Integrated CMOS active pixel sensor with low capacitance large area photodiodes

A novel CMOS X-ray active pixel sensor for indirect C.T. X-ray detection has been developed. A Cadmium tungstate (CdWO4) scintillator array glued on top is used is for the X-ray to light conversion. The array uses separation by white colored lead stripes to prevent pixel crosstalk and to shield the underlying CMOS electronics from direct radiation. Noise reduction by reducing the detector junction capacitance is applied to increase the SNR, instead of increasing the sensitivity. For this purpose a new low capacitance, low dark current dot type photodiode based on minority diffusion has been developed. The dynamic range is expanded to 17 bit by the use of individual in-pixel automatic gain control. A photon noise limited detector exhibiting a 20 x 10 pixel array and integrated temperature sensor has been realized in a standard 1.2µm CMOS process, which can be read out with a frame rate of 3000 frames/sec.