Punchthrough Enhanced Phototransistor Fabricated in Standard CMOS Process

A simple lateral structure phototransistor, combined with a normal phototransistor and a punchthrough transistor, has been successfully designed and fabricated in standard commercial CSMC 0.5- mum CMOS process. The proposed punchthrough enhancement mechanism provides a high optical gain of close to 10⁷ for a low-level optical power of 7.0 times10^-15W at a wavelength of 650 nm. Compared with conventional punchthrough phototransistors, a lower dark current of around 1 muA is obtained at a 2.0-V operating voltage.