CMOS-Integrated Single-Photon-Counting X-Ray Detector using an Amorphous-Selenium Photoconductor with $11\times 11-\boldsymbol{\mu}\mathbf{m}^{2}$ Pixels

We report, for the first time, results from a single-photon-counting X-ray detector monolithically integrated with an amorphous semiconductor. Our prototype detector combines amorphous selenium (a-Se), a well-known X-ray photoconductive material suitable for large-area applications, with a 0.18-μm-CMOS readout integrated circuit containing two 26×196 photon counting pixel arrays. The detector features 11×11-μm² pixels to overcome a-Se count-rate limitations by unipolar charge sensing of the faster charge carriers (holes) via a unique pixel geometry that leverages the small pixel effect for the first time in an amorphous semiconductor. Measured results from a mono-energetic radioactive source are presented and demonstrate the untapped potential of using amorphous semiconductors for high-spatial-resolution photon-counting X-ray imaging applications.