Innovative direct manufacturing of tungsten carbide superconducting nanowires for photon detection applications via pulsed focused ion beam induced deposition
Cristina García-Pérez, Fernando J. Urbanos, Gabriel Caballero, Manuel Rodríguez Osorio, A. Gómez, Ramón Bernardo Gavito, Daniel Granados
We present the development and optical characterization of tungsten carbide superconducting nanowire devices for photon detection. They are nanofabricated by direct deposition via pulsed focused ion beam induced deposition (PFIBID) using Tungsten Hexacarbonyl (W(CO)₆) as precursor. The nanowires exhibit a critical temperature of 4.71 K and demonstrate a notable response to low-intensity CW or pulsed laser illumination . For the first time, in-operando photoresponse low-temperature maps reveal hotspot distributions under low power illumination and localized superconductivity suppression upon high fluence photon absorption at higher powers. Dynamic response measurements under 1 MHz repetition rate, 640 nm pulsed laser excitation highlight the fast temporal response of the detectors and high operation stability near saturation. While currently operating in the multi-photon regime (9 photons/output-pulse), the findings emphasize their potential for single-photon detection with further optimization of material thickness (target <25 nm) and excitation schemes. This work demonstrates the significant promise to direct nanofabricate superconducting devices based on WC for advanced quantum applications.
We present the development and optical characterization of tungsten carbide superconducting nanowire devices for photon detection. They are nanofabricated by direct deposition via pulsed focused ion beam induced deposition (PFIBID) using Tungsten Hexacarbonyl (W(CO)₆) as precursor. The nanowires exhibit a critical temperature of 4.71 K and demonstrate a notable response to low-intensity CW or pulsed laser illumination . For the first time, in-operando photoresponse low-temperature maps reveal hotspot distributions under low power illumination and localized superconductivity suppression upon high fluence photon absorption at higher powers. Dynamic response measurements under 1 MHz repetition rate, 640 nm pulsed laser excitation highlight the fast temporal response of the detectors and high operation stability near saturation. While currently operating in the multi-photon regime (9 photons/output-pulse), the findings emphasize their potential for single-photon detection with further optimization of material thickness (target <25 nm) and excitation schemes. This work demonstrates the significant promise to direct nanofabricate superconducting devices based on WC for advanced quantum applications.
We evaluate the performance of hybrid microwave resonators made by combining sputtered Nb thin films with Tungsten nanowires grown with a He-beam induced deposition technique. Depending on growth conditions, the nanowires have a typical width w [35 - 75] nm and thickness t [5 - 40] nm. We observe a high normal state resistance R [65 - 150] Ω / which together with a critical temperature T c [4 - 6] K ensures a high kinetic inductance making the resonator strongly nonlinear. Both lumped and coplanar waveguide resonators were fabricated and measured at low temperature exhibiting internal quality factors up to 3990 at 4.5 GHz in the few photon regime. Analyzing the wire length, temperature, and microwave power dependence, we extracted a kinetic inductance for the W nanowire of L K 15 pH / which is 250 times higher than the geometrical inductance, and a Kerr non-linearity as high as K W, He / 2 π = 200 ± 120 Hz / photon at 4.5 GHz. The nanowires made with the helium focused ion beam are thus versatile objects to engineer compact, high impedance, superconducting environments with a mask and resist free direct write process.
We evaluate the performance of hybrid microwave resonators made by combining sputtered Nb thin films with Tungsten nanowires grown with a He-beam induced deposition technique. Depending on growth conditions, the nanowires have a typical width w∈[35−75] nm and thickness t∈[5−40] nm. We observe a high normal state resistance R◻∈[65−150] Ω/◻ which together with a critical temperature Tc∈[4−6] K ensures a high kinetic inductance making the resonator strongly nonlinear. Both lumped and coplanar waveguide resonators were fabricated and measured at low temperature exhibiting internal quality factors up to 3990 at 4.5 GHz in the few photon regime. Analyzing the wire length, temperature, and microwave power dependence, we extracted a kinetic inductance for the W nanowire of LK≈15 pH/◻, which is 250 times higher than the geometrical inductance, and a Kerr non-linearity as high as KW,He/2π=200±120 Hz/photon at 4.5 GHz. The nanowires made with the helium focused ion beam are thus versatile objects to engineer compact, high impedance, superconducting environments with a mask and resist free direct write process.
We present an alternative approach to the fabrication of highly efficient superconducting nanowire single-photon detectors (SNSPDs) based on tungsten silicide. Using well-established technologies for the deposition of dielectric mirrors and anti-reflection coatings in conjunction with an embedded WSi bilayer photon absorber structure, we fabricated a bandwidth-enhanced detector. It exhibits system detection efficiencies (SDE) higher than (87.1±1.3)% in the range from 1450nm to 1640nm, with a maximum of (92.9±1.1)% at 1515nm. Our measurements indicate SDE enhancements of up to (18.4±1.7)% over a single-absorber WSi SNSPD. The latter has been optimized for 1550 nm for comparison and exhibits maximum SDE of (93.5±1.2)% at 1555 nm. We emphasize that our technological approach has been tested with, but is not limited to, the wavelengths and absorber material presented here. It could be adapted flexibly for multi-color detector systems from the ultraviolet to the mid-infrared wavelength range. This bears the potential for significant improvements in many current quantum optical experiments and applications as well as for detector commercialization.
We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1−x) nanowire. Our device made from a uniform a-WxSi1−x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates.
Superconducting detectors have become essential devices for high-performance single-photon counting over a wide wavelength range with excellent time resolution. Detector fabrication typically relies on resist-based lithography processes, which can limit possibilities for device integration, e.g., on unconventional substrates. Here, we demonstrate a resist-free fabrication route for realizing superconducting nanowire single-photon detectors based on focused electron beam-induced deposition. Utilizing direct writing of a Pt–C mask, we achieved nanowire meanders with linewidths below 100 nm, operated them as superconducting devices for the detection of visible and near-infrared photons, and showed detector integration on side-polished optical fibers. Being compatible with device fabrication on curved irregular surfaces, our approach could enable superconducting detector integration in complex configurations.
Superconducting nanowires have been used to detect single photons for more than 20 years. The basic principle is that photons can perturb superconducting Cooper pairs and thereby create a resistive hotspot, which produces a current-crowding effect. This current-crowding effect reduces the superconducting energy gap near the hotspot, which results in the nanowire changing from a superconducting to a normal state near the hotspot. The resulting high impedance causes the current to be squeezed into a high frequency coaxial wire connected in parallel with it, which finally produces a measurable voltage pulse. Thanks to the maturity of current micro- and nano- fabrication techniques, high quality superconducting thin films and nano-wires have been realized in a variety of materials such as NbN, WSi, MoSi and others. These techniques include magnetron sputtering, physical vapor deposition, electron beam lithography, optical lithography, reactive ion etching, wafer cutting, etc. Measurements of superconducting single-photon detectors require cryogenic refrigeration systems, ranging from the initial liquid helium cold tank, to modern dry dilution refrigerators. On one hand, a superconducting device needs to be cooled down below its critical temperature to work. On the other hand, photon-detection events generate hot spots, which release heat to the device substrate, which the refrigerator needs to efficiently take away. Research on superconducting nanowire single-photon detectors (SNSPDs) has made significant advancements over the past two decades, including high detection efficiency, low dark counts, and broad wavelength range capabilities. Beyond improvements in traditional NbN, WSi and MoSi superconducting nanowires, there have been numerous efforts to develop high-temperature superconducting nanowires, such as MgB2 and Bi2Sr2CaCu2O8 (BSCCO), due to the operational limitations imposed by low-temperature superconducting materials. Typically, single-photon detectors require operation temperatures below the critical temperature. High-temperature superconducting nanowire single-photon detectors have currently reported to exhibit the highest operating temperature around 20 K in BSCCO, which is much lower than its critical temperature of 80 K, showing that large-gap superconductors have a comparably low sensitivity to low-energy photons. In recent years since 2018, several groups have reported that micrometer-wide superconducting wires can also be used for single-photon detection, unlike the conventional nanometer-wide superconducting wires. In general, as long as the bias current is uniformly distributed in superconducting wires and approaches the critical Cooper pair-breaking current, the hot spots generated by photon absorption can induce vortices and anti-vortices, and their motion under the action of the Lorentz force generates resistance and voltage, which ultimately produces a normal state region. An increase of the wire width to the micron scale offers more freedom to design new detectors based on current nano- and microfabrication techniques. In this doctoral dissertation, I will first introduce the basic Ginzburg-Landau theory of superconductivity and the measurement theory of superconducting circuits related to single-photon detection. I will then provide a detailed description of the equipment construction and sample fabrication techniques used in the experiment. Finally, I will present my two main studies: in one project I examined the photon-detection performance of superconducting micro-wires with a multi-pinhole structure, the correlation between dark counts and magnetic vortices, as well as the properties of critical current in magnetic fields. In a subsequent study I conducted numerical simulations using the time dependent Ginzburg-Landau equation, to analyze the dynamics of vortices in superconducting micro-strips with regular large-area perforations by pinholes as a function of magnetic field and bias current. The thus obtained predictions were then successfully confirmed in a detailed experimental study on a series of microwires.