High-performance low-temperature solution-processable ZnO thin film transistors by microwave-assisted annealing

Abstract

Oxide semiconductors afford a promising alternative to organic semiconductors and amorphous silicon materials in applications requiring transparent thin film transistors (TFTs). We synthesized an aqueous inorganic precursor by a direct dissolution of zinc hydroxide in ammonium hydroxide solution from which a dense and uniform ZnO semiconducting layer is achieved. Solution-processed ZnO-TFTs prepared at 140 C by microwave irradiation have shown enhanced device characteristics of $1.7 cm 2 V À1 s À1 mobility and a $10 7 on/off current ratio, with good air stability. Spectroscopic analyses confirmed that such a device improvement originates from accelerated dehydroxylation and better crystallization at low temperature by microwave irradiation. Our results suggest that solutionprocessable oxide semiconductors have potential for low-temperature and high-performance applications in transparent devices.

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

“…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.…”

“…By combining the demonstrated process with available UV-based low-temperature annealing schemes, [ 8,15,21 ] roll-printed metal-oxide TFT devices and circuits on low-cost plastic substrates can be achieved in the future. [ 22 ] the solution was stirred at 75 °C for more than 12 h and fi ltered prior using with a 0.45 µm pore size glass fi bre fi lter. The water content of the ready ink was measured to be ≈1 wt% with Karl Fischer titration (Mettler Toledo DL37), thus indicating the presence 2.5 of crystal H 2 O per In-atom.…”

Overview of electroceramic materials for oxide semiconductor thin film transistors

“…In addition, the starting Zn solutions were prepared by directly dissolving Zn(OH) 2 in aqueous ammonia solutions, to produce a so-called 'impurity-free precursor'. The use of zinc hydroxide allowed for low-temperature ZnO formation, indicating rapid, low-energy kinetics of metal-amine dissociation and simple dehydration and condensation reactions to form ZnO films [61,62]. The undoped ZnO (140°C under microwave-assisted annealing) and Li doped ZnO TFTs (300°C annealing) exhibited remarkable performance: μ fe~1 .7 cm 2 /V · s and 11.45 cm 2 /V · s for undoped and Lidoped devices, respectively.…”

“…The third process is a simple and novel 'aqueous route' for fabricating oxide TFTs at annealing temperatures below 200°C, suggested by several researchers [60][61][62]. The suggested aqueous route provides low-temperature oxideformation and good stability by restricting the hydrolysis and condensation reactions within a solution state.…”

Zinc Oxide Thin-Film Transistors Fabricated at Low Temperature by Chemical Spray Pyrolysis

“…There has been encouraging progress with ZnO. Using spin-coating, Yu et al 4 achieved a mobility of 4 cm 2 /Vs for devices fabricated at 300 °C, while Xu et al 5 and Jun et al 6) have demonstrated mobilities of approximately 0.5 cm 2 /Vs using the same processing method, but with a 150 °C annealing temperature.…”