Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors with a Low-Temperature Polymeric Gate Dielectric on a Flexible Substrate

Abstract

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a solution-processed polymeric gate dielectric of cross-linked poly(4-vinylphenol) (c-PVP) film were fabricated on a poly(ethylene terephthalate) (PET) substrate on which an a-IGZO film, as the active channel layer, was deposited by radio frequency (RF) sputtering. The entire TFT fabrication process was carried out at a temperature below 110 °C. The device exhibited an on/off ratio of 1.5×106 and a high field-effect mobility of 10.2 cm2 V-1 s-1, which is, to our knowledge, the best result ever achieved among a-IGZO TFTs with polymeric gate dielectrics on a plastic substrate.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Due to their properties and their availability, polymers are the natural choice and the most commonly used substrate materials. Among the different polymers, polyimide (PI) foils with thicknesses (t S ) between 5 lm and 125 lm are the most frequently utilized substrates, 135,145,152,157,158,160,165,172,177,180,184,188,189 together with PI and nano silica. 142,144 This is because of the numerous advantages of PI (commercially known as Kapton V R ), like a small coefficient of thermal expansion (CTE) of 12 Â 10 À6 K, a small humidity expansion coefficient (HEC) (9 Â 10 À6 %RH), a high T G of %360 C, and a surface roughness in the nanometer range.…”

“…114,155 Since standard PI exhibits a yellowish to brownish color, other polymeric substrates have been introduced to benefit from their transparency in the visual wavelength range. These materials, which are, in general, also cheaper and more easily available, include PET, 29,69,96,165,171,180,184,188 polyethylene naphthalate (PEN), 38,40,41,134,136,139,149,153,158,163,[166][167][168]173,181,202 polyetheretherketone (PEEK), 203 polycarbonate (PC), 154,157 polypropylene (PP) based synthetic paper, 204 parylene, 80,141 polyethersulfone (PES), 178 water-soluble polyvinyl alcohol (PVA), 82 as well as polydimethylsiloxane (PDMS). 78,132,147,[205][206][207] In particular, PDMS is also stretchable and biocompatible, but at the same time hard to process using standard fabrication techniques.…”

“…134,142,159,160 Besides metal oxide dielectrics, also organic materials have been used as gate dielectric, such as layers made from olefin polymers, 38 or cross-linked PVP (c-PVP). 165 To this regard, a direct comparison of c-PVP and SiO 2 showed that both materials have a comparable R and result in flexible IGZO TFTs with similar performance parameters, 165 although the thick c-PVP layer (t ox ¼ 280 nm) reduces C ox if compared with the thinner SiO 2 (t ox ¼ 170 nm). A third class of gate dielectrics is ferroelectric materials, in particular, poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)].…”

“…79 This is because the dielectric properties are determined by an arbitrary serial and parallel combination of discrete fiber capacitors within the paper substrate. The large choice concerning possible dielectrics results in a big variety of published C ox values ranging from 1.2 Â 10 À4 F m À2 measured for an organic layer 165 up to 1.3 Â 10 À1 F m À2 for a solid electrolyte. 184 Finally, ZnO was sandwiched between two layers of Al 2 O 3 to create a charge trapping layer in the gate dielectric, leading to non-volatile memory TFTs.…”

“…90 Multi-layer metals offer, in general, a compromise between good adhesion and high conductivity, especially in the case of Ti/Au, 23,96,181 Ti/Cu, 135 Cr/Au, 174 or Ti/Au/Ti gate stacks. 162 Besides metals and metal alloys, ITO, 29,69,78,80,135,139,165,177,180,184,188,205 IZO, 77,79,133,160,208 In 2 O 3 , 171 and aluminum zinc oxide (AZO) have been used to fabricate transparent gate contacts. 93,134 Furthermore, duallayers of metal and ITO 40 or IZO have also been employed.…”