Study On Gate Dielectric And Electrode Materials Of Flexible Amorphous In GaZnO Thin Film Transistors

With the advantages of low process temperature and high carrier mobility,amorphous indium gallium zinc oxide thin film transistor(a-IGZO TFT)is very suitable for making flexible TFT backplanes,and then driving flexible display devices.On the other hand,a flexible a-IGZO TFT manufacturing process suitable for practical production has yet to be researched and developed.This paper focuses on the most important gate insulating layer and electrode layer in flexible oxide TFTs.The relevant experimental data and theoretical analysis results have important reference significance for the actual production of flexible TFT backplanes.The material of the insulating layer plays an important role in the thin film transistor,but in the context of the trend of flexibility,the mechanism of the effect of bending stress on the gate insulating layer is not clear.Related tests were made to analyze the influence of the bending stress of the insulating layer on the stability of a-IGZO TFT devices.We used plasma-enhanced chemical vapor deposition(PECVD)deposited silicon oxide and silicon nitride,the most commonly used insulating layer materials,to test the operating characteristics,positive and negative bias stability characteristics of TFT devices in flat and bent states,respectively.Through the analysis and comparison of the results,the following conclusions are reached:in flat state,compared to Si O_X device(PBS+6.5V,NBS-3.0V),Si N_X device has better stability(PBS+3.5V,NBS-0.5V);in bent state,both devices have become more stable,but the stability of Si O_X devices(PBS+2.5V,NBS-1.0V)has changed more than Si N_X(PBS+1.0V,NBS-0.5V).It is suggested that this result is related to the charge trapping mechanism at the front channel.The data showed that the surface roughness of the Si N_X film is smaller than that of Si O_X,so we speculate that the interface defect states between Si N_X and IGZO is less and the sensitivity to bending stress is lower.In addition,due to the Young's modulus of Si N_X is greater than that of Si O_X,Si N_X devices will bear less mechanical stress while being bent.The materials of electrode also affect the electrical characteristics of flexible TFT devices significantly.Reducing the resistivity of flexible electrodes is of vital significance.We selected the most commonly used Mo electrode in production as the research object,and tried to improve its conductivity by introducing a"seed layer".W and Mo W were used as“seed layers”to prepare Mo/W and Mo/Mo W double-layer structures.The comparison of the square resistance measured by the pattern obtained by dry etching,proved that the double-layer structure indeed reduces the square resistance by about 30%.Based on this,we analyzed the related physical mechanism of the Mo electrode's resistivity reduction.In addition,in order to meet the needs of practical applications,we also explored the dry etching process of double-layer electrodes,improved the film etching angle,and obtained the dry etching process conditions that meet the needs of device fabrication.Finally,Mo/W electrode was fabricated on PI flexible substrate,and the decrease of the sheet resistance of the electrode was also observed...