A novel amplified image sensor with a-Si:H photoconductor and MOS transistors

An image sensor and a 16×16 pixel test device consisting of a MOS transistor array overlaid with an a-Si:H photoconductive film are presented. The sensor operates by applying the potential induced on the surface of a a-Si:H film directly to the gates of the MOS transistors, and then reading out the modulated drain currents. Photosensitivity is 4-5.6 μA/(nJ/cm²) for incident light of λ=0.6 μm, dynamic range is over 85 dB, and γ≃1. The sensor can be constructed in four configurations, depending on whether the carriers of image information in the a-Si:H film or MOS transistor channel are electrons or holes. The properties of signal and gain for the sensors of low and high pixel density, respectively, are analyzed, and it is pointed out that two distinct amplifying effects can exist in the sensor simultaneously