Back-illuminated single-photon avalanche diode with superior temporal resolution for next-generation solid-state LiDAR

We report on a back-illuminated (BI) single-photon avalanche diode (SPAD) based on 40 nm CIS technology specialized for both temporal resolution and photon detection probability (PDP). The proposed SPAD utilizes an optimized epitaxial layer and an isolated carrier-collection region to enhance timing resolution while maintaining high PDP in the near-infrared (NIR) region. To further improve its performance, various guard-ring (GR) structures were investigated, and a virtual GR configuration demonstrated superior trade-offs in terms of dark count rate (DCR), timing jitter, and PDP. A dedicated technology computer-aided design simulation and light emission test and laser scanning microscope measurements confirm strong electric-field confinement within the planar junction. Comprehensive electrical characterizations reveal a low breakdown voltage of 15 V and excellent timing jitter of 46 ps [full width at half maximum (FWHM)] at 940 nm under 5 V excess bias voltage. The measured PDP reaches 21% at 940 nm, making it highly effective for a wide-range of light detection and ranging (LiDAR) applications where both depth resolution and NIR sensitivity are critical. Furthermore, the device maintains relatively a low DCR, 2.7 kcps at 25 °C, robust temperature stability (−30 to 90 °C), and negligible afterpulsing. Compared to previously reported state-of-the-art BI SPADs, the proposed device achieves significant improvements in timing precision and NIR efficiency while maintaining compact pixel architecture. These results demonstrate the suitability of the SPAD for integration into compact, low-power depth-sensing systems in emerging platforms, such as mobile LiDAR and AR/VR/XR devices.