【作者】 黄海琴；

【导师】 张希清；

【作者基本信息】 北京交通大学 ， 光学， 2012， 博士

【摘要】 ZnO基薄膜晶体管因其在平板显示器领域的广泛应用前景而吸引了越来越多的关注和研究。由于ZnO中存在O空位、Zn填隙等缺陷,因此常规制备的未掺杂ZnO趋向于具有较大的载流子浓度,这使得制备的ZnO-TFT关态电流较大,易为耗尽型晶体管。因此ZnO基TFT的研制中需要解决的问题之一就是控制ZnO有源层的载流子浓度。针对这一问题,本论文主要制备了ZnO基TFT,并通过优化薄膜的沉积条件,提高ZnO基TFT的电学性能。主要研究工作如下：1、利用射频磁控溅射在石英衬底上沉积了ZnO薄膜,研究了ZnO薄膜厚度与薄膜质量的关系。以SiO2/p-Si为衬底制作了ZnO-TFT,研究了ZnO薄膜厚度,退火温度对器件性能的影响,并探讨了不同的沟道宽长比对器件开态电流和迁移率的影响。实验结果表明,ZnO厚度为40nm,退火温度为950℃时,器件性能最好,阈值电压为-2.4V,迁移率为27.5cm2/V s,开关比为7×103,关态电流为8.33×10-7A。发现随着沟道宽长比的增加,器件的开态电流增加,迁移率减小。2、利用射频磁控溅射在石英衬底上沉积ZnO:Ga (GZO)薄膜,研究了衬底温度和氧气分量对GZO薄膜性能的影响。在此基础上,以SiO2/p-Si为衬底制备了GZO-TFT,研究了衬底温度,氧氩比,退火温度和GZO薄膜厚度对TFT电学性能的影响,探索了GZO-TFT随时间的稳定性。实验结果表明,当衬底温度为500℃,氧气分量为1SCCM,退火温度为800℃,GZO厚度为35nm时,器件性能最好,阈值电压为14.7V,迁移率为10.13cm2/V s,开关比为1.07×106,关态电流为1.34×10-9A。未采取任何保护措施的GZO-TFT,在8个月后电学性能变化很小,但在12个月后,电学性能发生了严重退化,退化主要与空气中的水汽有关。3、利用rf-MBE在石英衬底和SiO2/p-Si衬底上生长了MgZnO薄膜,研究了衬底温度、Mg源温度和MgO缓冲层厚度对MgZnO薄膜性能的影响,并在此基础上制备了MgZnO-TFT,研究了MgO缓冲层厚度对MgZnO-TFT电学性能的影响。实验结果表明,加入4nm厚的MgO缓冲层的MgZnO-TFT的电学性能最好,其阈值电压为28.6V,迁移率为1.85cm2/Vs,开关比大于106,关态电流小于10-10A。更多还原

【Abstract】 ZnO-based thin film transistors (TFTs) have attracted much attention due to the wide range of application in driving flat panel displays. However, ZnO films tend to display high carrier concentration in the as-prepared state due to the existence of Vo and Zni, even in nominally undoped films, leading large off-current in ZnO-based TFTs and making they operate in depletion mode. Thus, one of the main problems in ZnO-based TFTs is the control of the carrier concentration in the active layers. In this doctoral dissertation, ZnO-based TFTs were fabricated and the electrical properties of the TFTs were improved by optimize the depotion condition. The details are as follows:The ZnO thin films were deposited on quartz and SiO2/p-Si substrates by radio frequency magnetron sputtering and ZnO-TFTs were fabricated on SiO2/p-Si substrates. The effect of ZnO films’ thickness on the optical properties of the films and the effect of ZnO films’thickness and annealing temperature on the electrical properties of the TFTs were investigated. The influence of W/L on the mobility of TFTs was also discussed. The results indicated that the transistor with an40nm thick ZnO and annealed at950℃exhibited the best performance, with a threshold voltage of-2.4V, a field effect mobility of27.5cm2/V s, an on/off ratio of7×103, and an off-current of8.33×10-7A. The on current increased and the mobility decreased as the W/L increased.The ZnO:Ga (GZO) thin films were deposited on quartz and SiO2/p-Si substrates by radio frequency magnetron sputtering and GZO-TFTs were fabricated on SiO2/p-Si substrates. The effect of substrate temperature and sputtering Oxygen flow on the optical properties of the films and the effect of substrate temperature, sputtering Oxygen flow, annealing temperature and GZO films’thickness on the electrical properties of the TFTs were investigated. The time-dependent instability of the TFT was studied. The results indicated that when the substrate temperate was950℃, Oxygen flow was1SCCM, annealing temperature was800℃, and the GZO films’thickness was35nm, the transistor exhibited the best performance, with a threshold voltage of14.7V, a field effect mobility of10.13cm2/V s, an on/off ratio of1.07×106, and an off-current of1.34×10-9A. The transistor stored in ambient air without any protection showed little difference after8months, but degenerated after12months, the degeneration was main related with the humidity in air. The MgZnO thin films were deposited on quartz and SiO2/p-Si substrates by rf-MBE and MgZnO-TFTs were fabricated on SiO2/p-Si substrates. We investigated the effect of substrate temperature, Mg temperature and MgO buffer layers’ thickness on the optical properties of the films and the effect of MgO buffer layers’ thickness on the electrical properties of the TFTs. The results indicated the MgZnO TFT with4nm MgO buffer layer exhibit the best performance, with a threshold voltage of28.6V, a field effect mobility of1.85cm2/V s, an on/off ratio of above106and an off-current lower than10-10A.更多还原