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

摘要

We have been developing monolithic active pixel sensors series, named"XRPIX," based on the silicon-on-insulator (SOI) pixel technology, for futureX-ray astronomical satellites. The XRPIX series offers high coincidence timeresolution ({\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, wesuccessfully demonstrated X-ray detection by event-driven readout of XRPIX2b.We here report recent improvements in spectroscopic performance. Wesuccessfully increased the gain and reduced the readout noise in XRPIX2b bydecreasing the parasitic capacitance of the sense-node originated in the buriedp-well (BPW). On the other hand, we found significant tail structures in thespectral response due to the loss of the charge collection efficiency when asmall BPW is employed. Thus, we increased the gain in XRPIX3b by introducingin-pixel charge sensitive amplifiers instead of having even smaller BPW. Wefinally achieved the readout noise of 35 e{\rm ^{-}} (rms) and the energyresolution of 320 eV (FWHM) at 6 keV without significant loss of the chargecollection efficiency.