Preparation And Properties Of Amorphous Tin Dioxide Transparent Thin Film Transistor

With the upgrading of computers,mobile phones,pads,wearable bracelets and other electronic devices,in addition to the upgrading of chips,batteries and other hardware,display technology is showing a leap forward development.Thin film transistor(TFT),as the core component responsible for driving in display,has been the key to the development of the display field.Amorphous oxide thin film transistor(AOS TFT)has the advantages of high field-effect mobility,high transparency in visible light region,good uniformity of amorphous structure and large area preparation,which makes up the shortcomings of traditional silicon TFT in transparent display field,and is expected to become the core driving element of the next generation display technology.At present,among AOS TFTs,amorphous InGaZnO(a-IGZO)based TFTs have the best performance and begin commercial application.However,its constituent elements contain rare metals such as In and Ga,resulting in high fabrication cost.Therefore,the development of AOS TFTs with little or no rare metals has become one of the key research directions in this field.SnO2 is an n-type transparent oxide semiconductor material.Because its conduction band bottom is dominated by highly overlapping Sn 5 s orbitals,it can show high mobility and good uniformity in amorphous structure.At the same time,it has a wide energy gap?3.6 eV,high transparency in visible light,rich storage capacity and low preparation cost.Therefore,the a-SnO2 based TFT shows great research prospects in the field of new generation display technologies such as transparent display and flexible display.In this study,amorphous tin dioxide thin film transistor(a-SnO2 TFT)was selected as the research object.Firstly,based on the first principle of density functional theory(DFT),the band structure and density of states of ideal SnO2 crystal and SnO2 with different concentrations of oxygen vacancy defects were analyzed.The results showed that SnO2 was a direct band gap semiconductor,and its conduction band bottom was dominated by the contribution of 5S orbital of Sn,while the valence band top was dominated by the 2p orbital of O.The intrinsic SnO2 was an n-type semiconductor,and most carriers are electrons.These indicated that a-SnO2 can be used as the channel layer to fabricate thin film transistors with high field effect mobility.A-SnO2 TFT was prepared by pulsed laser deposition method.In view of the lack of working mechanism,we first analyzed the working mechanism of a-SnO2 TFT with bottom gate structure using electric field modulation thermopower method.The carrier depletion region of 2.5 nm on the top surface of a-SnO2 films was confirmed.The phase structure,optical and electrical properties of SnO2 films with different thicknesses were studied.Combined with the method of electric field modulation thermopower method,the optimal channel thickness of a-SnO2 TFT for the preparation of bottom gate structure was determined to be 4.2 nm,and the TFT showed the highest on-off current ratio?105 and high field-effect mobility?20 cm2 V-1 s-1.Considering the strong gas sensitivity of SnO2,a-SnO2 TFT with top gate structure was prepared,and the thickness of channel layer and insulating layer were optimized.Finally,a-SnO2 TFT with high performance was successfully prepared.The TFT showed high on-off current ratio?105,high field-effect mobility?10 cm2 V-1 s-1,low threshold voltage?+ 0.65 V,small subthreshold slope?230 mV decade-1.The ambient atmosphere stability and voltage bias stability tests indicated that a-SnO2 TFT with top gate structure showed good ambient atmosphere stability,which effectively improves the problem of poor ambient atmosphere stability of aSnO2 TFT.