On-chip sensor for light direction detection

We present an on-chip optical sensor capable of detecting the direction of incident light. No off-chip optical or mechanical components or modifications-for example, baffles, slit structures, mirrors, etc.-are needed. The sensor was implemented in a standard 0.5 ìm complementary metal-oxide semiconductor process. A pair of on-chip photodiodes separated by a metal "wall" (created by stacking all metal layers, contacts, and vias available in the process) is used to detect the direction of the incident light. This metal stack wall creates on-chip shadowing to facilitate detection so that the two photodiodes produce different amounts of photocurrent. A model for this device is presented. The analysis indicts that the ratio of the difference of these two currents to the larger of the two currents has a linear relationship with the angle of the incident light. Moreover, we also demonstrate this ratio is almost independent of the incident light intensity. Test results verify these two conclusions and show good sensitivity to light direction and immunity to light intensity. An accuracy of 1.6 deg over a 100 deg range is achieved by the linear relationship.