Capacitance-voltage characteristics and two-dimensional numerical analysis of hydrogenated amorphous silicon thin film transistors
Abstract
The analytic model for the frequency-dependent C-V characteristics of an a-Si:H MIS capacitor are presented along with the direct measurement method on TFTs. The C-V model is derived based on the static I-V model developed using the simplified CFO band model for the a-Si bulk band gap states and the simplified Davis-Mott model for the surface states. The frequency variation of the measured capacitance, using a somewhat modified TFT, is modeled with the lateral flow transmission line model. These models show good agreement with the experiments. The inter-electrode capacitance-voltage characteristics of amorphous silicon thin film transistor were modeled and measured. The gate or induced channel charge was derived on the basis of the parameters and basic expressions of the static I-V model. The analytical expressions for the C-V characteristics of an a-Si:H MIS capacitor were applied to obtain an inter-electrode C-V model of an a-Si:H TFT. As the second part of the research, a computer program, TFTSP, has been developed for the two-dimensional simulation of a-Si:H TFTs, which provides ability in the choice of physical parameters so that different models can be evaluated and compared. It can handle distributed donor, acceptor, and dangling-bond states, as well as exponential tails. This computer program was employed to verify its validity by simulating the current-voltage characteristics of an a-Si:H TFT. The simulated results show good agreement with the experimental data indicating that this computer simulations are realistic. The program was used for the theoretical study of the ambipolar behavior of a-Si:H TFTs, which was observed and modeled on the basis of the curve-fitting parameters of the experimental data. The simulation results of the ambipolar characteristics of the a-Si:H TFT were presented only to show the possibility for the developed program to be refined and used for the optimal modeling and design of the ambipolar a-Si:H TFTs.
Degree
Ph.D.
Advisors
Neudeck, Purdue University.
Subject Area
Electrical engineering|Condensation
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