JPH1051044A - Lamination type piezoelectric transformer element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conversion efficiency, by constituting each inner electrode of Ag-Pd mixture containing Pd of specified wt.%, which has a specified thickness. SOLUTION: Inner electrodes 6a and 6b which are alternately laminated in the input region 2 of a lamination type piezoelectric transformer element 1 are electrically connected every other electrode. In a piezoelectric transformer element having viaconductor in the element, the viaconductor is apt to absorb natural vibration of the piezoelectric transformer element, similarly to the inner electrodes, and deteriorates conversion efficiency. Each inner electrode is constituted of Ag-Pd mixture containing Pd of 20-80wt.%, and the thickness is made 1-5μm. Thereby the inner electrode is made hard to absorb the vibration, and Qm of the whole element is improved, so that the conversion efficiency of the element can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer element suitable for use as a power source of a cold cathode fluorescent lamp for a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art A cold cathode tube is usually used as a light source for a backlight for a liquid crystal display device used in a portable notebook personal computer or the like. A high voltage of 1 kV or more is required to light this cold cathode tube, and a voltage of several hundred volts is required to maintain light emission.

[0003] Due to the nature of the above-mentioned products such as notebook personal computers, there is a high demand for downsizing and power saving of a boosting module for lighting a backlight. A step-up module using a piezoelectric transformer element is used. The step-up module using such a piezoelectric transformer has an advantage that the thickness of the entire module can be reduced as compared with the step-up module using a winding transformer having the same output.

However, for example, a length of 30 mm and a width of 3
In a piezoelectric transformer element using a single-plate ceramic piezoelectric body having a size of 2 mm and a thickness of 2 mm, for example, the step-up ratio (output voltage-input voltage ratio) at the time of outputting 2 watts is as low as about 4 to 6 times. Therefore, it was necessary to connect a small-sized winding transformer to the preceding stage of the piezoelectric transformer.

Therefore, recently, a laminated piezoelectric transformer element has been proposed. The laminated piezoelectric transformer element is composed of a ceramic piezoelectric body having a thickness of about 50 to 300 μm in which input regions are alternately laminated, and internal electrodes, and the laminated internal electrodes are electrically connected every other layer and electrically connected. It has a structure in which two groups are connected, and the two groups of internal electrodes are electrically connected to two external electrodes provided on both surfaces of the input area, respectively (for example, JP-A-7-302938). That is, such a laminated piezoelectric transformer element is equivalent to a plurality of single-plate piezoelectric transformer elements connected in parallel, and is intended to obtain a high step-up ratio.

In the above-described laminated type piezoelectric transformer element, the step-up ratio under load is greatly improved, and the present inventors made a single piezoelectric layer having a thickness of about 80 μm, laminated 25 layers, and set a length of 30 layers.
When a laminated piezoelectric transformer element having a thickness of 3 mm and a width of 3 mm and a thickness of 2 mm was manufactured and tested, a boost ratio at a power output of 2 Watts of about 80 times was obtained, which was an order of magnitude higher. However, in such a laminated piezoelectric transformer element, the conversion efficiency of the transformer, that is, the value obtained by dividing the output power by the input power is 70 to 80%, which is smaller than the conversion efficiency of the single-plate element being 90% or more. Was small.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated piezoelectric transformer element having high conversion efficiency.

[0008]

The inventors of the present invention have concluded that the above-mentioned laminated piezoelectric transformer element is given to the piezoelectric transformer element when it contains a larger amount of conductive material than the ceramic piezoelectric substance used. It has been found that vibrations are easily absorbed, and as a result, the conversion efficiency is reduced. That is, they have found that the conversion efficiency of the multilayer piezoelectric transformer element can be improved by making the internal electrode as hard as possible and reducing its thickness. Therefore, based on the above findings, the present invention provides a multilayer piezoelectric transformer element having an input area composed of a plurality of ceramic piezoelectric bodies and a plurality of internal electrodes alternately stacked, wherein
Consisting of an Ag-Pd mixture containing ~ 80 wt% Pd,
Another object of the present invention is to provide a laminated piezoelectric transformer element having a thickness of 1 to 5 μm.

In the above-described multilayer piezoelectric transformer element, when a plurality of internal electrodes are electrically connected every other layer, the connection is preferably obtained at a portion exposed on the side surface of the piezoelectric transformer element. When the polarization processing of the piezoelectric transformer element is performed in the air, there is a problem that a discharge occurs between the internal electrodes exposed on the side surfaces of the element and the insulation is destroyed, so that the polarization processing may not be completely performed. In order to solve this problem, the present inventors have tried to prevent the internal electrode from being exposed on the side surface of the element, and to fill the hole provided in advance at the position where the internal electrode of the piezoelectric material is laminated with a conductor (via conductor). A multilayer piezoelectric transformer element having a structure for obtaining electrical connection between them has already been proposed (Japanese Patent Application No. 8-52553).

Although such a structure can be used in the present invention, in the piezoelectric transformer element having the above-described via conductor inside, like the internal electrode, the via conductor reduces the natural vibration of the piezoelectric transformer element. It was found that it was easy to absorb and reduced the conversion efficiency. The problem is that, like the internal electrodes described above, the via conductor is made as hard as possible and the diameter of the via conductor is reduced to a certain value or less, so that the conversion efficiency of the laminated piezoelectric transformer element having such a structure can be improved. Is found.

Therefore, a preferred embodiment of the multilayer piezoelectric transformer element of the present invention is such that the internal electrodes are not exposed on the side surfaces of the element, and the internal electrodes are formed by a conductor filled in a hole provided in the ceramic piezoelectric body in the input area. Ag-P, wherein the electrodes are electrically connected and the conductor comprises 20-80% by weight of Pd
d mixture and the conductor has a diameter of 50 to 200
μm.

[0012]

The conversion efficiency of the piezoelectric transformer is closely related to the element Qm (mechanical quality factor). The relational expression between energy loss and Qm can be derived using the formula of the step-up ratio of the Rosen-type piezoelectric transformer. According to this, as Qm increases, energy loss decreases and conversion efficiency improves.

Qm represents the difficulty of a given vibration to attenuate. If the given vibration is difficult to attenuate, the energy that must be given to continue the vibration can be small, and the conversion efficiency increases. It is.

It is common sense to use a material having a high Qm for the piezoelectric material itself used for the piezoelectric transformer element. For example, in the case of a PZT-based piezoelectric ceramic, FeZ
By adding Mn or Mn in a measured amount, a piezoelectric material having a high Qm can be obtained. However, in the case of a laminated piezoelectric transformer element, an internal electrode inserted between the piezoelectric bodies is necessarily required.

In the multilayer piezoelectric transformer element of the present invention, the internal electrode has a specific composition of Ag-
By using a Pd mixture and having a specific thickness, the Qm of the entire device is increased, and the conversion efficiency of the device is increased.

In a preferred embodiment of the present invention, the internal electrodes are electrically connected by a conductor filled in a hole provided in the ceramic piezoelectric body in the input area, and the conductor also absorbs vibration. Therefore, the conversion efficiency of the element is increased by setting the composition of the conductor to be the same as that of the above-mentioned internal electrode and making the diameter smaller than a specific size.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The structure of the multilayer piezoelectric transformer element of the present invention can be any conventionally known structure. For example, it is a Rosen type piezoelectric transformer element that vibrates in the λ mode as shown in FIG. be able to.

The laminated piezoelectric transformer element 1 of the present invention shown in FIG. 1 is a Rosen-type piezoelectric transformer element having a rectangular plate (flat rectangular parallelepiped) shape as a whole, and has an input having a size almost half each. An area 2 and an output area 3 are provided. In the input area 2, the ceramic piezoelectric bodies 7 and the internal electrodes 6 a and 6 b are alternately laminated (the ceramic piezoelectric bodies are laminated one more than the number of the internal electrodes), and the input external electrodes 4 are formed on the upper and lower surfaces. And the piezoelectric body is polarized in the thickness direction (vertical direction in FIG. 1). The output region 3 has an output external electrode 5 on the end surface on the side opposite to the input region.
The piezoelectric body is polarized in the length direction (the left-right direction in FIG. 1).

The internal electrodes 6 alternately stacked in the input area 2
a and 6b are electrically connected every other, that is, two groups in which the internal electrodes 6a are electrically connected to each other and the internal electrodes 6b are electrically connected to each other, a group of the internal electrodes 6a and the internal electrodes. 6b are formed, and each group is electrically connected to each of the upper and lower electrodes 4 in the input area.

In the piezoelectric transformer element shown in FIG. 1, the corner of the internal electrode is cut into a right-angled triangle at one of the two corners on the input area side of the element (the internal electrodes 6a and 6b and Except that the opposite corner is cut away), the internal electrode and the piezoelectric body in the input area have the same planar shape, and the internal electrode is exposed on the element side surface. Internal electrode connection conductors 8 are provided outside the two corners of the end portion on the input region side of the element, and electrically connect between the internal electrodes 6a and between the internal electrodes 6b. Each is electrically connected to one.

The internal electrodes may be electrically connected at the ends of the internal electrodes exposed on the side surfaces of the piezoelectric transformer element by the internal electrode connecting conductors 8 as shown in FIG. As disclosed in the above-mentioned Japanese Patent Application No. 8-52553, the conductive material is filled in a hole provided in the input area plane of the piezoelectric body. And by making the planar shape of the internal electrode slightly smaller than that of the piezoelectric body, and by preventing the internal electrode from being exposed on the element side when laminated, the internal electrode as described above is exposed on the element side. The problems that occur can be avoided.

In such a configuration, each piezoelectric body in the input area has two holes for receiving two conductors for each of two groups of electrically connected internal electrodes. The two holes of these piezoelectric bodies are brought into contact with the internal electrodes on each of which the conductor filled therein is laminated, and are integrated at a later firing so that the internal electrodes can be electrically connected. Although it can be provided at an arbitrary position within the piezoelectric input region, usually, it is a via hole provided at the same position of each of the stacked piezoelectric materials. These holes are filled with a conductor (via conductor) as described above.

Internal electrodes are laminated between portions corresponding to the input regions of these piezoelectric bodies. Each internal electrode is provided with one hole having a diameter larger than the conductor at a position corresponding to one of the two conductors in the laminated piezoelectric body. The holes of the internal electrodes are provided such that, when the internal electrodes are stacked via the piezoelectric body, the holes are alternately provided at positions corresponding to the two conductors of the piezoelectric body in the order in which the internal electrodes are stacked. Make electrical connections every other one. That is, in one internal electrode, a hole having a diameter larger than that of the conductor is provided at a position corresponding to one of the conductors of the piezoelectric body, and the internal electrode is formed of a conductor at that position of the piezoelectric body on both sides. On the other hand, no hole is provided in a position corresponding to the other conductor of the piezoelectric body, and the piezoelectric body is connected to the conductor at that position in the piezoelectric bodies on both sides. In the adjacent internal electrode, holes are provided in the opposite pattern for the two conductors in each of the piezoelectric bodies. With such a structure, every other electrical connection of the internal electrodes can be obtained. In particular, when the electrical connection of the internal electrodes is obtained by such a structure, the dimensions are slightly smaller than the piezoelectric body so that the internal electrodes are not exposed to the outside as described above.

FIG. 2 is a schematic cross-sectional view in the longitudinal direction of the multilayer piezoelectric transformer element of the present invention having the above-described structure, including one via hole and a portion of the via conductor 9 filled therein. FIG. 3 is a schematic cross-sectional view in the width direction of the device, including two via holes and a portion of the via conductor 9 filled therein. In the multilayer piezoelectric transformer element of the present invention shown in these figures, a plurality of internal electrodes 6a 'and 6b' provided with holes in two different patterns as described above are alternately stacked via the piezoelectric body 7. The internal electrodes 6a 'and the internal electrodes 6b' are electrically connected to each other.

In the laminated piezoelectric transformer element of the present invention having the above-described structure, a frequency corresponding to the resonance frequency determined from the material of the element and the length in the vibration direction is provided between the two input external electrodes 4. When an AC voltage is applied, the entire piezoelectric transformer element mechanically vibrates at the resonance frequency due to the inverse piezoelectric effect, and a standing wave is formed. When oscillating in the λ mode, a node (node point) of the oscillation of the standing wave is a quarter of the element length from both ends of the element (the element length is L
Then, it exists at the position of L / 4). By the piezoelectric effect of the standing wave, an AC voltage can be extracted from between the input external electrode 4 and the output external electrode 5. Since the piezoelectric transformer element is formed so that the distance between the input electrode and the output electrode is longer than the distance between the input electrodes, the voltage generated between the input electrode and the output electrode is applied between the input electrodes. Is boosted from the applied voltage.

The dimensions and the like of the laminated piezoelectric transformer element of the present invention may be the same as those of a conventionally known laminated piezoelectric transformer element, and are generally 20 to 50 mm in length and 4 to 15 m in width.
m, having a size of about 1 to 3 mm, and a piezoelectric body having a thickness of about 50 to 300 μm in the input area.
About layers are laminated. The ceramic itself forming the piezoelectric body may be a conventionally known one, and is formed of, for example, lead zirconate titanate (PZT) ceramic.

In the multilayer piezoelectric transformer element of the present invention, the internal electrode is made of Ag-P containing 20 to 80% by weight of Pd.
d. It shall consist of a mixture.

In the case of laminating ceramic dielectrics, Ag, Ag-Pd mixture, Ag-Pt mixture, Pd, Pt, Cu, Ni and the like are generally used as electrode materials.
However, a Pb-based piezoelectric material (Pb
(Zr, Ti) O ₃ etc.) in an atmosphere where oxygen is present
Since it is necessary to fire at a temperature of 00 ° C. or more, Ag, Cu, and Ni cannot be used when firing is performed together with the firing. In addition, Pt is expensive and is therefore rarely used alone. Usually, Ag-Pt mixture or Ag-Pt is used.
Conductors in the form of d mixtures are often used.

In the present invention, an Ag-Pd mixture is particularly selected from the viewpoint of improving conversion efficiency, and a mixture containing Pd in an amount of 20% by weight or more and 80% by weight or less is used.

The Ag—Pd mixture generally has a higher hardness than the Ag—Pt mixture. However, even in the Ag—Pd mixture, if the Pd content is less than 20% by weight, the “hardness” of the internal conductor (electrode) is reduced. Qm, which is considered to be due to the shortage, occurs, and the effect of improving the conversion efficiency decreases. Also,
If the amount of Pd exceeds 80% by weight, the conductor does not become fine after firing, so that Qm also decreases and the conversion efficiency does not improve.

The thickness of the internal electrode similarly affects Qm, and the degree of this effect depends on the dimensions of the piezoelectric transformer element itself,
Although it depends on the number of laminated internal electrodes, the thickness is particularly 1 to 5 μm in the laminated piezoelectric transformer element of the present invention having the general dimensions and the number of laminated layers as described above.

When the Ag-Pd conductor is laminated between the ceramic piezoelectric bodies, it is basically Q
m decreases. In the piezoelectric transformer element having the dimensions and the number of layers as described above, if the thickness of one internal electrode is more than 5 μm, this decrease cannot be ignored and the conversion efficiency cannot be tolerated. On the other hand, if it is thinner than 1 μm, the conductor metal tends to be rounded due to surface tension when fired at the same time as the piezoelectric body, resulting in a net-like conductor, resulting in a continuous conductor. It will not work. It is impossible to uniformly apply an electric field to such a conductor, and the electric-to-mechanical energy conversion capability of the piezoelectric body cannot be sufficiently brought out, resulting in lower conversion efficiency.

When the internal electrodes are electrically connected by the via conductor as described above, the via conductor absorbs the vibration of the element, and the conversion efficiency of the element decreases.
Therefore, in the case of such a structure, the via conductor also has a Pd of 2 for the same reason as described above for the internal electrode.
It is preferable to use an Ag-Pd mixture containing 0% by weight or more and 80% by weight or less. Also, as the diameter of the via conductor increases, the vibration of the element is easily absorbed, so that the diameter is set to 200 μm or less in the present invention. Also,
If the diameter is smaller than 50 μm, the conductor resistance becomes so high that it cannot be ignored, the impedance of the whole element becomes high, and as a result, the Q value decreases and the conversion efficiency decreases.

When the via conductor is provided for connection between the internal electrodes as described above, the via conductor can be provided at any position in the plane of the input area of the element, but preferably at the position of the node of the vibration of the element. To be provided. By providing the via conductor at the position where the vibration of the element is minimized, the deterioration due to the vibration of the conductor can be minimized. Further, the absorption of the vibration of the element by the via conductor can be minimized.

The method for manufacturing the multilayer piezoelectric transformer element of the present invention having the above-mentioned structure is not particularly limited, but it is preferable to use, for example, a known method for manufacturing a low-temperature fired multilayer ceramic substrate. The outline of the method for manufacturing the piezoelectric transformer element of the present invention using a known method for manufacturing a low-temperature fired multilayer ceramic substrate will be described below.

In the case of the piezoelectric transformer element of the present invention having a structure in which electrical connection is made between internal electrodes by external conductors as shown in FIG. 1, first, a piezoelectric ceramic tape formed by a doctor blade method or the like is fired, and then the desired element is obtained. Prepared is one that is cut to a size such that the plane size of is obtained. In this case, the piezoelectric ceramic tape has dimensions (lamination, firing and cutting) corresponding to the planar dimensions of a desired number of elements such that a plurality of elements can be obtained by cutting a laminate formed after laminating a plurality of piezoelectric bodies. The dimensions may be such that a desired number of elements of a desired size will be obtained later). A paste of a conductor for an internal electrode is printed on such a ceramic tape in a shape of an internal electrode on a piezoelectric ceramic tape using a mesh mask. At this time, the internal electrodes are provided on the entire surface of the input region except that a notch is provided at one corner of the element input region side end. In this case, two patterns of notches of the internal electrodes are provided at the right corner or the left corner of the input area side end. A desired number of piezoelectric ceramic tapes on which the internal electrodes are printed in the two patterns are alternately laminated in a desired number, and finally, a piezoelectric ceramic tape on which the internal electrodes are not printed is laminated on the side where the internal electrodes are exposed. Then, the piezoelectric ceramic tapes having the laminated internal electrodes are thermocompression-bonded to each other, fired, cut if necessary,
The laminated piezoelectric transformer element of the present invention can be obtained by performing processing such as grinding, baking an Ag paste or the like to provide external electrode and internal electrode connection conductors, and performing polarization processing.

In the case of the piezoelectric transformer element of the present invention having a structure in which the internal electrodes are connected by via conductors as shown in FIGS. 2 and 3, first, the doctor blade method corresponding to one layer of the piezoelectric material in the input area is used. A piezoelectric ceramic tape formed by forming a hole corresponding to a via hole is prepared. Also in this case, the piezoelectric ceramic tape has a size corresponding to a planar dimension of a desired number of elements such that a plurality of elements can be obtained by cutting a laminated body formed after laminating a plurality of piezoelectric bodies. be able to. The piezoelectric ceramic tape 10 shown in FIG. 4 was provided with eight holes 11 in pairs to obtain four piezoelectric transformer elements by baking and cutting the laminated body obtained by laminating. Things. Next, these holes are filled with a via conductor paste by a printing method using a metal mask or the like. FIG. 5 is a partial cross-sectional view showing a state where the hole 11 of the piezoelectric ceramic tape 10 is filled with the paste 12 of the via conductor. Thereafter, a paste of the conductor for the internal electrode is printed on the piezoelectric ceramic tape in the shape of the internal electrodes 6a 'and 6b' using a mesh mask (FIG. 6). At this time, the outer shape is made smaller than that of the piezoelectric body so that the internal electrodes 6a 'and 6b' are not exposed to the side surfaces of the element when the layers are stacked. In addition, in the portion of the two holes, a hole larger than the via conductor is provided when the via conductor passing through the hole is not connected to the electrode. Then, solid printing is performed at a position corresponding to the other via conductor so that the electrode is connected to the via conductor. One having two types of electrode patterns in which holes are provided in either one of the two via conductors (for example, FIG.
(Shown in (a) and (b)) and alternately stacking them. With the internal electrode side as the upper surface, for example, FIG.
And (b) are patterns A and B respectively, for example, BABA. . . A desired number of layers such as BAB are stacked such that patterns B are arranged vertically, and via conductors are formed below the layers at positions corresponding to the holes of the pattern A having no electrodes. It is the same as above, where the piezoelectric ceramic is laminated and the position corresponding to the via conductor on the side to which the electrode of pattern B is connected is the piezoelectric ceramic and the internal electrode is not provided Are laminated. Then, the laminated piezoelectric ceramic tape is thermo-compressed, baked, processed as necessary, such as cutting and grinding, external electrodes are provided by baking Ag paste or the like, and the laminated piezoelectric transformer of the present invention is subjected to polarization processing. An element can be obtained.

[0039]

The present invention will be described in more detail with reference to non-limiting examples and comparative examples.

Examples 1 to 5 25 parts by weight of water and 10 parts by weight of an emulsion-type acrylic binder were mixed with 100 parts by weight of a Pb (Zr, Ti) O ₃ -based piezoelectric material powder, and a slurry was prepared by a ball mill. . A tape having a thickness of 130 μm after drying was formed from the slurry using a doctor blade device, and the thickness of the tape after firing was adjusted to about 100 μm.

The obtained tape was 100 mm long and 10 mm wide.
After cutting into a 0 mm rectangle, paste it on the printing frame,
Using a screen mask, the Ag /
An internal electrode having a Pd weight ratio was printed on a portion serving as an input area of the device. However, after laminating, firing, and cutting the laminate, a notch of a right-angled triangular internal electrode having two sides of 2 mm and having a vertex at one of the right and left corners of the input area side end is formed. As described above, printing was performed in two types of patterns.

Printing was performed while changing the emulsion thickness of the screen mask and the solid content concentration of the paste so that the thickness of the internal electrode after firing became the predetermined thickness shown in Table 1.

A tape on which internal electrodes are printed in the above two types of patterns is alternately layered by 10 layers each, and on the side where the internal electrodes are exposed, the same piezoelectric ceramic tape as above without the internal electrodes printed thereon Were laminated.

This was thermocompressed under the conditions of 100 ° C. and 30 MPa, and fired in air at 1150 ° C. for 2 hours.

The obtained fired body was 48 mm long and 10 m wide.
m, and the external electrodes on the upper and lower surfaces of the input region and the end surface of the output region were printed with Ag paste and baked at 700 ° C. Regarding the input external electrodes, the same right-angled triangular cutouts were provided in the left and right inverted patterns of the adjacent internal electrodes. Further, a connection conductor for an internal electrode having a width of 1 mm is printed on the side in the width direction and the length direction over the entire thickness direction outside the two corners of the end of the input area, using Ag paste in the same manner as the external electrode. And 700 ° C
Baked in.

As a result, an unpolarized element in which the internal electrodes were electrically connected to the external electrodes in the form shown in FIG. 1 was obtained.

The element before the polarization is applied to the input region as follows:
At 250 ° C. in air, an electric field strength of 3 MV / m (300 V / m
(100 μm), further short-circuit the input electrode, and in air at 250 ° C., an electric field strength of 0.8 MV / m (1
The output region was polarized at 9 kV / 24 mm) to obtain a multilayer piezoelectric transformer element of the present invention.

A load resistance of 50 kΩ, an ammeter, and a voltmeter were connected to the output side of the multilayer piezoelectric transformer element thus obtained, and a power supply and similarly an ammeter and a voltmeter were connected to the input side. The input power and output power were measured while maintaining a constant output of watts, and the conversion efficiency was calculated. Table 1 shows the results.

After measuring the conversion efficiency, the laminated piezoelectric transformer element was cut, and the thickness of the internal electrodes was measured with an electron microscope to confirm that each was at a predetermined value. Comparative Examples 1 to 5 Using the composition ratio of Ag-Pd shown in Table 1, the thickness of the internal electrode was as shown in Table 1, and a laminated piezoelectric transformer element was formed in the same manner as in Example. Manufactured.

The conversion efficiency was measured in the same manner as in the example, and the thickness of the internal electrode was measured. The results are also shown in Table 1.

[0051]

[Table 1] As can be seen from the results shown in Table 1, Ag / Pd of the internal electrode
When the ratio is in the range of 80/20 to 20/80 and the thickness is in the range of 1 to 5 μm, the conversion efficiency of the piezoelectric transformer becomes 85% or more. It is clear that there is a significant improvement.

Examples 6 to 12 25 parts by weight of water and 10 parts by weight of an emulsion type acrylic binder were mixed with 100 parts by weight of a Pb (Zr, Ti) O ₃ -based piezoelectric material powder, and a slurry was prepared by a ball mill. . A tape having a thickness of 130 μm after drying was formed from the slurry using a doctor blade device, and the thickness of the tape after firing was adjusted to about 100 μm.

The obtained tape was 100 mm long and 10 mm wide.
After cutting into a 0 mm rectangle, paste it on the printing frame,
Conductor for interlayer connection (via conductor) using punching device
Circular holes (via holes) for filling were formed at predetermined positions in a size such that the diameters shown in Table 1 were obtained after firing. After firing and cutting, the via hole is located at a position of a node when the element is vibrated in the λ mode, at a position 12 mm from an end in the longitudinal direction of the element, with a space of 2 mm in the width direction. Provided.

Ag-P having different composition ratios as shown in Table 2
d. A via conductor paste prepared by adding an organic binder or the like to the mixture is filled in the holes by a printing method using a metal mask, dried, and further, on a screen mask having the same Ag / Pd ratio as that of the via conductor. Internal electrodes
Fig. 6 so that it does not protrude to the side when cut out later
In the form (patterns A and B) as shown in (a) and (b), it has dimensions of 23.5 mm in length and 9 mm in width after firing and is concentric with the corresponding via conductor and about 1 mm more than the via conductor Printed with one large diameter circular hole.

Printing was performed while changing the emulsion thickness of the screen mask and the solid content of the paste so that the internal electrodes had the predetermined thickness shown in Table 2.

Ten patterns B and nine patterns A are alternately laminated such that the pattern B is vertically arranged with the internal electrode side as the upper surface.
However, the via conductor to which the electrode of pattern A is connected is not provided (as a piezoelectric ceramic)
The same ceramic tape having no internal electrode printed thereon as the uppermost layer, except that only the via conductor to which the electrode of pattern A was connected was formed thereon.

This was thermocompression-bonded at 100 ° C. and 30 MPa, and fired in air at 1150 ° C. for 2 hours.

These samples were cut to a length of 48 mm and a width of 10 mm so that the internal electrodes were not exposed on the side surfaces. The external electrodes on the upper and lower surfaces of the input region and the end surfaces of the output region were printed with an Ag paste and baked at 700 ° C. Was. As a result, an unpolarized element in which the internal electrodes were electrically connected to the external electrodes in the form shown in FIGS. 2 and 3 was obtained.

The element before the polarization is connected to the input region (lamination side).
About 250 ℃ in the air, polarization treatment with an electric field strength of 3 MV / m (300 V / 100 μm), further short-circuit the input electrode, and in the air at 250 ° C., an electric field strength of 0.8 MV / m (19 kV / 24 mm) Then, the output region was polarized to obtain a multilayer piezoelectric transformer element of the present invention.

A load resistance of 50 kΩ, an ammeter and a voltmeter were connected to the output side of the multilayer piezoelectric transformer element thus obtained, and a power supply and similarly an ammeter and a voltmeter were connected to the input side. The input power and output power were measured while maintaining a constant output of watts, and the conversion efficiency was calculated. Table 2 shows the results.

After measuring the conversion efficiency, the laminated piezoelectric transformer element was cut, and the diameter of the via hole and the thickness of the internal electrode were measured with an electron microscope, and it was confirmed that each value was a predetermined value.

Comparative Examples 6 to 13 Using the composition ratios of Ag-Pd shown in Table 2, the thicknesses of the internal electrodes and the diameters of the via holes were adjusted to those shown in Table 2, and Examples 6 to 13 were used. As in the case of No. 12, a laminated piezoelectric transformer element was manufactured.

The conversion efficiency was measured in the same manner as in Examples 6 to 12, and the diameter of the via hole and the thickness of the internal electrode were measured. The results are also shown in Table 2.

[0064]

[Table 2] As can be seen from the results shown in Table 2, Ag / Pd of the internal electrode
When the ratio is in the range of 80/20 to 20/80, the thickness is in the range of 1 to 5 μm, and the via conductor diameter is in the range of 50 to 200 μm, the conversion efficiency of the piezoelectric transformer exceeds 85%. It is clear that there is a significant improvement.

[0065]

As described above in detail, the multilayer piezoelectric transformer element of the present invention exhibits a high energy conversion efficiency, and enables the multilayer piezoelectric transformer element to be applied to more applications. .

Further, as in a preferred embodiment of the present invention, when the electrical connection between the internal electrodes is obtained by the via conductor provided inside the element, the internal electrodes can be prevented from being exposed to the outside. Even if the polarization treatment of the element is performed in air, the insulation is not broken, which is advantageous in manufacturing.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of one embodiment of a multilayer piezoelectric transformer element of the present invention.

FIG. 2 is a schematic sectional view showing the structure of one embodiment of the multilayer piezoelectric transformer element of the present invention.

FIG. 3 is a schematic sectional view showing the structure of one embodiment of the multilayer piezoelectric transformer element of the present invention.

FIG. 4 is a diagram showing a manufacturing process of the multilayer piezoelectric transformer element of the present invention.

FIG. 5 is a diagram showing a manufacturing process of the multilayer piezoelectric transformer element of the present invention.

FIG. 6 is a diagram showing a manufacturing process of the multilayer piezoelectric transformer element of the present invention.

[Explanation of symbols]

 1. . . . 1. a multilayer piezoelectric transformer element; . . . 2. input area of the multilayer piezoelectric transformer element; . . . 3. output area of the multilayer piezoelectric transformer element; . . . 4. input external electrode; . . . Output external electrode, 6a. . . Internal electrode, 6b. . . Internal electrode, 6a '. . Internal electrode, 6b '. . 6. internal electrode; . . . 7. ceramic piezoelectric body, . . . 8. conductor for connecting the internal electrode; . . . 9. Via conductor for internal electrode connection, . . 10. Piezoelectric ceramic tape, . . Via holes, 12. . . Conductor paste.

Claims (3)

[Claims] 1. A multilayer piezoelectric transformer element having an input region consisting of a plurality of ceramic piezoelectric bodies and a plurality of internal electrodes alternately stacked, wherein each internal electrode contains 20 to 80% by weight of Ag-Pd mixture containing Pd. Consisting of, and 1 to 5
A multilayer piezoelectric transformer element having a thickness of μm. 2. The internal electrode is not exposed on the side surface of the element, and the internal electrode is electrically connected by a conductor filled in a hole provided in the ceramic piezoelectric body. 2. The multilayer piezoelectric transformer element according to claim 1, comprising a Ag—Pd mixture containing 80% by weight of Pd, and the conductor having a diameter of 50 to 200 μm. 3. 3. The multilayer piezoelectric transformer element according to claim 2, wherein holes for filling the conductor of the ceramic piezoelectric body are provided at positions of nodes of vibration of the element.