Valérie Madrangeas

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

The dielectric properties of a KTa0.65Nb0.35O3 (KTN) 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.

Invited Article: Dielectric material characterization techniques and designs of high-Q resonators for applications from micro to millimeter-waves frequencies applicable at room and cryogenic temperatures

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.

Towards achieving strong coupling in three-dimensional-cavity with solid state spin resonance

We investigate the microwavemagnetic 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 microwaveresonantcavity 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 resonatorcavity, 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.

Ultra-High Tunability of

We report the high-frequency electrical characterization of Ba(2/3)Sr(1/3)TiO3 (BST) thin films exhibiting a very high dielectric tunability with low losses at 2.45 GHz under very low applied electrical fields. BST layers were integrated in out-of-plane Metal-Insulator-Metal (MIM) devices with optimized Ir/MgO(100) bottom electrodes. The high frequency properties of BST films with thicknesses of 200 nm, 450 nm and 1450 nm were thoroughly investigated in the 100 MHz-10 GHz domain and exhibit extremely high capacitance tuning abilities of 82%, 81% and 70% respectively, under applied voltages as low as 10 V. MIM devices responses show the onset of acoustic resonances associated with the BST electrostrictive behavior under an electric field. By combining high tunability with low resistive losses under low applied voltages, these devices are opening promising avenues for their integration in high-performance tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used ISM (industrial, scientific and medical) frequency band.

\text{Ba}_{(2/3)}\text{Sr}_{(1/3)}\text{TiO}_{3}

This paper deals with a tunable bandpass Bulk Acoustic Waves (BAW) filter architecture that uses integrated negative capacitors. In previous papers, the filter architecture was realized with inductances. The drawbacks of this solution were the generation of a second parasitic shunt resonant frequency and then the low-Q factor of the inductance that finally degrades the high-Q factor of BAW resonators. The proposed solution with a negative capacitance only tunes the shunt resonance of the BAW resonator without creating a parasitic one. The circuit consists of a flip-chip assembly of a BAW Solidly Mounted Resonator (SMR) die on the top of a BiCMOS 0.25 mum chip. The potentialities of such filter architecture has been tested for the WCDMA standard.

-Based Capacitors Under Low Electric Fields

A two-pole combline band-pass filter loaded by ferroelectric MIM (Metal-Insulator-Metal) varactors is designed, fabricated and tested. The varactors use new Mn-doped Barium Strontium Titanate (BST) ferroelectric ceramics developed to improve the performances at microwave frequencies (i.e. compromise between tuning capabilities and losses). The filter measurements demonstrate a frequency tuning of more than 16% in the 370–430-MHz frequency range under an applied field of 2 kV/mm.

A tunable bandpass BAW-filter architecture using negative capacitance circuitry

Superconducting planar microwave filters manufactured without tuning functionality often do not rigorously agree with their specifications. This paper suggests a method for adjusting the center frequencies of microstrip superconducting filters without using tuning screws in the device packages. Trimming with laser ablation is judiciously used to change the resonant frequencies of cross open-loop resonators and thus adjust the center frequencies of filters. A technique for adjusting the interresonator coupling is also proposed.

Tunable RF-Filter Using Mn-Doped BST Ceramic Varactors

We report for the first time the microwave characterization of 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3 (BNT–BT0.08) ferroelectric thin films fabricated by the sol-gel method and integrated in both planar and out-of-plane tunable capacitors for agile high-frequency applications and particularly on the WiFi frequency band from 2.4 GHz to 2.49 GHz. The permittivity and loss tangent of the realized BNT-BT0.08 layers have been first measured by a resonant cavity method working at 12.5 GHz. Then, we integrated the ferroelectric material in planar inter-digitated capacitors (IDC) and in out-of-plane metal-insulator-metal (MIM) devices and investigated their specific properties (dielectric tunability and losses) on the whole 100 MHz–15 GHz frequency domain. The 3D finite-elements electromagnetic simulations of the IDC capacitances are fitting very well with their measured responses and confirm the dielectric properties determined with the cavity method. While IDCs are not exhibiting an optimal tunability, the MIM capacit...

Tuning of Superconducting Filters With Laser Ablation Technique

A new 2D and 3D software, using the method of line, has been proposed in this paper to analyze planar tunable microwave devices including ferroelectric thin-films. Next, a dynamic characterization method of ferroelectric layers and some first experimental results have been presented.

Microwave dielectric properties of BNT-BT0.08 thin films prepared by sol-gel technique

The characterization of ferroelectric thin-film planar microwave devices using the method of Line (MoL) has been summarized in this paper. Because the permittivity-dc electric field dependence in ferroelectric materials is used to tune microwave devices, it is necessary to develop a suitable analysis method to accurately characterize ferroelectric materials. This paper presents first results of 2D analysis of tunable planar devices.