JPH0253315A - Piezoelectric filter - Google Patents

Abstract

PURPOSE:To eliminate the need for the material and parts for cascade connection by integrating a filter element in cascade connection by a single common piezoelectric base physically and using a common electrode formed to the common piezoelectric base so as to connect electrically the common electrode. CONSTITUTION:Two filter elements 21, 22 are formed to both sides of a slot 25 formed to the common piezoelectric base 23. Then electrodes 34, 36 placed to an upper face are used as input/output electrodes in both the filter elements 21, 22, both the filter elements 21, 22 are connected electrically by a common electrode 24 formed to the lower face of the common piezoelectric base 23 and in cascade connection. Thus, it is not required to apply electric connection to two separate filter elements through the use of wire bonding or a connection terminal or the like different from a conventional example.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a piezoelectric filter constructed using an energy-trapping type piezoelectric resonator, and particularly to a piezoelectric filter constructed by bonding two piezoelectric resonators together. It relates to a structure in which a plurality of filter elements are cascaded.

(Prior Art) Fig. 2 is a perspective view showing a conventionally used energy confinement type filter element. It has a structure in which these are pasted together using adhesive 4.

The first piezoelectric resonator 2 has an amphiboid surface of a piezoelectric substrate 5.
Electrodes 6 and 7 are formed extending from opposing edges toward the center and partially overlapping each other in the center region. Second
In the piezoelectric resonator 3 as well, electric currents ff19 and 10 are similarly formed at the center of the bidirectional surface of the piezoelectric substrate 8, with the front and back partially facing each other. The first and second piezoelectric resonators 2 and 3 are arranged so that their electrodes 7 and 10 overlap each other, and the adhesive 4
are physically integrated.

In this piezoelectric filter 1, the electrode 6 of the first piezoelectric resonator 2 and the electrode 9 of the second piezoelectric resonator 3 constitute input and output electrodes, respectively. Further, the stacked electrodes 10 are connected to a ground potential, and are electrically connected to a ground electrode 11 formed on the end face of the filter element 1.

Incidentally, depending on the application, the filter element 1 shown in FIG. 2 may have insufficient selectivity outside the passband. Therefore, conventionally, two filter elements 1 are prepared and connected in series. This dependent connection is between the input and output electrodes of the first filter element and the second stage filter element, for example, the second stage filter element.
The electrode 9 in the figure and the input side bridge of the next stage filter element are
This was accomplished by electrically connecting using connection terminals, wire bonding, or conductive patterns formed on a circuit board.

[Technical problem to be solved by the invention] However,
When two filter elements 1 are cascaded as described above, in order to cascade their input and output electrodes,
A complicated connection process as described above had to be performed.

Moreover, between two filter elements connected in series,
When the operating frequencies of the two are different, there is also the problem that the passband width fluctuates due to the frequency difference. However, regarding this point, it may be sufficient to prepare two filter elements 1 having the same operating frequency.

However, in order to prepare filter elements with uniform operating frequencies, it is necessary to perform the complicated work of measuring the operating frequencies of mass-produced filter elements in advance, classifying them, and selecting them. Therefore, the cost of piezoelectric filters was high because a selection process based on the operating frequency was required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cascade-connected piezoelectric filter that can be obtained through a relatively simple process and has a structure in which variations in passband width are unlikely to occur.

(Means for Solving Technical Problems) The present invention provides a piezoelectric substrate and a first piezoelectric substrate formed on one main surface of the piezoelectric substrate so as to extend from a first edge toward a central region.
and a second electrode extending from a second edge side opposite to the first edge toward the center on the other main surface of the piezoelectric substrate, and formed so as to partially face the first electrode on the front and back sides. Regarding a piezoelectric filter formed by cascadingly connecting two energy-trapping type piezoelectric resonators having two energy-trapping type piezoelectric resonators and a plurality of filter elements configured by stacking and bonding first or second electric bridges, the following configuration It is characterized by having the following.

That is, among the cascade-connected filter elements, the piezoelectric substrate of one piezoelectric resonator of one filter element and the piezoelectric substrate of one piezoelectric resonator of the next stage filter element are constituted by a single common piezoelectric substrate. In order to prevent vibration interference between both filter elements, this common piezoelectric substrate has grooves formed on the main surface of the side on which the other piezoelectric resonator of each filter element is stacked, and a common piezoelectric substrate. The electrode formed on the other main surface of is used as a common electrode for both filter elements, and the fact that both filter elements are electrically connected by the common electrode is expressed as 'vf@'.

[Effect]

In the present invention, the piezoelectric substrate constituting one piezoelectric resonator of the filter element is shared by the filter elements connected in a subordinate manner, so that the filter elements connected in a subordinate manner are physically integrated. Therefore, the electrical characteristics of both can be made to a considerable extent.

Moreover, since both filter elements are electrically connected by using a common electrode formed on the other main surface of the common piezoelectric substrate, a complicated subordinate connection process is not necessary.

Further, since the groove is formed in the common pressure substrate 1i, vibration interference between both filter elements due to integration is also prevented.

[Description of Embodiment] FIG. 1 is a perspective view showing an embodiment of the present invention. In this embodiment, filter elements 21 and 22, which are constructed by overlapping two energy-trapping piezoelectric resonators, are integrated using a common piezoelectric substrate 23, and a common electrode 24, which will be described later, is integrated with a common piezoelectric substrate 23.
are subordinated to each other.

That is, as shown in an exploded perspective view in FIG. 3, a groove 25 is formed on the upper surface of the common piezoelectric substrate 23 so as to extend from one edge to the other edge. The groove 25 is provided to prevent vibration interference between filter elements formed on both sides of the groove 25.

On both sides of the groove 25, electrodes 26, 27 are connected to the common piezoelectric substrate 2.
It is formed so as to extend from one edge of 3 to the central region. On the other hand, a common electrode 2 is provided on the back side of the common piezoelectric substrate 23.
4 is formed extending from the edge side facing the electrodes 26.27 to the central region, and is arranged so as to partially overlap with the electrodes 26.27 in the thickness direction via the common piezoelectric substrate 23. .

Vibration regions of one resonator of each filter element 21.22 are formed in the overlapping portions of the common electrode 24 and the electrodes 26.27, respectively.

On the other hand, a piezoelectric resonator 3132 is attached to the upper surface of the piezoelectric substrate 23 using an adhesive 2829 (see FIG. 1). This piezoelectric resonator 3132 is connected to the common piezoelectric substrate 23
With piezoelectric resonators configured on both sides of the groove 25 using
Each constitutes a filter element 21, 22 (see FIG. 1).

The piezoelectric resonator 31 extends from the opposing edges of the piezoelectric substrate 33 to the central region, and is formed by forming electrodes facing each other in the central region (only the electrode 34 located on the upper side is shown in FIG. 3). It is configured. Similarly, the piezoelectric resonator 32 is also constructed by forming electrodes 36 and 37 that overlap in the central region of the reproduction surface of the piezoelectric substrate 35.

The energy-trapping piezoelectric resonators 31, 32 are pasted onto the piezoelectric resonators configured on both sides of the groove 25 formed in the common piezoelectric substrate 23 using an adhesive 28, 29, as described above.

As described above, as shown in FIG. 1, filter elements 21 and 22, which are formed by bonding two piezoelectric resonators in the vertical direction, are integrally formed on both sides of the groove 25.

Note that ground electrodes 38 and 39 are provided on one end surface of each filter element 21 and 22. Ground electrode 38.39
are the electrodes 26, 27, 37 that are overlapped when two resonators are overlapped in each filter element 21, 22.
It is designed to draw out the Ground electrode 3
8.39, as shown in FIG. 3, electrodes are formed in advance on one end surface of the common piezoelectric substrate 23 and on one end surface of each piezoelectric resonator 31, 32, and after stacking, conductive adhesive or the like is applied. Alternatively, after the piezoelectric resonators 31 and 32 are stacked and adhesively fixed on the piezoelectric substrate 23, a ground electrode 38 shown in FIG. 1 may be formed on one end surface.
．． 39 may be applied and formed in a separate process.

By the way, in the embodiment shown in FIG. 1, two filter elements 21 and 22 are formed on both sides of the groove 25 formed in the common piezoelectric substrate 23, but in both filter elements 21 and 22, the electrodes located on the upper surface 34 and 36 are input/output electrodes, and both filter elements 21 and 22 are electrically connected by a common electrode 24 formed on the lower surface of a common piezoelectric substrate 23, and are connected in a subordinate manner.

Therefore, it can be seen that there is no need to electrically connect two separate filter elements using wire bonding, connection terminals, etc. as in the conventional example. Furthermore, since the two filter elements 21 and 22 are physically integrated by the common piezoelectric base Vi23, handling is easy.

Furthermore, since both the filter elements 21 and 22 are constructed using the common piezoelectric substrate 23, the difference in electrical characteristics between them can be made very small.

This will be explained in more detail with reference to FIG.

In actual mass production, as shown in FIG.
4, 45, and 46 are pasted together using an adhesive 47, and then cut along the cutting line schematically indicated by A to pierce the piezoelectric substrate 41 located above and cut the piezoelectric substrate 4 located below.
By forming a groove reaching an intermediate depth of 2, the depth 25 of the embodiment of FIG. 1 is formed.

Thereafter, by cutting and separating the laminate along cutting line B in FIG. 5, a plurality of the embodiments in FIG. 1 can be obtained. Therefore, it is not only possible to mass-produce the piezoelectric substrates 23, 33.3 of FIG.
4 is composed.

Therefore, the electrical characteristics of the piezoelectric substrates 23, 33, and 34 are also very similar, making it easy to match the electrical characteristics of the filter element 21 and the filter element 22.

Next, specific experimental results will be explained. A piezoelectric material with an electromechanical coupling coefficient of 58% and an electrical quality factor Q of 700 is used, and the length is 5. 1rra, width 2.75mm, groove width 0.
A piezoelectric filter of the embodiment shown in FIG. 1 was prepared with a total thickness of 15 mm and a total thickness of 0.47 mm. The thickness of each resonator used was 0.225a11, and the overlapping length of the electrodes facing each other via the piezoelectric substrate was 1°1M. Metal leads 51, 52, and 53 are soldered to the thus obtained piezoelectric filter as shown in FIG. After that, the filter characteristics were measured. The results are shown in Figure 6.

In addition, a large number of piezoelectric filters prepared as described above were prepared, and their average electrical characteristics were investigated.

The results are shown in the table below.

(Hereinafter, blank space) In addition, in the conventional example in which two filter elements shown in Fig. 2 are prepared and connected in series, the dispersion value σ-6 of the 3 dB attenuation bandwidth is
3KHz, but in this example, σ-38K
It was Hz. Therefore, it can be seen that the variation in frequency bandwidth is improved by about 60% compared to the conventional example. In addition, it was found that variations in insertion loss and center frequency were significantly reduced compared to the conventional example.

In the embodiment of FIG. 1, two filter elements 21.2
It should be pointed out that although two filter elements are cascade-connected using the piezoelectric substrate 23, the present invention can also be applied to cascade-connection of three or more filter elements. That is, if, for example, three filter elements are connected in series, the structure shown in FIG. By making the substrate 35 a common piezoelectric substrate like the piezoelectric substrate 23, the third stage filter element can be configured on the opposite side from the filter element 21.

[Effects of the Invention] As described above, in the present invention, a single common piezoelectric substrate is used.
The filter elements that are cascaded are physically integrated, and the filter elements are electrically connected by a common electrode formed on the common piezoelectric substrate. Therefore, unlike the conventional example, materials and parts for the subordinate connection are not required, and additional steps for making the subordinate connection can also be omitted.

Therefore, it is possible to effectively reduce the cost of the cascade type piezoelectric filter.

In addition, since the filter elements that are connected in series are integrally configured using a common piezoelectric substrate, it is easy to match the electrical characteristics. It is also possible to effectively reduce variations in characteristics.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a perspective view showing an example of a filter element used in a conventional example, FIG. 3 is an exploded perspective view of the embodiment shown in FIG. Figure 1 is a perspective view for explaining the reduction process of the embodiment; Figure 5 is a perspective view showing the state in which leads are attached for measuring the characteristics of the embodiment of Figure 1; It is a figure which shows the attenuation amount-frequency characteristic of a figure Example. In the figure, 21.22 is a filter element, 23 is a common piezoelectric substrate, 24 is a common electrode, 25 is a groove, 26.27.34
, 36 and 37 are electrodes, and 3335 is a piezoelectric substrate. Patent applicant Mura Co., Ltd. 1) Manufacturing agent
Patent Attorney Lord Miyajima Tax Figure 1 Figure 2 Figure 5 Figure 4

Claims (1)

[Scope of Claims] A piezoelectric substrate polarized in a direction perpendicular to the thickness direction; a first electrode formed on one main surface of the piezoelectric substrate so as to extend from a first edge to a central region; , extending from a second edge side opposite to the first edge to the center on the other main surface of the piezoelectric substrate, and formed so as to partially face each other through the first electrode and the piezoelectric substrate. A piezoelectric filter in which a plurality of filter elements are cascade-connected, each of which is constructed by bonding two energy-trapping piezoelectric resonators having two electrodes with their first or second electrodes stacked on top of each other. Among the filter elements connected in a dependent manner, the piezoelectric substrate of one piezoelectric resonator of one filter element and the piezoelectric substrate of one piezoelectric resonator of the next stage filter element are constituted by a single common piezoelectric substrate. , in the common piezoelectric substrate, a groove is formed on the main surface of the side on which the other piezoelectric resonator of each filter element is overlapped, in order to prevent vibration interference between both filter elements, and the common piezoelectric substrate The first or second electrode formed on the main surface opposite to the groove-formed side of the piezoelectric substrate is used as a common electrode between both filter elements, and both filter elements are electrically connected to each other by the common electrode. A piezoelectric filter, characterized in that it is connected to.