Improvement of Spectroscopic Performance using a Charge-sensitive Amplifier Circuit for an X-Ray Astronomical SOI Pixel Detector

TL;DR

This paper reports on enhancements in spectroscopic performance of XRPIX SOI pixel detectors for X-ray astronomy, achieving higher gain, lower noise, and improved energy resolution through circuit modifications.

Contribution

The study introduces in-pixel charge sensitive amplifiers to improve gain and energy resolution without sacrificing charge collection efficiency.

Findings

Achieved a readout noise of 35 e^- (rms).

Attained an energy resolution of 320 eV (FWHM) at 6 keV.

Improved spectroscopic performance by circuit modifications.

Abstract

We have been developing monolithic active pixel sensors series, named "XRPIX," based on the silicon-on-insulator (SOI) pixel technology, for future X-ray astronomical satellites. The XRPIX series offers high coincidence time resolution ({\rm \sim}1 {\rm \mu}s), superior readout time ({\rm \sim}10 {\rm \mu}s), and a wide energy range (0.5--40 keV). In the previous study, we successfully demonstrated X-ray detection by event-driven readout of XRPIX2b. We here report recent improvements in spectroscopic performance. We successfully increased the gain and reduced the readout noise in XRPIX2b by decreasing the parasitic capacitance of the sense-node originated in the buried p-well (BPW). On the other hand, we found significant tail structures in the spectral response due to the loss of the charge collection efficiency when a small BPW is employed. Thus, we increased the gain in XRPIX3b by introducing in-pixel charge sensitive amplifiers instead of having even smaller BPW. We finally achieved the readout noise of 35 e{\rm ^{-}} (rms) and the energy resolution of 320 eV (FWHM) at 6 keV without significant loss of the charge collection efficiency.