JP5340112B2 - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a filter characteristic in a surface acoustic wave device using an IDT electrode of a serial division type. <P>SOLUTION: Each of SAW elements 12, 13 includes IDT electrodes 1-5 where each IDT electrode includes: a central bus bar electrode; a plurality of first floating electrodes each having one end connected to a one-side long side, and arranged by being spaced apart from one another; a plurality of second floating electrodes each having one end connected to the other-side long side, and arranged by being spaced apart from one another; first electrodes arranged to be located between the first floating electrodes; and second electrodes arranged to be located between the second floating electrodes. The SAW element is constituted so that ways of changes of electrode finger pitches from one end of the IDT electrode to the other end thereof are made different from each other in a region where the first floating electrodes and the first electrodes are arranged across the center line of the central bus bar electrode and in a region where the second floating electrodes and the second electrodes are arranged. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a surface acoustic wave device used for mobile communication equipment and the like. Hereinafter, a surface acoustic wave may be abbreviated as “SAW”.

  In recent years, communication devices used for mobile communication have come to be used in higher frequency bands in response to services such as WLAN (Wireless Local Area Network) that transmits and receives data using wireless communication. Yes. Along with the higher frequency of this communication device, electronic components used therefor are required to operate at higher frequencies.

  There is a surface acoustic wave device (SAW device) as a key part of communication equipment. The SAW device is used as an element for constituting a ladder type surface acoustic wave filter (SAW filter), for example. This filter is excellent in power durability, and is used in an antenna duplexer or the like in a frequency band that operates at a high frequency. However, the conventional ladder-type SAW filter can sufficiently secure the electrical characteristics such as the attenuation characteristics in the vicinity of the pass band, the insertion loss characteristic of the pass band, and the attenuation outside the pass band, which are required for communication equipment operating at high frequencies. It was difficult.

  Therefore, there has been proposed a SAW device that can operate at a high frequency by using a multi-mode SAW filter and that has improved electrical characteristics such as attenuation characteristics near the pass band and out-of-band attenuation. However, the conventional multi-mode SAW filter may not be able to ensure sufficient power durability when operated at a high frequency.

  FIG. 13 is a plan view of an essential part showing a conventional SAW device. Therefore, as shown in FIG. 13, IDT (Inter Digital Transducer) electrodes for exciting the SAW formed on the piezoelectric substrate constituting the multi-mode SAW filter are divided in series in order to sufficiently secure the power durability. Thus, there has been proposed a SAW device in which the electric power supplied to the IDT electrode is divided (see, for example, Patent Document 1).

JP 2006-311180 A

  Although the multimode SAW filter shown in FIG. 13 can improve power durability by adopting a configuration in which IDT electrodes are divided in series, there is room for improvement in filter characteristics. Does not mention the relationship of the pitch for improving the filter characteristics.

  The present invention has been invented in view of such a situation, and aims to improve filter characteristics in a surface acoustic wave device using a series-divided IDT electrode.

  A SAW device according to an embodiment of the present invention is a surface acoustic wave device including a piezoelectric substrate and a surface acoustic wave element disposed on the piezoelectric substrate, wherein the surface acoustic wave element includes an elastic surface N IDT electrodes having a serially divided structure (N ≧ 3 or more) arranged in the wave propagation direction, each IDT electrode including a central bus bar electrode and one of the central bus bar electrodes One end is connected to the long side of the plurality of first floating electrode fingers arranged at intervals, and one end is connected to the other long side of the central bus bar electrode and spaced from each other. A plurality of second floating electrode fingers arranged; a floating electrode; a first electrode having a plurality of electrode fingers arranged so as to be positioned between the plurality of first floating electrode fingers; Arranged to be located between the second floating electrode fingers A second electrode having a plurality of electrode fingers which comprises a. The surface acoustic wave element is divided into a first region and a second region with a center line of the central bus bar electrode as a boundary, and the first region is a region where the first floating electrode finger and the first electrode are disposed. When the second region is the region where the second floating electrode finger and the second electrode are disposed, the IDT electrode has a method of changing the electrode finger pitch from one end to the other end in the first region. And the method of changing the electrode finger pitch from one end to the other end in the second region is different.

  According to the SAW device described above, it is possible to improve the filter characteristics of the surface acoustic wave device using series-divided IDT electrodes.

It is a top view which shows one Embodiment of the SAW apparatus of this invention. It is the top view to which a part of SAW element of the SAW apparatus shown in FIG. 1 was expanded. It is a top view of the SAW element which comprises the SAW apparatus shown in FIG. (A) is a graph which shows the electrode finger pitch in the 1st area | region of each IDT electrode of the SAW element shown in FIG. 3, (b) is the electrode finger pitch in the 2nd area | region of each IDT electrode of the SAW element shown in FIG. It is a graph which shows. It is the top view which expanded a part of SAW element in the modification of the SAW apparatus shown in FIG. It is a block circuit diagram which shows one Embodiment of the communication apparatus using the SAW apparatus shown in FIG. (A) is a graph which shows the electrode finger pitch of each IDT electrode of Example 1, (b) is a graph which shows the electrode finger pitch of each IDT electrode of the comparative example 1. 6 is a graph showing frequency characteristics of VSWR in Example 1 and Comparative Example 1. 3 is a graph showing frequency characteristics of attenuation in Example 1 and Comparative Example 1. (A) is a graph which shows the electrode finger pitch of each IDT electrode of Example 2, (b) is a graph which shows the electrode finger pitch of each IDT electrode of the comparative example 2. 6 is a graph showing frequency characteristics of VSWR in Example 2 and Comparative Example 2. It is a graph which shows the frequency characteristic of the attenuation amount in Example 2 and Comparative Example 2. It is a top view which shows the conventional SAW apparatus.

  Hereinafter, the example of embodiment about the SAW device of the present invention is explained in detail based on a drawing. Note that the drawings used in the following embodiments are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

  FIG. 1 is a plan view showing a SAW device according to an embodiment of the present invention. In addition, in the following drawings, the same code | symbol is attached | subjected to the same site | part and the description may be abbreviate | omitted.

  As shown in FIG. 1, the SAW device of this embodiment mainly includes a piezoelectric substrate 100 and two SAW elements 12 and 13 formed on the piezoelectric substrate 100.

The piezoelectric substrate 100 is made of, for example, a LiNbO ₃ substrate or a LiTaO ₃ substrate. In an actual product, the SAW elements 12 and 13 are hermetically sealed on the main surface of the piezoelectric substrate 100 along the outer periphery of the signal electrodes for extracting the signals of the SAW elements 12 and 13 to the outside and the main surface of the piezoelectric substrate. An annular electrode or the like for stopping is provided, but the illustration is omitted.

  The SAW elements 12 and 13 provided on the main surface of the piezoelectric substrate 100 have the same configuration, and have five IDT electrodes 1, 2, 3, 4, and 5 having a series-divided structure, Reflector electrodes 8 and 9 are provided on both sides of these five IDT electrodes.

  FIG. 2 is a plan view of the IDT electrode 1 having a series division type structure. As shown in the figure, the IDT electrode 1 has a configuration including a floating electrode 20, a first electrode 21, and a second electrode 22. The floating electrode 20 has one end connected to the central bus bar electrode 20o and one long side of the central bus bar electrode 20o, and a plurality of electrode fingers (first floating electrode fingers) 20a arranged at intervals. One end is connected to the other long side of the central bus bar electrode 20o, and a plurality of electrode fingers (second floating electrode fingers) 20b arranged at intervals are provided. In addition, the first electrode 21 includes a plurality of electrode fingers 21a disposed so as to be positioned between the plurality of electrode fingers 20a extending from the central bus bar electrode 20o, and the second electrode 22 includes a plurality of electrode fingers 21a extending from the central bus bar electrode 20o. A plurality of electrode fingers 22a are provided so as to be positioned between the electrode fingers 20b. These electrode fingers are arranged along the propagation direction (X direction in the figure) of the SAW propagating on the piezoelectric substrate 100 and are formed so as to extend in a direction perpendicular to the propagation direction.

  L indicated by a dotted line in FIG. 2 is a center line of the central bus bar electrode 20o. With this center line L as a boundary, the SAW element is divided into a first region and a second region. In this embodiment, the side where the electrode finger 20a of the floating electrode 20 extends from the center line L is the first region, and the side where the electrode finger 20b of the floating electrode 20 extends is the second region. Therefore, the first electrode 21 and the electrode finger 20a are disposed in the first region, and the second electrode 22 and the electrode finger 20b are disposed in the second region.

  For example, any one of an input signal potential, an output signal potential, and a ground potential is applied to the first electrode 21 and the second electrode 22. The floating electrode 20 is in a floating state to which no potential is applied. That is, the IDT electrode 1 has a serially divided structure in which an IDT composed of the electrode fingers 20a and the electrode fingers 21a and an IDT composed of the electrode fingers 20b and the electrode fingers 22a are connected in series. Yes. The IDT electrodes 2 to 5 also have a series-divided structure like the IDT electrode 1.

  The SAW elements 12 and 13 having such series-divided IDT electrodes 1 to 5 are connected in parallel to each other. As described above, the two SAW elements 12 and 13 are connected in parallel, and each SAW element 12 and 13 includes the series-divided IDT electrodes 1 to 5 so that it can be applied to the SAW device. Since the generated power is distributed to the two SAW elements and also to each IDT electrode, energy is less concentrated on a specific IDT electrode, and the power durability of the SAW device is improved. Can do. Further, by connecting the two SAW elements 12 and 13 in parallel, the cross width of the serially divided IDT electrodes 1 to 5 can be reduced, and the SAW device can be downsized.

  Further, unbalanced signal terminals 10 and 11 are connected to the two SAW elements 12 and 13 as shown in FIG.

  3 and 4 are diagrams for explaining electrode finger pitches of IDT electrodes constituting the SAW element according to the present embodiment. FIG. 3 is a plan view of the SAW element 12 shown in FIG. ) Is a diagram in which the pitches of electrode fingers arranged in the first region of the IDT electrodes 1 to 5 constituting the SAW element 12 are plotted, and FIG. 4B is a second view of the IDT electrodes 1 to 5 constituting the SAW element 12. It is the figure which plotted the pitch of the electrode finger arrange | positioned in the area | region. In FIG. 3, N1 indicated by a dotted line is a boundary between IDT electrode 1 and IDT electrode 2, N2 is a boundary between IDT electrode 2 and IDT electrode 3, N3 is a boundary between IDT electrode 3 and IDT electrode 4, and N4 is IDT. This is a boundary between the electrode 4 and the IDT electrode 5.

As can be seen by comparing FIG. 4A and FIG. 4B, the way of changing the electrode finger pitch of the SAW element according to this embodiment differs between the first region and the second region. For example, paying attention to the IDT electrodes 2, looking changes in electrode finger pitch from the boundary N1 toward the boundary N2, in the first region, the first electrode finger pitch Pb ₁ boundary N1 of the IDT electrodes 2 of the first region Among them, the pitch increases so as to increase monotonously up to the maximum electrode finger pitch Pm1, and the pitch slightly decreases in the central portion, and the pitch is maintained for a certain interval. Then, after becoming a maximum pitch Pm1 again, the pitch is reduced so as to monotonously decreases to the first electrode finger pitch Pb ₁ boundary N2. On the other hand, in the second region of the IDT electrodes 2, the greater the pitch so that monotonously increases from the second electrode finger pitch Pb ₁ boundary N1 up of the electrode finger pitch Pm2 in the second region of the IDT electrodes 2, after keeping the maximum of the electrode finger pitch Pm2 the constant interval in the central portion, the pitch as monotonically decreasing smaller second to the electrode finger pitch Pb ₂ boundary N2. In other words, when the electrode finger pitch of the first region and the electrode finger pitch of the second region at the same position are compared in the same IDT electrode, there are different parts (for example, the center electrode of the IDT electrode 2). When the finger pitch is compared between the first region and the second region, the electrode finger pitch between the two is different).

  By adopting such an electrode finger pitch, the filter characteristics of the SAW device using series-divided IDT electrodes are improved, for example, the frequency characteristics of VSWR (Voltage Standing Wave Ratio), the passband is widened, the ripple Reduction and the like can be realized.

  Considering the phase of SAW propagating in the first region and the second region, it is considered that the filter characteristics are improved when the electrode finger pitch in the first region and the electrode finger pitch in the second region are all the same. By making the electrode finger pitch of the first region and the electrode finger pitch of the second region all the same, the phase of the SAW propagating in the first region becomes equal to the phase of the SAW propagating in the second region. This is because the filter characteristics of the area and the filter characteristics of the second area are equal, and the generation of ripple due to interference and the narrowing of the band due to the deterioration of the shoulder characteristics of the pass band can be suppressed. However, as a result of extensive research on the relationship between the filter characteristics and the electrode finger pitch, the present inventor has found that this is not the case. That is, in a SAW element using series-divided IDT electrodes, the electrode finger pitch in the first region and the second electrode finger pitch in the first region are set to be the same as the electrode finger pitch in the first region and the second electrode finger pitch in the second region. It has been found that the filter characteristics are improved by making the electrode finger pitches of the two regions different.

  As one of the reasons, it is considered that the SAW propagating through the piezoelectric substrate is affected by the parasitic inductance based on the input / output wiring and the ground wiring connected to the IDT electrode. When the electrode finger pitch in the first region and the electrode finger pitch in the second region are all the same, the phase of the SAW that propagates in the first region and the phase of the SAW that propagates in the second region are surely considered only by the SAW element. However, in an actual product, various wirings are connected to the IDT electrode constituting the SAW element, and the SAW phase that propagates through the first region and the second are affected by the parasitic inductance of the wiring. It is considered that the phase of the SAW propagating in the region actually deviates. Therefore, it is presumed that by separately adjusting the electrode finger pitch in the first region and the electrode finger pitch in the second region, the effect of the phase shift is reduced and the filter characteristics are improved.

In the SAW element of the present embodiment, the electrode finger pitch changes so that the first electrode finger pitch Pb _{1 at} the boundary of the adjacent IDT electrodes on the first region side is minimized. For example, when focusing on the vicinity of the boundary N2 in the first region, the electrode finger pitch gradually decreases as the electrode finger pitch on both sides of the boundary N2 moves toward the boundary N2, and the electrode finger pitch (first electrode finger pitch at the boundary N2). Pb ₁ ) is minimal.

Further, when the first electrode finger pitches Pb _{1 at the} boundaries of the first region are compared with each other, as shown in FIG. 4A, the first electrode finger pitches Pb ₁ are not equal in size. The first electrode finger pitch Pb ₁ of specifically boundary N2, N3 is greater than the first electrode finger pitch Pb ₁ boundary N1, N4. Thus, by making the first electrode finger pitch Pb ₁ different at each boundary, the filter characteristics can be improved as compared with the case where all the first electrode finger pitches are aligned.

The second electrode finger pitch Pb ₂ is the pitch of the boundary in the second region, it has the same pitch relationship between the first electrode finger pitch Pb _1. That is, the electrode finger pitch changes so that the second electrode finger pitch Pb ₂ is minimized, and when the sizes of the second electrode finger pitches Pb ₂ in the second region are compared, The two-electrode finger pitch Pb ₂ is larger than the second electrode finger pitch Pb ₂ at the boundaries N1 and N4.

Further comparing the first electrode finger pitch Pb ₁ on the same border and the second electrode finger pitch Pb _2, both the size is different. For example, when the first electrode finger pitch Pb ₁ in the first region at the boundary N2 is compared with the second electrode finger pitch Pb ₂ in the second region, the second electrode finger pitch Pb _{2 in} the second region is larger. Thus, by making the first electrode finger pitch Pb ₁ and the second electrode finger pitch Pb ₂ on the same boundary different from each other, the filter characteristics can be improved as compared with the case where both are equal.

  Each IDT electrode has main pitch portions M1 and M2 in each of the first region and the second region. Here, the main pitch portion refers to a portion having the largest number of the same pitch among electrode finger pitches of one IDT electrode. For example, when focusing on the IDT electrode 2 in FIG. 4A, the portion surrounded by the alternate long and short dash line is the portion where the same pitch is the most among the electrode finger pitches in the first region of the IDT electrode 2, and this portion is It becomes the main pitch portion (first main pitch portion M1) in the first region of the IDT electrode 2. On the other hand, when focusing on the IDT electrode 2 in FIG. 4B, the portion surrounded by the alternate long and short dash line is the portion where the same pitch is the most among the electrode finger pitches in the second region of the IDT electrode 2, and this portion is This is the main pitch portion (second main pitch portion M2) in the second region of the IDT electrode 2.

In the present embodiment, the first and second main pitch portions M1 and M2 and the first and second electrode finger pitches Pb ₁ and Pb ₂ are set to satisfy a predetermined relationship. For example, paying attention to the IDT electrodes 2, the electrode finger pitch in the boundary N1 is smaller first electrode finger pitch Pb ₁ in the first region than the second electrode finger pitch Pb ₂ in the second region, likewise, at the boundary N2 The electrode finger pitch is such that the first electrode finger pitch Pb ₁ in the first region is smaller than the second electrode finger pitch Pb ₂ in the second region. Thus the first electrode finger pitch Pb ₁ at the boundary of the both sides of the IDT electrodes 2, when the second electrode finger pitch Pb ₂ smaller, even first main pitch portion M1 of the IDT electrode 2 from the second main pitch region M2 It is getting smaller. By arranging the electrode fingers so that the first and second electrode finger pitches Pb ₁ and Pb ₂ and the first and second main pitch portions M1 and M2 satisfy such a relationship, both end portions of the pass band of the SAW filter The passband can be widened while keeping the VSWR at low.

  In the present embodiment, the electrode finger pitch is changed while the duty of the electrode fingers is kept constant. In the present embodiment, the “electrode finger pitch” refers to the distance between the centers of adjacent electrode fingers (see FIG. 2).

Next, an example of a method for manufacturing the SAW device shown in FIG. 1 will be described. First, a mother substrate made of a large number of piezoelectric materials is prepared. The mother substrate is made of, for example, a LiTaO ₃ single crystal that propagates in the X direction with a 38.7 ° Y-cut or 42 ° Y-cut. Next, various electrodes such as IDT electrodes and reflector electrodes are formed in each SAW element region of the mother substrate. These electrodes are, for example, an Al (99 mass%)-Cu (1 mass%) alloy or a laminated film of an Al (99 mass%)-Cu (1 mass%) alloy and Ti in order to improve power durability. Etc. Various electrodes are formed by performing photolithography using such a metal material by a sputtering apparatus, a reduction projection exposure machine (stepper), and a RIE (Reactive Ion Etching) apparatus.

Next, a protective film is formed on a predetermined region of the electrode. The protective film is formed by depositing a SiO ₂ film on each electrode and piezoelectric substrate by a CVD (Chemical Vapor Deposition) apparatus, and then patterning by photolithography, and etching of a flip chip window opening by an RIE apparatus or the like. It is formed by doing. Thereafter, a pad electrode having a structure in which a Cr layer, a Ni layer, and an Au layer are stacked is formed on the flip chip window opening using a sputtering apparatus. Thereafter, using a printing method and a reflow furnace, solder bumps for flip-chiping the SAW device to an external circuit board or the like are formed on the pad electrodes.

Next, the mother substrate is diced along the dividing line, and is divided for each SAW device. Thereafter, each chip is accommodated in an external package and bonded with a flip chip mounting apparatus with the pad electrode forming surface as the bottom surface. Finally, the packaged SAW device is completed by baking in an N ₂ gas atmosphere.

[Modification]
FIG. 5 is a plan view (a diagram corresponding to FIG. 2) showing a serially divided IDT electrode 1 according to a modification of the SAW device shown in FIG. The floating electrode 20 in FIG. 5 includes a first dummy electrode finger 20c and a second dummy electrode finger 20d in addition to the structure of the floating electrode 20 in FIG.

  The first dummy electrode finger 20c protrudes from the central bus bar electrode 20o to the first region (first electrode 21 side) between the electrode fingers 20a, and the tip thereof is more central bus bar than the tip of the electrode finger 21a of the first electrode 21. It is located on the electrode 20o side. Similarly, the second dummy electrode finger 20d protrudes from the central bus bar electrode 20o to the second region (on the second electrode 22 side) between the electrode fingers 20b, and the tip thereof is from the tip of the electrode finger 22a of the second electrode 22. Is also located on the central bus bar electrode 20o side.

  Further, the first electrode 21 in FIG. 5 has a configuration having dummy electrode fingers 21c in addition to the configuration of the first electrode 21 in FIG. The dummy electrode finger 21c protrudes from the bus bar electrode of the first electrode 21 to the floating electrode 20 side between the electrode fingers 21a, and the tip thereof is closer to the bus bar electrode side of the first electrode 21 than the tip of the electrode finger 20a of the floating electrode 20 Is located.

  Similarly, the second electrode 22 of FIG. 5 has a configuration having dummy electrode fingers 22c in addition to the configuration of the second electrode 22 of FIG. The dummy electrode finger 22c extends from the bus bar electrode of the second electrode 22 to the floating electrode 20 side between the electrode fingers 22a, and the tip thereof is closer to the bus bar electrode side of the second electrode 22 than the tip of the electrode finger 20b of the floating electrode 20 Is located.

  By providing the first dummy electrode fingers 20c, the SAW is prevented from leaking from the first region to the second region beyond the central bus bar electrode 20o. As a result, noise due to electrical connection between the first region and the second region via the floating electrode 20 is reduced, and it is easy to obtain intended characteristics.

  Similarly, by providing the second dummy electrode finger 20d, the SAW is prevented from leaking from the second region to the first region beyond the central bus bar electrode 20o. The first dummy electrode finger 20c and the second dummy electrode finger 20d prevent the SAW from leaking in both the first region and the second region, so that the floating electrode 20 between the first region and the second region can be formed. The noise can be more reliably reduced with respect to the electrical connection.

  Furthermore, by providing the dummy electrode finger 21c and the dummy electrode finger 22c, leakage from the SAW IDT electrode 1 is suppressed, and a decrease in insertion loss is suppressed.

  Note that the position, width, protrusion amount, and shape of the dummy electrode fingers 20c (or 20d, 21c, 22c) between the electrode fingers 20a (or 20b, 21a, 22a) vary depending on the frequency of the passband. Depending on the circumstances, it may be set appropriately. The positions, widths, protrusion amounts, and shapes of the plurality of dummy electrode fingers may be the same or different. However, if the tip of the dummy electrode finger 20c (or 20d, 21c, 22c) protrudes beyond the tip of the electrode finger 21a (or 22a, 20a, 20b) extending from the opposite side, the intended characteristics are obtained. Therefore, it is preferable that the tip of the dummy electrode finger is opposed to the tip of the electrode finger extending from the opposite side with a predetermined gap, and the gap G is, for example, 0 <G ≦ 0. It is set in the range of 25λ (λ is the wavelength of SAW).

〔Communication device〕
FIG. 6 is a block diagram showing an embodiment of a communication device using the above-described SAW device. In FIG. 6, a transmission circuit Tx and a reception circuit Rx are connected to an antenna 140 via a filter 101 and a switch 150. The high-frequency signal to be transmitted is removed from the unnecessary signal by the filter 210, amplified by the power amplifier 220, and then radiated from the antenna 140 through the isolator 230 and the switch 150. The high-frequency signal received by the antenna 140 is amplified by the low-noise amplifier 160 through the switch 150, the unnecessary signal is removed by the filter 170, re-amplified by the amplifier 180, and converted to a low-frequency signal by the mixer 190. The If, for example, the filter 101 is configured using the SAW device in the above-described embodiment, the filter 101 has excellent filter characteristics, and the communication quality of the communication device is improved.

[Example 1]
Next, a first embodiment (SAW filter) of the SAW device according to the present invention will be described.

  For the SAW filter formed by connecting two SAW elements as shown in FIG. 3 in parallel, the frequency characteristics of VSWR and the frequency characteristics of insertion loss were calculated by simulation. The simulation was performed by a mode coupling method (COM method). In the present embodiment, SAW elements 12 and 13 composed of seven IDT electrodes 1 to 7 are used.

  FIG. 7A is a diagram in which the electrode finger pitch of the SAW element 20 constituting the SAW filter of Example 1 is plotted, and the horizontal axis indicates the order from one end of the reflector electrode 8 to the other end of the reflector electrode 9. This is the number of electrode fingers counted, and the vertical axis is the electrode finger pitch (μm). In the figure, the state of the change of the electrode finger pitch in the first region is indicated by a solid line, and the state of the change of the electrode finger pitch in the second region is indicated by a broken line. As shown in the figure, the SAW element 20 of Example 1 is different in the electrode finger pitch from one end to the other end in the first region and the electrode finger pitch from one end to the other end in the second region. The electrode fingers are arranged in such a way that the change of the difference is different.

  FIG. 7B is a diagram in which the electrode finger pitch of the SAW element 20 constituting the SAW filter of Comparative Example 1 is plotted. The change of the electrode finger pitch in the first region is indicated by a solid line, and the second region The change of the electrode finger pitch is indicated by a broken line. In the SAW element of Comparative Example 1, the way of changing the electrode finger pitch in the first region is the same as the way of changing the electrode finger pitch in the second region, and the wavy line indicating the change in the electrode finger pitch in the second region is This overlaps the solid line indicating the change in the electrode finger pitch in the first region.

  FIG. 8 shows the frequency characteristics of the VSWR calculated by simulation for the SAW filters of Example 1 and Comparative Example 1. In the figure, the VSWR frequency characteristic of the SAW filter of Example 1 is indicated by a solid line, and the VSWR frequency characteristic of Comparative Example 1 is indicated by a broken line. As can be seen from FIG. 8, the SAW filter of Example 1 has an improved VSWR in the passband (2400 MHz to 2500 MHz) compared to the SAW filter of Comparative Example 1.

  FIG. 9 is a diagram showing a simulation result of frequency characteristics of insertion loss, and is an enlarged view of a pass band (2400 MHz to 2500 MHz) portion. In the figure, the frequency characteristic of the insertion loss of the SAW filter of Example 1 is indicated by a solid line, and the frequency characteristic of the insertion loss of Comparative Example 1 is indicated by a broken line. As can be seen from FIG. 8, the SAW filter of Example 1 has a wider band than the SAW filter of Comparative Example 1. It can also be seen that the occurrence of ripples is also suppressed.

  From this result, in the SAW element using the series-divided IDT electrode, the change in the electrode finger pitch in the first region and the change in the electrode finger pitch in the second region are the same as the change. It was confirmed that the filter characteristics were improved by using different methods.

[Example 2]
Next, a second embodiment (SAW filter) of the SAW device according to the present invention will be described.

  Similar to the first embodiment, the frequency characteristics of the VSWR and the frequency characteristics of the attenuation are simulated for the SAW filter formed by connecting two SAW elements (seven IDT electrodes) in parallel as shown in FIG. Calculated by

FIG. 10A is a diagram in which the electrode finger pitch of the SAW element 20 constituting the SAW filter of Example 2 is plotted. The change of the electrode finger pitch in the second region is indicated by a solid line, The change of the electrode finger pitch is indicated by a broken line. As shown in the figure, the SAW element 20 of Example 2 has a method of changing the electrode finger pitch from one end to the other end in the first region and the electrode finger pitch from one end to the other end in the second region. The electrode fingers are arranged in such a way that the change of the difference is different. When attention is paid to the electrode finger pitches (first and second electrode finger pitches Pb ₁ and Pb ₂ ) at the boundaries N1 to N6 between the IDT electrodes, the size of the first electrode finger pitches Pb ₁ in the first region is one. The electrode fingers are arranged so that they are the same and partially different, and similarly, the electrode fingers are arranged so that the sizes of the second electrode finger pitches Pb ₂ in the second region are also the same and partially different. Specifically, the first electrode size of the finger pitch Pb ₁ at each boundary of the first region, N1: 0.7498 (μm), N2: 0.7509 (μm), N3: 0.7504 (μm) , N4: 0.7504 (μm), N5: 0.7509 (μm), N6: a 0.7498 (μm), the size of the first electrode finger pitch Pb ₂ at each boundary of the second region, N1 : 0.7520 (μm), N2: 0.7532 (μm), N3: 0.7540 (μm), N4: 0.7540 (μm), N5: 0.7532 (μm), N6: 0.7520 ( μm).

FIG. 10B is a diagram in which the electrode finger pitch of the SAW element 20 constituting the SAW filter of Comparative Example 2 is plotted. The change of the electrode finger pitch in the first region is shown by a solid line, The change of the electrode finger pitch is indicated by a broken line. In the SAW element of Comparative Example 2, the first electrode finger pitch Pb ₁ in the first region is all set to the same value. Specifically, the first electrode finger pitch Pb ₁ in the first region is set to 0.7531 (μm) at all the boundaries N1 to N6. On the other hand, the second electrode finger pitch Pb ₂ in the second region is different from the first electrode finger pitch Pb ₁ , but is the same at all boundaries in the second region, and its value is 0.7513 (μm ).

  FIG. 11 shows the frequency characteristics of the VSWR calculated by simulation for the SAW filters of Example 2 and Comparative Example 2. In the figure, the VSWR frequency characteristic of the SAW filter of Example 2 is indicated by a solid line, and the VSWR frequency characteristic of Comparative Example 2 is indicated by a broken line. As apparent from FIG. 11, it can be seen that the SAW filter of Example 2 has an improved VSWR in the passband (2400 MHz to 2500 MHz) as compared with the SAW filter of Comparative Example 2.

  FIG. 12 is a diagram showing a simulation result of frequency characteristics of insertion loss, and is an enlarged view of a passband (2400 MHz to 2500 MHz) portion. In the figure, the insertion loss frequency characteristic of the SAW filter of Example 2 is indicated by a solid line, and the insertion loss frequency characteristic of Comparative Example 2 is indicated by a broken line. As can be seen from FIG. 12, the SAW filter of Example 2 has a wider band than the SAW filter of Comparative Example 2. It can also be seen that the occurrence of ripples is also suppressed.

From this result, in the SAW element using the serially divided IDT electrodes, the first electrode finger pitch Pb ₁ in the first region and the second electrode finger pitch Pb ₂ in the second region are all the same, It was confirmed that the filter characteristics were improved by differentiating.

DESCRIPTION OF SYMBOLS 100 ... Piezoelectric substrate 1-5 ... IDT electrode 8, 9 ... Reflector electrode 10, 11 ... Unbalanced signal terminal 12, 13 ... Surface acoustic wave element 20 ... Floating electrode 21 ... First electrode 22 ... Second electrode

Claims (5)

A surface acoustic wave device comprising: a piezoelectric substrate; and a surface acoustic wave element disposed on the piezoelectric substrate,
The surface acoustic wave device includes IDT electrodes having N (an integer greater than or equal to 3) series-divided structure arranged along the propagation direction of the surface acoustic wave,
Each IDT electrode is
A central bus bar electrode, a plurality of first floating electrode fingers, one end of which is connected to one long side of the central bus bar electrode and spaced from each other, and the other long side of the central bus bar electrode A plurality of second floating electrode fingers connected at one end to each other and spaced apart from each other;
A first electrode having a plurality of electrode fingers disposed between the plurality of first floating electrode fingers;
A second electrode having a plurality of electrode fingers arranged to be positioned between the plurality of second floating electrode fingers,
The surface acoustic wave element is divided into a first region and a second region with a center line of the central bus bar electrode as a boundary, and the first region is a region where the first floating electrode finger and the first electrode are disposed, When the second region is a region where the second floating electrode finger and the second electrode are disposed,
The IDT electrode is different in elasticity between the electrode finger pitch changing from one end to the other end in the first region and the electrode finger pitch changing from one end to the other end in the second region. Surface wave device. The electrode finger pitch of the IDT electrode changes so that the first electrode finger pitch Pb _{1 at} the boundary of the adjacent IDT electrode on the first region side is minimized, and
When the sizes of all the first electrode finger pitches Pb ₁ in the first region are compared, the size of at least one first electrode finger pitch Pb _{1 is} the size of the other first electrode finger pitch Pb ₁ . The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is different. The electrode finger pitch of the IDT electrode changes so that the second electrode finger pitch Pb _{2 at} the boundary of the adjacent IDT electrode on the second region side is minimized,
When the sizes of all the second electrode finger pitches Pb ₂ in the second region are compared, the size of at least one second electrode finger pitch Pb _{2 is} the size of the other second electrode finger pitch Pb ₂ . The surface acoustic wave device according to claim 2, wherein the surface acoustic wave device has a size different from that of the surface acoustic wave device. Wherein said first electrode finger pitch Pb ₁ located on the same border second and electrode finger pitch Pb ₂ is a surface acoustic wave device according to claim 3 are different in size. The IDT electrode has a first main pitch portion M1 in the first region and a second main pitch portion M2 in the second region,
The size of the first electrode finger pitch Pb ₁ is smaller than the size of the second electrode finger pitch Pb ₂ , and the size of the first main pitch portion M 1 is smaller than the size of the second main pitch portion M 2. The surface acoustic wave device according to claim 4.