Preparation And Properties Studies Of ZnO TFT Based On Al₂O₃ Gate Dielectric

Thin film transistors(TFT)have a wide range of applications in flat panel display,graphic imaging,array sensing and other fields.The first-generation TFT use hydro-genated amorphous silicon(a-Si:H)as the active layer material,but its development is hampered by the low mobility and electrical instability of a-Si:H;the appearance of high temperature polysilicon improves the performance of TFT to some extent,but the high temperature required for preparation has limited its application range;organic thin-film transistors(OTFT)can be prepared at low temperature with low cost and simple craft,however,the mobility of OTFT is difficult to improve,and the nature of organic mate-rials is not stable enough.In recent years,metal oxides represented by ZnO have been considered as the most promising semiconductor materials for replacing Si-based TFT because of their high mobility,transparency to visible light,low-temperature preparation,and high stability,and they has broad application prospects in flexible devices and wear-able electronics.Thermal silicon oxide wafer,i.e.Si02/Si substrate,is commonly used in laboratory research on TFT,however,due to the limitation of the process level,low leakage current and high insulation Si02/Si are still dependent on imports,which hinders TFT laboratory research on a new type of active layer material with high cost.In this dis-sertation,the ZnO TFTs with different aspect ratios are first simulated and the transistor performance is obtained,on this basis,the ZnO TFTs are tested;after that,the deposi-tion process of ZnO thin films with excellent carrier transport properties was obtained by studying the performance of ZnO TFTs sputter deposited under different conditions;on this basis,the atomic layer deposition(ALD)high-K dielectric Al2O3 as an insulating layer on the Si wafer was used to verify the ALD growth of Al2O3 have significant perfor-mance improvements prepared to the Si02 medium;finally,the two-dimensional electron gas model of the double active layer ZnO/MgZnO TFT is compared with the ZnO TFT,The threshold voltage was reduced by 30%and the switching ratio was increased by an order of magnitude,TFTs with Gd-doped ZnO active layers were tried and prepared,and the reasons for their degradation were analyzed.(1)The ZnO TFT device was simulated by TCAD software,the effect of the aspect ratio of different devices on the performance of the device was studied;on this basis,the TFTs with different aspect ratios were prepared by laser direct write technology,the test results were consistent with the simulation rules.(2)Using ALD method,ZnO TFT was prepared by depositing a 100 nm Al2O3 substrate and a 100 nm thick Si02/Si substrate on a Si wafer with trimethyl aluminum(C3H9Al)and water(H20)as sources.The test results show that the mobility of ZnO TFTs with high-K dielectric Al2O3 is 22 times higher than that of ZnO TFT with Si02 as the insulating layer,the sub-threshold swing is reduced by 6 times,the on-off ratio increased by an order of magnitude to 104.(3)The ZnO TFT were prepared under three different sputtering conditions using magnetron sputtering method with metal Zn as the target and Al2O3/SiO2 as the dual di-electric layer,the performance of TFT devices was compared.The best preparation pro-cess under the conditions of our laboratory:the ratio of 02 and Ar in the sputtering process is 1:5,the pressure is 0.3 Pa,the temperature is 300?,the sputtering power is 100 W,and the sputtering time is 30 min.(4)The ZnO/MgZnO dual active layer TFT were prepared by magnetron sputtering with MgZnO target and ZnO target,the performance were compared with those of ZnO TFT,the reasons for the change of properties were analyzed;the ZnO doped Gd TFT was prepared with Zn target,analyzes the cause of the degradation of performance.