JP2003046157A - Laminated piezoelectric device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric device which is markedly improved in durability even if it is driven in a strong electric field for a long term by effectively preventing internal electrodes from being disconnected from external electrodes, and to provide its manufacturing method. SOLUTION: Piezoelectric bodies 26 and internal electrodes 28a and 28b are alternately laminated into a device body 24, and external electrodes 34a and 34b are provided on the sides of the device body 24 and alternately connected to the internal electrodes 28a and 28b for the formation of a laminated piezoelectric device. Protuberant conductive terminals 29a and 29b protruding from the side of the device body 24 are provided to every other end of the internal electrodes 28a and 28b, and the conductive terminals 29a and 29b are embedded in the external electrodes 34a and 34b respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element and a method for manufacturing the same, and for example, an AC adapter and a DC-DC converter used in various electronic devices, and a liquid crystal display used in a notebook computer, a portable terminal and the like. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element used for a backlight cold cathode fluorescent lamp inverter and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recently, in response to miniaturization of various electronic devices,
It is an important issue to reduce the size and height of the switching power supply device. In particular, in order to reduce the size and height, it is important to reduce the size and height of the transformer that boosts or lowers the voltage.

In general, miniaturization is achieved by a method of miniaturizing an electromagnetic transformer as the frequency of a circuit increases, or by using a piezoelectric transformer. In particular, when the height of the electromagnetic transformer is reduced, the loss of the electromagnetic transformer is increased due to the miniaturization of the electromagnetic transformer. Therefore, a piezoelectric transformer capable of obtaining a high power density has been used as an effective component. For example, it has been put into practical use as a step-up piezoelectric transformer of a cold cathode tube lighting inverter used for a liquid crystal backlight.

In the structure of the boosting piezoelectric transformer, conventionally, about half of the rectangular piezoelectric substrate 81 shown in FIG. 3 (a) in the longitudinal direction is the primary side, and the electrodes 82, 8 are arranged in the thickness direction.
3 is formed and polarized in the thickness direction, and the other half is the secondary side, the electrode 84 is formed on the end face in the longitudinal direction and is polarized in the longitudinal direction, and a high boost ratio is obtained. For this reason, the Rosen type laminated piezoelectric transformer shown in FIG. 3B, which has a structure in which the primary side is laminated, is also known.

When the primary side is laminated, in order to connect the inner electrodes 85 every other layer to the same potential, the outer electrodes 8 are formed on the side surfaces.
7 must be formed, and the internal electrode 85 and the external electrode 87 must be formed.
It is necessary to make a reliable connection.

Since the Rosen type piezoelectric transformer has a high step-up ratio and a high impedance of output side impedance of several 100 KΩ, it has characteristics suitable for a backlight lighting inverter in which impedance matching is easily achieved. However, there is a problem that the step-down characteristic cannot be obtained. In particular, when used as a step-down transformer for an AC-DC converter or a DC-DC converter, the impedance of the load is as low as less than 1 KΩ, which makes impedance matching difficult, resulting in low output power and efficiency. There was a problem.

As a piezoelectric transformer that solves such a problem, for example, one disclosed in Japanese Patent Laid-Open No. 11-4026 is known. FIG. 3C shows such a piezoelectric transformer, which has a feature that impedance matching is easy by stacking the primary side and the secondary side, but the internal electrode 85 has the same potential every other layer. In this case, it is necessary to form an external electrode 87 on the side surface in order to connect the internal electrode 85 and the external electrode 87 in this case as well.

FIG. 4 shows a connection structure of an internal electrode 85 and an external electrode 87 in a conventional piezoelectric transformer, in which a piezoelectric body 89 and an internal electrode 85 are alternately laminated to form an element body 91.
From the side surface of the element body 91.
Are exposed every other layer, and the internal electrodes 85 are formed on the exposed side surfaces of the element body 91 by vacuum vapor deposition, baking of silver paste, and application of a conductive resin to form the external electrodes 87. And the internal electrode 85 was electrically connected.

[0009]

However, in the above-described conventional piezoelectric transformer, when continuously driven in a high electric field for a long time, the internal electrode 85 formed between the piezoelectric bodies 89 and the external electrode 87 are formed. Peeling occurs and some of the piezoelectric body 89
There was a problem that the voltage was not supplied to the output and the output decreased during driving.

In order to solve such a problem, for example, in Japanese Patent Laid-Open No. 5-29680, after exposing the internal electrodes by etching, every other layer is plated on the end portions of the exposed internal electrodes by plating. By coating with a base metal, it protrudes,
The other internal electrodes between the protrusions are covered with an insulating layer, and a paste made of a conductive material is applied to the side surface of the element body on which the protrusions are formed and baked to form external electrodes, which are electrically connected to the internal electrodes. There is disclosed a laminated piezoelectric element for achieving the above.

However, since it is necessary to ionize the metal to be deposited by plating, the metal forming the protruding portion needs to be a base metal, and when the laminate is exposed to a high temperature environment, the coated base metal is oxidized. As a result, there is a problem in that electrical continuity with the external electrode cannot be secured. In addition, in order to make the protrusion, etching
There are many manufacturing processes such as plating, heat treatment, oxide film removal, and there is a problem that it takes time to manufacture. In addition, since the protrusion is made of an alloy of the internal electrode and the plated electrode, the Young's modulus of the protrusion is higher than that of silver, which is the main component of the internal electrode, and it is difficult to absorb the stress acting on the external electrode. There is a problem that peeling still easily occurs between the external electrode and the external electrode.

The present invention provides a laminated piezoelectric element capable of effectively preventing disconnection between the external electrode and the internal electrode even when continuously driven in a high electric field for a long period of time, and greatly improving durability, and a method for producing the same. The purpose is to

[0013]

A laminated piezoelectric element of the present invention comprises an element body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and a side surface of the element body. A laminated piezoelectric element having a pair of external electrodes in which electrodes are alternately connected to every other layer, and a protrusion made of a noble metal protruding from the side surface of the element body every other layer at an end of the internal electrode. Conductive terminals are provided, and the protruding conductive terminals are embedded in the external electrodes.

Such a laminated piezoelectric element is formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes,
A step of manufacturing an element body in which the end portions of the internal electrodes are exposed on the side surface every other layer, and a terminal paste mainly composed of a noble metal and glass is applied to the side surface of the element body in which the end portions of the internal electrode are exposed. And baking at a temperature equal to or higher than the softening point of the glass in the terminal paste, and at a temperature at which a noble metal can move in the glass to form a protruding conductive terminal at the end of the internal electrode, By forming an external electrode on the side surface of the element body on which the protruding conductive terminal is formed so as to embed the protruding conductive terminal,
The protruding conductive terminal can be easily formed.

The external electrode is formed by applying an external electrode paste containing metal and glass as a main component on the side surface of the element body on which the protruding conductive terminal is formed, and at a temperature higher than the softening point of the glass in the external electrode paste. It is also desirable that the baking is performed at a temperature lower than the forming temperature of the protruding conductive terminals.

In the laminated piezoelectric element of the present invention, protruding conductive terminals projecting from the side surface of the columnar laminated body are provided at every other end of the internal electrode, and the protruding conductive terminals are embedded in the external electrode. Therefore, it is possible to secure a large bonding area between the protruding conductive terminal and the external electrode, and to prevent disconnection between the protruding conductive terminal and the external electrode even when operated continuously for a long time under a high electric field. It is possible to significantly improve durability.

Further, in the present invention, it is desirable that the protruding conductive terminals and the internal electrodes have the same metal element. For example, the metal element of the protruding conductive terminal and the internal electrode is silver,
It is preferably composed of palladium or platinum. This is because by making the main component of the protruding conductive terminal the same as the metal component of the internal electrode, it is possible to strengthen the bonding strength between the protruding conductive terminal and the internal electrode, and Even when driven under a high electric field, the external electrode and the internal electrode are not disconnected, and the durability can be greatly improved.

Further, by using silver having a low Young's modulus as the main component of the protruding conductive terminal, the stress generated during driving under a high electric field can be sufficiently absorbed and the external electrode and the internal electrode are not disconnected. The durability can be greatly improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a laminated piezoelectric element comprising a piezoelectric transformer of the present invention. (A) is a perspective view, (b) is a line AA of (a). Cross section along,
(C) is an enlarged sectional view of a part of (b).

In the piezoelectric transformer of the present invention, as shown in FIG. 1, a voltage input portion 21, a voltage output portion 22, and a voltage input portion 23 are sequentially formed in the length direction of a piezoelectric substrate 20 having both rectangular main surfaces. The input electrodes 21a and 21b, the input electrodes 23a and 23b, and the output electrodes 22a and 22b are formed on both main surfaces of the piezoelectric substrate 20 in the voltage input portions 21 and 23 and the voltage output portion 22, respectively. The element body 24 is formed.

In the piezoelectric substrate 20 of the voltage output section 22, six layers of internal electrodes 28a, 28b for the output section are provided alternately at predetermined intervals in the thickness direction. Internal electrode 2
The end portions of 8a and 28b are exposed at the side surfaces of the voltage output portion 22 which are alternately opposed to each other, and the exposed inner electrodes 28a and 2b are exposed.
At the ends of 8b, protruding conductive terminals 29a, 2a made of the same metal component as that of the internal electrodes 28a, 28b, respectively.
9b are formed, and these protruding conductive terminals 29a, 2
9b is an external electrode 3 provided on the side surface of the voltage output section 22.
4a, 34b, and these external electrodes 34a,
34b is connected to the output electrodes 22a and 22b.

A glass layer 37 based on glass in the terminal paste is formed between the element body 24 and the external electrodes 34a and 34b, as shown in FIG. 1 (c). The glass layer 37 can insulate the internal electrode 28b that is not exposed on the side surface of the element body 24, and at the same time reduce the stray capacitance that does not contribute to vibration generated between the external electrode 34a and the internal electrode 28b that is not exposed. Can be made.

The external electrodes 34a and 34b are the internal electrodes 28.
The projecting conductive terminals 29a, 29b are provided on a part of the side surface of the voltage output section 22 where the ends of a, 28b are exposed.
Are formed only on the portions where the external electrodes 34a and 34b are formed.

Further, the piezoelectric layers 25 and 27 in the voltage input sections 21 and 23 are polarized in the thickness direction, and the voltage output section 22.
The piezoelectric layer 26 is polarized in the thickness direction, and the piezoelectric layers 26 adjacent to each other via the internal electrodes 28a and 28b have opposite polarization directions.

The piezoelectric layer 26 is composed of general piezoelectric ceramics such as PZT type piezoelectric ceramics, and has internal electrodes 28a, 28b and protruding conductive terminals 29a, 29.
b has the same metal element and is composed of silver and palladium or platinum. Input portion electrodes 21a, 21b, 23a, 23 formed on both main surfaces of the piezoelectric substrate 20.
b, the electrodes 22a and 22b for the output section are made of Ag and glass, and the external electrodes 34a and 34b are also made of Ag and glass.

A method for manufacturing the piezoelectric transformer of the present invention will be described. The PZT-based piezoelectric ceramic mixed with a desired composition is pre-baked at 900 to 1050 ° C. This calcined powder is pulverized, a binder, a plasticizer, etc. are added and dispersed in an organic solvent to prepare a slurry. The obtained slurry is made into a ceramic green sheet having a desired thickness by using a doctor blade method or the like.

Next, a binder, a plasticizer and the like are added to and mixed with Ag and Pd powder to prepare a conductive paste for internal electrodes, which is screen-printed at a predetermined position on the ceramic green sheet. A plurality of green sheets coated with conductive paste are laminated and integrated by hot pressing,
After heating at ~ 500 ° C and degreasing, 1000 ~ 11
Sinter at 50 ° C. At this stage, the opposing element body 24
Ends of the internal electrodes 28a and 28b are alternately exposed on the side surface of the.

After that, the internal electrodes 28a of the element body 24,
By applying the terminal paste for the protruding conductive terminals 29a and 29b containing Ag and glass as the main components to the opposite side surfaces where the ends of 28b are exposed, and baking at 700 to 950 ° C., the protruding conductive terminals are formed. The terminals 29a and 29b are formed.

That is, such a protruding conductive terminal 29
In order to form a and 29b, in particular, a glass powder having a softening point of 500 ° C. to 800 ° C. is dispersed in a terminal paste containing Ag as a main component, and the terminal paste is applied to the side surface of the element body 24. And softens the glass,
The diffusion rate of Ag in the glass can be increased by heating to a temperature at which the g particles can move in the glass, and particularly by maintaining the temperature at 100 ° C. or more higher than the softening temperature of the glass of the terminal paste. In this state, Ag, which is difficult to diffuse into the piezoelectric body, diffuses and gathers at the ends of the internal electrodes 28a and 28b, so that the protruding conductive terminals 29a and 29b as shown in FIG. 1C can be formed. At this time, Pd in the internal electrodes 28a, 28b is changed to the protruding conductive terminals 29a, 2b.
9b, and the protruding conductive terminals 29a and 29b are Ag.
And an alloy of Pd.

Part of the glass in the terminal paste is 29a,
29b are gathered around the base of the element 29b, and part of the element body 24
Present on the surface of.

After that, as shown in FIG. 1, a conductive paste containing silver and glass as the main components is applied and baked on both main surfaces of the element body 24, and the electrodes 21a, 21b and 23 for the input portion are applied.
a, 23b and the electrodes 22a, 22b for the output part are formed, and then the external electrode paste is applied and baked on the side surface of the element body 24 on which the protruding conductive terminals 29a, 29b are formed. 34b is formed. The baking temperature at this time is higher than the softening temperature of the glass in the external electrode paste, but it is important to keep the diffusion rate of Ag and Pd low, that is, lower than the protruding conductive terminal forming temperature. is there. Thereby, the protruding conductive terminal 29
The a and 29b are embedded and present in the external electrodes 34a and 34b.

Here, the input electrodes 21a, 21b, 2
The electrodes 3a and 23b, the output electrodes 22a and 22b, and the external electrodes 34a and 34b are formed by baking a conductive paste containing silver and glass as main components, but they are formed by a method such as vapor deposition, sputtering, or plating. Is also good. Also, a conductive material other than Ag may be used. The external electrodes 34a and 34b are
It may be formed by applying a conductive resin.

After that, a DC voltage is applied to each of the input electrodes 21a, 21b, 23a, 23b and the output electrodes 22a, 22b in silicone oil at 120 ° C. to obtain about 3
The piezoelectric transformer of the present invention is obtained by performing the polarization treatment for 0 minutes.

Although the PZT-based piezoelectric ceramic material and Ag / Pd are used as the piezoelectric ceramic material and the internal electrode material here, the piezoelectric ceramic material having piezoelectricity and the electrode material containing silver which can be integrally fired with the piezoelectric ceramic material. It goes without saying that other combinations are also possible.

In the piezoelectric transformer of the present invention, the voltage input section 2
1, 23 between the input part electrodes 21a and 21b, and 23
When an AC voltage having a frequency near the resonance frequency of the piezoelectric substrate 20 is applied between a and 23b, the piezoelectric substrate 20 is excited by the inverse piezoelectric effect, and the voltage output unit 2 is again activated by the positive piezoelectric effect.
A voltage having the same frequency as the input voltage is generated between the second output inner electrodes 28a and 28b. At this time, the output voltage depends on the load resistance and the driving frequency.

That is, when the piezoelectric transformer is driven, the piezoelectric substrate 20
Are vibrating, and the piezoelectric substrate 20 is distorted due to the vibration. If the protruding conductive terminals 29a and 29b are not provided, the adhesion area of the internal electrodes of the external electrodes 34a and 34b is small. Therefore, if stress caused by deformation of the porcelain is generated for a long period of time, peeling easily occurs. Conductive terminals 29a, 2
When 9b is formed, the internal electrodes 28a, 28b and the protruding conductive terminals 29a, 29b are firmly joined with the same component, and the external electrodes 34a, 34b and the protruding conductive terminals 29 are formed.
Since the adhesive area of a and 29b is widened and the main component of the protruding conductive terminals 29a and 29b is mainly silver having a low Young's modulus, the stress generated by the porcelain deformation can be sufficiently absorbed, and the external electrode 34a , 34b and the internal electrode 28
It is possible to suppress disconnection between a and 28b.

[0037]

EXAMPLES As an example, the piezoelectric transformer shown in FIG. 1 was manufactured by the green sheet method. First, a PZT-based piezoelectric ceramic material is used as the piezoelectric ceramic material, Ag / Pd is used as the internal electrode material, and the Ag / Pd conductive paste is screen-printed on the green sheet made of the PZT-based piezoelectric ceramic material to form the internal electrode. A pattern is formed, six layers of green sheets having such internal electrode patterns are laminated, and a green sheet having no internal electrode pattern is laminated thereon, and then they are integrated by hot pressing. After degreasing by heating at ~ 500 ° C, 1
Sintered at 100-1300 ° C.

This sintered body was processed into a shape having a length L of 25.74 mm, a width W of 19.8 mm and a thickness of 3.3 mm, and Ag and glass (softening point 550 ° C.) were mainly formed on both side surfaces of the sintered body. By applying the component paste for the terminals and baking at 800 ° C., the protruding conductive terminals 29a, 29b were formed.

After that, as shown in FIG. 1, a conductive paste containing Ag and glass as main components is applied and baked on both main surfaces, and input electrodes 21a, 21b, 23a, 23b and output electrode 22a are formed. , 22b are formed, and at the same time, an external electrode paste containing Ag and glass (softening point 475 ° C.) as main components is applied to both side surfaces and baked to form external electrodes 34a,
34b was formed. The baking temperature at this time was 520 ° C.

Observing the cross section of the external electrodes 34a, 34b, the protruding conductive terminals 29a, 29b are formed at the ends of the internal electrodes 28a, 28b, and the protruding conductive terminals 29a, 29b are formed. It was in a state of being embedded in the external electrodes 34a and 34b. Protruding conductive terminals 29a, 2
9b was composed of Ag / Pd.

Next, a direct current voltage of 1.6 kV / mm was applied to the piezoelectric transformer in silicone oil at 120 ° C., and 3
Polarization was performed for 0 minutes to polarize in the thickness direction of the piezoelectric substrate.

For comparison, the projecting conductive terminals were not formed, and the processed porcelain was applied to the input portion electrode, the output portion electrode,
A sample having an external electrode formed by baking at 600 ° C. was prepared.

As shown in FIG. 2, the measuring circuit receives the input side electrode (primary side electrode) of the piezoelectric transformer and outputs the output side electrode (secondary side electrode) as an output, and the load resistance is applied to this output side electrode. The RL was connected. Here, RL = 10Ω. Input voltage is 141 Vpp, frequency 110 kHz to 12
Applying a 5kHz sine wave from the input power supply to the input side electrode,
The input power (W) was obtained by measuring the input current (App) and the phase.

On the other hand, the output voltage (Vp
p), the output current (App) and the phase were measured to determine the output power (W). The efficiency (%) was calculated from the maximum output power and the maximum input power.

From the measurement results of the piezoelectric transformer of the present invention, it was found that the output power was 1.5 to 17.6 W and the efficiency was 91.2% or more, and the maximum output power was as high as 17.6 W.
The comparative example also showed similar characteristics in the initial measurement.

However, when the input voltage was continuously driven for 24 hours at 300 Vpp and re-measured with 141 V input, the piezoelectric transformer of the present invention showed the same characteristics as the initial characteristics, whereas in the comparative example, The output power dropped extremely and the efficiency also dropped. When the capacitance of the output part was measured, it decreased to 3/7 of the initial value, and as a result of the analysis, it was revealed that the external electrode and the internal electrode were separated at two locations.

[0047]

In the multi-layer piezoelectric element of the present invention, the protruding conductive terminals protruding from the side surface of the element body are provided at the end portions of the internal electrodes every other layer, and the protruding conductive terminals are embedded in the external electrodes. Therefore, when driven in a high electric field, the protruding conductive terminals deform and absorb the stress generated by the deformation of the element body. It is possible to suppress disconnection from the electrode and significantly improve durability.

[Brief description of drawings]

FIG. 1 is a view showing a laminated piezoelectric element of the present invention, (a)
In a perspective view, (b) is a sectional view taken along the line AA of (a), and (c) is a partially enlarged view of (b).

FIG. 2 is an explanatory diagram showing a measuring circuit of a piezoelectric transformer.

FIG. 3A is a conventional Rosen type piezoelectric transformer,
(B) is a perspective view showing a conventional Rosen type laminated piezoelectric transformer, and (c) is a conventional laminated type piezoelectric transformer.

FIG. 4 is a cross-sectional view showing a connection structure of internal electrodes and external electrodes of a conventional laminated piezoelectric transformer.

[Explanation of symbols]

20 .. Piezoelectric substrate 24: Element body 25, 26, 27 ... Piezoelectric body 28a, 28b ... internal electrodes 29a, 29b ... Protruding conductive terminals 34a, 34b ... External electrodes

Claims (5)

[Claims] 1. An element body formed by alternately laminating a plurality of piezoelectric bodies and a plurality of internal electrodes, and a pair of external electrodes provided on the side surface of the element body and in which the internal electrodes are alternately connected to each other. A laminated piezoelectric element comprising an electrode, wherein a protruding conductive terminal made of a noble metal protruding from a side surface of the element body is provided at each end of the internal electrode, and the protruding conductive terminal is provided. Is embedded in the external electrode. 2. The laminated piezoelectric element according to claim 1, wherein the protruding conductive terminals and the internal electrodes are made of the same metal element. 3. The protruding conductive terminal and the internal electrode are made of silver and palladium or platinum.
The laminated piezoelectric element described. 4. A step of manufacturing an element body in which a plurality of piezoelectric bodies and a plurality of internal electrodes are alternately laminated, and the end portions of the internal electrodes are exposed on the side surface every other layer, and the end of the internal electrodes. On the side surface of the element body where the part is exposed, a terminal paste containing a noble metal and glass as main components is applied, and the temperature is equal to or higher than the softening point of the glass in the terminal paste and at which the noble metal can move in the glass. Baking to form a protruding conductive terminal at the end of the internal electrode, and an external surface so that the protruding conductive terminal is embedded on the side surface of the element body on which the protruding conductive terminal is formed. And a step of forming an electrode. 5. The external electrode is formed by applying an external electrode paste containing metal and glass as a main component on a side surface of an element body on which a protruding conductive terminal is formed, the softening point of glass in the external electrode paste being equal to or higher than the softening point. 5. The method for manufacturing a laminated piezoelectric element according to claim 4, wherein the laminated piezoelectric element is formed by baking at a temperature lower than the forming temperature of the protruding conductive terminals.