【作者】 赵志刚；

【导师】 牛憨笨；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2010， 博士

【摘要】 数字X射线探测器能够将不可见的X射线信号转换为数字式电信号,是X射线成像系统中的关键器件。“基于光栅微分干涉的X射线相衬成像系统”对数字X射线探测器提出了大面积和高空间分辨率这两个要求。但是目前的X射线探测器因存在两个主要问题而难以满足上述要求。第一个问题是探测器中X射线转换屏的空间分辨率因荧光的侧向扩散而大大降低。第二个问题是探测器中图像传感器的感光面积远小于实际应用中75×75mm2的最低需求。为了解决以上两个问题,本论文开展了大面积高分辨率数字X射线探测器的研制工作,主要内容分为以下两个部分：第一个部分是制作像素化X射线转换屏,以提高X射线转换屏的分辨率。像素化X射线转换屏适合于使用硅基深孔阵列来制作。硅基深孔阵列是一种高深宽比的微结构,而光助电化学刻蚀是制作硅基深孔阵列的理想方法。为了能在整个5英寸硅片上制作出均匀的深孔阵列,自行设计并制作了一套新型大面积硅片光助电化学刻蚀装置。该装置借助一个水冷隔热系统和一个花洒式溶液循环系统,解决了传统光助电化学刻蚀装置中溶液升温和气泡堆积的问题。所制作的深孔阵列边长有5μm和1.5μm两种,深宽比分别达到了30和100。深孔阵列经高温热氧化和X射线荧光材料CsI:T1的填充之后,完成了像素化X射线转换的制作。经测试,像素化X射线转换屏的空间分辨率达到了201p/mm,满足最初的设计要求。另外,还利用新型大面积硅片光助电化学刻蚀装置,通过逐步加大刻蚀电流的方法补偿侧向腐蚀给微结构形貌带来的不利影响,制作了两种形貌一致性很好的高深宽比深槽阵列,用于X射线光栅的制作。第二个部分是开发基于4颗CMOS芯片拼接的数据采集系统,以扩大探测器的成像面积。4颗CMOS芯片LUPA-4000与一个2×2光锥阵列耦合后,能够拼接成完整的图像,成像面积达到98.5×98.5mm2。受光锥阵列结构尺寸的制约,在本课题中只能使用CMOS芯片,从底层开始完成整个数据采集系统的开发。数据采集系统采用了基于以太网远程控制,并对4颗LUPA-4000芯片单独用DDR2 SDRAM进行数据缓存的方案。用基于Verilog的FPGA设计实现LUPA-4000芯片的驱动时序和DDR2 SDRAM芯片的控制器,用ARM作为整个系统的微控制器,采集到的图像数据在PC机中存储。为了便于LUPA-4000芯片与光锥小端的耦合,为每一颗LUPA-4000制作了一块独立的PCB板,各PCB板之间留有一定量的调整间隙。本论文完成了数据据采集系统从电路原理图设计和PCB板图设计,到FPGA设计、ARM软件设计和PC机软件设计的全过程。在实现了LUPA-4000拍照与图像数据存储等基本功能的基础上,开发了一套参数可调整的数据采集系统,实现了拍照参数可调整和开窗读出等实用的附加功能。更多还原

【Abstract】 Digital X-ray detectors, which can convert invisible X-ray into digital electronic signal, are important components in X-ray imaging systems. High spatial resolution and large-area digital X-ray detectors are required in "Grating-differential Interference based X-ray Phase-contrast Imaging System". But nowadays X-ray detectors can hardly meet these requirements, because there are two main problems existing. The first problem comes from the fact that the spatial resolution of X-ray converter degrades seriously due to the lateral spreading of fluorescence. The second problem is that the area of light-sensitive part of the image sensor in X-ray detector is much less than the lowest requirement of 75 x 75mm2.To resolve these problems, research works were performed to manufacture a large-area high resolution digital X-ray detector. The works have emphases on two parts:The first part is the manufacture of a pixellated X-ray converter, in order to improve the spatial resolution.Silicon based pore arrays are essential for manufacturing pixellated X-ray converters. Silicon based pore arrays are high aspect ratio microstructure, which are suitable of manufactured by photoelectrochemical etching of silicon. To obtain uniform pore arrays in full 5 inch silicon wafers, a novel large area silicon wafer photoelectrochemical etching setup was established. With the help of a water-cooling system and a shower-head shaped circulator, the novel photoelectrochemical etching setup resolved the problems of electrolyte temperature going high and hydrogen bubbles assembling. There were two kinds of pore arrays manufactured, with side of 5μm and 1.5μm, and aspect ratio of 30 and 100 respectively. After high temperature oxidation and CsI:T1 filling of the pore arrays, the pixellated X-ray converter was finally manufactured. The spatial resolution of the pixellated X-ray converter was 201p/mm under test, which can meet the requirements of initial design. Additionally, by means of increasing the etching current gradually to compensate the influences of lateral etching, two kinds of high aspect ratio wall arrays with good morphology consistency were manufactured for X-ray gratings’fabrication by the novel photoelectrochemical etching setup.The second part is the development of a data acquisition system based on 4 CMOS chips’combination, in order to enlarge the imaging area. Four CMOS chips LUPA-4000 coupled with a 2×2 taper array can form a full image, with the area of 98.5×98.5mm2. Because the size of the taper array was fixed, the data acquisition system can only be developed from bare CMOS chips. The data acquisition system’s scheme was that it can be controlled far-distance by Ethernet, and the four CMOS chips’data were temporarily stored each by a DDR2 SDRAM. LUPA-4000’s driving timing and DDR2 SDRAM controller were accomplished by Verilog based FPGA design, and ARM was used as MCU, and image data were stored in PC. Every LUPA-4000 has an independent PCB board. There is some space between two boards, so it is convenient for LUPA-4000’s coupling to taper’s litter end. Besides the basic functions of taking photos and image data’s storing, a parameters adjustable data acquisition system was developed, with additional some useful functions, such as photo parameters’adjusting and windowing readout.更多还原