JP2014146887A - Elastic wave element, branching filter and communication module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave element capable of suppressing an influence of a distorted wave.SOLUTION: The elastic wave element includes a plurality of first electrode fingers 63A each of which includes: a first front half portion 21 whose one end is connected to a first busbar electrode 61A and which extends from the first busbar electrode 61A to a second busbar electrode 61B in a direction orthogonal to a propagation direction, and whose the other end is positioned apart from the second busbar electrode 61B; a first rear half portion 23 which is disposed beside the first front half portion 21 with a gap between them and extends in a direction orthogonal to the propagation direction, and whose both ends are positioned apart from the first and second busbar electrodes 61A, 61B; and a first folding portion 22 which connects the end portions of the first front half portion 21 and the first rear half portion 23 on the second busbar side, to each other. The elastic wave element further includes a plurality of second electrode fingers 63B of the similar configuration as the first electrode fingers 63A. The first electrode finger 63A and the second electrode finger 63B are disposed in such a manner that hook-shaped portions engage with each other.

Description

The present invention relates to an acoustic wave device such as a surface acoustic wave (SAW) device, a duplexer, and a communication module.

  2. Description of the Related Art An acoustic wave element having a piezoelectric substrate and an excitation electrode such as an IDT (InterDigital Transducer) provided on the main surface of the piezoelectric substrate is known. Such an acoustic wave element is used for, for example, a transmission filter and a reception filter of a duplexer.

  In an acoustic wave device, electrical characteristics may be deteriorated by an electrical distortion wave generated by the nonlinearity of the device. For example, in a duplexer using an elastic wave element, interference waves outside the transmission band and the reception band are mixed with the transmission wave, and a distorted wave is generated in the reception band. This distorted wave is called inter-modulation distortion (IMD: Inter-Modulation Distortion), and is one of the causes of lowering the communication quality (S / N ratio) of the wireless device. In addition, there is a possibility that harmonic distortion having a frequency that is an integral multiple of the transmission wave is generated, which may cause a problem that the communication of other wireless devices is interrupted.

  Therefore, in order to suppress a decrease in the S / N ratio due to a distorted wave, a method is known in which a series resonator or a parallel resonator of a ladder filter constituting a duplexer is divided without changing capacitance (for example, Patent Document 1). In this method, by dividing a series resonator or a parallel resonator, a voltage applied to the resonator is dispersed to suppress distortion waves.

JP 2007-074698 A

  However, if the resonator is divided without changing the capacitance, the resonator becomes larger and the elastic wave element becomes larger than before the division.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an elastic wave element, a duplexer, and a communication module that can suppress the influence of a distorted wave without dividing a resonator. .

The acoustic wave device of one embodiment of the present invention is an acoustic wave device including a piezoelectric substrate and at least one excitation electrode disposed on the upper surface of the piezoelectric substrate. The excitation electrode includes a first bus bar electrode extending in the propagation direction of the elastic wave propagating through the piezoelectric substrate, and a second bus bar electrode disposed facing the first bus bar electrode and extending in the propagation direction. The excitation electrode has one end connected to the first bus bar electrode and extends from the first bus bar electrode toward the second bus bar electrode in a direction perpendicular to the propagation direction, and the other end is connected to the second bus bar electrode. A first front half located away from the electrodes, and spaced apart from the first front half and extending in a direction perpendicular to the propagation direction, and both ends of the first and second bus bars A plurality of first rear portions located away from the electrodes, and a first folded portion connecting the first front half portion and the first second half portion on the second bus bar electrode side. Having a first electrode finger; The excitation electrode is connected at one end to the second bus bar electrode and extends from the second bus bar electrode toward the first bus bar electrode in a direction perpendicular to the propagation direction. The propagation direction is arranged between a second front half portion that is spaced apart from the first bus bar electrode and the other end is located away from the first bus bar electrode, and the first front half portion and the first second half portion. A second rear half portion that extends in a direction orthogonal to the first bus bar and has both ends positioned away from the first bus bar electrode and the first folded portion, and the first bus bar of the second front half portion and the second rear half portion. A plurality of second electrode fingers each having a second folded portion connecting the end portions on the electrode side.

  A duplexer according to an aspect of the present invention includes an antenna terminal, a transmission filter that filters a transmission signal and outputs the filtered signal to the antenna terminal, and a reception filter that filters a reception signal from the antenna terminal, The transmission filter includes the above acoustic wave element.

  A communication module according to one embodiment of the present invention includes an antenna, the above-described duplexer electrically connected to the antenna, and an RF-IC electrically connected to the duplexer.

  According to said structure, the influence of a distorted wave can be suppressed, without enlarging an elastic wave element.

It is a block diagram which shows the structure of the signal processing system of the communication module which concerns on embodiment of this invention. It is a circuit diagram which shows the structure of the duplexer which concerns on embodiment of this invention. It is a top view which shows the SAW element which concerns on embodiment of this invention. FIG. 4 is an enlarged view of a part of the SAW element shown in FIG. 3. It is a figure for demonstrating the effect | action of the SAW element of FIG. It is a graph which shows the measurement result of an Example. It is a top view which shows the modification of the SAW element of FIG.

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

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

<Communication module>
FIG. 1 is a block diagram showing a main part of a communication module 101 according to an embodiment of the present invention. The communication module 101 performs wireless communication using radio waves. The duplexer 1 has a function of demultiplexing a transmission frequency signal and a reception frequency signal in the communication module 101.

In the communication module 101, the transmission information signal TIS including the information to be transmitted is modulated and the frequency is raised (converted to a high frequency signal of the carrier frequency) by the RF-IC 103 to be a transmission signal TS. Unnecessary components other than the transmission passband are removed from the transmission signal TS by the bandpass filter 105, amplified by the amplifier 107, and input to the duplexer 1. Then, the duplexer 1 removes unnecessary components other than the transmission passband from the input transmission signal TS and outputs the result to the antenna 109. The antenna 109 converts the input electric signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

  In the communication module 101, the radio signal received by the antenna 109 is converted into an electric signal (reception signal RS) by the antenna 109 and input to the duplexer 1. The duplexer 1 removes unnecessary components other than the reception passband from the input reception signal RS and outputs the result to the amplifier 111. The output reception signal RS is amplified by the amplifier 111, and unnecessary components other than the reception passband are removed by the bandpass filter 113. The reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 103 to be a reception information signal RIS.

  The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) including appropriate information, for example, analog audio signals or digitized audio signals. The passband of the radio signal may be in accordance with various standards such as UMTS (Universal Mobile Telecommunications System). The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof. In FIG. 1, the direct conversion method is exemplified as the circuit method, but other appropriate methods may be used. For example, a double superheterodyne method may be used. FIG. 1 schematically shows only the main part, and a low-pass filter, an isolator or the like may be added at an appropriate position, and the position of an amplifier or the like may be changed.

<Demultiplexer>
FIG. 2 is a circuit diagram showing a configuration of the duplexer 1 according to the embodiment of the present invention. The duplexer 1 is used in the communication module 101 in FIG.

  The duplexer 1 includes a transmission terminal 3 to which the transmission signal TS from the amplifier 107 is input, a transmission filter 5 that removes unnecessary components other than the transmission passband from the transmission signal TS, and outputs them. And an antenna terminal 7 to which the above signal is input. The antenna terminal 7 is connected to the antenna 109.

  Further, the duplexer 1 removes unnecessary components other than the reception passband from the reception signal RS input from the antenna 109 via the antenna terminal 7 and outputs the received signal, and the signal from the reception filter 9 Is received. The reception terminal 11 is connected to the amplifier 111.

  The transmission filter 5 is configured by, for example, a ladder type SAW filter. That is, the transmission filter 5 includes one or more (3 in the present embodiment) first series resonator 15A-1 to third series resonator 15A-3 connected in series between the input side and the output side. And one or more (2 in the present embodiment) parallel resonators 15B provided between the series line and the reference potential portion. Hereinafter, the first series resonator 15A-1 to the third series resonator 15A-3 are simply referred to as “series resonator 15A” and may not be distinguished from each other, and the series resonator 15A and the parallel resonance may be omitted. The child 15B is simply referred to as “resonator 15”, and these may not be distinguished.

  The first series resonator 15 </ b> A- 1 is the resonator 15 closest to the antenna terminal 7 in the transmission filter 5. In addition, an impedance matching circuit may be inserted between the transmission filter 5 and the reception filter 9 and the antenna terminal 7.

  The reception filter 9 includes, for example, a multimode SAW filter 17 and an auxiliary resonator 15C connected in series on the input side thereof. In the present embodiment, the multiplex mode includes a double mode.

<SAW element>
FIG. 3 is a plan view of the SAW element 51 according to the embodiment of the present invention. The SAW element 51 constitutes the first series resonator 15A-1 in the duplexer 1 shown in FIG.

  Note that the SAW element 51 may be either upward or downward, but hereinafter, for convenience, the orthogonal coordinate system xyz is defined and the positive side in the z direction (the paper surface of FIG. 3). Terms such as the upper surface and the lower surface are used with the front side as the upper side.

  The SAW element 51 is configured as a 1-port SAW resonator, for example, and includes a piezoelectric substrate 53, an excitation electrode 55 provided on the upper surface 53 a of the piezoelectric substrate 53, and a reflector 57. In addition to the above, the SAW element 51 includes an additional film disposed on the upper surfaces of the excitation electrode 55 and the reflector 57, an adhesive layer interposed between the excitation electrode 55 and the reflector 57, and the piezoelectric substrate 53, and the piezoelectric substrate 53. There may be provided a protective layer or the like that covers the upper surface 53a of the substrate from above the excitation electrode 55 and the reflector 57. In FIG. 3, wirings and pads for inputting / outputting signals to / from the excitation electrode 55 are not shown.

The piezoelectric substrate 53 is a single crystal substrate having piezoelectricity, such as a lithium tantalate (LiTaO ₃ ) single crystal or a lithium niobate (LiNbO ₃ ) single crystal. More specifically, a 42 ° ± 10 ° YX cut LiTaO ₃ , a 128 ° ± 10 ° YX cut LiNbO ₃ substrate, or a 0 ° ± 10 ° YX cut LiNbO ₃ substrate is used. be able to. The planar shape and various dimensions of the piezoelectric substrate 53 may be set as appropriate.

  The excitation electrode 55 is made of a conductive layer formed on the upper surface 53a of the piezoelectric substrate 53, and includes a first bus bar electrode 61A, a second bus bar electrode 61B, a plurality of first electrode fingers 63A, a plurality of second electrode fingers 63B, and the like. doing. Hereinafter, for example, the first bus bar electrode 61A and the second bus bar electrode 61B are simply referred to as a bus bar electrode 61, and they may not be distinguished from each other. In addition, a member constituting the first bus bar electrode 61A or a member connected to the first bus bar electrode 61A may be given “first” and “A” like “first electrode finger 63A”. A member constituting the second bus bar electrode 61B or a member connected to the second bus bar electrode 61B may be given “second” and “B” like “second electrode finger 63B”. Further, when the corresponding ones such as the first electrode finger 63A and the second electrode finger 63B are collectively referred to, “first”, “second”, “A”, and “B” are omitted, It may be simply referred to as “electrode finger”.

  The first and second bus bar electrodes 61A and 61B have, for example, a long shape, and extend linearly in the SAW propagation direction (x direction) with a constant width. The first bus bar electrode 61A and the second bus bar electrode 61B oppose each other in the direction (y direction) orthogonal to the SAW propagation direction. The first bus bar electrode 61A and the second bus bar electrode 61B are, for example, parallel to each other, and the distance between them is constant in the SAW propagation direction.

  The plurality of first electrode fingers 63A and the second electrode fingers 63B are alternately arranged at regular intervals along the SAW propagation direction (x direction). The first and second electrode fingers 63A and 63B in the SAW element 51 are greatly different from the conventionally known electrode fingers in overall shape.

  A specific shape of the electrode finger in the SAW element 51 will be described with reference to FIG. FIG. 4 is an enlarged plane portion obtained by extracting a part of the excitation electrode 55 shown in FIG. The electrode finger 63 in the SAW element 51 has a linear portion extending from the bus bar electrode 61 and a portion turned back from the same as the conventional electrode finger.

  More specifically, the first electrode finger 63A includes a first front half 21, a first folded portion 22, and a first rear half 23, and the second electrode finger 63B includes a second front half 25 and The second folded portion 26 and the second second half portion 27 are configured.

  One end of the first front half 21 is connected to the first bus bar electrode 61A, and extends in the y direction toward the second bus bar electrode 61B. The other end of the first front half 21 is positioned in front of the second bus bar electrode 61B. The first second half portion 23 is disposed beside the first first half portion 21 with an interval, and extends in the y direction. Further, both ends of the first second half 23 are located away from the first and second bus bar electrodes 61A and 61B. The first folded portion 22 connects ends of the first front half portion 21 and the second rear half portion 27 on the first bus bar electrode side.

  One end of the second front half 25 is connected to the second bus bar electrode 61B, and extends in the y direction toward the first bus bar electrode 61A. The other end of the second front half 25 is located in front of the second bus bar electrode 61B. The second rear half 27 is disposed between the first front half 21 and the first rear half 23 and extends in the y direction. Further, both ends of the second second half portion 27 are located away from the first bus bar electrode 61 </ b> A and the first folded portion 22. The second folded portion 26 connects ends of the second front half portion 25 and the second rear half portion 27 on the first bus bar electrode side.

  The first and second electrode fingers 63A and 63B have a folded structure as described above, and have a bowl shape as a whole.

  In the SAW element 51, the first and second electrode fingers 63 </ b> A and 63 </ b> B having such a bowl shape are arranged so as to mesh with each other at the bowl shape portion. That is, the first second half portion 23 of the first electrode finger 63A is disposed so as to enter between the second front half portion 25 and the second second half portion 27 constituting the second electrode finger 63B. The second rear part 27 of 63B is disposed so as to enter between the first front part 21 and the first rear part 23 constituting the first electrode finger 63A.

  With the excitation electrode 55 having such a structure, distorted waves can be reduced as will be described later. Therefore, according to the SAW element 51, distortion waves can be reduced without dividing the resonator, so that the SAW element 51 is not greatly enlarged as in the case of dividing the resonator. Distorted waves can be reduced.

  In addition, the first electrode finger 63A and the second electrode finger 63B are alternately arranged with electrode fingers having different potentials in the intersecting region (the region where the first electrode finger 63A and the second electrode finger 63B overlap in the x direction). If the area portion is seen, it is not different from a normal SAW element. That is, the SAW excited by the excitation electrode 55 propagates through the intersection region between the first electrode finger 63A and the second electrode finger 63B.

  Returning to FIG. 3, the plurality of electrode fingers 63 are set so that the pitch p is equal to, for example, a half wavelength of the SAW wavelength λ at the frequency to be resonated. The pitch p is defined by, for example, the distance between the centers of the adjacent first electrode fingers 63A and the second electrode fingers 63B. The wavelength λ of the SAW is, for example, 1.5 μm to 6 μm.

  The entire lengths of the first and second electrode fingers 63A and 63B are, for example, equal to each other, and the lengths of corresponding constituent members are also equal to each other. That is, the first front half part 21 and the second front half part 25 have the same length, the first folded part 22 and the second folded part 26 have the same length, and the first latter part 23 and the second latter part. 27 have the same length. Note that the overall lengths of the first electrode fingers 63A and the second electrode fingers 63B may be different from each other, and the lengths of corresponding constituent members may be different.

  Further, the first and second electrode fingers 63A and 63B are formed with the same width w throughout, respectively, and have the same width w.

  These dimensions are appropriately set according to the electrical characteristics required for the SAW element 51. The width w of the electrode finger 63 is, for example, 0.4 p to 0.7 p with respect to the pitch p of the electrode finger 63. Note that the width w of the electrode fingers 63 may not be the same throughout the electrode fingers. For example, the front half, the folded portion, and the rear half of the electrode fingers may have different widths. Further, the width w may be different between the first electrode finger 63A and the second electrode finger 63B.

  In the SAW element 51, the first bus bar electrode 61A has a plurality of first dummy electrode fingers 65A, and the second bus bar electrode 61B has a plurality of second dummy electrode fingers 65B.

  The first dummy electrode finger 65A is a portion that slightly extends from the side surface of the first bus bar electrode 61A facing the second bus bar electrode 61B toward the second bus bar electrode 61B. The first dummy electrode finger 65 </ b> A is disposed at the center between the adjacent first electrode fingers 63 </ b> A, and is located in the same straight line as the first second half portion 23. The first dummy electrode fingers 65A may be arranged at positions shifted from the center between the adjacent first electrode fingers 63A, or arranged at positions shifted from the same straight line as the first second half portion 23. May be.

  Similarly, the second dummy electrode finger 65B is a portion slightly extended from the side surface of the second bus bar electrode 61B facing the first bus bar electrode 61A toward the first bus bar electrode 61A. The second dummy electrode finger 65B is arranged at the center between the adjacent second electrode fingers 63B and is located in the same straight line as the second second half 27, but is not necessarily the same as the first dummy electrode finger 65A. It does not have to be in such a positional relationship.

  The width (x direction) of the first and second dummy electrode fingers 65A and 65B is equal to the width w of the electrode finger 63, for example. The length (y direction) of the dummy electrode finger 65 is shorter than the electrode finger 63, and is 2 μm to 5 μm, for example.

  The tip of the first dummy electrode finger 65A faces the second folded portion 26 of the second electrode finger 63B via the first gap 67A. The tip of the second dummy electrode finger 65B faces the first folded portion 22 of the first electrode finger 63A via the second gap 67B. The tip of the first electrode finger 63A (the tip of the first second half 23) is opposed to the second folded portion 26 via the third gap 63C. The tip of the second electrode finger 63B (tip of the second second half portion 27) faces the first folded portion 22 via the fourth gap 67D.

  The number of the plurality of first gaps 67A is the same as the number of the plurality of first dummy electrode fingers 65A. The number of the plurality of second gaps 67B is the same as the number of the plurality of second dummy electrode fingers 65B. The number of the plurality of third gaps 67C is the same as the number of the plurality of first second half portions 23. The number of the plurality of fourth gaps 67D is the same as the number of the plurality of second second half portions 27.

The width of the plurality of gaps 67 is equal to the width w of the plurality of electrode fingers 63. The lengths l _g of the plurality of gaps 67 (the size in the y direction. Hereinafter, the lengths of the gaps may be referred to as “gap lengths”) are the same as each other in the gaps 67, for example. Is appropriately set according to the electrical characteristics required for the SAW element 51. For example, the gap length _{l g} is a 0.1λ~0.6λ. It should be noted that the gap length l _g may be different for each gap 67.

The excitation electrode 55 is made of, for example, metal. As this metal, for example,
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 excitation electrode 55 may be composed of a plurality of metal layers. The thickness of the excitation electrode 55 may be set as appropriate.

  When an AC voltage is applied to the piezoelectric substrate 53 by the excitation electrode 55, SAW propagating in the x direction along the upper surface 53a is induced near the upper surface 53a of the piezoelectric substrate 53. The SAW is reflected by the electrode finger 63. And the standing wave which makes the pitch p of the electrode finger 63 a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as that of the standing wave, and is taken out by the electrode finger 63. In this way, the SAW element 51 functions as a resonator or a filter.

  The reflector 57 is composed of a conductive layer formed on the upper surface 53a of the piezoelectric substrate 53, and is formed in a lattice shape in plan view. That is, the reflector 57 includes a pair of bus bar electrodes facing each other in a direction crossing the SAW propagation direction, and a plurality of electrode fingers extending between the bus bar electrodes in a direction perpendicular to the SAW propagation direction (y direction). ing. The plurality of electrode fingers of the reflector 57 are arranged at substantially the same pitch as the plurality of electrode fingers 63 of the excitation electrode 55.

  Similarly to the excitation electrode 55, the reflector 57 is also formed of a metal such as Al. The excitation electrode 55 and the reflector 57 can be formed by forming a film made of a metal material on the upper surface 53a of the piezoelectric substrate 53 by a conventionally known film forming method and then patterning the metal film by a photolithography method or the like. it can.

  Next, a mechanism by which the SAW element 51 can suppress distortion waves will be described with reference to FIGS. 4 and 5. FIG. 5 is an enlarged plan view of a part of a conventional excitation electrode having a conventional electrode finger structure, and members corresponding to the SAW element 51 are denoted by the same reference numerals.

  4 and 5, each member connected to the first bus bar electrode 61A and the first bus bar electrode 61A has a higher potential than each member connected to the second bus bar electrode 61B and the second bus bar electrode 61B. Suppose you are in a state.

  First, the generation mechanism of the distorted wave will be described with reference to FIG. When the potential of the first bus bar electrode 61A is higher than the potential of the second bus bar electrode 61B, an electric field E in the direction indicated by the black arrow is generated as shown in FIG. That is, an electric field Ex along the SAW propagation direction (x direction) is generated in the intersection region of the electrode fingers 63, and an electric field Ey along the direction (y direction) orthogonal to the SAW propagation direction is generated in the gap 67 region. Occur.

When such an electric field is generated, a distorted current is generated due to nonlinearity of the piezoelectric substrate 53 made of a piezoelectric material. Of the distorted current, the current I ₂ resulting from the second-order nonlinearity is proportional to the square of the electric field E. That is, I ₂ = αE ²
A distortion current I ₂ expressed by the following formula is generated. In this equation, α is a coefficient depending on the crystal orientation of the piezoelectric substrate. Since the strain current I ₂ is proportional to the square of the electric field E, it flows in the same direction with respect to the crystal orientation of the piezoelectric substrate regardless of the polarity of the electric field E. That is, as shown in FIG. 5, a distorted current I _{2x in the} x direction flows for the electric field Ex in the x direction, and a distorted current I _{2y in the} y direction (the first gap 67A) for the electric field Ey in the y direction. the distortion current _{I 2y} a, a distortion current in the second gap 67B and _{I 2y} B in.) flows. Here, the case where α is a positive constant has been described, but actual α is a complex number depending on the material and crystal orientation of the piezoelectric substrate.

Here, when attention is paid to the distortion current _{I 2x} along the x-direction, the distortion current _{I 2x} flowing through the first electrode finger 63A is distorted current I flowing out from the distortion current _{I 2x} and the first electrode finger 63A which flows into the first electrode finger 63A _{Since 2x} is in the opposite direction, it cancels out and becomes 0. For this reason, a distorted wave based on the distorted current I _2x is not output to the outside of the SAW element. Similarly, the distortion current I _2x cancels out also in the second electrode finger 63B. Therefore, the distorted current I _{2 in the} entire intersecting region of the excitation electrode 55 cancels out and is not output as a distorted wave outside the SAW element.

On the other hand, focusing on the electric field E _y along the y direction, the strain current I _2y A in the first gap 67A between the first dummy electrode finger 65A and the second electrode finger 63B, the second dummy electrode finger 65B and the first electrode finger. Since the distortion current I _2y B in the second gap 67B with 63A is in the same direction, these distortion currents I _2y do not cancel each other.

Thus, it is considered that the distorted current I _2y in the gap 67 remaining without canceling is one of the causes of the distorted wave.

In view of this, the SAW element 51 has a structure in which the electrode finger 63 is folded back to cancel the strain current I _2y in the gap 67. The reason why the strain current I _2y in the gap 67 can be canceled by using the structure in which the electrode finger 63 is folded back will be described with reference to FIG.

Focusing on the first gap 67A in the upper left in FIG. 4, a strain current I _2y A based on the electric field Ey generated there between the first dummy electrode finger 65A and the second folded portion 26 of the second electrode finger 63B. Flows. Next, paying attention to the third gap 67C, a strain current I based on the electric field Ey generated there is between the first second half 23 of the first electrode finger 63A and the second folded portion 26 of the second electrode finger 63B. _2y C flows. As described above, since the strain current I ₂ flows in the same direction with respect to the crystal orientation of the piezoelectric substrate regardless of the polarity of the electric field E, the strain current I _2y A and the strain current I _2y C are in the same direction along the y direction. Flowing. Then, the distortion current I _2y A flowing from the first dummy electrode finger 65A to the second folded portion 26 and I _2y C flowing from the second folded portion 26 to the first second half portion 23 flow in opposite directions and cancel each other. .

Similarly, in the second gap 67B, the distorted current I _2y B generated in the second gap 67B is canceled by the distorted current I _2y D generated in the fourth gap 67D.

That is, in the SAW element 51, the first and second electrode fingers 63A and 63B have a bent structure and are engaged with each other at the bent portions, so that a strain current is generated in each of the third gap 67C and the fourth gap 67D. I _2y C and I _2y D are generated to cancel the distortion currents I _2y A and I _2y B generated in the first and second gaps 67A and 67B.

  Therefore, according to the SAW element 51, since the distorted current in the gap 67, which is considered to be one of the causes of the distorted wave, cancels out, the distorted current output to the outside can be reduced, resulting in the generation of the distorted wave. Can be suppressed.

Further, when focusing on one gap 67, the magnitude of the distortion current I _2y at the gap 67 is proportional to the width w _g of the gap is inversely proportional to the square of the length l _g of the gap. Therefore, in the SAW element 51, the widths of the first gap 67A and the third gap 67C and the lengths of the first gap 67A and the third gap 67C are the same. In other words, in the SAW element 51, the width of the first dummy electrode finger 65A is equal to the width of the first second half portion 23, and the distance from the tip of the first dummy electrode finger 65A to the second folded portion 26 is equal to the first second half portion. The distance from the tip of 23 to the second folded portion 26 is equal. Thereby, the magnitude of the distorted current I _2y A generated in the first gap 67A and the magnitude of the distorted current I _2y C generated in the third gap 67C become substantially equal, and the effect of suppressing the distorted wave can be further enhanced. .

  Similarly, the widths of the second gap 67B and the fourth gap 67D and the lengths of the second gap 67B and the fourth gap 67D are made equal to each other.

Here in view of suppressing the distortion wave, described in more detail gap width w _g and gap length l _g. Magnitude of the distortion current I _2y in the gap 67 as described above is proportional to the width w _g of the gap, inversely proportional to the square of the length l _g of the gap, for example, in the first gap 67A and the third gap 67C When the gap width of the first gap 67A is w _g1 , the gap length of the first gap 67A is l _g1 , the gap width of the third gap 67C is w _g3 , and the gap length of the third gap 67C is l _g3 .
(W _g1 / l _g1 ² ) = (w _g3 / l _g3 ² ) (1)
Is satisfied, the magnitude of the distortion current I _2y A generated in the first gap 67A can be made substantially equal to the magnitude of I _2y C generated in the third gap 67C.

In the SAW element 51, the first gap 67A and the third gap 67C have the same gap width and gap length. That is, w _g1 = w _g3 and l _g1 = l _g3 , the expression (1) is satisfied, and the magnitude of the distortion current I _2y A is substantially equal to the magnitude of I _2y C.

In addition, for example, the width of the first gap 67A is set to 1/2 of the width of the third gap (w _g1 = w _g3 / 2), and the length of the first gap 67A is set to 1 / of the length of the third gap. By setting 4 (l _g1 = l _g3 / 4), the expression (1) can be satisfied. In this case, since it is possible to narrow the gap length l _g1 of the first gap 67A, it is possible to reduce the size of the excitation electrode 55 while suppressing the strain wave.

However, even if the magnitude of the distortion current I _2y A generated in the first gap 67A and the magnitude of I _2y C generated in the third gap 67C are different, the third gap 67C exists with respect to the first gap 67A. Since this has the effect of canceling the distortion current, the expression (1) does not necessarily have to be satisfied.

  In the second gap 67B and the fourth gap 67D, the relational expression similar to the expression (1) is satisfied, so that the magnitudes of strain currents generated in both gaps can be made substantially equal.

  As described above, the SAW element 51 constituting the first series resonator 15A-1 in FIG. 2 has been described, but the second and third series resonators 15A-2, 15A-3 other than the first series resonator 15A-1, The configuration of the first and second parallel resonators 15B-1 and 15B-2 and the auxiliary resonator 15C is an excitation electrode made up of linear electrode fingers 63 as shown in FIG. Note that these resonators 15 may have a structure in which the electrode fingers 63 are bent in the same manner as the first series resonator 15A-1. Also, the multi-mode SAW filter 17 may be an electrode finger 63 having a similar bent structure.

  Since the intermodulation distortion is generated when the transmission wave input from the transmission terminal 3 and the interference wave input from the antenna terminal 7 are simultaneously applied to the SAW resonator, the intensity of both the transmission wave and the interference wave is increased. The large first series resonator 15A-1 often generates the strongest distorted wave. For this reason, the excitation electrode 55 of the first series resonator 15A-1 having the structure shown in FIG. 3 is most effective in suppressing the intermodulation distortion of the entire duplexer. However, since the other resonators, particularly the first parallel resonator 15B-1 and the auxiliary resonator 15C close to the antenna terminal 7, are also sources of distortion waves to some extent, the excitation electrodes in these resonators have the same structure. By doing so, it is possible to further suppress distortion waves.

  As schematically shown in FIG. 2, the multimode SAW filter 17 is, for example, of a vertically coupled type, and includes a plurality (three in this embodiment) of excitation electrodes 55 arranged in the SAW propagation direction. And reflectors 57 disposed on both sides thereof. The multi-mode SAW filter 17 is, for example, an unbalanced input-balanced output type that converts an input unbalanced signal into a balanced signal and outputs it.

  The plurality of resonators 15 and the multimode SAW filter 17 are provided together on the upper surface 53a of one piezoelectric substrate 53, for example.

A SAW element was actually fabricated and the effect of reducing distortion waves was confirmed. More specifically, the SAW element W _E embodiment the excitation electrode is made of the structure shown in FIG. 3, the SAW element C of the comparative example excitation electrode is made of the same as conventional structure as shown in FIG. 5, strain wave The second harmonic (H2) which is a kind of the above was measured with a spectrum analyzer.

SAW element C of the comparative example and the SAW element W _E examples differ only structure of the excitation electrodes 55, otherwise to produce all under the same conditions. Fabricated SAW element W _E and the SAW element C as main common conditions in are as follows.
-Material of the piezoelectric substrate 53: LiTaO ₃
Excitation electrode 55 material: Al—Cu alloy Electrode finger 63 width: 1.15 μm
・ Width of dummy electrode finger 65: 1.15 μm
・ Duty: 0.5
Furthermore, SAW device _{W E} is the number of electrode fingers 63 80 (first electrode finger 40 present, the second electrode fingers 40 present), and the number of electrode fingers 63 of the SAW element C 160 (first electrode fingers: 80, second electrode finger: 80). Thus was the number of the electrode fingers 63 of the SAW element _{W E} 1/2 of the number of the SAW element C of the electrode fingers 63, the SAW element _{W E} has one electrode fingers and a first half and a second half portion This is because one electrode finger plays the role of two electrode fingers of the SAW element C. Therefore, if you look only intersections of the electrode fingers, the number of electrode fingers of the number and the SAW element C of the electrode fingers of the SAW element W _E can be regarded as the same.

Further, in the SAW element _{W E,} the first gap 67A, second gap 67B, and both the gap length _{l g} of the third gap 67C and the fourth gap 67D and 0.75 .mu.m. On the other hand, the gap length, which is the distance between the tips of the electrode fingers and the dummy electrode fingers in the SAW element C, was 0.75 μm.

FIG. 6 shows the measurement result of the second harmonic. A measurement result of the SAW element W _E solid lines Example 6, the measurement results of the SAW element C of broken lines comparative example. The measurement results SAW device as apparent from W _E is the second harmonic is lower than the SAW device C. That is, it was confirmed that can reduce the distortion wave by the SAW element W _E of Example.

The present invention is not limited to the above embodiment, and may be implemented in various aspects.
For example, the SAW element 51 in the above-described embodiment has the dummy electrode fingers 65, but may have no dummy electrode fingers 65 as shown in FIG.

Further, the shape of the excitation electrode 55 is not limited to that shown in the figure, and may be, for example, a so-called apodized one. Further, the excitation electrode 55 may be one in which the bus bar electrode 61 is inclined or bent, and the magnitude of the direction (y direction) orthogonal to the propagation direction of the elastic wave of the bus bar electrode 61 is changed. Also good. Further, the excitation electrode 55 may be provided with a portion where the pitch of the electrode fingers 63 is not constant but becomes narrow. Further, the electrode finger 63 or the dummy electrode finger 65 may have a chamfered corner at the tip thereof, or may have a wide tip width (x direction).

  Further, the first folded portion 22 and the second folded portion 26 may have a shape other than a linear shape. For example, the entire shape of the electrode finger 63 may be a J shape with an arc shape.

DESCRIPTION OF SYMBOLS 21 ... 1st front half part 22 ... 1st folding | turning part 23 ... 1st second half part 25 ... 2nd front half part 26 ... 2nd folding | turning part 27 ... 2nd latter half part 51 ... SAW element 53 ... Piezoelectric substrate 53a ... Upper surface 55 ... Excitation Electrode 61A ... first bus bar electrode 61B ... second bus bar electrode 63A ... first electrode finger 63B ... second electrode finger 65A ... first dummy electrode finger 65B ... second dummy electrode finger 67A ... first gap 67B ... second gap 67C ... 3rd gap 67D ... 4th gap

Claims (6)

An acoustic wave device having a piezoelectric substrate and at least one excitation electrode disposed on the upper surface of the piezoelectric substrate,
The excitation electrode is
A first bus bar electrode extending in the propagation direction of the elastic wave propagating through the piezoelectric substrate;
A second bus bar electrode disposed facing the first bus bar electrode and extending in the propagation direction;
One end is connected to the first bus bar electrode and extends from the first bus bar electrode toward the second bus bar electrode in a direction perpendicular to the propagation direction, and the other end is located away from the second bus bar electrode. A first front half portion that is spaced apart from the first front half portion and extends in a direction perpendicular to the propagation direction, and both ends are located apart from the first and second bus bar electrodes. A plurality of first electrode fingers having a first second half part, and a first folded part connecting ends of the first second half part and the first second half part on the second busbar electrode side;
One end is connected to the second bus bar electrode, extends from the second bus bar electrode toward the first bus bar electrode in a direction orthogonal to the propagation direction, and is spaced apart from the first second half portion. The other end of the second half is located away from the first bus bar electrode, and the second half is disposed between the first front half and the first second half and extends in a direction perpendicular to the propagation direction. And both ends of the second rear half part located away from the first bus bar electrode and the first folded part, and the end parts of the second front half part and the second rear half part on the first bus bar electrode side A plurality of second electrode fingers each having a second folded portion connecting the elastic wave elements. A first dummy electrode finger extending from the first bus bar electrode toward the second folded portion and having a tip located at a position having a first gap with respect to the second folded portion;
2. The second dummy electrode finger further extending from the second bus bar electrode toward the first folded portion and having a tip located at a position having a second gap with respect to the first folded portion. The elastic wave element as described. The width of the first gap in the propagation direction is equal to the width of the third gap, which is a gap between the tip of the first second half and the second folded portion, in the propagation direction,
The length of the first gap in the direction perpendicular to the propagation direction is equal to the length of the third gap in the direction perpendicular to the propagation direction,
The width of the second gap in the propagation direction is equal to the width of the fourth gap, which is a gap between the tip of the second second half and the first folded portion, in the propagation direction,
3. The acoustic wave device according to claim 2, wherein a length of the second gap in a direction orthogonal to the propagation direction is equal to a length of the fourth gap in a direction orthogonal to the propagation direction. The width of the first gap in the propagation direction is smaller than the width of the third gap, which is the gap between the tip of the first second half and the second folded portion, in the propagation direction,
The length of the first gap in the direction perpendicular to the propagation direction is smaller than the length of the third gap in the direction perpendicular to the propagation direction,
The width of the second gap in the propagation direction is smaller than the width of the fourth gap, which is a gap between the tip of the second second half and the first folded portion,
3. The acoustic wave device according to claim 2, wherein a length of the second gap in a direction orthogonal to the propagation direction is smaller than a length of the fourth gap in a direction orthogonal to the propagation direction. A duplexer comprising an antenna terminal, a transmission filter that filters a transmission signal and outputs the filtered signal to the antenna terminal, and a reception filter that filters a reception signal from the antenna terminal,
The duplexer having the acoustic wave element according to any one of claims 1 to 4, wherein the transmission filter.   A communication module comprising: an antenna; the duplexer according to claim 5 electrically connected to the antenna; and an RF-IC electrically connected to the duplexer.

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