Oxide Electric-double-layer Thin Film Transistor With Nafion Dielectric

In recent years,electric double-layer transistors(EDLTs),as a new type of device,have received widespread attention due to their large capacitance,low voltage,and multi-gate regulation characteristics.However,slow switching characteristics and low operating frequency are still the primary problems faced by EDLTs after years of development,which restrict their practical applications.As the core part of the EDLTs,various ion gate dielectrics including ionic liquids,polymer electrolytes and inorganic oxides have been explored,but there is no ion gate dielectric material with absolute advantages.Nafion is the most classic and also the mostly used proton exchange membrane material for polymer electrolyte fuel cells.It has excellent proton transport property and chemical-physical stability.As an important parameter index to measure the performance of EDLTs,transient characteristics have meaningful research significance.At the same time,with simple operation and rich functions,including various physical models and basic semiconductor formulas,Technology Computer Aided Design(TCAD)software is widely used in modeling and simulation of various semiconductor devices.The combination of TCAD software and EDLTs research is of great help to the optimization research of the transient characteristics of the device.This study covers several aspects such as device preparation,performance testing and software simulation.The specific research contents are as follows:(1)Preparation and testing of Nafion-gated dielectric oxide EDLTs.The Nafion precursor solution was prepared with nano-Al₂O₃ particles to enhance the mechanical strength,followed by the H₂O₂ and H₂SO₄ solution pretreatment to optimize the Nafion film.Next,SEM and AFM characterized the morphology of the film,and the internal characteristics were characterized by FTIR,XRD and Capacitance-Frequency.It was concluded that the pretreatment enhanced the capacitance characteristic and the water absorption of the Nafion film.According to impedance analysis,the Nafion proton conductivity of nontreated,H₂O₂+0.1 M H₂SO₄,H₂O₂+3.5 M H₂SO₄ were 0.11 m S/cm,0.25 m S/cm and 0.33 m S/cm,respectively.The IGZO channel and IZO source/drain electrodes were prepared by magnetron sputtering technology,and the transfer characteristics and output characteristics of the device were tested by the probe platform.It shows that the field-effect mobility increases from 1.2cm²V^-1s^-1 to 16.9 cm²V^-1s^-1,the threshold voltage decreases from 1.37 V to 0.57 V,and the counter-clockwise hysteresis width gradually becomes smaller after pretreatment.Besides,the device output characteristic curve shows good ohmic contact and saturation characteristics.(2)TCAD modeling and simulation of EDLTs.At the same time,according to the experimental data,the structure model of the Nafion-gated dielectric EDLTs was established by using TCAD software.Firstly,the IGZO density of state model is set up,which mainly considers the parameters of the conduction band tail state,mobility,and dielectric constant.Then set up the ion drift-diffusion model of proton conducting electrolyte,which mainly includes proton concentration,proton diffusion coefficient and dielectric constant.The proton concentration and diffusion coefficient were obtained by comparing simulated capacitance-frequency characteristics with experimental data,which were 1×10¹⁷cm^-3and6.8×10^-8cm²/s,respectively.Next,the device transfer and output characteristic curves are obtained,and the threshold voltage is obtained near 0.4 V.The influence of structural parameters such as the thickness of the channel and gate dielectric,the channel W/L ratio,and the area of the bottom gate electrode on the the threshold voltage V_thand I_on/offratio were studied.Finally,the simulation shows that the lower the channel/gate dielectric interface defect and the higher the gate dielectric proton concentration,the better the electrical characteristics of the device.(3)TCAD simulation of EDLTs transient characteristics.The transient switching time of Nafion-gated EDLTs was tested through the reverse circuit.The transient time of the device pretreated by 3.5 M H₂SO₄ shows the best performance of less than 10 ms.The transient characteristics of EDLTs were simulated by TCAD software,and it mainly includes two types of key factors:one is the proton characteristics of the gate dielectric;the other is the influence of the parasitic capacitance between the source/drain electrodes and the gate dielectric.It is obtained through simulation that increasing the proton concentration and proton diffusion coefficient can improve the transient switching characteristics.At the same time,reducing the source and drain electrodes can also effectively shorten the turn-on and turn-off time.The transient time of the device under ideal conditions can be calculated of 2 k Hz.For other factors,it was found that reducing the channel length and channel/gate dielectric interface defects can also improve the transient performance of the device.