Kevin Nadaud

Effect of Manganese Doping of BaSrTiO 3 on Diffusion and Domain Wall Pinning

In the present paper, the influence of manganese doping on the dielectric properties of BaSrTiO 3 thin films is presented. The real and imaginary parts of the materials permittivity have been measured in a large frequency range (100 Hz – 1 MHz) and as a function of the electric field. The tunability and the figure of merit of the material have been obtained from the measurement of the permittivity under an applied DC bias electric field. For the undoped material, the dielectric losses become important for a large DC bias which leads to breakdown. At a suitable dopant rate, this effect disappears. In order to better understand the origin of the related phenomena, we measure the permittivity as a function of the AC excitation amplitude and we decompose the obtained permittivity with the hyperbolic law. This enables to extract the different contributions of the bulk (low frequency diffusion and high frequency lattice relaxation) and of the domain wall motions (vibration and pinning/unpinning) to the materials dielectric permittivity and to understand the effect of manganese doping on each contribution. Knowledge of the related mechanisms allows us to establish the optimum dopant rate (mainly conditioned by the lattice contribution) and to reduce the domain wall motion, which finally is beneficial for the desired properties of the ferroelectric thin film. A particular attention is paid to low frequency diffusion, an especially harmful effect when a DC biasing is mandatory (tunable electronic component in mobile telecommunication devices for example).

A new method of dielectric characterization in the microwave range for high-k ferroelectric thin films

In this paper we propose a new method of dielectric characterization of high-k thin films based on the measurement of coplanar capacitor inserts between two coplanar waveguide transmission lines. The measurement geometry is deposed on the thin film which is elaborate on an insulating substrate. The thin film permittivity is extracted with the help of a mathematical model describing the capacitance between two conductor plates deposed on a 2-layers substrate. A simple correction is proposed in order to enhance the matching between the model and the full wave simulation. The results of the proposed measurement method are compared to those of a classical characterization technique using parallel plate capacitor geometry.

A simple phase-shifting cell for reflectarray using a slot loaded with a ferroelectric capacitor

A tunable reflectarray phase-shifting cell, designed for a resonance frequency of 5.6 GHz, is presented. The cell is based on a simple slot topology and loaded by a ferroelectric thin film capacitor of 60% tunability under 400 kV/cm bias electric field. The cell provides 245 degrees of phase-shifting.

Decomposition of the different contributions to permittivity, losses, and tunability in BaSrTiO3 thin films using the hyperbolic law

In this paper, the different contributions to the permittivity of a 1% manganese-doped BaSrTiO3 thin film are presented as a function of the applied DC field. The hyperbolic law has been used to discern the lattice, domain wall vibration, and pinning/unpinning contributions. This decomposition permits us to study the weight of the respective contribution in the total permittivity, the losses, and the tunability. By determining the figure of merit (FoM) of each contribution, the ratio between tun-ability and losses, it is possible to identify the phenomenon which should be limited or enhanced in order to optimize the materials dielectric properties. It is shown that the tunability of the domain wall contribution (approximately 80%) is very important compared to the lattice contribution (41%), the associated dissipation factor, however, is also much larger (0.2 instead of 0.014). Even if the domain wall contribution has been shown to be weak in the investigated thin film (less than 3% in permittivity and tunability), the weight of the losses is not negligible (around 18%). Hence, the domain contribution has to be limited in order to conserve a high FoM for the material. Moreover, it is shown that the AC field used for the materials characterization is important because it governs the weight of the domain wall losses and thus the FoM.

Domain wall motions in BST ferroelectric thin films in the microwave frequency range

The existence of domain wall motion at microwave frequencies and its contribution to the ferroelectric complex permittivity is shown by evaluating the dielectric properties of BaSrTiO 3 (BST) thin films as a function of the incident power. Even at low AC field amplitudes, the presence of the domain walls and the correlated motions (vibration and jumps) result in sensitivity of the dielectric properties to the incident field amplitude. Although the contribution of domain wall motion to the real part of the permittivity is not preponderant (less than 10 %), it represents more than 50 % of the materials global dielectric losses. This illustrates the importance to consider domain wall motion even in the microwave frequency region and the necessity to take into account the applied AC field amplitude (and thus the incident power) when characterizing ferroelectric materials. The present study has been realized on BST thin films, elaborated by pulsed laser deposition on MgO/Ir substrates.

Realization and characterization of manganese doped BST thin films for reflectarray applications

In the present work, Mn-doped Ba1-xSrxTiO3 (BST) thin films were realized by Chemical Solution Deposition (CSD) on alumina as the foreseen application for a reflect array needs integration of the ferroelectric on an insulating substrate. The optimum dopant rate to be inserted depending on the materials defect density, we have studied BST doping with a manganese content ranging from 0% to 2%. The dielectric and electrical characteristics were investigated as a function of the Mn content in the frequency range of 100 Hz to 5 GHz.

Effect of the incident power on permittivity, losses and tunability of BaSrTiO 3 thin films in the microwave frequency range

Domain wall motions in ferroelectrics participate to the materials complex permittiv-ity and are responsible for their sensitivity of the dielectric properties to the driving electric field and thus to the incident power at microwave frequencies. In the present study, the dependence of the permittivity, the dielectric losses and the tunability of Ba 2/3 Sr 1/3 TiO 3 (BST) thin films on the incident power and on the bias fields is examined at a frequency of 500 MHz. While, the domain wall motion participates only slightly to the permittivity (< 5 %), it strongly influences the losses due to its very dissipative behavior. As a consequence, the Figure of Merit (FoM , ratio between tunability and dielectric losses) of the material depends on the applied microwave power. In the present study, a decrease of the FoM from 29 to 21 is observed for an incident power varying from −20 dBm to 5 dBm. When characterizing ferroelectric materials, the incident power has to be considered; moreover, domain wall motion effects should be limited in order to achieve a high FoM and less power sensitivity.

Modified approach for high frequency dielectric characterization of thinly metallized soft polymer film using grounded coplanar waveguide

In this paper, we introduce the dielectric characterization of soft polymer, polyurethane (PU), between 1 and 31 GHz frequency band using Grounded CoPlanar Waveguide (GCPW) lines with a modified analytical method. The unavoidable thin metallization (1 μm) of GCPW lines on polyurethane yields high conductor losses, which contribute to the extracted global losses up to 58% at 4 GHz. In order to get more precisely the dielectric losses, a modification of an already existing analytical model by coupling it with 3D electromagnetic simulations is proposed, which allows to estimate and subtract quickly the conductor losses. The measurements indicated that polyurethane relative permittivity ranges from 3.49 to 2.65 and the loss tangent was about 0.08, which is in agreement with the state of the art on this grade of PU as well as the Metal-Insulator-Metal capacitors characterizations (from 10−1 to 107 Hz and from 2 × 108 to 5 × 109 Hz). The proposed approach may open a fast and simple way for precisely determining...

Stacked slot antenna for wireless communication

This paper presents a study of a printed rectangular slot antenna that has been folded twice by using a multilayer printed circuit board (PCB) structure. The investigation carried out show there is an optimal way to fold the slot antenna while keeping its intrinsic electrical behavior and achieving an interesting size reduction. The potential of the proposed concept is demonstrated with the design of a folded slot antenna devoted for WLAN or Bluetooth applications operating in the 2.4GHz band, using low-cost multilayer FR4 substrate.