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.