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Aerosol Jet Printing of Electronics: An Enabling Technology for Wearable Devices

Additive manufacturing has revolutionized the way products are designed and fabricated to include the field of printed electronics. Direct write (DW) technologies used to print three-dimensional (3D) electronic and sensor devices have experienced spectacular growth due to their capability to offer rapid prototyping of high-performance devices for a broad range of applications. This growth is driven by many factors to include significantly reduced design-to-product lead time and fabrication of complex geometries on conformal and flexible substrates. Originally developed by the Defense Advanced Research Projects Agency (DARPA) Mesoscopic Integrated Conformal Electronics (MICE) Program for the fabrication of mesoscale electronics, DW technologies have been explored for a range of applications including active and passive components, sensors, 3D structures, as well as applications in biology. This paper focuses on one emerging DW approach, Aerosol Jet Printing (AJP), as a non-contact method to print fine features using different types of materials over various surfaces. Aerosol Jet systems are able to print a wide variety of electronically, optically, and biologically functional materials on geometrically complex substrates that can be conformal, flexible, and stretchable. The Aerosol Jet process utilizes printable inks based on solutions or nanoparticle suspensions and can include metals, alloys, ceramics, polymers, adhesives, and/or biomaterials. A wide variety of substrates, to include silicon, polyimide, glass, FR-4 and aluminum oxide can be used to print these materials provided the ink is compatible with the substrate. Like other DW technologies, the AJP process offers the distinct benefit of fabrication without conventional masks, with a reduction in material consumption due to selective deposition of inks at digitally defined locations on the substrate. Use of this additive process eliminates the waste of hazardous materials used in the etching processes employed by subtractive methods. AJP systems use an atomizer to create a dense aerosol of micro-droplets that are focused into an aerosol stream, resulting in deposits that can be one tenth the size of the nozzle opening at a standoff height of up to 5 millimeters. These capabilities enable the fabrication of highly integrated devices expanding from the originally targeted mesoscale application to micro- and nano-scale applications. Design and innovative fabrication of more connected and “smart” products can be realized using AJP to meet the miniaturized, flexible, and conformal form factors desired in today's Internet of Things (IoT) global marketplace. AJP technology has opened up new avenues for bio-integrated electronics to include electronic textiles, wearable electrochemical systems, electronic epidermal tattoos, and permanent and dissolvable implantable devices. While it has been demonstrated that AJP is an enabling technology in the growing field of wearable devices, there are major challenges in widespread adoption of this innovative approach. This paper provides an overview of AJP technology and summarizes the historical underpinning of its development, underlying principles of its technique, and challenges presented in widening its adoption with industry.