Performance studies of a monolithic scintillator-CMOS image sensor for X-ray application

We proposed the direct deposition of CsI(Tl) scintillator layer with pixelated structure on a CMOS image sensor (CIS) in order to improve the spatial resolution. CMOS sensors developed for test have a 128×128 photodiode array with 50 μm pixel pitch and integrated readout-electronics including a 10 bit pipe-lined ADC. CsI(Tl) layer has thickness of 50 μm. The modulation transfer function, the noise power spectrum, and the detective quantum efficiency of pixelated and non-pixelated CsI(Tl) X-ray image sensors (XIS) were estimated with a 50 kVp X-ray beam. At 10% of modulation transfer function (MTF), the spatial resolution of pixelated and non-pixleated XIS are about 8 and 6 lp/mm, respectively. It implies that pixelation enhances the spatial resolution by reducing the lateral light diffusion. Though the NPS of pixelated XIS was slightly higher than the non-pixelated XIS, its detective quantum efficiency (DQE) values were much better than non-pixelated XIS especially at high spatial frequencies.