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High fill-factor miniaturized SPAD arrays with a guard-ring-sharing technique
Optics Express
|May 15, 2020
Summary
Researchers developed a novel guard-ring-sharing technique, enabling the smallest single-photon avalanche diode (SPAD) pixels at 2.2 µm pitch. This breakthrough facilitates compact, high-resolution SPAD arrays for advanced imaging applications.
Area of Science:
- Photonics and Semiconductor Devices
- Integrated Circuit Design
Background:
- Single-photon avalanche diode (SPAD) technology is crucial for low-light imaging.
- Pixel miniaturization is a key challenge for increasing SPAD array resolution and density.
Purpose of the Study:
- To introduce a novel guard-ring-sharing technique for SPAD pixel miniaturization.
- To demonstrate the operation and performance of SPAD arrays with record-small pixel pitches.
Main Methods:
- Device simulations and preliminary tests were conducted.
- 4x4 SPAD arrays were designed using 180 nm CMOS technology with parallel selective readout circuits.
- SPAD characteristics (fill factor, PDP, DCR, jitter, crosstalk, afterpulsing) were systematically measured for various pixel pitches (2.2, 3, and 4 µm).
Main Results:
- The smallest reported SPAD pixel pitch of 2.2 µm was achieved.
- For a 4 µm-pitch SPAD, key performance metrics included a 42.4% fill factor, 33.5% maximum PDP, 2.5 cps median DCR, 88 ps timing jitter, 3.57% crosstalk, and 0.21% afterpulsing.
- Electrical isolation was confirmed for SPADs utilizing guard-ring sharing.
Conclusions:
- The guard-ring-sharing technique successfully enables SPAD pixel miniaturization.
- The demonstrated SPAD arrays show promising performance, validating the technique for compact, multi-megapixel 3D-stacked SPAD arrays.
