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

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.