Fill-factor improvement of Si CMOS single-photon avalanche diode detector arrays by integration of diffractive microlens arrays.

Giuseppe Intermite,Ryan E Warburton,Aongus Mccarthy,Andrew J Waddie,Ximing Ren,Franco Zappa,Alberto Tosi,Federica Villa,Gerald S Buller,Rudi Lussana,Mohammad R Taghizadeh

doi:10.1364/oe.23.033777

Abstract

Single-photon avalanche diode (SPAD) detector arrays generally suffer from having a low fill-factor, in which the photo-sensitive area of each pixel is small compared to the overall area of the pixel. This paper describes the integration of different configurations of high efficiency diffractive optical microlens arrays onto a 32 × 32 SPAD array, fabricated using a 0.35 µm CMOS technology process. The characterization of SPAD arrays with integrated microlens arrays is reported over the spectral range of 500-900 nm, and a range of f-numbers from f/2 to f/22. We report an average concentration factor of 15 measured for the entire SPAD array with integrated microlens array. The integrated SPAD and microlens array demonstrated a very high uniformity in overall efficiency.

Highlights

Picosecond-resolution detection of single-photons in the visible and near-infrared (NIR) spectral range below a wavelength of 1 μm is required in many photon-starved applications such as time-of-flight ranging and imaging and time-resolved biomedical science [1,2,3,4,5].In this spectral range, detection of low–light level optical signals with picosecond timing resolution can be achieved using time-correlated single photon counting approaches [6], where a variety of single-photon detector options are available
Scaling down of the CMOS process may offer some advantages in reduced jitter through device miniaturization, it usually results in higher dark count rate (DCR) and it may not necessarily result in increased single-photon detection efficiency (SPDE) compared with custom processed Single-photon avalanche diode (SPAD) [16,17]
To evaluate the performance of infinite and finite conjugate diffractive microlenses resulting from the integration on the 32 × 32 SPAD array, the concentration factor used previously in [19] was applied: E CF = 0 (2)

Summary

Introduction

Picosecond-resolution detection of single-photons in the visible and near-infrared (NIR) spectral range below a wavelength of 1 μm is required in many photon-starved applications such as time-of-flight ranging and imaging and time-resolved biomedical science (e.g. fluorescence lifetime imaging, and positron emission tomography) [1,2,3,4,5]. Si SPAD detectors can be classified into two distinct groups: those fabricated using customized processing techniques and those fabricated using CMOS compatible approaches The former devices are based on tailored processing with the aim of obtaining the best performance from the photodiode when operated in Geiger-mode. From the early 2000s, several research groups have explored the design of a monolithically integrated single-photon imaging systems in high-voltage (HV) and standard deep-sub-micron (DSM) CMOS technologies [12,13,14,15,16] This efficient integration allows the possibility of fabrication of two-dimensional SPAD-based focal plane arrays. To the best of our knowledge, we report the highest value of the concentration factor for a full microlens array integrated with a SPAD array, with the best reported value for uniformity across the whole detector array after integration of the microlens and SPAD arrays

HV-CMOS Si SPAD Array

Results

Conclusions