TlBr Films for Direct Digital Radiography

The detector that converts X-ray intensity into a digitized electronic signal, processed into an image, often limits the performance of modern X-ray imaging systems, whether for medical, research, or industrial applications. Digital radiography (DR) uses the following two types of detectors: 1) indirect detectors, where a scintillating film converts X-rays into an optical signal read by an optical detector, and 2) direct detectors using semiconductors. Semiconductor X-ray detector technology typically uses a silicon wafer, an amorphous selenium (a-Se) film, or a relatively thin cadmium zinc telluride (CZT) crystal bump bonded to a readout platform. Although the use of a-Se and CZT improves the attenuation coefficient beyond that of silicon, a further increase in performance is highly desirable for improved imaging of higher-energy X-rays (greater than 20 keV). This article presents results on thallium bromide (TlBr) films coupled to a read-out integrated circuit (ROIC). TlBr, an attractive material for hard X-ray imaging due to its high atomic number and high density, achieves an image resolution of20 μm as a 1 cm² × 100-μm-thick columnar film deposited on CMOS ROIC.