a-Si:H TFT array driven linear image sensor with capacitance coupling isolation structure

A new linear image sensor integrating a-Si:H photodiode (PD) array, a-Si:H thin film transistor (TFT) array, multiplex circuits and an analog multiplexer on a single substrate has been developed. The photodiode has an Cr/a-Si:H/ITO sandwich structure. A photo to dark current ratio is 10⁴under 100 Ix green fluorescent lamp illumination. The TFT has an inverted staggered structure and SiNx is used as a gate insulator. ON-current is 2 µA and ON/OFF ratio is 10⁶(W/L = 4). In order to prevent capacitance couplings between data lines, the sensor has a ground line between each data line and ground metal layer between the bottom and upper conductive layer. The output voltage of the sensor is 43 mV at the exposure of 0.5 Ix.s and has uniformity better than ± 15%.