A SPAD Depth Sensor Robust Against Ambient Light: The Importance of Pixel Scaling and Demonstration of a 2.5μm Pixel with 21.8% PDE at 940nm

Abstract

We present scaled down Single Photon Avalanche Diode (SPAD) pixels to prevent Photon Detection Efficiency (PDE) degradation under high ambient light. This study is carried out on Back-Illuminated (BI) 3D-stacked SPAD array sensors with 3.3, 3.0, and 2.5μm pixel pitches fabricated using a CMOS 300mm platform. To achieve pixel scaling, the developed pixels introduce a sub-micron avalanche region to prevent premature edge breakdown while allowing for a low Dark Count Rate (DCR). Moreover, optimized optical lenses enable scaled down pixels to achieve approximately 100% fill factor, thereby boosting the PDE at λ=940nm beyond 20%, even under sunlight conditions. These sensors offer cost-efficient and high accuracy depth-sensing capabilities, even under challenging ambient light conditions.