Design and Performance of Hybrid Arrays of Mo/Au Bilayer Transition-Edge Sensors

Abstract

For future X-ray astrophysics missions, X-ray microcalorimeters can be optimized with different properties in different regions of the focal plane. This approach has the potential to improve microcalorimeter instrument capabilities with efficient use of instrument resources. For example a point-source array optimized for high angular resolution, high count-rate observations could be accompanied by a main array to expand the field of view for diffuse observations. In this approach, it is desirable to be able to simultaneously optimize different transition-edge sensor (TES) geometries on a single wafer design. The key properties of TESs such as transition temperature and shape are a strong function of size and geometry due to the complex interplay between the proximity effect from the superconducting bias electrodes and the normal metal features used for noise suppression and absorber contact. As a result, devices fabricated with the same deposited layer but with different sizes will have different transition temperatures and Manuscript

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

“…An excellent energy resolution of 1.58 ± 0.12 eV at 5.9 keV was reported with a small, 50 × 50 µm 2 , bare TES with T c = 95.6 mK, coupled to a Bi(4.04 µm)/Au(1.49 µm) 240 × 240 µm 2 absorber with heat capacity C = 0.69 pJ/K. The stripe-less small device had much larger values of α(∼1600), β(∼86) and M 2 (∼6) with respect to the larger size TESs with stripes (α ∼ 75, β ∼ 1.25 and M 2 ∼ 0) [114], which showed energy resolution around 2 eV and were under consideration for X-IFU.…”

“…The star symbol is the expected demonstration of the readout of 3168 pixels with the XIFU/Athena flight model (FM). The data points are taken from the following publications, as annotated in the bottom plot: a =[195], b =[196], c =[9], d =[133], e =[197], f =[128] (32 TESs + 8 repeats of the last row), g =[134], h =[135], i =[10], j =[198], k =[127], l =[148], m =[149], n =[114], o =[157].…”

Fabrication of X-Ray Microcalorimeter Focal Planes Composed of Two Distinct Pixel Types

“…The reflow acts consistently on all scales down to 3 μm circles used as single point attachments to the SPA pixels, though sharp interior corners have been observed to lead to nonideal photoresist sidewalls. The LPA pixels are attached to both the TES and nitride membrane through a "T" shaped stem [9]. Next, we electroplated an additional ~ 1.5 μm uniform Au film over the entire wafer to provide protection to the sacrificial resist supporting the added metal layers.…”

“…Uniform test arrays have demonstrated that we are able to fabricate SPA pixels on a 75 μm pitch with a 36×33 μm rectangular TES capable of achieving energy resolution ~1eV based upon a spectrum from a 1.5 KeV Al Kα X-rays [12], and LPA pixels on a 250 μm pitch with a 140 μm square TES capable of achieving energy resolution ~2 eV [9]. We will report the results of our efforts at achieving the target T 0 and energy resolution in a future publication.…”

Electroplating Deposition of Bismuth Absorbers for X-ray Superconducting Transition Edge Sensors

“…TES has been widely used in the field of X-ray detection [ 1 , 2 ]. X-ray TES is a very sensitive thermometer based on the transition between the superconducting and normal state of a superconducting metal film due to the thermal transfer from the absorber, which absorbs the energy of incident X-ray photons [ 3 , 4 , 5 ]. The energy resolution (Δ E ) in the strong electro-thermal feedback is related to ~ C 1/2 , C is the heat capacity of superconducting thin films and the absorber [ 6 , 7 , 8 ].…”