Some strategies to (co)-sinter refractory functional oxides at low temperature by spark plasma sintering

The sintering at high temperatures (1000-1400°C) of refractory oxides widely used in electronic devices, raises several issues related to defects, chemistry, microstructure and interface control. Reducing sintering temperatures below 900°C is a major challenge in particular when high relative densities, optimal microstructure and the control of reactivity at interfaces (grain boundaries, multi-materials) are mandatory. In this context, we propose to highlight some strategies focused on interfaces and phases control through two different illustrations of our recent works. The first one is focused on Micro-Electromechanical System (MEMS) energy harvesters (EH) using piezoelectric materials[1]. We will show the potentiality of SPS to co-sinter in one step and below 900°C complex devices such as screen-printed PbZrTiO3 in sandwich between two gold electrodes and supported on a stainless steel substrate. Here, the sintering aids in the pastes should be removed if possible or adapted for good adhesion, and delamination and bending of the multilayer EH must be avoided. We also intent to get rid of the annealing process after the SPS sintering. The second illustration reports on the ambitious goal to sinter zirconia ceramics at temperatures below 400°C. Recently, the exploration of non-equilibrium sintering, through transient liquid phase, hydrated precursors, or by using solvent assisted sintering, Flash sintering and Spark Plasma Sintering has been investigated to sinter ZnO and thermodynamically unstable materials at very low temperature [2-5]. Here, our approach is based on the use of specific precursors and deals with the control of transient non-equilibrium phases to find the driving force to establish the most favorable pathway for enhanced densification. [1]. M. I. Rua-Taborda, O. Santawitee, A. Phongphut, B. Chayasombat, C. Thanachayanont, S. Prichanont, C. Elissalde, J. Bernard, H. Debéda, Printed PZT Thick Films Implemented for Functionalized Gas Sensors , Key Engineering Materials, 777,158, 2018 [2].B. Dargatz, J. Gonzalez Julian, M. Bram, P. Jakes, A. Besmehn, L. Schade, R. Röder, C. Ronning and O. Guillon, “FAST/SPS sintering of nanocrystalline zinc oxide—Part I: Enhanced densification and formation of hydrogen-related defects in presence of adsorbed water, J. Eur. Ceram Soc. 36, 1207, 2016 [3]. S. Funahashi, J. Guo, H. Guo, K. Wang, A. L. Baker, K. Shiratsuyu, and C. A. Randall, Demonstration of the cold sintering process study for the densification and grain growth of ZnO ceramics, Journal of the American Ceramic Society, 100, 546, 2017. [4]. Luo J., “The scientific questions and technological opportunities of Flash sintering: from a case study of ZnO to others ceramics”, Scripta Mater., 146, 260, 2018 [5]. T. Herisson de Beauvoir, A Sangregorio, I. Cornu, C. Elissalde and M. Josse, “Cool-SPS: an opportunity for low temperature sintering of thermodynamically fragile materials” J. Mater. Chem. C, 6, 2229, 201

Feasibility of Screen-Printed PZT Microceramics for Structural Health Monitoring Applications

Using the association of low-cost screen-printing technology with the sacrificial layer method, the feasibility of totally released piezoelectric thick-film microceramics of gold-electroded PZT type is studied. After the deposition of the sacrificial layer on an alumina substrate and subsequent printing and drying of gold/PZT/gold layers, the final firing is performed at low temperature. This is followed by the releasing step of the Au/PZT/Au in a diluted acidic solution. Impedance analysis shows that the electrical properties and electromechanical coefficients of poled PZT thick films are still lower than those of PZT ceramics. This result is correlated with the high porosity rate of the PZT layer. However, these piezoelectric microceramics present desirable electromechanical behavior and can therefore be used as dynamic-mode sensors or as actuators to generate vibrations in a structure on which they are bonded. Moreover, the successful fabrication and the electromechanical impedance (EMI) levels obtained on a metallic structure suggest possible structural health monitoring applications of these screen-printed PZT microceramics

Study of Free-Standing Electroded PZT Thick-Films: From Materials to Microsystems

Free-standing electroded piezoelectric PZT thick-films are straightforward fabricated thanks to the association of the low-cost screen-printing technology with the sacrificial layer method. Au/PZT/ Au bridges are directly attached onto the alumina substrate on top of it they are processed. In addition, completely released disks are also processed. A study of the behaviour of these components shows the influence of both the releasing process and the densification on the piezoelectric properties of the PZT layer. From the electromechanical measurements, electroded PZT cantilevers and disks are promising for actuator, sensor or SHM applications

Printed piezoelectric materials for vibration-based damage detection

Piezoelectric materials are of high interest for many applications, e.g. vibrations measurement, active vibration control or vibration-based damage detection in Structural Health Monitoring (SHM). In this paper, thin electroded microceramics of piezoelectric material are straighforward fabricated thanks to the association of the screen-printing technology to the sacrificial layer method. After subsequent printing and drying of a stack of sacrificial, Au, PZT and Au layers on a substrate, piezoelectric disks are fired at 900°C and then released from the substrate. Studies of the electromechanical behaviour of these components obviously show the influence of the sacrificial layer composition on their densification and consequently their piezoelectric properties, favourable for detection of vibrations and SHM applications. Moreover, printing process might lead to lower cost of microceramics implementation than traditional ceramic process

Etude et microstructuration de composants et microsystèmes en couches épaisses

Ces activités de recherche sont principalement orientées vers la conception et la microstructuration des composants et microsystèmes à l'aide de technologies alternatives mais souvent complémentaires à la technologie Silicium. Elles comportent quatre périodes principales. En 1992, mes travaux de thèse au Laboratoire IXL de Bordeaux (devenu IMS) concernent la mise au point de dispositifs multi-capteurs sélectifs au méthane fiables, la technologie couche épaisse de sérigraphie ayant été utilisée pour la fabrication de ces microcapteurs. En 1996, lors d'un séjour post-doctoral en Allemagne à l'IMT Karlsruhe (Institut de MicroTechnologie), je m'intéresse aux microactionneurs piézoélectriques et m'initie à la technologie LIGA pour le développement d'un nouveau procédé technologique intégrant des microstructures sur un substrat piézoélectrique. En 1998, de retour au laboratoire IXL devenu ensuite IMS, je travaille à nouveau sur la technologie couches épaisses sérigraphiées avec des études sur l'influence de la porosité des couches et des interactions entre les éléments constituant les composants (électrodes, couches sensibles) sur les propriétés de composants. Puis en 2003, je me focalise plutôt sur les procédés de mise en œuvre de microstructures mobiles avec un nouveau procédé breveté dit de la couche sacrificielle et les applications en découlant. En parallèle avec ces études, une mise en valeur de matériaux novateurs de taille micrométrique ou nanométrique est réalisée avec le développement de composants basés sur des couches composites sérigraphiées. Enfin, depuis Juin 2012, une évolution naturelle vers l'électronique organique se fait puisque l'équipe PRIMS (Printed Microelectromechanical Systems) à laquelle je suis rattachée fait partie du groupe Electronique Organique et MEMS, et participe au LABEX AMADEUS et à l'EQUIPEX ELorprintec

Screen-Printed Microcantilevers for Environmental Sensing

This work investigates different geometries for fully screen-printed self-actuated self-readout microcantilevers made using a sacrificial layer process. The microcantilevers are made of PZT sandwiched between two gold electrodes. Q-factors as high as 1300 are reported. Promising theoretical sensitivities are reported (1000 Hz/µg at 620 kHz) and applications as humidity, temperature and particles sensor are explored in this work

Chapter 9: Resonant Micro-cantilever devices for gas sensing

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Les cartes d’extension PCBmod : conception et applications pédagogiques VHDL et microassemblage

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