The present disclosure relates to acoustic wave devices that each include a piezoelectric layer.
For example, an acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2012-257019 includes a support body, a piezoelectric substrate, and an IDT electrode. The acoustic wave device is disclosed in which the support body is provided with a hollow portion. The piezoelectric substrate is provided on the support body to overlap the hollow portion. The IDT electrode is provided on the piezoelectric substrate to overlap the hollow portion. In the acoustic wave device of Japanese Unexamined Patent Application Publication No. 2012-257019, a plate wave is excited by the IDT electrode.
In recent years, there has been a demand for an acoustic wave device that can reduce or prevent deterioration in characteristics.
Example embodiments of the present invention provide acoustic wave devices each with reduced or prevented deterioration in characteristics.
An acoustic wave device according to an example embodiment of the present invention includes an input terminal, an output terminal, a series arm electrically connected between the input terminal and the output terminal, at least one parallel arm electrically connected between the series arm and a ground potential, and acoustic wave resonators including one or more series arm resonators located at the series arm and one or more parallel arm resonators located at the parallel arm. The acoustic wave resonators include a support including a support substrate having a thickness in a first direction, a piezoelectric layer extending in the first direction of the support, an IDT electrode on one principal surface in the first direction of the piezoelectric layer, a first dielectric film on the one principal surface of the piezoelectric layer, and a second dielectric film on the first dielectric film. A thickness of one of the first dielectric film of the series arm resonator and the first dielectric film of the parallel arm resonator is larger than a thickness of another one of the first dielectric film of the series arm resonator and the first dielectric film of the parallel arm resonator. A thickness of one of the second dielectric film of the series arm resonator and the second dielectric film of the parallel arm resonator is smaller than a thickness of another one of the second dielectric film of the series arm resonator and the second dielectric film of the parallel arm resonator.
According to example embodiments of the present invention, it is possible to provide acoustic wave devices each with reduced or prevented deterioration in characteristics.
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.
Acoustic wave devices according to example embodiments of the present invention include a piezoelectric layer made of lithium niobate or lithium tantalate, for example, and a first electrode and a second electrode facing each other in a direction intersecting with a thickness direction of the piezoelectric layer.
A thickness-shear mode bulk wave is used in an acoustic wave device according to an example embodiment of the present invention.
In an acoustic wave device according to an example embodiment, the first electrode and the second electrode are electrodes located adjacent to each other. When a thickness of the piezoelectric layer is defined as d and a center-to-center distance between the first electrode and the second electrode is defined as p, d/p is set equal to or less than about 0.5, for example. Accordingly, it is possible to increase a Q factor even in the case where size reduction is provided.
In the meantime, a Lamb wave as a plate wave is used in an acoustic wave device according to an example embodiment. Thus, resonance characteristics attributed to the Lamb wave can be obtained.
An acoustic wave device of an example embodiment of the present includes a piezoelectric layer made of lithium niobate or lithium tantalate, for example, and an upper electrode and a lower electrode facing each other in a thickness direction of the piezoelectric layer while interposing the piezoelectric layer therebetween and uses a bulk wave.
The present invention will be clarified below by explaining example embodiments of acoustic wave devices according to the present invention with reference to the drawings.
The example embodiments described in the present specification are illustrative examples and it should be noted that portions of the configurations illustrated in different example embodiments can be substituted for one another or combined with one another.
An acoustic wave device 1 includes a piezoelectric layer 2 made of, for example, a LiNbO3. The piezoelectric layer 2 may be made of, for example, LiTaO3 instead. Cut-angles of LiNbO3 and LiTaO3 are provided by Z-cut in the present example embodiment. However, the cut-angles may be provided by rotated Y-cut or X-cut instead. Preferably, for example, a preferred propagation orientation is Y-propagation and X-propagation±about 30°. Although a thickness of the piezoelectric layer 2 is not limited to a particular thickness, the thickness is, for example, preferably set equal to or greater than about 50 nm and equal to or less than about 1000 nm in order to bring about effective excitation in the thickness-shear mode.
The piezoelectric layer 2 includes first and second principal surfaces 2a and 2b facing each other. An electrode 3 and an electrode 4 are provided on the first principal surface 2a. Here, the electrode 3 is an example of a “first electrode” and the electrode 4 is an example of a “second electrode”. In
The electrodes 3 and the electrodes 4 each have a rectangular or substantially rectangular shape and include a length direction. An electrode 3 and an adjacent electrode 4 face each other in a direction orthogonal or substantially orthogonal to this length direction. The multiple electrodes 3 and 4, the first busbar 5, and the second busbar 6 define interdigital transducer (IDT) electrodes. Each of the length direction of the electrodes 3 and 4 and the direction orthogonal or substantially orthogonal to the length direction of the electrodes 3 and 4 is a direction intersecting with a thickness direction of the piezoelectric layer 2. In this regard, the electrode 3 and the adjacent electrode 4 can also be deemed to face each other in the direction intersecting with the thickness direction of the piezoelectric layer 2.
The length direction of the electrodes 3 and 4 may be interchanged with the direction orthogonal or substantially orthogonal to the length direction of the electrodes 3 and 4 illustrated in
Moreover, pairs of structures each including the electrode 3 connected to one potential and the electrode 4 connected to another potential being located adjacent to each other are provided in the direction orthogonal or substantially orthogonal to the length direction of the electrodes 3 and 4 mentioned above. Here, the state of the electrode 3 and the electrode 4 being located adjacent to each other does not represent a case where the electrode 3 and the electrode 4 are disposed in such a way as to be in direct contact but represents a case where the electrode 3 and the electrode 4 are disposed with a clearance therebetween.
When the electrode 3 and the electrode 4 are located adjacent to each other, electrodes inclusive of other electrodes 3 and electrodes 4 to be connected to a hot electrode or a ground electrode are not disposed between the relevant electrode 3 and the electrode 4. The number of pairs does not always have to be an integer but may also be any of 1.5 pairs, 2.5 pairs, and so forth. A center-to-center distance, that is to say, a pitch between the electrodes 3 and 4 is, for example, preferably in a range from equal to or greater than about 1 μm and equal to or less than about 10 μm. The center-to-center distance between the electrodes 3 and 4 is a distance of connection between the center in a width dimension of the electrode 3 in the direction orthogonal to the length direction of the electrode 3 and the center in a width dimension of the electrode 4 in the direction orthogonal to the length direction of the electrode 4. Moreover, when at least two or more the electrodes 3 or two or more electrodes 4 are present (when there are 1.5 pairs or more of electrode sets assuming that each electrode set includes a pair of the electrode 3 and the electrode 4), the center-to-center distance between the electrodes 3 and 4 is an average value of the respective center-to-center distances of the adjacent electrodes 3 and 4 in the 1.5 pairs or more. The widths of the electrodes 3 and 4, that is to say, dimensions of the electrodes 3 and 4 in a direction in which the electrodes 3 and 4 face each other are, for example, preferably in a range from equal to or greater than about 150 nm and equal to or less than about 1000 nm. Here, the center-to-center distance between the electrodes 3 and 4 is equivalent to a distance of connection between the center in a dimension (the width dimension) of the electrode 3 in the direction orthogonal or substantially orthogonal to the length direction of the electrode 3 and the center in a dimension (the width dimension) of the electrode 4 in the direction orthogonal or substantially orthogonal to the length direction of the electrode 4.
Since the Z-cut piezoelectric layer is used in the present example embodiment, the direction orthogonal or substantially orthogonal to the length direction of the electrodes 3 and 4 is equivalent to a direction orthogonal or substantially orthogonal to a direction of polarization of the piezoelectric layer 2. This is not applicable when a piezoelectric body having a different cut-angle is used as the piezoelectric layer 2. Here, the term “orthogonal” is not limited only to a case of being strictly orthogonal but may also include a case of being substantially orthogonal (where an angle formed between the direction orthogonal to the length direction of the electrodes 3 and 4 and the direction of polarization may be equivalent to about 90°±10°, for example).
A support substrate 8 is laminated on the second principal surface 2b side of the piezoelectric layer 2 while interposing an insulating (intermediate) layer 7 therebetween. The insulating layer 7 and the support substrate 8 define a support. The insulating layer 7 and the support substrate 8 each have a frame shape and include cavities 7a and 8a as illustrated in
The insulating layer 7 is made of silicon oxide, for example. Nonetheless, an appropriate insulating material such as, for example, silicon oxynitride and alumina can be used in addition to silicon oxide. The support substrate 8 is made of Si, for example. A plane orientation on a surface on the piezoelectric layer 2 side of Si may be (100), (110), or (111). Preferably, for example, high-resistance Si having a resistivity equal to or greater than about 4 kΩ is desired. Nevertheless, the support substrate 8 can also be made using, for example, an insulating material or a semiconductor material as appropriate. For example, as the material of the support substrate 8, it is possible to use piezoelectric bodies such as aluminum oxide, lithium tantalate, lithium niobate, and quartz crystal, various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, dielectric bodies such as diamond and glass, semiconductors such as gallium nitride, and so forth.
The multiple electrodes 3 and 4 as well as the first and second busbars 5 and 6 are made of a metal or an alloy such as, for example, Al and AlCu alloy as appropriate. In the present example embodiment, the electrodes 3 and 4 as well as the first and second busbars 5 and 6 have a structure including an Al film laminated on a Ti film. Here, an adhesion layer other than the Ti film may be used instead.
In driving, an alternating-current voltage is applied between the multiple electrodes 3 and the multiple electrodes 4. To be more precise, the alternating-current voltage is applied between the first busbar 5 and the second busbar 6. Accordingly, it is possible to obtain resonance characteristics by using the thickness-shear mode bulk wave excited in the piezoelectric layer 2.
When the thickness of the piezoelectric layer 2 is defined as d and the center-to-center distance between the electrodes 3 and 4 located adjacent to each other among the multiple pairs of the electrodes 3 and 4 is defined as p in the acoustic wave device 1, d/p is set equal to or less than about 0.5, for example. For this reason, the thickness-shear mode bulk wave can be effectively excited, so that favorable resonance characteristics can be obtained. More preferably, for example, d/p is set equal to or less than about 0.24. In this case, it is possible to obtain even more favorable resonance characteristics.
Here, when at least one of the electrodes 3 and 4 include more than one as in the present example embodiment, or in other words, in the case where the pair of the electrodes 3 and 4 and one of the electrodes 3 and 4 define 1.5 pairs or more, the center-to-center distance p of the electrodes 3 and 4 located adjacent to one another is an average distance between the center-to-center distances of the respective sets of the electrodes 3 and 4 located adjacent to each other.
Since the acoustic wave device 1 of the present example embodiment has the above-described configuration, a drop in Q factor is less likely to occur even when the number of pairs of the electrodes 3 and 4 is decreased in an attempt to reduce size. This is because the acoustic wave device 1 is a resonator which does not require a reflector on each side and causes a small propagation loss. The acoustic wave device 1 does not require the reflectors because the acoustic wave device 1 uses the thickness-shear mode bulk wave.
A difference between the Lamb wave used in the acoustic wave device of the related art and the above-described thickness-shear mode bulk wave will be described with reference to
On the other hand, as illustrated in
Here, as illustrated in
As described above, at least one pair of electrodes including the electrode 3 and the electrode 4 are disposed in the acoustic wave device 1. However, since the acoustic wave device 1 is not configured to propagate the wave in the X direction, the number of pairs including the electrodes 3 and 4 does not always have to be multiple pairs. That is to say, at least one pair of electrodes needs to be provided therein.
For example, the electrode 3 is an electrode to be connected to a hot potential and the electrode 4 is an electrode to be connected to a ground potential. Nevertheless, the electrode 3 may be connected the ground potential and the electrode 4 may be connected to the hot potential instead. In the present example embodiment, at least the one pair of electrodes includes either the electrode to be connected to the hot potential or the electrode to be connected to the ground potential as mentioned above, and no floating electrodes are provided therein.
Here, the length of the excitation region C is a dimension of the excitation region C in the length direction of the electrodes 3 and 4.
In the present example embodiment, all of the distances between the electrodes among the electrode pairs including the electrodes 3 and 4 are set equal or substantially equal. In other words, the electrodes 3 and the electrodes 4 are disposed at regular pitches.
As apparent from
When the thickness of the piezoelectric layer 2 is defined as d and the center-to-center distance of the electrodes between the electrode 3 and the electrode 4 is defined as p, d/p is equal to or less than about 0.5 or more preferably equal to or less than about 0.24 in the present example embodiment as described above. This will be described with reference to
As with the acoustic wave device that obtained the resonance characteristics depicted in
As apparent from
Here, as described above, at least one pair of electrodes may include one pair and the p is defined as the center-to-center distance between the electrodes 3 and 4 that are located adjacent to each other in the case of one pair of electrodes. Meanwhile, in the case of the electrodes of 1.5 pairs or more, an average distance of the center-to-center distances of the electrodes 3 and 4 that are located adjacent to one another may be defined as p.
Regarding the thickness d of the piezoelectric layer as well, a value obtained by averaging thicknesses may be used in a case where the piezoelectric layer 2 has variations in thickness.
Preferably, in the acoustic wave device 1, a metallization ratio MR of certain electrodes 3 and 4 that are located adjacent to each other among the multiple electrodes 3 and 4 relative to the excitation region, which is the region where the electrodes 3 and 4 being located adjacent to each other overlap when viewed in a direction in which the electrodes 3 and 4 face each other, preferably satisfies, for example, MR≤about 1.75(d/p)+0.075. Specifically, the region where the first electrode fingers and the second electrode fingers being located adjacent to one another overlap when viewed in the direction in which the first electrode fingers and the second electrode fingers face each other is the excitation region (an intersecting region), and when the metallization ratio of the first electrode fingers and the second electrode fingers relative to the excitation region is defined as MR, MR preferably satisfies MR≤about 1.75(d/p)+0.075, for example. In this case, it is possible to reduce the spurious response effectively.
This will be described with reference to
The metallization ratio MR will be described with reference to
Here, when two or more pairs of the electrodes are provided, the ratio of the metallization portions included in the entire excitation region relative to a sum of the areas of the excitation regions may be defined as MR.
The spurious response grows as large as about 1.0 in a region surrounded by an ellipse J in
Accordingly, the range of Euler angles represented by Expression (1), Expression (2), or Expression (3) above is preferable because the fractional bandwidth can be sufficiently widened.
In the acoustic wave device 81, the Lamb wave as the plate wave is excited by applying an alternating-current electric field to the IDT electrode 84 above the hollow portion 9. Then, since the reflectors 85 and 86 are provided on both sides, it is possible to obtain the resonance characteristics attributed to the Lamb wave.
As described above, an acoustic wave device according to an example embodiment of the present invention may be configured to use the plate wave.
An acoustic wave device of a second example embodiment of the present invention will be described. In the second example embodiment, explanations of contents overlapping with those in the first example embodiment will be omitted as appropriate. The second example embodiment can apply the contents described in the first example embodiment.
A problem of an acoustic wave device of the related art will be described.
For example, an acoustic wave device 600 including a circuit as illustrated in
In the acoustic wave device 600 of the related art, a thickness t10 of the series dielectric film 731 is different from a thickness t20 of the parallel dielectric film 732. In
However, a difference in amount of frequency variation (such as an amount of frequency drop) is generated between the series arm resonator 620 and the parallel arm resonator 630 due to moisture absorption by the dielectric film 730 in a humid environment. Specifically, an amount of variation on a low-pass side is increased. In the case of the configuration illustrated in
As illustrated in
The acoustic wave device of the second example embodiment of the present invention can reduce the difference in amount of frequency variation between the series arm resonator and the parallel arm resonator attributed to the moisture absorption by the dielectric film as compared to the above-mentioned configuration of the related art.
As illustrated in
The one or more series arm resonators 120 and the one or more parallel arm resonators 130 are connected as in the circuit diagram illustrated in
As illustrated in
The multiple IDT electrodes 300 are laminated on the support 200. The laminated electrode 400 is laminated on the support 200 and is electrically connected to the multiple IDT electrodes 300. Thus, the multiple IDT electrodes 300 are electrically connected to one another with the laminated electrode 400. The dielectric film 500 is laminated on the support 200.
Each of the acoustic wave resonators 110 includes one IDT electrode 300, and the support 200 in addition to the dielectric film 500 located in a region overlapping the one IDT electrode 300 when viewed in the direction of lamination D11 (in other words, in plan view in the direction of lamination D11) and in a region in the vicinity of the aforementioned region (see
As illustrated in
As illustrated in
In the second example embodiment, for example, the support substrate 210 is made of silicon (Si), the joining layer 220 is made of silicon oxide (SiOx), and the piezoelectric layer 230 is made of lithium niobate (LN, LiNbOx). The materials of the respective portions defining the support 200 are not limited to the aforementioned materials. For example, the piezoelectric layer 230 may be made of lithium tantalate (LiTaOx) instead.
The joining layer 220 includes a recess 221. The recess 221 is recessed in the direction of lamination D11 from a principal surface 220A of the joining layer 220. A space defined by the recess 221 and another principal surface 230A of the piezoelectric layer 230 defines a hollow portion 220B. The hollow portion 220B is an example of a space portion.
The piezoelectric layer 230 is laminated on the joining layer 220. The other principal surface 230A of the piezoelectric layer 230 is in contact with the principal surface 220A of the joining layer 220. The piezoelectric layer 230 occludes the recess 221 of the joining layer 220. That is to say, the piezoelectric layer 230 is provided on the joining layer 220 so as to cover the hollow portion 220B.
As illustrated in
A shape of the membrane 231 in plan view in the direction of lamination D11 depends on a shape of the hollow portion 220B. The shapes of the membrane 231 and the hollow portion 220B are not limited to the shapes illustrated in
As illustrated in
As illustrated in
The first busbar electrode 310 corresponds to the first busbar 5 of the first example embodiment. The second busbar electrode 320 corresponds to the second busbar 6 of the first example embodiment. The first electrode finger 330 corresponds to the electrode 3 of the first example embodiment. The second electrode finger 340 corresponds to the electrode 4 of the first example embodiment.
In plan view in the direction of lamination D11, at least a portion of the IDT electrode 300 is provided on the one principal surface 230B of the piezoelectric layer 230 at a position overlapping the hollow portion 220B. In plan view in the direction of lamination D11, the first electrode fingers 330 and the second electrode fingers 340 of the IDT electrode 300 are provided at the position overlapping the hollow portion 220B in the second example embodiment.
As illustrated in
Similarly, the multiple second electrode fingers 340 are disposed to extend from the second busbar electrode 320 in the electrode finger extension direction D13. The multiple second electrode fingers 340 are arranged at intervals in the electrode finger facing direction D12. That is to say, the second busbar electrode 320 and the multiple second electrode fingers 340 define a comb-shaped electrode.
The electrode finger facing direction D12 is a direction intersecting with the direction of lamination D11 and is a direction along the one principal surface 230B of the piezoelectric layer 230. The electrode finger extension direction D13 is a direction intersecting with the direction of lamination D11 and is a direction intersecting with the electrode finger facing direction D12. In the second example embodiment, the directions of lamination D11, the electrode finger facing direction D12, and the electrode finger extension direction D13 are orthogonal or substantially orthogonal to one another.
The multiple first electrode fingers 330 and the multiple second electrode fingers 340 are disposed to overlap one another when viewed in the electrode finger facing direction D12 (in other words, in side view in the electrode finger facing direction D12). Meanwhile, in plan view in the direction of lamination D11, the multiple first electrode fingers 330 and the multiple second electrode fingers 340 are disposed adjacent to one another. Specifically, the multiple first electrode fingers 330 and the multiple second electrode fingers 340 are alternately arranged in the electrode finger facing direction D12. The first electrode finger 330 and the second electrode finger 340 located adjacent to each other are disposed to face in the electrode finger facing direction D12, thus defining a pair of electrodes.
As described above, the IDT electrode 300 includes a pair of comb-shaped electrodes including one comb-shaped electrode provided with the first busbar electrode 310 and the multiple first electrode fingers 330 and another comb-shaped electrode provided with the second busbar electrode 320 and the multiple second electrode fingers 340. Respective comb-shaped portions of the pair of comb-shaped electrodes are interdigitated with one another. As described above, the IDT electrode 300 is the IDT electrode. That is to say, the pair of comb-shaped electrodes define the IDT electrode.
The multiple first electrode fingers 330 and the multiple second electrode fingers 340 include an excitation region C1 and gap regions C2. The excitation region C1 is a region where the first electrode fingers 330 and the second electrode fingers 340 located adjacent thereto overlap in side view in the electrode finger facing direction D12. Each gap region C2 is a region where the first electrode fingers 330 and the second electrode fingers 340 located adjacent thereto do not overlap in side view in the electrode finger facing direction D12. That is to say, regarding the multiple first electrode fingers 330, the gap region C2 is a region on the first busbar electrode 310 side relative to the excitation region C1. Meanwhile, regarding the multiple second electrode fingers 340, the gap region C2 is a region on the second busbar electrode 320 side relative to the excitation region C1.
As illustrated in
As illustrated in
As illustrated in
In the second example embodiment, for example, the first dielectric film 510 is made of silicon oxide (SiO2) and the second dielectric film 520 is made silicon nitride (SiN). That is to say, in the second example embodiment, the first dielectric film 510 is, for example, a silicon oxide film and the second dielectric film 520 is a silicon nitride film. Here, the first dielectric film 510 may be made of a material other than silicon oxide such as, for example, silicon nitride, silicon oxynitride, and tantalum pentoxide, while the second dielectric film 520 may be made of a material other than silicon nitride such as, for example, diamond, silicon, silicon nitride, aluminum nitride, and aluminum oxide.
In the second example embodiment, hygroscopicity of the second dielectric film 520 is lower than hygroscopicity of the first dielectric film 510. Here, the hygroscopicity is equivalent to a water absorption rate. The water absorption rate is a ratio of an amount of increase in weight of a dielectric film relative to its original weight when the dielectric film is soaked in distilled water for a predetermined period of time under a certain temperature.
The first dielectric film 510 includes a first series dielectric film 511 that defines a portion of the series arm resonator 120, and a first parallel dielectric film 512 that defines a portion of the parallel arm resonator 130. The first series dielectric film 511 and the first parallel dielectric film 512 have different thicknesses and configurations thereof other than the thicknesses are the same or substantially the same. The thickness of one of the first series dielectric film 511 and the first parallel dielectric film 512 is larger than the thickness of the other one of the first series dielectric film 511 and the first parallel dielectric film 512. In the second example embodiment, a thickness t2 of the first parallel dielectric film 512 is larger than a thickness t1 of the first series dielectric film 511. Here, the thickness t1 may be larger than the thickness t2 instead.
The second dielectric film 520 includes a second series dielectric film 521 that constitutes a portion of the series arm resonator 120, and a second parallel dielectric film 522 that constitutes a portion of the parallel arm resonator 130. The second series dielectric film 521 and the second parallel dielectric film 522 have different thicknesses and configurations thereof other than the thicknesses are the same. The thickness of one of the second series dielectric film 521 and the second parallel dielectric film 522 is smaller than the thickness of the other one of the second series dielectric film 521 and the second parallel dielectric film 522.
To be more precise, of the series arm resonator 120 and the parallel arm resonator 130, the resonator including the thicker first dielectric film 510 includes the thinner second dielectric film 520. In the meantime, of the series arm resonator 120 and the parallel arm resonator 130, the resonator including the thinner first dielectric film 510 includes the thicker second dielectric film 520. In the second example embodiment, the thickness t2 of the first parallel dielectric film 512 is larger than the thickness t1 of the first series dielectric film 511. That is to say, the thickness of the first dielectric film 510 of the parallel arm resonator 130 is larger than the thickness of the first dielectric film 510 of the series arm resonator 120. Accordingly, in the second example embodiment, a thickness t4 of the second parallel dielectric film 522 is smaller than a thickness t3 of the second series dielectric film 521. In other words, the thickness of the second dielectric film 520 of the parallel arm resonator 130 is smaller than the thickness of the second dielectric film 520 of the series arm resonator 120. Here, in contrast to the second example embodiment, the thickness t3 is set to be smaller than the thickness t4 when the thickness t1 is set to be larger than the thickness t2.
In the second example embodiment, by setting the respective thicknesses t1, t2, t3, and t4 as described above, it is possible to reduce the difference in amount of frequency variation (such as the amount of frequency drop) between the series arm resonator 120 and the parallel arm resonator 130 due to the moisture absorption by the dielectric film 500, which will be described below in detail.
The difference in frequency between the series arm resonator 120 and the parallel arm resonator 130 is obtained by using the difference between the thicknesses t1 and t2. In FIG. 22, the thickness t2 (the thickness in the parallel arm resonator 130) of the first parallel dielectric film 512 is larger than the thickness t1 (the thickness in the series arm resonator 120) of the first series dielectric film 511 (t2>t1).
In the first example embodiment, the second dielectric film 520 having the low hygroscopicity is provided on the first dielectric film 510 having the high hygroscopicity. In this way, the amount of frequency variation is reduced or prevented as a whole.
Meanwhile, when the thickness t2 is larger than the thickness t1, the amount of frequency variation attributed to the moisture absorption of the first parallel dielectric film 512 having the thickness t2 is larger than the amount of frequency variation attributed to the moisture absorption of the first series dielectric film 511 having the thickness t1. That is to say, the amount of frequency variation attributed to the moisture absorption in the first dielectric film 510 is larger in the parallel arm resonator 130 than in the series arm resonator 120.
Given the circumstances, the difference in amount of frequency variation is reduced in the first example embodiment by setting the thicknesses t3 and t4 in the second dielectric film 520 as described below in detail.
The configurations of the second dielectric films 520 in the series arm resonator 120 and the parallel arm resonator 130 are appropriately set based on frequency sensitivity attributed to the configurations of the second dielectric film 520, respectively, such that the amount of frequency variation after moisture absorption of the series arm resonator 120 becomes equal to that of the parallel arm resonator 130.
In contrast to the configurations of the first dielectric films 510 (the difference between the thicknesses t1 and t2), the configurations of the second dielectric films 520 are set such that the amount of frequency variation in the series arm resonator 120 is larger than that in the parallel arm resonator 130. That is to say, the thicknesses of the second series dielectric film 521 and the second parallel dielectric film 522 are set such that a magnitude relationship in thickness between the second series dielectric film 521 and the second parallel dielectric film 522 is opposite to a magnitude relationship in thickness between the first series dielectric film 511 and the first parallel dielectric film 512. Specifically, as described above, the thickness t4 of the second parallel dielectric film 522 (the thickness of the second dielectric film 520 in the parallel arm resonator 130) is smaller than the thickness t3 of the second series dielectric film 521 (the thickness of the second dielectric film 520 in the series arm resonator 120) (t4<t3).
As a consequence, the amount of frequency variation in the second dielectric film 520 in the series arm resonator 120 is larger than that in the parallel arm resonator 130. Here, as described above, the amount of frequency variation in the first dielectric film 510 in the parallel arm resonator 130 is larger than that in the series arm resonator 120. Accordingly, the thicknesses t3 and t4 are adjusted in response to the thicknesses t1 and t2 so as to reduce the difference in amount of frequency variation between the series arm resonator 120 and he parallel arm resonator 130 in total.
Here, t2>t1 and t4<t3 are satisfied in the first example embodiment. In contrast, t2<t1 and t4>t3 may be satisfied instead.
Meanwhile, composition ratios of the materials of the second series dielectric film 521 and the second parallel dielectric film 522 are the same or substantially the same in the first example embodiment. However, the composition ratios may be different as in a second dielectric film 530 of a third example embodiment of the present invention to be described below. In this case, the respective thicknesses of the second series dielectric film 521 and the second parallel dielectric film 522 are set as appropriate depending on the difference in composition ratio of the materials.
An acoustic wave device 100A according to the third example embodiment is different from the acoustic wave device 100 according to the second example embodiment in that the second dielectric film 530 is provided instead of the second dielectric film 520. Different features from those in the second example embodiment will be described below. Features in common to those of the acoustic wave device 100 according to the second example embodiment will be denoted by the same reference signs and explanations thereof will be basically omitted or explained when necessary.
As illustrated in
The second dielectric film 530 includes a second series dielectric film 531 that defines a portion of the series arm resonator 120, and a second parallel dielectric film 532 that defines a portion of the parallel arm resonator 130. A composition ratio of materials of the second series dielectric film 531 is different from a composition ratio of materials of the second parallel dielectric film 532. A thickness t5 of the second series dielectric film 531 and a thickness t6 of the second parallel dielectric film 532 are equal or substantially equal. Except for the above-described configurations, the second dielectric film 530 has the same or substantially the same configurations as those of the second dielectric film 520.
For example, a composition percentage of silicon in one silicon nitride film of the second dielectric film 530 of the series arm resonator 120 and the second dielectric film 530 of the parallel arm resonator 130 is higher than a composition percentage of silicon in the other silicon nitride film out of the second dielectric film 530 of the series arm resonator 120 and the second dielectric film 530 of the parallel arm resonator 130.
In the third example embodiment, the composition percentage of silicon in the second dielectric film 530 of the resonator including the thick first dielectric film 510 is set to be higher than the composition percentage of silicon in the second dielectric film 530 of the resonator including the thin first dielectric film 510. Here, the thickness t2 of the first parallel dielectric film 512 of the parallel arm resonator 130 is larger than the thickness t1 of the first series dielectric film 511 of the series arm resonator 120. Accordingly, the composition percentage of silicon in the second parallel dielectric film 532 of the parallel arm resonator 130 is higher than the composition percentage of silicon in the second series dielectric film 531 of the series arm resonator 120.
The amount of frequency variation of the second dielectric film 530 becomes smaller as the composition percentage of silicon is higher and becomes larger as the composition percentage of silicon is lower. Accordingly, the amount of frequency variation in the second dielectric film 530 is larger in the series arm resonator 120 than in the parallel arm resonator 130. Here, as described above, the amount of frequency variation in the first dielectric film 510 is larger in the parallel arm resonator 130 than in the series arm resonator 120. That is to say, of the series arm resonator 120 and the parallel arm resonator 130, the composition percentage of the second dielectric film 530 is set in the resonator having the larger amount of frequency variation in the first dielectric film 510 to reduce the amount of frequency variation. This makes it possible to reduce the difference in amount of frequency variation in total by using the series arm resonator 120 and the parallel arm resonator 130.
In the third example embodiment, the composition percentage of silicon in the second parallel dielectric film 532 of the parallel arm resonator 130 is higher than the composition percentage of silicon in the second series dielectric film 531 of the series arm resonator 120. However, the present invention is not limited to this configuration. For example, when the thickness t2 of the first parallel dielectric film 512 is smaller than the thickness t1 of the first series dielectric film 511 in contrast to the above-described configurations illustrated in
In the third example embodiment, for example, the second dielectric film 530 is made of silicon nitride and the composition ratios of the materials of the second series dielectric film 531 and the second parallel dielectric film 532 involve the composition percentage of silicon. However, the composition ratios of the materials are not limited to the composition ratio of silicon but may be set as appropriate depending on the materials of the second dielectric film 530.
In the third example embodiment, the thickness t5 of the second series dielectric film 531 is equal or substantially equal to the thickness t6 of the second parallel dielectric film 532. However, without limitation to the foregoing, the thickness t5 may be larger or smaller than the thickness t6. In this case, the composition ratios of the respective materials of the second series dielectric film 531 and the second parallel dielectric film 532 may be set as appropriate depending on the difference in thickness between the thicknesses t5 and t6.
An acoustic wave device 100B according to the fourth example embodiment is different from the acoustic wave device 100 according to the second example embodiment in that the dielectric film 500 includes a third dielectric film 540 and a fourth dielectric film 550. Different features from those in the second example embodiment will be described below. Features in common to those of the acoustic wave device 100 according to the second example embodiment will be denoted by the same reference signs and explanations thereof will be basically omitted or explained when necessary.
The third dielectric film 540 is laminated on the other principal surface 230A of the piezoelectric layer 230. In the present example embodiment, the third dielectric film 540 has the same or substantially the same configuration as that of the first dielectric film 510. For example, the third dielectric film 540 is a silicon oxide film as with the first dielectric film 510.
The fourth dielectric film 550 is laminated on the third dielectric film 540. In the present example embodiment, the fourth dielectric film 550 has the same or substantially the same configuration as that of the second dielectric film 520. For example, the fourth dielectric film 550 is a silicon nitride film as with the second dielectric film 520. Here, as with the second dielectric film 520, the fourth dielectric film 550 may be made a material other than silicon nitride such as, for example, diamond, silicon, silicon nitride, aluminum nitride, and aluminum oxide.
Hygroscopicity of the fourth dielectric film 550 is lower than hygroscopicity of the third dielectric film 540.
The third dielectric film 540 includes a third series dielectric film 541 that defines a portion of the series arm resonator 120, and a third parallel dielectric film 542 that defines a portion of the parallel arm resonator 130. The third series dielectric film 541 corresponds to the first series dielectric film 511 of the second example embodiment. The third parallel dielectric film 542 corresponds to the first parallel dielectric film 512 of the second example embodiment.
That is to say, in the present example embodiment, the third series dielectric film 541 has the same or substantially the same configuration as that of the first series dielectric film 511, and the third parallel dielectric film 542 has the same or substantially the same configuration as that of the first parallel dielectric film 512.
Meanwhile, in the present example embodiment, a relative magnitude relationship between a thickness of the third series dielectric film 541 and a thickness of the third parallel dielectric film 542 is the same or substantially the same as the relative magnitude relationship between the thickness of the first series dielectric film 511 and the thickness of the first parallel dielectric film 512. In the fourth example embodiment, the third series dielectric film 541 has the same or substantially the same thickness t1 as the first series dielectric film 511, and the third parallel dielectric film 542 has the same or substantially the same thickness t2 as the first parallel dielectric film 512. Here, these thicknesses are mere examples. That is to say, the third series dielectric film 541 may have a different thickness from that of the first series dielectric film 511, or the third parallel dielectric film 542 may have a different thickness from that of the first parallel dielectric film 512.
The fourth dielectric film 550 includes a fourth series dielectric film 551 that defines a portion of the series arm resonator 120, and a fourth parallel dielectric film 552 that defines a portion of the parallel arm resonator 130. The fourth series dielectric film 551 corresponds to the second series dielectric film 521 of the second example embodiment. The fourth parallel dielectric film 552 corresponds to the second parallel dielectric film 522 of the second example embodiment.
That is to say, in the present example embodiment, the fourth series dielectric film 551 has the same or substantially the same configuration as that of the second series dielectric film 521, and the fourth parallel dielectric film 552 has the same or substantially the same configuration as that of the second parallel dielectric film 522.
Meanwhile, a relative magnitude relationship between a thickness of the fourth series dielectric film 551 and a thickness of the fourth parallel dielectric film 552 is the same or substantially the same as the relative magnitude relationship between the thickness of the second series dielectric film 521 and the thickness of the second parallel dielectric film 522. In the fourth example embodiment, the fourth series dielectric film 551 has the same or substantially the same thickness t3 as the second series dielectric film 521, and the fourth parallel dielectric film 552 has the same or substantially the same thickness t4 as the second parallel dielectric film 522. Here, these thicknesses are mere examples. That is to say, the fourth series dielectric film 551 may have a different thickness from that of the second series dielectric film 521, or the fourth parallel dielectric film 552 may have a different thickness from that of the second parallel dielectric film 522.
Meanwhile, the thicknesses of the third dielectric film 540 and the fourth dielectric film 550 are not always different between the series arm resonator 120 and the parallel arm resonator 130. That is to say, when the acoustic wave device includes the third dielectric film 540 and the fourth dielectric film 550, the thickness of the third dielectric film 540 and the thickness of the fourth dielectric film 550 may be set arbitrarily. This also applies to a third dielectric film 560 and a fourth dielectric film 570 in a fifth example embodiment of the present invention to be described below.
An acoustic wave device 100C according to the fifth example embodiment is different from the acoustic wave device 100A according to the third example embodiment in that the acoustic wave device 100C includes a third dielectric film and a fourth dielectric film. Different features from those in the third example embodiment will be described below. Features in common to those of the acoustic wave device 100A according to the third example embodiment will be denoted by the same reference signs and explanations thereof will be basically omitted or explained when necessary.
The third dielectric film 560 is laminated on the other principal surface 230A of the piezoelectric layer 230. The third dielectric film 560 has the same or substantially the same configuration as that of the first dielectric film 510. For example, the third dielectric film 560 is a silicon oxide film as with the first dielectric film 510.
The fourth dielectric film 570 is laminated on the third dielectric film 560. The fourth dielectric film 570 has the same or substantially the same configuration as that of the second dielectric film 530. For example, the fourth dielectric film 570 is a silicon nitride film as with the second dielectric film 530. Here, as with the second dielectric film 530, the fourth dielectric film 570 may be made of a material other than silicon nitride such as, for example, diamond, silicon, silicon nitride, aluminum nitride, and aluminum oxide.
Hygroscopicity of the fourth dielectric film 570 is lower than hygroscopicity of the third dielectric film 560.
The third dielectric film 560 includes a third series dielectric film 561 that defines a portion of the series arm resonator 120, and a third parallel dielectric film 562 that defines a portion of the parallel arm resonator 130. The third series dielectric film 561 corresponds to the first series dielectric film 511 of the third example embodiment. The third parallel dielectric film 562 corresponds to the first parallel dielectric film 512 of the third example embodiment.
That is to say, the third series dielectric film 561 has the same or substantially the same configuration as that of the first series dielectric film 511, and the third parallel dielectric film 562 has the same or substantially the same configuration as that of the first parallel dielectric film 512.
Meanwhile, a relative magnitude relationship between a thickness of the third series dielectric film 561 and a thickness of the third parallel dielectric film 562 is the same or substantially the same as the relative magnitude relationship between the thickness of the first series dielectric film 511 and the thickness of the first parallel dielectric film 512. In the fifth example embodiment, the third series dielectric film 561 has the same or substantially the same thickness t1 as the first series dielectric film 511, and the third parallel dielectric film 562 has the same or substantially the same thickness t2 as the first parallel dielectric film 512. Here, these thicknesses are mere examples. That is to say, the third series dielectric film 561 may have a different thickness from that of the first series dielectric film 511, or the third parallel dielectric film 562 may have a different thickness from that of the first parallel dielectric film 512.
The fourth dielectric film 570 includes a fourth series dielectric film 571 that defines a portion of the series arm resonator 120, and a fourth parallel dielectric film 572 that defines a portion of the parallel arm resonator 130. The fourth series dielectric film 571 corresponds to the second series dielectric film 531 of the second example embodiment. The fourth parallel dielectric film 572 corresponds to the second parallel dielectric film 532 of the second example embodiment.
That is to say, the fourth series dielectric film 571 has the same or substantially the same configuration as that of the second series dielectric film 531, and the fourth parallel dielectric film 572 has the same or substantially the same configuration as that of the second parallel dielectric film 532. Specifically, a composition ratio of materials of the fourth series dielectric film 571 is different from a composition ratio of materials of the fourth parallel dielectric film 572. A thickness t5 of the fourth series dielectric film 571 and a thickness t6 of the fourth parallel dielectric film 572 are equal or substantially equal. Here, the fourth series dielectric film 571 may have a different thickness from that of the second series dielectric film 531, or the fourth parallel dielectric film 572 may have a different thickness from that of the second parallel dielectric film 532.
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.
This application claims the benefit of priority to Provisional Application No. 63/333,307 filed on Apr. 21, 2022 and is a Continuation Application of PCT Application No. PCT/JP2023/015798 filed on Apr. 20, 2023. The entire contents of each application are hereby incorporated herein by reference.
Number | Date | Country | |
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63333307 | Apr 2022 | US |
Number | Date | Country | |
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Parent | PCT/JP2023/015798 | Apr 2023 | WO |
Child | 18918786 | US |