JP2018133615A - Elastic wave element, filter element, and communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave element, a filter element and a communication device capable of improving the characteristics of withstand power. An elastic wave element 1 of the present invention has a piezoelectric substrate 2 and an IT electrode arranged on the piezoelectric substrate 2. The following relationship is satisfied when the cut angle of the piezoelectric substrate is α, the total thickness which is the wavelength ratio of elastic waves of the IDT electrode is t, and the ratio of the Cu electrode is p. at2 + bt + c-0.1 ≦ p ≦ at2 + bt + c + 0.1 However, a = 6.073α2-594.6α + 14600b = −0.5997α2 + 54.46α-1497c = 0.006700α2-0.6505α + 17.960 <p ≦ 1 [Selection diagram] 2

Description

  The present invention relates to an acoustic wave element, a filter element, and a communication device.

  In recent years, in a communication apparatus such as a mobile terminal, an acoustic wave element is used as a duplexer for filtering a signal transmitted / received from an antenna. The acoustic wave element includes a piezoelectric substrate and excitation electrodes formed on the main surface of the piezoelectric substrate. The acoustic wave element utilizes a characteristic capable of mutually converting an electric signal and a surface acoustic wave by the relationship between the excitation electrode and the piezoelectric substrate.

  The duplexer includes, for example, a reception filter and a transmission filter by using a plurality of acoustic wave elements (see, for example, Patent Document 1). In the duplexer, a reception band and a transmission band are set by combining a plurality of acoustic wave elements.

JP 2007-214902 A

  In such a duplexer, one of the problems is to increase the power resistance. In order to increase the withstand power of the duplexer, it is necessary to increase the withstand power of the elastic wave element constituting the duplexer.

  Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide an acoustic wave element, a filter element, and a communication device having high power resistance.

An acoustic wave device according to an embodiment of the present disclosure includes a piezoelectric substrate and an IDT electrode that is disposed on the piezoelectric substrate and has a Cu electrode or a stacked structure of the Cu electrode and an Al electrode. When the cut angle of the piezoelectric substrate is α, the total thickness, which is the wavelength ratio of the elastic wave of the IDT electrode, is t, and the ratio of the Cu electrode is p, the following relationship is satisfied.
at ² + bt + c−0.1 ≦ p ≦ at ² + bt + c + 0.1
However, a = 6.073α ² −594.6α + 14600
b = −0.5997α ² + 54.46α-1497
c = 0.006700α ² -0.6505α + 17.96
0 <p ≦ 1
It is.

  A filter element according to an embodiment of the present invention includes the acoustic wave element described above and a series resonator and a parallel resonator disposed on the piezoelectric substrate, each of which is connected in a ladder shape. Yes.

  A communication apparatus according to an embodiment of the present invention includes an antenna, the above-described filter element electrically connected to the antenna, and an RF-IC electrically connected to the filter element.

  According to the elastic wave device, the filter device, and the communication device of the present invention, it is possible to increase power resistance.

It is a top view which shows the structure of the elastic wave element which concerns on one Embodiment of this invention. In the elastic wave element of FIG. 1, it is the principal part enlarged view of the cross section cut | disconnected by the II-II line | wire. It is the principal part expanded sectional view which expanded a part of IDT electrode. FIG. 2 is a diagram showing the relationship between the total thickness of IDT electrodes 3 and the ratio of Cu electrodes therein in the acoustic wave device of FIG. 1. FIG. 5A is a diagram showing the relationship between the total thickness of the IDT electrode 3 and the FOM, and FIG. 5B is the total thickness of the IDT electrode 3 in consideration of the FOM in FIG. 4 and the Cu electrode therein. It is a diagram which shows the relationship with the ratio. FIG. 6A is a diagram showing the relationship between the total thickness of the IDT electrode 3 and the maximum stress, and FIG. 6B shows the total thickness of the IDT electrode 3 in consideration of the maximum stress in FIG. It is a diagram which shows the relationship with the ratio of Cu electrode. It is the schematic explaining the communication apparatus which concerns on one Embodiment of this invention. It is a circuit diagram explaining the duplexer concerning one embodiment of the present invention. 9A and 9B are diagrams showing the frequency characteristics of the SAW elements according to the example and the comparative example, and FIG. 9A is a diagram showing the absolute value of the impedance with respect to the frequency. FIG. 9B is a diagram showing phase characteristics with respect to frequency.

  Hereinafter, an acoustic wave device, a filter device, and a communication device according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

  The elastic wave element may be either upward or downward, but in the following, for convenience, the orthogonal coordinate system xyz is defined and the upper side and the lower side are defined with the positive side in the z direction as the upper side. The terms such as are used.

<Outline of configuration of acoustic wave element>
FIG. 1 is a plan view showing a configuration of an acoustic wave (SAW) device 1 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part taken along line II-II in FIG. As shown in FIG. 1, the SAW element 1 includes a piezoelectric substrate 2, an excitation (IDT: Interdigital Transducer) electrode 3 and a reflector 4 provided on the upper surface 2 </ b> A of the piezoelectric substrate 2.

The piezoelectric substrate 2 is composed of a piezoelectric single crystal substrate (hereinafter referred to as an LT substrate) made of a lithium tantalate (LiTaO ₃ ) crystal. The cut angle of the LT substrate will be described later. The planar shape and various dimensions of the piezoelectric substrate 2 may be set as appropriate. As an example, the thickness (z direction) of the piezoelectric substrate 2 is 0.2 mm or more and 0.5 mm or less.

  As shown in FIG. 1, the IDT electrode 3 includes two comb electrodes 30. As shown in FIG. 1, the comb electrode 30 includes two bus bars 31 facing each other and a plurality of electrode fingers 32 extending from each bus bar 31 to the other bus bar 31 side. The pair of comb-shaped electrodes 30 are arranged so that the electrode fingers 32 connected to one and the electrode fingers 32 connected to the other mesh with each other in the propagation direction of the elastic wave. .

  Further, the comb electrode 30 has dummy electrode fingers 33 facing the respective electrode fingers 32. The dummy electrode fingers 33 may not be arranged.

  The bus bar 31 is, for example, formed in a long shape extending linearly with a substantially constant width. Accordingly, the edges of the bus bars 31 facing each other are linear. For example, the plurality of electrode fingers 32 are formed in an elongated shape extending in a straight line with a substantially constant width, and are arranged at substantially constant intervals in the propagation direction of the elastic wave.

  The plurality of electrode fingers 32 of the pair of comb electrodes 30 constituting the IDT electrode 3 is set to have a pitch Pt1. The pitch Pt1 is provided, for example, so as to be equal to a half wavelength of the wavelength λ of the elastic wave at the frequency to be resonated. The wavelength λ (that is, 2 × Pt1) is, for example, not less than 1.5 μm and not more than 6 μm. The IDT electrode 3 is arranged so that most of the plurality of electrode fingers 32 have a pitch Pt1, so that the plurality of electrode fingers 32 have a constant period, and therefore elastic waves can be generated efficiently. Can do.

  Here, the pitch Pt1 indicates a distance from the center of one electrode finger 32 to the center of the other electrode finger 32 adjacent to the one electrode finger 32 in the propagation direction. In each electrode finger 32, the width w1 in the propagation direction of the elastic wave is appropriately set according to the electrical characteristics required for the SAW element 1. For example, the width w1 of the electrode finger 32 is not less than 0.3 times and not more than 0.7 times the pitch Pt1.

  By arranging the electrode fingers 32 in this way, an elastic wave propagating in a direction orthogonal to the plurality of electrode fingers 32 is generated. Accordingly, in consideration of the crystal orientation of the piezoelectric substrate 2, the two bus bars 31 are disposed so as to face each other in a direction intersecting the direction in which the elastic wave is desired to propagate. The plurality of electrode fingers 32 are formed to extend in a direction orthogonal to the direction in which the elastic wave is desired to propagate. The propagation direction of the elastic wave is defined by the orientation of the plurality of electrode fingers 32, but in the present embodiment, for convenience, the orientation of the plurality of electrode fingers 32 will be described with reference to the propagation direction of the elastic wave. There are things to do.

  The number of each electrode finger 32 is 50 to 350 per side. The lengths of the plurality of electrode fingers 32 (the length from the bus bar to the tip) are set to be approximately the same, for example. The length (intersection width) with which the opposing electrode fingers 32 are engaged is 10 to 300 μm.

  The IDT electrode 3 is composed of, for example, a metal conductive layer 15. The metal material and the thickness S (z direction) of the metal layer 15 will be described later.

  The IDT electrode 3 may be disposed directly on the upper surface 2A of the piezoelectric substrate 2 or may be disposed on the upper surface 2A of the piezoelectric substrate 2 via a base layer made of another member. Another member is made of, for example, Ti, Cr, or an alloy thereof. When the IDT electrode 3 is disposed on the upper surface 2A of the piezoelectric substrate 2 via the underlayer, the thickness of another member has a thickness that does not substantially affect the electrical characteristics of the IDT electrode 3 (for example, in the case of Ti, IDT Within 5% of the thickness of the electrode 3).

  The underlayer may have a width in contact with the piezoelectric substrate 2 larger than a width in contact with the electrode finger 32 of the IDT electrode 3 in a cross-sectional view. In that case, the power durability can also be improved by the underlayer.

  When a voltage is applied, the IDT electrode 3 excites an elastic wave propagating in the x direction in the vicinity of the upper surface 2A of the piezoelectric substrate 2. The excited elastic wave is reflected at the boundary with the non-arranged region of the electrode fingers 32 (the long region between the adjacent electrode fingers 32). And the standing wave which makes the pitch Pt1 of the electrode finger 32 a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as that of the standing wave, and is taken out by the electrode finger 32. In this way, the SAW element 1 functions as a 1-port resonator.

  The reflector 4 is disposed so as to sandwich the IDT electrode 3 in the propagation direction of the elastic wave. The reflector 4 is generally formed in a slit shape.

  As shown in FIG. 2, the protective layer 5 is provided on the piezoelectric substrate 2 so as to cover the IDT electrode 3 and the reflector 4. Specifically, the protective layer 5 covers the surfaces of the IDT electrode 3 and the reflector 4, and covers the portion of the upper surface 2 </ b> A of the piezoelectric substrate 2 that is exposed from the IDT electrode 3 and the reflector 4. The thickness of the protective layer 5 is, for example, 1 nm or more and 20% or less of the thickness of the IDT electrode 3.

The protective layer 5 is made of an insulating material and contributes to protection from corrosion and the like. Preferably, the protective layer 5 is made of a material such as SiO ₂ that increases the propagation speed of the elastic wave when the temperature rises, thereby suppressing a change in electrical characteristics due to a change in the temperature of the elastic wave element 1. You can also. Further, a material such as SiNx may be used for improving the moisture resistance.

(Relationship between piezoelectric substrate 2 and IDT electrode 3)
At present, in an acoustic wave device, considering the excitation efficiency of the acoustic wave, radiation loss, electrical resistance, etc., the thickness of the wavelength ratio of the acoustic wave (= 2 × Pt1) is about 8% on the LT substrate having a cut angle of 42 °. In general, an IDT electrode made of Al is provided (hereinafter, the acoustic wave device of this configuration is referred to as a comparative model).

  On the other hand, in recent years, since the power of the high-frequency signal input to the acoustic wave element has been increased, an electrode having higher power durability than the electrode made of Al is required.

  However, simply replacing the electrode material with high strength such as Mo has a trade-off relationship between the excitation efficiency of the elastic wave, the radiation loss, and the electrical resistance, and the characteristics sufficient to replace the electrode made of Al are expressed. I couldn't make it.

Therefore, in the SAW element 1 according to the present embodiment, first, Cu was selected as a material capable of improving the power durability and exhibiting the same characteristics as the current Al electrode. Then, the relationship between the cut angle of the piezoelectric substrate 2 and the material and thickness of the IDT electrode 3 satisfies the conditions shown in the following formula (1), so that the excitation efficiency and radiation loss of elastic waves are achieved. It has been found that the characteristics such as are improved.
at ² + bt + c−0.1 ≦ p ≦ at ² + bt + c + 0.1 (1)

Here, the IDT electrode 3 is configured by a combination of an Al electrode 35 and a Cu electrode 36 as shown in FIG. The ratio of the Cu electrode 36 can be changed. When the IDT electrode 3 is composed of a plurality of electrodes, it is assumed that the Al electrode 35 and the Cu electrode 36 are stacked. In the formula (1), t represents the thickness (wavelength ratio) of the IDT electrode 3, and p represents the ratio of the Cu electrode to the total thickness of the IDT electrode 3, and takes a value greater than 0 and 1 or less. That is, the case where the IDT electrode 3 is composed of only the Cu electrode 36 is included. In FIG. 3, since the cross-sectional shape of the IDT electrode 3 is rectangular, p can be a ratio of the film thickness of the Cu electrode 36. And a, b, and c are the following constants, respectively.
a = 6.073α ² −594.6α + 14600
b = −0.5997α ² + 54.46α-1497
c = 0.006700α ² -0.6505α + 17.96
Where α represents the cut angle (°) of the LT substrate.

  When the above relationship is satisfied, the presence of the Cu electrode 36 made of a material having a higher tensile strength than that of the Al electrode 35 can increase the power resistance of the IDT electrode 3 and suppress the radiation loss of the elastic wave. The excitation efficiency can be increased. From the above, it is possible to provide the SAW element 1 having excellent power resistance and low loss.

  The above-described relationship is obtained by calculating a value that minimizes the radiation loss of the elastic wave at the resonance frequency when the cut angle of the piezoelectric substrate 2 and the material (laminate structure) of the IDT electrode 3 are changed. Is a mathematical expression. In addition, the validity is verified by actual measurement values.

FIG. 4 shows the relationship of equation (1). In FIG. 4, the horizontal axis represents the total thickness t of the IDT electrode 3 (unit: dimensionless, ratio to the wavelength λ (= 2 × Pt)), and the vertical axis represents the ratio of the thickness of the Cu electrode 36 to the total thickness t (unit). : Dimensionless). The legend is the condition that the radiation loss of the elastic wave at the resonance frequency confirmed by the simulation is the minimum, and the line is a plot of the center value of Equation (1). That is, the values satisfying p = at ² + bt + c are plotted. The cut angle α of the piezoelectric substrate 2 is changed from 42 ° to 50 °.

  From FIG. 4, it can be confirmed that the expression (1) accurately expresses the correlation such as the cut angle of the piezoelectric substrate 2, the total thickness of the IDT electrode 3, the ratio of the Cu electrode 36, and the like, which are complicatedly related.

  As such an Al electrode 35, Al or an Al alloy containing Al as a main component can be used. For example, an Al—Cu alloy in which about 1% to 3% of Cu is added to Al can be used. As the Cu electrode 36, Cu or a Cu alloy containing Cu as a main component can be used. For example, a Cu—Ag alloy in which about 1% to 20% of Ag is added to Cu can be used.

  FIG. 3 shows an example in which the Cu electrode 36 is disposed on the side close to the piezoelectric substrate 2, but the present invention is not limited to this example. For example, the Al electrode 35 may be disposed on the piezoelectric substrate 2 side.

  In the case where the Cu electrode 36 is disposed on the piezoelectric substrate 2 side, the strong Cu electrode 36 can be provided on the side close to the strong piezoelectric substrate 2, so that the SAW element 1 having excellent power durability can be provided. It will be a thing. In addition, since the center of gravity of the IDT electrode 3 can be moved downward, the electromechanical coupling coefficient can be reduced and the propagation loss can be reduced.

  The radiation loss of the elastic wave is also related to the density of the material constituting the IDT electrode 3, so that a so-called mass addition film is provided on the IDT electrode 3 or the IDT electrode 3 is embedded in an insulating material. In such a case, the above relationship is not established. “Embedded” means, for example, a case where the thickness of the insulating material is half or more of the thickness of the IDT electrode 3.

(Modification 1)
A modification of the SAW element 1 will be described with reference to FIG.

  As the proportion of the Cu electrode increases, the power durability increases. However, as shown in FIG. 4, when the proportion of the Cu electrode is increased, the total thickness t of the IDT electrode 3 is decreased, the electrical resistance as the electrode is increased, and as a result, the electrical loss is increased. On the other hand, it can be seen that the total thickness t can be increased as the cut angle of the piezoelectric substrate 2 is increased.

  As described above, the electric resistance may be decreased by increasing the cut angle of the piezoelectric substrate 2 while increasing the power resistance by increasing the ratio of the Cu electrode. Specifically, the electrical resistance as an electrode may be set to the same level or less as compared with the comparative model.

  In order to compare the electrical resistance characteristics as electrodes, FOM (Figure of Merit) is introduced. In this example, a value obtained by multiplying the conductivity and the electrode thickness is used as the FOM. In the case of a laminated structure, the FOM of the entire electrode is calculated by adding the electrode material multiplied by the conductivity and the electrode thickness for each electrode material. When the FOM is defined in this manner, the larger the FOM, the smaller the electric resistance per unit thickness of the electrode.

  In the calculation, the conductivity is expressed in μS / cm (Cu conductivity: 0.588 μS / cm, Al conductivity: 0.370 μS / cm), and the electrode thickness is wavelength λ (= 2 × Expressed as a ratio to Pt). For example, when the film thickness is 8% in terms of wavelength with a pure Al electrode, FOM = 0.370 × 0.08 = 0.0296. When the Cu film thickness is 3% and the Al film thickness is 4%, FOM = 0.588 × 0.03 + 0.370 × 0.04 = 0.0325.

  Here, FIG. 5A shows the FOM value when the cut angle of the piezoelectric substrate 2 is varied for the IDT electrode 3 having the center value of the equation (1). In FIG. 5A, the horizontal axis represents the total thickness t of the IDT electrode 3, and the vertical axis represents FOM. The FOM of the comparative model is 0.0296.

  As can be seen from FIG. 5A, the FOM value increases as the cut angle α is increased, and it can be seen that the SAW element 1 having excellent electrical characteristics can be provided. In particular, when α = 47 ° or more, the FOM exceeds the comparative model for any ratio of the Cu electrode to the Al electrode.

Here, the relationship between the cut angle α of the piezoelectric substrate 2 and the value of the total thickness t of the IDT electrode 3 having the same FOM as the FOM of the comparative model is expressed by Expression (2).
t = 0.0006429α ² −0.06314α + 1.595 (2)
In equation (2), α is 47 ° or less.

That is, when t ≧ 0.0006429α ² −0.06314α + 1.595 (when the total thickness t takes a value equal to or greater than the formula (2)), the SAW element 1 having improved electrical characteristics as compared with the conventional model is provided. be able to.

In the case where the FOM value is improved by 5% or more than the conventional model, it is preferable that the total thickness t be a value equal to or greater than the formula (3). In this case, even if the crystallinity of the IDT electrode 3 is slightly deteriorated, the electrical characteristics can be made good.
t = 0.0006429α ² −0.06314α + 1.605 (3)

  FIG. 5B shows the condition that satisfies the condition that the total thickness t is equal to or greater than the values of the expressions (2) and (3). A value satisfying the expression (2) is indicated by a line L11, and a value satisfying the expression (3) is indicated by a line L12. In the region located on the thicker side than the lines 11 and 12, the electrical characteristics of the SAW element 1 can be improved.

(Modification 2)
As shown in FIG. 3, by disposing the Cu electrode 36 on the side closer to the piezoelectric substrate 2, the SAW element 1 having excellent power durability can be provided, but in order to further improve the power durability, IDT It is good also considering the total thickness t of the electrode 3 as the value shown in Formula (4) or less.
t = 0.0046α−0.113 (4)
That is, t ≦ 0.0046α−0.113 may be set.

  FIG. 6A shows the result of simulating the maximum stress in the Al electrode 35 when the IDT electrode 3 has the configuration shown in FIG. The IDT electrode 3 satisfies the formula (1) and takes its center value.

  In FIG. 6A, the horizontal axis represents the total thickness t of the IDT electrode 3, and the vertical axis represents the maximum stress (unit: MPa) in the Al electrode 35. Here, the relationship between the IDT electrode 3 having the same stress as the standard model (about 60 MPa) and the cut angle α is expressed by Equation (4). For this reason, when the total thickness t of the IDT electrode 3 is smaller than the formula (4), the stress transmitted to the Al electrode 35 on the weaker side can be reduced to the standard model or less, and the SAW excellent in power durability. Element 1 can be provided.

In order to reduce the maximum stress of the Al electrode 35 by 20% from the standard model, the total thickness t of the IDT electrode 3 may be equal to or less than the value shown in Formula (5).
t = 0.0049α−0.1444 (5)
That is, t ≦ 0.0049α−0.1444 may be set.
In this case, the SAW element 1 having further excellent power durability can be provided. Specifically, the breakdown limit power is expected to improve by 2 dB at the maximum.

Further, in order to reduce the maximum stress of the Al electrode 35 by half as compared with the standard model, the total thickness t of the IDT electrode 3 may be equal to or less than the value shown in Expression (6).
t = 0.00475α−0.1257 (6)
That is, t ≦ 0.00475α−0.1257 may be set.
In this case, the SAW element 1 having further excellent power durability can be provided. Specifically, the breakdown limit power is expected to improve by up to 6 dB.

  FIG. 6B shows the condition that satisfies the condition that the total thickness t is equal to or greater than the values of the expressions (4) to (6). A value satisfying Expression (4) is indicated by a line L21, a value satisfying Expression (5) is indicated by a line L22, and a value satisfying Expression (6) is indicated by a line L23. The power durability of the SAW element 1 can be improved in a region located on the thinner side than the lines L21 to L23.

  In addition, it is good also as what satisfies the above-mentioned modification 1 and this modification 2 simultaneously. In that case, the SAW element 1 excellent in both electrical characteristics and power durability can be provided.

(Modification 3)
Although FIG. 3 shows an example in which the thickness of the Al electrode 35 is larger than the thickness of the Cu electrode 36, the present invention is not limited to this example. In view of the electrical characteristics and power durability, it may be adjusted as appropriate within a range satisfying the formula (1).

  In the case where the thickness of the Al electrode 35 is larger than the thickness of the Cu electrode 36, it is possible to provide the SAW element 1 that is particularly excellent in electric characteristics while improving power durability. Further, by increasing the thickness of the Al electrode 35, crystal growth in the <111> direction can be promoted, and the Al electrode 35 having excellent crystallinity can be obtained. For this reason, generation | occurrence | production of the defect used as the destruction origin can be suppressed, and power durability can be improved. Further, the crystallinity of the Al electrode 35 may be higher than the crystallinity of the Cu electrode 36. In this case, stress is concentrated on the Cu electrode 36 side by providing a stress transmission path to the Cu electrode 36 having a high tensile strength and a high strength as a material, thereby transmitting the stress to the Al electrode 35 having a low strength. Can be suppressed.

  On the other hand, when the thickness of the Al electrode 35 is smaller than the thickness of the Cu electrode 36, it is possible to provide a SAW element that is particularly excellent in power resistance while maintaining the electrical characteristics. In particular, when the cut angle α of the piezoelectric substrate 2 is 47 ° or more, it has been confirmed that even if the IDT electrode 3 is configured only by the Cu electrode 36, it exceeds the FOM of the conventional model, so that only the power resistance is achieved. Even when the thickness of the Cu electrode 36 is increased by paying attention to the above, it is possible to provide the SAW element 1 excellent in both power durability and electrical characteristics. In particular, when the cut angle α of the piezoelectric substrate 2 is 48 ° or more, even if the crystallinity of the Cu electrode 36 is slightly lowered, the SAW element 1 having excellent electrical characteristics can be provided that can exceed the FOM of the conventional model. It will be possible.

(Other variations)
In the example shown in FIG. 3, the cross-sectional shape of the IDT electrode 3 is rectangular, but it may be trapezoidal. In this case, the thickness ratio between the Al electrode 35 and the Cu electrode 36 is corrected according to the volume.

  In the example shown in FIG. 2, the case where a sufficiently thick piezoelectric substrate 2 is used has been described as an example. However, a so-called bonded substrate in which a support substrate is bonded to the lower surface of the thin piezoelectric substrate 2 is used. May be. In this case, the thickness of the piezoelectric substrate 2 may be about 0.5 μm to 20 μm, and the support substrate may be thick enough to support the piezoelectric substrate 2. In particular, when the sapphire substrate is a Si substrate or the like as the support substrate, deformation due to temperature change of the piezoelectric substrate 2 can be suppressed, so that a SAW element having excellent temperature characteristics can be provided.

  Furthermore, in the above-described example, the IDT electrode 3 has been described as having a uniform layer configuration and thickness. However, in the region where the electrode fingers 32 intersect with each other, it is sufficient that the electrode fingers 32 satisfy the above-described relationship. Absent. For example, the bus bar 31 may be thicker than the electrode fingers 32 or may have a different layer configuration.

  Note that the characteristics of each equation derived in the above example confirm that the tendency of the total thickness of the IDT electrode 3 to increase is the same even when the cut angle of the piezoelectric substrate 2 is 50 ° or more. However, the consistency between the measured value and the simulation value is confirmed until the cut angle α is 50 °.

<Filter element and communication device>
FIG. 7 is a block diagram showing a main part of the communication apparatus 101 according to the embodiment of the present invention. The communication device 101 performs wireless communication using radio waves. The duplexer 7 has a function of demultiplexing a signal having a transmission frequency and a signal having a reception frequency in the communication apparatus 101.

  In the communication apparatus 101, a transmission information signal TIS including information to be transmitted is modulated and increased in frequency (conversion to a carrier wave frequency to a high frequency signal) by the RF-IC 103 to be a transmission signal TS. Unnecessary components other than the transmission passband are removed from the transmission signal TS by the bandpass filter 105, amplified by the amplifier 107, and input to the duplexer 7. The duplexer 7 removes unnecessary components other than the transmission passband from the input transmission signal TS and outputs the result to the antenna 109. The antenna 109 converts the input electric signal (transmission signal TS) into a radio signal and transmits it.

  In the communication apparatus 101, the radio signal received by the antenna 109 is converted into an electric signal (reception signal RS) by the antenna 109 and input to the duplexer 7. The duplexer 7 removes unnecessary components other than the reception passband from the input reception signal RS and outputs the result to the amplifier 111. The output reception signal RS is amplified by the amplifier 111, and unnecessary components other than the reception passband are removed by the bandpass filter 113. The reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 103 to be a reception information signal RIS.

  The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) including appropriate information, and are, for example, analog audio signals or digitized audio signals. The passband of the radio signal may be in accordance with various standards such as UMTS (Universal Mobile Telecommunications System). The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof.

  FIG. 8 is a circuit diagram showing a configuration of the duplexer 7 according to one embodiment of the present invention. The duplexer 7 is a duplexer used in the communication apparatus 101 in FIG. The duplexer 7 includes filter elements that constitute the transmission filter 11 and / or the reception filter 12. The filter elements constituting the transmission filter 11 and / or the reception filter 12 are composed of a SAW element 1 and a resonator disposed on the piezoelectric substrate 2.

  The SAW element 1 is, for example, a SAW element that constitutes a part of a ladder type filter circuit of the transmission filter 11 in the duplexer 7 shown in FIG. As shown in FIG. 8, the transmission filter 11 includes a piezoelectric substrate 2, and series resonators S <b> 1 to S <b> 3 and parallel resonators P <b> 1 to P <b> 3 formed on the piezoelectric substrate 2.

  The duplexer 7 includes an antenna terminal 8, a transmission terminal 9, a reception terminal 10, a transmission filter 11 disposed between the antenna terminal 8 and the transmission terminal 9, and between the antenna terminal 8 and the reception terminal 10. The reception filter 12 is mainly configured.

  The transmission signal TS from the amplifier 107 is input to the transmission terminal 9, and the transmission signal TS input to the transmission terminal 9 is output to the antenna terminal 8 by removing unnecessary components other than the transmission passband in the transmission filter 11. Is done. Further, the reception signal RS is input from the antenna 109 to the antenna terminal 8, and unnecessary components other than the reception passband are removed by the reception filter 12 and output to the reception terminal 10.

  The transmission filter 11 is configured by, for example, a ladder type SAW filter. Specifically, the transmission filter 11 includes three series resonators S1, S2, and S3 connected in series between the input side and the output side, and a series arm that is a wiring for connecting the series resonators to each other. And three parallel resonators P1, P2, and P3 provided between the reference potential portion Gnd and the reference potential portion Gnd. That is, the transmission filter 11 is a ladder filter having a three-stage configuration. However, the number of stages of the ladder filter in the transmission filter 11 is arbitrary.

  An inductor L is provided between the parallel resonators P1, P2, and P3 and the reference potential unit Gnd. By setting the inductance of the inductor L to a predetermined magnitude, an attenuation pole is formed outside the band of the transmission frequency of the transmission signal to increase the out-of-band attenuation. The plurality of series resonators S 1, S 2, S 3 and the plurality of parallel resonators P 1, P 2, P 3 are each composed of a SAW resonator such as the SAW element 1.

  The reception filter 12 includes, for example, a multimode SAW filter 17 and an auxiliary resonator 18 connected in series on the input side thereof. In the present embodiment, the multiplex mode includes a double mode. The multimode SAW filter 17 has a balanced-unbalanced conversion function, and the receiving filter 12 is connected to two receiving terminals 10 that output balanced signals. The reception filter 12 is not limited to the multimode SAW filter 17 and may be a ladder filter or a filter that does not have a balanced-unbalanced conversion function.

  Between the connection point of the transmission filter 11, the reception filter 12, and the antenna terminal 8 and the ground potential part G, an impedance matching circuit made of an inductor or the like may be inserted.

  The SAW element of this embodiment may be used for any of the series resonators S1 to S3 or any of the parallel resonators P1 to P3. By using the SAW element 1 for at least one of the parallel resonators P1 to P3, the power durability of the filter can be improved.

  In order to confirm the effect of changing the material of the IDT electrode 3 and the cut angle of the piezoelectric substrate 2 as in the SAW element 1 of this embodiment and the modified example, the SAW element was manufactured and evaluated. The basic configuration of the SAW element is as follows.

[Piezoelectric substrate 2]
Material: Rotating Y-cut X-propagating LiTaO ₃ substrate [IDT electrode 3]
Electrode finger 32 of IDT electrode 3:
(Number) 150 (Pitch Pt1) 2.7 μm
(Duty: w1 / Pt1) 0.5
(Intersection width W) 20λ (λ = 2 × Pt1)
Material: Al electrode 35 ... Pure Al
Cu electrode 36 ... Pure Cu
(However, there is an underlayer 6 made of 6 nm Ti between the piezoelectric substrate 2 and the conductive layer 15.)
[Reflector 4]
Material and Layer Configuration: Same as IDT electrode Number of reflective electrode fingers 42: 30 Pt2 of reflective electrode fingers 42: Pt1
Distance G from IDT electrode 3: Pt1
[Protective layer 5]
Material: SiO ₂
Thickness: 15nm
With respect to such a basic configuration, a SAW element in which the cut angle of the piezoelectric substrate 2 and the combination of the electrode material of the IDT electrode 3 and its thickness were as follows was produced.
[Combination of cut angle of piezoelectric substrate 2 and electrode film thickness]
Comparative example: Cut angle: 42 °, electrode film thickness: Al 8%
Example 1: Cut angle: 46 °, electrode film thickness: Cu 2% / Al 7%
Example 2: Cut angle: 46 °, electrode film thickness: Cu 4% / Al 2%
Example 3: Cut angle: 48 °, electrode film thickness: Cu 6%

  As a result of measuring the breakdown power values of the SAW elements according to the comparative example and the example, the SAW element according to the comparative example is 32 dB, whereas the SAW element according to the example 1 is 34.5 dB, and 2.5 dB. It was confirmed that the power durability can be improved. In Examples 2 and 3, the breakdown power value was measured, and it was confirmed that the power durability was improved as compared with the comparative example.

  Furthermore, the electrical characteristics of the SAW elements according to the comparative example and the example were measured. FIG. 9 shows the characteristics of a SAW resonator using the acoustic wave device of the present invention. In FIG. 9, the horizontal axis indicates the frequency. 9A shows the absolute value of the impedance, and FIG. 9B shows the phase of the impedance.

  As is clear from FIG. 9, all the three types of the examples show the same or better characteristics as compared with the Al 8% product of the comparative example. In particular, the phase is closer to −90 ° than the comparative example on the high frequency side (750 MHz or more) with respect to the antiresonance frequency. This indicates that the loss is small in this frequency band. This is because the reflection coefficient of the elastic wave at the IDT electrode 3 is increased by using Cu having a high density as the electrode material. From this result, it was found that a SAW element having superior power durability and electrical characteristics compared to the configuration of the conventional model can be provided.

1 Elastic wave device (SAW device)
2 Piezoelectric substrate 2A Upper surface 3 Excitation (IDT) electrode 35 Al electrode 36 Cu electrode 4 Reflector 5 Protective layer 7 Demultiplexer 8 Antenna terminal 9 Transmission terminal 10 Reception terminal 11 Transmission filter 12 Reception filter 15 Conductive layer 17 Multimode SAW Filter 18 Auxiliary resonator 101 Communication device 103 RF-IC
105 Band Pass Filter 107 Amplifier 109 Antenna 111 Amplifier 113 Band Pass Filters S1 to S3 Series Resonators P1 to P3 Parallel Resonators

Claims (11)

A piezoelectric substrate;
An IDT electrode having a Cu electrode or a laminated structure of the Cu electrode and an Al electrode, disposed on the piezoelectric substrate;
An acoustic wave device satisfying the following relationship, where α is a cut angle of the piezoelectric substrate, t is a total thickness which is a wavelength ratio of elastic waves of the IDT electrode, and p is a ratio of the Cu electrode.
at ² + bt + c−0.1 ≦ p ≦ at ² + bt + c + 0.1
However, a = 6.073α ² −594.6α + 14600
b = −0.5997α ² + 54.46α-1497
c = 0.006700α ² -0.6505α + 17.96
0 <p ≦ 1
It is. t ≧ 0.0006429α ² −0.06314α + 1.595
The acoustic wave device according to claim 1, wherein: t ≧ 0.0006429α ² −0.06314α + 1.605
The elastic wave device according to claim 2, wherein t ≦ 0.0046α−0.113
The elastic wave device according to claim 1, wherein: t ≦ 0.0049α−0.1444
The acoustic wave device according to claim 4, wherein: t ≦ 0.00475α-0.1257
The acoustic wave device according to claim 4, wherein:   The acoustic wave device according to claim 1, wherein the Cu electrode and the Al electrode are located in order from the piezoelectric substrate side of the IDT electrode.   The acoustic wave device according to claim 1, wherein the IDT electrode includes the Al electrode and the Cu electrode having lower crystallinity than the Al electrode. An underlayer having conductivity between the upper surface and the IDT electrode;
The acoustic wave device according to claim 1, wherein the base layer has a width in contact with the piezoelectric substrate wider than a width in contact with the electrode finger in a cross-sectional view.   A filter element in which at least one acoustic wave element according to any one of claims 1 to 9 and at least one resonator disposed on the piezoelectric substrate are connected in a ladder shape. An antenna,
The filter element of claim 10 electrically connected to the antenna;
A communication device comprising: an RF-IC electrically connected to the filter element.