Patent Application
20220385271
The present invention relates to an acoustic wave device.
Acoustic wave devices have been widely used in filters for mobile phones and the like. Japanese Unexamined Patent Application Publication No. 2015-073331 discloses an example of an acoustic wave device. In this acoustic wave device, a piezoelectric film is laminated above a support substrate, and an interdigital transducer (IDT) electrode is provided on the piezoelectric film. When a wavelength defined by an electrode finger pitch of the IDT electrode is λ, a thickness of the piezoelectric film is 1λ or less. In Japanese Unexamined Patent Application Publication No. 2015-073331, silicon is disclosed as an example of a material of the support substrate.
However, in the acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2015-073331, it is difficult to sufficiently suppress spurious influence due to higher-order modes in a wide band.
Preferred embodiments of the present invention provide acoustic wave devices that are each able to reduce or prevent higher-order modes in a wide band.
An acoustic wave device according to a preferred embodiment of the present invention includes a support substrate, a piezoelectric film directly or indirectly on the support substrate, and an IDT electrode on the piezoelectric film, in which when a wavelength defined by an electrode finger pitch of the IDT electrode is λ, a thickness of the piezoelectric film is about 1λ or less, the piezoelectric film is a lithium tantalate film or a lithium niobate film, the piezoelectric film has crystal axes [XP, YP, ZP], the support substrate includes a first silicon layer and a second silicon layer on the first silicon layer, and the second silicon layer is closer to the piezoelectric film than the first silicon layer is in the support substrate, a plane orientation of each of the first silicon layer and the second silicon layer is one of (100), (110), and (111), in a silicon layer having a plane orientation of (111), when a direction vector obtained by projecting the ZP axis onto a (111) plane of the silicon layer is k111, an angle between the direction vector k111 and a [11-2] direction of silicon of the silicon layer is an angle α111, in a silicon layer having a plane orientation of (110), when a direction vector obtained by projecting the ZP axis onto a (110) plane of the silicon layer is k110, an angle between the direction vector k110 and a [001] direction of silicon of the silicon layer is an angle α110, in a silicon layer having a plane orientation of (100), when a direction vector obtained by projecting the ZP axis onto a (100) plane of the silicon layer is k100, an angle between the direction vector k100 and the [001] direction of silicon of the silicon layer is an angle α100, when an angle between the plane orientation of the first silicon layer and the crystal axes of the piezoelectric film is an angle α1, and an angle between the plane orientation of the second silicon layer and the crystal axes of the piezoelectric film is an angle α2, each of the angle α1 and the angle α2 is one of three types of angles of the angle α100, the angle α110, and the angle (Xiii, and a type of the angle α1 is different from a type of the angle α2 and/or a value of the angle α1 is different from a value of the angle α2.
Acoustic wave devices according to preferred embodiments of the present invention are each able to reduce or prevent higher-order modes in a wide band.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Hereinafter, the present invention will be clarified by describing preferred embodiments of the present invention with reference to the drawings.
Each of the preferred embodiments described in the present specification is illustrative and partial replacement or combination of configurations of different preferred embodiments can be provided.
As illustrated in
An IDT electrode 8 is provided on the piezoelectric film 7. By applying an AC voltage to the IDT electrode 8, acoustic waves are excited. As illustrated in
As illustrated in
The IDT electrodes 8, the reflector 9A, and the reflector 9B may include a single-layer metal film or a multi-layer metal film.
Referring back to
Here, when a wavelength defined by an electrode finger pitch of the IDT electrode 8 is λ, a thickness of the piezoelectric film 7 is, for example, about 1λ or less. This can suitably increase a Q factor. The electrode finger pitch refers to a distance between the centers of electrode fingers adjacent to each other. Specifically, the electrode finger pitch refers to a distance between center points of the adjacent electrode fingers in the acoustic wave propagation direction, that is, the X direction. When the distance between the centers of the electrode fingers is not constant, the electrode finger pitch is defined as an average value of the distances between the centers of the electrode fingers.
The first intermediate layer 5 is, for example, a silicon oxide film. The silicon oxide can be represented by SiOx. x is a positive number. In the present preferred embodiment, the first intermediate layer 5 is, for example, a SiO2 film. However, x is not limited to 2. The first intermediate layer 5 may include silicon oxide. Thus, the frequency-temperature characteristic can be improved.
In the acoustic wave device 1, the piezoelectric film 7 is provided directly on the first intermediate layer 5. The piezoelectric film 7 may be indirectly provided on the first intermediate layer 5 with another intermediate layer interposed therebetween. Alternatively, the acoustic wave device 1 does not necessarily include the first intermediate layer 5. The piezoelectric film 7 may be provided directly on the support substrate 2.
The support substrate 2 includes a first silicon layer 3 and a second silicon layer 4. The second silicon layer 4 is laminated on the first silicon layer 3. Here, an adhesive layer having a thickness of, for example, approximately 30 nm or less may be provided between the first silicon layer 3 and the second silicon layer 4. In the support substrate 2, the second silicon layer 4 is located closer to the piezoelectric film 7 than the first silicon layer 3 is.
Here, an angle between a plane orientation of the silicon layer and crystal axes of the piezoelectric film is defined as an angle α. Further, an angle α defined by a relationship between a plane orientation of the first silicon layer 3 and crystal axes of the piezoelectric film 7 is defined as an angle α1. An angle α between a plane orientation of the second silicon layer 4 and the crystal axes of the piezoelectric film 7 is defined as an angle α2. Details of the angle α1 and the angle α2 will be described later.
The present preferred embodiment is characterized in that the support substrate 2 includes the first silicon layer 3 and the second silicon layer 4, and the angle α1 and the angle α2 are different from each other. “The angle α1 and the angle α2 are different from each other” means that the types of angles determined by the plane orientation of the silicon layer are different from each other or the values of the angles are different from each other. This makes it possible to reduce or prevent higher-order modes in a wide band. Details of this advantageous effect will be described below together with definitions of the crystal axes, the plane orientation, the angle α1 and the angle 062, and the like.
The first silicon layer 3 and the second silicon layer 4 are silicon single crystal layers. As illustrated in
The plane orientation of the first silicon layer 3 of the present preferred embodiment is (111). The plane orientation being (111) indicates that the substrate or layer is cut in the (111) plane orthogonal or substantially orthogonal to crystal axes represented by Miller indices [111] in the crystal structure of silicon having a diamond structure. The (111) plane is a plane illustrated in
The plane orientation of the second silicon layer 4 of the present preferred embodiment is (100). The plane orientation being (100) indicates that the substrate or layer is cut in the (100) plane orthogonal or substantially orthogonal to crystal axes represented by Miller indices [100] in the crystal structure of silicon having a diamond structure. The crystal structure has in-plane four-fold symmetry in the (100) plane and becomes an equivalent crystal structure when rotated by 90°. The (100) plane is a plane illustrated in
On the other hand, the plane orientation being (110) indicates that the substrate or layer is cut in the (110) plane orthogonal or substantially orthogonal to crystal axes represented by Miller indices [110] in the crystal structure of silicon having a diamond structure. The crystal structure has in-plane two-fold symmetry in the (110) plane and becomes an equivalent crystal structure when rotated by 180°. The (110) plane is a plane illustrated in
In the following, the angle α and a direction vector k described later will be described in detail. The angle α is one of three types of angles: α111, α110, and α100. The direction vector k is one of k111, k110, and k100.
Here, as illustrated in
As illustrated in
On the other hand, in the silicon layer having the plane orientation of (110), a direction vector obtained by projecting the ZP axis onto the (110) plane of the silicon layer is defined as k110. The angle α110 is an angle between the direction vector k110 and a [001] direction of silicon of the silicon layer. The [001] direction, a [100] direction, and a [010] direction are equivalent due to the symmetry of the silicon crystal.
In the silicon layer having the plane orientation of (100), a direction vector obtained by projecting the ZP axis onto the (100) plane of the silicon layer is defined as k100. The angle α100 is an angle between the direction vector k100 and a [001] direction of silicon of the silicon layer.
The definitions of the direction vector k and the angle α are the same regardless of whether the silicon layer is laminated directly on the piezoelectric film or laminated indirectly on the piezoelectric film with another layer interposed therebetween. In the case illustrated in
However, the plane orientations of the first silicon layer 3 and the second silicon layer 4 are not limited to those described above. The plane orientation of each of the first silicon layer 3 and the second silicon layer 4 may be one of (100), (110), and (111). Each of the angle α1 and the angle α2 is one of three types of angles: the angle α100, the angle α110, and the angle α111.
More specifically, when the plane orientation of the first silicon layer 3 is (100), the angle α1 is the angle α100 angle. When the plane orientation of the first silicon layer 3 is (110), the angle α1 is the angle α110. When the plane orientation of the first silicon layer 3 is (111), the angle α1 is the angle α111.
Similarly, when the plane orientation of the second silicon layer 4 is (100), the angle α2 is the angle α100. When the plane orientation of the second silicon layer 4 is (110), the angle α2 is the angle α110. When the plane orientation of the second silicon layer 4 is (111), the angle α2 is the angle α111.
In the case in which the plane orientation of the first silicon layer 3 is (100) or (110), the behavior of the acoustic wave device when the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7 is the same or substantially the same as the behavior of the acoustic wave device when the IDT electrode 8 is provided on the negative surface. The same applies to the second silicon layer 4.
On the other hand, in the case in which the plane orientation of the first silicon layer 3 is (111), the behavior of an acoustic wave device 1 when the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7 is different from the behavior of an acoustic wave device 1 when the IDT electrode 8 is provided on the negative surface. More specifically, both of the acoustic wave devices 1 have behaviors in which the angles α1 are shifted by about 60° from each other. For example, the behavior when the value of the angle α1 satisfies α1=α in the case in which the IDT electrode 8 is provided on the negative surface is the same as the behavior when the value of the angle α1 satisfies α1=a+60° in the case in which the IDT electrode 8 is provided on the positive surface. The same applies to the second silicon layer 4.
The plane orientations of the first silicon layer 3 and the second silicon layer 4 may be the same or different. When the plane orientations of the first silicon layer 3 and the second silicon layer 4 are the same, the angle α1 and the angle α2 are the same type of angles. In this case, the values of the angle α1 and the angle α2 may be different. On the other hand, when the plane orientations of the first silicon layer 3 and the second silicon layer 4 are different, the angle α1 and the angle α2 are different types of angles. In this case, the value of the angle α1 and the value of the angle α2 may be the same or different. In this manner, the type of the angle α1 may be different from the type of the angle α2 and/or the value of the angle α1 may be different from the value of the angle α2.
Comparison of the present preferred embodiment with a first comparative example and a second comparative example shows that the higher-order modes can be reduced or prevented in a wide band in the acoustic wave device 1.
As illustrated in
Impedance frequency characteristics of the acoustic wave device having the configuration of the first preferred embodiment and the acoustic wave devices of the first comparative example and the second comparative example were compared. Design parameters of the acoustic wave device having the configuration of the first preferred embodiment are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, about 0°), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (about 0°, about 0°, about 45°), thickness: about 1 μm
First intermediate layer 5; material: SiO2, thickness: about 300 nm
Piezoelectric film 7; material: 40° Y-cut X-propagation LiTaO3, Euler angles (about 0°, about 130°, about 0°), thickness: about 400 nm
Angle α1; type: angle α111, value: about 0°
Angle α2; type: angle α100, value: about 45°
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
The first comparative example has design parameters the same as or similar to those of the acoustic wave device having the configuration of the first preferred embodiment, except that the plane orientation of the support substrate 102 is (111) and the Euler angles are (about −45°, about −54.7°, about 73°). The second comparative example has design parameters the same as or similar to those of the acoustic wave device having the configuration of the first preferred embodiment, except that the plane orientation of the support substrate 102 is (100) and the Euler angles are (about 0°, about 0°, about 0°).
As indicated by arrow A in
Here, in an acoustic wave device having a configuration the same as or similar to that illustrated in
The crystal structure has in-plane four-fold symmetry in the (100) plane of the silicon layer and becomes an equivalent crystal structure when rotated by about 90°. Thus, when the plane orientation of the first silicon layer 3 is (100), the value of the angle α1 satisfies α1=α1100+about 90×n. n is an integer (0, ±1, ±2, . . . ). When the plane orientation of the second silicon layer 4 is (100), the value of the angle α2 satisfies α2=α2100+about 90×m. m is an integer (0, ±1, ±2, . . . ). n and m may be the same or different.
The crystal structure has in-plane two-fold symmetry in the (110) plane of the silicon layer and becomes an equivalent crystal structure when rotated by about 180°. Thus, when the plane orientation of the first silicon layer 3 is (110), the value of the angle α1 satisfies α1=α1110+about 180×n. When the plane orientation of the second silicon layer 4 is (110), the value of the angle α2 satisfies β2=β2110+about 180×m.
In the case in which the plane orientation of the first silicon layer 3 is (100) or (110), the behavior of the acoustic wave device when the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7 is the same or substantially the same as the behavior of the acoustic wave device when the IDT electrode 8 is provided on the negative surface. The same applies to the second silicon layer 4. Thus, when the plane orientation of the first silicon layer 3 is (100) or (110), the value of the angle α1 is expressed as the same or substantially the same value regardless of whether the IDT electrode 8 is provided on the positive surface or the negative surface. When the plane orientation of the second silicon layer 4 is (100) or (110), the value of the angle α2 is expressed as the same or substantially the same value regardless of whether the IDT electrode 8 is provided on the positive surface or the negative surface.
The crystal structure has in-plane three-fold symmetry in the (111) plane of the silicon layer and becomes an equivalent crystal structure when rotated by about 120°. Further, in the acoustic wave device used to measure the phase of the higher-order mode, the IDT electrode 8 is provided on the negative surface of the piezoelectric film 7. Thus, in the case in which the plane orientation of the first silicon layer 3 is (111), the value of the angle α1 when the IDT electrode 8 is provided on the negative surface of the piezoelectric film 7 satisfies α1=α1111+about 120×n. Here, in the case in which the plane orientation of the first silicon layer 3 is (111), the acoustic wave device when the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7 and the acoustic wave device when the IDT electrode 8 is provided on the negative surface exhibit behaviors in which the angles α1 are shifted by about 60° from each other. Thus, when the plane orientation of the first silicon layer 3 is (111) and the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7, the value of the angle α1 satisfies α1=α1111+about 60+about 120×n. Similarly, in the case in which the plane orientation of the second silicon layer 4 is (111), the value of the angle α2 when the IDT electrode 8 is provided on the negative surface of the piezoelectric film 7 satisfies α2=α2111+about 120×m. When the plane orientation of the second silicon layer 4 is (111) and the IDT electrode 8 is provided on the positive surface of the piezoelectric film 7, the value of the angle α2 satisfies α2=α2111+about 60+about 120×m.
Ranges in which the angle α1 and the angle α2 are varied will be described in detail. The plane orientation of the first silicon layer 3 was set to (100), (110), or (111), and the angle α1 was varied. When the plane orientation of the first silicon layer 3 was (100), α1100 was varied in 5° increments in a range of about 0° to about 45°. When the plane orientation of the first silicon layer 3 was (110), α1110 was varied in 10° increments in a range of about 0° to about 90°. When the plane orientation of the first silicon layer 3 was (111), α1111 was varied in 5° increments in a range of about 0° to about 60°. Further, the plane orientation of the second silicon layer 4 was set to (100), (110) or (111), and the angle α2 was varied. When the plane orientation of the second silicon layer 4 was (100), α2100 was varied in 5° increments in a range of about 0° to about 45°. When the plane orientation of the second silicon layer 4 was (110), α2110 was varied in 10° increments in a range of about 0° to about 90°. When the plane orientation of the second silicon layer 4 was (111), α2111 was varied in 5° increments in a range of about 0° to about 60°. The higher-order modes were measured each time the angle α1 and the angle α2 were varied. The measured higher-order modes are higher-order modes at about 3.0 times or less the resonant frequency.
In the following, a range for the angle α1 and the angle α2 in which the phase of the higher-order mode is about −70 deg or less is shown in the drawings and tables. In the present specification, [deg] and [° ] are the same units.
Table 1 shows the range in which the phase of the higher-order mode is about −70 deg or less shown in
It is known that the angle α within the range of about ±2.5° or about ±5° does not significantly affect the higher-order mode. Thus, in Table 1, all α1100 and α2100 are described as being within the range of about ±2.5°. In the present specification and each table, for example, 0±about 2.5(°) indicates a range of −about 2.5° to about 2.5°. In tables other than Table 1, the angle α may be described as being within the range of about ±5°.
When α1100 and α2100 are any of the combinations shown in Table 1, the phase of the higher-order mode can be reduced or prevented to about −70 deg or less. Thus, the higher-order modes can be effectively reduced or prevented under the conditions shown in Table 1.
When α1100 and α2110 are any of the combinations shown in Table 2, the higher-order modes can be effectively reduced or prevented.
When α1100 and α2111 are any of the combinations shown in Table 3, the higher-order modes can be effectively reduced or prevented.
When α1110 and α2100 are any of the combinations shown in Table 4, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2100 are any of the combinations shown in Table 5, the phase of the higher-order mode can be reduced to about −80 deg or less. Thus, the higher-order modes can be further reduced or prevented under the conditions shown in Table 5.
When α1110 and α2110 are any of the combinations shown in Table 6, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2110 are any of the combinations shown in Table 7, the higher-order modes can be further reduced or prevented.
When α1110 and α2111 are any of the combinations shown in Table 8, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2111 are any of the combinations shown in Table 9, the higher-order modes can be further reduced or prevented.
When α1111 and α2100 are any of the combinations shown in Table 10, the higher-order modes can be effectively reduced or prevented. Further, when α1111 and α2100 are any of the combinations shown in Table 11, the higher-order modes can be further reduced or prevented.
When α1111 and α2110 are any of the combinations shown in Table 12, the higher-order modes can be effectively reduced or prevented. Further, when α1111 and α2110 are any of the combinations shown in Table 13, the higher-order modes can be further reduced or prevented.
When α1111 and α2111 are any of the combinations shown in Table 14, the higher-order modes can be effectively reduced or prevented.
As illustrated in
A thickness of the second silicon layer 4 is preferably equal to or less than a thickness of the first silicon layer 3. The thickness of the second silicon layer 4 is more preferably smaller than the thickness of the first silicon layer 3. In these cases, since waves excited by the IDT electrode 8 suitably propagate to the first silicon layer 3, the advantageous effect of reducing or preventing the higher-order modes in a wide range is suitably achieved.
The present preferred embodiment is different from the first preferred embodiment in that a second intermediate layer 26 is provided between the first intermediate layer 5 and the piezoelectric film 7. Except for the above point, the acoustic wave device according to the present preferred embodiment has a configuration the same as or similar to that of the acoustic wave device 1 according to the first preferred embodiment.
The plane orientation of the first silicon layer 3 in the present preferred embodiment is (111), the Euler angles are (−about 45°, about −54.7°, about 0°), the angle α1 is the angle α111, and the value of the angle α1 is about 0°. The plane orientation of the second silicon layer 4 is (100), the Euler angles are (about 0°, about 0°, about 45°), the angle α2 is the angle α100, and the value of the angle α2 is about 45°. The second intermediate layer 26 is, for example, a silicon nitride film. The second intermediate layer 26 may be, for example, a film including silicon nitride.
Also in the present preferred embodiment, the higher-order modes can be reduced or prevented in a wide band. This will be demonstrated in the following by comparing the second preferred embodiment with the first preferred embodiment. Design parameters of the acoustic wave device having the configuration of the second preferred embodiment are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, about 0°), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (about 0°, about 0°, about 45°), thickness: about 1 μm
First intermediate layer 5; material: SiO2, thickness: about 300 nm
Second intermediate layer 26; material: SiN, thickness: about 50 nm
Piezoelectric film 7; material: 40° Y-cut X-propagation LiTaO3, Euler angles (about 0°, about 130°, about 0°), thickness: about 400 nm
Angle α1; type: angle α111, value: about 0°
Angle α2; type: angle α100, value: about 45°
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
In both of the first preferred embodiment and the second preferred embodiment, it is possible to reduce or prevent the higher-order modes in a wide band indicated by a long dashed short dashed line in
The piezoelectric film 7 may be, for example, a lithium tantalate film or a lithium niobate film. On the other hand, the second intermediate layer 26 is, for example, a silicon nitride film. In this case, the acoustic velocity of the bulk wave propagating through the second intermediate layer 26 is higher than the acoustic velocity of the acoustic wave propagating through the piezoelectric film 7. Thus, the second intermediate layer 26 is a high acoustic velocity film. In the present preferred embodiment, since the second intermediate layer 26 as a high acoustic velocity film is laminated, the higher-order modes can be further reduced or prevented.
Here, the phase of the higher-order mode was measured for different thicknesses of the second silicon layer 4. The measured higher-order modes are higher-order modes at about 3.0 times or less the resonant frequency. More specifically, the thickness of the second silicon layer 4 was varied in 0.1 μm increments in a range of about 0.1 μm to about 3 μm. The wavelength λ was set to about 2 μm. Thus, when expressed based on λ, the thickness of the second silicon layer 4 is varied in 0.05λ increments in a range of about 0.05λ to about 1.5λ. Design parameters of the acoustic wave device for which the phase of the higher-order mode were measured are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, about 0°), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (0°, 0°, 45°), thickness: varied in 0.1 μm increments in the range of 0.1 μm to 3 μm.
First intermediate layer 5; material: SiO2, thickness: about 300 nm
Second intermediate layer 26; material: SiN, thickness: about 50 nm
Piezoelectric film 7; material: about 40° Y-cut X-propagation LiTaO3, Euler angles (about 0°, about 130°, about 0°), thickness: about 400 nm
Angle α1; type: angle α111, value: about 0°
Angle α2; type: angle α100, value: about 45°
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
As shown in
Further, by varying θ in Euler angles (φ, θ, ψ) of the piezoelectric film 7, a phase of Rayleigh waves as unwanted waves was measured. Note that φ and γ in the Euler angles were set to about 0°. Design parameters of the acoustic wave device for which the phase of Rayleigh waves was measured are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, about 0°), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (about 0°, about 0°, about 45°), thickness: about 1 μm
First intermediate layer 5; material: SiO2, thickness: about 300 nm
Second intermediate layer 26; material: SiN, thickness: about 50 nm
Piezoelectric film 7; material: Y-cut X-propagation
LiTaO3, cut-angles: varied in 5° increments in a range of about 0° to about 60°. θ in Euler angles (0°, θ, 0°): varied in 5° increments in a range of about 900 to about 150°. Thickness: about 400 nm
Angle α1; type: angle α111, value: about 0°
Angle α2; type: angle α100, value: about 450
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
As shown in
Here, in an acoustic wave device having a configuration the same as or similar to that illustrated in
When α1100 and α2100 are any of the combinations shown in Table 15, the phase of the higher-order mode can be suppressed to about −70 deg or less. Thus, the higher-order modes can be effectively reduced or prevented under the conditions shown in Table 15.
When α1100 and α2110 are any of the combinations shown in Table 16, the higher-order modes can be effectively reduced or prevented.
When α1100 and α2111 are any of the combinations shown in Table 17, the higher-order modes can be effectively reduced or prevented. Further, when α1100 and α2111 are any of the combinations shown in Table 18, the phase of the higher-order mode can be suppressed to about −80 deg or less. Thus, the higher-order modes can be further reduced or prevented under the conditions shown in Table 18.
When α1110 and α2100 are any of the combinations shown in Table 19, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2100 are any of the combinations shown in Table 20, the phase of the higher-order mode can be suppressed to about −80 deg or less. Thus, the higher-order modes can be further reduced or prevented under the conditions shown in Table 20.
When α1110 and α2110 are any of the combinations shown in Table 21, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2110 are any of the combinations shown in Table 22, the higher-order modes can be further reduced or prevented.
When α1110 and α2111 are any of the combinations shown in Table 23, the higher-order modes can be effectively reduced or prevented. Further, when α1110 and α2111 are any of the combinations shown in Table 24, the higher-order modes can be further reduced or prevented.
When α1111 and α2100 are any of the combinations shown in Table 25, the higher-order modes can be effectively reduced or prevented. Further, when α1111 and α2100 are any of the combinations shown in Table 26, the higher-order modes can be further reduced or prevented.
When α1111 and α2110 are any of the combinations shown in Table 27, the higher-order modes can be effectively reduced or prevented. Further, when α1111 and α2110 are any of the combinations shown in Table 28, the higher-order modes can be further reduced or prevented.
When α1111 and α2111 are any of the combinations shown in Table 29, the higher-order modes can be effectively reduced or prevented.
In the above, an example in which the piezoelectric film 7 is a lithium tantalate film is described. In the following, an example in which the piezoelectric film 7 is a lithium niobate film will be described with reference to
A third preferred embodiment of the present invention is different from the second preferred embodiment in that the piezoelectric film 7 is a lithium niobate film. Except for the above point, the acoustic wave device according to the third preferred embodiment has a configuration the same as or similar to that of the acoustic wave device according to the second preferred embodiment.
Here, phase characteristics were compared between the acoustic wave device having the configuration of the third preferred embodiment and a third comparative example. The third comparative example is different from the third preferred embodiment in that the support substrate includes a single silicon layer. Design parameters of the acoustic wave device having the configuration of the third preferred embodiment in which the phase characteristic was measured are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, about 0°), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (about 0°, about 0°, about 45°), thickness: about 1 μm
First intermediate layer 5; material: SiO2, thickness: about 300 nm
Second intermediate layer 26; material: SiN, thickness: about 50 nm
Piezoelectric film 7; material: about 0° Y-cut X-propagation LiNbO3, Euler angles (about 0°, about 120°, about 0°), thickness: about 400 nm
Angle α1; type: angle α111, value: about 0°
Angle α2; type: angle α100, value: about 45°
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
As shown in
The fourth preferred embodiment is different from the second preferred embodiment in that the second intermediate layer 26 is provided between the first intermediate layer 5 and the support substrate. Except for the above point, the acoustic wave device according to the fourth preferred embodiment has a configuration the same as or similar to the acoustic wave device according to the second preferred embodiment.
Here, as an example, it is shown that the higher-order modes can be effectively reduced or prevented when 40° Y-cut X-propagation LiTaO3 is used for the piezoelectric film 7. In the acoustic wave device having the configuration of the fourth preferred embodiment, the phase of the higher-order mode was measured by varying specific parameters. Thus, a relationship between the specific parameters and the phase of the higher-order mode was obtained. As the specific parameters mentioned above, ψ in Euler angles (φ, θ, ψ) of the first silicon layer 3 is Si_psi [deg], ψ in Euler angles (φ, θ, ψ) of the second silicon layer 4 is si_psi_2 [deg], the thickness of the second silicon layer 4 is t_Si2[λ], the thickness of the second intermediate layer 26 is t_SiN[λ], the thickness of the first intermediate layer 5 is t_SiO2[λ], and the thickness of the piezoelectric film 7 is t_LT [X]. The phase of the higher-order mode is represented by Pkj [deg]. As described above, [deg] and [° ] are the same units. Design parameters of the acoustic wave device for which the phase of the higher-order mode was obtained are as follows.
First silicon layer 3; plane orientation: (111), Euler angles (about −45°, about −54.7°, Si_psi), thickness: about 20 μm
Second silicon layer 4; plane orientation: (100), Euler angles (about 0°, about 0°, si_psi_2), thickness: t_Si2
Second intermediate layer 26; material: SiN, thickness: t_SiN
First intermediate layer 5; materials: SiO2, thickness: t_SiO2
Piezoelectric film 7; material: about 40° Y-cut X-propagation LiTaO3, Euler angles (about 0°, about 130°, about 0°), thickness: t_LT
Angle α1; type: angle α111, value: varied in 5° increments in a range of about 0° to about 60°.
Angle α2; type: angle α100, value: varied in 5° increments in a range of about 0° to about 45°.
Layer configuration of IDT electrode 8; layer configuration: (Ti layer)/(AlCu layer (Cu-1 wt. %))/(Ti layer) from piezoelectric film 7 side, thickness: (about 12 nm)/(about 100 nm)/(about 4 nm) from piezoelectric film 7 side
Wavelength λ of IDT electrode 8; about 2 μm
Duty ratio of IDT electrode 8; about 0.5
The specific parameters were varied in the following ranges:
Si_psi; the angle α1 was varied as described above by varying in 5 deg increments in a range of about 0 deg to about 60 deg.
si_psi_2; the angle α2 was varied as described above by varying in 5 deg increments in a range of about 0 deg to about 45 deg.
t_Si2; varied 0.05λ increments in a range of about 0.05λ to about 1λ.
t_SiN; varied in 0.1λ increments in a range of about 0.05λ to about 0.35λ.
t_SiO2; varied in 0.025λ increments in a range of about 0.1λ to about 0.2λ.
t_LT; varied in 0.025λ increments in a range of about 0.15λ to about 0.2Δ.
In the acoustic wave device for which the phase of the higher-order mode was obtained, the IDT electrode 8 is provided on the negative surface of the piezoelectric film 7. The measured higher-order modes are higher-order modes at about 3.0 times or less the resonant frequency. Equation 1, which is a relational equation between the specific parameters and the phase of the higher-order mode, was derived from the above measurements.
Pkj[deg]=(−71.2068602606219)+331.629446317838×(t_LTλ]−0.173291148291141)+(−22.7224910522243)×(t−SiO2[λ]1−0.133361933361938)+70.1603362058α21×(t_SiN[λ]1−0.0694258544258521)+20.4186870884974×(t_Si2[λ]−0.432632632632632)+(−0.0795718195965644)×(si_psi_2[deg]−15.1794651794652)+(−0.0801661426763212)×(Si_psi[deg]−21.3234663234663)+(−8265.27531314391)×((t−LTλ]−0.173291148291141)×(t_LTλ]−0.173291148291141)−0.000254658833416191)+(−702.352467513552)×((t_LTλ]−0.173291148291141)×(t_SiO2[λ]−0.133361933361938))+(−159.217489977571)×((t_SiO2[λ1]−0.133361933361938)×(t_SiO2[λ]−0.133361933361938)−0.00220941097478356)+1181.94608028125×((t_LTλ]−0.173291148291141)×(t_SiN[λ]−0.0694258544258521))+148.194177052574×((t_SiO2[λ1]−0.133361933361938)×(t_SiN[λ]−0.0694258544258521))+(−138.414297240254)×((t_SiN[λ]−0.0694258544258521)×(t_SiN[λ]−0.0694258544258521)−0.00607933216152169)+(−73.8108320642126)×((t_LT[λ]−0.173291148291141)×(t_Si2[λ]−0.432632632632632))+22.3596977549241×((t_SiO2[λ]−0.133361933361938)×(t_Si2[λ]−0.432632632632632))+(−180.302445874872)×((t_SiN[λ]−0.0694258544258521)×(t_Si2[λ]−0.432632632632632))+58.1189523422145×((t_Si2[λ]−0.432632632632632)×(t__Si2[λ]−0.432632632632632)−0.0206911530435046)+(−0.0892573877283934)×((t_LT[λ]−0.173291148291141)×(si_psi−2[deg]−15−1794651794652))+0.1α2191016582739×((t_SiO2[λ]−0.133361933361938)×(si_psi_2[deg]−15.1794651794652))+(−0.566877950267944)×((t_SiN[λ]−0,0694258544258521)×(si_psi_2[deg]−15.1794651794652))+(−0.523218662939604)×((t_Si2[λ1]−0.432632632632632)×(si_psi_2[deg]−15.1794651794652))+0.0α111049675010859×((si_psi_2[deg]−15.1794651794652)×(si_psi_2[deg]−15.1794651794652)−260,117227398797)+2.43575857272564×((t_LTλ]−0.173291148291−141)×(Si_psi[deg]−21.3234663234663))+(−0.269547003578196)×((t_SiO2[λ]−0.133361933361938)×(Si_psi[deg]−21.3234663234663))+(−0.235856493743728)×((t_SiN[λ]−0.0694258544258521)×(Si_psi[deg]−21.3234663234663))+0.475976492439799×((t_Si2[λ]−0.432632632632632)×(Si_psi[deg]−21.3234663234663))+0.00288777512919308×((si_psi_2[deg]−15.1794651794652)×(Si_psi[deg]−21.3234663234663))+0.00174948079902691×((Si_psi[deg]−213234663234663)×(Si_psi[deg]−21.3234663234663)−553.32136696361) Equation 1
It is preferable that Si_psi, si_psi_2, t_Si2, t_SiN, t_SiO2, and t_LT are within ranges of angles and thicknesses in which Pkj in Equation 1 is about −70 deg or less. This makes it possible to reduce or prevent higher-order modes more reliably and effectively.
Further, it is shown that the higher-order modes can be effectively reduced or prevented when, for example, 35° Y-cut X-propagation LiTaO3 is used for the piezoelectric film 7. Euler angles of this piezoelectric film 7 are (about 0°, about 125°, about 0°). In the acoustic wave device having the configuration of the fourth preferred embodiment, Equation 2, which is a relational equation between the specific parameters and the phase of the higher-order mode, was derived. Design parameters of the acoustic wave device other than the cut-angles and the Euler angles of the piezoelectric film 7 were the same or substantially the same as those used when Equation 1 was derived. The ranges of variations of the specific parameters were the same as when Equation 1 was derived.
Pkj[deg]=(−68.3045028100257)+148.009830991658×(t_LT[λ]−0.182938408896478)+(−31.7023619287189)×(t_SiO2[λ1]−0.131180496150558)+59.9941−196381256×(t_SiN[λ]−0.0722326775621397)+28.3891130547491×(t_Si2[λ]−0.457408041060735)+(−0.0551187486931435)×(si_psi_2[deg]−23.8177929854577)+0.00621179951505866×(Si_psi[deg]−33.7339606501283)+(−307.104268249355)×((t_LT[λ]−0,182938408896478)×(t_SiO2[λ]−0.131180496150558))+k(−221.090307531174)×((t_SiO2[λ]−0.131180496150558)×(t_SiO2[λ]−0131180496150558)−0.00245634808837649)+3.0630243958978×((t_LT[λ]−0.182938408896478)×(t_SiN[λ]−0.0722326775021397))+26.3784321839523×((t_SiO2[λ1]−0.131180496150558)×(t_SiN[λ]−0.0722326775021397))+(−149.210462980265)×((t_SiN[λ]−0.0722326775021397)×(t_SiN[λ]−0.0722326775021397)−0.00538017340609054)+16.5185556736186×((t_LT[λ]−0.182938408896478)×(t_Si2[λ]−0.457408041060735))+56.1146358518209×((t_SiO2[λ]−0.1311804961.50558)×(t_Si2[λ]−0.457408041060735))+(−231.9230984773)×((t_SiN[λ]−0.0722326775021397)×(t_Si2[λ]−0.457408041060735))+(−9,26166386908678)×((t_Si2[λ]−0.457408041060735)×(t_Si2[λ]−0.457408041060735)−0.00796565129547814)+(−0.0982556479630247)×((t_LT[λ]−0.182938408896478)×(si_psi_2[deg]−23.8177929854577))+(−0.144777667964478)×((t_SiO2[λ]−0.131180496150558)×(si_psi_2[deg]−23.8177929854577))+(−0.121859651665675)×((t_SiN[λ]−0.0722326775α21397)×(si_psi_2[deg]−23.8177929854577))+(−0.337942081738039)×((t_Si2[λ]−0.457408041060735)×(si_psi_2[deg]−23.8177929854577))+0.0000092550445874239×((si_psi_2[deg]−23.8177929854577)×(si_psi_2[deg]−23.8177929854577)−211.955679987944)+1.28762234468537×((t_LT[λ]−0.182938408896478)×(Si_psi[deg]−33.7339606501283))+(−0.350061531387324)×((t_SiO2[λ]−0.131180496150558)×(Si_psi[deg]−33.7339606501283))+(−0.155177588775029)×((t_SiN[λ]−0.0722326775α21397)×(Si_psi[deg]−33.7339606501283))+0.305377220918695×((t_Si2[λ]−0.457408041060735)×(Si_psi[deg]−33.7339606501283))+0.00184222592354461×((si_psi_2[deg]−23.8177929854577)×(Si_psi[deg]−33.7339606501283))+0.00210385689952457×((Si_psi[deg]−33.7339606501283)×(Si_psi[deg]−33.7339606501283)−454.804329993321) Equation 2
It is preferable that Si_psi, si_psi_2, t_Si2, t_SiN, t_SiO2, and t_LT are within ranges of angles and thicknesses in which Pkj in Equation 2 is about −70 deg or less. This makes it possible to reduce or prevent higher-order modes more reliably and effectively.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-024257 | Feb 2020 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2020-024257 filed on Feb. 17, 2020 and is a Continuation Application of PCT Application No. PCT/JP2021/005611 filed on Feb. 16, 2021. The entire contents of each application are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/005611 | Feb 2021 | US |
| Child | 17880848 | US |
