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[0001] The development of advanced integrated circuit devices and architectures has been spurred by the ever increasing need for speed. For example, microwave, fiber optical digital data transmission, high-speed data acquisition, and the constant push for faster digital logic in high speed computers and signal processors has created new demands on high-speed electronic instrumentation for testing purposes.
[0002] Conventional test instruments primarily include two features, the integrated circuit probe that connects the test instrument to the circuit and the test instrument itself. The integrated circuit probe has its own intrinsic bandwidth that may impose limits on the bandwidth achievable. In addition, the probe also determines an instrument's ability to probe the integrated circuit due to its size (limiting its spatial resolution) and influence on circuit performance (loading of the circuit from its characteristic and parasitic impedances). The test instrument sets the available bandwidth given perfect integrated circuit probes or packaged circuits, and defines the type of electric test, such as measuring time or frequency response.
[0003] Connection to a test instrument begins with the external connectors, such as the 50 ohm coaxial Kelvin cable connectors (or APC-2.4). The integrated circuit probes provide the transitions from the coaxial cable to some type of contact point with a size comparable to an integrated circuit bond pad. Low-frequency signals are often connected with needle probes. At frequencies greater than several hundred megahertz these probes having increasing parasitic impedances, principally due to shunt capacitance from fringing fields and series inductance from long, thin needles. The parasitic impedances and the relatively large probe size compared to integrated circuit interconnects limit their effective use to low-frequency external input or output circuit responses at the bond pads.
[0004] Therefore, electrical probes suffer from a measurement dilemma. Good high-frequency probes use transmission lines to control the line impedance from the coaxial transition to the integrated circuit bond pad to reduce parasitic impedances. The low characteristic impedance of such lines limits their use to input/output connections. High-impedance probes suitable for probing intermediate circuit nodes have significant parasitic impedances at microwave frequencies, severely perturbing the circuit operation and affecting the measurement accuracy. In both cases, the probe size is large compared to integrated circuit interconnect size, limiting their use to test points the size of bond pads. Likewise sampling oscilloscopes, spectrum analyzers, and network analyzers rely on connectors and integrated circuit probes, limiting their ability to probe an integrated circuit to its external response. For network analysis, a further issue is de-embedding the device parameters from the connector and circuit fixture response, a task which grows progressively more difficult at increasing frequencies.
[0005] With the objective of either increased bandwidth or internal integrated circuit testing with high spatial resolution (or both) different techniques have been introduced. Scanning electron microscopes or E-beam probing uses an electron beams to stimulate secondary electron emission from surface metallization. The detected signal is small for integrated circuit voltage levels. The system's time resolution is set by gating the E-beam from the thermionic cathodes of standard SEM'S. For decreasing the electron beam duration required for increased time resolution, the average beam current decreases, degrading measurement sensitivity and limiting practical systems to a time resolution of several hundred picoseconds. Also, SEM testing is complex and relatively expensive.
[0006] Valdmanis et al., in a paper entitled "Picosecond Electronics and Optoelectronics", New York: Springer-Verlag, 1987, shows an electro-optic sampling technique which uses an electrooptic light modulator to intensity modulate a probe beam in proportion to a circuit voltage. Referring to
[0007] Weingarten et al. in a paper entitled, "Picosecond Optical Sampling of GaAs integrated Circuits", IEEE Journal of Quantum Electronics, Vol. 24, No. 2, February 1988, disclosed an electro-optic sampling technique that measures voltages arising from within the substrate. Referring to
[0008] A microwave generator
[0009] Referring to
[0010] Since the system taught by Weingarten et al. does not include a probe proximate the circuit under test the limitations imposed by capacitive loading of the circuit to be tested is avoided. However, the system taught by Weingarten et al. is limited to "point probing," by the lens
[0011] Various other techniques by which semiconductors may be characterized, using electromagnetic radiation of different wavelengths under different conditions is cataloged by Palik et al. in "Nondestructive Evaluation of Semiconductor Materials and Device," Plenum Press, New York, 1979, chapter 7, pp. 328-390. Specifically, treatment is given of (1) infrared reflection of GaAs to obtain the optical parameters n and k and then the carrier density N and mobility u; (2) infrared transmission in GaAs to determine k from which is determined the wavelength dependence of free carrier absorption; (3) infrared reflection laser (spot size) scanning of and transmission through GaAs to determine free carrier density in homogeneity, including local mode vibrations; (4) far infrared impurity spectra; (5) infrared reflection and transmission from thin films on a GaAs substrate; microwave magnetoplasma reflection and transmission; (6) submillimeter-wave cyclotron resonance in GaAs to determine magnetotransmission; (7) ruby laser radiation to form a waveguide in a GaAs film on a GaAs substrate, the propagation features of which are then measured using infrared radiation; (8) infrared reflectance from multilayers of GaAs on a GaAs substrate; (9) reflectance measurements of graded free carrier plasmas in both PbSnTe films on PbSnTe substrates and InAs on GaAs substrates; (10) interferometric measurements of ion implanted layers; (11) infrared restrahlen spectra, also to determine lattice damage effects; (13) ellipsometric measurements of ion-implanted GaP; (14) determination of optical constants by internal reflection spectroscopy; (15) laser raster scanning of semiconductor devices to measure photoconductivity, to track the flow of logic in a MOS shift register (because of current saturation, the effect of the laser light differs in cells in the 0 or 1 logic state), and with a more intense laser power level to change those logic states (i.e., to write to the circuit); (16) laser raster scanning of semiconductor devices to determine variations in resistivity and carrier lifetimes; (17) thermal imaging of circuits to find hot spots; (18) Raman backscattering to determine free carrier density; (19) carrier injection to study the band edge; (20) birefringence measurements in monolayers of GaAs and AlAs on GaAs to characterize the resultant strain; (21 ) photoluminescence and cathodoluminescence measurements of implanted layers and acceptor and donor densities. With the exception of (7) above which relates to waveguide transmission, and also of (15) and (17), these techniques relate to the characterization of static systems. While (15) relates to a spot scanning technique of the operational integrated circuit and (17) relates to hot-characterization of the device temperature.
[0012] What is desired, therefore, is a non-invasive technique to measure voltage levels within a device.
[0013] The present inventor came to the realization that the single point non-invasive probing technique of semiconductor materials could be enhanced if both the phase and amplitude, or polarization and amplitude properties of light transmitted thorough or reflected off of a semiconductor material could be recorded or otherwise preserved in some manner. Semiconductor materials generally exhibit electro-optic (generally 3/5 semiconductor materials) or photo-refractive effects (generally silicon based expitaxal circuits), which can be made to become birefringent by the application of an electric field, either as such or as embodied in electromagnetic radiation. Also, surface reflection and/or transmission probing, of semiconductor materials, such as for example, GaAs, germanium or silicon, can be modulated by for example, cathode refections modulation (E-beam), an electric field, voltage, heat, pressure, x-ray radiation, magnetic fields, and photo injection. The present inventor then came to the realization that if an object in a state in which it is not birefringent, but such birefringence can then be brought about in some manner such as electrical or electromagnetic techniques, the nature of the birefringence so introduced can be studied to determine characteristics of the material. Upon further consideration the present inventor then came to the realization that holographic techniques can record both the phase and amplitude, or the polarization and amplitude properties of light, such as that passing through or reflected off a semiconductor material, which can then be reconstructed. Holographic techniques provide the ability to examine materials using a wave front that is greater than, and typically substantially greater than, the physical focal point of the wavelength of the light. Further, the present inventor came to the realization that using field based interference patterns detail regarding the structure and operating characteristics of semiconductor devices considerably smaller than the physical focal point of the applied light or applied signal may be determined. Likewise, obtaining such holographic information will enable the development of other devices, such as for example, lenses, filters, and optical devices, which are based on, at least in part, the operating characteristics of semiconductors.
[0014] A hologram is created by a coherent light beam being transmitted through or reflected from an object onto a recording medium, which at the same time the original beam is also directed onto that recording medium as a reference beam. Various characteristics of the resultant transmitted or reflected beam, herein called the "object wave," are recorded in the resultant interference pattern between the object wave and the reference beam, i.e., as a hologram. These characteristics can later be observed by illumination of the hologram by that reference beam alone. That is to say, inasmuch as the phases or polarizations of the reference beam and the object wave have been recorded in that interference pattern along with their intensities, the wave produced by illuminating the hologram with the reference beam is essentially an exact replica of the object wave. Those characteristics are in part a consequence of the physical structure (i.e., "appearance") of the illuminated object, hence the wave so observed appears as a three dimensional image of that object. Optical Holography, Second Edition, by P. Hariharan, 1996 describes some general optical holographic techniques, and is incorporated by reference herein in its totality.
[0015] The present inventor also realized that particular semiconductor materials are generally transparent to light of particular wavelengths so that the light may freely pass through and reflect back though all or a portion of the semiconductor, or otherwise pass through the semiconductor, substantially "unaffected" when the semiconductor is not stressed, such as by no applied voltage, not subject to a electromagnetic (e.g. radio wave) field or signal, magnetic field, x-ray radiation, gravity wave, sub-atomic partical radiation, pressure, temperature, photo-generated carriers, subject to electron- or ion-beam devices, bioelectric, or chemical. Likewise, when the semiconductor material, such as one including an integrated circuit, is stressed by applying a voltage therein by energizing a circuit fabricated therein, or by applying a different energy level, the same light will reflect or otherwise pass through the semiconductor material, while being affected by the changes imposed by the applied voltage, thereby resulting in a different pattern. The stressed and unstressed states may be recorded as different holographic images. In addition, it is within the scope of the present invention to make a comparison between two different stressed states. The two holographic images may then be compared to one another to determine the actual operating characteristics within the semiconductor material. In addition, by its nature, holographic imaging techniques record a significant spatial region much larger than a single wavelength simultaneously which is important for characterizing regions of the semiconductor material. For example, the operational characteristics of two different regions may be interrelated which is unobtainable using techniques limited to a wavelength in "spot size." The present inventor's realization that the application of holographic techniques for the testing of semiconductor devices was only after at least the culmination of the aforementioned realizations.
[0016] Of particular interest is the "real time" characterization of operating characteristics of integrated circuits where such birefringence is introduced by the electro-optic effect, i.e., the imposition of a voltage onto the object (as in the ordinary operation of the integrated circuit) causes birefringence therein. Birefringence in 3/5 materials generally imposes a rotation of the polarization which is primarily a polarization and/or amplitude shift. Voltage induced changes in silicon materials generally imposes a refractive index shift which is primarily a phase and/or amplitude shift. Both of these occurrences are detectable, such as for example, with a polarized beam, a polarization recording hologram, an amplitude hologram, and/or a phase hologram. In other words, upon application of an electric field the material, such as GaAs or silicon, introduces an anisotropy and the ordinary complex refractive index n* of the material is decomposed into n
[0019] Plane wave
[0020] Consequently,
[0021] To permit such a procedure, the in line apparatus of
[0023] As to the case in which the TO
[0024] Alternatively, a second hologram can be recorded using the apparatus in the in line configuration shown in
[0025] One of the sources of error as just noted is removed when recording a first hologram onto an infrared thermoplastic plate. For example, if a holographic recorder is used in conjunction with an installed thermoplastic plate, after exposure the thermoplastic plate is developed in situ, i.e., the plate is not removed from the optical path for such purposes. The error brought about by removing the recording medium for development and then replacing that medium back into the experimental apparatus is thus eliminated. Also, holographic image reconstruction from an voltage pattern or a microwave signal in the thermplastic device recorded at a wavelength of 1.15 μm may be obtained using a shorter wavelength such as 0.633 μm by increasing the image by a factor of two. Also, differences in the spectral sensitivity and optical resolution (lines per unit of length) of the thermoplastic plate and CCD camera
[0026] A CCD camera
[0027] For the purpose of processing such a data stream,
[0028] In order to illustrate the uses of the aforesaid components and those to be describe hereinafter, it is appropriate to outline in greater detail the characteristics of an exemplary representative TO
[0030] For purposes of future reference, the standard definitions of the planes in a cubic crystal are shown
[0032] The symmetry aspects of applying external forces to crystals have been discussed by J. F. Nye in
[0033] An electric field that is normal to the exposed (001) face of a GaAs crystal would have the effect of defining the corresponding z axis as the optic axis. An electric field that is tangential to that (001) face will define an optic axis lying somewhere in that face, i.e., either coincident with one or the other of the x and y axes or lying at some angle thereto. The indicatrix for the resultant uniaxial "structure," which will then determine the directions of propagation of the transmitted rays that would result from imposing an incident beam of light thereon, will have a corresponding orientation relative to the x and y axes. Because of the induced birefringence, there will be two rays, linearly polarized at right angles to each other, that transmit through the uniaxial crystal so formed, and by conservation principles the corresponding rays that reflect therefrom will likewise be so polarized. As will be seen below, this combination of events lends itself to direct determination by the present invention, since the apparatus that embodies the invention preserves not only the amplitude and phase of the reflected radiation as in a normal hologram, but also the polarization.
[0035] With regard to another aspect of holographic apparatus
[0036] Different embodiments of the invention as described also differ in the nature of the elements used to transmit appropriately structured laser beams onto the TO
[0037] Including the additional laser module
[0038] That is, in apparatus
[0039] The fabrication of integrated circuits typically uses structures, such as metal lines and ground planes, that are not generally transmissive, unless sufficiently thin. Using a transmissive holographic technique requires the light to pass through the test device. On extremely high density devices the feature density may be too high to permit sufficient transmission. The presence of a ground plane may also restrict transmission. To accommodate structures that are not sufficiently transmissive a reflection technique may be employed. Transmissive and reflective techniques typically require different holographic systems. Referring to
[0040] Unfortunately, the in-line holographic techniques result in the virtual image and the coherent source being viewed in-line and are superimposed upon one another making analysis difficult. The present inventor realized that an off-axis technique results in two images that are separated, as in the reference beam. This results in a clearer unobscured image that may be readily used, such as for interferometry. One example of an off axis technique is shown in
[0041] Another example of an off axis transmissive beam technique is shown in
[0042] Referring to
[0043] The present inventor came to the further realization that interferometric testing, as described by Weingarten et al. in a paper entitled, "Picosecond Optical Sampling of GaAs Integrated Circuits", IEEE Journal of Quantum Electronics, Vol. 24, No. 2, February 1988, is limited to the rules of conventional microscopy. Such limitations include the inability to resolve particles with a limited depth of field. In addition, the system described by Weingarten et al. requires accurate alignment of the polarization wave plates in order to interfere the light, which is difficult at best to achieve. Referring to
[0044] The present inventor came to the realization that if the CCD camera resolution and sensitivity to photo-generated voltages could be enhanced together with increasing the ability of the CCD camera to resolve individual pixels, then the system would not be directly limited to the physical attributes of the CCD camera. To achieve such enhancements the present inventor determined that using both holographic microscopy and/or holographic interferometry of the voltage displacement contours or interferometric fringes of the CCD camera may be used to substantially enhance the resolution. The optical image on the CCD produces a varying electric field on the pixels and associated structures which in result modulates the refractive index of the semiconductor crystals through the electro-optic effect or rotates the polarization of the incident beam. If the incident light distribution light changes the crystal in a manner that is different than was obtained by the CCD at rest, then a new charge pattern and thus a modified image may be obtained. A second sensor that is sensitive to a different wavelength of light than the first sensor (CCD) is used to sense the voltage patterns imposed on the first sensor. The second sensor may then observe the fringes in the voltage patterns of the first sensor representative of the variations of voltage as a result of stressing the test device. Inspection of the fringe pattern gives considerable amount of information about the stressed test device. Referring to
[0045] The inventor then realized, holographic microscopy when combined with conventional microscopy offers much greater usefulness in recording both phase and amplitude than is obtainable with conventional optical lens elements and devices. Likewise, optical holography offers the means to eliminate cumbersome optics, beam polarizers, and filters and permit in situ placement of more sensitive optics within the ergometric dimensions of conventional semiconductor packaging.
[0046] Holographic measurements of dynamic voltage patterns in semiconductors and freecarrier, devices distributed throughout an appreciable volume and area are not possible with a conventional optical microscopic system. This is because a conventional microscope which can resolve particles of diameter d has a limited depth of field as shown in the following equation:
[0047] Holography permits storing a high resolution, three-dimensional image of the whole field at any instant. The sationary image reconconstructed by the hologram can be examined subsequently in detail, throughout its volume by a conventional IR microscope.
[0048] In-line holography can be used for such examinations whenever a sufficient amount (>80%) is directly transmitted to serve as a refernce beam. This premites very simple optical system as shown in
[0049] where the diffracted field field due to the voltage induced refractive index or polarization shifts is its Fraunhofer diffraction pattern.
[0050] To give a satisfactory reconstructed image of a semiconductor device under test, the hologram should record the central maximum and at least sidelobe of its diffraction pattern. This would correspond to IR waves travelling at a maximum angle
[0051] to the directly transmitted wave, and hence, to a maximum fringe frequency of 4/d, which is independent of the values of λ and z. Accordingly, for a device under test with 10 μm lithography, the recording material should have a modulation transfer function which extends beyond 400 mm
[0052] Recording devices and films with lower resolution, which are faster and easily employed, can be used effectively if a hologram is recorded of a magnified image of the device under test. For this, the imaged area of the device under test is imaged near the holographic plane, as shown in
[0053] The inventor then realized from this material that the depth of the field is also limited by the dimensions of the recording material. Examination of the previvious expression for calculating the maximum angle, it follws that x, the half-wigth of the hologram, must be greater than 4zλ/d. Hence, the maximum depth of field over which the required resolution can be maintained is given by the relation
[0054] Determining film or recording medium resolution requirments for off-axis multiple beam holographic recording setups.
[0055] Holographic interferometry of phase objects provides a very simple approach to In-line holography when a sufficent amount of light is directly transmitted throught the device under test serves as a reference beam. Even in applications such as flow visualization and heat transfer studies, where conventional interfermetry has been used for many years, holographic interferometry has practical advantages.
[0056] In this first instance, mirrors and windows of relatively low optical quality can be used. [e.g., the 1 cm holographic plate is much larger than the 10 μm object. Since the phase errors due to these contribute equally to both interfering wavefronts, they cancel out, and only the effects changes in the optical path are seen. However, a significant advantage is the possibility of incorporating a diffusing screen (a ground glass plate) in the interferometer. This gives an interference pattern that is localized near the phase object, and can be viewed and photographed over a range of angles. This makes it possible to study three-dimensional refractive index distributions.
[0057] If the refractive index gradients in the test section are assumed to be small, so that rays propagate through it along straight lines parallel to the z axis, φ(x,y) the phase difference at any point in the interference pattern is given by the relation:
[0058] where no is the refractive index of the medium in the test section in its initial unpreturbed state and n(x, y, z) is the final refractive index distribution.
[0059] The simplest case is that of a two-dimensional phase object with no variation of refractive index in the z direction. In this case the refractive index distribution can be calculated directly from (64) This is a valid approximation to many practical situations.
[0060] Another case which lends to analytic treatment is that of a refractive index distribution f(r) which is radially symmetric about an axis normal to the line of sight (for convenience say, the y axis).
[0061] For a ray traveling in the z direction at a distance x from the center, we then have:
[0062] so that (64) becomes:
[0063] This is the Abel transform of f(r), and it can be inverted to find f(r).
[0064] The evaluation of an asymmetric refractive index distribution f(r,θ) is much more difficult and is possible only by recording a large number of interfergrrams from different directions. The problem becomes even more complicated when the effects of ray curvature due to refraction cannot be neglected.
[0065] Holographic interferometry has been found particularly useful in high energy plasma diagnostics. Since, unlike a neutral gas, a plasma is highly dispersive, measurements of the refractive index distribution at [different] two wavelengths make it possible to determine the electron density directly. This has shown that "the interference fringes are contours of constant dispersion and, hence of constant electron density." Both these approaches while demonstrating plasma diagnostics, are limited in their utility because of the inability of the two holograms to provide real-time interferometry, as needed.
[0066] When using Real-Time holographic interferometry techniques, the hologram is replaced, after processing, in exactly the same position in which it was recorded. When it is illuminated with the original reference beam, the virtual image coincides with the object. If, however, the shape of the object changes very slightly, two sets of light waves reach the observer, one being the reconstructed wave (corresponding to the object before the change) and the other directly transmitted wave form its present state (e.g., changes in the index of refraction will alter the reflected optical path).
[0067] The two wave amplitudes will add at the points where the difference in optical paths is zero or a whole number of wavelengths, and cancel at some other points in between. As a result, an observer, photodetector or device viewing the reconstructed image sees it covered with interference fringes, which is a contour map of the changes in shape of the object. These changes can be observed in real-time.
[0068] Considering an off-axis holographic recording system, the intensity at the photographic plate when the hologram is recorded is:
[0069] where r(x,y) is the complex amplitude due to the reference beam and o(x,y)=|(x,y)|exp[−1φ(x,y)] is the complex amplitude due to the object in its normal state.
[0070] Assuming that the amplitude transmittance of the photographic plate after processing is linearly related to the exposure, the amplitude transittance of the hologram is:
[0071] An alternative to
[0072] A two-beam microscopic holographic transmission probing system shown in
[0073] The arrangements shown in
[0074] By analyzing the position of the holographic fringes and the shifts reveals information as to the nature of the voltages in the CCD or within the Joesphson devices. The result is that the holographic fringes provide a high sensitivity to changes in voltage of the test device. Also the fringes increase the density of the sampling points of the CCD not directly provided by the pixels themselves. Analysis of the data from the CCD may provide information regarding the structure of the test device substantially smaller than the wavelength of the light used.
[0075] Referring to
[0076] Factors limiting the resolution holographic lithography and photography are not so much limited by the quality optics as in conventual photography and lithographic techniques but, upon the coherent nature of the hologram's interfering coherent beams or wavefronts upon the recording medium.
[0077] For infrared testing it may be desirable to include an infrared sensitive photo-conductor as the holographic recording medium. Generally such an infrared sensitive photo-conductor generates a photo-current when exposed to infrared light. Such a photo-conductor may be, for example, silicon (for creating photogenerated voltages up to short infrared wavelengths of 1.1 μm), Lead Selenide, Indium Arsenide, GaAs, PbTe, GaAs doped with zinc, and Lead Sulfide. Accordingly, the photo-current generated in the infrared sensitive photo-conductor is generally less than one electron volt. The photo-current then performs the step of reducing the surface potential, as in standard visible light photo-thermoplastics for in-line and off-axis holographic techniques.
[0078] The unique capabilities of holographic interferometry are due to the fact that holography permits storing a wave front for reconstruction at a later time and are suitable for electrical measurement. Wavefronts which were originally separated in time or space or even wavefronts of different wavelengths can be compared by holographic interferometry. It is possible to observe holographic interferometry in real time. After processing the first hologram, leaving the holographic material in place or replacing it, when it is illuminated with the original reference beam, it reconstructs the object wave, and the virtual image coincides with the object. If, however, the characteristics of the object changes very slightly, two sets of light waves reach the observer, one being the reconstructed wave (corresponding to the object before the change) and the other the directly transmitted wave from the object in its present state. The two wave amplitudes add the points where the difference in optical paths is zero, or a whole number of wavelengths, and cancel at some other points in between. As a result, an observer viewing the reconstructed image sees it covered with a pattern of interference fringes, which is a contour map of the changes in shape of the object. These changes can be observed in real time. In addition, by viewing at multiple angles, a three dimensional model may be developed of the object. One general limitation of real-time holographic interferometry is that while the light diffracted by the hologram is linearly polarized, the light scattered by a diffusely reflecting object is largely depolarized, resulting in a significant drop in the visibility of the fringes. To avoid this, it is helpful to use a polarizer when viewing or photographing the fringes.
[0079] In double exposure holographic interferometry which may be used to test electronic devices, interference takes place between the wavefronts reconstructed by two holograms of the object recorded on the same photographic plate. Typically, the first exposure is made with the object in its initial, unstressed condition, and the second is made with a stress applied to the object. When the processed hologram is illuminated with the original reference beam, it reconstructs two images, one corresponding to the object in its unstressed state, and the other corresponding to the stressed object. The resulting interference pattern reveals the changes in shape of the object between the two exposures. Double exposure holographic interferometry has an advantage over real-time holographic interferometry, because the two interfering waves are always reconstructed in exact register. Distortions of the emulsion affect both images equally, and no special care need be taken in illuminating the hologram when viewing the image. In addition, since the two diffracted wavefronts are similarly polarized and have almost the same amplitude, the visibility of the fringes is good. However, double-exposure holographic interferometry has certain limitations. The first of which is that where the object (or object's refractive index) has not moved between the exposures, the reconstructed waves, both of which have experienced the same phase-shift, add to give a bright image of the object. As a result it is difficult to observe small displacements or changes in the material's index of refractive or polarization state. A dark field, and much higher sensitivity, can be obtained by holographic subtraction, which merely involves shifting the phase of the reference beam by 180 degrees between the two exposures. An alternative method, which also helps to resolve ambiguities in the sense of changes, is to shift the phase of the reference beam by 90 degrees between the two exposures, or, better, to introduce a very small tilt in the wave-front illuminating the object between the two exposures. In the latter technique, equally spaced reference fringes are obtained, whose change is modulated by the phase shifts being studied. Another limitation of the double-exposure technique is that information on the intermediate states of the object is lost. This problem can be overcome to some extent by multiplexing techniques using spatial division of the hologram. In the latter procedure, a series of masks are used in which the apertures overlap in a systematic fashion, and a sequence of holograms is recorded at different stages of loading. The images can then be reconstructed, two at a time, so that interference patterns between any two images can be studied. An alternative is to use thermoplastic recording material, by which real-time fringes can be observed and the fringe pattern subsequently frozen to give a permanent holographic record.
[0080] Control of the fringes, to compensate for rigid body motion and eliminate ambiguities in interpretation, is not normally possible with a doubly exposed hologram. However, it is possible with two holograms recorded with different angularly separated reference waves. These holograms may be either on the same plate or different plates.
[0081] The testing of electronic devices in semiconductor materials may likewise be tested using stroboscopic holographic interferometry where a holograph of a stressed test object is recorded using a sequence of light pulses that are triggered at different times during the stressing of the test object.
[0082] A surface relief hologram can be recorded in a thin layer of thermoplastic which is combined with a photo-conductor and charged to a high voltage. On exposure, a spatially varying electrostatic field is created. The thermoplastic is then heated so that it becomes soft enough to be deformed by the field and, finally, cooled to fix the pattern of deformation. Such materially have a reasonably high sensitivity over the whole visible spectrum and yield a thin phase hologram with fairly high diffraction efficiency. In addition, they have the advantage that they do not require wet processing. If a glass substrate is used, the hologram can be erased and the material re-used a number of times. One structure of a photo-thermoplastic is a multi-layer structure consisting of a substrate (e.g., glass, Kodar, or Mylar) coated with a thin, transparent, conducting layer, an infrared sensitive photo-conductor, and a thermoplastic. Referring to
[0083] An infrared semi-transparent material, such as a thin gold layer or a transarent electrode, or a suitable organic photoconductor, may be deposited on the exterior surface of the thermoplastic. Besides serving as an electrode to the photo-conductor it also acts in a manner to filter the image. The stressed or unstressed states of the infrared image from the test device is exposed and fixed in the thermoplastic material. Thereafter, if an infrared sensitive camera views the thermoplastic material when exposed to the opposite of the stressed or unstressed state of the infrared image from the test device. The result is a set of fringes on the thermoplastic material corresponding to the maximum and minimum intensity distribution. Computer aided evaluation of the resulting thermoplastic holographs or inferograms may be used, as desired. If an infrared semi-transparent material is used then the infrared camera may be used to view the thermoplastic material from the front side through the transparent photo-conductor, as the infrared semi-transparent material, such as thin semiconductor material or glass, will make it simpler to detect the fringes.
[0084] One approach to making thin-phase thermoplastic holographic recordings is to sensitize the photoconductor to 1.15 μm infrared light. The photoconductor is formed by adding a sensitizer to to polyvinylcabazole (PVK); the dye 2,4,7,-trinitro-9-fluorenone is widely used as a sensitizer with visiable light. Since the photoconductor formed with this dye in complex with PVK is not sensitive to radiate at 1.15 μm, other dyes must be used. The PVK can be sensitized to near infrared by either of two sensitizers, 2.4,5,7-tetranitrofluorenone or (2,4,7-trinitrofluorenylidene)-malononitrile. A photoconductor solution is prepared by dissolving PVK in tetrahydrofuran and adding sensitizer at a wieght ratio of one part sensitzer to four to ten parts PVK. The holographic device is prepared by dip coating the glass substrate and its transparent electrode with the photoconductor. A thermoplastic layer is added by a second dip coating with an ester resin dissolved in naptha. Solution concentrations and dip speeds are adjusted to photoconductor and thermoplastic layer thicknesses of approximately 2 and 0.8 μm, respectively. The sensitizer forms a complex with the PVK that appears to the eye as dark brown or gray.
[0085] Referring to FIGS.
[0086] While it is potentially conceivable to use infrared photographic films as a recording medium they are not especially suitable for several reasons. First, infrared photographic films sense and record the infrared light as visible light when developed, and not as non-viewable to the human eye infrared light. Typical infrared films record the infrared light to a maximum of 1,314 nm, where the developed image (Bragg cells) on the film is in visible light (550-800 nm) and hence the visible image cannot refract or defract infrared light. Second, typical infrared photographic films have limited sensitivity and tend to fog due to chemical sensitivity. The fogging is principally because of background thermal radiation. Third, after its spectral sensitization, a photographic plate is subject to thermal background radiation during its preparation and storage, and the various stages in the photographic process. This gives rise to a fog and reduces the "lifetime" of a plate, and is the main obstacle to the achievement of reasonable photographic sensitivity. What would be desirable is an infrared "film" type recorder that senses infrared light and records the infrared light as an infrared image.
[0087] In addition to recording ultraviolet holograms of voltages and plasmas in free-metals with conventual photographic and holographic films, the present inventor has identified serveral infrared holographic recording mediums for recording plasma and voltages in semiconductors using single and dual wavelength for Gabor-type, in-line holography, off-axis holography, and holographic interferograms. A Bismuth recording film has demostrated good senistivity for recording infrared holography for wavelengths from 1.06 μm to 10.6 μm. A film of Magnesium-Bismuth (MnBi) has demonstrated good recording characteristics at 1.06 μm. Plexiglas has been used to record infrared holograms at 10.6 μm.
[0088] The present inventor came to the realization that a controlling factor should be included with the recording medium to permit the recording of infrared light only while the medium is "turned on," so that the recording material is sensitive only when a useful image is projected on it. In addition, at the end of the exposure, the factor should be "switched off" so that the material remains insensitive throughout the subsequent storage of the exposed material. Thus the basic principle of controllable sensitivity is the sensitization of a photographic material only during its exposure. Also, if desirable, the controlled sensitivity may be switched on and off only in a certain spectral region (controlled spectral sensitization). The present inventor further came to the realization that semiconductor materials exhibiting a photoelectric sensitivity in the infrared range may be used as a recording device. It needs to be understood that in electro-photograph recording techniques charge dispursion and diffusion are limiting factors on image resolution. The use of voltage channeling conductive elements and their subsequent arrangements are to be applied to the recording devices described herein, as desired.
[0089] One potential semiconductor material may include bringing into contact, during the exposure time, two separate parts of a photographic system, each of which is not photographically sensitive on its own but only when in contact with the other material. For example, a thin photosensitive semiconducting film may be brought into contact with an aqueous electrolytic solution. However, the electrolytic solution and the photosensitive semiconducting film tends to be, by itself, insensitive to infrared light. When the two materials are brought into contact, an oxidation-recombination reaction takes place at the semiconductor-electrolyte interface. The rate of the reaction is dependant, at least in part, on the electron (hole) density in the semiconductor, i.e., on the intensity of illumination falling on the semiconducting film. The reaction may be ended by breaking the contact of the two pieces, or any other suitable technique. Thus, the semiconductor film is again insensitive to infrared radiation. Alternatively, a semitransparent film of lead sulfide evaporated on a glass substrate could also be used as a photographic plate. Combined with a germanium filter, this plate may be exposed to obtain an optical image, or the exposure stopped in the latent image stage and the optical density could then be increased by "physical" development. Alternatively, a thin semiconductor plate of n-type gallium arsenide in contact with an electrolyte solution containing HNO
[0090] An alternative structure includes electrically controlled processes where an "electric shutter" is used to "switch on" the photosensitivity during exposure. There are two general techniques to electrically control the photographic process with a self-contained current-sensitive film, namely, a liquid process and a process with a self-contained current-sensitive film. Referring to
[0091] Another further embodiment of the image is not formed on the surface of a semiconductor but in a self-contained current-sensitive film. Referring to
[0092] Yet another alternative embodiment of a semiconductor as the basis of the film consists of the following. A charge is uniformly distributed across the surface of a high-resistivity semiconductor placed on a conducting substrate. The charge leaks away from the illuminated regions because of their photoconductivity and a latent electrophotographic image is formed on the plate. The image is made visible by development involving the precipitation of the charged colored particles of the developer on the unilluminated parts of the image. The photographic sensitivity of the plate is absent during its preparation and is imparted by charging the plate. The charging process acts as a controlling factor which "switch on" the sensitivity. However, the latent image has only a limited lifetime and the sensitivity can not be "switched off" after the exposure. The process can be completed by electrostatic development.
[0093] There are additional techniques that may be employed. The effect on a photographic plate of the background thermal radiation during the plate's storage and preparation before its exposure and during its subsequent treatment can be suppressed by exploiting the uniform illuminance of this radiation. A process can be developed in which the photographic effect is obtained only by projection of an image with regions of different illuminance but not by uniform illumination. A photographic process of this type may ensure insensitivity of a photographic material to the fogging effect of the thermal radiation and still give an optical image. One of possible variants of such a process involves the use of the photo emf in semiconductors, p-n, n-p-n, or p-n-p, junctions for the purpose of obtaining a photographic image. Referring to
[0094] Other suitable materials for this process include a base layer of n-material Aluminum overlaid by layer of p-material silicon which would a photovoltaic response from ultraviolet to approximately an infrared wavelength of 1.1 μm. Since the Aluminum layer is reflective to infrared radiation, it is useful in making films for infrared reflection (non-transmission) holograms. Both layers can be plasma deposited onto a high refractive index wafer or quartz (glass) surface (with the Aluminum layer outward) so that the hologram is recording through the quartz. The image quality of the developed hologram can be enhanced by the addition, a thin (or at wavelength specific thichness) dark infrared light absorbing layer of either p-, n-semiconductor or dielectric materials can be sandwiched between the silicon and aluminum layers. In infrared-transparent semiconductor materials, the materials' higher index of refraction gives a higher line resolution per millimeter in the processed film.
[0095] It is possible to increase the resolution of the aforementioned semiconductor based recording devices by the combination of an infrared wave front (or a relatively equal ultraviolet wave front strength to the infrared wave front) and e-beam convergence on the semiconductor in place of an applied voltage.
[0096] A further embodiment includes a recording device including a polycrystalline film, and in particular polycrystalline film including lead sulfide and selenide.
[0097] Another embodiment includes a lead sulfide recording device including sensitivity-controlling by an electric field applied to a semiconductor-electrolyte system where the image is formed directly on the semiconductor surface. A lead sulfide film may be prepared by vacuum evaporation followed by annealing. For example, the films may be deposited on a glass substrate with semitransparent tin dioxide electrodes (such as a surface resistance below 50 ohms/square). During exposure the semiconductor film is brought into contact with an electrolyte. The exposure is made through a film, such as a germanium filter. The light is focused onto the surface of the PbS film. For best results the electrolyte should have the following characteristics: (1) the effect of light should not result in the formation of an image in the absence of an electric field; (2) the selectivity of the electrolyte should be high in contrast to the electrolytes employed in electroplating; (3) the electrolyte should have a high current efficiency and the electrolysis should give rise to heterogeneous catalysis centers necessary for efficient development, (4) the electrolyte should produce an image with a high color contrast on the gray background of the semiconductor film. One potential electrolyte is a solution of simple salts, such as lead or silver nitrates, copper sulfate, or calcium chloride. A potential explanation of the mechanism of formation includes consideration of the semiconductor-electrolyte interface in an electric field. Cathodic polarization of the semiconductor surface produces a negative space-charge region and a corresponding blocking barrier at the surface of the p-type semiconductor. The selection of the elements of the light sensitive PbS-electrolyte system consists of addition of oxidizing or reducing agents to the electrolyte in accordance with the type of conduction of PbS. Referring to
[0098] Yet another alternative infrared recording medium is a photo-conduct-o-graphic system. The principal advantage of such a system is the formation of an image in a separable film and the consequent reusability of the photosensitive layer. One potential material utilizes high-resistivity gallium arsenide without a protective coating which is a compromise between photo-conduct-o-graphic and semiconductor-electrolyte systems, combining the advantages of both. Referring to
[0099] The counter-electrode (anode) is located at such a distance from the photo-conductor that the products of the anodic reaction in the current-carrying film near the counter-electrode can not diffuse into the main part of the assembly and spoil the useful image by accidental blackening.
[0100] The use of high-resistivity gallium arsenide eases the requirements that the electrolyte must satisfy in respect of the differential resistance in cathodic reactions, i.e., the resistance of the current-carrying film can be relatively high. When a high-resistivity photo-conductor is used in direct contact with a current-carrying film (without a protective layer) it is found that the system described above operates more or less efficiently with electrolytes. It follows that the protective layer need not be used, if desired.
[0101] The principal photographic characteristics of the system are a function of the electrolyte used and particularly of the ability of the latent-image centers to become localized in the current-carrying film during exposure and to remain in this film for some time after the exposure. These characteristics depend also on the process responsible for the visualization of the nonmetallic latent-image centers. For example, if a Phenidone electrolyte is used, the latent-image centers localized in the film may remain for several minutes and during this time the latent image is not affected by ordinary or acidified water. When the electrolyte is a weak aqueous solution of a neutral salt, the latent-image centers localized in the film have a sufficient degradation time. This time is sufficient for retention of the latent image from the end of the exposure to the beginning of the visualization process.
[0102] There may be at least two general types of reactions between a semiconductor material and molecules of an adsorbed reactant, controlled by active radiation. First, the chemical reaction between the components of the reagent is catalyzed by non-equilibrium carriers from the semiconductor. The visual image is produced by heterogeneous-catalysis reaction products. Second, the reaction or oxidation of the reagent on the semiconductor surface, involving non-equilibrium electrons or holes, respectively, and the chemical reaction of the products with the semiconductor material. The image is produced either through local etching of the surface, when the reaction products are soluble or gaseous and are removed from the surface, or by colored insoluble reaction products adsorbed on the surface. For example, a gas photo-corrosion of thin semiconducting films of indium antimonide may be used. Since the bonds in A
[0103] An extension of the aforementioned semiconductor based photography into infrared wavelengths may be achieved if the photo-sensitive element is cooled. For example, consider a film of semi-insulating GaAs is doped with zinc, 100 microns or less thick, and its resistivity generally 10
[0104] Referring to
[0105] Yet another recording material including semiconductor materials with forbidden bands narrower than the forbidden band of silicon. In addition, this may be extended to polycrystalline films, if desired. For example, a reaction of lead sulfide or selenide with an aqueous solution of AgNO
[0106] A two part system shown in
[0107] The inventor then realized that these two-part or three-part system films satisfies the requirements for making thin, phase, thin-amplitude, thin-phase, and thin-phase-reflection holograms, the films did not readily meet the requirements for creating volume- and volume-transmission, and volume reflection holograms. The inventor then realized that IR volume holograms could be readily achieved if an IR recording material could created which was able to record and resolve greater amplitude and refractive-index values.
[0108] Refering to
[0109] In
[0110] The present inventor came to the realization that temporary transient volume holograms utilizing a spatially modulated free carrier pattern would be useful in providing real-time hologram recording and interferometric evaluation of TO
[0111] Shown in
[0112] The effects which can be obtained with a nonuniformly excited insulator. As indicated in
[0113] A similar set up for the type of photocurrent (primary or secondary) to be expected from nonuniform illumination of a photoconductor. This discussion leads naturally to the reason why nonnegible photocurrents can occur in semiconductors with both carriers mobile, even for nonuniform illumination. Shown in
[0114] (1) only electron current need be considered, the holes being rapidly trapped at or near the site of their creation, and
[0115] (2) electron-hole pairs are generated at a distance x from the anode by a pulse of excitation.
[0116] The trapped holes from a space-charge of +Q cm{circumflex over ( )}−2, and their presence causes electrons to enter the crystal from the cathode. If the excess electrons which this enter the crystal constitute a charge of −aQ cm{circumflex over ( )}−2, the effect of the net charge is to increase the field at the cathode
[0117] where electrostatic units have been used, Eo is the field in the absence excitiation, and e is the diaelectric constant. The increase in current density corresponding to the increase in fild is given by
[0118] This increase in current may also expressed as
[0119] Equating these two relationships for Dj shows that
[0120] where
[0121] If strongly absorbed light or radiation is used to excite the material, x˜d, and then examination of the pevivous expression β shows that quanity b can be expressed as the ratio of two times
[0122] (1) the transit time, and:
[0123] (2) the the dielectric relaxiation time [81] (essentially the RC time constant) of the material:
[0124] where we have inserted the numerical factor to make the expression usable with conventional units for the resistivity r and e. Thus
[0125] so that the ratio of secondary to primary photocurrent is
[0126] To measure a primary photocurrent without any contribution from the secondary photocurent, then β must be much less than unity; i.e., tr>>tn. All other quanties being about the same, this means that a pure primary photocurrent can be observed in material only with a resistivity, i.e., insulators.
[0127] The same kind of reasoning is involved in determining the type photoconductivity which results from nonuniform illumination of a material in which both carriers are mobiles. The key question is this: When electron-hole pairs are generated in a material by nonuniform illumination, do the electrons and holes separate, each going to the appropriate electrode, or do the photoeexcited minority carriers move toward their approapriate electrode and taske along with them an equal number of majority carriers to maintain an absence of space charge. The answer is that, tr>>t
[0128] If t
[0129] In holographic filtering descrete voltage levels can be targeted, allowing for voltage induced jittering or timing; giving optional optical filtering conditions, i.e., negitive (low) background voltage level permites target photocurents, a large voltage exceeds the targeted voltage level recorded by the holographic filter.
[0130] Shown in
[0131] The free-carrier pattern acting as a pure-phase volume hologram and decays by diffusion of the free carriers using an apparatus as shown in
[0132] Two-wavelength holographic image production utilizes the interaction of photovoltages to produce computer generated holograms into voltage patterns on the free-carrier optical element to create a free-carrier image by a visible or UV wavelength which is subsequently read by another wavelength of non-photoelectric generating IR light. Serveral suitable techniques are discribed later is in this disclosure for making computer generated holograms of devices and conditions to be holographically tested. The amplitude and phase patterns of the short photogenerating wavelength are optically enlarged so that they correspond directly to the wave front dimensions of the IR optically read hologram. The photogenerating wavelength incident to free-carrier recording medium can be created or generated using, but not limited to, display devices such as cathode, liquid crystals, gas-plasma, or other free-carrier based devices.
[0133] Holographic filters in conjunction with holographic (initial polarization recording) mapping of the active optical surface are used to observe by non-invasive polarized light—the facsimile voltage patterns correspond to the optical amplitudes and phases that create the optical wavefront of the holographic image to be displayed. An electron lens or a cathode-ray element can be used to electrically reduce the voltage patterns down and transfer them to another optically active surface to increase image resolution if necessary.
[0134] Another approach is to use the following holographic technique of four-wave mixing utilizing free carriers and optical frequency doubling to enable real-time phase-conjunctent (4-wave mixing) examination of TO
[0135] In addition, other films may be used, as desired.
[0136] Additional recording mediums also include Bi
[0137] IR volume holograms offer to semiconductor voltage test and characterization, the ability to record two different transparencies (each formed by a different recording wavelength) on the same recording medium for subsequent reconstruction without crosstalk. The IR volume hologram recording process can be varied to also enable same-wavelength multiple hologram storage by rotating the recording medium after each exposure. Another suitable technique of essentially multiplexing multiple-images on a single recording medium is by considering the context of color holography; different non-overlapping regions of the same photographic plate can be utilized to record IC (TO
[0138] Pattern Recognition
[0139] Holograms created by computer calculations provide opportunity to generate wavefronts of any prescribed amplitude and phase distribution; this has been demonstrated to be extremely useful for generating three-dimensional images, testing optical surfaces, optical spatial-filtering, laser scanning, as well as pattern recognition of semiconductor devices and substrate voltage waveforms. Production of these holograms employs a discrete Fourier transform to generate the complex amplitude and phase distributions of an array of N
[0140] Digital Processing
[0141] The Fourier transform describes functions into different dimensions or coordinates such as Cartesian to spherical. For example, a function could be represented in the domains of time and frequency. The concept of the 3-D FFT has the same form as the mathematical representation of the 2-D FFT utilizing a 1-D FFT. Here, an element (n1, n2, n3) of the 3-D array (N1, N2, N3) would be defined in a 1-D device where:
[0142] Similarly, the 3-D FFT can derive from a time sample x(k1, k2, k3) a frequency sample X(k1, k2, k3). The parameter N can be expressed as:
[0143] Character & Condition Recognition
[0144] This property of associative storage has been used for recognizing a character with a hologram, it is applied to recognize the presence of a specific electronic circuit and detect specific voltage levels within the TO circuit. It makes it also possible to use an isochromatic hologram to perform a recognition of voltage condition(s) present in temporal voltage waveforms and in selected microelectronic devices and circuits. Like the previous section, this technique is essentially a spatial filtering operation in which the hologram functions as a matched filter. The approach here is to (1) couple invasive beam(s) to an electrooptic modulator to a prism, (2) invasively write the spectrally resolved beam(s) to the optically active surface to spatially filter, (3) read this with a noninvasive beam, (4) correlate the spatially resolved beam with the hologram (either a fixed hologram or a temporal photogenerated voltage field) with this noninvasive beam which is transmitted to invasively write the temporal photoelectric-pattern's correlation with the hologram on another optically active surface.
[0145] A optical system for this is shown in
[0146] where f(y−cj)j is the complex amplitude due to a typical character centered at cj, while that due to the reference source is δ(y+b).
[0147] If we assume linear recording, the transmittance of the hologram can be written as
[0148] where
[0149] The hologram is replaced, after processing, in exactly the same position in which it was recorded and illuminated by single character of the set centered on the axis. A computer generated hologram (CGH) of TO can be created utilizing IC layout tools and experimental data as well as theoretical test conditions can be subsisted in its place. If the amplitude due to the target device and its operating characteristics in the input plane is f(y)1, the transmittance of the hologram is
[0150] Shown is
[0151] The complex amplitude in the input output plane is then the Fourier transform of (86), which is
[0152] the only term of interest in (87) is the last but one on the right hand side which corresponds to the correlation of f(y)1 with all the characters of the set. If we ignore the constant factor βT, this can be expanded as
[0153] If the auto correlation function of the character presented is sharply peaked, the first term on the right hand side of (90) represents a bright spot of light, which is the reconstructed image of the reference source, located at
[0154] The presence of this bright spot in the output plane corresponds to recognition of the targeted microeleclectronic circuitry and accompanying voltage conditions present as one belonging to the original set. The fact that this image is reconstructed at a distance −c1 from its correct identifies the character presented as f(y−c1)1.
[0155] This basic circuit test condition recognition technique has been extended to permit simultaneous identification of all the circuit test targets and conditions on a single recording medium to allow multiple device and condition tests to be carried out in parallel. Shown in
[0156] When real-time operation is not required, a more direct technique can be used. This involves the use two transparencies in the input plane. One of these f(y+b)1 is a transparency of the character to be located, while the other f(y+b)2 is a transparency of the recording medium of the circuits and voltage conditions to be searched. The transmittance of the Fourier hologram formed with these two sources is then
[0157] where
[0158] and
[0159] If this hologram is illuminated with a plane wave, the complex amplitude in the output plane is proportional to the Fourier transform of t(η). As before, the only term of interest is the third within the square brackets which, if we neglect a constant factor, is
[0160] If F(y)2 is identical to F(y)1, this term will result in a bright auto correlation peak at y=−b. If, however, F(y)2 contains more than one such character f(y−c1)1, identical with f(y)1 but located at different positions and equal number of auto correlation peaks will be formed at locations y=−b−c1, corresponding to the centers of these patterns.
[0161] In isochromatic electron-shading, this approach is very useful for providing pattern and condition recognition both continual and real-time monitoring (using non-invasive light) for targeted devices and operating conditions in either temporal voltage waveforms, analogue and digital operations. This can be used to initiate various software and hardware functions such as: initiating both "stop" and "load" codes, program and node addresses, and initiating "link" operations for individual nodes (both star and cascade architecture's) in parallel processors. The limiting factors on system performance and operating bandwidth, are the physical dimensions hence, optical transit time, the physical dimensions of the voltage waveforms, and the compactly of the holographic storage medium.
[0162] Data-Access Techniques
[0163] Local optical archival of information offers virtual immunity of binary code for computers from degradation. For IR-based holography and optoelectronic devices, holography provides storage opportunities to similarly record and preserve the spectral and spatial integrity of light used for optical filters and waveguides.
[0164] The simplest approach of optical access employs a space variant approach. Here, the location and position(s) of the input field determines the composition of the output field from the hologram. The basic properties of such a system has been investigated for its applications in data processing.
[0165] To carry out a two-dimensional linear space-variant operation it is necessary to have a system having impulse response is a function of four independent variables (two more than a normal optical system). Two methods based on holographic techniques are described here.
[0166] The first is a simple method to perform the coordinate transformation
[0167] This transformation is effected with the optical shown in Figure No. (b), which uses a computer-generated hologram whose spatial frequencies at any point (u,v) are
[0168] Light from a point in the input plane having coordinates (u,v) is then diffracted at an angle such that an image of this point is formed in the back focal plane of the lens L2 at a point whose coordinates (x,y) satisfy (a) and (b).
[0169] More general operations can be realized, in principle, by a hologram array. Each input pixel is backed by a hologram element which generates the desired response for the targeted device and voltage conditions. However, there are serious limitations on the number of devices and conditions which can be handled in this fashion due to the limited resolution of hologram elements when targets are made very small.
[0170] Another method of obtaining a space-variant impulse response is to use a thick holographic element such as shown in
[0171] In
[0172] Higher selectivity can be obtained by the use of coded reference beams. For this, a diffuser is inserted into the input plane, and each of the holograms in the filter is recorded with a reference derived from a small area on this diffuser. Since the auto correlation functions of the reference beam are sharply peaked, each point in the input produces an output from the corresponding holographic filter. The diffuse background arising from the cross-correlation functions of the elementary diffusers is minimized by using a thick recording medium.
[0173] Holographic Image Generation
[0174] Holograms or computer generated holograms surface mounted on either frontside or backside can be made of IR absorbing materials to form transmission holograms, in the case of reflection-probing of TO
[0175] Holograms created by computer calculations provide opportunity to generate wavefronts of any prescribed amplitude and phase distribution; this has been demonstrated to be extremely useful for generating three-dimensional images, testing optical surfaces, optical spatial-filtering as well as laser scanning. Production of these holograms employs a discrete Fourier transform to generate the complex amplitude and phase distributions of an array of N
[0176] Many techniques have been developed for creating computer generated holograms (CGHs) and holographic lens elements (HLEs). CGHs are representations of the image's optical diffraction structure that has been calculated from either a mathematical description (e.g., Fourier analysis) of the wavefront or from samples. Several methods exist for creating and calculating HLEs and CGHs.
[0177] In conventional approaches to performing CGH calculations, the amplitude and relative phase of waveforms are plotted and optically reduced and transferred to holographic film. Illumination of the developed film creates the three dimensional image of the object calculated for viewing. Similar rules apply for creating HLEs such as concave, convex, cylindrical and achromatic lenses, prisms, beam gratings, etc. See
[0178] Replicating CGH plots by using a shorter (½ or ¼ of the IR wavelength) photogenerating wavelength so that free-carrier voltage waveforms or patterns approximating optically by a 2-times enlargement of the image. This technique eliminates the need for photo reduction of amplitude and wave phases since the voltage wave patterns directly correlate to IR and UV optical interference waveforms. Also, the reflection brightness value (+70%) of the metal mirror surface is greater than the light transmission values of presently available holographic transmission films (1% to 10%).
[0179] A Binary Detour-Phase Hologram has only two levels—either zero or one, the binary hologram is easily computed and projected onto the optically active projection surface by an invasive optical beam. Projection does not require the use of a reference wave or bias other than non-invasive polarized beam utilized to read the surface.
[0180] To produce the hologram, the surface area of the optically active projection surface is divided into array of N×N cells. Each cell corresponds to the N×N coefficients of the discrete Fourier transform of the complex amplitude of the in the object plane. Each Fourier coefficient is then represented by a single transparent area within the corresponding cell, whose size is determined by the modulus of the Fourier coefficient. This method derives its name from the fact that a shift of the transparent area in each cell results in light traveling a longer or short path to the reconstructed image. The effect here is achieved through the modulation of the TO material's polarization phase or in the refractive of the image. An example showing both the cells and the image of a typical binary detour-phase hologram of the letters ICO is shown in
[0181] This method of encoding the phase works, by a rectangular opening (a×b) in an opaque sheet (the hologram) centered on the origin of the coordinates, as shown on
[0182] Illustration showing the configuration of the cells in a binary detour-phase hologram shown in
[0183] (84)
[0184] where:
[0185] We now assume that the center of the rectangular opening is shifted to a point (Δxo, Δyo) and the sheet is illuminated by a plane wave incident at an angle. If the complex amplitude of the incident wave at the sheet is exp[i(αΔxo+βΔyo)], the complex amplitude of the diffraction pattern becomes:
[0186] continuing on . . .
[0187] If axi<λz, byi<λz, equation (87) reduces to:
[0188] If then, the computed complex amplitude of the object wave at a point (nΔx
[0189] its modulus and phase at this point can be encoded, as shown in equation ( ), by making the area of the opening located in this cell equal to the modulus so that
[0190] and displacing the center of the opening from the center by an amount given by the relation
[0191] To show the validity of this method of encoding, we consider the complex amplitude in the far field due to this opening, which is obtained by summing the complex amplitudes due to all the N×N openings, is therefore
[0192] If the dimensions of the cells and the angle of illumination are chosen so that
[0193] and
[0194] equation (92) reduces to
[0195] This is the discrete Fourier transform of the computed complex amplitude in the hologram plane, or in other words, the desired reconstructed image.
[0196] Illustration of a typical cell in a binary detour-phase hologram showing the configuration of a single cell in the binary detour-phase hologram shown in
[0197] Binary detour-phase holograms have several attractive features. It is possible to use a simple pen-and-ink plotter to prepare the binary master, and problems of linearity do not arise in the photographic reduction process. Their chief disadvantage is that they are very wasteful of plotter resolution, since the number of addressable plotter points in each cell must be large to minimize the noise due to quaintization of the modulus and the phase of the Fourier coefficients. When the number of quanitization levels is fairly large, this noise is effectively spread over the whole image field, independent of the form of the signal. However, when the number of phase-quaintization levels are small, the noise terms become shifted and self-convolved versions of the signal, which are much more annoying.
[0198] Generalized Binary Detour-Phase Holograms
[0199] In this method, as shown in
[0201] Phase Randomization
[0202] The Fourier transforms of the wavefronts corresponding to simple electronic circuits and their voltage levels have very large dynamic ranges, because the coefficients of the dc and low-frequency terms have much larger moduli than those of the high-frequency terms. This results in nonlinearity because of the limited dynamic range of the recording media.
[0203] To minimize this problem, it is convenient, where the phase of the final reconstructed image is not important, to multiply the complex amplitude at the original sampled object points by a random phase factor before calculating the Fourier transform. In transmission holography, this is optically analogous to placing a diffuser in front of the object transparency and has the effect of making the magnitudes of the Fourier coefficients much more uniform, as shown in
[0204] The Kinoform
[0205] In the case where the object is diffusely illuminated, the magnitudes of the Fourier coefficients are relatively unimportant, and the object can be reconstructed using only the values of their phases. This led to the concept of a completely different type of hologram called a kinoform.
[0206] This a computer generated hologram in which all the cells are completely transparent so that the moduli of all the Fourier coefficients are arbitrarily set equal to unity, and only the phase of the transmitted light is controlled in accordance with the phase of the computed Fourier coefficients. Thus, the amplitude transmittance tnm of the cell corresponding to a Fourier coefficient with modulus Onm and phase φnm would be:
[0207] However, to simplify recording, integral multiples of 2π radians are subtracted from the computed phases, so that they vary only between 0 and 2π over the entire kinoform.
[0208] Kinoforms have the advantage that they can diffract all the incident light into the final image. However, to achieve this, care is necessary to ensure that the phase matching condition expressed by (97) is satisfied accurately. Any error in the recorded phase shift, as altered by subsequent non-functionalities from the ideal test values of the TO, results in light diffracted into the zero order which can spoil the image and thus signal the presence of test failure conditions being present in the TO.
[0210] Computer Generated Interfergrams
[0211] Problems can arise with detour-phase holograms when encoding wavefronts with large phase variations since, when the phase of the wavefront moves through a multiple of 2π rad, the two apertures near the crossover may overlap. This has led to an alternative approach to the production of binary holograms based on the fact that an image hologram of a wavefront that has no amplitude variations is essentially similar to an interferogram, so that the exact locations of the transparent elements in the binary hologram can be determined by solving a grating equation which correlates with the TO circuitry and operating voltage parameters of the test.
[0212] Different methods can be used to incorporate information on the amplitude variations in the object wavefront into the binary fringe patterns. In one, the two-dimensional nature of the Fourier transform hologram used is used to record the phase information along the x-direction, while the fringe heights in the y-direction are adjusted to correspond to the amplitude. In another, the phase and the amplitude are recorded by the position and width of the fringes along the direction of the carrier frequency, while in the third, the phase and amplitude of the object wave are encoded by the superposition of two phase-only holograms.
[0213] This approach can be duplicated by plotter and photo reduction, or contentionual photolightographic, techniques as well as implimention in a free-carrier recording medium. Here the computer calculates the hologram at two levels of its amplitude transmittance—either one or zero (top). The reconstructed image appears in the lower illustration
[0214] Creating the voltage patterns with invasive light is accomplished by optically retrieving indexed patterns (matrices) that correspond to x, y, and z, coordinates of the holograph image field to be generated as well as Fourier transform functions. It is important to note in creating optical grating patterns metal mirror's photo-active surface using voltage waveform patterns, that the wavelength of electrons is less than 100,000 times shorter than visible light so no photo-reduction is necessary. The electron shadow that is created on the photovoltaic cell proportionally corresponds 1:1 to the interference lines of the real image upon the electro-optic surface. In this application, the isochromatic element serves as a mapping filter of the voltage waveforms.
[0215] One approach to display a holographic image for viewing is to generate multiple voltage patterns so that they are transposed beside each other in such a way that they bisect the active optical surface and interfere with each other in parallel to provide a parallax composite image.
[0216] In effect, the image's optical targets or input registers can also serve as index keys to retrieve multiple stored optical patterns that serve as precalculated optical patterns (copyrightable). These elements serve as templates to create the complex features (multiple Bragg cell conditions present) of the electro-static surface topographic electro-optic surface that goes into making three dimensional holographic images for display within a defined field (e.g., 6 mm×6 mm [width]×3 μm [depth]).
[0217] The inventor then realized that the abilty to resolve supra resolution in CCD detector devices disclosed in
[0218] The inventor then realized that the ability to resolve supra resolution in CCD detector and sensing devices previously disclosed in
[0219] In contrast to conventional lithography techniques and design conventions where more expitaxal devices are packed closer together onto a single chip to form more complex semiconductor devices, the inventor realized that the solution to developing higher operating frequencies was not in creating more descrete exptitraxal devices but, instead creating individual devices which would have more functionality if one could be able to resolve and alter the dynamic free carrier structure within a single, simple or complex expitaxal device. Instead of each binary expitaxal device modulating between two voltage levels, the device would be host to an array of voltage patterns. These descrete devices can be subsequently joined operationally together to form complex devices and systems which are disclosed later. By fashioning components in this manner it would be possible to create devices which in term would be equivalent to billions and/or trillions of conventional expitaxal devices are simulated within the device's free-carriers as either digital words or matrices, analogue waveforms, or symbolic characters. Timing of the free carrier patterns is controlled by microwave signal waveforms within the circuit and by discrete infrared (semiconductor materials)and ultraviolet (free-metal materials) holographic filters, beamsplitters, and holographic optical elements disclosed earlier. The free carrier patterns can be invasively written using specific photovoltaic wavelengths of light to the device's material, or by other sources of electromagnetic radiation such as x-rays, UV-light, magnetic fields, and other circuit devices in proximity or working in conjunction to the device. The functional electrical characteristics and physical dimensions of the free-carrier host device determine its operating frequency, phase cycle, sampling period window, stability or lifetime of the free-carrier pattern(s), and subsequent rewrite cycle.
[0220] The inventor then realized that the electrical characteristics at p-n junctions would serve as an effective free-carrier host device.
[0221] Forward-Bias Processes
[0222] Band-to-Band Tunneling
[0223] Photon-Assisted Tunneling
[0224] Injection
[0225] Tunneling to Deep Levels
[0226] Band Filling
[0227] Optical Refrigeration—optical pulse modulation and control systems for temperature control, good until approximately 30° K.
[0228] Hetrojunctions
[0229] Zener Breakdown
[0230] Avalanche Breakdown
[0231] Photoelectric Emission
[0232] Effect of Surface Conditions
[0233] Photovoltaic Effects
[0234] The solar or fast photocell
[0235] The Schottkey Barrier
[0236] Photovoltaic Effects at the Schottkey Barrier
[0237] Bulk Photovoltaic Effects—Dember Effect
[0238] Photomagnetoelectric Effect—useful for supra-resolution of magnetic fields in MRI devices.
[0239] Angular Dependence of Photovoltaic effects—useful for multivalue logic devices with multiple inputs and outputs on a single substrate and on multi-substrate systems.
[0240] "Photangular Effect"—useful for multivalue logic devices with multiple inputs and outputs on a single substrate and on multi-substrate systems.
[0241] Optically Induced barriers
[0242] Photovoltaic effect at a graded energy gap
[0243] Photopiezoelectric Effect
[0244] Macro-device host circuits—utilize microwave multvibrator and oscillator electronic circuits and macro devices having optical path and circuit phase/mode matching.
[0245] SAW devices—signal processing and conversion
[0246] Optical associative memories
[0247] Optical pattern & condition recognition
[0248] UV reads free metals, photowrites to IR
[0249] Four-wave mixing in free-carrier mediums which target character and voltage specific conditions in infrared stimulated luminescence, carriers can be excited out of traps by optical excitation. Since in most semiconductors the depth of the trap is less than 1.5 eV, the excitation can be obtained by infrared illumination. After the carrier is excited out of the trap, it makes a radiative transition, emitting a photon hv. E
[0250] The present invention relates to improved voltage test systems.


text:
Possible Duplicate:
Lost power during upgrade, how do I recover?
while upgrading from 12.04 to 12.10, after completion of downloading packages, installation of packages was going on.Due to power cut, it was inevitable to me shutting my computer down. Hence, the next steps of installing, cleaning and restarting could not be completed. The next time I logged in, I could see only a black screen. Please guide me to retrieve my ubuntu. (For your kind information, though I am a ubuntu lover, not a technically strong person)

subset: commoncrawl


text:
Aviva Premiership
Saracens bolster front-row options
ESPN Staff
June 7, 2012
Lorenzo Romano on the charge for Aironi © Getty Images
Saracens have announced the singing of Italian prop Lorenzo Romano ahead of next season.
The tight-head is currently on tour with Italy in the Americas ahead of their Tests against Argentina, Canada and the United States. Romano was turning out for Aironi in the RaboDirect PRO12 last season but the club are going to be replaced in next year's competition by another Italian franchise due to Aironi's financial difficulties.
Saracens have moved quickly to secure their man and he will vie with Carlos Nieto and Matt Stevens for a spot in the front-row next term.
Talking of Romano's signing, Saracens director of rugby Mark McCall said: "He is a young prop with immense potential, and we are looking forward to providing an environment where he can develop into one of the leading prop forwards in Europe."
© ESPN Sports Media Ltd.
Communication error please reload the page.


text:
Difference between revisions of "E17"
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== Installing E17 ==
== Installing E17 ==
=== From the
=== From the repository ===
To install e17:
To install e17:
pacman -S
pacman -S
You might also want to install additional [[Fonts]]. You need at least 1 True Type Font.
You might also want to install additional [[Fonts]]. You need at least 1 True Type Font.
If you need/want an e17 package which is not (yet) available in [
If you need/want an e17 package which is not (yet) available in [], see if it is available in the [[AUR]].
=== Compiling and packaging with ArchE17 script ===
=== Compiling and packaging with ArchE17 script ===
Revision as of 18:12, 21 November 2012
zh-CN:E17 Template:Article summary start Template:Article summary text Template:Article summary text Template:Article summary heading Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary end
From the Enlightenment wiki:
- The Enlightenment desktop shell provides an efficient yet breathtaking window manager based on the Enlightenment Foundation Libraries along with other essential desktop components like a file manager, desktop icons and widgets. It boasts a unprecedented level of theme-ability while still being capable of performing on older hardware or embedded devices.
E17 is the development release 17 (DR17) of the Enlightenment Desktop Environment. It comprises both the Enlightenment window manager and Enlightenment Foundation Libraries (EFL), which provide additional desktop environment features such as a toolkit, object canvas, and abstracted objects. E17 has been under development since 2005, but in February 2011 the core EFLs saw their first stable 1.0 release. Enlightenment the window manager is still in the beta stages, but is already quite usable. Many people currently use E17 as a day-to-day desktop environment without problems.
- 1 Installing E17
- 2 Starting E17
- 3 Configuring the Network
- 4 Installing Themes
- 5 Modules and Gadgets
- 6 Troubleshooting
- 7 External Links
Installing E17
From the extra repository
To install e17:
pacman -S enlightenment17
You might also want to install additional Fonts. You need at least 1 True Type Font.
If you need/want an e17 package which is not (yet) available in [extra], see if it is available in the AUR.
Compiling and packaging with ArchE17 script
You can build your own Arch Linux e17 packages with a small python script called ArchE17.
Compiling with easy_e17.sh
easy_e17.sh compiles E17 from source and installs it in
/opt/e17. It does not create packages and therefore does not install dependencies automatically.
- Get it from the AUR: easy-e17AUR.
- Edit
/etc/easy_e17.confif you want.
- Run it as user, so it downloads to ~/e17_src and builds as user, to install E17 (the script will immediately ask for your password so it can install in the end):
# easy_e17.sh -iWarning: This will install the latest svn version. For a stable result add the --srcrev= parameter with the latest stable revision. For beta 3 use 55246 as argument. For the revision with the 1.0 release of the core libraries, use 56361, and for the 1.1 release use 65800 (2 Dec. 2011).
- Put
/opt/e17/binin your
PATHby editing
/etc/profile. For example, you can add this line at the end of the file:
- If, after completing the install, xinitrc complains that it cannot find enlightenment upon starting, you may need to add these lines to the end of /etc/profile as well:
If you encounter any errors while trying to install E17, first check to make sure it is not a dependency problem. If it is, install the dependency and continue installing e17.
To update E17 without using the program mentioned below, run this command as root:
# easy_e17.sh -u
update_e17.sh is a zenity script which is made to accompany
easy_e17.sh. It makes several aspects of updating e17 easier as it can backup and restore your E17 svn tree (in case there is breakage), as well as roll it back to a specific revision (again, in case of breakage) or even let you know when a new revision has come around on E17's svn tree. See this page for more information on this optional component. You can get it from the AUR: oz-e17-toolsAUR.
Starting E17
If you use
startx or a simple Display Manager like XDM or SLiM, add or uncomment the following command in xinitrc:
exec enlightenment_start
Nowadays E17 has a new display manager called Elsa, you can download it from AUR elsa-svn-archAUR.
Elsa is quite sophisticated and its configuration is controlled by
To start Elsa add the following line to your
and change your default runlevel to 5.
More advanced display managers like GDM and KDM will automatically detect E17 thanks to the
/usr/share/xsessions/enlightenment.desktop file provided by the
e-svn package.
Configuring the Network
You can use networkmanager to manage your network connections.
pacman -S networkmanager
Then you need to follow the instructions on NetworkManager to do the configuration. You may also need network-manager-applet to help with your settings.
pacman -S network-manager-applet
You may want to add it to the start up programs so every time your E17 starts it appears on systray.
Settings -> Settings Panel -> Apps -> Startup Applications -> System -> Network
Another available network manager is Connman, you can download it from AUR connmanAUR. You do not need to follow any of the other instructions on the Connman wiki page. The current build of ConnMan already includes network policy group section (although with only one statement, not three).
Next, edit your
/etc/rc.conf. Remove network from your DAEMONS line. Add connmand (do not forget the d) after dbus and hal.
ConnMan loads very quickly and appears to handle DHCP quite nicely. If you have installed Wpa_supplicant, ConnMan latches onto that shows all available wireless connections.
Installing Themes
More themes to customize the look of e17 are available from:
- exchange.enlightenment.org, for which you can use the e17-themesAUR AUR package
- e17-stuff.org
You can install the themes (coming in .edj format) from the configuration dialog. During 2010 there was a change in how themes work, so for older themes you may need to do the following:
edje_convert <theme>.edj
You can also change the theme for the etk toolkit (the one which is used by exhibit). You can start the dialog to change the etk toolkit by starting
Modules and Gadgets
- Module
- Name used in enlightenment to refer to the "backing" code for a gadget.
- Gadget
- Front-end or user interface that should help the end users of E17 do something.
Many Modules provide Gadgets that can be added to your desktop or on a shelf. Some Modules (such as CPUFreq) only provide a single Gadget while others (such as Composite) provide additional features without any gadgets. Note that certain gadgets such as Systray can only be added to a shelf while others such as Moon can only be loaded on the desktop.
E17 offers two modules for compositing, Composite and Ecomorph, depending on your hardware and preference.
The Composite module is the standard compositing manager provided in enlightenment. It provides some minimal compositing effects such as transparency, fade and shadow. Composite provides the more stable module and is supported on a lot hardware through either OpenGL or compositing software rendering.
The Ecomorph module is a full-featured compositing manager which was ported from Compiz for E17. It can be downloaded from AUR ecomorph-gitAUR. Some experience instability with Ecomorph while others use it without a problem. Ecomorph requires 3D acceleration, while Composite does not.
From the current source code README for Places:
- Places module
- This module manage the volumes device attached to the system.
In other words, Places is a gadget that will help you browse files on various devices you might plug into your computer, like phones, cameras, or other various storage devices you might plug into the usb port.
Scale Windows
The Scale Windows module, which requires compositing to be enabled, shrinks all open windows and brings them all into view. It can be added to the desktop as a gadget or set as a key binding.
Some people like to change the standard window selection key binding
ALT + Tab to use Scale Windows to select windows. To change this setting, you navigate to
Menu > Settings > Settings Panel > Input > Keys. From here, you can set any key binding you would like.
To replace the window selection key binding functionality with Scale Windows, scroll through the left panel until you find the "ALT" section and then find and select
ALT + Tab. Then, scroll through the right panel looking for the "Scale Windows" section and choose either
Select Next or
Select Next (All) depending on whether you would like to see windows from only the current desktop or from all desktops and click "Apply" to save the binding.
If you find some unexpected behavior, there are a few things you can do:
- try to see if the same behavior exists with the default theme
- backup
~/.eand remove it (e.g.
mv ~/.e ~/.e.back).
If you are sure you found a bug please report it directly upstream. http://trac.enlightenment.org/e/report
If X complains about X cursors not being available, install the libxcursor package.
Screen unlocking does not work
If screenlock does not accept your password add the following to
auth required pam_unix_auth.so
Unreadable fonts
If fonts are too small and your screen is unreadable, be sure the right font packages are installed:
pacman -S ttf-dejavu ttf-bitstream-vera
udisks vs. HAL
Modules may need to use underlying libraries or daemons to interact with various devices connected to your computer. Currently there are at least two choices for these underlying libraries or daemons to interact with connected devices. The two that will be considered here are udisks and HAL. At the time of this entry the HAL page says:
- HAL (Hardware Abstraction Layer) is a daemon that allows desktop applications to readily access hardware information, to locate and use such hardware regardless of bus or device type. In this way a desktop GUI can present all resources to its user in a seamless and uniform manner. HAL has become deprecated in favor of udev, udisks, upower, etc. and is no longer developed. Currently, a small number of programs still rely on and use HAL, though development is heading toward utilizing udev as a replacement.
So, apparently E17 now tries to use udisks instead of HAL. But some of the modules and gadgets, such as Places, have not been updated to use udisks yet.
Places does not work
If Places gadget look something like a blank grey area with no Gadget in it and not detecting new device, it may because the Places is still trying to use HAL. Here is the procedure to get the HAL daemon running:
Install hal-infoAUR and hal-gitAUR from the Arch User Repository. Note that hal-infoAUR is a dependency for hal-gitAUR, so you may want to install it with pacman's
--asdeps flag.
Start the hal daemon
# rc.d start hal
Now you must remove the "Places" gadget from my shelf, and unload the Places module from menu
settings -> modules -> Places -> unload
Restart enlightenment, reload the Places module and add the Places gadget to my shelf. Then Places will work normally.
Failure in mounting internal partitions
Check if user is in storge group:
# groups <user>
If user is not in storage group:
# groupadd storage # gpasswd -a <user> storage
Then create this file as root:
# nano /etc/polkit-1/localauthority/50-local.d/10-storage-group-mount-override.pkla
And write into the file:
[storage group mount override] Identity=unix-group:storage Action=org.freedesktop.udisks2.filesystem-mount-system ResultAny=yes ResultInactive=yes ResultActive=yes
For more information, see: http://bbs.archbang.org/viewtopic.php?id=2720