A Backside-Illuminated Charge-Focusing Silicon SPAD with Enhanced Near-Infrared Sensitivity

TL;DR

This paper introduces a backside-illuminated silicon SPAD with charge focusing, achieving enhanced near-infrared sensitivity, high detection efficiency, and good timing resolution, suitable for large-scale ToF imaging arrays.

Contribution

The paper presents a novel BSI silicon SPAD with charge focusing and integrated CMOS electronics, improving near-infrared sensitivity and scalability for ToF applications.

Findings

Photon detection efficiency of 27% at 905 nm

Timing resolution of 240 ps

Potential for scalable pixel pitch reduction

Abstract

A backside-illuminated (BSI) near-infrared enhanced silicon single-photon avalanche diode (SPAD) for time-of-flight (ToF) light detection and ranging applications is presented. The detector contains a 2 $\mu$m wide multiplication region with a spherically-uniform electric field peak enforced by field-line crowding. A charge-focusing electric field extends into a 10 $\mu$m deep absorption volume, whereby electrons generated in all corners of the device can move efficiently towards the multiplication region. The SPAD is integrated with a customized 130 nm CMOS technology and a dedicated BSI process. The device has a pitch of 15 $\mu$m, which has the potential to be scaled down without significant performance loss. Furthermore, the detector achieves a photon detection efficiency of 27% at 905 nm, with an excess bias of 3.5 V that is controlled by integrated CMOS electronics, and a timing resolution of 240 ps. By virtue of these features, the device architecture is well-suited for large format ToF imaging arrays with integrated electronics.