JP4688572B2 - Surface acoustic wave resonator, surface acoustic wave device, and communication device - Google Patents

Description

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

  Conventionally, a surface acoustic wave filter has been widely used as a frequency selection filter used in the RF stage of mobile communication devices such as mobile phones and automobile phones. In general, characteristics required for a frequency selective filter include various characteristics such as a wide passband, low loss, and high attenuation. In recent years, there has been an increasing demand for lower loss for surface acoustic wave filters in order to improve reception sensitivity and lower power consumption particularly in mobile communication devices. The reason for this is that, in recent years, in mobile communication devices, the antenna has shifted from a conventional whip antenna to a built-in antenna using dielectric ceramics for miniaturization, so that sufficient gain of the antenna can be obtained. This is because the demand for improving the insertion loss further increases for the surface acoustic wave filter.

  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. 5B shows a plan view of an electrode structure of a conventional resonator type surface acoustic wave filter. FIG. 5A 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.

  Note that reference numerals 210, 211, 212, and 213 in FIG. 5 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. In addition, 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 resonator type surface acoustic wave filter, when the LiTaO ₃ substrate, which is often used as a piezoelectric substrate, is cascaded in two stages, the specific bandwidth (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 (for example, see 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 devices 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. Therefore, it has been insufficient to improve the insertion loss while improving the flatness of the filter characteristics in the passband and increasing the bandwidth.

  Further, in the surface acoustic wave device as disclosed in Patent Document 6, the propagation path length increases only by inserting the reflector electrode between the IDT electrodes, so that the propagation loss increases, 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.

  Thus, as a means that has been conventionally used to improve the insertion loss and broaden the band, the distance between adjacent IDTs is shortened or a narrow pitch part is provided at the end of the IDT electrode. By simply providing a portion with a short electrode finger pitch at the end of the IDT electrode, the resonance mode generated in the pass band cannot be optimally adjusted, so the pass band width of the filter characteristic in the pass band is kept wide. In addition, the insertion loss and flatness could not be sufficiently improved.

  Generally, in a resonator type surface acoustic wave filter, the distribution of the surface acoustic wave amplitude determines the frequency at which the resonance mode appears. The amplitude distribution of the surface acoustic wave appropriately determines the IDT electrode arrangement and the electrode finger pitch of the IDT electrode. Control can be performed by selecting. In particular, when the electrode finger pitch of the IDT electrode is appropriately selected, the appearance of the amplitude distribution of a specific surface acoustic wave can be suppressed or increased, so that the resonance peak in the pass band is placed at an optimal position. Can be adjusted.

  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). An object of the present invention is to provide a surface acoustic wave device that also functions as a high-quality balanced surface acoustic wave filter and a communication device using the same.

  The surface acoustic wave resonator according to the present invention includes: (1) A number of electrode fingers that are long in the direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate. A plurality of IDT electrodes having a plurality of IDT electrodes, and two adjacent IDT electrodes among the plurality of IDT electrodes are each a part from the other end and the electrode finger pitch is the remaining part of the electrode finger. A first portion different from the pitch and a second portion which is the remaining portion and has a constant electrode finger pitch, and an average value of the electrode finger pitch of the first portion is an electrode of the second portion The electrode finger pitch of the first portion is shorter toward the boundary between the two adjacent IDT electrodes, and the electrode finger pitch is minimized in the two first portions. It has multiple parts The features.

  In the surface acoustic wave resonator according to the present invention, (2) in the configuration of (1), the minimum part of the electrode finger pitches in the two first parts and the minimum part of the plurality of minimum parts Is on one side of the boundary between the two adjacent IDT electrodes.

  In the surface acoustic wave resonator according to the present invention, (3) in the configuration of (2), in the two adjacent IDT electrodes, the electrode finger pitch of the second portion of one IDT electrode is the other IDT. It is longer than the electrode finger pitch of the second part of the electrode, and the minimum part of the electrode finger pitch of the first part is on the one IDT electrode side.

  In the surface acoustic wave device according to the present invention, (4) in each of the configurations (1) to (3), in the two adjacent IDT electrodes, the electrode finger pitch of the second portion of one IDT electrode Is longer than the electrode finger pitch of the second part of the other IDT electrode, and the average value of the electrode finger pitch of the first part of the one IDT electrode is equal to that of the first part of the other IDT electrode. It is shorter than the average value of the electrode finger pitch.

  The surface acoustic wave device according to the present invention includes (5) the IDT electrode in series or in parallel with the IDT electrode constituting the surface acoustic wave resonator in each of the configurations (1) to (4). It comprises a reflector that sandwiches the IDT electrode, and is connected to a resonator that generates one or more mode resonances.

  The communication device of the present invention is characterized in that (6) in each of the above configurations (1) to (4), at least one of a reception circuit and a transmission circuit having the surface acoustic wave resonator of the present invention is provided. And

  A communication apparatus according to the present invention includes (7) at least one of a reception circuit and a transmission circuit having the surface acoustic wave resonator according to the present invention in each of the configurations (1) to (4). .

  A communication apparatus according to the present invention is characterized in that (8) in each of the above configurations (5) or (6), the communication apparatus includes at least one of a reception circuit and a transmission circuit having the surface acoustic wave device of the present invention.

  According to the surface acoustic wave device of the present invention, two adjacent IDT electrodes among the plurality of IDT electrodes are each a part from the other end, and the electrode finger pitch is different from the remaining part of the electrode finger pitch. 1 part and the remaining part and a second part having a constant electrode finger pitch, and the average value of the electrode finger pitch of the first part is shorter than the electrode finger pitch of the second part. The electrode finger pitch of the first portion is shortened toward the boundary between two adjacent IDT electrodes, so that the area on the substrate of the electrode finger of the IDT electrode is adjusted at the location where the IDT electrode is adjacent This can further prevent radiation loss of the surface acoustic wave to the bulk wave, and further increase the frequency spacing between the first-order mode, the third-order mode, and their harmonic modes. It is possible to adjust, it can be realized a surface acoustic wave device having good electrical characteristics in a wide band and low loss.

  Also, by providing a plurality of electrode finger pitch minimum portions in the two first portions, a plurality of surface acoustic wave resonance modes are generated between adjacent IDT electrodes, and the surface acoustic wave resonance modes are appropriately set. Therefore, it is possible to arrange the resonance frequencies with a certain frequency interval, that is, it is easy to arrange the resonance frequencies suitable for the wide band characteristics, and as a result, it is advantageous for widening the band. In addition, since the appearance of the amplitude distribution of a specific surface acoustic wave can be suppressed or increased, it is possible to control to arrange a plurality of resonance peaks in the pass band at the optimum frequency position. As a result, it is possible to control the filter characteristics such as improving the flatness and insertion loss while increasing the bandwidth.

  Further, in the above configuration, since the minimum part of the electrode finger pitch in the two first portions is on one side deviating from the boundary between the two adjacent IDT electrodes, the elastic surface generated between the adjacent IDT electrodes The resonance peak of the wave can be controlled to be arranged at an appropriate frequency, and the flatness and the insertion loss can be improved while the filter characteristic of the pass band is widened.

  In the above configuration, in two adjacent IDT electrodes, the electrode finger pitch of the second part of one IDT electrode is longer than the electrode finger pitch of the second part of the other IDT electrode, Since the minimum part of the electrode finger pitch is on one IDT electrode side, the resonance peak of the generated surface acoustic wave can be controlled to be arranged at an appropriate frequency between adjacent IDT electrodes. It is possible to optimally prevent radiation loss at the time of mode conversion of waves into bulk waves, and it is possible to improve flatness and insertion loss while broadening the passband filter characteristics.

  In the above configuration, in two adjacent IDT electrodes, the electrode finger pitch of the second part of one IDT electrode is longer than the electrode finger pitch of the second part of the other IDT electrode, and Since the average value of the electrode finger pitch of the first part is shorter than the average value of the electrode finger pitch of the first part of the other IDT electrode, a plurality of surface acoustic waves further generated between adjacent IDT electrodes The resonance peak can be controlled so as to be arranged at an optimum frequency, and the flatness and insertion loss can be improved while broadening the filter characteristics of the pass band.

  In each of the above configurations, the IDT electrode that constitutes the surface acoustic wave resonator includes a IDT electrode and a reflector that sandwiches the IDT electrode in series or in parallel, and generates one or more mode resonances. By connecting the element (surface acoustic wave resonator), impedance matching between the input signal terminal and the output signal terminal can be achieved, and it is possible to form an attenuation pole by connecting the surface acoustic wave resonator. Yes, the characteristics can be controlled so that the out-of-band attenuation amount satisfies the specifications required for high attenuation.

  In addition, by connecting the surface acoustic wave resonators having the above-described structure in two stages, it is possible to increase the number of paths connected from the first stage to the second stage, for example. The degree of freedom in design increases, the attenuation amount outside the band can be increased, and the flatness and insertion loss can be improved while maintaining a wider passband width more effectively.

  Further, for example, by dividing a part of the common electrode of the IDT electrode in the surface acoustic wave element unit to make each electrode connected to the output balanced signal, the function of the unbalanced-balanced signal converter can be achieved. The surface acoustic wave device can be provided.

  The communication device according to the present invention includes at least one of the reception circuit and the transmission circuit having the surface acoustic wave resonator or the surface acoustic wave device according to any one of the above-described inventions. By using a wave resonator or surface acoustic wave device as a communication device, a device that can satisfy the severe insertion loss that has been required in the past can be obtained, reducing the power consumption and realizing a much better sensitivity device. can do.

  Embodiments of a surface acoustic wave resonator and 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 resonator and 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.

  FIG. 1B is a plan view showing the electrode structure of the surface acoustic wave resonator according to the present invention. As an example, FIG. 1A shows a diagram of changes in the electrode finger pitch of the IDT electrode in the part A of the electrode structure of the surface acoustic wave resonator shown in FIG.

  As shown in FIG. 1B, the surface acoustic wave resonator of the present invention is formed on the piezoelectric substrate 1 along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate 1 with respect to the propagation direction. A plurality of IDT electrodes 2 to 7 (in the case of FIG. 1B, three IDT electrodes 2 to 4 and three IDT electrodes 5 to 7) having a plurality of long electrode fingers in a direction orthogonal to each other. At the same time, two adjacent IDT electrodes (IDT electrodes 2 and 3, IDT electrodes 3 and 4, IDT electrodes 5 and 66, and IDT electrodes 6 and 7) of each of the plurality of IDT electrodes are partially formed from the other end. The electrode finger pitch is composed of a first part that is different from the electrode finger pitch of the remaining part and a second part that is the remaining part and the electrode finger pitch is constant (in the example of FIG. 1B, In FIG. 1A, the L1 and L4 parts are the second part, and the L2 and L3 parts are the first. The average value of the electrode finger pitch of the first part is shorter than the electrode finger pitch of the second part (corresponding to the part) (in the example of FIG. 1B, the first part L2 and L3 The electrode finger pitch of the first part is shorter than the electrode finger pitch of the second part L1 and the part L4, respectively, and the electrode finger pitch of the first part becomes shorter toward the boundary between two adjacent IDT electrodes. In the example shown in FIG. 1 (b), the minimum portion C of the electrode finger pitch is the IDT electrode as shown in FIG. 1 (a). 3) and a plurality of IDT electrodes 4 side).

  Specifically, the minimum portion C of the electrode finger pitch is preferably 2 to 4 in order to appropriately arrange the resonance peak in the pass band to increase the bandwidth and improve the insertion loss.

  The two IDT electrodes 2 and 4 of the first surface acoustic wave resonator (surface acoustic wave resonator on the input terminal 13 side in FIG. 1B) are respectively connected to the second surface acoustic wave resonator (FIG. 1). In (b), the two IDT electrodes 5 and 7 of the surface acoustic wave resonator on the output terminal 14 side are cascade-connected.

  With this configuration, the position, number, and electrode finger pitch of the minimum part of the electrode finger pitch in the first part are set to optimum values, and a plurality of surface acoustic wave resonance modes are generated between adjacent IDT electrodes, It is possible to arrange the resonance modes of the surface acoustic waves optimally and arrange the resonance frequencies with a certain frequency interval, that is, it is easy to arrange the resonance frequencies suitable for the broadband characteristics, and as a result, the broadband It is advantageous to make it.

  In addition, since the appearance of the amplitude distribution of a specific surface acoustic wave can be suppressed or increased, control is performed so that a plurality of resonance peaks in the pass band are arranged at the optimal frequency position, and the surface acoustic wave The number of resonance peaks and the intensity distribution thereof can be controlled. As a result, it is advantageous to control the filter characteristics such as improving the flatness of the passband and the insertion loss while increasing the bandwidth.

  As shown in FIG. 1B, the IDT electrode 3 of the first surface acoustic wave resonator and the IDT electrode 6 of the second surface acoustic wave resonator each have a first portion formed at both ends. Needless to say, the IDT electrodes 3 and 6 having this configuration also correspond to the IDT electrodes having the first and second portions of the present invention. That is, the IDT electrodes 3 and 6 have a configuration in which a first portion is formed at both ends and a second portion is formed at the center.

  In the above configuration, the minimum part of the electrode finger pitch in the two first parts and the minimum part of the plurality of minimum parts is on one side deviated from the boundary between two adjacent IDT electrodes ( In the example of FIG. 1B, as shown in FIG. 1A, the minimum part of the electrode finger pitch in the first part and the minimum part of the plurality of minimum parts is the IDT electrode 3 and the IDT electrode. 4), a resonance mode of a plurality of surface acoustic waves is generated, the resonance modes of the surface acoustic waves are arranged at an optimum frequency, and a frequency interval of a certain degree or more is provided. Therefore, it is possible to arrange the resonance frequency, that is, it is easy to arrange the resonance frequency suitable for the wide band characteristics, and as a result, it is advantageous for widening the band.

  In addition, by inserting a wide pitch region with a wide electrode finger pitch into the first portion which is a narrow pitch portion as a whole, the minimum portion of the electrode finger pitch in the first portion is arranged at an optimal frequency position. Because it is possible to suppress or increase the appearance of the amplitude distribution of a specific surface acoustic wave, it is possible to control multiple resonance peaks in the passband to be placed at optimal frequency positions, and to generate elasticity It is possible to control the number of resonance peaks of the surface wave and its intensity distribution. As a result, it is possible to control the filter characteristics such as improving the flatness of the passband and the insertion loss while further increasing the bandwidth.

  In the above configuration, in the two adjacent IDT electrodes 2, 3, IDT electrodes 3, 4, IDT electrodes 5, 6 and IDT electrodes 6, 7, the electrode finger pitch of the second portion of one IDT electrode is the other. Longer than the electrode finger pitch of the second portion of the IDT electrode (in the example of FIG. 1B, as shown in FIG. 1A, the L1 portion which is the second portion on the IDT electrode 3 side is The electrode finger pitch is longer than the L4 part which is the second part on the IDT electrode 4 side), and the minimum part of the electrode finger pitch of the first part is one IDT electrode side (in the example of FIG. As shown in FIG. 1 (a), when the minimum part B of the electrode finger pitch is on the IDT electrode 3 side, the resonance peak of the generated surface acoustic wave is arranged at an appropriate frequency between adjacent IDT electrodes. The number of resonance peaks of the generated surface acoustic wave and The intensity distribution can be controlled, comprising a filter characteristic of the pass band advantageous for improving the flatness and insertion loss with wideband.

  In the above configuration, in two adjacent IDT electrodes, the electrode finger pitch of the second part of one IDT electrode is longer than the electrode finger pitch of the second part of the other IDT electrode, and The average value of the electrode finger pitch of the first part is shorter than the average value of the electrode finger pitch of the first part of the other IDT electrode (in the example of FIG. 1B, the first part L2 of the IDT electrode 3). The average value of the electrode finger pitch of the portion is shorter than the average value of the electrode finger pitch of the first portion L3 portion of the IDT electrode 4), so that the adjacent IDT electrodes (in the example of FIG. 1B, IDT (Between the electrode 3 and the IDT electrode 4), it is possible to control the plurality of resonance peaks of the generated surface acoustic wave to be arranged at an optimum frequency, and at the time of mode conversion of the surface acoustic wave to a bulk wave. To prevent radiation loss optimally Becomes ability can be improved flatness and insertion loss filter characteristic of the pass band while broadband.

  Further, FIG. 2 shows a plan view of the electrode structure of the surface acoustic wave device of the present invention.

  As shown in FIG. 2, in the surface acoustic wave resonator having the above configuration, the IDT is connected in series or in parallel with the IDT electrode 3 constituting the surface acoustic wave resonator (in the example of FIG. 1B) in series. It is composed of an electrode and a reflector sandwiching the IDT electrode, and by connecting a resonator (surface acoustic wave resonator) 12 that generates one or more mode resonances, impedance matching can be improved and an elastic surface By connecting the wave resonator 12, an attenuation pole can be formed, and a surface acoustic wave device that can control the characteristics so that the out-of-band attenuation satisfies the specifications required for high attenuation is realized.

  Further, by connecting the surface acoustic wave resonators having the above-described structure in two stages, the degree of freedom in selecting the resonance mode is increased by the cascade connection between the stages, and therefore the degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased. Therefore, it can be used for controlling 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. In other words, the number of paths connected from the first stage to the second stage can be increased, and the resonance modes of the generated surface acoustic waves can be superposed to increase the degree of freedom in the design of the pass band, and the out-of-band attenuation can be increased. Therefore, it is possible to provide a surface acoustic wave device that is more effective in improving flatness and insertion loss while maintaining a wide passband width.

  Since the number of electrode fingers of the IDT electrodes 2 to 7, the reflector electrodes 8 to 11 and the resonator 12 ranges from several to several hundreds, the shapes are simplified in the figure for simplicity. ing. Note that 13 is an input terminal, and 14 and 15 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.

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

  FIG. 3 shows a plan view of the electrode structure of the surface acoustic wave device of the present invention. In this example, one common electrode of the IDT electrode 6 at the center of the second-stage surface acoustic wave resonator is divided into two so that the electrode is connected to the two balanced output terminals. A surface acoustic wave device having a function of a balanced signal converter can be provided.

  As described above, it is possible to provide an excellent communication device that includes a reception circuit and a transmission circuit having an excellent surface acoustic wave resonator or surface acoustic wave device and that has extremely good sensitivity.

  In the description of the above-described embodiment, for the sake of simplicity, there are many electrode fingers that are long in the direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate 3. Although an example in which two IDT electrodes are arranged has been shown, the present invention is not limited to this, and a plurality of IDT electrodes other than three may be arranged. Changes can be made as appropriate without departing from the scope.

  Examples of the present invention will be described below.

An example in which the surface acoustic wave device shown in FIG. 1B is specifically manufactured will be described. 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. The electrode finger pitch of the IDT electrode between adjacent IDT electrodes has a profile of the electrode finger pitch of the IDT electrode as shown in FIG. The average value of the electrode finger pitch of the first portion L2 portion on the IDT electrode 3 side was 2.01 μm, and the electrode finger pitch of the second portion L1 portion was 2.12 μm. Moreover, the average value of the electrode finger pitch of the first portion L3 portion on the IDT electrode 4 side was 2.05 μm, and the electrode finger pitch of the second portion L4 portion was 2.10 μm. The two first portions as shown in FIG. 1 (a) are provided with a plurality of minimum portions C of electrode finger pitch. Further, the minimum portion B of the plurality of minimum portions, which is the minimum portion of the electrode finger pitch in the two first portions, is positioned on one IDT electrode side that is out of the boundary between two adjacent IDT electrodes. is doing.

  Two surface acoustic wave resonators are cascade-connected in two stages by IDT electrodes 2 and 5 and IDT electrodes 4 and 7.

  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 0.33 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 device was obtained.

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

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

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

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

  Moreover, as a comparative sample, two adjacent IDT electrodes as shown in FIG. 1B are each a part from the other end, and the electrode finger pitch is different from the remaining part of the electrode finger pitch. A surface acoustic wave device in which the electrode finger pitch in the IDT electrode is constant, and the remaining part and the second part in which the electrode finger pitch is constant, is manufactured in the same process as described above. The average electrode finger pitch of the reflector electrodes 8 to 11 arranged on both sides of each surface acoustic wave resonator 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 near the passband is shown in FIG. FIG. 4 is a graph showing the frequency dependence of the insertion loss representing the transmission characteristics of the filter. The filter characteristics of this example product were very good. That is, as shown by the solid line in FIG. 4, the insertion loss of this example product was 1.74 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. 4, the insertion loss of the comparative product was 2.00 dB, the ripple was 1.80 dB, and the specific bandwidth was 3.6%.

  Thus, in this example, a surface acoustic wave device with improved flatness and insertion loss while maintaining a wide passband could be realized.

1 shows an example of an embodiment of a surface acoustic wave device according to the present invention, where (a) is a graph showing the relationship between the position of each electrode and the electrode finger pitch in adjacent IDT electrodes, and (b) is a pattern of each electrode. It is a top view of the surface acoustic wave resonator shown. It is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention. It is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention. It is a graph which shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave apparatus of the Example and comparative example of this invention, and its vicinity, respectively. (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: Piezoelectric substrates 2-7, 203-209: IDT electrodes 8-11, 210-213: Reflector electrodes
12: Resonator
13: Input terminal
14, 15, 216, 217: Output terminals

Claims (7)

  A plurality of IDT electrodes having a plurality of long electrode fingers in a direction orthogonal to the propagation direction are disposed on the piezoelectric substrate along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate. The two adjacent IDT electrodes among the plurality of IDT electrodes are respectively a part from the other end, and the electrode finger pitch is different from the electrode finger pitch of the remaining part. And the second part having a constant electrode finger pitch, the average value of the electrode finger pitch of the first part being shorter than the electrode finger pitch of the second part, and the first part The electrode finger pitch of the portion is shortened toward the boundary between the two adjacent IDT electrodes, and the two first electrode portions include a plurality of minimum portions of the electrode finger pitch. Finger pitch Minimum portion, the surface acoustic wave resonator, characterized in that on the one side deviated from the boundary of the two IDT electrodes adjacent ones of the plurality of local minima a small part. A plurality of IDT electrodes having a plurality of long electrode fingers in a direction orthogonal to the propagation direction are disposed on the piezoelectric substrate along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate. The two adjacent IDT electrodes among the plurality of IDT electrodes are respectively a part from the other end, and the electrode finger pitch is different from the electrode finger pitch of the remaining part. And the second part having a constant electrode finger pitch, the average value of the electrode finger pitch of the first part being shorter than the electrode finger pitch of the second part, and the first part In the two adjacent IDT electrodes, the electrode finger pitch of the portion is shortened toward the boundary between the two adjacent IDT electrodes, the two first electrode portions include a plurality of minimum portions of the electrode finger pitch, on the other hand The electrode finger pitch of the second part of the IDT electrode is longer than the electrode finger pitch of the second part of the other IDT electrode, and the average value of the electrode finger pitch of the first part of the one IDT electrode is the other surface acoustic wave resonator you being shorter than the average value of the electrode finger pitch of the first portion of the IDT electrode.   In the two adjacent IDT electrodes, the electrode finger pitch of the second part of one IDT electrode is longer than the electrode finger pitch of the second part of the other IDT electrode, and the electrode of the first part 2. The surface acoustic wave resonator according to claim 1, wherein a minimum part of a finger pitch is on the one IDT electrode side.   The IDT electrode which comprises the surface acoustic wave resonator in any one of Claims 1 thru | or 3 consists of a reflector which pinches | interposes an IDT electrode and this IDT electrode in series or in parallel, One or more A surface acoustic wave device characterized in that a resonator for generating mode resonance is connected.   A surface acoustic wave device, wherein the surface acoustic wave resonators according to any one of claims 1 to 3 are cascade-connected in two stages.   A communication apparatus comprising at least one of a reception circuit and a transmission circuit having the surface acoustic wave resonator according to any one of claims 1 to 3. 6. A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave device according to claim 4.

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