Esposito M, Anaxagoras T, Konstantinidis A C, Zheng Y, Speller R D, Evans P M, Allinson N M, Wells K
Centre for Vision, Speech and Signal Processing, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK. School of Computer Science, University of Lincoln, Lincoln, LN6 7TS, UK.
Phys Med Biol. 2014 Jul 7;59(13):3533-54. doi: 10.1088/0031-9155/59/13/3533. Epub 2014 Jun 9.
Recently CMOS active pixels sensors (APSs) have become a valuable alternative to amorphous silicon and selenium flat panel imagers (FPIs) in bio-medical imaging applications. CMOS APSs can now be scaled up to the standard 20 cm diameter wafer size by means of a reticle stitching block process. However, despite wafer scale CMOS APS being monolithic, sources of non-uniformity of response and regional variations can persist representing a significant challenge for wafer scale sensor response. Non-uniformity of stitched sensors can arise from a number of factors related to the manufacturing process, including variation of amplification, variation between readout components, wafer defects and process variations across the wafer due to manufacturing processes. This paper reports on an investigation into the spatial non-uniformity and regional variations of a wafer scale stitched CMOS APS. For the first time a per-pixel analysis of the electro-optical performance of a wafer CMOS APS is presented, to address inhomogeneity issues arising from the stitching techniques used to manufacture wafer scale sensors. A complete model of the signal generation in the pixel array has been provided and proved capable of accounting for noise and gain variations across the pixel array. This novel analysis leads to readout noise and conversion gain being evaluated at pixel level, stitching block level and in regions of interest, resulting in a coefficient of variation ⩽1.9%. The uniformity of the image quality performance has been further investigated in a typical x-ray application, i.e. mammography, showing a uniformity in terms of CNR among the highest when compared with mammography detectors commonly used in clinical practice. Finally, in order to compare the detection capability of this novel APS with the technology currently used (i.e. FPIs), theoretical evaluation of the detection quantum efficiency (DQE) at zero-frequency has been performed, resulting in a higher DQE for this detector compared to FPIs. Optical characterization, x-ray contrast measurements and theoretical DQE evaluation suggest that a trade off can be found between the need of a large imaging area and the requirement of a uniform imaging performance, making the DynAMITe large area CMOS APS suitable for a range of bio-medical applications.
近年来，在生物医学成像应用中，互补金属氧化物半导体有源像素传感器（CMOS APS）已成为非晶硅和硒平板探测器（FPI）的一种有价值的替代方案。借助掩膜拼接工艺，CMOS APS现在可以扩展到标准的20厘米直径晶圆尺寸。然而，尽管晶圆级CMOS APS是单片式的，但响应不均匀性和区域变化的来源可能仍然存在，这对晶圆级传感器的响应构成了重大挑战。拼接传感器的不均匀性可能源于与制造工艺相关的多个因素，包括放大倍数的变化、读出组件之间的差异、晶圆缺陷以及由于制造工艺导致的整个晶圆上的工艺变化。本文报道了对晶圆级拼接CMOS APS的空间不均匀性和区域变化的研究。首次对晶圆CMOS APS的电光性能进行了逐像素分析，以解决因用于制造晶圆级传感器的拼接技术而产生的不均匀性问题。提供了像素阵列中信号生成的完整模型，并证明该模型能够解释整个像素阵列中的噪声和增益变化。这种新颖的分析导致在像素级、拼接块级和感兴趣区域评估读出噪声和转换增益，变异系数≤1.9%。在典型的X射线应用即乳腺摄影中，进一步研究了图像质量性能的均匀性，结果表明，与临床实践中常用的乳腺摄影探测器相比，其在对比度噪声比（CNR）方面的均匀性处于最高水平。最后，为了将这种新型APS的检测能力与目前使用的技术（即FPI）进行比较，对零频率下的检测量子效率（DQE）进行了理论评估，结果表明该探测器的DQE高于FPI。光学表征、X射线对比度测量和理论DQE评估表明，在大成像面积需求和均匀成像性能要求之间可以找到平衡，这使得DynAMITe大面积CMOS APS适用于一系列生物医学应用。
