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p { margin-bottom: 0.1in; line-height: 120%; }a:link { }Smarttextiles or Electronic textiles is the combination of electronics andtextiles into fabrics and clothing which are able to sense, compute,communicate and so many other features. These days, fabrics are thenew silicon wafers;they have generated much interest due to theadvent of soft computing and portable devices. An applied approach tofabricate electronic textiles is to combine textile substrates withrigid printed circuit boards (PCBs), allowing the integration oftransistors, logic gates, sensors, microprocessors, storage units andother communication interfaces into textiles. Amorphousindium-gallium-zinc-oxide (IGZO) as semiconductor material hasattracted a lot of awareness as the material is quite flexible andallows the fabrication of various transistors having increasedswitching speed compared to amorphous silicon TFTs due to the higherelectron mobility of IGZO.

The strips called e-strips fabricated withthese transistors are made and can be situated inside yarn or fabricfor circuit applications. The e-strips are woven into textiles inweft direction using an industrial weaving machine. These e-stripshave Thin film transistors fabricated on it and can be used toconnect circuits allowing circuitry for various logic gates likeAND,NAND,EXOR etc. The application of flexible e- strips assubstrates for electronic devices allows the integration of a varietyof thin-film devices such as interconnect lines and integratedcircuits (ICs) based on silicon and surface mount devices (SMDs) . INTRODUCTIONTheconvergence of electronics with textiles offers variety ofapplications in all scenarios. Electronic or smart textiles alsoknown as e-textiles assures to have a significant impact in areassuch as wearable computing, large-area electronics and fashiontextiles . Potential areas of application include health care,sports, fashion industry .

Here, the vision is of an e-textileconsisting of a fabric that maintain all the properties of textilefibers, like comfort, washability, drapability ,softness orstretchability and combines them with electronic functionality forbetter results. The foregoing electronic functionality often refersto different sensors like for temperature strain, posture, or otherphysiological signals but also includes the associated conditioningcircuits, power supply, signal processing or transmissionelectronics. To a certain extent, the span of e-textiles ranges fromconventional electronics attached to textiles to electroniccomponents build from active textile yarns. A measured approach forfabrication of transistors on fabrics is the integration of flexibleelectronics into a woven textile. Here, the use of flexible plasticstripes as carriers for thin-film devices and standard silicon chips,represents a good compromise between the electrical and mechanicalproperties of the final textile device . Addition to that, theintegration of electronic fibers and conductive yarns in the weft andwarp direction of a woven fabric also enables the fabrication of morecomplex systems inside a textile.

We can also fabricate themechanically flexible active electronic devices directly on circularfibers. Additionally,yarns usable for the fabrication of textiles exhibit diameterssignificantly below 1 mm, which results in a highly curved surface.These challenges can be addressed by new developments in the area offlexible electronics.

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In particular the use of oxide semiconductors,such as amorphous In-Ga-ZnO (IGZO) , promises to realize highperformance active electronic devices on a variety of substrates.Here, we evaluated how IGZO thin-film transistors (TFTs),representing the most important andbasic building block of all electronic systems, can be fabricated ona variety of different yarns. It is shownthat high performance TFTs, on glass fibers with a radius of 62.5 ?mand on polymer fibers with aradius of 125 ?m, are fully functional and can be integrated intotextiles for wearable or industrial applications.

THINFILM TRANSISTORS (TFTs)Flexibleelectronics and in particular flexible thin-film transistors are keycandidates for integration into textiles. Amorphous Indium-Gallium-Zinc-Oxide (IGZO) was presented for the first time in 2004 as asemiconductor material for thin-film transistors (TFTs) on flexibleplastic substrates. IGZO TFTs are beneficial for fabrication onflexible plastic substrates, because IGZO can be sputtered at roomtemperature while the process temperatures to fabricate drain,source, gate contact and gate insulators are below 150 C. Processtemperatures not exceeding 300 C are imperative due to temperaturestability of for example polyimide foils.

Furthermore, the electronmobility of room temperature sputtered IGZO is about 10 times largerthan the electron mobility of amorphous silicon . IGZO TFTs can bedesigned to operate at 5 V with a threshold voltage around 0.5 V.Since IGZO TFTs can be fabricated on flexible plastic foils, theimpact of bending and hence applying strain in the TFT layers isinvestigated . Bending IGZO TFTs is mainly motivated to enableflexible displays. Bending radii as small as 3 mm corresponding to0.7 % strain in the TFT layers are reported. Due to the higherelectron mobility of IGZO TFTs compared to TFTs made of amorphoussilicon, faster switching speeds of the tran- sistors are possibleand the fabrication of circuits becomes attractive.

To demonstratethe switching speed of transistors, ring oscillators are commonlyapplied. In, five-stage and seven-stage ring oscillators werefabricated and propagation delays per stage of 240 ns and 48 ns arereported, while operating with supply voltages of 18 V and 25 V,respectively. Basic circuits such as shift registers, inverters andNAND gates are presented in 44, 45, 46. 44 demonstrates a shiftregister operated at 20 V, while in 45 inverters operating at 10 Vare shown. NAND gates and inverters representing the basic buildingblocks for digital circuits are demonstrated in 46. The circuitsoperate at 5 V and can be bent to a radius of 3.5 mm corresponding toa strain of 0.

6 %. The system on panel concept, described in 7, tointegrate sensors, actuators and the required control electronics ona single flexible foil, requires analog circuits and in particularamplifier circuits. Since mechanical strain changes thecharacteristics of single IGZO TFTs, it is important to characterizethe behavior of analog circuits subjected to mechanical strain. Athin-film transistor (TFT) isa special kind of field-effect transistor made by depositing of anactive semiconductor layer as well as the dielectric layer andmetallic contacts over a supporting (but non-conducting) substrate.

Acommon substrate is glass, because the primary application of TFTs isin liquid-crystal displays. This differs from the conventionaltransistor, where the semiconductor material typically isthe substrate, such as a silicon wafer.TFTscan be made using a wide variety of semiconductor materials. A commonmaterial is silicon.

The characteristics of a silicon-based TFTdepend on the silicon’s crystalline state; that is, the semiconductorlayer can be either amorphous silicon, microcrystalline silicon,or itcan be annealed into polysilicon.Other materials which have been used assemiconductors in TFTs includecompound semiconductors such as cadmium selenide, or metal oxidessuch as zinc oxide or hafnium oxide. An application for hafnium oxideis as a high-? dielectric.

TFTs have also been made usingorganic materials, referred to as organic field-effect transistors orOTFTs.TFTON FIBRESRather than regular substrates used for the creation of electronicthin-film devices, for example, semiconductor wafers, glass platesetc. the mechanical and geometrical properties of fibres and yarnsare less advantageous. Hence, the successful fabrication oftransistors requires a modification of the fabrication process and aproper selection of suitable yarns or fibers.a range of possible substrate fibers e.g. steel and cotton yarns,nylon fibers with different diameters, glass fibers, and thininsulated metal Cu wire.

All materials have certain advantages anddisadvantages concerning the fabrication of smart textiles but hereare most important parameters for the fabrication of TFTs inelectronic textiles:ChemicalpropertiesThe chemical stability of the fiber material is a key aspect sincethe fibers have to resist the etchants and solvents used during thefabrication process. In this respect the metal and glass fibersexhibit the most beneficial properties. TemperatureresistanceThe melting or glass transition temperature of the evaluatedmaterials can significantly limit the choice of usable depositiontechnologies. While the maximum temperature of cotton and nylon is inthe range of 200 ?C, the glass fiber can be processed attemperatures above 1000 ?C. FibersurfaceThin-film devices are made from active layers with thickness in thenanometer range, hence the surface of the fibers has to be as flat aspossible. While the steel and cotton yarns do not exhibit acontinuous surface, also the surface roughness of the other fibersvaries strongly.

ConductivityNon-conductive fibers (glass, cotton, nylon) have the advantage thatno additional insulation layer is needed, and all electronic deviceson their surface are decoupled from each other. Metallic substratefibers at the same time, could simplify the device structure byproviding electronic functionality themselves. Here an interestingoption could be the use the insulated Cu wire as substrate fiber,gate contact and gate insulator simultaneously. TextilepropertiesUnobtrusive smart textiles needs electronic fibers which are soft,bendable, and with dimensions comparable to the textile yarns of thefabric. In this respect cotton but also steel yarns have beneficialproperties.

Similarly, polymer fibers such as nylon are common.Anyway, the diameter of the nylon fibers should not be too large (750 ?m ). Furthermore, thin Cu wires are bendable and can be imperceptible whenintegrated into a textile . Glass fibers on the other hand exhibit asmall diameter, but their minimum bending radius is limited to ?5cm. FABRICATIONAPPROACHESTodetermine the most appropriate manufacturing process, we evaluatedtwo different approaches to fabricate TFTs on fibers. The first isdirect fabrication of devices on nylon and glass fibers usingstandard semiconductor manufacturing equipment. The second one istransfer of TFTs, fabricated on flat and thin substrates, todifferent fibers, and yarns.