Research On Amorphous Indium Tungsten Oxide Thin Film Transistors With High Mobility

Amorphous Oxide Semiconductor?AOS?thin film transistors?TFTs?are regarded as the potential active matrix addressing devices for next-generation flat panel displays?FPDs?due to their outstanding feathers such as high field-effect mobility(?_FE),low off-current?Ioff?,good transparency,low processing temperature and simple device structure.Especially,amorphous InGaZnO?a-IGZO?has been attracting the most attention and becoming the mainstream of the active layers for AOS TFTs.However,the field-effect mobility of a-IGZO TFTs?¹0 cm2/Vs?is not large enough to meet the more and more serious requirements from high-resolution displays.Therefore,developing the other AOS TFTs with larger?_FE seems necessary.Recently,amorphous indium tungsten oxide?a-IWO?was proposed,with which the TFT devices exhibited quite large field-effect mobility as well the low off-current.Accordingly,the IWO TFTs might be another choice for the electronic devices addressing high-resolution displays.First we did some research on deposition condition of a-IWO TFT,and electrical characteristics with changing annealing temperature and annealing time.Then we tried to pattern the IWO TFTs by photolithography and wet etching methods.First with the consideration of high carrier concentration,Oxygen content was set high when depositing IWO film.Then the influence of annealing conditions including annealing temperature and annealing time on a-IWO electrical characteristics were investigated detailedly.It is said that a-IWO film is not fit for high annealing temperature,several annealing temperatures around 200?were chosen in this study.From the results,the higher annealing temperatures lead to more oxygen in a-IWO and then the field-effect mobility of a-IWO TFTs increased gradually with the annealing temperature increasing.While the subthreshold swing and threshold voltage were the best at annealing temperature of 200?annealing temperature.With the consideration of all parameters,200?was considered as the most appropriate temperature for a-IWO film.Then using 200?as the annealing temperature,changing annealing time?0.5h,1h,1.5h,2h?.Using the same way like former,200?/2h was the best annealing condition.Then wet etching process of a-IWO TFT was studied.First appropriate materials of every layer should be chosen.In our research Mo was picked out to be the electrodes material,including gate,source and drain,Silicon oxide and a-IWO were used as gate insulator and active layer.Further,we tried several etchants of Mo,and finally NH_3·H₂O+H₂O₂ as Mo etchant.It has been reported that a-IGZO was sensitive to most strong acid such as hydrochloric acid.So the solution?10ml hydrochloric+100 ml deionized water?was chosen as the IWO etchant first.There was still residual tungsten on the surface of the SiO2 film after IWO being etched by hydrochloric acid.Then BOE was chosen to wipe off W residue.The inverted staggered TFT was fabricated at first,and after Mo being etched that there was residual Mo on the surface of IWO film.While there was no improvement on the problem of Mo residue after several ways being attempted.Based on the above discussion,we finally fabricated an inverted coplanar a-IWO TFT device as Fig.4 to avoid Mo residual on the surface of a-IWO film.In this study,we tried to pattern the IWO TFTs by photolithography and wet etching methods and finally fabricated the inverted coplanar devices with reasonably good performance.