Characterization results of the first small pixel high rate (SPHIRD) pixel detector prototypes

This work presents a summary of the experimental results and the performance obtained from a first set of p-type silicon SPHIRD prototypes. The SPHIRD project (Small Pixel High Rate photon counting Detector) targets a new generation of X-ray photon counting hybrid pixel detectors for synchrotron radiation applications, with small pixels and operating between 10 and 30 keV. The readout ASIC is designed to explore techniques that boost the count rate capabilities of the detector and methods to manage, or in some cases exploit, the effects of charge sharing that are unavoidable with small pixels in this type of detector. The achievement of high photon rates relies on the implementation of a fast charge-sensitive amplifier in the pixel in combination with pile-up compensation techniques, which have been compared experimentally. The obtained results show and quantify their effectiveness in increasing the count-rate handled by the detector. The readout chip also includes dedicated circuitry for the relocation of photon hits, a functionality necessary to reduce the photon losses that are observed in photon counting detectors due to charge sharing when the discrimination threshold is set to 50% of the photon energy. The circuitry is however not limited to full pixel relocation: it also implements resources to reassign X-ray hits within regions smaller than the physical pixel. All these operation modes were experimentally evaluated with a pencil beam and with full field images.