Study On ZnO Thin-Film Transistors With Electrolyte Dielectric

In recent years,the zinc oxide thin film transistor（ZnO-TFT）using an electrolyte material that has an electric double layer effect as the gate dielectric of has been widely concerned because it can greatly reduce the operating voltage of a TFT device.The ZnO-TFT was fabricated by using the non-toxic and easily degradable chitosan as the gate dielectric.This paper has further explored its electrical properties,neurogenic properties and stability.The inverter circuit which is based on the device was studied.Finally,the electrical characteristics of ZnO-TFT were optimized.The main research contents and achievements are as follows:（1）ZnO-TFT was fabricated by using chitosan as the gate dielectric and sputtering zinc oxide as the active layer.The carrier mobility of the device was 2.12 cm²/Vs;the threshold voltage was 1.06 V,and the switching current ratio was 5×10⁴.The subthreshold swing is only135 mV/Dec and the operating voltage can be as low as 1 V.The ultra-low operating voltage is mainly derived from the formation of the electrical dual-layer effect of the interface of the chitosan gate dielectric layer.The corresponding MIS capacitor has a capacitance per unit area(C_OX)of 11.2μF/cm² at a low frequency of 50 Hz.（2）The neurogenic properties and stability of chitosan ZnO-TFT were studied.In the neurobionic characteristic test,the device simulates the short-range characteristics of biological synapses well;under the action of constant gate compressive stress,the device exhibits certain instability,which is dominately manifested by the increase of its stress time.At first,the current increases and then decreases;the threshold voltage drifts left and then drifts immediately,and the electrical properties can be quickly restored to the initial state after the gate bias stress is removed.This is primarily related to electrostatic doping at the interface of the gate dielectric.（3）The resistance-loaded inverter being based on chitosan ZnO-TFT was fabricated.The DC and AC characteristics were tested and analyzed,and the DC characteristics were simulated.The test results show that the inverter has a full swing voltage transfering characteristic when VDD is 1 V⁵ V,and the voltage gain is 3.9 at VDD=5 V.The simulation results show that the RPI model can better fit the DC characteristics of the electrolyte ZnO-TFT by reducing the thickness of the gate dielectric.（4）ZnO-TFT was fabricated by using chicken albumen as the gate dielectric layer,deposing ZnO as a semiconductor active layer by sputtering and ALD,respectively.The change of the performance of the chicken albumen from the ionic liquid to the solid film during its forming process was studied,and the vertical dual-gate ZnO-TFT which is based on chicken albumen was fabricated.The results show that the device fabricated by ALD has better electrical properties than the sputtering method,in which the carrier mobility increases from1.52 cm²/Vs to 38 cm²/Vs;the mobility of chicken albumen ionic liquid ZnO-TFT is 0.53 cm²/Vs,the switching ratio is 2.1×10³,and after the chicken albumen is dried and filmed,the mobility of the device rises to 0.79 cm²/Vs,and the switching ratio increases to 2.2×10⁴.In the vertical dual-gate ZnO-TFT,the regulation of the performance of the bottom gate device of the chitosan gate dielectric by the egg-clearing gate dielectric top gate is achieved.In addition,the chitosan ZnO-TFT prepared by ALD method has a mobility of 28.2 cm²/Vs and a switching ratio which reaches up to 2.4×10⁶.The electrical performance is far superior to that of the device prepared by a sputtering method.