Performance limits of a 55 μm pixel CdTe detector

In this work the results from simulation of a CdTe pixel detector with a pixel size of 45 μm and a pitch of 55 μm are presented. Simulation of charge sharing between neighboring pixels has been compared with experimental results obtained by the use of the MEDIPIX-II single photon counting chip. Electrical simulations have been performed using the commercial software package DESSIS (ISETCAD) and combined with the Monte Carlo code GEANT4 to allow a method of complete interaction and subsequent charge transport of charges induced by radiation. This has allowed the analysis of charge sharing between pixel elements, an important limiting factor in imaging applications. Experimental results were obtained by the use of a 1 mm thick CdTe detector, with pixel electrodes at a pitch of 55 μm. Each of these pixel electrodes was connected to the corresponding readout pixel on the Medipix-II chip, via an indium bump-bond. The results obtained imply that very small pixel size, such as 25 μm and detector 1 mm thick, is unrealistic because such intrinsic fine spatial resolution cannot be attained in the corresponding image due to charge sharing.