A 4.2K CMOS optical detector

An integrated CMOS (Complementary Metal-Oxide-Semiconductor)-compatible optical detector for liquid-helium-temperature LHT (4.2K) operation is presented. The optical detector, which responds to 0.768- and 1.1-μm wavelength light sources, is built in the n-well of a 0.7μm CMOS integrated circuit technology. The optical detection is based on the photogeneration of carriers in the frozen n-well that changes its output resistance at a ratio of 1.79MΩ per mW of optical power. The cryo-optical system has been tested with and without a built-in preamplification, and has been proved to respond to 50MHz-optical pulses.