【作者】 韦维砚；

【导师】 徐征；

【作者基本信息】 北京交通大学 ， 光学工程， 2011， 硕士

【摘要】 近年来,随着大尺寸液晶显示器和有源有机发光二极管的发展,传统的非晶硅薄膜晶体管和有机薄膜晶体管已经很难满足要求,以铟镓锌氧化物(IGZO)为代表的透明非晶氧化物半导体(TAOS)具有迁移率高、均一性好、透明等优点,将有望成为下一代显示技术中薄膜晶体管的有源层材料。本论文重点对以IGZO作为有源层的薄膜晶体管进行研究。作为TFT的核心部分,有源层的成膜质量、厚度等因素直接影响到薄膜晶体管的器件性能,所以对IGZO-TFT有源层的研究具有重要的意义。另外,退火处理也是改善薄膜晶体管性能的一种重要途径。(1)首先,采用射频磁控溅射制备了IGZO薄膜并进行了薄膜特性研究。XPS结果表明IGZO薄膜的元素比例(In:Ga:Zn)与靶材保持一致,通过在溅射中加入少量的O2能够抑制氧空位的产生；在低温条件下(200℃以下)制备的IGZO薄膜属于非晶态,并具有良好的表面形貌,粗糙度较低；IGZO薄膜的透射光谱表明在可见光范围薄膜具有较高的透过率,并推算出IGZO薄膜的光学带隙大约为3.69 eV,且随着基底温度的提高,薄膜的光学带隙减小：另外,我们还研究了溅射功率对IGZO薄膜生长的影响,结果表明,功率为100W时制备的薄膜比50W制备的薄膜具有更加光滑平整的表面形貌和更高的可见光透过率。(2)其次,在优化IGZO薄膜制备条件的基础上,本文采用厚度分别为40、60、80、120 nm的IGZO薄膜作为薄膜晶体管的有源层,以底栅顶接触结构构筑器件。结果表明,所制备的器件为n沟道耗尽型器件,当IGZO厚度为80 nm时,器件的性能达到最优化,器件在饱和区的场效应迁移率为0.113 cm2/Vs,阈值电压为-12.99 V,开关比为2.56×102。(3)最后,研究了退火温度对IGZO-TFT器件性能的影响。结果表明,退火处理能够提高器件的场效应迁移率,同时使器件的阈值电压向负方向漂移,200℃退火处理的器件与400℃退火处理的器件的场效应迁移率相差不大,XRD测试结果表明,当退火温度达到400℃时,IGZO薄膜开始结晶,晶界使得薄膜表面的粗糙度增加,将影响源漏电极与有源层的接触,因此,200℃的退火处理在改善IGZO-TFT性能上比400℃更合理有效。更多还原

【Abstract】 Recently, with the development of large liquid crystal and organ-ic-light-emitting-diode displays, conventional silicon and organic TFTs cannot satisfy the requirements, transparent amorphous oxide semiconductors (TAOSs) represented by In-Ga-Zn-O (IGZO), which satisfy almost all the requirements, are expected to be the channel material of TFTs in next-generation flat-panel displays. Thin film transis-tors(TFTs) based on indium gallium zinc oxide as active layer were studied in this thesis. As a code part of the TFT, the characteristics of active layer, such as film quality, thick-ness, will strongly determine the performance of TFTs. In addition, annealing treatment is an important way to improve the performance of TFTs.Firstly, indium gallium zinc oxide (IGZO) thin films were deposited by magnetron sputtering and studied. X-ray photoelectron spectroscopy measurements were per-formed to find out the quantitative and qualitative chemical properties of the IGZO thin films. The atomic ratio of In:Ga:Zn of the IGZO thin films was consistent with the tar-get. It could be found that the introduction of O2 in the sputtering could inhibit oxygen vacancies. The result of XRD measurement indicated the structure of IGZO films depo-sited at lower substrate temperature (below 200℃) was amorphous. AFM results showed that the surface of IGZO films was smooth. IGZO thin films showed high opti-cal transmission in the visible region, the optical band gap was approximately 3.69eV and decreased with the substrate temperature improvement. Furthermore, we studied IGZO thin films deposited with different sputtering power (50W,100W), the results showed that the film deposited under 100W has a smoother surface and higher trans-mittance in the visible region.Secondly, on the basis of optimized sputtering parameters, IGZO-TFTs with dif-ferent IGZO thickness (40,60,80,120nm) were fabricated on SiO2/Si substrates using top contact configuration with bottom gate. The electrical properties of devices showed that TFTs with a 80nm thick active layer showed the best performance, such as field-effect mobility (0.113cm2/Vs), threshold voltage (-12.99V) and on/off-current ratio (2.56×102). All the devices operated in n-type depletion mode.Finally, in order to investigate the effect of annealing on the performance of IG-ZO-TFT, devices were annealed at different temperature (without annealed,200℃, 400℃) before the source and drain electrodes were deposited. The electrical properties of devices showed that the field-effect mobility of TFTs was increased after annealing treatment, but the threshold voltage exhibited small negative shifts. XRD results showed IGZO films annealed at 400℃began to crystallize and had a rougher surface according to the AFM measurement. It could be concluded that annealing at 200℃was more ef-fective than 400℃to improve the performance of IGZO-TFTs.更多还原