Semiconducting Microcalorimeter Innovation Pathway

This case describes the development of microcalorimeter detector arrays for applications in Xray astronomy. The key insight, which initiated the multi-decade (X-ray) microcalorimeter innovation pathway, is generally attributed to a particular Goddard (infrared) astrophysicist; however multiple institutions and individuals have played key roles over the last 30 years. The development of microcalorimeters has been motivated by the need for a high resolution X-ray spectrometer that has high intrinsic quantum efficiency for use in X-ray astronomy. The high quantum efficiency is important because of the very low X-ray fluxes characteristic of most celestial X-ray sources. Although microcalorimeters were first demonstrated in 1984, and selected for flight aboard the Advanced X-ray Astronomical Facility (AXAF) in 1986; due to a series of unfortunate circumstances (AXAF-S split, Astro-E launch failure, Astro-E2 cryogenic system failure, discussed in the previous pathways) the detectors have yet to return data from a space-based platform. This milestone will hopefully be achieved in early-2014 aboard Astro-H. During this 30 year history, three fundamentally different classes of microcalorimeters have emerged – one based on semiconductor thermometers, one based on superconducting transition edge sensors and one based on magnetic resonance. Figure Error! No text of specified style in document.-1 illustrates how the best-in-the-world detector performance has improved over time. We consider the three generations here as separate, albeit entangled, innovation pathways. Only the first two histories are presented in detail (as the third is still quite immature).