JP4637718B2 - 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.

  Conventionally, a surface acoustic wave filter has been widely used as a frequency selection filter (hereinafter also referred to as a filter) used in an RF (radio frequency) stage of a mobile communication device such as a mobile phone or a car phone. In general, characteristics required for a frequency selective filter include various characteristics such as a wide passband, low loss, and high attenuation outside the passband. 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.

  In order to realize such a broad band and low loss, for example, three IDT electrodes (Inter Digital Transducer) are provided on a piezoelectric substrate, and a dual mode elastic surface using a longitudinal primary mode and a longitudinal tertiary mode is used. Wave resonator filters have been proposed.

  In particular, by providing a narrow pitch portion of electrode fingers at the ends of adjacent IDT electrodes, the radiation loss of bulk waves between the IDT electrodes is reduced, and the state of the resonance mode is controlled to achieve a wider band and lower loss. (For example, refer to Patent Documents 4 and 5).

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

  Since the conventional surface acoustic wave filter is generally an unbalanced input-unbalanced output type surface acoustic wave filter (hereinafter referred to as an unbalanced surface acoustic wave filter), a circuit connected to the subsequent stage of the surface acoustic wave filter. When the electronic component is a balanced input type, a circuit configuration in which an unbalanced-balanced converter (hereinafter also referred to as a balun) is inserted between the surface acoustic wave filter and the subsequent stage is employed. Similarly, in the case where the circuit or electronic component in the previous stage of the surface acoustic wave filter is a balanced output type, the circuit configuration is such that a balun is inserted between the previous stage and the surface acoustic wave filter.

  Currently, an unbalanced input-balanced output type surface acoustic wave filter or balanced input-unbalanced output, in which a surface acoustic wave filter is provided with an unbalanced-balanced conversion function or balanced-unbalanced conversion function to eliminate the balun. A surface acoustic wave filter (hereinafter referred to as a balanced surface acoustic wave filter) has been put into practical use. In order to satisfy the requirement of the unbalance-balance conversion function, a longitudinally coupled double mode filter is often used. In addition, as an RF filter, there is a great demand to match one input terminal of an unbalanced connection with an input / output impedance of 50Ω and the other balanced connection with an input / output impedance of 100 to 200Ω.

  FIG. 7 shows a conventional resonator type surface acoustic wave filter corresponding to balanced input / output. The IDT electrode 203 disposed on the piezoelectric substrate 201 applies an electric field to a pair of comb-like electrodes opposed to each other to excite surface acoustic waves. According to the principle, the surface acoustic wave excited by applying an input signal to the IDT electrode 203 is propagated to the IDT electrodes 202 and 204 located on both sides of the IDT electrode 203. One comb-like electrode of IDT electrodes 202 and 204 is cascade-connected to one comb-like electrode of second-stage IDT electrodes 205 and 207, and finally one comb-like electrode of IDT electrode 206 at the center of the second stage. Is transmitted to the output signal terminal 222 and from the other to the output signal terminal 223, and balanced output is performed. Further, by connecting the electrode patterns of the resonator-type surface acoustic wave elements in two stages, the attenuation outside the passband of the filter characteristics can be improved.

  In the resonator-type surface acoustic wave filter as described above, the number of comb-teeth electrodes facing the IDT electrodes 202, 204, 205, and 206, the positions where they are arranged, or the peripheral elements that cause parasitic capacitance are generated. Since the structure of the electrode pattern or the like is different, the signals transmitted to the output signal terminals 222 and 223 have different amplitudes, and the phase is shifted from the opposite phase. As a result, only a resonator type surface acoustic wave filter with a deteriorated balance was obtained.

  In recent years, surface acoustic wave filters have played a role in downsizing and no adjustment of various communication devices. Higher performance is also required for the balance in the passband. For example, a filter for a 900 MHz band mobile phone has a high-performance balance with an amplitude balance of 0.5 dB or less and a phase balance of 5 degrees or less. A filter is requested.

  In addition, as shown in FIG. 8, among the first-stage longitudinally coupled double-mode surface acoustic wave filters having three IDT electrodes 202, 203, and 204 sandwiched between reflectors 210 and 211 on both sides, The unbalanced terminal 221 is connected to the first IDT electrode 203, the IDT electrodes 202 and 204 on both sides thereof are connected in cascade to the second-stage IDT electrodes 205 and 207, respectively, and the second-stage center IDT electrode 206 is divided into two. Thus, they are connected to the balanced signal terminals 222 and 223 so that signals of opposite phases are output. Accordingly, a configuration of 50Ω unbalanced input−200Ω balanced output has been proposed (see, for example, Patent Document 3).

  Further, in the conventional dual mode resonator type surface acoustic wave filter, the balance is improved by making the IDT electrodes arranged at the center of the three IDT electrodes arranged in the propagation direction of the surface acoustic wave an even pair. A structure has been proposed (see, for example, Patent Document 4).

In addition, as shown in FIG. 9, three IDT electrodes 202, 203, 204 are arranged close to each other along the surface acoustic wave propagation direction in the first stage, and an unbalanced terminal 221 is connected to the central IDT electrode 203. The IDT electrodes 202 and 204 on both sides are cascaded to the second-stage IDT electrodes 205 and 207, respectively, and the second-stage center IDT electrode 206 is divided into two parts, which are respectively connected to the balanced signal terminals 222 and 223. Connecting. Further, a structure has been proposed in which a balance component is improved by forming a reactance component 224 on the piezoelectric substrate 201 or inside or outside the package at one balanced signal terminal 222 that forms an electric field-free region (for example, Patent Documents). See 5).
Japanese Patent Laid-Open No. 2002-9587 Special table 2002-528987 gazette JP 11-97966 A JP 2002-84164 A JP 2004-96244 A

  Conventionally, as a means for increasing the attenuation of a surface acoustic wave filter, as shown in FIG. 7, three IDT electrodes are arranged close to each other along the propagation direction of the surface acoustic wave, and reflectors are arranged on both sides thereof. A method of forming a surface acoustic wave filter by connecting a plurality of coupled surface acoustic wave elements in cascade is widely used. When this structure is used, the surface acoustic wave elements are cascaded in a plurality of stages, so that the insertion loss in the pass band increases, but the outside of the pass band can be highly attenuated. However, when a surface acoustic wave filter having a wide pass bandwidth is obtained by using a configuration in which the longitudinally coupled resonator type surface acoustic wave elements are cascade-connected, it is insufficient to improve the required insertion loss. there were.

  In addition, in the surface acoustic wave devices disclosed in Patent Documents 1 and 2, 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 electrode pattern of the resonator type surface acoustic wave element in which reflector electrodes for efficiently resonating the surface acoustic wave are provided at both ends of the propagation path of the surface acoustic wave of the IDT electrodes arranged in parallel, There is a need for improved amplitude and phase balance within the band. Here, the degree of balance between amplitude and phase means that a signal is input or output as a potential difference between two signal lines. The greater the amplitude of the signal on each signal line, the better the degree of amplitude balance. In addition, it can be said that the degree of phase balance is better as the phase difference of each signal is equal to 180 °.

  However, in the surface acoustic wave device disclosed in Patent Document 1, a surface acoustic wave device having a balanced output (input) force terminal connected to the IDT electrode at the center of the second step in the conventional two-stage configuration described above. In order to reverse the phase, a structure in which the electrode finger pitch of the IDT electrode positioned on both sides of the central IDT electrode is changed, or the adjacent distance between the central IDT electrode and the IDT electrodes on both sides thereof. Therefore, the frequency dependence of the propagation characteristics of the surface acoustic wave is different from that of the other portions in the narrow pitch portion, and there is a problem that the balance is adversely affected.

  Further, in the surface acoustic wave element disclosed in Patent Document 3, the polarity of the outermost electrode finger of the central IDT electrode and the polarity of the outermost electrode finger of the IDT electrode adjacent thereto are different on the left and right. Since the parasitic capacitance formed at the signal terminal is different, the balanced surface acoustic wave filter having such a structure has a problem that the degree of balance is poor.

In the surface acoustic wave element disclosed in Patent Document 4, for example, when a piezoelectric substrate made of a LiTaO ₃ single crystal is used as the piezoelectric substrate, the amplitude balance is about 1.2 dB and the phase balance is only about 11 degrees. It was not obtained, and sufficient balance that satisfies the requirements was not obtained.

  Furthermore, the effect of the surface acoustic wave element disclosed in Patent Document 5 was verified. FIG. 10 is a diagram showing the frequency characteristics of the surface acoustic wave device shown in FIG. In the diagram of FIG. 10, the horizontal axis represents frequency (unit: MHz), the vertical axis represents attenuation (unit: dB), and the solid line characteristic curve shows the result when nothing is added to the balanced signal terminal. A broken line indicates a result when a capacitive component is connected in parallel as a reactance component to one of the balanced signal terminals. Since a capacitive component as a reactance component is connected in parallel to one of the balanced signal terminals, the ripple in the passband increases.

  FIG. 11 is a diagram showing the VSWR (Voltage Standing Wave Ratio) in the surface acoustic wave device of FIG. Similarly to FIG. 10, the solid characteristic curve shows the result when nothing is added to the balanced signal terminal, and the broken line shows the result when the capacitive component is connected in parallel as a reactance component to one of the balanced signal terminals. . It can be seen that when a capacitive component as a reactance component is connected in parallel to one balanced signal terminal, the VSWR is also degraded.

  In addition, FIG. 12A shows the phase balance in the vicinity of the pass band and FIG. 12B shows the amplitude balance in the surface acoustic wave element of FIG. Similarly to FIG. 10, the solid characteristic curve shows the result when nothing is added to the balanced signal terminal, and the broken line shows the result when the capacitive component is connected in parallel as a reactance component to one of the balanced signal terminals. . As is apparent from FIG. 12, even when a capacitive component as a reactance component is connected in parallel to one balanced signal terminal, no significant improvement was observed in the phase balance and the amplitude balance.

  Accordingly, the present invention has been proposed in view of the above-described conventional problems, and the object thereof is to improve the insertion loss of the surface acoustic wave filter and to improve the balance, and to achieve a high quality balance. It is an object of the present invention to provide a surface acoustic wave element that can function as a surface acoustic wave filter and a communication device using the same.

  The surface acoustic wave resonator according to the present invention includes 1) a plurality of electrode fingers which are long on the piezoelectric substrate along the direction of propagation of the surface acoustic wave propagating on the piezoelectric substrate. An electrode group comprising three or more odd number IDT electrodes and reflector electrodes each provided on both sides of the odd number IDT electrodes and provided with a plurality of long electrode fingers in a direction orthogonal to the propagation direction In the first stage, the electrode group in the first stage has the IDT electrode in the center connected to the unbalanced signal terminal, and the electrode group in the last stage has the IDT electrode in the center. Each of the opposing comb-like electrodes each having the electrode finger is a floating electrode in which one of the two is divided into two and the other is electrically floating, and the comb-like electrode divided into two Are each connected to a balanced signal terminal Both electrode fingers are adjacent to each other at the center of the center IDT electrode, and the last electrode group is the outermost electrode of each of the comb-shaped electrodes divided into two in the center IDT electrode. The fingers are adjacent to the electrode fingers of the IDT electrodes on both sides, and the side having the electrode finger adjacent to the outermost electrode finger among the comb-like electrodes in the IDT electrodes on both sides is connected to the ground terminal. It is characterized by being.

  In the surface acoustic wave device of the present invention, 2) In the configuration of 1) above, the IDT electrode and the IDT electrode are sandwiched in series or in parallel with the IDT electrode constituting the surface acoustic wave element of 1). A surface acoustic wave resonator including a reflector and generating one or more mode resonances is connected.

  In addition, the communication apparatus of the present invention includes 3) at least one of a reception circuit and a transmission circuit having the surface acoustic wave elements having the configurations of 1) and 2) above.

  According to the surface acoustic wave device of the present invention, a plurality of stages of electrode groups, each of which is arranged on both sides of an odd number of IDT electrodes of three or more and an odd number of IDT electrodes, and is formed of a reflector electrode, are cascaded. In the first stage electrode group, the center IDT electrode is connected to the unbalanced signal terminal, and the last stage electrode group has the comb teeth facing each other with the center IDT electrode having electrode fingers. One of the electrode electrodes is divided into two and the other is a floating electrode that is electrically floating, so that the electrode finger facing the electrode finger on the balanced output side of the central IDT electrode is at ground potential. Since the noise component of the surface acoustic wave propagating from the ground terminal can be cut by not falling, both the amplitude balance and the phase balance in the balanced output can be improved.

  Furthermore, according to the surface acoustic wave element of the present invention, the two comb-shaped electrodes are connected to the balanced signal terminal, and each electrode finger is adjacent to the central portion of the central IDT electrode. Therefore, when the electrode fingers having the ground potential are adjacent to each other at the center portion of the center IDT electrode, the electrode fingers act as reflector electrodes, and multiple reflections of surface acoustic waves are caused between the adjacent electrode fingers. However, in the case of the surface acoustic wave device according to the present invention, the adjacent electrode fingers at the center become balanced output signals, and multiple reflections of surface acoustic waves occur. Therefore, the balance does not deteriorate.

  Furthermore, according to the surface acoustic wave device of the present invention, the outermost electrode fingers of the comb-like electrodes divided into two in the central IDT electrode are connected to the electrode fingers of the IDT electrodes on both sides. Since the side having the electrode finger adjacent to the outermost electrode finger among the comb-like electrodes in the IDT electrodes on both sides is connected to the ground terminal, the balance characteristic of the surface acoustic wave filter is In addition, it is possible to dispose the depression-like region with a deteriorated degree of balance outside the pass band, and to improve the degree of balance within the pass band. Furthermore, multiple reflections of surface acoustic waves between adjacent electrode fingers are less likely to occur, and insertion loss in the passband can be improved. Moreover, according to each said structure, the surface acoustic wave filter which has an unbalance-balance conversion function can be comprised.

  Contrary to this configuration, of the comb-like electrodes in the IDT electrodes on both sides, the side having the electrode finger adjacent to the outermost electrode finger is connected to each signal terminal, and the comb divided into two in the center IDT electrode When the outermost electrode fingers of the tooth-shaped electrodes are not adjacent to the electrode fingers of the IDT electrodes on both sides, the degree of deterioration of the deteriorated portion of the indentation-like balance generated in the pass band increases. The insertion loss in the inside deteriorates.

  In the IDT electrodes adjacent to each other in the last-stage electrode group, when the adjacent electrode fingers are signal electrodes or ground electrodes, a recessed area with a deteriorated degree of balance is present in the passband. And the degree of balance in the passband deteriorates.

  In each of the above configurations, an elastic surface that generates one or more mode resonances in series or in parallel with an IDT electrode that constitutes a surface acoustic wave element, and includes an IDT electrode and a reflector that sandwiches the IDT electrode. By connecting a wave resonator, impedance matching can be achieved, and by connecting a surface acoustic wave resonator, an attenuation pole can be formed, resulting in high out-of-band attenuation, which is required. Properties can be controlled to meet specifications.

  The communication device of the present invention is capable of satisfying severe insertion loss that has been conventionally required 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. Thus, it is possible to realize a communication apparatus with reduced power consumption and extremely good sensitivity.

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

  FIG. 1 shows a plan view of an electrode structure of a surface acoustic wave device according to the present invention. As shown in FIG. 1, the surface acoustic wave device of the present invention is formed on a piezoelectric substrate 1 along the direction of propagation of surface acoustic waves propagating on the piezoelectric substrate 1 in a direction orthogonal to the propagation direction. Three or more odd-numbered IDT electrodes 2 to 7 having a plurality of long electrode fingers and a plurality of long electrode fingers arranged on both sides of the odd-numbered IDT electrodes 2 to 7 and perpendicular to the propagation direction A plurality of electrode groups composed of the reflector electrodes 8 to 11 provided are connected in cascade. In the first stage electrode group, the central IDT electrode 3 is connected to the unbalanced signal terminal 12, and in the final stage electrode group, the central IDT electrode 6 has electrode fingers and is opposed to each other. One of the electrodes is divided into two and the other is a floating electrode that is electrically floating.

  With this configuration, the noise component of the surface acoustic wave propagating from the ground terminal can be cut off because the electrode finger facing the balanced output side electrode finger of the comb-like electrode in the central IDT electrode 6 does not fall to the ground potential. Therefore, both the amplitude balance and the phase balance in the balanced output can be improved.

  Further, the comb-shaped electrodes divided into two are respectively connected to the balanced signal terminals 13 and 14, and the respective electrode fingers are adjacent to each other at the central portion 15 of the central IDT electrode 6.

  With this configuration, the electrode fingers adjacent in the central portion of the central IDT electrode 6 become balanced output signals, so that multiple reflections of surface acoustic waves do not occur, and therefore the degree of balance does not deteriorate.

  Further, in the final stage electrode group, the outermost electrode fingers 16 of the two comb-like electrodes in the central IDT electrode 6 are adjacent to the electrode fingers of the IDT electrodes 5 and 7 on both sides, and both sides Of the comb-like electrodes of the IDT electrodes 5 and 7, the side having the electrode finger 17 adjacent to the outermost electrode finger 16 is connected to the ground terminal 18.

  With this configuration, in the balance characteristic of the surface acoustic wave filter, it is possible to dispose a region in which the hollow balance is deteriorated outside the pass band, and to improve the balance within the pass band. Furthermore, multiple reflections of surface acoustic waves between adjacent electrode fingers are less likely to occur, and insertion loss in the passband can be improved. Moreover, according to each said structure, the surface acoustic wave filter which has an unbalance-balance conversion function can be comprised.

  Contrary to this configuration, the side having the electrode finger adjacent to the outermost electrode finger among the comb-like electrodes in the IDT electrodes 5 and 7 on both sides is connected to the signal terminal, and 2 in the IDT electrode 6 in the center. When the outermost electrode fingers of the divided comb-like electrodes are not adjacent to the electrode fingers of the IDT electrodes 5 and 7 on both sides, the degree of deterioration of the indented balance degree deterioration portion generated outside the passband And the insertion loss in the passband is degraded.

  In addition, in the IDT electrodes 5 and 6 and the IDT electrodes 6 and 7 adjacent to each other in the last-stage electrode group, when the adjacent electrode fingers are signal electrodes or ground electrodes, a hollow equilibrium is obtained. A region with a deteriorated degree is generated in the pass band, and the balance in the pass band is deteriorated.

  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 device having the above-described structure according to the present invention, the IDT electrode 3 and the IDT electrode 3 constituting the surface acoustic wave device are connected in series or in parallel (in the case of FIG. 2 in series) By connecting a resonator (surface acoustic wave resonator) 19 composed of reflector electrodes sandwiching the IDT electrode and generating one or more mode resonances, impedance matching can be satisfactorily obtained, and surface acoustic waves can be obtained. Attenuation poles can be formed by connecting the resonator 19, and a surface acoustic wave element capable of controlling the characteristics so that the attenuation outside the passband is high and satisfies the required specifications is realized. .

  In addition, since the electrode group (surface acoustic wave resonator) having the above-described configuration according to the present invention is connected in two stages, the degree of freedom in selecting a resonance mode is increased by the cascade connection between the stages. This increases the degree of freedom of control, and 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. 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. Thus, it is possible to provide a surface acoustic wave device with improved flatness and insertion loss while maintaining a wider passband width more effectively.

  Since the number of electrode fingers of the IDT electrodes 2 to 7, the reflector electrodes 8 to 11 and the resonator 19 is several to several hundreds, for simplicity, these shapes are simplified in the figure. ing. Note that 12 is an input terminal, and 13 and 14 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 Since the coefficient is small, it is preferable as the piezoelectric substrate 1. Of these pyroelectric piezoelectric single crystals, if the piezoelectric substrate 1 has a significantly reduced pyroelectric property due to solid solution of oxygen defects or Fe, the reliability of the device is good. The thickness of the piezoelectric substrate 1 is preferably about 0.1 to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate 1 becomes brittle, and if it exceeds 0.5 mm, the material cost and component dimensions become large, which is not suitable for use.

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

Furthermore, SiO ₂ , SiN _x , Si, Al ₂ O ₃ is formed as a protective film on the surface acoustic wave propagation portion on the surface of the surface acoustic wave filter and the piezoelectric substrate according to the present invention, and current is applied by conductive foreign matter. It is also possible to prevent or 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 device according to the present invention is employed, an excellent communication device with remarkably good sensitivity can be provided.

  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 an odd number of five or more IDT electrodes may be arranged, and the gist of the present invention is also possible in other configurations. It is possible to make appropriate changes without departing from the scope.

  Examples of the present invention will be described below.

An example in which the surface acoustic wave element shown in FIG. 1 is specifically manufactured will be described. An elastic surface made of Al (99% by mass) -Cu (1% by mass) on a LiTaO ₃ single crystal piezoelectric substrate (mother substrate for multiple production) 1 having a 38.7 ° Y-cut propagation in the X direction. A fine electrode pattern constituting a wave element was formed.

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

  First, the piezoelectric substrate 1 was ultrasonically cleaned with acetone, IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the piezoelectric substrate 1 with a clean oven, a metal layer to be each electrode was formed. A sputtering apparatus was used for forming the metal layer, and an Al (99 mass%)-Cu (1 mass%) alloy was used as the material of the metal layer. The thickness of the metal layer at this time was about 0.33 μm.

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

Thereafter, a protective film was formed on a predetermined region of the electrode. That is, SiO ₂ was formed with 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 was performed by photolithography, and the flip-chip window opening portion was etched by an RIE apparatus or the like. Thereafter, a pad electrode mainly composed of Al was formed on the flip-chip window opening using a sputtering apparatus. The film thickness of the pad electrode at this time was about 1.0 μm. Thereafter, the photoresist and the unnecessary portion of Al 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 onto 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 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. As the package, a 2.5 × 2.0 mm square laminated structure formed by laminating ceramic layers was used.

  As a sample of the comparative example, in the last stage electrode group as shown in FIG. 3, of the comb-like electrodes on the IDT electrodes 5 and 7 on both sides with respect to the central IDT electrode 6, A surface acoustic wave element in which the side having the electrode finger adjacent to the outermost electrode finger was connected to the signal electrode was manufactured in the same process as described above. The other structure of the surface acoustic wave element used as the sample of the comparative example is the same as the structure of the surface acoustic wave element shown in FIG.

  Next, the characteristics of the surface acoustic wave elements of this example and the comparative example were measured. A signal of 0 dBm was input, and measurement was performed under the 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 the product of this example was 1.30 dB, and the specific bandwidth was 4.7%.

  On the other hand, as shown by the broken line in FIG. 4, the insertion loss of the comparative product was 1.45 dB, and the specific bandwidth was 4.5%.

  Also, diagrams of amplitude balance and phase balance near the passband are shown in FIGS. 5 and 6, respectively. The balance of the present invention was very good. As shown by the solid line in FIG. 5, the amplitude balance of this example was 0.1 dB, and as shown by the solid line of FIG. 6, the phase balance of this example was 1.7 °. On the other hand, as shown by the broken line in FIG. 5, the amplitude balance of the comparative example was 0.5 dB, and as shown by the broken line of FIG. 6, the phase balance of the comparative example was 4.2 °. As described above, in this embodiment, the balance can be greatly improved in the passband.

  As described above, in this example, it was possible to realize a surface acoustic wave device with improved insertion loss and improved balance while maintaining a wide pass band.

It is a top view which shows one example of embodiment about the surface acoustic wave element of this invention. It is a top view which shows the other example of embodiment about the surface acoustic wave element of this invention. It is a top view which shows the electrode structure of the surface acoustic wave element of a comparative example. It is a diagram which respectively shows the frequency characteristic of the insertion loss in the pass band and its vicinity about the surface acoustic wave element of the Example and comparative example of this invention. FIG. 6 is a diagram showing the amplitude balance in the frequency dependence of the balance in the passband and in the vicinity thereof for the surface acoustic wave elements of the examples of the present invention and the comparative example. FIG. 3 is a diagram showing the phase balance of the surface acoustic wave devices of the examples of the present invention and the comparative example, showing the frequency dependence of the balance in the passband and the vicinity thereof. It is a top view which shows an example of the electrode structure of the conventional surface acoustic wave element. It is a top view which shows the other example of the electrode structure of the conventional surface acoustic wave element. It is a top view which shows the other example of the electrode structure of the conventional surface acoustic wave element. It is a diagram which shows the frequency characteristic of the insertion loss in the pass band of the conventional surface acoustic wave element, and its vicinity. It is a diagram which shows the frequency characteristic of VSWR in the pass band of the conventional surface acoustic wave element, and its vicinity. It is a diagram which shows the frequency dependence of the balance in the passband of the conventional surface acoustic wave element and its vicinity, (a) is a diagram which shows amplitude balance, (b) is a diagram which shows phase balance. is there.

Explanation of symbols

1, 201: Piezoelectric substrates 2 to 7, 202 to 207: IDT electrodes 8 to 11, 210 to 213: Reflector electrodes 12, 221: Unbalanced signal terminals (unbalanced input (out) force part)
13, 14, 222, 223: balanced signal terminals (balanced (input) force part)
18: Ground terminal 19: Resonator

Claims (3)

On the piezoelectric substrate, along with the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate, three or more odd-numbered IDT electrodes having a plurality of long electrode fingers in a direction orthogonal to the propagation direction; A plurality of electrode groups, each of which is arranged on both sides of the odd number of IDT electrodes and includes a plurality of reflector electrodes having a plurality of long electrode fingers in a direction orthogonal to the propagation direction, are arranged in cascade . A surface acoustic wave device,
In the first-stage electrode group, the center IDT electrode is connected to an unbalanced signal terminal,
The last-stage electrode group includes a central IDT electrode disposed at the center among odd-numbered IDT electrodes constituting the last-stage electrode group, and a first adjacent IDT electrode disposed adjacent to one side of the central IDT electrode. And a second adjacent IDT electrode disposed adjacent to the other side of the central IDT electrode,
The central IDT electrode includes a comb-shaped floating electrode that is electrically floated, and electrode fingers that are arranged so as to mesh with electrode fingers of the comb-shaped floating electrode. It is composed of two comb-shaped divided electrodes,
The first adjacent IDT electrode has a first comb-shaped ground electrode connected to a ground terminal;
The second adjacent IDT electrode has a second comb-shaped ground electrode connected to a ground terminal;
The first comb-like divided electrode is connected to a first balanced signal terminal;
The second comb-like divided electrode is connected to a second balanced signal terminal;
The electrode fingers of the first comb-shaped divided electrode and the electrode fingers of the second comb-shaped divided electrode are adjacent to each other at the center of the central IDT electrode ,
The outermost electrode fingers of the first comb-shaped divided electrodes and the electrode fingers of the first comb-shaped ground electrode with is adjacent at the boundary between the central IDT electrode and the first adjacent IDT electrode, wherein The outermost electrode finger of the second comb-shaped divided electrode and the electrode finger of the second comb-shaped ground electrode are adjacent to each other at the boundary between the center IDT electrode and the second adjacent IDT electrode. A surface acoustic wave device. A surface acoustic wave resonator that includes one or more IDT electrodes and a reflector that sandwiches the IDT electrodes is connected in series or in parallel to the IDT electrodes that constitute the first-stage electrode group. A surface acoustic wave device characterized by that. A communication apparatus comprising at least one of a reception circuit and a transmission circuit having the surface acoustic wave element according to claim 1.

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