Patent Application
20250158593
The present invention relates to acoustic wave devices and filter devices.
In the related art, acoustic wave devices are widely used for, for example, filters of mobile phones. International Publication No. 2011/108229 discloses an example of an acoustic wave device. In the acoustic wave device, an interdigital transducer (IDT) electrode is provided on a piezoelectric substrate. The shape of a plurality of electrode fingers of the IDT electrode includes a curved shape. More specifically, each electrode finger extends along a curve from the center of a region where the IDT electrodes intersect to a common electrode.
In an IDT electrode of an acoustic wave device described in International Publication No. 2011/108229, an electrode finger pitch in the central portion in the direction in which a plurality of electrode fingers extend is narrower than an electrode finger pitch at an end portion in the direction. Therefore, there is an effect of suppressing the response of the unnecessary wave to a certain degree. However, it is impossible to sufficiently reduce or prevent an unnecessary wave outside a pass band or a transverse mode.
Example embodiments of the present invention provide acoustic wave devices and filter devices each capable of sufficiently reducing or preventing an unnecessary wave outside a pass band and a transverse mode.
An acoustic wave device according to an example embodiment of the present invention includes a piezoelectric substrate including a piezoelectric layer, and an IDT electrode on the piezoelectric layer, wherein the IDT electrode includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers of which one end portion is connected to the first busbar, and a plurality of second electrode fingers of which one end portion is connected to the second busbar, and the plurality of first electrode fingers and the plurality of second electrode fingers are interdigitated with each other, shapes of the plurality of first electrode fingers and the plurality of second electrode fingers in a plan view include a shape of a circular arc or an elliptical arc, and when a virtual line formed by connecting tip ends of the plurality of second electrode fingers is defined as a first envelope, a virtual line formed by connecting tip ends of the plurality of first electrode fingers is defined as a second envelope, and a center of a circle including the circular arc or a midpoint of two focal points of an ellipse including the elliptical arc in the shapes of the first electrode fingers and the second electrode fingers is defined as a fixed point, a straight line connecting the fixed point and a tip end of a second electrode finger is not parallel to the first envelope, and a straight line connecting the fixed point and a tip end of a first electrode finger is not parallel to the second envelope.
A filter device according to an example embodiment of the present invention includes a plurality of acoustic wave resonators, in which at least one of the acoustic wave resonators is the acoustic wave device according to the above-described example embodiment of the present invention.
According to the acoustic wave devices and the filter devices according to example embodiments of the present invention, it is possible to sufficiently reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
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 example embodiments with reference to the attached drawings.
Hereinafter, the present invention will be elucidated by describing specific example embodiments of the present invention with reference to the drawings.
Each example embodiment described in the present specification is merely an example, and configurations can be partially replaced or combined with each other between different example embodiments.
As shown in
As shown in
Returning to
Furthermore, one end portion of each of the plurality of first offset electrodes 18 is connected to the first busbar 14. The first electrode finger 16 and the first offset electrode 18 are alternately arranged. Each one end portion of the plurality of second offset electrodes 19 is connected to the second busbar 15. The second electrode finger 17 and the second offset electrode 19 are alternately arranged.
Each of the plurality of first electrode fingers 16, the plurality of second electrode fingers 17, the plurality of first offset electrodes 18, and the plurality of second offset electrodes 19 includes a base end portion and a tip end portion. The base end portions of the first electrode finger 16 and the first offset electrode 18 are portions connected to the first busbar 14. The base end portions of the second electrode finger 17 and the second offset electrode 19 are portions connected to the second busbar 15. The tip end portion of the first electrode finger 16 and the tip end portion of the second offset electrode 19 face each other with a gap G2 interposed therebetween. On the other hand, the tip end portion of the second electrode finger 17 and the tip end portion of the first offset electrode 18 face each other with a gap G1 interposed therebetween.
Hereinafter, the first electrode finger 16 and the second electrode finger 17 may be simply referred to as an electrode finger. The first offset electrode 18 and the second offset electrode 19 may be simply referred to as an offset electrode. The first busbar 14 and the second busbar 15 may be simply described as a busbar. The pitch or duty ratio of the offset electrode may be different from, for example, the electrode finger pitch or duty ratio of the IDT electrode 8 in the intersection region described later.
The shapes of the plurality of electrode fingers in a plan view are respective shapes corresponding to the circular arcs of a plurality of concentric circles. Therefore, the centers of the circles including the circular arcs in the shapes of the plurality of electrode fingers match or substantially match each other.
When an elliptical coefficient of the circles or the ellipses including the arcs in the shapes of the plurality of electrode fingers is defined as α2/α1, the elliptical coefficient α2/α1 is 1, for example, in the present example embodiment. In a case where the shapes including the arcs in the shapes of the plurality of electrode fingers are the ellipses, the elliptical coefficient α2/α1 is other than 1, for example. The term α1 corresponds to a dimension along a direction of an axis passing through the intersection region D of the major axis and the minor axis of the ellipse. The term α2 corresponds to a dimension along a direction of an axis that does not pass through the intersection region D of the major axis and the minor axis of the ellipse. When r is an optional constant, the expression of the elliptical coefficient in the XY plane can be represented as (x/α1)2+ (y/α2)2=r2.
When the center of the circle including the circular arcs in the shapes of the plurality of electrode fingers is defined as the fixed point C, in the present example embodiment, neither the extension line of the first envelope E1 nor the extension line of the second envelope E2 passes through the fixed point C. Therefore, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1. Similarly, the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2.
As a material of the piezoelectric layer 6 of the acoustic wave device 1, a piezoelectric single crystal may be used, for example. In the piezoelectric layer 6, the propagation axis is the direction of X propagation. In the present example embodiment, among straight lines passing through the intersection region D and the fixed point C, a straight line extending parallel to the propagation axis is the reference line N. However, the reference line N need not necessarily extend for parallel substantially parallel to the propagation axis.
The propagation axis may be not only the direction of X propagation, but also a direction perpendicular to either the direction of 90° X propagation or the direction in which the electrode finger of the IDT electrode 8 extends. The direction in which the electrode fingers extend herein refers to a direction in which the tangent line of each portion of the electrode fingers extends. The direction in which the acoustic wave is excited is a direction perpendicular to a direction in which a tangent line of each portion of the electrode finger extends, a direction connecting the shortest distance between adjacent electrode fingers, or a direction parallel to an electric field vector generated between the electrode fingers. The direction in which the electrode finger extends herein specifically refers to a direction in which a tangent line of a curve connecting each portion of the electrode finger extends. In addition, each portion of the electrode finger can be represented by the center of gravity or an intermediate point between both ends. In an acoustic wave resonator used in the related art shown in
An angle formed between the straight line passing through the fixed point C and the reference line N is defined as θC. Although there are an infinite number of straight lines passing through the fixed point C,
By applying an AC voltage to the IDT electrode 8, an acoustic wave is excited in the intersection region D. The intersection region D has each portion located on an infinite number of straight lines passing through the fixed point C. In
An angle formed between the straight line passing through the fixed point C, the excitation portion, and the reference line N is the angle θC. In addition, an angle formed between a straight line passing through the fixed point C and the excitation portion in the intersection region D and the excitation direction of the acoustic wave at the intersection of the first electrode finger 16 or the second electrode finger 17, and the reference line N is defined as an excitation angle θC_prop. In the excitation portion through which the reference line N passes, the angle θC and the excitation angle θC_prop are 0°. In each of the excitation portions, the excitation angles θC_prop are different from each other, and thus the propagation characteristics of the acoustic waves are different from each other. On the other hand, in the present example embodiment, the duty ratios are different from each other between the plurality of excitation portions such that the resonant frequencies or the anti-resonant frequencies of all the excitation portions match or substantially match each other. The duty ratios are the same as each other between the excitation portions having the same absolute value of the excitation angle |θC_prop|. Since the IDT electrode 8 is configured as described above, the resonance characteristics are unlikely to deteriorate. However, the duty ratio may be constant.
Here, the angle θC in the excitation portion and the excitation angle θC_prop match or substantially match each other. Hereinafter, although any one angle of the angle θC and the excitation angle θC_prop is taken up and discussed, there is no difference to have an effect that reverses the action and effect. When the elliptical coefficient α2/α1 is 1, for example, that is, in a case of being a circle, the angle θC and the excitation angle θC_prop are equal or substantially equal to each other.
In the present specification, the fact that one frequency and the other frequency match or substantially match each other means that the absolute value of the difference between both frequencies is equal to or smaller than about 2% of a reference frequency, for example. The reference frequency is a frequency when the excitation angle θC_prop is 0°, for example. In the intersection region D, an absolute value of a difference between the highest resonant frequency and the lowest resonant frequency of the main mode is preferably about 18 or less with respect to the reference frequency, for example. Alternatively, in the intersection region D, an absolute value of a difference between the highest anti-resonant frequency and the lowest anti-resonant frequency of the main mode is preferably about 18 or less with respect to the reference frequency, for example.
In the IDT electrode 8 of the acoustic wave device 1, the electrode finger pitch is constant. Therefore, when the wavelength defined by the electrode finger pitch is λ, the wavelength λ in the IDT electrode 8 is constant regardless of the excitation angle θC_prop. The electrode finger pitch is the center-to-center distance of the first electrode finger 16 and the second electrode finger 17 adjacent to each other. When the electrode finger pitch is p, λ=2p, for example.
An angle θC formed between a straight line passing through the fixed point C and the end portion of the first envelope E1 on the fixed point C side, and the reference line N is defined as a first inner side portion intersection angle θC_AP1_in. An angle θC formed between a straight line passing through the fixed point C and the end portion of the first envelope E1 on the side far from the fixed point C, and the reference line N is defined as a first outer side portion intersection angle θC_AP1_out. An angle θC formed between a straight line passing through the fixed point C and the end portion of the second envelope E2 on the fixed point C side, and the reference line N is defined as a second inner side portion intersection angle θC_AP2_in. An angle θC formed between a straight line passing through the fixed point C and the end portion of the second envelope E2 on the side far from the fixed point C, and the reference line N is defined as a second outer side portion intersection angle θC_AP2_out. As described above, in the present example embodiment, the straight line connecting the fixed point C and the tip end of the second electrode finger 17 is not parallel to the first envelope E1. Therefore, θC_AP1_in≠θC_AP1_out. Similarly, a straight line connecting the fixed point C and the tip end of the first electrode finger 16 is not parallel to the second envelope E2. Therefore, θC_AP2_in≠θC_AP2_out.
In the IDT electrode 8, the first envelope E1 and the first busbar 14 extend parallel or substantially parallel to each other. Similarly, the second envelope E2 and the second busbar 15 extend parallel or substantially parallel to each other. When an angle formed by the reference line N and the busbar is defined as a busbar inclination angle, the busbar inclination angles of the first busbar 14 and the second busbar 15 are the same as each other. However, the busbar inclination angles of the first busbar 14 and the second busbar 15 may be different from each other. In the present specification, a positive direction of the busbar inclination angle is a counterclockwise direction in a plan view.
As shown in
A unique feature of the present example embodiment is that the acoustic wave device 1 has the following configuration. 1) The shapes of the plurality of electrode fingers in a plan view include the shapes of the circular arcs or the elliptical arcs. 2) A straight line connecting the fixed point C and the tip end of the second electrode finger 17 is not parallel to the first envelope E1, and a straight line connecting the fixed point C and the tip end of the first electrode finger 16 is not parallel to the second envelope E2. As a result, it is possible to sufficiently reduce or prevent the unnecessary wave outside the pass band and the transverse mode. In the present specification, the outside of the pass band in the acoustic wave device refers to a lower band side than the resonant frequency and a higher band side than the anti-resonant frequency. Details of the above-described effects will be described below by comparing the present example embodiment with a comparative example.
In the comparative example, as shown in
On the other hand, when a direction in which the plurality of electrode fingers extend is defined as an electrode finger stretching direction and a dimension of the intersection region along the electrode finger stretching direction is defined as an intersection width, the intersection width in the IDT electrode 108 of the acoustic wave device of the comparative example is 41.5λ. The number of pairs of electrode fingers of the IDT electrode 108 is 60 pairs, and the number of pairs of electrode fingers of each of the reflector 109A and the reflector 109B is 20 pairs. In the IDT electrode 108, the duty ratio is 0.5.
As shown in
In an example embodiment of the present invention, the above-described effect is obtained by utilizing the fact that the propagation characteristics of the acoustic wave are different from each other in each of the excitation portions. Details will be described below.
The phase velocity of the acoustic wave has a dependence on the excitation angle θC_prop and exhibits unique characteristics depending on the configuration of the substrate. The reciprocal of the phase velocity corresponds to the reverse-velocity surface. Therefore, the relationship between the excitation angle θC_prop and the phase velocity is equal or substantially equal to the reverse-velocity surface of the piezoelectric substrate. Therefore,
The x-axis shown in
As shown in
In this case, in the acoustic wave device 1 according to the first example embodiment, the resonant frequencies or the anti-resonant frequencies of the main mode match or substantially match each other in all the excitation portions. Therefore, in the different excitation portions, the frequencies of the unnecessary waves are different from each other. As a result, each of the unnecessary wave outside the pass band and the transverse mode is dispersed. Therefore, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
In the first example embodiment, since the resonant frequencies or the anti-resonant frequencies in each of the excitation portions match or substantially match each other, the main mode is suitably excited. Therefore, deterioration of the resonance characteristics can be reduced or prevented.
In addition, in the first example embodiment, the first inner side portion intersection angle θC_AP1_in and the first outer side portion intersection angle θC_AP1_out are different from each other. The second inner side portion intersection angle θC_AP2_in and the second outer side portion intersection angle θC_AP2_out are different from each other. Therefore, in each of the electrode fingers, the ranges of the excitation angles θC_prop of the excitation portion including the electrode finger are different from each other. For example, in the acoustic wave device 1 of the first example embodiment related to the comparison of
As described above, in the excitation portions having different excitation angles θC_prop, the intervals between reverse-velocity surfaces of the main mode and the unnecessary wave are different. However, in the first example embodiment, the resonant frequencies or the anti-resonant frequencies of the main mode match or substantially match each other in all the excitation portions. In the first example embodiment, the ranges of the excitation angles θC_prop of the excitation portions including each electrode finger are different from each other. Therefore, the range of variation in the frequency of the excited unnecessary wave varies for respective portions in which the electrode fingers are located. Therefore, the unnecessary wave can be effectively dispersed. Therefore, it is possible to effectively reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
Hereinafter, the fact that the resonant frequencies in the main mode match or substantially match each other will be described in detail. As described above, the phase velocity corresponds to the reciprocal of the reverse-velocity surface. Therefore, the relationship between the excitation angle θC_prop and the phase velocity is equal or substantially equal to the reverse-velocity surface of the piezoelectric substrate in the XY plane as shown in
However, when the shape of the electrode finger is simply made to be curved, the impedance frequency characteristics are obtained by superimposing the characteristics in which the resonant frequencies at each of the excitation angles θC_prop are significantly different from each other. Therefore, the impedance frequency characteristics significantly deteriorate. Therefore, as in the first example embodiment, by changing the duty ratio that affects the frequency according to the excitation angle θC_prop, the frequencies of the acoustic waves excited at each of the excitation angles θC_prop can match or substantially match each other. Therefore, in each of the excitation portions, the resonant frequencies can match or substantially match each other. In each of the excitation portions, the anti-resonant frequencies can also match or substantially match each other. Therefore, the impedance frequency characteristics are obtained in which the resonant frequencies or the anti-resonant frequencies match or substantially match each other.
In the first example embodiment, a relationship between the excitation angle θC_prop and the duty ratio is described in
In the first example embodiment, in a case where the excitation angle θC_prop is 0°, the duty ratio is at a maximum value, for example. That is, in the first example embodiment, the straight line passing through the excitation portion having the largest duty ratio and the fixed point C among all the excitation portions is the reference line N. In the first example embodiment, when the excitation angle θC_prop is 0°, the duty ratio is about 0.5, for example. The larger the absolute value of the excitation angle |θC_prop|, the smaller the duty ratio. As a result, the resonant frequencies or the anti-resonant frequencies match or substantially match each other in all the excitation portions.
Even in the first modification example and the second modification example, the larger the absolute value of the excitation angle | θC_prop|, the smaller the duty ratio. In the first modification example, the duty ratio is about 0.64 when the excitation angle θC_prop is 0°, for example. In the second modification example, the duty ratio is about 0.425 when the excitation angle θC_prop is 0°, for example. In the first modification example and the second modification example, the resonant frequencies or the anti-resonant frequencies match or substantially match each other in all the excitation portions. In addition, in the first modification example and the second modification example, the configuration is the same as that of the first example embodiment except for the duty ratio. Therefore, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
Incidentally, a semiconductor lithography method may be used for forming the IDT electrode 8, for example. When a resist and a metal wire pattern are formed using the semiconductor lithography method, and the duty ratio is less than about 0.2 or more than about 0.8, for example, it is not easy to form a pattern, and it is difficult to perform stable pattern processing with small manufacturing variations. According to
The relationship between the duty ratio and the frequency of each mode varies depending on the reverse-velocity surface of the piezoelectric substrate. Therefore, depending on the configuration of the piezoelectric substrate e or the configuration on the piezoelectric substrate, when the larger the absolute value of the excitation angle |θC_prop|, the larger the duty ratio, the resonant frequencies or the anti-resonant frequencies may match or substantially match each other in all the excitation portions. In this case, among all the excitation portions, a straight line passing through the excitation portion having the smallest duty ratio and the fixed point C is the reference line N. Examples thereof include an acoustic wave device in which an IDT electrode provided on a substrate including only LiNbO3 having a rotation Y-cut−4° X propagation is embedded in a SiO2 film having a thick thickness. Alternatively, in the excitation portion in which the reference line N passes and the excitation angle θC_prop is 0°, the duty ratio is not necessarily maximum or minimum.
In the first example embodiment shown in
However, as in the first example embodiment shown in
Non-limiting examples of the design parameters of the acoustic wave devices of the first example embodiment and the comparative example are the same as those in the comparison in
As shown in
As shown in
Returning to
In the IDT electrode 8, the duty ratio is changed in the region between the intersection region D and the first busbar 14 and the region between the intersection region D and the second busbar 15, similar to the intersection region D. Therefore, the duty ratio of the portion including the first offset electrode 18 on the extension line of any excitation portion and the excitation portion is constant. Similarly, the duty ratio of a portion including the second offset electrode 19 on the extension line of any excitation portion and the excitation portion is constant.
However, in the first example embodiment, focusing on the region between the first busbar 14 and the intersection region D, the closer to the first busbar 14 in the region, the larger the duty ratio. Similarly, in the region between the second busbar 15 and the intersection region, the closer to the second busbar 15, the larger the duty ratio.
The shapes of the plurality of first offset electrodes 18 and the plurality of second offset electrodes 19 are not limited to the above-described shapes. For example, in the region between the first busbar 14 and the intersection region D, the closer to the first busbar 14, the smaller the duty ratio may be. In the region between the second busbar 15 and the intersection region D, the closer to the second busbar 15, the smaller the duty ratio may be. Alternatively, the offset electrode need not necessarily be provided. Even in this case, the unnecessary wave can be reduced or prevented in example embodiments of the present invention. Furthermore, the shapes of the first electrode finger 16 and the second electrode finger 17 are not particularly limited in regions other than the intersection region D.
As described above, the tip end portion of the second electrode finger 17 and the tip end portion of the first offset electrode 18 face each other with the gap G1 interposed therebetween. The size of the gap G1 is a distance between the tip end portion of the second electrode finger 17 and the tip end portion of the first offset electrode 18. Similarly, the size of the gap G2 is a distance between the tip end portion of the first electrode finger 16 and the tip end portion of the second offset electrode 19. The sizes of the gap G1 and the gap G2 are desirably about 1λ or less and more desirably about 0.5λ or less, for example. When the gap G1 is larger than about 0.5λ, there is a tendency for the acoustic wave to easily leak from the intersection region D in a direction toward the first busbar 14. The same applies to a case where the gap G2 is larger than about 0.5λ. When the sizes of the gap G1 and the gap G2 exceed 1λ, the amount of leakage of the main mode increases, and the loss may be non-negligible.
In addition, the lengths of the first offset electrode 18 and the second offset electrode 19 are desirably about 1λ or more and more desirably about 1.3λ or more, for example. When the length of the first offset electrode 18 is shorter than about 1.3λ, there is a tendency for the acoustic wave to easily leak from the intersection region D in a direction toward the first busbar 14. The same applies to a case where the length of the second offset electrode 19 is shorter than about 1.3λ. When the lengths of the first offset electrode 18 and the second offset electrode 19 are shorter than about 1λ, the amount of leakage of the main mode increases, and the loss may be non-negligible.
Incidentally, as shown in
In the first example embodiment, in the piezoelectric substrate 2, the high acoustic velocity film, the low acoustic velocity film, and the piezoelectric layer 6 are laminated in this order. As a result, the energy of the acoustic wave can be effectively confined to the piezoelectric layer 6 side.
As the material of the high acoustic velocity film, for example, a media including the following material as a main component, such as silicon, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a diamond-like carbon (DLC) film, diamond, spinel, or sialon can be used.
As the material of the low acoustic velocity film, for example, glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or a material including a compound in which fluorine, carbon, or boron is added to silicon oxide as a main component can be used.
As the material of the piezoelectric layer 6, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or lead zirconate titanate (PZT) can also be used. As the material of the piezoelectric layer 6, it is preferable to use lithium tantalate or lithium niobate.
As a material of the support substrate 4, for example, a piezoelectric body such as aluminum nitride, lithium tantalate, lithium niobate, or quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, or sialon, a dielectric such as aluminum oxide, silicon oxynitride, diamond-like carbon (DLC), or diamond, a semiconductor such as silicon, or a material including the above-described material as a main component can be used. The above-described spinel includes an aluminum compound including one or more elements selected from Mg, Fe, Zn, Mn, oxygen, or the like. Examples of the spinel as the examples of the materials of the support substrate 4 and the high acoustic velocity film include MgAl2O4, FeAl2O4, ZnAl2O4, or MnAl2O4. Silicon is preferably used as the material of the support substrate 4.
In the present specification, the main component means a component whose occupied ratio exceeds 50% by weight. The material of the main component may exist in any one state of single crystal, polycrystal, and amorphous, or in a mixed state thereof.
The relationship between the acoustic velocities in the first layer 5a and the second layer 5b in the intermediate layer 5 is not limited to the above-described relationship. Furthermore, the layer configuration of the piezoelectric substrate 2 is not limited to the above-described configuration. Hereinafter, a fourth modification example and a fifth modification example of the first example embodiment which are different from the first example embodiment only in the configuration of the piezoelectric substrate 2 will be described. In the fourth modification example and the fifth modification example, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode, similar to the first example embodiment. Furthermore, the energy of the acoustic wave can be effectively confined to the piezoelectric layer 6 side.
In the fourth modification example shown in
The acoustic reflection film 7 is a multilayer body having a plurality of acoustic impedance layers. Specifically, the acoustic reflection film 7 includes a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers. The high acoustic impedance layer is a layer having a relatively high acoustic impedance. More specifically, the plurality of high acoustic impedance layers of the acoustic reflection film 7 are a high acoustic impedance layer 13a, a high acoustic impedance layer 13b, and a high acoustic impedance layer 13c. On the other hand, the low acoustic impedance layer is a layer having a relatively low acoustic impedance. More specifically, the plurality of low acoustic impedance layers of the acoustic reflection film 7 are a low acoustic impedance layer 12a and a low acoustic impedance layer 12b. The low acoustic impedance layer and the high acoustic impedance layer are alternately laminated. The high acoustic impedance layer 13a is a layer located closest to the piezoelectric layer 6 side in the acoustic reflection film 7.
The acoustic reflection film 7 includes two low acoustic impedance layers and three high acoustic impedance layers. However, the acoustic reflection film 7 may include at least one low acoustic impedance layer and at least one high acoustic impedance layer.
As a material of the low acoustic impedance layer, for example, silicon oxide or aluminum can be used. As a material of the high acoustic impedance layer, for example, metal such as platinum or tungsten, or a dielectric such as aluminum nitride or silicon nitride can be used. The material of the intermediate layer 5A may be the same as the material of the low acoustic impedance layer.
In the fifth modification example shown in
In the first example embodiment, by changing the duty ratio according to the excitation angle θC_prop, the resonant frequencies or the anti-resonant frequencies of all the excitation portions match or substantially match each other. However, the parameters such as the electrode finger pitch, the thickness of the electrode finger, the thickness of the piezoelectric layer, and the thickness of the intermediate layer in the piezoelectric substrate, which affect the frequency, may be changed according to the excitation angle θC_prop, without being limited to the duty ratio. In a case where a dielectric film is provided on the piezoelectric substrate to cover the IDT electrode, the thickness of the dielectric film may be changed according to the excitation angle θC_prop. A plurality of the parameters among the above parameters may be changed according to the excitation angle θC_prop. Even in these cases, the resonant frequencies or the anti-resonant frequencies can match or substantially match each other in all the excitation portions.
In the first example embodiment, the shapes of all the portions of the first electrode finger 16 and the second electrode finger 17 are curved. As a result, the unnecessary waves can be further reduced or prevented. However, the shapes of the first electrode finger 16 and the second electrode finger 17 need not necessarily be curved in all portions. The first electrode finger 16 and the second electrode finger 17 may include a portion having a linear shape.
However, as in the first example embodiment, it is particularly preferable that the shapes of the first electrode finger 16 and the second electrode finger 17 in a plan view are the shapes of the circular arcs. Alternatively, it is particularly preferable that the shapes of the first electrode finger 16 and the second electrode finger 17 in a plan view are the shapes of the elliptical arcs. In these cases, it is possible to more effectively reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
The duty ratio including the offset electrode located on the extension line of the excitation portion, the center-to-center distance between the offset electrode and the electrode finger, and the thickness of the offset electrode may also be changed according to the excitation angle θC_prop of the excitation portion, similar to the parameters of the electrode finger.
Hereinafter, an example in which the other than the duty ratio is changed according to the excitation angle θC_prop will be described. In each of the following examples, since the shape of the IDT electrode is different from that of the first example embodiment, the shape of the reflector is also different from that of the first example embodiment.
The present example embodiment is different from the first example embodiment in that the shapes of the plurality of electrode fingers in a plan view are the shapes of the elliptical arcs. The present example embodiment is different from the first example embodiment in that the duty ratio is constant and the electrode finger pitch is not constant in the IDT electrode 28. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
The shapes of the plurality of electrode fingers in a plan view are the shapes of the elliptical arcs. In this case, the shapes of the plurality of electrode fingers in a plan view are the respective shapes corresponding to the elliptical arcs of a plurality of ellipses having the same center of gravity. More specifically, as shown in
In the present example embodiment, similar to the first example embodiment, a straight line connecting the fixed point C and the tip end of the second electrode finger is not parallel to the first envelope E1. Therefore, θC_AP1_in≠θC_AP1_out. A straight line connecting the fixed point C and the tip end of the first electrode finger is not parallel to the second envelope E2. Therefore, θC_AP2_in≠θC_AP2_out. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
As described above, in the IDT electrode 28, the duty ratio is constant. Specifically, the duty ratio is about 0.5, for example. In the present example embodiment, the reference line N is a straight line passing through the excitation portion having the widest electrode finger pitch among all the excitation portions. The larger the absolute value of the excitation angle |θC_prop|, the narrower the electrode finger pitch. As a result, the resonant frequencies or the anti-resonant frequencies match or substantially match each other in all the excitation portions. Hereinafter, a relationship between the absolute value of the excitation angle |θC_prop| and the electrode finger pitch will be specifically described. Here, the electrode finger pitch in the excitation portion in which the excitation angle θC_prop is 0° is denoted by p0, the electrode finger pitch of any portion is denoted by p1, and {(p1−p0)/p0}×100 [%] is defined as the change rate of the electrode finger pitch Δpitch [%].
As shown in
In the present example embodiment as well, similar to the first example embodiment, a straight line connecting the fixed point C and the tip end of the second electrode finger is not parallel to the first envelope E1. Therefore, θC_AP1_in≠θC_AP1_out. A straight line connecting the fixed point C and the tip end of the first electrode finger is not parallel to the second envelope E2. In other words, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
Furthermore, non-limiting examples of the design parameters of the acoustic wave device of the present example embodiment will be described below.
The relationship between the electrode finger pitch and the frequency of each mode varies depending on the reverse-velocity surface of the piezoelectric substrate. Therefore, depending on the configuration of the piezoelectric substrate or the configuration on the piezoelectric substrate, when the larger the absolute value of the excitation angle |θC_prop|, the wider the electrode finger pitch, the resonant frequencies or the anti-resonant frequencies may match or substantially match each other in all the excitation portions. In this case, among all the excitation portions, the reference line N is a straight line passing through the excitation portion having the narrowest electrode finger pitch and the fixed point C. Examples thereof include an acoustic wave device in which an IDT electrode provided on a substrate including only LiNbO3 having a rotation Y-cut−4° X propagation is embedded in a SiO2 film having a thick thickness. Alternatively, in the excitation portion in which the excitation angle θC_prop through which the reference line N passes is 0°, the value of the electrode finger pitch is not necessarily maximum or minimum.
The present example embodiment is different from the first example embodiment in that the electrode finger pitch is not constant and an elliptical coefficient α2/α1 is larger than 1 in the IDT electrode 38. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment. In the present example embodiment, both the duty ratio and the electrode finger pitch are not constant.
More specifically, among all the excitation portions, in the present example embodiment, the straight line passing through the excitation portion having the narrowest electrode finger pitch and the fixed point C is the reference line N. At the same time, among all the excitation portions, the straight line passing through the excitation portion having the largest duty ratio, and the fixed point C is the reference line N. The larger the absolute value of the excitation angle |θC_prop|, the wider the electrode finger pitch. The larger the absolute value of the excitation angle |θC_prop|, the smaller the duty ratio. As a result, the resonant frequencies or the anti-resonant frequencies match or substantially match each other in all the excitation portions. In the present example embodiment, similar to the first example embodiment, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
In the IDT electrode 38, the elliptical coefficient α2/α1 in the shapes of the plurality of electrode fingers is larger than 1. As a result, it is possible to suppress the response at an upper end of a stop band and to increase a value of a fractional stop band width. Details will be described below. The stop band is a region in which the wavelength of the acoustic wave is constant when the acoustic wave is confined to the metal grating having a periodic structure. The fractional stop band width is a value obtained by dividing the band width of the stop band by the resonant frequency. The upper end of the stop band is an end portion of the stop band on the higher band side. The band width of the stop band is a difference between the frequency at the upper end of the stop band and the resonant frequency.
In a case where the elliptical coefficient α2/α1 is larger than 1, the frequency at the upper end of the stop band is dispersed. As a result, it is possible to reduce or prevent the response of the frequency at the upper end of the stop band. In addition, a dimension of the intersection region in a direction in which the first busbar 14 and the second busbar 15 face each other is larger than a dimension of the t intersection region in a direction orthogonal to the direction. Therefore, the curvature of the shapes of the plurality of electrode fingers in a plan view approaches 0. In this case, the band width of the stop band is widened. Therefore, the value of the fractional stop band width can be increased.
Furthermore, in the present example embodiment, by using only the duty ratio, the value of the fractional band width can be made larger than in a case where the frequencies of each of the excitation portions match or substantially match each other. The fractional band width is represented by |fa−fr|/fr when the resonant frequency is defined as fr and the anti-resonant frequency is defined as fa.
Non-limiting examples of the design parameters of the acoustic wave device according to the present example embodiment will be described below.
Number of pairs of electrode fingers of IDT electrode: 60 pairs
The present example embodiment is different from the first example embodiment in that the electrode finger pitch is not constant and an elliptical coefficient α2/α1 is smaller than 1 in the IDT electrode 48. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment. In the present example embodiment, both the duty ratio and the electrode finger pitch are not constant.
More specifically, in the present example embodiment, among all the excitation portions, the straight line passing through the excitation portion having the widest electrode finger pitch and the fixed point C is the reference line N. At the same time, among all the excitation portions, the straight line passing through the excitation portion having the largest duty ratio, and the fixed point C is the reference line N. The larger the absolute value of the excitation angle |θC_prop|, the narrower the electrode finger pitch. The larger the absolute value of the excitation angle |θC_prop|, the smaller the duty ratio. As a result, the resonant frequencies or the anti-resonant frequencies match or substantially match each other in all the excitation portions. In the present example embodiment, similar to the first example embodiment, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
In the IDT electrode 48, the elliptical coefficient α2/α1 of the shapes of the plurality of electrode fingers in a plan view is smaller than 1. As a result, it is possible to suppress the response at the upper end of the stop band and to increase the value of the fractional stop band width. Details will be described below.
In a case where the elliptical coefficient α2/α1 is smaller than 1, the frequency at the upper end of the stop band is dispersed. As a result, it is possible to reduce or prevent the response of the frequency at the upper end of the stop band. In addition, the dimension of the intersection region in a direction in which the first busbar 14 and the second busbar 15 face each other is smaller than the dimension of the intersection region in a direction orthogonal to the direction. Therefore, the curvature is larger than that in a case where the shapes of the plurality of electrode fingers in a plan view are the circular arc shapes. In this case, an interval between the frequency at which the main mode occurs and the frequency at which the unnecessary wave occurs is widened. Therefore, the unnecessary waves can be effectively reduced or prevented. In addition to the above configuration, the frequencies of the excitation portions match or substantially match each other by both the duty ratio and the electrode finger pitch. As a result, by using only the duty ratio, unnecessary waves can be reduced or prevented as compared with a case where the frequencies of each of the excitation portions match or substantially match each other.
Furthermore, in the present example embodiment, by using only the duty ratio, the value of the fractional band width can be made smaller than in a case where the frequencies of each of the excitation portions match or substantially match each other.
Non-limiting examples of the design parameters of the acoustic wave device according to the present example embodiment will be described below.
In the first to fourth example embodiments, by adjusting the duty ratio or the electrode finger pitch, the resonant frequencies or anti-resonant the frequencies match or substantially match each other in all the excitation portions. However, the resonant frequencies or the anti-resonant frequencies of all the excitation portions may match or substantially match each other by adjusting the thicknesses of the plurality of electrode fingers. The example will be described with reference to a fifth example embodiment.
The fifth example embodiment is different from the first example embodiment in that the duty ratio is constant and the thickness of the plurality of electrode fingers is not constant in the IDT electrode. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
In the fifth example embodiment, among all the excitation portions, the straight line passing through the excitation portion having largest thicknesses of the first electrode finger and the second electrode finger, and the fixed point C is the reference line N. As shown in
In addition, in the fifth example embodiment, similar to the first example embodiment, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
The relationship between the thicknesses of the first electrode finger and the second electrode finger and the frequency of each of the modes varies depending on the reverse-velocity surface of the piezoelectric substrate. Therefore, depending on the configuration of the piezoelectric substrate or the configuration on the piezoelectric substrate, when the larger the absolute value of the excitation angle |θC_prop|, the larger the thicknesses of the first electrode finger and the second electrode finger, the resonant frequencies or the anti-resonant frequencies may match or substantially match each other in all the excitation portions. In this case, among all the excitation portions, the straight line passing through the excitation portion with smallest thicknesses of the first electrode finger and the second electrode finger, and the fixed point C is the reference line N. Examples thereof include an acoustic wave device in which an IDT electrode provided on a substrate including only LiNbO3 having a rotation Y-cut−4° X propagation is embedded in a SiO2 film having a thick thickness. Alternatively, in the excitation portion in which the reference line N passes and the excitation angle θC_prop is 0°, the values of the thicknesses of the first electrode finger and the second electrode finger are not necessarily maximum or minimum.
In the first to fifth example embodiments, the resonant frequencies or the anti-resonant frequencies of all the excitation portions match or substantially match each other due to the configuration of the IDT electrode. However, the resonant frequencies or the anti-resonant frequencies of all the excitation portions may match or substantially match each other by adjusting the thickness of the dielectric film covering the IDT electrode. This example will be described with reference to a sixth example embodiment and a modification example thereof.
The present example embodiment is different from the first example embodiment in that the duty ratio is constant in the IDT electrode 58. The present example embodiment is also different from the first example embodiment in that the dielectric film 55 is provided on the piezoelectric layer 6 to cover the IDT electrode 58. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
The acoustic velocity of the transversal wave propagating through the dielectric film 55 of the present example embodiment is lower than the acoustic velocity of the main mode propagating through the dielectric film 55. The thickness of the dielectric film 55 varies depending on the excitation angle θC_prop of the excitation portion of the IDT electrode 58 covered with the dielectric film 55.
In the present example embodiment, among all the excitation portions, the straight line passing through the excitation portion in which the portion having the largest thickness in the dielectric film 55 is located and the fixed point C is the reference line N. As shown in
In addition, in the present example embodiment, similar to the first example embodiment, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
In the sixth example embodiment, the acoustic velocity of the transversal wave propagating through the dielectric film 55 is lower than the acoustic velocity of the main mode propagating through the dielectric film 55. However, the relationship of the acoustic velocity of the wave propagating through the dielectric film is not limited to the above-described relationship. A modification example of the sixth example embodiment in which only the acoustic velocity of the transversal wave propagating through the dielectric film is different from that of the sixth example embodiment will be described below.
In the modification example of the example embodiment, the acoustic velocity of the transversal wave propagating through the dielectric film is higher than the acoustic velocity of the main mode propagating through the dielectric film. In the present modification example, a relationship between the absolute value of the excitation angle |θC_prop| in the excitation portion in the IDT electrode covered with the dielectric film and the thickness of the dielectric film is shown in
Depending on the configuration of the piezoelectric substrate, the value of the thickness of the portion in which the reference line N passes among the thicknesses of the portions covering the excitation portion in the dielectric film is not necessarily maximum or minimum.
The present example embodiment is different from the first example embodiment in that by changing at least the parameter other than the duty ratio according to the excitation angle θC_prop, the resonant frequencies or the anti-resonant frequencies of all the excitation portions match or substantially match each other. The duty ratio in a portion in which the tip end portions of the plurality of first electrode fingers 66 are arranged is constant. Similarly, the duty ratio in a portion in which the tip end portions of the plurality of second electrode fingers 67 are arranged is constant. In the present example embodiment, the configuration of the region between the intersection region and the first busbar 14 and the region between the intersection region and the second busbar is also different from that of the first example embodiment. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
The widths of the plurality of first offset electrodes 68 are constant. The widths of the plurality of first electrode fingers 66 are also constant in the region in the outer side portion of the intersection region. More specifically, the widths of the plurality of first offset electrodes 68 are the same as the widths of the tip end portions of the plurality of second electrode fingers 67. The widths of the plurality of first electrode fingers 66 are the same as the widths of the plurality of first offset electrodes 68 in the region in the outer side portion of the intersection region. The shapes of the plurality of first offset electrodes 68 in a plan view are curved. The shapes of the plurality of first electrode fingers 66 in the region in the outer side portion of the intersection region in a plan view are also curved. The duty ratio in the region between the intersection region and the first busbar 14 is the same as the duty ratio in the portion in which the tip end portions of the plurality of second electrode fingers 67 are arranged.
Although not shown, the widths of the plurality of second offset electrodes are the same as the widths of the tip end portions of the plurality of first electrode fingers 66 and are constant. The widths of the plurality of second electrode fingers 67 are the same as the widths of the plurality of second offset electrodes in the region in the outer side portion of the intersection region. The shapes of the plurality of second offset electrodes in a plan view are curved. The shapes of the plurality of second electrode fingers 67 in the region in the outer side portion of the intersection region in a plan view are also curved. The duty ratio in the region between the intersection region and the second busbar is the same as the duty ratio in the portion in which the tip end portions of the plurality of first electrode fingers 66 are arranged.
In the present example embodiment, the widths of the plurality of first offset electrodes 68 and the plurality of first electrode fingers 66 are not narrowed in the region between the intersection region and the first busbar 14. The widths of the plurality of second offset electrodes and the plurality of second electrode fingers 67 are also not narrowed in the region between the intersection region and the second busbar. As a result, the series resistance can be reduced.
In addition, in the present example embodiment, similar to the first example embodiment, the straight line passing through the fixed point C and the first envelope E1 is not parallel to the first envelope E1, and the straight line passing through the fixed point C and the second envelope E2 is not parallel to the second envelope E2. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
Hereinafter, a first modification example and a second modification example of the seventh example embodiment will be described, in which only the configurations of the region between the intersection region and the first busbar 14 and the region between the intersection region and the second busbar are different from those of the seventh example embodiment. In the first modification example and the second modification example, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode and to reduce the series resistance, similar to the seventh example embodiment.
In the first modification example shown in
Therefore, in the present modification example, the duty ratio in the region between the intersection region and the first busbar 14 is larger than the duty ratio in the portion in which the tip end portions of the plurality of second electrode fingers 67A are arranged. Similarly, the duty ratio in the region between the intersection region and the second busbar is larger than the duty ratio in the portion in which the tip end portions of the plurality of first electrode fingers 66A are arranged.
In the second modification example shown in
Acoustic wave devices according to various example embodiments of the present invention can be used, for example, in filter devices. Examples will be described below.
The filter device 70 according to the present example embodiment is a ladder filter. The filter device 70 includes a first signal terminal 72, a second signal terminal 73, a plurality of series arm resonators, and a plurality of parallel arm resonators. In the filter device 70, all the series arm resonators and all the parallel arm resonators are acoustic wave resonators. Furthermore, all the series arm resonators and all the parallel arm resonators are the acoustic wave devices according to one or more example embodiments of the present invention. However, at least one acoustic wave resonator of the plurality of acoustic wave resonators of the filter device 70 may be one of the acoustic wave devices according to example embodiments of the present invention.
The first signal terminal 72 is an antenna terminal. The antenna terminal is connected to an antenna. However, the first signal terminal 72 need not necessarily be an antenna terminal. The first signal terminal 72 and the second signal terminal 73 may be configured as, for example, electrode pads, or may be configured as wirings.
Specifically, the plurality of series arm resonators of the present example embodiment are a series arm resonator S1, a series arm resonator S2, and a series arm resonator S3. The plurality of series arm resonators are connected in series to each other between the first signal terminal 72 and the second signal terminal 73. Specifically, the plurality of parallel arm resonators are a parallel arm resonator P1 and a parallel arm resonator P2. The parallel arm resonator P1 is connected between a connection point between the series arm resonator S1 and the series arm resonator S2, and a ground potential. The parallel arm resonator P2 is connected between a connection point between the series arm resonator S2 and the series arm resonator S3, and the ground potential. The circuit configuration of the filter device 70 is not limited to the above-described configuration. The filter device 70 may include, for example, a longitudinally coupled resonator-type acoustic wave filter.
The acoustic wave resonator in the filter device 70 is the acoustic wave device according to an example embodiment of the present invention. Therefore, in the acoustic wave resonator of the filter device 70, it is possible to suppress the transverse mode and reduce or prevent the unnecessary wave outside the pass band. As a result, it is also possible to reduce or prevent the unnecessary wave outside the pass band of the filter device 70.
Incidentally, for example, in the acoustic wave device of the reference example shown in
In the present example embodiment, a plurality of acoustic wave resonators are configured on the piezoelectric substrate. Each acoustic wave resonator is the acoustic wave device 1 according to the first example embodiment. The sum of absolute values of inclination angles of the first busbar and the second busbar in each of the acoustic wave resonators is about 5° or less, for example. As a result, the plurality of acoustic wave resonators can be disposed such that the busbars of the adjacent acoustic wave resonators extend parallel or substantially parallel to each other. As a result, the area of the portion in which the plurality of acoustic wave resonators are configured can be reduced. Therefore, the size of the filter device 80 can be reduced.
The disposition of each acoustic wave resonator in the modification example of the ninth example embodiment shown in
A frame of the two-dot chain line shown in
In the ninth example embodiment and the modification example thereof, each acoustic wave resonator in the filter device is the acoustic wave device 1 according to the first example embodiment. Therefore, in each of the acoustic wave resonators of the filter device, it is possible to suppress the transverse mode and reduce or prevent the unnecessary wave outside the pass band. As a result, it is also possible to reduce or prevent the unnecessary wave outside the pass band of the filter device.
Incidentally, the curve in the shapes of the plurality of electrode fingers in a plan view in the acoustic wave device according to each of the above-described example embodiments is a smooth curve. The curve in the shapes of the plurality of electrode fingers in a plan view may be a shape formed by connecting straight lines having a minute size. The curve in the shapes of the plurality of electrode fingers in a plan view may be a shape in which a plurality of vertices are connected to each other by the curve. Alternatively, the curve in the shapes of the plurality of electrode fingers in a plan view need not necessarily be a smooth curve. This example is described as a sixth modification example of the first example embodiment.
In the IDT electrode 8A in the sixth modification example shown in an enlarged manner in
The shape of each of the second electrode fingers 17A in a plan view is also the same as the shape of each of the first electrode fingers 16A in a plan view. In the present modification example, similar to the first example embodiment, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
The present example embodiment is different from the first example embodiment in that the IDT electrode 8 is embedded in a protection film 99. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
Specifically, the protection film 99 is provided on the piezoelectric layer 6 to cover the IDT electrode 8. The thickness of the protection film 99 is larger than the thickness of the IDT electrode 8. The IDT electrode 8 is embedded in the protection film 99. As a result, the IDT electrode 8 is unlikely to be damaged.
The protection film 99 includes a first protection layer 99a and a second protection layer 99b. The IDT electrode 8 is embedded in the first protection layer 99a. The second protection layer 99b is provided on the first protection layer 99a. In this manner, a plurality of advantageous effects can be achieved by the protection film 99. Specifically, in the present example embodiment, silicon oxide is used as the material of the first protection layer 99a. As a result, the absolute value of a temperature coefficient of frequency (TCF) in the acoustic wave device can be reduced. Therefore, the temperature characteristics of the acoustic wave device can be improved. Silicon nitride is used for the second protection layer 99b. As a result, the humidity resistance of the acoustic wave device can be improved.
In addition, in the present example embodiment, the IDT electrode 8 is also configured in the same manner as the first example embodiment. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
The materials of the first protection layer 99a and the second protection layer 99b are not limited to the above-described example. The protection film 99 may be a single layer, or may be a multilayer body having three or more layers.
The present example embodiment is different from the first example embodiment in that the IDT electrode 8 is provided on both main surfaces of the piezoelectric layer 6. Except for the above points, the acoustic wave device according to the present example embodiment has the same configuration as the acoustic wave device 1 according to the first example embodiment.
The piezoelectric layer 6 includes a first main surface 6a and a second main surface 6b. The first main surface 6a and the second main surface 6b face each other. It is noted that the piezoelectric layer 6 in each of the above-described example embodiments similarly has the first main surface 6a and the second main surface 6b. In each of the above-described example embodiments and the present example embodiment, the IDT electrode is provided on the first main surface 6a. In the present example embodiment, the IDT electrode 8 is also provided on the second main surface 6b. The IDT electrode 8 provided on the second main surface 6b is embedded in the second layer 5b of the intermediate layer 5.
The IDT electrode 8 provided on the first main surface 6a and the IDT electrode 8 provided on the second main surface 6b of the piezoelectric layer 6 face each other with the piezoelectric layer 6 interposed therebetween. In the acoustic wave device according to the present example embodiment, the IDT electrode 8 is configured in the same manner as the first example embodiment on the first main surface 6a. As a result, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode.
For example, the IDT electrodes 8 provided on the first main surface 6a and the second main surface 6b of the piezoelectric layer 6 may have different design parameters.
Hereinafter, first to third modification examples of the eleventh example embodiment, which are different from the eleventh example embodiment in at least one of the configuration of the electrode provided on the second main surface of the piezoelectric layer and the multilayer structure of the piezoelectric substrate will be described. Even in the first to third modification examples, it is possible to reduce or prevent the unnecessary wave outside the pass band and the transverse mode, similar to the eleventh example embodiment.
In the first modification example shown in
The support substrate 4 blocks one of the through-holes of the dielectric layer 95. The piezoelectric layer 6 blocks the other of the through-holes of the dielectric layer 95. As a result, a hollow portion 92c is formed in the piezoelectric substrate 92. A portion of the piezoelectric layer 6 and a portion of the support substrate 4 face each other with the hollow portion 92c interposed therebetween. The IDT electrode 8 provided on the second main surface 6b of the piezoelectric layer 6 is located inside the hollow portion 92c.
In the second modification example shown in
In the third modification example shown in
In the tenth example embodiment, the eleventh example embodiment, and each of the modification examples, an example of a case where the IDT electrode 8 has the same configuration as that in the first example embodiment is shown. However, each of the configurations of the tenth example embodiment, the eleventh example embodiment, and each modification example can also be adopted in a case where the configuration of the IDT electrode is the configuration of the present invention other than the first example embodiment.
While example 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 |
|---|---|---|---|
| 2022-125004 | Aug 2022 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2022-125004 filed on Aug. 4, 2022 and is a Continuation application of PCT Application No. PCT/JP2023/026613 filed on Jul. 20, 2023. The entire contents of each application are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2023/026613 | Jul 2023 | WO |
| Child | 19024548 | US |
