JP6825822B2 - 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 Unexamined Patent Publication 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 invention includes a substrate made of a piezoelectric crystal and an electrically connected first capacitive portion and a second capacitive portion. In the first capacitance portion and the second capacitance portion, 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 are alternately spaced apart from each other. It is arranged with a gap. The arrangement direction of the first electrode finger and the second electrode finger has a plane direction component in which the Z-axis component of the piezoelectric crystal is projected onto the upper surface. The first capacitance portion is an electrode finger located at the end on the start point side when viewed along the forward direction of the surface direction component. The first end electrode finger is the first electrode finger. .. The second capacitance portion is an electrode finger located at the end on the start point side when viewed along the forward direction of the surface direction component, and the second end electrode finger is the second electrode finger.

The capacitive element of another aspect of the present invention includes a substrate made of a piezoelectric crystal and an electrically connected first capacitive portion and a second capacitive portion. In the first capacitance portion and the second capacitance portion, 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 are alternately spaced apart from each other. It is arranged with a gap. The first capacitance portion and the second capacitance portion have an odd total number of the first electrode finger and the second electrode finger, respectively, and the arrangement of the first electrode finger and the second electrode finger. The potentials of the electrode fingers located at the ends in the direction are different from each other.

The elastic wave device according to one aspect of the present invention 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 invention 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 invention described above has a first capacitive portion and a second capacitive portion that cancel each other's second-order nonlinear strains to suppress distortion and provide high electrical characteristics. It becomes a thing. 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 invention. It is sectional drawing of the capacitive element shown in FIG. It is a top view which shows the modification of the capacitance element shown in FIG. It is a top view which shows the modification of the capacitance element shown in FIG. It is a top view which shows the modification of the capacitance element shown in FIG. It is a top view which shows the modification of the capacitance element shown in FIG. 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 second harmonic measurement results of Examples and Comparative Examples, respectively. (A) and (b) are diagrams showing the second harmonic measurement results of Examples, Comparative Examples and Reference Examples, respectively.

Hereinafter, embodiments of the capacitive element, elastic wave device, and elastic wave module of the present invention 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.

<Capacitive element>
FIG. 1 is a plan view of the capacitance element 1 according to the embodiment of the present invention, 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 first capacitive portion 10a and a second capacitive portion 10b provided on the upper surface 2A thereof. The first capacitance section 10a and the second capacitance section 10b are electrically connected in parallel. In this example, both terminals T1 and T2 are electrically connected by wiring 4. Since the basic configurations of the first capacitance section 10a and the second capacitance section 10b are similar, they may be simply referred to as the capacitance section 10 hereafter without distinguishing them. Hereinafter, other configurations may be described without distinguishing them by omitting the description of the first, second, and the like.

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 composed of 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 portion 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 S (D3 direction) of the comb tooth electrode 30 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 ₂ , 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 first electrode finger 32a connected to the first bus bar 31a. The number of the first electrode fingers 32a is at least one. 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 at least one.

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 center spacing (pitch) of the electrode finger widths of the first comb tooth electrode 30a and the second comb tooth electrode 30b and the widths of the adjacent electrode fingers 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).

Then, the first end electrode finger 32x of the first capacitance portion 10a and the second end electrode finger of the second capacitance portion 10b located on the starting point side along the surface direction component Zd2 in the forward direction. 32y is an electrode finger connected to different potentials. Specifically, the first end electrode finger 32x is the first electrode finger 32a, and the second end electrode finger 32y is the second electrode finger 32b. The "starting point side" along the forward direction refers to the minus side in the surface direction component Zd2.

In this example, the total number of the first capacitance section 10a and the second capacitance section 10b, which is the sum of the first electrode finger 32a and the second electrode finger 32b, is an even number, respectively. That is, in the first capacitance section 10a, the number of the first electrode fingers 32a and the number of the second electrode fingers 32b is the same, and the total number of the sum of these is an even number. The same applies to the second capacitance section 10b. The total number of the first capacitance section 10a and the second capacitance section 10b may be the same or different. Then, the above-described configuration is realized by reversing the meshing method of the comb tooth electrode 30 between the first capacitance portion 10a and the second capacitance portion 10b.

With such a configuration, when a high frequency signal is applied between the terminals T1 and T2, the distorted wave is canceled between the first capacitance section 10a and the second capacitance section 10b, and the distorted wave is suppressed. Capacitive element 1 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 to the outside as a distorted wave. 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. When the rotational Y-cut-X-propagated piezoelectric crystal illustrated here is used, the component in the Z-axis direction 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. Further, since it is a part that forms a capacitance as a capacitance element, it may not be possible to take measures to reduce the occurrence of distortion such as widening the interval in design.

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 reversing the magnitude relationship between the number Na and the number Nb in the first capacitance section 10a and the magnitude relationship between the number Na and the number Nb in the second capacitance section 10b, it is caused by the D2 component of the electric field. The strain current can be offset and suppressed.

The capacitance unit 10 is composed of an even number of electrode fingers 32. In this case, one of the electrode fingers 32 located outside each capacitance portion 10 is the first electrode finger 32a and the other is the second electrode finger 32b. Therefore, the strain current due to the asymmetrical shape of the electric field in the thickness direction appears on both the first electrode finger 32a and the second electrode finger 32b and is canceled out in one capacitance portion 10.

From the above, when the total number of electrode fingers 32 of each capacitance portion 10 is an even number and the arrangement direction L1 of the electrode fingers 32 includes the Z-axis component of the piezoelectric crystal, the first end electrode fingers 32x and the second electrode fingers 32x. It was found that the distorted wave output of the capacitive element 1 can be suppressed by arranging the end electrode fingers 32y so as to be connected to different potentials.

In other words, in the capacitance element 1, the first capacitance section 10a and the second capacitance section 10b generate distorted waves having different polarities and are electrically connected so as to cancel each other out.

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.

<Capacitive element 1A>
Although the case where the total number of electrode fingers 32 of the capacitance units 10a and 10b is an even number is described above, the capacitance element 1 may be an odd number of capacitance elements 1A. 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. 3 shows a plan view of the capacitive element 1A. As shown in FIG. 3, the total number of electrode fingers 32 of each of the capacitance portions 10a and 10b is an odd number. The first-end electrode fingers 32x and the second-end electrode fingers 32y of the capacitance portions 10a and 10b are arranged so as to be connected to different potentials as in the capacitance element 1. In other words, comparing the number of the first electrode fingers 32a and the number of the second electrode fingers 32b, the smaller number of electrode fingers is different between the first capacitance portion 10a and the second capacitance portion 10b.

With this configuration, the polarities of the distorted wave generated in the first capacitance section 10a and the distorted wave generated in the second capacitance section 10b can be made different, and as a result, the distortion wave generated in the entire capacitance element 1A is generated. Can be suppressed. The mechanism will be described below.

In the capacitive element 1A, 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 is an even number in each capacitance portion 10, 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 unit 10. That is, the output of the distorted wave caused by the surface direction component can be 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 each capacitance portion 10, an 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 1A 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 into both electrodes is not completely canceled, and the strain current is output to the outside.

Here, in the capacitance element 1A, the electrode fingers 32 located outside each capacitance portion 10 are electrode fingers having the same polarity. For example, in FIG. 3, the first capacitance portion 10a is the first electrode finger 32a, and the second capacitance portion 10b is the second electrode finger 32b. Therefore, the change in the strain current due to the asymmetrical shape of the electric field in the D3 direction appears on both the first electrode finger 32a and the second electrode finger 32b, and a distortion wave having a different polarity is generated in each capacitance portion 10, and the capacitance is generated. The distorted wave can be canceled out and the output of the distorted wave can be suppressed for the element 1A as a whole.

As described above, the capacitive element 1 suppresses the output of the distorted wave by combining the two capacitive portions 10 in which the distorted waves caused by the plane direction component Zd2 of the crystal Z axis are different from each other. In the capacitive element 1A, the output of the distorted wave is suppressed by combining the two capacitive portions 10 in which the distorted waves caused by the thickness direction component Zd3 of the crystal Z axis are different from each other. As described above, it was confirmed that the capacitance elements 1 and 1A can suppress the distorted wave output with the same configuration, although the difference is in which direction the distorted waves caused by the electric field are different in the two capacitance units 10.

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 1A has a smaller distorted wave itself generated in the first capacitance section 10a and the second capacitance section 10b than the capacitance element 1, and the distorted wave output can be further suppressed.

<Capacitive element 1B>
In the above-mentioned capacitance elements 1 and 1A, the case where the odd and even numbers of the total number of the electrode fingers 32 of the capacitance units 10a and 10b match has been described, but the total number of the electrode fingers 32 of one of the capacitance units 10 is an odd number. The other capacitive element 1B may have an even number of electrode fingers 32. 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 capacitance element 1B. As shown in FIG. 4, the total number of electrode fingers 32 of each of the capacitance portions 10a and 10b is an odd number and an even number, respectively. The first-end electrode fingers 32x and the second-end electrode fingers 32y of the capacitance portions 10a and 10b are arranged so as to be connected to different potentials as in the capacitance element 1.

With this configuration, the polarities of the distorted wave generated in the first capacitance section 10a and the distorted wave generated in the second capacitance section 10b can be made different, and as a result, the distortion wave generated in the entire capacitance element 1B is generated. Can be suppressed. The mechanism will be described below.

In this example, the total number of electrode fingers 32 of the first capacitance section 10a is an odd number, and the total number of electrode fingers 32 of the second capacitance section 10b is an even number. In the first capacitance section 10a, a distorted wave is output by the thickness direction component Zd3 as described in the capacitance element 1A. Specifically, in the first capacitance section 10a, the electrode finger having the larger number of the first electrode finger 32a and the second electrode finger 32b becomes the electrode fingers 32x on both outer sides. Therefore, the distorted wave is output from the electrode finger side having the larger number to the electrode finger side having the smaller number. In this example, a distorted wave is output from the first electrode finger 32a to the second electrode finger 32b side.

In the second capacitance section 10b, as described in the capacitance element 1, a distorted wave is output by the plane direction component Zd2. That is, the number Na from the first electrode finger 32a to the second electrode finger 32b and the number Nb from the second electrode finger 32b toward the first electrode finger 32a are different along the forward direction of the surface direction component Zd2. Distortion current is output in the direction of the larger number. Here, since the total number of the electrode fingers 32 is even, the number of the electrode fingers 32 (second end electrode finger 32y) on the starting point side in the forward direction of the surface direction component Zd2 in the direction toward the adjacent electrode finger. Will be more. That is, the number from the second electrode finger 32b to the first electrode finger 32a increases, and the distorted wave is output in this direction.

In this way, the polarities of the distorted waves can be made different between the first capacitance section 10a and the second capacitance section 10b, and the distorted waves in the entire capacitance element 1B can be suppressed.

In the capacitance element 1B, the first capacitance section 10a outputs a distorted wave caused by the thickness direction component Zd3, and the second capacitance section 10b outputs a distorted wave caused by the surface direction component Zd2. Therefore, the absolute value of the magnitude of the distorted wave output from both capacitance units 10 may be different. Therefore, the crossing width of the electrode fingers 32 may be different between the capacitance portions 10 and adjusted so that the absolute values approach each other. For example, 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. The crossing width of the electrode fingers 32 of the first capacitance portion 10a may be larger than that of the second capacitance portion 10b.

<Capacitive elements 1C, 1D>
Although the above-mentioned capacitance elements 1, 1A and 1B have been described in the case where the arrangement direction L1 has the plane direction component Zd2, the capacitance elements 1C and 1D in which the arrangement direction L1 has the X-axis component may be used. 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. 5 shows a plan view of the capacitive element 1C. As shown in FIG. 5, the arrangement direction L1 has an X-axis component. In this example, the arrangement direction L1 and the X axis are substantially parallel. In such a case, the arrangement direction L1 of the electrode fingers 32 has no Z-axis component or becomes extremely small. On the other hand, in the electrode finger 32 at the end of the capacitance portion 10, the electric field in the thickness direction has asymmetry as in the previous example.

For this reason, in the capacitance element 1C, the total number of electrode fingers 32 of each capacitance section 10 is an odd number, and when viewed along the arrangement direction L1, the first capacitance section 10 and the second capacitance section 20 are arranged. The polarities of the electrode fingers 32 located at the ends are different from each other. The capacitive element 1C is a configuration in which the configuration related to the electrode finger of the capacitive element 1A is rotated by 90 °.

With such a configuration, the capacitive element 1C can suppress the output of the distorted wave by combining the two capacitive portions 10 in which the distorted waves caused by the thickness direction component Zd3 are different from each other.

Further, the capacitive element 1D shown in FIG. 6 may be used. The capacitance elements 1 to 1C arrange each capacitance portion 10 along the arrangement direction L1, while the capacitance element 1D arranges each capacitance portion 10 along the arrangement direction of the bus bar 31. With such a configuration, the bus bars can be shared between the capacitance units 10 to be electrically connected, so that wiring becomes easy.

Further, when the arrangement direction L1 is the X-axis direction (D1 direction), a distorted wave in the arrangement direction of the bus bar 31 may be generated. That is, an electric field of the surface direction component Zd2 is generated between one bus bar 31 and the tip of the other electrode finger 32. Therefore, by using the capacitance element 1D, between the first capacitance section 10a and the second capacitance section 10b, from the high potential side to the low potential side with respect to the plane direction component Zd2 as shown by the black arrow in the figure. You can go in different directions. As a result, the distorted waves generated in the respective capacitance units 10 can be offset, and the capacitance element 1D that further suppresses the distortion waves can be provided.

<Capacitive element 1E>
In the above-mentioned capacitive elements 1 to 1D, each capacitive portion 10 is electrically connected via the bus bar 31, but the capacitive element 1E may be connected via the electrode finger 32.

7 (a) and 7 (b) show a plan view of a capacitance element 1E connecting each capacitance portion 10 via an electrode finger 32 and a modified example thereof.

As shown in FIG. 7, in the capacitance element 1C, the two capacitance portions 10 are electrically connected by integrally forming and sharing a part of the electrode fingers 32. It can be considered that the two capacitance portions 10 are combined as a pair of comb tooth electrodes, and at least the electrode fingers located on both outer sides are shorter than the other electrode fingers. As shown in FIG. 7 (a), one of the short electrode fingers may be a part of the first capacitance portion 10a and the other may be a part of the second capacitance portion 10b, or FIG. 7 (b). ), Both may be a part of one capacitance portion 10 (first capacitance portion 10a in this example).

Such a configuration can be realized when the total number of electrode fingers 32 of each capacitance portion 10 is an odd number. The capacitance element 1E shown in FIG. 7A and the capacitance element 1A shown in FIG. 3 have the same electric circuit configuration.

<Others>
When the second capacitance portion 10b is arranged so as to overlap with each other when viewed along the arrangement direction L1 of the electrode fingers 32 of the first capacitance portion 10a, the second capacitance portion 10b side of the first capacitance portion 10a The distance between the electrode finger located in the first capacitance section 10b and the electrode finger located closest to the first capacitance section 10a of the second capacitance section 10b is the pitch of the electrode finger of the first capacitance section 10a and the electrode finger of the second capacitance section 10b. It may be larger than any of the pitches of. That is, the interval x3 shown in FIG. 3 may be larger than the pitches p1 and p2 of the capacitance unit 10. In this case, the electric field can be made asymmetric at the end of each capacitance section 10. As a result, when the output of the distorted wave due to the asymmetry of the electric field with respect to the thickness direction component Zd3 is used as in the capacitive elements 1A to 1D, a sufficient distorted wave can be output.

Further, in the above example, each capacitance unit 10 is electrically connected in parallel, but both may be connected in series.

Further, although the capacitance elements 1 to 1C are electrically connected to each capacitance portion 10 by the wiring 4, they may be electrically connected by sharing the bus bar 31. In that case, the distance between the first capacitance section 10a and the second capacitance section 10b may be adjusted so that the electric field can be made asymmetric at the end of each capacitance section 10.

Further, in the above-mentioned capacitive element, the case where the arrangement direction L1 is set to the plane direction component Zd2 or the X-axis component direction has been described, but it suffices to have those components with respect to the D2 direction and the D1 direction. It may be angled.

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, such as the capacitance elements 1, 1A and 1B, L1 and Zd2 are used. The angle formed may be 45 ° or less (that is, −45 ° to + 45 °, including the threshold value), and by setting the angle to 10 ° or less (that is, −10 ° to + 10 °, including the threshold value), two more effectively. The distortion current can be canceled between the capacitance units 10.

Similarly, in the case of a configuration in which the distortion current is canceled between the two capacitance portions 10 by having the arrangement direction L1 having an X-axis direction component as in the capacitance elements 1C and 1D, L1 and X (D1) are used. The angle may be less than 45 ° (-45 ° to + 45 °, not including the threshold value), and 10 ° or less (-10 ° to + 10 °, including the threshold value) may be set to more effectively two capacities. The distortion current can be canceled between the parts 10.

<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. 8, 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 IDT electrode 50 to be connected, 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 and the resonance frequency of the resonator 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 each 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 capacitance 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. Further, as long as the first capacitance section 10a and the second capacitance section 10b are electrically connected, they do not need to be arranged close to each other and may be arranged separately.

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

<Basic configuration>
Substrate 2: 42 ° Y-cut-X propagation LiTaO ₃ substrate Conductive film 15: AlCu 400 nm thickness Connection method of each capacitance part 10: Parallel <Each example configuration>
Example 1 (Structure of Capacitive Element 1)
Arrangement direction L1: Zd2, D2 direction Electrode finger 32 pitch p1, p2: 5 μm
32 electrode fingers of each capacitance unit 10: 8 fingers, 8 fingers Example 2 (configuration of capacitive element 1A)
Arrangement direction L1: Zd2, D2 direction Electrode finger 32 pitch p1, p2: 5 μm
32 electrode fingers of each capacitance unit 10: 7, 7, Example 3 (configuration of capacitive element 1C)
Arrangement direction L1: X, D1 direction Electrode finger 32 pitch p1, p2: 2.3 μm
32 electrode fingers of each capacitance part 10: 15, 15 Reference example 1
Arrangement direction L1: X, D1 direction Electrode finger 32 pitch p1, p2: 2.3 μm
Number of electrode fingers 32 of each capacitance portion 10: 10, 10 Also, as Comparative Examples 1 to 3, the first end electrode fingers 32x and the second end electrode fingers 32y with respect to the configurations of Examples 1 to 3. A capacitive element having the same polarity as the above was manufactured. Further, as Reference Example 2 with respect to Reference Example 1, a capacitive element in which the polarities of the first end electrode finger 32x and the second end electrode finger 32y are not different was produced. The polarities of the first end electrode finger 32x and the second end electrode finger 32y of Reference Example 1 are different.

The second harmonic (H2) was measured as distortion due to the second-order nonlinearity of the capacitive elements of Examples 1 to 3, Reference Examples 1 and 2, and Comparative Examples 1 to 3. The second harmonic measurement system is shown in FIG. As shown in FIG. 10, in this measurement system, the signal from the transmitter SG is passed through the power amplifier (PA), the isolator (ISO), the bandpass filter (BPF) that passes only the fundamental wave from the PA, and the directional coupling (Coupler). ), A signal is applied to the object to be measured (DUT) via the 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 the Coupler, the fundamental wave component was removed by the HPF, and the frequency component (second harmonic H2) twice that of the fundamental wave was measured.

The measurement results are shown in FIGS. 11 and 12. Specifically, FIG. 11A shows the measurement results of Example 1 and Comparative Example 1, and FIG. 11B shows the measurement results of Example 2 and Comparative Example 2 (FIG. 12). A) shows the measurement results of Example 3 and Comparative Example 3, and FIG. 12B shows the measurement results of Reference Examples 1 and 2, respectively.

In these figures, 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. Further, the measurement results of Examples 1 to 3 and Reference Example 1 are shown by broken lines, and the measurement results of Comparative Examples 1 to 3 and Reference Example 2 are shown by solid lines.

As shown in FIGS. 11A and 11B, in Examples 1 and 2 in which the polarities of the end electrode fingers of the respective capacitance portions 10 are different, H2 is significantly reduced as compared with Comparative Examples 1 and 2. I understand. Comparing FIG. 11A and FIG. 11B, the distorted wave (caused by the plane direction component Zd2) generated when the total number of electrode fingers 32 of each capacitance portion 10 is an even number (Comparative Example 1). It can be seen that the distorted wave) is larger than the distorted wave (distorted wave caused by the depth direction component Zd3) generated when the total number of electrode fingers 32 of each capacitance portion 10 is an odd number (Comparative Example 2).

Since the noise level of the measurement system used this time is about -70 to -80 dBm, it is considered that the H2 level of the actual Examples 1 and 2 is further reduced (theoretically -∞ d).
Bm).

Further, as shown in FIG. 12A, even in Example 3 in which the arrangement direction L1 is different, when the polarities of the end electrode fingers of each capacitance portion 10 are different, H2 is higher than that in Comparative Example 3. It was found to be significantly reduced.

As shown in FIG. 12B, H2 of Reference Examples 1 and 2 is small, and there is almost no difference between the two. This is because the distortion generation mechanism described above does not generate a distortion wave due to the second-order nonlinearity in the capacitance portion where the arrangement direction L1 is the D1 direction and the number of electrode fingers is an even number. Is. That is, since there is no electric field of the surface direction component Zd2, the distorted wave caused by the surface direction component Zd2 does not occur, and the distorted wave caused by the depth direction component Zd3 is within one capacitance section 10 when the number of electrode fingers is even. Is offset by. In FIG. 12B, since H2 was small in both Reference Examples 1 and 2 and there was no difference between them, it was confirmed that the above-mentioned strain generation mechanism was correct.

1: Capacitive element 2: Substrate 10: Capacitive portion 32: Electrode finger 100: Elastic wave device 210: Elastic wave module

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 are arranged alternately at intervals, a first capacitance portion and a first portion. Equipped with 2 capacity parts
The arrangement direction of the first electrode finger and the second electrode finger is a direction different from the propagation direction of the elastic wave in the substrate, and has a plane direction component in which the Z-axis component of the piezoelectric crystal is projected onto the upper surface. ,
The first capacitance portion and the second capacitance portion are electrically connected to each other by the first electrode fingers.
The first capacitance portion is an electrode finger located at the end on the start point side when viewed along the forward direction of the surface direction component. The first end electrode finger is the first electrode finger.
The second capacitance portion is an electrode finger located at the end on the start point side when viewed along the forward direction of the surface direction component. The second end electrode finger is the second electrode finger.
The first capacitance portion and the second capacitance portion are arranged side by side in the arrangement direction, and the electrode finger located at the end of the first capacitance portion on the second capacitance side side and the second capacitance portion. The distance between the electrode finger located at the end of the capacitance portion on the first capacitance portion side is the distance between the first electrode finger and the second electrode finger of the first capacitance portion and the distance between the second capacitance portion and the second electrode finger. Larger than the distance between the first electrode finger and the second electrode finger,
Capacitive element. The IDT electrode, which includes the electrode fingers provided on the upper surface and whose arrangement direction is along the X axis of the piezoelectric crystal,
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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