High sensitivity readout of 2D a-Si image sensors

A highly sensitive charge-sensitive amplifier IC was used to read out large-area two-dimensional arrays of amorphous silicon (a-Si) p-i-n photodiodes addressed by a-Si thin film transistors (TFTs). At the highest sensitivity mode, the random noise of the sensor was equivalent to an input charge of 1500 electrons rms. Feedthrough charge injection associated with TFT switching had to be avoided at the expense of the signal charge. Image lag caused by charge trapping in a-Si was suppressed by limiting the input light intensity. A simple model was developed for the noise contribution from a pixel and compared with measurements.