A Pixelated CsI (Tl) Scintillator for CMOS-based X-ray Image Sensor

Direct and indirect imaging detectors for digital radiography have been developed during the past a few years. Among scintillators, columnar CsI(Tl) screens are used for indirect digital X-ray imaging for industrial and medical radiography. By the help of recent developments CMOS (Complementary Metal Oxide Semiconductor) is replacing the CCD (Charge Coupled Devices) in X-ray image sensor because of low operating power, standard CMOS manufacturing process, and low cost. An X-ray imaging detector consisting of pixelated CsI(Tl) scintillator and CMOS imaging sensor for application in dental radiography was developed. The manufactured CMOS imaging sensor has 128 by 128 pixels with the pitch size of 50 mum and gap width of 5 mum. A 0.5 mum CMOS process was used for sensor fabrication. Pixel structured CsI(Tl) scintillator was directly deposited on the patterned CMOS imaging sensor by thermal evaporation and photo-lithography process. The fabricated monolithic X-ray imaging sensor showed dramatic improvement in spatial resolution due to enhancement of the scintillation light guiding effect and reduction of the light cross-talk between scintillator pixels.