Fabrication And Modulation On Electrical Properties Of Indium Oxide Thin Nanofiber Film Transistors

Thin film transistors（TFTs）are mainly used in liquid crystal displays in computers and smartphones.Nowadays,many large factories produce millions of displays every year,and each of which contains millions of TFTs.Electrospinning technology and solution spin-coating method are considered as the most promising technologies for preparing TFTs due to their simple operation,low cost,and large-scale production advantages.Metal oxide semiconductors（MOS）are widely used in experimental research and industrial production due to their high carrier concentration,large bandgap,and good chemical stability.At the same time,indium oxide（In₂O₃）as a kind of new N-type semiconductor with a wide bandgap is usually used as an active channel layer for TFTs devices.However,the large amount of oxygen vacancies generated by In₂O₃ itself makes the TFT device have high off-state current,small on-state current,negative threshold voltage,and large sub-threshold swing.In order to improve the electrical performance of In₂O₃TFTs and promote their practical application,this work focuses on doping,optimizing the annealing temperature of In₂O₃ nanofibers and improving the annealing temperature of gallium oxide（Ga₂O₃）dielectric films to regulate the surface roughness of thin films,carrier concentration,and electrical performance of TFT devices.The research content and experiments of this paper are mainly carried out in the following three aspects:（1）This work combines electrospinning technology and doping method to prepare In₂O₃ nanofiber TFT doped with different contents of gadolinium（Gd）.The main purpose is to realize the transformation of TFT device operation mode（from depletion type to enhancement type）and improve its electrical properties through Gd doping.It was found that In₂O₃ nanofiber TFT made with 7mol%Gd doping concentration has excellent electrical properties,which including 10⁵ current switch ratio,0.38 cm²/Vs mobility,15 V threshold voltage,and 9.5 V/Dec subthreshold swing.It is an effective way to get low operating voltage by using high dielectric constant（high-k）dielectric as dielectric layer of TFT,but high-k materials treated at high temperature have poor dielectric brittleness,which will lead to deterioration of film performance.As a solution,this work combines organic polymer material polyvinyl alcohol（PVA）with inorganic high-k material aluminum oxide（Al₂O₃）,and uses solution spin-coating method to prepare PVA-Al₂O₃ organic-inorganic composite dielectric film as TFT dielectric layer material.Experimental results show that In₂O₃/PVA-Al₂O₃ nanofiber TFT made with 7mol%Gd doping concentration has a working voltage ten times lower than before,as well as high current switch ratio of 10⁵,threshold voltage of 1.0 V,high mobility of 0.5 cm²/Vs and subthreshold swing of 0.13 V/Dec.（2）In this work the electrical properties of the device are controlled by controlling the annealing temperature of In₂O₃ nanofibers.The experimental results show that In₂O₃ nanofiber TFT annealed at550℃exhibits excellent electrical properties,which including 10⁵ current switch ratio,1.6×10^-3 cm²/Vs mobility,6.7 V threshold voltage,and 0.2 V/Dec subthreshold swing.Similarly,we also use PVA-Al₂O₃organic-inorganic composite dielectric film prepared by solution spin-coating method as the insulating layer of TFT device,successfully realizing the preparation of low-voltage and low-power In₂O₃/PVA-Al₂O₃TFT device.（3）The use of high-k dielectric as the insulating layer of TFT device is an effective way to enhance capacitance coupling and achieve low operating voltage.Considering that gallium oxide（Ga₂O₃）high-k material has the characteristics of wide bandgap,large dielectric constant,and excellent thermal stability,as well as the simple operability of solution spin-coating method,in this work we use solution spin-coating method to prepare Ga₂O₃ high-k dielectric film.Since annealing conditions have a great influence on the chemical composition and physical properties of Ga₂O₃ dielectric treated by solution,in this work,high-k Ga₂O₃ dielectric was mainly prepared by simple solution process method,and then annealed at 250℃,350℃,450℃,and 550℃respectively.Finally,low-voltage and low-power In₂O₃ TFT with high-performance solution-processed was integrated on optimized amorphous Ga₂O₃ dielectric.The optimized In₂O₃/Ga₂O₃ TFT device has a mobility of 8.5 cm²/Vs,a threshold voltage of-1.4V,a current switch ratio of 10⁴,a subthreshold swing of 0.41 m V/Dec,and excellent bias stability.