Integrated Cascade of Photovoltaic Cells as a Power Supply for Integrated Circuits

ICs can be powered directly by light when a supply voltage source capable of generating a multiple of the open clrcult voltage of one pnqnctlon 1s available on a chip Two schemes have been mvestlgated for cascading photovoltalc cells on the chip The structures can be made compatible with standard bipolar processes Deep Ion lmplantatlons have been used here to realize the multiple-Junction structure Power losses due to photocurrents ongmatmg from msulatlon Junctions m the cascade can be kept to a mm+ mum The surface areas of two adJacent cells have to satisfy a definite relation to ensure the build-up of output voltage Operating under sunlight condltlons, 0 6 mW/cm2 has been generated m a cascade of three cells With appropnate optical coatmgs on the slhcon surface and optimized cell dlmenslons, It should be possible to generate a few mllhwatts per cm2 The structures may have apphcatlons m electronic clrcults for glass flbres or can be used to power small CMOS clrcults