11  EP 2 000 008 B1 12  rated from isolation zone 120 by a third divider and po- sitionedopposite second precursor zone 116. In the em- bodiment shown, the third divider is a middle section of upper divider 134, which includes a series of third pas- sageways 192 therethrough, spaced apart along third precursor zone 190. Similarly, a fourth precursor zone 194 for receiving a fourth precursor gas (Precursor 4) is positioned opposite secondprecursor zone 116 andsep- arated fromisolation zone 120 byan endsection of upper divider 134,throughwhicha seriesof spaced-apart fourth passageways196 are provided. Precursor 4ispreferably different from Precursor 1, Precursor 2, and Precursor 3, but may alternatively be the same as Precursor 1 to achieve deposition of alternating layers of thin film ma- terials.Third precursor zone190is isolatedfromfirst and fourth precursor zones 114, 194 by a pair of partition walls 198 at opposite ends of third precursor zone 190, each extending between upper divider 134 and an outer reaction chamber wall 132 of vessel 30. [0036] In the embodiment of FIG. 2, more than two precursor zones are utilized to fabricate multiple layers of distinct materials -for example a first ten serpentine paths may traversebetweenfirst precursor zone114and second precursor zone 116, respectively, and the next ten serpentine paths may traverse between third precur- sor zone 190 and second precursor zone 116, finally, etc., resulting in multi-layer film stacks. [0037] In one example, the system 110 illustrated in FIG. 2 may utilize TMA as Precursor 1, water as Precur- sor 2, TiCl$_{4}$ as Precursor 3, and TMA as Precursor 4 to coat 3 cycles of Al$_{2}$O$_{3}$ (approximately 0.3 nm (3Å), fol- lowed by 4 cycles of titania (TiO $_{2}$) (approximately 0,2nm (2Å)), followed by another 3 cycles of Al$_{2}$O$_{3}$. [0038] In another example, a thin film of aluminum- doped zincoxide(ZnO) may beformed utilizing a system similar tothe one shown in FIG. 2. Aluminum-dopedZnO isan opticallytransmissive conductive oxide filmthat may be useful as a substitute for more expensive indium-tin- oxide(ITO)electrodescommonlyused inelectronics and solar cells. In thisexample,diethylzinc(DEZn) or dimeth- ylzinc (DMZn) are used as Precursor 1 and Precursor 4, andeachof the first andfourthprecursor zones 114, 194 includes between 50 and 100 turning guides (i.e., the substrate transits between 50 and 100 times in each of the first and fourth precursor zones). An oxidant, such aswater, or morepreferablyozone, is used as Precursor 2, and TMA is used as Precursor 3. The third precursor zone 190 may include onlyaverysmall number of turning guides (and transits) - for example two - to deposit only a dopingamount of Aluminum oxidewithinthe bulkZnO. The substrate may then be transported through the sys- tem multiple times, in multiple passes, to achieve the desired mechanical, electrical, and optical properties. [0039] In an alternative embodiment (not illustrated), third precursor zone 190may be positionedbetweenfirst and second precursor zones 114, 116 so that isolation zone 120 straddles third precursor zone 190 and sub- strate 112 traverses across third precursor zone 190 as [0042] FIG. 4 illustrates a system 310 according to a fourth embodiment, wherein the last two digits of 300- series reference numerals designating precursor zones 314, 316, isolation zone 320, and components of sub- it is transported between first and second precursor zones 114, 116. Other variations on the configuration of system 110 are also possible, the variety of configura- tionspreferablyhaving theirvariousprecursor zonesiso- lated from each other by one or more isolation zones, to prevent precursor gases from reacting in any of the zones, except at the surface of substrate 112. [0040] A system 200 shown in FIG. 3 isnot anembod- iment according to the claimed inv ention. The system 200may be configured without rollers, yet achieve ALD- type deposition on a long thin substrate 212, such as a web, bypassing thesubstrate 212alongalinear transport path between alternating zones 202, 204, 206, etc., of precursor 1, inert gas, precursor 2, inert gas, precursor 1, inert gas, etc.InFIG. 3,exhaust or pumpinglines from precursor zones 202, 206, etc. are omitted for simplicity. Whilesystem200 wouldlikelybe much longerthanthose of FIGS. 1 and 2 for a given layer count, the system 200 of FIG. 3 could be made very thin, for example if config- ured as a straight-line system such as ones used for ar- chitectural glass coating systems. Accordingly, system 200 could be used to coat both flexible substrates and rigid substrates. It could also reduce issues arising, in the systems 10 and 110 of FIGS. 1 and 2, from contact between substrate 12 and the turn guides 64, 66 of sub- strate transport mechanism 60. In oneembodiment, pre- cursor 1 is TMA and precursor 2 is water vapor, and one pass of the substrate 212 through the system completes three ALD cycles to deposit approximately 0,3nm (three angstroms (3 Å)) of aluminium oxide (Al$_{2}$O$_{3}$). One vari- ation on the configuration of FIG. 3 would be to have a chamber with as few zones as four, e.g., precursor 1, inert gas isolation, precursor 2, and inert gas isolation, to provide one full ALD cycle. A closed-loop substrate of flexible material (not shown) could be circulated through such a system, and the number of trips or circulations of the loop substrate through the chamber would deter- mined the resulting coating thickness. [0041] Some systems and methods of the kind de- scribedhereinmay notnecessarily require highlyspecific geometry or mechanical configuration. For instance, in addition to theconfigurations illustrated inFIGS. 1-3, the substrate could be wound through a path that looks like a "zig-zag" or a sine wave, or any path, as long as the substratewinds sequentiallythrough regions that provide at least the following: (1) exposure to one precursor; (2) an isolation zone, wherein the substrate is not exposed to one of the primary precursors; (3) exposure at least a second precursor; and (4) a second isolation zone as in step (2), which may be a common zone as that used for step (2). The substrate doesnot necessarily have topass over rollers - essentially any mechanical arrangement that allows the traversal or threading of the substrate through the sequential zones would work. 7