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A Monolithic Amorphous-Selenium/CMOS Small-Pixel-Effect-Enhanced X-Ray-Energy-Discriminating Quantum-Counting Pixel for Biomedical Imaging

Reza Mohammadi, Peter M. Levine, Karim S. Karim

IEEE Symposium on VLSI Technology and Circuits (VLSI Technology and Circuits), 2023

Abstract

We demonstrate the first dual-energy-discriminating quantum-counting-detector (ED-QCD) pixel with an amorphous X-ray-sensitive semiconductor, amorphous selenium (a-Se), monolithically integrated with a custom CMOS readout IC (ROIC). Our $92\times 92\mu \mathrm{m}^{2}$ large-area scalable pixel is also the first to exploit the small pixel effect (SPE) in amorphous semiconductors for dual-X-ray-energy quantum counting. SPE enables 7.9keV energy resolution and $35\mathrm{Mcps}/\mathrm{mm}^{2}$ count rate density that can satisfy even demanding medical-imaging applications like dedicated breast computed tomography (DBCT). Our novel pixel architecture achieves the design objectives by leveraging (1) area-efficient SPE-enhanced sub-pixels with shared counters, and (2) a partially-shared foreground input-offset-correction circuit employing a (3) new area-efficient current-steering calibration DAC.

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