JP2005101569A - Manufacturing method of piezoelectric thin film and piezo-resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a piezoelectric thin film having excellent piezoelectric properties, and also to provide a piezo-resonator using the thin film, which has excellent piezoelectric properties and is suitable for high frequency. <P>SOLUTION: The piezo-resonator 50 comprises a substrate 1 and a vacuum film-forming device 3b. A piezoelectric thin film 2 and excitation electrodes 3a, 3b constitute a piezoelectric element. The substrate 1 is provided with a cavity portion 4 at its rear, and its upper surface is provided with a thin-film support 5 constituted of a portion of the substrate. The piezoelectric thin film 2 is formed with the moisture pressure of the vacuum film-forming device being 2×10<SP>-5</SP>Pa or more during film formation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a diaphragm type piezoelectric resonator used in a high frequency region, and more particularly to a method for manufacturing a piezoelectric thin film used for a piezoelectric resonator.

  The resonance frequency of the piezoelectric resonator utilizing the longitudinal vibration of the piezoelectric substrate is inversely proportional to the thickness of the piezoelectric substrate. For this reason, when used in a high frequency region, it is necessary to process the piezoelectric substrate very thinly in correspondence with the frequency. However, to reduce the thickness of the piezoelectric substrate itself, due to the problem of mechanical strength, in the basic mode, several hundred MHz has been the limit of the practical high frequency region.

  Therefore, in order to solve such problems, the following piezoelectric resonator has been proposed. According to this method, a thin film supporting portion is formed on a part of the surface of the substrate by etching a part of the substrate made of an insulating material from the back side. It is a piezoelectric resonator formed by forming a single layer or a plurality of piezoelectric thin film layers and an electrode layer on a thin film support.

The thin film support can be thinned using a microfabrication technique. In addition, since the piezoelectric thin film layer can also be thinly formed using a vacuum film forming apparatus, the piezoelectric thin film layer is a piezoelectric resonator capable of extending high frequency characteristics from several hundred MHz to several thousand MHz (for example, see Patent Document 1).
JP 58-121817 A

  However, the piezoelectric resonator according to the related art described above has the following problems.

  In Patent Document 1, a ZnO film is formed as a piezoelectric thin film by a vacuum thin film forming method such as sputtering, ion plating, or CVD.

  The piezoelectric characteristics of the piezoelectric thin film are significantly affected by the orientation and crystallinity of the formed piezoelectric thin film. In the vacuum thin film forming method, it is difficult to accurately control the orientation and crystallinity of the film to be formed, and therefore, there is a problem that the piezoelectric characteristics of the formed piezoelectric thin film vary.

In order to solve the above problems, the piezoelectric thin film manufacturing method and the piezoelectric resonator of the present invention use a vacuum film forming apparatus, and in the piezoelectric thin film manufacturing method mainly comprising a piezoelectric oxide, the piezoelectric thin film is a vacuum film forming apparatus. The method of manufacturing a piezoelectric thin film is characterized in that the moisture pressure during film formation is 2 × 10 ⁻⁵ Pa or more. Further, the moisture pressure during film formation is larger than 3 × 10 ⁻⁵ Pa and smaller than 3 × 10 ⁻³ Pa. Further, the nitrogen partial pressure during film formation is smaller than 1 × 10 ⁻⁴ Pa. The piezoelectric thin film is characterized by containing ZnO as a main component.

  Furthermore, a piezoelectric resonator using the piezoelectric thin film formed by the manufacturing method described above. The piezoelectric filter is characterized by using at least one piezoelectric resonator. The duplexer is characterized by using the piezoelectric filter.

  According to the method for manufacturing a piezoelectric thin film of the present invention as described above, a piezoelectric thin film with small variations in orientation and crystallinity of the piezoelectric thin film can be formed, and a piezoelectric thin film with improved piezoelectric characteristics and small variations in piezoelectric characteristics can be formed. It becomes possible.

  In addition, by using the piezoelectric thin film formed by the piezoelectric thin film manufacturing method of the present invention as a piezoelectric resonator, using this piezoelectric resonator as a piezoelectric filter, and further using this piezoelectric filter as a duplexer, piezoelectric characteristics corresponding to high frequencies can be obtained. It is possible to provide a piezoelectric resonator, a piezoelectric filter, and a duplexer that are excellent and have small variations in piezoelectric characteristics.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view of an embodiment of a piezoelectric resonator according to the present invention.

  In FIG. 1, a piezoelectric resonator 50 includes a substrate 1, a piezoelectric thin film 2, an excitation electrode 3 a on one main surface side of the piezoelectric thin film 2, and an excitation electrode 3 b on the other main surface of the piezoelectric thin film 2. The piezoelectric thin film 2 and the excitation electrodes 3a and 3b constitute a piezoelectric element. The substrate 1 has a hollow portion 4 on the back surface side, and includes a thin film support portion 5 formed of a part of the substrate on the upper surface.

  Details of the method for manufacturing the piezoelectric resonator of the present invention will be described with reference to a schematic process flow shown in FIG.

  First, as shown in FIG. 2A, a resist pattern 6 is formed on the upper surface of a substrate 1, for example, a Si substrate, using a photolithography technique. Specifically, the resist is applied to a predetermined film thickness using a spin coater or the like. Next, a resist pattern 6 is formed by exposing and developing the resist through a photolithography mask on which a desired pattern is formed.

  Next, an excitation electrode 3a is formed on the substrate 1 as shown in FIG. Specifically, an electrode metal film is formed on the substrate 1 on which the resist pattern 6 is formed by a vapor deposition method or the like. Next, the excitation electrode 3a is formed by a lift-off method in which the resist pattern 6 and an unnecessary metal film on the resist pattern 6 are simultaneously peeled off.

Next, as shown in FIG. 2C, a piezoelectric thin film 2 having a predetermined film thickness corresponding to a desired frequency is formed on the substrate 1 on which the excitation electrode 3a is formed. For example, ZnO is used for the piezoelectric thin film 2. The piezoelectric thin film 2 corresponds to the desired piezoelectric characteristics, and BaTiO ₃ , BaTiO ₃ —SrTiO ₃ , PbTiO ₃ —PbZrO ₃ , Ta ₂ O ₅ or the like may be used.

The piezoelectric thin film 2 is formed by a vacuum thin film forming method such as a sputtering method or a CVD method using a metal mask or the like. At this time, the piezoelectric thin film 2 is formed at a moisture pressure of 2 × 10 ⁻⁵ Pa or more in the vacuum film forming apparatus during film formation. That is, when the moisture pressure is 3 × 10 ⁻⁵ Pa or more, the piezoelectric characteristic K ² (electromechanical coupling coefficient) can be secured by 2% or more, and thus a wide band filter can be manufactured. On the other hand, when the water pressure is 3 × 10 ⁻³ Pa or more, the ZnO film is cracked and the defect rate of the ZnO film is increased. For this reason, the water pressure is preferably larger than 3 × 10 ^{−5 and} smaller than 3 × 10 ⁻³ Pa. Further, the water pressure in the vacuum film forming apparatus during film formation may be controlled by the water pressure of the back pressure, but more preferably, the water pressure in the vacuum film forming apparatus during film formation is controlled. The water pressure in the vacuum film-forming apparatus during film formation is monitored by a partial pressure meter, a mass spectrometer, or the like, and controlled by introducing a water component from a predetermined path so as to achieve the above-described desired water pressure. Furthermore, the nitrogen partial pressure in the vacuum apparatus during film formation is preferably less than 1 × 10 ⁻⁴ Pa in order to prevent deterioration of piezoelectric characteristics.

  Next, an excitation electrode 3b is formed on the piezoelectric thin film 2 as shown in FIG. Since the excitation electrode 3b is formed by the same method as the excitation electrode 3a, detailed description thereof is omitted.

  Next, the piezoelectric resonator 50 shown in FIG. 1 is formed by forming the cavity 4 in the substrate 1. The cavity 4 is formed by partially etching from the back side of the substrate 1 by wet etching or reactive ion etching (RIE) using a mask or the like. Thereby, the thin film support 5 is formed on a part of the piezoelectric substrate 1.

FIG. 3 shows the relationship between the water pressure in the vacuum film forming apparatus during film formation and the piezoelectric characteristic K ² of the formed piezoelectric thin film 2. From FIG. 3, it can be clearly confirmed that the piezoelectric characteristic K ² tends to be improved as the water pressure in the vacuum film forming apparatus increases. The moisture pressure in the vacuum film forming apparatus is 2 × 10 ⁻⁵ Pa, and the piezoelectric characteristic K ² shows a value of 1% or more. Further, when the water pressure in the vacuum film forming apparatus becomes larger than 3 × 10 ⁻³ Pa, the piezoelectric characteristic K ² shows a value of 2% or more. Although not shown in FIG. 3, the reproducibility is also confirmed, and variations in piezoelectric characteristics are reduced. Further, when the moisture pressure in the vacuum film forming apparatus is 2 × 10 ⁻³ Pa, the piezoelectric characteristic K ² shows a large value of 4.5% when the nitrogen partial pressure is 2.8 × 10 ⁻⁷ Pa. However, if the nitrogen partial pressure is 1 × 10 ⁻⁴ Pa at the same moisture pressure, the piezoelectric characteristic K ² becomes as small as 0.4%. Thus, by lowering the nitrogen partial pressure in the vacuum film forming apparatus, it is possible to prevent deterioration of piezoelectric characteristics. The value of the piezoelectric characteristic K ^{2 is} a value of the piezoelectric characteristic that can be applied to a high frequency band for a communication system.

In addition, the effect of moisture pressure during film formation on a piezoelectric thin film containing piezoelectric oxide as a main component is not recognized when the water pressure during film formation is 1 × 10 ⁻⁵ Pa, for example, and is recognized according to the conditions of the present invention. It has also been confirmed from the presence of OH groups in the film.

  According to the method for manufacturing a piezoelectric thin film of the present invention as described above, a piezoelectric thin film with small variations in orientation and crystallinity of the piezoelectric thin film can be formed, and a piezoelectric thin film with improved variations in piezoelectric characteristics can be formed. Become.

  In addition, by using the piezoelectric thin film formed by the method for manufacturing a piezoelectric thin film of the present invention as a piezoelectric resonator, it is possible to provide a piezoelectric resonator that has excellent piezoelectric characteristics corresponding to a high frequency and has small variations in piezoelectric characteristics.

  FIG. 4 shows a schematic cross-sectional view of another embodiment of the piezoelectric resonator of the present invention.

  In FIG. 4, the piezoelectric resonator 60 includes a substrate 1, an insulating thin film 7, a piezoelectric thin film 2, an excitation electrode 3 a on one main surface side of the piezoelectric thin film 2, and an excitation on the other main surface of the piezoelectric thin film 2. And an electrode 3b. The piezoelectric thin film 2 and the excitation electrodes 3a and 3b constitute a piezoelectric element. The substrate 1 has a hollow portion 4 on the back surface side, and has a thin film support portion 8 constituted by a part of the insulating thin film 7 on the upper surface thereof.

  Details of the method for manufacturing the piezoelectric resonator of the present invention will be described with reference to a schematic process flow shown in FIG.

First, as shown in FIG. 5A, an insulating thin film 7 is formed on the upper surface of a substrate 1, for example, a Si substrate. The insulating thin film 7 may be a SiO ₂ thin film formed using, for example, a sputtering method or a thermal oxidation method. The insulating thin film 7 is not limited to the SiO ₂ thin film, and an aluminum oxide thin film or an aluminum nitride thin film formed by an electron beam method or a sputtering method may be used. The insulating thin film 7 is not limited to a single layer, and may be a laminated structure in which at least two of the SiO ₂ thin film, the aluminum oxide thin film, and the aluminum nitride thin film are in any order.

  Next, as shown in FIG. 5B, the excitation electrode 3 b, the piezoelectric thin film 2, and the excitation electrode 3 b are formed on the insulating thin film 7. Since this is the same as that shown in FIGS. 2A to 2D, detailed description thereof is omitted. Next, by forming the cavity 4 in the substrate 1, the piezoelectric resonator 60 shown in FIG. 4 is formed. The cavity 4 is formed by partially etching from the back side of the substrate 1 by wet etching or reactive ion etching (RIE) using a mask or the like. Thereby, the thin film support portion 8 is formed on a part of the insulating thin film 7.

The piezoelectric thin film 2 is formed at a moisture pressure of 2 × 10 ⁻⁵ Pa or more in a vacuum film forming apparatus during film formation. That is, when the water pressure is 3 × 10 ⁻⁵ Pa or more, the piezoelectric characteristic K ² can be secured by 2% or more, and thus a wide band filter can be manufactured. On the other hand, when the water pressure is 3 × 10 ⁻³ Pa or more, the ZnO film is cracked and the defect rate of the ZnO film is increased. For this reason, the water pressure is preferably larger than 3 × 10 ^{−5 and} smaller than 3 × 10 ⁻³ Pa. The water pressure in the vacuum film forming apparatus during film formation may be controlled by the water pressure of the back pressure, but more preferably, the water pressure in the vacuum film forming apparatus during film formation is controlled. The water pressure in the vacuum film forming apparatus during film formation is monitored by a partial pressure meter, a mass spectrometer, or the like, and controlled by introducing a water component from a predetermined path so as to achieve the above-described desired water pressure. Further, the nitrogen partial pressure in the vacuum apparatus during film formation is preferably smaller than 1 × 10 ⁻⁴ Pa in order to eliminate deterioration of piezoelectric characteristics.

  Therefore, a piezoelectric thin film with improved piezoelectric characteristics of the piezoelectric thin film 2 and small variations in piezoelectric characteristics is formed.

  According to the method for manufacturing a piezoelectric thin film of the present invention, a piezoelectric thin film with small variations in orientation and crystallinity of the piezoelectric thin film can be formed, and a piezoelectric thin film with improved variations in piezoelectric characteristics can be formed. In addition, by using the piezoelectric thin film formed by the method for manufacturing a piezoelectric thin film of the present invention as a piezoelectric resonator, it is possible to provide a piezoelectric resonator that has excellent piezoelectric characteristics corresponding to a high frequency and has small variations in piezoelectric characteristics.

  Moreover, you may comprise a piezoelectric filter using the piezoelectric resonator of this invention.

  FIG. 6 shows a schematic equivalent circuit diagram of a piezoelectric filter in which the piezoelectric resonators of the present invention are ladder-connected.

  FIG. 6A shows an equivalent circuit diagram of the T-type ladder filter, and FIGS. 6B and 6C show an equivalent circuit diagram of the L-type ladder filter.

  As shown in FIG. 6A, the T-type ladder filter includes three piezoelectric resonators 8. One end of each of the three piezoelectric resonators 8 is connected to each other. The other end of one piezoelectric resonator 8 is connected to the input terminal IN, the other end of the other piezoelectric resonator 8 is grounded, and the other end of the remaining one piezoelectric resonator 8 is connected to the output terminal OUT. Connected to. Further, a π-type ladder filter may be configured.

  Next, as shown in FIG. 6B, the L-type ladder filter includes four piezoelectric resonators 8. Two piezoelectric resonators 8 on the series side and two piezoelectric resonators 8 are connected in parallel. Moreover, as shown in FIG.6 (c), it may be comprised with the two piezoelectric resonators 8. FIG. Therefore, a ladder filter having excellent filter characteristics and small variations in filter characteristics can be provided by using a piezoelectric resonator having excellent piezoelectric characteristics and small variations in piezoelectric characteristics for the ladder type filter.

Further, a duplexer may be configured using the piezoelectric filter of the present invention.
FIG. 7 shows a schematic block diagram of an embodiment of a duplexer using the piezoelectric filter of the present invention. As shown in FIG. 7, the duplexer 80 includes a transmitter filter and a reception filter. For the transmission side filter, a T-type ladder filter 70 shown in FIG. 6A is used as a piezoelectric filter. Similarly, a T-type ladder filter 70 is used for the reception side filter. Therefore, it is possible to provide a duplexer that has excellent duplexer characteristics and small variations in duplexer characteristics by using a ladder filter having excellent filter characteristics and small variations in filter characteristics for the duplexer.

It is a schematic sectional drawing in one Example of the piezoelectric resonator of this invention. (Example 1) It is a general | schematic manufacturing process flow in one Example of the manufacturing method of the piezoelectric resonator of this invention. (Example 1) It is a graph which shows the effect of the present invention. (Example 1) It is a schematic sectional drawing in another Example of the piezoelectric resonator of this invention. (Example 2) It is a general | schematic manufacturing process flow in another Example of the manufacturing method of the piezoelectric resonator of this invention. (Example 2) It is a schematic circuit diagram in one Example of the piezoelectric filter using the piezoelectric resonator of this invention. Example 3 It is a schematic block diagram in one Example of the duplexer using the piezoelectric filter of this invention. (Example 4)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Piezoelectric thin film 3a, 3b Excitation electrode 4 Cavity part 5, 8 Piezoelectric thin film support part 6 Resist pattern 7 Insulating thin film 8, 50, 60 Piezoelectric resonator 70 T-type ladder filter 80 Duplexer

Claims (7)

In the method for manufacturing a piezoelectric thin film mainly composed of piezoelectric oxide using a vacuum film forming apparatus, the piezoelectric thin film is formed at a moisture pressure of 2 × 10 ⁻⁵ Pa or more during film formation of the vacuum film forming apparatus. A method for producing a piezoelectric thin film, comprising: 2. The method of manufacturing a piezoelectric thin film according to claim 1, wherein a moisture pressure during the film formation is greater than 3 × 10 ⁻⁵ Pa and less than 3 × 10 ⁻³ Pa. ³ . In the method of manufacturing a piezoelectric thin film mainly composed of piezoelectric oxide using a vacuum film forming apparatus, the piezoelectric thin film has a nitrogen partial pressure during film formation of the vacuum film forming apparatus in a range smaller than 1 × 10 ⁻⁴ Pa. The method for manufacturing a piezoelectric thin film according to claim 2, wherein the piezoelectric thin film is formed by:   The method for manufacturing a piezoelectric thin film according to any one of claims 1 to 3, wherein the piezoelectric thin film contains ZnO as a main component.   A piezoelectric resonator using the piezoelectric thin film formed according to any one of claims 1 to 4.   A piezoelectric filter using at least one piezoelectric resonator according to claim 5.   A duplexer using the piezoelectric filter according to claim 6.

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