Integrated Ambient Light Sensor With Nanocrystalline Silicon on a Low-Temperature Polysilicon Display Panel

A novel integrated ambient light sensor using nanocrystalline silicon fabricated using low-temperature polysilicon technology has been developed on a display panel. The photosensing structure of the silicon nanocrystals embedded in a dielectric film sandwiched between the bottom metal and top indium-thin-oxide electrodes perfectly eliminates backlight noise, which is a problem typical of conventional p-i-n photodiodes integrated into a liquid-crystal display. Experimental results indicate that the Si-nanocrystal photosensor has better performances in dark current and quantum efficiency than those of the p-i-n diode. The Si-nanocrystal photosensor also exhibited response linearity and speed comparable to the p-i-n diode. In terms of long-term operation and reliability, the lifetime of the Si-nanocrystal photosensor is roughly two orders longer than that of the p-i-n diode. The Si-nanocrystal ambient light sensor has considerable flexibility in the design of spectrum, geometry, and the readout circuit, which is achieved by adjusting the nanocrystal size and applying a vertical stacking structure. The Si-nanocrystal photosensor can be a promising low-cost PMOS-only solution for various photosensing applications on display panels.