The submicrometer resolution printing of various metal acetylacetonate complex inks including Fe, V, Mn, Co, Ni, Zn, Zr, Mo, and In was enabled by a robust ink formulation scheme which adopted a ternary solvent system where solubility, surface wettability, and drying as well as absorption behavior on a polydimethylsiloxane sheet were optimized. Hydrogen plasma in heated conditions resulted in bombarded, resistive, or conductive state depending on the temperature and the metal species. With a conductivity-bestowed layer of MoO and a plasma-protecting layer of ZrO situated on the top of an IGZO layer, a solution-processed TFT exhibiting an average mobility of 0.17 cm/(V s) is demonstrated.
We fabricated solution-processed indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) by microwave (MW) annealing an IGZO precursor film followed by irradiating with vacuum ultraviolet (VUV) light. MW annealing allows more rapid heating of the precursor film than conventional annealing processes using a hot plate or electric oven and promotes the crystallization of IGZO. VUV irradiation was used to reduce the duration and temperature of the post-annealing step. Consequently, the IGZO TFTs fabricated through MW annealing for 5 min and VUV irradiation for 1 min exhibited an on/off current ratio of 108 and a field-effect mobility of 0.3 cm2 V−1 s−1. These results indicate that MW annealing and photoirradiation is an effective combination for annealing solution processed IGZO precursor films to prepare the semiconductor layers of TFTs.
We designed an aqueous-fluoroalcoholic InGaZnO precursor for obtaining thin-film transistors (TFTs) on a flexible plastic film by spin-coating and low-temperature annealing processes without inert gas conditions. The precursor shows a low surface tension (23.7 mN m −1 ), which is advantageous for homogeneous coating onto plastic film. Thermal analysis of the precursor indicates formation of metal oxides at less than 300 °C. InGaZnO TFTs were obtained from the precursor by annealing at 300 °C via UV irradiation under humid atmosphere on a transparent polyimide film as well as on a p-Si substrate. The bottom-gate top-contact TFTs on the p-Si show 5.1 cm 2 V −1 s −1 of the average saturation mobility. The top-gate top-contact TFTs on the transparent polyimide film drive with 0.99 cm 2 V −1 s −1 of the average saturation mobility. The transparent polyimide film maintains flexibility even after humid-UV irradiation and annealing processes. The InGaZnO TFTs on the transparent polyimide film show more than 80% transmittance in the visible light region between 400 and 780 nm.
We fabricated a thin-film transistor (TFT) using amorphous indium gallium zinc oxide (a-IGZO), which was formed through annealing of an IGZO precursor film with a single-mode cavity microwave at 2.45 GHz. The transisitor fabricated with the a-IGZO film prepared by microwave annealing for 15 min showed higher device performance, i.e., a field effect mobility of 5.75 × 10−2 cm2·V−1·s−1, an on/off ratio of 106, and a threshold voltage of 20 V, than that prepared by annealing with a conventional oven for 120 min. The Raman spectra confirm that the device improvement originates from the decrease in the number of –OH groups and removal of organic species for 15 min by microwave annealing. These results suggest that the microwave annealing method has an advantage as the annealing process of solution-processed oxide semiconductors to reduce the process time. It can be applied to the fabrication of TFTs.
We synthesized viscous precursors to indium gallium zinc oxide (IGZO) using three kinds of alcoholamines, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA), by a simple process. The viscous precursors are obtained just by vigorous stirring of alcoholamine and urea in an aqueous solution containing the metal nitrates during heating at 150-160 ºC. The precursor containing EA (EA-precursor) is a pale-orange suspension containing aggregates of the metal hydroxides and shows pseudoplastic flow. The precursors containing DEA (DEAprecursor) and TEA (TEA-precursor) are transparent pale-yellow and dark-orange sols, respectively. They give Newtonian flow in the lower shear rate and pseudoplastic flow in the higher shear rate. Higher concentration of metal salts leads to higher viscosity of the precursors. According to thermogravimetry-differential thermal analysis (TG-DTA) for the EA-and DEAprecursors, evaporation of alcoholamine occurs at around each boiling point and subsequently formation of metal oxides occur at around 300 ºC. In the case of the TEA-precursor, formation of metal oxides occurs before pyrolysis of TEA attributed to the higher boiling point of TEA. The thin IGZO film, which is prepared by spin-coating of the diluted DEA-precursor and subsequent sintering at 450 ºC for 30 min, shows 0.02 cm 2 ·V -1 s -1 of the mobility and 10 -5 of the on/off ratio. The highly viscous DEA-precursor containing high concentration of metal ions allows patterning in an area of 100 cm 2 onto a surface of a silicon wafer with screen printing.
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