DE102004036703B4 - Piezoelectric transformer - Google Patents

Abstract

Piezoelectric transformer - comprising a body (1) containing a piezoelectric material, - electrodes (31, 32, 41, 42) arranged inside the body, - an inner contact layer (61, 62, 63, 64), a plurality of the electrodes (31, 32, 41, 42) on an inner side of an insulating layer (2) electrically merges, - wherein the inner contact layer (61, 62, 63, 64) between the body (1) and the insulating layer (2 ), which comprises a vitreous material, wherein the insulating layer (2) is applied to the inner contact layer (61, 62, 63, 64), - wherein a via (7) of the insulating layer (2) between the inner contact layer (61 , 62, 63, 64) and an outer contact layer (51, 52, 53, 54) is arranged.

Description

The invention relates to a piezoelectric transformer having a body containing a piezoelectric material.

From the publication US 2,830,274 A a piezotransformer of the aforementioned type is known, which has a tubular piezoelectric body.

From the publication JP 2000-183 417A For example, a piezoelectric transformer is known in which an insulator made of glass is provided between two outer electrodes arranged next to one another and partially covers the outer electrodes.

From the publication US Pat. No. 6,577,044 B1 For example, a piezoelectric transformer covered by an insulating polymer layer is known.

From the publication WO 01/91 276 A1 is a miniature power supply with a multilayer actuator is known, which is surrounded by a plastic insulation.

From the pamphlets DE 42 24 284 A1 and JP 61-234 580 A piezoelectric transducers are known in which internal electrodes are alternately connected by galvanically applied metal precipitates with external electrodes and insulated by an insulating material from the external electrodes. The insulating material may according to the DE 42 24 284 A1 contain a glass powder.

From the publication DE 102 07 530 A1 a piezoelectric actuator is known in which an outer electrode in the form of a glass frit-containing screen printing paste is brought up.

From the publication DE 103 22 947 A1 For example, a multi-mode bulk wave filter is known in which excitation electrodes are alternately isolated by an insulating material from an input electrode and electrically connected to the input electrode.

It is an object of the invention to provide a piezoelectric transformer having good insulation properties.

This object is achieved by a transformer according to claim 1. Advantageous embodiments of the transformer are the subject of dependent claims.

In accordance with at least one embodiment, a piezoelectric transformer is provided, which has a body which contains a piezoelectric material.

A piezoelectric material may be, for example, a lead zirconate titanate ceramic (PZT).

In this context, the inverse piezoelectric effect is understood to mean that the piezoelectric ceramic, which may still need to be polarized for use of the component, undergoes deformation when an electric field is applied in parallel or in anti-parallel or at an angle to the polarization direction.

The direct piezoelectric effect is understood to mean that a voltage drops in the body when deformations occur.

Advantageously, input electrodes may be provided in the body. With the aid of the input electrodes, a mechanical deformation of the body can be caused when a voltage is applied to the input electrodes.

In another advantageous embodiment, output electrodes are provided which are in contact with the body. By means of the output electrodes, an electrical voltage occurring upon deformation of the body can be tapped.

The input electrodes and the output electrodes can also be combined with each other within a component. Then, when an alternating voltage is applied to the input electrodes, a periodically recurring deformation of the body can be produced. This periodically recurring deformation of the body may in turn cause a periodically varying voltage in the output electrodes. By suitable arrangement of the electrodes can be achieved that the output voltage is different from the input voltage. In this case, one obtains a transformer with a ratio of the voltages corresponding transmission ratio.

Preferably, the input electrodes and the output electrodes, henceforth also referred to as electrodes, are provided with connection lines in order to be able to contact the electrodes with an input voltage source or with an output voltage tap.

According to at least one embodiment, there is provided a piezoelectric transformer having a body containing a piezoelectric material. The surface of the body is at least partially covered with an insulating layer containing a vitreous material.

Covering the surface with a vitreous insulating layer has the advantage that surface currents on the surface of the body can be reduced, which would otherwise lead to a surface discharge between the electrical poles to be connected to the body. As a result, electrical malfunctions can be avoided.

In another embodiment of the transformer, electrodes are provided which are in contact with the body. For contacting the electrodes, an outer contact layer is provided, which is arranged on the outside of the insulating layer.

Such a contact layer makes it possible for electrodes, which are in contact with the body, and which are arranged, for example, inside the body, to be accessible from the outside for the purpose of contacting.

According to another embodiment, electrodes are arranged in the interior of the main body. Further, a via of the insulating layer between the contact layer and an electrode is provided. It can thereby be ensured that the electrode arranged on one side of the insulating layer can be contacted from the outside, that is to say from the outside of the insulating layer.

Such a plated-through hole can be produced, for example, by diffusing material of the contact layer or the electrode into the insulating layer or displacing it. Preferably, the material is diffused so far that it at least partially traverses the insulating layer and thus allows a current path through the insulating layer.

According to another embodiment, an inner contact layer is provided between the insulating layer and the base body, which is conductively connected to electrodes. Thus, it is possible to combine a plurality of electrodes on the inside of the insulating layer and to continue on the outside of the insulating layer only the contact from the inside of the insulating layer to the outside.

Accordingly, it is provided in another embodiment that a through-connection of the insulating layer between the outer contact layer and the inner contact layer is provided.

According to a further embodiment, at least two inner contact layers and at least two outer contact layers are provided on a side surface of the base body. The distance between the outer contact layers is greater than the distance between the inner contact layers.

This can advantageously be achieved that the distance between the electrical contacts on the surface of the transformer is further increased, whereby the electrical insulation of different electrical poles of each other is further improved.

According to another embodiment, the body has a plurality of side surfaces, wherein on each side surface at most one outer contact layer is arranged.

Such a design of the transformer can be achieved that the outer contact layers have a large distance from each other, whereby the electrical insulation of the device can be further improved.

According to another embodiment, the body is additionally covered with a layer of an insulating organic composite material.

An organic insulating material may be, for example, an insulating varnish or other material of this type commonly used in the electronics industry for protection against breakdown. The advantage is that this additional insulating layer provides better protection against electrical breakdown between external contacts.

According to another embodiment of the transformer, the body has recesses on the outer surface which are filled with the material of the insulating layer.

By filling open pores, depressions or cracks on the surface of the body, enlargement and propagation of these pores, depressions and cracks and thus mechanical damage to the transformer can be largely prevented.

In accordance with at least one embodiment, a piezoelectric transformer is disclosed, which is divided into two parts. The first part is the input part and the second part is the output part. The two parts are mechanically firmly connected. Each part has internal electrode layers that allow electrical energy to be converted into mechanical energy and vice versa. Preferably, the internal electrodes are perpendicular to the polarization direction of the respective part of the transformer. Only by the polarization, the utilization of the piezoelectric effect is made possible. Advantageously, in each Part of the transformer provided a plurality of electrode layers, wherein each adjacent electrode layers overlap each other and wherein each adjacent electrode layers are connected to different poles of an input voltage source or with different terminals of a Ausgangspannungsabgriffs. By using several electrodes, the space requirement of the piezotransformer can be reduced.

An electrical input signal is converted in the input part of the piezoelectric transformer into mechanical vibrations of the body of the transformer. Due to the mechanical coupling of the input part and the output part both parts are affected by the mechanical vibration. The conversion of electrical energy into mechanical energy occurs due to the inverse piezoelectric effect. In the output part, the mechanical vibrations generated in the input part are transformed back into an electrical signal due to the direct piezoelectric effect.

The piezoelectric transformer is preferably made by sintering a stack of overlying green sheets containing a piezoelectric ceramic. Between the green sheets electrode layers are arranged, which are applied in the form of a metal-containing paste. This results in piezoelectric transformers with a laminated structure, which are produced by common sintering and thus have a monolithic structure.

For cost reasons, copper electrodes are preferably used. However, these require special process control because copper, because of its low melting point and its strong tendency to oxidize, can not readily be processed with ceramic materials having a piezoelectric effect.

By the measure described here of covering the body with an insulating layer, in particular a good electrical insulation between the input part and the output part of the transformer can be achieved. Good insulation, which is characterized by a high electrical breakdown voltage, is particularly important for piezoelectric transformers intended for applications where a mains voltage is applied to the input side of the transformer.

In particular, the surface discharge plays a major role in the electrical breakdown. In particular, to minimize the breakdown voltage between the input and the output of the transformer, it is important to minimize the surface discharge. For this purpose, according to the invention described herein, an insulating layer is provided on the surface of the transformer. An insulating layer containing a vitreous material has two major advantages:
The first advantage is that a good electrical insulation between the primary side and the secondary side of the transformer can be achieved.

The second advantage is that vitreous materials are hard materials which are very slightly deformable below the transformation temperature, and thus only minimally dampen the vibrations of the body needed to convert electrical to mechanical energy and back.

Another aspect of the transformers described herein is that the reliability of the transformer during operation can be improved. One failure mechanism is that cracks, which tend to form on the surface of the body due to small mechanical defects, can grow, propagate inwardly, and then result in mechanical damage to the transformer. The starting point of such growing, propagating cracks may also be pores, cracks or other openings in the ceramic which may be formed during the process of manufacturing the body.

The growth of such cracks occurs in particular during the operation of the transformer, since the electric field and thus the mechanical stress in the immediate vicinity of such defects is significantly increased. Thus, the risk of mechanical failure of the device is particularly high where there are defects on the surface of the transformer. This is because the electric field on the surface has a particularly large inhomogeneity and therefore a greater field strength than inside the material. The filling of such cracks, pores or other depressions on the surface of the body can therefore reduce inhomogeneities in terms of electric fields and thus also inhomogeneities with respect to mechanical loads and thus also reduce the risk of propagating cracks into the interior of the body.

The insulating layer may preferably cover the entire body.

For producing the outer contact layers, the body may first be produced, for example, by sintering ceramic green sheets together with electrode layers formed by printing metal-containing paste. Subsequently, the body is surrounded with a vitreous material, and then, in turn, a conductive paste is applied to the surface of the vitreous layer by screen printing. Glassy material and screen printing paste are baked together.

The position of the outer contact layers in monolithic or single-layer transformers is determined by the geometry of the electrodes. In the case of multilayer transformers, i. H. in the case of laminated transformers, the position of the outer contact layer is determined by those positions where the inner electrodes of the primary side and the secondary side of the transformer reach the surface of the body. During the thermal fixation of the electrode paste, which forms the outer contact layers, and the insulating layer, diffusion of the metal contained in the electrode paste through the insulating layer, that is through the glass-containing layer can be achieved, which finally leads to a via through the insulating layer.

Transformers will be explained in more detail below on the basis of exemplary embodiments and the associated figures:

1 shows by way of example a piezoelectric transformer in a perspective view.

2 shows another exemplary piezoelectric transformer in a perspective view.

3 shows a section of the transformer 2 in a detailed sectional view.

4 shows a transformer with a square plan in a perspective view.

Elements which are identical to one another or which have the same function are provided with the same reference numerals.

1 shows a transformer with a body 1 , which is made of a piezoelectric ceramic, such as a PZT ceramic. He has an entrance part 11 and an output part 12 on. Each of these parts contains a plurality of electrodes. Between the entrance part 11 and the output part 12 is an insulation layer 13 appropriate. The entrance part 11 and the output part 12 are mechanically coupled together by the insulating layer 13 , The body 1 is surrounded by an insulating layer 2 which contains a vitreous material or which may also consist entirely of a vitreous material.

1 should show the following structure:
On the ceramic body 1 is an insulating layer 2 made of glass. On the insulating layer 2 are external electrodes 51 . 52 . 53 . 54 applied.

The glassy material may, for example, have the following chemical composition: 20.5% by weight B ₂ O ₃ + 6.8% by weight PbO + 0.3% by weight Sb ₂ O ₃ + 10.4% by weight SiO ₂ + 62.0% by weight ZnO. Materials with other compositions are also possible, as far as they are insulating.

Through the insulating layer 2 can be a good electrical insulation between the input part 11 and the output part 12 getting produced.

The input part contains a plurality of input electrodes 31 . 32 , These include input electrodes 31 the first variety, all with a common external contact 52 are contacted. The input electrodes 32 the second variety are with another common external contact 51 contacted. input electrodes 31 The first variety alternate in the layer sequence with input electrodes 32 of the second variety. The same applies to the output electrodes 41 . 42 in the output part of the transformer.

At the exit part 12 is for the output electrodes 41 as common contacting the outer contact surface 54 intended. For the output electrodes 42 the second variety is the outer contact as common contact 53 intended.

Indicated in the figure is still an additional insulating layer 9 which can surround the body and which consists of an insulating organic composite material. At the points of contact 51 . 52 . 53 . 54 assigns the layer 9 Breakthroughs on.

2 shows a component, a transformer, which is constructed similar to the transformer 1 , In contrast to 1 are inner contact layers 61 . 62 . 63 . 64 provided with the aid of which each belonging to a variety electrodes are contacted. The inner contact layers 61 . 62 . 63 . 64 are covered with the insulating layer 2 , For contacting the inner contact layers are outer contact layers 51 . 52 . 53 . 54 provided on the outside of the insulating layer 2 are attached. Otherwise, the structure of the transformer corresponds to 2 that of the transformer 1 ,

The inner contact layers thus ensure that the electrodes of a variety initially all receive a common contact and thus are at the same potential. The outer contact layer is used in each case to lead this common contact from the interior of the device to the outside, to connect from there electrical power sources or voltage taps.

The polarization of each lying between two electrodes piezoelectric layer is indicated by the arrows. From the 1 and 2 shows that adjacent piezoelectric layers are each polarized in the opposite direction. Overall, the polarization is perpendicular to the input electrodes 31 . 32 or to the output electrodes 41 . 42 and in the longitudinal direction of the body 1 ,

2 It can also be seen that the distance di of the inner contact layers is smaller than the distance da the outer contact layers. As a result, the insulation resistance between the outer contact layers can be advantageously increased again.

Indicated in the figure is still an additional insulating layer 9 which can surround the body and which consists of an insulating organic composite material. At the points of contact 51 . 52 . 53 . 54 assigns the layer 9 Breakthroughs on.

3 shows in detail the connection of the input electrodes 31 to the outer contact layer 51 , The to the outside of the body 1 led out input electrodes 31 are first contacted by the inner contact layer 61 , This also fills a depression 10 on. On the inner contact surface 61 Applied is the insulating layer 2 , On the outside of the insulating layer 2 Finally, the outer contact surface is applied 51 , By means of the via 7 may be an electrically conductive connection between the outer contact layer 51 and the inner contact layer 61 getting produced. The contact 7 is achieved by diffusing metal from the outer contact layer 51 through the insulating layer 2 through or into the insulating layer 2 into it.

The transformer off 3 is similar to the one in 2 ,

Furthermore, in 3 to realize that even the insulating layer 2 is capable of a recess 10 to fill up on the surface of the body of the transformer and thus for a smooth surface of the body 1 to provide, whereby the danger of cracks can be reduced.

4 shows a piezoelectric transformer with a square plan. The entrance part 11 is located in the upper part of the transformer. The starting part 12 is located in the lower part of the transformer. The entrance part 11 and the output part 12 are mechanically coupled together by the insulating layer 13 ,

On every side surface 81 . 82 . 83 . 84 of the body 1 is an outer contact layer 51 . 52 . 53 . 54 arranged. The contact layers 51 . 52 each contact exactly one type of output electrode. The outer contact layers 53 . 54 In each case, exactly one type of input electrode makes contact in the input part of the transformer. By positioning the outer contact layers 51 . 52 . 53 . 54 a maximum distance and thus optimum isolation of the contacts from each other can be achieved.

LIST OF REFERENCE NUMBERS

1

body

2

insulating

31, 32

input electrode

41, 42

output electrode

51, 52, 53, 54

outer contact layer

61, 62, 63, 64

inner contact layer

7

via

81, 82, 83, 84

side surface

9

additional layer

10

deepening

11

introductory

12

output portion

13

insulating

di

Distance of the inner contact layers

there

Distance of the outer contact layers

Claims (6)

Piezoelectric transformer - with one body ( 1 ) containing a piezoelectric material, - with electrodes ( 31 . 32 . 41 . 42 ), which are arranged in the interior of the body, - with an inner contact layer ( 61 . 62 . 63 . 64 ) containing a plurality of electrodes ( 31 . 32 . 41 . 42 ) on an inner side of an insulating layer ( 2 ), whereby - the inner contact layer ( 61 . 62 . 63 . 64 ) between the body ( 1 ) and the insulating layer ( 2 ), which contains a vitreous material, wherein the insulating layer ( 2 ) on the inner contact layer ( 61 . 62 . 63 . 64 ) is applied, - wherein a via ( 7 ) of the insulating layer ( 2 ) between the inner contact layer ( 61 . 62 . 63 . 64 ) and an outer contact layer ( 51 . 52 . 53 . 54 ) is arranged. Transformer according to Claim 1, in which the material of the outer contact layer ( 51 . 52 . 53 . 54 ) in the insulating layer ( 2 ) has diffused. Transformer according to one of claims 1 or 2, - in which a first inner contact layer ( 61 ) and a second inner contact layer ( 63 ) on a side surface of the body ( 1 ) is arranged, - in which on this side surface of the body ( 1 ) a first outer contact layer ( 51 ) and a second outer contact layer ( 53 ), and - in which the distance (da) between the first and the second outer contact layer ( 51 . 53 ) is greater than the distance (di) between the first and second inner contact layers (FIG. 61 . 63 ). Transformer according to one of claims 1 or 2, in which the body ( 1 ) several side surfaces ( 81 . 82 . 83 . 84 ), wherein on each side surface ( 81 . 82 . 83 . 84 ) at most one outer contact layer ( 51 . 52 . 53 . 54 ) is arranged. Transformer according to one of Claims 1 to 4, in which the body ( 1 ) additionally with a layer ( 9 ) is covered by an insulating, organic composite material. Transformer according to one of Claims 1 to 5, in which the body ( 1 ) on the outside recesses ( 10 ), which with the material of the insulating layer ( 2 ) are filled.

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