JP2008136022A - Surface acoustic wave device and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device that reduces an insertion loss by suppressing small ripples in a passband. <P>SOLUTION: A surface acoustic wave element 14 has n electrode fingers for ground between electrode fingers for a signal at both ends of a central IDT electrode 3 and electrode fingers for a signal at the ends on the IDT electrode 3 sides of the IDT electrodes 2 and 4, wherein polarities of adjacent electrode fingers between the IDT electrodes are symmetrical with respect to the IDT electrode 3. A surface acoustic wave element 15 has (n-1) electrode fingers for ground between electrode fingers for a signal at one end of the central IDT electrode 6 and electrode fingers for a signal at the end on one end side of an IDT electrode 5 and has (n+1) electrode fingers for ground between electrode fingers for a signal on the other end of the IDT electrode 6 and electrode fingers for a signal at an end on the other end side of an IDT electrode 7, wherein the polarities of adjacent electrode fingers between the IDT electrodes are symmetrical with respect to the centers C and D of gaps between electrode fingers between the IDT electrodes. Electrode finger pitches of the IDT electrodes are symmetrical with respect to the center E of a gap between central electrode fingers of the IDT electrode 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 (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 selection 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 recent years, in mobile communication devices, the antenna has shifted from a conventional whip antenna to a built-in antenna using dielectric ceramics or the like for miniaturization. For this reason, it is difficult to obtain a sufficient antenna gain, and there is an increasing demand for further improving the insertion loss of the surface acoustic wave filter.

  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 Document 1).

  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.

  Further, as shown in FIG. 8, among the first-stage vertically coupled double mode filters having three IDT electrodes 202, 203, and 204 sandwiched between reflector electrodes 210 and 211 on both sides, the center IDT The unbalanced terminal 221 is connected to the electrode 203, the IDT electrodes 202 and 204 on both sides thereof are cascade-connected to the second-stage IDT electrodes 205 and 207, respectively, and the second-stage central IDT electrode 206 is divided into two parts, The phase is connected to the balanced signal terminals 222 and 223. Accordingly, a configuration has been proposed in which an unbalanced input with an input impedance of 50Ω and a balanced output with an output impedance of 200Ω are used (see, for example, Patent Document 2). In FIG. 8, reference numerals 212 and 213 denote reflector electrodes.

  FIG. 9 is a plan view schematically showing an electrode structure of a surface acoustic wave filter having a conventional balance-unbalance conversion function. The surface acoustic wave filters 212 and 213 connected in parallel on the piezoelectric substrate 201 are arranged, and the longitudinally coupled resonator type surface acoustic wave elements 212 and 213 include three IDT electrodes 202, 203, 204 and 205, 206, respectively. 207, and reflector electrodes 208, 209 and 210, 211 arranged on both sides thereof.

The longitudinally coupled resonator type surface acoustic wave elements 212 and 213 are connected in parallel and connected to the unbalanced signal terminal 214. In the IDT electrodes 202 and 204 and the IDT electrodes 205 and 207 connected to the unbalanced signal terminal 214, an electric field is applied to a pair of mutually opposed comb-like electrodes to excite surface acoustic waves. The excited surface acoustic wave propagates to the center IDT electrodes 203 and 206. In addition, the phase of the center IDT electrode 203 is a reverse phase that is 180 ° different from the phase of the center IDT electrode 206, and finally from one of the comb-like electrodes of the center IDT electrodes 203 and 206. A signal is transmitted to the balanced output signal terminals 215 and 216 and is output in a balanced manner. With such a configuration, a balanced-unbalanced conversion function is realized. Compared with the longitudinally coupled resonator type surface acoustic wave filter of the two-stage cascade connection type shown in FIG. 8, the crossing width of the electrode fingers of the IDT electrode is reduced to half that of the prior art, and further connected in parallel. The resistance loss in the longitudinally coupled resonator type surface acoustic wave filter can be reduced, and a low-loss longitudinally coupled resonator type surface acoustic wave filter can be realized. (For example, see Patent Document 3).
Japanese Patent Laid-Open No. 2002-9587 JP 11-97966 A JP 2002-84164 A

  By using a conventional surface acoustic wave filter as shown in FIG. 9, an unbalance-balance conversion function can be realized. However, depending on the polarity of the electrode fingers adjacent to each other between adjacent IDT electrodes, that is, the arrangement and combination of whether the adjacent electrode fingers are for signal or ground, and the distribution of the electrode finger pitch of each IDT electrode As shown in the frequency characteristics in the vicinity of the 10 passbands, there is a problem that the insertion loss in the passband deteriorates because minute ripples (arrow portions in FIG. 10) are generated in the passband in the filter characteristics.

  Conventionally, as a means for increasing the attenuation of the surface acoustic wave filter outside the pass band, three IDT electrodes are arranged close to each other along the propagation direction of the surface acoustic wave, and reflector electrodes are arranged on both sides thereof. A configuration in which a coupled resonator type surface acoustic wave element is cascade-connected to form a surface acoustic wave filter is widely used. When this configuration is used, the longitudinally coupled resonator type surface acoustic wave elements are cascaded in a plurality of stages, so that the insertion loss in the passband increases, but the attenuation outside the passband can be increased. 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 connected in cascade, it is insufficient to improve the required insertion loss. It was.

  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.

  Accordingly, the present invention has been proposed in view of the above-described conventional problems, and its purpose is to improve spike loss (micro ripple) in the pass band of the surface acoustic wave filter and improve insertion loss characteristics. Another object of the present invention is to provide a surface acoustic wave device that can also function as a high-quality balanced surface acoustic wave filter and a communication device using the same.

The surface acoustic wave device of the present invention includes three IDTs each having a plurality 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. There are formed first and second surface acoustic wave elements each having an electrode and a reflector electrode that is disposed on both sides of each of the electrodes and includes a plurality of long electrode fingers in a direction orthogonal to the propagation direction, The first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal and are each a balanced output section or a balanced input section, and the respective centers of the first and second surface acoustic wave elements are A surface acoustic wave device in which a balanced signal terminal is connected to the IDT electrode.
One of the first and second surface acoustic wave elements includes a signal electrode finger on both ends of the central IDT electrode and an end on the IDT electrode side in the center of the IDT electrode on both sides of the central IDT electrode. The number of ground electrode fingers arranged between each of the signal electrode fingers is n, and the polarity of the electrode fingers adjacent to each other between the adjacent IDT electrodes is centered on the IDT electrode at the center. The electrode finger pitch of the three IDT electrodes is a symmetrical distribution centering on the electrode finger located at the center of the center IDT electrode,
The other of the first and second surface acoustic wave elements includes a signal electrode finger at one end of the central IDT electrode and the one end of one IDT electrode adjacent to the central IDT electrode on the one end side. The number of ground electrode fingers arranged between the signal electrode fingers on the side end is n−1, the signal electrode fingers on the other end of the center IDT electrode, and the center on the other end side. The number of ground electrode fingers arranged between the other electrode side electrode finger of the other IDT electrode adjacent to the IDT electrode is n + 1 and between the adjacent IDT electrodes The polarities of the electrode fingers adjacent to each other are arranged symmetrically with respect to the center of the gap between the electrode fingers between the adjacent IDT electrodes, and the electrode finger pitch of the IDT electrodes is set to the center of the center IDT electrode. To the center of the gap between the electrode fingers Characterized in that it is a symmetrical distribution.

  In the surface acoustic wave device according to the present invention, preferably, the electrode finger pitch distribution of the three IDT electrodes in one of the first and second surface acoustic wave elements, and the first and second The electrode finger pitch distribution of the three IDT electrodes in the other of the surface acoustic wave elements is the same.

  In the surface acoustic wave device according to the present invention, preferably, the first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal via a surface acoustic wave resonator. .

  In the surface acoustic wave device according to the present invention, it is preferable that the first and second surface acoustic wave elements include one reflector electrode formed integrally with a reflector electrode at a location where they are adjacent to each other. It is characterized by.

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

The surface acoustic wave device of the present invention includes three IDT electrodes each having a plurality 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. The first and second surface acoustic wave elements having reflector electrodes provided with a plurality of long electrode fingers in the direction orthogonal to the propagation direction are respectively formed on both sides of the first and second surface acoustic wave elements. These surface acoustic wave elements are connected in parallel to the unbalanced signal terminal and are each a balanced output section or a balanced input section, and are balanced with the IDT electrodes at the center of the first and second surface acoustic wave elements. A surface acoustic wave device to which a signal terminal is connected,
One of the first and second surface acoustic wave elements includes a signal electrode finger at both ends of the central IDT electrode and a signal electrode finger at the end of the IDT electrode on both sides of the central IDT electrode on the central IDT electrode side. The number of grounding electrode fingers arranged between each electrode is n, and the polarity of the electrode fingers adjacent to each other between adjacent IDT electrodes is symmetrical with respect to the center IDT electrode. Further, the electrode finger pitch of the three IDT electrodes is symmetric with respect to the electrode finger located at the center of the center IDT electrode,
The other of the first and second surface acoustic wave elements is a signal electrode finger at one end of the center IDT electrode and a signal at one end of one IDT electrode adjacent to the center IDT electrode on one end side. The number of ground electrode fingers arranged between the electrode fingers is n−1, the other electrode electrode finger of the other end of the center IDT electrode and the other IDT adjacent to the center IDT electrode on the other end side. IDT electrodes in which the number of ground electrode fingers arranged between the signal electrode fingers on the other end side of the electrodes is n + 1 and the polarities of the electrode fingers adjacent to each other between adjacent IDT electrodes are adjacent to each other The electrode finger pitch of the IDT electrodes is symmetrically distributed with respect to the center of the gap between the electrode fingers located at the center of the center IDT electrode. Therefore, the following effects are achieved.

  That is, when the polarity arrangement of the electrode fingers is asymmetric in the adjacent portion of the IDT electrode, the distribution of higher-order modes of the excited surface acoustic wave becomes asymmetric, and the excitation field of the surface acoustic wave becomes asymmetric. In addition, a problem that minute ripples are generated due to deterioration of excitation efficiency in the IDT electrode (excitation electrode) and the reflector electrode of the surface acoustic wave occurred, but the electrode finger was connected to the ground terminal in the adjacent portion With the above configuration of the present invention in which the number of electrode fingers is constant and the symmetry of the electrode finger pitches of the two surface acoustic wave elements is ensured, the problem of generation of minute ripples can be solved.

  When the polarity arrangement of the electrode fingers has symmetry as in the present invention, the distribution of the higher-order modes of the excited surface acoustic wave is symmetric, the excitation field of the surface acoustic wave is symmetric, Since the reflection coefficient of the IDT electrode and the reflector electrode is not reduced and the reflection characteristics are improved and the excitation efficiency is not deteriorated, there is no problem that a minute ripple is locally generated.

  In the surface acoustic wave device of the present invention, it is preferable that the electrode finger pitch distribution of the three IDT electrodes in one of the first and second surface acoustic wave elements and the first and second surface acoustic waves. The distribution of the electrode finger pitches of the three IDT electrodes on the other of the elements is the same, so that the distribution of the excited surface acoustic waves can be made symmetric in the two surface acoustic wave elements, so that it passes therethrough. Generation of minute ripples in the band can be prevented more effectively.

  In the surface acoustic wave device according to the present invention, preferably, the first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal via the surface acoustic wave resonator, thereby causing surface acoustic wave resonance. Attenuation poles can be formed by connecting the elements, and characteristics can be controlled to meet the required specifications by adjusting the period of the electrode fingers. Furthermore, by connecting multiple surface acoustic wave resonators and making their electrode finger periods different, it is possible to form multiple attenuation poles and control the frequency position of the attenuation poles. It can be configured to meet the required specifications.

  Further, when a high frequency signal is input or output to an unbalanced signal terminal with an impedance of 50Ω, it is difficult to connect to the first and second surface acoustic wave elements with an impedance of 50Ω, and it is difficult to obtain the required impedance matching. become. However, when the first stage is a surface acoustic wave resonator (surface acoustic wave element comprising a single IDT electrode and a reflector electrode), impedance matching can be easily taken.

  The surface acoustic wave element according to the present invention is preferably configured such that each of the first and second surface acoustic wave elements includes one reflector electrode formed integrally with a reflector electrode at a location where they are adjacent to each other. Surface acoustic waves excited by two surface acoustic wave elements further pass through the integrally formed reflector electrode by canceling out the phases on the plus side and minus side, respectively, and improving the reflection characteristics. Generation of minute ripples in the band can be suppressed.

  The communication device according to the present invention can satisfy the severe insertion loss that has been conventionally required by including at least one of the reception circuit and the transmission circuit having any one of the surface acoustic wave devices according to the present invention. Thus, it is possible to realize a communication device with reduced power consumption and significantly improved sensitivity.

  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 addition, in drawing demonstrated below, the same code | symbol shall be attached | subjected to the same structure. 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. 1 shows a plan view of an example of an embodiment 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 has an electrode finger that is long on a piezoelectric substrate 1 along the direction of propagation of surface acoustic waves propagating on the piezoelectric substrate 1. First and second having three IDT electrodes 2 to 7 having a plurality of electrodes and reflector electrodes 8 to 11 each having a plurality of long electrode fingers arranged on both sides thereof and orthogonal to the propagation direction. The surface acoustic wave elements 14 and 15 are formed, and the first and second surface acoustic wave elements 14 and 15 are connected in parallel to the unbalanced signal terminal 21 and each is connected to a balanced output section or a balanced input section. The balanced signal terminals 22 and 23 are connected to the IDT electrodes 3 and 6 at the center of the first and second surface acoustic wave elements 14 and 15, respectively.

  Further, one of the first and second surface acoustic wave elements 14 and 15 (for example, the surface acoustic wave element 14) includes signal electrode fingers at both ends of the central IDT electrode 3 and both sides of the central IDT electrode 3. The number of ground electrode fingers arranged between the IDT electrodes 2 and 4 and the signal electrode fingers at the end on the center IDT electrode 3 side is n (one in the case of FIG. 1) and adjacent to each other. The polarities of the electrode fingers adjacent to each other between the matching IDT electrodes (between the IDT electrodes 2 and 3 and between the IDT electrodes 3 and 4) are arranged symmetrically with respect to the center IDT electrode 3.

  Note that the symmetrical arrangement means that the surface acoustic wave element 14 in FIG. 1 is line symmetric with respect to the axis of the center A of the IDT electrode 3 (the axis along the direction orthogonal to the propagation direction of the surface acoustic wave). Refers to the arrangement. The same shall apply hereinafter.

  Here, when the electrode finger connected to the balanced signal terminal (balanced signal output (input) terminal: signal line) is S and the electrode finger connected to the ground terminal is G, for example, the first surface acoustic wave element 14 is used. Is the arrangement of SGS and SGS from the left side of the figure at the adjacent location, and the number of ground electrode fingers is one each. Further, as shown in FIG. 1B, the electrode finger pitch of the three IDT electrodes 2 to 4 is symmetric with respect to the electrode finger located at the center A of the center IDT electrode 3. . In FIG. 1B, the unit of the electrode finger pitch p (X) on the vertical axis is μm. The same applies to FIGS. 2B to 5B.

  The other of the first and second surface acoustic wave elements 14 and 15 (for example, the surface acoustic wave element 15) includes a signal electrode finger at one end of the central IDT electrode 6 and a central IDT at one end thereof. The number of ground electrode fingers arranged between the signal electrode fingers on one end side of one IDT electrode 5 adjacent to the electrode 6 is n−1 (0 in the case of FIG. 1). The ground electrode disposed between the signal electrode finger on the other end of the IDT electrode 6 and the signal electrode finger on the other end side of the other IDT electrode 7 adjacent to the center IDT electrode 6 on the other end side. The number of electrode fingers is n + 1 (two in the case of FIG. 1), and the polarity of electrode fingers adjacent to each other between adjacent IDT electrodes (between IDT electrodes 5 and 6 and between IDT electrodes 6 and 7) is adjacent. The electrode finger gap between the matching IDT electrodes (between IDT electrodes 5 and 6 and between IDT electrodes 6 and 7). Center C of flops, are arranged symmetrically with respect to relative D.

  For example, the second surface acoustic wave element 15 has an arrangement of GSSG and SGGS from the left side of the drawing in the adjacent portion, and the signal electrode finger at one end of the center IDT electrode 6 and the center at the one end side. The number of ground electrode fingers arranged between the signal electrode fingers at one end of one IDT electrode 5 adjacent to the IDT electrode 6 is n−1, that is, 1-1 = 0. The signal electrode finger at the other end of the center IDT electrode 6 and the signal electrode finger at the other end of the other IDT electrode 7 adjacent to the center IDT electrode 6 on the other end side are disposed. The number of ground electrode fingers is n + 1, that is, 1 + 1 = 2.

  Furthermore, as shown in FIG. 1B, the electrode finger pitch of the IDT electrodes is symmetric with respect to the center E of the gap between the electrode fingers located at the center of the center IDT electrode 6.

  n should be as small as possible, in which case the number of grounding electrode fingers that perform vibrations (vibrations corresponding to nodes of surface acoustic waves) that are not vibrations (vibrations corresponding to antinodes of surface acoustic waves) due to input / output signals is reduced. Excellent steepness of attenuation on the low frequency side, and wide bandwidth. Accordingly, n is preferably 1 to 3. If n exceeds 3, the number of electrode fingers for grounding that is not vibration (vibration corresponding to antinodes of surface acoustic waves) due to input / output signals increases (vibration corresponding to nodes of surface acoustic waves) increases. The steepness of the attenuation on the side deteriorates and the bandwidth becomes narrower.

  With the above-described configuration of the present invention in which the symmetry of the electrode finger pitch between the two surface acoustic wave elements 14 and 15 is ensured, the problem of minute ripples generated in the passband can be solved. That is, when the polarity arrangement of the electrode fingers has symmetry as in the present invention, the distribution of the higher-order modes of the excited surface acoustic wave is symmetric, the excitation field of the surface acoustic wave is symmetric, Since the reflection coefficient of the IDT electrode and the reflector electrode is not reduced, the reflection characteristics are improved, and the excitation efficiency is not deteriorated. Therefore, the problem of generating minute ripples does not occur.

  In the surface acoustic wave device according to the present invention, preferably, the electrode finger pitch distribution of the three IDT electrodes in one of the first and second surface acoustic wave elements 14 and 15 and the first Since the distribution of the electrode finger pitches of the three IDT electrodes in the other of the first and second surface acoustic wave elements 14 and 15 is the same, the distribution of the excited surface acoustic waves is changed to two surface acoustic waves. The elements 14 and 15 can be symmetric, so that the generation of minute ripples in the passband can be more effectively prevented.

  Note that the distribution of the electrode finger pitch is the same as long as it is within the range of the accuracy of electrode finger pattern formation by photolithography (about 0.1 μm or less). In that case, the distribution of the excited surface acoustic waves becomes substantially the same.

  FIG. 2 shows a plan view of another example of the embodiment of the electrode structure of the surface acoustic wave device of the present invention. As shown in FIG. 2, the first and second surface acoustic wave elements 14 and 15 are preferably connected in parallel to the unbalanced signal terminal 21 via the surface acoustic wave resonator 16. Thereby, the attenuation pole can be formed by connecting the surface acoustic wave resonator 16, and the characteristics can be controlled to satisfy the required specifications by adjusting the period of the electrode fingers. Furthermore, by connecting a plurality of surface acoustic wave resonators 16 so that their electrode periods are different, it is possible to form a plurality of attenuation poles and to control the frequency position of the attenuation poles. Can be designed to meet the specifications.

  Further, when a high frequency signal is input or output to the unbalanced signal terminal 21 with an impedance of 50Ω, it is difficult to connect to the first and second surface acoustic wave elements 14 and 15 with an impedance of 50Ω, and the required impedance matching is achieved. It becomes difficult to take. However, when the first stage is a surface acoustic wave resonator (surface acoustic wave element comprising a single IDT electrode and reflector electrode) 16 as in the present invention, impedance matching can be easily achieved.

  FIG. 3 shows a plan view of another example of the embodiment of the electrode structure of the surface acoustic wave device of the present invention. As shown in FIG. 3, each of the first and second surface acoustic wave elements 14 and 15 is composed of a single reflector electrode 30 in which the reflector electrodes 30 are integrally formed at a location where they are adjacent to each other. It is good. With this configuration, the surface acoustic waves excited by the two surface acoustic wave elements 14 and 15 cancel each other on the plus side and the minus side in the integrally formed reflector electrode 30, and the reflection characteristics are good. As a result, the generation of minute ripples in the passband can be further suppressed. As a result, it is possible to provide a surface acoustic wave filter that further improves the insertion loss in the pass band, which is strictly required in the filter characteristics of the surface acoustic wave filter.

  FIG. 4 shows a plan view of another example of the embodiment of the electrode structure of the surface acoustic wave device of the present invention. As shown in FIG. 4, a reflector electrode (intermediate reflector electrode) composed of electrode fingers that are long in a direction perpendicular to the propagation direction of the surface acoustic wave is disposed between adjacent IDT electrodes in the propagation direction of the surface acoustic wave. It should be done. That is, the reflector electrode 61 is provided between the IDT electrodes 2 and 3, the reflector electrode 62 is provided between the IDT electrodes 3 and 4, the reflector electrode 63 is provided between the IDT electrodes 5 and 6, and the reflector is provided between the IDT electrodes 6 and 7. Electrodes 64 are respectively disposed. With this configuration, the difference in the amplitude of the surface acoustic wave between the first surface acoustic wave element 14 and the second surface acoustic wave element 15 can be reduced, and good amplitude balance characteristics can be obtained. .

  FIG. 5 shows a plan view of another example of the embodiment of the electrode structure of the surface acoustic wave device of the present invention. As shown in FIG. 5, the surface acoustic wave elements 52 and 53 are preferably cascade-connected to the first and second surface acoustic wave elements 14 and 15, respectively. With this configuration, there is no problem that a minute ripple is locally generated in the pass characteristic of the surface acoustic wave device. Furthermore, since the surface acoustic wave elements 52 and 53 are connected in cascade, a good attenuation characteristic outside the pass band can be obtained.

  In FIG. 5, 42 to 44 and 45 to 47 are IDT electrodes, and 48 to 51 are reflector electrodes.

  The number of electrode fingers of the IDT electrodes 2 to 7, the reflector electrodes 8 to 11, 17, 18, and 30 and the surface acoustic wave resonator 16 ranges from several to several hundreds. Shows the shapes in a simplified manner.

  Further, 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-propagating lithium niobate single crystal, 41 ° ± 3 ° Y-cut X-propagating lithium niobate single crystal, 45 ° ± 3 ° X-cut Z-propagating lithium tetraborate single crystal has a large electromechanical coupling coefficient and frequency Since the temperature 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 desired 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 1 according to the present invention. It is also possible to prevent energization and improve power durability.

  Further, the surface acoustic wave filter of the present invention can be applied to the communication device 90 (FIG. 11). That is, at least one of a receiving circuit and a transmitting circuit is provided and used as a bandpass filter included in these circuits. For example, as shown in FIG. 11, a transmission signal output from the transmission circuit is put on a carrier frequency by a mixer, an unnecessary signal is attenuated by a band pass filter (surface acoustic wave filter) 91, and then transmitted by a power amplifier 92. A communication device including a transmission circuit capable of amplifying a signal and transmitting from the antenna 99 through the duplexer 94 through the isolator 93, or a reception signal received by the antenna 99, and a reception signal passing through the duplexer 94 being low noise Amplified by an amplifier 95, and then an unnecessary signal is attenuated by a band pass filter (surface acoustic wave filter) 96. A received signal is amplified by a power amplifier 97. A signal is separated from a carrier frequency by a mixer 98. The present invention can be applied to a communication device including a receiving circuit that transmits to a receiving circuit to be extracted. Therefore, if the surface acoustic wave device of the present invention is employed, the insertion loss of the surface acoustic wave device is improved, so that it is possible to provide an excellent communication device with reduced power consumption and remarkably good sensitivity.

  Examples of the present invention will be described below.

Example 1 in which the surface acoustic wave device shown in FIG. 1 is specifically manufactured will be described. A fine electrode pattern made of Al (99 mass%)-Cu (1 mass%) on a piezoelectric substrate (mother substrate for multiple production) 1 made of LiTaO ₃ single crystal for X-direction propagation of 38.7 ° Y-cut. 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 0.18 μm.

  Next, a photoresist is spin-coated on the metal layer to a thickness of about 0.5 μm, patterned into a desired shape with a reduction projection exposure apparatus, and an unnecessary portion of the photoresist is dissolved with an alkaline developer by a developing device, The desired pattern was revealed. 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 unnecessary Al were removed at the same time by a lift-off method, and a pad electrode for forming a conductor bump for flip-chipping the surface acoustic wave device on an external circuit board or the like was completed.

  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. As the package, a 2.5 × 2.0 mm square laminated structure formed by laminating ceramic layers was used.

  In addition, as a sample of Comparative Example 1, a surface acoustic wave device having the configuration shown in FIG. In the surface acoustic wave device of Comparative Example 1, in the first surface acoustic wave element 212, the polarity of electrode fingers adjacent to each other between adjacent IDT electrodes (between IDT electrodes 202 and 203 and between IDT electrodes 203 and 204) is Is a configuration in which the IDT electrode 203 at the center is asymmetrical, and the number of electrode fingers connected to the ground terminal is different from that in FIG. In 212, the electrode finger pitch of the three IDT electrodes 202 to 204 is asymmetrically distributed around the electrode finger located at the center of the center IDT electrode 203. In the second surface acoustic wave element 213, the polarities of electrode fingers adjacent to each other between adjacent IDT electrodes (between IDT electrodes 205 and 206 and IDT electrodes 206 and 207) are set between adjacent IDT electrodes (IDT). Asymmetric arrangement with respect to the center of the gap between the electrode fingers between the electrodes 205 and 206 and between the IDT electrodes 206 and 207).

  The other configuration of the surface acoustic wave device of Comparative Example 1 is the same as that of the surface acoustic wave device shown in FIG.

  Next, the characteristics of the surface acoustic wave devices of Example 1 and Comparative Example 1 were measured. A signal of 0 dBm was input, and the pass band characteristics (insertion loss) were measured under the conditions of a frequency of 1640 to 2140 MHz and a measurement point of 801 points. The number of samples is 30, and the measuring instrument is a multi-port network analyzer (“E5071A” manufactured by Agilent Technologies).

  FIG. 6 shows a graph of frequency characteristics in the vicinity of the pass band obtained as a result of the measurement. FIG. 6 is a graph showing the frequency dependence of the pass characteristic (insertion loss) of the pass band representing the transmission characteristic of the filter. The filter characteristics of the surface acoustic wave device of Example 1 were very good. That is, as shown by the solid line in FIG. 6, the generation of minute ripples was not observed in the pass band of the surface acoustic wave device of Example 1, and good filter characteristics with improved insertion loss were obtained.

  On the other hand, as shown by a broken line in FIG. 6, a minute ripple was generated in the pass band of the surface acoustic wave device of Comparative Example 1, and the insertion loss was deteriorated.

  As Example 2, a surface acoustic wave device having the configuration shown in FIG. 3 was produced and evaluated in the same manner as in Example 1.

  As Comparative Example 2, in the configuration of FIG. 3, both the first and second surface acoustic wave elements 14 and 15 have IDT electrodes 2 to 4 and 5 to 7 having electrode finger pitches in the center of the IDT electrode 3. , 6 is produced with a symmetrical distribution around the electrode finger located at the center of the.

  Next, the characteristics of the surface acoustic wave devices of Example 2 and Comparative Example 2 were measured. A signal of 0 dBm was input, and the pass band characteristics (insertion loss) were measured under the conditions of a frequency of 1640 to 2140 MHz and a measurement point of 801 points. The number of samples is 30, and the measuring instrument is a multi-port network analyzer (“E5071A” manufactured by Agilent Technologies).

  FIG. 7 shows a graph of frequency characteristics in the vicinity of the passband obtained as a result of the measurement. As in the case of the first embodiment, as shown by the solid line in FIG. 7, the generation of minute ripples is not observed in the passband of the surface acoustic wave device of the second embodiment, and a good filter with improved insertion loss is obtained. Characteristics were obtained.

  On the other hand, as shown by the broken line in FIG. 7, a minute ripple was generated in the pass band of the surface acoustic wave device of Comparative Example 2, and the insertion loss was deteriorated.

  As described above, according to the surface acoustic wave device of the present invention, it is possible to realize the surface acoustic wave device that suppresses the generation of minute ripples generated in the passband and improves the insertion loss.

(A) is a top view which shows an example of embodiment about the surface acoustic wave apparatus of this invention, (b) shows the relationship between the electrode finger position of the surface acoustic wave apparatus of (a), and electrode finger pitch. It is a graph. (A) is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention, (b) shows the relationship between the electrode finger position and electrode finger pitch of the surface acoustic wave apparatus of (a). It is a graph. (A) is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention, (b) shows the relationship between the electrode finger position and electrode finger pitch of the surface acoustic wave apparatus of (a). It is a graph. (A) is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention, (b) shows the relationship between the electrode finger position and electrode finger pitch of the surface acoustic wave apparatus of (a). It is a graph. (A) is a top view which shows the other example of embodiment about the surface acoustic wave apparatus of this invention, (b) shows the relationship between the electrode finger position and electrode finger pitch of the surface acoustic wave apparatus of (a). It is a graph. It is a graph which respectively shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave apparatus of Example 1 of this invention and the surface acoustic wave apparatus of the comparative example 1, and its vicinity. It is a graph which respectively shows the frequency characteristic of the insertion loss in the pass band of the surface acoustic wave apparatus of Example 2 of this invention, and the surface acoustic wave apparatus of the comparative example 2 and its vicinity. It is a top view which shows typically an example of the electrode structure of the conventional surface acoustic wave apparatus. It is a top view which shows typically an example of the electrode structure of the surface acoustic wave apparatus of a prior art example (comparative example 1). It is a graph which shows the frequency characteristic of the insertion loss in the pass band of the conventional surface acoustic wave apparatus, and its vicinity. It is a block circuit diagram of the communication apparatus of this invention.

Explanation of symbols

1: Piezoelectric substrate 14: First surface acoustic wave element 15: Second surface acoustic wave element 16: Surface acoustic wave resonators 52, 53: Cascaded surface acoustic wave elements 2-7, 42-47: IDT Electrodes 8-11, 17, 18, 48-51, 61-64: Reflector electrode 21: Unbalanced signal terminal 22, 23: Balanced signal terminal

Claims (5)

Three IDT electrodes having a plurality of long electrode fingers in the direction orthogonal to the propagation direction along the propagation direction of the surface acoustic wave propagating on the piezoelectric substrate on the piezoelectric substrate, and arranged on both sides thereof, respectively And the first and second surface acoustic wave elements having a reflector electrode provided with a plurality of long electrode fingers in a direction orthogonal to the propagation direction. Are connected in parallel to the unbalanced signal terminal and each is used as a balanced output unit or a balanced input unit, and a balanced signal terminal is connected to the IDT electrode at the center of each of the first and second surface acoustic wave elements. A connected surface acoustic wave device,
One of the first and second surface acoustic wave elements includes a signal electrode finger on both ends of the central IDT electrode and an end on the IDT electrode side in the center of the IDT electrode on both sides of the central IDT electrode. The number of ground electrode fingers arranged between each of the signal electrode fingers is n (n is an integer of 1 or more), and the polarity of the electrode fingers adjacent to each other between the adjacent IDT electrodes is the center. And the electrode finger pitch of the three IDT electrodes is symmetrically distributed about the electrode finger located at the center of the center IDT electrode. Has been
The other of the first and second surface acoustic wave elements includes a signal electrode finger at one end of the central IDT electrode and the one end of one IDT electrode adjacent to the central IDT electrode on the one end side. The number of ground electrode fingers arranged between the signal electrode fingers on the side end is n−1, the signal electrode fingers on the other end of the center IDT electrode, and the center on the other end side. The number of ground electrode fingers arranged between the other electrode side electrode finger of the other IDT electrode adjacent to the IDT electrode is n + 1 and between the adjacent IDT electrodes The polarities of the electrode fingers adjacent to each other are arranged symmetrically with respect to the center of the gap between the electrode fingers between the adjacent IDT electrodes, and the electrode finger pitch of the IDT electrodes is set to the center of the center IDT electrode. To the center of the gap between the electrode fingers A surface acoustic wave device which characterized by being a symmetrical distribution.   Distribution of electrode finger pitches of the three IDT electrodes in one of the first and second surface acoustic wave elements, and the three in the other of the first and second surface acoustic wave elements 2. The surface acoustic wave device according to claim 1, wherein the electrode finger pitch distribution of the IDT electrodes is the same.   3. The surface acoustic wave device according to claim 1, wherein the first and second surface acoustic wave elements are connected in parallel to the unbalanced signal terminal via a surface acoustic wave resonator.   The said 1st and 2nd surface acoustic wave element consists of one reflector electrode in which the reflector electrode in the location which adjoins them is formed integrally, The one of the Claims 1 thru | or 3 characterized by the above-mentioned. Surface acoustic wave device.   A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave device according to claim 1.

Images