基于3D堆叠结构的CMOS单光子雪崩光电二极管像素的高信噪比研究

As an important means of extreme visual perception, the CMOS single photon avalanche photodiode (SPAD) image sensor, with the advantages of single photon sensitivity, picoseconds temporal resolution and micron space resolution, is currently the mainstream ideal device for transient imaging requiring single photon sensitivity. However, within the CMOS SPAD pixel, the SPAD could not obtain low dark count rate, high quantum efficiency and high fill factor, simultaneously. Besides, the functions of quenching the recharge circuit are relatively limited. Based on the back-illuminated SPAD structure compatible with 3D-stacked pixels and the 180nm CMOS process, the project is intended to achieve a SPAD with low dark count rate and high quantum efficiency, through the innovation of the photosensitive region and anti-reflection film of the device. The innovative structure of quenching and recharge circuit would be proposed, which could effectively suppress the effects of after-pulse, dark count and optical crosstalk of the SPAD, and ensure the output signal with good time resolution. The 3D-stacking technologies is used to realize the 3D integration between the SPAD and the quenching and recharge circuit, which makes the SPAD with high fill factor. Finally, high signal-to-noise ratio would be realized for the CMOS SPAD pixel based on 3D-stacked architecture.

作为极限视觉感知的重要手段，CMOS单光子雪崩光电二极管（SPAD）图像传感器兼具单光子灵敏度、皮秒量级时间分辨率和微米级空间分辨率，是目前实现单光子、瞬态成像的主流理想器件。然而，CMOS SPAD像素中SPAD器件还无法兼具较低暗计数率、较高量子效率和较高填充因子，而且淬灭充电电路功能也比较局限。本项目基于与3D堆叠结构像素相兼容的背入射SPAD器件结构和180nm CMOS工艺，拟通过创新器件的光敏区和减反膜，使其兼具较低暗计数率和较高量子效率。拟通过创新淬灭充电电路的电路结构，使其可有效抑制SPAD器件的后脉冲、暗计数和光学串话效应，保证输出信号具有较好时间分辨率。利用3D堆叠技术实现SPAD器件与淬灭充电电路之间的3D集成，使SPAD器件具有较高填充因子。最终使基于3D堆叠结构的CMOS SPAD像素实现较高的信噪比。

作为极限视觉感知的重要手段，CMOS单光子雪崩光电二极管（SPAD）图像传感器兼具单光子灵敏度、皮秒量级时间分辨率和微米级空间分辨率，是目前实现单光子、瞬态成像的主流理想器件。然而，CMOS SPAD像素中SPAD器件还无法兼具较低暗计数率、较高量子效率和较高填充因子，而且淬灭充电电路功能也比较局限。本项目基于与3D堆叠结构像素相兼容的SPAD器件结构和180nm CMOS工艺，通过创新器件的光敏区结构，提出了基于PIN结构的正入射、背入射SPAD器件，常温下暗计数率低于0.5Hz/um2，850nm处探测效率达到20%；提出了基于超表面增强吸收的增透结构，将850nm处量子效率提升2倍以上，并提出了基于表面等离子共振效应的近红外增强吸收结构，实现了1550nm处的高探测效率。通过创新淬灭充电电路的电路结构，提出了被动淬灭、主动淬灭以及多通道被动淬灭等多种电路，使其可有效抑制SPAD器件的后脉冲、暗计数和光学串话效应，保证输出信号具有较好时间分辨率，时间分辨率达到38.9ps。结合光学定制化设计，本项目研制出的SPAD单光子探测器的探测极限高于其他SPAD近30倍。通过片间3D集成，实现了高信噪比的CMOS SPAD像素的研制。