Bolometric Response Research Articles

Resonator-bolometer theory, microwave read out, and kinetic inductance bolometers

Kinetic inductance bolometers and calorimeters, each consisting of a kinetic inductance device suspended on a membrane and embedded in a resonant circuit, are being developed for applications such as planetary science, climate science, and X-ray spectroscopy. Arrays of these resonator-bolometers, each with a unique resonance frequency, are coupled to a single feedline, allowing many bolometers or calorimeters to be multiplexed using microwave read out. We derive coupled linear differential equations describing resonator-bolometers and means for calculating responses to signal and noise sources. By employing the bolometer matrix formalism, the model compactly describes the effects of demodulation, detuning, electrothermal feedback, resonator to feedline coupling, and bolometer sensitivity to changes in temperature and bias current. Based on this theory, estimates for the bolometer response to phonon noise, Johnson noise, and microwave bias quasiparticle generation noise are derived. The model is represented in terms of accessible parameters, most of which are measurable using a network analyzer. It is applicable to other types of devices such as dielectric bolometers or alternating current biased transition edge sensors and is readily extendible to more complex bolometers or to unsuspended kinetic inductance devices.

Carbon nanotube microbolometers on suspended silicon nitride via vertical fabrication procedure

We report on carbon nanotube membrane microbolometers, operating uncooled in the near-infrared (IR) and mid-IR band, with speed of 10 ms and responsivity of several kV/W. The microbolometers were fabricated using a vertical process on a thin suspended silicon nitride film for thermal isolation. The measured detectivity was ∼5.5 × 106 cm Hz1/2 W−1 at 40 Hz. The broadband spectral responses measured at room temperature over the entire band of the IR illumination source are characteristic of bolometric response. These results are indicative of the potential of this platform for uncooled IR sensing and thermal imaging. The measured device noise indicated a relatively strong 1/f contribution, which is common of carbon nanotube devices operated in atmospheric conditions. The observed responses suggest, however, that oxygen adsorption/desorption reported by some researchers did not play a significant role in these devices.

Nonlinear vs. bolometric radiation response and phonon thermal conductance in graphene-superconductor junctions

Graphene is a promising candidate for building fast and ultra-sensitive bolometric detectors due to its weak electron-phonon coupling and low heat capacity. In order to realize a practical graphene-based bolometer, several important issues, including the nature of radiation response, coupling efficiency to the radiation and the thermal conductance need to be carefully studied. Addressing these issues, we present graphene-superconductor junctions as a viable option to achieve efficient and sensitive bolometers, with the superconductor contacts serving as hot electron barriers. For a graphene-superconductor device with highly transparent interfaces, the resistance readout in the presence of radio frequency radiation is dominated by non-linear response. On the other hand, a graphene-superconductor tunnel device shows dominantly bolometric response to radiation. For graphene devices fabricated on SiO2 substrates, we confirm recent theoretical predictions of T2 temperature dependence of phonon thermal conductance in the presence of disorder in the graphene channel at low temperatures.

Analysis of bolometer operation near the superconducting transition edge using microwave readout

The results of pioneering experiments on using a new method of microwave recording the bolometric response from a metal film near its superconducting transition edge are analyzed. Experiments are carried out at 4.5 K using a thin-film niobium absorber with a critical temperature of 6.7 K. The validity of the adopted electrodynamic model is confirmed. The chip contains a miniature antenna tuned to approximately 600 GHz and integrated into a planar resonator with a frequency of 6 GHz, which is weakly coupled with a pump line. Based on the experimental and model data, the presence of electrothermal feedback is shown, stability criteria are found, and I–V characteristics at microwaves are obtained. Bulk experimental samples with an absorber measuring 5 μm × 2.5 μm × 15 nm are fabricated with optical photolithography. At an amplifier channel noise of 3 K, the optical sensitivity of a prototype receiver can be expected at a level of 10−15 W/Hz1/2.

PACS photometer calibration block analysis

The absolute stability of the PACS bolometer response over the entire mission lifetime without applying any corrections is about 0.5% (standard deviation) or about 8% peak-to-peak. This fantastic stability allows us to calibrate all scientific measurements by a fixed and time-independent response file, without using any information from the PACS internal calibration sources. However, the analysis of calibration block observations revealed clear correlations of the internal source signals with the evaporator temperature and a signal drift during the first half hour after the cooler recycling. These effects are small, but can be seen in repeated measurements of standard stars. From our analysis we established corrections for both effects which push the stability of the PACS bolometer response to about 0.2% (stdev) or 2% in the blue, 3% in the green and 5% in the red channel (peak-to-peak). After both corrections we still see a correlation of the signals with PACS FPU temperatures, possibly caused by parasitic heat influences via the Kevlar wires which connect the bolometers with the PACS Focal Plane Unit. No aging effect or degradation of the photometric system during the mission lifetime has been found.

The Herschel-PACS photometer calibration

This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ∼2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF ν = λF λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.

Photothermal response in dual-gated bilayer graphene.

The photovoltaic and bolometric photoresponse in gapped bilayer graphene was investigated by optical and transport measurements. A pulse coincidence technique at 1.5 μm was used to measure the response times as a function of temperature. The bolometric and photovoltaic response times were found to be identical implying that the photovoltaic response is also governed by hot electron thermal relaxation. Response times of τ ∼ 100-20 ps were found for temperatures from 3-100 K. Above 10 K, the relaxation time was observed to be τ = 25 ± 5 ps, independent of temperature within noise.

Junction array carbon nanotube bolometer

Vertically aligned arrays of multi-walled carbon nanotubes (MWNT forests) irradiated with low-intensity near-infrared laser exhibited bolometric response that became significant with decreasing temperature down from room to about 84 K. High responsivity of 42 V/W with signal bandwidth of about 2600 Hz was observed in the region with a surprisingly small temperature coefficient of resistance. This fact along with peculiar current dependences of material differential photoresistance can be explained by lifting Coulomb blockade in carbon nanotube junctions irradiated with light. A combination of significant bolometric response and nonlinear electrical transport are believed to be characteristic features of the nanostructured junction array system. Investigated material also revealed quite substantial noise with equivalent power of 3 * 10−6 WHz−½ that can be reduced by optimization of nanotube junction network in the forest structure.

Graphene terahertz uncooled bolometers

We propose the concept of a terahertz (THz) uncooled bolometer based on n-type and p-type graphene layers (GLs), constituting the absorbing regions, connected by an array of undoped graphene nanoribbons (GNRs). The GLs absorb the THz radiation with the GNR array playing the role of the barrier region (resulting in nGL-GNR-pGL bolometer). The absorption of the incident THz radiation in the GL n- and p- regions leads to variations of the effective temperature of electrons and holes and of their Fermi energy resulting in the variation of the current through the GNRs. Using the proposed device model, we calculate the dark current and the bolometer responsivity as functions of the GNR energy gap, applied voltage and the THz frequency. We demonstrate that the proposed bolometer can surpass the hot-electron bolometers using traditional semiconductor heterostructures.

Few layer graphene to graphitic films: infrared photoconductive versus bolometric response

We report a comparative study of the performance of infrared (IR) photoconductive and bolometric detectors fabricated from few layer graphene (FLG) to graphitic films obtained by different methods. FLG films grown directly on insulating substrates with the aid of residual hydrocarbons and polymethylmethacrylate (PMMA) carbon sources show an IR photoresponse of 73% which is far higher compared to the FLG films (6-14%) obtained by CVD and Scotch tape methods. The photoconductive nature of FLG films is due to generation of photoexcited charge carriers. On the other hand, the photoresponse of the bulk graphitic films is bolometric in nature where the resistance changes are due to thermal effects. The IR photoresponse from these graphitic films is correlated with the Raman peak intensities which are very sensitive to the nature of the FLG.

Semiconducting YBaCuO films grown on silicon substrates: IR room temperature sensing and fast pyroelectric response

YBa2Cu3O6+x (YBCO) oxides, well known as superconductors for x > 0. 5, are semiconductors (SC) for lower oxygen content. SC films DC sputtered at 150 °C in amorphous form (a-YBCO) exhibited a temperature coefficient of resistance competitive with other bolometric sensing materials. Such deposition conditions are highly beneficial to integrate a radiation detector on a silicon chip bearing already processed readout electronics. IR detector structures have been processed: simple planar or more advanced metal/a-YBCO/metal trilayers. IR response was investigated at 850 nm as a function of the modulation frequency. The planar structure exhibited a regular bolometric response below 100 Hz, then a pyroelectric high-pass response up to 100 kHz. The trilayer device only exhibited the pyroelectric behavior up to 100 kHz . In the pyroelectric regime, detectivity values peaked above 2×108 cm Hz½/W with time constants in the μs range, under both DC biased and unbiased conditions.

Terahertz response of thin-film YBCO bolometers

The bolometric response of high-temperature thin-film YBCO superconducting detectors to an electromagnetic radiation with a frequency of 2.5 THz is measured for the first time. The minimum value of the noise-equivalent power of the detectors is 3.5 × 10−9 W/\( \sqrt {Hz} \). The feasibility of further increasing the sensitivity of the detectors is discussed.

Distributed bolometric effect in optical antennas and resonant structures

Universidad Autonoma de San Luis Potosi, Coordinacion para la Innovacion y,Aplicacion de la Ciencia y la Tecnologia, San Luis Potosi, Mexico 78210Abstract. Nanoantennas coupled to nanobolometers have been used as detectors of opticalradiation. They are typically manufactured using two different materials: one for the nano-antenna and another for the nanobolometer. However, those metals used to fabricate nano-antennas also present a bolometric response. Therefore, antenna-coupled detectors using thebolometriceffectdistributedalongthedevicewerecomparedwiththeresultspreviouslyreportedfor nanobolometers coupled with dipole antennas in the infrared regime. We modeled therelevant physical mechanisms and also simulated the simple case of a dipole antenna usinga multi-physics computational tool. The simulation results were compared with experimentalresults. The advantage in performance when using a dedicated material to enhance the bolo-metric effect, is balanced with the easiness of the fabrication of resonant structures involvingonly one material where the bolometric effect is distributed along the device.

Bolometric response in graphene based superconducting tunnel junctions

We fabricate graphene-TiOx-aluminum tunnel junctions and characterize their radio frequency response. Below the superconducting critical temperature of aluminum and when biased within the superconducting gap, the devices show enhanced dynamic resistance which increases with decreasing temperature. Application of radio frequency radiation affects the dynamic resistance through electronic heating. The relation between the electron temperature rise and the absorbed radiation power is measured, from which the bolometric parameters, including heat conductance, noise equivalent power, and responsivity, are characterized.

A weakly coupled semiconductor superlattice as a potential for a radio frequency modulated terahertz light emitter

The bolometer response to THz radiation from a weakly coupled GaAs/AlGaAs superlattice biased in the self-oscillations regime has been observed. The bolometer signal is modulated with the frequency equal to the fundamental frequency of superlattice self-oscillations. The frequency spectrum of the bolometer signal contains higher harmonics whose frequency is a multiple of fundamental frequency of self-oscillations.

Achieving High Mid‐IR Bolometric Responsivity for Anisotropic Composite Materials from Carbon Nanotubes and Polymers

AbstractAn anisotropic carbon nanotube (CNT)‐polymer composite for bolometric applications in the mid‐IR spectral range (2.5–20 μm) is studied. Composite alignment in conjunction with non‐uniform distribution of CNTs in the polymer matrix allows for a significant enhancement of the temperature coefficient of resistance (0.82% K−1) with respect to uniform composite (0.24% K−1). As a result a responsivity of ≈ 500 V W−1 is reached, which is the highest for CNT‐based bolometers reported to date. Such remarkable optical and thermal characteristics are explained in terms of fluctuation tunneling theory taking into account the composite anisotropy and the gradient of the CNT concentration. Flatness of the photoresponse in the broad spectral mid‐IR range and enhanced responsivity provide a great potential for the use of such novel composite for applications in IR spectroscopy and thermal imaging.

Effect of Substrate Thickness on Responsivity of Free-Membrane Bolometric Detectors

The effect of substrate thickness and its Debye temperature on the bolometric response of the freestanding-membrane type of superconductor transition-edge detectors is investigated. The investigation is based on the calculation of the variation of the specific heat per unit volume and the heat conductivity using the finite-size scaling method for different Debye temperatures and micron size thickness of substrate. We also calculated the heat capacity and time constant for various materials with Debye temperatures in the range of 600-1400 K. The calculated results are compared with previously reported response values obtained theoretically and experimentally for the thermal-based infrared (IR) detectors. The IR response versus substrate thickness of these types of devices for different modulation frequencies is also presented. This inspected response at low thicknesses of substrate shows anomalistic behavior with respect to the previously reported results of response analyses. Here, we also obtained the optimized substrate thickness and Debye temperatures for maximum responsivity of these types of devices.

Radiofrequency dielectric properties of amorphous semiconducting Y–Ba–Cu–O oxide thin films for bolometric detection

We report the study of dielectric properties of amorphous semiconducting YBCO thin films measured in a broad frequency range, from 40Hz to 2GHz and in the 210 to 430K temperature range, using a coaxial discontinuity technique. At all temperatures, dielectric permittivity and conductivity spectra exhibit typical features of dielectric relaxation processes. A first relaxation at low frequency (300Hz–2kHz), observed only at high temperature, might be attributed to interfacial effects. Polarization in the grains of the YBCO thin films could lead to the second relaxation observed at higher frequency (800Hz–660kHz). The relaxation frequencies increase with temperature and follow a thermally activated behavior of the Arrhenius-type. Optical near-infrared response of YBCO bolometers exhibits a corner frequency around 40kHz. Above this frequency, the thermal diffusion is localized inside the YBCO thin film. This frequency is in good agreement with the relaxation frequency attributed to YBCO grains in the thin film, i.e. around 40kHz at 300K.

Bolometer with high-frequency readout for array applications

A new method of bolometer response readout is proposed, whereby a resistive temperature sensor with a miniature antenna for terahertz range is integrated into a planar terahertz-range resonator weakly coupled to a pumping line, in which the amplitude of a gigahertz signal depends on the sensor resistance that changes under the action of a terahertz radiation received by the antenna. The proposed method can be used to create detector arrays with the number of elements above 1000, which implement the frequency multiplexing method and require only one physical channel of amplification for the gigahertz range. Results of numerical simulations show that, using nanosized transition-edge sensors operating at 300 mK and an amplification channel with 3 K noise temperature, it is possible to achieve a record high sensitivity of 1.6 × 10−19 W/Hz1/2.

Relationships Between Complex Impedance, Thermal Response, and Noise in TES Calorimeters and Bolometers

Complex impedance measurements are widely used to characterize superconducting transition edge sensors (TESs) in bolometers and microcalorimeters. Typically, models are fit to impedance data to find parameters which pertain to the performance of these detectors. After the parameters are determined, the models are then used to compute the response and noise of these devices. In this paper, we present general relationships between the measured impedance, the thermal response to power in the TES, and noise. We describe a method for measuring αI and βI of the superconducting phase transition, which does not require model fitting. We find bolometer response is determined from the impedance provided that the absorber is strongly coupled to the TES electron system. We also demonstrate how to calculate upper and lower limits on the noise directly from the impedance data without modeling. Additionally, the relations can be used to check the validity of the models and to understand what information can and cannot be obtained from measurements of impedance, response, and noise.