This paper presents device designs, circuit demonstrations, and dissolution kinetics for amorphous indium–gallium–zinc oxide (a-IGZO) thin film transistors (TFTs) comprised completely of water-soluble materials, including SiNx, SiOx, molybdenum, and poly(vinyl alcohol) (PVA). Collections of these types of physically transient a-IGZO TFTs and 5-stage ring oscillators (ROs), constructed with them, show field effect mobilities (∼10 cm2/Vs), on/off ratios (∼2 × 106), subthreshold slopes (∼220 mV/dec), Ohmic contact properties, and oscillation frequency of 5.67 kHz at supply voltages of 19 V, all comparable to otherwise similar devices constructed in conventional ways with standard, nontransient materials. Studies of dissolution kinetics for a-IGZO films in deionized water, bovine serum, and phosphate buffer saline solution provide data of relevance for the potential use of these materials and this technology in temporary biomedical implants.

Water-soluble thin film transistors and circuits based on amorphous indium-gallium-zinc oxide.

Nitrogen-doped amorphous oxide semiconductor thin film transistors with double-stacked channel layers

Development and analysis of nitrogen-doped amorphous InGaZnO thin film transistors

The nitrogen-doped amorphous oxide semiconductor (AOS) thinfilm transistors (TFTs) with double-stacked channel layers (DSCL) were prepared and characterized. The DSCL structure was composed of nitrogen-doped amorphous InGaZnO and InZnO films (a-IGZO:N/a-IZO:N or a-IZO:N/a-IGZO:N) and gave the corresponding TFT devices large field-effect mobility due to the presence of double conduction channels. The a-IZO:N/a-IGZO:N TFTs, in particular, showed even better electrical performance (µFE = 15.0 cm2・V−1・s−1, SS = 0.5 V/dec, VTH = 1.5 V, ION/IOFF = 1.1 × 108) and stability (VTH shift of 1.5, −0.5 and −2.5 V for positive bias-stress, negative bias-stress, and thermal stress tests, respectively) than the a-IGZO:N/a-IZO:N TFTs. Based on the X-ray photoemission spectroscopy measurements and energy band analysis, we assumed that the optimized interface trap states, the less ambient gas adsorption, and the better suppression of oxygen vacancies in the a-IZO:N/a-IGZO:N hetero-structures might explain the better behavior of the corresponding TFTs.

Amorphous Oxide Thin Film Transistors with Nitrogen-Doped Hetero-Structure Channel Layers

Flexible InGaZnO (IGZO) thin-film transistors (TFTs) having more than 85% optical transparency in the visible regime were fabricated on polyethylene naphthalate substrates using a selective wet etching process at a maximum temperature of 150 °C. An etch selectivity of >15 was used to pattern Al-doped ZnO S/D contacts on IGZO channel layers in a back-channel etch process. Flexible IGZO TFTs exhibited a field-effect mobility of ∼9.5 cm2/V s, threshold voltage of ∼4 V, subthreshold swing of 0.5 V/decade, and an Ion/Ioff ratio of ∼107. Similar I-V characteristics were measured for flexible TFTs under flat, tensile and compressive strain while a 3.8 V threshold voltage shift was observed after application of a dc gate-bias for 3600 s with the TFTs operating in the linear regime.

Selective wet-etch processing of optically transparent flexible InGaZnO thin-film transistors

Effect of the oxygen flow rate for active-layer deposition on the thermal stability of amorphous InGaZnO thin film transistors (a-IGZO TFTs) was investigated. The transfer characteristics of a-IGZO TFTs were measured at temperatures ranging from 298 to 398 K and a simple analytical model was used to relate the threshold voltage $({\rm V}_{\rm th})$ decrease with increasing temperature to the formation of the point defects in a-IGZO films. Lower oxygen flow rate for active-layer deposition was proved to improve the thermal stability of a-IGZO TFTs, as was confirmed to be due to the increase in defect formation energy with the oxygen flow rate decreasing by the related theoretical analysis and XPS measurements.

Thermal Stability of Amorphous InGaZnO Thin-Film Transistors With Different Oxygen-Contained Active Layers

The present invention provides a method for manufacturing a thin-film transistor substrate, which has a simple process and achieves an excellent contact interface between an oxide semiconductor layer and source/drain terminals through successive film forming so as to prevent crowding effect resulting from excessive contact resistance. Further, by using a metallic material containing tantalum to make the source/drain terminals and applying an etchant solution containing hydrogen peroxide to carry out etching in an etching process of the source/drain terminals, damages of the oxide semiconductor layer caused by traditional etchant solution can be prevented and quality of the thin-film transistor substrate can be enhanced. Further, it is not necessary to additionally form an etch stopper layer to protect the oxide semiconductor layer in the back channel so as to achieve relatively high channel width/length ratio (W/L), and also simplify the structure of the thin-film transistor substrate, simplify the manufacturing process, reduce the manufacturing cost, and enhance yield rate.

Method for manufacturing thin-film transistor substrate

Anomalous degradation behaviors under illuminated gate bias stress in a-Si:H thin film transistor

Tantalum etched by H2O2 solution shows best performance to be the source/drain electrodes of inverted staggered amorphous Indium Gallium Zinc Oxide thin film transistors among the investigated five metal materials. In addition, the etching property is improved significantly by adding aqueous ammonia properly.

46.3: Development of Source/Drain Electrodes for Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Comparative study of amorphous indium gallium zinc oxide thin film transistors passivated by sputtered non-stoichiometric aluminum and titanium oxide layers

Tzu-Chieh Lai

Papers

Thermal Stability of Amorphous InGaZnO Thin-Film Transistors With Different Oxygen-Contained Active Layers

Method for manufacturing thin-film transistor substrate

Anomalous degradation behaviors under illuminated gate bias stress in a-Si:H thin film transistor

46.3: Development of Source/Drain Electrodes for Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Comparative study of amorphous indium gallium zinc oxide thin film transistors passivated by sputtered non-stoichiometric aluminum and titanium oxide layers