Yoshio Nishihara

a-Si:H TFT Driven Linear Image Sensor

A new contact type linear image sensor, which has 8.5 inches in length and 300 dot/inch, has been developed. By using a thin film transistor (TFT) array as a switching device, it requires only one IC chip compared with 20 ICs in conventional sensor. The new sensor integrates a-Si:H photodiode (PD) array, a-Si:H TFT array, multiplex circuits and an analog multiplexer on a single substrate. The TFT has an inverted staggered structure and amorphous silicon nitride (SiNx) is used as a gate insulator. The PD has a Cr/a-Si:H/ITQ sandwich structure and each PD is completely isolated by photolithography. In the multiplex circuits, a ground line is inserted between each signal line to reduce a capacitive coupling between them. A new custom LSI has also been developed. It has 64-ch input terminals to detect small signal with amplification and 41-ch output terminals to control the gates of TFT array. The sensor with the new LSI has achieved 2MHz clock frequency operation and proved to be used as a high speed device.

Methodology in design of a page width a-Si TFT linear image sensor

Abstract A circuit design method for a matrix driven linear image sensor has been developed. Relations between the circuit parameters and the performance of the sensor are resolved by analysis of the equivalent circuit. Optimizing for gray scale performance is accomplished by adjustment of circuit parameters. The effectiveness of this method has been demonstrated by the development of an actual sensor having the capability of resolving 16 levels of gray scale.