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The paper presents an electronic thinning method for hybrid pixel detectors(HPD) used in electron microscopy. Theoretically, the spatial resolution of a pixel detector improves with decreasing pixel pitch. However, as the pixel size diminishes, a single incident particle may induce signals across multiple adjacent pixels caused by scattering, the charge-sharing effect makes it difficult to determine the actual point of particle entry.
To improve the spatial resolution of HPDs, some researchers have created super resolution techniques, such as Center-of-Gravity(CoG) method and position interpolation algorithms[1-2]. However, the results calculated by these methods often depart from the particle’s exact incident position because the algorithms are based on statistical distributions and the results are maximum likelihood estimates.
Although high-energy incident particles follow complex trajectories within the sensor layer, we noticed that the distribution of energy deposited by particles in the shallow layer of the incident surface is always highly correlated with the incident position. Energy deposited within the layer of interest can be filtered by a well-designed integration time window. This achieves an effect similar to the back grind of a monolithic active pixel sensor(MAPS), thus improving the spatial resolution of HPDs. Meanwhile, the design preserves the original amplitude of the detector signal in circuit, enhancing the signal-to-noise ratio and energy resolution for individual particles.
To validate this, we conducted Monte Carlo simulations using the standard simulation tool Allpix2. Considering the feasibility of subsequent experimental verification, we have developed a simulation model similar to EMPIX2[3]. By studying the patterns of energy deposition and induced current signals generated by 300 keV electrons in a 500 μm silicon sensor, we compared the spatial resolution before and after applying the electronic thinning method. The results indicate that electronic thinning method can effectively improve the position resolution of the detector; under certain conditions, position resolution as high as 54.69 μm (with a pixel size of 150 μm) can be achieved. We also verified the generality of this method by examining parameters such as pixel pitch and detector bias. In addition, algorithms have been developed to identify and handle events of wide-angle scattering. Future work will involve designing readout chips and constructing a test system based on these simulation results to conduct real-world experiments, while experiments using existing HPDs are also underway.
Figures are shown in attached pdf.
[1] Litwinek T et al, Journal of Instrumentation, 2025, 20(12): P12034.
[2] Ramilli M et al, Journal of Instrumentation, 2017, 12(01): C01071.
[3] Tong Wei et al, Journal of Instrumentation, 2023, 18(12): C12007.