JP2005094542A - High frequency piezoelectric vibrator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency piezoelectric vibrator, and its manufacturing method which is easily manufacturable even when mass production is performed, and moreover does not have variations in characteristics. <P>SOLUTION: In the high frequency piezoelectric vibrator 12, a recession 3 is formed by etching in the center of one surface of a crystal substrate 2 by etching, and a thick annular surrounding portion 5 is formed in the peripheral brim portion of a thin oscillator 4 formed on the bottom surface of the recession 3 integrally with the oscillator 4. An exciting main electrode 13, a lead electrode 14 and a pad electrode 15 led out from the main electrode are formed approximately at the center of the thin oscillator 4 on the flat side of the crystal substrate 2. Besides, an annular electrode having an inside diameter with a size larger than the size of the main electrode, is formed at the oscillator 4 in the recess of the crystal substrate 2 as a suppression electrode 16 using material the same as that of the exciting main electrode 13, in opposition to the exciting main electrode 13 formed on the flat side of the crystal substrate 2. Moreover, a whole surface electrode 17 is formed on the whole surface on the recession side of the crystal substrate 2, and a high frequency piezoelectric device is made. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency piezoelectric vibrator and a method of manufacturing the same, and in particular, prevents CI value deterioration and unnecessary spurious generation of a high-frequency piezoelectric vibrator having a high resonance frequency of 100 MHz or more by fundamental vibration, and provides good resonance characteristics. The present invention relates to an improvement of an electrode configuration to obtain and a manufacturing method thereof.

In recent years, in various electronic devices, communication devices, etc., with the increase in the amount of information to be handled and the speeding up, high frequency is also applied to piezoelectric devices such as piezoelectric vibrators and piezoelectric filters used as reference frequency sources and frequency selection functions. And high frequency stability are required.
Conventional AT-cut quartz resonators that have been widely used as piezoelectric devices have excellent frequency-temperature characteristics, but the resonance frequency is inversely proportional to the thickness of the quartz substrate. From the viewpoint of crystal resonator manufacturing technology and mechanical strength, the resonance frequency is limited to about 50 MHz.

  In addition, overtone oscillation means that extracts harmonic components of an AT-cut crystal resonator and obtains an odd multiple of the fundamental resonance frequency is widely used, but requires an LC tuning circuit that includes a coil in the oscillation circuit. For this reason, there is a disadvantage in that the oscillation circuit is not integrated into a semiconductor integrated circuit, and the capacitance ratio is large and the impedance level is high, so that oscillation may be difficult.

  On the other hand, the surface acoustic wave resonator whose resonance frequency is determined by the electrode finger pitch of the interdigital transducer electrode has been capable of a frequency output of about 1 to 2 GHz due to the advancement of photolithography technology. There has been a problem that the frequency temperature characteristic of the obtained piezoelectric substrate is significantly inferior to that of the AT-cut quartz resonator.

  Therefore, in order to solve such a problem, the conventional high-frequency piezoelectric vibrator has a concave portion formed on one surface of an AT-cut quartz crystal substrate with a predetermined dimension by means of machining or etching, and the thin portion of the concave portion is thin. The excitation electrode is formed with the bottom surface of the substrate as the vibration part.

  On the other hand, in order to improve the spurious characteristics of an AT-cut crystal resonator, a piezoelectric resonator capable of arbitrarily controlling the spurious generation frequency to some extent regardless of the electrode length and film thickness is disclosed in Japanese Patent Laid-Open No. 2001-244778. . According to this, a spurious suppression electrode is formed as a second electrode with a predetermined gap so as to surround the periphery of the main electrode formed on the main surface of the piezoelectric substrate. Therefore, if the mass load (film thickness) of the suppression electrode is appropriately set according to the mass load (film thickness) of the main electrode, the energy confinement factor can be easily controlled, and a crystal resonator with less spurious is realized. It becomes possible.

  4A and 4B are structural examples of a conventional high-frequency piezoelectric vibrator. FIG. 4A is a top view, and FIG. 4B is a cross-sectional view taken along A-A ′. In the high-frequency piezoelectric vibrator 1, a concave portion 3 is formed on one surface of a quartz substrate 2 by etching or machining, and a thick annular surrounding portion 5 is formed on a peripheral portion of a thin vibrating portion 4 provided on the bottom surface of the concave portion 3. Is formed integrally with the vibrating portion 4 and the thin plate-like vibrating portion 4 is mechanically supported.

  Therefore, a conductor film is formed on the entire surface including the side wall in the concave portion 3 of the quartz substrate 2 having the above-described structure to form a full-surface electrode 6, and the main electrode is provided at the approximate center of the thin vibrating portion 4 on the flat side of the quartz substrate 2. 7, and further, the lead electrode 8 derived from this and the pad electrode 9 for conducting with the external package terminal are formed, and then the suppression electrode 10 for suppressing spurious due to the inharmonic mode is used as the main electrode and the like. Different electrode materials are used to surround the main electrode 7 with a predetermined gap therebetween.

Next, a method for manufacturing the conventional high-frequency piezoelectric vibrator as described above will be described.
FIG. 5 is a diagram illustrating an example of a manufacturing process of a conventional high-frequency piezoelectric vibrator. In order to manufacture a high-frequency piezoelectric vibrator, a protective film 11 is formed at a predetermined position on the surface of the AT-cut quartz crystal substrate 2 by photolithography and then etched (step 1). The portion not formed is recessed into a predetermined shape, and the thin plate-like vibrating portion 4 and the annular surrounding portion 5 supporting the periphery thereof are integrally formed to peel off the protective film 11 (step 2).

Next, the entire surface electrode 6 on the recessed portion 3 side of the quartz substrate 2, the main electrode 7 positioned substantially at the center of the vibrating portion 4 on the flat side of the facing quartz substrate 2, the lead electrode 8 and the external package terminal derived therefrom Are simultaneously formed by vacuum vapor deposition or the like (step 3), and then a suppression electrode for suppressing spurious is similarly formed by vacuum vapor deposition or the like using an electrode material different from the main electrode or the like. Form (step 4).
By configuring the piezoelectric vibrator in this way, a high-frequency piezoelectric vibrator having a very high resonance frequency and suppressing spurious can be obtained.
JP 2001-244778 A

  The conventional high-frequency piezoelectric vibrator needs to have the conditions disclosed in Japanese Patent Application Laid-Open No. 2001-244778 described above in order to suppress spurious due to the inharmonic mode. Therefore, in order to set only the main electrode to the energy confinement mode, the spurious suppression electrode is thicker than the excitation main electrode, but the cutoff frequency of the main electrode is f1, and the gap between the main electrode and the suppression electrode If the cut-off frequency of f2 is f2 and the cut-off frequency of the suppression electrode is f3, the relationship between the cut-off frequencies needs to be f1 <f2 <f3. An electrode having a high predetermined shape, film thickness, and position was required.

  However, the conventional high-frequency piezoelectric vibrator has a main electrode for excitation, a lead electrode, a bonding pad electrode, which are the same electrode material formed on the flat side of the piezoelectric substrate, and an entire surface electrode formed on the concave side of the piezoelectric substrate. Must be formed simultaneously with a predetermined film thickness, and a suppression electrode for spurious suppression must be formed by a mask vapor deposition method with a predetermined film thickness using a material different from these electrodes. The distance and position accuracy between the main electrode for excitation and the suppression electrode for suppressing spurious noise cannot be obtained, so that stable high-frequency piezoelectric vibrator characteristics cannot be obtained. This led to an increase in manufacturing cost due to a decrease in yield.

  The present invention has been made in order to solve the above-described problems, and can be easily manufactured even during mass production, and can easily control the electrode film thickness without causing variations in characteristics. An object of the present invention is to provide a high-frequency piezoelectric vibrator having an electrode structure that can prevent deterioration and unnecessary spurious generation, and a method for manufacturing the same.

In order to achieve the above object, a high-frequency piezoelectric vibrator and a manufacturing method thereof according to the present invention have the following configurations.
The high-frequency piezoelectric vibrator according to claim 1 is formed by forming a concave portion on one surface of the piezoelectric substrate by etching or machining, and a thick annular surrounding portion that mechanically supports the periphery thereof. A high-frequency piezoelectric vibrator integrally configured with
A main electrode for excitation having a predetermined shape formed at a substantially central portion of the vibration portion of the flat main surface of the piezoelectric substrate, and an annular suppression electrode is provided on the concave portion side of the piezoelectric substrate; The main electrode for excitation formed on the flat side of the piezoelectric substrate is arranged so as to surround the periphery thereof without overlapping, and the entire surface on the concave side of the piezoelectric substrate is covered with the entire surface electrode.

  The high-frequency piezoelectric vibrator according to claim 2, wherein the electrode film thickness of the suppression electrode is formed in accordance with the electrode film thickness of the main electrode, thereby controlling the energy confinement coefficient and reducing spurious generation. To do.

  The high-frequency piezoelectric vibrator according to claim 3 is configured such that the piezoelectric substrate is an AT-cut quartz crystal substrate.

  According to a fourth aspect of the present invention, there is provided a method for producing a high-frequency piezoelectric vibrator, wherein a concave portion is formed by etching on one main surface of a piezoelectric substrate, whereby a thin plate-like vibrating portion and an annular surrounding portion supporting the periphery thereof are integrated. A first film forming step of forming a metal film with a predetermined film thickness on both surfaces of the piezoelectric substrate, and a metal film with a predetermined film thickness only on the flat side surface of the piezoelectric substrate. A main film for excitation in a predetermined shape at the substantially central part of the vibrating part on the flat side of the piezoelectric substrate, and the main electrode for the concave part of the piezoelectric substrate overlapping the main electrode. Forming an annular suppression electrode so as to surround the surrounding without using a photolithographic technique and an etching technique, and forming an entire surface electrode almost entirely on the concave side of the piezoelectric substrate on which the suppression electrode is formed To include To.

  As described above, according to the first to fourth aspects of the present invention, the annular suppression electrode is provided on the concave side of the piezoelectric substrate so as to surround the main electrode for excitation formed on the flat side of the piezoelectric substrate without overlapping. The same material as the main electrode for excitation is disposed on the surface, and then the entire surface electrode is formed on the entire recess side of the piezoelectric substrate, so that it has good resonance characteristics with less spurious and mass production by batch processing method. Since this is possible, the manufacturing cost is reduced, and a remarkable effect is exhibited in mass production of high-frequency piezoelectric vibrators.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.
In this embodiment, an annular suppression electrode is formed on the concave side of the piezoelectric substrate integrally formed with a thin vibrating portion and a thick annular surrounding portion that mechanically supports the periphery of the vibrating portion. For excitation with sufficient energy confinement due to the mass load effect using the same material as the excitation main electrode, which is arranged to surround the excitation main electrode formed on the flat side without overlapping. A suppression electrode having a film thickness difference corresponding to the electrode film thickness of the main electrode was formed, and then the substantially entire surface on the concave side of the piezoelectric substrate was covered with the entire surface electrode. By the way, the difference in film thickness between the main electrode for excitation is about 0.2% in terms of frequency, and when gold is used as the electrode material at a frequency of 156 MHz, the difference in film thickness between the main electrode for excitation and the suppression electrode is The thickness of the main electrode for excitation is 50 nm, and the thickness of the suppression electrode is 48 nm.

  FIG. 1 is an example showing the structure of a high-frequency piezoelectric vibrator according to the present invention, where (a) shows a top view and (b) shows a cross-sectional view taken along A-A ′. The high-frequency piezoelectric vibrator 12 has a concave portion 3 formed on one side of a quartz substrate 2 by etching or machining, and a thick annular surrounding portion 5 on a peripheral portion of a thin vibrating portion 4 provided on the bottom surface of the concave portion 3. Is formed integrally with the vibrating portion 4 and the thin plate-like vibrating portion 1 is mechanically supported.

Therefore, a pad electrode 15 for conducting the main electrode 13 for excitation, the lead electrode 14 derived therefrom, and the external package terminal is formed in the approximate center of the thin vibrating portion 4 on the flat side of the quartz substrate 2. ing. In addition, the suppression electrode 16 is arranged on the vibration part 4 on the concave side of the quartz substrate 2 so as to surround the excitation main electrode 13 formed on the flat side of the quartz substrate 2 so as not to overlap, and the electrode material is The same material as the main electrode 13 for excitation is used. Further, a full surface electrode 17 is formed on the entire surface including the inner wall of the annular surrounding portion 5 on the concave portion side of the quartz crystal substrate 2 to obtain a high frequency piezoelectric device.

  According to the present embodiment, the excitation main electrode and the suppression electrode are formed using the same electrode material, batch processing is possible at the time of forming the electrode film, and the formation of the excitation main electrode and the suppression electrode is possible. High-frequency electrode structure that can form electrode patterns with high gap accuracy and position accuracy between both electrodes using photolithography technology, can easily control electrode film thickness, and prevent CI value deterioration and unnecessary spurious generation A piezoelectric vibrator can be obtained.

Next, the manufacturing method of the high frequency piezoelectric vibrator in the present embodiment will be described.
FIG. 2 is a diagram illustrating a first manufacturing process example of the high-frequency piezoelectric vibrator according to the present invention, and FIG. 3 is a diagram illustrating a second manufacturing process example of the high-frequency piezoelectric vibrator according to the present invention.
FIG. 2 shows a manufacturing process of a high frequency crystal substrate processed into a predetermined shape, and FIG. 3 shows a process of forming each electrode film. Also, in this process example, gold is used as the material of all electrode films as an example of each electrode film, the film thickness difference between the main electrode for excitation and the suppression electrode is about 2 nm, the main electrode for excitation, the lead electrode, The film thickness of the bonding pad electrode was 50 nm, and the film thickness of the suppression electrode was 48 nm.

  Referring to FIG. 2, in order to manufacture a high-frequency piezoelectric vibrator, a protective film 11 is formed at a predetermined position on the surface of the AT-cut quartz crystal substrate 2 by a photolithography technique (step 1), and etching is performed. A portion of the substrate 2 where the protective film 11 is not formed is recessed into a predetermined shape, and the thin plate-like vibrating portion 4 and the annular surrounding portion 5 supporting the periphery thereof are integrally formed (step 2), and thereafter Then, the protective film 11 is peeled off to obtain a quartz substrate having a predetermined shape (step 3).

Next, FIG. 3 will be described. On the both surfaces of the quartz substrate processed into a predetermined shape in the previous step, gold is used as the electrode film material over the entire surface as the first vapor deposition, and the entire surface is formed with a film thickness of 48 nm using a vacuum vapor deposition machine. After the electrode film 18 is formed (Step 4), only the flat side surface (formation surface of the main electrode) of the quartz substrate is further vacuumed over the entire surface with a film thickness of 2 nm by using gold as an electrode film material and second deposition. A full-surface electrode film 19 is formed using a vapor deposition machine, and the electrode film thickness on the flat surface side is set to 50 nm (step 5). At this time, since the general accuracy of the film thickness control of the vacuum vapor deposition machine is about ± 10%, a film formation error of ± 4.8 nm occurs during the first vapor deposition. The film formation error is ± 0.2 nm.

  Next, a main electrode for excitation having a predetermined shape is led out from the main electrode to a substantially central portion of the vibration part on the flat side of the crystal substrate on a quartz substrate having full-surface electrodes formed on both sides thereof, and lead electrodes and pad electrodes An annular suppression electrode is formed on the concave side so as to surround the main electrode without overlapping with the main electrode by using a photolithography technique and an etching technique at the same time (step 6). As described above, by using the photolithography technique and the etching technique in combination, it is possible to form an electrode with high accuracy, and to reduce an error in gap size and position accuracy between the main electrode and the suppression electrode. As described above, the electrode film thickness difference between the main electrode for excitation and the suppression electrode is 2 nm through the manufacturing process as in the present embodiment, but the error in the electrode film thickness difference is ± 0. .2 nm or less, and an electrode film necessary to prevent CI value deterioration and unnecessary spurious generation can be formed.

Next, as the last step, the entire surface electrode is applied to the concave side of the quartz substrate on which the suppression electrode is formed, thereby completing the high-frequency piezoelectric vibrator (step 7).
Therefore, in the manufacturing method of this embodiment, the electrode film formation and the electrode formation can be batch-processed, and all the electrodes can be formed with high accuracy in both electrode film thickness and electrode shape using the same electrode film material. Therefore, it is possible to provide a high-frequency piezoelectric vibrator that is suitable for mass production of high-frequency piezoelectric vibrators and that operates with basic vibrations in a high-frequency band at a low price.

Although the present invention has been described above using the high-frequency piezoelectric vibrator using an AT-cut quartz substrate as an example, the present invention is not limited to this, and an etchable piezoelectric substrate such as a langasite (La ₃ Ga ₅ SiO _14), or, it is obvious that may be used, such as piezoelectric material lithium tetraborate _{(Li 2 B 4 O 7)} .
Furthermore, in the present embodiment, the case where the electrode shape is rectangular has been described, but the present invention can also be applied to a circular electrode and an elliptical electrode.

1 is an example showing the structure of a high-frequency piezoelectric vibrator according to the present invention. It is a figure which shows the 1st example of a manufacturing process of the high frequency piezoelectric vibrator concerning this invention. It is a figure which shows the 2nd example of a manufacturing process of the high frequency piezoelectric vibrator concerning this invention. It is a structural example of a conventional high-frequency piezoelectric vibrator. It is a figure which shows the example of a manufacturing process of the conventional high frequency piezoelectric vibrator.

Explanation of symbols

1 .... high frequency piezoelectric vibrator, 2 .... quartz substrate,
3 .... concave, 4 .... vibrating part,
5 .... Annular go, 6 .... Full-surface electrode,
7 ・ ・ Main electrode, 8 ・ ・ Lead electrode,
9 .... Pad electrode, 10 .... Suppression electrode,
11 .... Protective film, 12 .... High frequency piezoelectric vibrator,
13 .... Main electrode, 14 .... Lead electrode,
15 .... Pad electrode, 16 .... Suppression electrode,
17. Full-surface electrode, 18. Full-surface electrode film,
19 .. Full-surface electrode film

Claims (4)

A high-frequency piezoelectric vibrator in which a thin vibrating portion and a thick annular surrounding portion that mechanically supports the peripheral edge thereof are integrally formed by forming a concave portion on one surface of a piezoelectric substrate by etching or machining. Because
A main electrode for excitation having a predetermined shape formed at a substantially central part of the vibration part of the flat main surface of the piezoelectric substrate;
On the concave side of the piezoelectric substrate, an annular suppression electrode is arranged so as to surround the main electrode for excitation formed on the flat side of the piezoelectric substrate without overlapping, and on the concave side of the piezoelectric substrate, A high-frequency piezoelectric vibrator characterized in that almost the entire surface is covered with a full-surface electrode.   2. The high-frequency piezoelectric vibration according to claim 1, wherein the generation of spurious is reduced by controlling the energy confinement coefficient by forming the electrode film thickness of the suppression electrode in accordance with the electrode film thickness of the main electrode. Child.   The high-frequency piezoelectric vibrator according to claim 1, wherein the piezoelectric substrate is an AT-cut quartz substrate. Forming a concave portion by etching on one main surface of the piezoelectric substrate to integrally form a thin plate-like vibrating portion and an annular surrounding portion supporting the periphery thereof;
A first film forming step of forming a metal film with a predetermined film thickness on both surfaces of the piezoelectric substrate;
A second film forming step of forming a metal film over the entire surface with a predetermined film thickness only on the flat side surface of the piezoelectric substrate;
A main electrode for excitation having a predetermined shape is provided at a substantially central portion of the vibration portion on the flat side of the piezoelectric substrate, and an annular suppression electrode is provided on the concave portion side of the piezoelectric substrate so as to surround the main electrode without overlapping with the main electrode. Forming using photolithography technique and etching technique;
A method of manufacturing a high-frequency piezoelectric vibrator, comprising: forming a full-surface electrode over substantially the entire surface of the concave portion of the piezoelectric substrate on which the suppression electrode is formed.

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