JP2007110342A - Surface acoustic wave element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent surface acoustic wave element capable of reducing insertion loss deterioration and improving shoulder characteristics. <P>SOLUTION: An IDT electrode 3 comprising a pair of parallel bus bar electrodes 31a, 31b and a plurality of electrode fingers 32a, 32b is formed on a piezoelectric substrate 10, and the surface of the IDT electrode 3 is covered with a protective film 6. The protective film 6 is formed so that its thickness on a bus bar electrode region B on the bus bar electrodes 31a, 31b and its thickness on an electrode finger non-crossing region R in the electrode fingers 32a, 32b are thicker than its thickness on an electrode finger crossing region S in the electrode fingers 32a, 32b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave element used in a communication device such as a mobile phone.

In recent years, surface acoustic wave devices have been used in various types of communication devices, but due to the higher frequency and higher functionality of communication devices, inherent loss caused by piezoelectric substrate materials Therefore, the demand for reducing the loss of the surface acoustic wave device is increasing.
Further, the electrode finger pitch of the IDT (Inter Digital Transducer) electrode becomes smaller as the frequency becomes higher, and the film thickness of the IDT electrode becomes thinner. For example, the thickness of the IDT electrode of a 1.9 GHz surface acoustic wave element is designed to be about half that of a 900 MHz surface acoustic wave element, and there is no ohmic loss in a transmission line such as an extraction electrode connecting between filters. The higher the frequency, the larger. Therefore, the insertion loss tends to further deteriorate.

In order to avoid such deterioration of insertion loss, various proposals have been made. For example, a dual-mode surface acoustic wave resonator filter using three IDT electrodes on a piezoelectric substrate and utilizing two resonance modes of a longitudinal first-order mode and a longitudinal third-order mode having different resonance frequencies of the surface acoustic wave to be excited The following means for improving the insertion loss have been proposed.
FIG. 14A shows a plan view of an electrode structure of a conventional resonator type surface acoustic wave element. An IDT electrode 204 having a plurality of electrode fingers is disposed on the piezoelectric substrate. The IDT electrode 204 is composed of a pair of comb-like electrodes facing each other and meshed, and an electric field is applied to the pair of comb-like electrodes to generate a surface acoustic wave. When an electric signal is input from an input terminal 215 connected to the IDT electrode 204, the excited surface acoustic wave is propagated to the IDT electrodes 203 and 205 disposed on both sides of the IDT electrode 204. In addition, an electric signal is transmitted from each of the IDT electrodes 203 and 205 to the IDT electrodes 206 and 209 through the inter-stage connection electrodes, and surface acoustic waves are respectively excited. The surface acoustic wave is propagated to the IDT electrodes 207 and 208, and electrical signals are output to the output terminals 216 and 217 through the IDT electrodes 207 and 208.

As described above, the surface acoustic wave elements having the same characteristics are configured in a two-stage cascade connection, whereby mutual interference between the first-stage and second-stage standing waves can be reduced. Further, the signal attenuated at the first stage is further attenuated at the second stage, and the out-of-band attenuation can be improved by about twice.
In the figure, 210, 211, 212, and 213 are reflector electrodes, respectively, and surface acoustic waves are reflected by these reflector electrodes 210, 211, 212, and 213, and standing waves are formed between the reflector electrodes at both ends. Become. This standing wave mode includes a primary mode and its higher-order (third-order) mode by three IDT electrodes. Since the pass characteristics are obtained by the resonance generated in these modes, the insertion loss in the passband can be improved by controlling the peak position of the resonance frequency generated in these modes.

Conventionally, as shown in FIG. 14 (b), by providing narrow pitch portions of electrode fingers at the ends of adjacent IDT electrodes 207 and 208, the radiation loss of bulk waves between IDT electrodes is reduced, and the insertion loss is reduced. (See, for example, Patent Documents 1 and 2).
FIG. 15 is a plan view of an electrode structure of another conventional surface acoustic wave element. As another means for realizing the low loss, at least one of the bus bar electrodes (a wide electrode connected to one side of the electrode finger. The electrode finger extends in a direction perpendicular to the side surface of the bus bar electrode) 303 in the IDT electrode. The thickness of the part 315 is made larger than the thickness of the electrode finger 304. With this structure, the sound velocity of the surface acoustic wave propagating from the bus bar electrode 303 toward the outer side P becomes slower than the sound velocity of the surface acoustic wave propagating through the electrode finger, and the energy of the surface acoustic wave is reduced to the IDT electrode. It is said that it is easy to be confined in the inside, and low loss can be realized (for example, refer to Patent Document 3).
Japanese Patent Laid-Open No. 2002-9587 Special Table 2002-528987 Japanese Patent Laid-Open No. 2002-100532 Masanori Ueda, "High Performance SAW Antenna Duplexer using Ultra-Low-Loss Ladder Filter and DMS for 1.9GHz US PCS", in: Second International Symposium on Acoustic Wave Devices for Future Mobile Communication Systems 2004

  However, in the surface acoustic wave devices disclosed in Patent Documents 1 and 2, the surface acoustic wave between the IDT electrodes is inserted by mode conversion into a bulk wave (which means an elastic wave traveling inward from the surface of the piezoelectric substrate). Although it is possible to suppress the deterioration of the loss, it is almost perpendicular to the propagation direction of the surface acoustic wave in the IDT electrodes, between the adjacent IDT electrodes, and between the adjacent IDT electrodes and reflector electrodes (indicated by W in FIG. 5). The confinement of the surface acoustic wave energy in this direction (direction P shown in FIG. 15) is incomplete.

  That is, in the propagation direction of the surface acoustic wave, the reflector electrode can reflect the surface acoustic wave to confine energy. However, not only the propagation direction of the surface acoustic wave but also the optical observation of the propagation leakage of the surface acoustic wave causes leakage in the direction P substantially perpendicular to the propagation direction. Further, as a result of the simulation, when the sound velocity Vg on the electrode finger of the IDT electrode is slower than or equal to the sound velocity Vb on the bus bar electrode of the IDT electrode, leakage in a direction substantially perpendicular to the propagation direction of the surface acoustic wave occurs. It has been reported that this occurs (for example, see Non-Patent Document 1).

For this reason, it is necessary to sufficiently confine the energy of the surface acoustic wave even in a direction substantially perpendicular to the propagation direction of the surface acoustic wave.
In short, it is not sufficient to improve the insertion loss only by providing the narrow pitch portion of the electrode finger at the end of the adjacent IDT electrode like the surface acoustic wave devices disclosed in Patent Documents 1 and 2, Furthermore, it is necessary to suppress deterioration of insertion loss due to leakage in a direction perpendicular to the propagation direction of the surface acoustic wave.

  Further, in the surface acoustic wave device as disclosed in Patent Document 3, the region up to the other bus bar electrode 303 opposite to the tip of the electrode finger 304 formed on one bus bar electrode of the IDT electrode (“electrode finger non- The “intersection region R” (indicated by R in FIG. 15) is a region where no electrode is formed and does not contribute to the excitation of the surface acoustic wave. Therefore, the speed of sound in the electrode finger non-intersecting region R is faster than that of the electrode finger crossing portion S. The acoustic velocity of the electrode finger non-intersecting region R is faster than the acoustic velocity of the electrode intersecting region S that contributes to surface acoustic wave excitation, thereby suppressing leakage in a direction substantially perpendicular to the propagation direction of the surface acoustic wave. I can't do enough.

  The present invention has been proposed in view of the above-described conventional problems. The object of the present invention is to provide a high-quality surface acoustic wave device having excellent filter characteristics without causing deterioration of insertion loss and a communication using the same. To provide an apparatus.

  The surface acoustic wave device of the present invention includes a piezoelectric substrate, a pair of parallel bus bar electrodes formed on the piezoelectric substrate, and an IDT electrode including a plurality of electrode fingers alternately extending from the bus bar electrodes and meshing with each other. A surface acoustic wave element formed on the piezoelectric substrate and covering the surface of the IDT electrode, and the electrode finger non-intersection between the tip of the electrode finger and the bus bar electrode facing the surface acoustic wave element The thickness of the protective film in the region R and the thickness of the protective film on the bus bar electrode are larger than the thickness of the protective film in the electrode finger crossing region S where the electrode fingers extending from the pair of bus bar electrodes intersect. (Signs such as R and S are shown in the drawing. The same applies hereinafter).

FIG. 2 and FIG. 3 are schematic diagrams of the sound velocity distribution of the surface wave at the cross-sectional position of the IDT electrode (the cross-sectional direction is perpendicular to the propagation direction of the surface acoustic wave (hereinafter also referred to as “surface wave”)). .
FIG. 3 shows the sound velocity distribution when the thickness of the protective film in the conventional structure is the same for the bus bar electrode and the electrode finger (including when the protective film thickness is 0, that is, when the protective film is not formed). .
FIG. 2 shows the surface of the IDT electrode of the present invention when the thickness of the protective film on the bus bar electrode and on the electrode finger non-crossing region R is larger than the thickness of the protective film on the electrode finger crossing region S of the IDT electrode. It is the figure which represented the sound velocity distribution of the wave typically.

  In the case of FIG. 3, the speed of sound on the bus bar electrodes is equal to or faster than that of the electrode finger crossing region S that contributes to surface wave excitation. Therefore, the energy in the direction perpendicular to the propagation direction of the surface acoustic wave cannot be sufficiently confined. Furthermore, since the sound speed of the surface wave in the electrode finger non-intersection region R of the IDT electrode is higher than that in the electrode finger cross region S, it becomes difficult to suppress the leakage of the surface acoustic wave energy. Yes.

  On the other hand, in the case of FIG. 2, the film thickness of the protective film on the bus bar electrode of the IDT electrode and on the electrode finger non-crossing region R is larger than the film thickness of the protective film on the electrode finger crossing region S. The speed of sound is slow. With this structure, the sound velocity in the bus bar electrode of the IDT electrode that does not contribute to the excitation of the surface acoustic wave and the electrode finger non-intersection region R can be made slower than the sound velocity in the electrode finger intersection region S that contributes to the excitation of the surface acoustic wave, It is possible to provide a surface acoustic wave device in which the energy of the surface acoustic wave can be confined, the insertion loss is reduced, and the steepness of the filter characteristics in the pass band is improved.

  Further, according to the surface acoustic wave device of the present invention, as shown in FIG. 4, in the above-described configuration, the plurality of IDT electrodes are formed adjacent to each other with their bus bar electrodes aligned, and are further formed of an insulator. A film covers the piezoelectric substrate over the IDT interelectrode region U of the adjacent IDT electrode, and in the IDT interelectrode region U, the thickness of the protective film at the extension T of the bus bar electrode is the bus bar. When the thickness is greater than the thickness of the portion other than the extension portion of the electrode, the speed of sound of the surface acoustic wave of not only the IDT electrode but also the extension portion of the bus bar electrode in the IDT interelectrode region U is extended in the propagation direction of the electrode finger. It becomes slower than the sound velocity of the surface acoustic wave at the part. Accordingly, it is possible to provide a surface acoustic wave device that can prevent leakage of energy in a direction perpendicular to the propagation direction of surface acoustic waves even at locations where IDT electrodes are adjacent, and can sufficiently reduce insertion loss in filter characteristics. Can do.

  Further, according to the surface acoustic wave element of the present invention, as shown in FIG. 5, in the above configuration, the piezoelectric substrate is connected to a pair of parallel bus bar electrodes and the bus bar electrodes facing each other from the bus bar electrodes. A reflector electrode including a plurality of electrode fingers is formed adjacent to the IDT electrode with the bus bar electrode aligned with the bus bar electrode of the IDT electrode, and the protective film includes the adjacent IDT electrode and the The IDT electrode-reflector electrode region W between the reflector electrode and the surface of the reflector electrode are covered, and the bus bar electrode extension V in the IDT electrode-reflector electrode region W and the reflection The thickness of the protective film on the bus bar electrode of the reflector electrode is a portion other than the extension portion of the bus bar electrode in the IDT electrode-reflector electrode region W and the electrode of the reflector electrode. If in the area S 'on is larger than the thickness of the protective film, the following effects. That is, the speed of sound at the bus bar electrode extension in the IDT electrode-reflector electrode area W that does not contribute to excitation can be made slower than the speed of sound at the electrode finger area S ′. Therefore, the surface acoustic wave element can be provided in which the effect of confining the surface acoustic wave energy is improved, and the insertion loss in the filter characteristics is sufficiently reduced.

Further, according to the surface acoustic wave element of the present invention, in each of the configurations, it is desirable that the ratio of the thick part to the thin part of the protective film is 1.5 to 20 times.
According to the surface acoustic wave device of the present invention, in each of the above configurations, it is desirable that a dummy electrode be formed on the other bus bar electrode facing the tip of the electrode finger formed on one bus bar electrode of the IDT electrode. .

  FIG. 8 shows a schematic diagram of the sound velocity of the surface wave in the structure. By increasing the thickness of the protective film of the surface finger of the surface acoustic wave non-intersecting region R and intentionally forming a dummy electrode, the speed of sound in the electrode finger non-intersecting region R of the IDT electrode can be reduced. The speed of sound at locations that do not contribute to the excitation of surface acoustic waves can be sufficiently slowed, so that the effect of confining the energy of surface acoustic waves can be further improved, and the filter characteristics can be improved. It is possible to provide a surface acoustic wave device that has a significantly improved insertion loss.

  Further, according to the method for manufacturing a surface acoustic wave element of the present invention, the IDT electrode is covered with a protective film, and a portion of the protective film on the electrode finger crossing region S is etched and thinned. The surface acoustic wave device of the invention can be manufactured. With this manufacturing method, the thickness of the protective film on the electrode finger crossing region S can be controlled while keeping the thickness of the electrode finger constant without affecting the electrode finger of the IDT electrode by etching. By controlling the film thickness of the protective film, it is possible to obtain a surface acoustic wave device in which the acoustic velocity of the surface acoustic wave in the non-excited portion can be made slower than the acoustic velocity of the excited portion, and the insertion loss in the filter characteristics is improved. it can.

  When forming a plurality of adjacent IDT electrodes with the bus bar electrodes aligned with each other in the surface acoustic wave element, the piezoelectric substrate in the region U between adjacent IDT electrodes is covered with a protective film, and the region between the IDT electrodes A surface acoustic wave element can be manufactured by etching and thinning the portion between the electrode fingers of U. Also in this case, the film thickness of the protective film on the electrode finger crossing region S and in the inter-IDT electrode region U is controlled while keeping the film thickness of the electrode finger constant without affecting the electrode finger of the IDT electrode. be able to. Thereby, the speed of sound in the non-excited portion of the surface acoustic wave can be made slower than the speed of sound in the excited portion, and a surface acoustic wave element with improved insertion loss in the filter characteristics can be obtained.

  When a reflector electrode is further formed, a protective film covers the reflector electrode and the piezoelectric substrate between the adjacent IDT electrode and the reflector electrode, and the electrode finger of the reflector electrode is formed. A surface acoustic wave element can be manufactured by etching and thinning a region on the region of the region and a region of the region between the electrode fingers of the adjacent IDT electrode and the reflector electrode. Also in this case, similarly to the above, the thickness of the protective film at the above-described region can be controlled efficiently without affecting the electrode fingers of the IDT electrode by etching. Thereby, the speed of sound in the non-excited portion of the surface acoustic wave can be made slower than the speed of sound in the excited portion, and a surface acoustic wave element with improved insertion loss in the filter characteristics can be obtained.

  The communication device of the present invention is a communication device including a reception circuit and / or a transmission circuit (at least one of a reception circuit and a transmission circuit), and the surface acoustic wave element is connected to a circuit component of the reception circuit and / or a transmission circuit. It is included in circuit components. According to this communication device, by using the surface acoustic wave element of the present invention as described above for a communication device, a device that can satisfy the severe insertion loss that has been conventionally required can be obtained, and the sensitivity is remarkably good. A communication device can be realized.

Hereinafter, an embodiment of the present invention will be described taking a resonator type surface acoustic wave element as an example.
In the following drawings, the size of each electrode, the distance between the electrodes, the number of electrode fingers, the interval, and the like are schematically illustrated for explanation.
FIG. 1A shows a planar structure of a longitudinally coupled resonator type electrode formed on the piezoelectric substrate 10. FIG. 1B shows a cross-sectional structure taken along line AA in FIG.

The surface acoustic wave element has a plate-like piezoelectric substrate 10 and an IDT electrode 3 and reflector electrodes 1 and 5 formed on the main surface of the piezoelectric substrate 10.
The “main surface” in this specification refers to a surface on which the IDT electrode 3 and the reflector electrodes 1 and 5 on the surface of the piezoelectric substrate 10 are formed.
The piezoelectric substrate 10 is made of a piezoelectric material such as LiTaO ₃ single crystal, LiNbO ₃ single crystal, LiB ₄ O ₇ single crystal. By selecting these highly piezoelectric materials, the electromechanical coupling coefficient of the piezoelectric substrate 10 can be increased, and the group delay time temperature coefficient can be decreased.

  Moreover, the pyroelectric effect which arises in the piezoelectric substrate 10 can be remarkably reduced by generating oxygen defects or dissolving Fe or the like in these piezoelectric materials. As a result, the discharge due to the pyroelectric effect generated in the piezoelectric substrate 10 can be reduced, and the discharge breakdown of the electrode fingers of the IDT electrode 3 and the reflector electrodes 1 and 5 can be prevented. As a result, the reliability of the surface acoustic wave device is improved. Can be kept good.

  As shown in FIG. 1A, on the piezoelectric substrate 10, a pair of parallel bus bar electrodes 31a and 31b (referred to collectively as “bus bar electrodes 31”) and the inner surfaces of the bus bar electrodes 31a and 31b are perpendicular to each other. An IDT electrode 3 comprising a plurality of electrode fingers 32a and 32b (collectively referred to as “electrode fingers 32”) is formed. The plurality of electrode fingers 32 are arranged to engage with each other. The number of electrode fingers 32 actually ranges from several to several hundred.

Further, on the outside of the IDT electrode 3 in the surface acoustic wave propagation direction, a pair of parallel bus bar electrodes 11a and 11b (collectively referred to as “bus bar electrode 11”) and the bus bar electrodes 11a and 11b are adjacent to the IDT electrode 3. A reflector electrode 1 having a plurality of electrode fingers 12 formed therebetween is formed.
Further, on the outside of the other surface acoustic wave propagation direction of the IDT electrode 3, a pair of parallel bus bar electrodes 51a and 51b (collectively referred to as “bus bar electrode 51”) and the bus bar electrode 51a are adjacent to the IDT electrode 3. , 51b, the reflector electrode 5 in which a plurality of electrode fingers 52 are formed is formed.

The pair of bus bar electrodes 11a and 11b of the reflector electrode 1, the pair of bus bar electrodes 31a and 31b of the IDT electrode 3, and the pair of bus bar electrodes 51a and 51b of the reflector electrode 5 are aligned in the same direction. Is formed.
The IDT electrode 3 on the piezoelectric substrate 10 and the reflector electrodes 1 and 5 form a longitudinally coupled resonator type electrode.

  A region where the electrode fingers 32a and 32b extending from the pair of bus bar electrodes 31a and 31b intersect each other is referred to as an “electrode finger crossing region S”. A region from the tip of the electrode finger 32a, 32b formed on one bus bar electrode 31a or 31b of the IDT electrode 3 to the other bus bar electrode 31b or 31a opposite to the electrode finger 32a, 32b is referred to as an “electrode finger non-crossing region”. R ". A region where the bus bar electrodes 31a and 31b are formed is referred to as a “bus bar electrode region B”.

The IDT electrode 3 of the piezoelectric substrate 10 is covered with a protective film 6 made of a material such as SiO ₂ , SiN _x , Si, Al ₂ O ₃ or the like. With this protective film 6, it is possible to prevent energization due to conductive foreign substances and to improve power resistance. The protective film 6 also has a function of limiting the sound velocity of the surface acoustic wave, as will be described in detail later.
A rectangular frame-shaped annular electrode (not shown) is formed on the main surface of the piezoelectric substrate 10 so as to surround the surface acoustic wave element.

On the other hand, a mounting substrate (not shown) for mounting the surface acoustic wave element is provided with a predetermined conductor pad at a position facing the input / output terminal of the piezoelectric substrate 10. A predetermined annular conductor (not shown) is provided at a position facing the electrode.
The surface acoustic wave element on which these surface acoustic wave elements are formed is mounted face-down on a mounting substrate. That is, the annular electrode on the main surface of the piezoelectric substrate 10 is bonded to a predetermined annular conductor on the mounting substrate using a metal bonding material such as solder, and the main surface of the piezoelectric substrate 10 and the mounting surface of the mounting substrate The surface acoustic wave element is confined in the space surrounded by the annular electrode, and the input / output terminal is electrically connected to a predetermined conductor pad (not shown) on the mounting substrate side.

In this manner, a surface acoustic wave device including a surface acoustic wave element is manufactured. This surface acoustic wave element can cope with the recent miniaturization of communication devices, and as a result, the chip size can be reduced. Note that the mounting structure of the surface acoustic wave device of the present invention is not limited to the above-described sealing structure surrounded by the annular electrode or the like.
Hereinafter, a characteristic structure of the surface acoustic wave element will be described.

The electrode finger crossing region S, the electrode finger non-crossing region R, and the bus bar electrode region B of the IDT electrode 3 are covered with a protective film 6. As shown in FIG. 1B, the protective film 6 has a thickness on the bus bar electrode region B and a thickness on the electrode finger non-intersecting region R larger than the thickness on the electrode finger intersecting region S.
Due to the structure of the protective film 6 having the thickness changed in this way, the sound velocity in the bus bar electrode region B and the electrode finger non-intersection region R of the IDT electrode 3 that does not contribute to the surface acoustic wave excitation contributes to the surface acoustic wave excitation. It can be slower than the sound speed of the finger crossing region S.

FIG. 2 is a graph showing the sound velocity distribution of the surface acoustic wave. The vertical axis represents the sound velocity, and the horizontal axis represents the position on the cross section along the line AA of the surface of the piezoelectric substrate 10. It is shown that the acoustic velocity of the surface acoustic wave is lower than that of the electrode finger crossing region S by increasing the thickness of the protective film 6 on the bus bar electrode region B and the electrode finger non-crossing region R. .
On the other hand, FIG. 3 is a graph showing the sound velocity distribution of a conventional surface acoustic wave, and shows a case where a protective film is not formed on the IDT electrode. In this case, the sound speed is the same on the electrode finger crossing region S and the bus bar electrode region B, and the sound speed is increasing on the electrode finger non-crossing region R. Even when the protective film 6 is formed with the same thickness on the IDT electrode 3, a graph similar to that in FIG. 3 can be obtained.

By setting a step in the thickness of the protective film 6 as in the present invention, it is possible to confine the energy of the surface acoustic wave in the electrode finger crossing region S and suppress its leakage, and particularly reduce the insertion loss of the filter characteristics. In addition, shoulder characteristics in the pass band can be improved.
In particular, the ratio of the thick part to the thin part of the protective film 6 is preferably 1.5 to 20 times. When the thickness of the thick part of the protective film 6 is less than 1.5 times that of the thin part, the effect of confining the energy of the surface acoustic wave does not appear. When the thickness of the thick part of the protective film 6 is larger than 20 times that of the thin part, the film forming process of the protective film 6 requires a long time for film formation, which is not a practical process.

FIG. 4 shows a plan view of another structure of the surface acoustic wave device of the present invention.
In this figure, on the piezoelectric substrate 10, three IDT electrodes 2, 3, and 4 have one bus bar electrode 21a, 31a, 41a aligned so that the propagation directions of the surface acoustic waves are the same direction, and The other bus bar electrodes 21b, 31b, 41b are arranged to be aligned. Further, reflector electrodes 1 and 5 are arranged outside the IDT electrodes 2 and 4 at both ends.

The central IDT electrode 3 has one bus bar electrode 31a connected to the input terminal IN. The output from the other bus bar electrodes 21b and 41b of the IDT electrodes 2 and 4 at both ends are combined into one and connected to the output terminal OUT.
Each IDT electrode 2, 3 and 4 is opposed to the electrode fingers 22a, 32a and 42a formed on one of the bus bar electrodes 21a, 31a and 41a of the IDT electrodes 2, 3 and 4 in the same manner as described above. The region to the other bus bar electrode 21b, 31b, 41b and the region from the tip of the electrode fingers 22b, 32b, 42b formed on the other bus bar electrode 21b, 31b, 41b to the one bus bar electrode 21a, 31a, 41a facing each other Is referred to as “electrode finger non-intersecting region R”. A region where the electrode fingers 22, 32, 42 extending from the pair of bus bar electrodes 21, 31, 41 intersect is referred to as an “electrode finger crossing region S”. A region where the bus bar electrodes 21, 31 and 41 are formed is referred to as a “bus bar electrode region B”.

An area between adjacent IDT electrodes is referred to as an “IDT interelectrode area U”, and an area on the extension of the bus bar electrode area B among the IDT interelectrode areas U is an “IDT interelectrode bus bar electrode extension area T”. That's it.
In the longitudinally coupled resonator type electrode of FIG. 4, the electrode finger crossing region S, the electrode finger non-crossing region R, and the bus bar electrode region B of the IDT electrodes 2, 3, 4 are all made of SiO ₂ , as in the structure of FIG. 1. , SiN _x , Si, Al ₂ O ₃ or the like. Further, the protective film 6 is also formed in the IDT interelectrode region U between adjacent IDT electrodes.

As in the structure of FIG. 1, the thickness of the protective film 6 on the bus bar electrode region B and the thickness of the protective film 6 on the electrode finger non-intersection region R in the IDT electrodes 2, 3, and 4 It is thicker than the upper protective film 6.
Further, in the structure of FIG. 4, in the IDT interelectrode region U, in the IDT interelectrode bus bar electrode extension region T, the protective film 6 has a thicker structure than the remaining IDT interelectrode region U. ing.

  Thereby, in the IDT inter-electrode region U, the sound velocity of the surface acoustic wave in the IDT inter-electrode bus bar electrode extension region T becomes slower than the sound velocity of the surface acoustic wave in the IDT inter-electrode region U other than the IDT inter-electrode bus bar electrode extension region T. Also, leakage of energy from the propagation direction of the surface acoustic wave to the vertical direction can be prevented at the adjacent portions between the IDT electrodes 2 and 3 and between the IDT electrodes 3 and 4. Therefore, it is possible to suppress the leakage of the surface acoustic wave, and it is possible to provide a surface acoustic wave element in which the insertion loss of the filter characteristics is particularly reduced.

FIG. 5 is a plan view showing still another example of the surface acoustic wave device of the present invention.
In this figure, the arrangement of the IDT electrodes 2, 3, 4 and the reflector electrodes 1, 5 is the same as in FIG.
A region of the electrode fingers 12 and 52 formed between the bus bar electrodes 11a and 11b of the reflector electrodes 1 and 5 and between the bus bar electrodes 51a and 51b is referred to as an “electrode finger region S ′”.

An area where the bus bar electrodes 11a, 11b, 51a, 51b of the reflector electrodes 1 and 5 are formed is referred to as a “bus bar electrode area B”.
The region between the reflector electrodes 1 and 5 and the IDT electrodes 2 and 4 adjacent to the reflector electrode 1 and 5 is referred to as an “IDT electrode-reflector electrode region W”. The region on the extension of the bus bar electrodes 11a, 11b, 51a, 51b is referred to as “IDT electrode-reflector electrode bus bar electrode extended region V”.

The protective film 6 is not only formed over the IDT electrodes 2, 3, 4, but also covers the reflector electrodes 1, 5, and further covers the surface of the IDT electrode-reflector electrode region W.
In the IDT electrodes 2, 3, and 4, as in FIG. 4, the thickness of the protective film 6 on the bus bar electrode region B and the thickness on the electrode finger non-intersection region R are thicker than the thickness on the electrode finger intersection region S. In the IDT interelectrode region U, in the IDT interelectrode bus bar electrode extension region T, the protective film 6 is thicker than the remaining IDT interelectrode region U.

  Further, in the configuration of FIG. 5, the reflector electrodes 1 and 5 have a structure in which the thickness on the bus bar electrode region B is thicker than the thickness of the electrode finger region S ′, and the IDT electrode-reflector electrode bus bar electrode. The thickness of the protective film 6 in the extended region V is thicker than the thickness on the IDT electrode-reflector electrode region W excluding the IDT electrode-reflector electrode bus bar electrode extended region V.

  With this structure, the sound velocity on the bus bar electrode region B of the reflector electrodes 1 and 5 that do not contribute to excitation can be made slower than the sound velocity of the surface acoustic wave in the electrode finger region S ′ of the reflector electrodes 1 and 5. The sound velocity on the IDT electrode-reflector electrode bus bar electrode extension region V is made slower than the sound velocity on the IDT electrode-reflector electrode region W excluding the IDT electrode-reflector electrode bus bar electrode extension region V. be able to.

Therefore, the leakage of propagation of the surface acoustic wave energy in the form of a beam does not occur, it becomes possible to improve the confinement effect of the surface acoustic wave energy, and the insertion loss in the filter characteristics can be sufficiently reduced, and the passband It is possible to provide a surface acoustic wave device with improved shoulder characteristics.
FIG. 6 is a plan view showing a modification of the surface acoustic wave element according to the present invention.

In this configuration, in addition to the configuration of FIG. 5 described above, the IDT electrode 3 on the input side and the pair of IDT electrodes 2 and 4 adjacent to the IDT electrode 3 are arranged in a direction orthogonal to the propagation direction. Reflector electrodes 12 and 13 each having four or more long electrode fingers arranged in the propagation direction are provided.
The thickness of the protective film 6 on the bus bar electrodes of the reflector electrodes 12 and 13 and the thickness of the protective film 6 in the region between adjacent IDT electrodes on the extension of the bus bar electrode are determined by the electrode finger region S ′. The structure is thicker than the above thickness. As a result, similarly to the structures of FIGS. 1, 4, and 5, it is possible to improve the effect of confining the energy of the surface acoustic wave, and to improve the insertion loss in the filter characteristics.

Further, the distance between the electrode fingers adjacent to each other of the reflector electrode 12 is gradually shortened from the electrode fingers located at both ends of the reflector electrode 12 toward the electrode finger located at the center. The same applies to the reflector electrode 13.
Therefore, it becomes possible to prevent radiation loss of the surface acoustic wave to the bulk wave, and to further finely adjust the frequency between the first-order and third-order modes and their harmonic modes. Thus, a surface acoustic wave device having good electrical characteristics can be realized.

Next, FIG. 7A shows a plan view of still another embodiment of the surface acoustic wave device of the present invention, and FIG. 7B shows a cross-sectional view taken along the line AA of FIG. 7A. .
Explaining the difference between this configuration and the configuration shown in FIG. 5, the electrode 33b is projected from the other bus bar electrode 31b at a position facing the tip of the electrode finger 32a extending from one bus bar electrode 31a of the central IDT electrode 3. At the same time, the electrode 33a is protruded from the one bus bar electrode 31a at a position facing the tip of the electrode finger 32b extending from the other bus bar electrode 31b of the central IDT electrode 3. The protruding electrodes 33a and 33b are referred to as “dummy electrodes 33a and 33b”. The dummy electrodes 33a and 33b and the electrode fingers 32b and 32a opposed to the dummy electrodes 33a and 33b are close to each other but never come into contact with each other. The dummy electrodes 33a and 33b are also included in the electrode finger non-intersection region R.

Also in the IDT electrodes 2 and 4 arranged outside the central IDT electrode 3, a dummy electrode is formed as in the IDT electrode 3.
The protective film 6 is thicker than the thickness on the electrode finger intersection region S on the bus bar electrode region B of the IDT electrodes 2, 3 and 4 and on the electrode finger non-intersection region R.
Also in the IDT inter-electrode bus bar electrode extension region T, the protective film 6 has a structure thicker than the thickness of the IDT inter-electrode region U excluding the IDT inter-electrode bus bar electrode extension region T.

In the reflector electrodes 1 and 5, the thickness of the protective film 6 on the bus bar electrodes 11 and 51 and the thickness of the protective film 6 in the bus bar electrode extension region V between the IDT electrode and the reflector electrode are determined by the electrode finger region S '. The structure is thicker than the upper thickness and the thickness on the IDT electrode-reflector electrode region W excluding the IDT electrode-reflector electrode bus bar electrode extension region V.
With this structure, dummy electrodes 33a and 33b are intentionally formed, and the thickness of the protective film 6 in the electrode finger non-crossing region R is increased, whereby the IDT electrodes 2, 3, and 4 in the electrode finger non-crossing region R are formed. The speed of sound can be made slower than the speed of sound in the electrode finger crossing region S.

FIG. 8 is a graph showing the sound velocity distribution of the surface acoustic wave. The vertical axis represents the sound velocity, and the horizontal axis represents the position on the cross section along the line AA of the surface of the piezoelectric substrate 10. It is shown that the acoustic velocity of the surface acoustic wave is lower than that of the electrode finger crossing region S by increasing the thickness of the protective film 6 on the bus bar electrode region B and the electrode finger non-crossing region R. .
Accordingly, it is possible to further improve the effect of confining the energy of the surface acoustic wave, and it is possible to provide a surface acoustic wave element in which the insertion loss in the filter characteristics is remarkably improved.

FIG. 9 shows a modification of the embodiment of the surface acoustic wave device of the present invention.
9 is different from the configuration of FIG. 7 in that the IDT electrode bus bar electrode extension region T of the adjacent IDT electrodes 2 and 3 is extended to the extension portion of the electrode finger non-intersection region R and adjacent. This is that the IDT interelectrode bus bar electrode extension region T of the IDT electrodes 3 and 4 is extended to the extension portion of the electrode finger non-intersection region R. Hereinafter, these expanded IDT inter-electrode bus bar electrode extension regions T are referred to as “IDT inter-electrode bus bar electrode extension regions T ′”.

In addition, the IDT electrode-reflector electrode bus bar electrode extended region V is also extended to the extended portion of the electrode finger non-intersecting region R in the same manner as described above, and this IDT electrode-reflector electrode bus bar electrode is expanded. The extension region V is referred to as “IDT electrode-reflector electrode bus bar electrode extension region V ′”.
In the structure of FIG. 9, the region where the thickness of the protective film 6 is thicker is the IDT electrode bus bar electrode extension region T ′ and the IDT electrode-reflector electrode bus bar electrode extension compared to the structure of FIG. It extends to the region V ′.

Further, in the reflector electrodes 1 and 5, the region where the thickness of the protective film 6 is large extends to the extension of the electrode finger non-intersection region R.
Thereby, since the portion where the protective film 6 is formed is widened, the speed of sound of the surface acoustic wave in the electrode finger crossing region S is further reduced, and the energy of the surface acoustic wave can be confined more effectively. The insertion loss in the filter characteristics can be greatly improved.

Next, FIGS. 10A to 10D show a method for manufacturing a surface acoustic wave device according to the present invention in cross-sectional views for each process.
Hereinafter, the manufacturing process of the IDT electrode 3 in FIG. 1 will be described. However, the IDT electrode and the reflector electrode other than the IDT electrode 3 are formed at the same time as the IDT electrode 3, and the manufacturing process is exactly the same as the IDT electrode 3. .

10A to 10D are taken along the line BB in FIG. 1 parallel to the propagation direction of the surface acoustic wave.
First, as shown in FIG. 10A, the conductor layer 30 constituting the IDT electrode 3 is formed on the piezoelectric substrate 10. Here, as the piezoelectric substrate 10, a lithium tantalate single crystal, a lithium niobate single crystal, a lithium tetraborate single crystal, or the like can be used. Further, the conductor layer 30 on the piezoelectric substrate 10 is made of aluminum, aluminum alloy, copper, copper alloy, gold, gold alloy, tantalum, tantalum alloy, or a laminated film made of these materials, and these materials and titanium, chromium. A laminated film with a material such as can be used. As a method for forming the conductor layer 30, a sputtering method or an electron beam evaporation method can be used.

Next, the conductor layer 30 is patterned into a pair of parallel bus bar electrodes 31a, 31b and a plurality of electrode fingers 32a, 32b extending from the respective bus bar electrodes 31a, 31b to form an IDT electrode 3.
In FIG. 10B, a portion of the electrode finger 32 to be patterned is drawn.
As a method of patterning the conductor layer 30, there is a method of performing photolithography after the formation of the conductor layer 30, and then performing RIE (Reactive Ion Etching) or wet etching. Alternatively, a resist is formed on one main surface of the piezoelectric substrate 10 before the conductor layer 30 is formed and photolithography is performed to open a desired pattern. Then, the conductor layer 30 is formed, and then the resist is formed on unnecessary portions. You may perform the lift-off process which removes the whole conductor layer 30 formed into a film.

Next, as shown in FIG. 10C, the IDT electrode 3 is covered with a protective film 6. As the material of the protective film 6, silicon, silica, or the like can be used. As a film forming method, a sputtering method, a CVD (Chemical Vapor Deposition) method, an electron beam evaporation method, or the like can be used.
Next, as shown in FIG.10 (d), the part on the electrode finger crossing area | region S in the electrode fingers 32a and 32b of the protective film 6 is etched and thinned. As a method of etching the protective film 6, there is a method of performing dry etching such as RIE or wet etching. By using this manufacturing method, the film thickness of the protective film 6 on the electrode finger crossing region S is controlled while keeping the film thickness of the electrode finger 32 constant without affecting the electrode finger 32 of the IDT electrode 3 by etching. can do.

FIGS. 11A to 11D show another method for manufacturing the surface acoustic wave device of the present invention in cross-sectional views for each process.
In FIG. 11, the manufacturing process of the IDT electrode 4 and the reflector electrode 5 of FIG. 5 will be described. However, the IDT electrode and the reflector electrode other than the IDT electrode 4 and the reflector electrode 5 are the same as the IDT electrode 4 and the reflector electrode 5. They are formed at the same time, and their manufacturing processes are the same as those of the IDT electrode 4 and the reflector electrode 5.

11A to 11D are taken along the line BB in FIG. 5 which is parallel to the propagation direction of the surface acoustic wave.
First, as shown in FIG. 11A, the conductor layer 30 is formed on the piezoelectric substrate 10.
Next, the conductor layer 30 is patterned into a pair of parallel bus bar electrodes 41a, 41b and a plurality of electrode fingers 42a, 42b extending from the respective bus bar electrodes 41a, 41b to form the IDT electrodes 4, The conductor layer 30 is patterned into a pair of parallel bus bar electrodes 51a, 51b and a plurality of electrode fingers 52 extending from the respective bus bar electrodes 51a, 51b so that the bus bar electrodes 51a, 51b are the same as the IDT electrode 4 described above. A reflector electrode 5 adjacent to the IDT electrode 4 is formed so as to be aligned with the bus bar electrodes 41a and 41b.

FIG. 11B depicts a cross section of the electrode fingers 42 and 52 to be patterned. Between the IDT electrode 4 and the reflector electrode 5 is an IDT electrode-reflector electrode region W. Next, as shown in FIG. 11 (c), the IDT electrode 4 and the reflector electrode 5 and the IDT electrode-reflector electrode region W are covered with a protective film 6.
As shown in FIG. 11 (d), a part on the electrode finger crossing region S in the electrode finger 42 of the IDT electrode 4 of the protective film 6, a part on the electrode finger region S ′ of the electrode finger 52 of the reflector electrode 5, Further, the IDT electrode 4 and reflector electrode 5 adjacent IDT electrode-reflector electrode region W (excluding the bus bar electrode region B of the reflector electrode 5) are etched and thinned. As a result, as in FIG. 10, the film thickness of the protective film 6 in the above-described region can be efficiently controlled collectively without affecting the electrode fingers 42 of the IDT electrode 4 by etching.

  In the method for manufacturing a surface acoustic wave element described above, the thickness of the electrode finger crossing region S is adjusted by cutting the conductor layer 30. However, by further laminating the conductor layer 30 in the electrode finger non-intersection region R and the bus bar electrode region B, it is possible to control the thickness to be increased. As a method for increasing the thickness of a part of the conductor layer 30, Al or a metal having a density higher than that of Al may be formed and stacked in the electrode finger non-intersection region R or the bus bar electrode region B.

The surface acoustic wave element of the present invention can be applied to a communication device.
That is, in a communication apparatus including one or both of a reception circuit and a transmission circuit, the surface acoustic wave element of the present invention can be used as a bandpass filter included in these circuits.
The transmission circuit is, for example, a circuit that places a transmission signal on a carrier frequency with a mixer, attenuates an unnecessary signal with a bandpass filter, then amplifies the transmission signal with a power amplifier, and transmits it from an antenna through a duplexer. is there. The receiving circuit receives the received signal with an antenna, amplifies the received signal that has passed through the duplexer with a low noise amplifier, then attenuates an unnecessary signal with a bandpass filter, and separates the signal from the carrier frequency with a mixer. A circuit for extracting a signal.

If the surface acoustic wave element of the present invention is employed, an excellent communication device with improved sensitivity can be provided.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, in the example described so far, the protective film 6 is formed on the electrode finger crossing region S of the IDT electrode and the reflector electrode, but the protective film 6 is not formed on the electrode finger crossing region S. It may be adopted. In addition, various modifications can be made within the scope of the present invention.

Next, an embodiment that further embodies the present invention will be described.
<Production>
The surface acoustic wave device shown in FIGS. 5 and 7 was specifically manufactured.
The one having the electrode finger pattern shown in FIG. 5 is referred to as Example 1, and the one using the dummy electrode shown in FIG.

In both Examples 1 and 2, IDT electrodes 2, 3 and 4 made of Al (99% by mass) -Cu (1% by mass) are formed on a LiTaO ₃ single crystal piezoelectric substrate 10 having a 38.7 ° Y-cut in the X direction. A fine electrode pattern of the reflector electrodes 1 and 5 was formed.
For pattern production, photolithography was performed using a sputtering apparatus, a reduction projection exposure machine (stepper), and an RIE (Reactive Ion Etching) apparatus.

  First, the piezoelectric substrate 10 was ultrasonically cleaned with acetone / IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the piezoelectric substrate 10 with a clean oven, an electrode was formed. A sputtering apparatus was used for film formation of the electrode, and a material composed of an Al (99 mass%)-Cu (1 mass%) alloy was used. The electrode film thickness at this time was about 0.15 μm.

Next, a photoresist is spin-coated to a thickness of about 0.5 μm, patterned into a desired shape by a reduction projection exposure apparatus (stepper), and an unnecessary portion of the photoresist is dissolved with an alkaline developer by a developing device, and then desired. After revealing the pattern, the electrode film was etched by the RIE apparatus to finish the patterning, and the electrode pattern of the longitudinally coupled resonator type electrode was obtained.
Thereafter, a protective film 6 was formed on predetermined regions of the IDT electrodes 2, 3, 4 and the reflector electrodes 1, 5. That is, SiO ₂ was formed to a thickness of about 1.0 μm on the electrode pattern and the piezoelectric substrate 10 by a CVD (Chemical Vapor Deposition) apparatus.

  Thereafter, the photoresist is patterned by photolithography, and the portion of the protective film on the electrode finger crossing region S and the portion of the region between the electrode fingers of the IDT interelectrode region U and the IDT electrode-reflector electrode region W are formed by the RIE apparatus. The thickness of the protective film 6 was reduced by etching. The film thickness after etching was 0.01 μm. At the same time, the protective film 6 in the electrode pad portion in the flip chip mounting was opened.

Thereafter, an electrode mainly composed of Al was formed using a sputtering apparatus. The electrode film thickness at this time was about 1.0 μm. Thereafter, the photoresist and unnecessary portions of Al were simultaneously removed by a lift-off method to complete a pad for forming a flip chip bump.
Next, a flip-chip bump made of Au was formed on the pad using a bump bonding apparatus. The bump had a diameter of about 80 μm and a height of about 30 μm.

Next, the piezoelectric substrate 10 was diced along dicing lines and divided into chips. Thereafter, each chip was bonded to the mounting substrate with the flip-chip mounting apparatus with the electrode formation surface facing down. Thereafter, baking was performed in an N ₂ atmosphere to complete a surface acoustic wave device. The package used was a 2.5 × 2.0 mm square ceramic laminated structure.
As a comparative sample, there is also a comparative example in which the fine electrode pattern of the IDT electrodes 2, 3, 4 and the reflector electrodes 1, 5 shown in FIG. 5 is formed, and the film thickness of the protective film 6 to be coated is made constant at 0.01 μm. Fabrication was performed in the same process as described above.

<Measurement / Evaluation>
Next, the characteristics of the surface acoustic wave device in this example were measured.
A signal of 0 dBm was input to the surface acoustic wave element, and measurement was performed under the conditions of a frequency of 1760 MHz to 2160 MHz and a measurement point of 800 points. The number of samples is 30, and the measuring instrument is a multiport network analyzer E5071A manufactured by Agilent Technologies.

The frequency characteristic graph of the insertion loss near the passband is shown in FIGS.
As shown by the solid line in FIG. 12, the filter characteristic of Example 1 is an insertion loss of 2.23 dB, and the ripple (difference between the maximum value and the minimum value of the attenuation in the passband) is 0.20 dB, which is very high. It showed good characteristics. On the other hand, in the filter characteristics of the comparative example, the insertion loss was 2.35 dB and the ripple was 0.30 dB as shown by the broken line in FIG.

Further, FIG. 13 shows a frequency characteristic graph in the vicinity of the passband comparing Example 2 and the comparative example.
The insertion loss of Example 2 was 2.13 dB as shown by the solid line in FIG. 13, and the ripple was 0.30 dB. The insertion loss of Example 2 is reduced as compared with the insertion loss of Example 1, and it can be seen that the insertion loss can be further improved by adding a dummy electrode.
As described above, in this example, it was possible to realize a surface acoustic wave device with reduced insertion loss and ripple in the filter characteristics and improved shoulder characteristics in the passband.

It is a figure which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film, (a) is a top view of the piezoelectric substrate in which the electrode was formed, (b) is an AA sectional view. is there. FIG. 2 is a diagram schematically showing a sound velocity distribution of a surface acoustic wave in a structural example of an electrode and a protective film of the surface acoustic wave element of the present invention. It is a diagram which shows typically the sound velocity distribution of the surface acoustic wave in the electrode structure of the conventional surface acoustic wave element. It is a top view which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film. It is a top view which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film. It is a top view which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film. It is a figure which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film, (a) is a top view of the piezoelectric substrate in which the electrode was formed, (b) is an AA sectional view. is there. FIG. 2 is a diagram schematically showing the speed of sound of a surface acoustic wave in a structural example of an electrode and a protective film of the surface acoustic wave element of the present invention. It is a top view which shows typically the structural example of the electrode of the surface acoustic wave element of this invention, and a protective film. (A)-(d) is sectional drawing for every process which shows an example of the manufacturing method of the surface acoustic wave element of this invention, respectively. (A)-(d) is sectional drawing for every process which shows an example of the manufacturing method of the surface acoustic wave element of this invention, respectively. It is a diagram which shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave element in Example 1, and its vicinity. It is a diagram which shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave element in Example 2, and its vicinity. It is a figure which shows typically the example of an electrode structure of the conventional surface acoustic wave element, (a) is a top view of an electrode structure, (b) is a diagram which illustrates typically the relationship between an electrode position and an electrode finger pitch. It is. It is a top view which shows typically the example of an electrode structure of the conventional surface acoustic wave element.

Explanation of symbols

1, 5 Reflector electrodes 2, 3, 4 IDT electrode 6 Protective film 10 Piezoelectric substrates 11a, 11b, 21a, 21b, 31a, 31b, 41a, 41b, 51a, 51b Bus bar electrodes 12, 22a, 22b, 32a, 32b, 42a, 42b, 52 Electrode fingers 33a, 33b Dummy electrodes

Claims (9)

A piezoelectric substrate;
An IDT electrode including a pair of parallel bus bar electrodes formed on the piezoelectric substrate and a plurality of electrode fingers alternately extending from the bus bar electrodes;
A surface acoustic wave device comprising a protective film formed on the piezoelectric substrate and covering a surface of the IDT electrode,
The electrode in which the thickness of the protective film in the electrode finger non-intersection region between the tip of the electrode finger and the bus bar electrode facing the electrode finger, and the thickness of the protective film on the bus bar electrode extend from the pair of bus bar electrodes A surface acoustic wave device characterized by being thicker than the thickness of the protective film in an electrode finger crossing region where fingers cross each other.   A plurality of the IDT electrodes are formed adjacent to each other with their bus bar electrodes aligned, and the protective film covers the piezoelectric substrate over the region between the IDT electrodes of the adjacent IDT electrodes, and between the IDT electrodes 2. The surface acoustic wave device according to claim 1, wherein in the region, the thickness of the protective film in the extended portion of the bus bar electrode is larger than the thickness in a portion other than the extended portion of the bus bar electrode. On the piezoelectric substrate, a reflector electrode including a pair of parallel bus bar electrodes and a plurality of electrode fingers connected from the respective bus bar electrodes to the opposite bus bar electrode aligns the bus bar electrode with the bus bar electrode of the IDT electrode. And adjacent to the IDT electrode,
The protective film covers the IDT electrode-reflector electrode region between the adjacent IDT electrode and the reflector electrode, as well as the surface of the reflector electrode,
The extension of the bus bar electrode in the IDT electrode-reflector electrode region and the thickness of the protective film on the bus bar electrode of the reflector electrode are other than the extension of the bus bar electrode in the IDT electrode-reflector electrode region. 3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave element is thicker than a thickness of the protective film on a portion and a region of the electrode finger of the reflector electrode.   The surface acoustic wave device according to any one of claims 1 to 3, wherein a ratio of a thickness of the thick part to the thin part of the protective film is 1.5 to 20 times.   The elastic surface according to any one of claims 1 to 4, wherein a dummy electrode facing the tip of the electrode finger formed on one of the bus bar electrodes of the IDT electrode is formed on the other bus bar electrode. Wave element. (A) forming a conductor layer on the piezoelectric substrate;
(B) forming the IDT electrode by patterning the conductor layer so as to form a pair of parallel bus bar electrodes and a plurality of electrode fingers extending from the bus bar electrodes alternately;
(C) coating the IDT electrode with a protective film;
(D) A method of manufacturing a surface acoustic wave device, comprising: a step of etching and thinning a portion of the protective film on the electrode finger crossing region. The step (b) includes a step of forming a plurality of adjacent IDT electrodes by aligning the bus bar electrodes.
The step (c) includes a step of covering the piezoelectric substrate in a region between adjacent IDT electrodes with a protective film,
The method of manufacturing a surface acoustic wave device according to claim 6, wherein the step (d) includes a step of etching and thinning a portion between the electrode fingers in the adjacent IDT electrode region. In the step (b), the conductor layer is patterned so as to form a pair of parallel bus bar electrodes and a plurality of electrode fingers extending from the bus bar electrodes to the bus bar electrodes facing each other. Forming a reflector electrode adjacent to the IDT electrode in alignment with the bus bar electrode of an electrode;
The step (c) includes a step of coating a protective film on the reflector electrode and on the piezoelectric substrate between the adjacent IDT electrode and the reflector electrode,
The step (d) includes a step of etching and thinning a portion of the reflector electrode on a region of the electrode finger and a portion of the region between the electrode finger of the IDT electrode and the reflector electrode adjacent to each other. A method for manufacturing a surface acoustic wave device according to claim 6 or 7. A communication device including a receiving circuit and / or a transmitting circuit,
A communication device comprising the surface acoustic wave device according to claim 1 in a circuit component of a receiving circuit and / or a circuit component of a transmitting circuit.

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