JP2001016068A - Piezoelectric resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric resonator long in seice life, few in malfunctions due to damage and deformation and capable of being inexpensively and easily manufactured with simple configuration by vibrating a piezoelectric body in the thickness direction of a supporting wall. SOLUTION: A base 11 and a supporting wall 12 protruded from the surface of the base 11 are integrally installed. A first electrode 14, a piezoelectric body 15 formed on the first electrode 14 and a second electrode 16 formed on the piezoelectric body 15 are installed on the side of the supporting wall 12. A vibrator 17 where the first electrode 14 and the second electrode 16 sandwich the piezoelectric body 15 is formed on the side of the supporting wall 12. Here, the supporting wall 12 protruded from the surface is installed on the base 11 and the vibrator 17 is formed on the side of the supporting wall 12. The vibrator 17 vibrates in the thickness direction of the supporting wall 12, and vibration is hardly transmitted to the base 11. Thus, it is not necessary to install a vibration space, and structure without a supporting film can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable telephone and a wireless LA.
The present invention relates to a piezoelectric resonator used for N and the like, and more particularly, to a piezoelectric resonator utilizing resonance of a thickness longitudinal vibration of a piezoelectric body.

[0002]

2. Description of the Related Art As the frequencies used for wireless communication and electric circuits have become higher, filters used for these electric signals have been developed to correspond to higher frequencies.

[0003] In particular, in the radio communication, microwaves in the vicinity of 2 GHz are becoming mainstream, and there is already a movement to establish standards of several GHz or more. Therefore, an inexpensive and high-performance filter corresponding to the high frequency is required. ing.

Recently, a filter using a surface acoustic wave resonator (SAWR) utilizing resonance of a surface acoustic wave, which is an acoustic wave transmitted on the surface of a solid, has been widely used.
That is, the SAWR applies a high-frequency electric field between comb-shaped electrodes formed on a solid surface, and utilizes resonance with a surface acoustic wave. This filter has very excellent frequency selection characteristics as a bandpass filter.

[0005] However, the SAWR has a 1G because the distance between the comb-shaped electrodes and the resonance frequency are in inverse proportion.
In the frequency region exceeding Hz, the distance between the comb-shaped electrodes was 1 μm or less, and it was very difficult to manufacture the electrodes.

Accordingly, in recent years, a bulk acoustic wave resonator (BAWR) utilizing thickness longitudinal vibration of a thin film exhibiting piezoelectricity has been proposed. This is a resonator using the fact that the piezoelectric body vibrates in response to an input high-frequency electric signal and resonates in the thickness direction of the piezoelectric body. Since the piezoelectric material constituting the BAWR can be controlled with high accuracy even at a film thickness of 1 μm or less, it is expected that a resonator having a higher resonance frequency than that of the SAWR can be manufactured. Have been.

As shown in FIG. 5, a conventional BAWR includes a base 1 and a support film 2 formed on the surface of the base 1.
A buffer layer 3 formed on the support film 2; a first electrode 4 formed on the buffer layer 3; a piezoelectric body 5 formed on the first electrode 4; (USP4, USP4)
320, 365). The first electrode 4, the piezoelectric body 5, and the second
A vibrating body is constituted by the electrodes, and a high-frequency electric field is applied between the first electrode 4 and the second electrode 6, whereby the vibrating body, the buffer layer 3 formed below the vibrating body, and the support film 2 are formed. Vibrates and becomes a vibrating part. The vibrating portion of the support film 2 is exposed to the vibration space A.

[0008] Further, instead of removing a part of the base, a hollow structure in which a part of the support film is separated from the surface of the base is formed to realize acoustic separation between the vibrating part and the base. It is disclosed in JP-A-61-127216.

[0009] This structure, as shown in FIG.
A support film 2 formed on the surface of the base 1; a first electrode 4 formed on the support film 2; a piezoelectric body 5 formed on the first electrode 4; And two second electrodes 6 formed thereon. In this example, instead of removing the substrate, the layer formed under the support film 2 after the formation of the support film is removed to form a hollow structure.
A vibration space A is formed between the substrate and the supporting film 2.

[0010]

However, in the above-described thin film piezoelectric resonator, it is necessary to form a vibration space below the vibrating body via a supporting film, and the structure and process are complicated. There was a problem that a supporting film having sufficient strength to support it could not be obtained.

That is, a residual stress is generated between the substrate and the support film due to a difference in thermal expansion, and the support film, the first electrode, the piezoelectric body, and the second electrode have internal stress in the film itself by the thin film forming process. Occurs and this internal stress is further increased by stacking. On the other hand, since the supporting film is exposed to the vibration space, the vibrating body is supported by the supporting film, and the residual stress and the internal stress substantially reduce the strength of the supporting film, and during manufacturing, during handling, or There has been a problem that the support film is easily broken during operation, the production yield is low, and the life of the product is short.

Further, there is a problem in that warping or bending of the entire piezoelectric resonator is induced in an attempt to relieve the above-mentioned residual stress and internal stress.

Further, in the conventional thin-film resonator shown in FIGS. 5 and 6, after forming a thin film such as a support film by a vacuum process, a vibration space is formed by a chemical wet process involving alkali treatment in the atmosphere. Then, an inefficient treatment of returning to a vacuum process to form a vibrator was required. This has resulted in complicated processes and high costs.

An object of the present invention is to provide a long-life piezo-resonator which is less likely to malfunction due to breakage or deformation, has a simple structure, and can be easily manufactured at low cost.

[0015]

According to the present invention, there is provided a piezoelectric resonator comprising:
A base, a support wall protruding from the surface of the base, and a vibrator provided on a side surface of the support wall and having a pair of electrodes sandwiching a piezoelectric body. And the piezoelectric body vibrates in the thickness direction of the support wall.

Further, the piezoelectric resonator of the present invention comprises: a base; a conductive support wall protruding from the surface of the base; and a piezoelectric body provided on a side surface of the support wall.
And an electrode provided on the piezoelectric body, and the piezoelectric body vibrates in a thickness direction of the support wall.

[0017]

In the piezoelectric resonator of the present invention, the base is provided with a support wall protruding from the surface thereof, and a vibrator is provided on the side surface of the support wall. Since the vibration is caused in the direction and the vibration is hardly transmitted to the base, there is no need to provide a vibration space as in the related art. Therefore, according to the present invention, since a structure without a supporting film is possible, the manufacturing process can be simplified with a simple structure, and further, the problem of cracks caused by the supporting film can be avoided.

Further, since the support wall is provided with conductivity and the piezoelectric body and the electrode are sequentially laminated on the side surface of the conductive support wall, the vibrator vibrates in the thickness direction of the support wall as described above. Vibration is hardly transmitted to the base, so that it is not necessary to provide a vibration space as in the prior art, and the manufacturing process can be simplified with a simple structure. In addition, the support wall itself can also serve as the electrode of the vibrating body, thereby reducing the number of layers to reduce the occurrence of stress, reducing warpage, and contributing to further cost reduction by reducing the number of steps.

In the present invention, since there is no need to provide a vibration space as in the prior art, all the manufacturing processes can be handled by a vacuum process by omitting the treatment in the atmosphere, an automation process can be constructed, and the processing time can be reduced. it can. as a result,
Further, cost reduction and productivity improvement can be achieved.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric resonator according to the present invention comprises a support wall protruding above a base, and a vibrator provided on a side surface of the support wall and sandwiching a piezoelectric body between a pair of electrodes. This is a thin film piezoelectric resonator. That is, in the piezoelectric resonator of the present invention, as shown in FIG. 1, a base 11 and a support wall 12 protruding from the surface of the base 11 are integrally provided. The first electrode 14 and the first electrode 1
A piezoelectric body 15 formed on the piezoelectric element 4 and a second electrode 16 formed on the piezoelectric body 15 are provided. Here, on the side surface of the support wall 12, a vibrating body 17 formed by sandwiching the piezoelectric body 15 between the first electrode 14 and the second electrode 16 is formed.

The support wall 12 can be formed by, for example, removing a block constituting the base body by etching except for a portion where the support wall is formed. Support wall thickness t
Is preferably 3 to 10 μm. This is because when the thickness is smaller than 3 μm, the strength is low, and when the thickness is larger than 10 μm, the resonance frequency is low.

The piezoelectric body 15 can be formed by a sol-gel method, a gas phase synthesis method represented by a sputtering method, or the like. The thickness of the piezoelectric body 15 depends on the frequency band of the resonator to be used, but is preferably 2 μm or less. this is,
This is because the interval between the first electrode 14 and the second electrode 16 needs to be 2 μm or less in order to obtain a resonance frequency of 1 GHz or more by the thickness longitudinal vibration.

The first electrode 14 and the second electrode 16 are CV
It is produced and obtained by a gas phase synthesis method such as a D method, a sputtering method, a vacuum evaporation method, an ion plating method and the like. The electrode preferably has a thickness of 0.05 to 0.3 μm, and particularly preferably 0.1 to 0.2 μm.

The substrate 11 is made of an inorganic substance such as silicon or alumina. The material is not particularly limited as long as it has a flat surface capable of forming a protruding support wall on the surface of the substrate. However, in order to form a support wall that is a rectangular convex protrusion, a single crystal is preferable. That is, the support wall 12 is preferably formed integrally with the base 11 because it is necessary to increase the strength of the support wall 12,
Further, a single crystal is suitable for forming the support wall by removing the periphery of the support wall of the base 11 by etching.

The ease of processing and accumulation of basic data,
Considering the uniformity of characteristics, etc., a silicon substrate is desirable. On the other hand, from the viewpoint of increasing the resonance frequency, a material having a high sound velocity, that is, a material having a large Young's modulus, for example, a sapphire substrate is desirable.

When a resonator is formed by using a piezoelectric material such as ZnO or AlN that is not a ferroelectric material as the piezoelectric material 15, the area becomes large and a small resonator cannot be realized. 15 is suitable for a ferroelectric substance having a large relative permittivity.

In particular, a ferroelectric thin film having a perovskite structure, such as Pb (Zr ₁ -x Ti _x ) O ₃ , has a large spontaneous polarization and a large piezoelectric property.
The relative dielectric constant is about 100 times larger than that of a non-ferroelectric piezoelectric substance such as ZnO or AlN, and the electrode area, which is one of the factors determining impedance, can be reduced to about 1/100. Can be smaller.

Examples of the ferroelectric having a perovskite structure include Pb (Zr ₁ -x Ti _x ) O ₃ and PbTi.
O ₃ and BaTiO ₃ . Further, a ferroelectric thin film other than the perovskite structure, for example, Sr ₂ KNb ₅ O ₁₅ having a tungsten bronze structure can be used.

Among ferroelectrics, Pb (Zr _{1 -X} T
i _X ) Those having a basic composition of O ₃ are preferred. Pb (Z
This is because those having the basic composition of r _1-x Ti _x ) O ₃ show a large piezoelectricity and a relative dielectric constant even in a thin film.

The first electrode 14 sandwiching the piezoelectric body 15 and the second electrode
The electrode 16 is made of Al, Au,
And the like. Al is desirable because the mass load on the piezoelectric body 15 is small and it is difficult to suppress the piezoelectric vibration, and the electrical resistivity is small and the decrease in the Q value of the resonator is small.

Needless to say, an extraction electrode is formed and used for electrical connection between the first electrode 14 or the second electrode 16 and the external electrode.

In the piezoelectric resonator configured as described above,
The base 11 is provided with a support wall 12 projecting from the surface thereof, and a vibrating body 17 is formed on a side surface of the supporting wall 12, so that the vibrating body 17 is supported as indicated by an arrow in FIG. Since it vibrates in the thickness direction of the wall 12 and almost no vibration is transmitted to the base 11, there is no need to provide a vibration space as in the related art, and a structure without the support film 12 is possible. Accordingly, the manufacturing process can be simplified, and it is not necessary to consider the cracking of the support film 12 and the like, and the life can be prolonged.

The support wall 1 provided on the surface of the base 11
2 has a three-dimensional structure, and a ferroelectric material is used for the piezoelectric body 15, so that the vibrator 1
Since the installation area of 7 can be reduced and the number or size of the support walls 12 can be arbitrarily determined, the area of components as a filter can be reduced.

FIG. 2 shows another embodiment of the present invention, in which a conductive support wall 1 is provided protruding from a base 11.
2, a piezoelectric body 15 formed on the side surface of the support wall 12, and an electrode 26 formed on the piezoelectric body 15. Here, since the support wall 12 has conductivity, it can be used as the first electrode in FIG.

By using conductive silicon or the like doped with a high concentration of carriers for the base 11, FIG.
The structure in which the first electrode is omitted and the substrate also serves as the electrode can be obtained. That is, the base 11 is made of a conductive silicon wafer, and the support wall 12 is formed using a semiconductor process such as lithography or plasma etching. Next, by sequentially forming the piezoelectric body 15 and the electrode 26 on the side surface of the support wall 12, the piezoelectric resonator of the present invention can be obtained.

In such a piezoelectric resonator, as described above,
Since a structure without a supporting film becomes possible, the manufacturing process can be simplified with a simple structure, furthermore, there is no need to consider cracking of the supporting film, etc., and a longer life can be promoted, and the formation of electrodes is omitted, The stress generated by reducing the number of layers can be reduced, and warpage can be reduced. Further, the cost can be further reduced by reducing the number of man-hours during manufacturing.

As another example, as shown in FIG. 3, the first electrode 14, the piezoelectric body 15, and the second electrode 16 are
By not being formed on the upper surface of the two, by forming them on two opposing surfaces, the two vibrations can be controlled independently, and the vibration characteristics as a resonator can be easily controlled. Note that the first electrode 14, the piezoelectric body 15, and the second electrode 16 may be formed on only one of the side surfaces of the support wall 12 without any problem.

As shown in FIG. 4, a vibrating body 17 composed of a first electrode 14, a piezoelectric body 15, and a second electrode 16 is formed on the side surface of the support wall 12, and the vibrating body 17 is It is formed at the center of the side surface of the support wall 12, and there is an unformed portion on the base 11 side and the upper surface side. Since the vibrating body 17 is not formed on the base 11 side and the upper surface side opposite thereto, the efficiency of confining vibration to the support wall 12 is increased, and unnecessary vibration can be suppressed.

[0039]

EXAMPLE 1 Using a (100) silicon wafer, a pattern was formed using a photoresist, and selective etching was performed to form a substrate 1 on which a support film 12 as shown in FIG. 1 was formed.
1 was produced. The support wall 12 has a width of 5 μm on the silicon wafer.
m, after forming an etching mask of 100 μm length,
RIE using a mixed gas of CF ₄ and O ₂ , width 5
A support wall having a thickness of 100 μm, a length of 100 μm, and a height of 100 μm was formed.

Next, the first electrode 14 was manufactured. An Al electrode was formed by MOCVD using Al (C ₂ H ₅ ) ₃ as a source gas. The reason why the MOCVD method is used is that relatively good film thickness uniformity can be obtained even with a complicated shape as compared with the sputtering method or the vapor deposition method. The thickness of the first electrode 14 was about 0.3 μm. Further, in order to increase the adhesion between the aluminum electrode and the silicon, titanium may be thinly formed between the support wall 12 and the first electrode 14.

Next, the piezoelectric body 15 was formed on the first electrode. Pb (Zr _0.47 Ti _0.53 ) O ₃ is used as a piezoelectric material. The film formation method is MOCVD, and TiO (DP
A thin film having a thickness of about 0.4 μm was formed using M) ₂ , Zr (DPM) ₄ , and Pb (DPM) ₂ . DPM is dipivaloyl methanate.

The second electrode 16 is placed on the piezoelectric body 15.
An Al thin film was formed in the same manner as the first electrode 14. The thickness is about 0.3 μm.

As a result of measuring the high-frequency characteristics of the resonator structure manufactured as described above, a result having a fundamental resonance frequency of 480 MHz was obtained for a sample having a piezoelectric film thickness of about 0.4 μm. From this result, considering the sound speed of the silicon substrate, it is considered that the vibration waves reflected at the second electrode ends on both sides resonate.

Each of the manufactured devices was cut out from one wafer by dicing, and the state of damage was observed. 3mm
When 100 pieces were cut out at a size of 3 mm, breakage was observed in 11 pieces.

In the electrodes and piezoelectric bodies formed by the thin film process, internal stress is generated in the films.
Of the pieces, the peeling at the interface between the base and the support film and the warpage of the piezoelectric resonator were 0 out of 100 pieces.

COMPARATIVE EXAMPLE First, a Si wafer was used as a substrate, and after cleaning by an RCA method, a thin film serving as a support film was formed. That is, a SiO ₂ film was formed on a Si substrate by a sputtering method. next,
A pattern was formed on the back surface of the Si substrate by using a photoresist method, and etching was selectively performed using a KOH solution to produce a vibration space A in FIG. In this solution treatment, the sample was immersed in a high-concentration alkaline solution for 24 hours and washed with pure water. A silicon nitride film is used as a protective film for etching. The shape of the vibration space becomes a trapezoidal concave portion due to the anisotropic etching of KOH.

Next, the first electrode, the piezoelectric material, the second
Each layer of the electrode was formed using a sputtering method. Pt was used for the electrode material and PZT was used for the piezoelectric material. A metal mask was used for pattern formation.

When dicing was performed to cut out each manufactured device from one wafer, 100 devices of 3 mm × 3 mm size were cut out, and 94 devices were damaged. Further, since the support film was formed by a thin film process, internal stress was generated in the film, and peeling occurred at the interface between the substrate and the support film. Out of 100 prototypes, 58
Peeling was observed in the individual.

Example 2 A piezoelectric resonator having the structure shown in FIG. 2 was manufactured. Base 11
An n-type low electric resistance silicon substrate was used. The method of manufacturing the support wall 12, the piezoelectric body 15, and the electrodes is the same as that of the first embodiment, but the conductive support wall 12 is the first method of the first embodiment.
The formation of the first electrode is omitted because it is used as an electrode. The thickness of the piezoelectric body 15 was about 0.4 μm, and the thickness of the electrode 16 was about 0.3 μm.

As a result of measuring the high-frequency characteristics of the resonator structure manufactured as described above, a result having a fundamental resonance frequency of 480 MHz was obtained for a sample having a piezoelectric film thickness of about 0.4 μm.

When dicing was performed to cut out each manufactured device from one wafer, 100 devices were cut out in a size of 3 mm × 3 mm, and nine devices were damaged. Further, at the interface between the substrate and the support film, peeling or warping was 0 out of 100 pieces.

[0052]

The piezoelectric resonator of the present invention is used in a conventional piezoelectric resonator by providing a support wall protruding from the surface on a base and forming a vibrator on the side surface. Since no support film is required, it is possible to prevent breakage during manufacturing with a simple structure, to suppress warpage, and to simplify the manufacturing process, thereby greatly reducing costs.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piezoelectric resonator of the present invention.

FIG. 2 is a perspective view showing another piezoelectric resonator of the present invention.

FIG. 3 is a perspective view showing still another piezoelectric resonator of the present invention.

FIG. 4 is a perspective view showing still another piezoelectric resonator of the present invention.

FIG. 5 is a sectional view showing a conventional piezoelectric resonator.

FIG. 6 is a cross-sectional view showing another conventional piezoelectric resonator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Base 12 ... Support wall 14 ... 1st electrode 15 ... Piezoelectric body 16 ... 2nd electrode 17 ... Vibration body

Claims (2)

[Claims] 1. A base, a support wall provided on the base so as to protrude from a surface thereof, and a vibrator provided on a side surface of the support wall and sandwiching a piezoelectric body between a pair of electrodes. A piezoelectric resonator, comprising: the piezoelectric body vibrates in a thickness direction of the support wall. 2. A base, a conductive support wall protruding from the surface of the base, a piezoelectric body provided on a side surface of the support wall, and an electrode provided on the piezoelectric body. Wherein the piezoelectric body vibrates in the thickness direction of the support wall.