Flexography‐Printed In₂O₃ Semiconductor Layers for High‐Mobility Thin‐Film Transistors on Flexible Plastic Substrate

Abstract

uniform, continuous and dense layers and is thus more suitable for printed TFTs with larger channel dimensions. Several precursor routes for solution-processed metal-oxide semiconductor layers based on metal alkoxides, [ 14,15 ] and on metal salts such as acetates, nitrates, and chlorides have been reported. [ 16,17 ] Precursors based on metal nitrates have been shown to convert into metal oxides generally at lower temperatures than acetateor chloride-based precursors. [ 17,18 ] In contrast to metal alkoxides, metal nitrates are less sensitive to air humidity and can be processed via an aqueous precursor route. [ 7 ] Based on these advantages, metal nitrates show promise as potential precursor materials for printed low-temperature-processed metal-oxide semiconductors. A large amount of work has concentrated on lowering the conversion temperature of the precursor solutions to semiconducting metal-oxide layers. Functional TFTs have been obtained at ≈200 °C or below (1) via the careful design of precursor chemistry utilizing metal alkoxides with controlled hydrolysis, [ 14,15 ] combustion process, [ 11,19 ] or the addition of oxidizing agents, [ 20 ] (2) via the use of additional energy in conversion such as various wavelengths of UV light, [ 8,15,21 ] or microwaves, [ 22 ] or (3) by employing conditions during annealing that promote effi cient precursor conversion such as ozone or vacuum. [ 6,7,20 ] After the fi rst report on inkjet-printed metal oxide layers from metal chloride precursors by Lee et al. in 2007, [ 16 ] the deposition of metal-oxide semiconductor layers for TFTs has been successfully performed via several printing techniques. [ 4 ] In addition to inkjet-printing, [ 12,16,17,19,23 ] metaloxide TFTs have been fabricated with electrodynamic-jet, [ 24 ] spray pyrolysis, [ 9 ] gravure (glass substrate, 550 °C annealing), [ 25 ] and fl exographic printing (Si wafer, 450 °C annealing). [ 26 ] The inkjet, electrodynamic jet, and spray pyrolysis techniques are typically utilized in noncontact sheet-to-sheet batch processes while the contact gravure and fl exographic printing are readily available also as continuous high-throughput roll-to-roll processes. Also novel combinations of conventional vacuum processes and techniques well known from the fi eld of printing have been proposed to prepare metal-oxide TFTs on fl exible substrates such as inkjet-printed growth inhibitors for the patterning of atomic-layer-deposited (ALD) metal-oxide layers, [ 27 ] and transferring of vacuum-processed functional TFTs from rigid to fl exible substrates by a roll-transfer method. [ 28 ] The previous results clearly indicate the challenges in the processability of materials that need to be overcome to enable large-area electronics fabrication using the industrial high-throughput additive printing processes on fl exible low-cost substrates.In this work, for the fi rst time, the metal-oxide TFT fabrication process was performed on fl exible substrate using process technologies that are roll-to-roll-compatible and industrially...

Metal oxide semiconductor thin-film transistors for flexible electronics

“…83 Recently, promising results of the first roll-to-roll compatible fabrication of In 2 O 3 patterns on PI substrates via flexographic printing have also been demonstrated. 250 f. Device configuration. The majority of the reported flexible n-type solution-processed metal oxide semiconductor TFTs are fabricated in BG staggered configuration with only few devices in BG coplanar, 145,196 TG staggered, 226 or TG coplanar setup.…”

“…. 191,[193][194][195][196][197]200,220,221,[223][224][225]250 (III) The third and last group presents a few examples of devices with l FE ! 10 cm 2 V À1 s…”

64-4:Invited Paper: Printed Metal Oxide Transistors

“…Most recently, Alastalo et al reported flexography-printed In 2 O 3 semiconductor layers for high-mobility thin-film transistors on flexible plastic substrate. Indium nitrate salt in 2ME was used as precursor solution [20]. The printing process resulted in an enhancement-mode In 2 O 3 TFTs on ALD-grown amorphous A l2 O 3 with a mobility value, P sat | 8 cm 2 /Vs.…”

Radiation‐Tolerant Flexible Large‐Area Electronics Based on Oxide Semiconductors

“…Only a dedicated processing technology and reduced thickness of oxide dielectrics [ 17 ] allows preparing radiation hard CMOS components withstanding 100 krad(Si), as necessary for example for space applications. [ 8,20 ] Importantly, HMSO can be considered an intrinsically stable semiconducting material class due to the high formation energy of the oxide based ionic lattice and their amorphous structure. HMSOs already fi nd commercial application in displays as they combine outstanding electronic transport properties with transparency.…”