Laminate structure detectors for low dark current with photoconductors in digital X-ray imaging

The Particle-In-Binder method is one of the excellent processes for a direct conversion X-ray detector. Although detectors coated by the particle-in-binder method provide high sensitivity in X-ray exposure, the dark current is quite high in medical devices. To decrease the dark current and improve the efficiency of detectors, we investigated the potential for a flat-panel X-ray detector with a laminate structure including a plurality of metal halide films. The dark current decreased by laminating the hexagonal lattice, matching the metal halide photoconductive layers and adjusting the Fermi level so it had a different band gap. Film samples of PbO on PbI2 and BiI3 on HgI2, 3 cm×3 cm in area, were deposited by the particle-in-binder process onto glass substrates with conductive coatings, and indium-tin oxide (ITO) was deposited onto laminate layers as a top electrode by using the sputtering process. They were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to observe structural and morphological properties. To also investigate electrical characteristics, dark current, and sensitivity to X-ray exposure in the energy range of chest radiography, diagnosis and signal lag were measured at the range of operating voltage. As a result, although the sensitivity of the film decreased, the efficiency of the film improved due to a decrease in dark current. It is proposed that a laminate structure of photoconductors to reduce dark current in flat-panel detector for image quality in digital radiography can be used.