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Malcolm Durkin , Joseph S. Adams, Simon R. Bandler, James A. Chervenak, Saptarshi Chaudhuri, Carl S. Dawson, Edward V. Denison, William B. Doriese , Shannon M. Duff, Fred M. Finkbeiner , Connor T. FitzGerald, Joseph W. Fowler, Johnathon D. Gard, Gene C. Hilton, Kent D. Irwin, Young Il Joe, Richard L. Kelley, Caroline A. Kilbourne , Antoine Miniussi, Kelsey M. Morgan , Galen C. O���Neil, Christine G. Pappas, Frederick S. Porter, Carl D. Reintsema, David A. Rudman, Kazuhiro Sakai, Stephen J. Smith, Robert W. Stevens, Daniel S. Swetz, Paul Szypryt, Joel N. Ullom, Leila R. Vale, Nicholas Wakeham , Joel C. Weber, and Betty A. Young, Time-division multiplexing (TDM) is the backup readout technology for the X-ray Integral Field Unit (X-IFU), a 3168-pixel X-ray transition-edge sensor (TES) array that will provide imaging spectroscopy for european space agency���s Athena satellite mission. X-IFU design studies are considering readout with a multiplexing factor of up to 40. We present data showing 40-row TDM readout (32 TES rows + 8 repeats of the last row) of TESs that are of the same type as those being planned for X-IFU, using measurement and analysis parameters within the ranges specified for X-IFU. Single-column TDM measurements have best-fit energy resolution of (1.91 �� 0.01) eV for the Al K�� complex (1.5 keV), (2.10 �� 0.02) eV for Ti K�� (4.5 keV), (2.23 �� 0.02) eV for Mn K�� (5.9 keV), (2.40 �� 0.02) eV for Co K�� (6.9 keV), and (3.44 �� 0.04) eV for Br K�� (11.9 keV). Three-column measurements have best-fit resolution of (2.03 �� 0.01) eV for Ti K�� and (2.40 �� 0.01) eV for Co K��. The degradation due to the multiplexed readout ranges from 0.1 eV at the lower end of the energy range to 0.5 eV at the higher end. The demonstrated performance meets X-IFU���s energy-resolution and energy-range requirements. True 40-row TDM readout, without repeated rows, of kilopixel scale arrays of X-IFU-like TESs is now under development.

F. T. Jaeckel , C. V. Ambarish, N. Christensen, R. Gruenke, L. Hu, D. McCammon, M. McPheron, M. Meyer, K. L. Nelms, A. Roy, D. Wulf, S. Zhang, Y. Zhou, J. S. Adams, S. R. Bandler, J. A. Chervenak, A. M. Datesman , M. E. Eckart, A. J. Ewin, F. M. Finkbeiner , R. Kelley, C. A. Kilbourne, Antoine Miniussi, F. S. Porter, J. E. Sadleir, Kazuhiro Sakai, Stephen J. Smith, Nicholas Wakeham, E. Wassell , W. Yoon , K. M. Morgan, D. R. Schmidt, D. S. Swetz, and J. N. Ullom, With the improving energy resolution of transition-edge sensor (TES) based microcalorimeters, performance verification and calibration of these detectors have become increasingly challenging, especially in the energy range below 1 keV where fluorescent atomic X-ray lines have linewidths that are wider than the detector energy resolution and require impractically high statistics to determine the gain and deconvolve the instrumental profile. Better behaved calibration sources such as grating monochromators are too cumbersome for space missions and are difficult to use in the lab. As an alternative, we are exploring the use of pulses of 3 eV optical photons delivered by an optical fiber to generate combs of known energies with known arrival times. Here, we discuss initial results of this technique obtained with 2 and 0.7 eV resolution X-ray microcalorimeters. With the 2 eV detector, we have achieved photon number resolution for pulses with mean photon number up to 133 (corresponding to 0.4 keV).

Fred Michael Finkbeiner, Joseph S. Adams, Simon R. Bandler, Gabriele L. Betancourt-Martinez, Ari David Brown, Meng-Ping Chang, James A. Chervenak, Meng P. Chiao, Aaron M. Datesman, Megan E. Eckart, Richard L. Kelley, Caroline A. Kilbourne, Antoine Miniussi, Samuel J. Moseley, Frederick Scott Porter, John E. Sadleir, Kazuhiro Sakai, Stephen James Smith, Nicholas A. Wakeham, Edward J. Wassell, and Wonisk Yoon, We are exploring the properties of electron-beam evaporated molybdenum thin films on silicon nitride coated silicon wafers at substrate temperatures between room temperature and 650 ��C. The temperature dependence of film stress, transition temperature, and electrical properties are presented. X-ray diffraction measurements are performed to gain information on molybdenum crystallite size and growth. Results show the dominant influence of the crystallite size on the intrinsic properties of our films. Wafer-scale uniformity, wafer yield, and optimal thermal bias regime for TES fabrication are discussed.

Edward J. Wassell, Joseph S. Adams, Simon R. Bandler, Gabriele L. Betancourt-Martinez, Meng P. Chiao, Meng Ping Chang, James A. Chervenak, Aaron M. Datesman, Megan E. Eckart, Audrey J. Ewin, Fred Michael Finkbeiner, Jong Yoon Ha, Richard Kelley, Caroline A. Kilbourne, Antoine Miniussi, Kazuhiro Sakai, Frederick Scott Porter, John E. Sadleir, r, Stephen James Smith, Nicholas Wakeham, and Wonisk Yoon, 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 ��m 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-��m2 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.