基于硅孔阵列高分辨率像素化CsI(Tl)闪烁转换屏的研究

Digital x-ray imaging has been widely used in the fields of non-destructive testing, medical diagnosis, macromolecular crystallography, plasma diagnostics, x-ray astronomy and so on. With the development of the application, a scintillation conversion screen is usually required to have a better spatial resolution for x-ray imaging than ever. CsI(Tl) is the most widely used scintillation screen material. In recent years, the emergence of the pixelated CsI(Tl) scintillation screen based on silicon pore array makes the spatial resolution of x-ray imaging given by the screen can be compared with that of optical imaging given by the high end optoelectronic device. However, the light yield of this kind of scintillation screen is still far lower than expected which leads to a poor detective quantum efficiency so that the screen is lack of application value. The reason of the problem results from the lack of systematical design of the structure and properties of the screen and imperfect preparation technique. This project intends to carry out the research on the pixelated CsI(Tl) scintillation screen based on silicon pore array in the aspects of physical design, preparation technique and performance characterization. In order to give an optimal design of the pixelated CsI(Tl) scintillation screen, they will be studied that the relation between structure of pixel array and spatial resolution as well as light yield, the effect of x-ray energy on spatial resolution, and the relation between light yield and screen thickness. According to the physical design, the pixelated CsI(Tl) scintillation screen based on silicon pore array will be fabricated with the research on the preparation process of silicon pore array and the technique for filling CsI(Tl). It is expected that the pixelated CsI(Tl) scintillation screen not only has a outstanding spatial resolution, but also has a high light yield so as to promote the application of the pixelated screen in x-ray imaging.

数字X射线成像在现代科技、医学诊断等领域有着广泛的应用，随着应用的深化，需要拥有更高X射线成像分辨率的闪烁屏。CsI(Tl)是应用最为广泛的闪烁屏材料，近年来基于硅孔阵列像素化CsI(Tl)闪烁屏制备技术的出现，使得其空间分辨率可与高端可见光成像光电器件的相当。然而，目前此种闪烁屏的光产额还远低于预期，以致量子探测效率过低而缺少应用价值，其问题还在于性能和结构设计以及制备工艺的不足。本课题拟从基于硅孔阵列像素化CsI(Tl)闪烁屏的物理设计、制备工艺和性能表征等方面，通过闪烁屏像素尺寸/壁厚/排列结构与其成像空间分辨率和光产额的量化关系、X射线能量对像素化闪烁屏空间分辨率的影响、光产额与X射线能量和闪烁屏厚度间的关系、硅孔阵列制备工艺和致密/均匀/无气泡CsI(Tl)填充技术等的深入研究，在追求更高空间分辨率的同时，着力增强闪烁屏的光产额，提升高分辨率像素化CsI(Tl)闪烁屏的应用价值。

基于硅孔阵列模板的结构化CsI(Tl)闪烁转换屏可以有效提升数字X射线成像的空间分辨率，为了追求更高的成像分辨率，研究逐渐向小周期、大深宽比方向发展。随着转换屏的结构周期小至微米量级，CsI(Tl)的填充面积占整个转换屏面积的比例受到了明显的压缩，结构化闪烁转换屏在X射线成像空间分辨率与探测量子效率需求间的矛盾变得突出；同时制备结构紧凑、周期小、深宽比大的硅孔阵列模板，提高在这种模板条件下CsI微柱的填充质量既颇具挑战又至关重要。为此，开展了基于硅孔阵列模板的CsI(Tl)转换屏的结构和性能设计、硅孔阵列模板及其SiO2全反射层的制备、结构化CsI转换屏的研制和性能表征等。通过研究，系统地掌握了结构化CsI(Tl)转换屏阵列周期、排列结构、孔壁厚度、微柱形状等与其光输出、成像空间分辨率和探测量子效率间的量化关系；认识了X射线能量对结构化CsI(Tl)转换屏空间分辨率的影响，以及光输出与X射线能量和闪烁屏厚度间的关系，为高性能结构化CsI(Tl)转换屏的研制提供了理论指导。通过紫外光刻、感应耦合等离子体预刻蚀、电化学刻蚀和热氧化技术等，得到了稳定的制备周期小、深宽比大、壁厚有限、孔壁光滑、SiO2层均匀可控的硅孔阵列模板的工艺条件。发展了真空熔融气压填充技术，通过优化制备工艺、克服闪烁微柱透明性分析的困难等，确保了CsI的填充质量，研制出周期小、深宽比大、填充致密、无气泡、具有六角和正方阵列结构的CsI闪烁转换屏，在结构周期小至4μm的情况下，转换屏闪烁微柱的深度可达100μm，深宽比远越优于已有报道。所研制的结构化CsI转换屏X射线成像的空间分辨率可超过110 lp/mm，零频探测量子效率可超过0.20，性能指标处于国际前列，为超高分辨率X射线成像创造了优越的条件。此外，还开展了结构化Lu2O3:Eu3+纳米线阵列闪烁转换屏研制、应用光子晶体提高闪烁转换屏光提取效率等拓展性研究，取得了积极的成果。