High responsivity photo-sensor using gate-body tied SOI MOSFET

SOI technology has proven to be advantageous in many applications compared to conventional bulk technology. However, the progress for use of SOI technology in low power imaging applications is relatively slow, despite the significant advancements achieved in bulk CMOS active pixel sensing circuits. It is difficult to fabricate optical sensors on SOI substrates due to the limited depth of silicon available on the top film, resulting in limited photon absorption capability. To overcome such limitations, CMOS compatible devices with self-amplification have been reported (Zhang et al. 1997; Yamamoto et al. 1996). However, the amplification is still not very satisfactory. In this paper, we have investigated the performance of a newly developed gate-body tied SOI MOSFET optical sensor fabricated with a DTMOS (dynamic threshold MOSFET) process (Assaderaghil et al. IEDM94, pp. 809-12, 1994). With dimensions of 5 /spl mu/m width by 2 /spl mu/m length, the optical current generated is of the order of micro-amperes, which can be directly read out for processing. The optical current can be further increased by reducing the channel length, and thus dimension reduction and performance enhancement can be achieved at the same time.