Front and Back Illuminated Dynamic and Active Pixel Vision Sensors Comparison

Back side illumination has become standard image sensor technology owing to its superior quantum efficiency and fill factor. A direct comparison of front and back side illumination (FSI and BSI) used in event-based dynamic and active pixel vision sensors (DAVIS) is interesting because of the potential of BSI to greatly increase the small 20% fill factor of these complex pixels. This brief compares identically designed front and back illuminated DAVIS silicon retina vision sensors. They are compared in term of quantum efficiency (QE), leak activity and modulation transfer function (MTF). The BSI DAVIS achieves a peak QE of 93% compared with the FSI DAVIS, peak QE of 24%, but reduced MTF, due to pixel crosstalk and parasitic photocurrent. Significant “leak events” in the BSI DAVIS limit its use to controlled illumination scenarios without very bright light sources. Effects of parasitic photocurrent and modulation transfer functions with and without IR cut filters are also reported.

I. Introduction

Event-based neuromorphic vision is an emerging field of machine vision. The Dynamic Vision Sensor (DVS) [1] has applications stemming from its high temporal resolution, low latency, high dynamic range, and sparse output. Each DVS pixel reports brightness change (log intensity change) events. The latency and amount of transferred data is reduced compared with conventional image sensors. The high dynamic range, due to the logarithmic phototransduction, allows application with less controlled lighting.