Nonlinear mechanisms in passive microwave devices

Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria de les TICThe telecommunications industry follows a tendency towards smaller devices, higher power and higher frequency, which imply an increase on the complexity of the electronics involved. Moreover, there is a need for extended capabilities like frequency tunable devices, ultra-low losses or high power handling, which make use of advanced materials for these purposes. In addition, increasingly demanding communication standards and regulations push the limits of the acceptable performance degrading indicators. This is the case of nonlinearities, whose effects, like increased Adjacent Channel Power Ratio (ACPR), harmonics, or intermodulation distortion among others, are being included in the performance requirements, as maximum tolerable levels. In this context, proper modeling of the devices at the design stage is of crucial importance in predicting not only the device performance but also the global system indicators and to make sure that the requirements are fulfilled. In accordance with that, this work proposes the necessary steps for circuit models implementation of different passive microwave devices, from the linear and nonlinear measurements to the simulations to validate them. Bulk acoustic wave resonators and transmission lines made of high temperature superconductors, ferroelectrics or regular metals and dielectrics are the subject of this work. Both phenomenological and physical approaches are considered and circuit models are proposed and compared with measurements. The nonlinear observables, being harmonics, intermodulation distortion, and saturation or detuning, are properly related to the material properties that originate them. The obtained models can be used in circuit simulators to predict the performance of these microwave devices under complex modulated signals, or even be used to predict their performance when integrated into more complex systems. A key step to achieve this goal is an accurate characterization of materials and devices, which is faced by making use of advanced measurement techniques. Therefore, considerations on special measurement setups are being made along this thesis.Award-winningPostprint (published version

The effects of granularity on the microwave surface impedance of high kappa superconductors

The microwave surface impedance of granular high temperature superconductors is an important figure of merit for technological applications. Because the behavior of the granular materials deviates significantly from that of the ideal defect free superconductors, the loss mechanisms are not fully understood. This dissertation seeks to quantify the contribution of granularity to centimeter wave and millimeter wave losses. By understanding these losses, the superconductive coupling between neighboring grains can also be understood.;The weakly coupled grain model is used as a phenomenological description of the microwave surface impedance. The granular superconducting surface is modelled as an effective resistively shunted Josephson junction. The measured surface impedance is compared to the model by plotting the normalized surface resistance versus the normalized surface reactance.;The model offers a quantitative explanation of many features observed in the surface impedance data including a local maximum in the surface reactance versus static magnetic field. The model also predicts the weaker than quadratic BCS frequency dependence of the surface resistance. The surface impedance of granular superconductors is always observed to saturate in high static magnetic fields. From analysis with the weakly coupled grain model it is concluded that the saturation is due to superconducting microshorts with properties which are independent of magnetic field.;Finally, measurement of surface resistance with an open Fabry-Perot resonator is treated within as a mini-dissertation. The loss mechanisms in the open resonator geometry are considered. The ohmic losses are computed numerically from a vector theory, and Bethe diffraction theory is used to compute a lower limit for losses arising from mode mixing

Noise and dissipation in superconducting granular aluminum circuits

In recent years, granular aluminum has emerged to a promising candidate to fill the gap of a high performance, high kinetic inductance material in superconducting detectors, amplifiers, and qubits. In this work, the noise properties of superconducting resonators made from granular aluminum films are studied in detail. The fluctuations of their fundamental frequency are analyzed, and electric fields are employed to investigate dielectric loss, revealing strongly coupled, microscopic two-level defects. The findings lead to a better understanding of disordered materials in the context of superconducting qubits and other quantum circuits

MICROWAVE STUDY OF THE PROPERTIES OF UNCONVENTIONAL SUPERCONDUCTING SYSTEMS

Microwave techniques have been widely used to characterize properties of conventional superconducting systems. Examples include characterizing the magnetic penetration depth of bulk crystals and thin films, residual resistance of superconducting radio-frequency cavity systems for use in particle accelerators, and resonance properties of superconducting microwave electronic circuit components such as coplanar waveguides and Josephson junction devices. In recent decades, new types of superconducting systems have appeared and massive characterization efforts have been made through low frequency techniques such as transport resistivity measurement, quantum oscillations in electrical resistance and magnetic susceptibility, scanning tunneling microscopy, optical frequency techniques, X-ray, angle-resolved photoemission spectroscopy, and Raman spectroscopy. On the other hand, microwave characterization of these new systems has been less frequent. As the diversity of an ecosystem helps the system to be more robust, the diversity of scientific measurements provides a more thorough understanding of a physical system because of the complimentary advantages of each measurement. The advantages of the microwave technique are first, it is non-destructive since the measurement does not require galvanic contact between the probe and the sample. Second, it has a good signal-to-noise ratio because it employs sensitive high frequency instruments and techniques. Third, the microwaves only marginally perturb the system under investigation since the photon energy of the probing signal is typically much lower than the maximum superconducting energy gap, which is not the case for optical techniques. In this thesis, unconventional superconducting systems, such as superconductors with non-s-wave pairing symmetry and superconductors with non-trivial topology, are investigated by means of microwave techniques. The thesis consists of two parts. In Part 1, I will discuss a newly developed microwave superconducting gap spectroscopy system. Using a combination of resonant microwave transmission technique and laser scanning microscopy, I demonstrated that the new technique can directly image the pairing symmetry of superconductors with unconventional pairing symmetries. During the demonstration with an example d-wave superconductor, a signature of Andreev bound states was also found. A phenomenological model to explain the observed properties of the Andreev bound states is also discussed. Lastly, an effort to broaden the adaptability of the new technique to samples of more general morphology is discussed. In Part 2, I describe a microwave surface impedance technique and its application to the characterization of topological superconducting systems. A thickness dependent surface reactance study of an artificial topological superconductor SmB6/YB6 (topological insulator / superconductor bilayer) was used to determine the characteristic lengths of the system (normal coherence length, penetration depth, and thickness of the topological surface state), and revealed robust bulk insulating properties of SmB6 thin films. A surface resistance and reactance study on the candidate intrinsic topological superconductor UTe2 revealed the existence of residual normal fluid and a chiral spin-triplet pairing state, which together point out the possible existence of an itinerant Majorana normal fluid on the surface of chiral superconductors

NASA developments in solid state power amplifiers

Over the last ten years, NASA has undertaken an extensive program aimed at development of solid state power amplifiers for space applications. Historically, the program may be divided into three phases. The first efforts were carried out in support of the advanced communications technology satellite (ACTS) program, which is developing an experimental version of a Ka-band commercial communications system. These first amplifiers attempted to use hybrid technology. The second phase was still targeted at ACTS frequencies, but concentrated on monolithic implementations, while the current, third phase, is a monolithic effort that focusses on frequencies appropriate for other NASA programs and stresses amplifier efficiency. The topics covered include: (1) 20 GHz hybrid amplifiers; (2) 20 GHz monolithic MESFET power amplifiers; (3) Texas Instruments' (TI) 20 GHz variable power amplifier; (4) TI 20 GHz high power amplifier; (5) high efficiency monolithic power amplifiers; (6) GHz high efficiency variable power amplifier; (7) TI 32 GHz monolithic power amplifier performance; (8) design goals for Hughes' 32 GHz variable power amplifier; and (9) performance goals for Hughes' pseudomorphic 60 GHz power amplifier

Magnetic, DC transport, and microwave properties of high temperature superconductors

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994.Includes bibliographical references (p. 147-156).by Paul Phong Nguyen.Ph.D

Superconducting quantum circuits for hybrid architectures

Im Bestreben nach neuen Quantentechnologien gehören supraleitende Quantenschaltkreise (SQS) zu den weltweit führenden Hardware-Plattformen, und finden bereits Anwendung in den Bereichen der Quanteninformationsverarbeitung, Quantenkommunikation und –kryptographie, sowie in der Quantensensorik. Obwohl die Kohärenz solcher Schaltkreise in den vergangenen zwei Jahrzehnten enorm gesteigert werden konnte, existieren konkurrierende Plattformen, die teilweise in bedeutenden Aspekten noch immer überlegen sind. Gerade deshalb erscheint eine Verknüpfung unterschiedlicher Implementierungen zu einer Quantenhybridarchitektur reizvoll, mit dem Ziel, die Stärken der individuellen Plattformen zu kombinieren und gleichzeitig vorhandene Schwächen auszugleichen. In diesem Zusammenhang habe ich im Rahmen meiner Dissertation eine nichtlineare Induktivität für die Verwendung in SQSs entwickelt, die, basierend auf dem ungeordneten Supraleiter „granulares Aluminium“ (grAl), auch in hohen Magnetfeldern verwendet werden kann, was eine Grundvoraussetzung für die Anwendbarkeit in Hybridstrukturen darstellt. Als Machbarkeitsnachweise habe ich den konventionellen Josephson-Kontakt in einem Transmon-Qubit mit dieser grAl-Induktivität ausgetauscht, und die Mikrowelleneigenschaften des Systems im Magnetfeld charakterisiert. Um das Signal-Rausch-Verhältnis der Messung zu verbessern, habe ich zudem einen nicht-entarteten parametrischen Verstärker entwickelt, der auf langen Ketten von Josephson-Kontakten basiert. Die Neuheit des zugrundeliegenden Konzeptes ist dabei die Verwendung von mehreren Eigenmodpaaren der Josephson-Kette, um den Frequenzbereich zwischen 1 und 10 GHz möglichst mit einem einzigen Verstärker abzudecken