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Abstract: The South Pole Telescope (SPT) is a 10–m mm/sub-mm telescope at the Amundsen-Scott South Pole Station. It''s primary science goals consist of a galaxy cluster survey for understanding Dark Energy and probing the physics of Inflation through the CMB polarization. Both science goals require exceptional sensitivity necessitating focal planes with many optical elements. The focal planes of the SPT utilize Transition Edge Sensor (TES) bolometers to build arrays of nearly 1000 detectors. In this talk, I will present the TES bolometer technology for both the first SPT focal plane and its upcoming upgrade to a polarization sensitive array. [Copyright &y& Elsevier]

Abstract: We report an absorber-coupled superconducting Transition Edge Sensor (TES) bolometric polarimeter for measuring Cosmic Microwave Background (CMB) B-mode polarization. The polarimeter consists of a dipole-like PdAu absorber and a Mo/Au bi-layer TES on a suspended silicon nitride rectangle. Its design, fabrication, thermal properties, and optical performance are presented. [Copyright &y& Elsevier]

Abstract: We are developing a gamma-ray microcalorimeter for Positron Annihilation Spectroscopy. Our detector composed of a transition edge sensor (TES) thermometer and an epoxy coupled bulk Pb absorber has been reported an energy resolution of 4.7keV FWHM at 662keV with a tens of milliseconds long response time. To enhance the detector properties, we designed a new attachment method in the focus of improving the thermal coupling between the absorber and the TES. In the new design, we created epoxy-posts both on the TES film and on the absorber, and then they were connected together using an epoxy-dot put on the epoxy-post on the absorber. Measured current signal of this epoxy-post TES gamma-ray detector showed an ultra fast response with 80μs fall time. [Copyright &y& Elsevier]

One of the critical limits on the sensitivity of direct neutrino mass experiment, such as MARE, is the background generated by unidentified double pulses. In our work developing an analysis system for MARE we have focused on comparing algorithms, and developing and testing an optimum algorithm for the identification (and removal) of double pulses. To test the algorithms we developed a Monte Carlo simulation that, based on the detectors physical parameters, generates realistic single and double events with known characteristics. In this paper we present our preliminary results on two algorithms used for double pulse identification and their efficiency as a function of pulse heights and separation. [ABSTRACT FROM AUTHOR]

Frequency-domain multiplexing has been used for reading out ∼1000 detectors on the APEX-SZ and South Pole Telescope receiver for half a decade and produced many high-impact science papers. A new digital FPGA-based backend reduces the power consumption and system-size by an order of magnitude. This Digital Frequency-domain Multiplexer (DfMUX) was operated successfully in a space-like environment during the stratospheric balloon test-flight of the EBEX polarimeter, saw first light on the POLARBEAR experiment in 2010, and will be deployed for the South Pole Telescope polarimeter and ASTE sub-mm continuum camera. We are presently developing a new generation DfMUX targeting a factor 5 lower power consumption and robustness for satellite platforms. The system will incorporate new technology for identifying and correcting radiation induced errors in the FPGA logic, higher bandwidth to accommodate a multiplexing factor of 64, and Digital Active Nulling (DAN) feedback. DAN linearizes the SQUID system response while dramatically reducing its input impedance. [ABSTRACT FROM AUTHOR]

Upcoming experiments aim to produce high fidelity polarization maps of the cosmic microwave background. To achieve the required sensitivity, we are developing monolithic, feedhorn-coupled transition edge sensor polarimeter arrays operating at 150 GHz. We describe this focal plane architecture and the current status of this technology, focusing on single-pixel polarimeters being deployed on the Atacama B-mode Search (ABS) and an 84-pixel demonstration feedhorn array backed by four 10-pixel polarimeter arrays. The feedhorn array exhibits symmetric beams, cross-polar response <−23 dB and excellent uniformity across the array. Monolithic polarimeter arrays, including arrays of silicon feedhorns, will be used in the Atacama Cosmology Telescope Polarimeter (ACTPol) and the South Pole Telescope Polarimeter (SPTpol) and have been proposed for upcoming balloon-borne instruments. [ABSTRACT FROM AUTHOR]

We have built a versatile, compact He test facility to evaluate high-purity Ge (HPGe) SuperCDMS (Cryogenic Dark Matter Search) detectors. We are able to rapidly identify photolithographic or other defects in the thousands of W-Al transition edge sensors (TESs) on each detector and to evaluate the performance of the underlying substrate. We describe our simple method to measure current-voltage ( I- V) characteristics and R vs. T behavior of HPGe detector crystals with resistances up to 100 GΩ. This provides a way to quickly perform diagnostic physics studies. Results provide critical data that give early warning that a crystal may not be suitable for the SuperCDMS underground experiment. Data from tests made on several kg-scale detectors are presented. [ABSTRACT FROM AUTHOR]

We present results of the analysis of electrical noise in a transition edge sensor (TES) as a resistively shunted conducting junction (the RSJ model). We derive an expression for the spectral density of voltage fluctuations taking into account weak superconductivity of a TES. We analyse and discuss differences in voltage noise in a TES compared to the familiar situation for the Josephson junction. The spectral density of voltage noise in the RSJ model has a unique analytical structure and cannot be reduced to the expression for the nonlinear Johnson noise near equilibrium. [ABSTRACT FROM AUTHOR]

We have developed a model for the resistive transition in a transition edge sensor (TES) based on the model of a resistively shunted junction, taking into account phase-slips of a superconducting system across the barriers of the tilted washing board potential. We obtained analytical expressions for the resistance of the TES, R( T, I), and its partial logarithmic derivatives α and β as functions of temperature and current. We have shown that all the major parameters describing the resistive state of the TES are determined by the dependence on temperature of the Josephson critical current, rather than by intrinsic properties of the S-N transition. The complex impedance of a pristine TES exhibits two-pole behaviour due to its own intrinsic reactance. [ABSTRACT FROM AUTHOR]

We have constructed a test facility for characterizing the focal plane arrays of SAFARI, the far-infrared imaging spectrometer for the SPICA satellite. SAFARI's three bolometer arrays are populated with extremely sensitive ( $\mathit{NEP}\sim 2\times 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$) transition edge sensors with a transition temperature close to 100 mK. The extreme sensitivity and low saturation power (∼4 fW) of SAFARI's detectors present challenges to characterizing them. In optimizing the SAFARI Detector System Test Facility we have paid careful attention to stray-light exclusion as well as electrical, magnetic, and mechanical isolation. We present measurements verifying the facility's performance and analyze them in terms of a two-fluid model of the TES current on the transition to investigate the background power level. We have measured a detector NEP of (5.1±0.4)×10 W Hz, showing that the facility is ready to test the SAFARI prototype arrays and is approaching the performance needed for testing the flight arrays. [ABSTRACT FROM AUTHOR]

Transition edge sensors (TES) are the chosen detector technology for the SAFARI imaging spectrometer on the SPICA telescope. The TES are required to have an NEP of $2\mbox{--}3\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ to take full advantage of the cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30-60 μm). The TES are on SiN membranes, in which long and narrow legs act as thermal links between the TES and the bath. We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing low noise detectors. We report our latest results that include a measured dark NEP of $4.2\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ and a saturation power of about 10 fW. [ABSTRACT FROM AUTHOR]

We report initial measurements on our first MoAu transition edge sensors (TESs). The TESs formed from a bilayer of 40 nm of Mo and 106 nm of Au showed transition temperatures of about 320 mK, higher than identical TESs with a MoCu bilayer which is consistent with a reduced electron transmission coefficient between the bilayer films. We report measurements of thermal conductance in the 200 nm thick silicon nitride SiN support structures at this temperature, TES dynamic behaviour and current noise measurements. [ABSTRACT FROM AUTHOR]

We have developed a process to integrate microstripline wiring with transition edge sensors (TES). The process includes additional layers for metal-etch stop and dielectric adhesion to enable recovery of parameters achieved in non-microstrip pixel designs. We report on device parameters in close-packed TES arrays achieved with the microstrip process including R, G, and T uniformity. Further, we investigate limits of this method of producing high-density, microstrip wiring including critical current to determine the ultimate scalability of TES arrays with two layers of wiring. [ABSTRACT FROM AUTHOR]

Transition-edge-sensor (TES) bolometers are the chosen detector technology for the SAFARI Imaging Spectrometer on the SPICA telescope. For this mission, SRON is developing bolometers, each consisting of a TiAu TES that is weakly coupled to the thermal bath through thin legs of silicon nitride. In order to understand and optimize the bolometer and to verify our detector models, we characterize the devices using a series of complex impedance measurements. We apply equivalent bolometer analysis (EBA) in combination with model fitting to these data. From this analysis, we obtain important parameters that give us confidence in our understating of the response and noise of these sensitive detectors. [ABSTRACT FROM AUTHOR]

We describe a process route to fabricate arrays of Ultra-low-Noise MoAu Transition Edge Sensors (TESs). The low thermal conductance required for space applications is achieved using 200 nm-thick Silicon Nitride (SiN) patterned to form long-thin legs with widths of 2.1 μm. Using bilayers formed on SiN islands from films with 40 nm-thick Mo and Au thicknesses in the range 30 to 280 nm deposited by dc-sputtering in ultra-high vacuum we can obtain tunable transition temperatures in the range 700 to 70 mK. The sensors use large-area absorbers fabricated from high resistivity, thin-film β-phase Ta to provide impedance-matching to incident radiation. The absorbers are patterned to reduce the heat capacity associated with the nitride support structure and include Au thermalizing features to assist the heat flow into the TES. Arrays of 400 detectors at the pixel spacing required for the long-wavelength band of the far-infrared instrument SAFARI are now being fabricated. Device yields approaching 99% are achieved. [ABSTRACT FROM AUTHOR]

We are developing bulk lead absorber coupled transition edge sensor gamma-ray detectors that can be applied to positron annihilation spectroscopy at 511 keV. We observe a double exponential decay in the signal response curves of our detectors. Here, we characterize this signal response using three gamma-ray detectors with different thermal conductance values. [ABSTRACT FROM AUTHOR]

A number of groups have produced TES bolometers and other devices using dielectric membranes for thermal isolation in which excess heat capacity is reported. We have fabricated a series of TES devices using large area membranes and narrow legs for thermal isolation to study the scaling of intrinsic parameters like the heat capacity of the membrane. The devices are arranged on a single chip to ensure similarity of devices parameters (i.e., film thicknesses) and processing history. Measurements (non-multiplexed) of the current-voltage characteristic and complex impedance are made using a well-characterized, highly uniform, multichannel SQUID setup. We have developed model for non-ideal transition edge sensor performance that enables extraction of heat capacities and thermal conductances identified in the models. We report on the magnitude of excess heat capacity in the dielectric membrane and thermal conductance of the metal-to-dielectric interface in each of the designs. [ABSTRACT FROM AUTHOR]

We are developing arrays of 150 GHz transition edge sensor (TES) polarimeters for the South Pole Telescope polarimeter (SPTpol). Prototype devices use an aluminum manganese (Al-Mn) alloy TES with a normal resistance Rn suited to frequency domain multiplexing (fMUX) used in SPTpol. Using the fMUX readout, the devices exhibit noise performance consistent with expectations when R>0.8Rn. Below 0.8Rn, the detectors have high loopgain and become unstable, which is predicted by use of a compound TES model. We address this issue in a recent fabrication with increased TES heat capacity and normal metal structures on the TES to tune the temperature sensitivity. [ABSTRACT FROM AUTHOR]

Time-division SQUID multiplexers are used in many applications that require exquisite control of systematic error. One potential source of systematic error is the pickup of external magnetic fields in the multiplexer. We present measurements of the field sensitivity figure of merit, effective area, for both the first stage and second stage SQUID amplifiers in three NIST SQUID multiplexer designs. These designs include a new variety with improved gradiometry that significantly reduces the effective area of both the first and second stage SQUID amplifiers. [ABSTRACT FROM AUTHOR]

Results of study optical performance of single pixel transition edge sensor (TES) bolometer presented at wavelength band 30–60 \mum are presented. FIR radiation is coupled into a multimode horn with entrance aperture of 450 \mum, length 4.5 mm and exit aperture of 45 \mum, which feeds a metal integrating cavity containing the detector. The radiation band is defined by a pair of lowpass and highpass mesh filters in front of the horn. Here we present measurements of optical noise equivalent power (NEP), optical efficiency, dynamic range and time constant. The results show that measured TES detectors are close to meeting the requirement of the “Band S” of SAFARI FTS imaging instrument [1] on the SPICA mission [2]. [ABSTRACT FROM AUTHOR]

Single photon detectors are fundamental tools for quantum metrology, e.g. to calibrate both detectors and sources, as for quantum information. One of the most promising detectors able to resolve single photons is the transition-edge sensor (TES). We report our last results obtained with Ti/Au TES deposited on SiN substrate. Photon counting measurements, obtained by using pulsed sources, in the NIR-visible wavelength range, show the ability to resolve up to fourteen photons with an energy resolution of 0.44 eV at 690 nm (1.80 eV) and 0.38 eV at 1310 nm (0.95 eV), with a good linearity. A preliminary measurement obtained by using a parametric down conversion (PDC) heralded single photon source, at 812 nm (1.53 eV), is also reported. [ABSTRACT FROM AUTHOR]

Abstract: Transition edge sensors (TESs) are high-sensitivity thermometers used in cryogenic microcalorimeters which exploit the steep gradient in resistivity with temperature during the superconducting phase transition. Practical TES devices tend to exhibit a white noise of uncertain origin, arising inside the device. We discuss two candidate models for this excess noise, phase slip shot noise (PSSN) and percolation noise. We extend the existing PSSN model to include a magnetic field dependence and derive a basic analytical model for percolation noise. We compare the predicted functional forms of the noise current vs. resistivity curves of both models with experimental data and provide a set of equations for both models to facilitate future experimental efforts to clearly identify the source of excess noise. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a Transition Edge Sensor (TES) – Energy Dispersive Spectroscopy (EDS) for Transmission Electron Microscope (TEM) based on a dilution refrigerator. The dilution refrigerator was cooled by liquid helium (L-He), which was supplied from an L-He container separated from the dilution refrigerator. We adopted the hybrid magnetic shields combining a permalloy shield and a NbTi/Nb/Cu superconducting shield to operate the TEM–TES system under a magnetic field of 200mT. The permalloy shield was used to prevent the ambient magnetic field until the NbTi superconducting shield cooled from room temperature (RT) to 2K. The critical magnetic field was 220mT for the TES change from a superconducting state to a normal state. The SQUID – current vs. bias current curve, under the condition that the snout was inserted in the TEM, was equal to the curve of the snout that was out of the TEM. The C (002) planes could be observed at 120kV under the condition the snout was inserted in the TEM. [Copyright &y& Elsevier]

We present results from the largest array of gamma-ray microcalorimeters operated to date. The microcalorimeters consist of Mo/Cu transition-edge sensors with attached Sn absorbers. The detector array contains 66 pixels each with an active area 2.25 mm2. Out of 66 pixels, 55 are active, and 31 were used to acquire a high statistics Pu gamma-ray spectrum. The energy resolution of the best 21 pixels was found to be 120 eV FWHM. The array is read out using time domain SQUID multiplexing. Here, we describe the multiplexing and present a high statistics Pu spectra. Because of the large collecting area of our array, the statistical error in the 240Pu line intensity is approximately 0.7%, which is comparable to the systematic error in a measurement with a 500 eV germanium sensor. Hence, we have reached an important threshold for demonstrating improved isotopic measurements with microcalorimeter sensors. With straightforward changes, we plan to achieve a resolution of about 50 eV FWHM with 256 multiplexed detectors. Finally, we present early estimates of on-chip heating within our sensor array. [ABSTRACT FROM AUTHOR]

We fabricated 16 × 16 format arrays of 180 μm square Ti/Au superconducting transition edge X-ray microcalorimeters of which transition temperatures range from 130 to 220 mK. All pixels are wired with Al, and stand on SiO2 and SiNx membranes that work as a weak thermal link. The membrane structure is formed by deep reactive ion etching. Energy resolution of a pixel in the array without a Au absorber was 11 eV (FWHM) at 5.9 keV, while the baseline resolution is about 3.7 eV. [ABSTRACT FROM AUTHOR]

Abstract: Bi films that we fabricated with vacuum-evaporation deposition show a crystal structure very similar to that of bulk Bi. However they have granular structure on sub-micron scales, and the electrical resistance increases at low temperatures, which is opposite to bulk Bi. A TES microcalorimeter with a Bi absorber shows an energy resolution significantly degraded compared to the baseline resolution. A thermal model of the calorimeter based on the present experimental results indicates that a position dependence of the pulse height and rise time degrades the energy resolution. The position dependence is further considered to be due to mismatch between the rise time of pulse which is mostly determined by the thermal conductance between Bi and TES and the thermal diffusion time in the Bi absorber. [Copyright &y& Elsevier]