一个非晶InGaZnO薄膜晶体管线性区陷阱态的提取方法

非晶InGaZnO(a-IGZO)薄膜在制备过程中形成的缺陷和弱键以陷阱态的形式非均匀分布在a-IGZO的带隙中, 这些陷阱态会俘获栅压诱导的电荷, 影响a-IGZO薄膜晶体管线性区迁移率、沟道电子浓度等, 进而影响线性区的电学性能. 本文基于线性区沟道迁移率与沟道内的自由电荷与总电荷的比值成正比, 分离出自由电荷以及陷阱态电荷. 由转移特性和电容电压特性得到自由电荷以及陷阱态电荷对表面势的微分, 分离出自由电子浓度和陷阱态浓度. 通过对沟道层与栅绝缘层界面运用泊松方程以及高斯定理, 考虑了沟道表面势与栅压的非均匀性关系, 得出自由电子浓度以及陷阱态浓度与表面势的关系, 最后通过陷阱态浓度与表面势求导得到线性区对应的态密度.

A technique for extracting the density of states of the linear region in an amorphous InGaZnO thin film transistor

Defects and weak bonds generated in the fabricating process of amorphous InGaZnO(a-IGZO) films distribute non-uniformly in the band gap of the a-IGZO film in the form of traps. These traps would capture the charges induced by gate voltage, and affect the linear region mobility, channel carrier density and so on, then the electrical properties in the linear region of a-IGZO thin film transistor. The model used is based on the mobility in linear region which is in direct proportion to the ratio of the free charge to the total induced charge in the channel, and then the free charge and the trapped charge are separated. From the ratio of the density of free carriers to that of the trapped, a direct relationship with the derivative of the free charge with respect to surface potential, and the derivative of the trapped charge with respect to surface potential is calculated by bringing in the gate voltage that serves as an intermediate variable between the linear region mobility and the total induced charge. In this way, the free carrier density and the trapped carrier density can be separated by using the transfer characteristic and capacitor-voltage characteristic. Poisson's equation and Gauss theorem are applied to the interface between the channel layer and the insulating layer. In consideration of the non-uniform characteristic between the surface potential and the gate voltage, the relationship between the free carrier density and the surface potential, the trapped carrier density and the surface potential are obtained. Finally, the density of states in the linear region could be gained by differentiating the trapped carrier density with respect to surface potential.