Park, Eunsung Park, Hyo-Sung Choi, Hyun-Seung Choi, Woo-Young Lee, Myung-Jae 2026-02-19T07:30:13Z 2026-02-19T07:30:13Z 2026-02-19 2026-03 1077-260X https://pubs.kist.re.kr/handle/201004/154332 Single-photon avalanche diode (SPAD) pixel scaling is essential to meet the increasing demands for high-resolution, compact, and power-efficient time-of-flight (ToF) sensing. In particular, the 3D-stacked approach enables aggressive pixel scaling by separating the SPAD and readout circuits into different wafers, thus maximizing the fill factor while minimizing the pixel pitch. However, pixel miniaturization often leads to degraded SPAD performance due to the premature edge breakdown (PEB) and the reduced number of photon-generated carriers that go through the avalanche multiplication region. In this work, we overcome these challenges by optimizing the doping profile to enhance the carrier collection in the device. We present a detailed analysis of the optimization progress by evaluating breakdown voltage (VB), dark count rate (DCR), and photon detection probability (PDP), highlighting the trade-offs and recovery achieved through successive doping refinements. The optimized device achieves a PDP of 37% and a timing jitter of 85 ps at 940 nm. Compared to prior 3D-stacked back-illuminated (BI) SPADs, our work exhibits one of the smallest pixel pitches to date, yet retains competitive PDP and jitter characteristics. This combination of aggressive scaling and robust performance positions the proposed SPAD as a promising solution for LiDAR, 3D imaging, and future wearable sensing systems. English Institute of Electrical and Electronics Engineers 3D-Stacked Back-Illuminated Single-Photon Avalanche Diode Pixel With a Pitch of 3.5 μm Article 10.1109/JSTQE.2026.3651682 1 IEEE Journal on Selected Topics in Quantum Electronics, v.32, no.2 IEEE Journal on Selected Topics in Quantum Electronics 32 2 N scie scopus 001681369900001 2-s2.0-105027775268 Engineering, Electrical & Electronic Quantum Science & Technology Optics Physics, Applied Engineering Physics Optics Article TIME-RESOLVED FLUORESCENCE SPAD LINE SENSOR RESOLUTION Single-photon avalanche diodes Photonics Optimization Silicon Laser radar Performance evaluation Doping profiles Three-dimensional displays Metals Electric breakdown 3D imaging 3D photonics 3D-stacked SPAD sensor back-illuminated SPAD LiDAR photon detection probability (PDP) pixel pitch pixel scaling resolution single-photon avalanche diode (SPAD) timing jitter