Flexible ultrathin-body single-photon avalanche diode sensors and CMOS integration.

Pengfei Sun,Edoardo Charbon,Ryoichi Ishihara

doi:10.1364/oe.24.003734

Abstract

We proposed the world's first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively and we extend this work to the first flexible SPAD image sensor with in-pixel and off-pixel electronics integrated in CMOS. Experimental results show that dark count rate (DCR) by band-to-band tunneling can be reduced by optimizing multiplication doping. DCR by trap-assisted avalanche, which is believed to be originated from the trench etching process, could be further reduced, resulting in a DCR density of tens to hundreds of Hertz per micrometer square at cryogenic temperature. The influence of the trench etching process onto DCR is also proved by comparison with planar ultrathin-body SPAD structures without trench. Photon detection probability (PDP) can be achieved by wider depletion and drift regions and by carefully optimizing body thickness. PDP in frontside- (FSI) and backside-illumination (BSI) are comparable, thus making this technology suitable for both modes of illumination. Afterpulsing and crosstalk are negligible at 2µs dead time, while it has been proved, for the first time, that a CMOS SPAD pixel of this kind could work in a cryogenic environment. By appropriate choice of substrate, this technology is amenable to implantation for biocompatible photon-counting applications and wherever bended imaging sensors are essential.

Highlights

Solid-state single-photon avalanche diode (SPAD) technology has existed for decades and is receiving wide attention for applications such as time-of-flight vision, time-correlated singlephoton counting, fluorescence lifetime sensing and biomedical imaging
We demonstrated the world’s first flexible SPAD fabricated in an ultrathin-body silicon-on-insulator (SOI) process followed by transfer post-processing to flexible substrate [12], and we achieved a flexible SPAD with dual-side illumination for the first time [13]
We investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively: dark count rate (DCR), VBD and photon detection probability (PDP) are studied based on different junction parameters, operation temperature and device structures

Summary

Introduction

Solid-state single-photon avalanche diode (SPAD) technology has existed for decades and is receiving wide attention for applications such as time-of-flight vision, time-correlated singlephoton counting, fluorescence lifetime sensing and biomedical imaging. A typical application in the field of biomedical sensing is the retinal prosthesis [6,7,8], where a single-photon imaging device, integrated with CMOS circuitry on flexible substrate, could be implanted into the eye and bent to match the curvature of the eyeball. Another application is chronic biomedical monitoring [9], where a wearable or implantable miniaturized single-photon sensor could be left in situ to continuously monitor a person’s health status, providing more accurate information about the progression of diseases such as cancer and other inflammatory or chronic ailments.

Device structure and fabrication flowchart

Measurement results

Comparison between flexible trench-isolated SPAD and planar SOI SPAD

Findings

Conclusions