9  EP 2 000 008 B1 10  will therefore require tension control and/or drive control systemsof thekindwellknownin theart of webhandling andcoilhandling systems.Additionalturning guidesmay be provided for determining the transport path of sub- strate 12 through, and in some embodiments, into, the vessel 30. For example, additional turning guides (not shown) may be required to compensate for changes in the diameter of the input and take-up rolls 74, 86 during operation of system 10. [0031] Depending on the configuration of substrate transport mechanism 60 and passageways 54, 56, the transport path of substrate 12 may have a serpentine profile, a sawtooth profile, or any other suitable shape for transporting substrate between first and second pre- cursor zones 14, 16. Substrate 12 preferably threads through passageways 54, 56 and traverses isolatio zone 20 in a direction normal to the plane of dividers 32, 34,such thatopposingpairsof first and second passage- ways 54, 56 are aligned with a traversal axis normal to dividers32,34.However,otherarrangementsandtrans- port path configurations may also be utilized. [0030] Turning guides 64, 66 may comprise rotating guide supports, such as rollers, pulleys, sprockets, or pinch rollers,aswellasnon- rotating guidesupports, such as guide bars, rails, or channels. Suitable rotating guide supports include both idlers, e.g. idler rollers, and driven rotatingsupports- the latter beingdrivenbya drive mech- anism (not shown) that may include means for synchro- nizing the rotating guide supports with each other and withpayout spool72and/or take-up spool 82. Non- rotat- ingguide supports maypreferablyinclude abearing sur- face made of or coated with a low-friction material, such as PTFE (TEFLON™). In one embodiment, turn guides64, 66may comprisefluid bearings(e.g. gasbear- ings) that support substrate 12 on a dynamic cushion of fluid, such as precursor gas and/or inert gas inject ed through small perforations in a bearing race of the fluid bearing. [0032] Intheembodimentshown,eachofthefirstturn- ingguides64 ispositionedwithinthefirst precursor zone 14 and supports substrate 12 as it turns 180° about the turning guide 64 toward the second precursor zone 16. Similarly, each of the second turning guides 66 is posi- tionedwithinthe second precursorzone16 andsupports substrate 12 as it turns 180° about the turning guide 66 toward the first precursor zone 14. In an alternative em- bodiment (not shown), only some of the turning guides 64, 66 may support substrate 12 as it turns toward the opposite precursor zone. For example, two turn guides may be used for asingle 180° turn, each support- ingthe substrate through 90° ofthe turn. In other embod- iments, substrate 12 may turn through somewhat more or less than 180° between traversals of isolation zone 20. A turn of greater than 180° could be implemented to fit more turning guides, and therefore more deposition cycles, within a systemof agiven overall length.A transit path ofsubstrate 12through precursor zones14, 16may be curved and/or straight. In one embodiment  shown), someorallof the first and secondturningguides may be located outboard of the respective first and sec- ond precursor zones such that the substrate follows a straight transit path completelyacrosstherespective pre- cursor zone nearest the turning guide and through pas- sagewaysin dividers bordering the inboard and outboard sides of the respective precursor zone. [0033] The system 10 illustrated in FIG. 1 includes ten first turning guides 64 and ten second turning guides 66, providing ten full cycles of ALD growth. In one example, the system of FIG. 1 may be used to deposit a coating of aluminum oxide (Al$_{2}$O$_{3}$) approximately 1,0 nm (ten angstroms (10 Å)) thick using trimethylaluminum (TMA) asPrecursor1 andwaterasPrecursor 2.AdditionalALD cycles may be added to system 10 by adding pairs of turning guides. For example, a 100- cycle system may have 200 turning guides -100 first turning guides 64 and 100 second turning guides 66. By using small-diameter guide rollers or other turning guides, suchasystem could be as small as one meter long from the input roll 74 to the take-up roll 86, approximately 50 cm high, and only slightly wider than the width of substrate 12. Systems capable of 500, 1000, 5000, or more ALD cycles in a single pass are also envisioned. Similar expansions are possible in the systems of FIGS. 2 and 4, described be- low. [0034] To increase film thickness beyond what is de- posited ina single passthrough system10 bythe number of ALD cycles defined by transport mechanism 60, the substrate10 maybepassed through the systemmultiple times, either by moving the take-up roll 86 from the sec- ond end 84 to the first end 76 after a pass, by reversing the transport direction of the substrate 12 to send it back through the system, or by using a closed-loop substrate that circulates back to the input side 76 for achieving multiple passes through the system without movement or handlingofthe bulkroll. Inbetween sequential passes, oneor more ofthe precursors withinthe precursor zones 14, 16 may be changed to provide a multi-layer coating stack of two or more thin film materials. [0035] FIG. 2 illustrates a system 110 and method ac- cording to a second embodiment for depositing layers of different materials on a flexible substrate 112 in a single pass through system 110. In the embodiment of FIG. 2, multiple separate precursor zones are located in se- quence along the lengthof the reaction chamber. In FIG. 2, 100-series reference numerals with the last two digits similar to the reference numerals of FIG. 1 designate similar components. For example, system 110 includes a first precursor zone 114 supplied by a first precursor delivery system 124, a second precursor zone 116 sup- plied by a second precursor delivery system 126, and an isolation zone 120 supplied by an inert gas delivery sys- tem 128. System 110 of FIG. 2 further includes a third precursor zone190 intowhicha thirdprecursor gas(Pre- cursor 3) different from the first and second precursor gases (Precursor 1 and Precursor 2) is introduced when the system is in use. Third precursor zone 190 is sepa- 6