A detailed study on spectroscopic performance of SOI pixel detector with a pinned depleted diode structure for X-ray astronomy

TL;DR

This study evaluates the spectroscopic performance of an optimized SOI pixel detector with a pinned depleted diode structure for X-ray astronomy, achieving record energy resolution and analyzing factors affecting performance.

Contribution

It provides a detailed analysis of the XRPIX detector's spectroscopic performance with an optimized PDD structure, highlighting the impact of gain non-linearity and charge injection.

Findings

Achieved best energy resolution of 178 eV at 6.4 keV for single-pixel events.

All-pixel event resolution of 291 eV, including charge-sharing events.

Identified gain non-linearity due to charge injection as a limiting factor.

Abstract

We have been developing silicon-on-insulator (SOI) pixel detectors with a pinned depleted diode (PDD) structure, named "XRPIX", for X-ray astronomy. In our previous study, we successfully optimized the design of the PDD structure, achieving both the suppression of large leakage current and satisfactory X-ray spectroscopic performance. Here, we report a detailed study on the X-ray spectroscopic performance of the XRPIX with the optimized PDD structure. The data were obtained at $-60^\circ\mathrm{C}$ with the "event-driven readout mode", in which only a triggering pixel and its surroundings are read out. The energy resolutions in full width at half maximum at 6.4 keV are $178\pm1$ eV and $291\pm1$ eV for single-pixel and all-pixel event spectra, respectively. The all-pixel events include charge-sharing pixel events as well as the single-pixel events. These values are the best achieved in the history of our development. We argue that the gain non-linearity in the low energy side due to excessive charge injection to the charge-sensitive amplifier is a major factor to limit the current spectroscopic performance. Optimization of the amount of the charge injection is expected to lead to further improvement in the spectroscopic performance of XRPIX, especially for the all-pixel event spectrum.