JP6072604B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave (SAW) element.

  A SAW element having a piezoelectric substrate and an IDT (InterDigital Transducer) provided on the main surface of the piezoelectric substrate is known (for example, Patent Document 1). Such a SAW element is used, for example, as a duplexer reception filter or transmission filter. In Patent Document 1, a piezoelectric substrate is not used alone for a SAW element, but a bonded substrate obtained by bonding a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient than that of the piezoelectric substrate is used for the SAW element. . By using such a bonded substrate, for example, a temperature change in the electrical characteristics of the SAW element is compensated.

JP 2007-214902 A

  However, when a bonded substrate is used as described above, spurious characteristics that do not occur when the bonded substrate is not used may occur with respect to the electrical characteristics of the SAW element. Therefore, it is desirable to provide a surface acoustic wave device that can reduce such spurious.

A surface acoustic wave device according to an aspect of the present invention is located on a piezoelectric substrate, a support substrate bonded to the lower surface of the piezoelectric substrate, and an upper surface of the piezoelectric substrate, and has an equivalent electrode finger pitch and is elastic. It has the 1st IDT electrode and 2nd IDT electrode which were arranged in the propagation direction of surface wave, and a plurality of reflectors provided between these IDT electrodes and on the both outsides, and satisfies the following (1) formula.
60 ° ≦ φ ≦ 300 ° and 0.05 ≦ L ₁ / (L ₁ + L ₂ ) ≦ 0.95 (1)
Where φ is the phase difference between the _first IDT electrode and the second IDT electrode, and L ₁ and L ₂ are the lengths of the first IDT electrode and the second IDT electrode in the propagation direction of the surface acoustic wave.

Preferably, the following equation (2) is satisfied: 0.15 ≦ L ₁ / (L ₁ + L ₂ ) ≦ 0.85 (2)

A surface acoustic wave device according to an aspect of the present invention is located on a piezoelectric substrate, a support substrate bonded to the lower surface of the piezoelectric substrate, and an upper surface of the piezoelectric substrate, and has an equivalent electrode finger pitch and is elastic. A first IDT electrode, a second IDT electrode and a third IDT electrode arranged in order in the propagation direction of the surface wave, and a plurality of reflectors provided between and outside the IDT electrodes, the first IDT electrode and The third IDT electrode has no phase difference between them and is equal in length in the propagation direction of the surface acoustic wave, and satisfies the following expression (3).
100 ° ≦ φ ≦ 260 ° and 0.01 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.49 (3)
Where φ is the phase difference between the _first IDT electrode and the second IDT electrode, and L ₁ and L ₂ are the lengths of the first IDT electrode and the second IDT electrode in the propagation direction of the surface acoustic wave.

Preferably, the following expression (4), expression (5) or expression (6) is satisfied.
140 ° ≦ φ ≦ 220 ° and 0.10 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.25 (4)
110 ° ≦ φ ≦ 140 ° and 0.14 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.36 (5)
220 ° ≦ φ ≦ 250 ° and 0.14 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.36 (6)

A surface acoustic wave device according to an aspect of the present invention is located on a piezoelectric substrate, a support substrate bonded to the lower surface of the piezoelectric substrate, and an upper surface of the piezoelectric substrate, and has an equivalent electrode finger pitch and is elastic. It has a plurality of IDT electrodes arranged in the propagation direction of the surface wave and a plurality of reflectors provided between and outside these IDT electrodes, and OI _max / OI _V defined below is 0.975 It is as follows. For an arbitrary IDT electrode, a surface acoustic wave that indicates an electric field applied by the IDT electrode and that has a first periodic function with a position in the propagation direction of the surface acoustic wave as a variable, and a bulk wave that propagates through the piezoelectric substrate. The overlap integral obtained by integrating the product of the second periodic function with the position in the propagation direction is a variable over the length of the IDT electrode in the propagation direction of the surface acoustic wave is defined as OI. For the i-th IDT electrode among the plurality of IDT electrodes, the function of overlap integral OI with the frequency and phase of the bulk wave propagating through the piezoelectric substrate as variables is defined as OI _i . The frequency and phase of the bulk wave are common among the plurality of IDT electrodes, and the phase of the first periodic function is the sum of OI _i calculated by making the phase difference between the plurality of IDT electrodes different among the plurality of IDT electrodes. _i . The maximum value of ΣOI _i having the frequency and phase of the bulk wave as variables is defined as OI _max . One virtual IDT electrode is assumed in which the phase differences of the plurality of IDT electrodes are eliminated and coupled together. For this virtual IDT electrode, the maximum value of the overlap integral OI with the frequency and phase of the bulk wave as variables is defined as OI _V. A value obtained by dividing OI _max by OI _V and normalizing is OI _max / OI _V described above.

Preferably, OI _max / OI _V is 0.75 or less.

  Preferably, two reflectors are provided between two adjacent IDT electrodes, and each of the two reflectors has 30 strip electrodes extending in a direction perpendicular to the propagation direction of the surface acoustic wave. One reflector is provided between two adjacent IDT electrodes, or the number of strip electrodes extending in a direction perpendicular to the propagation direction of the surface acoustic wave is 60 or more. It is.

  According to said structure, the spurious which arises when using a bonded substrate can be suppressed.

1 is a plan view showing a configuration of a SAW element according to a first embodiment of the present invention. It is sectional drawing in the II-II line of FIG. FIGS. 3A and 3B are schematic views for explaining the operation of the SAW element of FIG. FIG. 2 is a contour map showing the result of calculating a maximum overlap integral value OI _max for the SAW element of FIG. 1. 5A and 5B are cross-sectional views at various positions in FIG. 6A to 6F are diagrams showing measurement results of impedance characteristics of SAW elements according to the comparative example and the example. FIGS. 7A to 7F are enlarged views of a part on the high frequency side of the pass band in FIGS. 6A to 6F. FIG. 8A to FIG. 8E are diagrams showing measurement results of impedance characteristics of SAW elements according to comparative examples and other examples. 9 (a) to 9 (e) are enlarged views of a part on the high frequency side of the pass band in FIGS. 8 (a) to 8 (e). FIG. 10A to FIG. 10C are diagrams for explaining the influence of the bulk wave on the impedance characteristics of the SAW element according to the example. It is a top view which shows the structure of the SAW element which concerns on the 2nd Embodiment of this invention. FIG. 12 is a contour diagram showing a result of calculating a maximum overlap integral value OI _max for the SAW element of FIG. 11. 13A and 13B are cross-sectional views at various positions in FIG. 14A to 14C are diagrams showing measurement results of impedance characteristics of SAW elements according to the comparative example and the example. FIG. 15A to FIG. 15C are diagrams showing a part of the high frequency side of the pass band in FIG. 14A to FIG. 14C in an enlarged manner. It is a top view which shows the structure of the SAW element which concerns on the 3rd Embodiment of this invention. FIGS. 17A and 17B are diagrams illustrating measurement results of impedance characteristics of SAW elements according to the comparative example and the example. 18 (a) and 18 (b) are enlarged views showing a part on the high frequency side of the pass band in FIGS. 17 (a) and 17 (b).

  Hereinafter, SAW elements according to embodiments of the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

  The SAW element may have either direction upward or downward, but in the following, for convenience, the orthogonal coordinate system xyz is defined, and the positive side in the z direction is the upper side, the upper surface, the lower surface, etc. The following terms shall be used.

  In the second and subsequent embodiments, configurations that are the same as or similar to the configurations of the already described embodiments may be denoted by the same reference numerals as those of the already described embodiments, and description thereof may be omitted.

<First Embodiment>
(Overview of SAW element configuration)
FIG. 1 is a plan view showing a configuration of a SAW element 1 according to the first embodiment of the present invention. 2 is a cross-sectional view taken along line II-II in FIG.

  The SAW element 1 has a bonded substrate 3 and a first resonator 9A and a second resonator 9B provided on the upper surface 5a of the bonded substrate 3. The bonded substrate 3 has a piezoelectric substrate 5 and a support substrate 7 (FIG. 2) bonded to the lower surface 5 b of the piezoelectric substrate 5.

  Hereinafter, the first resonator 9A and the second resonator 9B are simply referred to as “resonator 9”, and they may not be distinguished from each other. In addition, “A” is added to the name of the configuration related to the first resonator 9A, and “A” is added to the reference symbol, and “Second” is added to the name of the configuration related to the second resonator 9B. In some cases, “B” may be added to the reference numeral, and “first”, “second”, “A”, and “B” may be omitted as in the resonator 9. The same applies to the resonators of the second and subsequent embodiments, and the same applies when three or more resonators are provided.

In addition to the above, the SAW element 1 is made of SiO ₂ or the like, and may have a protective layer or the like that covers the resonator 9. 1 and 2, the wiring for inputting and outputting signals to the resonator 9 is not shown.

The piezoelectric substrate 5 is composed of a single crystal substrate having piezoelectricity such as tantalum niobate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ) single crystal, or the like. More preferably, the piezoelectric substrate 5, 42 ° ± 10 ° Y- X cut LiTaO3,128 ° ± 10 ° Y-X cut LiNbO ₃ substrate or 0 ° ± 10 ° Y-X cut LiNbO ₃ substrate, etc. It is constituted by. In addition, quartz (SiO ₂ ) single crystal can be used.

  The thickness of the piezoelectric substrate 5 is, for example, constant, and the size thereof may be appropriately set according to the technical field to which the SAW element 1 is applied, the specifications required for the SAW element 1, and the like. As an example, the thickness of the piezoelectric substrate 5 is 20 to 30 μm. The planar shape and various dimensions of the piezoelectric substrate 5 may be set as appropriate.

  The support substrate 7 is formed of, for example, a material having a smaller thermal expansion coefficient than the material of the piezoelectric substrate 5. This makes it possible to compensate for temperature changes in the electrical characteristics of the SAW element 1 as will be described later. Examples of such a material include a single crystal such as sapphire, a semiconductor such as silicon, and a ceramic such as an aluminum oxide sintered body. The support substrate 7 may be configured by laminating a plurality of layers made of different materials.

  The thickness of the support substrate 7 is, for example, constant, and the size thereof may be appropriately set similarly to the thickness of the piezoelectric substrate 5. However, the thickness of the support substrate 7 is set in consideration of the thickness of the piezoelectric substrate 5 so that temperature compensation is suitably performed. As an example, the thickness of the support substrate 7 is 100 to 300 μm while the thickness of the piezoelectric substrate 5 is 10 to 30 μm. The planar shape and various dimensions of the support substrate 7 are, for example, equivalent to the piezoelectric substrate 5.

The piezoelectric substrate 5 and the support substrate 7 are bonded to each other through an adhesive layer (not shown), for example. The material of the adhesive layer may be an organic material or an inorganic material. Examples of the organic material include a resin such as a thermosetting resin. Examples of the inorganic material include SiO ₂ . Alternatively, the bonding surface may be bonded by so-called direct bonding, in which the bonding surface is bonded with no bonding layer after being activated by plasma or the like.

  Each resonator 9 has an IDT electrode 11 and a pair of reflectors 13 located on both sides of the IDT electrode 11.

  The IDT electrode 11 is constituted by a conductive pattern (conductive layer) formed on the upper surface 5a of the piezoelectric substrate 5, and has an input side comb electrode 15C and an output side comb electrode 15D as shown in FIG. Yes. In the following, this is simply referred to as “comb electrode 15”, and the two may not be distinguished. Further, the pair of comb electrodes 15 refers to a combination of the input side comb electrode 15C and the output side comb electrode 15D.

  The pair of comb-shaped electrodes 15 includes a bus bar 17 (FIG. 1) facing each other and a plurality of electrode fingers 19 extending from the bus bar 17 in the facing direction. The pair of comb electrodes 15 are arranged so that the plurality of electrode fingers 19 mesh with each other (intersect).

  Note that the SAW propagation direction is defined by the orientation of the plurality of electrode fingers 19, but in the present embodiment, for convenience, the orientation of the plurality of electrode fingers 19 will be described with reference to the SAW propagation direction.

  For example, the bus bar 17 is formed in a long shape having a substantially constant width and extending linearly in the SAW propagation direction (x direction). The bus bars 17 of the pair of comb electrodes 15 oppose each other in the direction (y direction) intersecting the SAW propagation direction.

  The plurality of electrode fingers 19 are formed in an elongated shape extending in a straight line in a direction (y direction) perpendicular to the SAW propagation direction with a substantially constant width, and are substantially constant in the SAW propagation direction (x direction). Arranged at intervals. The plurality of electrode fingers 19 of the pair of comb-tooth electrodes 15 have a pitch p (for example, a distance between the centers of the electrode fingers 19) equal to, for example, a half wavelength of the SAW wavelength λ at a frequency to be resonated. Is provided. The wavelength λ is, for example, not less than 1.5 μm and not more than 6 μm.

  In some of the plurality of electrode fingers 19, the pitch p may be relatively small, or conversely, the pitch p may be relatively large. It is known that providing such a narrow pitch portion or a wide pitch portion improves the frequency characteristics of the SAW element. In the present embodiment, when the pitch p (electrode finger pitch) is simply referred to, the pitch p of the portion excluding the pitch p of the narrow pitch portion and the wide pitch portion (most part of the plurality of electrode fingers 19) unless otherwise specified. Or it shall mean the average value. Similarly, unless otherwise specified, the term “electrode finger 19” refers to the electrode finger 19 other than the narrow pitch portion or the wide pitch portion.

  The number, length (y direction), and width (x direction) of the plurality of electrode fingers 19 may be appropriately set according to electrical characteristics required for the SAW element 1. As an example, the number of the plurality of electrode fingers 19 in the entire first resonator 9A and the second resonator 9B is 100 or more and 400 or less. The length and width of the plurality of electrode fingers 19 are, for example, equal to each other.

  The reflector 13 is constituted by, for example, a conductive pattern (conductive layer) formed on the upper surface 5a of the piezoelectric substrate 5, and is formed in a lattice shape in plan view. That is, the reflector 13 includes a pair of bus bars 21 (FIG. 1) facing each other in a direction intersecting the SAW propagation direction, and a plurality of reflectors 13 extending in a direction (y direction) perpendicular to the SAW propagation direction between the bus bars 21. Strip electrode 23.

  For example, the bus bar 21 is formed in a long shape having a substantially constant width and linearly extending in the SAW propagation direction (x direction). The pair of bus bars 17 oppose each other in the direction (y direction) intersecting the SAW propagation direction.

  The strip electrodes 23 are arranged at the same pitch as the plurality of electrode fingers 19 of the IDT electrode 11. The pitch between the electrode fingers 19 adjacent to each other and the strip electrode 23 (the pitch between the IDT electrode 11 and the strip electrode 23) is also equal to the pitch of the plurality of electrode fingers 19. The number, length (y direction) and width (x direction) of the strip electrodes 23 may be appropriately set according to the electrical characteristics required for the SAW element 1.

  In general, the number of strip electrodes 23 is about 20 in each reflector 13. However, in the present embodiment, the reflectors 13 positioned between the first resonator 9A and the second resonator 9B have 30 or more strip electrodes 23, respectively. In each of the reflectors 13 positioned outside the first resonator 9A and the second resonator 9B, the number of strip electrodes 23 may be a general number.

  The two resonators 9 are arranged in the SAW propagation direction (x direction). For example, the two resonators 9 have substantially the same configuration except for the number of electrode fingers 19. Specifically, for example, the length, width and pitch of the plurality of electrode fingers 19 and the intersection of the plurality of electrode fingers 19 of one comb-tooth electrode 15 and the plurality of electrode fingers 19 of the other comb-tooth electrode 15 The width is the same between the two resonators 9.

  The two resonators 9 are connected in parallel with each other. That is, the input-side comb electrode 15C of the first resonator 9A and the input-side comb electrode 15C of the second resonator 9B are connected, and the output-side comb electrode 15D of the first resonator 9A and the second resonance The output side comb-tooth electrode 15D of the child 9B is connected. The electric signal is input to the two input side comb electrodes 15C and output from the two output side comb electrodes 15D.

  Further, the input-side comb-tooth electrode 15C of the first resonator 9A and the input-side comb-tooth electrode 15C of the second resonator 9B are positioned on the same side (y-direction positive side) with respect to the intersecting region of the plurality of electrode fingers 19. The output-side comb-tooth electrode 15D of the first resonator 9A and the output-side comb-tooth electrode 15D of the second resonator 9B are located on the same side (y-direction negative side) with respect to the intersecting region of the plurality of electrode fingers 19. doing. However, as long as the resonators 9A and 9B are arranged so as to satisfy the spurious suppression method described later, the combing electrode connection method and which side may be selected arbitrarily.

  The conductor layer constituting the resonator 9 is made of metal, for example. Examples of the metal include Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al—Cu alloy. The conductor layer constituting the resonator 9 may be composed of a plurality of metal layers. The resonator 9 may have an insulating layer on the upper surface or the lower surface of the conductor layer for the purpose of increasing the reflection coefficient of the SAW resonator 9.

(Overview of spurious suppression methods)
FIG. 3A and FIG. 3B are schematic diagrams for explaining the operation of the SAW element 1. Specifically, FIG. 3 shows a cross section of the piezoelectric substrate 5 and the resonator 9 with the number of the electrode fingers 19 and the plurality of strip electrodes 23 being reduced from that of FIG.

  In FIG. 3, in order to show the potential difference between the pair of comb electrodes 15, for convenience, the electrode fingers 19 of the input side comb electrodes 15C are marked with +, and the electrodes of the output side comb electrodes 15D. The finger 19 is marked with-. Actually, since a high-frequency signal that is alternating current is input, + and-shown in the figure are potentials at a certain moment. Further, the potential of the input-side comb electrode 15C may be positive or negative with respect to the reference potential, and the potential of the output-side comb electrode 15D is positive with respect to the reference potential. It may be negative or negative. Further, the output-side comb electrode 15D may be connected to the reference potential portion.

  First, as shown in FIG. 3A, in each resonator 9, when an electric signal is input to the input-side comb electrode 15C and a voltage is applied to the piezoelectric substrate 5 by the plurality of electrode fingers 19, the piezoelectric substrate 5 is induced in the vicinity of the upper surface 5a. The SAW is reflected by the plurality of electrode fingers 19 and the plurality of strip electrodes 23. As a result, as shown by the line Ls, a SAW standing wave having a half wavelength of the pitch p of the plurality of electrode fingers 19 is formed. The standing wave generates an electric charge (an electric signal having the same frequency as that of the standing wave) on the upper surface 5a, and the electric signal is taken out by the plurality of electrode fingers 19 of the output-side comb electrode 15D.

  Here, when a voltage is applied to the piezoelectric substrate 5 by the plurality of electrode fingers 19, not only SAW but also a bulk wave propagating inside the piezoelectric substrate 5 is excited in the piezoelectric substrate 5, as indicated by a line Lb. Is done.

  As a result of intensive studies, the inventor of the present application has estimated that spurious generated when the bonded substrate 3 is used is caused by this bulk wave. The bulk wave is excited even when the bonded substrate 3 is not used. Nevertheless, the reason why the spurious wave is generated only when the bulk wave uses the bonded substrate 3 is as follows.

  First, the piezoelectric substrate 5 of the bonded substrate 3 is often made thinner than a piezoelectric substrate used alone without being bonded to the support substrate 7. For example, the thickness of the piezoelectric substrate 5 is about 1/10 that of a piezoelectric substrate used alone. This is because the required strength of the bonded substrate 3 is obtained by the support substrate 7.

  The bulk wave forms a standing wave between the front surface and the back surface of the piezoelectric substrate 5 in the depth direction of the piezoelectric substrate 5 and propagates as a traveling wave in the direction along the surface (SAW propagation direction). The so-called waveguide mode is considered. When the wave number in the direction along the surface of the waveguide mode coincides with the wave number (π / p) obtained from the period of the IDT, strong coupling between the IDT electrode and the waveguide mode of the bulk wave occurs, resulting in spurious. It is thought that it appears in the electrical characteristics. Since the piezoelectric substrate 5 is thin, the order of the standing wave in the depth direction of the guided mode of the bulk wave is reduced. As a result, in the piezoelectric substrate 5, it is considered that the frequency interval of the waveguide mode coupled with the IDT electrode becomes wide, and as a result, spurious due to the bulk wave becomes clear. When the piezoelectric substrate is thick, the frequency interval of the waveguide mode coupled with the IDT electrode is narrowed, and as a result, no clear spurious is observed.

  Further, since the piezoelectric substrate 5 is thin, bulk waves are concentrated in a narrow range in the depth direction. As a result, it is considered that the bulk wave is strongly coupled with the IDT electrode 11 and the mode is strongly excited.

  Further, the lower surface 5b of the piezoelectric substrate 5 is often flatter than the lower surface of the single-use piezoelectric substrate. By making the lower surface 5b flat, bulk waves are less likely to be scattered on the lower surface 5b. As a result, it is considered that the spurious of the bulk wave increases.

  In the present embodiment, based on the assumption that the spurious factor generated when the bonded substrate 3 is used is the coupling between the bulk wave waveguide mode and the IDT, the bulk waves are canceled out as a method of reducing spurious. Adopt the method to make it.

  Specifically, the two IDT electrodes 11 are arranged at certain intervals in the bulk wave propagation direction (SAW propagation direction). Thereby, the bulk waves excited in the two IDT electrodes 11 cancel each other.

  However, a reflector 13 is disposed between the two IDT electrodes 11 so as not to cancel up to SAW. Of course, reflectors 13 are arranged on both outer sides of the two IDT electrodes 11 in order to make the SAW less likely to be scattered outside. Since the bulk wave propagates inside the piezoelectric substrate 5, it is not significantly affected by the reflector 13 provided on the surface. For this reason, the SAW hardly propagates between the two IDT electrodes 11, and the bulk wave guided mode propagates. By such a mechanism, it is possible to cancel the bulk wave while suppressing the influence on the SAW.

  The IDT electrode 11 has a plurality of electrode fingers 19 periodically with a pitch p, and the electrode fingers 19 of the input side comb electrode 15C and the electrode fingers 19 of the output side comb electrode 15D are alternately arranged in the x direction. Has been placed. That is, the IDT electrode 11 has a periodic structure in which the pitch p is a half cycle. Therefore, the positional relationship between the two IDT electrodes 11 may be represented by the phase difference φ (FIG. 3B) of the periodic structure.

  Here, when the numerical value is changed, the phase difference φ is also the polarity of the two IDTs when each IDT electrode is virtually extended in the SAW propagation direction while maintaining the periodic structure of the IDT electrode. It is defined by the deviation of the included periodic structure. If two IDTs that are virtually extended overlap with each other, including the polarity, the phase difference is 0 °, and the IDT electrodes themselves overlap, but if the polarities of the electrodes are reversed, the phase difference is 180 °. . Hereinafter, the phase difference is used in the same meaning.

  On the other hand, the bulk wave is excited by the plurality of electrode fingers 19 of the IDT electrode 11 as shown in FIG. 3B, and thus has a periodicity due to the periodic structure of the IDT electrode 11. it is conceivable that. Therefore, if the phase difference φ is adjusted appropriately, it is predicted that the cancellation of the bulk wave is suitably performed. Therefore, as will be discussed in detail later, the phase difference φ is adjusted to an appropriate size.

  The phase difference φ is, for example, the distance (center between the arbitrary electrode finger 19 of the input-side comb electrode 15C of the first IDT electrode 11A and the arbitrary electrode finger 19 of the input-side comb electrode 15C of the second IDT electrode 11B. The distance is calculated by 2π × (Lt / 2p) where Lt (FIG. 3A) is set. This value may be adjusted to a value in the range of 0 to 2π by adjusting 2πn (n is an integer).

  For example, if Lt is p × (2m) (m is an integer), the phase difference φ is 0 °, and if Lt is p × (2m + 1), the phase difference φ is 180 °. This phase difference φ is also the phase difference between the standing waves of SAW excited in the two IDT electrodes 11. Therefore, for example, if the reflector 13 between the IDT electrodes 11 is not provided, the SAW excited by the two IDT electrodes 11 is out of phase when the phase difference φ is 180 ° and cancels out. It will be.

  Since the phase difference φ is appropriately set between the two IDT electrodes 11, the reflector located between the two IDT electrodes 11 needs to have a plurality of strip electrodes 23 corresponding to the phases of the IDT electrodes 11. is there. Accordingly, two reflectors 13 are arranged between the two IDT electrodes 11.

  If the resonator is configured to reduce spurious in accordance with the above-described concept, as a result, the two resonators 9 arranged in the SAW propagation direction as described above with reference to FIGS. A SAW element 1 having an IDT electrode 11 and a reflector 13 on each side thereof is configured.

  However, when the phase difference φ between the two IDT electrodes 11 is 180 °, the reflector 13 between the two IDT electrodes 11 can be shared. That is, in the SAW element 1, the number of reflectors 13 can be three. In the description of the embodiment, the number of the reflectors 13 between the IDT electrodes 11 is two even when φ is 180 ° unless otherwise specified.

  The two resonators 9 of the present embodiment are obtained by dividing one resonator that originally satisfies desired electrical characteristics in order to enable cancellation of bulk waves. That is, the number of electrode fingers 19 and the like are not designed separately for each resonator 9 but are designed so as to satisfy desired electrical characteristics in the entire two resonators 9. However, the bulk wave may be canceled between separately designed resonators.

(Method of setting phase difference φ, etc.)
Hereinafter, a method for calculating the magnitude of the bulk wave and a method for setting the phase difference φ based on the calculation method will be described.

  In the SAW element 1, as the overlap integral (OI: Overlap Integral) between the electric field (excitation effect by the IDT electrode 11) applied to the piezoelectric substrate 5 by the IDT electrode 11 and the bulk wave propagating through the piezoelectric substrate 5 increases, the IDT electrode 11 and the bulk wave are strongly coupled, and the bulk wave is considered to be large. Therefore, this overlap integral is calculated as follows.

First, only an arbitrary i-th IDT electrode 11 among the plurality of IDT electrodes 11 will be considered. A periodic function having an x-direction position as a variable indicating an electric field applied by the IDT electrode 11 is approximated by a sine wave, and is expressed by the following equation.
sin (k ₀ x + α _i )
However, _{k 0} is the wave number, a _{k 0} = _π / p. x is a position in the x direction. α _i is a phase, and is determined by the relationship between the reference position in the x direction (position where x = 0) and the positions of the plurality of electrode fingers 19. Note that the position of x = 0 may be an arbitrary position.

In addition, a periodic function having a variable in the position in the x direction indicating a bulk wave is approximated by a sine wave, and is expressed by the following equation.
sin (k _B x + α _B )
Here, k _B is the wave number of the bulk wave. α _B is the phase of the bulk wave and is determined by the positional relationship between the reference position in the x direction and the bulk wave.

For example, k _B may be calculated by the following equation assuming that there is no bulk wave dispersion.
k _B = ω _B / V _B = 2πf _B / V _B
Where ω _B is the angular frequency of the bulk wave, f _B is the frequency of the bulk wave, and V _B is the phase velocity of the propagation mode of the bulk wave. V _B is generally determined by the material and thickness of the piezoelectric substrate 5.

The overlap integral OI _i in the i-th IDT electrode 11 is obtained by integrating the product of the periodic function of the IDT electrode 11 and the periodic function of the bulk wave over the length of the i-th IDT electrode 11 in the x direction. Is represented by the following formula (A).

ただし、ｘ_ａｉおよびｘ_ｂｉは、ｉ番目のＩＤＴ電極１１のｘ方向の一方端および他方端の位置である（図１のｘ_ａ１、ｘ_ｂ１、ｘ_ａ２、およびｘ_ｂ２参照。）

Here, x _ai and x _bi are the positions of one end and the other end in the x direction of the i-th IDT electrode 11 (see x _a1 , x _b1 , x _a2 , and x _{b2 in} FIG. 1).

The overlap integral in the entire resonator 9 having a plurality of IDT electrodes 11 is represented by the sum ΣOI _i of the overlap integral OI _i of each IDT electrode 11. In this sum ΣOI _i , the phase difference of α _i is the same as the phase difference between the IDT electrodes 11. For example, if the phase difference φ between the first IDT electrode 11A and the second IDT electrode 11B is 180 °, α ₂ −α ₁ = φ = 180 °.

The total sum ΣOI _i of the overlap integral OI _i in the SAW element 1 varies depending on the values of x _ai , x _bi , k ₀ , k _B (f _B ), α _i, and α _B. Among these, x _ai , x _bi , k ₀ and α _i are determined by the configuration of the SAW element 1.

Therefore, regarding the SAW element 1 having various dimensions, the maximum value IO _max of the sum ΣOI _i is specified by calculating the sum ΣOI _i while changing the frequency f _B and the phase α _B of the bulk wave in various ways. .

It is considered that the bulk wave having the frequency f _{B at which} the maximum value IO _max is obtained is the bulk wave that most affects the occurrence of spurious. Further, it is considered that the spurious increases as the maximum value IO _max increases.

If the maximum value IO _max is calculated by changing the dimensions of the SAW element 1 in various _ways , the configuration of the SAW element 1 that can reduce the maximum value IO _max , that is, the configuration of the SAW element 1 that can reduce spurious due to bulk waves. Can be identified.

Specifically, x _ai and x _bi are defined by the length L _i of the IDT electrode 11 in the x direction (see L ₁ and L _{2 in} FIG. 1), and α _i is the phase difference φ between the IDT electrodes 11. Therefore, the maximum value OI _max may be calculated by variously changing L _i and φ.

(Calculation result of bulk wave size)
Hereinafter, a result of calculating the maximum value OI _max while varying the L _i and φ as described above.

Figure 4 is a contour diagram showing the result of calculating the maximum value OI _max of the overlap integral and the L _i and φ changed variously.

In FIG. 4, the horizontal axis indicates the normalized length L ₁ ^* in the x direction of the first IDT electrode 11A. The normalized length L ₁ ^* is a value L obtained by dividing the length L ₁ of the first IDT electrode 11A in the x direction by the total length (L ₁ + L ₂ ) of the _first IDT electrode 11A and the second IDT electrode 11B in the x direction. ₁ / (L ₁ + L ₂ ). Therefore, for example, L ₁ ^* = 0 corresponds to the case where only the second IDT electrode 11B is provided, and L ₁ ^* = 0.5 is equivalent in size to the first IDT electrode 11A and the second IDT electrode 11B. This corresponds to a case where L ₁ ^* = 1 corresponds to the case where only the first IDT electrode 11A is provided.

In FIG. 4, the vertical axis indicates the phase difference φ between the two IDT electrodes 11. FIG. 4 shows a range where the phase difference φ is 0 ° or more and 180 ° or less. Incidentally, the maximum value _{OI max} in the range of 180 ° 360 ° or more or less the same as the maximum value _{OI max} ranging from 0 ° or 180 ° or less (axisymmetrically 180 ° to the boundary).

In FIG. 4, the height of the contour line indicates the normalized maximum value OI _max ^* of the overlap integral. Normalized maximum value _{OI max} ^* is a value obtained by dividing the maximum value _OI max (OI _v) in the case of the maximum value _{OI max L} ¹ * = 0 (or 1). As described above, L ₁ ^* = 0 corresponds to the case where only one IDT electrode 11 is provided (comparative example). Contour lines are drawn in increments of 0.025.

From FIG. 4, it can be seen that OI _max ^* decreases as φ approaches 180 ° (reverse phase) and L ₁ ^* approaches 0.5, and the bulk wave cancels out. However, the minimum value of OI _max ^* occurs when L ₁ ^* is about 0.2 or about 0.8. This result is different from the intuitive prediction, that is, the prediction that the bulk wave is most canceled at L ₁ ^* = 0.5.

Note that even if the value of L ₁ + L ₂ is decreased or increased, FIG. 4 is normalized, so the same diagram as FIG. 4 can be obtained.

FIG. 5A shows the relationship between φ (horizontal axis) and OI _max ^* (vertical axis) when L ₁ ^* = 0.1, 0.2, 0.3, 0.4, and 0.5. And corresponds to the cross-sectional view of FIG. 4 at L ₁ ^* = 0.1, 0.2, 0.3, 0.4, and 0.5.

As shown in this figure, in general, OI _max ^* gradually decreases as φ increases, and a sudden change or the like does not occur. Therefore, it can be seen that a preferable range of φ can be appropriately set on the 180 ° side in accordance with the desired degree of effect (the desired reduction amount of OI _max ^* ).

FIG. 5B is a diagram showing the relationship between L ₁ ^* (horizontal axis) and OI _max ^* (vertical axis) in the case of φ = 60 °, 120 °, and 180 °, and φ = 60 °, 120 It corresponds to the cross-sectional view of FIG.

As shown in this figure, in any φ, OI _max ^* is large when L ₁ ^* is near 0 or near 1. When L ₁ ^* is slightly larger than 0 or L ₁ ^* is slightly smaller than 1, OI _max ^* is rapidly decreased. Therefore, it can be seen that a preferable range of L ₁ ^* can be set in a range slightly larger than 0 and slightly smaller than ₁ .

Also in FIG. 5B, as in FIG. 4, when L ₁ ^* is about 0.2 or 0.8, and L ₁ ^* is 0.5 (the most OI in intuitive prediction). _max ^* is appeared that the _{OI max} ^* is smaller than when) becomes smaller.

(Preferable range of φ and L ₁ ^* )
With reference to FIG. 4 and FIG. 5 described above, preferred ranges of φ and L ₁ ^* will be examined.

First, the normalized maximum value OI _max ^* of the overlap integral in the SAW element 1 is preferably small enough to confirm the effect of bulk wave cancellation compared to the comparative example (OI _max ^* = 1). Here, the minimum value of OI _max ^* is 0.5 from the theory. In other words, the maximum reduction amount of OI _max ^* is 0.5 (= 1−0.5). Therefore, for example, the OI _max ^* of the SAW element 1 is 5% to 10% (0.025 to 0.05) or more of the maximum reduction amount compared to the OI _max ^* (= 1) of the comparative example. It is preferable that the difference is small.
That is, preferably
OI _max ^* ≦ 0.975
And more preferably
OI _max ^* ≦ 0.95
It is.

Referring to FIG. 4 from such a viewpoint, for example, when the following expression is satisfied, OI _max ^* is preferably 0.975 or less.
60 ° ≦ φ ≦ 300 °
0.05 ≦ L ₁ ^* ≦ 0.95

Furthermore, for example, when the following formula is satisfied, OI _max ^* is approximately 0.95 or less, which is more preferable.
70 ° ≦ φ ≦ 290 °
0.10 ≦ L ₁ ^* ≦ 0.90

Further, it can be said that the effect of canceling the bulk wave is sufficiently obtained if the value is lower by half or more (0.25 or more) than the maximum reduction amount as compared with the comparative example.
That is, more preferably,
OI _max ^* ≦ 0.75
It is.

With reference to FIG. 4 and FIG. 5A from this point of view, when φ is approximately 170 ° or more (190 ° or less) except for L ₁ ^* = 0.1 in FIG. 5A, OI _max ^As is understood from the fact that ^* is 0.75 or less, it is preferable that the following expression is satisfied.
170 ° ≦ φ ≦ 190 °
0.13 ≦ L ₁ ^* ≦ 0.87

In addition, as an intuitive prediction, since OI _max ^* when L ₁ ^* = 0.5 is minimum, it is preferable that OI _max ^* is equal to or less than OI _max ^* when L ₁ ^* = 0.5. It can be said. From this point of view, referring to FIG. 4 and FIG. 5B, it is preferable that the following expression is satisfied.
0.15 ≦ L ₁ ^* ≦ 0.85
The preferred range of L ₁ ^* may be combined with any of the preferred ranges of φ described above.

Furthermore, L ₁ ^* may be set to the following range not including L ₁ ^* = 0.5.
0.15 ≦ L ₁ ^* ≦ 0.40, or 0.60 ≦ L ₁ ^* ≦ 0.85

(Example)
The effect of spurious suppression by bulk wave cancellation was confirmed by fabricating SAW elements according to comparative examples and examples and measuring their impedance characteristics. Specifically, it is as follows.

First, conditions common to the comparative example and the example are as follows.
Piezoelectric substrate 5:
Material: LiTaO ₃
Thickness: 20μm
Smoothness of the lower surface 5b: Ra = 0.2 nm
Support substrate 7:
Material: Si
Electrode finger 19:
Material: Al-Cu alloy
Pitch p: 1 μm
Width (x direction): 300 μm (300 pieces)
Length (y direction): 60 μm
Number: 300 (total)
Strip electrode 23:
Material, pitch p, width (x direction): same as electrode finger 19
Length (y direction): 60 μm
Number: 30 in each reflector 13 Resonance band: 1850-1910 MHz (UMTS BAND-2 transmission band)
The number (300) of the electrode fingers 19 is the number of the IDT electrodes 11 in the comparative example having only one IDT electrode 11, and the comparative example or example having two IDT electrodes 11. Is the total number of the two IDT electrodes 11.

Conditions for each of the comparative examples and the examples are as follows.
Comparative Example 1: Having only one IDT electrode (L ₁ ^* = 1)
Comparative Example 2: L ₁ ^* = 0.5, φ = 0 °
Examples 1-4:
L ₁ ^* : 0.5
φ: 45 °, 90 °, 135 ° or 180 °
Examples 5-9:
L ₁ ^* : 0.5, 0.4, 0.3, 0.2, 0.1
φ: 180 °
As described above, the influence of φ was examined in Comparative Example 2 and Examples 1 to 4, and the influence of L ₁ ^* was examined in Examples 5 to 9.

  FIGS. 6A to 6F are diagrams showing measurement results of impedance characteristics of Comparative Examples 1 and 2 and Examples 1 to 4. FIG. In these drawings, the horizontal axis represents frequency (MHz), and the vertical axis represents impedance phase (°).

  As shown in these figures, in both of the comparative example and the example, a clear spurious is generated on the high frequency side from the resonance band (1850-1910 MHz). Actually, spurious is generated from a frequency slightly lower than the resonance band, but it is difficult to confirm the effect because of the impedance change accompanying resonance and the spurious inherent to the resonator. For this reason, the effects of the present invention will be described below by analyzing spurious frequencies on the higher frequency side than the resonance band. Spurious generated in the resonance band or at a frequency slightly lower than the resonance band is also reduced by the same action.

  FIGS. 7A to 7F are enlarged views of a part on the high frequency side of the pass band in FIGS. 6A to 6F.

As shown in the frequency range of 2300 to 2350 MHz in these figures, the spurious peaks are lower in Examples 1 to 4 than in Comparative Examples 1 and 2. Further, as φ becomes larger, the spurious peak becomes smaller. On the other hand, as shown in FIGS. 4 and 5A, the maximum value OI _max ^* of the overlap integral decreases as φ increases. Therefore, the change tendency of the spurious peak coincides with the change tendency of the maximum value OI _max ^* .

  FIG. 8A to FIG. 8E are the same views as FIG. 6 showing the measurement results of the impedance characteristics of Examples 5-9. 9 (a) to 9 (e) are enlarged views of a part on the high frequency side of the passband in FIGS. 8 (a) to 8 (e), similarly to FIG. It is.

As shown in these figures and the frequency range of 2300 to 2350 MHz in FIGS. 7A and 7B, the spurious peak decreases when L ₁ ^* is slightly increased, and L ₁ ^* is 0. .Minimum when near 2. On the other hand, as shown in FIG. 4 and FIG. 5B, the maximum value OI _max ^* of the overlap integral decreases when L ₁ ^* becomes slightly larger, and becomes minimum when L ₁ ^* becomes around 0.2. It becomes. Therefore, the change tendency of the spurious peak coincides with the change tendency of the maximum value OI _max ^* .

As described above, the change tendency of the spurious peak actually measured in the comparative example and the example coincides with the change tendency of the maximum overlap integral OI _max ^* , and the effect of suppressing the spurious due to the cancellation of the bulk wave is confirmed. It was done.

(Supplementary discussion on examples)
As shown in the frequency range of 2300 to 2350 MHz in FIG. 7A to FIG. 7F, the spurious constituting one peak in the comparative example 1 is 2 in the first to fourth examples. It is divided into two mountains. Furthermore, as φ increases, the two peaks approach the same size, and as a result, the peak decreases.

Further, as shown in the frequency range of 2300-2350 MHz in FIGS. 9A to 9E, when L ₁ ^* is 0.5, the two spurious peaks whose boundaries are clear are As L ₁ ^* approaches 0.2, the boundary becomes ambiguous and, as a result, the peak is smaller.

  These phenomena can also be explained by the cancellation of bulk waves. Specifically, it is as follows.

Consider a SAW element 1 with various dimensions. That is, in the formula (A), x _ai , x _bi , k ₀ and α _i are set to predetermined values. Next, the frequency f _B is an arbitrary value, by calculating the sum ShigumaOI _i by a phase alpha _B while varying the frequency f _B to identify the maximum value OI _f of the sum ShigumaOI _i when the arbitrary value . By performing this particular for various values of frequency f _B, the relationship between the frequency f _B and the maximum value OI _f are specified.

FIG. 10A shows the relationship between the frequency f _B calculated as described above and the maximum value OI _f . The horizontal axis indicates the frequency f _B , and the vertical axis indicates the maximum value OI _f . The two lines show the calculation results of the maximum value OI _f for each φ = 0 ° (corresponding to Comparative Example 2) and phi = 180 ° (corresponding to Example 4).

  One peak (peak) that appears when φ = 0 ° is divided into two peaks when φ = 180 °. And when φ = 180 °, the total area of the mountain is not changed compared to φ = 0 °, but the peak value is smaller.

FIG. 10B shows the calculation result of the maximum value OI _f for φ = 45 °, 90 °, and 135 ° (corresponding to Examples 1 to 3) in addition to the calculation result shown in FIG. FIG.

  When φ = 180 °, the sizes of the two peaks are the same, but when φ becomes smaller than 180 °, the sizes of the two peaks become non-uniform, and the degree of non-uniformity is It is getting bigger.

10 (a) and 10 (b), the tendency of the change of the peak of the maximum value OI _f with respect to the change of φ, and the change of the spurious peak with respect to the change of φ shown in FIG. 7 (b). This is consistent with the trend.

FIG. 10C shows the calculation result of the maximum value OI _f for φ = 180 ° and L ₁ ^* = 0.2 (corresponding to Example 8).

As can be understood from the comparison between FIG. 10A and FIG. 10C, the boundary between the two peaks that was clear when L ₁ ^* = 0.5 is L ₁ ^* = 0.2. It is ambiguous. The tendency of the change of the peak of the maximum value OI _f with respect to the change of L ₁ ^* = coincides with the tendency of the change of the spurious peak with respect to the change of L ₁ ^* shown in FIG. 9B.

  As described above, it was confirmed from the tendency of the change in the spurious peaks appearing in the comparative example and the example that the spurious suppression effect was caused by the cancellation of the bulk wave.

<Second Embodiment>
(Overview of SAW element configuration)
FIG. 11 is a plan view similar to FIG. 1 showing the SAW element 201 of the second embodiment.

  The SAW element 201 includes three resonators 9 arranged in the SAW propagation direction (x direction).

Similar to the two resonators 9 of the first embodiment, the three resonators 9 have substantially the same configuration except for the number of electrode fingers 19. The first resonator 9A and the third resonator 9C have substantially the same number of electrode fingers 19 (lengths L ₁ and L _{3 of the} IDT electrode 11). The first resonator 9A and the third resonator 9C have a difference of 1 to 2 or a difference of 5% or less of the number of electrode fingers 19 of the first resonator 9A. May be different from each other. Also in this case, the first resonator 9A and the third resonator 9C have the same number. The first resonator 9A and the third resonator 9C may be line symmetric in the x direction.

  The first IDT electrode 11A and the second IDT electrode 11B are arranged such that the phase difference φ is a value other than 0 ° (360 °). Similarly, the phase difference φ of the second IDT electrode 11B and the third IDT electrode 11C is set to a value other than 0 ° (360 °). The first IDT electrode 11A and the third IDT electrode 11C have a phase difference φ of 0 °. In other words, the phase difference φ between the first IDT electrode 11A and the second IDT electrode 11B and the phase difference φ between the second IDT electrode 11B and the third IDT electrode 11C are the same.

  Even in such a configuration, as in the first embodiment, the cancellation of the bulk wave occurs between the first IDT electrode 11A and the second IDT electrode 11B, and the bulk occurs between the second IDT electrode 11B and the third IDT electrode 11C. Since waves cancel out, the occurrence of spurious when the bonded substrate 3 is used is suppressed.

  As in the first embodiment, the number of reflectors 13 between the IDT electrodes 11 may be one when the phase difference φ between the IDT electrodes on both sides thereof is 180 °.

(Calculation result of bulk wave size)
Similar to the first embodiment, the SAW element 201 also uses the equation (A) and sets the phase difference of α _i by the phase difference φ between the IDT electrodes 11, and the overlap integral for the three IDT electrodes 11. The sum ΣOI _{i of} OI _i can be calculated. Also, the maximum value IO _max of the sum ΣOI _i and its frequency f _B can be specified by calculating the sum ΣOI _i by varying the frequency f _B and the phase α _B of the bulk wave. Furthermore, if the maximum value OI _max is calculated by changing L _i and φ variously, a suitable range of L _i and φ can be specified. The calculation results are shown below.

In the following description, the length L3 of the _third IDT electrode 11C may be indicated as the length L1 of the _first IDT electrode 11A without any notice. In addition, the phase difference φ refers to the phase difference between the first IDT electrode 11A (or the third IDT electrode 11C) and the second IDT electrode 11B unless otherwise specified.

Also, the normalized length L ₁ ^* is different from the first embodiment,
L ₁ ^* = L ₁ / (L ₁ + L ₂ + L ₃ ) = L ₁ / (2L ₁ + L ₂ )
It is. Thus, for _example, corresponds to the case ^{L 1} * = 0, only the first 2IDT electrode 11B corresponds if _provided, ^L 1 * = 1/3, it is equivalent to the size of the three IDT electrodes 11 L ₁ ^* = 0.5 corresponds to the case where only the first IDT electrode 11A and the third IDT electrode 11C are provided.

FIG. 12 is a contour diagram showing the result of calculating the normalized maximum value OI _max ^* by changing L ₁ ^* and φ variously, and is a diagram corresponding to FIG. 4 of the first embodiment. Incidentally, ^* is the normalized maximum value _{OI max,} similarly to FIG. 4, the maximum value _OI max _{(OI v)} divided by the value _OI max / OI _v when the maximum value _{OI max L} ¹ * = 0.

From FIG. 12, it can be generally seen that OI _max ^* decreases as the phase difference φ approaches 180 ° (reverse phase) and as L ₁ ^* approaches 0.25. However, the minimum value of OI _max ^* occurs when φ is about 135 ° and L ₁ ^* is about 0.16, or φ is about 225 ° and L ₁ ^* is about 0.16. This result differs from the intuitive prediction, that is, the prediction that the bulk wave cancels most at φ = 180 ° and L ₁ ^* = 0.25.

FIG. 13A shows the relationship between φ (horizontal axis) and OI _max ^* (vertical axis) in the case of L ₁ ^* = 0.06, 0.14, 0.3, 0.4, and 0.44. And corresponds to the cross-sectional view of FIG. 12 at L ₁ ^* = 0.06, 0.14, 0.3, 0.4, and 0.44. Note that the line L ₁ ^* = 0.06 and the line L ₁ ^* = 0.44 overlap (the line with the highest OI _max ^* ).

As shown in this figure, in the vicinity of φ = 100 ° or φ = 260 °, OI _max ^* becomes smaller as φ approaches 180 °. In addition, OI _max ^* is sufficiently small when φ is in the range of 100 ° to 260 °. Therefore, it can be seen that a preferable φ range can be set in a range of 100 ° to 260 ° or a range close thereto.

FIG. 14B is a diagram showing the relationship between L ₁ ^* (horizontal axis) and OI _max ^* (vertical axis) when φ = 100 °, 125 °, 135 °, and 180 °, and φ = 100 It corresponds to the cross-sectional view of FIG. 13 at °, 125 °, 135 °, and 180 °.

As shown in this figure, in any φ, OI _max ^* is large when L ₁ ^* is near 0 or near 0.5. When L ₁ ^* is slightly larger than 0 or L ₁ ^* is slightly smaller than 0.5, OI _max ^* is rapidly decreased. Therefore, it can be seen that a preferable range of L ₁ ^* can be set in a range slightly larger than 0 and slightly smaller than 0.5.

14B, similarly to FIG. 13, when L ₁ ^* is about 0.15, L ₁ ^* is 0.25 (L ₁ having the smallest OI _max ^* in intuitive prediction). ^* ) ^Indicates that OI _max ^* is smaller than that in the case of

(Preferable range of φ and L ₁ ^* )
With reference to FIG. 12 and FIG. 13, the preferred ranges of φ and L ₁ ^* are examined.

Similar to the first embodiment, the maximum value OI _max ^* is preferably small enough to confirm the effect of bulk wave cancellation compared to the comparative example (OI _max ^* = 1). That is, the OI _max ^* of the SAW element 201 is preferably 0.975 or less or 0.95 or less.

From this point of view, referring to FIG. 12, for example, when the following expression is satisfied, OI _max ^* is preferably 0.975 or less.
100 ° ≦ φ ≦ 260 °
0.01 ≦ L ₁ ^* ≦ 0.49

Furthermore, for example, when the following formula is satisfied, OI _max ^* is approximately 0.95 or less, which is more preferable.
0.02 ≦ L ₁ ^* ≦ 0.48 (φ range is the same as above)

Further, similarly to the first embodiment, the value is not less than half (0.25 or more) lower than the maximum reduction amount (OI _max ^* ≦ 0.75) as compared with the comparative example (OI _max ^* = 1). In other words, it can be said that the effect of canceling the bulk wave was sufficiently obtained.

From this point of view, referring to FIG. 12, it is preferable that the following expression is satisfied.
110 ° ≦ φ ≦ 250 °
0.10 ≦ L ₁ ^* ≦ 0.40

Further, if as the intuitive predictions, because phi = 180 ° and _L ¹ * = 0.25 _{OI max} when the ^* (about 0.66) is minimal, the _{OI max} ^* following _{OI max} ^* a This is preferable. From this point of view, referring to FIG. 12 and FIG. 13 (b), it is preferable that one of the following expressions is satisfied.
140 ° ≦ φ ≦ 220 ° and 0.10 ≦ L ₁ ^* ≦ 0.25, or 110 ° ≦ φ ≦ 140 ° and 0.14 ≦ L ₁ ^* ≦ 0.36, or 220 ° ≦ φ ≦ 250 ° and 0.14 ≦ L ₁ ^* ≦ 0.36

Of the above equations, the first equation is 140 ° ≦ φ ≦ 220 ° and 0.10 ≦ L ₁ ^* ≦ 0.24 so that φ = 180 ° and L ₁ ^* = 0.25 are not included.
It may be said.

(Example)
Similar to the first embodiment, the SAW elements according to the comparative example and the example were prototyped, and the impedance characteristics were measured, thereby confirming the effect of suppressing spurious due to bulk wave cancellation. Specifically, it is as follows.

Conditions common to the comparative example and the example are the same as those of the example of the first embodiment. Conditions for each of the comparative examples and the examples are as follows.
Comparative Example 1: Same as Comparative Example 1 of the first embodiment (only one IDT electrode)
Example 10:
L ₁ ^* : 1/3
φ: 180 °
Example 11:
L ₁ ^* : 1/3
φ: 120 °

  14A to 14C are diagrams showing measurement results of impedance characteristics of Comparative Example 1 and Examples 10 and 11. FIG. FIGS. 15A to 15C are diagrams showing a part of the high frequency side of the pass band in FIGS. 14A to 14C in an enlarged manner.

  Similar to the first embodiment, the spurious peaks are lower in Examples 10 and 11 than in Comparative Example 1 in the frequency range of 2300 to 2350 MHz. In Examples 10 and 11, the spurious peaks are divided. As described above, the effect of suppressing spurious due to the cancellation of the bulk wave was confirmed.

<Third Embodiment>
(Overview of SAW element configuration)
FIG. 16 is a plan view similar to FIG. 1 showing the SAW element 301 of the third embodiment. In the figure,

  In the SAW element 1 of the first embodiment, the two resonators 9 are connected in parallel. On the other hand, in the SAW element 301, the two resonators 9 are connected in series.

  Specifically, the output-side comb electrode 15D of the first resonator 9A and the input-side comb electrode 15C of the second resonator 9B are connected. Then, as indicated by the arrow y1, the input signal is input to the input-side comb electrode 15C of the first resonator 9A. The input signal passes through the output-side comb-tooth electrode 15D of the first resonator 9A and the input-side comb-tooth electrode 15C of the second resonator 9B, and the output of the second resonator 9B as shown by the arrow y2. Output from the side comb electrode 15D.

  Further, the input-side comb-tooth electrode 15C of the first resonator 9A and the output-side comb-tooth electrode 15D of the second resonator 9B are located on the same side (y-direction negative side) with respect to the intersecting region of the plurality of electrode fingers 19. The output-side comb-tooth electrode 15D of the first resonator 9A and the input-side comb-tooth electrode 15C of the second resonator 9B are located on the same side (y-direction positive side) with respect to the intersecting region of the plurality of electrode fingers 19. doing.

  As described in the description of the first embodiment, the phase difference φ between the IDT electrodes 11 is, for example, an arbitrary electrode finger 19 of the input-side comb-tooth electrode 15C of the first IDT electrode 11A and the input of the second IDT electrode 11B. It is calculated by 2π × (Lt / 2p) where Lt is the distance (center-to-center distance) between the side comb electrode 15C and any electrode finger 19.

  Accordingly, as in the first embodiment, the bulk wave is not canceled when the phase difference φ is 0, and the bulk wave is canceled when the phase difference φ is 180 °.

The preferable ranges of φ and L ₁ ^* in the SAW element 301 are the same as the preferable ranges of φ and L ₁ ^* in the SAW element 1 of the first embodiment from the theory of overlap integral.

(Example)
Similar to the other embodiments, the SAW elements according to the comparative example and the example were prototyped, and the impedance characteristics were measured, thereby confirming the effect of suppressing spurious due to bulk wave cancellation. Specifically, it is as follows.

Conditions common to the comparative example and the example are the same as those of the example of the first embodiment. Conditions for each of the comparative examples and the examples are as follows.
Comparative Example 3:
L ₁ ^* : 0.5
φ: 0 °
Example 12:
L ₁ ^* : 0.5
φ: 180 °

  FIG. 17A and FIG. 17B are diagrams showing measurement results of impedance characteristics of Comparative Example 3 and Example 12. FIG. FIGS. 18 (a) and 18 (b) are enlarged views of a part on the high frequency side of the pass band in FIGS. 17 (a) and 17 (b).

  Similar to the other embodiments, in the frequency range of 2300 to 2350 MHz, the spurious peak is lower in Example 12 than in Comparative Example 3. In the twelfth embodiment, the spurious peaks are divided. As described above, the effect of suppressing spurious due to the cancellation of the bulk wave was confirmed.

<Application to other aspects>
In the first to third embodiments, the preferable ranges of the phase difference φ and the normalized length L ₁ ^* of the IDT electrode 11 have been described in the case where there are two or three IDT electrodes 11. However, as understood from the description of these embodiments, even if the number of IDT electrodes 11 and the like are changed, the phase difference and the normalized length are changed as in the first and second embodiments. A preferable range can be set.

That is, even in the modes other than the first to third embodiments, the formula (A) is used and the phase difference of α _i is set by the phase difference φ between the IDT electrodes 11, so that the plurality of IDT electrodes 11 The total sum ΣOI _i of the overlap integral OI _i can be calculated. Also, the maximum value IO _max of the sum ΣOI _i and its frequency f _B can be specified by calculating the sum ΣOI _i by varying the frequency f _B and the phase α _B of the bulk wave. Furthermore, if the maximum value OI _max is calculated by changing L _i and φ variously, a suitable range of L _i and φ can be specified.

In the second embodiment, while the _{L i} of the 1IDT electrode 11A and the 3IDT electrode 11C and the same, both the phase difference α was 0 °. However, it is clear that even if the two L _i are different from each other and / or the phase difference φ is different from each other, suitable L _i and φ can be obtained by the above procedure. However, since the number of parameters increases, the amount of calculation increases. The same applies when the number of IDT electrodes is four or more.

  Further, when a SAW element in which a plurality of IDT electrodes are arranged in the SAW propagation direction with a reflector interposed therebetween is manufactured or sold, whether the SAW element uses the idea of the present invention or not It can be specified as follows.

First, materials of various members of the SAW element are specified and various dimensions of the SAW element are measured. Next, coefficients other than f _B and α _B in the equation (A) are specified based on the specifying result and the measurement result. The specification of the coefficient includes specification of α _i in consideration of the phase difference φ necessary for calculating the total sum ΣOI _i of the overlap integral OI _i . Then, by calculating the sum ShigumaOI _i with the frequency _{f B} and phase alpha _B of the bulk wave is variously changed, calculates a maximum value _{IO max} summation ΣOI _i.

In addition, in an actual SAW element in which material specification and dimension measurement have been performed, one virtual IDT electrode is assumed that is coupled to each other without a phase difference between a plurality of IDT electrodes. This corresponds to L ₁ ^* = 0 in the first and second embodiments. For this virtual IDT electrode, the bulk wave frequency f _B and phase α _B are variously changed to calculate the OI of the formula (A), and the maximum value is OI _v .

Divide OI _max by OI _V to calculate the normalized maximum value OI _max ^* . As described in the embodiment, if OI _max ^* is 0.975 or less or 0.95 or less, it can be said that the bulk wave is canceled and the idea of the present invention is used. Further, if OI _max ^* is 0.75 or less, it can be said that the bulk waves are sufficiently canceled.

  The present invention may be implemented in various modes as described below.

  The SAW element may be used in an appropriate device such as a duplexer reception filter or transmission filter. Further, the SAW element may constitute a part of a ladder type SAW filter.

  When a plurality of IDT electrodes are connected in parallel, the plurality of input-side comb electrodes (or the plurality of output-side comb electrodes) are not on the same side (the same side in the y direction) with respect to the plurality of electrode fingers. Also good. Conversely, when a plurality of IDT electrodes are connected in series, the plurality of input side comb electrodes (or the plurality of output side comb electrodes) may be disposed on the same side with respect to the plurality of electrode fingers.

  The IDT electrode may have a so-called dummy electrode that extends from one bus bar to the other bus bar and that has a tip opposite to the tip of the electrode finger via a gap. Further, the IDT electrode may be of a so-called apodized type in which the shape of the region between the pair of bus bars changes with respect to the position in the SAW propagation direction. The bus bar may be inclined with respect to the SAW propagation direction. The lengths of the plurality of electrode fingers may be different from each other.

  Bus bars may be connected to two reflectors between two adjacent IDT electrodes. As described in the embodiment, when the phase difference between the IDT electrodes is 180 °, only one reflector between the IDT electrodes is required. That is, the SAW element of the first embodiment only needs to have at least three reflectors, and the SAW element of the second embodiment only needs to have at least four reflectors. However, it is preferable that only one reflector between two IDT electrodes has 60 or more strip electrodes. In this case, the binding of SAW between the two IDT electrodes can be suppressed.

  DESCRIPTION OF SYMBOLS 5 ... Piezoelectric substrate, 5b ... Lower surface, 7 ... Support substrate, 11A ... 1st IDT electrode, 11B ... 2nd IDT electrode, 13A ... 1st reflector, 13B ... 2nd reflector, p ... Pitch (electrode finger pitch).

Claims (5)

A piezoelectric substrate;
A support substrate bonded to the lower surface of the piezoelectric substrate;
A first IDT electrode and a second IDT electrode, which are located on the upper surface of the piezoelectric substrate, have electrode finger pitches equivalent to each other, and are arranged in the propagation direction of the surface acoustic wave;
A plurality of reflectors provided between and outside these IDT electrodes;
Have
A surface acoustic wave element that satisfies the following equation (1).
60 ° ≦ φ ≦ 300 ° and 0.05 ≦ L ₁ / (L ₁ + L ₂ ) ≦ 0.95 (1)
Where φ is the phase difference between the _first IDT electrode and the second IDT electrode, and L ₁ and L ₂ are the lengths of the first IDT electrode and the second IDT electrode in the propagation direction of the surface acoustic wave. The surface acoustic wave device according to claim 1, wherein the following equation (2) is satisfied.
0.15 ≦ L ₁ / (L ₁ + L ₂ ) ≦ 0.85 (2) A piezoelectric substrate;
A support substrate bonded to the lower surface of the piezoelectric substrate;
A first IDT electrode, a second IDT electrode, and a third IDT electrode, which are located on the upper surface of the piezoelectric substrate, have the same electrode finger pitch, and are sequentially arranged in the propagation direction of the surface acoustic wave;
A plurality of reflectors provided between and outside these IDT electrodes;
Have
The first IDT electrode and the third IDT electrode have no phase difference between them, and the lengths of both in the propagation direction of the surface acoustic wave are equal.
A surface acoustic wave element that satisfies the following formula (3).
100 ° ≦ φ ≦ 260 ° and 0.01 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.49 (3)
Where φ is the phase difference between the _first IDT electrode and the second IDT electrode, and L ₁ and L ₂ are the lengths of the first IDT electrode and the second IDT electrode in the propagation direction of the surface acoustic wave. The surface acoustic wave device according to claim 3, wherein the following expression (4), expression (5), or expression (6) is satisfied.
140 ° ≦ φ ≦ 220 ° and 0.10 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.25 (4)
110 ° ≦ φ ≦ 140 ° and 0.14 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.36 (5)
220 ° ≦ φ ≦ 250 ° and 0.14 ≦ L ₁ / (2L ₁ + L ₂ ) ≦ 0.36 (6) Two reflectors are provided between two adjacent IDT electrodes, and in each of the two reflectors, the number of strip electrodes extending in a direction orthogonal to the propagation direction of the surface acoustic wave is 30 or more. Alternatively, one reflector is provided between two adjacent IDT electrodes, and in the reflector, the number of strip electrodes extending in a direction perpendicular to the propagation direction of the surface acoustic wave is 60 or more.
The surface acoustic wave element according to any one of claims 1 to 4 .

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