【作者】 姚绮君；

【导师】 李德杰；

【作者基本信息】 清华大学 ， 电子科学与技术， 2009， 博士

【摘要】 本文针对有源驱动表面传导电子发射显示器(SED)对薄膜晶体管工作电流的需求,研究了基于ZnO半导体的薄膜晶体管,并在此基础上改进晶体管的半导体层材料,设计制作了基于In2O3半导体的薄膜晶体管。在全程工艺温度满足“柔性电子”应用需求的基础上,制作的In2O3薄膜晶体管在性能上超越了目前在这方面广泛采用的有机半导体材料薄膜晶体管。文中的ZnO半导体薄膜晶体管在普通制版玻璃上制作,整个制作过程全部使用常规薄膜工艺。器件采用薄膜晶体管的底栅结构,绝缘层为直流反应溅射的Ta2O5,半导体层为射频溅射沉积的ZnO。在ZnO膜层的沉积过程中采用了衬底加温、加入栅网屏蔽和优化溅射气氛等工艺手段,有效的改善了器件的性能。最终器件的场致迁移率达到3.8cm2/Vs,开关比105,沟道宽长比为5的器件在晶体管输出特性线性区工作时,工作电流达到160μA,可满足SED在工作电流上对薄膜晶体管的要求。器件的工作特性在耐压范围内稳定,没有发现阈值漂移问题。大气中退火可以提高ZnO薄膜晶体管的场致迁移率,经过400°C处理的器件场致迁移率达到了24cm2/Vs。此外,文中利用Levinson公式成功拟合了器件在低漏极电压下的转移特性,从拟合参数可以推算出器件中ZnO膜层晶粒内电子迁移率和掺杂浓度的信息。为降低器件制作的工艺温度,本文提出了基于In2O3半导体的薄膜晶体管,并探索了全程工艺温度低于140°C的器件制作方法。器件绝缘层采用直流反应溅射的Ta2O5,半导体层由In靶直流反应溅射沉积得到。采用向沟道界面扩散Bi的方法钝化界面处的载流子陷阱,使器件的稳定性得到了很大程度的改善,底栅结构In2O3薄膜晶体管器件的场致迁移率达到12cm2/Vs,开关比大于103,顶栅结构In2O3薄膜晶体管器件场致迁移率达到5cm2/Vs,开关比104。研究结果表明利用氧化物半导体作为薄膜晶体管的半导体层可以获得足够高的场致迁移率和稳定的器件特性,这个结果为实现下一代有源驱动平板显示器提供了技术基础。针对低温工艺器件还可以开发出“柔性电子”等更为广泛的应用。更多还原

【Abstract】 Thin film transistors (TFT) based on ZnO and In2O3 semiconductors are demonstrated in this dissertation to meet the demands for switching devices in active matrix Surface-conduction Electron-emitter Display (SED) and flexible electronics, respectively.ZnO TFT was fabricated on glass substrate, and only conventional thin film processing technology was used. Bottom-gated structure with reactive sputtered Ta2O5 insulator layer and rf sputtered ZnO semiconductor layer was adopted in the device. The performance of ZnO TFT was effectively improved by shielding the substrates with a metal mesh and tuning the Ar/O2 flow ratio during sputtering deposition of ZnO layer. Field effect mobility of 3.8cm2/Vs and on-off ratio of 105 was obtained. On-state current of the device with width/length ratio of 5 reached 160μA when the device worked in the linear region of the output characteristics. Magnitude of the current meets the demands in application of SED. The devices showed stable performance below the breakdown voltage, and no threshold voltage shift was found. Field effect mobility of the device was further improved by annealing in atmosphere. Devices annealed at 400°C had a field effect mobility of 24cm2/Vs. Levinson expression is successfully employed to simulate the transfer characteristics of the device for low drain voltage. Electron mobility and donor concentration in ZnO crystallite are obtained by matching the curve parameters.In2O3 is one of the semiconductor materials that can be treated at lower temperature and shows higher carrier mobility. In2O3-TFT with the whole fabrication process carried out at temperature lower than 140°C is demonstrated. Reactive sputtered Ta2O5 film was adopted as insulator layer of the device, and the semiconductor layer was deposited by reactive dc sputtering of an indium target. Stability of the device was greatly improved by passivating the carrier traps at the channel interface by diffusing bismuth into the channel. For bottom-gated structure In2O3 TFT, field effect mobility of 12cm2/Vs and On-Off ratio of 103 was obtained. For top-gated structure In2O3 TFT, field effect mobility of 5cm2/Vs and On-Off ratio of 104 was obtained.The results show that by using oxide semiconductor as the semiconductor layer in thin film transistors, high field effect mobility and stable performance can be obtained. The devices are expected to be used in the next generation active matrix flat panel display. Applications such as "flexible electronics" can be developed based on devices fabricated with low temperature processing technology.更多还原