JP2006128927A - Surface acoustic wave element and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic surface wave element having an imbalance-balance conversion function and excellent in degree of balance in a passband, and also to provide a communication device using the same. <P>SOLUTION: In the surface acoustic wave element, IDT electrode groups 21, 22, in which a plurality of first IDT electrodes 31-34 are electrically connected in the propagation direction of an acoustic surface wave, and first reflector electrodes 2, 3 are arranged on a piezoelectric substrate 1. The acoustic surface wave element is provided with an acoustic surface wave element in which one kind or more of either second IDT electrodes or second reflector electrodes 41, 42, which are not electrically connected with the first IDT electrodes 31-34, are arranged between at least two of the first IDT electrodes 31-34 in the IDT electrode groups 21, 22 as a first isolation electrode and third IDT electrodes 51, 52 which are not electrically connected with the IDT electrode groups 21, 22, are arranged between the IDT electrode groups 21, 22 and the first reflector electrodes 2, 3 as a second isolation electrode. The third IDT electrodes 51, 52 are connected with each other and made as an unbalanced input 4. Each of the IDT electrode groups 21, 22 is made as a balanced output 5 or 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 of a non-passband with respect to 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). When the circuit or electronic component to be connected 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 unbalanced surface acoustic wave filter and the subsequent stage. I took it. Similarly, when the circuit or electronic component in the previous stage of the unbalanced 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 unbalanced surface acoustic wave filter.

  Currently, in order to delete the balun, an unbalanced surface acoustic wave filter is provided with an unbalanced-balanced conversion function or a balanced-unbalanced conversion function. An unbalanced output 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.

  For example, as shown in FIG. 9, three IDT (Inter Digital Transducer) electrodes are arranged along the propagation direction of the surface acoustic wave, the central IDT electrode is connected to the unbalanced input terminal, and both sides of the central IDT electrode are connected. The IDT electrode is connected to a balanced output terminal to increase the impedance and realize an unbalanced-balanced conversion function. The IDT electrode 203 disposed on the piezoelectric substrate 201 applies an electric field to a pair of comb-like electrodes opposed to each other to excite surface acoustic waves. Therefore, by applying an input signal to the IDT electrode 203, the excited surface acoustic wave is propagated to the IDT electrodes 202 and 204 for output signals located on both sides of the IDT electrode 203. A signal is transmitted from one comb-shaped electrode of the IDT electrode 202 to the output signal terminal 212, and a signal is transmitted from the one comb-shaped electrode of the IDT electrode 204 to the output signal terminal 213, and these signals are balanced and output (for example, (See Patent Document 1).

  Further, as shown in FIG. 10, three IDT electrodes 202, 203, and 204 are arranged close to each other along the propagation direction of the surface acoustic wave, and the central IDT electrode 203 is divided into two, and acoustically connected in cascade. Electrically connected in series and connected to balanced signal terminals 212 and 213, IDT electrodes 202 and 204 having inverted polarities are arranged on both sides of the central IDT electrode 203, and unbalanced signal terminals Connected to 211. With this configuration, an unbalanced-balanced conversion function can be provided, and the impedance on the balanced signal terminals 212 and 213 side is about four times (200Ω) that of the unbalanced signal terminal 211 side (50Ω). What can be done has been proposed (see, for example, Patent Document 2).

  Moreover, in the conventional dual mode surface acoustic wave resonator filter, the balance is improved by making the IDT electrodes arranged in the center out of the three IDT electrodes arranged in the propagation direction of the surface acoustic wave. The structure which performs is proposed (for example, refer patent document 3).

  Further, as shown in FIG. 11, three IDT electrodes 202, 203, and 204 are arranged close to each other along the propagation direction of the surface acoustic wave, and the central IDT electrode 203 is divided into two parts, and the balanced signal terminals 212, 213, IDT electrodes 202 and 204 having reversed polarities are arranged on both sides of the central IDT electrode 203, connected to the unbalanced signal 211, and further to one balanced signal terminal 212 that forms an electric field-free region A configuration has been proposed in which the balance is improved by forming a reactance (capacitance) component 214 on the piezoelectric substrate 201 or inside or outside the package (see, for example, Patent Document 4).

Resonator-type electrodes in which reflector electrodes for efficiently resonating a surface acoustic wave are provided at both ends of a surface acoustic wave propagation path of a plurality of IDT electrodes arranged side by side as shown in FIGS. In the pattern, it is required to improve the balance between the amplitude and the phase in the pass band. Here, the amplitude and phase balance means that a signal is input or output as a potential difference between two signal lines, and the amplitude balance is better as the amplitude of the signal on each signal line is equal. In addition, the closer the phase difference of each signal is to 180 °, the better the phase balance.
Japanese Patent Laid-Open No. 6-204781 JP-A-11-97966 JP 2002-84164 A JP 2004-96244 A

  However, in the surface acoustic wave element disclosed in Patent Document 1, in order to reverse the phases of the signals output from the IDT electrodes located on both sides of the central IDT electrode, Since the structure of the IDT electrode positioned such as the electrode finger pitch is changed or the adjacent distance between the center IDT electrode and the IDT electrodes on both sides is changed, the degree of balance deteriorates. There was a problem that it was easy.

  In the surface acoustic wave element disclosed in Patent Document 2, the polarity of the outermost electrode finger of the central IDT electrode and the polarity of the outermost electrode finger of the adjacent IDT electrode are different on the left and right. Since the parasitic capacitance generated at the terminals is different, there is a problem that the balance is poor.

In the surface acoustic wave element disclosed in Patent Document 3, for example, when a LiTaO ₃ single crystal substrate is used as the piezoelectric substrate, the amplitude balance degree is about 1.2 dB (because the better the degree of balance, the closer the amplitude is). The phase balance is only about 11 degrees (the phase difference is closer to 0 degree as the degree of balance is better), and a sufficient degree of balance that satisfies the requirements has not been obtained.

  Furthermore, the effect of the surface acoustic wave device disclosed in Patent Document 4 was verified. FIG. 4 is a diagram (graph) showing frequency characteristics of the surface acoustic wave device shown in FIG. In FIG. 4, 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 indicates which The result when a capacitive component is connected in parallel as a reactance component to one of the balanced signal terminals is shown. Since a capacitive component as a reactance component is connected in parallel to one of the balanced signal terminals, the ripple in the passband increases.

  FIG. 5 is a diagram showing VSWR (Voltage Standing Wave Ratio) in the surface acoustic wave device of FIG. Similar to FIG. 4, the solid characteristic curve shows the result when nothing is added to the balanced signal terminal, and the broken line shows the result when the capacitive component is connected in parallel as a reactance component to one of the balanced signal terminals. . It can be seen that when a capacitive component as a reactance component is connected in parallel to one balanced signal terminal, the VSWR is also degraded.

  In addition, FIG. 6A shows the phase balance in the vicinity of the pass band and FIG. 6B shows the amplitude balance in the surface acoustic wave device of FIG. Similar to FIG. 4, 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 apparent from FIG. 6, even when a capacitive component as a reactance component was connected in parallel to one balanced signal terminal, no significant improvement was observed in the phase balance and amplitude balance.

  Accordingly, the present invention has been completed in order to solve the above-described problems in the prior art, and an object of the present invention is to improve the balance of the surface acoustic wave filter and to achieve a high quality balanced surface acoustic wave. It is an object to provide a surface acoustic wave element that functions as a filter and a communication device using the same.

  The surface acoustic wave device according to the present invention includes two first IDT electrodes each having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave on a piezoelectric substrate. An IDT electrode group is provided, and a plurality of electrode fingers that are long in the direction orthogonal to the propagation direction of the surface acoustic wave are provided outside both of the IDT electrode groups in the propagation direction of the surface acoustic wave. A first reflector electrode, and a second IDT electrode and a second IDT electrode electrically disconnected from the first IDT electrode between at least two first IDT electrodes of the IDT electrode group; One or more of the two reflector electrodes is disposed as a first separation electrode, and the IDT electrode group is electrically connected between the IDT electrode group and the first reflector electrode. A third IDT electrode that is not connected to the second separation electrode The third IDT electrodes are connected to form an unbalanced input unit or an unbalanced output unit, and each of the two IDT electrode groups is a balanced output unit or It is a balanced input unit.

  The surface acoustic wave device according to the present invention has a fourth IDT electrode electrically connected to the IDT electrode group between the IDT electrode group and the second separation electrode. One or more of the third reflector electrodes are arranged as a third separation electrode.

  In the surface acoustic wave device of the present invention, an IDT electrode and a surface acoustic wave of the IDT electrode that generate one or more mode resonances in series or in parallel with the third IDT electrode in each of the above configurations. A surface acoustic wave resonator composed of reflector electrodes disposed both outside in the propagation direction is connected.

  A communication apparatus according to the present invention is characterized by including at least one of a reception circuit and a transmission circuit having the surface acoustic wave element according to the present invention having any of the above-described configurations.

  According to the surface acoustic wave device of the present invention, the third IDT electrodes are connected to each other as an unbalanced input unit or an unbalanced output unit, and each of the two IDT electrode groups is used as a balanced output unit or a balanced input unit. And forming a surface acoustic wave device having an unbalance-balance conversion function by inserting a second IDT electrode or a second reflector electrode as a separation electrode between the first IDT electrodes. Can do. In addition, at least one of the second IDT electrode and the second reflector electrode that is not electrically connected to the first IDT electrode between at least two first IDT electrodes of the IDT electrode group. By arranging one or more as the first separation electrodes, it is possible to adjust the electric capacity of the electrodes in the two IDT electrode groups to be equal, and the deterioration of the balance can be suppressed. . 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.

  According to the surface acoustic wave device of the present invention, the fourth IDT electrode and the third reflector, which are electrically disconnected from the IDT electrode group, between the IDT electrode group and the second separation electrode. When any one or more of the electrodes are arranged as the third separation electrode, a surface acoustic wave device having the function of an unbalanced-balanced signal converter can be formed in the same manner as described above, and the degree of balance in the passband can be configured. 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.

  Further, according to the surface acoustic wave device of the present invention, the IDT electrode and the surface acoustic wave propagation direction of the IDT electrode generate one or more mode resonances in series or in parallel with the third IDT electrode. When a surface acoustic wave resonator consisting of both reflector electrodes on the outside is connected, the pass band width of the filter characteristics can be widened, and a surface acoustic wave element with excellent insertion quality and low quality is realized. can do. In addition, for example, impedance matching between the input unit / output unit of the surface acoustic wave resonator and the output unit / input unit (balanced output unit / balanced input unit) of the surface acoustic wave element can be satisfactorily performed. Attenuation poles can be formed by connecting surface wave resonators, and the characteristics can be controlled so as to satisfy specifications requiring a high attenuation of out-of-band attenuation.

  The communication apparatus according to the present invention includes at least one of the reception circuit and the transmission circuit having any one of the above-described surface acoustic wave elements according to the present invention, so that a balance degree that has been conventionally required can be satisfied. Obtained, and it is possible to delete the balun, it is possible to increase the mounting area of other components while utilizing the good filter characteristics by the surface acoustic wave device of the present invention, and the range of selection of the components is widened. 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. In addition, 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 device of the present invention includes first IDT electrodes 31 to 34 each having a plurality of long electrode fingers on a piezoelectric substrate 1 in a direction orthogonal to the propagation direction of the surface acoustic wave. Two IDT electrode groups 21 and 22 that are electrically connected to each other are arranged, and the IDT electrode groups 21 and 22 have both surface acoustic wave propagation directions outside the surface acoustic wave propagation direction. First reflector electrodes 2 and 3 having a plurality of long electrode fingers in a direction orthogonal to each other are disposed, and a first first electrode 31 to 34 of the IDT electrode group 21 and 22 is provided between the first IDT electrodes 31 to 34. One or more of the second IDT electrode and the second reflector electrode (reflector electrodes 41, 42), which are not electrically connected to the IDT electrodes 31 to 34, as a first separation electrode. Between the IDT electrode groups 21 and 22 and the first reflector electrodes 2 and 3, and the IDT electrode groups 21 and 22 are not electrically connected to each other. The third IDT electrodes 51 and 52 are arranged as second separation electrodes, and the third IDT electrodes 51 and 52 are connected to each other so that an unbalanced input section or an unbalanced output section ( In this example, it is an unbalanced input unit 4), and each of the two IDT electrode groups 21 and 22 is a balanced output unit or a balanced input unit (in this example, balanced output units 5 and 6).

  By adjusting the electrode finger pitch and the number of electrode fingers of the electrically non-connected reflector electrodes 41 and 42 disposed between the two IDT electrode groups 21 and 22, the phase difference between the balanced output units 5 and 6 is adjusted. Is equal to 180 °.

  With these configurations, the third IDT electrodes 51 and 52 are connected to each other as an unbalanced input unit or an unbalanced output unit, and each of the two IDT electrode groups 21 and 22 serves as a balanced output unit or a balanced input unit. And an elastic surface having an unbalance-balance conversion function by inserting a second IDT electrode or a second reflector electrode 41, 42 as a separation electrode between the first IDT electrodes 31-34. A wave element can be constructed. Further, the second IDT electrode and the second reflection, which are not electrically connected to the first IDT electrodes 31 to 34, between the at least two first IDT electrodes 31 to 34 of the IDT electrode groups 21 and 22. By arranging one or more of the electrode electrodes 41 and 42 as the first separation electrode, the electric capacity of the electrodes in the two IDT electrode groups 21 and 22 is adjusted to be equal. And the degree of 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.

  The number of electrode fingers of IDT electrodes 31 to 34, 51, 52 and reflector electrodes 2, 3, 41, 42 ranges from several to several hundreds. Simplified and illustrated. Further, the second IDT electrode or the second reflector electrodes 41 and 42 serving as the first separation electrode may be grounded or electrically floating. When the second reflector electrodes 41 and 42 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 substrate has a significantly reduced pyroelectric property due to solid solution of oxygen defects or Fe, the reliability of the device is good. The thickness of the piezoelectric substrate 1 is preferably about 0.1 to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate 1 becomes fragile, and if it exceeds 0.5 mm, the material cost and the component dimensions increase, which is not suitable for use.

  The IDT electrode and the reflector electrode are made of Al or an Al alloy (Al—Cu system, Al—Ti system), and are formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. 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 each electrode of the surface acoustic wave element of the present invention and the surface acoustic wave propagation portion on the piezoelectric substrate 1, and is formed of a conductive foreign material 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 signals or receiving a received signal with an antenna, amplifying the received signal that has passed through the duplexer with a low-noise amplifier, and then attenuating an unnecessary signal with a band-pass filter, and a carrier frequency with a mixer Can be applied to a communication apparatus including a receiving circuit that separates a signal from the signal and transmits the signal to a receiving circuit that extracts the signal. As described above, if the surface acoustic wave element of the present invention is employed in the communication device, it is possible to eliminate the balun necessary for the balanced output, while utilizing the good filter characteristics of the surface acoustic wave element of the present invention. Since the mounting area of other components can be increased and the range of component selection is widened, a highly functional communication device 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 device of the first example described above, between the IDT electrode groups 21 and 22 and the second separation electrode (between the IDT electrode group 21 and the IDT electrode 51, the IDT electrode Between the group 22 and the IDT electrode 52), one or more of the fourth IDT electrode and the third reflector electrode 61, 62 that are electrically disconnected from the IDT electrode group 21, 22 are connected. By providing the third separation electrode (in this example, the third reflector electrodes 61 and 62), a surface acoustic wave having the function of an unbalanced-balanced signal converter as in the first example is provided. An element can be realized 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.

  FIG. 3 shows a third 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. In the surface acoustic wave device of the second example described above, the IDT electrode and the surface acoustic wave of this IDT electrode that generate one or more mode resonances in series or in parallel with the third IDT electrodes 51 and 52. A surface acoustic wave resonator 7 composed of reflector electrodes disposed both outside in the propagation direction is connected. In this example, only the series resonator is connected.

  In this way, by connecting and adding the surface acoustic wave resonator 7 in series, parallel or series-parallel to the third IDT electrodes 51 and 52 constituting the IDT electrode groups 21 and 22, for example, surface acoustic waves are obtained. Impedance matching between the input unit / output unit of the resonator 7 and the output unit / input unit (balanced output unit / balanced input unit) of the surface acoustic wave element can be satisfactorily achieved, and the surface acoustic wave resonator can be obtained. By connecting 7, it becomes possible to form an attenuation pole, and the characteristics can be controlled so as to satisfy a specification that requires a high attenuation out-of-band attenuation.

  In addition, a surface acoustic wave device can be provided that has the function of an unbalanced-balanced signal converter as in the second example and can improve the degree of balance in the passband.

  As described above, it is possible to provide a communication device that includes a receiving circuit and a transmitting circuit having surface acoustic wave elements having excellent characteristics, and that has extremely excellent sensitivity.

  In the description of the above-described embodiment, for the sake of simplicity, the propagation direction of the second IDT electrode and the surface acoustic wave that are electrically unconnected to the IDT electrode group between at least two IDT electrodes of the IDT electrode group. Although an example in which one first separation electrode made of any of the second reflector electrodes having a plurality of electrode fingers that are long in a direction orthogonal to the above is disposed, is not limited thereto. The second IDT electrode and the second reflector electrode may be provided in plural, and other configurations may be appropriately changed without departing from the gist of the present invention. It is possible.

  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 in the X direction. The average electrode finger pitch and the number of electrode fingers of the IDT electrode and the reflector electrode constituting the surface acoustic wave element of the present invention shown in FIG. 1 are shown. The average electrode finger pitch of the first IDT electrodes 31, 32, 33, and 34 was 1.00 μm, 1.06 μm, 1.06 μm, and 1.00 μm, respectively. The number of electrode fingers of the first IDT electrodes 31, 32, 33, and 34 was 8, 18, 18, and 8, respectively. In addition, the average electrode finger pitch of the second reflector electrodes 41 and 42 serving as the separation electrodes was 0.92 μm. The number of electrode fingers of the second reflector electrodes 41 and 42 is two.

  In addition, the average electrode finger pitch of the third IDT electrodes 51 and 52 constituting the second separation electrode was both 1.03 μm. The number of electrode fingers of the third IDT electrodes 51 and 52 is both 18. The average electrode finger pitch of the reflector electrodes 2 and 3 disposed on both sides of the surface acoustic wave resonator portion was 1.03 μm, and the number of electrode fingers was 70.

  The surface acoustic wave device according to the embodiment of the present invention includes a plurality of first IDT electrodes 31 to 34 each having a plurality of electrode fingers that are long in the direction orthogonal to the propagation direction of the surface acoustic wave on the piezoelectric substrate 1. Two IDT electrode groups 21 and 22 that are electrically connected to each other are disposed, and the IDT electrode groups 21 and 22 are orthogonal to the surface acoustic wave propagation direction both outside the surface acoustic wave propagation direction. First reflector electrodes 2 and 3 having a plurality of electrode fingers long in the direction are disposed, and a first IDT electrode is provided between at least two first IDT electrodes 31 to 34 of the IDT electrode groups 21 and 22. One or more second reflector electrodes 41 and 42 that are not electrically connected to 31 to 34 are disposed as first separation electrodes, and the IDT electrode groups 21 and 22 and the first reflector electrodes 2 and 3 are disposed. The third IDT electrodes 51 and 52 that are not electrically connected to the IDT electrode groups 21 and 22 are arranged as second separation electrodes. The third IDT electrodes 51 and 52 are connected to each other as an unbalanced input unit 4, and the two IDT electrode groups 21 and 22 are respectively used as balanced output units 5 and 6. .

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

  First, the 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. A sputtering apparatus was used to form the metal film, and an Al (99 mass%)-Cu (1 mass%) alloy was used as the metal film material. The thickness of the metal film at this time was about 0.16 μm.

  Next, a photoresist layer is spin-coated on the metal film to a thickness of about 0.5 μm, patterned into a desired shape with a reduction projection exposure device (stepper), and an unnecessary portion of the photoresist layer is alkali-developed with a developing device. The desired pattern was exposed by dissolving with a liquid. Thereafter, the metal film was etched by the RIE apparatus, and the patterning was finished to obtain the pattern of each electrode of the surface acoustic wave element of the present invention.

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

  Thereafter, a photoresist layer is formed on the lower surface (the surface opposite to the upper surface on which each electrode pattern is formed) of the mother substrate, and a flip chip window opening is formed on the photoresist layer by photolithography. Then, the window opening was formed by etching with an RIE apparatus or the like. Thereafter, a sputtering apparatus was used to form a metal film containing Al as a main component on the photoresist layer on the lower surface of the mother substrate. The thickness of the metal film at this time was about 1.0 μm. Thereafter, the photoresist layer and the unnecessary portion of the Al metal film are simultaneously removed by a lift-off method, and an electrode for forming a conductive bump for flip-chip mounting the surface acoustic wave device on an external circuit board or the like in the window opening portion A pad was formed.

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

Next, the mother substrate was diced along the dividing line and divided into surface acoustic wave elements (chips). 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 produce a surface acoustic wave device. The package used was a 2.5 × 2.0 mm square laminate structure in which ceramic layers were laminated.

  As a sample of a comparative example, as shown in FIG. 7, a surface acoustic wave element in which a fine pattern of each electrode is formed without a second reflector electrode functioning as a separation electrode in the IDT electrode groups 21 and 22. It was produced in the same process as above.

  Next, the characteristics of the surface acoustic wave device in this example were measured. A signal of 0 dBm was input, and the frequency was measured from 1640 to 2140 MHz (FIG. 8 shows 1860 to 2060 MHz extracted) and the measurement points were 801 points. The number of samples is 30, and the measuring instrument is a multiport network analyzer (“E5071A” manufactured by Agilent Technologies).

  FIG. 8 shows a diagram (graph) of amplitude balance and phase balance in the passband (1930 to 1990 MHz). The balance of the examples of the present invention was very good. That is, as shown by the solid line in FIG. 8A, the amplitude balance of the embodiment is the most deteriorated value of 0.6 dB (the closer the amplitude of the two balanced signals is, the better the amplitude balance is and a value close to 0 dB). As shown by the solid line in FIG. 8 (b), the phase balance of the embodiment is the most deteriorated value of 3 ° (the phase balance is better as the phase difference between the two balanced signals approximates to 180 °). It was a value close to 0 °).

  On the other hand, as shown by a broken line in FIG. 8A, the amplitude balance of the comparative example is 1.0 dB, which is the most deteriorated value, and as shown by a broken line in FIG. 8B, the phase balance of the comparative example is The most deteriorated value was 15 °.

  Thus, in the embodiment of the present invention, the balance can be greatly improved in the pass band.

1 is a plan view schematically showing an electrode structure of a surface acoustic wave element according to a first example of an embodiment of a surface acoustic wave element of the present invention. FIG. 5 is a plan view schematically showing an electrode structure of a surface acoustic wave element according to a second example of an embodiment of the surface acoustic wave element of the present invention. FIG. 5 is a plan view schematically showing an electrode structure of a surface acoustic wave element according to a third example of an embodiment of the surface acoustic wave element of the present invention. 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 degree in a pass band and its vicinity about the surface acoustic wave element of the Example of this invention, and a comparative example, (a) is a diagram which shows an amplitude balance degree, (b) is a phase. It is a diagram which shows a balance degree. It is a top view which shows typically the electrode structure of the conventional surface acoustic wave element. It is a top view which shows typically the electrode structure of the conventional surface acoustic wave element. It is a top view which shows typically the electrode structure of the conventional surface acoustic wave element.

Explanation of symbols

1: Piezoelectric substrates 2, 3: First reflector electrode 4: Unbalanced force input / output portion 5, 6: Balanced force input / output force portion
21 and 22: IDT electrode group
31-34: 1st IDT electrode
41, 42: Second reflector electrode
51, 52: Third IDT electrode
61, 62: Third reflector electrode

Claims (4)

Two IDT electrode groups in which a plurality of first IDT electrodes having a plurality of long electrode fingers in a direction orthogonal to the propagation direction of the surface acoustic wave are electrically connected to each other are disposed on the piezoelectric substrate. In addition, a first reflector electrode having a plurality of long electrode fingers in a direction perpendicular to the propagation direction of the surface acoustic wave is disposed on both outer sides of the propagation direction of the surface acoustic wave of the IDT electrode group. Any one of the second IDT electrode and the second reflector electrode that is electrically disconnected from the first IDT electrode between at least two first IDT electrodes of the IDT electrode group. One or more types are disposed as one or more first separation electrodes, and a third IDT that is electrically disconnected from the IDT electrode group between the IDT electrode group and the first reflector electrode. Surface acoustic wave in which electrode is arranged as second separation electrode A third portion of the IDT electrode is connected to be an unbalanced input portion or an unbalanced output portion, and each of the two IDT electrode groups is a balanced output portion or a balanced input portion. A surface acoustic wave device. Between the IDT electrode group and the second separation electrode, one or more of the fourth IDT electrode and the third reflector electrode, which are electrically disconnected from the IDT electrode group, The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is provided as three separation electrodes. A reflector electrode disposed in both the IDT electrode and outside the propagation direction of the surface acoustic wave of the IDT electrode, which generates one or more mode resonances in series or in parallel with the third IDT electrode; 3. A surface acoustic wave device according to claim 1, wherein a surface acoustic wave resonator comprising: A communication apparatus comprising at least one of a receiving circuit and a transmitting circuit having the surface acoustic wave element according to any one of claims 1 to 3.

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