下一代光子计数型像素探测器中若干关键问题的研究

As a newly born detecting method, photon counting pixel detectors are different from the conventional charge integration mode. They are widely used in synchrotron radiation applications and radiation imaging. Large numbers of new experiment methods and new techniques are developed thereupon. Unfortunately, this type of detectors is totally relied on import before in China, thus the related domestic research are seriously restricted. In the recent two years, IHEP (the Institute of High Energy Physics) has developed a first prototype of silicon pixel detector which is fully localized in China. Its major performance is at the same level as the mainstream products in this field. However, gaps remain to the most advanced in the aspects like the pixel size and the variety of system functions. Based on the development experience and aiming at the next generation of photon counting pixel detectors, this project proposes to shrink the pixel size to the same level of the state-of-the-art product, so that the system can be capable for imaging applications. Several key issues are to be studied and solved, including the methodology of design and optimization for the circuitry in very small pixels, the mechanism of the charge sharing effect and solutions are to be given from the circuit level. It is also to be studied on the re-union from a small pixel array to a compound pixel, that some complicated functions, such as discrimination on multiple energy windows, can be realized thanks to the independent operation of individual pixels. In this way, the variety and practicability of the system can be further promoted. The final version of the readout chip for the next generation of photon counting pixel detectors are to be accomplished by the end of this project, only the dimension of the pixel matrix is limited. Therefore a good and ready basis is to be founded for the direct application in a real project.

光子计数型像素探测器作为一种有别于传统电荷积分方法的新探测模式，在同步辐射以及辐射成像应用中均有广泛应用，并随之产生了大量新实验方法和新技术。此前国内这类探测器完全依赖进口，严重限制了自主研究的开展。近两年针对高能光源应用，已由高能所实现了完全国产化的硅像素探测器原理样机。样机性能指标与主流探测器产品相当，但像素尺寸和系统功能与目前最先进产品相比还有一定差距。在此基础上，针对下一代光子计数型探测器，本课题计划将像素单元尺寸进一步减小至国际最好水平，使系统兼容成像应用，并着重解决与其相关的若干关键问题，包括小像素单元电路设计和优化方法，研究电荷共享效应机理并从电路级给出解决方案，同时通过将小像素阵列重编组成复合像素，利用小像素的相对独立工作实现多能量窗甄别等复合功能，进一步提高系统功能的多样性与实用性。本课题计划完成下一代光子计数探测器读出芯片的小尺寸定型版，为直接进行工程应用奠定基础。

本课题针对下一代光子计数型像素探测器，探索了高集成度、小像素尺寸像素读出芯片的设计方法。提出了改进型模拟前端电路结构，并采用全定制数字单元库实现了全部数字功能，成功的将像素单元尺寸缩小到55μm × 55μm，并保持主要性能不变。针对小像素尺寸探测器所不可忽略的电荷共享效应开展了研究，提出了片上电荷共享效应消除方案。针对像素读出芯片典型的大尺度、分布式数据源高速传输问题开展了研究，提出了分布式驱动和数据汇总方案，成功实现了高速数据串行接口。通过流片测试，验证了本项目所提出的设计方法和电路解决方案。在原型芯片的基础上进一步实现了工程批流片和探测器模组封装，并实现了单模块测试读出系统。在X光机和同步辐射光源上分别进行了成像实验，表明探测器模组能够实现高精度的位置分辨和成像功能。联调测试的结果表明探测器性能指标满足项目设计目标，并且实现了一定的实用性。