Coupling efficiency for phase locking of a spin transfer oscillator to a microwave current

The phase locking behavior of spin transfer nano-oscillators (STNOs) to an external microwave signal is experimentally studied as a function of the STNO intrinsic parameters. We extract the coupling strength from our data using the derived phase dynamics of a forced STNO. The predicted trends on the coupling strength for phase locking as a function of intrinsic features of the oscillators i.e. power, linewidth, agility in current, are central to optimize the emitted power in arrays of mutually coupled STNOs

Microwave detection with high T/sub c/ superconducting thin films

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Suppression of the “notch effect” in microwave surface resistance in

RHEED controlled ultra-thin buffer layers of SrTiO3 have been deposited on (100) MgO by pulsed laser deposition to growth YBaCuO films for microwave applications. A buffer layer with a thickness between 2 and 15 nm, i.e. 5 to 40 unit cells of SrTiO3, is sufficient to expand to more than 60 °C the range of deposition temperatures leading to low microwave surface resistance. The Rs values are as good as those obtained on LaAlO3 substrates with a slighly lower magnetic field dependency. The SrTiO3 seed layer induces an oriented epitaxial growth with YBCO [100] // MgO [100] over this range of deposition temperatures

Epitaxial YBa2Cu3O7-8/SrTiO3 heterostructures grown by pulsed laser deposition for voltage agile microwave filter applications

The performance of tunable microwave devices based on heteroepitaxial YBa2Cu3Ox/SrTiO3 films on (001) LaAlO3 substrate has been evaluated. It has been ascertained that 'out-of-plane' SrTiO3 lattice parameter is the relevant factor in determining both the agility and dielectric loss of the SrTiO3 layers. After high temperature annealing (1100 °C, 1 atm O2), only SrTiO3 layers deposited under low oxygen pressure (∼ 10-5 Torr) show an appreciable reduction of the dielectric losses whilst maintaining high agility. Annealed samples exhibit voltage independent losses of ∼ 5.10-3 simultaneously with 55% dielectric agility at 6 GHz and 77K

Active devices choice and design of an all cryogenic superconductor resonator oscillator

International audienceSeveral silicon-germanium bipolar transistors have been measured at cryogenic temperature regarding their gain and phase noise performance. The electrical model of the chosen device has been extracted. Using this model, the phase noise performance of a cryogenic superconductor oscillator has been simulated. The results are very promising, with a phase noise level of-155 dBc/Hz at 1 kHz offset from of a 1 GHz carrier

Concept of Superconducting Pipeline A/D Converter

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A low phase noise all cryogenic microwave oscillator based on a superconductor resonator

International audienceA 1 GHz full cryogenic oscillator is presented. The oscillator is based on a planar superconductor resonator featuring a loaded Q factor of 200 000 at low microwave input power (unloaded Q of 400 000) and on amplifying parts realized with SiGe bipolar transistors. The circuit is designed with an harmonic balance software and realized on alumina substrate. A nonlinear model is extracted at low temperature both for the transistor and the resonator. This double nonlinearity increases the difficulty of the oscillator design and implies a strategy to limit the power inside the resonator. The vibrations of the cryogenerator are also a serious issue to get high performance. Finally, the oscillator features a phase noise of-112 dBc/Hz at 100 Hz offset frequency and a phase noise floor of -170 dBc/Hz (100 kHz offset) at a temperature of 65 K

Advances in the application of high TcT_{\rm c} superconductors to microwave devices for analog signal processing

During the last five years, the surface resistance $R_{\rm s}$ (10 GHs, 77 K) of YBCO thin films has decreased from a value of about 10 to 20 milliohms — i.e. the same as cooled pure copper or as bulk YBCO — down to values lower than 200 micro-ohms, close to the theoretical value of 100 micro-ohms obtained by a straightforward calculation from BCS theory. This improvement of $R_{\rm s}$ is due to a better quality of the material from random grain ceramics to quasi epitaxial films. These highly textured films can be obtained by many deposition methods : sputtering, laser ablation, co-evaporation, molecular beam epitaxy, MOCVD, using heating sample holders in order to obtain in situ crystal oriented layers. The value of the surface resistance is about one hundred times lower than that of usual metallizations, which can be used either to improve the specifications of some components by two order of magnitude such as high $Q$ 3D resonators ($Q > 10^6$ for low phase noise oscillators) and high $Q$ inductances ($Q > 10^4$ for circuit matching of antennae in the MHz range) or to reduce the size of voluminous devices such as filter banks for multiplexing or spectral analysis