Low frequency noise in amorphous silicon thin-film transistors

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are used as charge switches in flat-panel X-ray detectors. The inherent noise in the TFTs contributes to the overall noise figure of the detectors and degrades the image quality. Measurements of the noise provide an important parameter for modeling the performance of the detectors and contribute to understanding the origins of the noise that could lead to improvements in TFT design. We have measured the low-frequency, conductance noise in a-Si:H TFTs with an inverted staggered structure. We find that the noise power density spectrum fits well to a 1/f^a power law with a near one. The noise power is inversely proportional to the gate voltage and also inversely proportional to channel length in both the linear and saturation regions. The results are in accord with theory. The Hooge parameter for the devices is approximately 1xW^-3