The Preparation And Performance Research Of Novel Amorphous SnO₂ Based Thin Film Transistors

Amorphous oxide films have many advantages such as high transparency,high mobility,low preparation temperature and high uniformity,so they are widely used in the channel layer of thin film transistors(TFT).So far,many excellent amorphous oxide films have been researched,among which the electrical properties of amorphous InGaZn O films are the most prominent,and TFTs based on this material are currently being used in industrial production.Most of the amorphous oxide films with excellent performance are based on indium oxide materials.But the abundance of indium on the earth is extremely low,it is expensive,and has a certain degree of toxicity.Therefore,it is imperative to develop some new-type amorphous oxide films with low-cost and high-performance,which are indium-free or low-indium.Since the ionic structure of Sn⁴⁺and In³⁺is similar,the amorphous tin oxide film also has a higher mobility.And because tin is far more abundant than indium,tin oxide becomes one of the best alternatives to In-based oxides.In this paper,a series of novel amorphous tin oxide-based(a-SnO₂:M,M=Ga,Eu,Si)thin film materials and the performance of their TFT devices have been studied.The specific work content is as follows:(1)Amorphous SnGaO TFT was prepared by sol-gel method.The study found that with the increase ofGaconcentration,the off-state current of the TFT decreases and the threshold voltage shifts towards positive voltage,indicating thatGadoping can effectively reduce the carrier concentration,which is mainly becauseGadoping can suppress the generation of oxygen vacancies in the film.The optimalGadoping concentration is about 20 at.%,the optimal annealing temperature is about 350?,the corresponding device's mobility is 5.2 cm²V^-1s^-1,the threshold voltage is-3.2 V,the subthreshold swing is 0.7 V/dec.,and the switch ratio is 1.5×10⁶.The higher annealing temperature can increase the mobility of the device,which is mainly attributed to the decrease of defects in the film and the increase of carrier concentration.(2)Rare earth elementEuwas selected as the dopant of amorphous SnO₂ channel layer,and it was found that rare earth elementEuis an effective carrier inhibitor.The amorphous SnEuO film prepared by the sol-gel method has a band gap of 3.87 e V.As the concentration ofEudoped increases,both the on-state current and off-state current of the TFT decrease,and the threshold voltage moves towards positive voltage.A certain concentration ofEudoped can improve the subthreshold swing,but the mobility is reduced.The optimalEudoping concentration is about 30 at.%,the annealing temperature is about 400?,the mobility of corresponding SnEuO TFT is 4.5 cm²V^-1s^-1,the switching ratio is 9.5×10⁶,the threshold voltage is-7.3 V,and the subthreshold swing is 0.8 V/dec..(3)Amorphous SnSiO TFT was fabricated by RF magnetron sputtering.The effects of annealing in different atmospheres on the bias stability of SnSiO TFTs were studied at an annealing temperature of 350?.The main factors that affect the bias stability of the device include the deep energy level defects in the channel layer,the defects in the channel/dielectric interface,as well as water and oxygen in the air.Annealing in air or oxygen will produce defects related to interstitial oxygen due to the presence of oxygen.At the same time,the roughness of the film will increase,resulting in a large number of interface state defects,which degrade the bias stability of SnSiO TFT.The nitrogen annealing process and argon annealing process make the SnSiO films have fewer defects and a smoother surface,so the stability of positive and negative bias is better.The TFT has the best bias stability after nitrogen annealing,and the corresponding electrical performance is also the best:its mobility is 8.6 cm²V^-1s^-1,the switching ratio is 1.5×10⁷,the threshold voltage is 0.2 V,and the subthreshold swing is0.7 V/dec..