A 64 × 128 3D-Stacked SPAD Image Sensor for Low-Light Imaging.

Area of Science:

• Photonics and Sensor Technology
• Image Processing
• Semiconductor Devices

Background:

• Low-light imaging is critical for applications like security, autonomous driving, and environmental monitoring.
• Single-Photon Avalanche Diode (SPAD) sensors offer high performance for low-light conditions.
• Existing sensors often struggle with sensitivity and noise in very dim environments.

Purpose of the Study:

• To develop and characterize a high-performance 64x128 SPAD image sensor optimized for low-light imaging.
• To enhance photosensitivity and reduce noise through advanced design techniques.
• To demonstrate effective 2D grayscale imaging capabilities under extremely low illumination.

Main Methods:

• Designed a 64x128 SPAD image sensor utilizing a 3D stacking architecture and microlens technology.
• Incorporated compact gated pixel circuits with thick-gate MOS transistors to boost photosensitivity.
• Implemented a configurable digital control circuit for adjustable exposure times and a dedicated SPAD denoising algorithm.

Main Results:

• Achieved very low dark noise levels, with an average Dark Count Rate (DCR) of 41.5 cps at 2.4 V excess bias.
• Successfully demonstrated 2D grayscale imaging under 6 × 10^-4 lux illumination.
• The sensor exhibits excellent low-light imaging performance, leveraging SPAD advantages.

Conclusions:

• The developed SPAD image sensor significantly enhances low-light imaging capabilities.
• The sensor's design effectively addresses challenges in sensitivity and noise.
• This technology shows strong potential for diverse applications requiring high-performance low-light vision.