Very recently, the hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) has shown its important application as an on-board driver for large-area flat-panel liquid crystal displays. It is also highly desirable to have on-board TFT logic circuits adjacent to the TFT driver matrix and have them implemented in the same technology on the same substrate. This reduces the number of lead connections to the display and hence the cost, and increases the reliability of the display. The first area to be investigated is the modeling of ID vs. VD static output characteristics of the n-channel a-Si:H TFT. Second, ambipolar characteristics of the a-Si:H TFT are investigated and modeled. Thereby device models for CAD circuit simulation programs are made available for circuit design. Third, a novel CMOS-like inverter circuit is presented as an application of the ambipolar a-Si:H TFT, and its static characteristics are analytically modeled. The transient response of the TFT is also characterized and modeled in order to understand its device limitations and to quantify its speed. Finally, the dynamic characteristics of the ambipolar a-Si:H TFT inverter are investigated and modeled so that its switching speed can be predicted and the optimized inverter can be designed.
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This work was supported by the AMOCO Research Center.