Suppression of Light Influx Into the Channel Region of Photosensitive Thin-Film Transistors

Analysis on the light influx into a bottom-gate, etch-stopper structure thin-film transistor is presented. Reduction of the light influx by means of structural changes in the device can lead to a universal improvement in negative-bias temperature illumination stress instability of metal-oxide transistors. When the devices are illuminated by a fixed light source from below, the dominant light influx occurs in the channel-width direction, due to light reflections off the boundary between the passivation layer and the ambient. Wave propagation into the channel can be suppressed by using thinner dielectric layers or applying an overlying coating layer with a larger refractive index than that of the passivation dielectric material.