Papers by Jean-Claude Villegier
HAL (Le Centre pour la Communication Scientifique Directe), 2008
International audienc
This conference was divided into the following sessions: high-{Tc} bolometers and applications; h... more This conference was divided into the following sessions: high-{Tc} bolometers and applications; high-speed detectors based on bolometric and nonbolometric effects; nonequilibrium and kinetic inductance detectors; SNS and grain boundary junctions; and poster presentations. Separate abstracts were prepared for 22 papers in this book.
The discovery of high Tc superconductors has revealed promising applications in optoelectronics. ... more The discovery of high Tc superconductors has revealed promising applications in optoelectronics. However a basic requirement for the development of successful novel optronic devices is the ability to fabricate high quality Josephson, tunnel or three terminal devices in a reproducible, controllable and reliable way. Large area deposition of YBCO multilayers, whole wafer processing techniques are essential and in great progress. Nevertheless, the degradation of the YBa2Cu3O7-x surface layer close to the junction contacts is observed and induces severe limitations in the devices performances. Experimental evidence of such problems and possible solutions will be presented. 1. INTEREST OF HTC JUNCTIONS FOR PHOTON DETECTION Optoelectronic applications using high-Tc superconducting oxides have recently attracted much attention [1-5J . For instance the feasibility of sensitive high-bandwidth infrared detectors with a wide optical band should provide important applications in the field of sp...
AIP Advances, 2011
A SWIFTS device (Stationary Wave Integrated Fourier Transform Spectrometer) has been realized wit... more A SWIFTS device (Stationary Wave Integrated Fourier Transform Spectrometer) has been realized with an array of 24 Superconducting Nanowire Single Photon Detectors (SNSPD), on-chip integrated under a Si3N4 monomode rib-waveguide interferometer. Colored light around 1.55μm wavelength is introduced through end-fire coupling, producing a counter-propagative stationary interferogram over the 40nm wide, 120nm spaced, 4nm thick epi-NbN nanowire array. Modulations in the source bandwidth have been detected using individual waveguide coupled SNSPDs operating in single photon counting mode, which is a step towards light spectrum reconstruction by inverse Fourier transform of the stationary wave intensity. We report the design, fabrication process and in-situ measurement at 4.2K of light power modulation in the interferometer, obtained with variable laser wavelength. Such micro-SWIFTS configuration with 160nm sampling period over 3.84μm distance allows a spectral bandwidth of 2μm and a wavelen...
Physical Review B, 2002
We examine the electrical transport behavior close to vortex "phase-transition-like" re... more We examine the electrical transport behavior close to vortex "phase-transition-like" region in YBa 2 Cu 3 O 7 - Φ films that have their c axes tilted from the film plane normal by angles of 0°, 5°, 10°, and 15°. The I-V isotherms for all films collapse accurately under the vortex-glass scaling algorithm, for magnetic fields of 0.01-1 T applied at angles θ of 0° to 90° with respect to the c axis. The critical exponent v lies in the range 1.3-1.7 for all films, field strengths and field orientations. The critical exponent z is magnetic-field strength dependent in all films and for B∥c is considerably larger for the group of tilted films than for the 0° film. z varies with magnetic-field angle in an opposite sense in the 0° film and in the group of tilted films. The "transition" temperatures, T t (B,θ), are broadly described by the expression (T c -T t )/T t (e θ B) β , where e θ = [cos 2 (θ)+e 2 sin 2 (θ)] 1 / 2 and e=(m a b /m c ) 1 / 2 . However, β≅½, for the 0° film while β1 for the group of tilted films. Thus, we find that the tilted films have a number of common behaviors that are quite distinct from those of the 0° film, indicating a dependence of the "phase-transition-like" behavior on film structure. The high and variable values of z and the lack of "universality" between film types does not allow an interpretation of the accurate I-V collapses as being evidence for a continuous equilibrium phase transition such as one between a vortex liquid and a vortex glass and we consider models based on flux creep and inhomogenous pinning due to defects.
High Tc Superconductor Thin Films, 1992
Communication presentee a : 'International Conference on advanced Materials', Strasbourg ... more Communication presentee a : 'International Conference on advanced Materials', Strasbourg (France), 27-31 mai 1991SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1020 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
In the future generations of telecommunication satellites, it will be necessary to reduce the ana... more In the future generations of telecommunication satellites, it will be necessary to reduce the analog part in reception systems and to achieve RF frontend at higher carrier frequencies with higher sensitivity and higher bandwidth. RSFQ (Rapid Single Flux Quantum) superconducting logic is suitable to process very high speed digital data processing with very low power dissipation and with performances well beyond what should be possible with CMOS technology in the next decades. The RSFQ circuit technology based on superconducting niobium nitride (NbN) presently developed at CEA-G involves NbN/Ta X N/NbN internally shunted Josephson junctions with high critical current density and high maximum switching frequency close to 1 THz, as required by ultra-fast RSFQ electronics. Very low power dissipation and very low noise level of fast NbN RSFQ gates designed and fabricated at CEA-G are presented. The RSFQ circuit for a sampling comparator has been studied operating in a sigma-delta modulator with a 30 GHz sinusoidal input carrier signal and a high sampling clock frequency of about 200 GHz. We will present the thermal noise and how it influences the phase fluctuations. Such a nitride technology has been recently demonstrated to be fully compatible with large scale integration on 200 mm diameter silicon wafer at reasonable fabrication cost in a micro-nano-electronic platform at CEA-Leti. The applicability of NbN RSFQ digital functions in the next decade Space Telecoms will finally be possible thanks to the development of reliable, low power consuming, space qualified cryocoolers operating at about 10K. Moreover semiconductor system design and integration techniques can be simply adapted to superconductivity, to fit the rules of any RSFQ library-foundry network, such as "CONNECT" for Japan and "FLUXONICS" for Europe. The need to increase traffic communications, i.e. the amount of information, requires a consequent increase in signal bandwidth and in carrier frequency. In the future generation of telecommunication satellites it will be necessary to reduce the analog part (LNA, RF filter, mixer, IF filter …) in reception systems to achieve a RF front-end at higher frequency with higher sensitivity, higher dynamics and increased range of linearity. The so called "Software Defined Radio" [1] reception systems will provide Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
Thin Solid Films, 1998
DC SQUIDs amplifiers based on Nb/Al–Al2O3/Nb Josephson junctions technology have been designed, f... more DC SQUIDs amplifiers based on Nb/Al–Al2O3/Nb Josephson junctions technology have been designed, fabricated and characterized. To compare the RF performances as a function of the device layout, several types of SQUIDs with various washer inductances and different input transformers have been fabricated on the same wafer. A seven mask process has been set up to fabricate the SQUID amplifiers without anodization steps. The geometric and electronic parameters of the different device elements and the spread of the fabrication parameters have been studied. Critical steps such as the reliable fabrication of 4 and 9 μm2 area Josephson junctions, the control of their critical current density between 300 and 1000 A/cm2, the SiO2 interlayers quality, and the step coverage have been characterized and optimized. Maximum voltage modulation ΔV and flux to voltage transfer function δV/δΦ as high as 450 μV and 1500 μV/Φ0, respectively, have been found. ΔV and δV/δΦ variation with the screening parameter βL=2LI0/Φ0 and with the McCumber parameter βC have been investigated and the dependence of a typical device gain with frequency in the 1–200 MHz range is presented.
Superconductor Science and Technology, 1994
The critical current density (Jc) for zero magnetic field has been measured as a function of temp... more The critical current density (Jc) for zero magnetic field has been measured as a function of temperature in c-oriented thin layers of YBa2CU3O7-x prepared by different synthesis methods. One direct and two indirect Jc(T) methods were employed for each film: transport measurements on patterned film constrictions, DC remanent magnetization studies using the Bean model and non-linear AC screening analysis. Results
physica status solidi (b), 1993
Transmission spectroscopy in the very far IR (10 to 50 cm−1) is shown to be efficient to get dc c... more Transmission spectroscopy in the very far IR (10 to 50 cm−1) is shown to be efficient to get dc conductivity, plasma frequency, and collision frequency at different temperatures in the normal state (e.g. 210 and 125 K), and the superconducting state (e.g. 79 to 65 and 8 K), for an YBa2Cu3O7—δ (YBaCuO) thin film. For a given sample a plasma frequency vp = 6500 ± 1000 cm−1 independent of temperature, a collision frequency depending linearly on temperature, vc = 0.69T (in cm−1) and a negligible transmission τ at v = 10 cm−1 for T = 8 K (τ < 2 × 10−4) are found, showing that the amount of YBa2Cu3O6 insulating impurity is very low. A two-fluid model is used to explain the spectra at T = 65 and 80 K, with a concentration Ns of superconductive electrons given by a T4 law, Ns = No[1 — (T/Tc)4], which seems to be acceptable as a first approximation where the collision frequency for normal electrons is assumed to be saturated around 40 cm−1 at T < 65 K, to fit the data. Such a collision frequency is corresponding to a mean free path l = 212 A if we take a Fermi velocity vF = 200 km s−1 and l = vF/2πcvc. La spectroscopie des supraconducteurs par transmission dans L' IR lointain (10 a 50 cm−1) permet d'obtenir la frequence de plasma et la frequence de collision avec une precision meilleure que ne donnet les mesures par reflection, si L'on peut disposer d'un film supraconducteur tres mince (p. ex. 30 nm). Pour un echantillon donne, on a trouve une frequence de plasma vp = 6500 ± 1000 cm−1 independante de la temperature, une frequence de collision dependant lineairement de T : vc = 0.69T (en cm−1) et une transmission a 8 K negligeable pour v = 10 cm−1, montrant que le film est relativement exempt d'impuretes isolantes. Un modele a deux fluides permet d'interpreter les spectres a 65 et 80 K en adoptant une loi en T4 pour la concentration en quasiparticules, en admettant que leur frequence de collision se sature a 40 cm−1 pour T < 65 K.
Physica C: Superconductivity, 1997
NQR spectra of 63'65Cu isotopes were measured in YBa2Cu306+x thin films at 1.4 K, which were prep... more NQR spectra of 63'65Cu isotopes were measured in YBa2Cu306+x thin films at 1.4 K, which were prepared by cathodic sputtering and chemical vapor deposition. By comparison with powder spectra, we show that the films obtained by cathodic sputtering are overdoped. We discuss the possible reasons of the lower T c commonly obtained in YBa2Cu306+ x thin films by comparison with powders and single crystals. Furthermore, we show that thin films synthesized by chemical vapor deposition could be affected by carbon retention.
Physica C: Superconductivity, 2000
Ž. Ž. Ž. a-axis YBa Cu O YBCO films have been grown on tetragonal 100 LaSrGaO LSGO substrates ove... more Ž. Ž. Ž. a-axis YBa Cu O YBCO films have been grown on tetragonal 100 LaSrGaO LSGO substrates over a 2 3 7 yd 4 Ž. Ž. PrBa Cu O PBCO template layer, using inverted cylindrical magnetron ICM sputtering. Detailed X-ray diffraction 2 3 7 yd studies showed that more than 98% of the grains are in-plane aligned with the substrate axes. We have studied the vortex-related phase-transition-like behaviour in these films from dc electrical measurements made with the transport current along the band c-axes, and in magnetic fields up to 1 T. Good scaling collapse of the current-voltage isotherms for a wide range of temperatures about the transition is observed when using an algorithm based upon a continuous thermodynamic phase transition such as that between a vortex-liquid and a vortex-glass. We note that the critical scaling exponents are by no means ''universal'' as expected by some authors and that the exponent z is far higher than expected from analogies with spin-glass systems. The wide range of temperature over which collapse occurs and the very high values of z make the usual association of z and zn with a length and a time scale implausible. Importantly, the observed ''transition'' temperature, T , t differs appreciably between the two transport current directions for the same magnetic field and field angle. These observations cast doubt on an interpretation for the vortex-related behaviour based on a continuous thermodynamic phase transition such as that between a vortex-liquid and a vortex-glass and alternative possibilities must be explored.
Physica C: Superconductivity, 1994
The nonlinearity in the flux-flow process due to the finite energy relaxation rate of the quasipa... more The nonlinearity in the flux-flow process due to the finite energy relaxation rate of the quasiparticles has been studied in the mixed state of epitaxial c-axis oriented YBa2Cu3074 ~ films. The inelastic quasiparticle scattering rate was found to decrease rapidly with decreasing temperature below T c.
Physica C: Superconductivity, 2006
The roadmap gives an overview on status and future developments in Superconducting Digital Electr... more The roadmap gives an overview on status and future developments in Superconducting Digital Electronics (SDE). Key areas in SDE under focus are applications, circuit simulation and design, circuit fabrication, interfacing and testing, cooling and system aspects, and new devices and materials. Care was taken to establish the vital link between research and development on the one hand and the industrial view on the other hand. The present roadmap is based on extensive input from the roadmap working group on SDE established by SCENET-the European Network for Superconductivity, intensified by the activities of the FLUXONICS Network-the European Foundry for Superconducting Electronics. It is the result of many years of discussion in the group and of consultations with experts in the field, on the way to bring together industrial expectations and visionary extrapolation and current status of technology.
International Journal of Infrared and Millimeter Waves, 1991
After several years, the Far IR (FIR) results
Journal of Applied Physics, 1993
Thin layers of YBa2Cu3O7−x (YBCO) deposited on LaAlO3 substrates have been prepared in situ by co... more Thin layers of YBa2Cu3O7−x (YBCO) deposited on LaAlO3 substrates have been prepared in situ by coevaporation of Y, Ba, and Cu. Incorporation of oxygen was accomplished by an atomic oxygen beam source with high cracking efficiency. The total oxygen flow at the substrate could be kept low enough to permit the use of a quadrupole mass spectrometer for evaporation rate monitoring. Films were strongly c-axis oriented with rocking curve full width at half-maximum values of 0.6°. Transport measurements on patterned films yielded critical current densities of 6×106 A/cm2 at 77 K. The deposition method was demonstrated to be feasible for preparation of Y2O3/YBCO heterostructures.
IEEE Transactions on Applied Superconductivity, 1993
A MOSFET-like device with a thin superconducting PrBaCuO/YBaCuO multilayer channel and SiO2 gate ... more A MOSFET-like device with a thin superconducting PrBaCuO/YBaCuO multilayer channel and SiO2 gate oxide was built. The effect of electric field applied on the gate was investigated as a function of temperature and drain-source current for different multilayers. It was shown that the critical temperature, as well as the density of the critical current could be enhanced or suppressed depending
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Papers by Jean-Claude Villegier
Moreover recently, deep submicron size (~0.01µm2), very low capacitance NbN-MgO-NbN SIS and SQUID circuits were achieved using a self-aligned process. Such junctions, beside their attracting properties for nitride IC, are able to emit or detect in a controllable way single microwave photons and could be a new building block of quantum information circuits.