Ari-David Brown

Bio: Ari-David Brown is an academic researcher from Goddard Space Flight Center. The author has contributed to research in topics: Bolometer & Transition edge sensor. The author has an hindex of 12, co-authored 40 publications receiving 461 citations.

Performance of TES X-ray Microcalorimeters with a Novel Absorber Design

Abstract: Superconducting transition-edge sensor (TES) microcalorimeters have demonstrated the Constellation-X requirements for spectral resolution, speed, and pixel size in a close-packed geometry. We will present our recent breakthrough energy resolution with sensors that have all gold and bismuth-gold absorbers. This has been enabled by cantilevered absorbers that make contact to the TES only in regions that are not part of the active thermometer. With this approach, rapid thermalization of the x-ray energy is achieved and interaction between the absorber and TES sensor films is avoided. This design allows us to obtain uniform high performance and is compatible with large-format, high fill-factor arrays. We will discuss this design, the results we have achieved in 8×8 arrays of these pixels, and the dependence of the performance on the geometry of the absorber contact area and on stress within the sensor.

Close-packed Arrays of Transition-edge X-ray Microcalorimeters with High Spectral Resolution at 5.9 keV

Abstract: We present measurements of high fill-factor arrays of superconducting transition-edge x-ray microcalorimeters designed to provide rapid thermalization of the x-ray energy. We designed an x-ray absorber that is cantilevered over the sensitive part of the thermometer itself, making contact only at normal metal-features. With absorbers made of electroplated gold, we have demonstrated an energy resolution between 2.4 and 3.1 eV at 5.9 keV on 13 separate pixels. We have determined the thermal and electrical parameters of the devices throughout the superconducting transition, and, using these parameters, have modeled all aspects of the detector performance.

JWST microshutter array system and beyond

Abstract: We have developed the Microshutter Array (MSA) system at NASA Goddard Space Flight Center (GSFC) as a multi-object aperture array for the Near Infrared Spectrograph (NIRSpec) instrument on the James Webb Space Telescope (JWST). The MSA system will enable NIRSpec to simultaneously obtain spectra from more than 100 targets, which, in turn, increases instrument efficiency one-hundred fold. Consequently, this system represents one of the three major innovations on the JWST, which has been selected by the National Research Council's 2001 decadal survey as the top-ranked space-based mission and is scheduled to be the successor to the Hubble Space Telescope. Furthermore, the MSA system will be one of the first MEMS devices serving observation missions in space. Microshutters are designed for the selective transmission of light with high efficiency and contrast and feature torsion hinges, light shields, deep-reactive ion-etched silicon windows, magnetic actuation, and electrostatic latching and addressing. Complete MSA quadrant assemblies consisting of 365 x 181 microshutters have been successfully fabricated. The assemblies have passed a series of critical reviews, which include programmable 2-D addressing, life tests, optical contrast tests, and environmental tests, required by the design specifications of JWST. Both the MSA and NIRSpec will be delivered to ESA for final assembly, and JWST is scheduled to launch in 2014. During final assembly and testing of the MSA system, we have begun to develop the Next Generation Microshutter Arrays (NGMSA) for future telescopes. These telescopes will require a much larger field of view than JWST's, and we discuss strategies for fabrication of a proof-of-concept NGMSA which will be modular in design and electrostatically actuated.

Absorber Materials for Transition-Edge Sensor X-ray Microcalorimeters

Abstract: Arrays of superconducting transition-edge sensors (TES) can provide high spatial and energy resolution necessary for x-ray astronomy. High quantum efficiency and uniformity of response can be achieved with a suitable absorber material, in which absorber x-ray stopping power, heat capacity, and thermal conductivity are relevant parameters. Here we compare these parameters for bismuth and gold. We have fabricated electroplated gold, electroplated gold/electroplated bismuth, and evaporated gold/evaporated bismuth 8x8 absorber arrays and find that a correlation exists between the residual resistance ratio (RRR) and thin film microstructure. This finding indicates that we can tailor absorber material conductivity via microstructure alteration, so as to permit absorber thermalization on timescales suitable for high energy resolution x-ray microcalorimetry. We show that by incorporating absorbers possessing large grain size, including electroplated gold and electroplated gold/electroplated bismuth, into our current Mo/Au TES, devices with tunable heat capacity and energy resolution of 2.3 eV (gold) and 2.1 eV (gold/bismuth) FWHM at 6 keV have been fabricated.

Fabrication of MKIDS for the MicroSpec Spectrometer

Abstract: Microspec is a new class of submillimeter and millimeter (250-700 μm wavelength) spectrometer, in which the wavelength separation and detection of incident light is done on a single substrate. The instrument is designed for space exploration by offering high spectral resolving power over a broad band, while being orders of magnitude smaller in mass and volume than the present state-of-the-art. The key enabling components for Microspec are background-limited microwave kinetic inductance detectors, which operate over the full bandwidth of the spectrometer. Here we present our fabrication strategy for making these sensitive detectors. A microstrip architecture utilizing a 0.45-μm crystalline silicon dielectric with a molybdenum nitride kinetic inductor material has been adopted. We have optimized wafer-scale lithographic patterning, and have developed processes that allow us to minimize surface roughness that may contribute to detector noise. Additionally, we have optimized the low-temperature wafer bonding process; this process allows us to build superconductors on both sides of the silicon dielectric layer. We present a final fabricated device and resonator operation at cryogenic temperatures.

Superconducting Microresonators: Physics and Applications

Abstract: Interest in superconducting microresonators has grown dramatically over the past decade. Resonator performance has improved substantially through the use of improved geometries and materials as well as a better understanding of the underlying physics. These advances have led to the adoption of superconducting microresonators in a large number of low-temperature experiments and applications. This review outlines these developments, with particular attention given to the use of superconducting microresonators as detectors.

Conceptual design of the International Axion Observatory (IAXO)

Abstract: The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4–5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few × 10−12 GeV−1 and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling gae with sensitivity — for the first time — to values of gae not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20 m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into ~ 0.2 cm2 spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for ~ 12 h each day.

Terahertz detectors and focal plane arrays

Abstract: Terahertz (THz) technology is one of emerging technologies that will change our life. A lot of attractive applications in security, medicine, biology, astronomy, and non-destructive materials testing have been demonstrated already. However, the realization of THz emitters and receivers is a challenge because the frequencies are too high for conventional electronics and the photon energies are too small for classical optics. As a result, THz radiation is resistant to the techniques commonly employed in these well established neighbouring bands.

Review of superconducting transition-edge sensors for x-ray and gamma-ray spectroscopy

Abstract: We present a review of emerging x-ray and gamma-ray spectrometers based on arrays of superconducting transition-edge sensors (TESs). Special attention will be given to recent progress in TES applications and in understanding TES physics.

Advanced Fabrication Processes for Superconducting Very Large-Scale Integrated Circuits

Abstract: We review the salient features of two advanced nodes of an 8-Nb-layer fully planarized process developed recently at MIT Lincoln Laboratory for fabricating single flux quantum (SFQ) digital circuits with very large-scale integration on 200-mm wafers: the SFQ4ee and SFQ5ee nodes, where “ee” denotes that the process is tuned for energy-efficient SFQ circuits. The former has eight superconducting layers with 0.5- $\mu\text{m}$ minimum feature size and a 2- $\Omega/\text{sq}$ Mo layer for circuit resistors. The latter has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm and a thin superconducting $\text{MoN}_{{x}}$ layer $(T_c \sim 7.5\ \text{K})$ with high kinetic inductance (about 8 pH/sq) for forming compact inductors. A nonsuperconducting $(T_{c} layer with lower nitrogen content is used for 6- $\Omega/\text{sq}$ planar resistors for shunting and biasing of Josephson junctions (JJs). Another resistive layer is added to form interlayer sandwich-type resistors of milliohm range for releasing unwanted flux quanta from superconducting loops of logic cells. Both process nodes use Au/Pt/Ti contact metallization for chip packaging. The technology utilizes one layer of Nb/AlOx-Al/Nb JJs with critical current density $J_{c}$ of 100 $\mu\text{A}/\mu\text{m}^{2}$ and minimum diameter of 700 nm. Circuit patterns are defined by 248-nm photolithography and high-density plasma etching. All circuit layers are fully planarized using chemical mechanical planarization of SiO2 interlayer dielectric. The following results and topics are presented and discussed: the effect of surface topography under the JJs on the their properties and repeatability, $I_c$ and $J_c$ targeting, effect of hydrogen dissolved in Nb, $\text{MoN}_{x}$ properties for the resistor layer and for high-kinetic-inductance layer, and technology of milliohm-range resistors.