Optical Properties of a-SiGe:H Thin Film Transistor for Infrared Image Sensors in Touch Sensing Display

We report the effects of monochromatic illumination on the electrical performance of a-SiGe:H thin-film transistor (TFT) and the use of this device as infrared (IR) image-sensing touch displays. In order to reduce the inevitable incidence of visible light into device, the visible cutting layer was designed, which played a critical role in reducing the optical noise from visible light. When the photo response was observed in real liquid crystal display (LCD) operation environment, it showed the display contents dependence, meaning that the supply of external IR light source for the touch sensing would be effective independent of any ambient light condition. Additionally, the optical noise from the display operation was eliminated using the block operation as well as the backlight IR light-emitting diode (LED) light modulation. From these, the clear touch images were successfully obtained in the a-SiGe:H photosensor embedded LCD panel.