Spectroscopic performance improvement of SOI pixel detector for X-ray astronomy by introducing Double-SOI structure

This paper reports the spectroscopic performance improvement of the silicon-on-insulator (SOI) pixel detector for X-ray astronomy, by introducing a double-SOI (D-SOI) structure. For applications in X-ray astronomical observatories, we have been developing a series of monolithic active pixel sensors, named as "XRPIXs," based on SOI pixel technology. The D-SOI structure has an advantage that it can suppress a parasitic capacitance between the sensing node and the circuit layer, due to which the closed-loop gain cannot be increased in our conventional XRPIXs with a single-SOI (S-SOI) structure. Compared to the S-SOI XRPIX, the closed-loop gain is doubled in the D-SOI XRPIX. The readout noise is effectively lowered to 33% (16 e(-) (rms)), and the energy resolution at 6.4 keV is improved by a factor of 1.7 (290 eV in FWHM). The suppression of the parasitic capacitance is also quantitatively evaluated based on the results of capacitance extraction simulation from the layout. This evaluation provides design guidelines for further reduction of the readout noise.