A review on the recent developments of solution processes for oxide thin film transistors

Abstract

This review article introduces the recent advances in the development of oxide semiconductor materials based on solution processes and their potential applications. In the early stage, thin film transistors based on oxide semiconductors fabricated by solution processes used to face critical problems such as high annealing temperatures (>400 °C) required to obtain reasonable film quality, and the relatively low field effect mobility (<5 cm 2 V −1 s −1 ) compared to devices fabricated by conventional vacuum-based techniques. In order to overcome such hurdles, the proper selection of high mobility amorphous oxide semiconductor materials is addressed first. The latter involves the combination of high mobility compounds and multilayered active stacks. Ensuing overviews are provided on the selection of optimum precursors and alternative annealing methods that enable the growth of high quality films at relatively low process temperatures (<200 °C). Reasonably high field effect mobility values (~10 cm 2 V −1 s −1 ) could thus be obtained by optimizing the above process parameters. Finally, potential applications of solution processed oxide semiconductor devices are summarized, involving, for instance, flexible displays, biosensors, and non-volatile memory devices. As such, further innovations in the solution process methods of oxide semiconductor devices are anticipated to allow the realization of cost effective, large area electronics in the near future.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…36,88 In particular, the possibility to replace vacuumprocessing techniques with higher throughput continuous processes is especially attractive in view of novel large-area and cost-effective applications, such as foldable and printable displays, disposable smart labels, and intelligent packaging. 87,116 To this aim, solution-processing techniques, especially spray pyrolysis (SP) or digitally controlled ondemand deposition methods like ink-jet printing, are gaining an increasing interest. 87 Another open issue is represented by the development of metal oxide semiconductor TFTs with good p-type conduction.…”

“…(B) Alternatively, the precursor solution is first deposited and then converted to the final metal oxide semiconducting material, most commonly via thermal annealing at temperatures in the range of 200 to 500 C, or alternatively via UV irradiation. 87,116,197,200,224,239 The benefit of approach (A) is that the deposition is decoupled from the synthesis, and therefore also from potentially high process temperatures. Using approach (A), crystalline metal oxide semiconductors can thus be easily synthesized and further tailored through their size and shape.…”

“…244 The commonly high thermal budget required in approach (B) strongly limits the choice of the flexible substrates to materials such as PI 145,193 or PAR. 192 Nevertheless, recent efforts have been devoted to the reduction of the annealing temperatures required to solution-process metal oxide semiconductors (and also gate dielectrics) 87,116,119,237,245 which consequently allows selecting a wider range of substrate materials, including PEN, 196,197,228 and PET. 194,229 c. Deposition methods.…”

Design, Properties, and TFT Application of Solution‐Processed In‐Ga‐Cd‐O Thin Films

“…In recent two decades, solution‐processed semiconductors and their devices have attracted increasing attentions, because the solution method allows deposition of thin films in air via a roll‐to‐roll process and/or by the directly patterning printing without incorporating photolithography for mass production, and possesses some other beneficial features such as the precise control of the cation‐anion stoichiometry together with metal cation ratios . To date, a variety of solution‐processable metal oxide semiconductors such as indium zinc oxide (In‐Zn‐O), zinc tin oxide (Zn‐Sn‐O), indium gallium zinc oxide (In‐Ga‐Zn‐O), and zinc indium tin oxide (Zn‐In‐Sn‐O), have been extensively explored as potential channel materials for thin‐film transistor (TFT) application providing reasonable electrical characteristics.…”

“…To date, a variety of solution‐processable metal oxide semiconductors such as indium zinc oxide (In‐Zn‐O), zinc tin oxide (Zn‐Sn‐O), indium gallium zinc oxide (In‐Ga‐Zn‐O), and zinc indium tin oxide (Zn‐In‐Sn‐O), have been extensively explored as potential channel materials for thin‐film transistor (TFT) application providing reasonable electrical characteristics. Among all of these oxide semiconductors, amorphous/nanocrystalline In‐Ga‐Zn‐O is investigated most frequently, because it demonstrates outstanding electrical performance and meter‐scale uniformity in vacuum‐based processing, and has been commercially used as the channel material of TFTs for backbone electronics of active matrix liquid crystal displays (AMLCDs) and active‐matrix organic light‐emitting diode displays (AMOLEDs) . However, the electrical performance of solution‐processed devices can not be competitive to that of vacuum‐based counterparts as yet.…”