arXiv subjects

Boris S. Karasik

Publications and source records attributed to Boris S. Karasik.

13 recordsLinked to original sources

arXiv2026

Enhancing Conversion Gain in HEB Mixers using Negative Differential Resistance

This work investigates how negative differential resistance (NDR) can be utilized to enhance conversion gain in superconducting niobium nitride (NbN) hot-electron bolometer (HEB) mixers. Conventional HEB operation avoids NDR regions due to parasitic oscillations caused by interactions between thermal inertia and bias-line reactance. Recent experimental results show that reducing the bias-T inductance suppresses these oscillations and enables stable biasing within the NDR regime, thereby increasing the mixer conversion gain beyond levels achievable under positive differential resistance (PDR) bias. Using a lumped thermal-electrical model, we interpret these experimental findings, derive stability conditions for NDR-biased operation, and predict the future performance limits achievable through optimized bias circuit designs. Our results indicate that further reductions in bias inductance, combined with appropriate load-line conditions, could yield several decibels of additional gain while maintaining practical IF bandwidths.

physics.ins-det↗

arXiv2026

Hot-electron bolometric mixer with negative differential resistance

We demonstrate that the conversion gain of a superconducting hot-electron bolometer (HEB) mixer can be increased by biasing the device within the negative differential resistance (NDR) region of its current-voltage characteristic. Although NDR biasing has historically been avoided due to MHz-range resistive oscillations, we show that these oscillations arise from an LC resonance formed by the bias-T inductance and the effective thermal capacitance of the HEB. By applying stability criteria analogous to those developed for tunnel diodes, we redesigned the embedding circuit to suppress this resonance and achieve stable NDR operation. Direct measurements using two monochromatic 2.5-THz sources confirm the predicted gain enhancement. These results establish NDR biasing as a viable method for improving HEB mixer performance and motivate further studies of noise behavior and circuit optimization.

physics.ins-det↗

arXiv2026

Lumped-Element Model of THz HEB Mixer Based on Sputtered MgB2 Thin Film

We present a comprehensive analysis and experimental study of THz hot-electron bolometer (HEB) mixers made from 40-nm-thick sputtered magnesium diboride (MgB2) thin films on high-resistivity silicon substrates. Using a lumped-element bolometric model, we achieve strong quantitative agreement with measurements of conversion gain, noise temperature, and local-oscillator (LO) coupling to the HEB devices. Our analysis shows that the sensitivity of current HEB devices is primarily limited by on-chip optical losses, with both Johnson and thermal-fluctuation noise contributing significantly to the overall noise temperature. Simulations of an optimized device with near-ideal optical coupling suggest that Johnson noise remains a substantial factor even with improved coupling. Further reduction of the noise temperature may require additional suppression of Johnson noise (via improved intrinsic conversion gain) beyond optimizing optical coupling efficiency. We emphasize the importance of accurate modeling to achieve good numerical agreement with experiments, thereby enabling understanding of the causes of sensitivity loss.

cond-mat.supr-con↗

arXiv2025

THz Metal-Mesh Bandpass Filters with Diamond-shaped Apertures for Sensitive THz Receivers

We present high-performance terahertz (THz) metal-mesh bandpass filters developed to mitigate direct detection effects in sensitive THz receivers based on superconducting hot-electron bolometer (HEB) mixers. These metal-mesh filters are free-standing 5-micron thick sheets of copper perforated with a periodic array of diamond-shaped apertures. The simple aperture design minimizes the effect of fabrication (rounding) errors on filter performance, allowing precise engineering of the center frequency (1.5-5.5 THz) while maintaining high (>90 %) peak power transmission at normal incidence and a relatively narrow bandwidth of 5-15 %. Based on finite-element method (FEM) simulation results, we provide simple design equations that can be used for rapid design with high accuracy. The measured transmission profiles of 1.9-THz, 2.5-THz, and 4.7-THz filters show excellent agreement with the simulation results. These filters are compatible with cryogenic operation and can substantially reduce the direct detection effects in HEB mixers.

physics.ins-det↗

arXiv2023

Indium-Bond-And-Stop-Etch (IBASE) Technique for Dual-side Processing of Thin High-mobility GaAs/AlGaAs Epitaxial Layers

We present a reliable flip-chip technique for dual-side processing of thin (<1 micron) high-mobility GaAs/AlGaAs epitaxial layers. The technique allows the fabrication of small (micron-scale with standard UV photolithography) patterned back gates and dual-gate structures on the thin GaAs/AlGaAs films with good alignment accuracy using only frontside alignment. The technique preserves the high-mobility (>10^6 cm^2 /V-s at 2 K) and most (>95%) of the charge density of the 2-dimensional electron gas (2DEG) systems, and allows linear control of the charge density with small (< 1 V) electrostatic gate bias. Our technique is motivated by a novel THz quantum-well detector based on intersubband transitions in a single, wide GaAs/AlGaAs quantum well, in which a symmetric, well-aligned dual-gate structure (with a typical gate dimension of ~5 micron by 5 micron) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch (IBASE) technique, we realize such dual-gate structure on 660-nm thick GaAs/AlGaAs epitaxial layers that contain a modulation-doped, 40-nm wide, single square quantum well. By independently controlling the charge density and the DC electric field set between the gates, we demonstrate robust tuning of the intersubband absorption behavior of the 40-nm quantum well near 3.44 THz at 30 K.

physics.ins-det↗

arXiv2014

Normal Metal Hot-Electron Nanobolometer with Johnson Noise Thermometry Readout

The sensitivity of a THz hot-electron nanobolometer (nano-HEB) made from a normal metal is analyzed. Johnson Noise Thermometry (JNT) is employed as a readout technique. In contrast to its superconducting TES counterpart, the normal-metal nano-HEB can operate at any cryogenic temperature depending on the required radiation background limited Noise Equivalent Power (NEP). It does not require bias lines; 100s of nano-HEBs can be read by a single low-noise X-band amplifier via a filter bank channelizer. The modeling predicts that even with the sensitivity penalty due to the amplifier noise, an NEP ~ 10$^{-20}$ - 10$^{-19}$ W/Hz$^{1/2}$ can be expected at 50-100 mK in 10-20 nm thin titanium (Ti) normal metal HEBs with niobium (Nb) contacts. This NEP is fairly constant over a range of readout frequencies ~ 10 GHz. Although materials with weaker electron-phonon coupling (bismuth, graphene) do not improve the minimum achievable NEP, they can be considered if a larger than 10 GHz readout bandwidth is required.

astro-ph.IM↗

arXiv2014

Monolayer graphene bolometer as a sensitive far-IR detector

In this paper we give a detailed analysis of the expected sensitivity and operating conditions in the power detection mode of a hot-electron bolometer (HEB) made from a few μm$^2$ of monolayer graphene (MLG) flake which can be embedded into either a planar antenna or waveguide circuit via NbN (or NbTiN) superconducting contacts with critical temperature ~ 14 K. Recent data on the strength of the electron-phonon coupling are used in the present analysis and the contribution of the readout noise to the Noise Equivalent Power (NEP) is explicitly computed. The readout scheme utilizes Johnson Noise Thermometry (JNT) allowing for Frequency-Domain Multiplexing (FDM) using narrowband filter coupling of the HEBs. In general, the filter bandwidth and the summing amplifier noise have a significant effect on the overall system sensitivity. The analysis shows that the readout contribution can be reduced to that of the bolometer phonon noise if the detector device is operated at 0.05 K and the JNT signal is read at about 10 GHz where the Johnson noise emitted in equilibrium is substantially reduced. Beside the high sensitivity (NEP < 10$^{-20}$ W/Hz$^{1/2}$, this bolometer does not have any hard saturation limit and thus can be used for far-IR sky imaging with arbitrary contrast. By changing the operating temperature of the bolometer the sensitivity can be fine tuned to accommodate the background photon flux in a particular application. By using a broadband low-noise kinetic inductance parametric amplifier, ~100s of graphene HEBs can be read simultaneously without saturation of the system output.

astro-ph.IM↗

arXiv2014

Prospective performance of graphene HEB for ultrasensitive detection of sub-mm radiation

Noise Equivalent Power and time constant of a submillimeter wave Hot-Electron Bolometer (HEB) made from monolayer graphene are analyzed using the lowest electron-phonon thermal conductance data reported to date. Frequency-domain multiplexed Johnson Noise Thermometry (JNT) is used for the detector readout. Planar microantennas or waveguides can provide efficient coupling of the graphene microdevice to radiation. The results show that the graphene HEB detector can be radiation background limited at very low level corresponding to the photon noise on a space telescope with cryogenically cooled mirror. Beside the high sensitivity, absence of a hard power saturation limit, higher operating temperature, and the ability to read 1000s of elements with a single broadband amplifier will be the advantages of such a detector.

physics.ins-det↗

arXiv2013

Graphene microbolometers with superconducting contacts for terahertz photon detection

We report on noise and thermal conductance measurements taken in order to determine an upper bound on the performance of graphene as a terahertz photon detector. The main mechanism for sensitive terahertz detection in graphene is bolometric heating of the electron system. To study the properties of a device using this mechanism to detect terahertz photons, we perform Johnson noise thermometry measurements on graphene samples. These measurements probe the electron-phonon behavior of graphene on silicon dioxide at low temperatures. Because the electron-phonon coupling is weak in graphene, superconducting contacts with large gap are used to confine the hot electrons and prevent their out-diffusion. We use niobium nitride leads with a $T_\mathrm{c}\approx 10$ K to contact the graphene. We find these leads make good ohmic contact with very low contact resistance. Our measurements find an electron-phonon thermal conductance that depends quadratically on temperature above 4 K and is compatible with single terahertz photon detection.

cond-mat.mes-hall↗

arXiv2012

Performance of Graphene Thermal Photon Detectors

We analyze the performance of graphene microstructures as thermal photon detectors and deduce the range of parameters that define a linear response. The saturation effects of a graphene thermal detector that operates beyond the linear range are described in detail for a single-photon detector (calorimeter). We compute the effect of operating beyond this linear range and find that sensitive detection occurs for such non-linear operation. We identify the optimum conditions and find that single-photon detection at terahertz (THz) frequencies should be feasible.

cond-mat.mes-hall↗

arXiv2012

Nanobolometers for THz Photon Detection

This article reviews the state of rapidly emerging terahertz hot-electron nanobolometers (nano-HEB), which are currently among of the most sensitive radiation power detectors at submillimeter wavelengths. With the achieved noise equivalent power close to 10^{-19} W/Hz^{1/2} and potentially capable of approaching NEP ~ 10^{-20} W/Hz^{1/2}, nano-HEBs are very important for future space astrophysics platforms with ultralow submillimeter radiation background. The ability of these sensors to detect single low-energy photons opens interesting possibilities for quantum calorimetry in the mid-infrared and even in the farinfrared parts of the electromagnetic spectrum. We discuss the competition in the field of ultrasensitive detectors, the physics and technology of nano-HEBs, recent experimental results, and perspectives for future development.

physics.ins-det↗

arXiv2012

Energy-resolved detection of single infrared photons with λ = 8 μm using a superconducting microbolometer

We report on the detection of single photons with λ = 8 μm using a superconducting hot-electron microbolometer. The sensing element is a titanium transition-edge sensor with a volume ~ 0.1 μm^3 fabricated on a silicon substrate. Poisson photon counting statistics including simultaneous detection of 3 photons was observed. The width of the photon-number peaks was 0.11 eV, 70% of the photon energy, at 50-100 mK. This achieved energy resolution is one of the best figures reported so far for superconducting devices. Such devices can be suitable for single photon calorimetric spectroscopy throughout the mid-infrared and even the far-infrared.

physics.ins-det↗

arXiv2010

Optical NEP in Hot-Electron Nanobolometers

For the first time, we have measured the optical noise equivalent power (NEP) in titanium (Ti) superconducting hot-electron nanobolometers (nano-HEBs). The bolometers were 2μmx1μmx20nm and 1μmx1μmx20nm planar antenna-coupled devices. The measurements were done at λ = 460 μm using a cryogenic black body radiation source delivering optical power from a fraction of a femtowatt to a few 100s of femtowatts. A record low NEP = 3x10^{-19} W/Hz^{1/2} at 50 mK has been achieved. This sensitivity meets the requirements for SAFARI instrument on the SPICA telescope. The ways for further improvement of the nano-HEB detector sensitivity are discussed.

astro-ph.IM↗