JP2008278546A - Surface wave device, and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface wave device capable of accurately manufacturing an IDT in which a propagation loss is nearly equal to zero in the IDT and a piezoelectric substrate. <P>SOLUTION: The IDT is composed of Au having a normalized film thickness H/λ=0.001 to 0.05 on a LiTaO<SB>3</SB>substrate having an Euler angle (0°, 125° to 137°, 0°±5°), and an SH wave having a small propagation loss is excited. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface wave device such as a surface wave resonator, a surface wave filter, and a duplexer, and more particularly to a surface wave device using SH waves.

  Conventionally, surface wave resonators have been widely used in bandpass filters and the like of mobile communication devices. As one of such surface wave resonators, a surface wave resonator having a structure in which an IDT (interdigital transducer) composed of comb-shaped electrodes arranged so that electrode fingers cross each other is formed on a piezoelectric substrate, or the surface thereof A surface wave device such as a surface wave filter using a wave resonator is well known.

As such a surface wave device, a leaky surface acoustic wave that propagates through a LiTaO ₃ substrate with Euler angles (0 °, −90 °, 0 °) is applied to a piezoelectric substrate, and Au, Ta, W are applied to the substrate surface. As described above, there is known a technique of converting an IDT having a predetermined film thickness from a metal having a large mass load into a Love wave type surface wave without propagation attenuation.

FIG. 11 shows Y-cut X propagation, that is, Euler angles are (0 °, −90 °, 0 °).
Shows how the electromechanical coupling coefficient k varies depending on the Au electrode thickness H / λ (electrode thickness / excited surface wave wavelength) when an Au electrode is formed on the LiTaO ₃ substrate. FIG.

  As shown in FIG. 11, a leaky surface acoustic wave is generated when the thickness of the Au electrode is H / λ = 0.03 or less, and a Love wave is generated when H / λ = 0.04 or more. I understand. FIG. 12 is a characteristic diagram showing the propagation loss (attenuation constant) of the leaky surface acoustic wave under the same conditions as in FIG. The solid line indicates the propagation loss when the electrode is electrically short-circuited, and the dotted line indicates the propagation loss when the electrode is electrically open. As shown in FIG. 12, the propagation loss is zero from around H / λ = 0.033 in the electrically shorted state and from around H / λ = 0.044 in the electrically open state. Therefore, in order to use an SH wave type surface wave having no propagation loss, although depending on the duty ratio of the IDT, the film thickness of the Au electrode in the electrically short-circuited state is at least H / λ = 0. It was necessary to make it thicker than 0.033. For example, in the case of materials such as Ta and W, since the density is smaller than that of Au, a film thickness larger than H / λ = 0.033 is required.

  However, as the thickness of the IDT is increased, the manufacturing accuracy is reduced as the thickness is increased. When the film thickness is Au to a certain extent, for example, if it is not thicker than H / λ = 0.033, there is a problem that the propagation loss does not become zero when the surface wave device is viewed from the viewpoint of propagation loss.

  Further, as the film thickness of the IDT, the film thickness H / λ (electrode thickness / excited SH wave wavelength) that can form the electrode finger of the IDT with general accuracy is assumed to be within 0.05. However, in order to reduce the propagation loss to 0, a film thickness larger than H / λ = 0.033 was required, and therefore the range of film thicknesses for forming IDT electrode fingers with high accuracy was narrow.

  Furthermore, when IDT is formed using, for example, Ta or W having a lower density than Au as an electrode material, a film thickness is required more than that of Au. Therefore, the propagation loss can be reduced to 0 in the range of film thickness that can be produced. There wasn't.

  Further, a material having a higher density such as Au than that of an electrode material generally used for an IDT of a surface wave device, such as Al, has a frequency variation due to slight variations in IDT film thickness, electrode finger width, and electrode finger pitch. Therefore, after the IDT is manufactured, the frequency is adjusted by trimming the IDT. However, for example, when an IDT of about H / λ = 0.034 is formed with Au and the frequency is lower than a desired frequency, the frequency adjustment is performed. As a result, the film thickness is from H / λ = 0.033. There has also been a problem that the propagation loss is not zero because it becomes smaller.

  In view of the above-described problems, the present invention provides a surface acoustic wave device that can manufacture an IDT with high accuracy, has substantially zero propagation loss in the IDT and the piezoelectric substrate, and can have a large frequency trimming adjustment range. The purpose is to do.

The surface acoustic wave device according to claim 1 includes a LiTaO ₃ substrate having an Euler angle (0 °, 125 ° to 137 °, 0 ° ± 5 °), and an IDT formed on the LiTaO ₃ substrate, The IDT is made of an electrode material containing Cu as a main component and is formed with a normalized film thickness H / λ = 0.003 to 0.05 to excite SH waves.

  The communication device according to claim 2 uses the surface acoustic wave device according to claim 1.

  With the configuration as described above, it is possible to obtain a surface acoustic wave device and a communication device with little leakage surface acoustic wave and small propagation loss.

As described above, according to the present invention, on a LiTaO ₃ substrate having an appropriate Euler angle,
By constructing an IDT with an appropriate film thickness, such as Au, Ag, Ta, Mo, Cu, Ni, Cr, Zn, Pt, W, etc., an IDT is configured to excite SH waves with low propagation loss. As a result, the surface acoustic wave component having a small propagation loss can be obtained because the leaky surface acoustic wave component is reduced.

  In addition, since the propagation loss becomes almost zero from the stage where the film thickness is extremely thin, even if the IDT is trimmed for frequency adjustment to change the film thickness, the propagation loss may be greatly deteriorated as in the prior art. In addition, the frequency trimming adjustment range can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a surface acoustic wave resonator cited as a surface acoustic wave device according to a first embodiment of the present invention. As shown in FIG. 1, the surface wave resonator 1 includes, for example, one IDT ₃ on a piezoelectric substrate 2 made of a LiTaO ₃ single crystal having Euler angles (0 °, 126 °, 0 °) and reflectors on both sides thereof. 4 and 4 are formed.

The IDT 3 has a pair of comb-shaped electrodes, each of which has at least one of Au, Ag, Ta, Mo, Cu, Ni, Cr, Zn, and W as a main component, and is arranged so that the respective comb-tooth portions face each other. It is constituted by.

Further, the electrode finger constituting the comb tooth portion of the IDT 3 has a normalized film thickness H / λ of 5%.
It is set to be within. That is, H / λ (electrode thickness / excited SH wave wavelength) ≦ 0.05 is set. This is the range in which the electrode fingers can be formed with high accuracy.

Next, a second embodiment of the present invention will be described. FIG. 2 is a plan view of a longitudinally coupled surface acoustic wave filter exemplified as a surface acoustic wave device showing a second embodiment of the present invention. As shown in FIG. 2, the longitudinally coupled surface wave filter 11 includes, for example, two IDTs 13a and 13b on both sides of a LiTaO ₃ single crystal having Euler angles (0 °, 126 °, 0 °) and both sides thereof. Are formed by forming the reflectors 14 and 14.

  The IDT 13 is formed of an electrode material mainly composed of at least one of Au, Ag, Ta, Mo, Cu, Ni, Cr, Zn, and W. It is comprised by arrange | positioning so that it may oppose. The IDTs 13a and 13b are arranged in parallel with a certain interval in the surface wave propagation direction. Also in the present embodiment, as in the first embodiment, the electrode fingers constituting the comb teeth of the IDTs 13a and 13b are set so that the normalized film thickness H / λ is within 5%. . That is, H / λ (electrode thickness / excited SH wave wavelength) ≦ 0.05 is set. This is the range in which the electrode fingers can be formed with high accuracy.

Next, a third embodiment of the present invention will be described. FIG. 3 is a plan view of a laterally coupled surface acoustic wave filter showing a third embodiment of the present invention. As shown in FIG. 3, the laterally coupled surface wave filter 21 includes, for example, two IDTs 23a and 23b on a piezoelectric substrate 22 made of a LiTaO ₃ single crystal having Euler angles (0 °, 126 °, 0 °) and its The reflectors 24a and 24b are formed on both sides.

  The IDTs 23a and 23b are made of an electrode material mainly composed of at least one of Au, Ag, Ta, Mo, Cu, Ni, Cr, Zn, and W, and a pair of comb-shaped electrodes is provided for each comb tooth portion. Are arranged so as to face each other. The IDTs 23a and 23b are arranged in a direction perpendicular to the surface wave propagation direction. Also in this embodiment, the electrode fingers constituting the comb teeth of the IDTs 23a and 23b are set so that the normalized film thickness H / λ is within 5% as in the first and second embodiments. Has been. That is, H / λ (electrode thickness / excited SH wave wavelength) ≦ 0.05 is set. This is the range in which the electrode fingers can be formed with high accuracy.

Next, a fourth embodiment of the present invention will be described. FIG. 4 is a plan view of a ladder-type surface acoustic wave filter cited as a surface acoustic wave device showing a fourth embodiment of the present invention. As shown in FIG. 4, a ladder-type surface acoustic wave filter 31 includes IDTs 33a and 33b on a piezoelectric substrate 32 made of a LiTaO ₃ single crystal having Euler angles (0 °, 126 °, 0 °) and reflectors on both sides thereof. It is configured by forming 34a and 34b.

  The IDTs 33a and 33b are formed of an electrode material containing at least one of Au, Ag, Ta, Mo, Cu, Ni, Cr, Zn, and W as a main component, and a pair of comb-shaped electrodes is provided for each comb tooth portion. Are arranged so as to face each other. Further, the IDT 33a is arranged on the serial arm, and the IDT 33b is arranged on the parallel arm, thereby forming a ladder type. Also in this embodiment, the electrode fingers constituting the comb tooth portions of the IDTs 33a and 33b are set so that the normalized film thickness H / λ is within 5% as in the first to third embodiments. ing. That is, H / λ (electrode thickness / excited SH wave wavelength) ≦ 0.05 is set. This is the range in which the electrode fingers can be formed with high accuracy.

  Next, fifth and sixth embodiments of the present invention will be described. FIG. 5 is a block diagram of a duplexer showing a fourth embodiment of the present invention and a communication device showing a fifth embodiment of the present invention.

  As shown in FIG. 5, in the communication device 41, the antenna terminal of the duplexer 44 having the reception surface wave filter 42 and the transmission surface wave filter 43 is connected to the antenna 45, and the output terminal is connected to the reception circuit 46. The input terminal is connected to the transmission circuit 47 and connected. For the reception surface wave filter 42 and the transmission surface wave filter 43 of the duplexer 44, any one or a combination of the surface wave filters 11 to 21 of the second to fourth embodiments is used.

Next, the normalized film thickness H / λ (electrode thickness / excited SH wave wavelength) of the IDT of the present invention will be described using examples. FIG. 6 shows the normalized film thickness H / λ (electrode thickness / excited) on the piezoelectric substrate including the case where the electrode is not formed on the LiTaO ₃ single crystal piezoelectric substrate with Euler angles (0 °, 126 °, 0 °). It is the figure which looked at the displacement of the propagation loss by changing the wavelength of the SH wave) between 0.00-0.05. Note that the electrodes are electrically short-circuited.

  As shown in FIG. 6, the propagation loss tends to gradually increase as the film thickness is increased for any material, but the value is smaller than that of the conventional Love wave filter indicated by the solid line in FIG. It is clear that there is. Further, as shown in FIG. 6, in Au, the propagation loss is the worst when H / λ = 0.025, but even in that case, the propagation loss is about 0.04 dB / λ. The propagation loss of the conventional Love wave filter shown by the solid line in FIG. 12 is 0.32 dB / λ when H / λ = 0.025, which is a propagation loss of 0.7 dB at the maximum. Is getting better.

Next, FIG. 7 shows the normalized film thickness H / λ (electrode thickness) on the piezoelectric substrate including the case where no electrode is formed on the LiTaO ₃ single crystal piezoelectric substrate with Euler angles (0 °, 126 °, 0 °). FIG. 5 is a diagram showing the displacement of the propagation loss by changing the wavelength of the excited SH wave) between 0.00 and 0.05. The electrodes are in an electrically open state.

  As shown in FIG. 7, the propagation loss tends to gradually increase as the film thickness is increased for any material, but the value is smaller than that of the conventional Love wave filter indicated by the dotted line in FIG. It is clear that there is. Further, as shown in FIG. 7, in Au, the propagation loss is the worst when H / λ = 0.029, but even in that case, the propagation loss is about 0.142 dB / λ. Compared with the propagation loss of the conventional Love wave filter indicated by the dotted line in FIG. 12 is 0.8 dB / λ at H / λ = 0.029 and 1.18 dB at the maximum, the propagation loss is remarkably higher. Is getting better.

These are SH waves with very small propagation loss in the surface wave device of the present invention, whereas Love waves are excited in the conventional LiTaO ₃ substrate of Euler angles (0 °, −90 °, 0 °). It is because it is used. Here, Au is explained, but not only Au but also other Ag, Ta, Mo, Cu, Ni, Cr, Zn, Pt, W, etc., the same SH wave can be used. Propagation loss is improved.

  Note that the film thickness at which the SH wave can be satisfactorily used in the surface wave device of the present invention varies depending on the electrode material. For example, H / λ = 0.001 in the case of Au, and H / λ = 0.002 in the case of Ag. In the case of Ta, H / λ = 0.002, in the case of Mo, H / λ = 0.005, in the case of Cu, H / λ = 0.003, in the case of Ni, H / λ = 0.006, In the case of Cr, H / λ = 0.003, in the case of Zn, H / λ = 0.003, and in the case of W, H / λ = 0.002, and these are considered in consideration of propagation loss and electromechanical coupling coefficient. A film thickness equal to or greater than the value of is appropriate.

  FIG. 8 is a characteristic diagram showing the change of the electromechanical coupling coefficient of each electrode material depending on the film thickness. Note that the same substrate material, cut angle, and propagation direction as those shown in FIGS. As shown in FIG. 8, it can be seen that a relatively large electromechanical coupling coefficient is obtained regardless of which metal material is used. Further, as shown in FIG. 8, other metal materials having a higher specific gravity have a larger electromechanical coupling coefficient than metal materials having a lower specific gravity such as Al.

  9 and 10 are characteristic diagrams showing the electrode film thickness and the cut angle θ at which the propagation loss becomes zero. FIG. 9 shows the cut angle θ at which the propagation loss is zero when the electrode is electrically short-circuited, and FIG. 10 is when the electrode is electrically open. An actual IDT has a portion with and without an electrode finger, and has a characteristic between FIG. 9 and FIG. 10 depending on its metallization ratio. The cut angle is set to (0 °, θ, 0 ° ± 5 °) in Euler angle display (φ, θ, ψ), and θ is changed. ψ indicates a propagation direction, and an error of about ± 5 ° is a propagation loss and is within an allowable range.

  9 and 10, when Au is used for an electrode such as IDT, the cut angles at which the propagation loss 0 can be realized are (0 °, 125 ° to 146 °, 0 °) in Euler angle display (φ, θ, ψ). ± 5 °).

In addition, when Ag is used for electrodes such as IDT, the cut angles that can achieve zero propagation loss are Euler angles (φ, θ, ψ) (0 °, 125 ° to 140 °, 0 ° ± 5 °).
It can be seen that it is.

  When Ta is used for an electrode such as IDT, the cut angle at which a propagation loss of 0 can be realized is Euler angle display (φ, θ, ψ) (0 °, 125 ° to 140 °, 0 ° ± 5 °). I understand that.

  When Mo is used for an electrode such as an IDT, the cut angles that can achieve zero propagation loss are Euler angles (φ, θ, ψ) (0 °, 125 ° to 134 °, 0 ° ± 5 °). I understand that.

  When Cu is used for an electrode such as IDT, the cut angles at which a propagation loss of 0 can be realized are Euler angles (φ, θ, ψ) (0 °, 125 ° to 137 °, 0 ° ± 5 °). I understand that.

  When Ni is used for an electrode such as IDT, the cut angles at which a propagation loss of 0 can be realized are Euler angles (φ, θ, ψ) (0 °, 125 ° to 133 °, 0 ° ± 5 °). I understand that.

  When Cr is used for an electrode such as IDT, the cut angles at which a propagation loss of 0 can be realized are Euler angles (φ, θ, ψ) (0 °, 125 ° to 147 °, 0 ° ± 5 °). I understand that.

  When Zn is used for an electrode such as an IDT, the cut angles at which a propagation loss of 0 can be realized are Euler angles (φ, θ, ψ) (0 °, 125 ° to 137 °, 0 ° ± 5 °). I understand that.

  When W is used for an electrode such as IDT, the cut angle at which zero propagation loss can be realized is (0 °, 125 ° to 138 °, 0 ° ± 5 °) in Euler angle display (φ, θ, ψ). I understand that.

Therefore, by using the LiTaO ₃ substrate having the cut angle shown in FIGS. 9 and 10 and the electrode material having such a film thickness, a surface wave device having substantially zero propagation loss can be obtained.

  In the first to sixth embodiments of the present invention, the surface wave device having a reflector has been described. However, the present invention is not limited to this and can be applied to a surface wave device having no reflector.

It is a top view of the surface wave resonator for demonstrating 1st Embodiment. It is a top view of the longitudinal coupling type surface acoustic wave filter for demonstrating 2nd Embodiment. It is a top view of the lateral coupling type surface acoustic wave filter for explaining a 3rd embodiment. It is a top view of the ladder type surface acoustic wave filter for explaining a 4th embodiment. It is a block diagram of the communication apparatus for demonstrating 5th, 6th embodiment. It is a characteristic view which shows the relationship between the normalized film thickness H / λ of the IDT and the propagation loss when the electrode of the surface acoustic wave device according to the present invention is electrically short-circuited. It is a characteristic view which shows the relationship between the normalized film thickness H / λ of the IDT and the propagation loss when the electrode of the surface acoustic wave device according to the present invention is in an electrically open state. It is a characteristic view which shows the relationship between the normalized film thickness H / λ of the IDT and the electromechanical coupling coefficient of the surface acoustic wave device according to the present invention. FIG. 6 is a characteristic diagram showing the relationship between the normalized film thickness H / λ of the IDT in which the electrode of the surface acoustic wave device according to the present invention is short-circuited and the cut angle at which the propagation loss becomes zero. It is a characteristic view which shows the relationship between the normalized film thickness H / λ of the IDT in which the electrode of the surface acoustic wave device according to the present invention is open and the electromechanical coupling coefficient. It is a characteristic view showing the relationship between the normalized film thickness H / λ of the IDT of the conventional surface wave device and the electromechanical coupling coefficient k. It is a characteristic view showing the relationship between the normalized film thickness H / λ of the IDT of the conventional surface wave device and the propagation loss.

Explanation of symbols

1 Surface Wave Resonator 2 Piezoelectric Substrate 3 IDT
4 reflectors

Claims (3)

A LiTaO ₃ substrate having an Euler angle (0 °, 125 ° to 137 °, 0 ° ± 5 °), and an IDT formed on the LiTaO ₃ substrate,
The IDT is made of an electrode material containing Cu as a main component, and is formed with a normalized film thickness H / λ = 0.003 to 0.05, thereby exciting the SH wave. Surface wave device.   The surface acoustic wave device according to claim 1, wherein the IDT is formed with a normalized film thickness H / λ = 0.04 to 0.05.   A communication apparatus using the surface acoustic wave device according to claim 1.

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