R. Ballabriga et al. "The Medipix3 Prototype, a Pixel Readout Chip Working in Single Photon Counting Mode With Improved Spectrometric Performance", in IEEE Transctions On Nuclear Science, Vol.54, No.5, pp.1824-1829, 2007
We have been developing a monolithic active pixel sensor with the 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, i.e. SOIPIX, for the X-ray imaging spectroscopy on future astronomical satellites. SOIPIX includes a thin CMOS readout layer and a thick high-resistivity Si-sensor layer vertically on a single chip, which would provide advantages in capabilities of direct and flexible readout circuitries over charge-coupled device (CCD). We have built INTPIX2/3 (2008/2009) and XRPIX1(2010). We successfully confirmed the capability of X-ray imaging and spectroscopy in a photon-counting mode by irradiating INTPIX2/3 with monochromatic X-rays. To reduce the readout noise, we designed and built XRPIX1, which has a correlated double sampling (CDS) readout circuit in each pixel to suppress the reset noise. We obtained an energy resolution of FWHM ~1.5 keV(7%)@22 keV with XRPIX1 cooled at 50 degree. Moreover, XRPIX1 offers intra-pixel hit trigger and one-dimensional hit-pattern outputs. We also confirmed the trigger capability by irradiating a single pixel of XRPIX1 with laser light.