JPH0435105A - Electrode structure for ultra thin plate piezoelectric resonator - Google Patents

Abstract

PURPOSE:To avoid disadvantage caused due to increase in a parallel capacitance of a resonator by forming a conductor film being an opposite electrode to a position other than a region corresponding to a lead pattern on an opposite face of a vibration part. CONSTITUTION:A part 16 corresponding to a region of a vibration part 3 of an electrode lead 7 prolonged from an opposite electrode 6 is eliminated from a full face electrode 5 added to a recessed part 2 of an ultra thin piezoelectric block 1. This is because the said vibration part 3 is very thin and a capacitor with a large capacitance is formed when a conductor film exists on the front and rear side of the said vibration part. In contrast with the above fact, an annular surrounding part 4 is thick and even if a conductor film exists on the front and rear face of the part 4, so much capacitance is not caused and no detrimental effect is given on the capacitance ratio of the resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention uses fundamental wave vibration to generate frequencies of several tens to several hundreds of MHz.
This invention relates to an electrode structure for an ultra-thin piezoelectric resonator that can obtain a high resonant frequency that extends to .

(Prior art) In recent years, demands for higher frequencies and higher frequency stability have become stricter in various electronic devices and communication devices. Although the cut crystal resonator has extremely excellent temperature-frequency characteristics, its resonance frequency is inversely proportional to the plate thickness, so from the viewpoint of manufacturing technology and mechanical strength, 40MH
The limit was about z.

Also, so-called overtone oscillation means that extracts harmonic components of an AT-cut crystal resonator to obtain a frequency that is an odd multiple of the fundamental resonance frequency is also widely used, but this method requires an LC tuning circuit that includes a coil in the oscillation circuit. In order to achieve this, the oscillation circuit is made into a semiconductor integrated circuit, which is inconvenient, and the space ratio is large and the impedance level is high, which may make oscillation difficult.

On the other hand, surface acoustic wave resonators, whose resonant frequency is determined by the electrode finger pitch of interdigital transducer electrodes, have become
Although it has become possible to achieve a certain degree of resonance, there is a problem in that the temperature-frequency characteristics of the piezoelectric substrate that can be used for this purpose are significantly inferior to that of AT-cut crystal.

In order to solve the above-mentioned problem, conventionally, the method shown in Fig. 4(a)
A piezoelectric resonator as shown in (b) has been studied.

That is, this piezoelectric resonator has a concave portion 2 formed in the center of one side of the AT-cut crystal block 1 by machining or etching.
At the same time, the thickness of the vibrating part 3 located at the bottom surface of the recessed part 2 is set to be about 17 μm if a fundamental resonance frequency of 100 M I-1z is to be obtained, for example.

As a result of forming the concave part 2, a thick annular surrounding part (rib) 4 is formed integrally with the vibrating part 3 on the peripheral edge of the ultra-thin plate-like vibrating part 3 on the block surface on the side of the concave part 2. mechanically supports the ultra-thin plate-shaped vibrating section.

A conductive film 5 is attached to the entire surface of the piezoelectric plate having the above-described structure, including the inner wall of the recess, and a partial electrode 6 and an electrode lead 7 extending therefrom are formed on the surface of the vibrating part 3 on the opposite side by vacuum evaporation or the like. If this method is used for attachment, it is possible to obtain a piezoelectric resonator with an extremely high resonance frequency.

A piezoelectric resonator having such a structure is suitable for being housed in a flat package as shown in FIG.

That is, the concave portion 2 of the crystal block 1 is housed in a case 9 made of ceramic or the like having a concave storage space 8 in the center with the concave portion 2 facing the bottom of the case, and one peripheral plane of the concave side of the annular surrounding portion 4 is placed toward the face. The conductive adhesive 10 applied in a linear manner mechanically connects the conductive film 11 that is exposed on the bottom surface of the storage space 8, passes through the wall of the case in an airtight manner, and is connected to the external lead that protrudes or is exposed outside the case. It would be common sense and advantageous to fix and electrically bond.

The conductive film I+ on the bottom of the storage cavity is connected to a terminal 12 formed at a corner of the bottom of the case via a connecting conductor that passes through the inside of the case 9 in an airtight manner.

Also, the butt 7a located at the end of the electrode lid 7 extending from the partial electrode 6 of the resonator is connected by wire bonding to a pad 14 formed on the stepped portion 13 inside the case, and this pad I4 is also connected to the case 9. Needless to say, it is connected to the terminal 15 formed at the corner of the bottom surface of the case via a connecting conductor that passes through the inside in an airtight manner.

The problem with the ultra-thin plate piezoelectric resonator constructed in this way is that since the entire surface on the side of the recessed portion 2 is covered with the conductor film 5, the electrode leat 7 extending from the partial electrode 6 becomes a problem.
As a result of forming a capacitor between the piezoelectric resonator and the piezoelectric resonator, the capacitance ratio of the piezoelectric resonator increases, and the range in which the frequency can fluctuate becomes smaller.

That is, when a capacitor is formed between the electrode lead 7 and the recessed conductor film 5, the parallel capacitance C6 in the equivalent circuit of the piezoelectric resonator shown in FIG. 6 increases, and the capacitance ratio γ of the piezoelectric resonator increases. -C8/C, increases, this type of resonator is limited in its application to oscillation circuits that need to vary the oscillation frequency within a predetermined range, such as voltage-controlled crystal oscillators (VCXOs). However, even if it is not applied to a multimode filter element, it is expected that it will be difficult to handle when a relatively wide bus band is required.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems predicted in ultra-thin plate piezoelectric resonators, and the present invention is to convert the bottom surface of a recess formed on the surface of a piezoelectric block such as crystal into an ultra-thin plate shape. In a piezoelectric resonator with a piezoelectric vibrating part, the electrode and the electrode reed pattern face each other through the ultra-thin vibrating part, forming a capacitor and increasing the parallel capacitance of the resonator. It is an object of the present invention to provide an electrode structure for an ultra-thin piezoelectric resonator that can eliminate various problems that occur.

(Summary of the Invention) In order to achieve the above object, a resonator according to the present invention includes an electrode and an electrode lead pattern extending from the electrode on at least one surface of an ultra-thin vibrating section, and a resonator on the opposite surface of the vibrating section. The present invention is characterized in that a conductive film serving as a counter electrode is formed at a position avoiding a region corresponding to the lead pattern.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

Before explaining the embodiments, in order to help understand the present invention, we will explain why the ultra-thin plate piezoelectric resonator, which is the basis of the present invention, has an electrode structure in which a front electrode is provided in the recessed part and a partial electrode is provided on the opposite surface side. Let me explain a little bit about whether to adopt .

First, from the viewpoint of vacuum deposition technology, it is possible to provide a partial electrode on the vibrating part of the recess of the piezoelectric substrate as described above, and to extend a narrow electrode lead from the electrode beyond the inner wall and step of the recess. It is extremely difficult to perform vapor deposition by tilting the face with respect to the horizontal plane, and there is a concern about ensuring continuity of the electrode lead. It was designed so that it could be secured.

Second, this type of resonator was originally intended for ultra-miniaturization of devices, and the size of the piezoelectric substrate was, for example, 3 mm x 3 mm.
I would like the following. If this is the case, a manufacturing method will be adopted in which a large number of chips are formed at once on a piezoelectric sea urchin heart using batch processing, and then the chips are finally cut into individual chips. In this case, if the above-mentioned type of electrode configuration is adopted, it is sufficient to simply deposit a conductive film on the entire surface of the wafer, and there is no need for delicate alignment of a photomask or photolithography mask, which improves production efficiency. , yield can be improved and costs can be reduced.

For the reasons described above, it should be noted that the ultra-thin piezoelectric resonators that have been studied by the inventors of the present invention are basically those in which electrodes are attached to the entire surface of the concave side.

However, if the electrode configuration as described above is used, a large capacitor is constructed between the electrode lead portion and the electrode lead portion on the entire surface of the vibrating portion, partly because the plate thickness of the vibrating portion is extremely small. As mentioned above, the capacitance ratio of the resonator increases, causing various problems.

In order to solve this problem, the ultra-thin plate piezoelectric resonator according to the present invention has the following electrode structure.

FIG. 1(a) is a plan view showing the basic configuration of the present invention, in which a vibrating portion of an electrode lead 7 extends from a full-surface electrode 5 attached to the recess 2 side of an ultra-thin piezoelectric block and a counter electrode 6 thereof. The portion 16 corresponding to the three regions is removed.

The reason for this is that the vibrating section 3 has an extremely small wall thickness, and if conductive films are present on the front and back sides of the section, it constitutes a capacitor with a large capacity.

In comparison, the annular surrounding portion 4 has a large wall thickness, and even if a conductive film is present on the front and back surfaces thereof, it will not have a very large capacitance, and this will have a significant effect on the capacitance ratio of the resonator. This is because it is thought that it does not give .

In order to construct the electrode with a blank space as described above, a suitable mask is attached to the recess 2 side of the piezoelectric block 1 and the conductor is vapor-deposited, or a photolithography technique is used after the conductor is vapor-deposited on the entire surface. It is necessary to remove unnecessary conductive films, which makes the process a little more complicated, but the cost required for this is more than compensated for by the improvements in the various characteristics of the resonator. .

In addition, in the same figure [b], when the width of the electrode lead 7 of the partial electrode 6 facing the full surface electrode is almost equal to the width of the electrode 6, the side edge of the electrode lead 7 and the full surface electrode facing this should be removed. This shows that by setting the distance d between the blank part 16 and the side edge to approximately the thickness of the annular surrounding part 4, the capacitance through the vibrating part 3 will become almost negligible. It is.

However, since a capacitor is formed between the lead part 7 of the partial electrode 6 and the opposing conductor film extending along the side edge of the partial electrode 6, in order to eliminate this, a conductor in the entire surface electrode is formed as shown in FIG. It may be effective to extend the area from which the membrane is to be removed to the area 17 corresponding to the side edge of the partial electrode 6.

By the way, as mentioned above, in order to remove the - part of the entire surface electrode attached to the concave side of the piezoelectric block 1, it is necessary to use an appropriately shaped vapor deposition mask or photolithography technique as mentioned above.

Therefore, as shown in (d) or (e) of the same figure, the range in which the conductive film should be removed from the entire surface electrode is expanded to the part facing the electrode lead 7 of the partial electrode 6 in the annular surrounding part 4 of the piezoelectric block l. If so, it would be more effective to reduce the capacitance ratio of the resonator without increasing the number of man-hours.

1. In the resonator as described above, as shown in FIG. The edges are mechanically fixed and electrically connected using a conductive adhesive lO, and the adhesive portion is the edge of the partial electrode 6 facing the extending direction of the electrode lead 7, as shown in FIG. 1(d). 20 may be used, and the electrode 6 may be connected to the lead terminal pad 1 of the cage at the tip of the lead 7.
In order to ensure bonding when connecting to 4 with a wire, the annular surrounding surface 18 on the side where the leat 7 of the partial electrode 6 is extended as shown in FIG. It will be like that.

The case where the present invention is applied to a piezoelectric vibrator has been described above, but the present invention can be similarly applied to an ultra-thin multi-moat filter as shown in FIG.

As is well known, the most common double moat piezoelectric filter among multiplex piezoelectric filters has a split electrode 19 close to the - side of the piezoelectric substrate (vibrating section 3 in this case), and a full electrode on the opposite side. is provided, acoustic coupling is produced between both electrodes of the divided electrode 19, and as a result, a bandpass filter is constructed by utilizing two vibration modes with different resonant frequencies that are excited.

Therefore, it is necessary to draw out the electrode leads 21 from the divided electrodes 19 to the edges of the piezoelectric block 1, as shown in FIG. 3(a).
The conductive film may be removed from the region 22 surrounded by the device 2I and the inner wall of the annular surrounding portion 4 as shown in FIG.

Furthermore, the region 2I may be extended to the surface of the annular surrounding portion 4, as shown in FIG. 2(b).

By doing so, it is possible to make the volume ratio γ of the piezoelectric resonator the same as that of a normal piezoelectric resonator. This makes it possible to form an ultra-small filter element having this frequency as the central layer e number, and to secure these characteristics, particularly the variable width of the resonant frequency and the band width of the filter, to a value 1 minute larger.

(Effects of the Invention) Since the present invention is constructed as described above, the volume ratio of the ultra-thin piezoelectric resonator or filter element can be kept to a low value, and the variable width of the resonant frequency of the vibrator can be controlled. In addition, the filter element has the considerable effect of reducing spurious waves and providing a wide passband, and this effect more than compensates for the increase in the number of beads required for electrode formation.

[Brief explanation of the drawing]

1(a) to 1(e) are plan views showing different embodiments of the electrode structure of the ultra-thin piezoelectric resonator according to the present invention, and FIG.
The figure is a cross-sectional view showing an example of a piezoelectric resonator packaging method according to the present invention, and FIGS. 3(a) and 3(b) respectively show different embodiments of an ultra-thin multimode filter element to which the present invention is applied. A plan view, FIGS. 4(a) and 4(b) are a perspective view and an XX cross-sectional view showing the structure of an ultra-thin piezoelectric resonator that has been studied in the past, and FIG. 5 is a cross-sectional view showing its packaging method. 6 are equivalent circuit diagrams of the resonator. l ・ ・ ・ 3 ・ ・ ・ Full-surface electrode I 0 16... Ultra-thin piezoelectric block 2... Concave vibrating part 4... Annular surrounding part 5... -6... Partial electrode 7... Electrode: Conductive adhesive 11: Conductor film/blank area Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] (1) In a piezoelectric resonator in which an ultra-thin vibrating part and a thick-walled annular surrounding part that supports the periphery of the vibrating part are integrally molded, an electrode and an electrode lead pattern extending from the electrode are provided on one surface of the vibrating part. an electrode structure for an ultra-thin piezoelectric resonator, characterized in that a counter electrode is formed at a position avoiding at least a region corresponding to the lead pattern on the opposing surface of the vibrating section.