JP2007097117A - Surface acoustic wave resonator, surface acoustic wave filter and surface acoustic wave duplexer, and communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave duplexers, their surface acoustic wave filters, and a communication apparatus using the surface acoustic wave duplexers or surface acoustic wave resonators in which isolation characteristics, insertion loss and power resistance are enhanced. <P>SOLUTION: A surface acoustic wave resonator comprises a piezoelectric substrate 19, an IDT (Inter Digital Transducer) electrode 1 formed on the piezoelectric substrate 19 and including bus bar electrodes 12a, reflector electrodes 2 disposed to be adjacent to both sides of the IDT electrode 1 in a main propagation direction F of surface acoustic waves at the IDT electrode 1, and auxiliary reflector electrodes 3 that includes electrodes formed repeatedly and are disposed at positions external to the reflector electrodes 2 on virtual straight lines extending from the bus bar electrodes 12a of the IDT electrode 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave resonator having improved Q, a surface acoustic wave filter having improved insertion loss, a surface acoustic wave duplexer having improved isolation characteristics, insertion loss and power durability, and these surface acoustic wave filters. The present invention relates to a communication device using a surface acoustic wave duplexer or a surface acoustic wave resonator. Such surface acoustic wave resonators, surface acoustic wave filters, and surface acoustic wave duplexers are collectively referred to as “surface acoustic wave elements”. A surface acoustic wave element has been widely used as a filter for an RF stage and an IF stage of a mobile phone, for example, in the mobile communication field.

  2. Description of the Related Art In recent years, surface acoustic wave elements that are compact and lightweight and have a sharp cutoff performance have been used as constituent elements for filters, delay lines, oscillators, and the like of electronic devices that use radio waves.

  As a type of surface acoustic wave element, a ladder type (ladder type) surface acoustic wave filter is known in which surface acoustic wave resonators composed of a plurality of one-terminal pairs are connected in series and parallel on the same piezoelectric substrate. ing.

  Usually, a surface acoustic wave resonator composed of one terminal pair includes an IDT (InterDigital Transducer) electrode 1 including a bus bar electrode 12a and electrode fingers 13, and an elastic surface excited from the IDT electrode 1, as shown in FIG. It consists of reflector electrodes 2 arranged adjacent to the IDT electrode 1 on both sides of the electrode finger repetition direction, which is the main propagation direction of waves.

  Ladder type surface acoustic wave filters are widely used as RF stage filters for cellular phones and the like because they are small in size, have a low loss in the pass band, and can realize a high attenuation filter outside the pass band.

  By using a total of two such ladder-type surface acoustic wave filters for the transmission side and the reception side, an antenna duplexer can be configured.

  The duplexer is a high frequency component having a function of separating a signal in a transmission side frequency band (for example, a low frequency side frequency band) and a signal in a reception side frequency band (for example, a high frequency side frequency band).

A large power exceeding 1 W is normally applied to the transmission filter of the duplexer, but a part of the surface acoustic wave excited by the IDT electrode of the surface acoustic wave resonator constituting the transmission filter is contained in the surface acoustic wave resonator. Without being sufficiently confined, it leaks out of the surface acoustic wave resonator, propagates on the piezoelectric substrate, and is received by the IDT electrode of the surface acoustic wave resonator constituting the reception filter. Since the leaked surface acoustic wave is converted again into an electric signal, a part of the signal from the input terminal of the transmission filter to the antenna terminal leaks into the reception filter, which is the S of the reception signal. The / N (signal / noise) ratio was deteriorated. The leakage power ratio from the input terminal of the transmission filter to the reception filter is referred to as “isolation”.
Japanese Utility Model Publication No. 6-9229 Satoshi Matsuda, Yasuyuki Saito, Osamu Kawauchi, Akinori Miyamoto, “Improvement of SAW surface acoustic wave device characteristics by elastic wave observation”, Proceedings of the 33rd EM Symposium, May 20, 2004, p. 77-82 J. Tsutsumi, S. Inoue, and Y. Iwamoto, “Extremly Low-Loss SAW Filter and Its Application to Antenna Duplexer for The 1.9GHz PCS Full-Band”, Proc. IEEE International Frequency Control Sympo. Pp.861-867, (2003) JVKnuuttila, J. Koskela, PTTikka, and MMSalomaa, 1999 IEEE Ultrasonics Sympo., P83

  In recent years, the required specifications on the communication system side have become stricter, and a duplexer having better isolation characteristics (smaller leakage power ratio) than the conventional one is desired.

  Moreover, since the number of parts constituting the communication device is increasing with the further enhancement of functions of the communication device, there is always a demand for downsizing the parts.

  Conventionally, in order to improve isolation characteristics, degradation of isolation characteristics due to acoustic coupling of surface acoustic waves leaked by cutting and separating the piezoelectric substrate itself into two filters, a transmission filter and a reception filter. (For example, see Non-Patent Documents 1 and 2).

  However, in the antenna duplexer configured in this way, the number of pieces to be taken per wafer is reduced by the area of the cutting allowance for cutting into two, and it is difficult to reduce the manufacturing cost. Further, since a mounting margin necessary for mounting the chip in the package is required for two chips, the size of the package increases, and it is difficult to satisfy the customer's demand for miniaturization.

  A surface acoustic wave element is an element that converts an electric signal into a mechanical wave (= surface acoustic wave) and processes the signal. The electric signal input to the surface acoustic wave filter is converted into an electric signal by a surface acoustic wave resonator. Leakage in the state of a surface acoustic wave converted from a signal means that the electric signal power input to the surface acoustic wave filter is lost in a state converted to a surface acoustic wave. There is also a problem that the insertion loss of the filter increases when the surface acoustic wave leaks from the surface wave resonator. For this reason, when such an antenna duplexer with a large insertion loss is mounted on a communication device, a larger output power is required to transmit an electric signal with a necessary transmission power, which has led to a reduction in power consumption in recent years. There was also a problem that the request could not be met.

  In addition, since the insertion loss of the filter is large, when a large amount of power is applied to the transmission side filter, there is a problem that the amount of heat generated in the transmission side filter is large, which shortens the power durability.

  Also, in order to realize a good insertion loss, the equivalent capacitance of each of the series resonator and the parallel resonator constituting the ladder type (= electricity determined by the number of electrode pairs of the comb-like electrode fingers, the crossing width, the electrode pitch, etc.) It is effective to reduce the capacity ratio determined by the ratio of capacity. However, since the attenuation amount of the conventional surface acoustic wave filter is almost determined by this capacitance ratio, if the capacitance ratio is decreased to achieve a good insertion loss, the attenuation amount deteriorates and the S / N ratio deteriorates. There was a problem.

  Here, the reason why the surface acoustic wave leaks outside the surface acoustic wave resonator will be described.

  The surface acoustic wave excited by the IDT electrode propagates in a direction substantially perpendicular to the longitudinal direction of the electrode finger. This direction is called the main propagation direction. If the electrode finger is in an ideal state with an infinite length in the longitudinal direction, a surface acoustic wave that propagates only in the main propagation direction is excited, but the actual element is actually excited because it has a finite size. The surface acoustic wave includes a component deviating from the main propagation direction.

  As shown in FIG. 32, a conventional surface acoustic wave resonator is formed so that the length in the longitudinal direction of the reflector electrode 2 at both ends of the IDT electrode 1 is approximately the same as the length in the longitudinal direction of the IDT electrode 1. The reflector electrode 2 cannot efficiently reflect the component deviated from the main propagation direction, and the component deviated from the main propagation direction leaks to the outside of the surface acoustic wave resonator.

  The surface acoustic wave excited by the IDT electrode 1 includes a plurality of frequency components. Usually, the reflector electrode 2 has the highest reflection efficiency with respect to a certain frequency among the frequency components excited by the IDT electrode 1. In order to improve the period, the period of the repetitive electrode (also referred to as the grating electrode) is designed so that surface acoustic waves of other frequency components are not reflected efficiently by the reflector but leak outside the surface acoustic wave resonator. End up.

  When the propagation mode existing in the main propagation path in the surface acoustic wave resonator and the propagation mode existing in the bus bar electrode 12a can be coupled, the surface acoustic wave excited at the intersection of the electrode fingers is transferred to the bus bar electrode 12a. Since there is no structure for confining the surface acoustic wave at the end of the bus bar electrode 12a, the surface acoustic wave leaks from the end of the bus bar electrode to the outside of the surface acoustic wave resonator (for example, Non-Patent Document 3). reference).

  The surface acoustic wave leaking to the outside of the surface acoustic wave resonator in this way causes the above-described problem. In a duplexer, such leakage has not been a problem in the past, but has become a problem due to recent strict requirements for characteristics.

  Patent Document 1 discloses that a reflector having a bent or curved shape is obtained by forming a reflector with a bent or curved shape so that a surface acoustic wave having an angle with respect to the main propagation direction of the IDT electrode is bent or curved. A structure has been proposed in which leakage of surface acoustic waves to the outside of the resonator can be prevented because it is efficiently reflected by the electrode and returned to the IDT electrode again.

  However, since the reflector electrode having the structure described in Patent Document 1 has a shape in which the end of the conventional reflector is extended as it is, the grating electrode period has the highest reflection efficiency with respect to the frequency in the band. I have to design it like this. For this reason, although the loss within the pass band of the filter is improved, in the adjacent frequency band outside the pass band (that is, the receiving side frequency band adjacent to the transmitting side frequency band) that is a problem in the antenna duplexer It was not possible to prevent the surface acoustic wave having a frequency affecting the isolation characteristics from leaking.

  In view of the above problems, an object of the present invention is to realize a high-Q surface acoustic wave resonator by preventing leakage of surface acoustic waves to the outside of the surface acoustic wave resonator.

  Another object of the present invention is to realize a surface acoustic wave filter having a small size and low insertion loss by using the surface acoustic wave resonator of the present invention.

  Another object of the present invention is to provide a surface acoustic wave duplexer that is small in size, excellent in isolation characteristics, low in insertion loss, and excellent in power durability by using the surface acoustic wave resonator of the present invention. Is to realize.

  Another object of the present invention is to provide a communication device with lower power consumption and good call quality by using the surface acoustic wave resonator, surface acoustic wave filter, and surface acoustic wave duplexer of the present invention. It is.

  The surface acoustic wave resonator according to the present invention includes a piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate and having a bus bar electrode, and formed on the piezoelectric substrate in the main propagation direction of the surface acoustic wave of the IDT electrode. A reflector electrode disposed adjacent to both ends, and an electrode formed on the piezoelectric substrate and repeatedly formed, wherein the bus bar electrode of the IDT electrode is virtually positioned at a position outside the reflector electrode. And an auxiliary reflector electrode arranged on an extended straight line.

  According to the surface acoustic wave resonator having this structure, the surface acoustic wave leaking in a direction other than the main propagation direction of the surface acoustic wave of the IDT electrode or the surface acoustic wave leaking from the bus bar electrode Therefore, it is possible to realize a high-Q surface acoustic wave resonator with less leakage loss of surface acoustic waves.

  The auxiliary reflector electrode is preferably formed such that the repeated direction of the electrode formed repeatedly (G shown in FIGS. 1 and 11) is directed toward the IDT electrode.

  In particular, it is desirable that an angle θ formed by the repetition direction of the repeatedly formed electrode of the auxiliary reflector electrode and the repetition direction of the electrode finger of the IDT electrode is greater than 0 degree and 20 degrees or less.

  Further, the number of the auxiliary reflector electrodes per one IDT electrode is not limited. For example, the auxiliary reflector electrodes may be arranged at four positions on the outer side of the reflector electrode.

  The auxiliary reflector electrode has two bus bar electrodes, and both end portions of the repeatedly formed electrode of the auxiliary reflector electrode are so-called ladder-type electrodes connected to the bus bar electrode. Also good.

  Further, the auxiliary reflector electrode may be a comb-shaped electrode having a shape in which one end of the repeatedly formed electrode is electrically opened.

  The auxiliary reflector electrode may be an electrode in which both ends of the repeatedly formed electrode are electrically opened.

  The auxiliary reflector electrode may be an IDT-type electrode having two bus bar electrodes and having electrode fingers extending from the bus bar electrode extending in a substantially right angle direction.

  Moreover, in the said structure, the pitch of the said auxiliary reflector electrode can be made to differ from the pitch of the said reflector electrode. As a result, the auxiliary reflector electrode can be designed so that the reflection efficiency is high at a wavelength different from that of the reflector electrode, and therefore, the surface acoustic wave has a wavelength that is not reflected by the reflector electrode. The auxiliary reflector electrode can also be efficiently reflected, and leakage of the surface acoustic wave to the outside of the surface acoustic wave resonator can be further suppressed.

  Further, according to the surface acoustic wave resonator of the present invention, the pitch of the auxiliary reflector electrode can be made different from the pitch of the IDT electrode. By doing so, it is possible to suppress unnecessary resonance generated between the auxiliary reflector electrode and the IDT electrode, and a surface acoustic wave resonator with less spurious resonance can be realized. Here, the pitch of the IDT electrodes means that one of the comb-like electrodes among the electrode fingers of one comb-like electrode and the electrode fingers of the other comb-like electrode meshed with the comb-like electrode. The distance between the centers of the electrode fingers adjacent to the electrode fingers is indicated.

  Further, since the second auxiliary reflector electrode is formed outside the reflector electrode and between the two auxiliary reflector electrodes, the elasticity that has not been completely reflected by the reflector. Surface waves can be reflected and confined within the IDT electrode. Thereby, a high-Q surface acoustic wave resonator with less surface acoustic wave leakage loss can be realized.

  In addition, the second auxiliary reflector electrode and the auxiliary reflector electrode are connected and integrally formed, thereby leaking between the second auxiliary reflector electrode and the auxiliary reflector electrode. The surface acoustic wave can be further reflected and confined in the surface acoustic wave resonator, and a surface acoustic wave resonator having a higher Q can be realized. Further, since the potentials of the second auxiliary reflector electrode and the auxiliary reflector electrode can be made equal, the fineness due to sparks that may occur between different portions due to the pyroelectric property of the piezoelectric substrate. An electrode can be prevented from being broken, and a high-Q surface acoustic wave resonator can be realized.

  Further, according to the surface acoustic wave filter using the surface acoustic wave resonator of the present invention, the surface acoustic wave filter having a small size and low insertion loss is realized by including the surface acoustic wave resonator having a high Q. can do. Conventionally, in order to prevent the surface acoustic wave leaked from the transmission filter from being combined with the reception filter, the substrate is divided into two by the transmission filter and the reception filter. For this reason, a margin for mounting is required. However, according to the present invention, since leakage of surface acoustic waves from the transmission filter can be prevented, there is no need to divide the board into two, and the mounting margin as described above. Can be reduced in size.

  According to the surface acoustic wave duplexer using the surface acoustic wave resonator of the present invention, in the surface acoustic wave duplexer having the transmission filter region and the reception filter region on the substrate, the surface acoustic wave resonator described above Is provided in at least one of the transmission filter region or the reception filter region, and by using a piezoelectric substrate as a common substrate, it is small but has excellent isolation characteristics and a small insertion loss. A surface acoustic wave duplexer with excellent power durability can be realized.

  And according to the communication device of the present invention provided with the surface acoustic wave duplexer of the present invention, because the filter has a low insertion loss, the input power necessary to obtain the same output power can be reduced, The power consumption of the power amplifier can be reduced, and therefore a communication device with reduced power consumption can be realized. In addition, since the surface acoustic wave duplexer is small, a mounting area for other components can be secured, and thus a highly functional communication device can be realized. In addition, high call quality can be obtained due to high isolation characteristics.

  Hereinafter, an example of an embodiment of a surface acoustic wave device of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol shall be attached | subjected to the same location in drawing. Further, 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, and are not limited to these.

  FIG. 1 shows a plan view of a surface acoustic wave resonator.

  This surface acoustic wave resonator is an element in which a plurality of electrodes made of a metal thin film are formed on one main surface of a piezoelectric substrate (see “19” in FIG. 2). The formed electrodes are the IDT electrode 1, the reflector electrode 2, the auxiliary reflector electrode 3, and the like.

  The IDT electrode 1 includes two bus bar electrodes 12a extending in parallel to the main propagation direction F of surface acoustic waves, and electrode fingers 13 that are formed to extend perpendicularly inward from each bus bar electrode 12a and engage with each other.

  The reflector electrode 2 is disposed adjacent to both ends of the main propagation direction F of the IDT electrode 1. The reflector electrode 2 includes two bus bar electrodes 12b extending in parallel and a grating electrode 14a formed extending from each bus bar electrode 12b at a right angle inward. The grating electrode 14a is also connected to the opposing bus bar electrode 12b and is short-circuited from the electrode finger 13 that is not connected to the opposing bus bar electrode 12b.

  Four auxiliary reflector electrodes 3 are arranged on the side of the reflector electrode 2 that is not adjacent to the IDT electrode 1, that is, on four positions outside the reflector electrode 2. These four positions are on a straight line H obtained by virtually extending the two bus bar electrodes 12 a of the IDT electrode 1. Similarly to the reflector electrode 2, the auxiliary reflector electrode 3 also includes a shorted grating electrode 14b.

  In addition, the installation positions of the auxiliary reflector electrode 3 are not limited to the four positions outside the reflector electrode 2. You may install only in one place among the four places, and may install in two places or three places. Even if it is installed in one to three places, it is possible to achieve the effect of the present invention that prevents leakage of surface acoustic waves to the outside and increases Q.

  Each of the auxiliary reflector electrodes 3 is disposed so as to be inclined so that the repeating direction of the grating electrode 14 b (hereinafter referred to as “direction G of the auxiliary reflector electrode 3”) faces the IDT electrode 1. That is, when viewed from the IDT electrode 1, the four auxiliary reflector electrodes 3 are arranged in directions extending outward. The inclination angle is indicated by θ.

  In the conventional structure without the auxiliary reflector electrode 3 (FIG. 32), there exists a surface acoustic wave that leaks outside the reflector electrode 2. This is because the reflector electrode 2 is formed with a single electrode pitch, and surface acoustic waves having wavelengths other than the wavelength reflected at this pitch leak.

  In addition, a surface acoustic wave may leak from the bus bar electrode 12a of the IDT electrode 1, but if the leaked surface acoustic wave is combined with a propagation mode from the bus bar electrode 12b of the reflector electrode 2, eventually the bus bar electrode 12b. The surface acoustic wave leaks from the end portion.

  Therefore, by forming the auxiliary reflector electrode 3 as shown in FIG. 1, it is possible to reflect such a leaky surface acoustic wave leaking in the oblique θ direction from the leaking main propagation direction F and reduce the leaking energy. it can.

  Therefore, the Q value of the surface acoustic wave resonator can be further increased, and effects such as improvement in the insertion loss of the surface acoustic wave filter and improvement in the isolation of the surface acoustic wave duplexer can be obtained.

  FIG. 2 is a schematic top view of a surface acoustic wave duplexer in which a transmission filter and a reception filter using the surface acoustic wave resonator having the structure of FIG. 1 are formed on the same piezoelectric substrate 19. In FIG. 2, the upper half shows a transmission filter area, and the lower half shows a reception filter area.

  A signal input from the input terminal 15 of the transmission filter is output from the output terminal 16 through three series surface acoustic wave resonators and two parallel surface acoustic wave resonators combined in a ladder shape.

  A signal input from the input terminal 17 of the reception filter is output from the output terminal 18 through two series surface acoustic wave resonators and three parallel surface acoustic wave resonators that are alternately combined in a ladder shape. Is done.

  Further, the auxiliary reflector electrode 3 is added to each of the surface acoustic wave resonators of the transmission side and the reception filter, and the surface acoustic wave leaks in an obliquely inclined direction with respect to the main propagation direction F. Is reduced.

  An annular electrode 21 is provided on the piezoelectric substrate 19. The annular electrode 21 is for hermetically sealing the piezoelectric substrate 19 to a mounting substrate (not shown) by flip chip mounting. Experiments have shown that even if the annular electrode 21 exists, propagation of the surface acoustic wave leaked from the surface acoustic wave resonator is hardly hindered.

  In the structure of FIG. 2, it is particularly effective to use the configuration of the present invention for the series surface acoustic wave resonator among the surface acoustic wave resonators constituting the transmission filter.

  This is because the high-power signal applied to the transmission filter passes through the series surface acoustic wave resonator, but the strong surface acoustic wave excited at this time can be efficiently confined by the present invention. .

  On the other hand, when the surface acoustic wave resonator according to the present invention is used as the parallel surface acoustic wave resonator of the reception filter, the surface acoustic wave leaked from the series surface acoustic wave resonator of the transmission filter is parallel to the parallel elasticity of the reception filter. Reflected by the auxiliary reflector electrode 3 used for the surface wave resonator. As a result, since it is difficult for the IDT electrode 1 constituting the parallel surface acoustic wave resonator of the reception filter to receive, there is an effect of improving isolation.

  The pitch of the grating electrodes 14b of the auxiliary reflector electrode 3 can be made different from the pitch of the grating electrodes 14a of the reflector electrode 2.

  For example, the pitch of the grating electrode 14b of the auxiliary reflector electrode 3 of the surface acoustic wave resonator used for the transmission filter is matched with the pitch of the electrode fingers 13 of the IDT electrode 1 of the surface acoustic wave resonator used for the reception filter. As a result, the isolation characteristics in the reception frequency band can be improved. This is because a surface acoustic wave having a wavelength in the reception frequency band that could not be completely reflected by the reflector electrode 2 is reflected by the auxiliary reflector electrode 3 and is confined in the surface acoustic wave resonator of the transmission filter. This is because the surface acoustic wave in the band does not leak.

  Further, a plurality of different pitches may be mixed in the grating electrode 14b of the auxiliary reflector electrode 3. By doing so, the surface acoustic wave leaking from the surface acoustic wave element can be suppressed not only in a specific frequency band but also in a wider band, so that the Q of the surface acoustic wave resonator is improved. In this case, the spatial arrangement of the plurality of pitches is not particularly important and can be set freely.

  In addition, in FIG. 1 etc., the IDT electrode 1 shows a case where the short dummy electrode 8 is formed on the other bus bar electrode 12a of the portion opposite to the tip of the electrode finger 13 formed on one bus bar electrode 12a. However, this makes it more difficult to couple the propagation mode of the main propagation path and the propagation mode of the bus bar electrode, so leakage from the main propagation path of the surface acoustic wave resonator to the outside through the bus bar electrode. The surface acoustic wave to be generated can be reduced, and a high-Q surface acoustic wave resonator can be obtained. And when a filter is comprised using this surface acoustic wave resonator, it can be set as a filter with a lower insertion loss. Furthermore, when a duplexer having a transmission filter region and a reception filter region on the same substrate is configured, the isolation characteristic is further improved.

  In addition, in FIG. 1 and the like, a ladder-like electrode (short reflector) in which the grating electrode 14b is electrically short-circuited at both ends is used as the structure of the auxiliary reflector electrode 3, but it is not limited to such a shape. For example, even if it is a shape (open reflector) in which both ends or one end is electrically opened, the isolation characteristics can be improved in the same manner.

  FIG. 3 shows an example of an open reflector with one end electrically open, and FIG. 4 shows an example of an open reflector with both ends electrically open.

  Furthermore, the shape of the auxiliary reflector electrode 3 may be a shape (IDT reflector) in which electrode fingers are alternately engaged like an IDT electrode. This structure will be described in detail later with reference to the drawings.

  The shape of the auxiliary reflector electrode 3 is not a grating electrode made of linear electrode fingers but a grating electrode made up of an arc having a certain curvature, a bent or curved shape, or a trapezoidal shape. You can also. By doing so, surface acoustic waves leaking over a wide range of angles can be reflected, so that it is possible to obtain more effects such as improvement of the Q value of the resonator, improvement of the insertion loss of the filter, and improvement of the isolation of the duplexer. it can.

  In the surface acoustic wave resonator of the present invention, a lithium tantalate single crystal, a lithium niobate single crystal, a lithium tetraborate single crystal, or the like can be used as the piezoelectric substrate.

  The IDT electrode, the reflector electrode, and the auxiliary reflector electrode according to the present invention include aluminum, an aluminum alloy, copper, a copper alloy, gold, a gold alloy, tantalum, a tantalum alloy, or a laminated film made of these materials. Alternatively, a laminated film of these materials and a layer made of a material such as titanium or chromium can be used. As a method for forming these laminated films, a sputtering method or an electron beam evaporation method can be used.

  As a method of patterning these electrodes, there is a method of performing photolithography after forming an electrode film, and then performing RIE (Reactive Ion Etching) or wet etching. Alternatively, after forming a pattern such as a desired IDT electrode or reflector electrode by applying a photoresist on the piezoelectric substrate and performing photolithography before forming the electrode film, a single layer film made of a material such as aluminum or the like A lift-off process may be performed in which a laminated film is formed, and then the resist is removed together with the single-layer film or laminated film formed in unnecessary portions.

  Hereinafter, modifications of the electrode shape of the surface acoustic wave resonator formed on the piezoelectric substrate will be described.

  As shown in FIG. 5, the second auxiliary reflector electrode 4 having the grating electrode 14 c may be disposed at a position adjacent to the reflector electrode 2 on the side opposite to the IDT electrode 1.

  The second auxiliary reflector electrode 4 propagates in a direction substantially perpendicular to the electrode finger of the IDT electrode 1, that is, along the main propagation direction F of the surface acoustic wave as described above, and is completely transmitted by the first reflector electrode 2. Can reflect surface acoustic waves that cannot be reflected.

  The pitch of the grating electrodes 14c of the second auxiliary reflector electrode 4 is preferably different from the pitch of the grating electrodes 14a of the reflector electrode 2. By doing in this way, the surface acoustic wave which was not able to be reflected by the reflector electrode 2 can be reflected efficiently.

  In FIG. 5, the second auxiliary reflector electrode 4 is shown as a ladder electrode (short reflector) made up of a bus bar electrode and a grating electrode, but an IDT electrode (IDT reflector made up of a bus bar electrode and an electrode finger). However, it may be composed only of the grating electrode (open reflector).

  Further, a plurality of different pitches may be mixed in the grating electrode 14c of the second auxiliary reflector electrode 4. By doing so, the surface acoustic wave leaking from the surface acoustic wave resonator can be suppressed not only in a specific frequency band but also in a wider band, so that the Q value of the surface acoustic wave resonator is improved. . In this case, the spatial arrangement of the plurality of pitches is not particularly important and can be set freely.

  Further, as shown in FIG. 6, the auxiliary reflector electrode 3 and the second auxiliary reflector electrode 4 which are adjacent to each other may be connected by a connecting portion 5 to be integrally formed. By doing so, the potentials of the auxiliary reflector electrode 3 and the second auxiliary reflector electrode 4 can be made equal, and therefore, by the spark generated between different portions due to the pyroelectric property of the piezoelectric substrate. The microelectrode can be prevented from being broken, and a high-Q surface acoustic wave resonator can be realized.

  In addition, when the auxiliary reflector electrode 3 and the second auxiliary reflector electrode 4 are connected and integrally formed, various connection structures are conceivable. For example, as shown in FIG. 6, it is possible to extend and connect the portions that originally existed in FIG.

  Further, as shown in FIG. 7, the grating electrode 14b of the auxiliary reflector electrode 3 and the grating electrode 14c of the second auxiliary reflector electrode 4 may be extended and integrated. At this time, the reflector bus bar electrode 25 for short-circuiting the grating electrode may be provided in the region of the connecting portion 5 or may not be provided as shown in FIG.

  Further, as shown in FIG. 9, a grating electrode 14 d may be provided in a region between the auxiliary reflector electrode 3 and the second auxiliary reflector electrode 4. By adopting such a structure, the surface acoustic wave leaking between the auxiliary reflector electrode 3 and the second auxiliary reflector electrode 4 can be further reflected and confined in the surface acoustic wave resonator. A high-Q surface acoustic wave resonator can be realized.

  Among the structures described above, the structure shown in FIG. 7 and the structure shown in FIG. 9 are particularly advantageous because the optimum pitch of the grating electrodes can be obtained in each direction.

  In addition, the shape of the second auxiliary reflector electrode 4 can be formed not by a grating electrode made of linear electrode fingers but by a circular arc having a certain curvature, or a grating electrode made up of a bent or curved shape. In this way, the surface acoustic wave leaking in a wide range of angles can be reflected, so that the Q value of the higher surface acoustic wave resonator, the insertion loss of the filter, the isolation of the duplexer, etc. can be improved. An effect can be obtained.

  Further, as shown in FIG. 10, instead of the reflector electrode 2 having the rectangular outer shape shown in FIG. 1, the reflector bar electrode 12 b is inclined toward the IDT electrode 1. A reflector electrode 2 'having a shape in which the end of the grating electrode 14a of the electrode is bent may be used.

  Further, in FIG. 10, the reflector electrode 2 ′ is shown in a bent shape, but may be a smoothly curved shape.

  By making such a bent or curved shape, the surface acoustic wave leaking from the IDT electrode 1 in a direction other than the main propagation direction F of the surface acoustic wave is reflected by the bent or curved reflector electrode 2 ′. And higher effects can be obtained.

  FIG. 11 shows an example in which, instead of the auxiliary reflector electrode 3 of FIG. 1, an IDT type auxiliary reflector electrode 3 ′ having bus bar electrodes 12 c and electrode fingers 13 b and alternately engaging the electrode fingers 13 b is arranged. It is a top view.

  The four positions where these IDT type auxiliary reflector electrodes 3 ′ are arranged are on a straight line obtained by virtually extending the bus bar electrode 12 a of the IDT electrode 1.

  Each of the IDT auxiliary reflector electrodes 3 ′ has a repeating direction of each IDT auxiliary reflector electrode 3 ′ (hereinafter referred to as “direction of the IDT auxiliary reflector electrode 3 ′) G directed toward the IDT electrode 1. It is arranged to be inclined.

  Since no signal line is connected to the IDT auxiliary reflector electrode 3 ', the surface acoustic wave itself is not excited.

  It is possible to form a surface acoustic wave duplexer, which is a surface acoustic wave element according to the present invention, by forming two ladder filters made using a plurality of surface acoustic wave resonators shown in FIG. 11 on a piezoelectric substrate 19. I can do it. The structure is shown in FIG. Instead of the auxiliary reflector electrode 3 in FIG. 1, the only difference is that an IDT type auxiliary reflector electrode 3 'is arranged.

  Note that the pitch of the electrode fingers 13b of the IDT auxiliary reflector electrode 3 'may be different from the pitch of the grating electrodes 14a of the reflector electrode 2. In this way, since the IDT auxiliary reflector electrode 3 'can be designed to have a high reflection efficiency at a wavelength different from that of the reflector electrode 2, a surface acoustic wave having a wavelength that is not reflected by the reflector electrode 2 can be used. Even so, it can be efficiently reflected by the IDT auxiliary reflector electrode 3 ', and leakage of the surface acoustic wave to the outside of the surface acoustic wave resonator can be further suppressed.

  Further, the pitch of the electrode fingers 13b of the IDT type auxiliary reflector electrode 3 'may be different from the pitch of the electrode fingers 13a of the IDT electrode 1. This makes it possible to suppress unnecessary resonance that occurs between the IDT-type auxiliary reflector electrode 3 ′ and the IDT electrode 1, thereby realizing a surface acoustic wave resonator with little ripple.

  In the case of the duplexer shown in FIG. 12, the pitch of the electrode fingers 13b of the IDT auxiliary reflector electrode 3 'of the surface acoustic wave resonator used for the transmission filter is set to the IDT of the surface acoustic wave resonator used for the reception filter. If the pitch is adjusted to the pitch of the electrode fingers 13a of the electrode 1, the isolation characteristic in the reception frequency band can be improved. This is because a surface acoustic wave having a wavelength in the reception frequency band that could not be completely reflected by the reflector electrode 2 is reflected by the IDT auxiliary reflector electrode 3 'and is confined in the surface acoustic wave resonator. This is because the surface acoustic wave does not leak from the surface acoustic wave resonator of the filter to the reception filter.

  Further, a plurality of different pitches may be mixed in the electrode finger 13b of the IDT type auxiliary reflector electrode 3 ′. By doing so, the surface acoustic wave leaking from the surface acoustic wave resonator can be suppressed not only in a specific frequency band but also in a wider band, so that the Q value of the surface acoustic wave resonator is improved. . In this case, the spatial arrangement of the plurality of pitches is not particularly important and can be set freely.

  The IDT auxiliary reflector electrode 3 ′ is not composed of a linear electrode finger but an electrode finger formed of an arc having a certain curvature, a bent or curved shape, or a trapezoidal shape. By doing so, surface acoustic waves leaking over a wide range of angles can be reflected, improving the Q value of higher surface acoustic wave resonators, improving filter insertion loss, and improving duplexer isolation. Etc. can be obtained.

  Further, in the IDT auxiliary reflector electrode 3 ′, a dummy electrode 8 is provided as in the IDT electrode 1 shown in FIG. 11, or the lengths of the electrode fingers 13a and the dummy electrodes 8 are different depending on the location. You may do. By doing this, it is possible to reflect surface acoustic waves leaking over a wider range of wavelengths, or to improve the reflection efficiency at a certain frequency, thereby improving the Q value of higher surface acoustic wave resonators. Effects such as improved filter insertion loss and improved duplexer isolation can be obtained.

  Further, the second auxiliary reflector electrode 4 may be disposed between two adjacent IDT type auxiliary reflector electrodes 3 ′, that is, on both outer sides of the reflector electrode 2. FIG. 13 is a diagram illustrating an arrangement example of the second auxiliary reflector electrode 4.

  The second auxiliary reflector electrode 4 can reflect a surface acoustic wave that propagates in a direction substantially perpendicular to the electrode finger 13a of the IDT electrode 1 as described above and cannot be completely reflected by the reflector electrode 2. .

  Note that when the second auxiliary reflector electrode 4 is a grating electrode 14b, the pitch may be different from the pitch of the grating electrode 14a of the reflector electrode 2, and the grating is also a IDT electrode (IDT reflector). As described with reference to FIG. 5, it may be composed of only electrodes (open reflectors) or may be configured by mixing a plurality of different pitches.

  Further, the IDT auxiliary reflector electrode 3 'and the second auxiliary reflector electrode 4 which are adjacent to each other may be connected and formed integrally.

  For example, as shown in FIG. 14, it is possible to connect the bus bar electrode of the IDT-type auxiliary reflector electrode 3 ′ and the bus bar electrode of the second auxiliary reflector electrode 4 by providing a connection portion 5a in an extended region.

  Further, as shown in FIG. 15, a connecting portion 5b, which is a region in which the grating electrode 14b of the second auxiliary reflector electrode 4 is extended until it contacts the electrode finger 13b of the IDT auxiliary reflector electrode 3 ', is provided. May be integrated. At this time, the reflector bus bar electrode 25 for short-circuiting the grating electrode 14b may be provided, or may not be provided as shown in FIG.

  Further, as shown in FIG. 17, a grating electrode 14 c may be further provided in the connection portion 5 d which is a region between the IDT auxiliary reflector electrode 3 ′ and the second auxiliary reflector electrode 4 in FIG. 13. Instead of the grating electrode 14c, an IDT electrode may be provided.

  With such a structure, the surface acoustic wave leaking between the IDT auxiliary reflector electrode 3 'and the second auxiliary reflector electrode 4 shown in FIG. A surface acoustic wave resonator that can be confined and has a higher Q can be realized.

  Among such structures, the structure shown in FIG. 15 and the structure shown in FIG. 17 are advantageous because an optimum grating electrode pitch can be obtained in each direction.

  In addition, the shape of the second auxiliary reflector electrode 4 is not a linear electrode finger, but an electrode finger constituted by an arc having a certain curvature, a bent or curved shape, or a trapezoidal shape. By doing so, surface acoustic waves leaking over a wide range of angles can be reflected, improving the Q value of higher surface acoustic wave resonators, improving filter insertion loss, and improving duplexer isolation. Etc. can be obtained.

  Further, instead of the reflector electrode 2 having the rectangular shape shown in FIG. 11, the bus bar electrode 12 b portion of the reflector electrode 2 is inclined toward the IDT electrode 1 in the same manner as shown in FIG. 10. As described above, a reflector electrode having a shape in which the end of the grating electrode 14a of the reflector electrode is bent may be used.

  Since the surface acoustic wave resonator or surface acoustic wave element of the present invention described above has a good in-passband characteristic of insertion loss, these can be applied to a communication device.

  That is, in a communication device including one or both of a reception circuit and a transmission circuit, the surface acoustic wave resonator or surface acoustic wave element of the present invention can be mounted on a bandpass filter or a duplexer.

  The transmission circuit is a circuit that places a transmission signal on a carrier frequency with a mixer, attenuates an unnecessary signal with a band-pass filter, amplifies the transmission signal with a power amplifier, and transmits the amplified signal from an antenna through a duplexer.

  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.

  A communication apparatus in which the duplexer or the bandpass filter is incorporated can reduce the input power necessary to obtain the same output power because the filter has a low insertion loss. For this reason, the power consumption of the power amplifier can be reduced, and therefore a communication device with reduced power consumption can be realized.

  In addition, by using the surface acoustic wave duplexer of the present invention having the transmission filter region and the reception filter region on the piezoelectric substrate, the surface acoustic wave duplexer is small, so that a mounting area for other components can be secured. For this reason, a small and highly functional communication device can be realized. In addition, high call quality can be obtained due to high isolation characteristics.

  The embodiment of the present invention is not limited to the above example, and various modifications can be made without departing from the scope of the present invention.

  For example, as shown in FIG. 18, the thick film portion 6 may be further provided on the bus bar electrode 12 a or the bus bar electrode 12 b of the reflector electrode 2. By doing in this way, since it can suppress that the mode of a main propagation path and a bus-bar electrode couple | bonds, the loss by the leakage of a surface acoustic wave can be suppressed more. Although FIG. 18 shows a shape in which the thick film portion 6 is provided symmetrically with respect to the electrode finger 13 and the grating electrode of the reflector electrode 2, the shape may be different up and down.

  Further, the outer shape of the IDT electrode may be apodized in a shape such as a triangle, a rhombus, or a trapezoid instead of the rectangle shown in FIGS.

  Further, the shape of the grating electrode region of the reflector electrode may be a triangle, a rhombus, a trapezoid, or the like.

  Further, the position of the auxiliary reflector electrode may be arranged on a straight line obtained by virtually extending the bus bar electrode on the side not adjacent to the IDT electrode of the reflector electrode, and the inclination angle θ exceeds 0 °, Although effective if the angle is 20 ° or less, the effective angle is a parameter depending on the substrate orientation, the film thickness of the IDT electrode, the pitch of the electrode fingers 13, and the like, and is not limited to this range.

  The ladder type filter has been described. However, the present invention can be applied to any surface acoustic wave element that handles surface acoustic waves, such as a DMS type filter, a transversal type filter, and an IDT type filter.

  First, Ti / Al-1 mass% Cu / Ti / Al is formed on one main surface of a piezoelectric substrate (substrate thickness is 250 μm) composed of a 38.7 ° Y-cut X propagation lithium tantalate single crystal substrate from the substrate side by sputtering. Four layers of the underlying conductor film made of −1 mass% Cu were formed. The film thicknesses are 6 nm / 104 nm / 6 nm / 104 nm, respectively.

  Next, the underlying conductor film is patterned by photolithography and RIE, and a plurality of surface acoustic wave resonators each including an IDT electrode having electrode fingers and bus bar electrodes, a reflector electrode, and an auxiliary reflector electrode are provided. Then, they were connected to a ladder type, and the surface acoustic wave duplexer of the present invention shown in FIG. 2 and FIG. A mixed gas of BCl3 and Cl2 was used as an etching gas at this time. Both the line width of the electrode fingers and the distance between adjacent electrode fingers are about 0.5 μm.

  In addition, as a comparative example of the conventional structure, a surface acoustic wave duplexer having the structure shown in FIG.

  Next, a new conductor layer made of Cr / Ni / Au is laminated on the input terminals 15 and 17, the output terminals 16 and 18, and the annular electrode 21, and the input terminals 15 and 17 and the output terminals 16 and 18 are stacked. An input pad and an output pad were formed on each of them.

  The thicknesses of the new conductor layers are 10 nm / 1000 nm / 100 nm, respectively.

  Thereafter, the piezoelectric substrate was diced along dicing lines and divided for each surface acoustic wave duplexer chip.

  Next, the surface acoustic wave duplexer of the example of the present invention and the surface acoustic wave duplexer of the comparative example were each mounted on a mounting base made of an LTCC (Low Temperature Co-fired Ceramics) substrate with one main surface facing each other. .

  Here, the LTCC substrate has a base-side annular conductor corresponding to the annular electrode 21 formed on one main surface of the piezoelectric substrate 19 and pad electrodes connected to the input / output pads of the surface acoustic wave duplexer. Solder was printed on the base-side annular conductor and the pad electrode.

  When mounting a surface acoustic wave duplexer on this, place the surface acoustic wave duplexer to match these solder patterns, temporarily fix it by applying ultrasonic waves, and then heat to melt the solder Thus, the annular electrode 21 and the base-side annular conductor were connected, and the input / output pad and the pad electrode were connected.

  As a result, each IDT electrode, reflector electrode, and input / output pad of the surface acoustic wave duplexer were completely hermetically sealed by the base-side annular conductor of the LTCC substrate and the annular electrode 21 connected thereto.

  The surface acoustic wave element mounting process described above was performed in a nitrogen atmosphere.

  Next, the other main surface (back surface) of the surface acoustic wave element is protected with a mold resin, and finally the LTCC substrate is diced between the surface acoustic wave duplexers, so that the surface acoustic wave duplexer of the embodiment of the present invention and the comparison are compared. A surface acoustic wave device having an example surface acoustic wave duplexer was obtained.

(1) Case with Auxiliary Reflector Electrode 3 (FIG. 2) FIG. 20 is a graph showing the isolation characteristics of the duplexer having the structure of FIG.

  In the graph of FIG. 20, the horizontal axis represents normalized frequency, and the vertical axis represents isolation (unit: dB). The dotted characteristic curve indicates the result of the conventional surface acoustic wave duplexer shown in FIG. 19 without the conventional auxiliary reflector electrode 3, and the solid characteristic curve indicates the auxiliary reflector electrode 3 with respect to the conventional surface acoustic wave duplexer. The result of the Example of this invention when adding is shown.

  As can be seen from the results shown in FIG. 20, the surface acoustic wave duplexer according to the embodiment of the present invention has a significant improvement of, for example, a maximum isolation characteristic of 5 dB at a normalized frequency of 0.95 compared to the comparative example. It was observed.

  It is considered that the duplexer having the configuration of the comparative example cannot obtain good characteristics because the surface acoustic wave resonator that constitutes the transmission filter includes a leaky surface acoustic wave that propagates in a leak.

  FIG. 21 shows an example in which the impedance characteristic (solid line) of a one-terminal surface acoustic wave resonator manufactured using the surface acoustic wave resonator of the present invention is compared with the impedance characteristic (dashed line) of a conventional surface acoustic wave resonator. It is a graph which shows.

  In FIG. 21, the horizontal axis represents a frequency normalized with an arbitrary frequency, and the vertical axis represents the absolute value | Z | (unit: Ω) of the impedance. The peak portion of the impedance | Z | is called anti-resonance resistance.

  As shown in FIG. 21, in the present invention, the peak value called the anti-resonance resistance value 11 can be increased to achieve a high Q. The anti-resonance resistance value 11 is a parameter that affects the insertion loss in the passband when a ladder type filter is configured. Can be reduced. Specifically, the anti-resonance resistance value 11 of the present invention is about 900Ω, whereas the conventional anti-resonance resistance value 10 without the auxiliary reflector electrode 3 is 840Ω, which is as large as about 60Ω according to the present invention. It has been improved.

  FIG. 22 shows the case where the horizontal axis represents the angle θ (unit: °) formed by the repeating direction G of the grating electrode 14 b of the auxiliary reflector electrode 3 and the main propagation direction F of the surface acoustic wave of the IDT electrode 1. FIG. 4 is a diagram showing an anti-resonance resistance value (unit: Ω) on the vertical axis.

  In this experiment, it was found that the anti-resonance resistance value was improved by about 62Ω by changing θ from 0 ° to 20 °.

  The angle formed between the direction G of the auxiliary reflector electrode 3 and the main propagation direction F of the surface acoustic wave of the IDT electrode 1 may be 20 ° or more according to desired characteristics.

  FIG. 23 is an enlarged view of the characteristics in the passband of the transmission filter. In FIG. 23, the horizontal axis represents a frequency normalized by an arbitrary frequency, and the vertical axis represents an attenuation amount (unit: dB).

  The angle θ (unit: °) formed by the direction G of the auxiliary reflector electrode 3 and the main propagation direction F of the surface acoustic wave of the IDT electrode 1 is taken as a parameter, the broken line is 5 °, the alternate long and short dash line is 10 °, The dotted line indicates 15 ° and the solid line indicates 20 °. In FIG. 23, the insertion loss is most improved when θ is 20 °, and an improvement of about 0.1 dB is seen as compared with the case of 5 °.

  Further, the surface acoustic wave of the present invention in which the pitch of the grating electrodes 14b of the auxiliary reflector electrode 3 and the pitch of the electrode fingers 13 of the IDT electrode 1 are made different in the same manner as described in the above embodiment. A surface acoustic wave duplexer using a resonator was fabricated and evaluated as described above.

  The result is shown in FIG. FIG. 24 is a schematic top view similar to FIG. 2, but shows a graph of isolation characteristics when the pitch of the grating electrodes 14 b of the auxiliary reflector electrode 3 is different from the pitch of the electrode fingers 13 of the IDT electrode 1. It is.

  In the graph of FIG. 24, the horizontal axis represents normalized frequency, and the vertical axis represents isolation (unit: dB). The dotted characteristic curve indicates the result of the comparative example having no conventional auxiliary reflector electrode 3, and the broken line and the solid characteristic curve indicate that the pitch of the grating electrode 14b with respect to the conventional surface acoustic wave resonator is IDT electrode 1 respectively. And the auxiliary reflector electrode 3 having the same pitch as that of the electrode finger 13 and the auxiliary reflector electrode 3 having a pitch of the grating electrode 14b that is twice the pitch of the electrode finger 13 of the IDT electrode 1. The result of the Example of invention is shown.

  As can be seen from the results shown in FIG. 24, the surface acoustic wave resonator of this example showed a significant improvement in isolation characteristics of about 6 dB at maximum as compared with the comparative example.

(2) Case of having IDT type auxiliary reflector electrode 3 '(FIG. 12) FIG. 25 is a graph showing the isolation characteristics of the manufactured Examples and Comparative Examples of the present invention.

  In the graph of FIG. 25, the horizontal axis represents normalized frequency, and the vertical axis represents isolation (unit: dB). The broken line characteristic curve shows the result of the comparative example of FIG. 19 that does not have the conventional IDT auxiliary reflector electrode 3 ', and the solid line characteristic curve shows the IDT auxiliary reflector electrode 3 with respect to the conventional surface acoustic wave duplexer. The result of the Example of this invention when adding 'is shown.

  As can be seen from the results shown in FIG. 25, the surface acoustic wave duplexer of this example showed a significant improvement in isolation characteristics, for example, about 9 dB at a normalized frequency of 1.005, compared to the comparative example. The duplexer of the comparative example is considered to have failed to obtain good characteristics because there is a leaky surface acoustic wave that propagates leaking from the surface acoustic wave resonator constituting the transmission filter.

  Further, when the impedance characteristic (solid line) of a one-terminal surface acoustic wave resonator manufactured using the surface acoustic wave resonator of the present invention is compared with the impedance characteristic (dashed line) of a conventional surface acoustic wave resonator, FIG. A graph as shown in FIG. As shown by the solid line, it can be confirmed that the peak value called the antiresonance resistance value 11 can be increased. Specifically, the anti-resonance resistance value of the present invention is about 819Ω, whereas the anti-resonance resistance value 10 of the conventional surface acoustic wave resonator without the IDT auxiliary reflector electrode 3 ′ is 812Ω. According to the present invention, about 7Ω can be improved.

  FIG. 27 shows anti-resonance when the horizontal axis represents the angle θ (unit: °) formed by the direction G of the IDT auxiliary reflector electrode 3 ′ and the main propagation direction F of the surface acoustic wave of the IDT electrode 1. It is the figure which showed resistance value (unit: ohm) on the vertical axis | shaft.

  In the experiment, it is found that the antiresonance resistance value is improved by about 14Ω by changing θ from 0 ° to 10 °. In addition, when angle (theta) is about 10 degrees, it turns out that it improves most.

  Therefore, from the viewpoint of optimizing the anti-resonance resistance value, the angle formed between the electrode finger repetition direction G of the IDT electrode type auxiliary reflector electrode 3 ′ and the main propagation direction F of the surface acoustic wave of the IDT electrode 1. It is desirable that θ be in the range of 5 ° to 10 °.

  When this angle is larger than 10 °, the anti-resonance resistance value is small. However, as will be described later with reference to FIG. 29, the isolation characteristics are improved regardless of the angle.

  FIG. 28 is an enlarged view showing the in-passband characteristics of the duplexer transmission filter shown in FIG.

  In FIG. 28, the horizontal axis represents the frequency normalized with an arbitrary frequency, and the vertical axis represents the attenuation (unit: dB).

  The angle θ (unit: °) is taken as a parameter, and the broken line is a graph of the angle θ = 0 °, whereas the solid line shows the case where the angle θ is 10 °. In FIG. 28, it can be seen that when θ = 10 °, the insertion loss is improved by about 0.1 dB compared to the conventional case.

  Further, regarding the position of the IDT electrode type auxiliary reflector electrode, the bus bar electrode on the side not adjacent to the IDT electrode of the reflector electrode is arranged on a virtually extended straight line, and the isolator when the inclination angle θ is changed is shown. FIG. 29 is a graph showing the effect on the distribution characteristics.

  The angle θ (unit: °) is taken as a parameter, the horizontal axis represents a normalized frequency, and the vertical axis represents isolation (unit: dB).

  As the tilt angle θ of the IDT electrode type auxiliary reflector electrode increases in the range of 0 ° to 20 °, the isolation characteristics improve over a wide frequency range. When θ is 20 °, θ is 0 ° compared to when 0 °. The maximum improvement was about 2 dB.

  Further, the surface acoustic wave duplexer in which the pitch of the electrode fingers 13b of the IDT type auxiliary reflector electrode 3 'and the pitch of the electrode fingers 13a of the IDT electrode 1 are made different in the same manner as described in the above embodiment. Was prepared and the evaluation was performed.

  As a result, as shown in FIG. 30, when the pitch of the electrode fingers 13b of the IDT type auxiliary reflector electrode 3 'is set to twice the pitch of the electrode fingers 13a of the IDT electrode 1, 1 is within the pass band of the transmission filter. At a frequency of 0.00, the isolation characteristic was improved by about 9 dB compared to the conventional case.

  FIG. 31 is a graph showing the isolation characteristics of the duplexer when the IDT auxiliary reflector electrode 3 ′ and the second auxiliary reflector electrode 4 shown in FIG. 14 are connected and integrally formed. The broken line indicates the structure shown in FIG. 13 in which the IDT auxiliary reflector electrode 3 ′ and the second auxiliary reflector electrode 4 are not connected, and the solid line indicates the IDT auxiliary reflector electrode 3 ′ and the second auxiliary reflector electrode. This is the case of the structure shown in FIG. The solid line shows that the normalized frequency is improved by about 1 dB over a wide range of 0.98 to 1.02 as compared to the case where there is no connection.

It is a top view which shows embodiment of the surface acoustic wave resonator of this invention. It is the upper surface schematic of the surface acoustic wave duplexer which is an example of the surface acoustic wave element of this invention. It is a schematic diagram which shows the auxiliary reflector electrode which open | released one end part electrically. It is a schematic diagram which shows the auxiliary reflector electrode which open | released both ends electrically. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is the upper surface schematic of the surface acoustic wave duplexer which is an example of the surface acoustic wave element of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is a top view which shows other embodiment of the surface acoustic wave resonator of this invention. It is the upper surface schematic of the conventional surface acoustic wave duplexer. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the impedance characteristic of the surface acoustic wave resonator for demonstrating the effect of this invention. It is a graph which shows the anti-resonance resistance value of the surface acoustic wave resonator produced in the Example of this invention. It is a graph which shows the pass-band characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the impedance characteristic of the surface acoustic wave resonator for demonstrating the effect of this invention. It is a figure which shows the anti-resonance resistance value of the surface acoustic wave resonator produced in the Example of this invention. It is a graph which shows the pass-band characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a graph which shows the isolation characteristic of the surface acoustic wave duplexer produced in the Example of this invention. It is a top view which shows the conventional surface acoustic wave resonator.

Explanation of symbols

1: IDT electrode 2: Reflector electrode 3: Auxiliary reflector electrode (grating electrode type)
3 ': IDT type auxiliary reflector electrode 4: second auxiliary reflector electrodes 5, 5a, 5b, 5c, 5d: connection portion 6: thick film portion 8: dummy electrode 10: anti-resonance resistance value (conventional)
11: Anti-resonance resistance value (present invention)
12a, 12b, 12c: bus bar electrodes 13, 13a, 13b: electrode fingers 14a, 14b, 14c, 14d: grating electrodes 15, 17: input terminals 16, 18: output terminals 19: piezoelectric substrate 21: annular electrode 25: reflector Bus bar electrode F: Main propagation direction of surface acoustic wave of IDT electrode G: Repeat direction of electrode formed repeatedly of auxiliary reflector electrode

Claims (17)

A piezoelectric substrate;
An IDT electrode formed on the piezoelectric substrate and having a bus bar electrode;
A reflector electrode formed on the piezoelectric substrate and disposed adjacent to both ends in the main propagation direction of the surface acoustic wave of the IDT electrode;
Auxiliary reflector formed on the piezoelectric substrate, having electrodes repeatedly formed, and arranged on a straight line that is outside the reflector electrode and virtually extends the bus bar electrode of the IDT electrode And a surface acoustic wave resonator including the electrode.   2. The surface acoustic wave resonator according to claim 1, wherein the auxiliary reflector electrode is formed such that a repeating direction of the repeatedly formed electrode is directed toward the IDT electrode.   3. The angle θ formed by the repeating direction of the repeatedly formed electrode of the auxiliary reflector electrode and the repeating direction of the electrode finger of the IDT electrode is more than 0 degree and 20 degrees or less. Surface acoustic wave resonator.   4. The surface acoustic wave resonator according to claim 1, wherein the auxiliary reflector electrode is disposed at four positions obliquely outside the reflector electrode. 5.   The surface acoustic wave resonator according to any one of claims 1 to 4, wherein both end portions of the repeatedly formed electrode of the auxiliary reflector electrode are short-circuited.   5. The surface acoustic wave resonator according to claim 1, wherein one end of the repeatedly formed electrode of the auxiliary reflector electrode is electrically open. 6.   5. The surface acoustic wave resonator according to claim 1, wherein both ends of the repeatedly formed electrode of the auxiliary reflector electrode are electrically open. 6.   5. The auxiliary reflector electrode has two bus bar electrodes, and the auxiliary reflector electrode has a shape in which electrode fingers extending in a substantially right angle direction from the bus bar electrode are engaged with each other. 6. Surface acoustic wave resonators.   The surface acoustic wave resonator according to any one of claims 1 to 8, wherein a pitch of the repeatedly formed electrodes of the auxiliary reflector electrode is different from a pitch of the reflector electrode.   10. The surface acoustic wave resonator according to claim 1, wherein a pitch of the repeatedly formed electrode of the auxiliary reflector electrode is different from a pitch of the IDT electrode.   The second auxiliary reflector electrode is formed between two auxiliary reflector electrodes formed at positions outside the reflector electrode, and any one of claims 5 to 10 according to claim 4. A surface acoustic wave resonator according to claim 1.   The surface acoustic wave resonator according to claim 11, wherein the second auxiliary reflector electrode and the auxiliary reflector electrode are connected and formed integrally.   A surface acoustic wave filter comprising a plurality of surface acoustic wave resonators according to claim 1, wherein the piezoelectric substrate is used as a common substrate. A surface acoustic wave duplexer having a transmission filter region and a reception filter region on a substrate,
A surface acoustic wave duplexer using the surface acoustic wave resonator according to claim 1 in at least one of the transmission filter region and the reception filter region, and using the piezoelectric substrate as the substrate.   The communication apparatus carrying the surface acoustic wave resonator in any one of Claims 1-12.   The communication apparatus carrying the surface acoustic wave filter of Claim 13. The communication apparatus carrying the surface acoustic wave duplexer of Claim 14.

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