Superconducting Transition Edge Sensor Research Articles

Correlated avalanches in transition edge sensor noise power spectra

The peaked structures of the excess noise observed in many superconducting transitionedge sensors are analyzed in both the normalized resistance and the frequency domains. Inthe framework of our dynamical percolation model we find high amplitude noise peaks inthe low normalized resistance range (0.2 approximately) and of much lower amplitude inthe high normalized resistance range (0.8), but no peaks are obtained in the power noisespectra in the very wide frequency range explored. The excess noise peaks experimentallyexplored are accounted for quantitatively by our statistical model of correlated avalanches.Our preliminary experimental noise results on a Ir thin film sensor are compared withliterature results.

Development of TES Microcalorimeter for high Precision Spectroscopy of LX-ray photons emitted from Transuranium Elements

A microcalorimeter with the superconducting transition edge sensor (TES) with a Au absorber of 5.0 μm thick was fabricated for the energy dispersive measurement of LX-ray photons emitted from transuranium elements. The TES microcalorimeter and a superconducting quantum interference device (SQUID) amplifier chips were cooled by operating a compact 3He-4He dilution refrigerator without consuming liquid helium by loading a Gifford-McMahon (GM) cooler. Since the cold stages of the GM cooler are tightly coupled to the heat exchangers of the dilution refrigerator, the TES and SQUID chips suffered from mechanical vibrations induced by a reciprocating motion of the displacer of the GM cooler. Detection signals of LX-ray photons emitted from an 241Am source were observed by operating the TES microcalorimeter in severe noise environment induced by mechanical vibrations.

Introduction to TES Physics

Superconducting Transition Edge sensors (TES) devices are now in use across a broad range of applications including dark matter searches, gamma ray and x-ray spectroscopy, UV-optical-IR spectroscopy, IR bolometry and CMB bolometers. We summarize the effects that must be taken into account in the design of TES devices. These include determining time constants, maintaining voltage bias, avoiding electrothermal oscillations, critical current limitations, saturation and preventing normal-superconducting phase separation. We summarize our understanding of excess noise seen in most TES devices.

Development of a Digital Signal Readout System for Large TES Arrays

We are developing a digital signal readout system for arrays of high-resolution gamma and fast-neutron detectors based on superconducting transition edge sensors (TESs). The readout system allows for real time data acquisition and analysis at count rates exceeding 100 Hz for pulses with several ∼ms decay times with minimal loss of energy resolution compared to optimum filtering. This digital signal processing system had originally been developed for gamma-ray analysis with HPGe detectors, and we have modified the hardware and firmware to accommodate the slower TES signals. Parameters of the filtering algorithm have been optimized to maximize either resolution or throughput. Here we present a summary of the digital signal processing hardware and discuss its initial performance.

GISMO, a 2 mm Bolometer Camera Optimized for the Study of High Redshift Galaxies

The 2 mm spectral range provides a unique terrestrial window enabling ground based observations of the earliest active dusty galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. We have built GISMO (the Goddard-IRAM Superconducting 2-Millimeter Observer), a 2 mm, 128 element superconducting Transition Edge Sensor (TES) based bolometer camera for the IRAM 30 m telescope in Spain. The camera uses an 8×16 planar array of multiplexed TES bolometers, which incorporates our recently designed Backshort Under Grid (BUG) architecture, described elsewhere. The optical design incorporates a 100 mm (4 inches) diameter silicon lens cooled to 4 K, which provides the required fast beam of 0.9 λ/D. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while the capability for diffraction-limited observations is preserved. With the background limited performance of the detectors, the camera provides significantly greater imaging sensitivity and mapping speed at this wavelength than has previously been possible. The major scientific driver for the instrument is to provide the IRAM 30 m telescope with the capability to rapidly observe galactic and extragalactic dust emission, in particular from high-z Ultra Luminous Infrared Galaxies (ULIRGs) and quasars, even in the summer season. The instrument will fill in the SEDs of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Our source count models predict that GISMO will serendipitously detect one galaxy every four hours on the blank sky, and that one quarter of these galaxies will be at a redshift of z 6.5. We expect to install GISMO at the 30 m telescope in the second half of 2007.

Superconducting Transition-Edge Sensor Bolometers with Integrated Electron-tunneling Refrigerators

We discuss the development of an array of superconducting Transition-Edge Sensor (TES) bolometers intended for use at millimeter wavelengths. Each bolometer in the array uses a proximity-effect TES sensing element and each has integrated Normal-Insulator-Superconductor (NIS) refrigerators to cool the bolometer below the reference bath temperature. The NIS refrigerators and bolometers are fabricated on a single Silicon substrate. Four short, thin and narrow legs suspend the millimeter wavelength radiation-absorbing element. The leg geometry is used to control and optimize the thermal conductance of the bolometer. Using the technology developed at NIST, we fabricated NIS refrigerators at the base of each of the suspension legs. These NIS refrigerators remove hot electrons by quantum-mechanical tunneling and should be capable of reducing the temperature of the biased (∼10 pW) bolometers by more than 100 mK when operating from a local thermal reservoir provided by a 3He system at ∼300 mK. This lower temperature at the bolometer will allow the detectors to approach background-limited performance despite the simple cryogenic system. In this paper we describe the progress toward the development of these detectors designed for use in observations at the 100 m Green Bank Telescope at 3 mm wavelength and the results of laboratory tests of a prototype detector.

Functional Description of Read-out Electronics for Time-Domain Multiplexed Bolometers for Millimeter and Sub-millimeter Astronomy

We have developed multi-channel electronics (MCE) which work in concert with time-domain multiplexors developed at NIST, to control and read signals from large format bolometer arrays of superconducting transition edge sensors (TESs). These electronics were developed as part of the Submillimeter Common-User Bolometer Array-2 (SCUBA2 ) camera, but are now used in several other instruments. The main advantages of these electronics compared to earlier versions is that they are multi-channel, fully programmable, suited for remote operations and provide a clean geometry, with no electrical cabling outside of the Faraday cage formed by the cryostat and the electronics chassis.

Simulation of Transient Response of Ir-TES for Position-Sensitive TES with Waveform Domain Multiplexing

We are developing a new x-ray microcalorimeter based on a superconducting transition edge sensor (TES) as an imaging sensor. Our measurement shows unique waveforms which we consider as an expression of thermal nonuniformity of TES films. This arises from the different thermal responses, so that response signal shapes would vary according to the position of the incident x-ray. This position dependency deteriorate the measured energy resolution, but with appropriate waveform analysis, this would be useful for imaging device. For more inspection, we have developed a simulation code which enables a dynamic simulation to obtain a transient response of the TES by finite differential method. Temperature and electric current distributions are calculated. As a result, we successfully obtained waveform signals. The calculated signal waveforms have similar characteristics to the measured signals. This simulation visualized the transition state of the device and will help to design better detector.

A Fabrication Process for Microstrip-Coupled Superconducting Transition Edge Sensors Giving Highly Reproducible Device Characteristics

Astronomical instruments for measuring Cosmic Microwave Background polarisation, such as CLOVER, require large arrays of Superconducting Transition Edge Sensors (TESs). We report recent results from a processing route development aimed at high yield fabrication of microstrip-coupled TESs. The incoming signal is delivered onto a silicon nitride membrane by means of a superconducting microstrip transmission line. This transmission line is then terminated with a thin-film load resistor. The wafer-based fabrication route of the Mo/Cu TESs gives highly reproducible device characteristics in terms of superconducting transition temperature, electrical and thermal characteristics. An overall device yield of 65% has been achieved for a multi-wafer processing run.

Accurate Thermal Conductance and Impedance Measurements of Transition Edge Sensors

Past measurements of the thermal coupling of superconducting transition edge sensor (TES) calorimeters suspended on SiN membranes produced wide-ranging values for the exponent of the thermal coupling through the membranes. We present a measurement technique that is less susceptible to current dependence of the phase transition than the previous measurements. An initial measurement produced the expected exponent for a 2-D phonon gas: thermal conductance is proportional to T 2. In doing these measurements, we employ a modification to Lindeman’s equivalent circuit technique for measuring TES complex impedance.

X-ray Microcalorimeter Based on Superconducting Transition Edge Sensors

We have tried to realize an X-ray imaging spectrometer based on the superconducting transition edge sensor (TES) with high energy resolution, a large pixel array, a relatively high absorption efficiency and a high count rate. Our single pixel of Ir/Au TES achieved an excellent energy resolution of 9.4 eV for 5.9 keV X-rays. We have also proposed a pixellated array of Ir-TES where we slightly modify the bias point of each pixel and identify the pixel from the response function of each pixel. Our 10-pixel device, where all pixels are parallel biased, obtained 13 eV (FWHM) at 3 keV energy resolution and 80 microm position resolution. So far, we could successfully operate a 20-pixels device. Further, we are now trying to improve the count rate and the absorption efficiency of TESes, by developing our original new TES geometry which having a radiation absorber that self-adjusts the operating temperature.

Frequency-Domain Multiplexed Readout for Superconducting Gamma-Ray Detectors

We are developing a frequency-multiplexed readout for arrays of high-resolution gamma detectors based on superconducting transition edge sensors (TESs). Each sensor is part of an LCR resonant circuit and is biased at an identifying carrier frequency. Several carrier signals are added and amplified with a single SQUID preamplifier at 4 K. Gamma absorption modulates the amplitude of the carrier, and demodulation at room temperature retrieves the initial temperature evolution of the sensor. This multiplexing system has originally been developed to read out large arrays of bolometers for cosmic microwave background studies. To accommodate the faster gamma-ray signals, its demodulator bandwidth is being extended to ~20 kHz to allow reading out up to eight TESs with a detector bandwidth of ~10 kHz. Here we characterize the system noise performance and show how this multiplexing scheme can be adapted to read out arrays of superconducting gamma-ray detectors.

Absolute Power Measurement with Transition Edge Sensors and SQUID amplifier

We have developed a new cryogenic radiometer for determining absolute power. This instrument is composed of a superconducting transition edge sensor as a thermometer, a silicon substrate as a heat absorber, and a SQUID amplifier as a readout. The input power is measured with electrical substitution of a heater on the device. By using very sharp transition of the thermometer, the device temperature is locked within its transition temperature. This device demonstrated very wide dynamic range of more than 105, very low noise equivalent power of 1.5 nW. These properties are very attractive to be used as highly precise power measurement instruments in metrological fields.

Energy calibration of superconducting transition edge sensors for x-ray detection using pulse analysis

Transition edge sensors (TESs) have been developed to be used as high-resolution x-ray detectors. They show excellent energy resolution and can be used in many applications. TESs are a special kind of calorimeters that can determine small temperature changes after x-ray absorption. Such a temperature change causes a strong resistance change (superconducting to normal-conducting phase transition) that can be measured. The energy calibration of a TES based spectrometer is problematic due to the nonlinear behavior of the detector response. In this article, a method is introduced to calibrate the energy scale of TES spectra. This is accomplished by calculating the energy dependence of the response of the detector operated in electrothermal feedback mode. Using this method a calibration accuracy of a few eV for an x-ray energy of 6keV can be achieved. Examples of energy dispersive x-ray spectroscopy (EDS) measurements demonstrate the high quality of this method for everyday use of TES EDS detectors in material analysis. However, because the method relies only on a few very general assumptions, it should also be useful for other kinds of TES detectors.

Fabrication of superconducting transition edge sensor based on Mo and Au bilayers

We report fabricated antenna-coupled superconducting transition edge sensor (TES) for millimeter-wave polarimetry. Superconducting microwave components for an antenna-coupled focal plane will be described in this work. We use low-loss Nb/SiO/Nb transmission line as base materials as a start, although changes in the dielectric may be possible to reduce loss further. Additionally, we have fabricated single- and double-element antennas, filters and detectors. We use TES bilayers consisting of Mo/Au thin films and Nb electrical contacts on a low-stress Si 3N 4 membrane. In this work, we report transition temperature as a function of Mo thicknesses and Au film composition.

Digital signal processing based on a clustering algorithm for Ir/Au TES microcalorimeter

In recent years, cryogenic microcalorimeters using their superconducting transition edge have been under development for possible application to the research for astronomical X-ray observations. To improve the energy resolution of superconducting transition edge sensors (TES), several correction methods have been developed. Among them, a clustering method based on digital signal processing has recently been proposed. In this paper, we applied the clustering method to Ir/Au bilayer TES. This method resulted in almost a 10% improvement in the energy resolution. Conversely, from the point of view of imaging X-ray spectroscopy, we applied the clustering method to pixellated Ir/Au-TES devices. We will thus show how a clustering method which sorts signals by their shapes is also useful for position identification

Optimizing the operating temperature of a transition edge sensor

We discuss the theory for optimizing the operating temperature of a voltage biased superconducting transition edge sensor (TES) in terms of energy resolution and speed, considering only internal detector noise sources. The noise processes included in the modeling are the unavoidable Johnson and phonon noise. The phonon noise is calculated for the case of ballistic transport. If other external and excess internal noise sources are not dominant, an optimal operating temperature can be found to minimize the energy resolution. The detector slows down by approximately a factor of two at the optimal energy resolution point.

X-ray microanalysis with microcalorimeters

The combination of high-energy-resolution spectrometers with high-spatial-resolution scanning electron microscopes provides a powerful tool for material analysis. X-ray spectrometers based on superconducting transition edge sensors combine the advantages of commonly used energy- and wavelength-dispersive spectrometers, i.e. a fast spectrum acquisition and a high-energy-resolution over a wide energy range. While the energies of the characteristic lines present in a spectrum contain the qualitative composition of the analyzed material, the corresponding mass fractions can be obtained from their intensities. In this work first quantitative measurements performed with the POLARIS spectrometer system are presented.

Building blocks for a polarimeter-on-a-chip

For the “Primordial Anisotropy Polarization Pathfinder Array (PAPPA)” balloon flight project, we have designed and made thin-film niobium microstrip circuits as building blocks for a “polarimeter-on-a-chip” in which superconducting transmission lines are used to couple millimeter wave signals from planar antennas to superconducting transition edge sensor (TES) detectors. Our goal is to demonstrate technology for precision measurements of the polarization of the cosmic microwave background. To enable characterization and verification of our microstrip components, we have incorporated waveguide probes on each chip that can bring millimeter wave signals from a room temperature vector network analyzer to the superconducting circuits on the chip and back again for S-parameter measurements. We have designed a planar antenna and RF choke on the probes to efficiently couple radiation between waveguide and thin-film microstrip. To support the probe antennas in waveguides, we sculpted thin silicon cantilevers that extend from an edge of each silicon chip into a pair of waveguides within a specially designed split-block mount. This technique will allow us to make calibrated measurements at low temperatures of the velocity, impedance, and loss properties of our niobium transmission lines, the frequency response of microstrip filters, hybrid couplers, or terminations, and the performance of integrated detectors.

Fabrication of antenna-coupled transition edge sensors for polarimeter applications

In this paper we describe the progress in the development of polarization sensitive superconducting, bolometric detector arrays targeted at cosmic microwave background (CMB) studies. Our implementation takes advantage of superconducting technology to reduce the complexity of the typical CMB bolometer focal plane by incorporating as many of the required elements as necessary on the detector itself. Each pixel in the array consists of a distributed dual-polarization beam forming antenna, a band pass filter, and power splitter/combiner delivering detected power to four separate superconducting transition edge sensors. This combination of elements detects the polarization of the incoming light uniquely while eliminating a large part of the cooled mass of the focal plane including feed horns, polarizers, and band pass filters. Of course this increases the fabrication complexity of the bolometric detector itself over previous implementations. We will describe our fabrication process consisting of eight front side mask levels and one back side layer designed to produce whole wafer array tiles suitable for CMB polarimeters.