JP2007081469A - Surface acoustic wave element and communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element with superior characteristic which can improve shoulder characteristics of a passband by reducing deterioration due to insertion loss. <P>SOLUTION: An IDT electrode 3 consisting of a pair of parallel common electrodes and a plurality of electrode fingers 4 extending from each of the common electrodes so as to mate with each other is formed on a piezoelectric substrate 1. Dummy electrode fingers 5 are each formed on the other common electrode so as to oppose each of the end of the electrode fingers 4 formed on the one common electrode of the IDT electrode 3. The dummy electrodes 5 are each formed so as to have a width smaller than the width of each of electrode fingers of the IDT electrode 3, and connection portions 8 with the common electrode in the electrode fingers of the IDT electrode 3 are each formed so as to have a width smaller than the width of each of the other parts 9 thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave element 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 apparatus including the same.

  In recent years, surface acoustic wave filters that can be miniaturized and non-adjusted have come to be used in various communication devices. With the progress of higher frequency and higher functionality of communication devices, surface acoustic wave filters have been reduced in loss. There is an ever-increasing demand for Since the intrinsic loss due to the piezoelectric substrate material increases as the frequency increases, for example, in a dual mode surface acoustic wave resonator filter, the insertion loss tends to deteriorate as the frequency increases.

  Further, the electrode finger pitch of the IDT electrode (Inter Digital Transducer) becomes smaller as the frequency becomes higher, and the film thickness of the IDT electrode becomes thinner. For example, the IDT electrode film thickness of a 1.9 GHz surface acoustic wave filter is designed to be about half that of a 900 MHz surface acoustic wave filter, and an ohmic in a transmission line such as an extraction electrode connecting the filters is used. The loss increases as the frequency increases. Therefore, the insertion loss tends to further deteriorate.

  In order to suppress such deterioration of insertion loss, various proposals have been made. For example, the following means for improving insertion loss has been proposed for a dual-mode surface acoustic wave resonator filter using three longitudinal ID modes and three longitudinal IDT electrodes provided on a piezoelectric substrate. ing.

  FIG. 5 shows a plan view of an electrode structure of a conventional resonator type surface acoustic wave filter. The IDT electrode 204 having a plurality of electrode fingers disposed on the piezoelectric substrate 202 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. It will cause. By inputting an electric signal from the input terminal 215 connected to one comb-like electrode of 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. The In addition, an electric signal is output from one comb-like electrode constituting each of the IDT electrodes 203 and 205 to the output terminals 216 and 217 through the IDT electrodes 206 and 209. In the figure, reference numerals 210, 211, 212, and 213 denote reflector electrodes.

  In this way, by connecting the resonator electrode patterns in two stages in cascade, the out-of-band attenuation is increased by the mutual interference between the first and second stage standing waves, and the out-of-band attenuation of the filter characteristics is increased. Can be improved. In other words, the surface acoustic wave filter having the same characteristics is configured in a two-stage cascade connection, so that the signal attenuated in the first stage is further attenuated in the second stage, and the out-of-band attenuation is approximately doubled. Can be made.

  Here, by inputting an electric signal to the input terminal 215 connected to the IDT electrode 204, the surface acoustic wave is excited, and the surface acoustic wave is propagated to the IDT electrodes 203 and 205 located on both sides of the IDT electrode 204. The electrical signals are output from the output terminals 216 and 217 connected to the IDT electrodes 207 and 208. In addition, surface acoustic waves are reflected by the reflector electrodes 210, 211, 212, and 213 located at both ends of the IDT electrodes 203 to 205 and both ends of the IDT electrodes 206 to 209, and become standing waves between the reflector electrodes at both ends. .

  This standing wave mode includes a primary mode and its higher-order (third-order) mode by three IDT electrodes 203 to 205. 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, by providing a narrow pitch portion of electrode fingers at the end of adjacent IDT electrodes, the radiation loss of bulk waves between IDT electrodes is reduced, and the insertion loss can be improved by controlling the resonance mode state. (For example, see Patent Documents 1 and 2).

FIG. 6 is a plan view of an electrode structure of a conventional surface acoustic wave filter. As another means for realizing a reduction in loss, since the thickness of at least a part of the common electrode in the IDT electrode is made thicker than the thickness of the electrode finger, the sound velocity of the surface acoustic wave propagating through the common electrode There has also been proposed an example of a surface acoustic wave filter that is slower than the speed of sound of a surface acoustic wave propagating through a finger, confines the energy of the surface acoustic wave, and achieves low loss (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 2002-9587 Special table 2002-528987 gazette JP 2002-1000095 A2 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, it is possible to suppress the deterioration of insertion loss due to the mode conversion of the surface acoustic wave between the IDT electrodes into a bulk wave. The confinement of the energy of the surface acoustic wave in the direction perpendicular to the propagation direction of the surface acoustic wave between the electrodes, between the adjacent IDT electrodes and between the adjacent IDT electrode and the reflector electrode is incomplete.

  That is, in the propagation direction of the surface acoustic wave, energy can be confined by reflecting the surface acoustic wave with the reflector electrode. However, not only the propagation direction of the surface acoustic wave, but also the optical direction of the propagation leakage of the surface acoustic wave, that is, the observation of the phenomenon that the light is polarized by the photoelastic effect when the surface acoustic wave element is irradiated with light, It is known that leakage occurs in a direction perpendicular to the electrode finger (in a direction parallel to the electrode finger). Further, as a result of computer simulation, the sound velocity Vb on the IDT electrode common electrode is higher than that on the electrode finger of the IDT electrode. When the sound velocity Vg is slow or equal, it is reported that leakage occurs in a direction perpendicular to the propagation direction of the surface acoustic wave (a direction parallel to the electrode finger) (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 the direction perpendicular to the propagation direction of the surface acoustic wave. As in the surface acoustic wave devices disclosed in Patent Documents 1 and 2, it is not sufficient to improve the insertion loss by providing the narrow pitch portions of the electrode fingers at the ends of the adjacent IDT electrodes. It is necessary to suppress degradation 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 disclosed in Patent Document 3, an electrode is formed in the region from the electrode finger tip formed on one common electrode of the IDT electrode to the other common electrode opposite to the electrode finger. This is a region that does not contribute to the excitation of surface acoustic waves. Therefore, the speed of sound in this region is faster than that of the electrode finger intersection. The sound velocity in the electrode finger non-intersection area is faster than the sound speed in the electrode intersection area that contributes to the excitation of the surface acoustic wave, thereby sufficiently suppressing leakage in the direction perpendicular to the propagation direction of the surface acoustic wave. Can not.

  Further, as a means for increasing the thickness of a part of the common electrode of the IDT electrode, a means for depositing a metal having a density higher than that of Al on the common electrode and laminating the IDT electrode with Al or Al alloy in advance. There is means for forming the electrode finger by reducing the thickness of the electrode finger by dry etching or the like after the film is formed to be thick, but in the former case, the surface acoustic wave device process is increased. In the latter case, it becomes difficult to uniformly control the film thickness of the electrode by uniformly controlling the etching.

  Accordingly, the present invention has been completed in view of the above-mentioned problems in the prior art, and the object thereof is as a high-quality surface acoustic wave filter having excellent filter characteristics without causing deterioration of insertion loss. Another object of the present invention is to provide a surface acoustic wave element that can function as well as a communication device using the same.

  In the surface acoustic wave device of the present invention, an IDT electrode including a pair of parallel common electrodes and a plurality of electrode fingers extending so as to mesh with each other is formed on a piezoelectric substrate. A dummy electrode finger is formed on the other common electrode so as to face the tip of the electrode finger formed on one common electrode, and the width of the dummy electrode finger is narrower than the width of the electrode finger of the IDT electrode. In addition, the width of the connection portion of the electrode finger of the IDT electrode with the common electrode is narrower than the width of the remaining portion.

  The surface acoustic wave device of the present invention is preferably characterized in that, in the above configuration, the duty of the dummy electrode finger is smaller than the duty of the electrode finger of the IDT electrode.

  A communication apparatus according to the present invention includes at least one of a receiving circuit and a transmitting circuit having any one of the surface acoustic wave elements according to the present invention.

  In the surface acoustic wave device according to the present invention, an IDT electrode including a pair of parallel common electrodes and a plurality of electrode fingers extending so as to mesh with each other is formed on a piezoelectric substrate, and one of the IDT electrodes is formed. A dummy electrode finger is formed on the other common electrode so as to face the tip of the electrode finger formed on the common electrode, and the width of the dummy electrode finger is narrower than the width of the electrode finger of the IDT electrode, This is a configuration in which the width of the connection portion of the electrode finger of the IDT electrode with the common electrode is narrower than the width of the remaining portion, thereby producing the following effects.

  FIG. 3 shows a graph for explaining the sound velocity anisotropy of the leaky wave SAW mode at the position of the IDT electrode. In FIG. 3, Vx is the sound velocity in the propagation direction (X direction), and Vy is the sound velocity in the direction perpendicular to the propagation direction (Y direction). In the leaky SAW mode, an unnecessary wave parallel to the propagation direction is generated as the first mode. Further, another unnecessary wave generation mode is the second generation mode, and an unnecessary wave in the normal direction to the sonic velocity curve in FIG. 3 (mode radiated obliquely with respect to the propagation direction) is generated.

  According to the present invention, by providing a dummy electrode finger short from the other common electrode to the vicinity thereof, unnecessary waves of the first mode parallel to the propagation direction of the surface acoustic wave can be suppressed, and the electrode of the dummy electrode finger can be suppressed. The width of the finger is formed narrower than the width of the electrode finger of the IDT electrode, and the width of the connection portion with the common electrode in the electrode finger of the IDT electrode is formed narrower than the width of the remaining portion. The speed of sound Vx is increased to shift the speed of sound curve itself, that is, the speed of sound curve is shifted from (a) to (b) in FIG. Mode radiated in an oblique direction with respect to the propagation direction) can be suppressed. Therefore, the shoulder characteristic of the pass band in the filter characteristic can be improved, and the insertion loss can be improved.

  Further, in the surface acoustic wave device as disclosed in Patent Document 3, it is necessary to further add a step of increasing the film thickness of the common electrode, which increases the number of steps, but according to the electrode structure of the present invention, By devising the electrode structure without changing the number of steps, it is possible to provide a surface acoustic wave device in which unnecessary waves in two modes are suppressed and insertion loss is improved.

  The surface acoustic wave device according to the present invention is preferably configured so that, in the above configuration, the duty of the dummy electrode fingers is smaller than the duty of the electrode fingers of the IDT electrodes, so that the IDT electrodes can be used even when the electrode widths of the dummy electrode fingers are not the same. By setting the dummy electrode finger duty smaller than the duty of the electrode fingers (line width ratio = line width / (line width + between lines)), the common direction parallel to the propagation direction of the surface acoustic wave is the same as above. Both the unnecessary wave of the first mode in the vicinity of the electrode and the unnecessary wave of the second mode radiated obliquely with respect to the propagation direction of the surface acoustic wave can be suppressed, and the insertion loss of the surface acoustic wave element can be suppressed. Can be improved.

  A communication apparatus according to the present invention includes at least one of a receiving circuit and a transmitting circuit having any one of the surface acoustic wave elements according to the present invention.

  Then, according to the communication device of the present invention, by using the surface acoustic wave element of the present invention as described above for the communication device, it is possible to obtain a device that can satisfy the severe insertion loss that has been conventionally required, and the sensitivity. However, a much better communication device can be realized.

  Hereinafter, embodiments of 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 site | part. 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.

  As an example of an embodiment of a surface acoustic wave device according to the present invention, FIG. 1 shows a plan view of an IDT electrode formed on a piezoelectric substrate. As shown in FIG. 1, the surface acoustic wave device of the present invention has an IDT electrode 3 comprising a pair of parallel common electrodes and a plurality of electrode fingers 4 extending from the common electrodes so as to mesh with each other. The dummy electrode finger 5 is formed on the other common electrode so as to face the tip of the electrode finger 4 formed on one common electrode of the IDT electrode 3, and the width of the dummy electrode finger 5 is equal to that of the IDT electrode 3. The width of the connection part 8 with the common electrode in the electrode finger of the IDT electrode 3 is narrower than the width of the remaining part 9.

  Here, the dummy electrode finger 5 is a small electrode projecting from the other common electrode at an interval between the tip of the electrode finger 4 extending from one common electrode and the other common electrode in the IDT electrode 3. Refers to electrode fingers.

  With the above configuration, the dummy electrode finger 5 is provided in the vicinity of the other common electrode, that is, the gap between the dummy electrode finger 5 and the electrode finger 4 of one common electrode in the other common electrode (which is a conventional gap). The common electrode and electrode finger non-intersecting region of the IDT electrode 3 that suppresses unnecessary waves of the first mode parallel to the propagation direction of the surface acoustic wave and does not contribute to the excitation of the surface acoustic wave. The speed of sound in (the area up to the other common electrode facing the tip of the electrode finger 4 formed on one common electrode of the IDT electrode 3) is made faster than the speed of sound in the electrode finger crossing region contributing to excitation of the surface acoustic wave. be able to.

  Further, the width of the dummy electrode finger 5 is formed narrower than the width of the electrode finger of the IDT electrode 3, and the width of the connection portion 8 with the common electrode in the electrode finger of the IDT electrode 3 is formed narrower than the width of the remaining portion 9. As a result, the sound velocity Vx in the vicinity of the common electrode is increased and the sound velocity curve itself is shifted (the sound velocity curve is shifted from (a) to (b) in FIG. 3). Mode unnecessary waves (modes of unnecessary waves radiated obliquely with respect to the propagation direction of the surface acoustic wave) can be suppressed. Therefore, a surface acoustic wave device with improved shoulder characteristics in the pass band and improved insertion loss of filter characteristics can be obtained.

  As another example of the embodiment of the surface acoustic wave device of the present invention, FIG. 2 shows a plan view of an electrode structure of a longitudinally coupled double mode surface acoustic wave device. In this example, three IDT electrodes are provided adjacent to each other in the propagation direction of the surface acoustic wave, and each dummy electrode finger is compared with the width of the electrode finger 4 of each IDT electrode as in the configuration shown in FIG. 5 is narrow, and the width of the connecting portion 8 of the electrode finger of the IDT electrode 3 with the common electrode is narrower than the width of the remaining portion 9, thereby suppressing the unnecessary wave of the surface acoustic wave and reducing the filter characteristics. A surface acoustic wave device with improved insertion loss can be provided.

  In the present invention, the width of the dummy electrode finger 5 is narrower than the width of the electrode finger 4 of the IDT electrode 3, but the width of the dummy electrode finger 5 is about 10% to 45% of the width of the electrode finger 4 of the IDT electrode 3. Is preferred. If it is less than 10%, it becomes difficult to control the line width in the photolithography process for forming the dummy electrode finger 5, and if it exceeds 45%, the sound speed at the dummy electrode portion 5 is difficult to increase. The effect of removing unnecessary waves in the second mode is reduced.

  The length of the dummy electrode finger 5 depends on the operating frequency, but is about 4.5 μm corresponding to about 1 wavelength at 800 to 900 MHz, and about 2 μm corresponding to about 1 wavelength at 1.8 to 1.9 GHz. .

  Moreover, although the width of the connection part 8 with the common electrode in the electrode finger of the IDT electrode 3 is formed narrower than the width of the remaining part 9, the width of the connection part 8 is about 10% to 45% of the width of the remaining part 9. It is preferable that If it is less than 10%, it is difficult to control the line width in the photolithography process for forming the connection portion 8, and if it exceeds 45%, the speed of sound at the dummy electrode portion 5 is difficult to increase. The effect of removing unwanted waves in mode 2 is reduced.

  The surface acoustic wave device according to the present invention preferably has an IDT electrode even in the case where the dummy electrode finger 5 has a duty smaller than that of the IDT electrode 3 in the above-described configuration, even if the electrode width of each dummy electrode finger 5 is not the same. By setting the duty of the dummy electrode finger 5 to be smaller than the duty of the third electrode finger 4, the unnecessary wave of the first mode near the common electrode in the direction parallel to the propagation direction of the surface acoustic wave and the elasticity Both unnecessary waves of the second mode radiated in an oblique direction with respect to the propagation direction of the surface wave can be suppressed, and the insertion loss of the surface acoustic wave element can be improved.

  Since the number of electrode fingers of the IDT electrodes 3, 6, 7 and the reflector electrode 2 ranges from several to several hundreds, the shape is simplified in the drawing for simplicity.

  In the present invention, the dummy electrode finger 5 has a quadrangular shape as shown in FIG. 1, but may have a trapezoidal shape (tapered at the tip side), in which case the sound speed gradually changes, There is an effect that unnecessary waves that cannot be taken into account can be removed by continuously changing the velocity of the surface acoustic wave.

  The surface acoustic wave device of the present invention has a conductor layer formed on a piezoelectric substrate 1 and a plurality of electrode fingers 4 and dummy electrode fingers that extend from the common electrode and each common electrode so as to mesh with each other. 5 to form an IDT electrode 3.

  Here, as the piezoelectric substrate 1, a lithium tantalate single crystal, a lithium niobate single crystal, a lithium tetraborate single crystal, or the like can be used.

  The conductor layer on the piezoelectric substrate 1 includes aluminum, aluminum alloy, copper, copper alloy, gold, gold alloy, tantalum, tantalum alloy, or a laminated film 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, a sputtering method or an electron beam evaporation method can be used.

  As a method for patterning the conductor layer, there is a method in which photolithography is performed after forming the conductor layer, and then RIE (Reactive Ion Etching) or wet etching is performed. Alternatively, before forming the conductor layer, a resist is formed on one main surface of the piezoelectric substrate 1 and photolithography is performed to open a desired pattern. Then, the conductor layer is formed, and then the resist is formed on an unnecessary portion. A lift-off process for removing the entire conductor layer may be performed.

  Next, a protective film for protecting the IDT electrode 3 is formed. Silicon, silica or the like can be used as the material for the protective film. 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. As a method of etching the protective film, there is a method of performing dry etching such as RIE or wet etching.

  In the surface acoustic wave device according to the present invention, the IDT electrode 3 is formed adjacent to each other so as to align the common electrodes, and a protective film is formed on the piezoelectric substrate 1 across the adjacent IDT electrodes 3. In the protective film between the IDT electrodes 3 that are covered, the thickness between the common electrodes is preferably larger than the thickness between the electrode fingers 4. Thereby, the speed of sound of the surface acoustic wave between the common electrodes not only in the IDT electrode 3 but also in the adjacent part of the IDT electrode 3 becomes slower than the speed of sound of the surface acoustic wave between the electrode fingers 4. 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 the surface acoustic wave and sufficiently reduce the insertion loss in the filter characteristics.

  The surface acoustic wave filter of the present invention can be applied to a communication device. That is, at least one of the receiving circuit and the transmitting circuit is provided and used as a band-pass 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. Communication device equipped with a transmission circuit capable of receiving the received signal with an antenna, the received signal that passed through the duplexer is amplified with a low noise amplifier, and then the unnecessary signal is attenuated with a band-pass filter, and then the carrier frequency is detected with a mixer. The present invention is applicable to a communication device having a receiving circuit that separates a signal and transmits the signal to a receiving circuit that extracts the signal. By adopting the surface acoustic wave device of the present invention, an excellent communication device with improved sensitivity can be obtained. Can be provided.

  As described above, it is possible to provide a communication device such as an excellent communication device that includes the reception circuit and the transmission circuit having the surface acoustic wave element having excellent characteristics, and whose sensitivity is remarkably good.

An embodiment in which the surface acoustic wave filter shown in FIG. A fine electrode pattern of an IDT electrode 3 made of Al (99% by mass) -Cu (1% by mass) was formed on a LiTaO ₃ single crystal piezoelectric substrate 1 having a 38.7 ° Y-cut propagation in the X direction. For pattern production, photolithography was performed using a sputtering apparatus, a reduction projection exposure machine (stepper), and an RIE apparatus.

  First, the mother substrate of the piezoelectric substrate 1 was ultrasonically cleaned with acetone, IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the substrate using a clean oven, the conductor layers to be the IDT electrodes 3, 6, 7 (including the connection portion 8 of the electrode finger 4), the dummy electrode 5, and the reflector electrode 2 are formed. went. A sputtering apparatus was used for film formation of these electrodes, and a material made of an Al (99 mass%)-Cu (1 mass%) alloy was used. The thickness of these electrodes at this time was about 0.15 μm.

  Next, a photoresist is spin-coated on the conductor layer 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 removed with an alkaline developer by a developing apparatus. Then, the conductive layer was etched by an RIE apparatus to complete the patterning, and an electrode pattern of the surface acoustic wave resonator constituting the surface acoustic wave filter was obtained.

Thereafter, a protective film was formed on a predetermined region of the piezoelectric substrate 1 including the IDT electrodes 3, 6 and 7 (there is a narrow connection portion 8 of the electrode finger 4), the dummy electrode 5 and the reflector electrode 2. That is, SiO ₂ was formed to a thickness of about 0.1 μm on the electrode pattern and the piezoelectric substrate 1 by a CVD apparatus. Thereafter, patterning of the photoresist is performed by photolithography, and a portion on the region of the intersection of the electrode fingers 4 of the IDT electrodes 3, 6 and 7 of the protective film and a portion on the region of the electrode fingers of the reflector electrode 2 by the RIE apparatus. In addition, the portion of the region between the electrode fingers of the adjacent IDT electrodes 3, 6, 7 and the reflector electrode 2 was etched to reduce the thickness of the protective film. At the same time, a protective film window was opened on the electrode pad portion in flip chip mounting.

  Thereafter, an electrode pad mainly composed of Al was formed using a sputtering apparatus. The electrode pad 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 form flip-chip electrode pads.

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

Next, the mother substrate of the piezoelectric substrate 1 was diced along dicing lines and divided into chips each having the surface acoustic wave element shown in FIG. Thereafter, each chip was bonded in a ceramic package with the flip-chip mounting apparatus with the electrode forming surface on the bottom surface. Thereafter, baking was performed in an N ₂ atmosphere to complete a surface acoustic wave filter. The package used was a 2.5 × 2.0 mm square laminate structure.

  As a sample of the comparative example, a dummy electrode finger 5 is formed with the same fine electrode pattern as that of the IDT electrodes 3, 6, 7 (no narrow connection portion 8 of the electrode finger 4) and the reflector electrode 2 shown in FIG. A surface acoustic wave filter having a structure in which an unpatterned electrode pattern was formed was produced in the same process as described above.

  Next, the characteristics of the surface acoustic wave filter in this example were measured. A signal of 0 dBm was input, and measurement was performed under 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 network analyzer (“Multiport Network Analyzer E5071A” manufactured by Agilent Technologies).

  FIG. 4 shows a frequency characteristic graph near the passband. Here, FIG. 4 is a graph showing the frequency dependence of the insertion loss representing the transmission characteristics of the filter. As shown by the solid line in FIG. 4, the insertion loss of the surface acoustic wave device of this example was 2.13 dB, and the ripple was 0.2 dB. On the other hand, as shown by the broken line in FIG. 4, the insertion loss of the surface acoustic wave element of the comparative example was 2.35 dB, and the ripple was 0.3 dB.

  As described above, in this example, it was possible to realize a surface acoustic wave device that reduced the insertion loss in the filter characteristics and improved the shoulder characteristics of the passband.

It is a top view which shows one example of embodiment about the surface acoustic wave element of this invention. It is a top view which shows the other example of embodiment about the surface acoustic wave element of this invention. It is a graph which shows the change of the sound speed of the surface acoustic wave in the IDT electrode of the surface acoustic wave element of this invention, (a) shows the sound speed of the surface acoustic wave of the conventional surface acoustic wave element, (b) is the present invention. It shows the speed of sound of a surface acoustic wave of a surface acoustic wave element. It is a graph which shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave element of a present Example and a comparative example, and its vicinity. It is the top view which shows the graph explaining the relationship between the electrode position of a conventional surface acoustic wave element, and an electrode finger pitch, and an electrode structure. It is a top view which shows the example of an electrode structure of the conventional surface acoustic wave element.

Explanation of symbols

1: Piezoelectric substrate 2: Reflector electrodes 3, 6, 7: IDT electrodes 4: Electrode fingers of IDT electrodes 5: Dummy electrode fingers 8: Connection portions with common electrodes in electrode fingers of IDT electrodes 9: Electrode fingers of IDT electrodes The remaining part of the connection with the common electrode

Claims (3)

An IDT electrode comprising a pair of parallel common electrodes and a plurality of electrode fingers extending so as to mesh with each other is formed on the piezoelectric substrate, and the IDT electrode formed on one common electrode of the IDT electrode A dummy electrode finger is formed on the other common electrode so as to face the tip of the electrode finger, the width of the dummy electrode finger is narrower than the width of the electrode finger of the IDT electrode, and the IDT electrode A surface acoustic wave device, wherein a width of a connection portion of the electrode finger with the common electrode is narrower than a width of the remaining portion. 2. The surface acoustic wave device according to claim 1, wherein a duty of the dummy electrode finger is smaller than a duty of the electrode finger of the IDT electrode. A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave element according to claim 1.

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