Fully 2D tileable photodiode detector for medical computed tomography imaging

摘要

This thesis presents a novel design of 2D tileable photodiode detector for medical CT imaging application. The novel design integrates the through-wafer interconnect (TWI) technology into the conventional photodiode structure to achieve 2D tileable capability. With respect to the TWI technology, a new development of the upside down "T" shape TWI is reported for the first time in this thesis comparing to the existing straight TWI, and it shows better electrical properties and allows more robust processing capability. This thesis describes two structures of the photodiode integration with the TWI: via-outside-pixel (VOP) and the via-inside-pixel (VIP). The VIP structure shows advantages over the VOP structure with compact photodiode pixel arrangement. Moreover, it allows sophisticated guard ring protections to further improve the photodiode characteristics. This thesis reports experimental and theoretical studies on the effect of two different guard ring designs to the photodiode application. Upon the design and the fabrication of the novel photodiode chip, the properties of the photodiode are characterized in three aspects (electrical, optical and thermal properties) in this thesis. All the measurement and simulation data show that the demonstrated photodiode samples with the novel design can either meet or exceed the requirements (better image resolution, faster scanning speed and higher coverage rate) of the modern CT detector.