Fully Transparent Ingazno₄ Thin Film Transistor

Recently, transparent oxide-based thin-film transistors (TFTs) have attracted much attention because of their high electron mobilities (>10 cm2/Vs) and because they can be processed at low temperatures to produce large-area displays with the potential of low production costs. Among various transparent oxide semiconductors, InGaZnO4 is preferred as a channel layer of TFTs due to its uniform structure, smooth surface, and high electron mobility (>10 cm2 /Vs) even for an amorphous film deposited at room temperature.In this paper, we fabricated transparent InGaZnO4 TFTs on a glass substrate at room temperature. First of all, 150-nm-thick indium tin oxide (ITO) film was deposited on glass substrate by radio-frequency magnetron sputtering and used as the common gate electrode. Next, a 4μm-thick SiO2 gate dielectric layer was deposited onto the ITO by plasma-enhanced chemical vapor deposition using SiH4 and O2 as reactive gases at room temperature. Then, a 50-nm-thick InGaZnO4 active layer was deposited by radio-frequency magnetron sputtering at room temperature. Finally, the ITO source/drain electrodes were deposited by direct current sputtering with a thickness of 200 nm. The entire process of device fabrication was performed at room temperature. All of the active channel and source/drain electrodes were patterned using nickel shadow masks. The electrical characteristics of the transistors were measured with a Keithley 4200 semiconductor parameter analyzer at a room temperature in the dark. Measurements were made on transistors with a channel length of 80μm and a width of 1000μm. The dielectric capacitance of InGaZnO4 TFTs were performed by the capacitance-frequency (C-f ) measurement using an Agilent 4294A precision impedance analyzer, which was based on an ITO/SiO2 /Al sandwich test structure. The optical transmission measurement was performed by UV/Vis spectrophotometer in the wavelength range between 200 and 1000 nm. The experimental results shows that the unit-area capacitance was 1.6μF/cm2, while the field-effect mobility, subthreshold swing and on-off ratio were 40.6cm2V-1s-1, 103mV/decade, 2.1×106, respectively. The device operating voltage is only 1.5V. The average transmittance in the visible portion of the electromagnetic spectrum (400–700 nm) is ~80%, indicating the TFTs are fully transparent to visible light.Fully-transparent room-temperature-fabricated InGaZnO4 TFTs are very promising for next generation display technologies based on transparent displays and flexible displays.