This review presents an overview of the thermal properties of mesoscopic structures. The discussion is based on the concept of electron energy distribution, and, in particular, on controlling and probing it. The temperature of an electron gas is determined by this distribution: refrigeration is equivalent to narrowing it, and thermometry is probing its convolution with a function characterizing the measuring device. Temperature exists, strictly speaking, only in quasiequilibrium in which the distribution follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur due to slow relaxation rates of the electrons, e.g., among themselves or with lattice phonons. Observation and applications of nonequilibrium phenomena are also discussed. The focus in this paper is at low temperatures, primarily below $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where physical phenomena on mesoscopic scales and hybrid combinations of various types of materials, e.g., superconductors, normal metals, insulators, and doped semiconductors, open up a rich variety of device concepts. This review starts with an introduction to theoretical concepts and experimental results on thermal properties of mesoscopic structures. Then thermometry and refrigeration are examined with an emphasis on experiments. An immediate application of solid-state refrigeration and thermometry is in ultrasensitive radiation detection, which is discussed in depth. This review concludes with a summary of pertinent fabrication methods of presented devices.

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Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

This review describes bolometric detectors for infrared and millimeter waves. The introduction sketches the history of modern bolometers, indicates how they fit into the more general class of thermal detectors, and describes the types of applications for which they are the optimum solution. Section I is a tutorial introduction to the elementary theories of bolometer response, of thermal radiation, and of bolometer noise. Important results are derived from the laws of thermal physics in the simplest possible way. The more rigorous theories of bolometer response and noise that are required for quantitative understanding and optimization are then summarized. This material is intended to provide the background required by workers who wish to choose the appropriate bolometer technology for a given measurement, or to evaluate a novel technology. Section II, then describes the various components of an efficient bolometer and gives details of the fabrication and performance of modern bolometers. This discussion f...

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Bolometers for infrared and millimeter waves

Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of metallic optical antennas based on the background of both well-developed radiowave antenna engineering and plasmonics. In particular, we discuss the role of plasmonic resonances on the performance of nanoantennas and address the influence of geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.

https://iopscience.iop.org/article/10.1088/0034-4885/75/2/024402/pdf

Nanoantennas for visible and infrared radiation.

Superconducting detectors will play an increasingly significant role in astrophysics, especially at millimeter through far-IR wavelengths, where the scientific opportunities include key problems in astronomy and cosmology. Superconducting detectors offer many benefits: outstanding sensitivity, lithographic fabrication, and large array sizes, especially through the recent development of multiplexing techniques. This paper describes the scientific opportunities, the basic physics of these devices, the techniques for radiation coupling, and reviews the recent progress in direct detectors, such as transition-edge bolometers, and the work on tunnel junction (superconductor-insulator-superconductor) and hot-electron mixers.

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Superconducting detectors and mixers for millimeter and submillimeter astrophysics

We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition‐edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and a rf signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (<0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (if) response. The mixer offers ≊4 GHz if bandwidth, ≊80 Ω rf resistive impedance, good match to the if amplifier, and requires only 1–20 nW of local oscillator power. The upper rf frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double‐sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.

Superconducting terahertz mixer using a transition-edge microbolometer

We have extended the high efficiency of lithographic antennas to mid‐infrared wavelengths. Pattern measurements made at 9.5 μm wavelength on a 65°, self‐complementary, spiral antenna exhibit a ratio of response to orthogonal linear polarizations of 1.35 dB, a beamwidth of 85° (3 dB full width), a directivity of 8.2 dB, and surprisingly, a close resemblance to the theoretical pattern for a 65° spiral in free space. Direct detection measurements made with an ambient temperature blackbody source yield an antenna efficiency of 52±7%, when corrected for incomplete filling of the antenna beam by the source, at a mean effective wavelength of 19 μm.

Lithographic spiral antennas at short wavelengths

Extremely sensitive far-infrared detectors suitable for both direct detection and heterodyne applications, based on mu m-sized thin films with thickness less than a superconducting penetration depth are possible. The penetration depth of such a film, and therefore its inductance, varies with temperature and with quasiparticle population (described by an effective temperature T*), resulting in both bolometric and nonequilibrium photoinductive responses. Incident radiation is coupled into the small-area kinetic inductor by a lithographic antenna, and the resulting inductance changes are amplified and converted to a voltage signal by an integrated microstrip DC SQUID. The device is sensitive because, unlike junction-based devices with large capacitive reactances, the kinetic inductor is naturally well matched to the antenna impedance at the far-IR frequency ( nu >2 Delta /h) and to the preamplifier (SQUID) impedance at microwave or video frequencies ( nu <<2 Delta /h). The best kinetic inductor materials are those with low electronic mean free path, large penetration depth, and high critical current density. Thus, common magnet alloys such as NbTi are the natural choice for liquid-He temperature operation. A detailed analysis predicts a (phonon-limited) NEP of 4*10/sup -17/ W/ square root Hz for a bolometer with an iridium kinetic inductor operated at 0.1 K. A heterodyne noise temperature of 2250 K (single-sideband) at 3 THz, with a 200-MHz bandwidth, is predicted for a Nb-Ti mixer operated at 4 K.

Far-infrared kinetic-inductance detectors

A bolometer that is based on a differential thermometer that senses temperature changes through changes in the kinetic inductance of a superconducting thin film is being developed. The temperature transducer is an inductance bridge patterned as an integrated circuit on a 1-cm/sup 2/ Si substrate. Two inductors from opposite arms of the bridge are patterned on a 2-mm/sup 2/ thermally isolated Si island which is supported by a 9- mu m thick Si:B membrane. The bridge is excited with audio-frequency current, and the bridge imbalance is detected with a commercial DC SQUID amplifier. The bridge is balanced by applying power to the thermally isolated island. This thermometer is the sensor for a prototype radiometer that will provide an absolute measure of IR power. The radiometer, which is designed for a NEP of about 10/sup -11/ W/ square root Hz, is intended to measure the spectrally dispersed power of a 300-K black body. This absolute radiometer is being developed for use at the Low Background Infrared (LBIR) Facility at NIST, Gaithersburg, MD. The noise floor of the temperature transducer for the radiometer has been measured to be 0.7 pW for a 100-s integration time. This is approximately 150 times lower noise than that of the commercial absolute radiometer currently used at the LBIR facility.

Superconducting kinetic inductance radiometer

A two‐dimensional, time‐dependent analysis is made of array‐compatible bolometers directly deposited onto a single substrate. It applies both to antenna‐coupled and surface‐absorbing configurations. Unlike previous spherically symmetric treatments, it allows analysis of thermal crosstalk between closely neighboring detectors, and of the effects of finite substrate thickness. In a closely packed array of surface‐absorbing detectors, thermal crosstalk generally degrades the array’s resolution more severely than optical (diffractive) crosstalk. Diffraction‐limited resolution with surface‐absorbing detectors is possible only by sacrificing either thermal resistance, and therefore sensitivity, or filling factor. With a minimum substrate thickness of Lmin, a closely packed, diffraction‐limited array is limited to a thermal resistance of Zt≤0.08(κLmin)−1, where κ is the thermal conductivity of the substrate. An array of antenna‐coupled bolometers is not subject to this limitation since the thermally and opticall...

J. E. Sauvageau

Papers

Lithographic spiral antennas at short wavelengths

Far-infrared kinetic-inductance detectors

Superconducting kinetic inductance radiometer

Two‐dimensional analysis of microbolometer arrays

Far-Infrared Kinetic-Inductance Detectors | NIST