JPH03185907A - Piezoelectric element - Google Patents

Abstract

PURPOSE:To improve the bonding strength and the operating reliability for a long time remarkably by providing a lowermost close contact metallic layer and an uppermost connection conductor layer to at least the electrode lead leadout part on a piezoelectric substrate in a piezoelectric element. CONSTITUTION:Exciting electrode parts 2, 3 are arranged to both major sides of a piezoelectric substrate 1 opposite to each other and electrode lead leadout parts 21, 31 are formed respectively to the electrode parts 2, 3. Moreover, metallic conductor wiring layers 8a, 8b are bonded and connected onto a ceramic substrate 9 by conductive bonding members 7a, 7b to form the piezoelectric element. Then the electrode lead leadout parts 21, 31 of the piezoelectric element are provided with a lowermost close contact metallic layer 4 and an uppermost connection conductor layer 5. The Ag paste of the bonding members 7a, 7b is brought into contact with and adhered to a Pd metallic film being the uppermost conductor layer 5 of the electrode lead leadout parts 21, 31 and element fixing parts 22, 32. Thus, the bonding strength is very strong and the operating reliability for a long time is remarkably improved.

Description

[Detailed Description of the Invention] [Summary] Regarding piezoelectric elements, in particular, the purpose of this invention is to improve the reliability of electrode connections in strip-type small thickness vibrators, and to provide excitation electrodes on both opposing principal surfaces of a piezoelectric substrate. In the piezoelectric element, the electrode lead lead-out portions of the excitation electrode portions on both sides are adhesively connected to a metal conductor wiring layer formed on a ceramic substrate using a conductive adhesive. The piezoelectric element is configured such that the lead lead-out portion includes a lowermost adhesive metal layer and an uppermost connecting conductor layer.

[Industrial application field]

The present invention relates to a piezoelectric element, particularly to an electrode structure of a strip-type small thickness vibrator using a LiTaO3 rotating X-plate.

In recent years, with the miniaturization of office automation equipment and communication equipment such as word processors and personal computers, extremely small piezoelectric elements such as piezoelectric vibrators have come to be used as elements for generating reference signals used in these devices. Ta. Such piezoelectric vibrators use a new artificial single crystal with a large electromechanical coupling coefficient, instead of using conventional crystal as a piezoelectric material. For example, LiTa03 (lithium tantalate) has come to be used, but in order to miniaturize the device, the lead extraction part of the excitation electrode part is directly attached to the metal conductor wiring layer on the ceramic vine board using conductive adhesive. In many cases, connections are made by gluing, and there is a need to improve the connection reliability.

[Conventional technology]

Recently, LiTa0+ single crystals have a large electromechanical coupling coefficient and a relatively small temperature coefficient, so they have often been used as extremely small piezoelectric vibrators and surface acoustic wave elements.

For example, FIG. 6 is a diagram showing an example of the appearance of a piezoelectric element.

In the figure, ■ is a piezoelectric substrate, for example, 0.55 mm thick.
, 3゛ rotation X-cut LiTaO3 plate processed into a rectangle with a width of 1 mm and a length of 8 mm, 2゛ is an excitation electrode part, and a thickness of 50 nm, for example, is placed on one of the main surfaces of the piezoelectric substrate 1.
NiCr with a thickness of 200 nm is placed on top of the NiCr base.
A predetermined electrode pattern shape with an electrode lead extension part 21' provided on one side is formed by vapor-depositing and using a normal photoetching technique.

Reference numeral 22' denotes an element fixing part, which is provided at the other end of the piezoelectric substrate 1 to be separated from the excitation electrode part 2', and has the same film structure as the excitation electrode part 2', and is made by photo-etching. They were formed at the same time.

3° was attached to the other main surface of the piezoelectric substrate 1. Similarly, it is made of a two-layer film of Au/NiCr, and has, for example, an electrode lead extension part 31' in the opposite direction to that of the excitation electrode part 2'. Similarly, the element fixing part 32'' is formed at the end opposite to the element fixing part 22''.

FIG. 7 is a cross-sectional view showing a piezoelectric element mounted state.

In the figure, reference numeral 4 denotes an adhesion metal layer, for example, a NiCr film provided at the bottom layer to improve adhesion to the piezoelectric substrate 1.
6 is a conductor film on which Au is deposited.

9 is a ceramic substrate, for example, and 8a and 8b are metal conductor wiring layers, for example, thick film wiring layers made of Ag--Pd. 7a and 7b are conductive adhesives, for example, Ag paste.

The conductive adhesives 7a and 7b are connected to the electrode lead extraction portion 21°.

This is for electrically and mechanically connecting and fixing 31 to the metal conductor wiring layers 8a and 8b. The element fixing parts 22'' and 32' are provided to more securely mechanically fix the piezoelectric element 1 to the ceramic substrate 9.

When an alternating voltage is applied to the excitation electrode portions 2' and 3' of the piezoelectric element as described above, for example, in this example, thickness shear vibration is excited and the piezoelectric element can function as a vibrator.

[Problem to be solved by the invention]

However, in the conventional piezoelectric element, the electrode lead extraction portion 21
', 31' is composed of a gold (Au) conductor layer 6, and this Au conductor layer 6 is connected to conductive adhesives 7a, 7b.
The adhesive strength with the Ag paste is very low, for example, according to actual measurements, it is only about 1g7mm, and when the surface of the element vibrates like a vibrator, the connection resistance increases and the connection There was a serious problem of instability that needed to be solved.

[Means to solve the problem]

The above problem is solved by the fact that the excitation electrode sections 2 and 3 are disposed on both opposing main surfaces of the piezoelectric substrate 1, and the electrode lead extension sections 21 and 31 of the excitation electrode sections 2 and 3, respectively,
In a piezoelectric element in which metal conductor wiring layers 8a and 8b formed on a ceramic substrate 9 are adhesively connected by conductive adhesives 7a and 7b, at least the electrode lead lead-out portions 21 and 31 are formed of the lowermost adhesive metal layer. This problem can be solved by a piezoelectric element characterized by comprising a layer 4 and an uppermost connecting conductor layer 5.

[Effect]

According to the present invention, the connection conductor layer 5, for example, P
d Since the metal film is used as a form, the adhesive strength with Ag paste is 5 g/mm'', which is approximately 5 times the adhesive strength with conventional Au metal layers, ensuring long-term operation reliability. This results in a marked improvement in performance.

〔Example〕

FIG. 1 is a side view showing an embodiment of the present invention.

Reference numeral 2 denotes an excitation electrode section, which is provided on one of the principal surfaces of the piezoelectric substrate 1.
For example, NiCr with a thickness of 50 nm is provided as the adhesive metal layer 4 on the bottom layer, Pd with a thickness of 1100 nm is formed on the top layer as the connection conductor layer 5 by sputtering, and then one side is formed with a normal photoetching technique. This is based on the shape of a predetermined electrode pattern in which the electrode lead extension portion 21 is provided. Reference numeral 22 denotes an element fixing part, which is provided at the other end of the piezoelectric substrate 1, separated from the excitation electrode part 2, and has the same film structure as the excitation electrode part 2, and is formed simultaneously using a photoetching technique. It is something.

3 was attached to the other main surface of the piezoelectric substrate 1. An excitation electrode part made of a two-layer film of the same structure and the same thickness of Pd/NiCr, for example, an electrode lead extraction part 31 is provided in the opposite direction to that of the excitation electrode part 2,
Similarly, the element fixing part 32 is formed at the end opposite to the element fixing part 22.

Note that the same reference numerals are given to the same parts as those explained in the various countries of the conventional example, and the explanation of the same parts will be omitted.

FIG. 2 is a sectional view showing a state in which elements are mounted according to an embodiment of the present invention.

In the embodiment of the present invention, the conductive adhesive bands 7a and 7b are made of Ag.
The paste is Pd, which is the connection conductor layer 5 that forms the top layer of the electrode lead extraction parts 21, 31 and the element fixing parts 22, 32.
Since the adhesive is in contact with the metal film, the adhesive strength is extremely strong as described above.

In this figure as well, the same reference numerals are given to the same parts as those explained in the various countries of the conventional example, and explanations of the same parts are omitted.

FIG. 3 is a diagram showing the relationship between operating time and cumulative failure rate, with the cumulative failure rate plotted on the vertical axis and the operating time plotted on the horizontal axis. The test conditions were as follows: The piezoelectric element described in FIG. 1 was mounted as shown in FIG. The device was operated, and if a predetermined level of vibration could no longer be obtained, it was determined to be defective.

Incidentally, the cumulative failure rate of the piezoelectric element with the conventional electrode configuration shown in FIG. 7 as a reference sample is shown by the broken line ■. In the conventional example, defects began to occur after 100 hours, and 1000
The time has reached approximately 10'&.

In contrast, in the case of the embodiment of the present invention, as shown by the solid line ■, failures began to occur only after 1,000 hours, and even after 2,000 hours, the occurrence of failures was less than 1%, and the operational reliability was high. It was confirmed that there was a significant improvement.

FIG. 4 is a diagram showing another embodiment of the present invention.

In this example, the bottom adhesive metal layer 4 has a thickness of 50 nm.
NiCr film with a thickness of 11 which is the top layer connecting conductor layer 5.
For example, between 00n Pd metal films with a thickness of 1100n
An Au conductor layer 6 is inserted as an intermediate layer. By using Au, which has a specific resistance of about 115 that of Pd, as the intermediate layer, it is particularly advantageous when it is necessary to reduce the resonance resistance of the vibrator depending on the purpose of use.

FIG. 5 is a diagram showing still another embodiment of the present invention, in which a connecting conductor layer 5 made of a Pd metal film is provided as the uppermost layer only in the electrode lead extraction part 21.31 and the element fixing part 22.32. This modification of the embodiment shown in FIG. 4 is suitable for similar purposes.

In the above embodiments, a Pd metal film was used as the connection conductor layer 5, but the invention is not limited to this, and similar effects can be obtained by using other metals, such as Ti.

The embodiments described above are merely examples, and materials, element configurations, combinations thereof, and films other than those shown in the embodiments may be used as long as they comply with the spirit of the present invention. As for the formation technology, other methods are used as appropriate,
It goes without saying that the piezoelectric element of the present invention may be configured as follows.

〔Effect of the invention〕

As described in detail above, according to the present invention, since the connection conductor layer 5 is formed of, for example, a Pd metal film on at least the top layer of the electrode lead extension parts 21 and 31, the adhesive strength with the Ag paste is 5g/mm” and conventional A
The adhesive strength with the u-conductor layer 6 is about 5 times higher than that of 0, and it greatly contributes to improving the quality and reliability of piezoelectric elements, such as piezoelectric vibrators.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the element mounting state of the embodiment of the present invention, FIG. 3 is a diagram showing the relationship between operating time and cumulative failure rate, and FIG. 4 5 is a diagram showing still another embodiment of the present invention, FIG. 6 is a diagram showing an example of the external appearance of a piezoelectric element, and FIG. 7 is a diagram showing a conventional piezoelectric element. FIG. 3 is a cross-sectional view showing a state in which elements are mounted. In the figure, 1 is a piezoelectric substrate, 2.3 is an excitation electrode part, 4 is an adhesive metal layer, 5 is a connection conductor layer, 6 is an Au conductor layer, 17 (7a, 7b) is a conductive adhesive, 8 ( 8a, 8b) are metal conductor wiring layers, 9 is a ceramic substrate, 21.31 is an electrode lead extraction part, and 22.32 is an element fixing part. 2 Expansion [effect/fraud (×)

Claims (1)

[Claims] Excitation electrode portions (
2, 3) are arranged, and metal conductor wiring layers (8a, 8b) formed on the respective electrode lead lead-out parts (21, 31) of the excitation electrode parts (2, 3) and the ceramic substrate (9).
) are adhesively connected to each other by a conductive adhesive (7a, 7b), in which at least the electrode lead lead-out portions (21, 31) are connected to the bottom adhesive metal layer (4) and the top connection conductor layer. (5) A piezoelectric element comprising: