XPAD3: A new photon counting chip for X-ray CT-scanner

The X-ray pixel chip with adaptable dynamics (XPAD3) circuit is the next generation of 2D X-ray photon counting imaging chip to be connected to a pixel sensor using the bump and flip-chip technologies. This circuit, designed in IBM 0.25 μm technology, contains 9600 pixels (130 μm×130 μm) distributed into 80 columns of 120 elements each. Its features have been improved to provide high-counting rate over 109 ph/pixel/mm2, high-dynamic range over 60 keV, very low-noise detection level of 100e− rms, energy window selection and fast image readout less than 2 ms/frame. An innovative architecture has been designed in order to prevent the digital circuits from bothering the very sensitive analogue parts placed in their neighbourhood. This allows to read the chip during acquisition while conserving the precise setting of the thresholds over the pixel array. Finally, the aim of this development is to combine several XPAD3 to form the PIXSCAN detector.