24.1: A 2 Inch a‐Si:H TFT‐LCD with Backlight Control TFT Sensors

Abstract We have developed a 2.0 inch a‐Si:H TFT‐LCD with the photosensors for detecting the brightness of backlight and outdoor daylight. Two kinds of sensors were embedded in the TFT backplane with a‐Si:H TFTs with bottom gate and top gate structures. A pixel has a switching TFT and a TFT sensor in addition to the capacitance. The TFT sensor exhibited the photo‐current of ∼10 −9 A and dark current of ∼10 −12 A in the operation region of backlight. The dynamic range is 60 dB which is high enough to sense the brightness of the backlight. The output signal saturates at ∼ 20000 Lux in the present work but it can be increased by decreasing the TFT size.