Estimate Threshold Voltage Shift in a-Si:H TFTs Under Increasing Bias Stress

A method of estimating threshold voltage shift in hydrogenated amorphous silicon (a-Si:H) transistors under increasing bias stress is proposed. Although the threshold voltage shift in a-Si:H thin-film transistor (TFT) has been modeled well under constant bias stress, its property with increasing bias stress, which occurs in many a-Si:H-based compensating circuits, still cannot be quantified without any restriction, such as constant overdrive bias or short stressing time. In this paper, we propose a model which is effective under an arbitrary increasing stress for a prolonged time. The proposed model reduces to the constant bias model if the stress bias remains unchanged. With this method, the lifetime of most compensating circuits based on a-Si devices can be estimated completely.