Abstract
Buried P-Well (BPW) technology was used in silicon-on-insulator pixels (SOIPIX) to suppress the back-gate effect, the major challenge in SOIPIX. In this work, we have designed and optimized two novel pixel structures, which are based on different BPW design layouts, to study the carrier collection efficiency and conversion gain of the pixel unit used in SOIPIX X-ray detectors. The first structure has an extended BPW region connected with a P+ node. In the second structure, a separated BPW ring region is formed surrounding the P+ node. Two X-ray sources with different photon energies have been applied in the simulation of excess carrier generation. The results indicated that the first structure had higher collection efficiency while the second structure had a slightly better conversion gain. As a result, the total photoelectric voltage of the first structure is about two times that of the second structure, where low doping concentration (<1 × 1016 cm‒3) in the BPW region is preferred. Such a study of design and optimization of BPW technology is very important for applications in SOIPIX detectors
Highlights
In the field of medical diagnostics, digital X-ray imaging systems have been under investigation and development for a long time [1]
By varying the size and position of the buried P-Well, we have studied the dependence of the collection efficiency and the conversion gain on device geometry
As the photodiode is reverse-biased a highpixel voltage, the depletion depletion region expands to nearly the whole substrate
Summary
In the field of medical diagnostics, digital X-ray imaging systems have been under investigation and development for a long time [1]. The SOI X-ray detectors have recently been integrated in the direct imaging system [5] Some progress in this area has been achieved by Miyoshi et al [6,7,8], who studied X-ray astronomy with SOI CMOS technology. Niemiec et al have researched monolithic X-ray detectors with thick film SOI technology [9] These detectors are composed of a thick, high-resistivity substrate (the X-ray absorption layer) and a relatively thin, low-resistivity Si layer (on which to build readout circuits) sandwiching a buried oxide (BOX) layer in a single wafer. In order to optimize the collection efficiency and the conversion gain, we have designed and optimized SOIPIX X-ray detectors with different BPW structures. We have studied the impact of BPW doping concentration on the pixel characteristics
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