JP2009219045A - Acoustic wave resonator and acoustic wave device - Google Patents

Abstract

In an elastic wave resonator weighted with the width of intersection of electrode fingers of an IDT electrode provided on a piezoelectric substrate, an elastic wave resonator capable of suppressing spurious based on a higher-order transverse mode and the elastic wave resonator are provided. The elastic wave device used is provided.
An elastic wave resonator is weighted by the width of an electrode finger of an IDT electrode provided on a piezoelectric substrate, and an envelope formed by connecting tips of electrode fingers connected to the bus bar is connected to the bus bar from the bus bar. The electrode finger group constituting the envelope passing through the adjacent local maxima and local minima is alternately arranged with at least three local maxima having a local maximum of at least two local maxima and at least two local minimums having this local minimum. Includes an electrode finger having an upper limit cross width in which a predetermined n-th order transverse mode (n is a predetermined odd number of 3 or more) does not occur, and an envelope passing through the tip of the electrode finger having the upper limit cross width The line is a straight line having an inclination angle in the range of 10 ° to 65 ° with respect to the propagation direction of the elastic wave.
[Selection] Figure 1

Description

  The present invention relates to an acoustic wave resonator using an acoustic wave such as SAW (Surface Acoustic Wave) and an acoustic wave device using the same, and more particularly to a technique for suppressing spurious caused by a higher-order transverse mode.

2. Description of the Related Art An acoustic wave resonator using an elastic wave is known as a resonator that is mounted on a mobile terminal such as a cellular phone and incorporated in, for example, a ladder type filter that discriminates a high frequency signal. FIG. 14 shows an example of a SAW resonator 100 using a surface acoustic wave (hereinafter referred to as SAW (Surface Acoustic Wave)) generated on the surface of a piezoelectric material such as quartz, LiTaO ₃ or LiNbO ₃ .

  The SAW resonator 100 includes a comb-shaped interdigitated electrode 2 (hereinafter referred to as an IDT (InterDigital Transducer) electrode 2) and a reflector disposed on both sides of the IDT electrode 2 on a piezoelectric substrate (not shown) made of a piezoelectric material. 3a and 3b are arranged. The IDT electrode 2 is made of, for example, aluminum and includes two bus bars 21 and 22 provided so as to face each other, and a large number of electrode fingers 231 connected to the bus bars 21 and 22 in a cross finger shape. ing. Then, frequency characteristics that cause resonance and anti-resonance according to the frequency using SAW excited between the adjacent electrode fingers 231 and 232 by electro-mechanical conversion of the frequency signal input to the bus bar 21 on one side. Have gained. The reflectors 3a and 3b are configured as a grating reflector including a number of electrode fingers 231 made of, for example, aluminum, and have a role of reflecting the SAW propagated outward from the IDT electrode 2 to the IDT electrode 2. Fulfill.

  The SAW excited between the electrode fingers 231 and 232 of the IDT electrode 2 propagates, for example, in the direction indicated by the arrow in FIG. 14 (referred to as the vertical direction), and the SAW traveling wave and the reflectors 3a on both sides. When the reflected wave of the SAW reflected at 3b overlaps, a transverse mode having an amplitude distribution in a direction perpendicular to the longitudinal direction (referred to as a transverse direction) is excited. The transverse mode includes a main resonance mode, a second-order mode, a third-order mode,..., A mode having an infinite number of orders, and among these, the main resonance whose amplitude distribution is schematically shown in FIG. Only the mode is used to obtain the frequency characteristics of the SAW resonator 100.

  On the other hand, among the higher-order modes than the main resonance mode, even-order modes cancel out vibration energy in each mode and do not affect the frequency characteristics, but odd-order modes such as third-order, fifth-order, etc. For example, the vibration energy corresponding to the area not shaded with diagonal lines in FIG. 15A remains without being canceled. Such non-cancelled vibration energy appears as spurious in the frequency characteristics of the SAW resonator 100 and causes ripples in the frequency characteristics of the ladder filter, for example.

  Therefore, various SAW resonators are known in which the crossing widths of the electrode fingers 231 and 232 are weighted in order to suppress the influence of such higher-order transverse modes. For example, in the SAW resonator 100a described in Non-Patent Document 1, the intersection width of the electrode fingers 231 and 232 is maximum in the central region of the IDT electrode 2 and minimum at both ends as shown in FIG. The shape of the envelope formed by connecting the tip portions of the electrode fingers 231 and 232 is a straight line.

  In the region where the intersection width of the electrode fingers 231 and 232 is reduced by weighting, the proportion of energy canceled out in the mode is increased as shown in FIG. As a result, as the crossing width is reduced, the influence of the higher order transverse mode is reduced in order from the lower order mode, and the spurious can be reduced in the frequency characteristics of the entire SAW resonator 100a. The electrode 233 that does not intersect the opposing electrode fingers 231 and 232 is a dummy electrode 233 for preventing the disturbance of the SAW phase.

In this way, the technique for weighting the intersection widths of the electrode fingers 231 and 232 to suppress the influence of the higher-order transverse mode to a smaller level is used to reduce the power consumption of the mobile terminal and the reception radio wave due to the downsizing of the receiving antenna The SAW resonators having various envelope shapes have been proposed in response to demands for weakening and the like. For example, in Patent Document 1, the envelope shape of the electrode fingers 231 and 232 is defined as “cos ⁻¹ (| ax |), where a is a constant” with respect to the origin of the x axis shown in FIG. The SAW resonator 100b is described in which the excitation intensity distribution is matched with the main resonance mode and the degree of suppression of the higher-order transverse mode is further increased.

  However, also in the SAW resonators 100a and 100b described in FIGS. 16 and 17, the high-order transverse vibration mode cannot be suppressed to a desired level as shown in the actual measurement results (experimental values) described later. This inventor has grasped this.

  Note that Patent Document 2 includes a plurality of local maximum points where the crossing width of electrode fingers is maximum and local minimum points where the crossing width is also minimum, and these local maximum points and local minimum points are alternately arranged. The child is listed. However, the technique described in Patent Document 2 sufficiently obtains the effect of suppressing higher-order transverse modes because the envelope inclination angle is out of the range of 10 ° to 65 ° and the envelope inclination is too large. It is not possible. In the SAW resonator, the minimum point of the envelope extends to the center of the IDT electrode, and there are many regions where the cross width of the electrode fingers is small. As will be described later, in a region where the crossing width of the electrode fingers is small, there is a possibility that excessive stress is applied to the electrode fingers when power is applied to the IDT electrodes, resulting in destruction of the electrode fingers, and the SAW resonator is provided. There is a problem that the insertion loss of the filter increases.

IEICE Transactions A Vol. 75-A No. 3 Page 464, left column, 8th line to right column, 7th line, FIG. Japanese Patent Laid-Open No. 7-22898: Paragraph 0002, FIG. JP 2007-60108 A: No. 0009, No. 0035, No. 0044, FIG.

  The present invention has been made based on such circumstances, and the object thereof is based on a high-order transverse mode in an elastic wave resonator weighted with the width of intersection of electrode fingers of an IDT electrode provided on a piezoelectric substrate. An object of the present invention is to provide an elastic wave resonator capable of suppressing spurious and an elastic wave device using the elastic wave resonator.

The elastic wave resonator according to the present invention is an elastic wave resonator in which the intersection width of electrode fingers of IDT electrodes provided on a piezoelectric substrate is weighted.
The envelope formed by connecting the tips of the electrode fingers connected to the bus bar on at least one side of the IDT electrode has at least three local maxima at which the distance from the bus bar is a maximum, and the distance is minimum. And at least two local minimum parts arranged alternately,
The electrode finger group constituting the envelope passing through these adjacent maximum and minimum portions has an upper limit cross width at which a predetermined n-th order transverse mode (n is a predetermined odd number of 3 or more) does not occur. The electrode fingers are included,
The envelope passing through the tip of the electrode finger having the upper limit crossing width is a straight line having an inclination angle in the range of 10 ° to 65 ° with respect to the propagation direction of the elastic wave, or the upper limit An envelope formed by connecting a predetermined number of tip ends of electrode fingers having a cross width and tip portions of electrode fingers having a cross width smaller than the electrode fingers is a tangent drawn with respect to the envelope The maximum inclination angle formed with the propagation direction is a curve having an inclination angle within the range.
Here, one of the local maximum points is preferably provided at a position where the maximum amplitude of the zeroth-order longitudinal mode excited in the IDT electrode is generated, and the nth-order transverse mode is a third-order transverse mode. The case is preferred. In addition, the shorter one of the intersection widths of the electrode finger located at the minimum portion and the left and right electrode fingers adjacent to the electrode finger with respect to the opening length between the inner ends of the bus bars facing the IDT electrode It is preferable that the ratio of the crossing width is 0.3 or more.

  The elastic wave device according to the present invention is an elastic wave device in which a plurality of elastic wave resonators are formed on a common substrate, and at least one of the plurality of elastic wave resonators is the above-described elastic wave resonator. It is characterized by being.

  According to the elastic wave resonator according to the present invention, the envelope formed by connecting the tip portions of the electrode finger group of the IDT electrode has at least three maximum portions where the distance from the bus bar is maximum, and this distance is minimum. At least two local minimums, so that the electrode fingers with the upper limit crossing width that can suppress the high-order transverse mode of a predetermined order are placed several times at intervals in the elastic wave propagation direction. Can be arranged. Further, the inclination angle of a straight line constituting an envelope connecting adjacent maximum points and minimum points, or the maximum inclination angle of a tangent line drawn with respect to the curve constituting the envelope line is within a range of 10 ° to 65 °. Therefore, a plurality of electrode fingers having an intersection width close to the upper limit intersection width can be arranged in the vicinity of the electrode fingers having the upper limit intersection width as described above, which affects the frequency characteristics. An elastic wave resonator having a small spurious can be obtained by effectively suppressing a large high-order transverse mode.

  The gist of the present invention will be briefly described below before describing a specific configuration example of the SAW resonator according to the present embodiment. As described in the background art, SAW resonators with various envelope shapes have been proposed for the purpose of suppressing the occurrence of spurious due to higher-order transverse modes, but there is a demand for lower spurious. It is getting stronger. Therefore, the present inventor has intensively studied to develop a higher performance SAW resonator, and has obtained the following knowledge.

  That is, (1) In the SAW resonators 100a and 100b described in FIG. 16 and FIG. 17 described above, there is no suppression for a high-order transverse mode of a specific order, such as a third-order transverse mode having a relatively large vibration energy. In many cases, it is not sufficient to cause spurious. (2) In order to sufficiently suppress a specific higher-order transverse mode that cannot be suppressed in this way, for example, the electrode fingers 231 and 232 are input while inputting a signal having a resonance frequency to the IDT electrode 2 having a constant crossing width. The number of electrode fingers 231 and 232 having an upper limit cross width (hereinafter referred to as an upper limit cross width) at which the specific higher-order transverse mode does not occur when the cross width of the electrode is gradually reduced is provided. It is preferable. (3) In the case where a large number of electrode fingers 231 and 232 having such an upper limit crossing width are arranged, the direction of propagation of elastic waves is greater than the arrangement of these electrode fingers 231 and 232 in one place. It is better to disperse them.

Based on the knowledge of (1) to (3) described above, for example, as schematically shown in FIG. 18, an electrode finger having an upper limit cross width “W _max ” capable of suppressing a specific higher-order transverse mode. It seems to be effective to adopt the IDT electrode 2 having the envelopes 41 and 42 in which 231 and 232 are widely arranged in the SAW propagation direction. However, the characteristics of the high-order transverse mode change due to subtle changes in the physical properties of the piezoelectric substrate and slight deviations in the distance between the inner ends of the bus bars 21 and 22 (referred to as opening lengths). There is variation every two. Therefore, even if a SAW resonator including electrode fingers 231 and 232 having a calculated upper limit intersection width “W _max ” as shown in FIG. 18 is manufactured, the intersection width deviates from the actual upper limit intersection width. If it is, it may not be useful for suppressing spurious.

As described above, in order to utilize the knowledge obtained in (1) to (3), even when the upper limit intersection width “W _max ” corresponding to the higher-order transverse mode to be suppressed fluctuates, A configuration that can stably suppress the higher-order transverse mode is required. The present invention is made from such a viewpoint. Hereinafter, the configuration of the SAW resonator 1 according to the present embodiment will be described in detail.

  FIG. 1 is a plan view of a SAW resonator 1 according to the present embodiment, which includes an IDT electrode 2 and reflectors 3a and 3b, and has an intersection width of electrode fingers 231 and 232 connected to bus bars 21 and 22, respectively. The weighting is the same as the SAW resonators 100a and 100b described above with reference to FIGS. The SAW resonator 1 has local maximum points P1 to P3 and Q1 to Q3, and local minimum points B1 and B2, which are local maximums, to an envelope formed by connecting the tip portions of the electrode fingers 231 and 232. , C1 and C2 are alternately provided, so that the influence of a predetermined higher-order transverse mode, for example, the third-order transverse mode can be suppressed, which is different from the conventional SAW resonators 100a and 100b.

Here, design variables related to the weighting of the intersection widths of the electrode fingers 231 and 232 are defined with reference to FIG. 2, and an IDT electrode is formed in a region (called a tap) of a piezoelectric substrate sandwiched between adjacent electrode fingers 231 and 232. When the numbers “1, 2, 3,...” Are sequentially assigned from the left end side of 2, the intersection width of the electrode fingers 231 and 232 forming the i-th tap is “W (i)”. Since the SAW is excited with a width equal to the intersection width “W (i)” at the i-th tap, when the excitation amplitude is “Y (i)”, the absolute value of the weighting coefficient “y (i)” is It is defined by the following equation (1).
| Y (i) | = Y (i) / W0 = W (i) / W0 = w (i) (1)
Here, W0 is the opening length of the IDT electrode 2, and w (i) is the ratio of the crossing width to the opening length of the electrode fingers 231 and 232 forming the i-th tap (referred to as relative crossing width).

The reason for taking the absolute value of the weighting coefficient in the equation (1) is that the direction of the weighting coefficient changes depending on the direction of the electric field formed between the electrode fingers 231 and 232. Now, when the electric field toward the right direction of the x axis shown in FIG. 2 is formed between the electrode fingers 231 and 232 forming the i-th tap, the electric field toward the left direction is formed. When is negative, the weighting coefficient is expressed by the following equation (2).
y (i) = sign * (Y (i) / W0) (2)
Here, “sign” returns “sign = 1” when the direction of the electric field formed between the electrode fingers 231 and 232 is positive, and “sign = −1” when the direction is negative.

  Thus, the weighting of the intersection widths of the electrode fingers 231 and 232 is performed to adjust the width of the SAW excited region. In the present embodiment, as described above, the higher-order transverse mode is weighted. The distribution of the weighting coefficient “| y (i) |” is set for the purpose of suppressing the influence, and the envelope formed by connecting the tips of the electrode fingers 231 and 232 so as to realize the distribution of the weighting coefficient. The shape of the line has been determined.

  FIG. 3B is a schematic diagram in which the envelopes 41 and 42 are drawn by omitting the description of the electrode fingers 231 and 232 of the IDT electrode 2 according to the embodiment. Assuming that the upper side is the front and the lower side is the rear as viewed in the drawing, 41 is an envelope formed by a group of electrode fingers 232 connected to the bus bar 22 on the rear side, and 42 is connected to the bus bar 21 on the front side. This is an envelope formed by a group of electrode fingers 231 that are formed.

  As shown in FIG. 3, when the x-axis is taken in the vertical direction (SAW propagation direction) and the y-axis is taken in the horizontal direction, the central left end of the two bus bars 21 and 22 is the origin, and the right end is the “L point”. The envelope 41 starts from the origin and has local maximum points P1 to P3, local minimum points B1, from the origin to the L point in the order of “origin vicinity position → P1 → B1 → P2 → B2 → P3 → L point vicinity position”. It is a bent line connecting B2 with a straight line.

  Here, it is known that when a frequency signal is inputted to the SAW resonator 1, the IDT electrode 2 is excited in the SAW propagation direction in addition to the above-described transverse mode. As shown in FIG. 3A, the main resonance mode (0th-order mode) of the longitudinal mode has a peak with the maximum amplitude at the center of the IDT electrode 2 in the x-axis direction. If the cross width of 231 and 232 is small, excessive stress is applied to the electrode fingers 231 and 232 when the frequency signal is subjected to electro-mechanical conversion, resulting in the destruction of the electrode fingers 231 and 232.

  Therefore, in the envelope 41, the crosswise width of the electrode fingers 231 and 232 is maximized at the position where the aforementioned peak occurs, so that the front and rear direction (y direction) is near the bus bar 21 and the left and right direction (x direction). Is a maximum point P2 at the center of the IDT electrode 2. The remaining two maximum points P1 and P3 are arranged at approximately the same position as the above-described maximum point P2 in the front-rear direction, and at about one third of the distance from both ends of the IDT electrode 2 to the center in the left-right direction. Has been.

On the other hand, the two minimum points B1 and B2 are the center position from the x-axis to the bus bar 21 in the front-rear direction, the position slightly closer to the outer end than the center position between the maximum points P1 and P2 in the left-right direction, and the maximum point. They are arranged at positions slightly closer to the outer end than the center between P2 and P3. As a result, the inclination angles θ1 to θ4 formed by the line segments P1-B1, B1-P2, P2-B2, and B2-P3 constituting the envelope 41 with respect to the SAW propagation direction are, for example, 10 ° or more and 65 ° or less. The inclination angle is within the range of. Further, with respect to the opening length W0 between the bus bars 21 and 22, one of the intersection widths of the electrode fingers 232 positioned at the respective minimum points B1 and B2 and the left and right electrode fingers 231 adjacent to the electrode fingers 232 is shorter. The ratio of the crossing width W (m _B ) is 0.3 or more, preferably 0.35 or more.

On the other hand, the maximum points Q1 to Q3 and the minimum points C1 and C2 constituting the other envelope 42 are slightly shifted because the tip portions of the electrode fingers 231 are discretely arranged. Are arranged at positions that are substantially line symmetric with respect to the maximum points P1 to P3 and the minimum points B1 and B2 constituting the envelope 41 described above. Therefore, the envelope 42 is formed by a bent line connecting these points with straight lines in the order of “near origin position → Q 1 → C 1 → Q 2 → C 2 → Q 3 → L point neighboring position”, and line segments Q 1 -C 1, C 1 -Q2, Q2-C2 and C2-Q3 are inclined with respect to the SAW propagation direction, and the inclination angles θ1 'to θ4' are within the above-described inclination range. The shorter cross width W (m _C ) of the cross widths of the electrode fingers 231 and the left and right electrode fingers 232 has a ratio of the length to the opening length W0 of 0.3 or more, preferably 0. 35 or more.

As described above, in each of the envelopes 41 and 42, the three local maximum points P1 to P3 and Q1 to Q3 and the two local minimum points B1, B2, C1, and C2 are alternately arranged. By being connected with a straight line, the weighting coefficient of the IDT electrode 2 according to the present embodiment satisfies the following formulas (3) to (6).
| Y (P1) | ≈ | y (P2) | ≈ | y (P3) | (3)
| Y (B1) | ≈ | y (B2) | (4)
| Y (Q1) | ≈ | y (Q2) | ≈ | y (Q3) | (5)
| Y (C1) | ≈ | y (C2) | (6)
The intersection widths of the electrode fingers 231 and 232 are the line segments included in the envelopes 41 and 42 (P1-B1, B1-P2, P2-B2, B2-P3, Q1-C1, C1-Q2, Q2-C2). , C2-Q3).

  Therefore, in the present embodiment, the upper limit intersection width corresponding to the tertiary transverse mode (the upper limit intersection width at which the tertiary transverse mode does not occur) is previously grasped at the design level, and is larger than the design upper limit intersection width. For example, the arrangement positions of the minimum points B1, B2, C1, and C2 in the y direction are set with a margin so that the electrode fingers 231 and 232 having a small intersection width are also included in the envelopes 41 and 42. Thereby, even if the actual upper limit intersection width deviates from this design value, the electrode fingers 231 and 232 having the intersection width corresponding to the actual upper limit intersection width are located at any position on the envelopes 41 and 42. Can exist in the number corresponding to the number of the line segments.

  Here, as described in the knowledge of (2), for example, in order to suppress the third-order transverse mode, a large number of electrode fingers 231 and 232 having upper limit intersection widths corresponding to the third-order transverse mode are arranged. It is preferable to do. However, the electrode fingers 231 and 232 whose crossing width is smaller than the upper limit crossing width does not abruptly reduce the effect of suppressing the third-order transverse mode. For example, if the crossing width is about several μm, It has been found that the transverse mode suppression effect which is not inferior to the electrode fingers 231 and 232 having the upper limit crossing width can be exhibited.

  Therefore, in the IDT electrode 2 according to the present embodiment, the inclination angle formed by each line segment constituting the envelopes 41 and 42 with respect to the SAW propagation direction is in the range of 10 ° to 65 °. For example, the electrode fingers 231 and 232 having an intersection width effective in suppressing the third-order transverse mode in each region denoted by reference numerals S1 to S4 in FIG. 3B. For example, it is possible to arrange a few to a dozen or so. As a result, the electrode fingers 231 and 232 having the intersecting width are arranged, for example, about ten to several tens at intervals in the SAW propagation direction in the entire regions S1 to S4.

  It should be noted that line segments constituting the envelopes 41 and 43 in the region on the left side of the local maximum points P1 and Q1 and the region on the right side of the local maximum points P3 and Q3 (origin point -P1, origin point -Q1, P3-L point, Q3) -L) is not designed so that the tilt angle with respect to the SAW propagation direction is within a predetermined range. However, the electrode fingers 231 and 232 constituting these line segments also have an effective crossing width for suppressing the third-order transverse mode in the regions labeled with the regions S0 and S0 ′ in FIG. Needless to say, the electrode fingers 231 and 232 are included, and together with the electrode fingers 231 and 232 in the other regions S1 to S4, the third transverse mode is suppressed.

  As described above, the occurrence of the higher-order transverse mode appears as spurious in the frequency characteristics of the SAW resonator 1 and becomes a ripple or the like of the frequency characteristics of the ladder filter using the SAW resonator 1. For this reason, the above-described range of the tilt angle of 10 ° or more and 65 ° or less is effective in suppressing the higher-order transverse mode so as to satisfy the insertion loss specification of a ladder filter using the SAW resonator 1, for example. The electrode fingers 231 and 232 having a wide intersection width are in a range where about ten to several tens of electrodes can be arranged.

  Here, the number of electrode fingers 231 and 232 that can be arranged within a unit length of a line segment having a certain inclination angle increases or decreases depending on the arrangement interval (hereinafter referred to as a pitch) between the adjacent electrode fingers 231 and 232, for example. The pitch of the electrode fingers 231 and 232 is determined by the resonance frequency of the SAW resonator 1 and the like. Therefore, in determining the actual inclination angles θ1 to θ4 and θ1 ′ to θ4 ′ within the above ranges, the pitch between the electrode fingers 231 and 232 is determined so as to have a desired frequency characteristic such as a resonance frequency, and the condition Below, the arrangement positions of the maximum points P1 to P3, Q1 to Q3, and the minimum points B1, B2, C1, and C2 are changed, and the frequency characteristics of the SAW resonator 1 are confirmed through simulations and experiments. For example, it may be determined by determining the arrangement positions of these local maximum points and local minimum points at a position where the spurious can be suppressed to the extent that the usage value of the insertion loss of the ladder filter is satisfied.

  By providing the above configuration, the SAW resonator 1 according to the present embodiment has the upper limit cross width effective for suppressing the third-order transverse mode and the electrode fingers 231 and 232 having a cross width close to the cross width. For example, as shown in FIG. 3B, these electrode fingers 231 and 232 are arranged at intervals in the regions S1 to S4 (further in the regions S0 and S0 ′). Will also be arranged). As a result, the SAW resonator 1 has the requirements described in the findings (2) and (3) described above, and a higher-order transverse mode of a predetermined order (the third-order transverse mode in the present embodiment). ) Can be effectively suppressed.

  The SAW resonator 1 according to the present embodiment has the following effects. The envelopes 41 and 42 formed by connecting the tips of the electrode fingers 231 and 232 of the IDT electrode 2 have three maximum points P1 to P3 and Q1 that are the distances from the bus bars 21 and 22, respectively. Since Q3 and two local minimum points B1, B2, C1, and C2 at which this distance is minimum are alternately arranged, it is possible to suppress a high-order horizontal mode of a predetermined order such as a tertiary horizontal mode. The electrode fingers 231 and 232 having the upper limit crossing width can be arranged a plurality of times at intervals in the SAW propagation direction. Furthermore, since the inclination angle of the straight lines (line segments) constituting the envelopes 41 and 42 connecting the adjacent maximum points and minimum points is within the range of 10 ° or more and 65 ° or less, the above-mentioned upper limit intersection width is set. A plurality of electrode fingers 231, 232 having a crossing width close to the upper limit crossing width can be arranged in the vicinity of the electrode fingers 231, 232, so that a high-order transverse mode having a large influence on frequency characteristics can be effectively Therefore, the SAW resonator 1 with small spurious can be obtained.

  In addition, by making the position where the peak of the main resonance mode (zero-order mode) of the SAW resonator 1 occurs matches the positions of the maximum points P2 and Q2, the intersection width of the electrode fingers 231 and 232 is maximized. Thus, it is possible to prevent the power durability in the region where the stress applied to the electrode fingers 231 and 232 is greatest when the power is applied to the IDT electrode 2 from being lowered. Furthermore, when the intersection width of the electrode fingers 231 and 232 at the minimum points B1, B2, C1, and C2 is at least 30% of the opening length between the bus bars 21 and 22, the intersection width is reduced. In addition, the power input to the IDT electrode 2 can have practically sufficient power resistance.

  The SAW resonator 1 according to the embodiment includes, for example, a ladder type filter in which a plurality of SAW resonators are connected in a ladder type, a duplexer that discriminates transmission / reception signals by combining two filters having different pass bands, and a resonance It can be applied to various SAW devices such as a child and a transmitter. Here, the SAW device including the plurality of SAW resonators 1 preferably employs the SAW resonator 1 according to the embodiment for all the resonators, but the SAW resonator 1 is included in the plurality of resonators. If one or more are provided, the effect of spurious suppression can be exhibited as compared with a SAW device not provided with the SAW resonator 1.

  Moreover, the local maximum where the distance from the bus bars 21 and 22 to the envelopes 41 and 42 is the maximum and the local minimum where the distance is minimum are not limited to the case where the distance is configured by the local maximum and the local minimum. For example, as in the SAW resonator 1a shown in FIG. 4, the minimum portions B1, B2, C1, and C2 may be configured by straight portions parallel to the SAW propagation direction. Further, like the SAW resonator 1b shown in FIG. 5, the maximum portions P2 and Q2 may be linear portions parallel to the SAW propagation direction.

  Further, the shapes of the two envelopes 41 and 42 are not limited to the case where the configurations are symmetrical with respect to the x axis as shown in the SAW resonator 1 of FIG. For example, as shown in the SAW resonator 1c in FIG. 6, the two envelopes may be asymmetric with respect to the x axis. Further, as shown in FIG. 7 (a), the SAW resonator 1d without the reflectors 3a and 3b, and the both ends of the electrode fingers 301 of the reflectors 3a and 3b as shown in FIG. Part of the SAW resonator 1e is also included in the technical scope of the present invention.

  Furthermore, the slope of the envelope 41 passing through the maximum points P1 to P3 and the minimum points B1 and B2 is not limited to a constant value. For example, as shown in the IDT electrode 2 in FIG. The slope of the straight line to be changed may change midway. In this case, an envelope passing through the tip portion of the electrode fingers 231 and 232 (existing in the regions S1 to S4 in FIG. 8A) having an upper limit intersection width capable of suppressing a predetermined higher-order transverse mode. It is only necessary that the inclination of the lines 41 and 42 is an angle within the range of 10 ° to 65 ° as described above.

  Next, FIG. 8B shows an example of the IDT electrode 2 in which the envelopes 41 and 42 are constituted by curves. In this case, for example, a predetermined number of electrode fingers 231 and 232 having different intersection widths that can suppress a predetermined higher-order transverse mode in the left-right direction of the electrode fingers 231 and 232 having the upper limit intersection width in design. For example, about ten to several tens of lines are arranged (represented by regions T1 to T4 in FIG. 8B), and curves of envelopes 41 and 42 formed at the tips of these electrode fingers 231 and 232 are shown. It is preferable that the maximum inclination angles θ1 to θ4 of the tangential line drawn with respect to the SAW propagation direction be an inclination angle within a predetermined range. At this time, if the number of electrode fingers 231 and 232 arranged in the regions T1 to T4 is larger than the necessary number necessary for suppressing the higher-order transverse mode, the actual upper limit crossing width varies. In this region, it is possible to arrange the electrode fingers 231 and 232 having the upper limit crossing width and the crossing width smaller than this crossing width by about several μm, with an interval of 10 to several dozen.

  In each of the above-described embodiments, the case where the cubic transverse spurious is suppressed has been described. However, the order of the predetermined n-order transverse mode is not limited to the third order. For example, in a SAW resonator in which the influence of the fifth-order transverse mode is large, the slope of the envelope passing through the tip portions of the electrode fingers 231 and 232 having the upper limit cross width corresponding to the mode is a straight line having the above-described slope angle. Alternatively, such a straight line may have an envelope shape arranged corresponding to each of the third-order transverse mode and the fifth-order transverse mode.

  Also, the number of local maximum parts and local minimum parts arranged on the envelopes 41 and 43 is not limited to the case of three local maximum parts and two local minimum parts shown in the embodiment, and these are alternately arranged. If so, the number of local maximums may be four or more, and the number of local minimums may be three or more.

Furthermore, in each of the above-described embodiments, a SAW resonator using SAW as an elastic wave resonator has been described. However, the types of elastic wave resonators applicable to the present invention are not limited thereto. For example, an elastic wave resonator of a type using boundary acoustic waves may be used.
In the transversal SAW resonator 110 shown in FIG. 9, the envelope passing through the minimum points D1 and D2 formed to invert the phase of the SAW and the maximum points R1 to R3 adjacent to these points is as follows. It is not included in the technical scope of the present invention.

(Experiment)
The SAW resonator 1 according to the embodiment and the conventional type SAW resonators 100, 100a, 100b are formed, and signals are sent to the bus bars on one side of these SAW resonators 1, 100, 100a, 100b while changing the frequency. Then, the reflection characteristic (S11 characteristic) of the input signal was actually measured.
A. Experimental conditions
Example 1
With respect to the SAW resonator 1 having the envelope shape shown in FIG. 1, the reflection characteristics were actually measured by changing the frequency of the input signal in the range of 1.1 to 2.7 [GHz].
(Comparative Example 1)
With respect to the SAW resonator 100 in which the electrode fingers 231 and 232 shown in FIG. 14 are not weighted, the reflection characteristics were actually measured by changing the frequency of the input signal in the range of 1.0 to 2.5 [GHz].
(Comparative Example 2)
With respect to the SAW resonator 100a having a diamond-shaped envelope shape shown in FIG. 16, the reflection characteristics were actually measured by changing the frequency of the input signal in the range of 1.0 to 2.4 [GHz].
(Comparative Example 3)
With respect to the SAW resonator 100b having the envelope shape of “cos ⁻¹ (| ax |)” shown in FIG. 17, the frequency of the input signal is changed in the range of 1.0 to 2.4 [GHz] to reflect characteristics. Was actually measured.

B. Experimental result
The experimental results of (Example 1) are shown in the Smith chart of FIG. 10, and the experimental results of (Comparative Examples 1 to 3) are shown in the Smith charts of FIGS. Note that the reflection response indicated by the thick arrow in each Smith chart is a response caused by a principle different from the high-order transverse mode, and is not an application target of the technique according to the present embodiment.

  In a SAW resonator having an ideal frequency characteristic without unnecessary spurious, the reflection characteristic of the SAW resonator draws a single circle along the outer circumference of the Smith chart. Compared with such ideal reflection characteristics, the SAW resonator 1 according to (Example 1) shown in FIG. 10 has a clean single-sided response except for the above-described response that is not related to the higher-order transverse mode. It draws a circle and has excellent frequency characteristics without spurious.

On the other hand, for example, in the SAW resonator 100 that is not weighted to suppress the higher-order transverse mode (Comparative Example 1), a relatively large unnecessary response is shown at the position indicated by the dashed arrow of the reflection characteristic shown in FIG. Are observed, and a spurious frequency response is obtained. In addition, as for the conventional SAW resonators 100a and 100b in which the electrode fingers 231 and 232 are weighted for the purpose of suppressing higher-order transverse modes, as can be seen from the reflection characteristics shown in FIGS. 12 and 13, respectively. Although the size of the unnecessary response is considerably small, it cannot be said that these have disappeared.
From the above results, the SAW resonator 1 according to the embodiment has excellent frequency performance compared to the conventional SAW resonators 100a and 100, and if a filter is configured using the SAW resonator 1, High performance filter characteristics with small ripples can be obtained.

It is a top view of the SAW resonator concerning embodiment. It is an enlarged plan view regarding the electrode finger of the SAW resonator. It is the top view which showed typically the IDT electrode of the said SAW resonator. It is a top view of the SAW resonator concerning 2nd Embodiment. It is a top view of the SAW resonator concerning a 3rd embodiment. It is a top view of the SAW resonator concerning a 4th embodiment. It is a top view of the SAW resonator concerning 5th, 6th embodiment. It is a top view of the SAW resonator concerning 7th, 8th embodiment. It is a top view of the SAW resonator which does not correspond to an embodiment. It is a characteristic view which shows the reflective characteristic of the SAW resonator concerning embodiment. It is a characteristic view which shows the reflective characteristic of the SAW resonator concerning a 1st comparative example. It is a characteristic view which shows the reflective characteristic of the SAW resonator concerning the 2nd comparative example. It is a characteristic view which shows the reflective characteristic of the SAW resonator concerning the 3rd comparative example. It is a top view which shows an example of the SAW resonator in which the electrode finger is not weighted. It is explanatory drawing which shows the principle which suppresses high order transverse mode. It is a top view which shows the 1st prior art example of the SAW resonator to which the electrode finger was weighted. It is a top view which shows the 2nd prior art example of the SAW resonator to which the electrode finger was weighted. It is a top view which shows the reference example of the SAW resonator to which the electrode finger was weighted.

Explanation of symbols

B1, B2, C1, C2, D1, D2
Minimum points P1 to P3, Q1 to Q3, R1 to R3
Maximum point 1, 1a-1e
SAW resonator 2 IDT electrodes 3a and 3b Reflectors 21 and 22 Bus bars 41 and 42 Envelopes 100 and 100a to 100b
SAW resonator 110 Transversal SAW resonator 231, 232
Electrode finger 233 Dummy electrode 301 Electrode finger

Claims (5)

In the acoustic wave resonator weighted with the crossing width of the electrode fingers of the IDT electrode provided on the piezoelectric substrate,
The envelope formed by connecting the tips of the electrode fingers connected to the bus bar on at least one side of the IDT electrode has at least three local maxima at which the distance from the bus bar is a maximum, and the distance is minimum. And at least two local minimum parts arranged alternately,
The electrode finger group constituting the envelope passing through these adjacent maximum and minimum portions has an upper limit cross width at which a predetermined n-th order transverse mode (n is a predetermined odd number of 3 or more) does not occur. The electrode fingers are included,
The envelope passing through the tip of the electrode finger having the upper limit crossing width is a straight line having an inclination angle in the range of 10 ° to 65 ° with respect to the propagation direction of the elastic wave, or the upper limit An envelope formed by connecting a predetermined number of tip ends of electrode fingers having a cross width and tip portions of electrode fingers having a cross width smaller than the electrode fingers is a tangent drawn with respect to the envelope An acoustic wave resonator comprising: a maximum inclination angle formed with the propagation direction is a curve having an inclination angle within the range.   One of the local maximum points is provided at a position where the maximum amplitude of the zeroth-order longitudinal mode excited in the IDT electrode is generated.   The acoustic wave resonator according to claim 1, wherein the nth-order transverse mode is a third-order transverse mode.   With respect to the opening length between the inner ends of the opposing bus bars of the IDT electrode, the shorter one of the intersection widths of the electrode fingers located in the minimum portion and the left and right electrode fingers adjacent to the electrode fingers The elastic wave resonator according to any one of claims 1 to 3, wherein a width ratio is 0.3 or more. An acoustic wave device in which a plurality of acoustic wave resonators are formed on a common substrate,
An elastic wave device, wherein at least one of the plurality of elastic wave resonators is the elastic wave resonator according to any one of claims 1 to 4.

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