| Among the various manufacturing processes of oxide semiconductor thin film transistor（TFT）,the solution process has been become the most potential method due to its low cost and simple process.However,the solution-processed metal oxide TFTs suffer from poor bias stress stability（especially the negative bias illumination stress stability）because of the presence of oxygen-related defect states,which hinders the practical applications.Moreover,researches of the solution-processed metal oxide TFT are mostly focused on the single device,but the TFTs used for display driver are as the pixel array,which has significantly different performance compared that of a single device.In order to meet the needs of display driver,it is urgent to enhance the bias stress stability of the solution-processed pixel-level TFT arrays.Based on this,indium zinc tin oxide（IZTO）TFT arrays with etching stopper layer（ESL）structure and back channel etched（BCE）structure are fabricated by solution process in this paper.And the influence of the passivation layer on the bias and illumination stress stability of IZTO TFTs with two structures are studied.The main work of this paper is as follows:（1）The IZTO TFT array with ESL structure is fabricated and the bias stress stability is studied.First,the device properties of IZTO TFTs are compared that using Al2O3 prepared by atomic layer deposition（ALD）and solution-processed hafnium aluminum oxide（HAO）prepared as gate dielectrics.The mobilities of Al2O3-IZTO TFT and HAO-IZTO TFT are 2.5 and 2.1 cm2·V-1·s-1,respectively.The mobilities of two devices are basically similar,that confirms the feasibility of solution-processed HAO film as the gate dielectric layer of TFT.Then,by optimizing the annealing temperature of the IZTO film,the device mobility increases from 2.1 to 17.7 cm2·V-1·s-1.And the thickness of the IZTO film is further optimized,the device mobility is improved to 33.56 cm2·V-1·s-1.Meanwhile,the device exhibits good stability under positive bias stress（PBS）and negative bias illumination stress（NBIS）.Finally,the effects of Si O2 and Si Nx as passivation layer on the bias stress and illumination stability of HAO-IZTO TFT are investigated and compared,indicating that the HAO-IZTO TFT with Si Nx passivation layer has the best stability.TheΔVth are 0.17 and-0.14 V under PBS and NBIS,respectively,which is attributed to the correlated H diffusion during from Si Nx deposition,a moderate amount of H passivate the defect states and reduces oxygen vacancies（VO）,thereby improving the performance and stability of HAO-IZTO TFTs.（2）The IZTO TFT array with BCE structure is fabricated and the bias stress stability is studied.First,theΔVth of HAO-IZTO TFT is 0.76 and-0.77 V under PBS and NBIS,respectively,that due to the exposure of the back channel to the adsorption of water and oxygen in the air.After the device with Si O2 passivation,theΔVth of HAO-IZTO TFT is reduced to 0.2 and-0.3 V under PBS and NBIS,respectively.It shows that the passivation layer can prevent the adsorption of water and oxygen on the surface of the IZTO film and improve the stability of the device.At the same time,the N2O or NH3 plasma treatment are used to passivate the surface defect states of the IZTO film,and the effects of two gas plasma treatments on the device performance and stability of IZTO TFT are compared.The results show that the performance of IZTO TFT is improved by N2O plasma treatment,especially the negative bias illumination stress stability,that the saturation mobility increases from25.12 to 51.52 cm2·V-1·s-1,and the Vth shift under NBIS increases from-0.3 to-0.1 V,which meets the requirements of the display driver.Moreover,the overall uniformity and stability of the devices in the pixel array are improved after N2O plasma treatment,which further indicates that a good solution-processed pixel-level IZTO TFT arrays can be obtained after N2O plasma treatment. |
