InZnO Electric-Double-Layer Thin Film Transistors And Their Applications In Low-Voltage Inverter

Ionic/electronic interaction has attracted much attention for it offers a new dimension in the recent advancements of solid state materials. Thin film transistors（TFTs） gated by ionic/electronic hybrid electrolyte have been developed. With the formation of an electric-double- layer（EDL） layer at the electrolyte/solid interface with the thickness of about 1 nm under an external electric field, a big EDL capacitance >1 μF/cm² is always obtained. Such value is much larger than that for the conventional dielectrics, such as SiO 2 and high dielectric constant oxides. The huge capacitance can improve the modulation of charge carrier density by the gate electrical field, thus reduce the device operating voltage（typically below 2 V）. So ionic/electronic hybrid electrolyte gated transistors ha ve potential applications in low-power sensors and portable electronics. C hitosan is a linear polysaccharide composed of randomly distributed β-（1-4）-linked D-glucosamine and N-acetyl-D-glucosamine. It has become of great interests as a new functional material of high potentials in various fields. Besides, due to its high proton conductivity when doping acid, chitosan has also attracted much attention as a solid electrolyte membrane. Considered of the merits of EDL TFTs and the properties of chitosan, we fabricated oxide EDL TFTs gated by chitosan. The EDL TFTs’ electrical properties and their applications in inverter were discussed. The main contents can be summarized as follows:（1） Solution-processed chitosan by acid doping was fabricated with spin coater. A high conductivity of ³×10^-3 S/cm at room temperature and a large protonic/electronic hybrid EDL capacitance of ⁴-7 μF/cm² were observed in solution-processed chitosan film. Then, protonic/electronic coupled indium- zinc-oxide（InZnO） thin- film transistors were fabricated by using solution processed chitosan as gate dielectrics. Good transistor performances were obtained with high stability due to the strong proton gating behavior, such as a low operating voltage of ¹.0 V, a high on/off ratio of about 3×10⁷, a very small subthreshold swing of ⁶5 mV?decade^-1 and a small threshold voltage of-0.28 V, etc. Then, the transient responses to square-wave pulses of the InZnO TFTs were investigated, which confirmed its protonic/electronic coupled EDL effects.（2） A low- voltage resistor- loaded inverter was built by using a chitosan-gated InZnO TFT in series with a load resistor. Good inverter per formances were obtained. The inverter had a voltage gain of 3.6 V/V at supplied voltage of 0.5 V and a voltage gain 20 V/V at supplied voltage of 3 V. A linear relationship between the voltage gain and the supplied voltage was obtained. Transient characteristics at different frequency of the inverter were discussed in detail. Moreover, the signal processing applications were also discussed, which indicated that the inverter can be used for decreasing noises of input signals.（3） To modulate the threshold vo ltage of TFTs and the transfer voltage of the inverter, we fabricated dual- gate TFTs with self-assembling process. The threshold voltage and the operation mode can be modulated effectively while supplied a voltage of-2 V⁺2 V on in-plane gate of the dual- gate TFTs. Results shows that the threshold voltage of the dual- gate TFTs shifted from ^-0.4 V to ⁰.1 V when the in-plane gate voltage varied from +2 V to-2 V. Then we investigated its application on inverter, results showed that the transfer voltage of the inverter can be modulated with a different voltage on in-plane gate. Furthermore, we obtained high and balance noise margin at a in-plane gate voltage of-2 V.These studies demonstrated that the solution-processed chitosan film have a high conductivity at room temperature and a large EDL capacitance. O xide protonic/electronic hybrid EDL TFTs have very potential applications in portable electronics and low-power biochemical sensors.