Abstract
In this paper, we report on the development of a monolithic active pixel sensor for X-ray imaging using 0.2 µm fully depleted silicon-on-insulator (SOI)-based technology to support next generation astronomical satellite missions. Detail regarding low-noise dual-gain SOI based pixels with a charge sensitive amplifier and pinned depleted diode sensor structure is presented. The proposed multi-well sensor structure underneath the fully-depleted SOI allows the design of a detector with low node capacitance and high charge collection efficiency. Configurations for achieving very high charge-to-voltage conversion gain of 52 µV/e− and 187 µV/e− are demonstrated. Furthermore, in-pixel dual gain selection is used for low-noise and wide dynamic range X-ray energy detection. A technique to improve the noise performance by removing correlated system noise leads to an improvement in the spectroscopic performance of the measured X-ray energy. Taken together, the implemented chip has low dark current (44.8 pA/cm2 at −30 °C), improved noise performance (8.5 e− rms for high gain and 11.7 e− rms for low gain), and better energy resolution of 2.89% (171 eV FWHM) at 5.9 keV using 55Fe and 1.67% (234 eV FWHM) at 13.95 keV using 241Am.
Highlights
Recent decades have witnessed considerable progress in the use of X-ray imaging and spectroscopy to enhance our understanding of the complexities of the universe, such as new insights into black holes, supernova remnants, and the evolution of stars through cosmic time of galaxies [1].X-ray detectors are considered to be fundamental and key components to any space missions.High energy astrophysics requires a detector with wide pass-band spectral response and high hit position pixel readout time.Sensors 2018, 18, 1789; doi:10.3390/s18061789 www.mdpi.com/journal/sensorsMost astronomical satellites employ charge-coupled device (CCD) detectors for X-ray imaging (e.g., Swift’s X-ray telescope, Chandra’s advanced CCDs imaging spectrometer, Suzaku’s X-ray imaging spectrometer, XMM-Newton’s European photon imaging camera) [2,3]
The CCD detector technology for space has reached its maturity with a near fano-limited energy resolution, high quantum efficiency, and low readout noise
At high event count rates, CCDs with large array are limited in their ability to measure X-rays accurately
Summary
Recent decades have witnessed considerable progress in the use of X-ray imaging and spectroscopy to enhance our understanding of the complexities of the universe, such as new insights into black holes, supernova remnants, and the evolution of stars through cosmic time of galaxies [1]. Imaging Sensors has demonstrated an energy resolution of 156 eV at 5.9 keV [5] Another hybrid detector from MIT Lincoln Laboratory uses 3-D integration of silicon diode array with CMOS readout circuitry on a separate silicon-on-insulator (SOI) wafer [6]. MPI Semiconductor Laboratory has demonstrated the DEPFET monolithic pixel detector for high energy particle imaging [7] Another monolithic detector optimized for X-ray detection is being developed at the Smithsonian Astrophysical Observatory with SRI/Sarnoff [8]. The SOIPIX leverages the advantages of monolithic pixel detectors with high-resistivity silicon substrate used as a detector and SOI CMOS readout circuits implemented on thick insulating oxide layer Both the SOI circuit and detector can be optimized independently for achieving the best performance for low-noise wide-dynamic-range X-ray detection. Evaluation results from 55 Fe and 241 Am X-ray sources using the SOIPIX-PDD based dual-gain CSA pixel with improved X-ray spectroscopic performance are discussed
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