a-Si TFT亚阈特征参数与有源层的厚度效应

The Subthreshold Characterization Parameter and Active Layer Thickness Effect over a-Si TFT

从异质界面处的有效界面态出发 ,研究了 a-Si Nx:H/a-Si:H异质结 a-Si:H TFT的亚阈特征参数的界面效应和有源层的厚度效应 ,发现 a-Si:H的特性不仅与材料、工艺有关 ,而且其几何结构参数对 a-Si:H TFT的特性也有明显的影响。实验结果表明 :亚阈特征参数主要由异质界面的有效界面态密度决定 ,当 NH3/Si H4 比增加时亚阈特征参数下降 ,增加 a-Si Nx 材料的淀积温度 ,可使亚阈特性得到明显的改善 ,a-Si:H有源层的厚度减小 ,抑制了亚阈参数的增加 ,阈值电压也减小并趋于稳定 ,且 TFT的 ION/IOF F随有源层厚度呈现近似抛物线状变化规律。文中从理论上分析了有源层厚度与 TFT特性的关系 ,计算的最佳有源层的厚度约为 2 0 0 nm,这与实验结果基本一致。

In the paper we discussed the interface effect of subthreshold characterization parameter on a Si TFT with a Si:H/a SiN x :H heterojunction and the thickness effect of active layer by using effective interface state density. We found that a Si:H properties not only depend on the material and technology but also geometrical structure parameters. The experimental results show that the subthreshold characterization parameter is mainly decided by effective interface state density on heterointerface. When we improve NH 3/SiH 4 ratio the subthreshold characterization parameter would come down. If the illuviation temperature of a SiN x material is raised the subthreshold characterization would get better obviously. With decreasing of active layer thinkness, the increase of the subthreshold parameter would be restrained, subthreshold threshod voltage would decrease and tend towards stability, and the curve of I ON / I OFF of a Si:H TFT would be parabola approximately. The dependence of the TFT properties on the active layer thickness is also analysised, and the best active thickness is about 200 nm, which is basically consistent with experiment results.