Tunnel Junction Detectors Research Articles

Anatomy of Protein Electrospray Ionization Mass Spectra by Superconducting Tunnel Junction Mass and Energy Spectrometry.

Cryogenic superconducting tunnel junction (STJ) detectors have the advantage of single-particle sensitivity, high quantum efficiency, low noise, and the ability to detect the time and relative impact energy of deposited ions. This makes them attractive for use in mass spectrometry (MS) and as a form of energy spectrometry. STJ cryodetectors have been coupled to time-of-flight (TOF) mass spectrometers equipped with a matrix-assisted laser desorption ionization (MALDI) source and to an electrospray ionization (ESI) TOF mass spectrometer. Here, a lab-made linear quadrupole ion trap (LIT) mass spectrometer system was coupled to an ESI source and a 16-channel Nb-STJ array with improved readout electronics. The goal was to investigate fundamentals of ESI-generated protein ions by further exploiting the advantage of resolving these ions in a third dimension of the relative energy deposited into the STJs. The proteins equine cytochrome c, bovine carbonic anhydrase, bovine serum albumin, and murine immunoglobulin G were studied using this ESI-LIT-STJ-MS instrument. Multiply charged monomers, multimers, and fragments from metastable ions were resolved from monomer peaks by differences in ion deposition energy even when these ions have the same mass-to-charge ratio as the corresponding monomer. The determination of a fragment mass from metastable decomposition is accomplished without knowing the charge state of the fragment. The average charge state of the multimers is reduced with each addition of a protein which is presumed to be a direct reflection of the surface area available for charging. Multiply charged in-source fragments have also been observed and distinguished in the mass spectrum of carbonic anhydrase by using the differences in the energy deposited in the STJs.

350-GHz Bandpass Filters Using Superconducting Coplanar Waveguide

On-chip filters play an invaluable role in most detectors and instruments, blocking unwanted, harmonic, or mirrored signals. In this article, two coplanar waveguide bandpass filters working at 350 GHz are designed based on quarter-wavelength stepped impedance resonators, which can be easily integrated in on-chip systems. A second-order filter with a classical Chebyshev response and a fourth-order filter with quasi-elliptical characteristic is developed together to define the roll-off performance. Both filters are patterned based on superconducting niobium film by the optical lithography and lift-off process, which could reduce the significant metallic loss in high terahertz band. All the chips integrated with transitions are evaluated through a quasi-optical system, which is built based on the sensitive superconductor-insulator-superconductor tunnel junction detector at cryogenic temperature. The calibrated transmission responses, which are matched with simulations, have indicated that such superconducting coplanar waveguide filters can be enabled in future terahertz astronomical spectrometer.

Feasibility of Laboratory-Based EXAFS Spectroscopy with Cryogenic Detectors.

Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is a powerful technique that gives element-specific information about the structure of molecules. The development of a laboratory EXAFS spectrometer capable of measuring transmission spectra would be a significant advance as the technique is currently only available at synchrotron radiation lightsources. Here, we explore the potential of cryogenic detectors as the energy resolving component of a laboratory transmission EXAFS instrument. We examine the energy resolution, count-rate, and detector stability needed for good EXAFS spectra and compare these to the properties of cryogenic detectors and conventional X-ray optics. We find that superconducting tunnel junction (STJ) detectors are well-suited for this application.

Comment on “Observation of nuclear gamma resonance with superconducting tunnel junction detectors” [AIP Advances 6, 025315 (2016)

Comment on “Observation of nuclear gamma resonance with superconducting tunnel junction detectors” [AIP Advances 6, 025315 (2016)

Response to “Comment on ‘Observation of nuclear gamma resonance with superconducting tunnel junction detectors’” [AIP Advances 9, 059101 (2019)

Response to “Comment on ‘Observation of nuclear gamma resonance with superconducting tunnel junction detectors’” [AIP Advances 9, 059101 (2019)

Improving the spatial resolution of superconducting tunnel junction THz wave detectors using a modified LiNbO3 absorber

We proposed a superconducting tunnel junction (STJ) detector for terahertz (THz) waves with a modified substrate absorber. The absorber of each STJ was isolated by trenches in order to restrict the diffusion of phonons generated by THz waves, which are made with a dicing process. We evaluated the diffusion characteristics of phonons in the LiNbO3 substrate by detecting THz photons. We found that the phonon diffusion length in a 500-μm-thick LiNbO3 substrate was over 1 mm. No degradation of the current – voltage (I–V) characteristics of the STJ after performing the dicing process.

Registering the radiation spectrum of a Mössbauer 119mSn source using superconducting tunnel junction detectors

Radiation spectra from a 119m Sn Mossbauer source are registered using Nb-based superconducting tunnel junction detectors. Mossbauer and accompanying X-ray radiation are detected via escape peaks with high energy resolution.

超伝導で質量分析の限界を越える試み

Superconducting tunnel junction (STJ) detectors for ions and neutral molecules have the ability to overcome the limits of conventional mass spectrometry, utilizing the performance of kinetic energy measurement of individual atoms and molecules in an energy range of 100 eV–100 keV. This unusual performance is realized by a small superconducting energy gap of ～meV, which is lower than the energies of phonons that are the quanta of crystal lattice vibration. The superconducting detectors are sensitive to molecule impact on the surface of superconductors through lattice vibration generation instead of using secondary electron emission that is used in conventional molecule detectors. An output pulse height is determined by the energy deposited to the detector surface, which is proportional to the product of charge number and acceleration voltage (zV [eV]). Consequently, it is possible to simultaneously determine m/z and z values of individual ions in vacuum, which is an advantage over ion mobility mass spectrometry (IMS) in a drift gas or charge detection mass spectrometry (CDMS). The STJ detectors can overcome the two fundamental MS limits of “m/z overlap” in different charge states and “neutral loss” in tandem mass spectrometry. For example, no one has identified doubly-charged homonuclear diatomic molecular ions of 14N22+ before us. In this paper, we report the experimental results obtained by using double-focused-MS, MALDI-TOF-MS, and ESI-TOF-MS equipped with a STJ detector. The superconducting detectors are expected to be employed in space and in electrostatic ion storage rings for planetary science, interstellar chemistry (origin of life), atomic and molecular sciences, and life sciences.

Position-sensitive superconductor detectors

Superconducting tunnel junction (STJ) detectors and superconducting transition- edge sensors (TESs) are representative superconductor detectors having energy resolutions much higher than those of semiconductor detectors. STJ detectors are thin, thereby making it suitable for detecting low-energy X rays. The signals of STJ detectors are more than 100 times faster than those of TESs. By contrast, TESs are microcalorimeters that measure the radiation energy from the change in the temperature. Therefore, signals are slow and their time constants are typically several hundreds of μs. However, TESs possess excellent energy resolutions. For example, TESs have a resolution of 1.6 eV for 5.9-keV X rays. An array of STJs or TESs can be used as a pixel detector. Superconducting series-junction detectors (SSJDs) comprise multiple STJs and a single-crystal substrate that acts as a radiation absorber. SSJDs are also position sensitive, and their energy resolutions are higher than those of semiconductor detectors. In this paper, we give an overview of position-sensitive superconductor detectors.

Observation of nuclear gamma resonance with superconducting tunnel junction detectors

Nb-based superconducting tunnel junction detectors have been used for the registration of electrons following a nuclear gamma resonance (Mössbauer effect). Electrons were produced by a RhFe scatterer under irradiation by the 57Co(Rh) Mössbauer source. This observation demonstrates the role which can be played by superconducting tunnel junction detectors in the field of conversion electron Mössbauer spectroscopy and other types of electron spectroscopy.

Spin-Torque Diode-Based Radio-Frequency Detector by Utilizing Tilted Fixed-Layer Magnetization and In-Plane Free-Layer Magnetization

We report a novel spin-torque diode (STD) radio-frequency detector by utilizing tilted fixed-layer magnetization and in-plane free-layer magnetization. Through macrospin modeling and numerical simulation, we study both the direct current (dc) dependence and the perpendicular external field dependence of the output voltage of the detector. We systematically investigate both the fixed-layer magnetization tilt angle dependence and the dc dependence of the resonance detection regime of the detector. It is found that an ultrawide resonance detection regime 6.5 GHz can be achieved, which is 1200% higher than the traditional STD magnetic tunnel junction detector with in-plane fixed-layer magnetization.

Enhancement of phonon backscattering due to confinement of ballistic phonon pathways in silicon as studied with a microfabricated phonon spectrometer

In this work, the mechanism for enhanced phonon backscattering in silicon is investigated. An understanding of phonon propagation through substrates has implications for engineering heat flow at the nanoscale, for understanding sources of decoherence in quantum systems, and for realizing efficient phonon-mediated particle detectors. In these systems, phonons that backscatter from the bottom of substrates, within the crystal or from interfaces, often contribute to the overall detector signal. We utilize a microscale phonon spectrometer, comprising superconducting tunnel junction emitters and detectors, to specifically probe phonon backscattering in silicon substrates (∼500 μm thick). By etching phonon “enhancers” or deep trenches (∼90 μm) around the detectors, we show that the backscattered signal level increases by a factor of ∼2 for two enhancers versus one enhancer. Using a geometric analysis of the phonon pathways, we show that the mechanism of the backscattered phonon enhancement is due to confinement of the ballistic phonon pathways and increased scattering off the enhancer walls. Our result is applicable to the geometric design and patterning of substrates that are employed in phonon-mediated detection devices.

Charge Multiplication Factor in STJ Detectors

This work pays attention to the inconsistency of the commonly used formulae for the internal gain, and the multitunneling noise factor in superconducting tunnel junction (STJ) detectors with experimental data. The origin of this inconsistency is in the fact that these formulae give the mean value and the relative variance of the number of crossings of the insulating barrier by a quasiparticle, but not the net charge transferred through the barrier that actually determines the signal of an STJ detector. In this work, the theory of branching cascade processes was applied to the process of multiple tunneling in STJ. The duality nature of quasiparticles and the coupling of the quasiparticle and phonon subsystems were taken into account. The general formulae for time dependences of the moments of the charge multiplication factor were derived.

Superconducting Tunnel Junction Detectors for Analytical Sciences

Superconducting tunnel junction (STJ) detectors exhibit superior detection performance for photons and particles at a high spectroscopic resolution of ~ 10 eV, a short dead-time (decay time) of ~ μs, a high quantum efficiency of ~ 100%, and a low detection threshold energy of less than 1 eV, which cannot be achieved by conventional detectors. The outstanding detection performance originates from a small superconducting energy gap of ~ meV, which is three orders of magnitude smaller than ~ eV in semiconductors. This paper reports our recent progress in two applications of STJ detectors to fluorescence-yield X-ray absorption fine structure (XAFS) spectrometry for trace light elements in matrices and mass spectrometry (MS) for ions with the same mass/charge-number ratio (m/z) but different charge states and neutral fragments.

Development of Ta-based STJ X-ray Detector Arrays for Synchrotron Science

We are developing a cryogen-free Ta-based superconducting tunnel junction (STJ) detector for soft X-ray spectroscopy at synchrotrons. With an energy resolution 10 times higher than conventional solid-state X-ray detectors and count-rate capabilities above 5 kHz/pixel, STJ detectors offer potentially increased sensitivity for fluorescence-yield X-ray absorption spectroscopy (FY-XAS). We have developed 36-pixel arrays of 208 \(\times \) 208 \(\upmu \)m Ta STJs with an energy resolution of \(\sim \)9 eV FWHM at the 525 eV oxygen K line. Compared to earlier Nb-based STJs, Ta-STJs offer improved energy resolution and absorption efficiency and extend the operating range to several keV. Here we describe the integration of the 36-pixel arrays into a cryogen-free, user-friendly X-ray spectrometer. A computer-controlled adiabatic demagnetization refrigerator coupled to a two-stage pulse tube refrigerator allows operation below 100 mK. The detector chip is located at the end of a 42 cm shielded snout for insertion into the analysis chamber. The system is currently being commissioned at the Advanced Light Source synchrotron.

Toward 1000-Pixel Superconducting-Tunnel-Junction Detectors for X-Ray Absorption Fine Structure Spectroscopy

Superconducting tunnel junction (STJ) detectors have excellent energy resolution, high detection efficiency, and high counting rate in the soft X-ray energy range. These properties are suitable for synchrotron radiation facilities. However, in order to achieve a high throughput analysis for dopants with a lower concentration, the pixel number of STJ array detectors should be further increased to enlarge the sensitive area. As a first step, we have fabricated 400-pixel STJ array detectors and checked the operation yield and the uniformity of leakage current (\(I_{leak}\)) values. Fabricated STJs showed excellent current-voltage curves having low subgap current. The operation yield of STJs with \(I_{leak}\) values of less than 10 nA was 96 \(\%\). The average \(I_{leak}\) of 3.6 nA is roughly equivalent to that of the 100-pixel STJ array detector, which is open to users at synchroton radiation beam lines and have 12 eV energy resolution at 400 eV.

Time Dependence of Partial Integrated Charge Fluctuations in STJs

Multiple tunneling of quasiparticles in a superconducting tunnel junction (STJ) detector increases the fluctuations in the measured charge. To optimize the energy resolution of an STJ detector, it is necessary to know the time dependence of the integrated charge and its noise. In this work, the theory of branching cascade processes was applied to the process of quasiparticle multitunneling. The duality nature of quasiparticles and the coupling of the quasiparticle and the phonon subsystems were taken into account. The formulae for time dependences of the mean value and the relative variance of the integrated charge were derived. Influence of a shaping amplifier on the relative variance of an STJ detector was also considered.

Fast and High Dynamic Range Imaging with Superconducting Tunnel Junction Detectors

We have demonstrated a combined test of the submillimeter-wave SIS photon detectors and GaAs-JFET cryogenic integrated circuits. A relatively large background photo-current can be read out by fast-reset integrating amplifiers. An integration time of 1 ms enables fast frame rate readout and large dynamic range imaging, with an expected dynamic range of 8,000 in 1 ms. Ultimate fast and high dynamic range performance of superconducting tunnel junction detectors (STJ) will be obtained when photon counting capabilities are employed. In the terahertz frequencies, when input photon rate of 100 MHz is measured, the photon bunching gives us enough timing resolution to be used as phase information of intensity fluctuation. Application of photon statistics will be a new tool in the terahertz frequency region. The design parameters of STJ terahertz photon counting detectors are discussed.

Fully differential cryogenic transistor amplifier

We have constructed a dc-coupled differential amplifier capable of operating in the 4.2K–300K temperature range. The amplifier can be operated at high-bias setting, where it dissipates 5mW, has noise temperature TN≈0.7K at RS≈5kΩ and >40MHz bandwidth at 4.2K bath temperature. The bias setting can be adjusted: at our lowest tested setting the amplifier dissipates <100μW, has noise temperature TN≈2K at RS≈25kΩ and >2MHz bandwidth. The 1/f noise corner frequency is a few times 10kHz. We foresee the amplifier to have an application in the readout of Superconducting Quantum Interference Devices (SQUIDs), Superconducting Tunnel Junction Detectors (STJs) and Transition Edge Sensors (TESes). We have verified the practical use of the amplifier by reading out a 4.2K 480-SQUID array with 40MHz bandwidth and <8×10−8Φ0/Hz1/2 flux noise.

Evaluation of Submillimeter/Terahertz Camera Performance With the Cryogenic Multi-Channel Read Out System

The purpose of our development is to realize the terahertz camera with superconducting tunnel junction detectors and cryogenic integrated circuits made of gallium-arsenide junction field-effect transistors (GaAs-JFET). This paper presents the first demonstration of such system. First, we have combined cryogenic charge integrating amplifiers made of GaAs-JFETs with the superconductor-insulator-superconductor (SIS) photon detectors at 0.5 K, and the detector current was successfully read out by the cryogenic amplifiers. Secondly, we have demonstrated an operation of a 32-channel multi-chip module all made of the GaAs-JFET circuits. The module has 32-channel detector input ports and two read out multiplexers for fast sampling. The power dissipation is about 350 μW . Using 910 kΩ resistors in place of detectors we measured output voltage noise of 3 mVrms with a charge integration time of 1 ms,. From these results, we have proven the terahertz camera technologies using SIS photon detectors and cryogenic read out electronics with the noise equivalent power (NEP) of 3.8 × 10-15 W/Hz0.5 and 1 kHz frame rate.