Study of Polysilicon Position-Sensitive Detector (PSD)

Abstract

A position-sensitive detector (PSD) fabricated using polysilicon films by a standard LSI fabrication process has been designed and its basic characteristics for sensor applications have been evaluated, together with the electrical characteristics of polysilicon photodiodes. A polysilicon PSD can be used as an optical position sensor on LSI chips without additional areas or process steps. Although the optoelectric conversion efficiency of a polysilicon PSD with a thickness of 335 nm irradiated with a near-IR light source was very low owing to small absorption coefficients and a short diffusion length of minority carriers in polysilicon films, a linear relationship between light position and output current was obtained. Using polysilicon films with a thickness of 1 μm, we improved the optoelectric conversion by about one order and obtained a hyperbolic-sine position dependence.