JP6885533B2 - Manufacturing method of bulk elastic wave resonator - Google Patents

Manufacturing method of bulk elastic wave resonator Download PDF

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JP6885533B2
JP6885533B2 JP2017013227A JP2017013227A JP6885533B2 JP 6885533 B2 JP6885533 B2 JP 6885533B2 JP 2017013227 A JP2017013227 A JP 2017013227A JP 2017013227 A JP2017013227 A JP 2017013227A JP 6885533 B2 JP6885533 B2 JP 6885533B2
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王義 山崎
王義 山崎
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New Japan Radio Co Ltd
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Description

本発明は、温度補償型のバルク弾性波共振器の製造方法に関するものである。 The present invention relates to a method for manufacturing a temperature-compensated bulk elastic wave resonator.

近年、スマートフォンの世界的な普及や、ウェアラブルやIoT(Internet of Things)と通称されるマイクロ波を用いた無線通信サービスの留まることのない旺盛な需要の拡大に伴い、限られた資源である電波(マイクロ波)を有効に利用するため、空間にあふれるマイクロ波の中から必要な周波数の電波を選択的に抽出することが求められている。例えば、現在、2.5GHz帯以下の周波数帯だけでなく3GHz以上の高周波帯を利用するサービスも拡大しており、所定の周波数帯域の電波を選択的に抽出するため高周波フィルタが使用されている。この種の高周波フィルタでは、温度ドリフトがなく、急峻なスカート特性を有する等、高性能化が要求されている。 In recent years, with the worldwide spread of smartphones and the ever-increasing demand for wireless communication services using microwaves, commonly known as wearables and IoT (Internet of Things), radio waves are a limited resource. In order to make effective use of (microwaves), it is required to selectively extract radio waves of a required frequency from microwaves overflowing in space. For example, at present, services that use not only a frequency band of 2.5 GHz or less but also a high frequency band of 3 GHz or more are expanding, and a high frequency filter is used to selectively extract radio waves in a predetermined frequency band. .. High-frequency filters of this type are required to have high performance, such as having no temperature drift and having steep skirt characteristics.

また、世界各地で使用されている周波数帯域に対応できるようにするため、1台のスマートフォンに10個を超える高周波フィルタが搭載されるようになり、小型でフィルタ特性に優れていることから、高周波フィルタとして、SAW(表面弾性波)共振器が多用されている。 In addition, in order to support the frequency band used all over the world, more than 10 high-frequency filters are installed in one smartphone, and because of its small size and excellent filter characteristics, high-frequency waves are used. SAW (Surface Acoustic Wave) resonators are often used as filters.

一方、SAW共振器では3GHz以上の高周波帯域や広い通過帯域で使用するには限界があり、高性能を要求されるフィルタにはバルク弾性波(BAW)共振器が使われるようになってきている。今後、3GHz帯以上の高周波帯でも、使用される周波数帯域が込み合ってくるとの予測を踏まえると、バルク弾性波共振器の需要はさらに拡大することが期待される。 On the other hand, SAW resonators have a limit in being used in a high frequency band of 3 GHz or higher and a wide pass band, and bulk elastic wave (BAW) resonators are being used for filters that require high performance. .. In the future, it is expected that the demand for bulk elastic wave resonators will further increase, based on the prediction that the frequency bands used will be crowded even in the high frequency band of 3 GHz or higher.

現在、圧電膜を上部電極膜と下部電極膜で挟み、これら電極直上あるいは直下を空気層として、弾性波が上部電極膜あるいは下部電極膜の表面での弾性波の反射率を高めたバルク弾性波共振器が用いられている。 Currently, a piezoelectric film is sandwiched between an upper electrode film and a lower electrode film, and an air layer is formed directly above or below these electrodes, and the elastic wave is a bulk elastic wave in which the reflectance of the elastic wave on the surface of the upper electrode film or the lower electrode film is enhanced. Resonators are used.

ところで、バルク弾性波共振器では、圧電膜材料や電極膜材料が温度により熱膨張する効果と、弾性波の伝搬速度が温度により変化する効果が相まって、温度変化に伴い共振周波数が変化してしまう。その結果、バルク弾性波共振器で構成した高周波フィルタの通過帯域が、温度により変動してしまう。そのため、このような変動を考慮して、使用する周波数帯域を余裕を持って狭く設定せざるを得ず、有限の資源である電波を有効に活用できないという問題があった。また、所定の通過帯域を保証するような厳しいスペックを設定すると、製造歩留まりが低下するという問題がある。 By the way, in a bulk elastic wave resonator, the resonance frequency changes as the temperature changes due to the combination of the effect that the piezoelectric film material and the electrode film material thermally expand with temperature and the effect that the propagation speed of elastic waves changes with temperature. .. As a result, the pass band of the high-frequency filter composed of the bulk elastic wave resonator fluctuates depending on the temperature. Therefore, in consideration of such fluctuations, the frequency band to be used must be set narrow with a margin, and there is a problem that radio waves, which are a finite resource, cannot be effectively used. Further, if a strict specification that guarantees a predetermined pass band is set, there is a problem that the manufacturing yield is lowered.

そこで、温度補償のために圧電膜と逆符号の温度依存性を有する薄膜材料を積層したり、圧電膜と逆符号の温度依存性を有する電極膜材料を用いる等の手法が提案されている。 Therefore, methods such as laminating a thin film material having a temperature dependence of the inverse code with the piezoelectric film or using an electrode film material having a temperature dependence of the inverse code with the piezoelectric film have been proposed for temperature compensation.

図7に従来の温度補償型のバルク弾性波共振器の断面図を示す。図7に示すように、支持基板となるシリコン基板1上に下部電極膜2、圧電膜3、圧電膜3と逆符号の温度依存性を有する温度補償膜4および上部電極膜5が順に積層されている。また下部電極膜2の下には凹部6が形成され、この凹部6上の下部電極膜2、圧電膜3、温度補償膜4および上部電極膜5により共振部が形成されている。 FIG. 7 shows a cross-sectional view of a conventional temperature-compensated bulk elastic wave resonator. As shown in FIG. 7, a lower electrode film 2, a piezoelectric film 3, a temperature compensating film 4 having a temperature dependence opposite to that of the piezoelectric film 3, and an upper electrode film 5 are laminated in this order on a silicon substrate 1 serving as a support substrate. ing. A recess 6 is formed under the lower electrode film 2, and a resonance portion is formed by the lower electrode film 2, the piezoelectric film 3, the temperature compensation film 4, and the upper electrode film 5 on the recess 6.

ところで、薄膜バルク弾性波共振器の共振周波数は、共振部を構成する温度補償膜を含む積層膜の厚さにほぼ反比例する。そのため所望の共振周波数とするためには、それぞれの膜厚の均一性や再現性に優れた製造方法が望まれる。 By the way, the resonance frequency of the thin film bulk elastic wave resonator is substantially inversely proportional to the thickness of the laminated film including the temperature compensating film constituting the resonance portion. Therefore, in order to obtain a desired resonance frequency, a manufacturing method having excellent uniformity and reproducibility of each film thickness is desired.

しかし実際は、共振部を構成するそれぞれの膜の厚さを厳密に所望の厚さに形成することは難しく、共振周波数はばらついてしまう。そこで、所望の共振周波数となるような調整工程が必要となる。 However, in reality, it is difficult to strictly form the thickness of each film constituting the resonance portion to a desired thickness, and the resonance frequency varies. Therefore, an adjustment step for achieving a desired resonance frequency is required.

例えば特許文献1乃至3には、共振周波数の調整方法が開示されている。具体的には、図7に示すバルク弾性波共振器では、上部電極膜5表面の一部をエッチング除去することにより、共振周波数を調整できる。 For example, Patent Documents 1 to 3 disclose a method for adjusting the resonance frequency. Specifically, in the bulk elastic wave resonator shown in FIG. 7, the resonance frequency can be adjusted by removing a part of the surface of the upper electrode film 5 by etching.

しかし、上部電極膜5表面をエッチングすると上部電極膜5の電気抵抗値が高くなってしまい、このような薄膜バルク弾性波共振器によってフィルタを構成する場合には、その特性が劣化してしまうという問題があった。 However, when the surface of the upper electrode film 5 is etched, the electric resistance value of the upper electrode film 5 becomes high, and when the filter is constructed by such a thin film bulk elastic wave resonator, its characteristics are deteriorated. There was a problem.

また、予め上部電極膜5を薄く形成しておき、その表面に追加の金属膜を形成することにより共振周波数を調整する方法も提案されている。しかし、電極膜を厚くすることで圧電結合係数が劣化してしまい、この場合もフィルタ特性が劣化してしまうという問題があった。 Further, a method of adjusting the resonance frequency by forming the upper electrode film 5 thinly in advance and forming an additional metal film on the surface thereof has also been proposed. However, there is a problem that the piezoelectric coupling coefficient deteriorates due to the thickening of the electrode film, and the filter characteristics also deteriorate in this case as well.

このような問題点は、共振周波数の異なるバルク弾性波共振器を同一基板上に形成する場合でも同様で、その解決が迫られている。 Such a problem is the same even when bulk elastic wave resonators having different resonance frequencies are formed on the same substrate, and its solution is urgently needed.

特許第4008264号公報Japanese Patent No. 4808264 特許第4008265号公報Japanese Patent No. 408265 米国特許第5894647号明細書U.S. Pat. No. 5,894,647

従来提案されているバルク弾性波共振器は、共振周波数を調整する際、上部電極膜をエッチングしたり、追加の金属膜を積層していたため、特性が劣化してしまうという問題があった。本発明はこれらの問題点を解消し、温度による共振周波数の変動がなく、共振周波数を調整することができるバルク弾性波共振器の製造方法を提供することを目的とする。 The conventionally proposed bulk elastic wave resonator has a problem that its characteristics are deteriorated because the upper electrode film is etched or an additional metal film is laminated when adjusting the resonance frequency. An object of the present invention is to solve these problems and to provide a method for manufacturing a bulk elastic wave resonator capable of adjusting the resonance frequency without fluctuation of the resonance frequency due to temperature.

上記目的を達成するため、本願請求項1記載の発明は、圧電膜と、該圧電膜を挟む上部電極膜および下部電極膜と、前記圧電膜と逆符号の温度係数を持つ温度補償膜とを含む多層膜とが積層したバルク弾性波共振器の製造方法において、前記下部電極膜と前記圧電膜と前記上部電極膜とを、前記バルク弾性波共振器の共振周波数の波長の1/2の整数倍の厚さとなるように形成する工程と、前記上部電極膜上に前記温度補償膜として、選択除去可能な少なくとも2種類の第1の温度補償膜と第2の温度補償膜を交互に積層し、表面を前記第1の温度補償膜とする多層構造の膜であって、前記共振周波数の波長の1/2の整数倍より厚い膜を形成する工程と、前記多層構造の温度補償膜のうち、表面に形成された前記第1の温度補償膜を選択エッチングし、前記バルク弾性波共振器の共振周波数が所定の値に達していない場合は、前記多層構造の温度補償膜の表面となった前記第2の温度補償膜を選択エッチングし、前記バルク弾性波共振器の共振周波数が前記所定の値となるまで前記第1の温度補償膜の選択エッチングと前記第2の温度補償膜の選択エッチングを繰り返すことで、前記多層構造の温度補償膜の厚さを前記バルク弾性波共振器の共振周波数の波長の1/2の整数倍とし、前記バルク弾性波共振器の共振周波数を所定の値に調整する工程と、を含むことを特徴とする。 In order to achieve the above object, the invention according to claim 1 of the present application comprises a piezoelectric film, an upper electrode film and a lower electrode film sandwiching the piezoelectric film, and a temperature compensating film having a temperature coefficient opposite to that of the piezoelectric film. In a method for manufacturing a bulk elastic wave resonator in which a multilayer film including the multilayer film is laminated, the lower electrode film, the piezoelectric film, and the upper electrode film are formed by an integer of 1/2 of the wavelength of the resonance frequency of the bulk elastic wave resonator. In the step of forming the film so as to have twice the thickness, at least two types of the first temperature compensating film and the second temperature compensating film that can be selectively removed are alternately laminated on the upper electrode film as the temperature compensating film. Among the steps of forming a film having a multilayer structure having the surface as the first temperature compensating film, which is thicker than an integral multiple of 1/2 of the wavelength of the resonance frequency, and the temperature compensating film having the multilayer structure. , The first temperature compensating film formed on the surface was selectively etched, and when the resonance frequency of the bulk elastic wave resonator did not reach a predetermined value, the surface of the temperature compensating film having the multilayer structure was obtained. The second temperature compensating film is selectively etched, and the first temperature compensating film and the second temperature compensating film are selectively etched until the resonance frequency of the bulk elastic wave resonator reaches the predetermined value. By repeating the above, the thickness of the temperature compensation film having the multilayer structure is made an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator, and the resonance frequency of the bulk elastic wave resonator is set to a predetermined value. It is characterized by including a step of adjusting.

本願請求項2記載の発明は、請求項1記載のバルク弾性波共振器の製造方法において、少なくとも2つのバルク弾性波共振器を備え、一方のバルク弾性波共振器の前記多層構造の温度補償層の表面に形成された前記第1の温度補償膜を選択エッチングし、前記一方のバルク弾性波共振器の共振周波数が所定の第1の共振周波数に達していない場合は、前記多層構造の温度補償膜の表面となった前記第2の温度補償膜を選択エッチングし、前記一方のバルク弾性波共振器の共振周波数が前記第1の共振周波数となるまで前記第1の温度補償膜の選択エッチングと前記第2の温度補償膜の選択エッチングを繰り返すことで、前記一方のバルク弾性波共振器の共振周波数を他方のバルク弾性波共振器の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 2 of the present application includes at least two bulk elastic wave resonators in the method for manufacturing a bulk elastic wave resonator according to claim 1, and the temperature compensation layer having the multilayer structure of one bulk elastic wave resonator. When the resonance frequency of the one bulk elastic wave resonator does not reach a predetermined first resonance frequency by selectively etching the first temperature compensation film formed on the surface of the above-mentioned multilayer structure, the temperature compensation of the multilayer structure is performed. The second temperature compensating film that is the surface of the film is selectively etched, and the first temperature compensating film is selectively etched until the resonance frequency of the one bulk elastic wave resonator becomes the first resonance frequency. It is characterized by including a step of adjusting the resonance frequency of the one bulk elastic wave resonator to a value different from the resonance frequency of the other bulk elastic wave resonator by repeating the selective etching of the second temperature compensation film. And.

本願請求項3記載の発明は、請求項2記載のバルク弾性波共振器の製造方法において、前記他方のバルク弾性波共振器の前記多層構造の温度補償層の表面に形成された前記第1の温度補償膜を選択エッチングし、前記他方のバルク弾性波共振器の共振周波数が所定の第2の共振周波数に達していない場合は、前記多層構造の温度補償膜の表面となった前記第2の温度補償膜を選択エッチングし、前記他方のバルク弾性波共振器の共振周波数が前記第2の共振周波数となるまで前記第1の温度補償膜の選択エッチングと前記第2の温度補償膜の選択エッチングを繰り返すことで、前記他方のバルク弾性波共振器の前記第2の共振周波数を前記一方のバルク弾性波共振器の前記第1の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 3 of the present application is the first aspect of the method for manufacturing a bulk elastic wave resonator according to claim 2, which is formed on the surface of the temperature compensation layer having the multilayer structure of the other bulk elastic wave resonator. When the temperature compensation film is selectively etched and the resonance frequency of the other bulk elastic wave resonator does not reach a predetermined second resonance frequency, the second surface of the temperature compensation film having the multilayer structure is formed. The temperature compensating film is selectively etched, and the first temperature compensating film and the second temperature compensating film are selectively etched until the resonance frequency of the other bulk elastic wave resonator becomes the second resonance frequency. By repeating the above, the step of adjusting the second resonance frequency of the other bulk elastic wave resonator to a value different from the first resonance frequency of the one bulk elastic wave resonator is included. To do.

本願請求項4記載の発明は、請求項1または2いずれか記載のバルク弾性波共振器の製造方法において、少なくとも2つのバルク弾性波共振器を備え、一方のバルク弾性波共振器の前記温度補償膜の表面をエッチング除去し、または前記表面の温度補償膜を選択的に除去し、該一方のバルク弾性波共振器の共振周波数を他方のバルク弾性波共振器の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 4 of the present application includes at least two bulk elastic wave resonators in the method for manufacturing a bulk elastic wave resonator according to any one of claims 1 or 2, and the temperature compensation of one of the bulk elastic wave resonators. The surface of the film is removed by etching, or the temperature compensation film on the surface is selectively removed, and the resonance frequency of one bulk elastic wave resonator is adjusted to a value different from the resonance frequency of the other bulk elastic wave resonator. It is characterized by including a step of performing.

本願請求項5記載の発明は、請求項3記載のバルク弾性波共振器の製造方法において、少なくとも2つのバルク弾性波共振器を備え、一方のバルク弾性波共振器の前記温度補償膜表面に別の膜を積層形成し、該一方のバルク弾性波共振器の共振周波数を他方のバルク弾性波共振器の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 5 of the present application includes at least two bulk elastic wave resonators in the method for manufacturing a bulk elastic wave resonator according to claim 3, and is separately provided on the surface of the temperature compensation film of one bulk elastic wave resonator. It is characterized by including a step of laminating and forming the films of the above and adjusting the resonance frequency of the one bulk elastic wave resonator to a value different from the resonance frequency of the other bulk elastic wave resonator.

本願請求項6記載の発明は、請求項4または5いずれか記載のバルク弾性波共振器の製造方法において、前記他方のバルク弾性波共振器の前記温度補償膜の表面をエッチング除去し、または前記表面の温度補償膜を選択的に除去し、該他方のバルク弾性波共振器の共振周波数を前記一方のバルク弾性波共振器の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 6 of the present application etches and removes the surface of the temperature compensating film of the other bulk elastic wave resonator in the method for manufacturing a bulk elastic wave resonator according to any one of claims 4 or 5. It is characterized by including a step of selectively removing the temperature compensation film on the surface and adjusting the resonance frequency of the other bulk elastic wave resonator to a value different from the resonance frequency of the one bulk elastic wave resonator. ..

本願請求項7記載の発明は、請求項4または5いずれか記載のバルク弾性波共振器の製造方法において、前記他方のバルク弾性波共振器の前記温度補償膜表面に別の膜を積層形成し、該他方のバルク弾性波共振器の共振周波数を前記一方のバルク弾性波共振器の共振周波数とは異なる値に調整する工程を含むことを特徴とする。 The invention according to claim 7 of the present application is the method for manufacturing a bulk elastic wave resonator according to any one of claims 4 or 5, wherein another film is laminated on the surface of the temperature compensation film of the other bulk elastic wave resonator. It is characterized by including a step of adjusting the resonance frequency of the other bulk elastic wave resonator to a value different from the resonance frequency of the one bulk elastic wave resonator.

本願請求項8記載の発明は、請求項1乃至7いずれか記載のバルク弾性波共振器の製造方法において、前記共振周波数を調整する工程は、前記温度補償膜の厚さ、あるいは前記別の膜を積層形成する場合は前記温度補償膜と前記膜の積層膜との厚さをバルク弾性波共振器の共振周波数の波長の1/2の整数倍に調整する工程であることを特徴とする。 The invention according to claim 8 of the present application is the method for manufacturing a bulk elastic wave resonator according to any one of claims 1 to 7, wherein the step of adjusting the resonance frequency is the thickness of the temperature compensation film or the other film. The step is to adjust the thickness of the temperature compensating film and the laminated film of the film to an integral multiple of 1/2 of the wavelength of the resonance frequency of the bulk elastic wave resonator.

本願請求項9記載の発明は、請求項1乃至7いずれか記載のバルク弾性波共振器の製造方法において、前記共振周波数を調整する工程は、共振周波数を高くする場合は前記温度補償膜をエッチング除去し、共振周波数を低くする場合は前記温度補償膜に別の膜を積層形成する工程であることを特徴とする。 The invention according to claim 9 of the present application is the method for manufacturing a bulk elastic wave resonator according to any one of claims 1 to 7. In the step of adjusting the resonance frequency, the temperature compensating film is etched when the resonance frequency is increased. When removing and lowering the resonance frequency, it is a step of laminating another film on the temperature compensating film.

本発明によれば、下部電極膜、圧電膜および上部電極膜の全体の厚さを、共振周波数の波長の1/2の整数倍として、その表面に概ね共振周波数の波長の1/2の整数倍の厚さとなるように温度補償膜をエッチング除去あるいは別の膜を積層形成することで共振周波数の調整を行う構成としているので、共振特性に寄与する上部電極等の形状は変化せず、バルク弾性波共振器の特性を劣化させずに共振周波数の調整が可能となる。 According to the present invention, the total thickness of the lower electrode film, the piezoelectric film and the upper electrode film is set to an integral multiple of 1/2 of the resonance frequency wavelength, and the surface thereof is approximately 1/2 integer of the resonance frequency wavelength. Since the resonance frequency is adjusted by removing the etching of the temperature compensation film or laminating another film so that the thickness is doubled, the shape of the upper electrode, etc. that contributes to the resonance characteristics does not change, and the bulk. The resonance frequency can be adjusted without deteriorating the characteristics of the elastic wave resonator.

また、共振周波数の調整が行われた後の温度補償膜の厚さは、概ね共振周波数の波長の1/2の整数倍となるので、予め、温度補償膜の厚さが共振周波数の波長の1/2の整数場となるときに温度補償可能な膜を選択することで、共振周波数の調整と温度補償とを同時に行うことができるという利点がある。 Further, since the thickness of the temperature compensation film after the resonance frequency is adjusted is approximately an integral multiple of 1/2 of the wavelength of the resonance frequency, the thickness of the temperature compensation film is the wavelength of the resonance frequency in advance. By selecting a film capable of temperature compensation when the field becomes a 1/2 integer field, there is an advantage that the resonance frequency can be adjusted and the temperature compensation can be performed at the same time.

また本発明は、複数のバルク弾性波共振器が同一基板上に形成されている場合でも、個々のバルク弾性波共振器の共振周波数の調整が可能であり、量産性に優れた製造方法となる。 Further, according to the present invention, even when a plurality of bulk elastic wave resonators are formed on the same substrate, the resonance frequency of each bulk elastic wave resonator can be adjusted, which is a manufacturing method excellent in mass productivity. ..

本発明の第1の実施例のバルク弾性波共振器の温度補償膜をエッチングする前の断面図である。It is sectional drawing before etching the temperature compensation film of the bulk elastic wave resonator of 1st Example of this invention. 本発明の第1の実施例のバルク弾性波共振器の温度補償膜をエッチングした後の断面図である。It is sectional drawing after etching the temperature compensation film of the bulk elastic wave resonator of 1st Example of this invention. 本発明の第3の実施例のバルク弾性波共振器の温度補償膜に別の膜を積層する前の断面図である。It is sectional drawing before stacking another film on the temperature compensation film of the bulk elastic wave resonator of the 3rd Example of this invention. 本発明の第3の実施例のバルク弾性波共振器の温度補償膜に別の膜を積層した後の断面図である。It is sectional drawing after another film was laminated on the temperature compensation film of the bulk elastic wave resonator of the 3rd Example of this invention. 本発明の第4の実施例のバルク弾性波共振器を説明する図である。It is a figure explaining the bulk elastic wave resonator of the 4th Example of this invention. 本発明の第5の実施例のバルク弾性波共振器を説明する図である。It is a figure explaining the bulk elastic wave resonator of the 5th Example of this invention. 従来のバルク弾性波共振器の断面図である。It is sectional drawing of the conventional bulk elastic wave resonator.

本発明のバルク弾性波共振器は、下部電極膜と圧電膜と上部電極膜の全体の厚さを共振器の共振周波数の波長の1/2の整数倍とし、表面に形成した温度補償膜の厚さを調整することで、共振周波数を調整する構成としている。温度補償膜は、共振器の共振周波数の波長の概ね1/2の整数倍になったとき、所望の共振周波数となる。したがって、温度補償膜を共振器の共振周波数の波長の概ね1/2の整数倍のときに温度補償膜として機能する膜を選択すれば、温度補償と共振周波数の調整が同時に実現でき、しかも共振器としての特性維持を図ることが可能となる。以下、本発明の実施例について説明する。 In the bulk elastic wave resonator of the present invention, the total thickness of the lower electrode film, the piezoelectric film, and the upper electrode film is set to an integral multiple of 1/2 of the resonance frequency wavelength of the resonator, and the temperature compensation film formed on the surface thereof. The resonance frequency is adjusted by adjusting the thickness. The temperature compensation film has a desired resonance frequency when it is approximately an integral multiple of 1/2 the wavelength of the resonance frequency of the resonator. Therefore, if a film that functions as a temperature compensation film is selected when the temperature compensation film is approximately 1/2 of the wavelength of the resonance frequency of the resonator, temperature compensation and resonance frequency adjustment can be realized at the same time, and resonance can be achieved. It is possible to maintain the characteristics of the vessel. Hereinafter, examples of the present invention will be described.

図1は、本発明の第1の実施例のバルク弾性波共振器の断面図である。図1に示すように、支持基板となるシリコン基板1上に下部電極膜2、圧電膜3および上部電極膜5が順に積層している。この積層膜の厚さは、バルク弾性波共振器の共振周波数の波長の1/2の整数倍に設定している。 FIG. 1 is a cross-sectional view of a bulk elastic wave resonator according to a first embodiment of the present invention. As shown in FIG. 1, a lower electrode film 2, a piezoelectric film 3, and an upper electrode film 5 are laminated in this order on a silicon substrate 1 serving as a support substrate. The thickness of this laminated film is set to an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator.

ここで、圧電膜として窒化アルミニウム(AlN)、電極膜としてモリブデン(Mo)を用いると、それぞれ材料の温度係数は約−25ppm/℃、約−60ppm/℃であり、温度補償膜4を備えない従来構造の薄膜バルク弾性波共振器は、−40ppm/℃前後の負の温度係数をもち、温度上昇に伴って共振周波数が下がる傾向となる。 Here, when aluminum nitride (AlN) is used as the piezoelectric film and molybdenum (Mo) is used as the electrode film, the temperature coefficients of the materials are about -25 ppm / ° C. and about -60 ppm / ° C., respectively, and the temperature compensation film 4 is not provided. The thin film bulk elastic wave resonator having a conventional structure has a negative temperature coefficient of about -40 ppm / ° C., and the resonance frequency tends to decrease as the temperature rises.

そこで上部電極膜5上に、シリコン酸化膜からなる温度補償膜4を積層形成する。この温度補償膜4は、バルク弾性波共振器の共振周波数の波長の1/2の整数倍よりわずかに厚く形成する。図1では、温度補償膜4aが共振周波数の波長の1/2の整数倍に相当する部分を、温度補償膜4bがわずかに厚く積層した部分を表している。本実施例では、温度補償膜4aと温度補償膜4bは、いずれもシリコン酸化膜とし、連続して形成する。 Therefore, a temperature compensating film 4 made of a silicon oxide film is laminated on the upper electrode film 5. The temperature compensation film 4 is formed to be slightly thicker than an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator. In FIG. 1, a portion in which the temperature compensating film 4a corresponds to an integral multiple of 1/2 of the wavelength of the resonance frequency is represented by a portion in which the temperature compensating film 4b is slightly thickly laminated. In this embodiment, the temperature compensating film 4a and the temperature compensating film 4b are both formed as a silicon oxide film and are continuously formed.

このような構造のバルク弾性波共振器は、所望の共振周波数より低い共振周波数で共振する。そこで所望の共振周波数となるように調整するため、温度補償膜4aの表面の温度補償膜4bの厚さ分だけエッチング除去し、温度補償膜の厚さを薄くする(図2)。温度補償膜の厚さを薄くする方法としては、イオンビームミリング法や反応性ドライエッチング法などドライエッチング法が簡便な方法である。共振周波数は、共振周波数の測定とエッチングを繰り返すことで、所望の値に調整することができる。この調整により、温度補償膜4bがエッチング除去され、温度補償膜4aの厚さが共振周波数の波長の概ね1/2の整数倍に相当する厚さとなる。 A bulk elastic wave resonator having such a structure resonates at a resonance frequency lower than a desired resonance frequency. Therefore, in order to adjust the resonance frequency so as to be desired, the temperature compensation film 4a is etched and removed by the thickness of the temperature compensation film 4b on the surface to reduce the thickness of the temperature compensation film (FIG. 2). As a method for reducing the thickness of the temperature compensation film, a dry etching method such as an ion beam milling method or a reactive dry etching method is a simple method. The resonance frequency can be adjusted to a desired value by repeating the measurement and etching of the resonance frequency. By this adjustment, the temperature compensation film 4b is removed by etching, and the thickness of the temperature compensation film 4a becomes a thickness corresponding to approximately ½ of the wavelength of the resonance frequency.

このように形成されたバルク弾性波共振器では、下部電極膜2と圧電膜3と上部電極膜5の積層膜の厚さを共振器の共振周波数の波長の1/2の整数倍とするとともに、温度補償膜の厚さも共振器の共振周波数の波長の概ね1/2の整数倍となる。より具体的には、圧電性を有する結晶配向方向を有する場合には、下部電極膜2と圧電膜3と上部電極膜5の厚さを共振器の共振周波数の波長の概ね1/2の奇数倍となる。膜厚が概ね等しく互いに逆方向の圧電性を示す結晶配向方向を有する2層の圧電膜から構成される場合には、下部電極膜2と2層の圧電膜3と上部電極膜5の厚さを共振器の共振周波数の波長の概ね1/2の2倍となる。また、互いに逆方向の結晶配向方向を有する圧電膜3が交互に偶数層積層された多層構造からなる場合は、その厚さを共振器の共振周波数の波長の概ね1/2の層数倍となる。 In the bulk elastic wave resonator formed in this way, the thickness of the laminated film of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 is set to an integral multiple of 1/2 the wavelength of the resonance frequency of the resonator. The thickness of the temperature compensation film is also approximately ½ of the wavelength of the resonance frequency of the resonator. More specifically, when the crystal orientation direction has piezoelectricity, the thickness of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 is an odd number of approximately 1/2 of the wavelength of the resonance frequency of the resonator. Double. When the film is composed of two layers of piezoelectric films having substantially the same film thickness and exhibiting piezoelectricity in opposite directions, the thickness of the lower electrode film 2 and the two layers of the piezoelectric film 3 and the upper electrode film 5 Is approximately twice the wavelength of the resonance frequency of the resonator. Further, when the piezoelectric films 3 having crystal orientation directions opposite to each other have a multi-layer structure in which even-numbered layers are alternately laminated, the thickness thereof is set to be approximately 1/2 the number of layers of the wavelength of the resonance frequency of the resonator. Become.

簡単のため、圧電膜が単一の圧電性を示す結晶配向方向を有し、下層電極膜2と圧電膜3と上部電極膜5の積層膜の全体の厚さを共振周波数の波長の1/2とし、温度補償膜の厚さも共振周波数の概ね1/2となる一次共振の場合について説明する。なお、2以上の整数倍となる高次の共振の場合についても考え方は同様であるため、説明は省略する。 For simplicity, the piezoelectric film has a single piezoelectric crystal orientation direction, and the overall thickness of the laminated film of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 is 1 / of the wavelength of the resonance frequency. The case of primary resonance in which the thickness of the temperature compensation film is also approximately 1/2 of the resonance frequency will be described. Since the same concept applies to the case of high-order resonance that is an integral multiple of 2 or more, the description thereof will be omitted.

この場合、下部電極膜2の下面と上部電極膜5の上面(温度補償膜の下面と一致)および温度補償膜4aの上面が、バルク弾性波振動における歪あるいは応力分布の節となり、全体で1波長分の弾性波が励起されて共振状態となる。この下部電極膜2と圧電膜3と上部電極膜5の積層構造における歪分布は、温度補償膜4aのない下部電極膜2と圧電膜3と上部電極膜5からなるバルク弾性波共振器の歪分布と一致する。そのため、膜内の歪分布を決める圧電結合係数は概ね同一に保たれ、特性の劣化はない。先に説明した図7に示す従来例では、下部電極膜2、圧電膜3、温度補償膜4と上部電極膜5の積層構造で構成され、下部電極膜2の下面と上部電極膜5の上面を歪分布の節となる共振器の場合には、上部電極膜5の表面をエッチング除去して上部電極膜5の厚さが変化すると下部電極膜と2圧電膜3と上部電極膜5の歪分布が変化し、そのため圧電結合係数が劣化してしまうので、本発明の効果が大きいことがわかる。 In this case, the lower surface of the lower electrode film 2 and the upper surface of the upper electrode film 5 (corresponding to the lower surface of the temperature compensation film) and the upper surface of the temperature compensation film 4a form nodes of strain or stress distribution in bulk elastic wave vibration, and 1 as a whole. Elastic waves of wavelengths are excited to enter a resonance state. The strain distribution in the laminated structure of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 is the strain of the bulk elastic wave resonator composed of the lower electrode film 2 without the temperature compensation film 4a, the piezoelectric film 3, and the upper electrode film 5. Consistent with the distribution. Therefore, the piezoelectric coupling coefficients that determine the strain distribution in the film are kept substantially the same, and there is no deterioration in characteristics. In the conventional example shown in FIG. 7 described above, the structure is composed of a laminated structure of the lower electrode film 2, the piezoelectric film 3, the temperature compensation film 4, and the upper electrode film 5, and the lower surface of the lower electrode film 2 and the upper surface of the upper electrode film 5 are formed. In the case of a resonator that serves as a node of strain distribution, when the surface of the upper electrode film 5 is removed by etching and the thickness of the upper electrode film 5 changes, the strain of the lower electrode film, 2 piezoelectric film 3, and the upper electrode film 5 is distorted. It can be seen that the effect of the present invention is large because the distribution changes and the piezoelectric coupling coefficient deteriorates.

バルク弾性波共振器の最下面である下部電極膜2の下面と最上面である上部電極膜5の上面は温度によらず常に歪分布の節となる。圧電膜3と下部電極膜2、上部電極膜5の温度特性に対して温度補償膜4aの温度特性の符号が逆である。そのため、温度変動によって圧電膜3と各電極膜の波長が短くなると温度補償膜の波長が長くなり、互いに相殺することによって共振周波数が温度によらずほぼ一定に保たれ、あるいは共振周波数の温度による変動が緩和される。 The lower surface of the lower electrode film 2 which is the lowermost surface of the bulk elastic wave resonator and the upper surface of the upper electrode film 5 which is the uppermost surface are always nodes of strain distribution regardless of the temperature. The sign of the temperature characteristic of the temperature compensating film 4a is opposite to the temperature characteristic of the piezoelectric film 3, the lower electrode film 2, and the upper electrode film 5. Therefore, when the wavelengths of the piezoelectric film 3 and each electrode film become shorter due to temperature fluctuations, the wavelengths of the temperature compensating film become longer, and by canceling each other, the resonance frequency is kept substantially constant regardless of the temperature, or depends on the temperature of the resonance frequency. Fluctuations are mitigated.

なお、圧電膜に励起されるバルク弾性波が温度補償膜にしみ出し、温度補償膜の粘性等による弾性的損失が発生するため、Q値は幾分低下するが、従来例のような圧電膜と各電極膜の間に温度補償膜を挟む構造に比べて、その低減は軽微である。 The bulk elastic wave excited by the piezoelectric film seeps into the temperature compensation film, and elastic loss occurs due to the viscosity of the temperature compensation film. Therefore, the Q value decreases somewhat, but the piezoelectric film as in the conventional example. Compared with the structure in which the temperature compensation film is sandwiched between the electrode film and each electrode film, the reduction is slight.

以上説明したように、温度補償膜4aの上面および下面が歪分布の節になるようにすれば良いから、温度補償膜の厚さは共振周波数の波長の概ね1/2ばかりでなく、その整数倍であってもよい。 As described above, since the upper surface and the lower surface of the temperature compensation film 4a may be the nodes of the strain distribution, the thickness of the temperature compensation film is not only approximately 1/2 of the wavelength of the resonance frequency but also an integer thereof. It may be doubled.

温度補償膜4としては、二酸化シリコン膜の他、不純物をドーピングした二酸化シリコン酸化膜、酸素の組成を変えたシリコン酸化膜やシリコン酸化窒化膜(SiON)を用いることができ、温度補償膜4としてバルク弾性波共振器の共振周波数の波長の概ね1/2の整数倍の膜厚としたときに、下部電極膜2、圧電膜3および上部電極膜5で構成される共振周波数の波長の1/2の整数倍となる負の温度係数を持つ部分の温度依存性を補償するような特性の膜を選択すればよい。 As the temperature compensation film 4, in addition to the silicon dioxide film, an impurity-doped silicon dioxide oxide film, a silicon oxide film having a different oxygen composition, or a silicon oxide nitride film (SiON) can be used, and the temperature compensation film 4 can be used as the temperature compensation film 4. When the film thickness is approximately 1/2 of the wavelength of the resonance frequency of the bulk elastic wave resonator, it is 1 / of the wavelength of the resonance frequency composed of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5. A film having characteristics that compensate for the temperature dependence of the portion having a negative temperature coefficient that is an integral multiple of 2 may be selected.

次に第2の実施例について説明する。上記第1の実施例では、温度補償膜4は単一の材料で構成した場合について説明した。しかし、本発明はこれに限定されず、化学的性質の異なる多層膜としてもよい。例えば、シリコン酸化膜とシリコン膜、シリコン酸化膜と金属膜であるモリブデン(Mo)膜の積層膜構造等、選択的にエッチング除去可能な膜の組合わせとすればよい。また2種類の膜の多層構造とすることに限定されず、複数の膜の多層構造としてもよい。 Next, a second embodiment will be described. In the first embodiment described above, the case where the temperature compensating film 4 is made of a single material has been described. However, the present invention is not limited to this, and a multilayer film having different chemical properties may be used. For example, a combination of films that can be selectively etched and removed, such as a silicon oxide film and a silicon film, or a laminated film structure of a silicon oxide film and a molybdenum (Mo) film that is a metal film, may be used. Further, the structure is not limited to a multilayer structure of two types of films, and a multilayer structure of a plurality of films may be used.

一例として、シリコン酸化膜とシリコン膜の多層構造とした場合について説明する。温度補償膜は、膜厚全体を多層構造とすることは必ずしも必要はないが、少なくとも共振周波数の調整に必要な領域を多層構造とすると、簡便な共振周波数調整が可能となる。 As an example, a case where a silicon oxide film and a silicon film have a multilayer structure will be described. The temperature compensation film does not necessarily have a multi-layer structure over the entire film thickness, but if at least the region required for adjusting the resonance frequency has a multi-layer structure, simple resonance frequency adjustment becomes possible.

バルク弾性波共振器の共振周波数が所定の値より低い場合、例えば最表面のシリコン酸化膜をエッチング除去する。その際、共振周波数を調整するために除去する厚さに相当する厚さ、あるいはそれより薄くシリコン酸化膜を形成しておくと、共振周波数の調整のため、最表面シリコン酸化膜を完全に除去することになる。この除去工程では、シリコン酸化膜の下層のシリコン膜がエッチングストッパーとして機能し、確実にシリコン酸化膜だけを除去することができる。 When the resonance frequency of the bulk elastic wave resonator is lower than a predetermined value, for example, the outermost silicon oxide film is etched and removed. At that time, if a silicon oxide film having a thickness corresponding to or thinner than the thickness to be removed for adjusting the resonance frequency is formed, the outermost silicon oxide film is completely removed for adjusting the resonance frequency. Will be done. In this removal step, the silicon film underneath the silicon oxide film functions as an etching stopper, and only the silicon oxide film can be reliably removed.

シリコン酸化膜一層のエッチングだけでは所望の共振周波数に達していない場合には、最表面のシリコン膜をエッチング除去する。この場合、共振周波数を調整するために除去する厚さに相当する厚さ、あるいはそれより薄くシリコン膜を形成しておくと、共振周波数の調整のため、最表面となったシリコン膜を完全に除去することになる。シリコン膜の下層のシリコン酸化膜がストッパーとして機能し、確実にシリコン膜だけを除去することができる。以下、所望の共振周波数に達するまで、このエッチングを繰り返せばよい。所望の共振周波数に達したとき、残った温度補償膜の厚さは、バルク弾性波共振器の共振周波数の波長の概ね1/2の整数倍となる。 When the desired resonance frequency is not reached only by etching one layer of the silicon oxide film, the outermost silicon film is etched and removed. In this case, if a silicon film having a thickness corresponding to or thinner than the thickness to be removed for adjusting the resonance frequency is formed, the outermost silicon film is completely removed for adjusting the resonance frequency. It will be removed. The silicon oxide film under the silicon film functions as a stopper, and only the silicon film can be reliably removed. Hereinafter, this etching may be repeated until a desired resonance frequency is reached. When the desired resonance frequency is reached, the thickness of the remaining temperature compensation film is approximately an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator.

なお、上記のように温度補償膜を化学的に性質の異なる膜の多層構造とすると、温度補償膜として機能する場合に最適な厚さとは若干ずれる可能性がある。しかし、その差はわずかであり、最適な厚さから若干ずれても十分な温度補償機能を得ることが可能である。 If the temperature compensating film has a multilayer structure of films having chemically different properties as described above, the thickness may be slightly different from the optimum thickness when functioning as the temperature compensating film. However, the difference is small, and it is possible to obtain a sufficient temperature compensation function even if the thickness deviates slightly from the optimum thickness.

次に第3の実施例について説明する。上述の第1および第2の実施例では、温度補償膜4をエッチング除去して所望の厚さにする場合について説明したが、本発明はこれに限定されない。具体的には図3および図4に示すように別の膜を付加することで、所望の厚さにしてもよい。 Next, a third embodiment will be described. In the first and second examples described above, the case where the temperature compensating film 4 is etched and removed to obtain a desired thickness has been described, but the present invention is not limited thereto. Specifically, as shown in FIGS. 3 and 4, another film may be added to obtain a desired thickness.

上記実施例同様、支持基板となるシリコン基板1上に下部電極膜2、圧電膜3および上部電極膜5が順に積層している。これらの膜の厚さは、バルク弾性波共振器の共振周波数の波長の1/2の整数倍に設定している。その後、温度補償膜4cを積層形成する。この温度補償膜4cは、バルク弾性波共振器の共振周波数の波長の1/2の整数倍よりわずかに薄い(図3)。 Similar to the above embodiment, the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 are laminated in this order on the silicon substrate 1 serving as the support substrate. The thickness of these films is set to an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator. After that, the temperature compensation film 4c is laminated and formed. The temperature compensation film 4c is slightly thinner than an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator (FIG. 3).

このような構造のバルク弾性波共振器は、所望の共振周波数より高い共振周波数で共振する。そこで所望の共振周波数となるように調整するため、温度補償膜4cの表面に別の温度補償膜4dを追加し、温度補償膜を厚くする(図4)。別の温度補償膜4dとしては、シリコン酸化膜との他、温度補償膜として使用可能な不純物をドーピングした二酸化シリコン酸化膜、酸素の組成を変えたシリコン酸化膜やシリコン酸化窒化膜(SiON)等の誘電体膜や金属膜を使用する。 A bulk elastic wave resonator having such a structure resonates at a resonance frequency higher than a desired resonance frequency. Therefore, in order to adjust the desired resonance frequency, another temperature compensation film 4d is added to the surface of the temperature compensation film 4c to thicken the temperature compensation film (FIG. 4). As another temperature compensation film 4d, in addition to a silicon oxide film, a silicon dioxide oxide film doped with impurities that can be used as a temperature compensation film, a silicon oxide film having a changed oxygen composition, a silicon oxide nitride film (SiON), etc. Use a dielectric film or metal film of.

温度補償膜の厚さを厚くする方法としては、例えばスパッタ法による所望の膜の積層形成が簡便な方法である。共振周波数は、共振周波数の測定とエッチングを繰り返すことで、所望の値に調整することができる。この調整により、温度補償膜4dを付加され、温度補償膜の厚さが共振周波数の波長の概ね1/2の整数倍に相当する厚さとなる。 As a method for increasing the thickness of the temperature compensating film, for example, a simple method is to form a laminate of desired films by a sputtering method. The resonance frequency can be adjusted to a desired value by repeating the measurement and etching of the resonance frequency. By this adjustment, the temperature compensation film 4d is added, and the thickness of the temperature compensation film becomes a thickness corresponding to an integral multiple of approximately 1/2 of the wavelength of the resonance frequency.

本実施例においても、下部電極膜2と圧電膜3と上部電極膜5の積層膜の厚さを共振器の共振周波数の1/2の整数倍とするとともに、温度補償膜4cに温度補償膜4dを追加することで全体としての温度補償膜の厚さも共振器の共振周波数の波長の概ね1/2の整数倍となり、上記第1の実施例同様の効果が得られる。 Also in this embodiment, the thickness of the laminated film of the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 5 is set to an integral multiple of 1/2 of the resonance frequency of the resonator, and the temperature compensation film 4c is covered with the temperature compensation film. By adding 4d, the thickness of the temperature compensation film as a whole becomes approximately ½ of the wavelength of the resonance frequency of the resonator, and the same effect as that of the first embodiment can be obtained.

なお、上記実施例では、単一のバルク弾性波共振器を例にして説明したが、通常の製造工程では、ウエハ状のシリコン基板上に複数のバルク弾性波共振器を同時に形成することになる。その場合、ウエハの周辺部と中央部等ウエハの位置によって共振周波数がばらつく。そこで、上記実施例で説明した温度補償膜のエッチング量等は、共振周波数のばらつき等を考慮し、あるいは共振周波数の変化の傾向等を考慮し、適宜設定すればよい。この場合、温度補償膜の厚さは、温度補償膜として機能する最適な厚さとは若干ずれる可能性がある。しかし、その差はわずかであり、最適な厚さから若干ずれていても十分な温度補償機能を得ることができるので、ばらつきによる生じる歩留まり等を考慮し、最適な値に設定すればよい。 In the above embodiment, a single bulk elastic wave resonator has been described as an example, but in a normal manufacturing process, a plurality of bulk elastic wave resonators are simultaneously formed on a wafer-shaped silicon substrate. .. In that case, the resonance frequency varies depending on the position of the wafer such as the peripheral portion and the central portion of the wafer. Therefore, the etching amount and the like of the temperature compensating film described in the above embodiment may be appropriately set in consideration of the variation of the resonance frequency and the like, or the tendency of the change of the resonance frequency and the like. In this case, the thickness of the temperature compensating film may deviate slightly from the optimum thickness that functions as the temperature compensating film. However, the difference is small, and a sufficient temperature compensation function can be obtained even if the thickness deviates slightly from the optimum thickness. Therefore, the optimum value may be set in consideration of the yield caused by the variation.

次に第4の実施例について説明する。バルク弾性波共振器を用いてフィルタを形成する場合、異なる共振周波数を有する複数のバルク弾性波共振器を用いる。本発明はこのように同一基板に複数のバルク弾性波共振器を形成する場合にも適用可能である。例えば、同一基板に2つのバルク弾性波共振器を形成する場合について図5に示すように、支持基板となるシリコン基板1上に2つのバルク弾性波共振器10A、10Bが形成されている。図5に示すように、バルク弾性波共振器10Aは、シリコン基板1上に、下部電極膜2A、圧電膜3および上部電極膜5Aが順に積層している。一方バルク弾性波共振器10Bは、シリコン基板1上に、下部電極膜2B、圧電膜3および上部電極膜5Bが順に積層している。さらにそれぞれ温度補償膜4A、4Bが積層している。これらの温度補償膜4A、4Bは図5に示すように厚さが異なっている。このような温度補償膜は、一方のバルク弾性波共振器の温度補償膜の表面を選択的にエッチング除去したり、他方のバルク弾性波共振器の温度補償膜上に別の膜を積層することで形成することができる。 Next, a fourth embodiment will be described. When forming a filter using a bulk elastic wave resonator, a plurality of bulk elastic wave resonators having different resonance frequencies are used. The present invention is also applicable to the case where a plurality of bulk elastic wave resonators are formed on the same substrate in this way. For example, as shown in FIG. 5 in the case of forming two bulk elastic wave resonators on the same substrate, two bulk elastic wave resonators 10A and 10B are formed on a silicon substrate 1 serving as a support substrate. As shown in FIG. 5, in the bulk elastic wave resonator 10A, a lower electrode film 2A, a piezoelectric film 3 and an upper electrode film 5A are laminated in this order on a silicon substrate 1. On the other hand, in the bulk elastic wave resonator 10B, the lower electrode film 2B, the piezoelectric film 3 and the upper electrode film 5B are laminated in this order on the silicon substrate 1. Further, the temperature compensation films 4A and 4B are laminated, respectively. These temperature compensating films 4A and 4B have different thicknesses as shown in FIG. Such a temperature compensating film may selectively remove the surface of the temperature compensating film of one bulk elastic wave resonator by etching, or laminate another film on the temperature compensating film of the other bulk elastic wave resonator. Can be formed with.

具体的には、上記第1の実施例を適用する場合について説明する。まず、上部電極膜5A、5B上に、バルク弾性波共振器10Bの共振周波数の概ね1/2の整数倍の厚さの温度補償膜を積層する。その後、バルク弾性波共振器10B形成領域を覆い、バルク弾性波共振器10A形成領域を開口するようにレジスト膜をパターニングし、バルク弾性波共振器10Aの共振周波数の概ね1/2の整数倍の厚さとなるまで温度補償膜をエッチング除去する。その後、レジスト膜を除去すると図5に示すように、バルク弾性波共振器10Aの温度補償膜4Aの厚さとバルク弾性波共振器10Bの温度補償膜4Bの厚さとが異なる形状を同一基板上に形成することが可能となる。 Specifically, a case where the first embodiment is applied will be described. First, a temperature compensation film having a thickness approximately ½ of the resonance frequency of the bulk elastic wave resonator 10B is laminated on the upper electrode films 5A and 5B. After that, the resist film is patterned so as to cover the bulk elastic wave resonator 10B forming region and open the bulk elastic wave resonator 10A forming region, and is approximately an integral multiple of 1/2 of the resonance frequency of the bulk elastic wave resonator 10A. The temperature compensation film is etched and removed until it becomes thick. After that, when the resist film is removed, as shown in FIG. 5, the thickness of the temperature compensating film 4A of the bulk elastic wave resonator 10A and the thickness of the temperature compensating film 4B of the bulk elastic wave resonator 10B are different on the same substrate. It becomes possible to form.

次に第5の実施例について説明する。上記第4の実施例において、上記第3の実施例を適用する場合には、温度補償膜を化学的性質の異なる多層膜とすればよい。 Next, a fifth embodiment will be described. In the case of applying the third embodiment in the fourth embodiment, the temperature compensation film may be a multilayer film having different chemical properties.

具体的には、上記第3の実施例を適用する場合について説明する。まず、上部電極膜5A、5B上に、バルク弾性波共振器10Aの共振周波数の1/2の整数倍の厚さの温度補償膜を積層する。その後、バルク弾性波共振器10A形成領域を覆い、バルク弾性波共振器10B形成領域を開口するようにレジスト膜をパターニングし、バルク弾性波共振器10Bの共振周波数の概ね1/2の整数倍の厚さとなるまで別の膜、例えば金属膜を積層し、リフトオフすることで、図6に示すように、温度補償膜4B上に別の膜4eを形成することができる。 Specifically, a case where the third embodiment is applied will be described. First, a temperature compensation film having a thickness that is an integral multiple of 1/2 the resonance frequency of the bulk elastic wave resonator 10A is laminated on the upper electrode films 5A and 5B. After that, the resist film is patterned so as to cover the bulk elastic wave resonator 10A forming region and open the bulk elastic wave resonator 10B forming region, and is approximately an integral multiple of 1/2 of the resonance frequency of the bulk elastic wave resonator 10B. By laminating another film, for example, a metal film, and lifting it off until the thickness becomes thick, another film 4e can be formed on the temperature compensating film 4B as shown in FIG.

さらに別の実施例として、一方のバルク弾性波共振器の温度補償膜のみをエッチングする代わりに、両方の温度補償膜をそれぞれ所望の厚さだけエッチングすることで共振周波数を調整することも可能である。同様に、一方のバルク弾性波共振器の温度補償膜上のみに別の膜を積層する代わりに、両方のバルク弾性波共振器の温度補償膜上に別の膜をそれぞれ積層して共振周波数を調整することも可能である。さらに、温度補償膜のエッチングによる共振周波数の調整と別の膜を積層することによる共振周波数の調整を組み合わせても問題ない。 As yet another embodiment, it is possible to adjust the resonance frequency by etching both temperature compensation films to a desired thickness instead of etching only the temperature compensation film of one bulk elastic wave resonator. is there. Similarly, instead of laminating another membrane only on the temperature compensating membrane of one bulk elastic wave resonator, another membrane is laminated on the temperature compensating membrane of both bulk elastic wave resonators to obtain the resonance frequency. It is also possible to adjust. Further, there is no problem in combining the adjustment of the resonance frequency by etching the temperature compensation film and the adjustment of the resonance frequency by laminating another film.

以上本発明の実施例について説明したが、本発明は上記実施例に限定されるものでないことは言うまでもない。具体的には、圧電膜として窒化アルミニウムに限定されるものでなく、窒化スカンジウムアルミニウム(Al1-xScxN)、酸化亜鉛(ZnO)、チタン酸ジルコン酸鉛(PZT)も利用することが可能である。また、上部電極膜あるいは下部電極膜は、モリブデン(Mo)の代わりに、プラチナ(Pt)、チタン(Ti)、イリジウム(Ir)、ルテニウム(Ru)等の金属薄膜で形成することができる。同様に、温度補償膜として使用する金属膜についても、モリブデン(Mo)の代わりに、プラチナ(Pt)、チタン(Ti)、イリジウム(Ir)、ルテニウム(Ru)等の金属薄膜で形成することができる。 Although the examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above examples. Specifically, the piezoelectric film is not limited to aluminum nitride, and scandium aluminum nitride (Al 1-x Sc x N), zinc oxide (ZnO), and lead zirconate titanate (PZT) can also be used. It is possible. Further, the upper electrode film or the lower electrode film can be formed of a metal thin film such as platinum (Pt), titanium (Ti), iridium (Ir), and ruthenium (Ru) instead of molybdenum (Mo). Similarly, the metal film used as the temperature compensation film may be formed of a metal thin film such as platinum (Pt), titanium (Ti), iridium (Ir), ruthenium (Ru) instead of molybdenum (Mo). it can.

1:シリコン基板、2:下部電極膜、3:圧電膜、4:温度補償膜、5:上部電極膜、6:凹部 1: Silicon substrate 2: Lower electrode film 3: Piezoelectric film 4: Temperature compensation film 5: Upper electrode film, 6: Recessed

Claims (1)

圧電膜と、該圧電膜を挟む上部電極膜および下部電極膜と、前記圧電膜と逆符号の温度係数を持つ温度補償膜とを含む多層膜とが積層したバルク弾性波共振器の製造方法において、
前記下部電極膜と前記圧電膜と前記上部電極膜とを、前記バルク弾性波共振器の共振周波数の波長の1/2の整数倍の厚さとなるように形成する工程と、
前記上部電極膜上に前記温度補償膜として、選択除去可能な少なくとも2種類の第1の温度補償膜と第2の温度補償膜を交互に積層し、表面を前記第1の温度補償膜とする多層構造の膜であって、前記共振周波数の波長の1/2の整数倍より厚い膜を形成する工程と、
前記多層構造の温度補償膜のうち、表面に形成された前記第1の温度補償膜を選択エッチングし、前記バルク弾性波共振器の共振周波数が所定の値に達していない場合は、前記多層構造の温度補償膜の表面となった前記第2の温度補償膜を選択エッチングし、前記バルク弾性波共振器の共振周波数が前記所定の値となるまで前記第1の温度補償膜の選択エッチングと前記第2の温度補償膜の選択エッチングを繰り返すことで、前記多層構造の温度補償膜の厚さを前記バルク弾性波共振器の共振周波数の波長の1/2の整数倍とし、前記バルク弾性波共振器の共振周波数を所定の値に調整する工程と、を含むことを特徴とするバルク弾性波共振器の製造方法。
In a method for manufacturing a bulk elastic wave resonator in which a piezoelectric film, an upper electrode film and a lower electrode film sandwiching the piezoelectric film, and a multilayer film including the piezoelectric film and a temperature compensation film having a temperature coefficient of the opposite sign are laminated. ,
A step of forming the lower electrode film, the piezoelectric film, and the upper electrode film so as to have a thickness that is an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator.
As the temperature compensating film, at least two types of the first temperature compensating film and the second temperature compensating film that can be selectively removed are alternately laminated on the upper electrode film, and the surface thereof is used as the first temperature compensating film. A step of forming a film having a multi-layer structure, which is thicker than an integral multiple of 1/2 of the wavelength of the resonance frequency.
When the first temperature compensating film formed on the surface of the multi-layered temperature compensating film is selectively etched and the resonance frequency of the bulk elastic wave resonator does not reach a predetermined value, the multilayer structure is formed. The second temperature compensating film, which is the surface of the temperature compensating film, is selectively etched, and the first temperature compensating film is selectively etched until the resonance frequency of the bulk elastic wave resonator reaches the predetermined value. By repeating the selective etching of the second temperature compensating film, the thickness of the temperature compensating film having the multilayer structure is made an integral multiple of 1/2 the wavelength of the resonance frequency of the bulk elastic wave resonator, and the bulk elastic wave resonance is performed. A method for manufacturing a bulk elastic wave resonator, which comprises a step of adjusting the resonance frequency of the instrument to a predetermined value.
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