Patent ID: 12191840

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIGS.1to6,FIG.11, andFIGS.13to18referred to in the following preferred embodiments and the like are schematic diagrams, and ratios of sizes, thicknesses, and the like of elements in the drawing do not necessarily reflect actual dimensional ratios.

Preferred Embodiment 1

Hereinafter, an acoustic wave device1according to Preferred Embodiment 1 of the present invention will be described with reference toFIGS.1to3.

(1.1) Overall Configuration of Acoustic Wave Device

The acoustic wave device1according to Preferred Embodiment 1 includes a piezoelectric layer4, a first electrode51, and a second electrode52, as illustrated inFIG.1. The first electrode51and the second electrode52face each other in a direction D2(hereinafter, also referred to as a “second direction D2”) crossing a thickness direction D1(hereinafter, also referred to as a “first direction D1”) of the piezoelectric layer4, as illustrated inFIG.2A. The acoustic wave device1utilizes a bulk wave of a thickness-shear primary mode. The second direction D2is orthogonal or substantially orthogonal to a polarization direction PZ1of the piezoelectric layer4. The bulk wave of the thickness-shear primary mode is a bulk wave whose propagation direction is the thickness direction D1of the piezoelectric layer4produced by thickness-shear vibrations of the piezoelectric layer4, and the number of nodes of the wave is one in the thickness direction D1of the piezoelectric layer4. The thickness-shear vibrations are excited by the first electrode51and the second electrode52. The thickness-shear vibrations are excited in a defined region45between the first electrode51and the second electrode52in the piezoelectric layer4in a plan view from the thickness direction D1. In the acoustic wave device1, when the second direction D2is orthogonal or substantially orthogonal to the polarization direction PZ1of the piezoelectric layer4, an electromechanical coupling coefficient (hereinafter, also referred to as a coupling coefficient) of the bulk wave of the thickness-shear primary mode is large. Here, “orthogonal” is not limited to being strictly orthogonal, and may be substantially orthogonal (an angle between the second direction D2and the polarization direction PZ1is, for example, about 90°±10°).

As illustrated inFIG.1andFIG.2A, the first electrode51and the second electrode52intersect with each other when viewed from the second direction D2. The expression “intersect with each other when viewed from the second direction D2” means that the electrodes overlap each other when viewed from the second direction D2. The acoustic wave device1further includes a first wiring portion61connected to the first electrode51and a second wiring portion62connected to the second electrode52. The first wiring portion61is connected to a first terminal T1. The second wiring portion62is connected to a second terminal T2different from the first terminal T1. The acoustic wave device1includes a plurality of the first electrodes51and a plurality of the second electrodes52. That is, in the case where the first electrode51and the second electrode52define a set of paired electrodes, the acoustic wave device1includes a plurality of sets of paired electrodes. In the acoustic wave device1, the plurality of first electrodes51and the plurality of second electrodes52are alternately provided one by one in the second direction D2. In the acoustic wave device1, the plurality of first electrodes51is connected to one first wiring portion61, and the plurality of second electrodes52is connected to one second wiring portion62.

The acoustic wave device1includes a support substrate2, an acoustic reflection layer3, the piezoelectric layer4, the first electrode51, and the second electrode52, as illustrated inFIG.2A. The acoustic reflection layer3is provided on the support substrate2. The piezoelectric layer4is provided on the acoustic reflection layer3. The first electrode51and the second electrode52are in contact with the piezoelectric layer4. The acoustic reflection layer3includes at least one (for example, two) high acoustic impedance layer32and at least one (for example, three) low acoustic impedance layer31. The low acoustic impedance layer31has an acoustic impedance lower than that of the high acoustic impedance layer32. The acoustic wave device1includes, as a resonator, an acoustic wave resonator5including the first electrode51, the second electrode52, and the piezoelectric layer4. In the acoustic wave device1, the acoustic wave resonator5further includes the acoustic reflection layer3described above.

(1.2) Elements of Acoustic Wave Device

Next, each of the elements of the acoustic wave device1will be described with reference to the drawings.

(1.2.1) Support Substrate

As illustrated inFIG.2A, the support substrate2supports the piezoelectric layer4. In the acoustic wave device1according to Preferred Embodiment 1, the support substrate2also supports the acoustic reflection layer3, and supports the piezoelectric layer4and the first electrode51as well as the second electrode52with the acoustic reflection layer3interposed therebetween.

The support substrate2includes a first principal surface21and a second principal surface22facing each other. The first principal surface21and the second principal surface22face each other in a thickness direction of the support substrate2. The thickness direction of the support substrate2is a direction along the thickness direction D1of the piezoelectric layer4. In a plan view from the thickness direction D1of the piezoelectric layer4, the outer peripheral shape of the support substrate2is rectangular or substantially rectangular, but is not limited thereto, and may be, for example, a square or substantially square shape.

The support substrate2is, for example, a silicon substrate. The thickness of the support substrate2is, for example, about 120 μm, but is not limited thereto. The silicon substrate is according to Modification 1 of Preferred Embodiment 1 of the present invention, for example, a single crystal silicon substrate. When the support substrate2is a silicon substrate, the plane orientation of the first principal surface21may be, for example, a (100) plane, (110) plane, or (111) plane. The propagation direction of the bulk wave may be set without being restricted by the plane orientation of the silicon substrate. The resistivity of the silicon substrate is, for example, about 1 kΩcm or more, preferably about 2 kΩcm or more, and more preferably about 4 kΩcm or more.

The support substrate2is not limited to a silicon substrate, and may be, for example, a quartz substrate, a glass substrate, a sapphire substrate, a lithium tantalate substrate, a lithium niobate substrate, an alumina substrate, a spinel substrate, a gallium arsenide substrate, or a silicon carbide substrate.

(1.2.2) Acoustic Reflection Layer

The acoustic reflection layer3is provided on the first principal surface21of the support substrate2as illustrated inFIG.2A. The acoustic reflection layer3faces the first electrode51and the second electrode52in the thickness direction D1of the piezoelectric layer4.

The acoustic reflection layer3reduces or prevents the leakage of the bulk waves (bulk waves of the thickness-shear primary mode described above) excited by the first electrode51and the second electrode52into the support substrate2. By including the acoustic reflection layer3, the acoustic wave device1may improve an effect of confining acoustic wave energy in the piezoelectric layer4. Because of this, the acoustic wave device1may reduce the loss and increase the Q value as compared with a case of not including the acoustic reflection layer3.

The acoustic reflection layer3has a laminated structure including a plurality of (three) low acoustic impedance layers31and a plurality of (two) high acoustic impedance layers32alternately provided one by one in the thickness direction D1of the piezoelectric layer4. The acoustic impedance of the low acoustic impedance layer31is lower than the acoustic impedance of the high acoustic impedance layer32.

Hereinafter, for convenience of description, in the acoustic reflection layer3, the two high acoustic impedance layers32may be referred to as a first high acoustic impedance layer321and a second high acoustic impedance layer322in the order of closeness to the first principal surface21of the support substrate2. The three low acoustic impedance layers31may be referred to as a first low acoustic impedance layer311, a second low acoustic impedance layer312, and a third low acoustic impedance layer313in the order of closeness to the first principal surface21of the support substrate2.

In the acoustic reflection layer3, the first low acoustic impedance layer311, the first high acoustic impedance layer321, the second low acoustic impedance layer312, the second high acoustic impedance layer322, and the third low acoustic impedance layer313are provided in this order from the support substrate2side. Accordingly, the acoustic reflection layer3may reflect the bulk wave (bulk wave of the thickness-shear primary mode) from the piezoelectric layer4at each of an interface between the third low acoustic impedance layer313and the second high acoustic impedance layer322, an interface between the second high acoustic impedance layer322and the second low acoustic impedance layer312, an interface between the second low acoustic impedance layer312and the first high acoustic impedance layer321, and an interface between the first high acoustic impedance layer321and the first low acoustic impedance layer311.

The material of the plurality of high acoustic impedance layers32is, for example, platinum (Pt). The material of the plurality of low acoustic impedance layers31is, for example, silicon oxide. The thickness of each of the plurality of high acoustic impedance layers32is, for example, about 94 nm. The thickness of each of the plurality of low acoustic impedance layers31is, for example, about 188 nm. The acoustic reflection layer3includes two conductive layers because each of the two high acoustic impedance layers32is made of platinum.

The material of the plurality of high acoustic impedance layers32is not limited to Pt, and may be a metal such as, for example, tungsten (W) or tantalum (Ta). The material of the plurality of high acoustic impedance layers32is not limited to metal, and may be, for example, an insulator.

The plurality of high acoustic impedance layers32is not limited to being made of the same material, and may be made of mutually different materials, for example. The plurality of low acoustic impedance layers31is not limited to being made of the same material, and may be made of mutually different materials, for example.

Further, the number of low acoustic impedance layers31in the acoustic reflection layer3is not limited to three, and may be one, two, or four or more. The number of high acoustic impedance layers32in the acoustic reflection layer3is not limited to two, and may be one or three or more. The number of high acoustic impedance layers32and the number of low acoustic impedance layers31are not limited to being different, and may be the same, or the number of low acoustic impedance layers31may be less than the number of high acoustic impedance layers32by one.

The film thickness of each of the high acoustic impedance layers32and the low acoustic impedance layers31in the acoustic reflection layer3is appropriately set in accordance with the desired frequency of the acoustic wave device1and the material applied to each of the high acoustic impedance layers32and the low acoustic impedance layers31in order to obtain favorable reflection in the acoustic reflection layer3.

(1.2.3) Piezoelectric Layer

The piezoelectric layer4includes a first principal surface41and a second principal surface42facing each other, as illustrated inFIG.2A. The first principal surface41and the second principal surface42face each other in the thickness direction D1of the piezoelectric layer4. In the piezoelectric layer4, of the first principal surface41and the second principal surface42, the first principal surface41is located on the first electrode51side and the second electrode52side, and the second principal surface42is located on the acoustic reflection layer3side. Accordingly, in the acoustic wave device1, the distance between the first principal surface41of the piezoelectric layer4and the acoustic reflection layer3is longer than the distance between the second principal surface42of the piezoelectric layer4and the acoustic reflection layer3. The material of the piezoelectric layer4is, for example, lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). The piezoelectric layer4is, for example, a Z-cut LiNbO3or a Z-cut LiTaO3. With regard to the Euler angles (φ, θ, ψ) of the piezoelectric layer4, for example, φ is about 0°±10° and θ is about 0°±10°. Any angle may be used for ψ. From the viewpoint of increasing the coupling coefficient, the piezoelectric layer4is preferably made of a Z-cut LiNbO3or a Z-cut LiTaO3. The propagation orientation may be a Y-axis direction, an X-axis direction, or a direction rotated within a range of about ±90° from an X-axis in crystal axes (X, Y, Z) defined for the crystal structure of the piezoelectric layer4. The piezoelectric layer4is, for example, a single crystal, but is not limited thereto. For example, the piezoelectric layer4may be a twin crystal or ceramics.

The thickness of the piezoelectric layer4is, for example, in a range from about 50 nm to about 1000 nm, and is about 400 nm as an example.

The piezoelectric layer4includes the defined region45. In a plan view from the thickness direction D1of the piezoelectric layer4, the defined region45is a region intersecting with both the first electrode51and the second electrode52in a direction in which the first electrode51and the second electrode52face each other in the piezoelectric layer4, and located between the first electrode51and the second electrode52.

(1.2.4) Electrodes

In the acoustic wave device1, of the first electrode51and the second electrode52, the first electrode51is a hot electrode, and the second electrode52is a ground electrode. In the acoustic wave device1, the plurality of first electrodes51and the plurality of second electrodes52are alternately provided one by one being separated from each other. Accordingly, the first electrode51and the second electrode52adjacent to each other are separated from each other. The distance between the center lines of the first electrode51and the second electrode52adjacent to each other is, for example, in a range from about 1 μm to about 10 μm, and is about 3 μm as an example. In this case, the first electrode51and the second electrode52being “adjacent to each other” refers to a case in which the first electrode51and the second electrode52face each other with a gap interposed therebetween.

A group of electrodes including the plurality of first electrodes51and the plurality of second electrodes52is only required to have a configuration in which the plurality of first electrodes51and the plurality of second electrodes52are provided in the second direction D2being separated from each other, and may have a configuration in which the plurality of first electrodes51and the plurality of second electrodes52are not alternately provided are separated from each other. For example, a region in which the first electrodes51and the second electrodes52are provided one by one and separated from each other, and a region in which two first electrodes51or two second electrodes52are provided in the second direction D2may be mixed. In addition, for example, one or more of the plurality of first electrodes51or of the plurality of second electrodes52may be in an electrically floating state.

The plurality of first electrodes51and the plurality of second electrodes52each have an elongated (linear) shape in a plan view from the thickness direction D1of the piezoelectric layer4, where a third direction D3orthogonal or substantially orthogonal to the second direction D2is a longitudinal direction and the second direction D2is a width direction, as illustrated inFIG.1. The length of each of the plurality of first electrodes51is, for example, about 20 μm, but is not limited thereto. A width H1(first electrode width H1) of each of the plurality of first electrodes51is, for example, in a range from about 50 nm to about 1000 nm, and is about 500 nm as an example. The length of each of the plurality of second electrodes52is, for example, about 20 μm, but is not limited thereto. A width H2(second electrode width H2) of each of the plurality of second electrodes52is, for example, in a range from about 50 nm to about 1000 nm, and is about 500 nm as an example.

The first electrode51includes a first electrode principal portion510. The first electrode principal portion510is a portion of the first electrode51intersecting with the second electrode52in a direction in which the first electrode51and the second electrode52face each other. The second electrode52includes a second electrode principal portion520. The second electrode principal portion520is a portion of the second electrode52intersecting with the first electrode51in the direction in which the first electrode51and the second electrode52face each other.

Each of the plurality of first electrodes51includes a laminated film including a main electrode film511and a close contact film512, as illustrated inFIG.2A. Each of the plurality of second electrodes52includes a laminated film including a main electrode film521and a close contact film522, as illustrated inFIG.2A. The main electrode films511and521are provided on the close contact films512and522, respectively. That is, the main electrode films511and521are provided on the piezoelectric layer4with the close contact films512and522respectively interposed therebetween. The main electrode films511and521are each made of, for example, an Al film or AlCu film. The close contact films512and522are each made of, for example, a Ti film. The main electrode films511and521have a thickness of, for example, about 80 nm. The close contact films512and522have a thickness of, for example, about 10 nm. When the main electrode films511and521are, for example, AlCu films, it is preferable for Cu to be, for example, about 1 wt % to about 20 wt %. The main electrode films511and521are not limited to the Al films or AlCu films, and may be each include, for example, an alloy including aluminum (Al) as a main ingredient, and also including manganese (Mn) or silicon (Si). In the acoustic wave device1according to Preferred Embodiment 1, the main electrode films511and521are, for example, aluminum layers.

As illustrated inFIG.2B, in the acoustic wave device1according to Preferred Embodiment 1, the <111> direction of the crystal of the main electrode film511as an aluminum layer is a direction orthogonal or substantially orthogonal to a surface on the piezoelectric layer4side of the main electrode film511(here, a surface on the close contact film512side of the main electrode film511). In other words, the <111> direction of the crystal of the main electrode film511as an aluminum layer is a direction orthogonal or substantially orthogonal to a principal surface (in this case, the first principal surface41) of the piezoelectric layer4. A C-axis101of the piezoelectric layer4is a Z-axis direction in the crystal axes (X, Y, Z) defined for the crystal structure of the piezoelectric layer4. Here, “orthogonal” is not limited to being strictly orthogonal, and may be substantially orthogonal (an angle formed by the first principal surface41and the C-axis101of the piezoelectric layer4is, for example, about 90°±10°). The <111> direction of the crystal if the main electrode film511as an aluminum layer is an orientation direction of the crystal of the main electrode film511.

In the acoustic wave device1according to Preferred Embodiment 1, as illustrated inFIG.2B, an orientation axis102of the main electrode film (aluminum layer)521defining a portion of the second electrode52, an orientation axis103of the close contact film522defining a portion of the second electrode52, and the C-axis101of the piezoelectric layer4are oriented in the same or substantially the same direction. In other words, the <111> direction (orientation axis102) of the crystal of the main electrode film521as an aluminum layer is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer4side of the main electrode film521(here, the surface on the close contact film522side of the main electrode film521). To further rephrase, the <111> direction of the crystal of the main electrode film521as an aluminum layer is a direction orthogonal or substantially orthogonal to the principal surface (in this case, the first principal surface41) of the piezoelectric layer4.

In the acoustic wave device1according to Preferred Embodiment 1, the main electrode films511and521as aluminum layers are epitaxial layers. In this case, the “epitaxial layer” refers to a metal layer grown with the same or substantially the same orientation as that of a single crystal defining and functioning as the base material. In Preferred Embodiment 1, the orientation of the main electrode films511and521as the epitaxial layers is the same or substantially the same as the orientation of the piezoelectric layer4.

Herein, it is assumed that the orientation axis102of the main electrode films511and521is inclined with respect to the first principal surface41of the piezoelectric layer4. In this case, when the acoustic wave resonator5is excited, intermodulation distortion (IMD) is generated between an input signal and an output signal due to the inclination of the orientation axis102of the main electrode films511and521. In contrast, in the acoustic wave device1according to Preferred Embodiment 1, because the orientation axis102of the main electrode films511and521is orthogonal or substantially orthogonal to the first principal surface41of the piezoelectric layer4, it is possible to reduce or prevent the generation of distortion between the input signal and the output signal. In other words, the acoustic wave device1according to Preferred Embodiment 1 may improve distortion characteristics.

In the acoustic wave device1according to Preferred Embodiment 1, the plurality of first electrodes51has the same or substantially the same first electrode width H1, but is not limited to the same or substantially the same width, and may have different widths. In the acoustic wave device1according to Preferred Embodiment 1, the plurality of second electrodes52has the same or substantially the same second electrode width H2, but is not limited to the same or substantially the same width, and may have different widths. In the acoustic wave device1according to Preferred Embodiment 1, the first electrode width H1is equal or substantially equal to the second electrode width H2, but is not limited thereto. The first electrode width H1may differ in size from the second electrode width H2.

With regard to the acoustic wave device1according to Preferred Embodiment 1, although the number of first electrodes51and the number of second electrodes52are, for example, both five inFIG.1, each of the number of first electrodes51and the number of second electrodes52is not limited to five, and may be one, two to four, six or more, or fifty or more.

The second direction D2, in which the first electrode51and the second electrode52face each other, is preferably orthogonal or substantially orthogonal to the polarization direction PZ1of the piezoelectric layer4(seeFIG.2A), but is not limited thereto. For example, in a case where the piezoelectric layer4is not a Z-cut piezoelectric body, the first electrode51and the second electrode52may face each other in a direction orthogonal or substantially orthogonal to the third direction D3, which is the longitudinal direction. The first electrode51and the second electrode52are not rectangular or substantially rectangular in some case. In such case, the third direction D3, which is the longitudinal direction, may be a long side direction of a circumscribed polygon that circumscribes the first electrode51and the second electrode52in a plan view of the first electrode51and the second electrode52. In the case where the first wiring portion61and the second wiring portion62are connected to the first electrode51and the second electrode52, respectively, the “circumscribed polygon that circumscribes the first electrode51and the second electrode52” includes a polygon circumscribing at least portions of the first electrode51and the second electrode52excluding the portion connected to the first wiring portion61or the second wiring portion62.

In the acoustic wave device1, each of the plurality of first electrodes51is provided on the first principal surface41of the piezoelectric layer4, as illustrated inFIG.2A. In the acoustic wave device1, each of the plurality of second electrodes52is provided on the first principal surface41of the piezoelectric layer4. That is, in the acoustic wave device1, the first electrode51and the second electrode52are provided on the same principal surface (in this case, the first principal surface41) of the piezoelectric layer4, and face each other on the same principal surface.

In the acoustic wave device1according to Preferred Embodiment 1, the thickness of each of the plurality of first electrodes51is smaller than the thickness of the piezoelectric layer4. Each of the plurality of first electrodes51includes a first principal surface513and a second principal surface514crossing the thickness direction D1of the piezoelectric layer4, and two side surfaces515and515crossing the width direction of the first electrode51. In each of the plurality of first electrodes51, the second principal surface514of the first principal surface513and the second principal surface514is located on the acoustic reflection layer3side. Accordingly, in the acoustic wave device1, the shortest distance from the first principal surface513of the first electrode51to the acoustic reflection layer3is longer than the shortest distance from the second principal surface514of the first electrode51to the acoustic reflection layer3. In each of the plurality of first electrodes51, the second principal surface514is in planar contact with the piezoelectric layer4.

In the acoustic wave device1according to Preferred Embodiment 1, the thickness of each of the plurality of second electrodes52is smaller than the thickness of the piezoelectric layer4. Each of the plurality of second electrodes52includes a first principal surface523and a second principal surface524crossing the thickness direction D1of the piezoelectric layer4, and two side surfaces525and525crossing the width direction of the second electrode52. In each of the plurality of second electrodes52, the second principal surface524of the first principal surface523and the second principal surface524is located on the acoustic reflection layer3side. Accordingly, in the acoustic wave device1, the shortest distance from the first principal surface523of the second electrode52to the acoustic reflection layer3is longer than the shortest distance from the second principal surface524of the second electrode52to the acoustic reflection layer3. In each of the plurality of second electrodes52, the second principal surface524is in planar contact with the piezoelectric layer4.

(1.2.5) First Wiring Portion and Second Wiring Portion

The first wiring portion61includes a first busbar611. The first busbar611is a conductor portion configured to cause the plurality of first electrodes51to have the same potential. The first busbar611has an elongated shape (linear shape) whose longitudinal direction is in the second direction D2. The plurality of first electrodes51connected to the first busbar611extend toward a second busbar621. In the acoustic wave device1, a first conductor portion including the plurality of first electrodes51and the first busbar611has a comb shape in a plan view from the thickness direction D1of the piezoelectric layer4. The first busbar611is integrally provided with the plurality of first electrodes51, but is not limited thereto.

The second wiring portion62includes the second busbar621. The second busbar621is a conductor portion configured to cause the plurality of second electrodes52to have the same potential. The second busbar621has an elongated shape (linear shape) whose longitudinal direction is in the second direction D2. The plurality of second electrodes52connected to the second busbar621extend toward the first busbar611. In the acoustic wave device1, a second conductor portion including the plurality of second electrodes52and the second busbar621has a comb shape in the plan view from the thickness direction D1of the piezoelectric layer4. The second busbar621is integrally provided with the plurality of second electrodes52, but is not limited thereto.

The first busbar611and the second busbar621face each other in the third direction D3. The third direction D3is a direction orthogonal or substantially orthogonal to both the first direction D1and the second direction D2.

The first wiring portion61and the second wiring portion62are electrically conductive. The material of the first wiring portion61and the second wiring portion62is, for example, aluminum (Al), copper (Cu), platinum (Pt), gold (Au), silver (Ag), titanium (Ti), nickel (Ni), chromium (Cr), molybdenum (Mo), tungsten (W), or an alloy including any of these metals as a main ingredient. The first wiring portion61and the second wiring portion62may include a plurality of metal films made of these metals or alloys that are laminated. Each of the first wiring portion61and the second wiring portion62includes, for example, a laminated film of a close contact film made of a Ti film and a main wiring film made of an Al film or AlCu film provided on the close contact film. The close contact film is, for example, about 10 nm in thickness. The main wiring film is, for example, about 80 nm in thickness. In the AlCu film, it is preferable for Cu to be, for example, about 1 wt % to about 20 wt %.

In the acoustic wave device1, each of the first busbar611and the second busbar621may include a metal film on the main wiring film from the viewpoint of reducing the resistance of the first busbar611and the second busbar621.

(1.3) Manufacturing Method for Acoustic Wave Device

In a non-limiting example of a manufacturing method for the acoustic wave device1, for example, after the support substrate2is prepared, first step to fourth step are performed. In the first step, the acoustic reflection layer3is formed on the first principal surface21of the support substrate2. In the second step, a piezoelectric substrate from which the piezoelectric layer4is formed and the support substrate2are bonded with the acoustic reflection layer3interposed therebetween. In the third step, the piezoelectric layer4which is a portion of the piezoelectric substrate is formed by thinning the piezoelectric substrate. In the fourth step, the first electrode51, the second electrode52, the first wiring portion61, and the second wiring portion62are formed on the piezoelectric layer4. In the fourth step, the first electrode51, the second electrode52, the first wiring portion61, and the second wiring portion62are formed using, for example, a photolithography technique, an etching technique, a thin film forming technique, and the like. In the first step to the fourth step, a silicon wafer is used as the support substrate2, and a piezoelectric wafer is used as the piezoelectric substrate. In the manufacturing method for the acoustic wave device1, a wafer including a plurality of the acoustic wave devices1is cut with, for example, a dicing machine to obtain the plurality of acoustic wave devices1(chips).

The manufacturing method for the acoustic wave device1is an example and is not particularly limited. For example, the piezoelectric layer4may be formed using a film forming technique. In this case, the manufacturing method for the acoustic wave device1includes a step of film-forming the piezoelectric layer4instead of the second step and the third step. The piezoelectric layer4formed by the film forming technique may be, for example, a single crystal or twin crystal. Examples of the film forming technique include, but are not limited to, a chemical vapor deposition (CVD) method.

(1.4) Operations and Characteristics of Acoustic Wave Device

The acoustic wave device1according to Preferred Embodiment 1 utilizes a bulk wave of a thickness-shear primary mode. As described above, the bulk wave of the thickness-shear primary mode is a bulk wave whose propagation direction is in the thickness direction D1of the piezoelectric layer4produced by thickness-shear vibrations of the piezoelectric layer4, and the number of nodes of the wave is one in the thickness direction D1of the piezoelectric layer4. The thickness-shear vibrations are excited by the first electrode51and the second electrode52. The thickness-shear vibrations are excited in the defined region45between the first electrode51and the second electrode52in the piezoelectric layer4in a plan view from the thickness direction D1. The thickness-shear vibrations may be confirmed by, for example, a finite element method (FEM). More specifically, the thickness-shear vibrations may be confirmed by, for example, analyzing a displacement distribution by FEM using parameters of the piezoelectric layer4(such as, for example, material, Euler angles, and thickness), parameters of the first electrode51and the second electrode52(such as, for example, material, thickness, and distance between center lines of the first electrode51and the second electrode52), and analyzing distortion. The Euler angles of the piezoelectric layer4may be obtained by analysis. In the FEM, for example, Femtet (registered trademark) of Murata Manufacturing Co., Ltd. may be used as analysis simulation software.

Here, a difference between a Lamb wave utilized in an acoustic wave device of the related art and the bulk wave of the thickness-shear primary mode will be described with reference toFIGS.4A and4B.

FIG.4Ais a schematic elevational cross-sectional view for explaining a Lamb wave propagating through a piezoelectric substrate of an acoustic wave device such as a surface acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2012-257019. In the acoustic wave device of the related art, an acoustic wave propagates through a piezoelectric substrate400as indicated by an arrow. In this case, the piezoelectric substrate400includes a first principal surface401and a second principal surface402facing each other. InFIG.4A, the Z direction and X direction are illustrated in addition to the piezoelectric substrate400. InFIG.4A, the Z direction is a thickness direction connecting the first principal surface401and the second principal surface402of the piezoelectric substrate400. The X direction is a direction in which a plurality of electrode fingers of the IDT electrode is arranged. The Lamb wave is a plate wave in which an acoustic wave propagates in the X direction as indicated inFIG.4A. Accordingly, in the acoustic wave device of the related art, because the acoustic wave propagates in the X direction, two reflectors are respectively disposed on both sides of the IDT electrode to obtain desired resonance characteristics. Due to this, in the acoustic wave device of the related art, the propagation loss of the acoustic wave is generated. Therefore, when miniaturization is achieved, that is, when the number of pairs of electrode fingers is reduced, the Q value is reduced.

In contrast, as illustrated inFIG.4B, in the acoustic wave device1according to Preferred Embodiment 1, because the vibration displacement occurs a thickness-shear direction, the acoustic wave propagates in a direction connecting the first principal surface41and the second principal surface42of the piezoelectric layer4, that is, propagates in or substantially in the Z direction and resonates. Accordingly, an X-direction component of the acoustic wave is significantly smaller than a Z-direction component thereof. Because resonance characteristics are obtained by the propagation of the acoustic wave in the Z direction, reflectors are not required. This prevents the generation of propagation loss when the acoustic wave propagates to reflectors. Therefore, even when the number of electrode pairs each including the first electrode51and the second electrode52is reduced in order to achieve miniaturization, the decrease in the Q value is unlikely to occur.

In the acoustic wave device1according to Preferred Embodiment 1, an amplitude direction of the bulk wave of the thickness-shear primary mode in a first region451included in the defined region45of the piezoelectric layer4is opposite to an amplitude direction thereof in a second region452included in the defined region45, as illustrated inFIG.5. InFIG.5, a two-dot chain line schematically shows the bulk wave when a voltage to make the second electrode52have a higher potential than the first electrode51is applied between the first electrode51and the second electrode52. The first region451is a portion of the defined region45between the first principal surface41and a virtual plane VP1orthogonal or substantially orthogonal to the thickness direction D1of the piezoelectric layer4and dividing the piezoelectric layer4into two sections. The second region452is a portion of the defined region45between the virtual plane VP1and the second principal surface42.

Characteristics of a structural model1r(seeFIG.6) of an acoustic wave device according to a reference configuration utilizing a bulk wave of the thickness-shear primary mode were simulated. Regarding the structural model1r, the same or corresponding elements as those of the acoustic wave device1according to Preferred Embodiment 1 are denoted by the same reference signs, and description thereof will be omitted.

The structural model1rdiffers from the acoustic wave device1according to Preferred Embodiment 1 in that the first wiring portion61and the second wiring portion62are not included. In the simulation, the number of pairs of the first electrode51and the second electrode52was infinite, and the piezoelectric layer4was a 120° rotated Y-cut X-propagation LiNbO3.

In the structural model1r, the piezoelectric layer4is a membrane, and the second principal surface42of the piezoelectric layer4is in contact with air. In the structural model1r, in an optional cross section along the thickness direction D1of the piezoelectric layer4(FIG.6), the distance between the center lines of the first electrode51and the second electrode52adjacent to each other was denoted as p, and the thickness of the piezoelectric layer4was denoted as d. In the structural model1r, in a plan view from the thickness direction D1of the piezoelectric layer4, an area of the first electrode principal portion510was denoted as S1, an area of the second electrode principal portion520was denoted as S2, an area of the defined region45was denoted as S0, and a structural parameter defined by an expression of (S1+S2)/(S1+S2+S0) was denoted as MR. In a case where at least either multiple first electrodes51or multiple second electrodes52are provided in the piezoelectric layer4, the distance p between the center lines refers to each distance between the center lines of the first electrode51and the second electrode52adjacent to each other.

FIGS.7A and7Bare graphs showing a relationship between a fractional bandwidth and d/p when mutually different potentials are applied to the first electrode51and the second electrode52with regard to the structural model1r. In each ofFIGS.7A and7B, the horizontal axis represents d/p and the vertical axis represents the fractional bandwidth.FIGS.7A and7Bcorrespond to a case where the piezoelectric layer4is a 120° rotated Y-cut X-propagation LiNbO3, and the same or substantially the same tendency is observed in the cases of other cut-angles. In the structural model1rof the acoustic wave device, even when the material of the piezoelectric layer4is LiTaO3, the relationship between the fractional bandwidth and d/p has the same or substantially the same tendency as that ofFIGS.7A and7B. In the structural model1rof the acoustic wave device, the relationship between the fractional bandwidth and d/p has the same or substantially the same tendency as that ofFIGS.7A and7Bregardless of the number of pairs of the first electrode51and the second electrode52. In the structural model1rof the acoustic wave device, in addition to the case in which the second principal surface42of the piezoelectric layer4is in contact with air, in a case in which the second principal surface42of the piezoelectric layer4is in contact with the acoustic reflection layer3, the relationship between the fractional bandwidth and d/p has the same or substantially the same tendency as that ofFIGS.7A and7B.

It may be understood fromFIG.7Athat, in the structural model1rof the acoustic wave device, the value of the fractional bandwidth changes drastically taking a point at d/p=about 0.5 as an inflection point. In the structural model1rof the acoustic wave device, when d/p is greater than about 0.5, the coupling coefficient is low and the fractional bandwidth is less than about 5% no matter how much d/p is changed within a range of about 0.5<d/p 21 about 1.6. On the other hand, in the structural model1rof the acoustic wave device, when d/p is less than or equal to about 0.5, it is possible to increase the coupling coefficient and set the fractional bandwidth to be about 5% or more by changing d/p within a range of about 0<d/p about 0.5.

In the structural model1rof the acoustic wave device, when d/p is less than or equal to about 0.24, it is possible to further increase the coupling coefficient and set the fractional bandwidth to be larger by changing d/p within a range of about 0<d/p≤about 0.24. In the acoustic wave device1according to Preferred Embodiment 1, as illustrated inFIG.2A, in any cross section along the thickness direction D1of the piezoelectric layer4, in a case where the distance between the center lines of the first electrode51and the second electrode52is denoted as p, and the thickness of the piezoelectric layer4is denoted as d, the relationship between the fractional bandwidth and d/p has the same or substantially the same tendency as the relationship between the fractional bandwidth and d/p of the structural model1rof the acoustic wave device.

Furthermore, as is clear fromFIG.7A, when d/p is less than or equal to about 0.10, it is possible to further increase the coupling coefficient and set the fractional bandwidth to be larger by changing d/p within a range of about 0<d/p≤about 0.10.

FIG.7Bis an enlarged graph of a portion ofFIG.7A. As shown inFIG.7B, the fractional bandwidth changes taking a point at d/p=about 0.096 as an inflection point. Therefore, in a case of d/p≤about 0.096, it is possible to further increase the coupling coefficient and set the fractional bandwidth to be larger than in a case of about 0.096<d/p by changing d/p within a range of about 0<d/p≤about 0.096. Further, as shown inFIG.7B, the fractional bandwidth changes taking points at d/p=about 0.072 and about 0.048 as inflection points. Therefore, by satisfying a relationship of about 0.048≤d/p≤about 0.072, it is possible to reduce or prevent a change in the coupling coefficient due to a change in d/p and to set the fractional bandwidth to a constant or substantially constant value.

FIG.8is a graph in which plotted are spurious levels in a frequency band between a resonant frequency and an anti-resonant frequency in a case where the thickness d of the piezoelectric layer4, the distance p between the center lines of the first electrode51and the second electrode52, the first electrode width H1, and the second electrode width H2are changed in the structural model1rof the acoustic wave device according to the reference configuration utilizing the thickness-shear mode. InFIG.8, the horizontal axis represents the fractional bandwidth and the vertical axis represents the normalized spurious level. The normalized spurious level is a value obtained by normalizing the spurious level in the following manner: a spurious level at a fractional bandwidth (for example, about 22%) where the spurious level has the same or substantially the same value even when the thickness d of the piezoelectric layer4, the distance p between the center lines of the first electrodes51and the second electrodes52, the first electrode widths H1, and the second electrode widths H2are changed, is considered to be about 1.FIG.8shows a case where a Z-cut LiNbO3capable of more suitably exciting the thickness-shear mode is used as the piezoelectric layer4, and the same or substantially the same tendency is observed in the cases of other cut-angles. In the structural model1rof the acoustic wave device, even when the material of the piezoelectric layer4is LiTaO3, the relationship between the normalized spurious level and the fractional bandwidth has the same or substantially the same tendency as that ofFIG.8. In the structural model1rof the acoustic wave device, the relationship between the normalized spurious level and the fractional bandwidth has the same or substantially the same tendency as that ofFIG.8regardless of the number of pairs of the first electrode51and the second electrode52. In the structural model1rof the acoustic wave device, in addition to the case in which the second principal surface42of the piezoelectric layer4is in contact with air, in a case in which the second principal surface42of the piezoelectric layer4is in contact with the acoustic reflection layer, the relationship between the normalized spurious level and the fractional bandwidth has the same or substantially the same tendency as that ofFIG.8.

It may be understood fromFIG.8that when the fractional bandwidth exceeds about 17%, the normalized spurious level is aggregated to about 1. This indicates that, when the fractional bandwidth is about 17% or more, some sort of sub-resonance exists in a band between the resonant frequency and the anti-resonant frequency as in frequency characteristics of impedance exemplified inFIG.9.FIG.9shows the frequency characteristics of impedance when a Z-cut LiNbO3having Euler angles about (0°, 0°, 90°) is used as the piezoelectric layer4, and d/p equals about 0.08 and MR equals about 0.35. InFIG.9, a portion of the sub-resonance is surrounded by a broken line.

As described above, in the case where the fractional bandwidth exceeds about 17%, even when the thickness d of the piezoelectric layer4, the distance p between the center lines of the first electrode51and the second electrode52, the first electrode width H1, and the second electrode width H2are changed, large spurious signals are included in the band between the resonant frequency and the anti-resonant frequency. Such spurious signals are generated by overtones in a planar direction, mainly in a direction in which the first electrode51and the second electrode52face each other. Therefore, from the viewpoint of reducing or preventing the spurious signals in the band, the fractional bandwidth is preferably about 17% or less, for example. Because the acoustic wave device1according to Preferred Embodiment 1 exhibits the same or substantially the same tendency as that of the structural model1rof the acoustic wave device with regard to the relationship between the normalized spurious level and the fractional bandwidth, the fractional bandwidth is preferably about 17% or less, for example.

FIG.10shows, with regard to the structural model1rof the acoustic wave device, a first distribution region DA1with a fractional bandwidth exceeding about 17% and a second distribution region DA2with a fractional bandwidth not larger than about 17% while considering d/p and MR as parameters, in a case where a Z-cut LiNbO3is used as the piezoelectric layer4, and the thickness d of the piezoelectric layer4, the distance p between the center lines of the first electrodes51and the second electrodes52, the first electrode width H1, and the second electrode width H2are changed. InFIG.10, the first distribution region DA1and the second distribution region DA2have different dot densities, and the dot density of the first distribution region DA1is higher than the dot density of the second distribution region DA2. InFIG.10, an approximate straight line DL1of a boundary line between the first distribution region DA1and the second distribution region DA2is indicated by a broken line. The approximate straight line DL1is represented by a numerical expression of MR=1.75×(d/p)+0.075. Accordingly, in the structural model1rof the acoustic wave device, the fractional bandwidth may be about 17% or less by satisfying a condition of MR 1.75×(d/p)+0.075.

FIG.10shows a case where a Z-cut LiNbO3capable of more suitably exciting the thickness-shear mode is used as the piezoelectric layer4, and the same or substantially the same tendency is observed in the cases of other cut-angles. In the structural model1rof the acoustic wave device, even when the material of the piezoelectric layer4is LiTaO3, the approximate straight line DL1is the same or substantially the same. In the structural model1rof the acoustic wave device, the approximate straight line DL1is the same or substantially the same regardless of the number of pairs of the first electrode51and the second electrode52. In the structural model1rof the acoustic wave device, in addition to the case in which the second principal surface42of the piezoelectric layer4is in contact with air, in a case in which the second principal surface42of the piezoelectric layer4is in contact with the acoustic reflection layer, the approximate straight line DL1is the same or substantially the same. The acoustic wave device1according to Preferred Embodiment 1, similar to the structural model1rof the acoustic wave device, may cause the fractional bandwidth to be about 17% or less by satisfying the condition of MR≤1.75×(d/p)+0.075. InFIG.10, an approximate straight line DL2(hereinafter, also referred to as a second approximate straight line DL2) indicated by a chain line separately from the approximate straight line DL1(hereinafter, also referred to as the first approximate straight line DL1) is a line indicating a boundary for reliably setting the fractional bandwidth to be about 17% or less. The second approximate straight line DL2is represented by a numerical expression of MR=1.75×(d/p)+0.05. Accordingly, in the structural model1rof the acoustic wave device, it is possible to reliably set the fractional bandwidth to be about 17% or less by satisfying a condition of MR=1.75×(d/p)+0.05.

(1.5) Advantageous Effect

The acoustic wave device1according to Preferred Embodiment 1 includes the piezoelectric layer4, the first electrode51, and the second electrode52. The first electrode51and the second electrode52face each other in the direction D2crossing the thickness direction D1of the piezoelectric layer4. The acoustic wave device1utilizes a bulk wave of the thickness-shear primary mode. The material of the piezoelectric layer4is lithium niobate or lithium tantalate, for example. The first electrode51and the second electrode52include, for example, the aluminum layers (main electrode films)511and521, respectively, provided on the piezoelectric layer4. The <111> direction of the crystal of each of the aluminum layers511and521is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer4side of each of the aluminum layers511and521.

With the acoustic wave device1according to Preferred Embodiment 1, the Q value may be increased and the distortion characteristics may be improved even when the size of the device is reduced. In this case, the acoustic wave device1according to Preferred Embodiment 1 utilizes the bulk wave of the thickness-shear primary mode, and resonance characteristics are obtained by the wave propagation in the Z direction. Because of this, reflectors are not required. This prevents the generation of propagation loss when the wave propagates to reflectors. Therefore, even when the number of electrode pairs each including the first electrode51and the second electrode52is reduced in order to reduce the planar size, the decrease in the Q value is unlikely to occur. In the acoustic wave device1according to Preferred Embodiment 1, the <111> direction of the crystal of the aluminum layers (main electrode films)511and521is orthogonal or substantially orthogonal to the surfaces on the piezoelectric layer4side of the aluminum layers511and521. This improves the distortion characteristics when the acoustic wave resonator5is excited.

The acoustic wave device1according to Preferred Embodiment 1 includes the piezoelectric layer4, the first electrode51, and the second electrode52. The first electrode51and the second electrode52face each other in the direction D2crossing the thickness direction D1of the piezoelectric layer4. In the acoustic wave device1, in any cross section along the thickness direction D1of the piezoelectric layer4, when the distance between the center line of the first electrode51and the center line of the second electrode52is denoted as p, and the thickness of the piezoelectric layer4is denoted as d, d/p is not greater than about 0.5. The material of the piezoelectric layer4is lithium niobate or lithium tantalate, for example. The first electrode51and the second electrode52include, for example, the aluminum layers (main electrode films)511and521, respectively, provided on the piezoelectric layer4. The <111> direction of the crystal of each of the aluminum layers511and521is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer4side of each of the aluminum layers511and521.

With the acoustic wave device1according to Preferred Embodiment 1, the Q value may be increased and the distortion characteristics may be improved even when the size of the device is reduced.

In the acoustic wave device1according to Preferred Embodiment 1, the second principal surface42of the piezoelectric layer4may reduce or prevent unwanted waves by the acoustic reflection layer3. In the acoustic wave device1according to Preferred Embodiment 1, the material of the piezoelectric layer4is lithium niobate or lithium tantalate, for example, and the material of the low acoustic impedance layer31is, for example, silicon oxide. In this case, the frequency-temperature characteristics of each of the lithium niobate and lithium tantalate have a negative slope, and the frequency-temperature characteristics of the silicon oxide have a positive slope. Thus, in the acoustic wave device1according to the preferred embodiment, the absolute value of the temperature coefficient of frequency (TCF) may be reduced, and the frequency-temperature characteristics may be improved.

(1.6) Modifications

Preferred Embodiment 1 discussed above is merely one of various preferred embodiments of the present invention. Preferred Embodiment 1 discussed above may be modified in various ways in accordance with design and the like as long as the advantageous effects of the present invention are obtained.

(1.6.1) Modification 1

Hereinafter, an acoustic wave device1aaccording to Modification 1 of a preferred embodiment of the present invention will be described with reference toFIGS.11and12. With regard to the acoustic wave device1aaccording to Modification 1, the same or corresponding elements as those of the acoustic wave device1according to Preferred Embodiment 1 are denoted by the same reference signs, and description thereof will be omitted.

The acoustic wave device1aaccording to Modification 1 is an acoustic wave filter (in this case, a ladder filter). The acoustic wave device1aincludes an input terminal15, an output terminal16, a plurality of (for example, two) series-arm resonators RS1provided on a first path12connecting the input terminal15and the output terminal16, and a plurality of (for example, two) parallel-arm resonators RS2respectively provided on a plurality of (for example, two) second paths, the two second paths include a second path13and a second path14connecting a plurality of (for example, two) nodes, which are a node N1and a node N2on the first path12, to the ground (ground terminals17and18). The ground terminals17and18may be configured to be one ground and shared.

In the acoustic wave device1a, each of the plurality of series-arm resonators RS1and the plurality of parallel-arm resonators RS2is the acoustic wave resonator5. Each of a plurality of the acoustic wave resonators5is a resonator including the first electrode51and the second electrode52. In the acoustic wave device1a, the piezoelectric layer4is shared by the plurality of acoustic wave resonators5. In the acoustic wave device1a, the acoustic reflection layer3is shared by the plurality of acoustic wave resonators5. The resonant frequency of the parallel-arm resonator RS2is lower than that of the series-arm resonator RS1. In this case, the acoustic wave resonator5defining the parallel-arm resonator RS2includes, for example, a silicon oxide film provided on the first principal surface41of the piezoelectric layer4, whereas the acoustic wave resonator5defining the series-arm resonator RS1does not include a silicon oxide film on the first principal surface41of the piezoelectric layer4. The acoustic wave resonator5defining the series-arm resonator RS1may include, for example, a silicon oxide film on the first principal surface41of the piezoelectric layer4. In this case, it is sufficient that the silicon oxide film of the acoustic wave resonator5defining the series-arm resonator RS1is thinner than the silicon oxide film of the acoustic wave resonator5defining the parallel-arm resonator RS2.

In the acoustic wave device1a, the support substrate2and the acoustic reflection layer3are shared by the plurality of acoustic wave resonators5. However, of the plurality of high acoustic impedance layers32, the high acoustic impedance layer32(the second high acoustic impedance layer322) closest to the piezoelectric layer4may be isolated for each acoustic wave resonator5.

(1.6.2) Modification 2

Hereinafter, an acoustic wave device1baccording to Modification 2 of a preferred embodiment of the present invention will be described with reference toFIG.13. With regard to the acoustic wave device1baccording to Modification 2, the same or corresponding elements as those of the acoustic wave device1according to Preferred Embodiment 1 are denoted by the same reference signs, and description thereof will be omitted.

The acoustic wave device1baccording to Modification 2 differs from the acoustic wave device1according to Preferred Embodiment 1 in that two reflectors8are provided.

Each of the two reflectors8is a short-circuit grating. Each reflector8does not reflect a bulk wave of the first-order slip mode but reflects an unwanted surface acoustic wave propagating along the first principal surface41of the piezoelectric layer4. One reflector8of the two reflectors8is located on the opposite side to the second electrode52side of the first electrode51located at the end among the plurality of first electrodes51in a direction along the propagation direction of the unwanted surface acoustic wave of the acoustic wave device1b. The remaining one reflector8of the two reflectors8is located on the opposite side to the first electrode51side of the second electrode52located at the end among the plurality of second electrodes52in the direction along the propagation direction of the unwanted surface acoustic wave of the acoustic wave device1b.

Each reflector8includes a plurality of (for example, four) electrode fingers81, and one end of each the plurality of electrode fingers81is short-circuited to each other and the other end thereof is short-circuited to each other. In each reflector8, the number of electrode fingers81is not particularly limited.

Each reflector8is electrically conductive. The material of each of the reflectors8is, for example, Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or an alloy including any of these metals as a main component. Each reflector8may include a plurality of metal films made of these metals or alloys that are laminated. Each reflector8includes, for example, a laminated film including a close contact film made of a Ti film provided on the piezoelectric layer4and a main electrode film made of an Al film provided on the close contact film. The close contact film is, for example, about 10 nm in thickness. The main electrode film is, for example, about 80 nm in thickness.

In the acoustic wave device1baccording to Modification 2, each reflector8is a short-circuit grating, but is not limited thereto, and may be, for example, an open grating, a positive-negative reflection grating, or a grating in which a short-circuit grating and an open grating are combined. In the acoustic wave device1b, two reflectors8are provided, but only one of the two reflectors8may be provided.

(1.6.3) Modification 3

In the acoustic wave device1according to Preferred Embodiment 1, the cross section of each of the first electrode51and the second electrode52has a rectangular or substantially rectangular shape, but is not limited thereto. For example, the first electrode51and the second electrode52may have a shape such that the width of a lower end is wider than the width of an upper end as illustrated in any ofFIGS.14A to14D. This makes it possible to increase capacitance between the first electrode51and the second electrode52without increasing the width of an upper surface of each of the first electrode51and the second electrode52.

InFIG.14A, the first electrode51and the second electrode52include a portion where the width is constant substantially constant on the upper end side and a portion where the width is gradually increased on the lower end side. InFIG.14B, the first electrode51and the second electrode52have a trapezoidal or substantially trapezoidal cross-sectional shape. InFIG.14C, the first electrode51and the second electrode52have a shape that widens toward the lower end with both side surfaces thereof in the width direction being curved. InFIG.14D, the first electrode51and the second electrode52each include a portion with a trapezoidal or substantially trapezoidal cross-sectional shape on the upper end side, and on the lower end side, include a portion with a trapezoidal or substantially trapezoidal cross-sectional shape that is wider in size than the portion with the trapezoidal or substantially trapezoidal cross-sectional shape on the upper end side.

(1.6.4) Modification 4

In the acoustic wave device1according to Preferred Embodiment 1, the first principal surface41of the piezoelectric layer4, and the first electrode51and the second electrode52on the first principal surface41are exposed, but are not limited thereto. For example, as illustrated in any ofFIGS.15A to15C, the acoustic wave device1may include a dielectric film9covering the first principal surface41of the piezoelectric layer4, and the first electrode51and second electrode52on the first principal surface41.

InFIG.15A, the dielectric film9is thinner than the first electrode51and the second electrode52, and the surface of the dielectric film9has a concavo-convex shape along the shape of the base material. InFIG.15B, the surface of the dielectric films9is flattened to have a planar shape. InFIG.15C, the dielectric film9is thicker than the first electrode51and the second electrode52, and the surface of the dielectric film9has a concavo-convex shape along the shape of the base material.

(1.6.5) Other Modifications

In Preferred Embodiment 1, the first electrode51and the second electrode52are provided on the first principal surface41of the piezoelectric layer4, but is not limited thereto. The first electrode51and the second electrode52may be provided on the second principal surface42of the piezoelectric layer4. That is, the first electrode51and the second electrode52may be provided on the principal surface (in this case, the second principal surface42) of the piezoelectric layer4and may face each other on this principal surface.

In Preferred Embodiment 1, the first electrode51and the second electrode52are provided on the first principal surface41of the piezoelectric layer4, but is not limited thereto. At least a portion of each of the first electrode51and the second electrode52may be buried in the piezoelectric layer4.

In Preferred Embodiment 1, the cross-sectional shape of the first electrode51and the cross-sectional shape of the second electrode52are the same or substantially the same, but the cross-sectional shape of the first electrode51and the cross-sectional shape of the second electrode52may be different. In this case, the cross-sectional shape is, for example, a shape of a cross section orthogonal or substantially orthogonal to the thickness direction D1and the second direction D2of the piezoelectric layer4.

When an acoustic wave filter is configured as in the acoustic wave device1aof Modification 1 of Preferred Embodiment 1, the shapes of the first electrode51and the second electrode52may be different for each acoustic wave resonator5. The shapes of the first electrode51and the second electrode52may be different between the acoustic wave resonator5defining the series-arm resonator RS1and the acoustic wave resonator5defining the parallel-arm resonator RS2.

In Preferred Embodiment 1, the first electrode51and the second electrode52have a linear shape in a plan view from the thickness direction D1of the piezoelectric layer4, but are not limited thereto. The first electrode51and the second electrode52may have, for example, a curved shape, or a shape including a linear portion and a curved portion.

Instead of the acoustic wave resonator5in the acoustic wave device1aaccording to Modification 1 of Preferred Embodiment 1, any of the acoustic wave resonators5according to Modifications 2 to 4 of Preferred Embodiment 1, an acoustic wave resonator5of Preferred Embodiment 2 described below, and an acoustic wave resonator5according to Modification 1 of Preferred Embodiment 2 described below may be provided.

In Preferred Embodiment 1, each of the first electrode51and the second electrode52includes the main electrode films511,521and the close contact films512,522, but the close contact films512,522may be omitted. In other words, the first electrode51and the second electrode52may include only the main electrode films511and521, respectively.

In Preferred Embodiment 1, the close contact layer (close contact films512,522) includes one layer, but the close contact layer may include two or more layers. As an example, a case in which the close contact layer includes two layers may be provided. In this case, for example, when one of the two close contact layers is a Ti film and the other one thereof is a NiCr film, it is preferable that the piezoelectric layer4, the Ti film, the NiCr film, and the main electrode films511,521are laminated in this order.

Another metal film may be provided on the main electrode films511,521. As an example, the metal film may be a Ti film. In this case, it is sufficient that, for example, the piezoelectric layer4, the Ti film as a close contact layer, the main electrode films511,521, and the Ti film as another metal film are laminated in this order.

In Preferred Embodiment 1, the thickness of each of the plurality of first electrodes51is smaller than the thickness of the piezoelectric layer4, but the thickness of each of the plurality of first electrodes51may be equal or substantially equal to the thickness of the piezoelectric layer4or larger than the thickness of the piezoelectric layer4.

Modifications 1 to 4 and the other modifications described above may also be applied to acoustic wave devices1cand1daccording to Preferred Embodiment 2 described below.

Preferred Embodiment 2

Hereinafter, the acoustic wave device1caccording to Preferred Embodiment 2 of the present invention will be described with reference toFIGS.16and17. With regard to the acoustic wave device1caccording to Preferred Embodiment 2, the same or corresponding elements as those of the acoustic wave device1according to Preferred Embodiment 1 are denoted by the same reference signs, and description thereof will be omitted.

(2.1) Configuration of Acoustic Wave Device

The acoustic wave device1caccording to Preferred Embodiment 2 does not include the acoustic reflection layer3of the acoustic wave device1according to Preferred Embodiment 1. In the acoustic wave device1caccording to Preferred Embodiment 2, the piezoelectric layer4is provided on the support substrate2. In this case, the support substrate2is, for example, a silicon substrate. The piezoelectric layer4is bonded to the support substrate2with, for example, a silicon oxide film7interposed therebetween. The acoustic wave device1cfurther includes a cavity26. The cavity26is located immediately below the acoustic wave resonator5. That is, the cavity26is provided on the side opposite to the resonator5across the piezoelectric layer. The acoustic wave resonator5includes the first electrode51and the second electrode52in a plan view from the thickness direction D1of the piezoelectric layer4, and a portion (defined region45) between the first electrode51and the second electrode52in the piezoelectric layer4in the plan view from the thickness direction D1of the piezoelectric layer4. In the acoustic wave device1caccording to Preferred Embodiment 2, the cavity26is extends through the support substrate2and the silicon oxide film7, and exposes a portion of the piezoelectric layer4(a portion of the second principal surface42). In the acoustic wave device1caccording to Preferred Embodiment 2, the acoustic wave resonator5does not include the acoustic reflection layer3of the acoustic wave device1according to Preferred Embodiment 1. The cavity26overlaps a portion of each of the first wiring portion61and the second wiring portion62in the plan view from the thickness direction D1of the piezoelectric layer4. It is not necessary for the cavity26to overlap a portion of each of the first wiring portion61and the second wiring portion62in the plan view from the thickness direction D1of the piezoelectric layer4.

The thickness of the support substrate2is, for example, in a range from about 50 μm to about 500 μm. The thickness of the silicon oxide film7is, for example, in a range from about 0.01 μm to about 10 μm. The piezoelectric layer4has the same thickness as the piezoelectric layer4of the acoustic wave device1according to Preferred Embodiment 1.

(2.2) Manufacturing Method for Acoustic Wave Device

In a non-limiting example of a manufacturing method for the acoustic wave device1c, for example, after the support substrate2is prepared, first step to fifth step are performed. In the first step, the silicon oxide film7is formed on the first principal surface21of the support substrate2. In the second step, a piezoelectric substrate from which the piezoelectric layer4is formed and the support substrate2are bonded with the silicon oxide film7interposed therebetween. In the third step, the piezoelectric layer4made of a portion of the piezoelectric substrate is formed by thinning the piezoelectric substrate. In the fourth step, the plurality of first electrodes51, the plurality of second electrodes52, the first wiring portion61, and the second wiring portion62are formed on the piezoelectric layer4. In the fifth step, the cavity26is formed. In the fourth step, the plurality of first electrodes51, the plurality of second electrodes52, the first wiring portion61, and the second wiring portion62are formed using, for example, a photolithography technique, an etching technique, a thin film forming technique, and the like. In the fifth step, a region where the cavity26is expected to be formed in the support substrate2and the silicon oxide film is etched using, for example, a photolithography technique, an etching technique, and the like. In the fifth step, etching is performed using the silicon oxide film7as an etching stopper layer, and then an unnecessary portion of the silicon oxide film7is removed by, for example, etching so as to expose a portion of the second principal surface42of the piezoelectric layer4. In the first step to the fifth step, a silicon wafer is used as the support substrate2, and a piezoelectric wafer is used as the piezoelectric substrate. In the manufacturing method for the acoustic wave device1c, a wafer including a plurality of the acoustic wave devices1cis cut with, for example, a dicing machine to obtain the plurality of acoustic wave devices1c(chips).

The manufacturing method for the acoustic wave device1cis an example and is not particularly limited. For example, the piezoelectric layer4may be formed using a film forming technique. In this case, the manufacturing method for the acoustic wave device1cincludes a step of film-forming the piezoelectric layer4instead of the second step and the third step. The piezoelectric layer4formed by the film forming technique may be, for example, a single crystal or a twin crystal. Examples of the film forming technique include, but are not limited to, a CVD method.

(2.3) Advantageous Effects

The acoustic wave device1caccording to Preferred Embodiment 2, similar to the acoustic wave device1according to Preferred Embodiment 1, includes the piezoelectric layer4, the first electrode51, and the second electrode52. The first electrode51and the second electrode52face each other in the direction D2crossing the thickness direction D1of the piezoelectric layer4. The acoustic wave device1cutilizes a bulk wave of the thickness-shear primary mode. The material of the piezoelectric layer4is, for example, lithium niobate or lithium tantalate. The first electrode51and the second electrode52include, for example, the aluminum layers511and521, respectively, provided on the piezoelectric layer4. The <111> direction of the crystal of each of the aluminum layers511and521is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer4side of each of the aluminum layers511and521. With the configuration described above, in the acoustic wave device1caccording to Preferred Embodiment 2, the Q value may be increased and the distortion characteristics may be improved even when the size of the device is reduced.

The acoustic wave device1caccording to Preferred Embodiment 2, similar to the acoustic wave device1according to Preferred Embodiment 1, includes the piezoelectric layer4, the first electrode51, and the second electrode52. The first electrode51and the second electrode52face each other in the direction D2crossing the thickness direction D1of the piezoelectric layer4. In the acoustic wave device1c, in any cross section along the thickness direction D1of the piezoelectric layer4, when the distance between the center line of the first electrode51and the center line of the second electrode52is denoted as p, and the thickness of the piezoelectric layer4is denoted as d, d/p is not greater than about 0.5. The material of the piezoelectric layer4is, for example, lithium niobate or lithium tantalate. The first electrode51and the second electrode52include, for example, the aluminum layers511and521, respectively, provided on the piezoelectric layer4. The <111> direction of the crystal of each of the aluminum layers511and521is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer4side of each of the aluminum layers511and521. With the configuration described above, in the acoustic wave device1caccording to Preferred Embodiment 2, the Q value may be increased and the distortion characteristics may be improved even when the size of the device is reduced.

The acoustic wave device1caccording to Preferred Embodiment 2 includes the cavity26, such that the energy of the bulk wave is confined in the piezoelectric layer4and an improved Q value may be obtained.

In the acoustic wave device1caccording to Preferred Embodiment 2, the piezoelectric layer4is bonded to the support substrate2with the silicon oxide film7interposed therebetween, but the silicon oxide film7is not a necessary element. In addition to the silicon oxide film7, another layer may be laminated between the support substrate2and the piezoelectric layer4. In the acoustic wave device1caccording to Preferred Embodiment 2, the cavity26passes through the support substrate2in the thickness direction thereof, but is not limited thereto. The cavity26does not pass through the support substrate2, and may be defined by an internal space of a recess provided in the first principal surface21of the support substrate2. The acoustic wave resonator5may include another film (for example, a dielectric film such as the silicon oxide film7) laminated on the second principal surface42of the piezoelectric layer4.

(2.4) Modifications

Preferred Embodiment 2 is merely one of various preferred embodiments of the present invention. Preferred Embodiment 2 may be modified in various ways in accordance with design and the like as long as the advantageous effects of the present invention are obtained.

(2.4.1) Modification 1

Hereinafter, the acoustic wave device1daccording to Modification 1 of Preferred Embodiment 2 will be described with reference toFIG.18. With regard to the acoustic wave device1daccording to Modification 1 of Preferred Embodiment 2, the same or corresponding elements as those of the acoustic wave device1caccording to Preferred Embodiment 2 are denoted by the same reference signs, and description thereof will be omitted.

The acoustic wave device1daccording to Modification 1 of Preferred Embodiment 2 differs from the acoustic wave device1caccording to Preferred Embodiment 2 in that two reflectors8are included as in the acoustic wave device1baccording to Modification 2 of Preferred Embodiment 1. The configuration of each reflector8is the same as or similar to that of each reflector8of the acoustic wave device1b.

(2.4.2) Other Modifications

Modifications 1 to 4 and the other modifications of Preferred Embodiment 1 described above may be applied to the acoustic wave device1caccording to Preferred Embodiment 2 and the acoustic wave device1daccording to Modification 1.

The following preferred embodiments of the present invention are disclosed in the present specification based on the above-described preferred embodiments and the like.

An acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention includes the piezoelectric layer (4), the first electrode (51), and the second electrode (52). The first electrode (51) and the second electrode (52) face each other in the direction (D2) crossing the thickness direction (D1) of the piezoelectric layer (4). The first electrode (51) and the second electrode (52) are adjacent to each other. The acoustic wave device (1;1a;1b;1c;1d) utilizes a bulk wave of the thickness-shear primary mode. The material of the piezoelectric layer (4) is lithium niobate or lithium tantalate. The first electrode (51) and the second electrode (52) include the aluminum layers (511and521), respectively, on the piezoelectric layer (4). The orientation direction of the crystal of each of the aluminum layers (511and521) is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer (4) side of each of the aluminum layers (511and521).

According to the above-described preferred embodiment, it is possible to increase the Q value and improve the distortion characteristics even when the size of the device is reduced.

An acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention includes the piezoelectric layer (4), the first electrode (51), and the second electrode (52). The first electrode (51) and the second electrode (52) face each other in the direction (D2) crossing the thickness direction (D1) of the piezoelectric layer (4). In the acoustic wave device (1;1a;1b;1c;1d), when the distance between the center line of the first electrode (51) and the center line of the second electrode (52) is denoted as p, and the thickness of the piezoelectric layer (4) is denoted as d, d/p is not greater than about 0.5 in any cross section along the thickness direction (D1). The material of the piezoelectric layer (4) is lithium niobate or lithium tantalate. The first electrode (51) and the second electrode (52) include the aluminum layers (511and521), respectively, on the piezoelectric layer (4). The orientation direction of the crystal of each of the aluminum layers (511and521) is a direction orthogonal or substantially orthogonal to the surface on the piezoelectric layer (4) side of each of the aluminum layers (511and521).

According to the above-described preferred embodiment, it is possible to increase the Q value and improve the distortion characteristics even when the size of the device is reduced.

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, the first electrode (51) and the second electrode (52) face each other on the principal surface (for example, the first principal surface41) of the piezoelectric layer (4).

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, an orientation direction is orthogonal or substantially orthogonal to a principal surface (for example, the first principal surface41) of the piezoelectric layer (4).

According to the above-described preferred embodiment, it is possible to increase the Q value and improve the distortion characteristics even when the size of the device is reduced.

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, the aluminum layers (511and521) are epitaxial layers.

According to the above-described preferred embodiment, it is possible to increase the Q value and improve the distortion characteristics even when the size of the device is reduced.

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, Euler angles (φ, θ, ψ) of the piezoelectric layer (4) are about (0°±10°, 0°±10°, ψ).

According to the above-described preferred embodiment, it is possible to increase the Q value and improve the distortion characteristics even when the size of the device is reduced.

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, d/p is equal to or less than about 0.24.

According to the above-described preferred embodiment, it is possible to further increase the fractional bandwidth.

In an acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, the first electrode (51) and the second electrode (52) are adjacent to each other. The first electrode (51) includes the first electrode principal portion (510) intersecting with the second electrode (52) in a direction in which the first electrode (51) and the second electrode (52) face each other. The second electrode (52) includes the second electrode principal portion (520) intersecting with the first electrode (51) in the direction in which the first electrode (51) and the second electrode (52) face each other. In a plan view from the thickness direction (D1), the piezoelectric layer (4) includes the defined region (45) intersecting with both the first electrode (51) and the second electrode (52) in a direction in which the first electrode (51) and the second electrode (52) face each other in the piezoelectric layer (4), and located between the first electrode (51) and the second electrode (52). The acoustic wave device (1;1a;1b;1c;1d) satisfies a relationship of MR≤1.75×(d/p)+0.075. In this case, S1 is an area of the first electrode principal portion (510) in the plan view from the thickness direction (D1). S2 is an area of the second electrode principal portion (520) in the plan view from the thickness direction (D1). S0 is an area of the defined region (45) in the plan view from the thickness direction (D1). MR is a structural parameter defined by an expression of (S1+S2)/(S1+S2+S0).

According to the above-described preferred embodiment, it is possible to reduce or prevent spurious signals within the band.

An acoustic wave device (1;1a;1b;1c;1d) according to a preferred embodiment of the present invention, includes the first wiring portion (61) connected to the first electrode (51) and the second wiring portion (62) connected to the second electrode (52).

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.