JP4562517B2 - Surface acoustic wave element and communication device - Google Patents

Description

  The present invention relates to a resonator type surface acoustic wave filter or surface acoustic wave comprising a balanced signal electrode for performing balanced input or balanced output on a piezoelectric substrate and an unbalanced signal electrode for performing unbalanced output or unbalanced input. The present invention relates to a surface acoustic wave element such as a resonator and a communication apparatus including the same.

  Conventionally, a surface acoustic wave filter has been widely used as a frequency selection 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, in order to reduce the size, weight, and cost of mobile communication devices, the number of components 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 the signal lines 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.

  A conventional surface acoustic wave filter is generally an unbalanced input-unbalanced output type surface acoustic wave filter (hereinafter also referred to as an unbalanced surface acoustic wave filter), and is therefore connected to a subsequent stage of the surface acoustic wave filter. When the circuit or 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 has been adopted. Similarly, in the case where the circuit and electronic components in the previous stage of the surface acoustic wave filter are of the 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 also 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. Further, there are many demands for RF filters to match one of the connection terminals with an unbalanced connection and an input / output impedance of 50Ω, and the other with a balanced connection and an input / output impedance of 100 to 200Ω.

  FIG. 8 shows a conventional resonator type surface acoustic wave filter corresponding to balanced input / output. An IDT (Inter Digital Transducer) electrode 203 formed 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. Then, by applying an input signal to the IDT electrode 203, the excited surface acoustic wave is propagated to the IDT electrodes 202 and 204 located on both sides of the IDT electrode 203. One comb-like electrode of each of the IDT electrodes 202 and 204 is cascade-connected to one comb-like electrode of each of the second-stage IDT electrodes 205 and 207, and finally the IDT electrode 206 at the center of the second-stage A signal is transmitted from one comb-shaped electrode to the output signal terminal 222, and from the other comb-shaped electrode to the output signal terminal 223, and balanced output is performed. Further, by connecting the resonator type electrode patterns in two stages in cascade, the attenuation outside the passband, which is a filter characteristic, can be improved.

  In the resonator-type surface acoustic wave filter as described above, the IDT electrodes 202, 204, 205, 206, and 207 have the number and arrangement of opposing comb-shaped electrodes, and peripheral electrode patterns that cause parasitic capacitance. Because of the slightly different structures, the signals transmitted to the output signal terminals 222 and 223 have different amplitudes and are out of phase with each other. Only a filter 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 within the passband. For example, as a filter for a 900 MHz band mobile phone, a high-performance balance filter having an amplitude balance of 0.5 dB or less and a phase balance of 5 degrees or less. Is required.

  Further, as shown in FIG. 9, among the first-stage vertically coupled double mode 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 IDT electrode 203, and 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 center IDT electrode 206 is divided into two. These are connected to the balanced signal terminals 222 and 223 in the opposite phase. Accordingly, a configuration of 50Ω unbalanced input−200Ω balanced output has been proposed (see, for example, Patent Document 1).

  In the conventional dual mode surface acoustic wave resonator filter, the balance is improved by making the IDT electrodes arranged in the center of the three IDT electrodes arranged in the propagation direction of the surface acoustic wave an even pair. A configuration has been proposed (see, for example, Patent Document 2).

  Also, as shown in FIG. 10, three IDT electrodes 202, 203, 204 are arranged close to each other along the propagation direction of the surface acoustic wave 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 connected in cascade to the second-stage IDT electrodes 205 and 207, respectively, and the center IDT electrode 206 in the second-stage is divided into two parts, which are respectively connected to the balanced signal terminals 222 and 223. A configuration is proposed in which the balance is improved by adding a reactance (capacitance) component 224 on the piezoelectric substrate 201 or inside or outside the package to one balanced signal terminal 222 that is connected and further forms an electric field-free region. (For example, refer to Patent Document 3).

As shown in FIGS. 8 to 10, a resonator-type electrode pattern in which reflector electrodes for efficiently resonating surface acoustic waves are provided at both ends of a surface acoustic wave propagation path of a plurality of IDT electrodes arranged side by side. However, improvement in the balance between amplitude and phase within the passband is required. 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 closer the amplitude of the signal of each signal line is, the closer the degree of amplitude balance is. It can be said that the better the phase balance is, the closer the phase difference of each signal is to 180 °.
JP-A-11-97966 JP 2002-84164 A JP 2004-96244 A

  However, in the surface acoustic wave element disclosed in Patent Document 1, which is a surface acoustic wave element in which a balanced output (input) force terminal is connected to the IDT electrode at the center of the second stage in the conventional two-stage configuration described above. In order to reverse the phase, the structure in which the electrode finger pitches of the IDT electrodes located on both sides of the central IDT electrode are changed, and the adjacent distance between the central IDT electrode and the IDT electrodes on both sides thereof are determined. Since the left and right structure is adopted, there is a problem that the balance is deteriorated.

  In the surface acoustic wave element disclosed in Patent Document 1, 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 to the center are different on the left and right. Since the parasitic capacitance generated at the signal terminal is different, the balanced surface acoustic wave filter having such a configuration has a problem that the degree of balance is poor.

In the surface acoustic wave element disclosed in Patent Document 2, for example, when a LiTaO ₃ single crystal substrate is used as the piezoelectric substrate, the amplitude balance is about 1.2 dB and the phase balance is only about 11 degrees. A sufficient degree of equilibrium that satisfies the requirements was not obtained.

  Furthermore, the effect of the surface acoustic wave element disclosed in Patent Document 3 was verified. FIG. 3 is a diagram (graph) showing frequency characteristics of the surface acoustic wave device shown in FIG. In FIG. 3, the horizontal axis represents frequency (unit: MHz), the vertical axis represents attenuation (unit: dB), the solid characteristic curve shows the result when nothing is added to the balanced signal terminal, and the broken line is either The result when a capacitive component as a reactance component is connected in parallel to one balanced signal terminal is shown. When a capacitive component as a reactance component is connected in parallel to one balanced signal terminal, the ripple in the passband increases.

  4 is a diagram showing VSWR (Voltage Standing Wave Ratio) in the surface acoustic wave device of FIG. Similar to FIG. 3, 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.

  FIG. 5A shows the pass balance and the phase balance in the vicinity of the surface acoustic wave device of FIG. 9, and FIG. 5B shows the amplitude balance. Similar to FIG. 3, 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. 5, 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 completed in view of the above-mentioned problems of the prior art, and an object of the present invention is to improve the balance of the surface acoustic wave filter and to provide a high quality balanced surface acoustic wave filter. And providing a surface acoustic wave element that also functions as a communication device using the same.

The surface acoustic wave element of the present invention includes a piezoelectric substrate , a first surface acoustic wave element portion disposed on the piezoelectric substrate, and a second surface acoustic wave element portion disposed on the piezoelectric substrate. The first surface acoustic wave element section includes a plurality of electrode fingers that are long in a direction orthogonal to the propagation direction of the surface acoustic wave. a part side first first IDT electrode group in which a plurality of three electrically connected to each other in the IDT electrode is disposed on both the outer surface acoustic wave propagation direction of these first IDT electrode group A first reflector electrode on the first surface acoustic wave element side having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave, and at least two of the first IDT electrode group one of disposed between the first surface acoustic wave element part side of the first IDT electrode, said First surface acoustic wave consisting of any one or more of 1 second IDT electrode and a second reflector electrode is electrically disconnected to the first IDT electrode of the surface acoustic wave element portion A second separation surface having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave. Two second IDT electrode groups in which a plurality of first IDT electrodes on the wave element section side are electrically connected to each other, and both of the second IDT electrode groups on the outer side in the propagation direction of the surface acoustic wave. A first reflector electrode on the second surface acoustic wave element side having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave, and the second IDT electrode group Arranged between at least two first IDT electrodes on the second surface acoustic wave element side It is, the second and the first separation electrode of the second surface acoustic wave element portion which is electrically disconnected to the first IDT electrode of the surface acoustic wave element side, the second IDT electrode disposed between the first reflector electrode of the the group second surface acoustic wave element portion, and a third IDT electrodes electrically disconnected from said second IDT electrode group first includes a second separation electrode, said first IDT electrode group at both ends of the first surface acoustic wave element part is cascaded to the second separation electrodes of the second surface acoustic wave element part and which, said first IDT electrode group in the center of the first surface acoustic wave element part is an unbalanced input unit or unbalanced output section, two of said second of said second surface acoustic wave element part Each of the IDT electrode groups is a balanced output section or a balanced input section.

Further, the surface acoustic wave device of the present invention having the above structure, between the said second of said second IDT electrode group of the surface acoustic wave element part second separation electrode, said second IDT electrode The group is characterized in that one or more of the fourth IDT electrode and the third reflector electrode, which are not electrically connected, are arranged as the third separation electrode.

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

According to the surface acoustic wave element of the present invention, a surface acoustic wave element having an unbalance-balance conversion function can be configured. Further, it is possible to suppress degradation of the flat衡度. Further, the degree of freedom in selecting the resonance mode is widened, and the degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased. As a result, it is possible to control the filter characteristics such as widening the band while reducing the insertion loss and ripple. Further, the configuration in which the cascade connection is made in two stages can ensure a sufficient amount of attenuation outside the passband.

Further, according to the SAW device of the present invention, between the second surface acoustic wave element part the second IDT electrode group of the second separation electrode, the electrical and the second IDT electrode group By disposing any one or more of the fourth IDT electrode and the third reflector electrode that are not connected to each other as the third separation electrode, the function of the unbalanced-balanced signal converter can be similarly achieved. It is possible to provide a surface acoustic wave device having the same, and to improve the balance in the pass band. Furthermore, the degree of freedom in selecting the resonance mode is increased, the degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased, and as a result, it is possible to control the filter characteristics such as widening the band while reducing the insertion loss and ripple.

  The communication apparatus according to the present invention includes the above-described surface acoustic wave element according to the present invention and includes at least one of the reception circuit and the transmission circuit, thereby satisfying a good balance required conventionally. Can be obtained, and the balun can be eliminated, and the mounting area of other components can be increased while utilizing the good filter characteristics of the surface acoustic wave device of the present invention, and the range of selection of the components is expanded. Therefore, a communication device having high functions can be manufactured.

  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 the figure demonstrated below, the same code | symbol is attached | subjected to the same structure. Further, the size of each electrode, the distance between the electrodes, the number of electrode fingers, the interval, and the like are schematically illustrated for explanation.

FIG. 1 shows a first example of an embodiment of a surface acoustic wave element according to the present invention, and is a plan view of the surface acoustic wave element. As shown in FIG. 1, the surface acoustic wave element of the present invention includes a first surface acoustic wave element part A and a second surface acoustic wave element part B disposed on a piezoelectric substrate . The first surface acoustic wave element unit A includes three first IDT electrodes 31 to 42 each having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave. The IDT electrode groups 21, 22, and 23 (first IDT electrode group) are disposed, and the surface acoustic wave waves of both the IDT electrode groups 21, 22, and 23 are disposed outside the surface acoustic wave propagation direction. The first reflector electrodes 2 and 3 on the first surface acoustic wave element part A side having a plurality of long electrode fingers in a direction orthogonal to the propagation direction are arranged, and the IDT electrode groups 21, 22, 23 A second IDT electrode and a second reflector that are electrically unconnected to the first IDT electrodes 31 to 42 between the at least two first IDT electrodes on the first surface acoustic wave element section A side first separation of any one or more of the electrodes first surface acoustic wave element part a side Pole (in this example, reflector electrodes 51, 52, 53, 54) made by arranging one or more as. The second surface acoustic wave element part B includes two IDT electrode groups 24 and 25 (second IDT electrode group) and a second surface acoustic wave disposed outside the propagation direction of the surface acoustic wave. together formed by disposing a first separate electrodes (reflector electrodes) 55 and 56 of the first reflector electrodes 4 and 5 and the second surface acoustic wave element part B side of the element portion B side, IDT electrodes The third IDT electrodes 61 and 62 that are not electrically connected to the IDT electrode groups 24 and 25 are arranged as second separation electrodes between the first and second reflector electrodes 4 and 25. ing Te.

  The IDT electrode groups 21 and 23 at both ends of the first surface acoustic wave element portion A are connected in cascade with the second separation electrodes (IDT electrodes 61 and 62) of the second surface acoustic wave element portion B, respectively. The IDT electrode group 22 at the center of the first surface acoustic wave element unit A is used as an unbalanced input unit or an unbalanced output unit (unbalanced input unit 6 in this example). Each of the two IDT electrode groups 24 and 25 is a balanced output unit or a balanced input unit (in this example, balanced output units 7 and 8).

  With these configurations, the IDT electrode groups 21 and 23 at both ends of the first surface acoustic wave element A are connected in cascade with the second separation electrodes (IDT electrodes 61 and 62) of the second surface acoustic wave element B, respectively. Each of the two IDT electrode groups 24 and 25 is a balanced output unit or a balanced input unit, and a second IDT electrode or a second reflector electrode is used as a separation electrode between the first IDT electrodes. By inserting a surface acoustic wave element having an unbalance-balance conversion function can be configured.

  Furthermore, by inputting an unbalanced input signal to the IDT electrode group 22 at the center of the first surface acoustic wave element unit A, the excited surface acoustic waves are placed on both sides of the IDT electrode group 22, Propagated to 23. Further, the IDT electrode groups 21 and 23 are connected in cascade to the IDT electrodes 61 and 62 of the second surface acoustic wave element part B, respectively, and signals are transmitted to the IDT electrode groups 24 and 25 for balanced output. At that time, by adjusting the electrode finger pitch and the number of electrode fingers of the electrically non-connected reflector electrodes 55 and 56 disposed between the two IDT electrode groups 24 and 25, the balanced output units 7 and 8 are adjusted. The phase difference of is equal to 180 °. In addition, the impedance can be increased by an IDT electrode group composed of a plurality of IDT electrodes and separation electrodes. Therefore, when the input impedance of the unbalanced connection portion is 50Ω, the requirement that the input / output impedance is matched to 100 to 200Ω at the balanced connection portion can be satisfied.

  In addition, in order to take out a balanced signal (a signal in which the two signals have the same amplitude and opposite phases) from the balanced output units 7 and 8, a signal path from the balanced input unit 6 to the balanced output unit 7, What is necessary is just to provide the IDT electrode which mutually reversed the polarity in each of the signal path | route from the balanced input part 6 to the balanced output part 8. For example, in the case of FIG. 1, the polarities of the IDT electrode 33 and the IDT electrode 36, and the IDT electrode 32 and the IDT electrode 37 are reversed.

  Further, in the surface acoustic wave element part A, the first IDT electrodes 31, 32, 37, 38 are electrically connected between at least two first IDT electrodes 31, 32, 37, 38 of the IDT electrode groups 21, 23. By disposing one or more of the second IDT electrodes and the second reflector electrodes 51 and 54 as the first separation electrodes, the two IDT electrode groups 21 are not connected. , 23 can be adjusted equally, and the balance can be improved. Furthermore, the degree of freedom in selecting the resonance mode is increased, the degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased, and as a result, it is possible to control the filter characteristics such as widening the band while reducing the insertion loss and ripple.

  Since the number of electrode fingers of IDT electrodes 31 to 42, 61, 62 and reflector electrodes 2, 3, 4, 5, 51 to 56 ranges from several to several hundreds, These shapes are shown in a simplified manner. In addition, the first IDT electrode or the second reflector electrodes 51 to 54 serving as the first separation electrode may be grounded or electrically floating. When the second reflector electrodes 51 to 54 are not electrically connected and are in a floating state, there is an advantage that the wiring can be easily routed.

  Further, as the piezoelectric substrate 1 for the surface acoustic wave element, 36 ° ± 3 ° Y-cut X propagation lithium tantalate single crystal, 42 ° ± 3 ° Y cut X propagation lithium tantalate single crystal, 64 ° ± 3 ° Y Cut X Propagation Lithium Niobate Single Crystal, 41 ° ± 3 ° Y Cut X Propagation Lithium Single Crystal, 45 ° ± 3 ° X Cut Z Propagation Lithium Tetraborate Single Crystal has a large electromechanical coupling coefficient and frequency temperature coefficient Is preferable as the piezoelectric substrate 1. Of these pyroelectric piezoelectric single crystals, if the pyroelectricity is remarkably reduced by solid solution such as 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.

  Further, the IDT electrodes 31 to 42, 61, 62 and the reflector electrodes 2, 3, 4, 5, 51 to 56 are made of Al or an Al alloy (Al—Cu type, Al—Ti type), vapor deposition, sputtering. It is formed by a thin film forming method such as a CVD method or a CVD method. The thickness of each electrode is preferably about 0.1 to 0.5 μm for obtaining characteristics as a surface acoustic wave element.

Furthermore, SiO ₂ , SiN _x , Si, Al ₂ O ₃ or the like is formed as a protective film on the surface acoustic wave propagation part on the surface of the surface acoustic wave element and the piezoelectric substrate 1 according to the present invention. It is also possible to prevent energization and improve power durability.

  The surface acoustic wave element 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, or receiving a received signal with an antenna, amplifying the received signal that has passed through the duplexer with a low-noise amplifier, and then attenuating an unnecessary signal with a band-pass filter, and a carrier frequency with a mixer Can be applied to a communication apparatus including a receiving circuit that separates a signal from the signal and transmits the signal to a receiving circuit that extracts the signal. Therefore, if the surface acoustic wave device of the present invention is employed, it is possible to eliminate the balun necessary for the balanced output, and the mounting area of other components while utilizing the good filter characteristics of the surface acoustic wave device of the present invention. Since the range of component selection is widened, a communication device having high functionality can be provided.

  FIG. 2 shows a second example of the embodiment of the surface acoustic wave element of the present invention, and is a plan view of the surface acoustic wave element. As shown in FIG. 2, in the surface acoustic wave element of the first example described above, the IDT electrode groups 24 and 25 of the second surface acoustic wave element part B and the second separation electrode (third IDT electrode 61, 62) (between the IDT electrode group 24 and the third IDT electrode 61, and between the IDT electrode group 25 and the third IDT electrode 62), the IDT electrode groups 24, 25 are electrically Any one or more of the fourth IDT electrode and the third reflector electrodes 71 and 72 that are connected are arranged as a third separation electrode (in this example, the third reflector electrodes 71 and 72). Accordingly, a surface acoustic wave device having a function of an unbalanced-balanced signal converter as in the first example can be provided, and the degree of balance in the passband can be improved. Furthermore, the degree of freedom in selecting the resonance mode is increased, the degree of freedom in controlling the amplitude distribution of the surface acoustic wave is increased, and as a result, it is possible to control the filter characteristics such as widening the band while reducing the insertion loss and ripple.

  In the description of the above-described embodiment, for simplicity, the IDT electrode groups 21 to 23 are not electrically connected between at least two IDT electrodes 31, 32, 37, and 38 of the IDT electrode groups 21 to 23. A first separation electrode composed of any one of the second reflector electrodes 51 to 54 having a plurality of long electrode fingers in the direction orthogonal to the propagation direction of the second IDT electrode and the surface acoustic wave is 1 However, the present invention is not limited to this, and a plurality of two types of second IDT electrodes and second reflector electrodes 51 to 54 may be disposed. Other configurations can be changed as appropriate without departing from the gist of the present invention.

  Specific examples of the surface acoustic wave device 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. A fine electrode pattern made of Al (99 mass%)-Cu (1 mass%) was formed on a LiTaO ₃ single crystal piezoelectric substrate 1 having a 38.7 ° Y-cut propagation in the X direction. The average electrode finger pitch and the number of electrode fingers of the IDT electrode and reflector electrode constituting the surface acoustic wave element of FIG. 1 are shown below.

  The average electrode finger pitches of the first IDT electrodes 31, 32, 33, 34, 35, 36, 37, and 38 constituting the first surface acoustic wave element A are 2.10 μm, 2.01 μm, 1.96 μm, and 2.11, respectively. μm, 2.11 μm, 1.96 μm, 2.01 μm, and 2.10 μm were used, and the number of electrode fingers was 14, 8, 8, 18, 18, 8, 8, and 14, respectively. In addition, the average electrode finger pitch of the second reflector electrodes 51, 52, 53, and 54 serving as the first separation electrode was 2.15 μm, and the number of electrode fingers was two.

  Similarly, the average electrode finger pitch of the second stage first IDT electrodes 39, 40, 41, and 42 constituting the second surface acoustic wave element part B is 2.00 μm, 2.12 μm, 2.12 μm, and 2.00 μm, respectively. It was. The number of electrode fingers of the first IDT electrodes 39, 40, 41, and 42 was 8, 18, 18, and 8, respectively.

  Further, the uniform electrode finger pitch of the second reflector electrodes 55 and 56 was 2.15 μm, and the number of electrode fingers was two. The average electrode finger pitch of the third IDT electrodes 61 and 62 constituting the second separation electrode was 2.07 μm, and the number of electrode fingers was 18.

  In addition, the average electrode finger pitch of the first reflector electrodes 2, 3, 4 and 5 disposed on both sides of the surface acoustic wave resonators A and B is 2.13 μm, and the number of electrode fingers is 70. It was a book.

  The surface acoustic wave element electrically connects a plurality of first IDT electrodes 31 to 42 having a plurality of long electrode fingers on the piezoelectric substrate 1 in a direction orthogonal to the propagation direction of the surface acoustic wave. The three IDT electrode groups 21, 22, and 23 are disposed, and the IDT electrode groups 21, 22, and 23 are both outside the surface acoustic wave propagation direction with respect to the surface acoustic wave propagation direction. The first reflector electrodes 2 and 3 having a plurality of long electrode fingers in the orthogonal direction are arranged, and the first reflector electrodes 31 to 38 of the IDT electrode groups 21, 22 and 23 are arranged between the first IDT electrodes 31 to 38. A first surface acoustic wave element unit A in which one or more second reflector electrodes 51 to 54 are arranged as first separation electrodes, which are electrically unconnected to one IDT electrode 31 to 38; Two IDT electrode groups 24, 25 and a first reflector electrode 4, disposed both outside the propagation direction of the surface acoustic wave, In addition, a first separation electrode (second reflector electrodes 55 and 56) is disposed, and an IDT electrode group 24 is provided between the IDT electrode groups 24 and 25 and the first reflector electrodes 4 and 5. , 25 is provided with a second surface acoustic wave element portion B in which third IDT electrodes 61, 62 that are electrically unconnected are arranged as second separation electrodes.

  Further, the IDT electrode groups 21 and 23 at both ends of the first surface acoustic wave element part A are connected in cascade with the second separation electrodes (third IDT electrodes 61 and 62) of the second surface acoustic wave element part B, respectively. The IDT electrode group 22 at the center of the first surface acoustic wave element unit A is used as the unbalanced input unit 6, and each of the two IDT electrode groups 24 and 25 of the second surface acoustic wave element unit B is The balanced output units 7 and 8 are used.

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

  First, a mother substrate on which a large number of regions to be the individual piezoelectric substrates 1 were formed was ultrasonically cleaned with acetone, IPA (isopropyl alcohol) or the like to remove organic components. Next, after sufficiently drying the mother substrate with a clean oven, a metal film serving as each electrode was formed on the upper surface of the mother substrate. A sputtering apparatus was used to form the metal film, and an Al (99 mass%)-Cu (1 mass%) alloy was used as the material of the metal film. The thickness of this metal film was about 0.34 μm.

  Next, a photoresist layer is spin-coated on the metal film on the upper surface of the mother substrate to a thickness of about 0.5 μm, and each electrode is patterned into a desired shape by a reduction projection exposure device (stepper), which is not required by the developing device. After part of the photoresist layer is dissolved with an alkaline developer to reveal a desired pattern, the metal film is etched by an RIE apparatus, the patterning of each electrode is finished, and the pattern of each electrode of the surface acoustic wave element is changed. Obtained.

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

  Next, a photoresist layer is spin-coated on the lower surface of the mother substrate to a thickness of about 5 μm, and the photoresist layer is patterned by photolithography to form a window portion for flip chip mounting. Etching was performed. Thereafter, using a sputtering apparatus, an electrode pad mainly composed of Al was formed in the window opening portion. The thickness of this electrode pad was about 1.0 μm. Thereafter, the photoresist layer and the unnecessary portion of Al are simultaneously removed by a lift-off method, and electrode pads for forming conductive bumps for flip-chip mounting the surface acoustic wave element on an external circuit board or the like are provided on the individual piezoelectric substrates 1. Provided in the area.

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

Next, the mother substrate was diced along the dividing line, and divided into individual surface acoustic wave elements (chips). Thereafter, each chip was bonded to the inside of the package with the flip chip mounting apparatus with the lower surface, which is the electrode pad forming surface, facing down. Thereafter, baking was performed in an N ₂ atmosphere to complete the surface acoustic wave device. The package used was a 2.5 × 2.0 mm square laminate structure formed by laminating ceramic layers.

  As a sample of the comparative example, as shown in FIG. 6, in the second surface acoustic wave element portion B, the second reflector functioning as the first separation electrodes 55 and 56 (FIG. 1) in the IDT electrode groups 24 and 25. A surface acoustic wave device was used in which fine electrode patterns without electrodes were produced in the same process as described above.

  Next, the characteristics of the surface acoustic wave device in the example of the present invention were measured. A signal of 0 dBm was input and measurement was performed in the frequency range of 910 to 980 MHz. 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 diagram (graph) of amplitude balance and phase balance in the pass band (924 to 960 MHz). The balance of the examples was very good. That is, as shown by the solid line in FIG. 7A, the amplitude balance of the embodiment (the closer the amplitude of the two balanced outputs is, the closer the value is to 0 dB) is 0.41 dB, which is the most deteriorated value. As shown by the solid line in FIG. 7 (b), the phase balance of the example (the closer the phase difference between the two balanced outputs is to 180 °, the closer the value is to 0 °) is the most. The deteriorated value was 2.4 °.

  On the other hand, as shown by the broken line in FIG. 7A, the amplitude balance of the comparative example is 0.39 dB as the most deteriorated value, and as shown by the broken line in FIG. 7B, the phase balance of the comparative example is The most deteriorated value was 2.8 °.

  As described above, in this embodiment, the degree of phase balance can be improved in the pass band. Note that the difference in phase balance between 2.4 ° and 2.8 ° is actually a significant difference in terms of CNR (Carrier Noise Ratio) and the like.

1 is a plan view schematically showing an electrode structure according to a first example of an embodiment of a surface acoustic wave element of the present invention. It is a top view which shows the 2nd example of embodiment about the surface acoustic wave element of this invention, and shows an electrode structure typically. 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 degree in the pass band 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. It is a top view which shows typically the electrode structure of the surface acoustic wave element of a comparative example. It is a diagram which shows the frequency dependence of the balance in the pass band of the surface acoustic wave element of the Example of this invention and a comparative example, and its vicinity, (a) is a diagram which shows an amplitude balance, (b) is a phase It is a diagram which shows a balance degree. It is a top view which shows typically an example of the electrode structure of the conventional surface acoustic wave element. It is a top view which shows typically the other example of the electrode structure of the conventional surface acoustic wave element. It is a top view which shows typically the other example of the electrode structure of the conventional surface acoustic wave element.

Explanation of symbols

1: Piezoelectric substrates 2 to 5: First reflector electrode 6: Unbalanced input (out) force portion 7, 8: Balanced out (input) force portion
21-25: IDT electrode group
31-42: 1st IDT electrode
51-54: Second reflector electrode
55, 56: First separation electrode
61, 62: Third IDT electrode
71, 72: Third reflector electrode

Claims (3)

A surface acoustic wave device comprising: a piezoelectric substrate; a first surface acoustic wave element portion disposed on the piezoelectric substrate; and a second surface acoustic wave element portion disposed on the piezoelectric substrate. There,
The first surface acoustic wave element unit includes a plurality of first IDT electrodes on the first surface acoustic wave element unit side having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave. electrically connected to the three first IDT electrode group is disposed on both the outer surface acoustic wave propagation direction of these first IDT electrode group, orthogonal to the propagation direction of the surface acoustic wave a first of the first surface acoustic wave element part side of the reflector electrodes in which a plurality inborn long electrode fingers in the direction of, the first of at least two of said first surface acoustic wave element part side of the IDT electrode group disposed between the first IDT electrode, said first second IDT electrode and a second reflector electrode is electrically disconnected to the first IDT electrode of the surface acoustic wave element portion first separation electrode of the first SAW device portion consisting of the inner or 1 or more and It includes,
The second surface acoustic wave element unit includes a plurality of first IDT electrodes on the second surface acoustic wave element unit side having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave. Two second IDT electrode groups that are electrically connected to each other and outside the propagation direction of the surface acoustic wave of the second IDT electrode group , and orthogonal to the propagation direction of the surface acoustic wave A first reflector electrode on the second surface acoustic wave element portion side having a plurality of electrode fingers that are long in the direction, and at least two of the second surface acoustic wave element portion side of the second IDT electrode group The first surface acoustic wave element unit side first electrode disposed between the first IDT electrodes and electrically disconnected from the first IDT electrode on the second surface acoustic wave element unit side . and separate electrodes, a first reflection of said second IDT electrode group second surface acoustic wave element portion Disposed between the electrodes, wherein the second separate electrodes consisting of a third IDT electrodes electrically disconnected from said second IDT electrode group,
The first IDT electrode groups at both ends of the first surface acoustic wave element unit are connected in cascade with the second separation electrodes of the second surface acoustic wave element unit, respectively, and the first surface acoustic wave The first IDT electrode group at the center of the wave element unit is an unbalanced input unit or an unbalanced output unit, and each of the two second IDT electrode groups of the second surface acoustic wave element unit is a balanced output. A surface acoustic wave device, characterized in that the surface acoustic wave device is a part or a balanced input part. Wherein between the second of the said second IDT electrode group of the surface acoustic wave element part second separate electrodes, wherein the second IDT electrode groups electrically disconnected, the fourth IDT electrode 2. The surface acoustic wave device according to claim 1, wherein at least one of the third reflector electrode and the third reflector electrode is disposed as a third separation electrode. A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave element according to claim 1.

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