Preparation And Optoelectronic Properties Of Li Doped Oxide Thin Film Transistors

In recent years,thin film transistors（TFTs）have been widely used in the display field as switching and driving devices.Amorphous oxide semiconductors（AOS）are a promising new type of TFT material that has made significant progress in display applications in a short period of time.Compared to traditional amorphous silicon materials,AOS materials have advantages such as no grain boundaries,interface traps,scattering centers,and the ability to deposit over large areas at low temperatures.These advantages provide a comprehensive improvement in the electronic performance of AOS materials and do not affect the disorderliness of the thin films.Additionally,AOS materials can be used to manufacture high-transparency and high-mobility TFTs.Due to the absence of grain boundary restrictions,all of the above features make AOS TFTs a key research direction in many emerging fields such as flexible electronics.Currently,commercially available fifth-generation IGZO TFTs have good static characteristics and long-term reliability,and their mobility can reach 15 cm²/Vs,but they still cannot meet the requirements of next-generation higher-resolution and higher-response display devices,and the devices contain toxic rare metal elements In and Ga.Therefore,it is urgent to find more suitable oxide materials as the active layer of TFTs.Substituting Sn with similar electronic structure and abundant content for In is helpful for the large-scale application of TFTs.The effective increase of the carrier concentration and device mobility can be achieved by doping alkali metal Li,and the Li-O bond energy is relatively high,which helps to suppress oxygen vacancies and improve device stability.However,there are relatively few studies on Li-doping ZTO TFTs,and the impact of Li doping on the overall electrical performance of the devices needs to be studied.The performance enhancement of single-layer Li-doped ZTO TFTs in existing studies is limited.This paper carries out a series of studies on the above issues and explores the photoelectric properties of TFTs.Chapter 3 of this paper first studies the appropriate Sn valence state for sputtering ZTO TFT devices,and different ZTO TFTs were prepared by co-sputtering Sn with Zn O.By changing the sputtering power of Sn and adjusting the different Sn valence states in ZTO films,it is demonstrated that Sn exists in multiple ways in ZTO films,including Sn⁴⁺,Sn²⁺and Sn interstitials.Experimental studies have shown that the optimal ratio of Sn⁴⁺has a significant effect on improving the performance of the devices.Chapter 4 focuses on the study of Li-doping on ZTO TFTs by magnetron sputtering.Using XPS technology,the presence of Li in the thin film was confirmed,and the electrical properties analysis showed that Li doping effectively improved the quality of the thin film and increased the device mobility.Finally,Chapter 5 aims to further improve the performance of the devices by designing and preparing a structure of double active-layer TFTs.The high carrier concentration active layer is placed at the bottom layer,and the low carrier concentration active layer is placed at the top layer,to complement each other and improve device mobility.In order to match the lattice of the two active layers,Li-ZTO thin films are used for both the upper and lower layers,and a matching set of double active-layer structures is found through experimental.In order to further optimize the device performance,the thickness of the lower layer film is adjusted by changing the sputtering time of the lower layer film,thereby achieving an improvement in device mobility.Through experiments gradually reducing the sputtering time,the relationship between film quality and sputtering time is discovered.Analysis and research have shown that when the sputtering time is 4 minutes,the binding degree of M-O bonds in the film is the highest,and the device performance is also the best,with a mobility of up to 18 cm²/Vs.