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Description
Charge sharing constitutes a fundamental limitation in hybrid pixel detectors operating in single-photon-counting mode. As the charge cloud generated by an absorbed X-ray photon drifts toward the collection electrodes, it undergoes lateral diffusion. When the interaction occurs in proximity to pixel boundaries, the deposited charge is distributed among adjacent pixels. Consequently, instead of a single signal proportional to the photon energy being registered in one pixel, multiple reduced-amplitude signals are recorded in neighboring pixels, resulting in spectral distortion and degradation of energy resolution. A range of integrated circuit (IC) architectures has been proposed to mitigate charge-sharing effects [1–3]. These approaches differ primarily in the extent of interpixel communication, from schemes involving only nearest neighbors (e.g., four pixels) to those incorporating larger pixel clusters. However, increasing the number of participating pixels introduces important trade-offs, including increased analog noise and reduced count-rate capability—both critical parameters in high-flux imaging applications.
Furthermore, conventional X-ray imaging relies on time-integrated photon counting, where only the total number of detected photons is measured over a given acquisition period. In such measurements, individual photon interactions are neither spatially controlled nor resolved with respect to pixel boundaries, limiting the ability to directly observe and quantify charge-sharing phenomena. As a result, the spatial distribution of charge sharing can typically only be inferred indirectly. In this work, we present a detailed experimental characterization of charge-sharing distributions with subpixel resolution using a full-scale integrated circuit bump-bonded to silicon (Si) and cadmium telluride (CdTe) sensors of varying thicknesses. The measurements provide direct insight into the spatial behavior of charge sharing in pixelated detectors. The experimental results are systematically compared with theoretical models to assess their validity and to inform the optimization of interpixel communication algorithms for effective charge-sharing compensation.
This work is supported by the National Science Centre, Poland, project no. 2023/51/B/ST7/01782.
[1] A. Krzyzanowska, et al., Characterization of the Photon Counting CHASE Jr., Chip Built in a 40-nm CMOS Process With a Charge Sharing Correction Algorithm Using a Collimated X-Ray Beam, IEEE TNS. Vol. 64 (9), pp. 2561–2568, 2017.
[2] V. Sriskaran et al., High-rate, high-resolution single-photon X-ray imaging: Medipix4, 2024 JINST 19, P02024.
[3] M. Zoladz, et al. Tests of charge sharing compensation algorithm implemented in a single pixel counting integrated circuit operating with Si and CdTe pixel detectors, 2025 JINST 20, P12015.