2015/09/02 by Matsumura, Hideaki, Tsuru, Takeshi Go, Tanaka, Takaaki +8
#FOS: Physical sciences #Instrumentation and Detectors (physics.ins-det)
paper · doi:10.48550/arxiv.1509.00538
We have been developing X-ray SOIPIXs for next-generation satellites for X-ray astronomy. Their high time resolution (∼10~μs) and event-trigger-output function enable us to read out without pile-ups and to use anti-coincidence systems. Their performance in imaging spectroscopy is comparable to that in the CCDs. A problem in our previous model was degradation of charge-collection efficiency (CCE) at pixel borders. We measured the response in the sub-pixel scale, using finely collimated X-ray beams at 10~μmΦ at SPring-8, and investigated the non-uniformity of the CCE within a pixel. We found that the X-ray detection efficiency and CCE degrade in the sensor region under the pixel circuitry placed outside the buried p-wells (BPW). A 2D simulation of the electric fields shows that the isolated pixel-circuitry outside the BPW creates local minimums in the electric potentials at the interface between the sensor and buried oxide layers. Thus, a part of signal charge is trapped there and is not collected to the BPW. Based on this result, we modified the placement of the in-pixel circuitry so that the electric fields would converge toward the BPW. We confirmed that the CCE at pixel borders is successfully improved with the updated model.