Cold-electron Bolometers Research Articles

Measurements of dichroic bow-tie antenna arrays with integrated cold-electron bolometers using YBCO oscillators.

We consider properties of dichroic antenna arrays on a silicon substrate with integrated cold-electron bolometers to detect radiation at frequencies of 210 and 240 GHz. This frequency range is widely used in cosmic microwave background experiments in space, balloon, and ground-based missions such as BICEP Array, LSPE, LiteBIRD, QUBIC, Simons Observatory, and AliCPT. As a direct radiation detector, we use cold-electron bolometers, which have high sensitivity and a wide operating frequency range, as well as immunity to spurious cosmic rays. Their other advantages are the compact size of the order of a few micrometers and the effect of direct electron cooling, which can improve sensitivity in typical closed-loop cycle 3He cryostats for space applications. We study a novel concept of cold-electron bolometers with two SIN tunnel junctions and one SN contact. The amplitude-frequency characteristics measured with YBCO Josephson Junction oscillators show narrow peaks at 205 GHz for the 210 GHz array and at 225 GHz for the 240 GHz array; the separation of these two frequency bands is clearly visible. The noise equivalent power level at an operating point in the current bias mode is 5 × 10-16 W/√Hz.

A Bunch of YBCO Josephson Generators for the Analysis of Resonant Cold-Electron Bolometers

The resonant properties of Cold-Electron Bolometers (CEBs) located at a 0.3 K cryostat plate are measured using a 50 μm long high-temperature YBa2Cu3O7−δ (YBCO) Josephson junction oscillator, placed on a 2.7 K plate of the same cryostat. For these purposes, a bunch of YBCO Josephson oscillators with various lengths of dipole antennas and overlapping generation bands has been developed and investigated in 50–500 GHz frequency range. Two setups of Josephson junction placement were compared, and as a result, various narrow-band receiving systems with CEBs have been measured, demonstrating the feasibility of the presented approach.

Efficiency of electron cooling in cold-electron bolometers with traps.

Electron on-chip cooling from the base temperature of 300 mK is very important for highly sensitive detectors operating in space due to problems of dilution fridges at low gravity. Electron cooling is also important for ground-based telescopes equipped with 3He cryostats being able to function at any operating angle. This work is aimed at the investigation of electron cooling in the low-temperature range. New samples of cold-electron bolometers with traps and hybrid superconducting/ferromagnetic absorbers have shown a temperature reduction of the electrons in the refrigerator junctions from 300 to 82 mK, from 200 to 33 mK, and from 100 to 25 mK in the idle regime without optical power load. The electron temperature was determined by solving heat balance equations with account of the leakage current, sixth power of temperature in the whole temperature range, and the Andreev current using numerical methods and an automatic fit algorithm.

Numerical modeling of a multi-frequency receiving system based on an array of dipole antennas for LSPE-SWIPE.

Here we present the results of a numerical modeling of mode composition in the constriction of the Large Scale Polarization Explorer-Short-Wavelength Instrument for the Polarization Explorer (LSPE-SWIPE) back-to-back horn. These results are used for calculating the frequency response of arrays of planar dipole antennas with cold-electron bolometers for 145, 210, and 240 GHz frequencies. For the main frequency channel (i.e., 145 GHz) we have a 45 GHz bandwidth. For the auxiliary frequency channels (i.e., 210 and 240 GHz) placed on the same substrate, we have bandwidths of 26 and 38 GHz, respectively. We performed some optimizations for cold-electron bolometers to achieve a photon noise-equivalent power of 1.1 × 10−16 W/Hz1/2. This was achieved by replacing one of two superconductor–insulator–normal tunnel junctions with a superconductor–normal metal contact.

Optimization of the Cold-Electron Bolometer and a Quasiparticle Cascade Amplifier in the Voltage-Biased Mode

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*NEP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phot</sub> .

Spectral Characteristics of the Double-Folded Slot Antennas with Cold-Electron Bolometers for the 220/240 GHz Channels of the LSPE Instrument

We present the results of the experimental and theoretical study of the resonant properties and noise of a single cell of a receiving system based on cold-electron bolometers (CEB) with a double-folded slot antenna and coplanar lines. The system was designed to receive signals at 220/240 GHz frequencies with a 5% bandwidth. In measurements, we used the samples of the double-folded slot antennas with slot lengths of 162 um and coplanar line lengths from 185 to 360 um. Measurements of the resonance properties of CEB located at 0.3 K cryostat plate were carried out using a generator based on a high-temperature YBCO Josephson junction located inside the same cryostat at 4 K plate. This arrangement made it possible to obtain smooth amplitude-frequency characteristics with a clearly defined peak of a 15–21 GHz bandwidth at different frequencies. Based on these results, 2-D array of double-folded slot antennas with CEBs as 220/240 GHz LSPE channel prototype was calculated.The absorption efficiency of the array has reached 81% and 77% for 220 and 240 GHz channels, respectively.

Responsivity and Noise Equivalent Power of a Single Cold-Electron Bolometer

We have developed a single-pixel capacitively coupled Cold-Electron Bolometer (CEB) and characterized it in the current-biased regime. The most attractive feature of the CEB is effective electron self-cooling of the absorber, which leads to a lower bolometer noise and higher dynamic range. The bolometer responsivity was measured by determining the voltage response to an applied power through the absorber from a heating current, modulated at frequencies from 35 Hz to 2 kHz. The optimum responsivity of 1.5 × 1010 V/W was measured at a modulation frequency of 35 Hz. The noise equivalent power (NEP) was subsequently obtained from the estimated bolometer noise voltage with respect to the measured bolometer responsivity. The NEP of better 2 × 10−18 W/Hz1/2 was obtained for modulation frequencies greater than 100 Hz. The background power and the bolometer time constant were also estimated from the experimental results. The photon-noise-limited operation of CEB will dominate for a signal power of 10 fW and higher at frequency 80 GHz and higher.

A Distributed Terahertz Metasurface with Cold-Electron Bolometers for Cosmology Missions

We developed and tested a 2D periodic array of cold-electron bolometers arranged into a wideband frequency selective metasurface that absorbs more than 70% of the incident power in the frequency range 100–800 GHz. The array had 10 × 10 unit cells, each containing four bolometers incorporated into a ring. The chip with bolometers was mounted on the back side of the silicon lens without a back-reflector. Preliminary experiments demonstrated voltage responsivity as high as 109 V/W for the current-biased series array. Simulation of the noise performance shows realization of background noise-limited performance with NEPtot &lt; NEPphot for the optical power load P0 &gt; 15 pW. Results of numerical simulation made for the unit cell of the array are presented together with the equivalent diagram based on lumped network elements. The unit cell also was developed numerically to operate in two radiation modes.

Record electron self-cooling in cold-electron bolometers with a hybrid superconductor-ferromagnetic nanoabsorber and traps

The Cosmic Microwave Background (CMB) radiation is the only observable that allows studying the earliest stage of the Universe. Radioastronomy instruments for CMB investigation require low working temperatures around 100 mK to get the necessary sensitivity. On-chip electron cooling of receivers is a pathway for future space missions due to problems of dilution fridges at low gravity. Here, we demonstrate experimentally that in a Cold-Electron Bolometer (CEB) a theoretical limit of electron cooling down to 65 mK from phonon temperature of 300 mK can be reached. It is possible due to effective withdrawing of hot electrons from the tunnel barrier by double stock, special traps and suppression of Andreev Joule heating in hybrid Al/Fe normal nanoabsorber.

Response of a Cold-Electron Bolometer on THz Radiation from a Long YBa2Cu3O7−δ Bicrystal Josephson Junction

The response of the Cold-Electron Bolometers (CEBs), integrated into a 2-D array of dipole antennas, has been measured by irradiation from YBa2Cu3O7−δ (YBCO) 50 μm long Josephson junction into the THz region at frequencies from 0.1 to 0.8 THz. The possibility of controlling the amplitude-frequency characteristic is demonstrated by the external magnetic field in the traveling wave regime of a long Josephson junction. The YBCO junction has been formed on the bicrystal Zr1−xYxO2 (YSZ) substrate by magnetron sputtering and etching of the film. CEBs have been fabricated using an Al multilayer structure by a self-aligned shadow evaporation technique on Si substrate. Both receiver and oscillator have been located inside the same cryostat at 0.3 K and 2.7 K plates, respectively.

Wideband Double-Polarized Array of Cold-Electron Bolometers for OLIMPO Balloon Telescope

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.

Cold-Electron Bolometer as a 1-cm-Wavelength Photon Counter

We investigate theoretically the possibility of using the cold-electron bolometer (CEB) as a counter for 1-cm-wavelength (30-GHz) photons. To reduce the flux of photons from the environment that interact with the detector, the bath temperature is assumed to be below 50 mK. At such temperatures, the time interval between two subsequent photons of 30 GHz that hit the detector is more than 100 h, on average, for a frequency window of 1 MHz. Such temperatures allow the observation of the physically significant photons produced in rare events, such as axion conversion (or Primakoff conversion) in a magnetic field. We present the general formalism for the detector's response and noise, together with numerical calculations for proper experimental setups. We observe that the current-biased regime is favorable due to lower noise and allows for photon counting at least below 50 mK. For the experimental setups investigated here, the voltage-biased CEBs may also work as photon counters but with less accuracy and, eventually, may require smaller volumes of the normal-metal island.

Electromagnetic radiation detectors based on Josephson junctions: Effective Hamiltonian

We theoretically analyze two setups of low energy single-photon counters based on Josephson junctions (JJ). For this, we propose two simple and general models, based on the macroscopic quantum tunneling formalism (MQT). The first setup is similar to the photon counter based on the "cold electron bolometer" (CEB), where the JJ replaces the CEB in the center of the superconducting antenna. In the second setup, the JJ is capacitively coupled to the antenna. We derive the Hamiltonians for the two setups and we write the Schr\"odinger equations taking into account both, the antenna and the JJ. The quantum particles of the MQT models are in two-dimensional potential landscapes, which are parabolic along one direction and may have the form of a washboard potential along another direction. Such a potential landscape has a series of local minima, separated by saddle points. If the particle is prepared in the initial state in the metastable "ground state" of a local minimum, then the photon absorption causes it to jump into an excited state. If the excitation energy is bigger than the potential barrier seen by the quantum particle (the difference between the "ground state" and the saddle point), the photon is detected. The models are simple and allow us to do mostly analytical calculations. We show that the two setups are equivalent form the MQT point of view, since one Hamiltonian can be transformed into the other by changes of variables. For typical values of the JJ and antenna parameters, the setups may work as counters of photons of wavelengths up to 1 cm, at least.

A Study of a Narrow-Band Receiving System of Cold-Electron Bolometers for the 220 and 240 GHz Channels using an Oscillator Based on the High-Temperature YBCO Superconductor

We present the results of theoretical and experimental studies of the resonant properties of a single cell of a receiving system based on cold-electron bolometers (CEBs) with a double-slot antenna and curved coplanar lines, which is intended for receiving a signal in the range 220–240 GHz with a bandwidth of 5%. The resonant properties of a CEB located on the cryostat plate with a temperature of 0.3 K, are measured using an oscillator based on high-temperature superconductor (HTS) of yttrium barium copper oxide (YBCO), placed inside the same cryostat on a plate with a temperature of 4 K, which allows one to obtain smooth amplitude-frequency characteristics.

Photon-noise-limited cold-electron bolometer based on strong electron self-cooling for high-performance cosmology missions

Bolometers for balloon and space missions have seen extensive development because of their capacity to test primordial conditions of the Universe. The major improvements consist in lowering the operating temperature to reach higher sensitivities. Here we show that an array of 192 cold-electron bolometers (CEB) demonstrates photon-noise-limited operation at the cryostat temperature of 310 mK due to effective self-cooling of the absorber. The direct electron cooling of nanoabsorber placed between normal metal - insulator - superconductor junctions has considerably higher efficiency than indirect cooling through massive suspended platform, that requires overcoming a weak electron-phonon conductance. The electron temperature reached 120 mK without a power load, and 225 mK with a 60 pW power load with self-noise of a single bolometer below 3cdot 1{0}^{-18} {rm{W}} {{rm{Hz}}}^{-1/2} at a 0.01 pW power load. This bolometer works at electron temperature less than phonon temperature, thus being a good candidate for future space missions without the use of dilution refrigerators.

A dual-band cold-electron bolometer with on-chip filters for the 220/240 GHz channels of the LSPE instrument

We are developing multi-chroic double-slot antenna with cold-electron Bolometer (CEB) on-chip filters for the 220/240 GHz interstellar dust monitoring channels of the LSPE–SWIPE experiment. For this goal, we used a narrowband double-slot resonant antenna with CEBs connected by coplanar lines. The simulations show that we have achieved 5% bandwidth for 220 GHz and 5.5% bandwidth for 240 GHz in our numeric modeling for the single cells. A series array of unit cells using double-slot design and coplanar lines with CEBs shows proper frequency selection. Estimations of the noise properties of the CEB arrays in a voltage-biased mode with the SQUID readout show photon-noise limited operation for the optical power load of 6 pW for channel 220 GHz and 20 pW for channel 240 GHz.

Absorption and cross-talk in a multipixel receiving system with cold electron bolometers

In the article we compare two types of receiving pixels, based on cold electron bolometers, fabricated with different technology. Both pixels are designed for the 350 GHz frequency channel of the OLIMPO project. The first type of pixel is fabricated on a thin Si substrate, using an etching procedure, and the other on thick non-etched substrate. The individual antenna systems have been designed for both types of pixels. The investigation of absorption efficiency, amplitude–frequency characteristics and cross-talk has shown that the etched substrate has the highest absorption efficiency of 60% in the required frequency band and the lowest cross-talk of 0.2%. While the unetched 380 μm substrate leads to a slightly smaller absorption efficiency and a slightly larger cross-talk, it allows for rigid structures and the exclusion of complex technological operations.

Multichroic seashell antenna with internal filters by resonant slots and cold-electron bolometers

We have developed and realized a novel multichroic seashell antenna with internal bandpass filters by resonant slots and cold-electron bolometers (CEB). Slots and CEBs are connected by coplanar waveguides (CPW) instead of microstrip lines to realize the most reliable single-layer technology. The internal resonance is organized by a series resonance of slots with CPW and capacitances of superconductor/insulator/normal (SIN) tunnel junctions. In contrast, a conventional multichroic pixel consists of a wideband sinuous antenna coupled to TES detectors by long microstrip lines with overlap and external on-chip filters for different frequency bands. A common problem with a conventional multichroic pixel is that the beam width is frequency dependent for different frequency bands. Besides that, this system with external filters is quite large and includes long microstrip lines with unavoidable overlap and rater high losses. The multichroic seashell antenna with internal resonances avoids all these problems. The main advantage of this antenna is an opportunity to tune separate pairs of phased slots for each frequency band independently. We used pairs of λ/2 slots for 75 and 105 GHz, connected by CPW to CEBs. The connection of CPW to slots was shifted closer to the end of slots for proper RF matching. Each CEB included two SIN junctions and an absorber. SIN junctions had capacitances of 77 and 67 fF. Wave impedance of the antenna was near 50 Ohm and resistance of the absorber was matched to this value. RF testing was done at 314 mK irradiating this chip by frequency sweep of a generator from 78–118 GHz. The response curves have shown clear resonances around 75 and 105 GHz with a quality factor around 5. These experiments confirmed that the seashell antenna with the internal filters by resonant slots and CEBs could effectively be used for creating multiband elements.

Multifrequency seashell antenna based on resonant cold-electron bolometers with kinetic Inductance Nanofilters for CMB measurements

A novel type of the seashell slot antenna with internal filters by the capacitance of resonant cold-electron bolometers (RCEB) and kinetic inductance of the NbN superconducting nanostrip has been realized for multifrequency pixels. Seashell antenna gives the opportunity to connect opposite slots by coplanar waveguides (CPW) instead of microstrip lines (MSL). A conventional multifrequency pixel combines a wideband antenna and narrowband filters with long microstrip lines with unavoidable losses and overlaps. Another problem is the frequency dependent beam width due to a fixed pixel diameter for multiple frequencies. The main advantage of the seashell antenna with nano-filters is independent tuning of the separate pairs of slots for each frequency avoiding frequency dependence of the beam width. We used λ/2 slots for 75 and 105 GHz, feeding by CPW near the end of slots for RF matching. Each RCEB includes two SIN (Superconductor-Insulator-Normal) tunnel junctions with a nano-absorber and NbN kinetic inductance of 450 or 310 pH. SIN junctions had capacitances of 9.3 and 7.2 fF and absorber matched to a wave impedance of the antenna near 50 Ohm. Kinetic inductance value was estimated at the level of 35 pH/sq. RF testing was done at 300 mK irradiating this chip by sweep generator from 60 to 120 GHz. The response curves showed clear resonances at 75 and 105 GHz with a quality factor of 10 and 7. These experiments confirm that the seashell antenna with the internal RCEB filters can be used for frequency selection in compact multiband pixels.

Realization of the Resonant Cold-Electron Bolometer With a Kinetic Inductance Nanofilter for Multichroic Pixels

A novel type of the resonant cold-electron bolometer (RCEB) has been realized for multichroic pixels. The internal resonance is organized by a kinetic inductance of the NbN superconducting nanostrip and a capacitance of the superconductor-insulator-normal (SIN) tunnel junctions. The basic idea of a multichroic system is to combine a wideband antenna and narrow-band RCEBs. We used a single Lambda slot with two RCEBs for 75 and 105 GHz, placed in the middle. Each RCEB included two SIN junctions with absorber connected to NbN kinetic inductance of 420 and 240 pH. SIN junctions had capacitances of 11 and 8 fF. Wave impedance of the slot antenna was near 15 Ω and resistance of the absorber was matched to this value. Matching of antenna with an external system was done by placing Si lens on the back side of a Si substrate. RF testing was done at 300 mK irradiating this chip by sweep generator from 60 to 120 GHz. The response curves showed clear resonances at 75 and 105 GHz with quality factor of 10 and 7. Kinetic inductance value was estimated at the level of 35 pH/sq. These experiments confirmed that the RCEB can be effectively used to create multiband elements.