Characteristics of a-SiGe:H Thin Film Transistor Infrared Photosensor for Touch Sensing Displays

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

“…4(a). And then, the photo current at a bias of V was selected at each wavelength, because the increase of photo current at the off-state was more significant than at the on-state [14]. Before the illumination on the device, the optical power of incident light was measured and calibrated at every step.…”

“…However, it was observed that the overall TFT characteristics of the a-SiGe:H TFT was degraded due to the higher number of defects [25] contained in the active layer (see [14] for details). If the direction of polarization is perpendicular or parallel to the director at incidence, the polarization state of the light will follow the twist of the local director as the light propagates in the liquid crystal (LC).…”

“…The key to solving such a problem could be using an infrared (IR) as a touch sensing light source, which is not interfered by ambient visible light [13], [14]. For these, the materials sensitive to IR such as amorphous SiGe are necessary.…”

A $\alpha $ -Si:H Thin-Film Phototransistor for a Near-Infrared Touch Sensor

“…Key challenges for planar photosensor arrays involve large areal coverage at relatively low cost, high sensitivity, and rapid-response. Most of these requirements can be realized Manuscript in commercial products by implementing hydrogenated amorphous silicon (α-Si:H) devices, which are widely used in large-area applications such as flat panel display backplanes or photodetector arrays [3], [4]. Although α-Si:H is an excellent photosensor material for touch-sensing in displays, a major drawback involves its photo-sensitivity with respect to ambient sunlight while in external light mode, or light emanating from organic emissive layers in organic light emitting diode (OLED) panels.…”

“…Furthermore, in the sensor TFT, unlike the switching TFT, only the selective near IR light can be absorbed by the active channel through the band-pass filter metal layers, which have high transmittance in the near IR region [13]. Although our device has lower sensitivity than metal-oxide [7] or SiGe [4] phototransistors, the sensitivity of the a-Si:H phototransistor is just sufficient to prevent the incidence of unnecessary IR light from ambient light and transmit the intended IR signals only. By virtue of the block metal layers and band-pass filter layers, the a-Si:H phototransistor can sense the near IR light selectively and is not interrupted by external visible light.…”