JP2018207371A - Acoustic wave element and communication device - Google Patents

Abstract

To provide an acoustic wave element with excellent electric characteristics.SOLUTION: An acoustic wave element includes a piezoelectric substrate 7 having a first face 7a and an electrode part 5 disposed on the first face 7a for exciting an acoustic wave. The electrode part 5 includes a conductor layer composed of Al with Cu less than 5 wt% added, and, on its upper face, lots of particles composed of Cu are disposed, and a value of multiplying the number of particles by a particle diameter is 4.2×10pieces/m or more.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an elastic wave element using an elastic wave and a communication apparatus having the elastic wave element.

  A surface acoustic wave element (SAW element) having a piezoelectric substrate and an IDT (Interdigital Transducer) electrode provided on the upper surface of the piezoelectric substrate and exciting a surface acoustic wave (SAW) is known. (For example, Patent Document 1).

  In Patent Document 1, a piezoelectric substrate is not used alone as a SAW resonator, but a bonded substrate obtained by bonding a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient than that of the piezoelectric substrate is used as a SAW element. Yes. By using such a bonded substrate, for example, a change in the electrical characteristics of the SAW resonator due to a temperature change is compensated.

JP 2014-229916 A

  In such a SAW element, it is required to stably realize desired electrical characteristics. The present disclosure has been devised under such circumstances, and an object thereof is to provide a highly reliable SAW device that stably expresses desired electrical characteristics.

An acoustic wave device according to an aspect of the present disclosure includes a piezoelectric substrate and an electrode unit. The piezoelectric substrate has a first surface. The electrode portion is located on the first surface and excites an elastic wave. The electrode portion includes a conductor layer made of Al to which less than 5 wt% of Cu is added. A large number of Cu particles are located on the upper surface, and a value obtained by multiplying the number and the particle size is 4.2 × 10 ^5. Pieces / m or more.

  A communication apparatus according to an aspect of the present disclosure includes an antenna, the antenna terminal connected to the antenna, a duplexer including the reception filter and the transmission filter including the acoustic wave element, the transmission filter, and the reception And an IC connected to the filter.

  According to said structure, the highly reliable elastic wave element which expresses a desired electrical property stably can be provided.

It is a top view showing composition of an elastic wave device concerning an embodiment of this indication. It is principal part sectional drawing in the II-II line | wire of FIG. It is a diagram which shows the correlation with the value which multiplied the existence density of the particle | grain 51 with respect to the heat processing temperature, and the particle size, and the reduction rate of an electrical resistance value. (A)-(c) is a figure which shows the result of having observed the surface state of the conductor layer, respectively. It is sectional drawing which shows the modification of an electrode part. It is a schematic diagram which shows a duplexer. It is a block diagram which shows the communication apparatus as an example of use of a duplexer.

<Elastic wave device>
Hereinafter, an acoustic wave device according to an embodiment of the present disclosure will be described with reference to the drawings. In this example, a SAW element using SAW as an elastic wave element will be described. 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 SAW element may be either upward or downward, but in the following, for the sake of convenience, an orthogonal coordinate system including the D1 axis, the D2 axis, and the D3 axis is defined and the normal direction of the D3 axis is defined. In some cases, terms such as the upper surface and the lower surface are used with the side as the upper side.

(Overview of SAW element configuration)
FIG. 1 is a plan view showing a configuration of an acoustic wave device 1 (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.

  The SAW element 1 uses SAW as an elastic wave. Specifically, the configuration of the SAW element 1 is as follows.

The SAW element 1 includes, for example, a bonded substrate 3 and an electrode portion 5 configured on the upper surface of the bonded substrate 3. In addition, the SAW element 1 is made of SiO ₂ or the like, and may have a protective layer 6 that covers the electrode portion 5.

  The bonded substrate 3 includes, for example, a piezoelectric substrate 7 and a support substrate 9 (FIG. 2) bonded to the lower surface (second surface) 7 b of the piezoelectric substrate 7. 1 and 2 show examples of the X-axis, Y-axis, and Z-axis of the piezoelectric substrate 7.

The piezoelectric substrate 7 is composed of, for example, a single crystal substrate having piezoelectricity. The single crystal substrate is made of, for example, lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), or quartz (SiO ₂ ). The cut angle may be appropriate. For example, in the case of lithium tantalate, they are 42 ° ± 10 ° Y-X cut, 0 ° ± 10 ° Y-X cut, and the like. In the case of lithium niobate, it is 128 ° ± 10 ° YX cut or 64 ° ± 10 ° YX cut.

  In the following description, an example in which the piezoelectric substrate 7 is YX cut of 38 ° to 48 ° mainly made of lithium tantalate will be described. For confirmation, in this Y-X cut, the main surface is orthogonal to the Y ′ axis (not shown) rotated about the X axis from the Y axis to the Z axis at an angle of 38 ° to 48 °.

  The thickness of the piezoelectric substrate 7 is, for example, constant over the entire planar direction of the piezoelectric substrate 7 and can be exemplified by 0.2 μm to 30 μm.

  The support substrate 9 is formed of, for example, a material having a smaller coefficient of thermal expansion than the material of the piezoelectric substrate 7. Thereby, the temperature change of the electrical characteristics of the SAW element 1 can be compensated. Examples of such a material include a semiconductor such as silicon, a single crystal such as sapphire, and a ceramic such as an aluminum oxide sintered body. The support substrate 9 may be a laminated body in which a plurality of layers made of different materials are laminated, or may be configured by a plurality of layers laminated on a base substrate.

  For example, the thickness of the support substrate 9 is constant over the entire planar direction of the support substrate 9, and the size thereof may be appropriately set according to the specifications required for the SAW element 1. However, the thickness of the support substrate 9 is made larger than the thickness of the piezoelectric substrate 7 so that temperature compensation can be suitably performed and the strength of the piezoelectric substrate 7 can be reinforced. As an example, the thickness of the support substrate 9 is not less than 100 μm and not more than 300 μm. The planar shape and various dimensions of the support substrate 9 are, for example, equivalent to the piezoelectric substrate 7.

The piezoelectric substrate 7 and the support substrate 9 are bonded to each other through an adhesive layer (not shown), for example. The material of the adhesive layer may be an organic material or an inorganic material. Examples of the organic material include a resin such as a thermosetting resin. Examples of the inorganic material include SiO ₂ . In addition, the piezoelectric substrate 7 and the support substrate 9 may be bonded by so-called direct bonding, in which the bonding surface is bonded without a bonding layer after activation processing with plasma or the like. Furthermore, an intermediate layer may be provided between the piezoelectric substrate 7 and the support substrate 9.

  The configuration of the electrode unit 5 is, for example, the same configuration as the electrode unit for a so-called 1-port SAW resonator. That is, the electrode unit 5 includes an IDT electrode 11 and a pair of reflectors 13 located on both sides of the IDT electrode 11.

  The IDT electrode 11 is composed of a conductive pattern (conductive layer) formed on the upper surface (first surface) 7a of the piezoelectric substrate 7, and has a pair of comb-shaped electrodes 15 as shown in FIG. .

  The pair of comb-shaped electrodes 15 are, for example, a bus bar 17 (FIG. 1) facing each other, a plurality of electrode fingers 19 extending from the bus bar 17 in the opposing direction of the bus bar 17, and the bus bar 17 between the plurality of electrode fingers 19. And a protruding dummy electrode 21. The pair of comb electrodes 15 are arranged so that the plurality of electrode fingers 19 mesh with each other (intersect).

  For example, the bus bar 17 is formed in a long shape having a substantially constant width and extending linearly in the SAW propagation direction (D1-axis direction, X-axis direction). The bus bars 17 of the pair of comb electrodes 15 are opposed to each other in the direction (D2 axis direction) intersecting the SAW propagation direction.

  The plurality of electrode fingers 19 are, for example, formed in a long shape having a substantially constant width and extending linearly in a direction orthogonal to the SAW propagation direction (D2 axis direction), and the SAW propagation direction (D1 axis direction, Are arranged at substantially constant intervals in the X direction).

  In general, in the SAW resonator, the plurality of electrode fingers 19 of the pair of comb-tooth electrodes 15 have a pitch p (for example, the distance between the centers of the electrode fingers 19: see FIG. 2) of the SAW at the frequency to be resonated. It is provided so as to be equivalent to a half wavelength (λ / 2) of the wavelength λ. The SAW wavelength λ is, for example, not less than 1.5 μm and not more than 6 μm.

  Similar to the SAW resonator, in some of the plurality of electrode fingers 19, the pitch p may be relatively small, or conversely, the pitch p may be relatively large. So-called thinning may be performed in which p is an integral multiple of the normal pitch p. In the present embodiment, when the pitch is simply referred to as “p”, unless otherwise specified, a portion (such as a narrow pitch portion, a wide pitch portion, or a thinned portion) other than the above-described specific portion (a plurality of electrode fingers 19) is excluded. Most) pitch p or an average value thereof. Similarly, unless otherwise specified, the term “electrode finger 19” refers to the electrode finger 19 other than the specific portion.

  The number, length (D2 axis direction) and width (D1 axis direction: w1 in FIG. 2) of the plurality of electrode fingers 19 may be appropriately set according to the electrical characteristics required for the acoustic wave resonator 1 and the like. . As an example, the number of electrode fingers 19 is 100 or more and 400 or less. The length and width of the electrode fingers 19 are, for example, the same among the plurality of electrode fingers 19.

  For example, the dummy electrode 21 protrudes from the bus bar 17 at an intermediate position of the plurality of electrode fingers 19 in one comb-tooth electrode 15, and the tip thereof has a gap from the tip of the electrode finger 19 of the other comb-tooth electrode 15. Are facing each other. For example, the dummy electrodes 21 have the same length and width between the plurality of dummy electrodes 21.

  The reflector 13 is constituted by, for example, a conductive pattern (conductive layer) formed on the upper surface 7a of the piezoelectric substrate 7, and is formed in a lattice shape in plan view. That is, the reflector 13 includes a pair of bus bars (reference numerals omitted) facing each other in a direction crossing the SAW propagation direction, and a direction perpendicular to the propagation direction of the elastic wave (for example, SAW) (D2 axis direction) between these bus bars. And a plurality of strip electrodes (reference numerals omitted).

  The plurality of strip electrodes of the reflector 13 are arranged in the D1 axis direction so as to follow the arrangement of the plurality of electrode fingers 19. The number and width of the strip electrodes may be appropriately set according to electrical characteristics required for the acoustic wave resonator 1. The pitch of the plurality of strip electrodes is, for example, equal to the pitch of the plurality of electrode fingers 19. Further, the distance between the strip electrode at the end of the reflector 13 and the electrode finger 19 at the end of the IDT electrode 11 is, for example, equal to the pitch p of the plurality of electrode fingers 19 (may be an integer multiple of the pitch p). ).

  Examples of the conductor layer constituting the IDT electrode 11 and the reflector 13 include an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al—Cu alloy. A plurality of layers made of other material systems may be included below the conductor layer. The material of the conductor layer will be described later.

  The thickness of the IDT electrode 11 and the reflector 13 is, for example, constant throughout the whole.

  In the SAW element 1 configured as described above, first, an action similar to that of the SAW resonator occurs. Specifically, when an electric signal is input to one comb electrode 15 and a voltage is applied to the piezoelectric substrate 7 by the plurality of electrode fingers 19, it propagates along the upper surface in the vicinity of the upper surface of the piezoelectric substrate 7. SAW is induced. The SAW is reflected by the plurality of electrode fingers 19 and the plurality of strip electrodes of the reflector 13. As a result, a SAW standing wave having a pitch p of the electrode fingers 19 of approximately a half wavelength (λ / 2) is formed. The standing wave generates a charge (an electric signal having the same frequency as that of the standing wave) on the upper surface of the piezoelectric substrate 7, and the electric signal is taken out by the plurality of electrode fingers 19 of the other comb-tooth electrode 15.

(Regarding the precipitated particles of the electrode part 5)
Here, the electrode unit 5 will be described in detail. In the SAW element 1, the electrode portion 5 is made of Al to which Cu is added. Specifically, Cu is added to Al at a ratio of less than 5 wt%. By adding Cu at such a ratio, Cu can be dissolved in Al, and mixing of a plurality of different phases in the conductor layer constituting the electrode portion 5 can be suppressed. Thereby, stable electrical characteristics can be realized.

Furthermore, a large number of particles 51 are located on the surface of the electrode portion 5. These particles 51 are made of Cu, and are deposited from the conductor layer constituting the electrode portion 5. Here, in the SAW element 1, a value obtained by multiplying the number of particles 51 per unit area (existence density) and the particle size of the particles 51 (hereinafter referred to as F value) is 4.2 × 10. ⁵ pieces / m or more. By satisfying such a relationship, the electrical characteristics of the SAW element 1 can be improved and stabilized. Specifically, the electrical resistance of the electrode part 5 can be reduced, the migration of the electrode part 5 can be suppressed, and the power durability can be improved.

  Cu is generally added to increase the power durability of the conductor film. On the other hand, as a result of repeated studies by the inventors of the present application, a difference occurs in the resistance value and power durability of the conductor film depending on the solid solution state, dispersion state, and crystal grain boundary state of Cu inside the conductor film. I found out. The inventors have found that there is a correlation between the resistance value and power durability of the conductor film and the existence density and particle size of the precipitated particles 51.

  The existence density and particle size of the particles 51 can be controlled by the amount added and the heat treatment conditions during and after the formation of the conductor layer. Since the dispersion state of Cu inside the conductor layer and the state of the crystal grain boundary change depending on the heat treatment conditions, etc., the shape and number of particles 51 deposited on the surface and the state inside the conductor layer are considered to have a correlation. It is done.

That is, when the F value is 4.2 × 10 ⁵ pieces / m or more, the electrical characteristics of the conductor layer can be enhanced.

  Here, the electrical properties of the conductor layer were measured by changing the particle size and density of the particles deposited on the conductor layer. Specifically, a film formed by adding 1 wt% Cu to Al (no heat treatment) is used as a comparative example, and the F value is changed by changing the heat treatment temperature and heat treatment time for the conductor layer of this comparative example. The sheet resistance value was confirmed by making it different. The result is shown in FIG.

In FIG. 3, the horizontal axis represents the heat treatment temperature (unit: ° C.), the vertical axis represents the reduction rate from the resistance value (specific resistance) of the comparative example, and the right axis represents the F value. The heat treatment temperature shows the results of changing the reference temperature _{T 0} to _T 0 + 220 ° C.. When heat treatment is performed at T ₀ , the specific resistance value is reduced by about 0.5% compared to the specific resistance of the comparative example.

  As is clear from FIG. 3, it was confirmed that the resistance value decreased and took a minimum value as the heat treatment temperature was increased, and then increased from the minimum value to increase the resistance. That is, it was confirmed that the reduction rate of the resistance value took a maximum value as the temperature increased and then decreased. Further, it was confirmed that the F value took a maximum value as the heat treatment temperature was increased and then decreased. The resistance value and the F value show the same tendency with respect to the heat treatment temperature.

That is, by setting the F value to a certain value or more, the electric resistance value can be reduced, and the electric characteristics can be improved. Specifically, when the F value is 4.2 × 10 ⁵ pieces / m or more, the resistance value can be reduced by 10% or more compared to the comparative example.

  4A to 4C show the results of observing the surface of the conductor layer when the heat treatment conditions are varied. 4A shows the surface state of the conductor layer in the region A shown in FIG. 3, FIG. 4B shows the surface state of the conductor layer in the region B of FIG. 3, and FIG. 3 is a surface state of the conductor layer in the region C of FIG.

  In the region A, it can be confirmed that both the density and the particle size of the particles are smaller than those in the region B, and the particle size is smaller than that in the region C. Further, in the region A, as the heat treatment temperature is increased, both the abundance density and the particle size of the particles are increased.

  In the region B, the existence density was larger than those in the regions A and C. And in the area | region B, the particle size was substantially constant.

  In the region C, the particle size of the particles is larger than in the regions A and B, and the existence density is small. In the region C, as the heat treatment temperature was increased, the particle size was increased and the existence density was decreased.

As described above, in the region B, the amount of Cu in the conductor layer is optimized, and a large number of particles having a relatively small particle diameter are precipitated, so that the distribution of Cu and the state of the grain boundary in the conductor layer are biased. It is assumed that it can be in a state where there is no. For this reason, the electrical characteristics can be enhanced by setting the region B, that is, the F value to 4.2 × 10 ⁵ pieces / m or more.

  And by reducing the electrical resistance value of the conductor layer by 10% or more, heat generation when a high frequency signal is applied to the electrode portion 5 can be suppressed, and the power durability can be improved.

In addition, the same tendency was confirmed when the same measurement was performed by changing the addition amount of Cu within a range of less than 5 wt%. For this reason, it was confirmed that the electrical characteristics can be enhanced by setting the F value to 4.2 × 10 ⁵ pieces / m or more regardless of the amount of Cu added. In addition, it was confirmed that the reduction rate of the resistance value increased rapidly as the addition amount increased in the region where the addition amount of Cu was up to 1 wt%, and the degree of improvement in the reduction rate became moderate when it exceeded 1 wt%. From this result, it is good also considering the addition amount of Cu as 1 wt% or more. Note that the amount of Cu (the solid solution amount of Cu) in the conductor layer after the particles 51 are deposited may be 0.1 wt% or less. This is because, by calculation, it was confirmed that when the specific resistance was reduced by 10% or more when the Cu addition amount was 1 wt%, the residual Cu concentration in the solid solution was lowered to 0.1 wt% or less. In that case, the resistance value of the conductor layer can be reduced. The lower the residual solid solution concentration, the lower the resistivity.

  When the amount of Cu added is increased, the resistance value can be reduced by 10% or more even if the residual solid solution concentration is higher than 0.1 wt% while satisfying the above F value condition. On the other hand, when the residual solid solution concentration is 0.1 wt% or less while increasing the addition amount in the range of 1 wt% or more and less than 5 wt%, a higher resistance reduction rate can be realized.

  Furthermore, by reducing the particle size distribution of the particles 51, it is presumed that the distribution of Cu and the state of grain boundaries in the conductor layer can be made uniform, and the resistance value can be reduced.

In addition, as a result of measuring the value of the power durability when the particle size of the particles 51 was varied, it was confirmed that the power durability could be improved by reducing the particle size of the particles 51. Specifically, with respect to the comparative example, when the average particle size of the particles was reduced by 20%, the power durability could be increased from 27.3 dB to 27.5 dB. For this reason, by setting the F value to 4.2 × 10 ⁵ particles / m or more in a state where the particle size of the particles 51 is small, it is possible to reduce the resistivity and increase the power durability. Specifically, the average particle size may be 10 nm or less.

  In the above-described example, the particle 51 is measured by, for example, observing the surface state with a scanning electron microscope or the like, then capturing the image, and performing various processes such as binarization as necessary with image analysis software. To calculate. At this time, the “particle diameter” of the particle 51 is expressed by the average of the Ferret diameter. Even when the protective layer 6 is present above the conductor layer, it can be observed from above the protective layer 6. This is because the protective layer 6 is thin relative to the escape depth of the reflected electrons and secondary electrons. In order to facilitate identification of the particles 51, the surface state may be confirmed by a reflected electron image, if necessary.

(Modification)
In the example described above, the electrode unit 5 has been described using an example of a single layer film, but the electrode unit 5 may be a multilayer film. It may be a laminated film with a layer other than the Al—Cu alloy, or as shown in FIG. 5, a laminated body in which an underlayer 55 made of Ti or the like and a conductor layer 56 made of an Al—Cu alloy are repeatedly laminated. It may be. In that case, what is necessary is just to confirm the surface state of the conductor layer of the Al-Cu alloy located in the uppermost layer.

  In the above-described example, the example using the composite substrate of the support substrate and the piezoelectric substrate has been described. However, the present invention is not limited to this example. A thick piezoelectric substrate alone may be used, or a plurality of laminated films may exist between the support substrate and the piezoelectric substrate.

  Furthermore, the material which comprises a conductor layer is not limited to the example which adds only Cu to Al. For example, Mg may be added in addition to Cu to grow Al crystal grains and reduce grain boundaries.

<Usage example of SAW element>
Hereinafter, a duplexer and a communication device will be described as examples of use of the SAW element 1.

(Demultiplexer)
FIG. 6 is a schematic diagram showing a duplexer 101 as an example of use of the SAW element 1.

  The duplexer 101 filters, for example, the transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and filters the reception signal from the antenna terminal 103 and outputs it to the pair of reception terminals 107. A reception filter 111.

  The transmission filter 109 includes, for example, one or more series resonators S1 to S3 and one or more parallel resonators P1 to P3 connected in a ladder shape.

  The reception filter 111 is configured by, for example, a longitudinally coupled multiple mode (including a double mode) type resonator filter 17. A resonator 18 may be provided in the previous stage.

  At least one of the SAW resonators constituting the transmission filter 109 and the reception filter 111 is constituted by the SAW element 1.

(Communication device)
FIG. 7 is a block diagram showing a main part of the communication device 151 as an example of use of the SAW element 1.

  The communication device 151 performs wireless communication using radio waves. The communication device 151 uses the SAW element 1 by including the duplexer 101 described above. Specifically, it is as follows.

  In the communication device 151, a transmission information signal TIS including information to be transmitted is modulated and increased in frequency (converted to a high frequency signal of a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153, and is transmitted to the transmission signal TS. Is done. Unnecessary components other than the transmission passband are removed from the transmission signal TS by the bandpass filter 155, amplified by the amplifier 157, and input to the duplexer 101 (transmission terminal 105). Then, the duplexer 101 removes unnecessary components other than the transmission passband from the input transmission signal TS, and outputs the transmission signal TS after the removal from the antenna terminal 103 to the antenna 159. The antenna 159 converts the input electric signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

  In the communication device 151, a radio signal (radio wave) received by the antenna 159 is converted into an electric signal (reception signal RS) by the antenna 159 and input to the duplexer 101. The duplexer 101 removes unnecessary components other than the reception passband from the input reception signal RS and outputs the result to the amplifier 161. The output received signal RS is amplified by the amplifier 161, and unnecessary components other than the reception passband are removed by the band pass filter 163. Then, the reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 153 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, for example, analog audio signals or digitized audio signals. The passband of the radio signal may conform to various standards such as UMTS (Universal Mobile Telecommunications System). The transmission passband and the reception passband usually do not overlap each other. The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof. FIG. 7 schematically shows only the main part, and a low-pass filter, an isolator or the like may be added at an appropriate position, and the position of the amplifier or the like may be changed.

  DESCRIPTION OF SYMBOLS 1 ... Elastic wave element, 3 ... Bonded board | substrate, 5 ... Electrode part, 7 ... Piezoelectric substrate, 9 ... Support substrate, 11 ... IDT electrode

Claims (5)

A piezoelectric substrate having a first surface;
An electrode portion disposed on the first surface for exciting an elastic wave,
The electrode part includes a conductor layer made of Al to which less than 5 wt% of Cu is added, and a large number of particles made of Cu are located on the upper surface, and the value obtained by multiplying the number and the particle diameter is 4.2. The acoustic wave element which is × 10 ⁵ pieces / m or more.   The acoustic wave device according to claim 1, wherein the electrode part has a Cu solid solution concentration of 0.1 wt% or less.   3. The acoustic wave element according to claim 1, wherein the electrode portion includes a plurality of layers made of different materials, and the conductor layer is located on an uppermost layer thereof. The piezoelectric substrate has a second surface facing the first surface,
4. The acoustic wave device according to claim 1, further comprising a support substrate that is bonded to the second surface and is made of a material having a smaller linear expansion coefficient than a material constituting the piezoelectric substrate. 5. An antenna,
The antenna terminal is connected to the antenna, and a duplexer including a reception filter and a transmission filter including the elastic wave element according to any one of claims 1 to 7,
An IC connected to the transmission filter and the reception filter;
A communication device.