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Register a new userPassivation of Si(Li) detectors operated above cryogenic temperatures for space-based applications
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This work evaluates the viability of polyimide and parylene-C for passivation of lithium-drifted silicon (Si(Li)) detectors. The passivated Si(Li) detectors will form the particle tracker and X-ray detector of the General Antiparticle Spectrometer (GAPS) experiment, a balloon-borne experiment optimized to detect cosmic antideuterons produced in dark matter annihilations or decays. Successful passivation coatings were achieved by thermally curing polyimides, and the optimized coatings form an excellent barrier against humidity and organic contamination. The passivated Si(Li) detectors deliver $lesssim,4$ keV energy resolution (FWHM) for 20$-$100 keV X-rays while operating at temperatures of $-$35 to $-45,^{circ}$C. This is the first reported successful passivation of Si(Li)-based X-ray detectors operated above cryogenic temperatures.
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A Si(Li) detector fabrication procedure has been developed with the aim of satisfying the unique requirements of the GAPS (General Antiparticle Spectrometer) experiment. Si(Li) detectors are particularly well-suited to the GAPS detection scheme, in which several planes of detectors act as the target to slow and capture an incoming antiparticle into an exotic atom, as well as the spectrometer and tracker to measure the resulting decay X-rays and annihilation products. These detectors must provide the absorption depth, energy resolution, tracking efficiency, and active area necessary for this technique, all within the significant temperature, power, and cost constraints of an Antarctic long-duration balloon flight. We report here on the fabrication and performance of prototype 2-diameter, 1-1.25 mm-thick, single-strip Si(Li) detectors that provide the necessary X-ray energy resolution of $sim$4 keV for a cost per unit area that is far below that of previously-acquired commercial detectors. This fabrication procedure is currently being optimized for the 4-diameter, 2.5 mm-thick, multi-strip geometry that will be used for the GAPS flight detectors.
Electron tracking based Compton imaging is a key technique to improve the sensitivity of Compton cameras by measuring the initial direction of recoiled electrons. To realize this technique in semiconductor Compton cameras, we propose a new detector concept, Si-CMOS hybrid detector. It is a Si detector bump-bonded to a CMOS readout integrated circuit to obtain electron trajectory images. To acquire the energy and the event timing, signals from N-side are also read out in this concept. By using an ASIC for the N-side readout, the timing resolution of few us is achieved. In this paper, we present the results of two prototypes with 20 um pitch pixels. The images of the recoiled electron trajectories are obtained with them successfully. The energy resolutions (FWHM) are 4.1 keV (CMOS) and 1.4 keV (N-side) at 59.5 keV. In addition, we confirmed that the initial direction of the electron is determined using the reconstruction algorithm based on the graph theory approach. These results show that Si-CMOS hybrid detectors can be used for electron tracking based Compton imaging.
Schottky Barrier (SB)-MOSFET technology offers intriguing possibilities for cryogenic nano-scale devices, such as Si quantum devices and superconducting devices. We present experimental results on a novel device architecture where the gate electrode is self-aligned with the device channel and overlaps the source and drain electrodes. This facilitates a sub-5 nm gap between the source/drain and channel, and no spacers are required. At cryogenic temperatures, such devices function as p-MOS Tunnel FETs, as determined by the Schottky barrier at the Al-Si interface, and as a further advantage, fabrication processes are compatible with both CMOS and superconducting logic technology.
IDeF-X HD is a 32-channel analog front-end with self-triggering capability optimized for the readout of 16 x 16 pixels CdTe or CdZnTe pixelated detectors to build low power micro gamma camera. IDeF-X HD has been designed in the standard AMS CMOS 0.35 microns process technology. Its power consumption is 800 micro watt per channel. The dynamic range of the ASIC can be extended to 1.1 MeV thanks to the in-channel adjustable gain stage. When no detector is connected to the chip and without input current, a 33 electrons rms ENC level is achieved after shaping with 10.7 micro seconds peak time. Spectroscopy measurements have been performed with CdTe Schottky detectors. We measured an energy resolution of 4.2 keV FWHM at 667 keV (137-Cs) on a mono-pixel configuration. Meanwhile, we also measured 562 eV and 666 eV FWHM at 14 keV and 60 keV respectively (241-Am) with a 256 small pixel array and a low detection threshold of 1.2 keV. Since IDeF-X HD is intended for space-borne applications in astrophysics, we evaluated its radiation tolerance and its sensitivity to single event effects. We demonstrated that the ASIC remained fully functional without significant degradation of its performances after 200 krad and that no single event latch-up was detected putting the Linear Energy Transfer threshold above 110 MeV/(mg/cm2). Good noise performance and radiation tolerance make the chip well suited for X-rays energy discrimination and high-energy resolution. The chip is space qualified and flies on board the Solar Orbiter ESA mission launched in 2020.
The influence of the transient thermal effects on the partition of the energy of selfrecoils in germanium and silicon into energy eventually given to electrons and to atomic recoils respectively is studied. The transient effects are treated in the frame of the thermal spike model, which considers the electronic and atomic subsystems coupled through the electron - phonon interaction. For low energies of selfrecoils, we show that the corrections to the energy partition curves due to the energy exchange during the transient processes modify the Lindhard predictions. These effects depend on the initial temperature of the target material, as the energies exchanged between electronic and lattice subsystems have different signs for temperatures lower and higher than about 15 K. Many of the experimental data reported in the literature support the model.
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