Preparation And Performance Of H-doped And Mg/H Co-doped ZnO Thin Film Transistors

The zinc oxide thin film transistor(ZnO-TFT)has the advantages of large-area preparation at low temperature,high optical transparency,richness,non-toxicity,and low manufacturing cost.Therefore,it has attracted widespread attention in the field of liquid crystal display.There are a large number of oxygen-related defects and high-density grain boundaries in the ZnO material,which will increase the defect state density and electron scattering at the interface of the ZnO-TFT active layer and the dielectric layer,resulting in lower saturation mobility and lower current switching and at the same time being not conducive to the bias stability of the device.Hydrogen doping is an effective method to improve ZnO-TFT.And it can lead to the reduction of oxygen-related defect states in the film,improve the roughness of the film and effectively increase the carrier concentration in the film,while hydrogen doping won't increase the manufacturing cost of TFT devices.At present,in most of the literature adopting hydrogen plasma to treat the film surface is used to achieve the purpose of hydrogen doping,which belongs to the secondary treatment process.In this thesis,hydrogen doping was carried out at room temperature by passing argon and hydrogen mixed gas in a sputtering atmosphere.The preparation process was simple and there was no subsequent annealing treatment.The main research contents are as follows:The reasons for the influence of different hydrogen flow rates on the performance of ZnO:H-TFT devices were studied.It was found in the study that hydrogen acts as a defect passivator and shallow donor in the ZnO film.On the one hand,it provides a suitable carrier concentration,on the other hand,it reduces the interface trap state density.And hydrogen plasma can etch the film surface while reducing the roughness of the film to improve TFT performance.When H₂/(Ar+H₂)=0.1%,the best performance parameters of ZnO:H-TFT devices are:?_sat=5.17 cm²/V s,I_on/I_off=4.98×10⁶,SS=0.76 V/Dec,V_th=6.03 V.Our experimental results indicates that introducing hydrogen into the sputtering atmosphere to achieve hydrogen doping is a simple and effective way to improve the performance of ZnO-TFT.However,the addition of excessive hydrogen will cause the carrier concentration to be too high,causing the off-state current of the device to increase,and adversely affecting the performance parameters of the device.Compared with ZnO-TFT,Mg doping in Mg_0.03Zn_0.97O-TFT can increase the formation energy of V_O,resulting in the reduction of the V_O as a donor.As a result,the off-state current of the device is reduced,which is more suitable for hydrogen doping research than the former.When the gas flow rate is H₂/(Ar+H₂)=0.3%,the best performance parameters of the device are:?_sat=6.33 cm²/V s,I_on/I_off=4.46×10⁵,SS=1.21 V/Dec,V_th=4.25 V.Compared with the ZnO:H-TFT optimal performance device,the saturation mobility of the Mg_0.03Zn_0.97O:H-TFT optimal device increases,the threshold voltage decreases and its bias stability becomes better.And then positive and negative bias stability compared with the former are reduced by 0.5 V and 1.3 V respectively.The reason for the above results is that Mg/H co-doping can effectively reduce the oxygen-related defects.Therefore,the effective mass and scattering of electrons are reduced,and the carrier concentration is adjusted to a moderate level.The problems are the increase of the off-state current of the device,the decrease of the switching ratio and the sub-threshold swing which is too large.Compared with Mg_0.03Zn_0.97O-TFT,the off-state current of Mg_0.06Zn_0.94O-TFT is lower due to the increase of Mg content,which is also more suitable for hydrogen doping research.When H₂/(Ar+H₂)=0.39%,the best performance parameters of Mg_0.06Zn_0.94O:H-TFT are:?_sat=8.11 cm²/V s,I_on/I_off=6.17×10⁶,SS=0.42 V/Dec,V_th=2.78 V,the positive and negative bias voltage stability values are 0.5 V and 1 V.The performance of the device is significantly better than the optimal device of Mg_0.03Zn_0.97O:H-TFT and ZnO:H-TFT.It can be seen that the proper ratio of Mg/H co-doping can indeed effectively improve the performance of ZnO-based TFT devices.The spectrum test shows that our active layer film is suitable for the preparation of high-performance Mg ZnO:H-TFT transparent devices.