Electrical Noise Equivalent Power Research Articles

A terahertz detector based on superconductor-graphene-superconductor Josephson junction

Graphene is an attractive material for terahertz (THz) detectors due to its unique properties of extremely weak electron-phonon interaction and small electronic heat capacity. In this paper, we demonstrate a lens-antenna-coupled THz detector based on a diffusive superconductor-graphene-superconductor (SGS) junction, which has a sharp resistive transition at 1.4 K due to the proximity Josephson coupling. The SGS Josephson detector, measured with a dc superconducting quantum interference device (SQUID) readout, exhibits an electrical noise equivalent power (NEP) as low as 5 × 10−17 W/Hz0.5 at 0.1 K, which is still limited by the readout noise. Furthermore, the optical performance of the SGS Josephson detector is measured with a cryogenic blackbody radiation source, giving an optical NEP of 2.5–5 × 10−16 W/Hz0.5 at 1.4 THz in the temperature range from 0.1 K to 0.6 K.

Responsivity and NEP Improvement of Terahertz Microbolometer by High-Impedance Antenna.

The antenna-coupled microbolometer with suspended titanium heater and thermistor was attractive as a terahertz (THz) detector due to its structural simplicity and low noise levels. In this study, we attempted to improve the responsivity and noise-equivalent power (NEP) of the THz detector by using high-resistance heater stacked on the meander thermistor. A wide range of heater resistances were prepared by changing the heater width and thickness. It was revealed that the electrical responsivity and NEP could be improved by increasing the heater’s resistance. To make the best use of this improvement, a high-impedance folded dipole antenna was introduced, and the optical performance at 1 THz was found to be better than that of the conventional halfwave dipole antenna combined with a low-resistance heater. Both the electrical and optical measurement results indicated that the increase in heater resistance could reduce the thermal conductance in the detector, thus improved the responsivity and NEP even if the thermistor resistance was kept the same.

Noise equivalent power of a NbTiN-Al-based kinetic inductance detector for terahertz sensing

We have designed and fabricated a superconducting hybrid NbTiN-Al kinetic inductance detector (KID) over a broad band centered at 4.3 THz. The detector sensitivity is characterized by changing the bath temperature in a dark environment. Both amplitude and phase readouts are performed. The measured electrical noise equivalent power for phase readout is about 2.6 × 10−18 W · Hz−0.5 at 200 mK. This ultra-sensitive KID, which enables large arrays with frequency domain multiplexing, is promising for imaging instruments in space-based far-infrared observatories.

Ti Hot Electron Bolometers with Johnson Noise Readout for Terahertz Radiation Detection

A hot electron bolometer (HEB) with Johnson noise readout is an attractive technique for radiation detection due to its high sensitivity, wide operating temperature range, and large dynamic range. In this paper, we present the development of a terahertz HEB based on Johnson noise readout. The HEB consists of a titanium microbridge connected to two high-energy-gap niobium contacts for confining hot electrons. We measured the thermal conductance and noise equivalent power (NEP) of the HEB at different bath temperatures. We find that the thermal conductance due to the electron–phonon interaction increases with temperature as T2.5. At 3.0 K, the thermal conductance is found to be 37.9 ± 1.4 nW/K and the electrical NEP is as low as 23.0 ± 0.8 pW/$$ \sqrt {\text{Hz}} $$. In addition, we find that the HEB works efficiently up to 15 μW input power.

Nanostructured graphene for nanoscale electron paramagnetic resonance spectroscopy

The opening of a quantum confinement gap in nanostructured graphene yields extremely sensitive photodetectors, with electrical noise equivalent power lower than 10−15 W Hz−0.5 at temperatures below 3 K, for detection of radiation in a very broad frequency range, including ultraviolet, visible and terahertz. Here we demonstrate the operation of these detectors in the presence of magnetic field as high as 7 T, paving the way to in situ spectroscopy of molecular nanomagnets.

Fast and sensitive bolometric terahertz detection at room temperature through thermomechanical transduction

Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

Radiation Tolerance of Aluminum Microwave Kinetic Inductance Detector

Microwave kinetic inductance detector (MKID) is one of the candidates of focal plane detector for future satellite missions such as LiteBIRD. For the space use of MKIDs, the radiation tolerance is one of the challenges to be characterized prior to the launch. Aluminum (Al) MKIDs with 50 nm thickness on silicon substrate and on sapphire substrate were irradiated with a proton beam of 160 MeV at the heavy ion medical accelerator in Chiba. The total water-equivalent absorbed dose was $$\sim $$ 10 krad which should simulate the worst radiation absorption of 5 years observation at the Lagrange point L2. We measured characteristics of these MKIDs before and after the irradiation. We found no significant changes on resonator quality factor, responsivity, and recombination time of quasi-particles. The change on electrical noise equivalent power was also evaluated, and no significant increase was found at the noise level of $$O(10^{-18})$$ W/ $$\sqrt{ \mathrm{Hz} }$$ .

Sub-10 pW/Hz0.5 room temperature Ni nano-bolometer

In this letter, we report on room temperature Ni nano-bolometers with a measured electrical noise equivalent power of 8.7 pW/Hz0.5 based on air-suspended and self-aligned nano-stack (SiO2/Ni/SiO2) structures, which is an outstanding electrical performance among uncooled micro/nano-bolometers. This result, together with electrical resistances of 172.6 Ω and modulation frequencies of 15–30 kHz, shows that Ni nano-bolometers can be easily coupled to terahertz antennas and are appropriate for fast passive imaging applications.

Electrical Characteristics of Superconducting Ti Transition Edge Sensors

We have designed and fabricated superconducting Ti transition edge sensors (TES) with different microbridge lengths varying from 1 to 6 \(\upmu \)m. The current–voltage characteristics of the fabricated Ti TESs are measured at different bath temperatures using a commercial SQUID amplifier. The thermal conductance (G) is found to be about 300 pW/K for a 2.6-\(\upmu \)m-long device. In addition, the effective response time measured with a current pulse signal is about 3 \(\upmu \)s, and decreases with increasing the bias voltage because of negative electro-thermal feedback. The obtained electrical noise equivalent power from the measured current noise is about \(4 \times 10^{-17}\) W/Hz\(^{0.5}\), which is sufficiently low for TeSIA instrument.

Characterization of a Superconducting NbSi Transition Edge Sensor for TeSIA

We report on the performance of a superconducting NbSi transition edge sensor (TES), which is co-evaporated on a suspended SiO/SiN/SiO trilayer membrane. The temperature sensitivity coefficient (\alpha) calculated from the measured resistive transition curve is as high as 200. The current-voltage characteristics were measured at bath temperatures varying from 288 mK to 440 mK using a two-stage SQUID amplifier, from which the thermal conductance (G) was found to be 345 pW/K. We also measured the current noise at different bias voltages at 288 mK. The obtained electrical noise equivalent power (NEP) from its calculated current responsivity and measured current noise is about 8\times 10{-17} \hbox{W}/\surd{\hbox{Hz}}. In addition, the preliminary measurement results of time domain multiplexing scheme based on the superconducting quantum interference devices (SQUIDs) and an application specific integrated circuit (ASIC) are presented.

Equivalence of optical and electrical noise equivalent power of hybrid NbTiN-Al microwave kinetic inductance detectors

We have measured and compared the response of hybrid NbTiN-Al Microwave Kinetic Inductance Detectors (MKIDs) to changes in bath temperature and illumination by sub-mm radiation. We show that these two stimulants have an equivalent effect on the resonance feature of hybrid MKIDs. We determine an electrical noise equivalent power (NEP) from the measured temperature responsivity, quasiparticle recombination time, superconducting transition temperature, and noise spectrum, all of which can be measured in a dark environment. For the two hybrid NbTiN-Al MKIDs studied in detail, the electrical NEP is within a factor of two of the optical NEP, which is measured directly using a blackbody source.

Electrodynamic model of the field effect transistor application for THz/subTHz radiation detection: Subthreshold and above threshold operation

Developed in this work is an electrodynamic model of field effect transistor (FET) application for THz/subTHz radiation detection. It is based on solution of the Maxwell equations in the gate dielectric, expression for current in the channel, which takes into account both the drift and diffusion current components, and the equation of current continuity. For the regimes under and above threshold at the strong inversion the response voltage, responsivity, wave impedance, power of ohmic loss in the gate and channel have been found, and the electrical noise equivalent power (ENEP) has been estimated. The responsivity is orders of magnitude higher and ENEP under threshold is orders of magnitude less than these values above threshold. Under the threshold, the electromagnetic field in the gate oxide is identical to field of the plane waves in free-space. At the same time, for strong inversion the charging of the gate capacitance through the resistance of channel determines the electric field in oxide.

Toward a Detector/Readout Architecture for the Background-Limited Far-IR/Submm Spectrograph (BLISS)

We have built and tested 32-element linear arrays of absorber-coupled transition-edge sensors (TESs) read out with a time-division SQUID multiplexer. This detector/readout architecture is designed for the background-limited far-IR/submm spectrograph (BLISS) which is a broadband (35–433 \(\upmu \)m), grating spectrometer consisting of six wavebands each with a modest resolution of R \(\sim \) 700. Since BLISS requires the effective noise equivalent power (NEP) of the TESs to equal 1 \(\times \) 10\(^{-19}\) W/Hz\(^{1/2}\), our detectors consist of very long (1–2 mm), narrow (0.4 \(\upmu \)m), and thin (0.25 \(\upmu \)m) Si\(_{x}\)N\(_{y}\) support beams that reduce the thermal conductance G between the substrate and the optical absorber. The thermistors of our lowest noise TESs consist of iridium with \(T_{c}=130\) mK. We have measured the electrical properties of arrays of these Ir TESs with various meander and straight support beams and absorber shapes and found that G is \(\sim \)30 fW/K (meander) and \(\sim \)110 fW/K (straight), the electrical NEP is 2–3 \(\times \) 10\(^{-19}\) W/Hz\(^{1/2}\) (meander and straight), and the response time \(\tau \) is 10–30 ms (meander) and 2–5 ms (straight). To reduce spurious or “dark” power from heating the arrays, we mounted the arrays into light-tight niobium boxes and added custom L/R and L/C low-pass chip filters into these boxes to intercept dark power from the bias and readout circuit. We found the average dark power equals 1.3 and 4.6 fW for the boxes with L/R and L/C chip filters, respectively. We have built arrays with \(T_{c}= 70\) mK using molybdenum/copper bilayers and are working to lower the dark power by an order of magnitude so we can demonstrate NEP\(~=~1~\times \) 10\(^{-19}\) W/Hz\(^{1/2}\) with these arrays. PACS numbers: 85.25.Pb; 95.85.Gn; 95.85.Fm; 63.22.\(+\)m

Highly sensitive hot electron bolometer based on disordered graphene.

A bolometer is a device that makes an electrical resistive response to the electromagnetic radiation resulted from a raise of temperature due to heating. The combination of the extremely weak electron-phonon interactions along with its small electron heat capacity makes graphene an ideal material for applications in ultra-fast and sensitive hot electron bolometer. However, a major issue is that the resistance of pristine graphene weakly depends on the electronic temperature. We propose using disordered graphene to obtain a strongly temperature dependent resistance. The measured electrical responsivity of the disordered graphene bolometer reaches 6 × 106 V/W at 1.5 K, corresponding to an optical responsivity of 1.6 × 105 V/W. The deduced electrical noise equivalent power is 1.2 , corresponding to the optical noise equivalent power of 44 . The minimal device structure and no requirement for high mobility graphene make a step forward towards the applications of graphene hot electron bolometers.

Optical Efficiencies of Lens-Antenna Coupled Kinetic Inductance Detectors at 220 GHz

We have been developing a terahertz camera based on antenna-coupled superconducting resonators, the so-called microwave kinetic inductance detectors (MKIDs), and a silicon lens array. The MKID consists of a coplanar waveguide coupled to a double slot antenna and is patterned on a high-quality aluminum film grown by molecular beam epitaxy. The camera is sensitive at frequencies of 200-240 GHz. Its bandwidth is limited by the impedance properties of the double slot antenna. The design, fabrication, and optical evaluations of the planar antennas and silicon lens arrays are presented in this paper. The MKID camera has been evaluated both in dark conditions and under optical radiation in a 0.1-K dilution refrigerator. The electrical noise equivalent power was around 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> W/√(Hz) in dark conditions and 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> W/√(Hz), which is much lower than the photon noise level, with the optical load. The optical efficiency of the camera was estimated by three independent methods, and the results were consistent with each other and equal to 20%-25% without an anti-reflection coating on the lens surface.

MgB2 thin-film bolometer for applications in far-infrared instruments on future planetary missions

A SiN membrane based MgB2 thin-film bolometer, with a non-optimized absorber, has been fabricated that shows an electrical noise equivalent power of 2.56×10−13W/√Hz operating at 30Hz and a responsivity of 702kV/W. It is predicted that with the inclusion of a gold black absorber that an optical specific detectivity of 8.3×1010cm/√Hz/W at an operational frequency of 10Hz, can be realized for integration into future planetary exploration instrumentation where high sensitivity is required in the 17–250μm spectral wavelength range.

Design and Testing of Kinetic Inductance Detectors Made of Titanium Nitride

To use highly resistive material for Kinetic Inductance Detectors (KID), new designs have to be done, in part due to the impedance match needed between the KID chip and the whole 50 Ω readout circuit. Chips from two new hybrid designs, with an aluminum throughline coupled to titanium nitride microresonators, have been measured and compared to a TiN only chip. In the hybrid chips, parasitic temperature dependent box resonances are absent. The dark KID properties have been measured in a large set of resonators. A surprisingly long lifetime, up to 5.6 ms is observed in a few KIDs. For the other more reproducible devices, the mean electrical Noise Equivalent Power is \(5.4 \times 10^{-19}\ \mathrm{W}\sqrt{\mathrm{Hz}}\).

Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna

Two series/parallel arrays of ten cold-electron bolometers with superconductor-insulator-normal tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. To increase the dynamic range of the receiver, all single bolometers in an array are connected in parallel for the microwave signal by capacitive coupling. To increase the output response, bolometers are connected in series for dc bias. With the measured voltage-to-temperature response of 8.8 μV/mK, absorber volume of 0.08 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and output noise of about 10 nV/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , we estimated the dark electrical noise equivalent power (NEP) as NEP = 6 * 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> W/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The optical response down to NEP = 2 * 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-17</sup> W/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> was measured using a hot/cold load as a radiation source and a sample temperature down to 100 mK. The fluctuation sensitivity to the radiation source temperature is 1.3 * 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> K/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . A dynamic range over 43 dB was measured using a backward-wave oscillator, a variable polarization grid attenuator, and cold filters/attenuators.

Development of Crystal Al MKIDs by Molecular Beam Epitaxy

We report here the effect of film qualities in superconductors on the properties of Microwave Kinetic Inductance Detectors (MKIDs). The sensitivity of MKIDs between crystal aluminum films and amorphous aluminum films is compared. The good quality and crystallized aluminum films have been prepared by using molecular beam epitaxy. We have confirmed that epitaxial Al(111) films were grown on Si(111) substrates with X-ray diffraction and in-situ reflection high-energy electron diffraction measurements. The amorphous aluminum films on the Si(111) wafers have been deposited by electron beam evaporation. We have measured transmission losses of MKIDs, noise spectrum and relaxation time against optical pulses, changing MKIDs’ bath temperature from 0.11 K to 0.55 K in a dilution refrigerator. Despite of the improvement in normal resistivity, the quasiparticle decay time of both films are equivalent and 450 μs at 0.11 K. The electrical noise equivalent power of the both MKIDs are also comparable and around \(10^{-17}~\mbox{W}/\sqrt{\mbox{Hz}}\). Fabrication details and performance data of both films are presented.

Transition Edge Sensors (TES) Using a Low-G Spider-Web-Like SiN Supporting Structure

We fabricated and characterized a low thermal conductance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</i> ) transition edge sensor (TES). The device is based on a superconducting Ti/Au bilayer deposited on a suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</i> ) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> W/√Hz. The current noise and complex impedance are also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> W/√Hz, which is about a factor of 2 higher than what is expected from the thermal conductance that comes out of the IV curves analysis. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 62 μs and a thermal capacity of 3 fJ/K.