Cryogenic irradiations, a more realistic study of the impact of radiation on detectors in space

电荷耦合器件（ccd）长期以来一直是空间天文学任务的首选探测器。当放置在轨道上时，这些设备会经历恶劣的辐射环境。入射到探测器上的辐射会破坏硅晶格，产生导致“陷阱”形成的缺陷。形成的陷阱可以捕获设备外检测到的信号，导致ccd的涂抹和信号丢失，CMOS传感器的电荷损失和明亮像素，以及增加暗电流等噪声源。在发射任何任务之前，至关重要的是详细研究辐射的影响，以便使用适当的屏蔽，同时开发新的读出技术和校正算法，以减轻剩余的损害。目前，标准做法规定，设备的辐射测试是在室温下进行的，尽管探测器在轨道上运行期间将保持低温，温度通常低至零下120摄氏度。辐照后产生的空位在器件中迁移，直到它们达到稳定状态，但任何特定缺陷结构的稳定性强烈依赖于温度；在室温下存在的捕集器可能与设备在冷辐照和冷保存时存在的捕集器截然不同。关于所谓的“低温辐照”的文献很少，但有报道称室温下辐射的影响与更现实的低温辐照相比有2-3倍的差异，并且这种差异的方向（增加或减少影响）在不同的装置类型之间有所不同。欧几里得任务的目标是绘制暗物质和能量图，它依赖于对辐射对探测器的影响的全面和彻底的了解，从而允许对辐射进行校正，以减少高达300倍的涂抹。哈勃望远镜的校正精度约为30倍，比欧几里得高精度测量所需的校正精度低一个数量级。ESA的JUICE任务将需要充分了解木星附近恶劣的电子主导辐射环境对CMOS传感器的影响，而ESA的Plato任务的大型CCD基线将导致信号电荷在大面积辐射损坏的硅上转移。低温辐照带来了许多挑战，因为设备必须始终保持低温（因此处于真空状态），包括在辐照期间和辐照后的几周或几个月。在过去的12个月里，电子成像中心（CEI）开发了设备和技术，使我们的第一次低温照射得以进行。早期的结果表明，在低温下的结果与在室温下的结果有很大的不同，包括不同陷阱种类和种群密度的存在。

Charge-Coupled Devices (CCDs) have long been the detectors of choice for space astronomy missions. When placed in orbit, the devices can experience a harsh radiation environment. The radiation incident on the detector will act to damage the silicon lattice, creating defects that lead to the formation of "traps". The traps formed can capture signal that is being detected out of the device, leading to smearing and signal loss in CCDs and charge loss and bright pixels in CMOS sensors as well increasing sources of noise such as dark current.Before any mission is launched, it is vital that the impact of radiation is studied in detail such that appropriate shielding is used along with the development of novel readout techniques and correction algorithms to mitigate the damage that remains. Currently, standard practice dictates that radiation testing of devices is carried out at room temperature, despite the fact that the detectors will be kept cold during operation in orbit, with temperatures often as low as -120 degrees Celsius.The vacancies created after irradiation migrate through the device until they reach a stable state, but the stability of any particular defect structure is strongly dependent on temperature; the traps present at room temperature may be dramatically different to those present when a device is irradiated cold and kept cold. Literature on the so called "cryogenic irradiation" is sparse, but there are reports of a factor of 2-3 difference between the impact of radiation at room temperature compared to the more realistic cryogenic irradiation, with the direction of this difference (increased or decreased impact) varying between different device types.ESA's Euclid mission, aiming to map dark matter and energy, is dependent on a complete and thorough understanding of the impact of radiation on the detectors to allow for correction against radiation to reduce the smearing by up to 300 times. Hubble is able to correct by approximately a factor of 30, one order of magnitude less than that required for Euclid's high precision measurements. ESA's JUICE mission will require a full understanding of the impact on CMOS sensors of the harsh electron-dominated radiation environment near Jupiter and the large CCD's baselined for ESA's Plato mission will lead to the transfer of signal charge across large areas of radiation damaged silicon.Cryogenic irradiations present many challenges as the devices must be kept cold (and therefore under vacuum) at all times, including whilst irradiating and for a period of weeks or months after the irradiation. Equipment and techniques have been developed within the Centre for Electronic Imaging (CEI) over the past 12 months that have allowed our first cryogenic irradiations to take place. Early results demonstrate that there is a dramatic difference between the cryogenic results and those performed at room temperature, including the presence of different trap species and densities of populations.