Simulation Research Of Nitrogen-doping On Defect Regulation Of A-IGZO TFTs And Electrical Properties Of A-IZO/a-IGZO Composite Channel TFTs

Transparent amorphous indium gallium zinc oxide（a-IGZO）-based thin film transistors（TFTs）are used as core devices for next-generation display driver technology due to their strong driving ability,high optical transmittance,good uniformity in large-area fabrication,and low power consumption.Although a-IGZO TFTs exhibit excellent device performance,due to the disordered lattice structure of a-IGZO channel materials,there are high density of the sub-band state defects in the materials,which strongly affect the performance and reliability of a-IGZO TFTs.In recent years,in-situ nitrogen doping（N-doping）technology has been proposed to suppress sub-band state related defects in a-IGZO TFT,thereby improving the electrical performance and reliability of the devices.However,the effect of N-doping on the sub-band state defects density distribution in a-IGZO TFTs is unclear.In order to further reveal the mechanism of N-doping on device improved performance and reliability,it is necessary to deeply and systematically study the effect of N-doping on the defects state density of a-IGZO TFTs.Meanwhile,modern display technology evolves towards high resolution and large size,which requires thin film transistor technology to have the characteristics of high mobility and high stability.Therefore,in this thesis,TCAD simulation was used to study the effect of N-doping on the sub-band state defects density distribution of a-IGZO TFT and the effect of IZO/IGZO composite channel on the electrical properties of TFT.The main work and results are as below:1.Silvaco TCAD simulation tool is used to fit experimental data of the device performance and reliability（positive gate bias stress,monochromatic light illumination stress,and negative bias illumination stress）of a-IGZO TFTs with various N-doping ratios.The results show that the density of interface,band tail states,and deep-level oxygen vacancy-related defect states of a-IGZO TFTs are significantly decreased by appropriate N-doping ratio,which is consistent with the improved electrical performance and stability under stress conditions;When excess nitrogen is incorporated into a-IGZO TFTs,the associated defect density of the device increases,resulting in degradation of device performance and reliability;Meanwhile,it is confirmed that the tail-distributed acceptor-like N-related defects are formed by excessive N-doping ratio,which leads to the degradation of subthreshold swing in a-IGZO TFTs.2.In order to further improve the field effect electron mobility of a-IGZO TFT devices,the performance and reliability of highly conductive a-IZO and a-IGZO composite channel TFT devices are studied by using Silvaco TCAD simulation tool.Firstly,the effect of the channel material a-IZO/a-IGZO thickness ratio on the device characteristics is investigated.The results show that the optimal channel material thickness ratio is 5:40,and the device exhibits excellent electrical performance,such as threshold voltage of 1.0 V,subthreshold swing of0.09 V/dec,field-effect mobility of 31.1 cm²/V?s,and the current on-off ratio of 10¹⁰.Meanwhile,it is found that the improvement of the performance of a-IZO/a-IGZO TFT is related to the formation of electron conduction path（sub-channel）at the interface of the channel materials.Secondly,the effects of interfacial defects of the channel materials and the oxygen-related defects in the channel materials on the reliability of TFT devices are investigated.By establishing and adjusting the parameters of the density of states model,it is found that with the increase of the interface tail state acceptor defect density,the threshold voltage and subthreshold swing of the device increase;when the a-IZO layer is introduced,the related defect density of the TFT is passivated,and then the electrical reliability of a-IZO/a-IGZO TFTs is significantly improved.