WO2005067074A1

WO2005067074A1 - Electroactive component

Info

Publication number: WO2005067074A1
Application number: PCT/FI2004/000013
Authority: WO
Inventors: Jari Juuti; Pekka Moilanen; Seppo LEPPÄVUORI
Original assignee: Jari Juuti; Pekka Moilanen; Leppaevuori Seppo
Priority date: 2004-01-09
Filing date: 2004-01-09
Publication date: 2005-07-21

Abstract

The invention is concerned with a method of preparing an electroactive component and an electroactive component. In the solution, a component structure of at least one pre-sintered electroactive element (100) and at least one vitrifiable element (102) is formed, the bending, pre-stressing and permanent jointing together of which is performed by sintering.

Description

ELECTROACTIVE COMPONENT

FIELD

The invention is concerned with an electroactive component, which can be used e.g. as an actuator, a sensor, and a transformer, and a method for preparing an electroactive component.

BACKGROUND

An electroactive component performs an electromechanical transformation, wherein an electric signal modifies the form of a component or the modification of the form of the component causes an electric signal. Of this reason, electroactive components can be used as actuators, sensors, and transformers.

The function of electroactive components can be intensified by forming a biased structure, which comprises several layers fastened to eachother. The different layers of the biased components can be formed by laminating, bonding, gluing, reducing or sintering.

In the reduction technique, an example of which is the RAINBOW technique (Reduced And Internally Biased Oxide Wafer), the component chosen is a piezoelectric or electrorestrictive material containing lead, the lower surface of which is reduced with carbon (graphite) in a high temperature (600 - 1000°C). The reduction causes a layer of lead to be formed on the lower surface of the component, and due to the different thermal expansion coefficients of ceramics and lead, a bias (prestress) is formed in the structure, which is bent.

In connection techniques, such as e.g. the CRESCENT or CERAMBOW techniques (CERAMic Biased Oxide Wafer), a metal sheet is fastened with a ceramic electrode element in an elevated temperature (200 - 400°C). The stress state of the component depends on the different thermal expansion coefficients of ceramics and lead and possibly also on the pressure used in connection with the construction.

In the THUNDER technique (Thin layer Unimorph DrivER and sensor), metal sheets LARC™-SI of different thicknesses are glued or laminated on both sides of the ceramics by means of a polyimide adhesive in an elevated temperature without pressure or by means of pressure. Due to the different thermal expansion coefficients of ceramics and lead, a bias (prestress) is formed in the component, which is bent.

An electroactive component can also be prepared by laminating two pieces of the same thickness and size but of different ceramic materials together. As the pieces are not sintered, the bending and degree of stressing is controlled by regulating the kinetics of the joint sintering, which enables either a straight structure or a structure, which is bent into the desired direction. Components produced in this way have, however, poor performance characteristics.

These solutions have, however, several problems. None of the known solutions is suitable for mass production of electroactive components because of their complexity and arduousness.

BRIEF DESCRIPTION

The object of the invention is to realize an improved method of preparation and a component in accordance with the method.

This is achieved with a method of preparation of an electroactive component, in which method, the electroactive component comprises two electrodes with one electroactive element between them. In the method, there is furthermore formed a component structure comprising at least one pre-sintered electroactive element and at least one vitrifiable element; and bending, pre-stressing and a persistent jointing of the elements of the component structure is performed by sintering. The invention is also concerned with an electroactive component comprising two electrodes and an electroactive element between the electrodes. Furthermore, the electroactive component comprises a component structure of at least two elements for the purpose of the electroactive function, which structure has at least one pre- sintered electroactive element and at least one vitrifiable element, and bending, pre- stressing and persistent jointing of the elements of the component structure have been performed by sintering.

The preferable embodiments of the invention are described in the subclaims.

The invention is based on that at least one pre-sintered electroactive element and at least one element vitrifiable in the process are bent, pre-stressed and permanently joined together.

There are several advantages achieved with the solution of the invention. The solution enables a simple and linear preparation of the electroactive component in such a way that the solution can be applied also for mass production.

LIST OF FIGURES

The invention will now be described in connection with preferable embodiments, in which

Figures 1 A - 1 B presents the manufacturing of a two-part component structure Figures 2A - 2B presents the manufacturing of a three-part component structure

Figures 3A - 3B present the manufacturing of a multiple-part component structure, wherein the vitrifiable element is a ceramics

Figures 4A - 4B present the manufacturing of a multiple-part component structure with several conducting elements and wherein the vitrifiable element is a ceramics, and

Figures 5A - 5B present the manufacturing of a component structure with several conducting elements DESCRIPTION OF EMBODIMENTS

The presented method of manufacture is suitable for such electroactive components as actuators, sensors and transformers but not restricted to these.

Sintering can be defined as solidification of a substance in temperatures lower than the melting temperature. Glass is often used in electroactive ceramic materials to drop the sintering temperature to a more suitable level. This takes place through a melt phase of the glass, in other words, a part of the vitrifiable material is melt (the glass) and a part is not (the ceramic material). The amount of glass in the ceramics is 2 - 10 %. In the glass-ceramics mixture, the melt phase of the glass works as a sintering aid between the ceramic particles as it were a fluidizer.

Let us first study the manufacturing of the electroactive component by means of figure 1A. A vitrifiable element 102 has been put under a pre-sintered electroactive element 100. With pre-sintered component is meant a component that is sintered or almost completely sintered. The vitrifiable element 102 can be non-sintered and the vitrifiable element 102 can work as one of the electrodes of the component, whereby the vitrifiable element 102 can be of metal. When the elements 100 and 102, which are fastened to each other, are sintered, the elements adhere permanently to each other by forming a component structure, which is bent as presented in figure 1B. The sintering that fastens the elements 100 and 102 to each other is performed in a lower temperature than the pre-sintering of the electro active element 100. The sintering temperature can be ca 600°C - 1200°C. The bending of the component structure is a consequence of the fact that the sintering especially shrinks the element 102, but does not shrink the element 100, as that is pre-sintered, and the shrinking causes a pre-tension between the elements and a bending of the structure. The bending and the pre-stress are also influenced by the different coefficients of thermal expansion. When the temperature changes from the sintering temperature to ordinary room temperature, the temperature change also has an effect of the bending and the prestress. The bending and the pre-stressing of the component structure can thus be adjusted also by making use of the coefficients of thermal expansion in addition to the sintering. The component structure presented in figures 2A - 2B is otherwise similar to that presented in figures 1A - 1B, but in addition to the vitrifiable element 102 fastened below the pre-sintered electro active element 100, there is also a vitrifiable element 200 above the electro active element 100. The vitrifiable element 200 can be non- sintered and the vitrifiable elements 102, 200 can work as electrodes of the component, whereby the vitrifiable elements 102, 200 can be of metal or other conductive material. The vitrifiable elements 102, 200 can be of the same material but of different thickness. In such a way, the bending and the pre-stress can be influenced by means of the thickness of the vitrifiable elements. In addition to the thickness of the vitrifiable elements, also the thickness of the electroactive element and of other possible elements influence on the bending and the pre-stress. In alternative, the vitrifiable elements can be of different materials, whereby the vitrifiable elements 102, 200 can have the same thickness or different thickness. Thus, the bending and pre-stress can be affected also by the selection of the material for the vitrifiable elements. When the elements 100, 102, 200, which touch each other are sintered, the elements adhere permanently to each other and the component structure is bent as is presented in figure 2B. The bending is a consequence of that the elements 102, 200 shrink during the sintering, but as the elements 102, 200 either are of different thickness or of different materials, the shrinking of element 102 causes the bigger force (element 102 thought to be thicker or to shrink more of material reasons), which decides the bending direction.

In figures 3A - 3B, there is presented a component structure, wherein a vitrifiable ceramic element 102 is fastened to a pre-sintered electro active element 100. Furthermore, vitrifiable elements 300, 302 are fastened on both outer surfaces in this structure, which elements can work as electrodes of the components. Instead of metal elements, also other conductive vitrifiable elements can be used. When a component structure is sintered, the elements adhere permanently to each other and the component structure is bent as is presented in figure 3B. The bending and the pre-stressing are caused by the fact that especially the vitrifiable ceramic element shrinks during the sintering and bends the structure. Also other vitrifiable elements affect the bending and the pre-stressing. The advantage of this structure is e.g. that the temperature dependence is smaller because the difference of thermal expansion between the ceramic materials is smaller than for example between a metal and a ceramic material.

Figure 4A - 4B presents a structure, wherein three vitrifiable metal layers 400 - 404 are used. The pre-sintered electroactive element 100 is between the vitrifiable metal element 400, which can work as one of the electrodes of the component and the vitrifiable metal element 402. The metal element 402, in turn, is in contact with the vitrifiable ceramic element 102. The vitrifiable metal element 404 is lowest and it can work as the third electrode of the component. Instead of metal elements, also other conductive, vitrifiable elements can be used. The thin metal layers, which work as electrodes can be sintered in the structure before the pre-stressing (e.g. elements 400, 402, but not 404). If the metal stays outside the structure and does not cause a pre-stress, it can be added later. Also in this structure, it is especially the shrinking of the vitrifiable ceramic element 102 that causes the bending and the pre-stress during the sintering, even if also the other vitrifiable elements influence the bending and the pre-stress. The sintered structure is presented in figure 4B. Such a multilayer structure increases the mobility of the component and enables a pre-setting of the component. The pre-setting is made e.g. in such a way that the different poles of an electric power supply are connected to the metal elements 402 and 404, whereby an electric field is formed between the metal elements 402 and 404, which field bends the structure in the desired way. The sensor, actuator and the transformer functions themselves can be performed by means of the metal elements 400 and 402. The presetting enables e.g. a temperature compensation to be made.

Still one possible structure has been presented in figures 5A - 5B. In this structure, the metal elements 500 and 502, which are of pre-sintered (solid) metal, are lowest and topmost. The pre-sintered electroactive element 100 is between the vitrifiable metal element 200 and the vitrifiable metal element 102. The vitrifiable metal elements 102,200 are either of different thickness or of different materials as in the case of figures 2A -2B and instead of metal elements, also other sintered elements can be used. When the elements are sintered together, the structure is pre-stressed and bent as presented in figure 5B. The bending is due to the fact that the element 102 fastens the elements 500 and 100 together during the sintering. During the sintering, element 102 bends the structure a little, but the real pre-stressing is formed during the cooling down of the component due to the different coefficients of thermal expansion of the elements 100 and 102. The advantage with such a structure is e.g. that the vitrifiable material can be used a little, the structure becomes very strong and has a high pre-stress because of the solid metal.

In the presented solutions, the non-sintered metal and ceramic elements or other non-sintered elements can be fastened to each other in different ways known in themselves, e.g. by dipping, spraying, spreading with comb, thick layer printing, lamination of band cast material and so on. The materials used as the electro active elements can be piezoelectric compounds, such as e.g. PZT (lead zirconium titanate), PLZT (lead lantane zirconium titanate), PMN-PT (lead magnesium-niobate lead titanate) and PZN-PT (lead zink niobate-lead titanate) but with not restricting to these. Also electrorestrictive compounds can be used as electroactive elements. Furthermore, memory ceramics are possible electro active elements. The vitrifiable elements can e.g. be different metals, such as silver palladium, copper, aluminum or generally conductors used in electro technique. Furthermore, the vitrifiable elements used can be non-sintered electroactive elements. Even if the material thicknesses can be freely chosen, the design can be started from that the thickness of the pre- sintered electro active element is ca two-thirds of the thickness of the component structure and the thickness of the vitrifiable elements ca one-third of the component structure.

By means of the presented solution, components with a big mobility and a moderate load can be mass produced. The components reach the electro mechanical responses of modern pre-stressed components.

Due to the manufacturing method of the components in question, it can also be used in THUNDER, CERAMBOW, CRESCENT processes or in non-prestressed gluing processes (which also increases the performance of the component).

The pre-stressed electroactive component in question can be applied to load speakers and pumps because of the high responses of the component with relatively low frequencies. Applications are e.g. valves, regulators, relays, deflectors and scanners, optic regulators, linear transformers. As the structures are fast, exact, they work within a broad frequency area and big responses.

Even if the invention has been further described by referring to the examples of the accompanied drawings, it is clear that the invention is not restricted to them, but can be modified in many ways within the scope of the enclosed patent claims.

Claims

1. Method for preparing an electroactive component, in which method the electroactive component comprises two electrodes, between which there is at least one electroactive element (100), characterized in that a component structure is formed, which comprises at least one pre-sintered electroactive element (100) and at least one vitrifiable element (102, 200, 300, 302, 400-404); and bending, pre-stressing and persistent jointing of the elements together is performed.

2. Method of claim 1, characterized in that the bending and pre-stressing of the components structure in the sintering step is regulated by means of the thickness of at least one vitrifiable element (102, 200, 300, 302, 400 - 404).

3. Method of claim ^characterized in that the bending and pre-stressing of the components structure in the sintering step is regulated by means of the material choice of at least one vitrifiable element (102, 200, 300, 302, 400 - 404).

4. Method of claim 1, characterized in that at least one vitrifiable element (102, 200, 300, 302, 400 - 404) is of metal.

5. Method of claim ^characterized in that at least one vitrifiable element (102, 200, 300, 302, 400 - 404) is a piezoelectric or electrorestrictive compound.

6. Method of claim 1, characterized in that each pre-sintered element (100) is a piezoelectric or electrorestrictive compound.

7. Electroactive component, which comprises two electrodes and an electroactive element (100) between the electrodes, characterized in that, the the electroactive component comprises a component structure of at least two elements for an electroactive activity, which structure contains at least one pre- sintered element (100) and at least one vitrifiable element (102, 200, 300, 302, 400 - 404), and bending, pre-stressing and permanent jointing of the elements together has been performed by sintering.

8. Component of claim 7, characterized in that bending and pre-stressing of the component structure are dependent of the thickness of at least one vitrifiable element (102, 200, 300, 302, 400 - 404).

9. Component of claim 7, characterized in that bending and pre-stressing of the component structure are dependent of the material of at least one vitrifiable element (102, 200, 300, 302, 400 - 404).

10. Component of claim 7, ch a racterized in that at least one vitrifiable element (102, 200, 300, 302, 400 - 404) is of metal.

11. Component of claim 7, ch a racte rized in that at least one vitrifiable element (102, 200, 300, 302, 400 - 404) is a piezoelectric or electrorestrictive compound.

12. Component of claim 7, characterized in that at least one pre-sintered element (102, 200, 300, 302, 400 - 404) is a piezoelectric or electrorestrictive compound.