JP2008085720A - Surface acoustic wave apparatus and communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave apparatus which suppresses generation of spurious near a pass band and is compact, and to provide a communication apparatus. <P>SOLUTION: The surface acoustic wave apparatus includes three IDT electrodes 2-4, 5-7 along a propagation direction of a surface acoustic wave on a piezoelectric substrate 1 and reflector electrodes 8, 10 disposed at both sides of the IDT electrodes. First and second surface acoustic wave devices 14, 15 connected in parallel to an unbalanced signal terminal 21 are formed side by side in the propagation direction, balanced signal terminals 22, 23 are connected to the central IDT electrodes 3, 6 of the first and second surface acoustic wave devices 14, 15. For the first and second surface acoustic wave devices 14, 15, a reflector electrode at a position where they are adjacent to each other, is composed of a common reflector electrode 30 and an electrode finger pitch at its central portion is formed longer than electrode finger pitches of the IDT electrodes 4, 5 adjacent to the common reflector electrode 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device such as a surface acoustic wave filter or a surface acoustic wave resonator used in a mobile communication device such as a mobile phone, and a communication device including the surface acoustic wave device. The present invention relates to a surface acoustic wave device having excellent external damping characteristics.

  As mobile terminal devices have been reduced in size and weight, the number of built-in circuits has been increasing due to the multi-band and multi-functionality of mobile terminal devices corresponding to a plurality of communication systems. For this reason, there is a strong demand for small electronic components that can be surface-mounted to improve the mounting density of the electronic components used. A surface acoustic wave filter which is a key part of a portable terminal device is also required to have a small surface acoustic wave filter which can be surface-mounted with low loss and a cutoff characteristic outside the passband.

  In response to the demand for miniaturization, a surface acoustic wave device has conventionally been widely used as a ceramic package type in the mounting form. However, a configuration as shown in FIG. 6 has been widely used in recent years. Yes. That is, the main surface of the piezoelectric substrate 51 on which the surface pattern of the surface acoustic wave element is formed is opposed to the upper surface of the circuit board 52, and the electrode pattern of the surface acoustic wave element and the wiring conductor of the circuit board 52 are bumped. A CSP (Chip Scale Package) type surface acoustic wave device that is electrically connected through a connection body 53, flip-chip mounted by face-down mounting, and hermetically sealed with a sealing resin 54 or the like is surface mountable and compact. Can be realized.

  In recent years, in order to reduce the size, weight, and cost of mobile communication devices, the number of parts used has been reduced, and a new function has been required for the surface acoustic wave filter. One of the requirements is that it can be configured as an unbalanced input-balanced output type or a balanced input-unbalanced output type. Here, the balanced input or balanced output means that a signal is input or output as a potential difference between two signal lines, and the signals of each signal line have the same amplitude and the phases are reversed. On the other hand, unbalanced input or unbalanced output means that a signal is input or output as the potential of one line with respect to the ground potential.

  FIG. 5 is a plan view schematically showing an electrode structure of a surface acoustic wave filter having a conventional balance-unbalance conversion function. The longitudinally coupled resonator type surface acoustic wave elements 212 and 213 as surface acoustic wave filters connected in parallel on the piezoelectric substrate 201 are arranged, and each of the longitudinally coupled resonator type surface acoustic wave elements 212 and 213 includes three IDTs. The electrodes 202, 203, 204 and 205, 206, 207, and reflector electrodes 208, 209, 210, 211 arranged on both sides thereof are configured.

  The longitudinally coupled resonator type surface acoustic wave elements 212 and 213 are connected in parallel to the unbalanced signal terminal 214. The IDT electrodes 202 and 204 and the IDT electrodes 205 and 207 connected to the unbalanced signal terminal 214 apply an electric field to a pair of mutually opposed comb-like electrodes to excite surface acoustic waves. The excited surface acoustic wave propagates to the center IDT electrodes 203 and 206. In addition, the phase of the center IDT electrode 203 is a reverse phase that is 180 ° different from the phase of the center IDT electrode 206, and finally from one of the comb-like electrodes of the center IDT electrodes 203 and 206. A signal is transmitted to the balanced output signal terminals 215 and 216 and is output in a balanced manner. With such a configuration, a balanced-unbalanced conversion function is realized. In addition, compared with a longitudinally coupled resonator type surface acoustic wave filter of a type in which two stages are cascade-connected, the crossing width of the electrode fingers of the IDT electrode is reduced to half that of the conventional one, and further, the longitudinally coupled resonators are connected in parallel. Resistance loss in the surface acoustic wave filter can be reduced, and a low-loss longitudinally coupled resonator surface acoustic wave filter can be realized (see, for example, Patent Document 1).

As for downsizing of the surface acoustic wave element, one reflector electrode constituting a plurality of two-port surface acoustic wave resonators is shared as a reflector electrode of the plurality of two-port surface acoustic wave resonators. A configuration has been proposed in which the grating electrode of the reflector electrode is weighted (see, for example, Patent Document 2).
JP 2001-308672 A JP 2003-174350 A

  By using the conventional surface acoustic wave filter as shown in FIG. 6, the mounting form can be reduced in size, but in order to satisfy the demand for further reduction in size, the surface acoustic wave element chip itself needs to be further downsized. was there.

  Further, by using a conventional surface acoustic wave filter as shown in FIG. 5 described in Patent Document 1, an unbalance-balance conversion function can be realized. However, since two reflector electrodes exist at adjacent positions in two longitudinally coupled resonator type surface acoustic wave elements connected in parallel, the structure is disadvantageous for downsizing the surface acoustic wave device. In addition, since two longitudinally coupled resonator type surface acoustic wave elements connected in parallel to the unbalanced signal terminal are arranged adjacent to each other in the propagation direction of the surface acoustic wave, the elastic surface to be excited The waves interfere with each other, and in particular, there is a problem that the frequency characteristics of the surface acoustic wave device are deteriorated, such as spurious in the low frequency side out-of-passband attenuation characteristics near the passband.

  In addition, one reflector electrode constituting a plurality of conventional two-port surface acoustic wave resonators described in Patent Document 2 is used as a reflector electrode for a plurality of two-port surface acoustic wave resonators. As for the surface acoustic wave element miniaturization technology weighted to the grating electrode of the reflector electrode, the mutual interference of the surface acoustic waves in the adjacent surface acoustic wave elements is suppressed, A sufficient effect could not be obtained with respect to suppression of spurious generation in the low frequency side out-of-passband attenuation characteristic.

  Accordingly, the present invention has been completed in view of the above problems in the prior art, and its purpose is to reduce the size of the surface acoustic wave device and out of the low frequency side pass band near the pass band of the surface acoustic wave filter. An object of the present invention is to provide a surface acoustic wave device that can sufficiently suppress the occurrence of spurious in damping characteristics and a communication device using the same.

  The surface acoustic wave device according to the present invention includes: 1) three pieces having a plurality of electrode fingers that are long on the piezoelectric substrate in a direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate. IDT electrodes and reflector electrodes each provided on both sides of the three IDT electrodes and provided with a plurality of long electrode fingers in a direction orthogonal to the propagation direction, and connected in parallel to an unbalanced signal terminal First and second surface acoustic wave elements are formed side by side in the propagation direction, and each of the first and second surface acoustic wave elements is a balanced output unit or a balanced input unit, A surface acoustic wave device in which a balanced signal terminal is connected to the IDT electrode at the center of each of the second surface acoustic wave elements, wherein the first and second surface acoustic wave elements are adjacent to each other. The reflector electrode in It consists passing reflector electrodes, it is an the electrode finger pitch in the central portion of the common reflector electrode is characterized by longer than the electrode finger pitch of the IDT electrode adjacent to the common reflector electrodes.

  In the surface acoustic wave device according to the present invention, 2) in the configuration of 1) above, the electrode finger pitch at both ends of the common reflector electrode is substantially equal to the electrode finger pitch of the IDT electrode adjacent to the common reflector electrode. It is characterized by being the same.

  In the surface acoustic wave device according to the present invention, 3) in the above configuration 1) or 2), the first and second surface acoustic wave elements are connected to the unbalanced signal terminal via the surface acoustic wave resonator. It is characterized by being connected in parallel.

  In addition, the communication device of the present invention includes 4) at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave device according to any one of 1) to 3) above.

  According to the surface acoustic wave device of the present invention, three IDTs each having a plurality of electrode fingers that are long in the direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate. The first and second electrodes are arranged on both sides of each of the three IDT electrodes and have reflector electrodes each having a plurality of long electrode fingers in a direction orthogonal to the propagation direction, and connected in parallel to the unbalanced signal terminal. Two surface acoustic wave elements are formed side by side in the propagation direction, and each of the first and second surface acoustic wave elements serves as a balanced output section or a balanced input section. In the surface acoustic wave device, the balanced signal terminal is connected to the IDT electrode at the center of each of the first and second surface acoustic wave devices, and the reflector electrode at a location where they are adjacent is a common reflector electrode. A common reflector electrode Since the electrode finger pitch in the center is longer than the electrode finger pitch of the IDT electrode adjacent to the common reflector electrode, mutual interference of the excited surface acoustic waves can be suppressed in the two adjacent surface acoustic wave elements. Therefore, spurious generation can be suppressed particularly in the low frequency side out-of-band attenuation characteristic near the pass band, and the characteristic can be improved in the frequency characteristic of the surface acoustic wave device. Further, since the reflector electrodes of the adjacent first and second surface acoustic wave elements are integrally formed as a common reflector electrode, the surface acoustic wave filter chip can be miniaturized.

  Further, according to the surface acoustic wave device of the present invention, in the above configuration, the electrode finger pitch at both ends of the common reflector electrode is substantially the same as the electrode finger pitch of the IDT electrode adjacent to the common reflector electrode. The width of the low band side and the high band side of the pass band can be prevented from being narrowed, and the entire pass band can be made large.

  Further, according to the surface acoustic wave device of the present invention, in the above configuration, the first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal via the surface acoustic wave resonator. Similarly to the above, in the two adjacent surface acoustic wave elements, it is possible to further suppress the mutual interference of the excited surface acoustic waves. Therefore, particularly in the low passband attenuation characteristics on the low frequency side near the passband. Spurious generation can be further suppressed, and the frequency characteristics of the surface acoustic wave device can be improved.

  In addition, the first and second surface acoustic wave elements are connected in parallel via a surface acoustic wave resonator to which an unbalanced signal terminal (unbalanced input terminal or unbalanced output terminal) is connected. When the connection destination of the balanced signal terminal is the first and second surface acoustic wave elements that are longitudinally coupled resonator type surface acoustic wave elements, when a signal is input to and output from the unbalanced signal terminal at 50Ω, Impedance matching becomes difficult, but impedance matching is easy when the first stage is a surface acoustic wave resonator (surface acoustic wave element comprising a single IDT electrode and reflector electrode) as in the present invention. Can be taken to.

  The communication device of the present invention includes the above-described surface acoustic wave device of the present invention, and includes at least one of a reception circuit and a transmission circuit, and thus can satisfy severe attenuation characteristics that have been conventionally required. Is obtained, the sensitivity is remarkably good, and a small communication device can be realized.

  Hereinafter, embodiments of a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings. The surface acoustic wave device of the present invention will be described by taking a resonator type surface acoustic wave filter having a simple structure as an example. In addition, in drawing demonstrated below, the same code | symbol shall be attached | subjected to the same structure. In addition, the number of electrodes and the distance between the electrodes, such as the size of each electrode and the distance between the electrodes, are schematically illustrated for the purpose of explanation.

  FIG. 1A shows a plan view of an example of an embodiment of an electrode structure of a surface acoustic wave device according to the present invention. FIG. 1B shows a change in the electrode finger pitch of the common reflector electrode for the electrode structure of the surface acoustic wave device of the present invention. As shown in FIG. 1A, a surface acoustic wave device according to the present invention has an electrode that is long on a piezoelectric substrate 1 along the direction of propagation of surface acoustic waves propagating on the piezoelectric substrate 1 in a direction orthogonal to the propagation direction. Three IDT electrodes 2 to 4 and 5 to 7 having a plurality of fingers, and a plurality of electrode fingers that are arranged on both sides of the three IDT electrodes 2 to 4 and 5 to 7 and that are long in the direction orthogonal to the propagation direction And the first and second surface acoustic wave elements 14 and 15 connected in parallel to the unbalanced signal terminal 21 are formed side by side in the propagation direction. Each of the second surface acoustic wave elements 14 and 15 is used as a balanced output section or a balanced input section, and a balanced signal terminal is connected to the IDT electrodes 3 and 6 in the center of each of the first and second surface acoustic wave elements 14 and 15. (Balanced signal output terminal or balanced signal input terminal) 22, 2 Are connected to each other, and the first and second surface acoustic wave elements 14 and 15 are composed of one common reflector electrode 30 integrally formed with reflector electrodes at locations where they are adjacent to each other. The electrode finger pitch at the center of the electrode 30 is formed longer than the electrode finger pitch of the IDT electrodes 4 and 5 adjacent to the common reflector electrode 30.

  With this configuration, it is possible to suppress the mutual interference of the excited surface acoustic waves in the two adjacent surface acoustic wave elements 14 and 15, and therefore, particularly in the low-pass-side attenuation characteristics on the low frequency side near the pass band. Spurious generation can be suppressed, and the frequency characteristics of the surface acoustic wave device can be improved. Further, since the reflector electrodes of the adjacent first and second surface acoustic wave elements 14 and 15 are integrally formed as the common reflector electrode 30, the surface acoustic wave filter chip can be reduced in size. .

  In the surface acoustic wave device of the present invention, the electrode finger pitch at the central portion of the common reflector electrode 30 is formed longer than the electrode finger pitch of the IDT electrodes 4 and 5 adjacent to the common reflector electrode 30. When the electrode finger pitch at the center of the electrode 30 is x1, the number of electrode fingers at the center is N1, and the area other than the center of the common reflector electrode 30, that is, the electrode finger pitch at both ends is x3, N1 × { (X1 / x3) -1} is preferably about 0.003 to 0.8. If the value is less than 0.003, the above-described effect of the present invention is not exhibited. If the value exceeds 0.8, the frequency of the attenuation pole generated by the common reflector electrode 30 is significantly reduced, which is caused by mutual interference of surface acoustic waves. It becomes impossible to suppress spurious.

  For example, N1 is about several to several tens, x1 / x3 is more than 1 and about 2 or less, and N1 × {(x1 / x3) −1} is about 0.003 to 0.8. N1, x1 / x3 are controlled.

  In the present invention, the electrode finger pitch at both ends of the common reflector electrode 30 is preferably substantially the same as the electrode finger pitch of the IDT electrodes 4 and 5 adjacent to the common reflector electrode 30. In this case, when the electrode finger pitch at both ends of the common reflector electrode 30 is x2, x2 / x3 is preferably about 0.985 to 1.011, although it depends on the passband width. When x2 / x3 is less than 0.985, the high band side of the pass band is narrowed, and when x2 / x3 exceeds 1.011, the low band side of the pass band is narrowed. Therefore, by setting x2 / x3 to about 0.985 to 1.011, it is possible to prevent the width of the low band side and the high band side of the pass band from being narrowed and to increase the entire pass band.

  Further, the width in the propagation direction of the central portion of the common reflector electrode 30 is not particularly limited, but is, for example, about 20 to 80% of the entire width in the propagation direction of the common reflector electrode 30, and particularly About 60%. Therefore, the width in the propagation direction of both ends of the common reflector electrode 30 is about 80 to 20% of the entire width in the propagation direction of the common reflector electrode 30.

  FIG. 2A shows a plan view of another example of the embodiment of the electrode structure of the surface acoustic wave device of the present invention. FIG. 2B shows changes in the electrode finger pitch of the common reflector electrode 30 in the electrode structure of the surface acoustic wave device of the present invention. In the surface acoustic wave device according to the present invention, the first and second surface acoustic wave elements 14 and 15 are connected to the unbalanced signal terminal 21 via the surface acoustic wave resonator 16 in the configuration shown in FIG. It is formed in parallel connection.

  With this configuration, in the same manner as described above, it is possible to suppress the mutual interference of the excited surface acoustic waves in the two adjacent surface acoustic wave elements 14 and 15, and therefore, the low-frequency side pass particularly near the passband. Spurious generation can be suppressed in the out-of-band attenuation characteristic, and the characteristic can be improved in the frequency characteristic of the surface acoustic wave device.

  The first and second surface acoustic wave elements 14 and 15 are connected in parallel via a surface acoustic wave resonator 16 to which an unbalanced signal terminal (unbalanced input terminal or unbalanced output terminal) 21 is connected. Yes. Thereby, when the connection destination of the unbalanced signal terminal 21 is the first and second surface acoustic wave elements 14 and 15 which are longitudinally coupled resonator type surface acoustic wave elements, the unbalanced signal terminal 21 is 50Ω. However, it is difficult to achieve impedance matching when a signal is input to or output from a surface acoustic wave resonator (as in the present invention, the first stage is a surface acoustic wave resonator (elastic surface comprising a single IDT electrode 12 and reflector electrodes 17 and 18). In the case of the wave element 16, impedance matching can be easily taken.

  1 and 2, the number of electrode fingers of the IDT electrodes 2 to 7, the reflector electrodes 8, 10, 17, 18, 30 and the surface acoustic wave resonator 16 ranges from several to several hundreds. For simplicity, these shapes are simplified in the figure.

  Further, as the piezoelectric substrate 1 for the surface acoustic wave filter, 36 ° ± 3 ° Y-cut X propagation lithium tantalate single crystal, 42 ° ± 3 ° Y cut X propagation lithium tantalate single crystal, 64 ° ± 3 ° Y Cut X-propagating lithium niobate single crystal, 41 ° ± 3 ° Y-cut X-propagating lithium niobate single crystal, 45 ° ± 3 ° X-cut Z-propagating lithium tetraborate single crystal has a large electromechanical coupling coefficient and frequency Since the temperature coefficient is small, it is preferable as the piezoelectric substrate 1. Of these pyroelectric piezoelectric single crystals, if the piezoelectric substrate 1 has a significantly reduced pyroelectric property due to solid solution of oxygen defects or Fe, the reliability of the device is good. The thickness of the piezoelectric substrate 1 is preferably about 0.1 to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate 1 becomes brittle, and if it exceeds 0.5 mm, the material cost and component dimensions become large, which is not suitable for use.

  The IDT electrode and the reflector electrode are made of Al or an Al alloy (Al—Cu type, Al—Ti type), and are formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD (Chemical Vapor Deposition) method. . The electrode thickness is preferably about 0.1 to 0.5 μm for obtaining the desired characteristics as a surface acoustic wave filter.

Furthermore, SiO ₂ , SiN _x , Si, Al ₂ O ₃ is formed as a protective film on the surface acoustic wave propagation portion on the surface of the surface acoustic wave filter and the piezoelectric substrate 1 according to the present invention. It is also possible to prevent energization and improve power durability.

  The surface acoustic wave filter of the present invention can be applied to a communication device. That is, at least one of a receiving circuit and a transmitting circuit is provided and used as a bandpass filter included in these circuits. For example, the transmission signal output from the transmission circuit is put on the carrier frequency by the mixer, the unnecessary signal is attenuated by the band pass filter, and then the transmission signal is amplified by the power amplifier and transmitted from the antenna through the duplexer. A communication device equipped with a transmission circuit capable of receiving signals, or receiving a received signal with an antenna, amplifying the received signal that has passed through the duplexer with a low noise amplifier, and then attenuating an unnecessary signal with a band-pass filter, and a carrier frequency with a mixer Can be applied to a communication apparatus including a receiving circuit that separates a signal from the signal and transmits the signal to a receiving circuit that extracts the signal. Therefore, if the surface acoustic wave device of the present invention is employed, severe attenuation, which has been conventionally required, is provided by including at least one of the reception circuit and the transmission circuit having any one of the surface acoustic wave devices of the present invention. A device capable of satisfying the characteristics is obtained, the sensitivity is remarkably good, and a small communication device can be realized.

  Examples of the present invention will be described below.

An example in which the surface acoustic wave device shown in FIG. A fine electrode pattern made of Al (99 mass%)-Cu (1 mass%) on a piezoelectric substrate (mother substrate for multiple production) 1 made of LiTaO ₃ single crystal for X-direction propagation of 38.7 ° Y-cut. Formed.

  The pattern of each electrode was produced by photolithography using a sputtering apparatus, a reduction projection exposure machine (stepper), and an RIE (Reactive Ion Etching) apparatus.

  First, the piezoelectric substrate 1 was ultrasonically cleaned with acetone, IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the piezoelectric substrate 1 with a clean oven, a metal layer to be each electrode was formed. A sputtering apparatus was used for forming the metal layer, and an Al (99 mass%)-Cu (1 mass%) alloy was used as the material of the metal layer. The thickness of the metal layer at this time was about 0.18 μm.

  Next, a photoresist is spin-coated to a thickness of about 0.5 μm on the metal layer, patterned into a desired shape by a reduction projection exposure apparatus (stepper), and an unnecessary portion of the photoresist is removed with an alkaline developer by a developing apparatus. To dissolve the desired pattern. Thereafter, the metal layer was etched by an RIE apparatus, patterning was completed, and a pattern of each electrode constituting the surface acoustic wave element was obtained.

Thereafter, a protective film was formed on a predetermined region of the electrode. That is, a SiO ₂ layer having a thickness of about 0.02 μm was formed on each electrode pattern and the piezoelectric substrate 1 by a CVD (Chemical Vapor Deposition) apparatus.

  Thereafter, patterning was performed by photolithography, and the flip-chip window opening portion was etched by an RIE apparatus or the like. Thereafter, a pad electrode mainly composed of Al was formed on the flip chip window opening using a sputtering apparatus. The film thickness of the pad electrode at this time was about 1.0 μm. Thereafter, the photoresist and unnecessary Al were removed at the same time by a lift-off method, and a pad electrode for forming a conductor bump for flip-chipping the surface acoustic wave device on an external circuit board or the like was completed.

  Next, a flip-chip conductor bump made of Au was formed on the pad electrode using a bump bonding apparatus. The conductor bump had a diameter of about 80 μm and a height of about 30 μm.

Next, the piezoelectric substrate 1 was diced along a dividing line, and divided into each surface acoustic wave device (chip). Thereafter, each chip was accommodated in a package with a flip chip mounting apparatus with the electrode pad forming surface facing down and bonded. Thereafter, baking was performed in an N ₂ atmosphere to complete a packaged surface acoustic wave device. As the package, a 2.5 × 2.0 mm square laminated structure formed by laminating ceramic layers was used.

  Further, as a sample of the comparative example, as shown in FIG. 3A, one common reflection in which reflector electrodes at adjacent portions of the first and second surface acoustic wave elements 14 and 15 are integrally formed. A surface acoustic wave device including the reflector electrode 30a and having the electrode pitch of the common reflector electrode 30a constant as a whole was manufactured in the same process as described above.

  The other configuration of the surface acoustic wave device used as the sample of the comparative example is the same as the configuration of the surface acoustic wave element shown in FIG. FIG. 3B shows a state of change in the electrode finger pitch of the common reflector electrodes 30 and 30a of the surface acoustic wave device of the present invention and the comparative example. In the embodiment of the surface acoustic wave device of the present invention, the common reflector electrode 30 has a portion having a long pitch of 56 electrode fingers and a portion having a short pitch of 20 electrode fingers on both sides thereof. . On the other hand, the common reflector electrode 30a of the comparative example has 96 electrode fingers with a constant electrode finger pitch.

  Next, characteristic measurement was performed on the surface acoustic wave devices of the present example and the comparative example. A signal of 0 dBm was input, and measurement was performed under conditions of a frequency of 1640 to 2140 MHz and a measurement point of 801 points. The number of samples is 30, and the measuring instrument is a multi-port network analyzer (“E5071A” manufactured by Agilent Technologies).

  A graph of frequency characteristics near the passband is shown in FIG. FIG. 4 is a graph showing the frequency dependence of the insertion loss representing the transmission characteristics of the surface acoustic wave filter. The filter characteristics of this example product were very good. That is, as shown by the solid line in FIG. 4, in the attenuation characteristic on the low frequency side (1760 to 1785 MHz) in the vicinity of the pass band of the surface acoustic wave filter of the product of this example, a good filter characteristic in which spurious is sufficiently suppressed is obtained. Obtained.

  On the other hand, as indicated by the wavy line in FIG. 4, the spurious is greatly generated in the attenuation characteristic on the low frequency side (1760 to 1785 MHz) in the vicinity of the pass band of the surface acoustic wave device of the comparative example, and the filter characteristic is deteriorated.

  As described above, in this example, the surface acoustic wave device can be realized in which the spurious is sufficiently suppressed and the size is reduced in the attenuation characteristic on the low frequency side near the pass band.

1 shows an example of an embodiment of a surface acoustic wave device according to the present invention, where (a) is a plan view of the surface acoustic wave device, and (b) is an electrode finger pitch of a common reflector electrode of the surface acoustic wave device of (a). It is a graph which shows. The other example of embodiment is shown about the surface acoustic wave apparatus of this invention, (a) is a top view of a surface acoustic wave apparatus, (b) is the electrode finger pitch of the common reflector electrode of the surface acoustic wave apparatus of (a) It is a graph which shows. 1 shows a surface acoustic wave device of a comparative example, (a) is a plan view of the surface acoustic wave device, (b) is an electrode finger pitch of a common reflector electrode of the surface acoustic wave device of the embodiment, and (a) surface acoustic wave. It is a graph which shows the electrode finger pitch of the common reflector electrode of an apparatus. It is a graph which shows the frequency characteristic of the insertion loss in a pass band and its vicinity about the surface acoustic wave apparatus of an Example and a comparative example. It is a top view which shows typically the example of an electrode structure of the conventional surface acoustic wave apparatus. It is sectional drawing of the conventional packaged surface acoustic wave apparatus.

Explanation of symbols

1: piezoelectric substrate 14: first surface acoustic wave element 15: second surface acoustic wave element 16: surface acoustic wave resonators 2-7: IDT electrode 8, 10: reflector electrode 21: unbalanced signal terminal 22, 23: balanced signal terminal 30: common reflector electrode

Claims (4)

Three IDT electrodes each provided with a plurality of long electrode fingers in a direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate on the piezoelectric substrate, and the three IDT electrodes First and second surface acoustic wave elements connected in parallel to the unbalanced signal terminal, and having reflector electrodes each provided with a plurality of long electrode fingers in a direction orthogonal to the propagation direction. Formed side by side in the propagation direction,
Each of the first and second surface acoustic wave elements is used as a balanced output section or a balanced input section, and a balanced signal terminal is connected to the IDT electrode at the center of each of the first and second surface acoustic wave elements. A surface acoustic wave device comprising:
In the first and second surface acoustic wave elements, the reflector electrode at a location where they are adjacent to each other is composed of a common reflector electrode, and an electrode finger pitch at a central portion of the common reflector electrode is equal to the common reflector electrode. A surface acoustic wave device characterized by being longer than an electrode finger pitch of adjacent IDT electrodes.   2. The surface acoustic wave device according to claim 1, wherein the electrode finger pitch at both ends of the common reflector electrode is substantially the same as the electrode finger pitch of the IDT electrode adjacent to the common reflector electrode.   3. The surface acoustic wave device according to claim 1, wherein the first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal via a surface acoustic wave resonator.   A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave device according to claim 1.

Images