CMOS Image Sensor for the THESEUS X-ray Space Telescope

瞬态高能天空和早期宇宙探测器（THESEUS）是由欧洲航天局提出的一项空间望远镜使命，其任务是通过X射线、伽马射线和红外波长成像研究早期宇宙。THESEUS上将有一个工作在300 eV至6 keV能量范围内的软X射线成像仪，计划使用一系列专用CMOS图像传感器（CIS）作为有源器件。CIS由于其众多优点而越来越多地用于空间应用。与电荷耦合器件（CCD）不同，CIS在很大程度上不受辐射引起的电荷转移效率低下的影响，并且可以耐受大剂量的电离辐射。此外，CIS功耗更低，并在芯片上集成了数字化和其他功能，大大简化了航天器电子设备并减轻了其质量。对软X射线成像仪的要求决定了传感器建立在相对厚的、完全耗尽的硅衬底上，并且具有大的像素尺寸（例如40平方微米）以及非常低的读出噪声和图像滞后。由于现有CMOS技术的要求和限制之间的相互冲突，这对传感器设计提出了若干挑战。特别地，用于实现可忽略的图像滞后的解决方案使得完全耗尽更加困难，并且可以使得感测节点太大，这增加了读出噪声

Proposed by the European Space Agency, the Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space telescope mission tasked with studying the early Universe by imaging in the X-ray, gamma-ray and infrared wavelengths. Onboard THESEUS will be a soft X-ray imager working in the 300 eV to 6 keV energy range, which is planned to use an array of specialised CMOS image sensors (CIS) as active devices. CIS are increasingly used in space applications due to their numerous advantages. Unlike Charge Coupled Devices (CCDs), CIS are largely immune to radiation-induced charge transfer inefficiency and can tolerate large doses of ionising radiation. In addition, CIS dissipate less power and integrate digitisation and other functions on-chip, significantly simplifying spacecraft electronics and reducing its mass. The requirements for the soft X-ray imager dictate that the sensor is built on a relatively thick, fully depleted silicon substrate, and has large pixel size (e.g. 40 micrometres square) combined with very low readout noise and image lag. This poses several challenges to the sensor design due to the conflicting interplay between the requirements and the limitations of the available CMOS technologies. In particular, the solutions for achieving negligible image lag make full depletion more difficult, and can make the sense node too large, which increases the readout noise