We are developing ultra-low noise transition edge sensor (TES) bolometer arrays for the long-wavelength grating spectrometer modules of SAFARI, part of the cryogenically-cooled SPICA mission now in phase-A study in Europe. These devices target a per-pixel noise equivalent power (NEP) below 10^-19 WHz^-1/2 with a time-constant faster than 10ms. The SAFARI focal planes will be cooled to 50 mK, and we use a 100 mK thermistor formed from an annealed Titanium-Gold bilayer film. To minimize excess heat capacity, we have developed a new wet-release process which provides high yield in large (~250-pixel) sub-arrays. We will report on the fabrication, testing, and achieved performance of these detectors.
We will also present the focal plane assembly designed to support the 5 (spatial) x 180 (spectral) format coupled to spectrometers thru multimodes horns. The focal plane is composed of four monolithic sub-arrays with integrated backshorts, all integrated onto a large silicon substrate.
We report experimental progress toward demonstrating background-limited arrays of membrane-isolated transition-edge sensors (TESs) for the Background Limited Infrared/Sub-mm Spectrograph (BLISS). BLISS is a space-borne instrument with grating spectrometers for wavelengths λ= 35-435 μm and with R= λ/Δλ~500. The goals for BLISS TESs are: noise equivalent power (NEP) = 5×10-20 W/Hz1/2 and response time τ<30ms. We expect background-limited performance from bilayers TESs with TC=65mK and G=15fW/K. However, such TESs cannot be operated at 50mK unless stray power on the devices, or dark power PD, is less than 200aW. We describe criteria for measuring PD that requires accurate knowledge of TC. Ultimately, we fabricated superconducting thermistors from Ir (TC≥135mK) and Mo/Cu proximitized bilayers, where TC is the thermistor transition temperature. We measured the Ir TES arrays in our 45mK base temperature adiabatic demagnetization refrigerator test system, which can measure up to eight 1x32 arrays simultaneously using a time-division multiplexer, as well as our single-pixel test system which can measure down to 15mK. In our previous Ir array measurements our best reported performance was NEP=2.5×10-19 W/Hz1/2 and τ~5ms for straight-beam TESs. In fact, we expected NEP 1.5×10-19W/Hz1/2 for meander beam TESs, but did not achieve this previously due to 1/f noise. Here, we detail improvements toward measuring the expected NEP and demonstrate NEP=(1.3±0.2)×10-19W/Hz1/2 in our single-pixel test system and NEP=(1.6±0.3)×10-19W/Hz1/2 in our array test system.
We are developing the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) for SPICA to provide a breakthrough capability for far-IR survey spectroscopy. The 3.2-meter, actively-cooled (T<6K) SPICA telescope allows mid-IR to submm observations which are limited only by the natural backgrounds, and BLISS is designed
to operate near this fundamental limit. BLISS-SPICA provide a line sensitivity of 10-20 W m-2 , thereby enabling
spectroscopy of dust-obscured galaxies at all epochs back to the first billion years after the Big Bang (redshift
6), and study of all stages of planet formation in circumstellar disks.
BLISS covers the 35-430 micron waveband at moderate resolving power (300<R<700) in six grating spec trometer bands, each coupling at least two 2 sky positions simultaneously. The instrument is cooled with an on-board refrigerator to 50 mK for optimal sensitivity. The detector package in the goal implementation is 4200 silicon-nitride micro-mesh leg-isolated bolometers with superconducting transition-edge-sensed (TES) thermis tors, read out with a cryogenic time-domain multiplexer. The instrument is designed to fit within the stringent SPICA resource allocations for mass and heat lift, and to mitigate the impact of cosmic rays. We report on this design and our progress in prototyping and validating the BLISS spectrometers and prototype cooler. A companion paper in Conference 8452 (A. Beyer et al.) discusses in greater detail the progress in the BLISS TES bolometer development.
We are developing the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) for SPICA to provide
a breakthrough capability for far-IR survey spectroscopy. SPICAs large cold aperture allows mid-IR to submm
observations which are limited only by the natural backgrounds, and BLISS is designed to operate near this
fundamental limit. BLISS-SPICA is 6 orders of magnitude faster than the spectrometers on Herschel and
SOFIA in obtaining full-band spectra. It enables spectroscopy of dust-obscured galaxies at all epochs back to
the rst billion years after the Big Bang (redshift 6), and study of all stages of planet formation in circumstellar
disks.
BLISS covers 35 - 433 microns range in ve or six wavelength bands, and couples two 2 sky positions simultaneously.
The instrument is cooled to 50 mK for optimal sensitivity with an on-board refrigerators. The detector
package is 4224 silicon-nitride micro-mesh leg-isolated bolometers with superconducting transition-edge-sensed
(TES) thermistors, read out with a cryogenic time-domain multiplexer. All technical elements of BLISS have
heritage in mature scientic instruments, and many have own. We report on our design study in which we are
optimizing performance while accommodating SPICAs constraints, including the stringent cryogenic mass budget.
In particular, we present our progress in the optical design and waveguide spectrometer prototyping. A
companion paper in Conference 7741 (Beyer et al.) discusses in greater detail the progress in the BLISS TES
bolometer development.
We report on the characterization of SixNy (Si-N) optical absorbers and support beams for transition-edge sensors
(TESs). The absorbers and support beams measured are suitable to meet ultra-sensitive noise equivalent power
(NEP≤10-19W/√Hz) and effective response time (τ) requirements (τ≤100ms) for space-borne far-infrared(
IR)/submillimeter(sub-mm) spectrometers, such as the Background Limited far-Infrared/Sub-mm Spectrograph
(BLISS) and the SpicA FAR-infrared Instrument (SAFARI) for the SPace Infrared telescope for Cosmology and
Astrophysics (SPICA). The thermal response time (τ0) of an absorber suspended by support beams from a lowtemperature
substrate depends on the heat capacity (C) of the absorber and the thermal conductance (G) of the support
beams (τ0=C/G). In membrane-isolated TESs for BLISS, the effective response time τ is expected to be a factor of 20
smaller than τ0 because of voltage-biased electrothermal feedback operation and assumption of a reasonable open-loop
gain, LI≈20. We present design specifications for the arrays of membrane-isolated ultra-sensitive TESs for BLISS.
Additionally, we measured G and τ0 for two Si-N noise thermometry device (NTD) architectures made using different
fabrication processes: (1) a solid membrane Si-N absorber suspended by thin and long Si-N support beams and (2) a
wire-mesh Si-N absorber suspended by long, and even thinner, Si-N support beams. The measurements of G and τ0
were designed to test suitability of the Si-N thermal performance to meet the demands of the two SPICA instruments.
The solid membrane NTD architecture is similar to the TES architecture for SAFARI and the mesh membrane NTD is
similar to that of BLISS TESs. We report measured values of G and C for several BLISS and SAFARI NTD devices.
We observe that the heat capacity of the solid membrane devices can be reduced to the order of 1fJ/K at 65mK for
devices that are wet etched by KOH. However, C for these devices is found to be on the order of 100fJ/K for a dry XeF2
process. The heat capacity is similarly large for the mesh devices produced with a dry XeF2 etch.
A. Orlando, R. Aikin, M. Amiri, J. Bock, J. Bonetti, J. Brevik, B. Burger, G. Chattopadthyay, P. Day, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, K. Irwin, M. Kenyon, J. Kovac, C. L. Kuo, A. Lange, H. LeDuc, N. Llombart, H. Nguyen, R. Ogburn, C. Reintsema, M. Runyan, Z. Staniszewski, R. Sudiwala, G. Teply, A. Trangsrud, A. Turner, P. Wilson
BICEP2/Keck and SPIDER are cosmic microwave background (CMB) polarimeters targeting the B-mode polarization
induced by primordial gravitational waves from inflation. They will be using planar arrays of polarization
sensitive antenna-coupled TES bolometers, operating at frequencies between 90 GHz and 220 GHz. At 150 GHz
each array consists of 64 polarimeters and four of these arrays are assembled together to make a focal plane, for a
total of 256 dual-polarization elements (512 TES sensors). The detector arrays are integrated with a time-domain
SQUID multiplexer developed at NIST and read out using the multi-channel electronics (MCE) developed at
the University of British Columbia. Following our progress in improving detector parameters uniformity across
the arrays and fabrication yield, our main effort has focused on improving detector arrays optical and noise
performances, in order to produce science grade focal planes achieving target sensitivities. We report on changes
in detector design implemented to optimize such performances and following focal plane arrays characterization.
BICEP2 has deployed a first 150 GHz science grade focal plane to the South Pole in December 2009.
We present a concept for BLISS, a sensitive far-IR-submillimeter spectrograph for SPICA. SPICA is a JAXA-led mission featuring a 3.5-meter telescope actively cooled to below 5K, envisioned for launch in 2017. The low-background platform is especially compelling for moderate-resolution survey spectroscopy, for which BLISS is
designed. The BLISS / SPICA combination will offer line sensitivities below 10-20W m-2 in modest integrations, enabling rapid survey spectroscopy of galaxies out to redshift 5. The far-IR fine-structure and molecular transitions which BLISS / SPICA will measure are immune to dust extinction, and will unambiguously reveal these galaxies' redshifts, stellar and AGN contents, gas properties, and heavy-element abundances. Taken together, such spectra will reveal the history of galaxies from 1 GY after the Big Bang to the present day. BLISS is comprised of five sub-bands, each with two R ~ 700 grating spectrometer modules. The modules are configured with polarizing and dichroic splitters to provide complete instantaneous spectral coverage in two sky positions. To approach background-limited performance, BLISS detectors must have sensitivities at or below 5 × 10-20W Hz-1/2, and the format is 10 arrays of several hundred pixels each. It is anticipated that these requirements can be met on SPICA's timescale with leg-isolated superconducting (TES) bolometers cooled with a 50 mK magnetic refrigerator.
We describe the design and performance of polarization selective antenna-coupled TES arrays that will be used
in several upcoming Cosmic Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully
lithographic polarimeter arrays utilize planar phased-antennas for collimation (F/4 beam) and microstrip filters
for band definition (25% bandwidth). These devices demonstrate high optical efficiency, excellent beam shapes,
and well-defined spectral bands. The dual-polarization antennas provide well-matched beams and low cross
polarization response, both important for high-fidelity polarization measurements. These devices have so far
been developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave atmospheric windows for
CMB observations. In the near future, the flexible microstrip-coupled architecture can provide photon noise-limited
detection for the entire frequency range of the CMBPOL mission. This paper is a summary of the
progress we have made since the 2006 SPIE meeting in Orlando, FL.
We present scientific rationale, concepts and technologies for far-IR (λ=35-600 μm) instrumentation for the
cryogenic single-dish space telescopes envisioned for the next two decades. With the tremendous success of
Spitzer, the stage is set for larger (3-10 meter) actively-cooled telescopes and several are under consideration
including SPICA in Japan, and CALISTO/SAFIR in the US. The cold platforms offer the potential for far-IR
observations limited only by the zodiacal dust emission and other diffuse astrophysical foregrounds. Optimal
instrumentation for these missions includes large-format direct-detector arrays with sensitivity matched to the
low photon backgrounds. This will require major improvements relative to the current state of the art, especially
for wavelengths beyond the 38-micron silicon BIB cutoff, We review options and present progress with one
approach: superconducting bolometers.
We highlight in particular the scientific potential for moderate-resolution broadband spectroscopy. The large
cold telescopes can provide line sensitivities below 10-20 W m-2, enabling the first routine survey spectroscopy
of the redshift 0.5 to 5 galaxies that produced the cosmic far-IR background. These far-IR-bright dusty galaxies
account for half of the photon energy released since stars and galaxies began forming, and the new far-IR
spectroscopic capability will reveal their energy sources and chart their history. We describe concepts for the
background-limited IR-Submillimeter Spectrograph (BLISS) designed for this purpose. BLISS is a suite of
R~1000 spectrometer modules spanning the far-IR range, and is under study for SPICA; a similar but more
capable instrument can be scaled for CALISTO/SAFIR.
To determine the lowest attainable phonon noise equivalent power (NEP) for membrane-isolation bolometers, we fabricated and measured the thermal conductance of suspended Si3N4 beams with different geometries via a noise thermometry technique. We measured beam cross-sectional areas ranging from 0.35 × 0.5 μm2 to 135 × 1.0 μm2 and beam lengths ranging from 700 μm to 8300 μm. The measurements directly imply that membrane-isolation bolometers are capable of reaching a phonon noise equivalent power (NEP) of 4×10-20 W/Hz1/2. This NEP is adequate for the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) proposed for the Japanese SPICA observatory, and adequate for NASA's SAFIR observatory, a 10-meter, 4 K telescope to be deployed at L2. Further, we measured the heat capacity of a suspended Si3N4 membrane and show how this result implies that one can make membrane-isolation bolometers with a response time which is fast enough for BLISS.
We have developed a completely lithographic antenna-coupled bolometer
for CMB polarimetry. The necessary components of a millimeter wave radiometer - a beam forming element, a band defining filter, and the TES detectors - are fabricated on a silicon chip with photolithography. The densely populated antennas allow a very efficient use of the focal plane area. We have fabricated and characterized a series of prototype devices. We find that their properties, including the frequency and angular responses, are in good agreement with the theoretical expectations. The devices are undergoing optimization for upcoming CMB experiments.
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