Dental Imaging with a Quantum-dot-based Direct Conversion X-ray Image Sensor

X-ray imaging has been extensively used in medical diagnosis thanks to the ability of X-rays to penetrate through our body or a part for non-invasive imaging of internal structures. Nowadays, most commercial X-ray detectors including dental imaging instruments rely on a cesium iodide (CsI) scintillator to convert X-rays into visible light. However, they normally suffer from a low spatial resolution due to optical crosstalk among neighboring pixels. Pixelated detectors made of cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe) have shown excellent performance for X-ray imaging. Nevertheless, they require flip-chip hybridization to connect to silicon readout, adding assembly complexity, increasing fabrication cost, and restricting achievable pixel resolution. We have developed a direct conversion X-ray imager with a high-Z lead-sulfide (PbS) quantum-dot (QD) based photon absorber monolithically and directly deposited on a CMOS readout chip. The silicon readout has been designed with a standard 180-nm CMOS process and the photon absorber with a 120- $\mu$ m layer of PbS QDs has been deposited from solutions at low temperature. This approach takes advantages of CMOS technologies for a high pixel resolution, low-power consumption, and complex readout electronics. It also benefits from high X-ray absorption efficiency and low-temperature solution-based fabrication of PbS QDs. To our knowledge, this is the first direct conversion X-ray imager with an absorber stack of PbS QDs on silicon readout. Following an introduction to sensor design and fabrication, this paper demonstrates the potential use of this imager in medical imaging particularly dental imaging. This novel radiation detector has been used to produce high-quality tooth images while presenting a low dark current, high linearity, a low noise equivalent dose, and a high spatial resolution. The validation of this solution-based monolithic approach benefits realization of low-cost high-performance X-ray imagers.