Bolometric Detectors Research Articles

A polarized infrared thermal detector made from super-aligned multiwalled carbonnanotube films

Carbon nanotube (CNT) films, easily drawn from super-aligned CNT arrays with a largearea and a good compatibility with semiconductor technology, have been used as lightsensitive materials for infrared (IR) detection. A bolometric CNT detector madefrom one layer of super-aligned CNT film shows a 15.4% resistance change under10 mW mm − 2 of IR illumination and a fast characteristic response time of 4.4 ms due to its ultra-smallheat capacity per unit area in vacuum at room temperature. Besides the power intensitydetection, the anisotropic property of the super-aligned CNT films makes them idealmaterials to detect the polarization of IR light simultaneously, which provides greatpotential in infrared imaging polarimetry. Theoretical analyses have been carried out toinvestigate the influences of CNT film properties on the responsivity and response time ofthe detector.

Heteroepitaxy of Nd0.67Sr0.33MnO3 on silicon for bolometric x-ray detector application

We have recently reported the design concept and sensor fabrication for a novel bolometric x-ray detector based on a rare earth manganite material for application as a total energy monitor for the Linac Coherent Light Source (LCLS) free electron laser at the Stanford Linear Accelerator Center (SLAC). The detector employs epitaxial thin films of Nd(0.67)Sr(0.33)MnO(3) grown on Si by pulsed laser deposition. In this paper we report details of the fabrication of the actual detector, its response characteristics under photon illumination from LCLS, and improvements in the growth scheme of the sensor material on Si using a buffer/template layer scheme that employs yttria-stabilized zirconia, cerium oxide (CeO(2)), and bismuth titanate (Bi(4)Ti(3)O(12)). The thermal sensor response changes linearly with the energy of an optical calibration laser as expected, and the signals from optical and x-ray pulses at LCLS are very similar, thereby validating the design concept. To the best of our knowledge, the LCLS detector application reported here is the first practical use of colossal magnetoresistive manganite bolometers.

Model of the response function of large mass bolometric detectors

Large mass bolometers are used in particle physics experiments to search for rare processes. By operating at low temperature, they are able to detect particle energies from few keV up to several MeV, measuring the temperature rise produced by the energy released. This study was performed on the bolometers of the CUORE experiment. The response function of these detectors is not linear in the energy range of interest, and it changes with the operating temperature. The nonlinearity is found to be dominated by the thermistor and its biasing circuit, and is modeled using few measurable parameters. A method to obtain a linear response is the result of this work. It allows a great simplification of the data analysis.

Optimization of a bolometer detector for ITER based on Pt absorber on SiN membrane

Any plasma diagnostic in ITER must be able to operate at temperatures in excess of 200 °C and neutron loads corresponding to 0.1 dpa over its lifetime. To achieve this aim for the bolometer diagnostic, a miniaturized metal resistor bolometer detector based on Pt absorbers galvanically deposited on SiN membranes is being developed. The first two generations of detectors featured up to 4.5 μm thick absorbers. Results from laboratory tests are presented characterizing the dependence of their calibration constants under thermal loads up to 450 °C. Several detectors have been tested in ASDEX Upgrade providing reliable data but also pointing out the need for further optimization. A laser trimming procedure has been implemented to reduce the mismatch in meander resistances below 1% for one detector and the thermal drifts from this mismatch.

On the effect of cosmic rays in bolometric cosmic microwave background measurements from the stratosphere

Ultra-sensitive bolometric detectors in balloon-borne or satellite missions have the potential to discover low-level non gaussian features in the Cosmic Microwave Background (CMB), due to topological defects or to the inflation process. However, the space environment includes a population of cosmic rays (CR), which produce spurious spikes in bolometric signals. In this paper we analyze how CR affect these measurements and the estimates of non-gaussianity and of angular power spectra of the CMB. Using accurate simulations of noise and CR events in bolometric detectors, we find that a de-spiking technique based on outliers removal in the detector signals contributing to the same sky pixel works well in removing CR events larger than the noise. Low level events hidden in the noise produce skewness and kurtosis of the temperatures of the pixels, indicating low-level non-gaussianity. Moreover, when the low-level CR distribution is not known a-priori, the standard noise estimation pipeline produces a positive bias of the power spectrum at high multipoles. In experiments with detector sensitivity better than 100 $\mu K / \sqrt{Hz}$, in an environment less favorable than the earth stratosphere, the CR-induced non gaussianity is likely to affect significantly the results.

Development of Kinetic Inductance Detectors for Cosmic Microwave Background experiments

We describe the design, optimization, electrical and optical tests of Microwave Kinetic Inductance Detectors (MKIDs) for the mm-wave range. Our detectors are based on a novel resonator design, and are suitable for ground-based astronomical observations in the 143 GHz atmospheric window. The measured optical Noise Equivalent Power (NEP) at 0.3 K is \(\sim 10^{-16}~\text{W}/\sqrt{\rm Hz}\) under a 300 K background load. This is equivalent or better than the performance of the best current bolometric detectors for the 140 GHz atmospheric window, limited by atmospheric noise in the best available sites. We also describe which improvements can be introduced to reduce the NEP of our detector, for lower background applications (narrow band or space-based).

Modeling the intensity and polarization response of planar bolometric detectors

Far-infrared bolometric detectors are used extensively in ground-based and space-borne astronomy, and thus it is important to understand their optical behavior precisely. We have studied the intensity and polarization response of free-space bolometers and shown that when the size of the absorber is reduced below a wavelength, the response changes from being that of a classical optical detector to that of a few-mode antenna. We have calculated the modal content of the reception patterns and found that for any volumetric detector having a side length of less than a wavelength, three magnetic and three electric dipoles characterize the behavior. The size of the absorber merely determines the relative strengths of the contributions. The same formalism can be applied to thin-film absorbers, where the induced current is forced to flow in a plane. In this case, one magnetic and two electric dipoles characterize the behavior. The ability to model easily the intensity, polarization, and straylight characteristics of electrically small detectors will be of great value when designing high-performance polarimetric imaging arrays.

Energy resolution of terahertz single-photon-sensitive bolometric detectors

We report measurements of the energy resolution of ultrasensitive superconducting bolometric detectors. The device is a superconducting titanium nanobridge with niobium contacts. A fast microwave pulse is used to simulate a single higher-frequency photon, where the absorbed energy of the pulse is equal to the photon energy. This technique allows precise calibration of the input coupling and avoids problems with unwanted background photons. Present devices have an intrinsic full-width at half-maximum energy resolution of approximately 23 THz, near the predicted value due to intrinsic thermal fluctuation noise.

Structural, microchemical and superconducting properties of ultrathin NbN films on silicon

AbstractStructural, chemical and superconducting properties of thin NbN films used for development of fast and sensitive hot‐electron bolometer (HEB) detectors for wide spectra range are reported. The thin NbN films with a thickness between 4 and 10 nm were deposited on the (001)Si substrates by magnetron sputtering. In order to investigate the film morphology and microchemistry, diffraction‐contrast and high‐resolution transmission electron microscopy (TEM) in combination with scanning TEM and electron energy loss spectroscopy (EELS) were performed. In addition, the zero‐resistance critical temperature of the NbN films was measured and correlated to their thickness. The interrelations between fabrication conditions, crystalline and superconducting properties of the differently thick NbN films are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An approach for the performance analysis of an uncooled infrared bolometer imager

As an approach for analyzing an uncooled infrared bolometer imager, a method is introduced which supposes that a thermal system is built into the infrared radiation detection mechanism. In this analysis, the bi-directional radiation energy flows between two thermal elements are considered and a radiation thermal conductance between them is defined. Based on the values of the radiation thermal conductances and conventional material thermal conductance, an equivalent thermal circuit for a bolometer detector element is extracted. Calculations were carried out using software written in visual C++. The analysis shows a Noise Equivalent Temperature Difference (NETD) of 50 mK is obtained as a typical value, assuming that no additional noise other than temperature fluctuation noise exists, and that the NETD becomes better as the system time constant built into the equivalent thermal circuit increases.

FPN Sources in Bolometric Infrared Detectors

Low manufacturing cost and ease of use favor spreading of 2-D bolometric infrared detector arrays over various application domains such as predictive maintenance, medical imaging, automotive industry, and security. The infrared detector's main figure of merit has long been the noise equivalent temperature difference (NETD), which sets the minimum temperature difference distinguishable from background noise at sensor output. However, while nowadays uncooled detectors have achieved sufficient NETD, fixed pattern noise (FPN) is indeed becoming a crucial figure of merit especially when the focal plane array (FPA) is not regulated by a thermoelectric cooler (TEC). In this paper, we study the various sources of dispersion of infrared bolometric detectors and their respective impact on FPN in the resulting image. We propose an analytical model to identify main sources of nonuniformity, and the confrontation of results with actual measurements leads to the ability of a highly accurate on-chip thermal drift compensation.

Thermal Design and Characterization of Transition-Edge Sensor (TES) Bolometers for Frequency-Domain Multiplexing

In contemporary cosmic microwave background experiments, bolometric detectors are often background limited, and in this case the sensitivity of instruments can only be improved by increasing the number of background-limited detectors, and so contemporary TES receivers contain as many pixels as possible. Frequency-domain multiplexing (fMUX) is one strategy for reading out many detectors with one SQUID. For any readout system, it is important to carefully evaluate the thermal design of detector, in conjunction with the readout bandwidth, in order to ensure stable electro-thermal feedback (ETF). We demonstrate a novel technique for characterizing the thermal circuit of our detectors, using am AC-bias and the fMUX electronics. This technique is used to study the internal thermal coupling of a TES bolometer. We illustrate how the insights gathered by this technique have been instrumental in improving the stability of our multiplexed detectors for the south pole telescope (SPT).

A Microbolometer Asynchronous Dynamic Vision Sensor for LWIR

In this paper, a novel event-based dynamic IR vision sensor is presented. The device combines an uncooled microbolometer array with biology-inspired (ldquoneuromorphicrdquo) readout circuitry to implement an asynchronous, ldquospikingrdquo vision sensor for the 8-15 mum thermal infrared spectral range. The sensor's autonomous pixels independently respond to changes in thermal IR radiation and communicate detected variations in the form of asynchronous ldquoaddress-events.rdquo The 64times64 pixel ROIC chip has been fabricated in a 0.35 mum 2P4M standard CMOS process, covers about 4times4 mm2 of silicon area and consumes 8 mW of power. An amorphous silicon (a-Si) microbolometer array has been processed on top of the ROIC and contacted to the pixel circuits. We discuss the bolometer detector properties, describe the pixel circuits and the implemented sensor architecture, and show measurement results of the readout circuits. Subsequently, a DFT-based approach to the characterization of asynchronous, spiking sensor arrays is discussed and applied. Test results and analysis of sensitivity, bandwidth, and noise of the fabricated IR sensor prototype are presented.

Control of Membrane Thermal Transport Supporting Superconducting Detector Development

Because thermal transport determines the dynamic and static operation of bolometric detectors, control of the thermal conductance is critical for the implementation of detectors utilizing superconducting Transition Edge Sensors (TESs). For this reason, we have examined the use of partially perforated membranes for thermal management. This technique preserves the physical integrity of the membrane, and therefore maintains the mechanical robustness of the detector. This paper describes investigations of the thermal transport in trenched membranes.

Characterization of NbSi TES on a 23-Pixel Array

Instrumental progress allowed the development of bolometric detectors adapted to submillimeter and millimeter wavelengths. Superconducting transition-edge sensors (TESs) are currently under heavy development to be used as ultra sensitive bolometers. In addition to good performance, the choice of material depends on long term stability (both physical and chemical) along with a good reproducibility and uniformity in fabrication. For this purpose we are investigating the properties of NbSi thin films and have already developed arrays of NbSi TES. NbSi is a well-known alloy for use in resistive thermometers. We present a low temperature characterization of the NbSi films on a 23-pixel array. In order to tune the critical temperature of the NbSi thermometers down to the desired range, we have to adjust the concentration of Niobium in the NbSi alloy. In this experiment, we set for a Niobium concentration of 15 percent, to be able to run tests at a convenient temperature larger than 300 miliKelvin. Tests are made using Helium4-cooled cryostats, 300 miliKelvin Helium3 mini-fridges, resistance bridge and a commercial SQUID with its readout circuit. Parameters being measured are: critical temperature, resistance, sharpness of the transition given by the alpha parameter and noise measurements. The multiplexing is also developed to prepare the final chain for noise measurements on 23 pixel bolometers array.

2D Analysis of the Effects of Geometry on the Response of High-$T_{\rm c}$ Superconductive Bolometric Detectors

We present a new approach for analytical modeling and calculating the response of high-T c superconductive transition edge sensors in a wide range of modulation frequencies for different configurations of the film patterns. The method used here is based on solving the heat transfer differential equation for two different time varying heat sources, which are related to the absorbed radiated power. The used method employs two-dimensional boundary conditions for describing meander-line patterned devices. The results from the applied method are in better agreement with those obtained from the frequency response measurements of the characterized samples, than the previously developed models. In addition, the method is capable of being used for analysing the effect of the device configurative parameters on its ultimate sensitivity. Therefore, it has also been applied to investigate the effects of changing track and spacing width, substrate thickness, and absorption coefficient of the absorber layer on the magnitude of bolometric response. In this calculation, the effect of surface absorption caused by the superconducting thin film and absorber layer, as well as bulk absorption in the depth of the substrate are considered simultaneously. Analytical results are presented and compared with previous analytical works and measured data from YBCO samples. Through extensive numerical calculations, we demonstrate that the responsivity of superconductor bolometers is a strong function of geometry, and there exists an optimal track width to spacing ratio of about 0.2.

An efficient phase-shifting scheme for bolometric additive interferometry

<i>Context. <i/>Most upcoming CMB polarization experiments will use direct imaging to search for primordial gravitational waves through the B-modes. Bolometric interferometry is an appealing alternative to direct imaging that combines the advantages of interferometry in terms of systematic effects handling and those of bolometric detectors in terms of sensitivity.<i>Aims. <i/>We calculate the signal from a bolometric interferometer in order to investigate its sensitivity to the Stokes parameters paying particular attention to the choice of the phase shifting scheme applied to the input channels in order to modulate the signal.<i>Methods. <i/>The signal is expressed as a linear combination of the Stokes parameter visibilities whose coefficients are functions of the phase shifts.<i>Results. <i/>We show that the signal to noise ratio on the reconstructed visibilities can be maximized provided the fact that the phase shifting scheme is chosen in a particular way called “coherent summation of equivalent baselines”. As a result, a bolometric interferometer is competitive with an imager having the same number of horns, but only if the coherent summation of equivalent baselines is performed. We confirm our calculations using a Monte-Carlo simulation. We also discuss the impact of the uncertainties on the relative calibration between bolometers and propose a way to avoid this systematic effect.

Polarization modulators for CMBPol

We review a number of technologies that are candidates for active polarization modulators for CMBPol. The technologies are appropriate for instruments that use bolometric detectors and include birefringent crystal-based and metal-mesh-based half-wave plates, variable phase polarization modulator, Faraday rotator, and photolithographed modulators. We also give a current account of the status of millimeter-wave orthomode transducers.

Implosion dynamics and radiation characteristics of wire-array Z pinches on the Cornell Beam Research Accelerator

Experimental results are presented that characterize the implosion dynamics and radiation output of wire-array Z pinches on the 1-MA, 100-ns rise-time Cornell Beam Research Accelerator (COBRA) [J. B. Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)]. The load geometries investigated include 20-mm-tall cylindrical arrays ranging from 4to16mm in diameter, and consisting of 8, 16, or 32 wires of either tungsten, aluminum, or Invar (64% iron, 36% nickel). Diagnostics fielded include an optical streak camera, a time-gated extreme-ultraviolet framing camera, a laser shadowgraph system, time-integrated pinhole cameras, an x-ray wide-band focusing spectrograph with spatial resolution, an x-ray streak camera, a load voltage monitor, a Faraday cup, a bolometer, silicon diodes, and diamond photoconducting detectors. The data produced by the entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output on COBRA. The highest x-ray peak powers (300–500GW) and total energy yields (6–10kJ) were obtained using 4-mm-diameter arrays that stagnated before peak current. Additional findings include a decrease in soft x-ray radiation prior to stagnation as the initial wire spacing was changed from 1.6mmto785μm, and a timing correlation between the onset of energetic electrons, hard x-ray generation, and the arrival of trailing current on axis—a correlation that is likely due to the formation of micropinches. The details of these and other findings are presented and discussed.

Colossal Magnetoresistive Manganite Based Fast Bolometric X-ray Sensors for Total Energy Measurements of Free Electron Lasers

Bolometric detectors based on epitaxial thin films of rare earth perovskite manganites have been proposed as total energy monitors for X-ray pulses at the Linac Coherent Light Source free electron laser. We demonstrate such a detector scheme based on epitaxial thin films of the perovskite manganese oxide material Nd{sub 0.67}Sr{sub x0.33}MnO{sub 3}, grown by pulsed laser deposition on buffered silicon substrates. The substrate and sensor materials are chosen to meet the conflicting requirements of radiation hardness, sensitivity, speed and linearity over a dynamic range of three orders of magnitude. The key challenge in the material development is the integration of the sensor material with Si. Si is required to withstand the free electron laser pulse impact and to achieve a readout speed three orders of magnitude faster than conventional cryoradiometers for compatibility with the Linac Coherent Light Source pulse rate. We discuss sensor material development and the photoresponse of prototype devices. This Linac Coherent Light Source total energy monitor represents the first practical application of manganite materials as bolometric sensors.