JP4550549B2 - Surface acoustic wave element and communication device - Google Patents

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 been used in various communication devices, and the surface acoustic wave filters have become wider with the progress of higher frequency and higher functionality of communication devices. The demand to do is increasing. For example, as a 1.9 GHz band cellular phone filter, a high-performance broadband filter having an effective pass bandwidth of 80 MHz or more (specific bandwidth of about 4% or more) is desired.

  In order to realize such a wide band, for example, a dual-mode surface acoustic wave resonator filter using three IDT electrodes (Inter Digital Transducer) on a piezoelectric substrate and using a longitudinal first-order mode and a longitudinal third-order mode Has been proposed.

  FIG. 6B shows a plan view of an electrode structure of a conventional resonator type surface acoustic wave filter. FIG. 6A is a graph showing the relationship between the position of each electrode (horizontal axis) and the pitch of the electrode fingers (vertical axis) of the resonator type surface acoustic wave filter of FIG. 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. A surface acoustic wave is generated. By inputting an electric signal from an input terminal 215 connected to one comb-like electrode of the IDT electrode 204, the excited surface acoustic wave propagates to the IDT electrodes 203 and 205 disposed on both sides of the IDT electrode 204. . 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 FIG. 6, reference numerals 210, 211, 212, and 213 denote reflector electrodes. Thus, 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, a surface acoustic wave filter having similar 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 improved by about twice. 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 this 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. Further, the surface acoustic waves are reflected by the reflector electrodes 210, 211, 212, and 213 located at both ends, and become standing waves between the reflector electrodes 210, 211, 212, and 213 at both ends.

  This standing wave mode includes a first-order mode and its higher-order (third-order) mode by three IDT electrodes (for example, IDT electrodes 203, 204, and 205). Since the pass characteristics are obtained by the resonance generated in these modes, the pass band can be widened by controlling the interval between the resonance frequencies generated in these modes. Conventionally, in order to control the interval of the resonance frequency, a narrow pitch portion is provided at the end of the IDT electrode, thereby reducing the radiation loss of the bulk wave when the surface wave is converted into the bulk wave, thereby achieving a wider band. It was. As another method, the resonance frequency interval is controlled by controlling the interval d between the IDT electrodes. Further, as another means, a capacitance is added to the output IDT electrode to control the resonance frequency interval.

As described above, in the conventional dual-mode surface acoustic wave resonator filter, when two stages are cascaded using a LiTaO ₃ substrate often used as a piezoelectric substrate, the specific bandwidth (the value of the pass bandwidth with respect to the center frequency) is about 0.40% (see, for example, Patent Document 1), and even when a capacity is added, only about 2% can be obtained (see, for example, Patent Document 2). In addition, when the distance d between the IDT electrodes is controlled, a maximum bandwidth of 3.7% is obtained (see, for example, Patent Document 3), but the filter must take temperature fluctuation into account, and is manufactured. Since the frequency fluctuates due to the variation in the electrode shape, it has been difficult to apply to a communication device such as a mobile phone that requires a wide pass bandwidth.

  Therefore, by providing a narrow pitch portion of electrode fingers at the end of adjacent IDT electrodes, the radiation loss of bulk waves between the IDT electrodes is reduced, and the resonance mode state is controlled to increase the bandwidth and insertion loss. Improvement has been achieved (see, for example, Patent Documents 4 and 5).

In addition, in order to provide a surface acoustic wave filter with a wide band, low loss, and high out-of-band attenuation on the high band side, a configuration in which a reflector electrode is inserted between IDT electrodes has also been proposed (for example, Patent Document 6). reference).
JP-A-1-231417 Japanese Patent Laid-Open No. 4-40705 JP 7-58581 A Japanese Patent Laid-Open No. 2002-9587 Special Table 2002-528987 JP-A-8-250969

  However, in the surface acoustic wave elements disclosed in Patent Documents 4 and 5, when a narrow pitch portion is provided at the end of the IDT electrode, there are portions where the electrode finger pitch is different in a state where the surface acoustic waves are combined, The ripple of the filter characteristic in the pass band increases, the shoulder characteristic deteriorates, and the flat characteristic of the pass band cannot be obtained. Also, simply providing a narrow pitch portion at the end of the IDT electrode limits the number of basic resonance modes that can be used for excitation of surface acoustic waves to the longitudinal first-order mode and the longitudinal third-order mode. Since it cannot be used, the degree of freedom in design was small. For this reason, there is a limit to widening the bandwidth.

  Further, in the surface acoustic wave element disclosed in Patent Document 6, the propagation path length becomes long just by inserting the reflector electrode between the IDT electrodes, so that the propagation loss becomes large, and the insertion loss in the filter characteristics. Increases, and the pass bandwidth decreases, which is not preferable.

  Although it is conceivable to use five IDT electrodes in place of the three IDT electrodes in order to ensure a sufficient bandwidth, the propagation path length is similarly increased, resulting in an increase in propagation loss and in filter characteristics. This is not preferable because the insertion loss increases and the surface acoustic wave filter size increases.

  As described above, conventionally, as a means for widening the band, the distance between adjacent IDT electrodes is shortened or a narrow pitch portion is provided at the end of the IDT electrode. Since there are portions where the electrode finger pitch is different in the coupled state, the ripple is large.

  In addition, conventionally used IDT electrodes are connected via a bus bar every other electrode finger, but when the number of electrode fingers of the IDT electrode increases, a certain proportion will be occupied in the resonator, The resonance modes that are allowed to occur are restricted. However, in the design of a surface acoustic wave filter, it is desirable that the resonance mode that can be used to form the pass band has a degree of freedom.

  In general, in a resonator type surface acoustic wave filter, the amplitude distribution of the surface acoustic wave determines the frequency at which the resonance mode appears. The amplitude distribution of the surface acoustic wave is controlled by the arrangement of the IDT electrodes and the connection form of the IDT electrodes. Is possible. In particular, when a plurality of IDT electrodes arranged in the propagation direction of a surface acoustic wave are connected to each other, the appearance of the amplitude distribution of a specific surface acoustic wave can be suppressed or increased.

  Therefore, the present invention has been completed in view of the above-described conventional problems, and the object thereof is to provide excellent filter characteristics with a wide passband without causing deterioration of insertion loss (increasing insertion loss). It is an object of the present invention to provide a surface acoustic wave element that functions as a high-quality balanced surface acoustic wave filter and a communication device using the same.

The surface acoustic wave element of the present invention includes a piezoelectric substrate , a first surface acoustic wave element portion disposed on the piezoelectric substrate, and a second surface acoustic wave element portion disposed on the piezoelectric substrate. , Wherein the first surface acoustic wave element section has a plurality of electrode fingers extending in a direction orthogonal to the propagation direction of the surface acoustic wave. Three first IDT electrode groups formed by electrically connecting a plurality of first IDT electrodes on the part side and both outside of the three first IDT electrode groups in the propagation direction of the surface acoustic wave disposed in said the first of the first surface acoustic wave element part side of the reflector electrodes in which a plurality inborn electrode fingers extending in a direction perpendicular to the propagation direction of a surface acoustic wave, said first IDT electrode between at least two of said first surface acoustic wave element part side of the first IDT electrode of the group It is set, consisting of the first second of any one or more of the IDT electrode and the second reflector electrodes electrically disconnected to the first IDT electrode of the surface acoustic wave device side first A first separation electrode on the surface acoustic wave element portion side, and the second surface acoustic wave element portion has a plurality of electrode fingers extending in a direction orthogonal to the propagation direction of the surface acoustic wave. Two second IDT electrode groups formed by electrically connecting a plurality of first IDT electrodes on the second surface acoustic wave element portion side, and the surface acoustic waves of these two second IDT electrode groups arranged both outside the propagation direction of the, the second of the first surface acoustic wave element part side of the reflector electrodes in which a plurality inborn electrode fingers extending in a direction perpendicular to the propagation direction of the surface acoustic wave , At least two of the second surface acoustic wave element portions of the second IDT electrode group Disposed between the first IDT electrode, said second first surface acoustic wave element portion to the IDT electrode electrically disconnected and has been in the second surface acoustic wave element side first a separation electrode is disposed between the first reflector electrode of said second IDT electrode group and the second surface acoustic wave element side, and the electrically the second IDT electrode group anda second separate electrodes consisting of any one or more of the third IDT electrode and the third reflector electrodes disconnected, the three first of the first surface acoustic wave element part One IDT electrode group is arranged along the propagation direction of the surface acoustic wave, and two first IDT electrode groups arranged on both sides of the three first IDT electrode groups are provided. The third IDT electrode and the cascade connection that constitute the second separation electrode of the second surface acoustic wave element unit, respectively. The first IDT electrode group arranged in the center of the three first IDT electrode groups is connected to an input / output terminal, and the first separation electrode in the first surface acoustic wave element unit is connected. The electrode finger pitch is wider than the electrode finger pitch of the first IDT electrode on the side of the first surface acoustic wave element part adjacent to the second separation electrode in the second surface acoustic wave element part. Second
The electrode finger pitch of the first IDT electrode on the surface acoustic wave element portion side is wider than the electrode finger pitch of the second separation electrode.

In the surface acoustic wave device according to the present invention, in the configuration described above, the first IDT electrode group in the first surface acoustic wave element portion includes a first surface acoustic wave element portion side of the first surface acoustic wave element portion . The electrode finger pitch of each of the IDT electrodes is constant, and the average electrode finger pitch of the first IDT electrodes on the first surface acoustic wave element portion side located at at least one end of the first IDT electrode group is , characterized in that narrower than the average electrode finger pitch of the first IDT electrode group and the first of all the other electrodes of the electrode group composed of the first separate electrodes of the surface acoustic wave element portion is there.

In the surface acoustic wave device according to the present invention, in each of the above-described configurations, two electrode groups each including the first IDT electrode group and the first separation electrode on the first surface acoustic wave element portion side are adjacent to each other. which one of the first of the first and the first IDT electrode of the surface acoustic wave element part side of the first surface acoustic wave element part side of the separation electrode, characterized in that the average electrode finger pitches different from each other It is.

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

  According to the surface acoustic wave element of the present invention, any one of the second IDT electrode and the second reflector electrode in the IDT electrode group of the first surface acoustic wave element portion and the second surface acoustic wave element portion. By providing the first separation electrode composed of more than seeds, a new resonance mode can be generated in addition to the original resonance mode by the first separation electrode, so that the degree of freedom in selecting the resonance mode is widened. The degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased, and as a result, it is possible to control the filter characteristics such as widening the band while reducing the insertion loss and the ripple. Further, in the second surface acoustic wave element portion, by providing at least one of the third IDT electrode and the third reflector electrode as one or more second separation electrodes, the resonance mode can be similarly obtained. The degree of freedom of selection is widened, and the degree of freedom of control of the surface acoustic wave amplitude distribution is increased. As a result, it is possible to control the filter characteristics with reduced insertion loss and ripple while increasing the bandwidth.

Also, when you widen the spacing between the forcibly resonant mode trying broadband tends to S ₂₁ is a transmission characteristic between the resonance peak and the resonance peak is reduced. As described above, it is possible to arrange resonance frequencies with a certain degree of frequency interval when the degree of freedom in selecting a possible resonance mode is large, that is, arrangement of resonance frequencies suitable for wideband characteristics is easy. As a result, it is advantageous for widening the bandwidth.

  Further, the two IDT electrode groups provided with the first separation electrode in the first surface acoustic wave element unit are respectively connected in cascade with the second separation electrode of the second surface acoustic wave element unit. For example, the number of paths connected from the first stage to the second stage can be increased, the degree of freedom in the design of the passband is increased, and the insertion loss and ripple can be reduced while maintaining a wider passband width more effectively. .

  The electrode finger pitch of the first separation electrode in the first surface acoustic wave element unit is wider than the electrode finger pitch of the adjacent first IDT electrode, and the second separation electrode in the second surface acoustic wave element unit is By making the electrode finger pitch of the adjacent first IDT electrodes wider than the electrode finger pitch of the second separation electrode, it is possible to adjust the resonance peak position in the pass band and arrange it at the optimum position. As a result, it is possible to reduce the insertion loss and the ripple while keeping the pass band width of the filter characteristics in a wide band. Furthermore, by adopting the above configuration, the degree of impedance concentration is improved, and as a result, the VSWR (Voltage Standing Wave Ratio) of the filter characteristics can be reduced.

  According to the surface acoustic wave device of the present invention, in the above configuration, the electrode finger pitch of one or more first IDT electrodes is constant in the IDT electrode group in the first surface acoustic wave device portion, and the IDT The average electrode finger pitch of the first IDT electrode positioned at at least one end of the electrode group becomes narrower than the average electrode finger pitch of all other electrodes in the electrode group composed of the IDT electrode group and the first separation electrode. By doing so, it becomes possible to prevent the radiation loss at the time of conversion of the surface acoustic wave into the bulk wave, and as a result, the insertion loss of the filter characteristic can be reduced.

  According to the surface acoustic wave element of the present invention, in each of the above configurations, the electrode group including the IDT electrode group and the first separation electrode includes two adjacent first IDT electrodes and the first separation electrode. However, since the average electrode finger pitch is different from each other, the degree of freedom in selecting the resonance mode is increased, and the coupling of the surface acoustic wave is kept as it is and the electrical coupling is disconnected, thereby reducing the insertion loss and the ripple. In particular, the shoulder characteristic in the pass band of the filter characteristic can be improved.

  Further, for example, by connecting and adding surface acoustic wave resonators in series, parallel or series-parallel to IDT electrodes constituting the IDT electrode group, impedance matching can be achieved, and surface acoustic wave resonators are By connecting, an attenuation pole can be formed, and the characteristics can be controlled so that the out-of-band attenuation amount satisfies the specifications required for high attenuation.

  Further, for example, each of the two IDT electrode groups of the second surface acoustic wave element unit is an electrode whose output is a balanced signal, thereby providing an elastic surface having a function of an unbalanced-balanced signal converter. A wave element can be provided.

  According to the communication device of the present invention, the strict insertion loss that has been conventionally required is satisfied by including at least one of the reception circuit and the transmission circuit having any of the surface acoustic wave elements of the present invention. Can be obtained, and a communication device with much better sensitivity can be realized.

  Embodiments of a surface acoustic wave device according to the present invention will be described below 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 the drawings described below, the same components are denoted by the same reference numerals. 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 shown in FIG. 1C, the surface acoustic wave device of the present invention is a first IDT electrode having a plurality of electrode fingers extending on the piezoelectric substrate 1 in a direction orthogonal to the propagation direction of the surface acoustic wave. The three IDT electrode groups 21, 22, and 23, in which a plurality of 31 to 42 are electrically connected to each other, are disposed, and both of the IDT electrode groups 21, 22, and 23 outside the propagation direction of the surface acoustic wave. The first reflector electrodes 2 and 3 having a plurality of electrode fingers extending in a direction orthogonal to the propagation direction of the surface acoustic wave are disposed on at least two first IDT electrode groups 21, 22, and 23. Any one of the second IDT electrode and the second reflector electrode (in this example, the reflector electrodes 61 to 64) that is not electrically connected to the first IDT electrode between the IDT electrodes The first surface acoustic wave element portion A in which one or more of the above are disposed as the first separation electrode, and two IDs The first reflector electrodes 4 and 5 and the first separation electrode (in this example, the reflector electrodes 65 and 66) disposed both outside the electrode groups 24 and 25 and the propagation direction of the surface acoustic wave are provided. The IDT electrode groups 24 and 25 are electrically connected to at least one of the IDT electrode groups 24 and 25 and between the IDT electrode groups 24 and 25 and the first reflector electrodes 4 and 5. A second elastic member formed by disposing at least one of the third IDT electrodes 71 and 72 and the third reflector electrodes 73 and 74 as the second separation electrode. And a surface wave element portion B.

  Further, the two IDT electrode groups 21 and 23 of the first surface acoustic wave element part A are connected in cascade with the second separation electrodes (IDT electrodes 71 and 72) of the second surface acoustic wave element part B, respectively. Yes.

  Further, as shown in FIG. 1A (the horizontal axis indicates the reference numerals of the respective parts of the first surface acoustic wave element part A), the first separation electrode in the first surface acoustic wave element part A is shown. The electrode finger pitch of (reflector electrodes 61, 62, 63, 64) is such that the adjacent first IDT electrodes (IDT electrodes 31, 32 for reflector electrode 61, IDT electrodes 37, 38 for reflector electrode 64, reflector) It is wider than the electrode finger pitch of the IDT electrodes 33 and 34 for the electrode 62 and the IDT electrodes 35 and 36) for the reflector electrode 63.

  In addition, as shown in FIG. 1B (the horizontal axis indicates the reference numerals of the respective parts of the first surface acoustic wave element part B), the second separation electrode in the second surface acoustic wave element part B ( The electrode finger pitch of the first IDT electrodes (in this example, IDT electrodes 39 and 71 for the reflector electrode 73 and IDT electrodes 42 and 72 for the reflector electrode 74) adjacent to the reflector electrodes 73 and 74) is the second. Wider than the electrode finger pitch of the separation electrodes (reflector electrodes 73 and 74).

  The first surface acoustic wave element portion A according to the present invention includes the IDT electrode group including the first IDT electrodes and the first separation electrode, thereby increasing the degree of freedom in selecting the resonance mode. The degree of freedom in controlling the amplitude distribution of the wave increases, and it can be used to control the filter characteristics. When the degree of freedom in selecting the resonance mode is large, it is possible to arrange the resonance frequency with a certain frequency interval, which is advantageous for reducing insertion loss and ripple while keeping the passband in a wide band. Become.

  The two IDT electrode groups 21 and 23 of the first surface acoustic wave element part A are connected in cascade with the second separation electrodes (IDT electrodes 71 and 72) of the second surface acoustic wave element part B, respectively. As a result, the cascade connection between the IDT electrode groups 21 and 23 and the second separation electrode increases the degree of freedom in selecting the resonance mode, thereby increasing the degree of freedom in controlling the surface acoustic wave amplitude distribution and the filter characteristics. It becomes possible to use it for control. When the degree of freedom in selecting the resonance mode is large, it is possible to arrange the resonance frequency with a certain frequency interval. In other words, the number of paths connected from the first stage to the second stage can be increased, the degree of freedom in the design of the passband is increased, and the insertion loss and ripple can be reduced more effectively while keeping the passband width wide. .

  Furthermore, the electrode finger pitch of the first separation electrodes (reflector electrodes 61, 64) in the first surface acoustic wave element unit A is equal to the adjacent first IDT electrode (IDT electrodes 31, 32, The first IDT electrode (which is wider than the electrode finger pitch of the IDT electrodes 37, 38) with respect to the reflector electrode 64 and is adjacent to the second separation electrode (reflector electrodes 73, 74) in the second surface acoustic wave element part B ( Since the electrode finger pitch of the IDT electrodes 39 and 71 with respect to the reflector electrode 73 and the IDT electrodes 42 and 72 with respect to the reflector electrode 74 is wider than the electrode finger pitch of the second separation electrode (reflector electrodes 73 and 74), It is possible to arrange the resonance peak in the pass band at an optimum position, and as a result, it is possible to reduce the insertion loss and the ripple while keeping the pass band width of the filter characteristics in a wide band. Furthermore, by adopting the above configuration, the degree of concentration of impedance is improved, and as a result, the VSWR of the filter characteristics can be reduced.

  Further, in the IDT electrode groups 21, 22, and 23 in the first surface acoustic wave element unit A, the electrode finger pitch of one or more first IDT electrodes is constant, and at least the IDT electrode groups 21, 22, and 23 The average electrode finger pitch of the first IDT electrode (the IDT electrode 32 in the IDT electrode group 21, the IDT electrode 33 or the IDT electrode 36 in the IDT electrode group 22) located at one end is determined by the IDT electrode group and the first separation electrode. It is narrower than the average electrode finger pitch of all other electrodes in the electrode group consisting of This makes it possible to prevent radiation loss when converting surface acoustic waves into bulk waves, and as a result, insertion loss of filter characteristics can be reduced.

  In addition, the electrode group composed of the IDT electrode groups 21 to 25 and the first separation electrodes (reflector electrodes 61 to 66) has two adjacent first IDT electrodes and the first separation electrode as an average electrode. The difference in finger pitch increases the degree of freedom in selecting the resonance mode, and the surface acoustic wave coupling remains the same while the electrical coupling is disconnected, reducing the insertion loss and ripple, and especially the filter characteristics. The shoulder characteristics in the pass band can be improved.

  Since the number of electrode fingers of IDT electrodes 31 to 42, 71, 72 and reflector electrodes 2-5, 61-66, 73, 74 ranges from several to several hundreds, These shapes are shown in a simplified manner. In addition, the first IDT electrode or the second reflector electrode which is a separation electrode constituting the electrode group may be grounded, electrically floating, or used for interstage connection. . When the second reflector electrode is not electrically connected and is in a floating state, there is an advantage that the wiring can be easily routed. 6 is an input terminal, and 7 and 8 are output terminals.

  As the piezoelectric substrate 1 for the surface acoustic wave filter, 36 ° ± 3 ° Y-cut X propagation lithium tantalate single crystal, 42 ° ± 3 ° Y cut X propagation lithium tantalate single crystal, 64 ° ± 3 ° Y Cut X Propagation Lithium Niobate Single Crystal, 41 ° ± 3 ° Y Cut X Propagation Lithium Single Crystal, 45 ° ± 3 ° X Cut Z Propagation Lithium Tetraborate Single Crystal has a large electromechanical coupling coefficient and frequency temperature coefficient Is preferable as a piezoelectric substrate. Of these pyroelectric piezoelectric single crystals, if the substrate has a significantly reduced pyroelectric property due to solid solution of oxygen defects or Fe, the reliability of the device is good. The thickness of the piezoelectric substrate is preferably about 0.1 to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate becomes brittle, and if it exceeds 0.5 mm, the material cost and component dimensions increase, making it unsuitable for use.

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

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

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

  In addition, by connecting and adding surface acoustic wave resonators in series, parallel or series-parallel to the IDT electrodes constituting the IDT electrode group, impedance matching can be satisfactorily achieved, and the surface acoustic wave resonators By connecting, an attenuation pole can be formed, and the characteristics can be controlled so that the out-of-band attenuation amount satisfies the specifications required for high attenuation.

  Further, for example, by making each of the two IDT electrode groups 24 and 25 of the second surface acoustic wave element part B an electrode whose output is a balanced signal, the function of an unbalanced-balanced signal converter is achieved. The surface acoustic wave device having the above can be provided.

  As described above, it is possible to provide an excellent communication apparatus that includes a receiving circuit and a transmitting circuit having excellent surface acoustic wave elements and that has significantly improved sensitivity.

  In the description of the above-described embodiment, for the sake of simplicity, the propagation direction of the second IDT electrode and the surface acoustic wave that are electrically unconnected to the IDT electrode group between at least two IDT electrodes of the IDT electrode group. Although an example in which one first separation electrode made of any of the second reflector electrodes having a plurality of electrode fingers extending in a direction perpendicular to the first electrode is disposed is limited to this. Instead, a plurality of types of the second IDT electrode and the second reflector electrode may be provided as the first separation electrode, and other configurations are also possible without departing from the scope of the present invention. It is possible to change appropriately.

  Examples of the present invention will be described below.

An embodiment in which the surface acoustic wave element shown in FIG. A fine electrode pattern of Al (99% by mass) -Cu (1% by mass) was formed on a LiTaO ₃ single crystal piezoelectric substrate having a 38.7 ° Y-cut in the X direction. FIG. 1 (a) shows the average electrode finger pitch of the IDT electrode and the reflector electrode constituting the first surface acoustic wave element portion A of the present invention. The average electrode finger pitch of the first IDT electrodes 31, 32, 33, 35, 36, 37, 38 in the first stage is 2.10 μm, 2.01 μm, 1.96 μm, 2.11 μm, 1.96 μm, 2.01 μm, 2.10 μm, respectively. It was. Further, the average electrode finger pitch of the second reflector electrodes 61, 62, 63, 64 serving as the separation electrodes was 2.15 μm.

  Similarly, FIG. 1B shows the average electrode finger pitch of the IDT electrode and the reflector electrode constituting the second surface acoustic wave element portion B of the present invention. The average electrode finger pitch of the first IDT electrodes 39, 40, 41, and 42 in the second stage was set to 2.00 μm, 2.12 μm, 2.12 μm, and 2.00 μm, respectively. In addition, the average electrode finger pitch of the second reflector electrodes 65 and 66 serving as separation electrodes was 1.84 μm.

  The average electrode finger pitch of the third IDT electrodes 71 and 72 constituting the second separation electrode is 2.07 μm, and the average electrode finger pitch of the third reflector electrodes 73 and 74 is 1.79 μm. did. The average electrode finger pitch of the reflector electrodes 2, 3, 4 and 5 disposed on both sides of each surface acoustic wave element A and B was 2.13 μm.

  The second surface acoustic wave element unit B is provided with at least one IDT electrode group between the IDT electrode groups 24 and 25 and between the IDT electrode groups 24 and 25 and the first reflector electrodes 4 and 5. One or more of the third IDT electrodes (IDT electrodes 71 and 72) and the third reflector electrodes (reflector electrodes 73 and 74), which are not electrically connected to 24 and 25, are connected to the second One or more separation electrodes are arranged, and the two IDT electrode groups 21 and 23 of the first surface acoustic wave element portion A are respectively connected to the second separation electrodes (IDT electrodes) of the second surface acoustic wave element portion B. 71, 72).

  Further, the electrode finger pitch of the first separation electrode (reflector electrodes 61, 62, 63, 64) in the first surface acoustic wave element part A is wider than the electrode finger pitch of the adjacent first IDT electrode (IDT). Reflector electrode 61 for electrodes 31, 32, reflector electrode 62 for IDT electrodes 33, 34, reflector electrode 63 for IDT electrodes 35, 36, reflector electrode 64 for IDT electrodes 37, 38), second surface acoustic wave The electrode finger pitch of the first IDT electrode adjacent to the second separation electrode (reflector electrodes 73 and 74) in the element part B is wider than the electrode finger pitch of the second separation electrode (reflector electrode 73). IDT electrodes 39, 71 against IDT electrodes 42, 72 against reflector electrode 74).

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

  First, the piezoelectric substrate 1 was ultrasonically cleaned with acetone, IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the piezoelectric substrate 1 with a clean oven, a metal layer to be each electrode was formed. A sputtering apparatus was used for forming the metal layer, and an Al (99 mass%)-Cu (1 mass%) alloy was used as the material of the metal layer. The thickness of the metal layer at this time was about 0.34 μm.

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

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

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

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

  Further, as a comparative sample, a surface acoustic wave device having a fine electrode pattern as shown in FIG. As shown in FIG. 2A, the average electrode finger pitch of the first IDT electrodes 31, 32, 33, 35, 36, 37, 38 in the first stage is 2.10 μm, 2.01 μm, 1.96 μm, 2.11, respectively. μm, 1.96 μm, 2.01 μm, and 2.10 μm. Moreover, the average electrode finger pitch of the reflector electrodes 61, 62, 63, and 64 serving as the separation electrodes was 2.05 μm, 2.04 μm, 2.04 μm, and 2.05 μm, respectively.

  Similarly, as shown in FIG. 2B, the average electrode finger pitch of the first IDT electrodes 39, 40, 41, and 42 in the second stage is 1.91 μm, 2.12 μm, 2.12 μm, and 1.91 μm, respectively. . In addition, the average electrode finger pitch of the reflector electrodes 65 and 66 serving as separation electrodes was set to 2.02 μm. The average electrode finger pitch of the third IDT electrodes 71 and 72 was both 2.07 μm. The average electrode finger pitch of the third reflector electrodes 73 and 74 was both 1.99 μm. The average electrode finger pitch of the reflector electrodes 2, 3, 4 and 5 disposed on both sides of the surface acoustic wave element portions A and B was 2.13 μm.

  Next, the characteristics of the surface acoustic wave device in this example were measured. A signal of 0 dBm was input, and measurement was performed under conditions of a frequency of 780 to 960 MHz and a measurement point of 800 points. The number of samples was 30, and a multi-port network analyzer (“E5071A” manufactured by Agilent Technologies) was used as a measuring instrument.

  A graph of frequency characteristics in the vicinity of the passband is shown in FIG. FIG. 3 is a graph showing the frequency dependence of the insertion loss representing the transmission characteristics of the filter. The filter characteristics of this example product were very good. That is, as shown by the solid line in FIG. 3, the insertion loss of this example product was 2.2 dB, the ripple was 0.20 dB, and the specific bandwidth was 4.9%.

  On the other hand, as shown by the broken line in FIG. 3, the insertion loss of the comparative product was 4.8 dB, the ripple was 1.80 dB, and the specific bandwidth was 3.8%.

  Thus, in this example, a surface acoustic wave device with reduced insertion loss and ripple while maintaining a wide pass band could be realized.

  FIG. 4 is a Smith chart showing impedance characteristics as viewed from the input terminal 6 of the first surface acoustic wave element portion A of the embodiment of FIG. 3 and the comparative example. As can be seen from FIG. 4, the impedance matching is improved in the example than in the comparative example. As a result, as shown by the solid line in FIG. 5, the VSWR in the passband in the example was 1.7, which is the most deteriorated value.

  On the other hand, as shown by the broken line in FIG. 5, the VSWR in the passband in the comparative example was 3.9 as the most deteriorated value.

  As described above, in this example, a surface acoustic wave element with a reduced VSWR could be realized.

The example of embodiment about the surface acoustic wave element of this invention is shown, (a) And (b) is a graph which shows the relationship between the position of each electrode and electrode finger pitch in the 1st and 2nd surface acoustic wave element part (C) is a top view of the surface acoustic wave element which shows the pattern of each electrode. The surface acoustic wave element of a comparative example is shown, (a) and (b) are graphs showing the relationship between the position of each electrode and the electrode finger pitch in the first and second surface acoustic wave element parts, (c) It is a top view of the surface acoustic wave element which shows the pattern of an electrode. 4 is a graph showing the frequency characteristics of insertion loss in the passband and the vicinity of the surface acoustic wave elements of Examples and Comparative Examples of the present invention. It is a Smith chart which shows the impedance characteristic with respect to the input terminal of the surface acoustic wave element of the Example of this invention, and a comparative example, respectively. It is a graph which shows the frequency characteristic of VSWR in the pass band of the surface acoustic wave element of the Example of this invention, and a comparative example, and its vicinity. (A) is a graph which shows the relationship between the position of each electrode of the conventional resonator type surface acoustic wave filter, and the pitch of an electrode finger, (b) is a top view which shows about the electrode structure of the conventional resonator type surface acoustic wave filter It is.

Explanation of symbols

1,202: Piezoelectric substrate
21-25: IDT electrode group
31-42: 1st IDT electrode
71, 72: Third IDT electrode
61-66: Second reflector electrode
73, 74: third reflector electrodes 2-5: first reflector electrodes 6, 215: input terminals 7, 8, 216, 217: output terminals

Claims (4)

A surface acoustic wave device comprising: a piezoelectric substrate; a first surface acoustic wave element portion disposed on the piezoelectric substrate; and a second surface acoustic wave element portion disposed on the piezoelectric substrate. There,
The first surface acoustic wave element unit includes a plurality of first IDT electrodes on the first surface acoustic wave element unit side having a plurality of electrode fingers extending in a direction orthogonal to the propagation direction of the surface acoustic wave. Three first IDT electrode groups that are electrically connected, and these three first IDT electrode groups are disposed both outside the propagation direction of the surface acoustic wave, and the propagation direction of the surface acoustic wave. first and first reflector electrode of the surface acoustic wave device side, at least two of said first surface acoustic wave of the first IDT electrodes of a plurality inborn electrode fingers extending in a direction perpendicular to A second IDT electrode disposed between the first IDT electrodes on the element side and electrically disconnected from the first IDT electrode on the first surface acoustic wave element side; and a second IDT electrode the first surface acoustic wave element portion consisting of any one or more of the reflector electrodes Wherein the separation electrode,
The second surface acoustic wave element unit includes a plurality of first IDT electrodes on the second surface acoustic wave element unit side having a plurality of electrode fingers extending in a direction orthogonal to the propagation direction of the surface acoustic wave. Two electrically connected second IDT electrode groups and the two second IDT electrode groups are disposed both outside the propagation direction of the surface acoustic wave, and the propagation direction of the surface acoustic wave A first reflector electrode on the second surface acoustic wave element portion side having a plurality of electrode fingers extending in a direction orthogonal to the second surface acoustic wave , and at least two second surface acoustic waves of the second IDT electrode group A second surface acoustic wave element side disposed between the first IDT electrodes on the element side and electrically disconnected from the first IDT electrode on the second surface acoustic wave element side first separation electrode and said second IDT electrode group and the second surface acoustic wave element of the Disposed between the first reflector electrode, and one of the third IDT electrode and the third reflector electrodes wherein the second IDT electrode group is electrically disconnected 1 includes a second separate electrodes consisting of seeds above, to,
The three first IDT electrode groups of the first surface acoustic wave element unit are arranged side by side along the propagation direction of the surface acoustic wave, and among these three first IDT electrode groups Two first IDT electrode groups arranged on both sides are cascade-connected to the third IDT electrode constituting the second separation electrode of the second surface acoustic wave element part, respectively . A first IDT electrode group disposed in the center of one IDT electrode group is connected to an input / output terminal;
The electrode finger pitch of the first separation electrode in the first surface acoustic wave element unit is wider than the electrode finger pitch of the first IDT electrode on the side of the adjacent first surface acoustic wave element unit , and the second The electrode finger pitch of the first IDT electrode on the side of the second surface acoustic wave element adjacent to the second separation electrode in the surface acoustic wave element is wider than the electrode finger pitch of the second separation electrode. A surface acoustic wave device. The first one or more of the electrode finger pitch of the first surface acoustic wave element part side of the first IDT electrode on the first IDT electrode group in the surface acoustic wave element part is constant, respectively, the second average electrode finger pitch of the first IDT electrodes of at least the first of the first IDT electrode of the surface acoustic wave element portion located on one end, said first resilient surface and said first IDT electrode group 2. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is narrower than an average electrode finger pitch of all the other electrodes of the electrode group including the first separation electrode on the wave device section side . The electrode group consisting of the first IDT electrode group and the first separation electrode on the first surface acoustic wave element unit side is composed of two adjacent first IDTs on the first surface acoustic wave element unit side . 3. The surface acoustic wave element according to claim 1, wherein the electrode and the first separation electrode on the first surface acoustic wave element part side have different average electrode finger pitches.   A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave element according to any one of claims 1 to 3.

Images