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MAGNETOSTRICTION IN FILMS FOR INTEGRATED TECHNOLOGIES

Objective


A very successful approach in developing materials exhibiting low field large magentrostriction turned out to be with multilayers in which two magnetic layers of different nature alternate. One material has large room temperature magnetrostriction but low magnetisation while the other is magnetically soft and thinner than the magnetic exchange length. The saturation field of such of system can be considerably reduced while keeping relatively large values of the magnetostriction. The milestone values of the project were reached with this type of material.

Within the project, the influence of the substrate on the film properties was studied. Different substrates were considered : Havar, tantalum, sapphire and silicon. At the present state of knowledge, the substrate choice will strongly depend on the system function and design.
The properties of magnetrostrictive films on Si were examined in more detail. An interesting procedure consists in depositing the magnetrostrictive layer first, place a resist on top of it, pattern the resist and transfer the structure into the layer by appropriate etching process. Therefore, the resistance of magnetrostrictive layers to dry etching processes was examined in more detail. Success was obtained when room temperature etching was used.

Modelling magentrostrictive demonstrators:
Special modelling tools are required to describe the properties of magnetostrictive films which allows to take into account the non linearities of the existing strong static magneto-mechanical coupling. Thus, special emphasis was put on numerical improvement of finite element techniques. Special thin shell elements have been developed to cope with thin films unusually high length-to-thickness ratio. Different methods including iterative and strong numerical coupling have been developed and compared to adapt to the non linear strongly coupled characteristics of magentostriction. The limited data available for thin films has encouraged new solvings more adapted.
Two different cantilevers have been modelled and compared with experimental data. Similarily, two different structures of magnetostrictive micromembranes have been modelled. Results indicate that the modelling tools are very efficient to help design magnetrostrictive microstructures. They also have proved to be useful for inverse characterisation of the film properties.

Dynamic modelling was performed in a linear approximation, using the ATILA code. On the one hand, the code itself was improved, on the other hand calculation was performed on model bimorphs and on the different types of original demonstrators developed within the project : thermal-free type bimorph, micro-pump membrane and standing-wave ultrasonic demonstrators.

Building demonstrators:
A very specific objective of the project was going from the development of new high-performance magnetostrictive materials to their potential use. This was successfully achieved with the development of original demonstrators.

In Particular, a Linear Standing Wave Ultrasonic Motor (LSWUM) has been studied on detail and built. Due to stresses in the film, it was however found that the motor bends and breaks. This led to the design of the Rotating Standing Wave Ultrasonic Motor (RSWUM). This micro-motor was built in the last part of the project and very recently operated with great success.

Micro-pumps are key components for the development of integrated microanalysis systems which are one of the most promising micromachined products. A new approach to this are magnetostrictive thin film micro-membranes. Major expected advantages are the fast response time in comparison to thermal actuation and remote operation control.

Simulation of the mechanical behavior of membranes was made using the finite element method. This helped in designing. A pump was successfully developed using four Si-chips that were fabricated by laser cutting. A more original design was also examined in which the flow is produced by microdiffusers. Such a valve-less micro-pump was built with significantly increased performances.
The aims of this proposal are i) to obtain low-field, large magnetostriction in rare earth (R)-transition metal (M) based films and ii) to demonstrate the potential use of such materials in microsystems. The first aspect of this project concerns materials research which will develop along two main lines with a view to reaching the largest possible magnetostriction at fields of around 200 Oe in films prepared by sputtering techniques. The second aspect of the project is concerned with the incorporation of magnetostrictive films into microsystems. In this respect, an essential element is the compatibility of the materials and their fabrication processes involved, with the techniques needed for microsystems preparation (Si or LIGA (LIithorafie, Galvanformung, Abformung)). The third aspect concerns applications of magnetostrictive films. To illustrate possible applications, two demonstrators will be built in which the displacement of the active element will be mechanically amplified to lead to the desired effect. These will be a bimorph cantilever and a simple micro-motor. Other applications will be illustrated by constructing an acoustic resonator with magnetically-adjustable resonance frequency and a stress-controlled inductance.

The Consortium associates 7 partners from 3 European countries. Partners A, B and C are more specifically involved in materials research. They will share the work in developing films with large magnetostriction. Partners D and E will design the demonstrators and model their behaviour; both of them are very experienced in modelling and optimising the behaviour of magnetic materials within specific applications. Partners F and G which are micro-technology specialists, will be more specifically in charge of building the demonstrators and measuring their properties. The 2 endorsers are leading European industries which are closely concerned with the possible applications of magnetostrictive films, one of them being already engaged in research in this area.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
Address
Avenue Des Martyrs 25
38042 Grenoble
France

Participants (6)

CEDRAT TECHNOLOGIES SA
France
Address
Chemin Du Pre-carre 10 Zirst
38240 Meylan
Forschungszentrum Karlsruhe Technik und Umwelt GmbH
Germany
Address

76021 Karlsruhe
INSTITUT NATIONAL POLYTECHNIQUE DE GRENOBLE
France
Address
Rue De La Houille Blanche Domaine Universitaire
38402 Saint-martin-d'heres
MAX-PLANCK-GESELLSCHAFT ZUR FÖRDERUNG DER WISSENSCHAFTEN eV
Germany
Address
Heisenbergstraße 1
7000 Stuttgart
NCSR DEMOKRITOS
Greece
Address
Aghia Paraskevi Attikis
15310 Athens
Universität Gesamthochschule Kassel
Germany
Address
Heinrich-plett-straße 40
34109 Kassel