Additive manufacturing processes make it possible to produce increasingly complex 3D parts. In addition, these numerical processes can be usefully used to manufacture ceramic/metal parts of high dimensional resolution with thermal, electrical and electronic properties of interest for applications in the field of power electronics. In this context, a hybrid additive machine was developed to manufacture ceramic/metal parts. This machine consists in the combination of two additive manufacturing processes: stereolithography and robocasting. Using this hybrid process, the feasibility of HTCC components has been demonstrated by building dielectric alumina by stereolithography and molybdenum conductive network by robocasting. Molybdenum-based metallic formulation adapted to the process and allowing to obtain a high conductive metallic network has been developed. The co-debinding and co-sintering cycles have been optimized to minimize the content of residual carbon and to prevent the oxidation of molybdenum. The alumina/molybdenum interface has also been observed to conclude about a possible delamination between these two materials with different thermal expansion co-efficients (CTE). Sintered HTCC parts have been characterized in the domain of hyperfrequency. The frequency responses deviate from the simulation due to a lack of dimensional accuracy of the metallic network.

K0.5Na0.5NbO3 thin films were deposited by pulsed laser deposition on (100)MgO substrates for microwave device applications. A fine epitaxial growth of pure perovskite phase was evidenced by X-ray diffraction. Dielectric characterizations were performed from 1 to 40 GHz using coplanar microwave devices printed on the 500 nm-thick K0.5Na0.5NbO3 thin films. Dielectric permittivity epsilon(r) = 355 and loss tangent tan delta = 0.35 at 10 GHz were retrieved without biasing. A comparison of the results with those retrieved from the resonant cavity method (to characterize as-deposited films) showed no deleterious influence neither from the device patterning nor the thin film-device interface. A frequency tunability up to 22% was measured under a moderate external DC bias electric field E-b(ias) = 94 kV/cm. Temperature measurements from 20 degrees to 240 degrees C exhibited a permittivity increase up to epsilon(r) = 975 coupled to a loss decrease tan delta = 0.25 at 10 GHz. According to such measurements, an orthorhombic-tetragonal phase transition was evidenced close to 220 degrees C with an increase of the frequency tunability up to 34%. Comparison of the properties of such films with those grown on R-plane sapphire substrates demonstrated the benefit brought by the epitaxial growth of K0.5Na0.5NbO3 films on (100) MgO. (C) 2020 Elsevier B.V. All rights reserved.

Stereolithography is an additive manufacturing process, which makes it possible to fabricate useful complex 3D ceramic parts with a high dimensional resolution, a good surface roughness and properties close to those obtained by classical routes. Previous work concerning LTCC components, demonstrates that it is possible, by coupling the stereolithography with robocasting additive processes, to obtain multi-material components (e.g. ceramic / metal components). On the base of this previous work, the manufacturing of HTCC components using this innovative hybrid additive manufacturing process is described. Various complex and innovative geometries of HTCC alumina/tungsten components, in order to improve the characteristics of current circuits, are built and the mechanical and electrical properties characterized. Finally, hyper-frequency parameters of simulated HTCC complex micro strip resonators were compared to measured values on components manufactured by additive manufacturing.

Actuellement, les pieces HTCC et LTCC (High and Low Temperature Co-fired Ceramics) sont elaborees selon deux procedes : le coulage en bande pour le substrat dielectrique en ceramique et la serigraphie pour la realisation des pistes et vias metalliques. Un procede de fabrication additive hybride, capable de construire une piece 3D en ceramique / metal, pourrait trouver un interet majeur dans la fabrication de composants utilises en micro-electroniques. En effet, un des principaux avantages de la fabrication additive est de pouvoir realiser des geometries qui ne peuvent actuellement pas etre obtenues en micro-electronique, ce qui permettrait d’obtenir un gain de performances compare aux circuits actuels. L’objectif de ce travail est de proposer un nouveau procede d’obtention de pieces monolithiques multimateriaux utilisant le couplage de deux technologies de fabrication additive .Une strategie combinant la stereolithographie et la micro-extrusion est proposee pour la fabrication de pieces multimateriaux HTCC et LTCC. Les pieces modeles sont des circuits electroniques dans les trois dimensions de l’espace comprenant un substrat dielectrique ainsi que des pistes horizontales et des vias. Des structures innovantes ont egalement ete construites (blindage continus et vias obliques). La caracterisations de ces composants conduit a des valeurs similaires a celles des HTCC et LTCC realises par des procedes conventionnels.

Dielectric resonators are employed to build state-of-the-art low-noise and high-stability oscillators operating at room and cryogenic temperatures. A resonator temperature coefficient of frequency is one criterion of performance. This paper reports on predictions and measurements of this temperature coefficient of frequency for three types of cylindrically symmetric Bragg resonators operated at microwave frequencies. At room temperature, microwave Bragg resonators have the best potential to reach extremely high Q-factors. Research has been conducted over the last decade on modeling, optimizing, and realizing such high Q-factor devices for applications such as filtering, sensing, and frequency metrology. We present an optimized design, which has a temperature sensitivity 2 to 4 times less than current whispering gallery mode resonators without using temperature compensating techniques and about 30% less than other existing Bragg resonators. Also, the performance of a new generation single-layered Bragg resonator, based on a hybrid-Bragg-mode, is reported with a sensitivity of about −12 ppm/K at 295 K. For a single reflector resonator, it achieves a similar level of performance as a double-Bragg-reflector resonator but with a more compact structure and performs six times better than whispering-gallery-mode resonators. The hybrid resonator promises to deliver a new generation of high-sensitivity sensors and high-stability room-temperature oscillators.

We investigate the microwave magnetic field confinement in several microwave three-dimensional (3D)-cavities, using a 3D finite-element analysis to determine the best design and achieve a strong coupling between microwave resonant cavity photons and solid state spins. Specifically, we design cavities for achieving strong coupling of electromagnetic modes with an ensemble of nitrogen vacancy (NV) defects in diamond. We report here a novel and practical cavity design with a magnetic filling factor of up to 4 times (2 times higher collective coupling) than previously achieved using one-dimensional superconducting cavities with a small mode volume. In addition, we show that by using a double-split resonator cavity, it is possible to achieve up to 200 times better cooperative factor than the currently demonstrated with NV in diamond. These designs open up further opportunities for studying strong and ultra-strong coupling effects on spins in solids using alternative systems with a wider range of design parameters. The strong coupling of paramagnetic spin defects with a photonic cavity is used in quantum computer architecture, to interface electrons spins with photons, facilitating their read-out and processing of quantum information. To achieve this, the combination of collective coupling of spins and cavity mode is more feasible and offers a promising method. This is a relevant milestone to develop advanced quantum technology and to test fundamental physics principles. Published by AIP Publishing.

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba (1-x) Sr x TiO 3 , BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

We investigate the microwave magnetic field confinement in several microwave 3D-cavities, using 3D finite-element analysis to determine the best design and achieve strong coupling between microwave resonant cavity photons and solid state spins. Specifically, we design cavities for achieving strong coupling of electromagnetic modes with an ensemble of nitrogen vacancy (NV) defects in diamond. We report here a novel and practical cavity design with a magnetic filling factor of up to 4 times (2 times higher collective coupling) than previously achieved using 1D superconducting cavities with small mode volume. In addition, we show that by using a double-split resonator cavity, it is possible to achieve up to 200 times better cooperative factor than the currently demonstrated with NV in diamond. These designs open up further opportunities for studying strong and ultra-strong coupling effects on spins in solids using alternative systems with a wider range of design parameters.

Ferroelectric (FE) thin film capacitors can be a convenient technology for tuning microwave devices. The high agility of ferroelectric materials with an applied DC bias is presented to be employed for tunable systems. Existing reconfiguration solutions are based on varactor diodes, Micro-Electro-Mechanical systems (MEMS), PIN diodes, field effect transistors (FET) or on the introduction of tunable ferroelectric materials. Among these, PIN diodes present only two possible states (On/Off) and, like the FETs devices, have high power consumption. Varactor diodes present high capacitance tunability but have a very low power handling capability (although they are widely referenced for frequency tunable antennas). In this framework, two solutions with low power consumption are emerging for the conception of reconfigurable circuits: MEMS and ferroelectric materials. The potential of ferroelectric materials is evaluated within practical devices to meet the current requirements for highly reconfigurable, integrated, efficient and low power-consuming systems. In this context, the integration of agile capacitors based on ferroelectric materials within compact devices to be reconfigurable will be presented. Indeed, the high agility these materials with an applied DC bias voltage and their reasonable loss tangent values can be employed to develop tunable systems. Particularly, reconfigurable filters, phase shifters and frequency agile antennas based on different ferroelectric materials will be discussed. The characterization of their dielectric properties at RF frequencies will be presented followed by their integration inside the devices. Reconfigurable components could present either a 2D-shape, i.e. interdigital capacitors or a 3D-shape as the Metal- Ferroelectric-Metal tunable components. Designs and performances of the devices incorporating these two kinds of ferroelctric-based components will be presented and detailed.

Dielectric resonators are key elements in many applications in micro to millimeter wave circuits, including ultra-narrow band filters and frequency-determining components for precision frequency synthesis. Distributed-layered and bulk low-loss crystalline and polycrystalline dielectric structures have become very important for building these devices. Proper design requires careful electromagnetic characterization of low-loss material properties. This includes exact simulation with precision numerical software and precise measurements of resonant modes. For example, we have developed the Whispering Gallery mode technique for microwave applications, which has now become the standard for characterizing low-loss structures. This paper will give some of the most common characterization techniques used in the micro to millimeter wave regime at room and cryogenic temperatures for designing high-Q dielectric loaded cavities.

The dielectric properties of a KTa0.65Nb0.35O3 ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers.

La cavite de type Klystron est une structure volumique constituee d'une ligne coaxiale court-circuitee et fermee a l'autre extremite sur une charge capacitive. L'objectif de cette etude consiste a inserer un materiau dans la zone capacitive afin de modifier la frequence de resonance et le facteur de qualite du mode TEM pour determiner les caracteristiques dielectriques du materiau. Dans cet article nous presentons la structure, le principe de la methode utilisee pour la modelisation, les avantages de cette structure et enfin les premiers resultats.

Cylindrical re-entrant cavities are unique three-dimensional structures that resonate with their electric and magnetic fields in separate parts of the cavity. To further understand these devices, we undertake rigorous analysis of the properties of the resonance using in-house developed Finite Element Method (FEM) software capable of dealing with small gap structures of extreme aspect ratio. Comparisons between the FEM method and experiments are consistent and we illustrate where predictions using established lumped element models work well and where they are limited. With the aid of the modeling we design a highly tunable cavity that can be tuned from 2 GHz to 22 GHz just by inserting a post into a fixed dimensioned cylindrical cavity. We show this is possible as the mode structure transforms from a re-entrant mode during the tuning process to a standard cylindrical Transverse Magnetic (TM) mode.

We propose a scalable resonator structure based on two-dimensional out-of-plane photonic band gap crystal. This resonator offers the possibility to obtain a strong confinement at terahertz domain with high quality factor.