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Register a new userSingle pixel performance of a 32$times$32 Ti/Au TES array with broadband X-ray spectra
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We are developing a kilo-pixels Ti/Au TES array as a backup option for Athena X-IFU. Here we report on single-pixel performance of a 32$times$32 array operated in a Frequency Division Multiplexing (FDM) readout system, with bias frequencies in the range 1-5 MHz. We have tested the pixels response at several photon energies, by means of a $^{55}$Fe radioactive source (emitting Mn-K$alpha$ at 5.9 keV) and a Modulated X-ray Source (MXS, providing Cr-K$alpha$ at 5.4 keV and Cu-K$alpha$ at 8.0 keV). First, we report the procedure used to perform the detector energy scale calibration, usually achieving a calibration accuracy better than $sim$ 0.5 eV in the 5.4 - 8.9 keV energy range. Then, we present the measured energy resolution at the different energies (best single pixel performance: $Delta$E$_{FWHM}$ = 2.40 $pm$ 0.09 eV @ 5.4 keV; 2.53 $pm$ 0.10 eV @ 5.9 keV; 2.78 $pm$ 0.16 eV @ 8.0 keV), investigating also the performance dependency from the pixel bias frequency and the count rate. Thanks to long background measurements ($sim$ 1 day), we finally detected also the Al-K$alpha$ line at 1.5 keV, generated by fluorescence inside the experimental setup. We analyzed this line to obtain a first assessment of the single-pixel performance also at low energy ($Delta$E$_{FWHM}$ = 1.91 eV $pm$ 0.21 eV @ 1.5 keV), and to evaluate the linearity of the detector response in a large energy band (1.5 - 8.9 keV).
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Large format arrays of transition edge sensor (TES) are crucial for the next generation of X-ray space observatories. Such arrays are required to achieve an energy resolution of $mathrm{Delta}E<$3 eV full-width-half-maximum (FWHM) in the soft X-ray energy range. We are currently developing X-ray microcalorimeter arrays as a backup option for the X-IFU instrument on board of ATHENA space telescope, led by ESA and foreseen to be launched in 2031. In this contribution, we report on the development and the characterization of a uniform 32$times$32 pixel array with (length$times $width) 140$times$30 $mu$m$^2$ TiAu TESs, which have textcolor{black}{a 2.3 $mu$m} thick Au absorber for X-ray photons. The pixels have a typical normal resistance $R_mathrm{n}$ = 121 m$Omega$ and a critical temperature $T_mathrm{c}sim$ 90 mK. We performed extensive measurements on 60 pixels out of the array in order to show the uniformity of the array. We obtained an energy resolutions between 2.4 and 2.6 eV (FWHM) at 5.9 keV, measured in a single-pixel mode at AC bias frequencies ranging from 1 to 5 MHz, with a frequency domain multiplexing (FDM) readout system, which is developed at SRON/VTT. We also present the detector energy resolution at X-ray with different photon energies generated by a modulated external X-ray source from 1.45 keV up to 8.9 keV. Multiplexing readout across several pixels has also been performed to evaluate the impact of the thermal crosstalk to the instruments energy resolution budget requirement. This value results in a derived requirement, for the first neighbour, that is less than 1$times$10$^{-3}$ when considering the ratio between the amplitude of the crosstalk signal to an X-ray pulse (for example at 5.9 keV)
Uniform large transition-edge sensor (TES) arrays are fundamental for the next generation of X-ray space observatories. These arrays are required to achieve an energy resolution $Delta E$ < 3 eV full-width-half-maximum (FWHM) in the soft X-ray energy range. We are currently developing X-ray microcalorimeter arrays for use in future laboratory and space-based X-ray astrophysics experiments and ground-based spectrometers. In this contribution we report on the development and the characterization of a uniform 32$times$32 pixel array with 140$times$30 $mu$m$^2$ Ti/Au TESs with Au X-ray absorber. We report upon extensive measurements on 60 pixels in order to show the uniformity of our large TES array. The averaged critical temperature is $T_mathrm{c}$ = 89.5$pm$0.5 mK and the variation across the array ($sim$1 cm) is less than 1.5 mK. We found a large region of detectors bias points between 20% and 40% of the normal-state resistance where the energy resolution is constantly lower than 3 eV. In particular, results show a summed X-ray spectral resolution $Delta E_mathrm{FWHM}$ = 2.50$pm$0.04 eV at a photon energy of 5.9 keV, measured in a single-pixel mode using a frequency domain multiplexing (FDM) readout system developed at SRON/VTT at bias frequencies ranging from 1 to 5 MHz. Moreover we compare the logarithmic resistance sensitivity with respect to temperature and current ($alpha$ and $beta$ respectively) and their correlation with the detectors noise parameter $M$, showing an homogeneous behaviour for all the measured pixels in the array.
We report on the design and performance of a mixed-signal application specific integrated circuit (ASIC) dedicated to avalanche photodiodes (APDs) in order to detect hard X-ray emissions in a wide energy band onboard the International Space Station. To realize wide-band detection from 20 keV to 1 MeV, we use Ce:GAGG scintillators, each coupled to an APD, with low-noise front-end electronics capable of achieving a minimum energy detection threshold of 20 keV. The developed ASIC has the ability to read out 32-channel APD signals using 0.35 $mu$m CMOS technology, and an analog amplifier at the input stage is designed to suppress the capacitive noise primarily arising from the large detector capacitance of the APDs. The ASIC achieves a performance of 2099 e$^{-}$ + 1.5 e$^{-}$/pF at root mean square (RMS) with a wide 300 fC dynamic range. Coupling a reverse-type APD with a Ce:GAGG scintillator, we obtain an energy resolution of 6.7% (FWHM) at 662 keV and a minimum detectable energy of 20 keV at room temperature (20 $^{circ}$C). Furthermore, we examine the radiation tolerance for space applications by using a 90 MeV proton beam, confirming that the ASIC is free of single-event effects and can operate properly without serious degradation in analog and digital processing.
We have been developing monolithic active pixel sensors for X-rays based on the silicon-on-insulator technology. Our device consists of a low-resistivity Si layer for readout CMOS electronics, a high-resistivity Si sensor layer, and a SiO$_2$ layer between them. This configuration allows us both high-speed readout circuits and a thick (on the order of $100~mu{rm m}$) depletion layer in a monolithic device. Each pixel circuit contains a trigger output function, with which we can achieve a time resolution of $lesssim 10~mu{rm s}$. One of our key development items is improvement of the energy resolution. We recently fabricated a device named XRPIX6E, to which we introduced a pinned depleted diode (PDD) structure. The structure reduces the capacitance coupling between the sensing area in the sensor layer and the pixel circuit, which degrades the spectral performance. With XRPIX6E, we achieve an energy resolution of $sim 150$~eV in full width at half maximum for 6.4-keV X-rays. In addition to the good energy resolution, a large imaging area is required for practical use. We developed and tested XRPIX5b, which has an imaging area size of $21.9~{rm mm} times 13.8~{rm mm}$ and is the largest device that we ever fabricated. We successfully obtain X-ray data from almost all the $608 times 384$ pixels with high uniformity.
Transition-edge sensors (TESs) are used as very sensitive thermometers in microcalorimeters aimed at detection of different wavelengths. In particular, for soft X-ray astrophysics, science goals require very high resolution microcalorimeters which can be achieved with TESs coupled to suitable absorbers. For many applications there is also need for a high number of pixels which typically requires multiplexing in the readout stage. Frequency Domain Multiplexing (FDM) is a common scheme and is the baseline proposed for the ATHENA mission. FDM requires biasing the TES in AC at MHz frequencies. Recently there has been reported degradation in performances under AC with respect to DC bias. In order to assess the performances of TESs to be used with FDM, it is thus of great interest to compare the performances of the same device both under AC and DC bias. This requires two different measurement setups with different processes for making the characterization. We report in this work the preliminary results of a single pixel characterization performed on a TiAu TES under AC and afterwards under DC bias in different facilities. Extraction of dynamical parameters and noise performances are compared in both cases as a first stage for further AC/DC comparison of these devices.
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