Printed Oxide Thin Film Transistors: A Mini Review

Abstract

Compared to conventional amorphous silicon (a-Si) TFTs, amorphous metal oxide TFTs have superior device performance such as higher mobility, better sub-threshold swing, and lower off-state current. Amorphous metal oxide TFTs have an additional advantage on the device uniformity due to the lack of grain boundary issues in the poly-Si TFTs. Compared with sputtered oxide TFTs, metal oxide TFTs with solution processes have better flexibility and controllability to adjust the composition of chemical solution. Among various solution-based approaches, direct printing is a promising low-cost technique in fabricating TFTs. The printing technique offers several advantages in manufacturing electronics such as a direct writing of materials, reduction of chemical waste, and reproducibility with high-resolution scale, which are not affordable from other solution-based approaches. While many printed OTFTs have been reported, relatively fewer studies, associated with printed metal oxide TFTs, have been pursued. Interests to printed metal oxide TFTs have grown continuously since the first report of a general route toward printed oxide TFTs. A variety of metal oxide materials have been reported as the channel layer of printed metal oxide TFTs. In this mini review paper, the development of printed metal oxide TFTs was discussed including the ink formulations, the types and characteristics of the applied printers, and fabricated thin film transistor characteristics. Lastly the review is concluded with a concise summary and future outlook from an industry perspective. Thin film transistors (TFTs), first reported by Lilienfeld and Heil almost nine decades ago, have continuously being developed and improved for low cost electronic switches.1,2 Advanced fabrication techniques and materials expand its application to low cost, large size, high resolution, and high-speed flat panel displays.3 The greatest advancement was accompanied with the advent of a-Si:H as a semiconductor channel layer.4 Although a-Si:H semiconductor exhibited lower electronic properties (carrier mobility ≤ 1 cm 2 /Vs) than TFTs based on polycrystalline channel layers (e.g. CdS), the electronic transport properties of a-Si:H were sufficient as switching elements in Liquid Crystal Displays, along with other benefits such as lower cost, high uniformity and excellent reproducibility in large area fabrication. However, lower performances of a-Si:H TFTs limit its application in AMOLED display. Metal oxide semiconductors have been intensively researched over the past decade due to their superior electrical properties including high carrier mobility (∼1-100 cm 2 /Vs), high optical transparency, good thermal/environmental durability, and potentially low-manufacturing cost.5,6 Significant progress of metal oxide TFTs has demonstrated the advantages over a-Si:H TFTs as next candidate for high-performance display applications. 7,8 In terms of manufacturing metal oxide semiconductors as the active channel layers in TFTs, gas-phase deposition technique that requires high vacuum f...

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

“…[ 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.…”

“…[1][2][3][4] Metal-oxide TFTs offer advantages over organic TFTs such as a higher charge carrier mobility that leads to higher achievable current density and circuit speed. [ 3 ] In contrast to the widely used a-Si semiconductor, where the conduction band is based on covalently bonded Si atoms with highly directional hybridized sp 3 orbitals, n-type metal-oxide semiconductors such as In 2 O 3 , In-Zn-O (IZO), and In-Ga-Zn-O (IGZO), where the conduction band is made of spherical s -orbitals with lower dependence of interatom wave function overlap on the bond angles between neighboring metal atoms, have shown to exhibit nearly as high charge-carrier mobility in amorphous fi lms as in crystalline fi lms and typically beyond that of a-Si.…”

“…[6][7][8][9][10][11][12] Metal-oxide semiconductor layers can be solution processed from stabilized nanoparticle dispersions or from sol-gel-precursor solutions. [ 3,4 ] Nanoparticles typically require high temperature sintering (>400 °C) to allow a connected network of particles and to remove dispersion stabilizing encapsulants. Although recently, chemical removal of the stabilizing encapsulant of In 2 O 3 nanoparticles has been shown to enable low processing temperatures and allow good TFT performance when combined with short TFT channels (≈10 µm) and an electrolyte-gate, [ 13 ] the metal-oxide precursor route yields readily more semiconductor and dielectric layers, respectively.…”

P‐215: Organic‐Inorganic Hybrid Thin‐film Photo‐detector for Fingerprint Recognition

“…Except for the OPD part, driving part is indispensable to fulfill the function of fingerprint recognition. For this driving part, oxide (IGZO) TFT has been selected considering its superior performance such as higher mobility, better sub-threshold swing, and lower off-state current, compared to conventional amorphous silicon (a-Si) TFT [6].…”

All‐solution‐printed oxide thin‐film transistors by direct thermal nanoimprinting for use in active‐matrix arrays

“…In oxide TFTs, a lot of good oxide inks are available thanks to the studies of solution processing. As a result, TFTs with relative good performance have been developed by several kinds of printing methods [6][7][8][9][10][11][12]. However, when they come to scalability, printing technologies significantly lack scalability and pattern fidelity compared with photolithography.…”