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

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https://ieeexplore.ieee.org/abstract/document/7762854

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https://doi.org/10.1109/TASC.2016.2633783
 http://hdl.handle.net/11603/24027

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
UMBC Faculty Collection
UMBC Physics Department

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Author/Creator ORCID

https://orcid.org/0000-0003-0622-5174
 https://orcid.org/0000-0003-4096-4675
 https://orcid.org/0000-0002-9247-3010
 https://orcid.org/0000-0001-8397-9338

Date

2016-12-01

Type of Work

journal articles
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Citation of Original Publication

E. J. Wassell et al., "Fabrication of X-Ray Microcalorimeter Focal Planes Composed of Two Distinct Pixel Types," in IEEE Transactions on Applied Superconductivity, vol. 27, no. 4, pp. 1-5, June 2017, Art no. 2300205, doi: 10.1109/TASC.2016.2633783.

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0

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Abstract

We develop superconducting transition-edge sensor (TES) microcalorimeter focal planes for versatility in meeting the specifications of X-ray imaging spectrometers, including high count rate, high energy resolution, and large field of view. In particular, a focal plane composed of two subarrays: one of fine pitch, high count-rate devices and the other of slower, larger pixels with similar energy resolution, offers promise for the next generation of astrophysics instruments, such as the X-ray Integral Field Unit Instrument on the European Space Agency’s ATHENA mission. We have based the subarrays of our current design on successful pixel designs that have been demonstrated separately. Pixels with an all-gold X-ray absorber on 50 and 75 µm pitch, where the Mo/Au TES sits atop a thick metal heatsinking layer, have shown high resolution and can accommodate high count rates. The demonstrated larger pixels use a silicon nitride membrane for thermal isolation, thinner Au, and an added bismuth layer in a 250-µm2 absorber. To tune the parameters of each subarray requires merging the fabrication processes of the two detector types. We present the fabrication process for dual production of different X-ray absorbers on the same substrate, thick Au on the small pixels and thinner Au with a Bi capping layer on the larger pixels to tune their heat capacities. The process requires multiple electroplating and etching steps, but the absorbers are defined in a single-ion milling step. We demonstrate methods for integrating the heatsinking of the two types of pixel into the same focal plane consistent with the requirements for each subarray, including the limiting of thermal crosstalk. We also discuss fabrication process modifications for tuning the intrinsic transition temperature (Tc) of the bilayers for the different device types through variation of the bilayer thicknesses. The latest results on these “hybrid” arrays will be presented.