A physical based analytical current models of poly-Si TFT``s were developed: turn-on current model, leakage current model, and subthreshold current model.
The turn-on current model was expressed as the drift current over the potential barrier at the grain boundary. The model formulation is analytical, which makes it suitable for the simulation of circuits. The model parameter extraction method was also developed. The proposed models show good agreement with the experimental results over a wide range of gate and drain voltage and especially, including the temperature dependence of I-V characteristics. The intrinsic capacitance model of poly-Si TFT``s biased at the turn-on region was developed. The model was based on the turn-on current model.
Mechanisms of the leakage current were investigated and modeled using the unified resistance model. The leakage current was found to be greatly influenced by channel resistance and junction currents. The junction currents are the generation current enhanced by lateral electric field at the drain junction, the generation current enhanced by vertical electric field at the drain overlap region, and the recombination current at the source junction. Using the unified resistance model, the mechanisms of leakage current could be found correctly. The model is in good agreement with measured leakage current characteristics over wide ranges of gate and drain biases.
An analytical physical-based model for subthreshold current was developed. The model equation was expressed to the diffusion current, which have a physical and simple equation for the subthreshold identity factor to be obtained by considering the continuous density of states (DOS) in the grain boundary. The temperature dependence of the subthreshold current could be explained by the model.