Study On Materials Modification And Properties Of InSnZnO Thin-film Transistors

Metal oxide semiconductors are considered to be the most promising channel materials for TFTs instead of silicon-based materials.The metal oxide TFT has the following advantages:1)high carrier mobility;2)uniform device performance,suitable for large-area production;3)low preparation temperature and suitable for flexible display;4)forbidden bandwidth,transpareny under visible light and suitability for transparent display.At present,it fully meets the requirements of large-size,ultra-high-resolution displays,and is considered to be one of the most promising new technologies in the next generation of new display technologies.However,as the new display technology evolves into ultra-high definition,ultra-high resolution and flexible displays,they impose higher technical requirements on metal oxide TFTs:higher mobility,better reliability,lower process temperatures,and so on.In response to this demand,this thesis focuses on the development of metal oxide thin film transistors with high electrical characteristics,high stability and flexibility,and studies the relationship between material modification and the performance of the indium-tin-zinc oxide thin film transistors.The main research contents and achievements are as follows:In order to solve the problem of low mobility?¹0cm²/Vs?of traditional InGaZnO oxide materials,the high mobility InSnZnO?ITZO?quaternary material was successfully prepared by co-sputtering method,and a high mobility InSnZnO-TFT was fabricated using this material as an active layer.The effects of annealing process on the properties of InSnZnO semiconductor thin films and the performance of the TFT devices were also studied.The results show that controlling the inherent defects in the ITZO film is very important for improving the electrical performance of the ITZO TFT.Sn atoms can effectively inhibit the formation of oxygen vacancy defects in ITZO films,and different annealing temperatures can effectively adjust the content of oxygen vacancy defects in the active layer of the device.Finally,ITZO TFTs with high saturation mobility(?_sat²7.4cm²V^-1s^-1)and high environmental stability were successfully fabricated by optimizing the annealing temperature and other conditions.In order to solve the problem of poor stability of metal oxide TFTs,a method of gas phase self-assembled monolayers?SAMs?as a passivation layer was proposed.The effects of organic self-assembled monolayers with different chain lengths as passivation layers on the properties and environmental stability of InSnZnO TFT devices were investigated.It is found that the SAMs with long alkyl chain can provide an ordered and highly hydrophobic monolayer and achieve optimal performance of ITZO TFTs with a field-effect mobility(?_FE)up to 22.9 cm²V^-1s^-1,a threshold voltages(V_th)as low as-0.1 V,a subthreshold swing?SS?as low as 0.076V/dec,and an on-off current ratio(I_on/I_off)as high as 4.3×10⁸.In addition,the threshold voltage drifts only 0.4V at a bias voltage(V_gs=10V)for one hour,and the device performance is basically unchanged under different humidity conditions.At the same time,the study also combines both advantages of inorganic passivation materials and the organic silane to prepare ITZO TFT with double passivation of SAMs/Al₂O₃.The inorganic passivation material is dense enough to effectively inhibit oxygen atoms from escaping from the oxide semiconductor film to form oxygen vacancies?V_O?.Organosilane can form a superhydrophobic interface on the surface of the oxide by self-assembly,which can effectively prevent the adsorption and permeation of water molecules.In addition,we systematically studied the effects of Al₂O₃ passivation and SAMs/Al₂O₃ double passivation on device performance and stability,respectively.Compared with the Al₂O₃ passivated ITZO TFT,the SAMs/Al₂O₃ double passivated ITZO TFT exhibits superior performance with a field effect mobility(?_FE)of up to 19.8 cm²V^-1s^-1,an on-off current ratio(I_on/I_off)as high as8.7×10⁹,a threshold voltages(V_th)as low as 0.9V,and a subthreshold swing?SS?as low as0.04 V/dec.Due to the modification of Al₂O₃ passivation layer by SAMs,a superhydrophobic interface is formed while eliminating the surface hydroxyl and surface defects of Al₂O₃passivation layer,which enhances the barrier property of the passivation layer to water and oxygen in the air.Since the interface of the gate dielectric layer has a great influence on the performance of the device,the research work studies the effect of gate dielectric layer modification on the performance of MO-TFT.By introducing a self-assembled monolayer as a modifying layer of the gate dielectric layer between the gate dielectric layer and the active layer,the interface characteristics of the gate dielectric layer and the active layer are improved,the surface roughness and surface energy are reduced.At the same time,we also studied the effect of alkyl chain length of self-assemble molecules on the TFT device and explore the related mechanism.It has been found that the modification of the interface of the gate dielectric layer by SAMs with short alkyl chains is more favorable to the performance of the device than the SAMs with long alkyl chains.In order to solve the problem of metal oxide TFT applied to flexible flat panel display technology,a flexible metal oxide TFT with a curvature radius of up to 10 mm was fabricated on a polyimide?PI?substrate.At the same time,in order to solve the problem of poor stability of the metal oxide TFT,the back channel surface of the flexible ITZO-TFT was modified by the OTES self-assembled layer,and the hydroxyl group on the surface of the ITZO film was eliminated by chemical reaction.The self-assembled layer modification forms a long-range ordered high hydrophobic molecular layer on the back channel surface of the flexible ITZO-TFT,which reduces surface energy and surface polarity,and solves the problem of poor stability of ITZO-TFT from the root.The passivation layer greatly improves the stability of the flexibl ITZO TFT even after being subjected to positive bias stress?PBS?and negative bias stress?NBS?,and shows only a small threshold voltage shift of 0.8 V after PBS and 1.3 V after NBS.The prepared flexible ITZO-TFT device shows good bias stability and good flexibility.The device can maintain good performance under a certain radius of curvature.