Various layouts of analog CMOS optical position-sensitive detectors

Abstract

We report on the fabrication and characterization of analog multi-pixel optical position-sensitive detectors (PSD's) for sensing the two-dimensional position of a light spot over the sensor area. Computer simulations were performed to understand the influence of the geometrical layout of the device on the linearity of response. Standard CMOS technology was chosen for fabrication so that the detectors are compatible with reliable low-cost and low-power electronics for integration with processing electronics. Three chessboard-like 5x5-pixel structures, with different pixel layouts have been implemented. The response linearity was calculated and measured over 80% of the detector active area. It was shown that chessboard-like structures are not suitable for spot diameters below 2 pixels. For a light spot diameter comparable with the device size, the best linearity of response -RMS deviation of less than 4% -among all three structures is achieved by the structure with vertical phototransistors as the photo-sensing elements. We also implemented a PSD with two complementary spiral structures, providing sensing for both coordinates in each pixel. With this layout we achieved RMS non-linearity of less than 3.5% for a spot size comparable with pixel size in close agreement to the simulations. The computer model indicates that the non-linearity for all structures studied decreases with the number of pixels.

Fast Hartmann-Shack wavefront sensors manufactured in standard CMOS technology

“…The quad cell, alternating, chessboard-like, and spiral structures all yield the and coordinates of the light-spot centroid based on the relative photocurrents on rows and columns of photodetectors. The working principle of each of these structures and the performance of the respective implemented CMOS structures was given by de Lima Monteiro et al [7]. The main advantage of using PSDs is the nearly direct information about the positions of the spots, rendering image processing unnecessary.…”