Study Of Fabrication And Properties Of A-IGZO Thin Film Transistors Based On Composite Insulator

Since 2003,Professor Hosono Hideo firstly discovered and applied the amorphous indium gallium zinc oxide?a-IGZO?materials into the preparation of thin film transistor?TFT?.IGZO is considered as the next generation of TFT materials in large-size and flexible display applications with its characteristics of high mobility,visible light transparency and amorphous structure.In this thesis,the influence of a-IGZO TFT devices' fabrication process based on composite insulator was demonstrated,including a-IGZO TFT devices based on single Al₂O₃ insulator,single PMMA insulator and Al₂O₃-PMMA composite insulator,individually.The influence of DC sputtering power on the active layer and ultra-thin buffer layer of composite insulator a-IGZO TFT devices were demonstrated as well.The details are as follows:Firstly,the effects of oxygen partial pressure?OPP?and DC sputtering power on the surface morphology,electrical conductivity and visible light transparency of a-IGZO films were demonstrated to obtain the proper sputtering conditions.As the OPP changed from 0% to 4%,the surface roughness presents a down and up trend,and the optimum was 2%,the resistivity was significantly increased as well.As the sputtering power changed from 120 W to 210 W,the resistivity and surface roughness decreased slowly,and almost stopped after 180 W.The UV-VIS and XRD test showed that the IGZO thin film was fully visible light transparency and amorphous structure under these sputtering conditions.The 2% OPP and 180 W sputtering power was comsidered as proper result.Secondly,the a-IGZO TFT devices fabricated with reactive magnetron sputtering Al₂O₃ insulator and spin-coating PMMA insulator were studied,individually.For single Al₂O₃ insulator devices,we changed the sputtering OPP from 16% to 28%,and then the Al₂O₃ film's surface roughness presented a down and up trend.The best insulating performance was at 20% OPP when the corresponding TFT's off state leakage was down to 10-7A,and a saturation mobility up to 1.41cm2/V·s.After that,the influence of spin-speed on PMMA films and corresponding devices were studied.The PMMA films' roughness were less than 0.5 nm,far less than Al₂O₃ films.The off state performance of PMMA insulator TFT devices was down by 2 orders of magnitude compared to Al₂O₃,but the poor saturation output ability led to a saturation mobility down below 0.3cm2/V·s.Then,the a-IGZO TFT devices' electrical performance of Al₂O₃-PMMA composite insulator,single Al₂O₃ and signal PMMA insulator were studied after analysising the advantages and disadvantages of single insulator devices.The result showed that composite insulator effectively reduced the off state leakage and sub threshold swing?SS?.The current on/off ratio increased by nearly 10 times than single insulator TFT device.In addition,the influence of DC sputtering power of IGZO film that based on composite insulator devices was demonstrated.The current on/off and sub threshold performance presented a up and down trend,when the optimum power was 180 W,the carrier mobility reached 1.23cm2/V·s,current on/off ratio was 3×104,and sub threshold swing was 4.4V/dec.At last,the influence of a conductive a-IGZO buffer layer on the composite insulator TFT device was studied.The on/off performance was dramatically improved after adding a 3nm conductive a-IGZO buffer layer,the on state current output increased while off state leakage decreased 1 order of magnitude,individuality.The saturation mobility was 4.32cm2/V·s?3.43 times than without buffer later device?,current on/off ratio reached 3.8×106,the threshold voltage decreased by 36%,and sub threshold voltage was 1V/dec.The result showed that the a-IGZO buffer layer has effects of improving the channel interface performance based on the composite insulator a-IGZO TFT device.