Digital subpixel algorithm for small pixel photon counting devices

Hybrid pixel detectors are segmented devices widely used for photon detection. They consist of a sensor and readout electronics bonded together. Due to their hybrid structure, sensors of different materials can be used to register a wide range of photon energies. Moreover, the devices working in a single photon counting (SPC) mode allow registering each incoming photon separately, providing noiseless imaging. The spatial resolution of the detectors and photon count rate registered per unit area can be improved by reducing pixel size. However, small-pixel devices suffer from charge sharing. The charge sharing between pixels can be observed if the charge cloud generated in the photon-sensor event spreads due to diffusion and repulsion. Several anti-charge-sharing algorithms exist and some have been successfully implemented inside the ASICs readout. Even though they allow the allocation of the event to the proper pixel and reconstruction of the total photon energy, the detector resolution is limited by the readout channel area which must be large enough to fit the complex mixed-mode functionality. The article presents the simulations of an alternative solution which can improve both spatial resolution and high-count-rate performance. In the authors’ approach, charge sharing is regarded as a positive effect which can be used to estimate the photon interaction position with subpixel resolution. The algorithm is evaluated to improve detection efficiency and required pixel area for implementation in deep submicron technologies.