JP6767201B2 - Capacitive element, elastic wave element and elastic wave module - Google Patents

Description

The present invention relates to a capacitive element that suppresses distortion, an elastic wave device using the same, and an elastic wave module.

In recent years, with the miniaturization of electronic components, it has been required to provide a capacitive element on a piezoelectric substrate. For example, in an elastic wave device in which an excitation electrode for exciting an elastic wave is formed on a piezoelectric substrate, a configuration has been proposed in which a capacitive element is also provided on the piezoelectric substrate. Patent Document 1 discloses an example in which a capacitive element connected in parallel to a pair of excitation electrodes formed on a piezoelectric substrate is provided in order to improve the resonance characteristics of the excitation electrodes. The capacitive element of Patent Document 1 is composed of a pair of comb tooth electrodes having a plurality of electrode fingers extending in parallel.

Japanese Patent Application Laid-Open No. 05-167384

Here, in order to enhance the electrical characteristics of the elastic wave device, it is necessary to enhance the electrical characteristics of the capacitive element itself. That is, when a capacitive element is provided on a substrate having piezoelectricity, it is necessary to enhance the electrical characteristics of the capacitive element in order to enhance the characteristics of the entire electronic component including the capacitive element.

The present invention has been devised based on the above circumstances, and an object thereof is a capacitive element having high electrical characteristics formed on a substrate having piezoelectricity, and an elastic wave device using the capacitive element. And to provide elastic wave modules.

The capacitive element of one aspect of the present disclosure includes a substrate made of a piezoelectric crystal, and a plurality of first electrode fingers and a plurality of second electrode fingers arranged on the upper surface of the substrate. The second electrode finger is connected to a potential different from that of the first electrode finger, and has the same number as the first electrode finger. The first electrode finger and the second electrode finger are alternately arranged at intervals, and the arrangement direction has a plane direction component in which the Z-axis component of the piezoelectric crystal is projected onto the upper surface. .. Then, assuming that the gaps between the electrode fingers are the i-th (where i is a natural number excluding 0) in order from the end along the arrangement direction, at least one of the odd-numbered gaps has an even-numbered size. It is larger than the size of the gap.

The capacitive element of another aspect of the present disclosure includes a substrate made of a piezoelectric crystal and a plurality of first electrode fingers and a plurality of second electrode fingers arranged on the upper surface of the substrate. The second electrode finger is connected to a potential different from that of the first electrode finger, and is one more than the first electrode finger. The first electrode finger and the second electrode finger are alternately arranged at intervals, and the arrangement direction has a plane direction component in which the Z-axis component of the piezoelectric crystal is projected onto the upper surface. .. Then, at least one of the gaps from the first electrode finger to the second electrode finger along the forward direction of the surface direction component is larger than the size of the gap between the other electrode fingers.

The elastic wave device according to one aspect of the present disclosure includes an IDT electrode formed on the upper surface thereof and the capacitance element electrically connected to the IDT electrode.

The elastic wave module according to one aspect of the present disclosure includes the elastic wave device and a circuit board on which the elastic wave element device is mounted.

The capacitive element according to one aspect of the present disclosure described above suppresses distortion and has high electrical characteristics. Further, an elastic wave device and an elastic wave module provided with such a capacitive element have excellent electrical characteristics.

It is a top view which shows one Embodiment of the capacitive element which concerns on this disclosure. It is sectional drawing of the capacitive element shown in FIG. (A) and (b) are plan views showing a modified example of the capacitive element shown in FIG. 1, respectively. It is a top view which shows the modification of the capacitance element shown in FIG. It is a top view which shows the main part of one Embodiment of the elastic wave apparatus which concerns on this invention. It is a top view which shows one Embodiment of the elastic wave module which concerns on this invention. It is a block diagram which shows the structure of the measurement system of a second harmonic. (A) and (b) are diagrams showing the measurement results of the second harmonics of Examples and Comparative Examples, respectively. (A) and (b) are diagrams showing the second harmonic simulation results and measurement results of Examples and Comparative Examples, respectively.

Hereinafter, embodiments of the capacitive element, elastic wave device, and elastic wave module of the present disclosure will be described in detail with reference to the drawings. The figures used in the following description are schematic, and the dimensional ratios and the like on the drawings do not always match the actual ones.

Further, in the description of the modification and the like, the same or similar configurations as those of the embodiments already described may be designated by the same reference numerals as those of the embodiments already described, and the description may be omitted.

The capacitive element, the elastic wave device, and the elastic wave module may be in any direction upward or downward, but in the following, for convenience, the D1 direction, the D2 direction, and the D3 direction which are orthogonal to each other are defined. In addition, terms such as upper surface and lower surface shall be used with the positive side in the D3 direction facing upward. The Cartesian coordinate system defined in the D1 direction, the D2 direction, and the D3 direction described above is defined based on the shapes of the capacitive element, the elastic wave device, and the elastic wave module, and is a piezoelectric crystal constituting the substrate. It does not refer to the crystal axis (X-axis, Y-axis, Z-axis) of. Further, those having similar basic configurations may be described without distinguishing them by omitting the description of the first, second and the like.

<Capacitive element>
FIG. 1 is a plan view of the capacitance element 1 according to the embodiment of the present disclosure, and FIG. 2 is a cross-sectional view of the capacitance element 1 shown in FIG.

The capacitive element 1 includes a substrate 2 made of a piezoelectric crystal and a capacitive portion 10 provided on an upper surface 2A thereof.

The substrate 2 is composed of a piezoelectric single crystal (piezoelectric crystal) composed of an LN (lithium niobate: LiNbO ₃ ) crystal or an LT (lithium tantalate: LiTaO ₃ ) crystal. Specifically, for example, the substrate 2 is composed of a 36 ° to 48 ° YX cut LT substrate. The planar shape and various dimensions of the piezoelectric substrate 2 may be appropriately set. As an example, the thickness of the substrate 2 (in the D3 direction) is 0.2 mm or more and 0.5 mm or less.

The piezoelectric crystal of the substrate 2 has an XYZ axis as a crystal axis, and when an X propagation substrate is used, the X axis and the D1 direction coincide with each other. That is, the X-axis and the D1 direction are the propagation directions of elastic waves. Further, the Y-axis and the Z-axis do not have components in the D1 direction, but have components in the D2 and D3 directions. Here, focusing on the Z-axis, the Z-axis component is derived from the surface direction component Zd2 projected on the upper surface 2A and in the direction opposite to the D2 direction, and the thickness direction component and Zd3 projected in the thickness direction D3. Become.

A capacitance portion 10 is arranged on the upper surface 2A of such a substrate 2. The capacitance section 10 is composed of an interdigital electrode in which a pair of comb tooth electrodes 30 (30a, 30b) are meshed with each other to form a capacitor.

The comb tooth electrode 30 is composed of, for example, a metal conductive layer 15. The metal is not particularly limited as long as it is a conductive material, and examples thereof include Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al—Cu alloy. The comb tooth electrode 30 may be composed of a plurality of metal layers. The thickness of the comb tooth electrode 30 (in the D3 direction) may be, for example, 50 nm or more and 600 nm or less.

The comb tooth electrode 30 may be arranged directly on the upper surface 2A of the substrate 2, or may be arranged on the upper surface 2A of the substrate 2 via a base layer made of another member. Another member is made of, for example, Ti, Cr, or an alloy thereof. When the comb tooth electrode 30 is arranged on the upper surface 2A of the substrate 2 via the base layer, the thickness of another member is such that the electric characteristics of the comb tooth electrode 30 are hardly affected (for example, in the case of Ti). It is set to a thickness of 5% of the thickness of the comb tooth electrode 30).

Further, a dielectric material that protects the conductive layer 15 may be arranged on the comb tooth electrode 30. As the dielectric, for example, a resin material such as an epoxy resin, SiO _x , SiNx, or the like can be used.

Next, the shape of the comb tooth electrode 30 will be described. The first comb tooth electrode 30a includes a first bus bar 31a and a plurality of first electrode fingers 32a connected to the first bus bar 31a. The second comb tooth electrode 30b includes a second bus bar 31b and a second electrode finger 32b connected to the second bus bar 31b. The number of the second electrode fingers 32b is the same as that of the first electrode fingers 32a.

Here, the first bus bar 31a and the second bus bar 31b are connected to different potentials. As a result, the first electrode finger 32a and the second electrode finger 32b are connected to different potentials. Then, by arranging the first comb tooth electrode 30a and the second comb tooth electrode 30b so that the electrode fingers 32 alternately mesh with each other, the first electrode finger 32a and the second electrode finger 32b are spaced apart from each other. Are arranged. Here, the electrode finger widths of the first comb tooth electrode 30a and the second comb tooth electrode 30b may be constant. In FIG. 1, in order to facilitate understanding, a portion having the same potential as the second electrode finger 32b is shaded.

The arrangement direction L1 of such electrode fingers 32 has a plane direction component Zd2. In this example, the arrangement direction L1 and the plane direction component Zd2 are substantially parallel. In other words, the arrangement direction L1 is substantially the same as the direction orthogonal to the extending direction of the electrode finger 32 (the width direction of the electrode finger 32).

Here, the gaps Gp between the electrode fingers 32 are counted as the first, second ... I-th in order from the end along the arrangement direction L1, and each gap Gp is Gp1, Gp2 ..., Gpi. .. Note that i is a natural number excluding 0. In this example, Gp1 to Gp5 exist. The size of at least one of the odd-numbered gaps Gp1, Gp3, and Gp5 (two of Gp1 and Gp5 in this example) is larger than that of the even-numbered gap Gp (Gp2, Gp4). In this example, the gaps Gp (Gp2, Gp3, Gp4) other than Gp1 and Gp5 have the same size.

In this example, since the total number of electrode fingers 32 is even, the number of gaps Gp is an odd number, and the odd-numbered gap Gp and the even-numbered gap Gp are counted from either side in the arrangement direction. It will not be replaced.

With such a configuration, when a high frequency signal is applied between the terminals T1 and T2, the capacitance unit 10a cancels the distorted wave inside the terminal T1 and T2, and the capacitance element 1 in which the distorted wave is suppressed can be obtained. .. The mechanism will be described in detail below.

When an electric field is applied to the piezoelectric crystal by an electrode, a strain current corresponding to the electric field flows due to the second-order nonlinearity of the dielectric constant, and the strain current is output as a distorted wave to the outside. This basic principle is simple, but in an actual capacitive element, the electric field is excited inside the piezoelectric crystal by the interdigital electrode formed on the surface of the piezoelectric crystal, so the electric field is not a simple shape but parallel to the upper surface. It has a directional component and a depth directional component. The non-linearity of the anisotropic dielectric constant corresponds to this electric field, and the strain currents (plane effect, depth effect) caused by each are generated. The distorted waves actually observed are the sum of these distorted currents including their phases (polarities).

When a high frequency signal is applied to each electrode finger 32, an electric field E is excited inside the substrate 2. The electric field E is excited in a direction from the high potential side to the low potential side. For the sake of simplicity, it is described that a static voltage is applied to the electrode finger 32, but the signal actually applied to the electrode finger 32 is a high-frequency AC signal, which will be described in the future. Corresponds to the momentary state of the AC signal.

In the D1 direction, an electric field is generated between one bus bar 31 and the tip of the other electrode finger 32. In the D2 and D3 directions, an electric field is generated from one electrode finger 32 toward the other electrode finger 32 on both sides thereof.

For electrode fingers other than the end of each capacitance portion 10, electrode fingers having different potentials (for example, electrode fingers 32b) are symmetrically present on both sides of a certain electrode finger (for example, electrode finger 32a), so that the substrate 2 The electric field excited inward is symmetrical with respect to the D1-D3 plane when viewed from the central axis of the electrode finger. However, the electrode finger 32 located on the outermost side of each capacitance portion 10 is asymmetric with respect to the D1-D3 plane because an electric field is generated only between the electrode finger 32 and the electrode finger 32 located on the inner side.

Further, the direction (polarity) of the strain current due to the second-order nonlinearity does not depend on the direction of the electric field, but only on the orientation of the crystal. For example, considering the case where the electrode finger 32a has a high potential, when viewed from a certain electrode finger 32a, the D2 component of the electric field generated in the direction of the electrode finger 32b to the left and the electrode finger 32b to the right are generated. The D2 component of the electric field generated in the direction of is the same in magnitude and opposite in polarity. However, the strain current generated by this electric field flows in the same direction with respect to D2 (depending on the crystal, for example, in the positive direction of D2).

Therefore, when viewed from a certain electrode finger 32a, the strain current flowing from the electrode finger 32b on the left side and the strain current flowing out to the electrode finger 32b on the right side have the same magnitude, and these cancel each other out to distort the outside. No current is output.

Here, in the LiTaO ₃ substrate and the LiNbO ₃ substrate, the non-linearity of the permittivity of the crystal in the Z-axis direction is large, so that the electric field in the Z-axis direction greatly contributes to the strain current. The component in the Z-axis direction when the rotational Y-cut-X propagation piezoelectric crystal illustrated here is used is composed of a component in the D2 direction and a component in the D3 direction in the Cartesian coordinate system, and is composed of the component in the D1 direction. Will not contain the ingredients of.

Therefore, if the electric field E is divided into an electric field in the D1 direction, which is a component in the plane direction, an electric field in the D2 direction, and an electric field in the D3 direction, which is a component in the depth direction, the electric field E is divided into the D1 direction in the opposite direction of the two bus bars 31. The electric field is perpendicular to the Z-axis, has no Z-axis direction component, and contributes less to the strain current. The electric field component in the D3 direction of this portion contributes to the strain current. However, since this portion does not contribute much as a capacitance, for example, by widening the distance between the first bus bar 31a and the tip of the electrode finger 32b, the electric field can be reduced and the generation of strain current can be suppressed.

On the other hand, since the electric field in the D2 direction and the electric field in the D3 direction from one of the adjacent electrode fingers 32 to the other have a component in the Z-axis direction, they contribute to the generation of strain current.

Based on the above description, the mechanism of generating the strain current in the case of the capacitance portion 10 of FIG. 1 and the strain suppression method according to the present invention will be described. The capacitance unit 10 is composed of an even number of electrode fingers 32. In this case, the number between each electrode finger becomes an odd number, and a strain current due to the electric field in the D2 direction is generated. That is, the number Na from the first electrode finger 32a toward the second electrode finger 32b and the number Nb from the second electrode finger 32b toward the first electrode finger 32a along the forward direction of the plane direction component Zd2 of the crystal Z axis. Since the above-mentioned distortion currents do not completely cancel each other out, the distortion currents are output to the outside. Therefore, by widening the distance between the electrode fingers 32, which is larger depending on the magnitude of the numbers of several Na and several Nb, the electric field at the widened portion can be reduced and the strain current can be reduced. As a result, the difference in distortion current due to the difference in the magnitude relationship of the numbers can be canceled by reducing the distortion current of the larger number of several Na and several Nb.

The larger of several Na and several Nb always corresponds to the odd-numbered gap Gp. That is, the distortion current in the entire capacitance portion 10 can be reduced by widening the gap interval of the odd-numbered gap Gp.

Further, since the arrangement direction L1 is orthogonal to the X axis, it is possible to suppress the generation of an unintended elastic wave by the electrode finger 32.

Further, since the gaps (Gp2, Gp3, Gp4) other than Gp1 and Gp5 have the same size, it is possible to prevent the voltage from being excessively concentrated.

Furthermore, in this example, the gap interval is wider than the others at two locations, Gp1 and Gp5. As a result, since the distortion current is dispersed at two places to attenuate the strain current, the amount of widening the gap interval can be reduced, and as a result, the capacitance can be secured. In addition, the gap spacing is widened by forming a combination (Gp1, Gp5) between the electrode fingers 32 located on both outer sides of the array direction and the electrode fingers 32 located one inside of the electrode fingers 32. It is possible to suppress the decrease in the capacity value due to the expansion of. As a result, it is possible to provide the capacitive element 1 having a desired capacitance with a small distortion without increasing the size of the element shape.

However, the two places where the gap spacing is widened are not particularly limited as long as they are odd-numbered gaps Gp, and as in this example, the electrode fingers 32 located on both outer sides in the arrangement direction and one inside thereof are located. The combination with the electrode finger 32 (Gp1, Gp5) is not limited. For example, a combination of Gp3 and Gp5 may be used.

When the capacitance unit 10 is composed of an even number of electrode fingers 32, the difference between the number Na and the number Nb is one, so that one distortion current is generated. By widening the interval of one gap Gp, the distortion current for this one can be reduced, but in order to make it completely 0, the interval of the gap Gp needs to be infinite. However, the distortion current can be completely canceled by widening the interval between the two or more gaps Gp.

For example, by widening the interval between the two gaps Gp as in the above example and halving the distortion current generated at each of the two gaps Gp, the two gaps Gp are totaled for one gap Gp. It can be adjusted so that the distortion current of is generated. By doing so, the magnitudes of the strain currents generated at several Na and several Nb are virtually equal, and the strain currents can be offset.

However, if the interval between the gaps Gp is too wide, the distortion current obtained by adding the two gaps Gp becomes less than the distortion current for one gap Gp, and cannot be completely canceled. Therefore, the upper limit of the amount of widening the interval of the odd-numbered gap Gp can be estimated from the magnitude of the distortion current generated at one even-numbered gap Gp.

In addition, an electric field in the D3 direction, which is an electric field in the other direction having a Z-axis component, will be examined. In this example, the electrode fingers 32 other than the electrode fingers 32 located on both outer sides in the arrangement direction have the same number of the first electrode fingers 32a and the second electrode type 32b, and the strain output from the first electrode fingers 32a. The strain output from the second electrode finger 32b is offset. The electrode fingers 32 located on both outer sides in the arrangement direction have different polarities from each other. Therefore, the strain generated in the electrode fingers 32 on both outer sides is canceled out. From the above, when the total number of electrode fingers 32 is an even number, the shape shown in FIG. 1 may be obtained in consideration of the surface direction component of the Z-axis components.

<Capacitive elements 1A to 1B)
In the above example, the gap interval is wider than the others at two locations, Gp1 and Gp5, but this is not the case. For example, as shown in FIG. 3A, the gap interval may be widened at one place. In the capacitive element 1A shown in FIG. 3A, the gap interval is larger in the gap Gp3 than in other gaps. With such a configuration, the capacity can be secured because there is only one portion where the capacity is reduced. Further, since it can be regarded as a configuration divided into two capacitance portions having no distortion current due to the electric field in the plane direction, the distortion current can be reduced.

When widening the gap at one place, it may be at another position as long as it is an odd-numbered gap (Gp1, Gp5).

Further, the gap spacing of all the odd-numbered gaps Gp may be widened as in the capacitive element 1B shown in FIG. 3 (b). That is, the gap interval is wider than the others at three locations, Gp1, Gp3, and Gp5. In that case, since the strain current is attenuated by being dispersed at three places, the amount of widening the interval between the individual gaps Gp1, GP3, and Gp5 should be smaller than that of the capacitive element 1 shown in FIG. Can be done.

<Capacitive element 1C>
Although the case where the total number of electrode fingers 32 of the capacitance unit 10 is an even number has been described above, the capacitance element 1 may be an odd number of capacitance elements 1C. Hereinafter, the description of the same portion as that of the capacitive element 1 will be omitted, and only the different portion will be described.

FIG. 4 shows a plan view of the capacitive element 1C. As shown in FIG. 4, the total number of electrode fingers 32 of the capacitance unit 10 is an odd number. That is, the number of the first electrode fingers 32a is one less than the number of the second electrode fingers 32b. That is, the electrode fingers 32 located on both outer sides in the arrangement direction of the electrode fingers 32 are the second electrode fingers 32b.

Then, when viewed in the forward direction (direction from the − side to the + side) along the surface direction component Zd2, at least one of the gaps Gpx from the first electrode finger 32a to the second electrode finger 32b is the other. The gap interval is larger than the gap (for example, the gap Gpy from the second electrode finger 32b to the first electrode finger 32a).

In this example, any of Gp2 and Gp4 has a wider gap interval than Gp1 and Gp3. When the total number of the plurality of electrode fingers 32 is an odd number, the direction of the piezoelectric crystal with respect to the crystal axis becomes important, and the direction is opposite to Gpx when the direction is the forward direction of the Zd2 direction. It is not equivalent to Gpx at the time.

With this configuration, it is possible to suppress the generation of distorted waves generated in the capacitance section 10a. The mechanism will be described below.

In the capacitive element 1C, the relationship between the arrangement direction L1 of the electrode finger 32 and the Z-axis component of the piezoelectric crystal is the same as in the case of the capacitive element 1, so that the electric field in the D2 direction and the electric field in the D3 direction contribute to the distorted wave. .. Here, when the electric field in the D2 direction is examined, the number between the electrode fingers 32 in the capacitance portion 10 is an even number, and the generation of distorted waves is suppressed by the above-mentioned principle of cancellation. In other words, the number Na from the first electrode finger 32a toward the second electrode finger 32b and the number Nb from the second electrode finger 32b toward the first electrode finger 32a along the forward direction of the plane direction component Zd2 of the crystal Z axis. Since the above is the same, the distorted waves are canceled in one capacitance section 10. That is, the output of the distorted wave caused by the plane direction component can be basically ignored.

Next, the electric field in the D3 direction will be examined. Here, as described above, when viewed from a certain electrode finger 32a other than the electrode finger 32 located on the outermost side (end) of the capacitance portion 10, the electric field generated between the electrode finger 32b on the left side thereof is generated. The components in the D3 direction are antisymmetric with respect to the D1-D3 plane passing through the central portion between the electrode fingers 32. However, since the strain current flows not in the direction of the electric field but in the direction determined by the crystal axis, the strain current flowing into a certain electrode finger 32a and the strain current flowing into the electrode finger 32b to the left of the distortion current have the same magnitude. Therefore, this current cancels out and no external distortion current is generated. However, since there is no electrode finger next to the electrode finger 32 at the end of the capacitive element 1C and the electrode finger 32 next to it in the opposite direction, the electrode finger 32 at the end and the electrode finger 32 one inside The electric field is not completely antisymmetric with respect to the D1-D3 plane passing through the central portion. Therefore, the strain current flowing through both electrodes is not completely canceled, and the strain current is output to the outside.

Here, in the capacitance element 1C, the electrode fingers 32 located outside the capacitance section 10 are electrode fingers having the same polarity. For example, in FIG. 4, it is the second electrode finger 32b. Therefore, the polarity of the strain current due to the asymmetrical shape of the electric field in the D3 direction has a direction of being output from the first electrode finger 32a to the second electrode finger 32b.

The capacitive element 1C intentionally generates a distortion current having a polarity different from the output of the distortion current due to the D3 direction (thickness direction) in the D2 direction (plane direction), thereby canceling the distortion currents and canceling the distortion current as a whole. It suppresses the output of.

Specifically, the capacitance portion 10 composed of the original odd number of electrode fingers 32 can basically ignore the output of the distorted wave due to the surface direction component, but at least one of the gap Gpx should be increased. Then, the strain current output from the first electrode finger 32a to the second electrode finger 32b is reduced to break the balance, and a total strain current is generated from the second electrode finger 32b to the first electrode finger 32a.

As described above, since the capacitance element 1C has a different number of electrode fingers 32 from the capacitance elements 1, 1A and 1B, the direction of the distortion current generation factor is different. However, it is common in that the generated strain current is canceled by the same "adjustment of the electric field strength of the surface direction component".

When a 42 ° YX cut LT substrate is used as the substrate 2, the output of the distorted wave caused by the surface direction component Zd2 is larger than the output of the distorted wave caused by the thickness direction component Zd3. Therefore, the capacitance element 1C has a smaller distorted wave itself due to the thickness direction than the capacitance element 1, and the distorted wave output can be further suppressed. In addition, the amount of widening the gap interval of the gap Gpx can be reduced.

<Others>
In the above-mentioned capacitive element, the case where the arrangement direction L1 is set to the plane direction component Zd2 has been described, but it suffices to have those components, and the angles may be formed in the D2 direction and the D1 direction. Good.

Specifically, in the case of a configuration in which the arrangement direction L1 has the surface direction component Zd2 to cancel the distortion current between the two capacitance portions 10, the angle formed by L1 and Zd2 is 45 ° or less (that is, −45 °). ~ + 45 °, including the threshold value), and by setting it to 10 ° or less (-10 ° to + 10 °, including the threshold value), the distortion current can be more effectively canceled between the two capacitance sections 10. it can.

Further, a plurality of the above-mentioned capacitive elements may be provided. A desired capacitance can be realized by connecting a plurality of capacitance elements in parallel or in series.

<Elastic wave device>
Next, an embodiment of the elastic wave device of the present invention will be described with reference to FIG. As shown in FIG. 5, the elastic wave device 100 includes an IDT electrode 50 on the upper surface 2A of the substrate 2, and the IDT electrode 50 and the capacitance element 1 are electrically connected to each other. Further, in this example, an external terminal 60 electrically connected to the IDT electrode 50 and a cover 70 accommodating the IDT electrode 50 are provided. In FIG. 8, the portion where the cover 70 is arranged is shown by a broken line, and the state in which the cover is removed is shown.

The structure of the IDT electrode 50 is basically the same as that of the pair of comb tooth electrodes 30 of the capacitance portion 10, and includes a pair of bus bars 51, an electrode finger 52, and a reflector 53. In the IDT electrode 50, electrode fingers 52 connected to different potentials are arranged so as to intersect alternately. This arrangement direction is along the X axis of the piezoelectric crystal. With such a configuration, it becomes a 1-port type resonator in which elastic waves excite along the X axis. Normally, since the capacitive element 10 is formed at the same time as the connected IDT electrode 50, the above configuration (material, thickness, etc.) is generally the same as that of the capacitive element 10.

By connecting the capacitive element 1 in parallel to such an IDT electrode 50, the difference between the anti-resonance frequency of the resonator and the resonance frequency can be reduced.

The pitch of the electrode fingers 32 of each capacitance portion 10 of the capacitance element 1 may be different from the pitch Pt1 of the electrode fingers 52 of the IDT electrode 50. This is to suppress the influence on the capacitance section 10 when a high frequency signal for exciting elastic waves is input to the IDT electrode 50. In this example, by setting the arrangement direction L1 of the capacitance element 1 to a direction orthogonal to the X axis, it is possible to suppress the excitation of an unintended elastic wave in the capacitance element 1.

Further, the distance from the tip of one electrode finger 32 of the capacitance portion 10 of the capacitance element 1 to the other bus bar 31 is larger than the distance from the tip of one electrode finger 52 of the IDT electrode 50 to the other bus bar 51. You may. In this case, while the loss of elastic waves can be reduced in the IDT electrode 50, it is possible to suppress the occurrence of unintended distortion in the capacitive element 1.

Further, in this example, the capacitive element 1 is arranged outside the region in which the intersecting region of the electrode fingers 52 of the IDT electrode 50 is extended in the arrangement direction. With such a configuration, it is possible to prevent the vibration of the elastic wave excited by the IDT electrode 50 from being transmitted to the capacitive element 1 and improve the power resistance.

The elastic wave module 210 can be provided by mounting the elastic wave device 100 having a cap-shaped cover 70 on the upper surface 2A on the circuit board 200 via the terminal 120 as shown in FIG.

In the above example, the capacitance element 1 is also housed inside the cover 70, but the present invention is not limited to this. For example, the capacitance element 1 may be arranged outside the cover 70, or may be provided directly below the cover 70 so as to be sandwiched between the cover 70 and the upper surface 2A. By arranging the cover 70 on the capacitance element 1, the capacitance portion 10 of the capacitance element 1 comes into contact with the cover 70. In this case, even when the capacitive element 1 is provided in the region where the intersecting region of the electrode fingers 52 of the IDT electrode 50 is extended in the arrangement direction, the cover can suppress the vibration caused by the IDT electrode 50 and is resistant to vibration. It is possible to provide an elastic wave device having excellent electric power.

In the above example, the case where the capacitive element 1 is used has been described, but other capacitive elements may be used.

In order to confirm the effect of suppressing the strain current by the above-mentioned capacitive element, the capacitive element 1 was actually manufactured and the strain was measured. The capacitive element 1 was manufactured with the following specifications.

<Basic configuration>
Substrate 2: 42 ° Y-cut-X propagation LiTaO ₃ substrate Conductive film 15: AlCu 400 nm thick Electrode finger 32: Width 1 μm
Cross width 200 μm
Number of 10 Gp2-8 Size: 1 μm

<Structure of each example>
Sizes of Gp1 and Gp9: 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 5.0 μm, 8.0 μm
Hereinafter, the magnitude of Gp1 may be expressed as "Gp1 =".

<Comparative example configuration>
Comparative Example 1
Size of Gp1 and Gp9: Same as Gp2 Comparative Example 2
Size of Gp1 and Gp9: 0.75 μm

For the capacitive elements of such Examples and Comparative Example 1, the second harmonic (H2) was simulated and actually measured as distortion due to the second-order nonlinearity. The measurement system of the second harmonic is shown in FIG. As shown in FIG. 7, this measurement system is a bandpass filter (BPF) that passes the signal from the transmitter SG through only the fundamental wave from the power amplifier (PA), isolator (ISO), and PA.
A signal is applied to the object to be measured (DUT) via a directional coupling (Coupler) and an attenuator (ATT). Then, the reflected wave from the DUT is branched by the Coupler and input to the measuring instrument (SA) via the high-pass filter (HPF). Specifically, the output from the oscillator SG was amplified to 22 dBm by PA and applied to a capacitive element which is a DUT by a probe. Then, the reflected wave was taken out by Coupler, the fundamental wave component was removed by HPF, and the frequency component (second harmonic H2) twice that of the fundamental wave was measured.

Further, FIG. 8A shows the magnitude of the distortion output when the high frequency signals input in Comparative Examples 1 and 2 and Examples are changed. That is, it shows the magnitude of the distortion output when the input high frequency signal is changed when the magnitudes of Gp1 and Gp9 are 0.75 μm to 8 μm. In FIG. 8A, the vertical axis represents the output (unit: dBm) of the second harmonic H2, and the horizontal axis represents the frequency (unit: MHz) of the input signal. As is clear from this figure, it was confirmed that the distortion current was suppressed in all frequency bands by widening the gap.

Further, FIG. 8B shows a diagram showing the correlation between the average value of each strain current in FIG. 8A and the size of the gap. As shown in FIG. 8B, by widening the gap, the distortion output becomes smaller and the minimum value is taken when Gp1 = Gp9 = 1.5 μm. After that, it was confirmed that the distortion output increased by further widening the gap Gp and converged to the value of Comparative Example 1 of Gp1 = Gp9 = 1.0 μm. This is consistent with the theoretical expectation that when Gp1 and Gp9 become sufficiently wide, the distortion current generated at Gp1 and Gp9 disappears, and as a result, the distortion current for one gap remains without being offset.

Next, FIG. 9A shows the simulation results when the sizes of Gp1 and Gp9 are 0.5 μm to 2.5 μm, and FIG. 9B shows the results of the simulation when the sizes of Gp1 and Gp9 are 0.75 μm to 3 μm. The result of the actual measurement is shown. In FIG. 9, the horizontal axis represents the Gp1 and Gp9 gap intervals, and the vertical axis represents the output (unit: dBm) of the second harmonic H2.

The simulated and measured values are in good agreement, indicating that the mechanism of strain current generation and suppression is valid. Then, in both the simulation and the measured value, the distortion current becomes smaller than that of the comparative example by widening the gap Gp of the specific part (odd number), and the minimum value is taken when the size of the gap Gp is constant. That is, the distortion current can be made smaller by setting the gap interval to about 1.5 times the normal gap interval.

Further, it can be seen that when the magnitude of the odd-numbered gap Gp is reduced, the distortion current is larger than when the magnitudes of all the gap Gp are the same. From this result, the following can be inferred.

That is, from another point of view, this configuration can be regarded as a configuration in which the even-numbered gap Gp is widened. In particular, if the number of electrode fingers 32 is 4, the gap Gp becomes the gap Gp1 to Gp3, and the size of the gap Gp2 is larger than Gp1 and Gp3. Specifically, when the size of the odd-numbered gap Gp (Gp1, Gp3) is 0.75 μm, the size of the even-numbered gap (Gp2) is set to 1 μm. It can be seen that when the even-numbered gaps are large, the characteristics are worse than when all the other gaps are the same size. In other words, it is presumed that the characteristics deteriorate when the even-numbered gap is increased.

From this, it was confirmed that it is important to "increase" the "odd number" gap Gp.

According to the present disclosure, it has been confirmed that if the odd-numbered gap Gp is increased, the distortion output can be reduced as compared with the case where all the gap Gp have the same width.

When widening the widths of two gaps Gp among the odd-numbered gaps Gp, the distortion output can be minimized by setting the widening gap width to about 1.5 times the other gap widths. As the gap width is further widened, the distortion reduction effect decreases and converges to the value of Comparative Example 1 when all the gap widths are equal. If the gap width is made too wide, the size will increase. Therefore, when the widths of the two gaps are widened, the widened gap width is preferably 1.1 to 5 times the even-numbered gap width. From the viewpoint that the distortion output can be minimized, 1.25 to 2 times is more preferable. Even when the width of three or more gaps Gp is widened, the optimum width for minimizing the distortion output can be appropriately set.

1: Capacitive element 2: Substrate 10: Capacitive portion 32: Electrode finger 32a: First electrode finger 32b: Second electrode finger 100: Elastic wave device 210: Elastic wave module Gp: Gap

Claims (4)

A substrate made of piezoelectric crystals and
A plurality of first electrode fingers arranged on the upper surface of the substrate and a plurality of second electrode fingers connected to different potentials than the first electrode finger are provided.
The first electrode finger and the second electrode finger are alternately arranged at intervals, and the arrangement direction has a plane direction component in which the Z-axis component of the piezoelectric crystal is projected onto the upper surface.
A capacitive element in which at least one of the gaps from the first electrode finger to the second electrode finger along the forward direction of the surface direction component is larger than the size of the gap between the other electrode fingers. The IDT electrode provided on the upper surface and
The IDT electrode is electrically connected to the acoustic wave device and a capacitive element according to claim 1. Further provided with a cover disposed on the upper surface and accommodating the IDT electrode.
The elastic wave device according to claim 2 , wherein the cover is located on the capacitive element. The elastic wave device according to claim 2 or 3 ,
An elastic wave module having a circuit board on which the elastic wave device is mounted.

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