A fractal-based photodiode for on-chip energy harvesting

This paper presents the design and test of a photodiode with improved conversion efficiency for on-chip solar energy harvesting applications. The improved efficiency is achieved by exploiting the lateral photoresponse of the photodiode through the usage of diodes with fractal geometries. The fractal diodes have a large perimeter-to-area ratio which translates into more collected charges due to lateral photoresponse. An approximation of the quadric Koch island fractal has been designed and fabricated in a 0.5μm CMOS process along with a rectangular photodiode of equal area but different perimeter that serves as the control. Measurements of the fabricated chip show improvements in the charge collection of the fractal-based photodiode of up to 6% with respect to the rectangular control photodiode.