JPH0342805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to piezoelectric elements used in oscillators, filters, and the like.

<Conventional technology> Conventionally, piezoelectric elements used in the frequency range of around 190 to 1000 kHz are, for example, as shown in Fig. 5.
A piezoelectric substrate 5 made of a square flat plate is provided, and electrodes 6, 6 having a uniform thickness are formed on both main surfaces of the piezoelectric substrate 5. For example, as shown in FIG. 6, in the case 1, When the piezoelectric substrate 5 is held between the two terminal plates 3 and 4 that are in pressure contact with the vibration node points, and a voltage is applied between the two electrodes 6 and 6 via both terminal plates, the arrow a in FIG. 5... A device that generates a spreading vibration in the plane direction as shown in is known.

The conventional piezoelectric element 2' having such a structure is used, for example, by being incorporated into an oscillator or filter that utilizes the vibration component spreading in the plane direction. sometimes,
As shown in FIG. 7, apart from the spread vibration component in the planar direction, that is, the main vibration component A, a thickness longitudinal vibration component B that vibrates in the same direction as the polarization axis is also simultaneously excited.

<Problems to be Solved by the Invention> However, when the piezoelectric element 2' is used as an oscillation element, spurious vibrations caused by such thickness longitudinal vibrations cause equipment connected to the oscillator to be affected by the spurious frequency. There is a risk that so-called spurious responses may occur, causing malfunctions based on Furthermore, when this piezoelectric element 2' is used as a filter, a problem arises in that it causes insufficient attenuation in the short wave region.

In view of these conventional problems, it is an object of the present invention to reduce spurious responses by dispersing the thickness longitudinal vibration component.

<Means for solving the problems> In order to achieve such an object, the present invention includes the following steps:
The piezoelectric substrate is characterized by a structure in which the film thickness of each of the electrodes formed on both main surfaces of the piezoelectric substrate is regularly changed in a direction parallel to a diagonal line of each main surface of the piezoelectric substrate.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is an enlarged longitudinal sectional side view of an oscillator incorporating a piezoelectric element of this embodiment. In this figure, reference numeral 1 denotes a case, and a piezoelectric element 2 and two terminal plates 3 and 4 are housed in the case 1. This piezoelectric element 2 is a spread vibration mode element having electrodes 6, 6 formed on the entire main surfaces of a piezoelectric substrate 5 made of a square flat plate made of ceramic, and has a vibration node at its center. Each of the terminal plates 3 and 4 is in pressure contact with the vibration node point of the piezoelectric element 2 to sandwich the element 2, and among these, one terminal plate 4 is connected to the piezoelectric element 2 and the other terminal plate 3. This serves as a leaf spring terminal that presses and biases the terminal toward one side wall 1a of the case.

Figures 2 to 4 show the piezoelectric element 2 of this embodiment.
FIG. 2 is a perspective view, FIG. 3 is a plan view, and FIG. 4 is an enlarged longitudinal sectional side view. In these figures, each of the electrodes 6, 6 is a first electrode film 7, 7 having a uniform thickness over the entire main surface.
are formed, and second electrode films 8, 8 are formed on both first electrode films 7, 7. The second electrode films 8, 8 are striped electrodes 6, each consisting of a plurality of strips 8a formed at equal pitches in parallel directions along the diagonal of the main surface of the piezoelectric substrate 5. The strip portions 8a of each of the second electrode films 8, 8 are arranged in directions crossing each other on the front and back sides of the piezoelectric element.

Both electrodes 6, 6 configured in this manner are arranged in a direction parallel to the diagonal direction of each main surface by forming second electrode films 8, 8 on first electrode films 7, 7, respectively. It has two types of film thicknesses that change regularly. The first and second electrode films 8, 8 are each formed to have the same thickness. Therefore, the striped portions 8a... where the second electrode films 8, 8 overlap the first electrode films 7, 7 overlap with the other electrodes 6, 6.
The film thickness is set to twice that of that part.

In addition to silver (Ag), the constituent materials of these electrodes 6, 6 include gold (Au), silver-palladium alloy (Ag-Pd), nickel (Ni), or nickel-copper alloy (Ni-Cu). etc. are used.

When a voltage is applied to both electrodes 6, 6 of the piezoelectric element 2 having the above configuration, the spread vibration component along the diagonal line of the piezoelectric substrate 5, that is, the main vibration component, is excited without any practical problem, but in the longitudinal direction of the piezoelectric substrate 5. The vibration component, that is, the spurious vibration frequency component, is
It is dispersed by discontinuous changes in the film thickness of the electrodes 6, 6, and as a result, the occurrence of spurious responses can be considerably suppressed. in this regard,
When the inventor conducted an experiment, it was possible to reduce the noise by approximately 10 dB.

The present invention also includes those in which the piezoelectric substrate 5 is made of various piezoelectric materials other than ceramic dielectric.

<Effects of the Invention> As described above, according to the present invention, the film thickness of each of the electrodes formed on both main surfaces of the piezoelectric substrate is regularly arranged in a direction parallel to the diagonal direction of each main surface of the piezoelectric substrate. Therefore, the spreading vibration, which is the main vibration component, can be excited without any problem, and the thickness longitudinal vibration component, which causes spurious response, can be reduced.

[Brief explanation of drawings]

FIG. 1 is an enlarged longitudinal cross-sectional side view of an oscillator incorporating a piezoelectric element according to the present invention, FIGS. 2 to 4 show the piezoelectric element of this embodiment, and FIG. 2 is a perspective view,
Figure 3 is a plan view, Figure 4 is an enlarged vertical side view, Figure 5
The figure is a perspective view of a conventional example, FIG. 6 is a longitudinal cross-sectional side view of an oscillator incorporating a piezoelectric element of an embodiment, and FIG. 7 is a diagram showing vibration characteristics of a piezoelectric element of a conventional example. 5... Piezoelectric substrate, 6,6... Electrode.

Claims (1)

[Claims] 1. In a piezoelectric element comprising a rectangular flat piezoelectric substrate, electrodes are formed on both main surfaces of the substrate, and has a vibration mode extending in the plane direction of the substrate, each of the electrodes is formed on each main surface of the piezoelectric substrate. A piezoelectric element characterized by having a film thickness that changes regularly in a direction parallel to a diagonal direction of the piezoelectric element.