a-Si:H TFT-driven high-gray-scale contact image sensor with a ground-mesh-type multiplex circuit

An A4 page width and 300 dot/inch hydrogenated amorphous silicon thin film transistor (a- Si:H TFT) driven contact image sensor which can read more than 128 gray levels has been developed. Crosstalk due to the coupling between data lines in the multiplex circuit has prevented high gray scale reading. In order to eliminate crosstalk, a sensor with a new multiplex structure has been developed with a ground mesh shield layer inserted at the crossover points between each data line. The ground mesh shield pattern was designed to optimize the gray scale reproduction ratio R. With this sensor, R is more than 0.992 for a single bit, thus achieving 128 levels of gray. This design was compared to the performance of two other sensors, one without a ground mesh shield, the other using a data line meander pattern. This technology is also applicable to higher performance image sensors with greater than 400 dot/inch resolution.