Development and characterization of CMOS-based monolithic X-ray imager sensor

TLDR: In this article, the authors proposed a new design of CMOS-based X-ray image sensor with monolithically grown pixelated CsI(Tl) on photosensor area for securing the maximally achievable spatial resolution for a given sensitivity determined by the thickness at a certain Xray energy.

Abstract: We proposed a new design of CMOS-based X-ray image sensor with monolithically grown pixelated CsI(Tl) on photosensor area for securing the maximally achievable spatial resolution for a given sensitivity determined by the CsI(Tl) thickness at a certain X-ray energy The test version of a CMOS image sensor (CIS) was designed and fabricated using AMIS 05 mum standard CMOS process The chip includes an 128times128 CMOS active pixel sensor(APS) array with 50 mum pitch, a row/column decoder, a sample & hold circuit with buffers, an analog signal processor(ASP) and a 10 bit pipe-lined analog-to-digital converter(ADC) A data acquisition system (DAS) for operating the image sensor and for processing digital signals was also developed Then the X-ray image sensor was fabricated by depositing thermally evaporated CsI(Tl) blocks of 50 mum thick on each pixel sensor of CIS using a photo-resist pattern as a basis of CsI(Tl) deposition Linearity of the response, dark current noise, dynamic range and spatial resolution etc were measured with bare and scintillator-coupled CIS image sensors by green LED light and X-ray beam respectively The mean charge generation rate per pixel measured at room temperature in the dark was about 45,600 electrons/sec which results in the electronic noise of 210 electrons for 1 sec exposure time Therefore the dynamic range is ~67 dB if we consider the statistical noise together The spatial resolution of scintillator-coupled CMOS image sensor was measured to be ~7 lp/mm by a lead line pattern and 80 kVp X-ray This works was supported by Nuclear R&D Program of MOST, Korea through KOSEF