Via-in-pixel design of truly 2D extendable photodiode detector for medical CT imaging

This paper presents a new design of the silicon-based photodiode detector for medical imaging, especially for the X-ray computed tomography applications. The new structure of the photodiode includes a conventional front-illuminated photodiode and a through wafer interconnection. Moreover, the through wafer interconnection is integrated into the photodiode by being placed inside the active area of the photodiode. This new structure is called via-in-pixel design. Truly 2D photodiode detector can be designed with maximum free space or minimum gap between each two photodiode elements by using the via-in-pixel design. In addition, 2D photodiode detector arrays can be constructed by tiling more edgeless detectors. In the paper, the via-in-pixel photodiodes were demonstrated and the performances were measured. Together with the measurement data, a quasi-3D device simulation was performed to disclose the electrical characteristics of the via-in-pixel photodiode by using Synopsis Advanced TCAD software. The results show that the via-in-pixel design of the photodiode detector can either meet or exceed the medical imaging requirements.