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We propose a bolometer intended for room-temperature operation and based on a 100-nm-wide ruthenium (Ru) strip fabricated on a thin layer of cross-linked polymethyl methacrylate (XPMMA). This layer provides thermal isolation between the silicon substrate and the Ru nanostrip for increasing the nonlinearity of the bolometer ${I}-{V}$ curve due to more intensive self-heating by the biasing and an ac current. A number of bolometers with Ru strips of different dimensions and different thicknesses of XPMMA layer were fabricated and tested at dc. An estimate based on the dc tests gives the electrical voltage responsivity to radio frequency (RF) signal as much as 250 V/W, which makes the proposed bolometer attractive as a sensing element for a simple and low-cost microwave and terahertz detector. Numerical simulations of temperature distribution along the Ru strip and analysis of the bolometer noise performance are also presented. [ABSTRACT FROM AUTHOR]

An optimized concept of the Cold-Electron Bolometer (CEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junction and Andreev SN contact for voltage-bias mode has been developed. The responsivity of this design is much better than the widespread concept of the CEB with two SIN tunnel junctions for the current-biased mode (SINIS structure) due to degradation of responsivity by a factor of two in voltage-bias (VB) mode. Besides that, for the realization of the CEB with the same capacitance, we need twice larger junctions that lead to four times larger area and volume of the absorber. As a result, the NEP of one SIN junction CEB is half that of two SIN junction CEB. A novel concept of the quasiparticle cascade amplifier (QCA) based on harvesting the waste energy of relaxed quasiparticles without any additional voltage bias has been developed. The distinguish feature of the cascade principle is utilizing the same dc voltage as used for CEB. The cascade principle of signal amplification proved to be possible due to the conversion of electrons to holes in the second absorber. The amplifier is based on the optimized CEB with one SIN junction and one SN contact. The coefficient of power amplification of the incoming signal to the potential energy of hot quasiparticles is huge and can achieve a level of 140 at the optimal bias point. The coefficient of power amplification of the QCA can reach a value of 30 and more to overcome the noise of the SQUID amplifier. For a power load of 6 pW, the total NEP of the CEB is decreased to the level of photon noise NEP, down to 0.7*NEPphot. [ABSTRACT FROM AUTHOR]

Smooth and uniform epitaxial ultrathin MgB2 films are desired for various electronic applications including hot-electron bolometers and single-photon detectors. However, the growth of ultrathin MgB2 films on SiC substrates using the Hybrid Physical-Chemical Vapor Deposition was dominated by the Volmer-Weber or island growth mode, which limited the minimum thickness for a conductive MgB2 film. Here we show the results of a study on the very early stage of the MgB2 film growth. We find that the root-mean-squared roughness and grain connectivity of ultrathin MgB2 films grown on C-terminated 6H-SiC($000\bar{1}$) substrate is much better than those on Si-terminated substrate. The result provides a simple solution to growing high-quality ultrathin MgB2 films for applications. [ABSTRACT FROM AUTHOR]

Ali CMB Polarization Telescope (AliCPT) is the first Cosmic Microwave Background (CMB) polarimeter with a large focal plane camera to be deployed in the Northern Hemisphere, in the Tibetan Plateau. Here we present the design of a dichroic (90/150 GHz) focal plane camera capable of hosting up to 32,376 Transition-Edge Sensor (TES) bolometers operating from a base temperature of 280 mK. Detectors are fabricated as monolithic arrays of 1,704 feedhorn-coupled and polarization-sensitive TES bolometers that are packaged in independent modules and read out with a microwave multiplexing architecture. A custom RFSoC-based system manages the multiplexing readout. Prototype AliCPT pixels have been fabricated and characterized, demonstrating passband performance within 2.5% of design and cross-polarization systematic sensitivity $\leq$ 2%. [ABSTRACT FROM AUTHOR]

Future cosmic microwave background (CMB) experiments will deploy increasing numbers of superconducting detectors with requirements for increased sensitivity and reduced systematics. We report on the ongoing development of OMT-coupled CMB detectors at Argonne National Laboratory. Key areas of development include bolometers with dual Transition Edge Sensors (TES) for easier lab characterization, a hybrid SiN membrane fabrication process, a chemical vapor deposition (CVD) SiN dielectric process, and a new pixel design for improved compatibility with large scale fabrication. These developments enhance our ability to fabricate large-scale (150 mm diameter wafers) detector arrays with the performance necessary for future CMB experiments. [ABSTRACT FROM AUTHOR]

The AdvancedAtacama Cosmology Telescope Polarimeter (AdvACT) is an upgrade for the Atacama Cosmology Telescope using Transition Edge Sensor (TES) detector arrays to measure cosmic microwave background (CMB) temperature and polarization anisotropies in multiple frequencies. The low frequency (LF) array was deployed early 2020. It consists of 292 TES bolometers observing in two bands centered at 27 GHz and 39 GHz. At these frequencies, it is sensitive to synchrotron radiation from our galaxy as well as to the CMB, and complements the AdvACT arrays operating at 90, 150 and 230 GHz. We present the initial LF array on-site characterization, including the time constant, optical efficiency and array sensitivity. [ABSTRACT FROM AUTHOR]

In this article, we propose a novel type of a wideband 2-D array of cold-electron bolometers (CEBs) sensitive to both polarizations of the incoming optical signal. This array was developed for osservatorio per il lontano infrarosso e le microonde su pallone orientabile (OLIMPO) balloon telescope with a requirement on bandwidth more than 10%. Sensitivity to both polarization components was achieved by a special meander-type arrangement of orthogonal L/2 dipoles. We present theoretical estimations for the optimal arrangement of 2-D arrays of CEBs, which allows achieving maximum efficiency in a wide band with the lowest noise equivalent power (NEP). A pixel layout with an optimal density of CEBs, sensitive to dual polarizations, and having more than 10% FWHM bandwidth at around 350 GHz was proposed and numerically analyzed. The layout consists of a periodic sparse array of orthogonal dipoles sensitive to both polarization components of the incoming signal. The numerical analysis confirmed that the sparse array is the most promising for a combination of high absorbing efficiency and low noise of the system and satisfying the 10% bandwidth requirements for the OLIMPO instrument. Different combinations of series and parallel connections of bolometers were considered for better noise properties to achieve the photon noise-limited level. [ABSTRACT FROM AUTHOR]

We report on the response of a monolithic high $\mathrm{T_{c}}$ transition-edge bolometer to about 3 mmWave for the first time. The detector structure consisting of 400-nm $\mathrm{YBa_{2}Cu_{3}O_{7-x}}$ (YBCO) film on buffered yttria stabilized zirconia substrate without any coupled antenna, shows bolometric type responsivity to the 3-mmWave radiation at its transition temperature. The YBCO thin film and $\mathrm{Ce_{0.9}La_{0.1}O_{2}}$ buffer layer are both fabricated by the metal-organic deposition method. The meander line pattern of the bolometer is designed for obtaining maximum absorption and responsivity possible when the polarized radiation of the source is aligned with the pattern. Meander lines are 50 micrometers wide and 1.5-mm long. We have measured amplitude and phase of the response versus modulation frequency of the detector to the linearly polarized 95-GHz source, and the detector was biased at five distinct temperatures at the transition corresponding to five different electrical conductivities of the YBCO film. When the meander lines of the device are parallel to the incident beam polarization, the YBCO pattern is speculated to act as a dissipative antenna resulting in higher absorption leading to high magnitude of the response as observed. The results from the measured phase of the response versus modulation frequency are also in agreement with the discussed absorbed mechanism. The absorption of the YBCO pattern is also measured to depend on the electrical conductivity of the YBCO film and our results show that there is an optimum electrical conductivity for having maximum absorption for this detector. Simulation results for this structure confirm the experiments showing that at electrical conductivity value of $\mathrm{1.33\times 10^{5}}$ S/m we have the maximum absorption for our device. These observations promise design of versatile THz and millimeter-wave detectors with potential for applications in medical and security imaging. [ABSTRACT FROM AUTHOR]

A novel system to measure the time constant of microbolometer cameras per-pixel to create a 2-D time constant map is presented. The measurements take place at the camera level and do not require any special control of the camera beyond the ability to capture raw data. Detailed simulations are run for a broad range of variables and values to demonstrate the usefulness of the system in extracting even extremely fast time constants with high accuracy and repeatability. Measurements are taken on a proof of concept system with an example camera, and a 2-D time constant map is reported. These results are compared with measurements from a linear motion stage system. [ABSTRACT FROM AUTHOR]

A pinhole camera using four-channel resistive bolometers was designed and implemented on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) to measure the plasma radiated power. Quantification of the radiated power is required for comprehensive power balance assessments but faces unique challenges on linear plasma devices due to weak absolute signal, compared to typical use in toroidal fusion plasmas, and high neutral pressure changes. Around 1 mTorr, the pressure-driven signal contribution was shown to overwhelm the radiated power signal in Proto-MPEX, found to be $\sim 3~{\mu W}$. Since the pressure-driven signals could not be predicted from first principle arguments, the signals were corrected using empirical models that take two experimental pressure measurements and the raw bolometer signal to reveal the radiated power signals. Four “gas-only” Proto-MPEX shots were taken, without the radio frequency (rf) plasma discharge, to train, optimize, and validate empirical models. The data included two pressure measurements at different locations along with the bolometer signal. Multiple models were tested; partial least-squares regression with a cross correlation method to account for the time offset in the pressure measurements provided the best combination of accuracy and stability. The model was validated to have a modeling error of 0.0036 V, which was lower than 10% of the expected radiated power signal. The model was tested on a different “gas-only” shot with a complete time-series data. For plasma operation shots, the corrected bolometer measurements were compared with an absolute extreme ultraviolet photodiode measurement and similarities and differences are discussed. [ABSTRACT FROM AUTHOR]

Plasma radiation plays an important role in the operation and control of magnetic confinement fusion and is typically measured by bolometers. Here, we study the influence of mechanical vibration and magnetic field, which are typically present in magnetic confinement fusion devices, on the performance of a fiber-optic bolometer (FOB) based on silicon Fabry-Perot interferometer (FPI) demodulated by a scanning diode laser. It is found that both the vibration and magnetic field could cause large noise due to the birefringence of the silicon FPI. To mitigate the birefringence effects, we demonstrated two effective methods: polarization maintaining FOB and polarization scrambling. We show that two methods can be effective in mitigating the effect caused by the sensor birefringence: (1) replacing the regular single-mode fiber in the FOB system with polarization-maintaining fiber and (2) using a polarization scrambler after the laser source. For both methods, no significant increase in the noise was observed in the vibration and magnetic field tests. Our research highlights the importance of the polarization management for the FOB systems toward their practical applications in magnetic-confinement fusion systems. [ABSTRACT FROM AUTHOR]

The use of deep learning is facilitating a wide range of data processing tasks in many areas. The analysis of fusion data is no exception since there is a need to process large amounts of data collected from the diagnostic systems attached to a fusion device. Fusion data involve images and time series and are a natural candidate for the use of convolutional and recurrent neural networks. In this article, we describe how convolutional neural networks can be used to reconstruct the plasma radiation profile, and we discuss the potential of using RNNs for disruption prediction based on the same input data. Both approaches have been applied at the Joint European Torus (JET) using data from a multichannel diagnostic system. Similar approaches can be applied to other fusion devices and diagnostics. [ABSTRACT FROM AUTHOR]

Thermal sigma–delta modulator is a closed-loop measurement approach, where the sensing element performs part of the $\Sigma \Delta$ modulation in the thermal domain. A new architecture is proposed in this paper for measuring the thermal incident radiation using thermoresistive sensors, where the modulator input range is automatically adjusted to fit the complete thermal radiation. The proposed architecture is compared with a similar one, which uses the same transducer interface circuit but without range adjustment, and is validated experimentally with a reference pyranometer. The proposed architecture has the main advantage of presenting a signal-to-noise ratio and sensitivity that is independent of the ambient temperature range definition. Experimental results for an ambient temperature range of 45 °C show a gain of 13 dB over the similar one. [ABSTRACT FROM AUTHOR]

This paper describes the metrological characterization of a new type-N coaxial microcalorimeter and its associated thermistor-type transfer standard, which together are used as the primary standard for microwave power from 0.05 to 18 GHz at the Centro Nacional de Metrología, Queretaro, Mexico. The design characteristics, evaluation method, and measurement uncertainties of the primary standard are given and compared to recent realizations found in the open literature. The metrological characterization of the microcalorimeter is based on a comparison method to indirectly obtain its correction factor. The effective efficiency of the transfer standard, directly calibrated in the microcalorimeter by means of calorimetric measurements, is shown and compared against measurements performed by National Institute of Standards and Technology, showing good agreement within the estimated expanded uncertainties (0.21%–0.47%). The developed data acquisition system to automate the effective efficiency measurements and the proposed software leveling loop to keep the microwave power level constant are also discussed. This approach allows to keep an RF power stability of better than 100 ppm over several hours and is a straightforward solution to replace analog leveling systems which require obsolete hardware. Finally, the analysis followed to evaluate the uncertainty for the effective efficiency measurements is thoroughly described. [ABSTRACT FROM AUTHOR]

Methods increasing the sensitivity of uncooled metal bolometers have been analyzed. The dynamic responsivity mode that increases sensitivity and accuracy without changing the design of sensors and the measurement circuit of optical power is proposed for the operation of uncooled bolometers. Experiments studying the efficiency of the mode are carried out using a Ti50.5Ni49.5-bolometer that has better sensitivity than other identical metal bolometers. The results of the study have confirmed the theoretical estimates of a multiple increase in sensitivity using the proposed mode. In addition, the operation of the Ti50.5Ni49.5-bolometer in the two-phase high-temperature region of the alloy is shown to also contribute to a multiple increase in the sensitivity and precision of the sensor. This letter describes and tests a new method for compensating the self-heating power of uncooled bolometers. [ABSTRACT FROM AUTHOR]

InfraRed imaging video bolometer (IRVB) is a powerful diagnostic for the plasma radiation measurement. Study on plasma radiation phenomena, e.g., plasma detachment, is one of the crucial issues to realize a fusion reactor. In order to apply the IRVB to such a study, a shielding is required to protect an IR camera from neutron irradiation. In the large helical device (LHD), deuterium experiment has started in 2017. Then, the shielding was designed using MCNP6 code with the 3-D modeling of LHD. The guideline of the neutron flux for the design was determined by the operational experience in JT-60U tokamak and by the result of the irradiation in OKTAVIAN. The strong neutron flux due to the location close to the vacuum vessel and the influx through the lens hole were reduced sufficiently. The designed shielding was applied to the LHD deuterium experiments and the IRVB with the shielding could be operated successfully without any dead pixels in the neutron emission rate up to $3.3\times 10^{15}\,\,\text {n}\cdot \text {s}^{-1}$ , which is the maximum rate in the first experimental campaign and in the total neutron emission of $3.6\times 10^{18}$ n. These correspond to the neutron emission rate of $2.9\times 10^{7}\,\,\text {n}\cdot \text {s}^{-1}$ and the total neutron emission of $3.2 \times 10^{10}$ n at around the IR camera. [ABSTRACT FROM AUTHOR]

We present a technique for designing the angle-sensing infrared detectors with subwavelength dimensions. The proposed detector is composed of a two-element long-wave infrared (LWIR) biomimetic antenna array. The detector consists of two closely spaced and strongly coupled IR antennas whose natural mutual coupling is augmented by using an external coupling network. Each antenna is connected to a microbolometer to detect the incoming IR radiation. By controlling the mutual coupling between the antennas and designing an optimum coupling network, the ratio of the power absorbed in the two bolometers is made to a one-to-one function of the incidence angle. This allows for determining the angle of incidence of the incoming IR light by measuring the changes of the dc currents passing through the bolometers when the antennas are biased with a dc voltage source. A prototype of the proposed angle-sensing detector is designed to operate at $10.6~\mu \text{m}$ in the LWIR band. The prototype is fabricated and characterized. Measurement results show that the device has a one-to-one response function for transverse electric waves within a field of view of ±60°. The response of the device for incident waves having the transverse magnetic or random polarizations was also simulated and measured. In all cases, the measurement results are found to be in good agreement with the theoretical predictions. [ABSTRACT FROM AUTHOR]

We describe the first phase of experimental study of the superconducting bridge RFTES detector at temperatures 20-300 mK including the measurement of its thermal conductance, which fits the model of electron gas heating. We discuss the idea of the RFTES scheme, which is based on the probing of microwave loss near superconducting transition of the bridge. The heat applied to the bridge is generated by the probing signal at the frequency of the high-Q resonator. Since the real part is dominating in the nonlinear impedance of the bridge, the applied heat provides merely amplitude modulation of Q suggesting the suppression of phase jitter of the resonator. The bridge was made from a 50-nm-thick hafnium film (TC ≈ 380 mK) sized to 2.5 μm × 2.5 μm. The resonator and the rest of the circuit were made from 200-nm-thick film of niobium (TC ≈ 9 K) demonstrating the loaded Q-factor up to and above 10 000 at 1.5 GHz. A cryogenic semiconductor amplifier was used in the readout circuit. The thermal conductance was measured using the steady Q regime of the resonator and found to follow T5 down to and below G ≈ 1×10-13 W/K. The NEP below 10-18 W/√Hz is estimated for the electron temperature of the bridge about 300 mK. [ABSTRACT FROM AUTHOR]

This paper introduces an in-circuit performance evaluation system for SiGe microbolometer readout integrated circuits (ROICs) that can characterize the overall system noise performance by emulating microbolometers with MOSFETs biased in the triode region. Specifically, the proposed test platform is designed for the testing of imagers with high resistance SiGe microbolometers. The architecture of the ROIC is based on a bridge with active and reference bolometer pixels with a capacitive transimpedance amplifier input stage and column parallel integration with serial readout. Noise measurements along with simulated resistance curves of the dummy detectors are reported. The prototype with 17- $\mu \text{m}$ pixel pitch has been designed and fabricated in a 0.25- $\mu \text{m}$ SiGe BiCMOS process. [ABSTRACT FROM AUTHOR]

Reliable algorithms for disruption avoidance and prediction are foreseen to play a fundamental role in the JET control system for the successful operation of the machine in the upcoming deuterium-tritium campaigns. The integration of such algorithms is expected to be a key part also in the implementation of the ITER plasma control system. So far, most of the effort has been devoted to the prediction of disruptions, which is required to mitigate the effects of these transient events, protecting the integrity of in-vessel components. Nevertheless, in order to put in place recover strategies or to have the possibility of a soft landing for the plasma current, the paradigm must be shifted to avoiding disruptions. In this paper, plasma profile-based indicators will be statistically analyzed showing their potential in such a perspective, where warning times and reliability of detection are crucial. [ABSTRACT FROM AUTHOR]

Cloud radiative forcing climate signals cannot be detected and proved sufficiently by the existing space-based Earth Radiation Budget (ERB) measurements due to the insufficient instrument calibration accuracy, relative to the sizes of mere decadal-scale trends. This paper, therefore, introduces a new project called the Moon and ERB Experiment (MERBE). Its methodology is for all earth observations using broadband thermal detectors, such as bolometers, to adhere toward more traceable calibration standards based on scans of our moon. This traceability limits instrument-dependent biases and spurious drifts for the past decades of existing earth data measurements as well as future measurements. The goal of the MERBE project is to substantially increase existing satellite climate data accuracy; therefore, a reexamination of all aspects of space-based ERB device calibration was also warranted. This paper concentrates on the improvement of ERB data quality from the level of detector voltages and onward. A component model of bolometer thermal and electronic time response and offset effects is used to design an improved inversion filter, which deconvolves path direction dependence of a scanning thermal detector. For every ERB instrument on the TRMM, Terra, Aqua, and SNPP satellites, instantaneous error reductions are achieved in all recovered MERBE radiance measurements. This also will allow for more accurate results from ERB device lunar scans based on improved telescope field-of-view mapping, as presented in other MERBE work. [ABSTRACT FROM AUTHOR]

This letter represents a prototype of an intrinsic thermistor based on silicon-germanium/silicon (Si1−xGex/Si) multi quantum wells with varying Ge concentration in SiGe wells. Experimental results of the thermistor prototype are provided in terms of temperature coefficient of resistance (TCR) and noise constant (K1/f). The prototype with 50% Ge in SiGe wells exhibited an outstanding TCR of −5.5 %/K accompanied by a K1/f of $5.8\times 10^{-13}$ for $25~\mu \text{m} \times 25~\mu \text{m}$ and $3.4\times 10^{-15}$ for $200~\mu \text{m} \times 200~\mu \text{m}$ pixel size, showing the concurrent achievement of a very high TCR and a low 1/f noise performance. [ABSTRACT FROM AUTHOR]

The size and power dissipation of an infrared imaging system can be reduced by the use of uncooled microbolometers; but the nonuniformity of the microbolometer makes such imaging systems heavily reliant on complicated calibration techniques, incurring an overhead which is particularly significant in low-cost, compact devices. We therefore propose a shutter-based successive-approximation calibration loop, which avoids the need to implement correction tables in software on an external processor. Prototype imager, consisting of an $80 \times 82$ pixel infrared focal-plane array and readout circuitry, has been implemented, and the experimental results confirm that our on-chip autocalibration approach compensates effectively for fixed pattern noise caused by the nonuniformity of the microbolometers. [ABSTRACT FROM PUBLISHER]

A radio frequency bolometer was realized using a thermistor fabricated from a carbon nanotube thin-film deposited on a sapphire substrate. Power detection performance was characterized at room and liquid nitrogen temperatures. With the thermistor held at a temperature of 15 °C, the bolometer’s sensitivity of 915-MHz test signals was found to be 0.36 mV/mW, and power levels as low as −45 dBm could be detected with a 20-s integration time constant. The sensitivity increased to 2.3 mV/mW when the thermistor was cooled to −193 °C. Experiments over the temperature range of 15 °C–240 °C indicate that internanotube mechanisms dominate power detection at temperatures below a value of approximately 200 °C and that intrananotube mechanisms (primarily Joule-heating) dominate at higher temperatures. [ABSTRACT FROM AUTHOR]

In the current submm and mm cosmology experiments the focal planes are populated by kilopixel transition edge sensors (TESes). Varying incoming power load requires frequent rebiasing of the TESes through standard current–voltage (IV) acquisition. The time required to perform IVs on such large arrays and the resulting transient heating of the bath reduces the sky observation time. We explore a bias step method that significantly reduces the time required for the rebiasing process. This exploits the detectors' responses to the injection of a small square wave signal on top of the dc bias current and knowledge of the shape of the detector transition R(T,I). This method has been tested on two detector arrays of the Atacama Cosmology Telescope (ACT). In this paper, we focus on the first step of the method, the estimate of the TES %Rn [ABSTRACT FROM PUBLISHER]

The sensitivity of a bolometer is in principle limited by the phonon noise, which is a function of the conductance between its absorber and the thermal sink. However, practical issues limit the degree to which conductance can be minimized. For example, in a high-radiation environment, extremely low conductance, or, equivalently, long thermal recovery time, can lead to high data loss. To circumvent such limitations, we are developing a technique of modulating the conductance through the use of pixel-scale superconducting heat switches. We have fabricated bolometer-like test devices consisting of isolated regions connected to a thermal ground plane through narrow aluminum strips. Niobium coils are patterned around the aluminum strips. Flowing current through a coil allows the aluminum to be driven into the normal or high thermal conductance state. We have measured the conductance of these devices as a function of temperature and drive coil current. [ABSTRACT FROM AUTHOR]

We report on the development of a multipixel hot electron bolometer (HEB) receiver fabricated using silicon membrane technology. The receiver comprises a $2\,\times \,2$ array of four HEB mixers, fabricated on a single chip. The HEB mixer chip is based on a superconducting NbN thin-film deposited on top of the silicon-on-insulator (SOI) substrate. The thicknesses of the device layer and handling layer of the SOI substrate are 20 and 300 μm, respectively. The thickness of the device layer is chosen such that it corresponds to a quarter-wave in silicon at 1.35 THz. The HEB mixer is integrated with a bow-tie antenna structure, in turn designed for coupling to a circular waveguide, fed by a monolithic drilled smooth-walled horn array. [ABSTRACT FROM PUBLISHER]

We discuss performance of submicron size hot-electron bolometer mixers made from thin MgB2 superconducting films. With a superconducting transition temperature of ∼30 K, such terahertz (THz) mixers can operate with high sensitivity at temperatures up to 20 K. Due to very small dimensions local oscillator power requirements are rather low. In the intermediate frequency band of 1–3 GHz, the double sideband receiver noise temperature is 1600 K at 10 K operation temperature, 2000 K at 15 K, 2500–3000 K at 20 K. The gain bandwidth of such devices is 6 GHz and the noise bandwidth is estimated to be 6–8 GHz. [ABSTRACT FROM PUBLISHER]

Our new detector and readout concept brings together TES (Transition Edge Sensor) and MKID (Microwave Kinetic Inductance Detector) technologies and exploits the idea of a microwave-induced superconducting transition in a small thin-film microbridge. The superconducting transition of the bridge manifests itself as variation in the Q -factor of niobium resonators at 5–8 GHz, somewhat similar to MKID operation. We present data showing the potential for developing this concept into multipixel detector arrays. Single-pixel sensitivity was measured at 4.5 K for an input band of 600–700 GHz using a prototype 10-nm-thick Nb bridge of size 1 μm × 500 nm. Radiation from human skin was detected with a resolution better than 1 K/rtHz, which is encouraging for terahertz imaging applications. To further improve device sensitivity, we are also developing Hf-based devices that operate near 0.35 K. Details about the physics and stability of these devices are discussed. [ABSTRACT FROM PUBLISHER]

Frequency-division multiplexing (FDM) is the current baseline read-out system for the large array of superconducting transition edge sensors (TES's) under development for the X-ray instrument XIFU (Athena). In this multiplexing scheme the sensor operates as amplitude modulator of a MHz carrier. To achieve the best performance with these and similar instruments the detector physics and its interaction with the read-out circuit needs to be better understood. In particular we need an explanation for the dependence of the TES microcalorimeter nonlinear impedance on the bias point, because it directly affects the choice of the detector optimal working point. With the TES microcalorimeters fabricated at NASA-Goddard we observe current steps in the amplitude of the uncalibrated IV characteristics when the detectors are read-out in the frequency domain and are biased in the low-resistance part of the superconducting transition. In this paper, we report on the characterization under FDM of NASA-Goddard TES microcalorimeters under development for the XIFU instrument. We have measured several pixels with different size and geometry in the bias frequency range from 1 to 4 MHz and at different bath temperatures. The results will be discussed within the recently developed weak-link theoretical framework. [ABSTRACT FROM PUBLISHER]

Hot-electron bolometers (HEBs) made with MgB2 have proven to have a large intermediate frequency and have shown potential for a low noise into the terahertz range. Although practical results from these mixers have been achieved fairly quickly, effort is still needed to realize an MgB2 HEB with improved sensitivity to compete with state-of-the-art mixers. Here, we present the results of our mixer work to achieve MgB2 HEBs based on hybrid physical chemical vapor deposition grown films, with improved sensitivity and higher temperature operation. A new fabrication process is developed which utilizes even thinner films (<10 nm) allowing for the improvement of the impedance match of the mixer device with the Au spiral antenna. Integrated superconducting contacts prevent deterioration of the sensitivity due to the electron diffusion. The mixer noise temperature is 2000 and 3600 K at 600 and 1.9 THz, respectively, with minimal dependence on the bath temperature until over 20 K. The noise bandwidth of the mixer is 6.5 GHz at 4.2 K and is expected to be larger at higher operating temperature. [ABSTRACT FROM PUBLISHER]

Silicon nitride membrane based cryogenic bolometers exhibit high sensitivity and enable ultra-sensitive detector applications. Multi-pixel instruments were already introduced as devices for submillimeter-wave imaging. Nevertheless, the numbers of pixels are limited by the readout process which is typically a time-division multiplexing or code-division multiplexing technique. To overcome this challenge, a replacement of the transition-edge sensor as thermometer by a lumped-element resonance circuit seems to be a promising solution. Therefore, one can benefit from the intrinsic capability of frequency-division multiplexing that allows the readout of large detector arrays simultaneously and in real-time. The number of pixels is then limited by the available readout bandwidth and the quality factors of each individual resonance circuit. We successfully demonstrated, based on our feasibility study, the principal operation of such a device, what we call kinetic-inductance bolometer (KIBO). But the overall performance of the achievable noise-equivalent power (NEP) was limited by implementation and operation temperature of KIBO. Therefore, improved KIBO designs were developed and fabricated with niobium thin-film technology. In this paper, we describe the improvement procedure and estimate the expected NEP value. [ABSTRACT FROM AUTHOR]

In this paper, we describe the optimization of transition-edge-sensor (TES) detector arrays for the third-generation camera for the South Pole Telescope. The camera, which contains ∼16 000 detectors, will make high-angular-resolution maps of the temperature and polarization of the cosmic microwave background. Our key results are scatter in the transition temperature of Ti/Au TESs is reduced by fabricating the TESs on a thin Ti(5 nm)/Au(5 nm) buffer layer and the thermal conductivity of the legs that support our detector islands is dominated by the SiOx dielectric in the microstrip transmission lines that run along the legs. [ABSTRACT FROM PUBLISHER]

Background suppression plays a crucial role in particle physics experiments searching for rare events, such as neutrinoless double beta decay and dark matter interactions. Bolometers, that are among the most competitive devices in this field, would largely benefit from the development of ultrasensitive light detectors, as the combined readout of the bolometric and light signals enables the particle identification. The CALDER collaboration is developing superconducting light detectors that will match the requirements of next generation experiments: noise lower than 20 eV, large active area ($>$20 cm $^2$), wide temperature range of operation, high radiopurity, and ease in fabricating hundreds of channels. For this purpose, we are exploiting the excellent energy resolution and the natural multiplexed readout provided by kinetic inductance detectors (KIDs). KIDs have already demonstrated their potentiality as direct detectors of photons for different astrophysical applications. The aim of our project is to apply this technology in particle physics, using indirect detection. These devices can be operated in a phonon-mediated approach, in which KIDs are coupled to a large insulating substrates in order to increase the active surface from a few mm$^2$ to 25 cm $^2$. We have already demonstrated the feasibility of a phonon-mediated KIDs-based light detectors, using aluminium sensors. These device reached a baseline sensitivity of around 80 eV with an overall efficiency of about 20%. Currently, we are testing new materials (e.g., Ti-Al and nonstoichiometric TiN) to enhance the sensitivity and reach the goal of our project. We present our results and the physical interpretation of the device behavior. Finally, we also discuss the impact of this project on the most advanced bolometric experiments searching for neutrinoless double beta decay and dark matter. [ABSTRACT FROM PUBLISHER]

In order to design antennas for mid-infrared (MIR) hot electron bolometers (HEBs), the surface impedance of Au thin films at cryogenic temperatures was evaluated using Fourier transform infrared spectroscopy with a sample cooling system. We fabricated resonator arrays that were constructed by gold thin film strips. The length, width, and thickness of the resonators were set at 1300, 200, and 55 nm, respectively. As the temperature was lowered, the resonant frequency was shifted to the low-frequency side. By fitting the resonant frequency to simulated results, the corrected surface reactance was established for designing MIR nano-antennas. MIR HEBs with a twin-slot antenna were designed and fabricated using the corrected surface impedance. The design frequency was 61 THz. The HEBs were formed as a superconducting strip with Au antennas and electrodes. Here, the superconductivity under the Au electrodes was suppressed by a Ni thin film. For evaluating the mixer properties of the MIR HEBs, measurement setup without beam splitter was constructed. In this setup, local oscillator power was applied directly to the HEB, and we confirmed that the critical current of the HEB can be reduced to be almost zero by the LO irradiation. The HEB responses with clear polarization dependencies were also observed. [ABSTRACT FROM AUTHOR]

A new method is proposed to compare the sensitivity of uncooled metal bolometers. This method allows us to conduct a comparative analysis for the sensitivity of uncooled bolometers with metal and metal alloy resistive elements. The experiments showed a twofold superiority in the sensitivity of the TiNi alloy-based bolometer with a resistive element less than $10~\Omega $ in resistance over the identical bolometers based on technologically applicable metals due to improved electrophysical properties. The Ti50.5Ni49.5 bolometer developed to measure the total solar radiation has a higher sensitivity, a higher measuring efficiency, a smaller weight, and size compared with a serial CMP-11 pyranometer, as well as the best environmental protection. The highly sensitive uncooled metal bolometers are shown to be used as an integral part of the optical absorption gas analyzer to provide the control of background mercury vapors in the atmosphere. [ABSTRACT FROM PUBLISHER]

Bolometer antennas are required to have not only a large gain–bandwidth product but also a fast heating rate suitable for video rate operation. However, while the gain–bandwidth product of an antenna increases with the fraction of the antenna bulk volume occupied by its enclosing sphere, its heating rate decreases. In this paper, we show that for a typical heating rate requirement, wire antennas such as dipole and bow-tie antennas are preferable over planar antennas such as triangular and pentagonal antennas. More complex bent-wire antenna geometries achieved by a genetic algorithm are shown to yield better performance. [ABSTRACT FROM PUBLISHER]

This paper presents a very low noise suspended micro-bolometer with an in-situ vacuum micro-package so as to prevent thermal loss to the surrounding area and minimize the thermal conductivity of the ambient. Bolometer thermal models with respect to vacuum pressure are developed and verified by finite-element method (FEM) simulations. It is found that with the vacuum micro-package, a micro-scale (and not a nano-scale) size bolometer can achieve a noise equivalent power (NEP) close to the theoretical limit. Vacuum packaged Ni micro-bolometers with a sheet resistance of 6.2– 6.5~\Omega /\text sq , widths of 1.3 and 2.3~ \mu \text m , and a micro-vacuum ambient of 1 torr are fabricated using advanced micro-machining techniques. The measured responsivity (RESP) of a room-temperature micro-bolometer with w b =1.3~ \mu {\text {m}} is 922 V/W ( \beta =1.54~ \text M\Omega /\text W ) for R b =275 ~\Omega and I b =0.6 ~{\text {mA}} . The measured best NEP is 7.2 pW/Hz0.5 at 3-kHz modulation frequency for w b =1.3~ \mu {\text {m}} , l b =40 ~\mu {\text {m}} , and R b =230~ \Omega , and is the first demonstration resulting in <10 pW/Hz0.5 performance among uncooled micro-bolometers without any nano-patterning methods. The application areas are in low-cost THz imaging systems and wideband THz detectors. [ABSTRACT FROM PUBLISHER]

Two scintillating bolometers of LiF (33 g) and Al2O3 (50 g) at 20 mK, inside a lead shielding at the Canfranc Underground Laboratory, were irradiated with neutrons from a source of 252Cf. The analysis of nuclear recoils registered by sapphire and (\text n, \alpha ) captures by 6Li shows the feasibility of these cryogenic devices to measure the spectral flux of a neutron field. Data unfolding was done assuming that the spectral flux is a piecewise constant function defined on six energy groups. It can be solved by using non-negative least squares without additional assumptions on the neutron flux. The model provides consistent results with the spectra of the observed events in bolometers, giving a fast neutron flux of \Phi (\text E>\text 0.1~\text MeV)= \text 0.20~\text n~\text s^-\text 1\text cm^-\text 2 with a 15% uncertainty after 3 hours of live time. After our analysis, it can be concluded that nuclear recoils in sapphire are more useful than (\text n, \alpha ) captures in LiF for spectrometry of fast neutrons. [ABSTRACT FROM PUBLISHER]

This paper presents the influence of the surrounding air on air-suspended microbolometers and nanobolometers. If the air-suspended bolometer is long and thin due to a low sheet resistance, the thermal loss through the air can be comparable to that through the bolometer structure, and therefore, the surrounding air can greatly affect the bolometer performance. The thermal models with the surrounding air effect are newly developed and verified using finite-element method simulations, and it is seen that bolometers with widths < \1 \mum are required so as to minimize the effect of the surrounding air. Ni/Cr microbolometers and nanobolometers with the sheet resistance of 5.3–5.6 \Omega/sq. and widths of 2–0.6 \mum are fabricated and tested at room temperature. As the bolometer resistance increases, the microbolometer (w{b}=2 \ \mum) responsivity saturates at 83 V/W (limited by the surrounding air), while that of the nanobolometer (w{b}=0.6 \mum) continuously increases up to 315 V/W. Also, the 3-dB cutoff frequency of the nanobolometer (65 kHz) is three times higher than that of the microbolometer. The measured nanobolometer noise equivalent power is 14 pW/\surdHz for w{b}=0.6 \mum, l{b}=20 \mum, and R{b}=184 \Omega, which is \sim \2\times better than the previous state-of-the art. Application areas are in terahertz power measurements and room-temperature imaging systems. [ABSTRACT FROM PUBLISHER]

We propose an analog front-end integrated circuit (IC) design for a readout IC (ROIC), which applies a fixed-voltage-bias sensing method with a capacitance transimpedance amplifier (CTIA) to an input stage in order to simplify the circuit structure of the ROIC and the IR sensor characteristic control. For a sample-and-hold stage, in order to display and control a signal detected by the IR sensor using a 2-D focal plane array, a differential delta sampling circuit is proposed, which effectively removes the fixed pattern noise. In addition, a two-stage variable-gain amplifier equipped with a rail-to-rail fully differential operational amplifier is applied to the ROIC to achieve high voltage sensitivity. The output characteristic of the proposed device is 30.84 mV/K and the linearity error rate is less than 0.07%. After checking the performance of the ROIC using an HSPICE simulation, the chip is manufactured and measured using the United Microelectronics Corporation Japan 0.35- \mu\mboxm standard CMOS process to confirm that the simulation results from the actual design are in close agreement with the measurement results. [ABSTRACT FROM PUBLISHER]

In this paper, we have fabricated and characterized uncooled microbolometers using as infrared element intrinsic amorphous silicon–germanium films with embedded nanocrystals with a dimension in the range of \sim 2 –4 nm. The presence of nanocrystals in the amorphous films reduces the density of defects, improves the transport properties, and specially improves the films stability against radiation. On the other hand, the combination of silicon and germanium in one alloy allows to improve the film conductivity and the temperature coefficient of resistance (TCR), without the necessity of perform doping. Large values of TCR have been demonstrated in the microbolometers, as large as −6.6% \text{K}^{-1} , which in fact is the largest value reported for this kind of devices, and consequently large detectivity values were obtained in the reported devices ( 2\times 10^{9}$ cmHz ^{\vphantom {R^{R^{}}}{1/2}}\text{W}^{-1} ). [ABSTRACT FROM PUBLISHER]

Using a microwave probe as a tool, we have performed experiments aimed at understanding the origin of the output-power fluctuations in hot-electron-bolometer (HEB) mixers. We use a probe frequency of 1.5 GHz. The microwave probe picks up impedance changes of the HEB, which are examined upon demodulation of the reflected wave outside the cryostat. This study shows that the HEB mixer operates in two different regimes under a terahertz pump. At a low pumping level, strong pulse modulation is observed, as the device switches between the superconducting state and the normal state at a rate of a few megahertz. When pumped much harder, to approximate the low-noise mixer operating point, residual modulation can still be observed, showing that the HEB mixer is intrinsically unstable even in the resistive state. Based on these observations, we introduced a low-frequency termination to the HEB mixer. By terminating the device in a 50- $\Omega$ resistor in the megahertz frequency range, we have been able to improve the output-power Allan time of our HEB receiver by a factor of four to about 10 s for a detection bandwidth of 15 MHz, with a corresponding gain fluctuation of about 0.035%. [ABSTRACT FROM PUBLISHER]

Hot-Electron Bolometer (HEB) mixers have proven to be the best tool for high-resolution spectroscopy at the Terahertz frequencies. However, the current state of the art NbN mixers suffer from a small intermediate frequency (IF) bandwidth as well as a low operating temperature. \MgB2 is a promising material for HEB mixer technology in view of its high critical temperature and fast thermal relaxation allowing for a large IF bandwidth. In this work, we have fabricated and characterized thin-film ( $\sim$15 nm) <$ 4000 K at 9 K using a 600 GHz source. Using temperature dependencies of the radiation power dissipated in the device we have identified the optical loss in the integrated microantenna responsible as a cause of the limited sensitivity of the current mixer devices. From the analysis of the current-voltage (IV) characteristics, we have derived the effective thermal conductance of the mixer device and estimated the required local oscillator power in an optimized device to be \sim\!\! 1\ \mu\W. [ABSTRACT FROM PUBLISHER]

The frequency domain multiplexing (FDM) readout of arrays of transition edges sensors for the X-IFU/Athena and SAFARI/SPICA instruments requires SQUID amplifiers with low input inductance, low flux noise, high-dynamic range and low power consumption. We report the performance of two-stage SQUID amplifiers developed at VTT coupled to multiple high-Q LC resonators of the SRON FDM readout operating in the frequency range from 2 to 5 MHz. The SQUIDs have been tested in the following configurations: 1) the two SQUIDs at base temperature with open input; 2) the amplifier SQUID at 1K temperature and the front-end SQUID at base temperature in the FDM readout of low-G TES bolometers; and 3) and in the FDM readout of X-ray microcalorimeter arrays with both SQUIDS at base temperature. We measured an input flux noise equal to 0.18\ \mu\Phi0/\Hz^{1/2} at 20 mK, equivalent to an energy resolution of 9 $\hbar$. The measured current noise at the SQUID input is \sim\!\! 1\ \pA/Hz^1/2 at 20 mK, which corresponds to a coupled energy resolution of about 15 $\hbar$. [ABSTRACT FROM PUBLISHER]

In this paper, the design, fabrication, and testing of a CMOS compatible mid-infrared (mid-IR) thermopile sensor comprising a stacked double layer thermopile and an interferometric absorber is reported. The devices are all fabricated in CMOS compatible process. The length and width of the thermocouple are 600 and 12 μm, respectively. One thermopile consists of 96 thermocouple pairs. The thickness of the poly-Si strips is 300 nm and the thickness of the SiO2 electrical isolation layer is 150 nm. The interferometric absorber is formed by a stacked three layer of 7-nm TiN, 250-nm amorphous silicon, and 300-nm Al. The measurement using blackbody with temperature of 470 °C was conducted at ambient temperature from -50 °C to 300 °C. The results show that the responsivity and the detectivity of this thermopile mid-IR sensor vary from 130 to 463 V/W and 3.8 * 106 cm * Hz1/2 * W-1 to 1.3 * 107 cm * Hz1/2 * W-1, respectively. And the time constant of the mid-IR sensor is 33 ms. The maximum output voltage is measured at 190 °C, where the responsivity and the detectivity are 425.7 V/W and 1.25 * 107 cm * Hz1/2 * W-1, respectively. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance (FMR) of glass-coated amorphous Fe78Ni8P10B10 and Co67Fe4Cr7Si8B14 microwires was investigated at frequency 9.54 GHz by the standard FMR and the electrically detected FMR techniques. Static magnetic field was applied parallel to the wire axis and the resonance was driven by the microwave current passing through the wire. The field dependences of electrical resistance measured at different levels of microwave power were compared with the resonance curves obtained by the standard FMR method. It was found that the change of resistance observed at the resonance is caused by the increase of temperature due to the energy dissipation by the Gilbert damping of spin-precession motion. [ABSTRACT FROM AUTHOR]

In this paper, microbolometers with different geometric designs were fabricated using polycrystalline silicon (polysilicon) films from TSMC 0.35 μm (D35 type) and 0.18 μm (T18 type). D35 microbolometers with high-resistance films showed negative temperature coefficient of resistance (TCR) values, whereas T18 microbolometers with low-resistance films showed positive TCR values. Results indicate that conventional designs with large areas of infrared absorbers can be optimized using uniform suspended arms throughout the microbolometer in the two types of devices. Finite element modeling indicates that the heat flux of microbolometers with uniform beams is evenly distributed and thus results in improved TCR values. [ABSTRACT FROM PUBLISHER]