Low-voltage Electric-double-layers ITO Thin Film Transistors

Recently, wide bandgap-based oxide thin-film transistors （TFTs） have beenextensively investigated because of their high electron mobility and low processingtemperature, making them compatible with flexible substrates and because they can beprocessed at low temperatures to produce large-area displays with the potential of lowproduction costs. However, they usually require large operation voltage to achievehigh output currents and high mobilites. In this condition, oxide TFTs operated inlow-voltage have attracted much more attention. Among various oxide semiconductormaterials, InGaZnO4、ITO（indium tin oxide）are preferred as the channel layer of TFTsdue to their uniform structure, smooth surface, and high electron mobility（>10cm²/Vs）even for an amorphous film deposited at room temperature.We have developed microporpus SiO2film by plasma enhanced chemical vapordeposition（PECVD） using SiH4and O2as the reactive gases at room temperature. Wecan highly reduce the operation voltage by using this kind of SiO2as the gate dielectricof TFTs, so we can solve the high operation voltage problem of normal TFTs. Besides,we have attempted to give research on flexible TFTs. A new kind ofelectric-double-layers indium-tin-oxide （ITO） thin-film transistors was fabricated onpaper substrate by one-shadow-mask process. First of all，300-nm-thick ITO film wasdeposited on paper substrate by radio-frequency magnetron sputtering, as the gateelectrode. Next, a4μm-thick SiO2gate dielectric layer was deposited onto the ITO byPECVD using SiH₄and O₂as the reactive gases at room temperature. Finally, thechannel layer can be simultaneously self-assembled between ITO source/drainelectrodes by only one shadow mask during RF magnetron sputtering deposition atroom temperature. The thickness of the ITO source/drain electrodes was about200nm,and the measurements were made on transistors with a channel length of80μm and awidth of1000μm. The entire process of device fabrication was performed at roomtemperature. The electrical characteristics of the transistors were measured with aKeithley4200semiconductor parameter analyzer at a room temperature in the dark.These TFTs exhibit a good performance with an ultralow operation voltage of1.5V, afield-effect mobility of20.1cm²/Vs, a subthreshold swing of188mV/decade, a largeon-off current ratio of5×10⁵, and a threshold voltage of-1V, respectively. Besides,the influence of mechanical bending to the electrical performance of the flexible ITO TFTs was investigated. After bending, the saturation mobility, subthreshold swing,on-off current ratio and threshold voltage of ITO TFTs were14.2cm²/Vs，188mV/decade，1×10⁵and-0.84V, respectively.The full-room-temperature oxide TFTs on paper substrate by one-shadow-maskprocess show a lot of advantages，such as low operation voltage、simple deviceprocess、low cost, etc. And ccomparing the device performance before and afterbending, the attenuation of the device is not serious, within the acceptable range. SuchTFTs are very promising for the application of low-power and portable flexibleelectronic devices in the future.