A CMOS optical PSD with submicrometer resolution

This paper presents the design of an optical Position Sensing Detector (PSD) for application in biological material gene identification. The system is able to measure changes in the position of a light spot emitted by a Vertical Cavity Surface Emitting Laser (VCSEL). Changes in spot position are produced by the deflections of a microcantilever used to sense the hybridisation process of the biological material. Detection of these deflections requires submicrometer resolution. The photodetectors and the detection algorithm proposed in this paper have been designed and optimized for this resolution. A 0.35 μm CMOS prototype consisting of an array of 22 PSDs has been implemented and experimentally characterized. The obtained results confirm that displacements of the light spot position as low as 0.15 μm can be detected.