JP2017228882A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high reliability by stabilizing the resonator characteristics of each resonator, even if multiple resonators of different frequency characteristics are formed on one piezoelectric substrate.SOLUTION: A surface acoustic wave filter 10 includes a piezoelectric substrate 20, a resonator electrode 31, a resonator electrode 32, and a protection film 40. The piezoelectric substrate 20 is provided with a recess 21 in the surface 201. The resonator electrode 31 is formed on the bottom face of the recess 21. The resonator electrode 32 is formed in a region different from the recess 21 on the surface 201 of the piezoelectric substrate 20. The protection film 40 is formed on the surface 201 of the piezoelectric substrate 20, and covering the resonator electrodes 31, 32. Top surface 401 in the protection film 40, on the opposite side to the surface abutting against the surface 201 of the piezoelectric substrate 20, is flat.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface acoustic wave filter in which an IDT electrode is formed on the surface of a piezoelectric substrate.

Conventionally, various surface acoustic wave filters have been put into practical use. The surface acoustic wave filter has a structure as shown in Patent Document 1, for example. The surface acoustic wave filter of Patent Document 1 includes a piezoelectric substrate and a comb electrode (IDT electrode). The comb electrode is formed on the surface of the piezoelectric substrate. A first protective film that covers the comb-shaped electrode is formed on the surface of the piezoelectric substrate. The first protective film is made of, for example, SiO ₂ . A second protective film is formed on the surface of the first protective film. The second protective film is made of, for example, SiO ₂ .

  In the surface acoustic wave filter of Patent Document 1, two sets of comb electrodes are formed on the surface of the piezoelectric substrate. The thickness of the first protective film in the formation region of the first comb electrode is larger than the thickness of the first protective film in the formation region of the second comb electrode. As a result, the first resonator including the first comb electrode and the second resonator including the second comb electrode have different frequency characteristics. In the surface acoustic wave filter of Patent Document 1, the first resonator is set as a series arm resonator, and the second resonator is set as a parallel arm resonator.

JP-A-6-152299

  However, in the surface acoustic wave filter described in Patent Document 1, the first resonator portion and the second resonator portion have different thicknesses, and a step is generated on the surface of the first protective film.

  As described above, when a step is formed on the outer surface of the surface acoustic wave filter (an electronic component forming the surface acoustic wave filter), cracks are easily generated from the step, and the physical strength of the surface acoustic wave filter is reduced. Further, when the second protective film is formed on the surface of the first protective film, it is difficult to form the second protective film on the surface of the step, and the environment resistance and the like are deteriorated. In addition, the step difference causes problems such as generation of a resist residue during the planarization process of the surface of the first protective film, making it difficult to realize stable resonator characteristics and filter characteristics.

  Accordingly, an object of the present invention is to provide a highly reliable surface acoustic wave filter having stable resonator characteristics even when a plurality of resonators having different frequency characteristics are formed on one piezoelectric substrate.

  The surface acoustic wave filter of the present invention includes a piezoelectric substrate, a first resonator electrode, a second resonator electrode, and a first protective film. The piezoelectric substrate has a recess on the surface. The first resonator electrode is formed on the bottom surface of the recess. The second resonator electrode is formed in a region different from the concave portion on the surface of the piezoelectric substrate. The first protective film is formed on the surface of the piezoelectric substrate and covers the first resonator electrode and the second resonator electrode. The top surface of the first protective film opposite to the surface in contact with the surface of the piezoelectric substrate is flat.

  In this configuration, the thickness of the portion of the first protective film that covers the first resonator electrode is larger than the thickness of the portion of the first protective film that covers the second resonator electrode. Therefore, the frequency characteristic of the first resonator including the first resonator electrode is different from the frequency characteristic of the second resonator including the second resonator electrode.

  The surface acoustic wave filter according to the present invention preferably includes a wiring electrode for connecting the first resonator electrode and the second resonator electrode on the surface of the piezoelectric substrate.

  In this configuration, the first resonator electrode and the second resonator electrode are connected at a short distance, and the wiring electrode is protected by the first protective film.

  In the surface acoustic wave filter according to the present invention, the first resonator including the first resonator electrode and the second resonator including the second resonator electrode may form different filters. .

  In this configuration, a plurality of filters having different filter characteristics are formed by one piezoelectric substrate.

  In the surface acoustic wave filter according to the present invention, the first resonator including the first resonator electrode and the second resonator including the second resonator electrode are connected in a ladder shape. Two filters may be configured.

  In this configuration, the resonator characteristics of the series arm resonator and the parallel arm resonator constituting the ladder circuit can be made different from each other with a single piezoelectric substrate.

  In the surface acoustic wave filter according to the present invention, the first resonator including the first resonator electrode and the second resonator including the second resonator electrode are connected in a longitudinally coupled manner. One filter may be configured.

  In this configuration, the resonator characteristics of a plurality of resonators constituting the longitudinally coupled circuit can be made different with one piezoelectric substrate.

  In the surface acoustic wave filter of the present invention, the first resonator may be a series arm resonator, and the second resonator may be a parallel arm resonator.

  With this configuration, a temperature characteristic on the high frequency side of the pass band is excellent, and a filter having a wide pass band is realized.

  In the surface acoustic wave filter of the present invention, the first resonator may be a parallel arm resonator, and the second resonator may be a series arm resonator.

  With this configuration, a temperature characteristic on the low frequency side of the pass band is excellent, and a filter having a wide pass band is realized.

  The surface acoustic wave filter of the present invention preferably includes a second protective film formed on the top surface of the first protective film.

  With this configuration, the reliability of the surface acoustic wave filter is improved. Further, since the top surface of the first protective film is flat, it is easy to form the second protective film on the entire surface of the first protective film.

  According to the present invention, even if a plurality of resonators having different frequency characteristics are formed on one piezoelectric substrate, the respective resonator characteristics are stable and high reliability can be realized.

(A) is a side view which shows the structure of the surface acoustic wave filter which concerns on the 1st Embodiment of this invention, (B) is a plane which shows the structure of the surface acoustic wave filter which concerns on the 1st Embodiment of this invention FIG. It is a graph which shows a resonator characteristic, a horizontal axis shows a frequency and a vertical axis | shaft shows an impedance. It is a flowchart which shows an example of the manufacturing method of the surface acoustic wave filter which concerns on the 1st Embodiment of this invention. (A) is a side view which shows the structure of the surface acoustic wave filter which concerns on the 2nd Embodiment of this invention, (B) is a plane which shows the structure of the surface acoustic wave filter which concerns on the 2nd Embodiment of this invention. FIG. (A) is a top view which shows the structure of the surface acoustic wave filter which concerns on the 3rd Embodiment of this invention, (B) is an equivalent circuit schematic of the surface acoustic wave filter shown to (A).

  A surface acoustic wave filter according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a side view showing the configuration of the surface acoustic wave filter according to the first embodiment of the present invention. FIG. 1B is a plan view showing the configuration of the surface acoustic wave filter according to the first embodiment of the present invention. In FIG. 1B, illustration of the protective film 40 and the protective film 50 is omitted.

  As shown in FIGS. 1A and 1B, the surface acoustic wave filter 10 includes a piezoelectric substrate 20, a plurality of resonator electrodes 31, 32, a protective film 40, and a protective film 50.

  The piezoelectric substrate 20 is made of a lithium niobate substrate (LN substrate), a lithium tantalate substrate (LT substrate), a crystal substrate, or a ZnO substrate. The material of the piezoelectric substrate 20 is not limited to these materials as long as it is a material used as a surface acoustic wave filter.

  A recess 21 is formed on the surface 201 of the piezoelectric substrate 20. The surface 201 is flat except for the recess 21. The bottom surface of the recess 21 is flat. In addition, the bottom face of the recessed part 21 may be provided with the further recessed part. That is, the bottom surface of the recess 21 may be recessed in a plurality of steps.

  For the resonator electrode 31 and the resonator electrode 32, a material having a specific gravity greater than that of the protective film 40, for example, any one of Pt, Au, Cu, Ag, and W may be used. Further, the resonator electrode 31 and the resonator electrode 32 may be formed by laminating a highly conductive metal such as Al on the surface of any one of the above metals.

  The resonator electrode 31 is formed on the bottom surface of the recess 21. The resonator electrode 31 includes two IDT electrodes 311 and 312 and two reflector electrodes 313.

  The two IDT electrodes 311 and 312 are each formed by a bus bar electrode and a plurality of electrode fingers. The plurality of electrode fingers of the IDT electrode 311 and the plurality of electrode fingers of the IDT electrode 312 are disposed between the bus bar electrode of the IDT electrode 311 and the bus bar electrode of the IDT electrode 312. The plurality of electrode fingers of the IDT electrode 311 and the plurality of electrode fingers of the IDT electrode 312 are alternately arranged along a direction orthogonal to the arrangement direction of the two bus bar electrodes. The two reflector electrodes 313 are arranged so as to sandwich the arrangement area of the plurality of electrode fingers constituting the two IDT electrodes 311 and 312. The two reflector electrodes 313 are arranged at the respective end portions in the arrangement direction of the plurality of electrode fingers.

  The resonator electrode 32 is formed in a region different from the concave portion 21 on the surface 201 of the piezoelectric substrate 20. The resonator electrode 32 includes two IDT electrodes 321 and 322 and two reflector electrodes 323. The two IDT electrodes 321 and 322 correspond to the second IDT electrode of the present invention.

  The two IDT electrodes 321 and 322 are each formed by a bus bar electrode and a plurality of electrode fingers. The plurality of electrode fingers of the IDT electrode 321 and the plurality of electrode fingers of the IDT electrode 322 are disposed between the bus bar electrode of the IDT electrode 321 and the bus bar electrode of the IDT electrode 322. The plurality of electrode fingers of the IDT electrode 321 and the plurality of electrode fingers of the IDT electrode 322 are alternately arranged along a direction orthogonal to the arrangement direction of the two bus bar electrodes. The two reflector electrodes 323 are arranged so as to sandwich the arrangement area of the plurality of electrode fingers constituting the two IDT electrodes 321 and 322. The two reflector electrodes 323 are arranged at the respective end portions in the arrangement direction of the plurality of electrode fingers.

The protective film 40 is made of, for example, a SiO ₂ film. The material of the protective film 40 may be a material having temperature characteristics opposite to the temperature characteristics of the resonator composed of the resonator electrodes 31 and 32 and the piezoelectric substrate 20. The protective film 40 corresponds to the “first protective film” of the present invention.

  The protective film 40 is in contact with the entire surface 201 of the piezoelectric substrate 20. That is, the protective film 40 is filled not only in the portion other than the concave portion 21 on the surface 201 but also in the concave portion 21. The protective film 40 completely covers the resonator electrode 31 and the resonator electrode 32 and has a predetermined thickness. The top surface 401 of the protective film 40 (the surface opposite to the surface in contact with the surface 201 of the piezoelectric substrate 20) is flat. In other words, the top surface 401 of the protective film 40 has no step between a region that overlaps the recess 21 and a region that does not overlap the recess 21 (a region different from the recess 21).

  Therefore, the thickness of the region overlapping the recess 21 in the protective film 40 is larger than the thickness of the region different from the recess 21 in the protective film 40. In other words, the thickness of the region where the resonator electrode 31 is formed in the protective film 40 is larger than the thickness of the region where the resonator electrode 32 is formed in the protective film 30.

  Accordingly, the first resonator including the resonator electrode 31 and the second resonator including the resonator electrode 32 have different resonator characteristics. FIG. 2 is a graph showing the resonator characteristics, in which the horizontal axis indicates the frequency and the vertical axis indicates the impedance.

  Specifically, the first resonator has better temperature characteristics of the resonator than the second resonator. In addition, the first resonator has a smaller electromechanical coupling coefficient and a smaller specific bandwidth than the second resonator. In this case, it has the characteristic of the 1st resonator shown as the continuous line of FIG. That is, the impedance change at the resonance point fr31 and the antiresonance point fa31 is steeper than that of the second resonator, and the frequency difference between the resonance point fr31 and the antiresonance point fa31 is smaller than that of the second resonator.

  On the other hand, the temperature characteristics of the second resonator are deteriorated as compared with the first resonator. In addition, the second resonator has a larger electromechanical coupling coefficient and a larger specific bandwidth than the first resonator. In this case, it has the characteristic of the 2nd resonator shown by the broken line of FIG. That is, the impedance change at the resonance point fr32 and the antiresonance point fa32 is gentler than that of the first resonator, and the frequency difference between the resonance point fr31 and the antiresonance point fa31 is larger than that of the first resonator.

  As described above, the surface acoustic wave filter 10 according to this embodiment can include two resonators having different resonator characteristics by one piezoelectric substrate 20. And since there is no level | step difference in the top | upper surface 401 of the protective film 40, the crack by the said level | step difference can be prevented. Thereby, the physical strength of the surface acoustic wave filter 10 is improved. The surface acoustic wave filter 10 can realize high reliability.

  The first resonator and the second resonator may be different filter components or may be a single filter component (the second embodiment and the third embodiment). See embodiment).

The protective film 50 is made of, for example, an SiN film, an SiO ₂ film, an inorganic film such as glass, an organic film, an organic / inorganic hybrid film, or the like. The protective film 50 may be made of a film other than these depending on the desired reliability. The protective film 50 corresponds to the “second protective film” of the present invention.

  The protective film 50 covers the entire top surface 401 of the protective film 40. With this configuration, the surface acoustic wave filter 10 can achieve higher reliability or stable resonator characteristics depending on the material of the protective film 50.

  In the surface acoustic wave filter 10, the top surface 401 of the protective film 40 is flat. Therefore, the problem that the protective film 50 is not formed at the step does not occur, and the protective film 50 can be easily and reliably formed on the entire top surface 401 of the protective film 40. Thereby, the surface acoustic wave filter 10 having higher reliability and stable resonator characteristics can be easily realized.

  The surface acoustic wave filter 10 having such a configuration is manufactured as follows. FIG. 3 is a flowchart showing an example of a method for manufacturing a surface acoustic wave filter according to the first embodiment of the present invention.

  A recess 21 is formed on the surface 201 of the piezoelectric substrate 20 (S101). Specifically, a resist film is formed in a region other than the recess 21 on the surface 201 of the piezoelectric substrate 20. The piezoelectric substrate 20 with a resist film is immersed in an RIE method or an etching solution. Thereby, a part of the surface 201 of the piezoelectric substrate 20 is recessed, and the recess 21 is formed. After the formation of the recesses 21, the resist film is removed.

  The resonator electrode 31 is formed on the bottom surface of the recess 21 (S102). The resonator electrode 32 is formed in a region different from the concave portion 21 on the surface 201 (S102). As a method for forming the resonator electrode 31 and the resonator electrode 32, a vapor deposition method such as PVD or CVD, or a known method such as pattern plating may be used. The formation of the resonator electrode 31 and the formation of the resonator electrode 32 may be performed simultaneously.

A protective film (SiO ₂ film) 40 is formed to cover the surface 201 (including the recess 21) of the piezoelectric substrate 20 (S104). The top surface 401 of the protective film 40 is planarized using a CMP method or the like (S105).

A protective film 50 is formed on the top surface 401 of the planarized protective film (SiO ₂ film) 40 (S106). Since the top surface 401 of the protective film (SiO ₂ film) 40 is flattened, the protective film 50 can be easily and reliably formed on the entire top surface 401.

  In the configuration of FIG. 1, a mode is shown in which one resonator electrode is formed in each of the recess 21 and a region different from the recess 21 on the surface 201. However, a plurality of resonator electrodes may be formed in the recess 21, or a plurality of resonator electrodes may be formed in a region different from the recess 21 on the surface 201.

  Next, a surface acoustic wave filter according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 4A is a side view showing the configuration of the surface acoustic wave filter according to the second embodiment of the present invention. FIG. 4B is a plan view showing the configuration of the surface acoustic wave filter according to the second embodiment of the present invention. In FIG. 4B, illustration of the protective film 40 and the protective film 50 is omitted.

  As shown in FIGS. 4A and 4B, the surface acoustic wave filter 10A according to this embodiment includes a plurality of wiring electrodes 411, compared to the surface acoustic wave filter 10 according to the first embodiment. 412, 421, and 422 are different. Other configurations of the surface acoustic wave filter 10A are the same as those of the surface acoustic wave filter 10 according to the first embodiment, and description of the same portions is omitted.

  Each of the wiring electrodes 411, 412, 421, 422 is formed on the surface 201 of the piezoelectric substrate 20. The wiring electrodes 411, 412, 421, 422 are made of the same material as the resonator electrodes 31, 32. The wiring electrodes 411, 412, 421, 422 may be made of a material different from that of the resonator electrodes 31, 32.

  The wiring electrode 411 and the wiring electrode 412 are disposed so as to sandwich the resonator electrode 31 when the surface acoustic wave filter 10A is viewed in plan. The wiring electrode 411 is disposed close to the IDT electrode 311. The wiring electrode 412 is disposed close to the IDT electrode 312. The wiring electrode 411 and the wiring electrode 412 have a shape that leads to the bottom surface of the recess 21.

  The wiring electrode 411 is connected to the IDT electrode 311. An input / output terminal P11 is formed at the end of the wiring electrode 411 opposite to the side connected to the IDT electrode 311. The input / output terminal P11 is realized by a structure in which a part of the wiring electrode 411 is not covered with the protective film 40 and the protective film 50. The input / output terminal P <b> 11 is in a region different from the concave portion 21 on the surface 201.

  The wiring electrode 412 is connected to the IDT electrode 312. An input / output terminal P12 is formed at the end of the wiring electrode 412 opposite to the side connected to the IDT electrode 312. The input / output terminal P12 is realized by a structure in which a part of the wiring electrode 412 is not covered with the protective film 40 and the protective film 50. The input / output terminal P12 is in a region different from the concave portion 21 on the surface 201.

  The wiring electrode 421 and the wiring electrode 422 are arranged so as to sandwich the resonator electrode 32 when the surface acoustic wave filter 10A is viewed in plan. The wiring electrode 421 is disposed in the vicinity of the IDT electrode 321. The wiring electrode 422 is disposed in the vicinity of the IDT electrode 322.

  The wiring electrode 421 is connected to the IDT electrode 321. An input / output terminal P21 is formed at the end of the wiring electrode 421 opposite to the side connected to the IDT electrode 321. The input / output terminal P <b> 21 is realized by a structure in which a part of the wiring electrode 421 is not covered with the protective film 40 and the protective film 50. The input / output terminal P <b> 21 is in a region different from the concave portion 21 on the surface 201.

  The wiring electrode 422 is connected to the IDT electrode 322. An input / output terminal P22 is formed at the end of the wiring electrode 422 opposite to the side connected to the IDT electrode 322. The input / output terminal P22 is realized by a structure in which a part of the wiring electrode 422 is not covered with the protective film 40 and the protective film 50. The input / output terminal P22 is in a region different from the concave portion 21 on the surface 201.

  Even in such a configuration, as shown in FIG. 4A, in the surface acoustic wave filter 10A, the top surface 401 of the protective film 40 is flat. Thereby, the surface acoustic wave filter 10A has the same effects as the surface acoustic wave filter 10 according to the first embodiment.

  In addition, input / output terminals P11 and P12 of the first resonator including the resonator electrode 31 and input / output terminals P21 and P22 of the second resonator including the resonator electrode 32 are recessed portions on the surface 201 of the piezoelectric substrate 20. 21, but more preferably in a different region from the recess 21. In that case, the depth of the hole opened in the protective films 40, 50 for forming the input / output terminals P11, P12 is the same as the depth of the hole opened in the protective films 40, 50 for forming the input / output terminals P21, P22. Therefore, the process of forming the input / output terminals P11, P12, P21, and P22 is facilitated.

  Further, by connecting the input / output terminals P11 and P12 to the external circuit as input / output terminals of the first filter and the input / output terminals P21 and P22 as input / output terminals of the second filter, the surface acoustic wave filter 10 is Two filters having different frequency characteristics can be formed by one piezoelectric substrate 20. Further, by connecting the input / output terminal P11 and the input / output terminal P21 or the input / output terminal P22, one filter in which two resonators having different frequency characteristics are connected can be realized.

  Next, a surface acoustic wave filter according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 5A is a plan view showing a configuration of a surface acoustic wave filter according to the third embodiment of the present invention. In FIG. 5A, illustration of the protective film 40 and the protective film 50 is omitted. FIG. 5B is an equivalent circuit diagram of the surface acoustic wave filter shown in FIG.

  As shown in FIG. 5A, the surface acoustic wave filter 10B has the resonator electrode 33 and wiring electrodes 411B, 422, 432, and 440 added to the surface acoustic wave filter 10 according to the first embodiment. It differs in the point and the shape of the recess 21B. Other configurations of the surface acoustic wave filter 10B are the same as those of the surface acoustic wave filter 10, and the description of the same portions is omitted.

  The resonator electrode 33 includes two IDT electrodes 331 and 332 and two reflector electrodes 333. The two IDT electrodes 331 and 332 correspond to the first IDT electrode of the present invention. The basic structure and material of the resonator electrode 33 are the same as those of the resonator electrode 31 and the resonator electrode 32, and the description thereof is omitted.

  The piezoelectric substrate 20B includes a recess 21B on the surface 201. The resonator electrode 31 and the resonator electrode 33 are formed on the bottom surface of the recess 21B of the piezoelectric substrate 20B. The resonator electrode 32 is formed in a region different from the concave portion 21B on the surface 201 of the piezoelectric substrate 20B.

  The resonator electrodes 31, 32, and 33 are arranged so that the arrangement directions of a plurality of electrode fingers that constitute each of the resonator electrodes 31, 32, and 33 are parallel to each other. The resonator electrode 31 and the resonator electrode 33 are arranged at intervals along the extending direction of the plurality of electrode fingers. The resonator electrode 32 and the resonator electrode 33 are arranged at intervals along the arrangement direction of the plurality of electrode fingers.

  Each of the wiring electrodes 411B, 422, 432, 440 is formed on the surface 201 of the piezoelectric substrate 20B. The wiring electrodes 411 </ b> B, 422, 432, 440 are made of the same material as the resonator electrodes 31, 32, 33. The wiring electrodes 411B, 422, 432, and 440 may be made of a material different from that of the resonator electrodes 31, 32, and 33.

  The wiring electrode 411B and the wiring electrode 440 are disposed so as to sandwich the resonator electrode 31 when the surface acoustic wave filter 10B is viewed in plan. The wiring electrode 411B is disposed in the vicinity of the IDT electrode 311. The wiring electrode 440 is disposed close to the IDT electrode 312. The wiring electrode 411B and the wiring electrode 440 have a shape that leads to the bottom surface of the recess 21B.

  The wiring electrode 411B is connected to the IDT electrode 311. An input / output terminal P11 is formed at the end of the wiring electrode 411B opposite to the side connected to the IDT electrode 311. The input / output terminal P11 is realized by a structure in which a part of the wiring electrode 411B is not covered with the protective film 40 and the protective film 50. The input / output terminal P11 may be in the recess 21B on the surface 201, but it is more preferable that the input / output terminal P11 is in a different area from the recess 21B.

  The wiring electrode 440 and the wiring electrode 422 are arranged so as to sandwich the resonator electrode 32 in plan view of the surface acoustic wave filter 10B. The wiring electrode 440 is disposed in the vicinity of the IDT electrode 321. The wiring electrode 422 is disposed in the vicinity of the IDT electrode 322.

  An input / output terminal P22 is formed at the end of the wiring electrode 422 opposite to the side connected to the IDT electrode 322. The input / output terminal P22 is realized by a structure in which a part of the wiring electrode 422 is not covered with the protective film 40 and the protective film 50. The input / output terminal P22 may be in the concave portion 21B on the surface 201, but it is more preferable that the input / output terminal P22 is in a region different from the concave portion 21B.

  The wiring electrode 440 and the wiring electrode 432 are disposed so as to sandwich the resonator electrode 33 in plan view of the surface acoustic wave filter 10B. The wiring electrode 440 is disposed in the vicinity of the IDT electrode 331. The wiring electrode 432 is disposed in the vicinity of the IDT electrode 332.

  An input / output terminal P32 is formed at the end of the wiring electrode 432 opposite to the side connected to the IDT electrode 332. The input / output terminal P32 is realized by a structure in which a part of the wiring electrode 432 is not covered with the protective film 40 and the protective film 50. The input / output terminal P32 may be in the recess 21B on the surface 201, but is more preferably in a different area from the recess 21B.

  The wiring electrode 440 is connected to the IDT electrode 312, the IDT electrode 321, and the IDT electrode 331.

  Although not shown, a protective film 40 is formed on the surface 201 of the piezoelectric substrate 20B, including the recesses 21B, as in the surface acoustic wave filter 10 according to the first embodiment. The top surface 401 opposite to the surface 201 in the protective film 40 is flat. A protective film 50 is formed on the top surface 401 of the protective film 40.

  With such a configuration, the surface acoustic wave filter 10B has the same effects as the surface acoustic wave filter 10 according to the first embodiment and the surface acoustic wave filter 10A according to the second embodiment.

  In the surface acoustic wave filter 10 </ b> B, the plurality of resonator electrodes 31, 32, and 33 are connected by the wiring electrode 440. Therefore, the plurality of resonator electrodes 31, 32, 33 can be connected at a short distance as compared with a configuration in which the plurality of resonator electrodes 31, 32, 33 are individually formed and connected by an external conductor pattern. Thereby, the surface acoustic wave filter 10B can suppress transmission loss. In particular, as shown in FIG. 5, the transmission loss can be further suppressed by making the width of the wiring electrode 440 larger than that of the other wiring electrodes 440. Further, since the entire wiring electrode 440 is covered with the protective film 40, the surface acoustic wave filter 10B can improve the environmental resistance of the wiring electrode 440.

  Also, with such a configuration, the surface acoustic wave filter 10B realizes the circuit shown in FIG. The surface acoustic wave filter 10B includes resonators 310, 320, and 330, and input / output terminals P11, P22, and P32. The resonator 310 includes a resonator electrode 31. The resonator 320 includes a resonator electrode 32. The resonator 330 includes a resonator electrode 33.

  The resonator 310 and the resonator 330 are connected in series between the input / output terminal P11 and the input / output terminal P22. The resonator 310 is connected to the input / output terminal P11, and the resonator 330 is connected to the input / output terminal P33. A first end of the resonator 320 is connected to an end of the resonator 310 opposite to the input / output terminal P11 and an end of the resonator 330 opposite to the input / output terminal P33. A second end of the resonator 320 is connected to the input / output terminal P22.

  With this configuration, the surface acoustic wave filter 10 </ b> B includes a ladder type circuit including the resonators 310, 320, and 330.

  Here, by connecting the input / output terminal P22 to the ground potential, the resonators 310 and 330 become series arm resonators, and the resonator 320 becomes a parallel arm resonator. With this configuration, the surface acoustic wave filter 10B is a ladder-type filter including a series arm resonator having good temperature characteristics and a parallel arm resonator having a large electromechanical coupling coefficient. As a result, the attenuation characteristic of the surface acoustic wave filter 10B is steep on the high frequency side of the pass band of the desired communication band, and is excellent in temperature characteristics. Furthermore, even if the frequency difference between a desired communication band and a communication band adjacent thereto is small, the surface acoustic wave filter 10B can be adapted to this. The surface acoustic wave filter 10B can realize a pass band having a wide frequency range with respect to a desired communication band.

  Thereby, for example, the surface acoustic wave filter 10B can satisfy the conditions of the transmission filter corresponding to Band2 of UMTS. The surface acoustic wave filter 10 </ b> B can realize such filter characteristics with a single piezoelectric substrate 20.

  On the other hand, although not shown, the structure of the resonator 310 or the resonator 330 can be applied to the parallel arm resonator, and the structure of the resonator 320 can be applied to the series arm resonator. In this case, the surface acoustic wave filter is a ladder type filter including a series arm resonator having a large electromechanical coupling coefficient and a parallel arm resonator having a good temperature characteristic. As a result, the attenuation characteristic of the surface acoustic wave filter becomes steep on the low frequency side of the pass band of the desired communication band, and the temperature characteristic is excellent. Furthermore, even if the frequency difference between a desired communication band and a communication band adjacent thereto is small, the surface acoustic wave filter can be adapted to this. The surface acoustic wave filter can realize a pass band having a wide frequency range with respect to a desired communication band.

  Thereby, for example, the surface acoustic wave filter can satisfy the conditions of the reception filter corresponding to Band 2 of UMTS. The surface acoustic wave filter can realize such filter characteristics with one piezoelectric substrate 20.

  In the above description, the ladder-type circuit is formed by a plurality of resonators. However, a filter including a vertically coupled circuit may be formed by a plurality of resonators having the above-described configuration. Accordingly, the resonators constituting the longitudinally coupled circuit can be individually made to have desired characteristics, and a longitudinally coupled filter having desired filter characteristics can be easily realized by using one piezoelectric substrate.

10, 10A, 10B: surface acoustic wave filter 20, 20B: piezoelectric substrate 21, 21B: recess 30: protective film 31, 32, 33: resonator electrode 40: protective film 50: protective film 201: surface 310: resonator 311 312: IDT electrode 313: Reflector electrode 320: Resonator 321, 322: IDT electrode 323: Reflector electrode 330: Resonator 331, 332: IDT electrode 333: Reflector electrode 401: Top surface 411, 411B, 412 421, 422, 440: wiring electrodes P11, P12, P21, P22, P32, P33: input / output terminals

Claims (8)

A piezoelectric substrate having a recess on the surface;
A first resonator electrode formed on the bottom surface of the recess;
A second resonator electrode formed in a region different from the concave portion on the surface of the piezoelectric substrate;
A first surface formed on the surface of the piezoelectric substrate, covering the first resonator electrode and the second resonator electrode, and having a flat top surface opposite to the surface in contact with the surface of the piezoelectric substrate. A protective film;
A surface acoustic wave filter.   2. The surface acoustic wave filter according to claim 1, further comprising: a wiring electrode that connects the first resonator electrode and the second resonator electrode on the surface of the piezoelectric substrate. The first resonator including the first resonator electrode and the second resonator including the second resonator electrode constitute different filters.
The surface acoustic wave filter according to claim 1. The first resonator provided with the first resonator electrode and the second resonator provided with the second resonator electrode are connected in a ladder form to constitute one filter.
The surface acoustic wave filter according to claim 1. A first resonator including the first resonator electrode and a second resonator including the second resonator electrode are connected in a longitudinally coupled manner to form one filter.
The surface acoustic wave filter according to claim 1. The first resonator is a series arm resonator, and the second resonator is a parallel arm resonator.
The surface acoustic wave filter according to claim 4. The first resonator is a parallel arm resonator, and the second resonator is a series arm resonator;
The surface acoustic wave filter according to claim 4. A second protective film formed on the top surface of the first protective film;
The surface acoustic wave filter according to any one of claims 1 to 7.

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