Performance of the floating gate/body tied NMOSFET photodetector on SOI substrate

In this paper, we report the performance of a new photodetector fabricated on SOI substrate using a standard CMOS process. The photodetector is formed by connecting the gate and the body of a NMOSFET. The gate-body terminal is left floating so that the potential can be modulated by illumination. The depletion region induced by the floating gate separates the optically generated electron-hole pairs in the direction perpendicular to the current. This increases the body potential and induces positive charges to the gate due to the tied gate and body. It results in a further turn on of the NMOSFET and extra optical current. The gain behavior under different illumination is characterized and explained by transistor theory. A wide signal range of more than six orders of magnitude and a high responsivity of about 1000 A/W have been obtained with an operating voltage as low as 0.2 V. The device scaling properties, noise behavior and transient response are also studied.