High aspect ratio transition edge sensors for x-ray spectrometry

Abstract

We are developing large TES arrays in combination with FDM readout for the next generation of X-ray space observatories. For operation under AC-bias, the TESs have to be carefully designed and optimized. In particular, the use of high aspect ratio devices will help to mitigate non-ideal behaviour due to the weak-link effect. In this paper, we present a full characterization of a TES array containing five different device geometries, with aspect ratios (width:length) ranging from 1:2 up to 1:6. The complex impedance of all geometries is measured in different bias configurations to study the evolution of the small-signal limit superconducting transition parameters α and β , as well as the excess noise. We show that high aspect ratio devices with properly tuned critical temperatures (around 90 mK) can achieve excellent energy resolution, with an array average of 2.03 ± 0.17 eV at 5.9 keV and a best achieved resolution of 1.63 ± 0.17 eV. This demonstrates that AC-biased TESs can achieve a very competitive performance compared to DC-biased TESs. The results have motivated a push to even more extreme device geometries currently in development.

A Review of X-ray Microcalorimeters Based on Superconducting Transition Edge Sensors for Astrophysics and Particle Physics

“…We have to experimentally investigate the performance, under ac bias, of many high aspect ratio devices fabricated at SRON with high (T c 110 mK) [120], and low (T c 90 mK) [22] critical temperature. The energy resolution was shown to scale with T c as expected.…”

“…Figure 6. Current noise spectra of a Ti/Au 80 × 40 µm 2 TES X-ray calorimeter developed at SRON, biased at 2.5 MHz, at R/R n ∼ 0.2 with α ∼ 370 and β ∼ 5[22].…”

“…, we give an example of the mitigation of the Josephson effects achievable by using high aspect ratio (AR) TESs. From left to right, we show the I-V curves and the I Q /I I ratio of, respectively, an NASA-GSFC Mo/Au 75 × 17.5 µm 2 (AR = 4:1, R N = 120 mΩ), an SRON Ti/Au 80 × 20 µm 2 (AR = 4:1, R N 100 mΩ)[22], and an SRON Ti/Au 80 × 10 µm 2 (AR = 8:1, R N 200 mΩ). All the devices have a P sat ∼ 1-2 pW, compatible with the X-IFU requirement.…”

Thermal crosstalk of X-ray transition-edge sensor micro-calorimeters under frequency domain multiplexing readout

“…The bilayer dimensions are 50 × 10 µm 2 and 80 × 20 µm 2 for the array hosted in the XFDM and For further details about the TES array fabrication, see the study from Nagayoshi et al 7 . For further details about their AC operation and spectral performance, see the study from de Wit et al 8 .…”

Demonstration of MHz frequency domain multiplexing readout of 37 transition edge sensors for high-resolution x-ray imaging spectrometers

“…To reduce frequency dependent detector behaviour under AC bias, we use high aspect ratio TESs. This device was extensively investigated under AC bias with a lower inductance (L eff =1 µH) and demonstrated an excellent spectral resolution of 1.8 eV FWHM 20 .…”