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The X-ray integrated field unit (X-IFU) in European Space Agency's (ESA's) Athena mission will be the first high-resolution X-ray spectrometer in space using a large-format transition-edge sensor microcalorimeter array. Motivated by optimization of detector performance for X-IFU, we have conducted an extensive campaign of parametric characterization on transition-edge sensor (TES) detectors with nominal geometries and physical properties in order to establish sensitivity trends relative to magnetic field, dc bias on detectors, operating temperature, and to improve our understanding of detector behavior relative to its fundamental properties such as thermal conductivity, heat capacity, and transition temperature. These results were used for validation of a simple linear detector model in which a small perturbation can be introduced to one or multiple parameters to estimate the error budget for X-IFU. We will show here results of our parametric characterization of TES detectors and briefly discuss the comparison with the TES model.

Micro-X is a sounding-rocket experiment that will combine a transition edge sensor (TES) microcalorimeter array with an imaging mirror to obtain high-spectral-resolution images of astronomical X-ray sources. The instrument's resolution across the 0.3-2.5 keV band will be 2 eV. The first flight will target the region of the Bright Eastern Knot of the Puppis A supernova remnant and is slated for January 2011. The obtained high-resolution X-ray spectra will be used to ascertain the temperature and ionization state of the X-ray-emitting gas and to determine its velocity structure. The TES array is read out by a time-division superconducting quantum interference device (SQUID) multiplexing system. The detector front end assembly and the SQUID multiplexing circuit are cooled to the operating temperature of 50 mK with an adiabatic demagnetization refrigerator (ADR). The design of this refrigerator is tailored to the requirements of rocket flight. Stable operation of the TES array close to the ADR magnet will be achieved with a magnetic shielding system, which will be based on a combination of a bucking coil and high-permeability and superconducting shield materials to cancel out residual fields. We describe our progress in developing the Micro-X instrument.

We report on the development of position-sensitive transition-edge sensors (PoST's) for future X-ray astronomy missions such as the International X-ray Observatory (IXO), under study by NASA and ESA. PoST's consist of multiple absorbers each with a different thermal coupling to one or more transition-edge sensors (TESs). This results in a characteristic pulse shape for each absorber element and allows position discrimination. PoST development is motivated by a desire to achieve maximum focal-plane area with the fewest number of readout channels. We report detailed characterization of our single TES PoST's or Hydras, which consist of four electroplated Au/Bi absorbers coupled to a low noise Mo/Au TES. Using a numerical model of the Hydra we fit to measured complex impedance curves and determine device parameters that allow us to accurately reproduce the measured pulse shapes and noise spectra. Results from Hydras with different internal thermal conductances reveal the trade-offs in optimizing for energy resolution or position-sensitivity. We report a best achievable energy resolution of < 6.0 eV across all pixels for a device with transition temperature of 86 mK, coupled with straightforward position discrimination by rise-time.

We present fabrication details of our Mo/Au X-ray microcalorimeters, which are being developed as one of the candidate high resolution spectrometers for the Constellation-X mission. We have reproducibly fabricated Mo/Au transition-edge sensors with Tc's of /spl sim/100 mK on etched silicon nitride membranes and connected via superconducting Nb leads. Our single pixel devices have, so far, attained resolution of 3.7 eV at 3.3 keV. We also discuss our plans for fabrication and testing of fully functional multi-pixel array of X-ray microcalorimeters.

We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.

The transition between normal conduction and superconductivity in superconducting materials can be exploited as a highly sensitive thermometer. Transition temperatures can be tailored through the selection of materials, their component cases of more than one material. Two bilayer configurations, Ag/Al and Au/Mo, are examined, including details of preparation, testing, and encountered difficulties. Proposed designs for spaceflight detector applications are discussed.

The Micro-X sounding rocket program will fly a 128-pixel array of transition-edge-sensor microcalorimeters to enable high-resolution X-ray imaging spectroscopy of supernova remnants. To match the angular resolution of the optics while maximizing the field-of-view and retaining a high energy resolution (2-4 eV at 1 keV), we have designed the pixels using 590 × 590 μm2 Au/Bi absorbers, which overhang 140 × 140 μm2 Mo/Au sensors. Here we report experimental results from flight-candidate arrays, including measurements of energy resolution, uniformity, and absorber thermalization. We describe the reduction in pixel-to-pixel crosstalk afforded by an angle-evaporated Cu backside heatsinking layer, which provides Cu coverage on the four sidewalls of the silicon wells beneath each pixel. In addition, we present measurements of devices that have an identical pixel architecture but were fabricated with thin (sub-micron) all-Au absorbers.