Optoelectronic CMOS Power Supply Unit for Electrically Isolated Microscale Applications

This paper presents a CMOS power supply unit for electrically isolated microscale applications, where the provision of electrical power is not appropriate through wiring. A miniature fiberoptic platform consisting of an inclined silicon mirror fabricated using bulk micromachining is coupled to the monolithically integrated photodiode/dc-dc converter system, to yield a stand-alone optical power supply. In this approach, the dc/dc converter steps up the voltage of a single CMOS-integrated photodiode to a higher level. A test chip is fabricated using UMC 0.18-mu m triple-well CMOS technology to demonstrate the power supply unit. Two different types of photodiodes, namely, a triple-well photodiode and an n-well photodiode are compared. It is found that on-chip triple-well photodiode results in a projected responsivity of 26 mA/W. The dc/dc converter had a maximum efficiency of 56% and is able to boost an input voltage level of 0.5-to-1.2V. Silicon mirrors coated with 25-nm-thick aluminum are measured to have a reflectivity of 80% for a laser beam at a wavelength of 650 nm. Capability of the overall packaged optoelectronic system, consisting of the optical fiber, silicon mirror, CMOS photodiode, and the dc/dc converter, is demonstrated by generation of an electrical power of 60 mu W.