CMOS Sensor for Sun Tracking

We present an optical localization chip capable of detecting the direction of incident light. The chip requires no off-chip optical or mechanical components or post-processing (e.g. baffles, slits, mirrors, etc.). The chip was fabricated in a standard 0.5 mu m CMOS (complementary metal oxide semiconductor) process. Our approach employs 100 light sensing cells, each having two detectors separated by a metal "wall". The "wall" was created by stacking all metal layers, contacts and vias available in the process. This metal stack "wall" is used to create on-chip shadowing to facilitate detection. Each optical detection element produces a differential output with the normalized difference between the currents dependent upon the angle of the incident light. The width of the photodiodes is limited by the height of the metal wall to only a few micrometers. To achieve a good sensitivity, 100 cells are placed in parallel. Test results show good sensitivity to the direction and intensity of the incident light with accuracy of 1.9 degrees over a 100 degree range and 1.1 degrees over a 50 degree range.