PhD Seminar Notice: Monolithic Amorphous-Selenium/CMOS Small-Pixel-Effect-Enhanced Single-Photon-Counting Pixel for Dedicated Breast Computed Tomography

Friday, February 16, 2024 8:30 am - 9:30 am EST (GMT -05:00)

Candidate: Reza Mohammadi

Date: February 16, 2024

Time: 8:30 AM

Place: E5 5106

Supervisor(s): Levine, Peter

All are welcome!


We present the design and first experimental demonstration of a dual-energy-discriminating single-photon-counting (SPC) pixel with an amorphous-selenium (a-Se) X-ray sensor, monolithically integrated on a complementary metal-oxide-semiconductor (CMOS) readout integrated circuit (ROIC). Our proposed 92 × 92-μm2 pixel features a large-area-scalable design and is the first SPC X-ray pixel to exploit the small-pixel effect (SPE) using an amorphous sensor. By leveraging SPE, our pixel achieves a 7.9-keV energy resolution and 35-Mcps/mm2 maximum count rate, making it the first to use an amorphous sensor to meet the needs of demanding medical X-ray imaging applications like dedicated breast computed tomography. We achieve our objectives by integrating (1) a new area-efficient pixel architecture that exploits SPE, and (2) a novel partially-shared foreground input-offset-correction circuit for SPC which employs (3) a new area-efficient current-steering calibration digital-to-analog converter for our proposed energy-calibration circuit. We report electronic and X-ray characterization results from our custom-design ROIC, fabricated in a 0.18-μm 1.8-V analog/mixed-signal CMOS process. Our 1.5 × 2.5 mm2 ROIC contains a 5 × 8-pixel array, in which each pixel consumes 11 μW from a 1.8-V supply. We also post-process our ROIC to deposit a 115-μm-thick a-Se X-ray sensor using a simple thermal-evaporation process.