JP2006237750A - Surface acoustic wave device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device excellent in various characteristics (particularly, a temperature characteristic) and to provide an electronic apparatus with the surface acoustic wave device. <P>SOLUTION: The surface acoustic wave device 1 includes: a crystal substrate 2 wherein the Euler's angle is expressed as (0, θ, ψ); an IDT 3, reflectors 4, 5 provided on the substrate 2; and an insulation protection film selectively provided to upper faces of the reflectors 4, 5. The IDT 3 and the reflectors 4, 5 of the surface acoustic wave device 1 are laid out so that an angle ψ between a propagation direction of a surface acoustic wave and the X axis of the substrate 2 is 90±10° and a surface acoustic traversal wave is stimulated. Then it is characterized in that the cut angle θ is 126 to 150°and the normalized film thickness Hz/λ of the insulation protection film (wherein Hz is an average thickness of the insulation protection film, and λ is a wavelength of the surface acoustic traversal wave) is 0.02 to 0.4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave element and an electronic apparatus.

A wave that propagates with energy concentrated near the surface of the propagation medium is known as a surface acoustic wave (SAW).
A surface acoustic wave element is an element that uses such a surface acoustic wave, such as a band-pass filter for a communication device such as a mobile phone, a resonator as a reference clock, a signal processing delay element (in particular, a Fourier transform functional element). ), Various sensors such as pressure sensors and temperature sensors, and optical deflectors.

  For example, a surface acoustic wave element used as a filter or resonator is a piezoelectric substrate as a surface acoustic wave propagation medium, and an input device that is arranged on the piezoelectric substrate and applies a voltage that excites the surface acoustic wave to the piezoelectric substrate. And a pair of interdigital electrodes (IDT) for detecting and outputting surface acoustic waves propagating through the piezoelectric substrate, converting them into electrical signals, and a pair of IDTs disposed on both sides of the IDT And a reflector.

In such a surface acoustic wave element, when AC power (electric signal) is supplied to the input IDT, the piezoelectric base is distorted by the electric field generated by the AC power. At this time, the electrodes that generate this electric field have a comb-like shape, so that the piezoelectric substrate becomes dense, thereby generating surface acoustic waves.
This surface acoustic wave propagates to both sides of the IDT, is reflected by the reflector, and resonance occurs between the reflectors. The surface acoustic wave energy is converted into electrical energy by the output IDT and output.

Incidentally, as for the characteristics required of the surface acoustic wave device, (the temperature characteristic is good) that the frequency variation is small with respect to temperature changes, it electromechanical coupling coefficient k ² is large to some extent, also when using a reflector Has a large reflection coefficient of surface acoustic waves.
Among these, temperature characteristics are particularly important in a surface acoustic wave device used as a resonator or a narrow band filter.

As a surface acoustic wave element having excellent temperature characteristics, there is an element in which an IDT or a reflector is formed on a quartz substrate of ST cut 0 ° X-axis propagation and Rayleigh waves generated by the excitation of the IDT are used.
In general, the frequency of a surface acoustic wave is defined by f (frequency) = V (sound speed) / λ (wavelength). In order to increase the frequency when the comb electrodes have the same wavelength, it is desirable to use a substrate having a high sound speed.

Rayleigh waves usually have a slow sound speed of around 3000 m / s, which is desirable as an element of several hundred MHz, but for 1 GHz or more, the wavelength of the electrode pair of the comb-teeth electrodes must be shortened, and the accuracy of photolithography In addition, it is difficult to ensure electrode deposition accuracy and etching accuracy. For example, when the line width and space width of the comb electrode are set to 1: 1, the line width for realizing 1.5 GHz is 0.5 μm or less, which is difficult in terms of accuracy in consideration of mass production. .
In addition, as a surface acoustic wave element using a shear horizontal wave (SH wave), an element in which an IDT or a reflector is formed on an ST-cut 90 ° X-axis propagation quartz substrate has been proposed (for example, a patent) (Refer to Literature 1, Patent Literature 2, and Patent Literature 3.)

  On the quartz substrate, the SH wave using the transverse wave type surface acoustic wave is generally called STW (Surface Transversal Wave) (for example, refer to Patent Document 4), and the sound velocity is about 5000 m / second. The surface acoustic wave element using STW is applied to a surface acoustic wave element of 1 GHz or more because it has 1.6 times the ST cut and 1.6 times the high frequency of the same pattern. .

Further, it is widely known that a quartz substrate has a cut angle at which the frequency temperature characteristic (TCF), which is a first-order temperature coefficient, is “0” in STW.
However, the surface acoustic wave element described in Patent Document 4 uses a quartz substrate having a cut angle near θ of 128.4 °, and has a drawback that the second-order temperature coefficient is worse than the ST-cut Rayleigh wave.

Japanese Examined Patent Publication No. 61-45892 JP-A-10-233645 Japanese Patent Laid-Open No. 2000-323958 US Pat. 4965479

  An object of the present invention is to provide a surface acoustic wave element that is excellent in various characteristics (particularly temperature characteristics), and an electronic apparatus including the surface acoustic wave element.

Such an object is achieved by the present invention described below.
The surface acoustic wave device of the present invention includes a quartz substrate whose Euler angles are represented by (0, θ, ψ),
A function of converting an electrical signal into a surface acoustic wave propagating near the surface of the quartz substrate and / or a function of converting a surface acoustic wave propagating near the surface of the quartz substrate into an electrical signal provided on the quartz substrate; A comb electrode having a plurality of electrode fingers;
Having at least an insulating film provided on the surface of each electrode finger opposite to the quartz substrate;
The comb electrode is arranged so that an angle ψ formed by the propagation direction of the surface acoustic wave and the X axis of the quartz crystal substrate is 90 ± 10 °, and a transverse type surface acoustic wave is excited. A surface acoustic wave device,
The cut angle θ is 126 to 150 °,
The normalized film thickness Hz / λ (Hz indicates the average thickness of the insulating film, and λ indicates the wavelength of the transverse wave type surface acoustic wave) is 0.02 to 0.4. And
As a result, a surface acoustic wave element having excellent secondary temperature coefficient β (that is, temperature characteristics) and excellent insulation resistance can be obtained.

In the surface acoustic wave device of the present invention, the insulating film is composed of SiO ₂ as a main material,
The normalized film thickness Hz / λ of the insulating film is preferably 0.03 to 0.38.
Thereby, the secondary temperature characteristic β can be further improved, and the insulation resistance can be improved.
In the surface acoustic wave device of the present invention, the insulating film is composed of Al ₂ O ₃ as a main material,
The normalized film thickness Hz / λ of the insulating film is preferably 0.04 to 0.4.
Thereby, the secondary temperature characteristic β can be further improved, and the insulation resistance can be improved.

In the surface acoustic wave element according to the present invention, it is preferable that the insulating film is provided so as to cover an upper surface or a surface of each electrode finger.
Thereby, the internal stress of the insulating film acts in the direction in which the quartz substrate is bent, and the temperature characteristics of the surface acoustic wave element can be changed.
In the surface acoustic wave device according to the aspect of the invention, it is preferable that the insulating film is provided so as to cover a surface of each electrode finger and a portion of the quartz substrate exposed from each electrode finger.
As a result, the internal stress of the insulating film acts more greatly in the direction in which the quartz substrate is bent, and the temperature characteristics of the surface acoustic wave element can be changed more reliably.

In the surface acoustic wave device of the present invention, it is preferable that the comb electrode is composed of Al as a main material.
Since Al has a low electric resistance, energy loss is reduced by configuring the comb electrode with Al as the main material.
In the surface acoustic wave device of the present invention, the normalized film thickness H / λ of the comb electrode (H represents the average thickness of the comb electrode, and λ represents the wavelength of the transverse surface acoustic wave) is 0. 0.03 to 0.14 is preferable.
Thus, a more improved temperature characteristics, the electromechanical coupling coefficient k ² is large, it is possible to reduce the energy loss during the electromechanical transducer.

In the surface acoustic wave device of the present invention, it is preferable that the normalized film thickness H / λ of the comb electrode and the cut angle θ are set so as to satisfy the relationship A shown below.
[Relationship A]
θmin ≦ θ ≦ θmax
θmax = 3344.8 (H / λ) ² −143.65 (H / λ) +129.098
θmin = 2560.4 (H / λ) ² −147.18 (H / λ) +122.8
Thereby, the apex temperature in the temperature characteristics (hereinafter simply referred to as “apex temperature”) can be set at or near the actual use temperature range of the surface acoustic wave element. The temperature characteristics in the range become better.

In the surface acoustic wave device according to the present invention, a pair of reflectors provided via the comb electrodes and including a plurality of reflectors are provided.
The reflectors are arranged such that an angle ψ formed by the propagation direction of the surface acoustic wave and the X axis of the quartz crystal substrate is 90 ± 10 °.
It is preferable that the insulating film is further provided on at least a surface of each reflector opposite to the quartz substrate.
Thereby, various characteristics (especially temperature characteristics) of the surface acoustic wave element can be further improved.

In the surface acoustic wave device of the present invention, it is preferable that each of the reflectors is made of Al as a main material.
Thereby, various characteristics (especially temperature characteristics) of the surface acoustic wave element can be further improved.
In the surface acoustic wave device of the present invention, it is preferable that the normalized film thickness of each reflector is 0.03 to 0.14.
Thereby, various characteristics (especially temperature characteristics) of the surface acoustic wave element can be further improved.
In the surface acoustic wave device of the present invention, it is preferable that the normalized film thickness of each reflector and the cut angle θ are set so as to satisfy the relationship A.
Thereby, various characteristics (especially temperature characteristics) of the surface acoustic wave element can be further improved.
An electronic apparatus according to the present invention includes the surface acoustic wave element according to the present invention.
As a result, a highly reliable electronic device can be obtained.

Hereinafter, preferred embodiments of the surface acoustic wave device and the electronic apparatus of the present invention will be described.
<First Embodiment>
FIG. 1 is a perspective view schematically showing a first embodiment of a surface acoustic wave device according to the present invention, and FIG. 2 is a cross-sectional view of the surface acoustic wave device shown in FIG. In the following description, the upper side in FIG. 2 is referred to as “upper” and the lower side is referred to as “lower”.

A surface acoustic wave device 1 shown in FIGS. 1 and 2 includes a substrate 2, an IDT 3 provided on the substrate 2, a pair of reflectors 4 and 5 disposed on both sides of the IDT 3, and the IDT 3 and the reflector 4 5 and an insulating protective film (insulating film) 6 provided on the upper surface (surface opposite to the substrate 2).
This surface acoustic wave element 1 is a so-called one-port type element, and includes electrodes 3a and 3b having a function of applying a voltage to the substrate 2 to excite the surface acoustic wave on the substrate 2. . In the present embodiment, each of the electrodes 3a and 3b also has a function of converting a surface acoustic wave into an electric signal.
Each reflector 4, 5 has a function of reflecting the surface acoustic wave propagating to the substrate 2 and confining it between the reflector 4 and the reflector 5.

When a driving voltage is input to the IDT 3 (each electrode 3a, 3b), a surface acoustic wave is excited near the surface of the substrate 2, and an electrical signal having a specific frequency due to resonance is output from the IDT 3 (each electrode 3a, 3b). .
Each of the electrodes 3a and 3b has a plurality of electrode fingers 31 arranged in parallel at predetermined intervals, and has a comb-like shape as a whole.
Each reflector 4 and 5 has a plurality of reflectors 41 and 51 arranged in parallel at a predetermined interval, and has a grating shape as a whole. Thereby, each reflector 4 and 5 is each comprised so that a surface acoustic wave can be reflected efficiently.

By adjusting the width, interval, pitch, thickness, etc. of the electrode fingers 31 and the reflectors 41, 51, characteristics such as the oscillation frequency of the surface acoustic wave excited in the surface acoustic wave element 1 can be made desired. Can be set.
The configurations of the reflectors 4 and 5 may be the same or different from each other, but are preferably substantially the same. Thereby, a surface acoustic wave can be more reliably contained between the reflector 4 and the reflector 5, and as a result, a surface acoustic wave can be resonated more greatly.

The separation distance f between the IDT 3 and each reflector 4, 5, that is, the separation between the center point of the electrode finger 31 closest to the reflector 4 (5) and the center point of the reflector 41 (51) closest to the IDT 3. The distance f is preferably about 0.1 to 0.8 times the wavelength λ of the surface acoustic wave excited on the substrate 2 or a value obtained by adding an integral multiple of one half of the wavelength to 0. More preferably, it is about 4 to 0.6 times or its value plus an integral multiple of half the wavelength.
Further, the end face distance g between the IDT 3 and each of the reflectors 4 and 5 is about 0.05 to 0.4 times the wavelength λ of the surface acoustic wave excited on the substrate 2 or a value obtained by adding an integral multiple of the wavelength to that value. It is preferably about 0.2 to 0.3 times or a value obtained by adding an integral multiple of the wavelength to the value.
By setting as described above, the deviation between the phase of the surface acoustic wave at the IDT 3 and the phase of the surface acoustic wave at the reflectors 4 and 5 can be reduced. As a result, the reflectors 4 and 5 Resonance of the surface acoustic wave due to is more efficiently performed.

In the present invention, a quartz crystal substrate represented by Euler angles (0, θ, ψ) is used as the substrate 2.
By using a quartz substrate as the substrate 2, a surface acoustic wave having a large electromechanical coupling coefficient k ² is excited in the surface acoustic wave element 1.
Here, the general definition of Euler angles (φ, θ, ψ) is as follows. That is, the device coordinate system (X, Y, Z) is rotated by φ around the Z axis, then the device is rotated by θ around the new Y ′ axis after φ rotation, and finally the new after rotation by θ Each angle when rotating around the Z ″ axis by ψ.
In the present invention, the angle ψ is set to 90 ± 10 °. That is, in the surface acoustic wave element 1, the IDT 3 and the reflectors 4 and 5 are propagated in the vicinity of the surface of the substrate 2 by the IDT 3 (the direction substantially perpendicular to the longitudinal direction of the electrode fingers 31). ) Is arranged to be 90 ± 10 ° with respect to the X axis of the substrate 2.

Further, the cut angle θ is set to 126 to 150 °.
First, the reason why the angle ψ is set to 90 ± 10 ° will be described.
FIG. 3 is a graph showing the relationship between the angle ψ and the electromechanical coupling coefficient k ^{2 of} various surface acoustic waves.
As shown in FIG. 3, the Rayleigh wave decreases as the angle ψ increases and becomes almost zero at 90 °. On the other hand, the surface wave of shear wave (SH wave) (Surface Transversal Wave: STW) has a large peak when the angle ψ is in the range of 80 ° to 100 °.
Therefore, by setting the angle ψ to 90 ± 10 °, the surface acoustic wave mainly composed of STW is efficiently excited by the IDT 3. In the present invention, this shear wave type surface acoustic wave (STW) is used. Since this STW has a high sound speed, the surface acoustic wave element 1 can be made to have a higher frequency by using a surface acoustic wave having STW as a main component.

In particular, the angle ψ is preferably set to 90 ± 2 °. Thereby, STW can be efficiently used as a surface acoustic wave. Further, as the surface acoustic wave, it becomes particularly large waves electromechanical coupling coefficient k ² is excited, the energy loss during the conversion of the electrical signal and a surface acoustic wave (insertion loss) is suppressed.
In addition, since STW has a large reflection coefficient at each of the reflectors 4 and 5, the number of reflectors 41 and 51 can be suppressed to be small, and the surface acoustic wave element 1 can be downsized.

Next, the reason why the cut angle θ is set to 126 to 150 ° will be described.
FIG. 4 is a graph showing the relationship between the cut angle θ of the quartz substrate, the secondary temperature coefficient β, and the normalized film thickness Hz / λ of the insulating protective film.
Here, Hz indicates the average thickness of the insulating protective film 6, and λ indicates the wavelength of STW (transverse wave type surface acoustic wave).

The secondary temperature coefficient β is a characteristic value indicating a secondary fluctuation amount of the frequency with respect to a temperature change. The average thickness (film thickness) of the IDT 3 (comb electrode) is set to an optimum value, and the primary temperature coefficient is set. This is a temperature characteristic that appears when the value nears “0”.
Here, the primary temperature coefficient is generally labeled as a temperature coefficient (TCF or α), and TCF = “0” indicates that the primary temperature coefficient α is “0”.
Note that the closer the value of the secondary temperature coefficient β is to “0”, the better the temperature characteristics can be obtained.

As shown in FIG. 4, the secondary temperature coefficient β has a correlation with the cut angle θ of the quartz substrate, and becomes smaller as the cut angle θ increases.
Therefore, if a quartz substrate having a larger cut angle θ is selected, the surface acoustic wave device 1 with better temperature characteristics can be produced. In practice, however, the surface thickness between the cut angle θ and the standardized film thickness of the IDT 3 can be reduced. In addition, since there is a relationship as will be described later, in order to maintain good temperature characteristics, if the cut angle θ of the quartz substrate is set large, the film thickness of the IDT 3 must be increased.
For this reason, in the process of forming IDT 3 (during film formation or etching), there is a problem that the thickness of IDT 3 is likely to vary and a problem that a long time is required for film formation, and the cut angle θ is simply set. There is a limit to the increase.

Considering this, the cut angle θ of the quartz substrate is set in the range of 126 to 150 °. Thereby, the secondary temperature coefficient β can be brought close to “0”, and as a result, the temperature characteristics of the surface acoustic wave element 1 can be improved.
As shown in FIG. 4, the secondary temperature coefficient β varies depending on the film thickness (standardized film thickness) of the insulating protective film 6. In the present invention, the temperature characteristics of the surface acoustic wave element 1 are further optimized by setting the normalized film thickness Hz / λ of the insulating protective film 6. This point will be described later.
Although the thickness (average) of such a board | substrate 2 is not specifically limited, It is preferable that it is about 0.05-1 mm, and it is more preferable that it is about 0.1-0.8 mm.

The insulating protective film 6 has a function of preventing foreign matter from adhering to the surfaces of the IDT 3 and the reflectors 4 and 5 and preventing a short circuit between the electrode fingers 31 via the foreign matter.
In the present embodiment, the insulating protective film 6 is selectively provided on the upper surfaces of the IDT 3 (electrode finger 31) and the reflectors 4 and 5 (reflectors 41 and 51) as shown in FIG. The sides of the vessels 4 and 5 are exposed.

The present invention is characterized in that the normalized film thickness Hz / λ of the insulating protective film 6 is set to 0.02 to 0.4. As a result, the secondary temperature coefficient β can be reliably improved (improved), that is, the temperature characteristic (frequency fluctuation accompanying temperature change) can be reliably improved (improved). Incidentally, when the Hz / lambda is greater than 0.4, since the electromechanical coupling coefficient k ² becomes small, the characteristics of the surface acoustic wave device decreases.
Examples of the constituent material of the insulating protective film 6 include SiO ₂ (silicon oxide) or oxides such as SiO _x , Al ₂ O ₃ , Cu ₂ O, Ta ₂ O ₅ , and TiO ₂ , Si _x N _y , Examples thereof include nitrides such as AlN, carbides such as TiC and SiC, and one or more of these can be used in combination.

Among these, as a constituent material of the insulating protective film 6, a material containing at least one of SiO ₂ , Al ₂ O ₃ , and Si _x N _y as a main component is preferable. The insulating protective film 6 containing these materials as a main material is preferable because it can be formed relatively easily by a sputtering method or a CVD method and has a particularly high insulating property.
In particular, the insulating protective film 6 containing silicon oxide as a main material has a property that the frequency increases as the temperature increases. Therefore, there is an effect of setting the apex temperature higher. In addition, the insulating protective film 6 mainly composed of other materials has an effect of setting the apex temperature to be lower.

When the insulating protective film 6 is made of SiO ₂ as a main material, the normalized film thickness Hz / λ of the insulating protective film 6 is preferably set to 0.03 to 0.38.
When the insulating protective film 6 is made of Al ₂ O ₃ as the main material, the normalized film thickness Hz / λ of the insulating protective film 6 is preferably set to 0.04 to 0.4.
By setting the normalized film thickness Hz / λ of the insulating protective film 6 within such a range, temperature characteristics (frequency temperature characteristics) can be reduced while preventing or suppressing a decrease in the oscillation frequency of the STW accompanying an increase in mass. It can be improved (improved). Moreover, sufficient insulation is exhibited.

Next, the configuration of IDT 3 will be described.
As a constituent material of IDT3, for example, Al, Ta, W, Au, Pt or an alloy containing these can be used, and one or more of these can be used in combination.
Among these, as a constituent material of IDT3, a material mainly composed of Al is preferable. Since Al has a small electric resistance, energy loss is reduced by configuring IDT 3 with Al as a main material. For this reason, in the surface acoustic wave element 1, the resonance of the surface acoustic wave becomes sharper.

Moreover, since Al has a small specific gravity, a change in sound speed depending on the film thickness of IDT 3 can be suppressed to a small level. Therefore, variations in the center frequency can be suppressed.
In addition, since the film thickness of the IDT 3 can be easily controlled, the highly accurate surface acoustic wave element 1 can be obtained.
Furthermore, the migration resistance of IDT 3 can be improved by adding Cu, Si, Ti, Mo, Sc or the like to Al.

Such an IDT 3 may have a multilayer structure in which an electrode layer serving as a barrier metal is provided on at least one of the upper surface and the lower surface of the electrode layer serving as a skeleton.
IDT3 is I: the normalized film thickness H / λ (H is the average thickness of IDT3, λ is the STW wavelength), and II is the normalized film thickness H / λ and quartz. It is preferable that any one of the relations with the cut angle θ of the substrate satisfies the following conditions, and it is more preferable that both satisfy the following conditions.

I: The normalized film thickness H / λ of IDT3 is preferably about 0.03 to 0.14, and more preferably about 0.055 to 0.125. With the the normalized thickness H / lambda range of IDT 3, a more improved temperature characteristics, the electromechanical coupling coefficient k ² is large, it is possible to reduce the energy loss during the electromechanical transducer .
In addition, by setting the normalized film thickness H / λ of the IDT 3 within the above range, the mass loading effect of the IDT 3 is preferably exhibited, and the STW can be confined near the surface of the quartz substrate. As a result, in the surface acoustic wave element 1, the STW is favorably excited.

II: It is preferable that the normalized film thickness H / λ of IDT 3 and the cut angle θ of the substrate 2 satisfy the following relationship A.
[Relationship A]
θmin ≦ θ ≦ θmax
θmax = 3344.8 (H / λ) ² −143.65 (H / λ) +129.098
θmin = 2560.4 (H / λ) ² −147.18 (H / λ) +122.8
[Relationship A ']
θmin '≦ θ ≦ θmax'
θmax ′ = 2747.8 (H / λ) ² −72.4 (H / λ) +121.5
θmin ′ = 2560.4 (H / λ) ² −147.18 (H / λ) +122.8
FIG. 5 is a graph showing the relationship between the normalized film thickness H / λ of IDT and the cut angle θ of the quartz substrate.

The range satisfying the relationship A is a range indicated by a region X in FIG. 5, and the range satisfying the relationship A ′ is a range indicated by a region Y in FIG.
By setting the cut angle θ and the normalized film thickness H / λ of the IDT 3 to values that satisfy the relationship in the region X, the apex temperature is set at or near the actual operating temperature range of the surface acoustic wave device 1. Therefore, the surface acoustic wave device 1 has better temperature characteristics in the actual use temperature range. Further, by setting the value to satisfy the relationship in the region Y, the effect becomes more remarkable.

Each reflector 4 and 5 preferably has the same configuration as IDT 3. That is, each of the reflectors 4 and 5 is made of the same material as that of the IDT 3, the normalized film thickness is set in the range of 0.03 to 0.14, and the normalized film It is preferable that the thickness and the cut angle θ satisfy the relationship A (particularly, the relationship A ′).
Thereby, various characteristics of the surface acoustic wave element 1 can be further improved. Moreover, since each reflector 4 and 5 can be formed simultaneously with IDT3, the manufacturing process of the surface acoustic wave element 1 can also be simplified.

Moreover, the reflectance of STW can be made sufficiently large by making the normalized film thickness of each reflector 4 and 5 the same as that of IDT3. For this reason, the number of the reflectors 41 and 51 can be reduced, and there exists an advantage that size reduction of the surface acoustic wave element 1 can be achieved.
In addition, you may make it set the normalized film thickness of each reflector 4 and 5 so that it may differ from IDT3 as needed.

The surface acoustic wave element 1 as described above uses a quartz substrate as the substrate 2, the Euler angles (0, θ, ψ), the angle ψ, the cut angle θ, and the normalized film thickness Hz of the insulating protective film 6. Various characteristics (especially temperature characteristics) are improved by a synergistic effect by setting (defining) / λ.
Further, by setting (specifying) the IDT3 constituent material, the IDT3 normalized film thickness H / λ, and the relationship between the IDT3 normalized film thickness H / λ and the cut angle θ, the above effects can be further improved. Can be improved.
In the present embodiment, the case where the insulating protective film 6 is selectively provided on the upper surfaces of the IDT 3 and the reflectors 4 and 5 has been described. However, the configuration (shape) of the insulating protective film 6 is shown in FIGS. You may make it show.

FIG. 6 and FIG. 7 are diagrams showing other configuration examples of the insulating protective film, respectively. In the following description, the upper side in FIGS. 6 and 7 is referred to as “upper” and the lower side is referred to as “lower”.
6 is provided so as to cover the surfaces of the IDT 3 (each electrode finger 31) and the reflectors 4, 5 (each reflector 41, 51). Thereby, the internal stress of the insulating protective film 6 ′ acts in the direction in which the substrate 2 is bent, and the temperature characteristics can be changed as compared with the case where the insulating protective film 6 shown in FIG. 2 is provided.

7 includes the IDT 3 (each electrode finger 31) and the surfaces of the reflectors 4 and 5 (each reflector 41, 51), the IDT 3 (each electrode finger 31) and the reflection of the substrate 2. It is provided so as to cover the portions (surface acoustic wave propagation portions) exposed from the containers 4 and 5 (respective reflectors 41 and 51). By providing such an insulating protective film 6 ″, it acts more greatly in the direction in which the substrate 2 is bent, and the temperature characteristics can be changed more reliably than when the insulating protective film 6 shown in FIG. 2 is provided. it can.
In addition, the insulating protective film 6 ″ having such a configuration also has an advantage that it is easy to form a film having a relatively large thickness.
In addition to changing the normalized film thickness of the insulating protective film, the temperature characteristics of the surface acoustic wave element 1 can be further finely adjusted by changing the configuration of the insulating protective film.

Second Embodiment
Next, a second embodiment of the surface acoustic wave device of the present invention will be described.
FIG. 8 is a perspective view showing a second embodiment of the surface acoustic wave element of the present invention, and FIG. 9 is a cross-sectional view of the surface acoustic wave element shown in FIG. In the following description, the upper side in FIG. 9 is referred to as “upper” and the lower side is referred to as “lower”.

Hereinafter, the surface acoustic wave element according to the second embodiment will be described with a focus on differences from the surface acoustic wave element 1 according to the first embodiment, and description of similar matters will be omitted.
The surface acoustic wave element 7 according to the second embodiment is provided with an input IDT 8 and an output IDT 9 in place of the IDT 3 that functions to excite the surface acoustic wave and convert the surface acoustic wave into an electric signal. Except for this, it is the same as the surface acoustic wave element 1 of the first embodiment.

The IDT (input side electrode) 8 has a function of applying a voltage to the substrate 2 to excite a surface acoustic wave near the surface of the substrate 2, while the IDT (output side electrode) 9 is a substrate 2. The surface acoustic wave propagating in the vicinity of the surface is detected, and the surface acoustic wave is converted into an electrical signal and output to the outside.
Therefore, when a driving voltage is input to the IDT 8, a surface acoustic wave is excited in the substrate 2, and an electrical signal having a specific frequency due to resonance is output from the IDT 9.
Each IDT 8 and 9 has a comb-like shape having a plurality of electrode fingers 81 and 91 arranged in parallel at a predetermined interval, and the width, interval, pitch and thickness of the electrode fingers 81 and 91 of each IDT 8 and 9. By adjusting the thickness and the like, it is possible to set characteristics such as the oscillation frequency of the surface acoustic wave to a desired one.

Also in the surface acoustic wave element 7 of the second embodiment, a quartz substrate is used as the substrate 2, its Euler angles (0, θ, ψ), the angle ψ, the cut angle θ, and the normalized film of the insulating protective film 6. For example, excellent performance as a narrow band filter can be obtained and energy loss can be reduced by the synergistic effect by setting (specifying) the thickness Hz / λ.
Further, the constituent materials of IDTs 8 and 9, the normalized film thickness H / λ of IDTs 8 and 9, and the relationship between the normalized film thickness H / λ of IDTs 8 and 9 and the cut angle θ are set (specified), respectively. Thus, the effect can be further improved.
Also in this embodiment, instead of the insulating protective film 6, insulating protective films 6 ′ and 6 ″ can be provided.
The surface acoustic wave elements 1 and 7 as described above can be applied to various electronic devices, and the obtained electronic devices have high reliability.

Next, an electronic apparatus including the surface acoustic wave element according to the present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 10 is a perspective view showing a configuration of a mobile (or notebook) personal computer to which an electronic device including the surface acoustic wave element of the present invention is applied.
In this figure, a personal computer 1100 includes a main body 1104 having a keyboard 1102 and a display unit 1106. The display unit 1106 is supported by the main body 1104 via a hinge structure so as to be rotatable. Yes.
Such a personal computer 1100 includes a surface acoustic wave element 1 (or 7) and an antenna 1101 that function as a filter, a resonator, a reference clock, and the like.

FIG. 11 is a perspective view showing a configuration of a mobile phone (including PHS) to which an electronic apparatus including the surface acoustic wave element of the present invention is applied.
In this figure, a cellular phone 1200 includes an antenna 1201, a plurality of operation buttons 1202, an earpiece 1204, and a mouthpiece 1206, and a display unit is disposed between the operation buttons 1202 and the earpiece 1204.
Such a cellular phone 1200 incorporates a surface acoustic wave element 1 (or 7) that functions as a filter, a resonator, or the like.

FIG. 12 is a perspective view illustrating a configuration of a digital still camera to which an electronic apparatus including the surface acoustic wave element according to the invention is applied. In this figure, connection with an external device is also simply shown.
Here, an ordinary camera sensitizes a silver halide photographic film with a light image of a subject, whereas a digital still camera 1300 photoelectrically converts a light image of a subject with an imaging device such as a CCD (Charge Coupled Device). An imaging signal (image signal) is generated.

A display unit is provided on the back of a case (body) 1302 in the digital still camera 1300, and is configured to display based on an imaging signal from the CCD. The display unit is a finder that displays an object as an electronic image. Function.
A light receiving unit 1304 including an optical lens (imaging optical system), a CCD, and the like is provided on the front side (the back side in the drawing) of the case 1302.
When the photographer confirms the subject image displayed on the display unit and presses the shutter button 1306, the CCD image pickup signal at that time is transferred and stored in the memory 1308.

In the digital still camera 1300, a video signal output terminal 1312 and an input / output terminal 1314 for data communication are provided on the side surface of the case 1302. As shown in the figure, a television monitor 1430 is connected to the video signal output terminal 1312 and a personal computer 1440 is connected to the input / output terminal 1314 for data communication as necessary. Further, the imaging signal stored in the memory 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation.
Such a digital still camera 1300 incorporates a surface acoustic wave element 1 (or 7) that functions as a filter, a resonator, or the like.

  In addition to the personal computer (mobile personal computer) shown in FIG. 10, the mobile phone shown in FIG. 11, and the digital still camera shown in FIG. (For example, inkjet printers), laptop personal computers, televisions, video cameras, video tape recorders, car navigation devices, pagers, electronic notebooks (including those with communication functions), electronic dictionaries, calculators, electronic game devices, word processors, workstations , Video phone, crime prevention TV monitor, electronic binoculars, POS terminal, medical equipment (eg electronic thermometer, blood pressure monitor, blood glucose meter, electrocardiogram measuring device, ultrasonic diagnostic device, electronic endoscope), fish detector, various measuring devices , Instrumentation (e.g., vehicle, aircraft, ship Vessels acids), it can be applied to a flight simulator or the like.

As described above, the surface acoustic wave element and the electronic apparatus of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these.
For example, in the surface acoustic wave device of the present invention, the number of reflectors and comb electrodes may be changed according to the application, and the reflectors may be omitted.
For example, the comb electrode and the reflector may be configured such that portions other than the electrode fingers and the reflector are exposed from the insulating film, respectively.
In addition, the surface acoustic wave device of the present invention may be compounded with semiconductor devices having various functions.

Next, specific examples of the present invention will be described.
1. Fabrication of surface acoustic wave device (Example 1)
First, a quartz substrate having an average thickness of 0.4 mm was prepared as a substrate. The Euler angles of this quartz substrate are (0, 133, 90).

Next, aluminum was deposited on the quartz substrate by a vacuum deposition method to form an aluminum film (conductive material film).
Next, a resist layer having a shape corresponding to the IDT (comb electrode) and the reflector was formed by photolithography.
Next, by using this resist layer as a mask, unnecessary portions of the aluminum film were removed to form IDTs and reflectors, and then the resist layer was removed.
Next, silicon oxide (SiO ₂ ) was deposited by CVD on the entire surface of the quartz substrate so as to cover the IDT and the reflector, thereby forming a silicon oxide film (insulating protective film).

As a result, the surface acoustic wave device shown in FIGS. 8 and 7 was obtained.
Note that the normalized film thicknesses of the IDT and the reflector were each 0.08.
The normalized film thickness of the insulating protective film was 0.2.
In addition, the separation distance g between the IDT and each reflector is 0.25 times the wavelength of the surface acoustic wave, and the distance f is 0.5 times the wavelength of the surface acoustic wave.

(Examples 2-6, Comparative Examples 1-4)
A quartz substrate having the Euler angle shown in Table 1 is used, and the constituent material of the insulating protective film, the shape of the insulating protective film, the normalized film thickness of the insulating protective film, the IDT and the normalized film thickness H / λ of the reflector are set. The surface acoustic wave device shown in FIG. 1 was obtained in the same manner as in Example 1 except that the changes were made as shown in Table 1.
In the case where the shape of the insulating protective film is as shown in FIGS. 2 and 6, after forming the insulating protective film so as to cover the IDT and the reflector, a predetermined resist layer is formed thereon. Then, unnecessary portions of the insulating protective film were removed using this resist layer as a mask.

2. Evaluation For each surface acoustic wave element of each example and each comparative example, the frequency variation with respect to the temperature change was examined.
The result is shown in FIG.
As is apparent from FIG. 13, the surface acoustic wave elements of the respective examples (surface acoustic wave elements of the present invention) all had small frequency fluctuations with respect to temperature changes.
On the other hand, each of the surface acoustic wave elements of the comparative examples had a large frequency variation with respect to a temperature change.
In each surface acoustic wave element of each example, sharp resonance was obtained. Typically, FIG. 14 shows the characteristics of the surface acoustic wave device of Example 1.

The surface acoustic wave elements shown in FIGS. 1 and 9 were produced in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 4, and for these, as a result of examining the frequency variation with respect to the temperature change, And almost the same result was obtained. Further, in each of the surface acoustic wave devices of the respective examples (the present invention), a low impedance was obtained and sufficient resonance was confirmed.
Further, except that the configuration of the insulating protective film is changed to that shown in FIGS. 2 and 6, surface acoustic wave elements are prepared in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 4, and these are respectively As a result of examining the frequency fluctuation with respect to the change, it was confirmed that this can be changed.

1 is a perspective view schematically showing a first embodiment of a surface acoustic wave element of the present invention. It is sectional drawing of the surface acoustic wave element shown in FIG. It is a graph showing the relationship between the electromechanical coefficient k ² of the angle ψ and various surface acoustic wave. It is a graph which shows the relationship between the cut angle (theta) of a quartz substrate, secondary temperature coefficient (beta), and the normalization film thickness Hz / (lambda) of an insulating protective film. It is a graph which shows the relationship between the normalized film thickness H / λ of IDT and the cut angle θ of the quartz substrate. It is a figure which shows the other structural example of an insulating protective film. It is a figure which shows the other structural example of an insulating protective film. It is a perspective view which shows 2nd Embodiment of the surface acoustic wave element of this invention. It is sectional drawing of the surface acoustic wave element shown in FIG. It is an electronic device (notebook type personal computer) provided with the surface acoustic wave element of the present invention. It is an electronic device (cellular phone) provided with the surface acoustic wave element of the present invention. It is an electronic apparatus (digital still camera) provided with the surface acoustic wave element of the present invention. It is a graph which shows the frequency fluctuation with respect to the temperature change in the surface acoustic wave element of each Example and each comparative example. 3 is a graph showing characteristics of the surface acoustic wave element of Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 7 ... Surface acoustic wave element 2 ... Substrate 3 ... IDT 3a, 3b ... Electrode (comb electrode) 31 ... Electrode finger 4, 5 ... Reflector 41, 51 ... Reflector 6, 6 ', 6 "... Insulating protective film 8 ... IDT (input side electrode) 81 ... Electrode finger 9 ... IDT (output side electrode) 91 ... Electrode finger 1100 ... Personal computer 1101 ... Antenna 1102 ... Keyboard 1104 ... Main body 1106 ... Display unit 1200 ... Mobile phone 1201 ... Antenna 1202 ... Operation buttons 1204 ... Earpiece 1206 ... Mouthpiece 1300 ... Digital still camera 1302 ... Case (body) 1304 Light receiving unit 1306 Shutter button 1308 Memory 1312 Video signal output terminal 1314 Input and output terminal 1430 ‥‥ television monitor 1440 ‥‥ personal computer over data communication

Claims (13)

A quartz substrate whose Euler angle is represented by (0, θ, ψ);
A function of converting an electrical signal into a surface acoustic wave propagating near the surface of the quartz substrate and / or a function of converting a surface acoustic wave propagating near the surface of the quartz substrate into an electrical signal provided on the quartz substrate; A comb electrode having a plurality of electrode fingers;
Having at least an insulating film provided on the surface of each electrode finger opposite to the quartz substrate;
The comb electrode is arranged so that an angle ψ formed by the propagation direction of the surface acoustic wave and the X axis of the quartz crystal substrate is 90 ± 10 °, and a transverse type surface acoustic wave is excited. A surface acoustic wave device,
The cut angle θ is 126 to 150 °,
The normalized film thickness Hz / λ (Hz indicates the average thickness of the insulating film, and λ indicates the wavelength of the transverse wave type surface acoustic wave) is 0.02 to 0.4. A surface acoustic wave device. The insulating film is composed of SiO ₂ as a main material,
2. The surface acoustic wave device according to claim 1, wherein the normalized film thickness Hz / λ of the insulating film is 0.03 to 0.38. The insulating film is composed of Al ₂ O ₃ as a main material,
2. The surface acoustic wave device according to claim 1, wherein the normalized film thickness Hz / λ of the insulating film is 0.04 to 0.4.   The surface acoustic wave device according to claim 1, wherein the insulating film is provided so as to cover an upper surface or a surface of each electrode finger.   5. The surface acoustic wave device according to claim 1, wherein the insulating film is provided so as to cover a surface of each electrode finger and a portion of the quartz substrate exposed from the electrode finger.   The surface acoustic wave device according to any one of claims 1 to 5, wherein the comb electrode is composed of Al as a main material.   The normalized film thickness H / λ of the comb-teeth electrode (H represents the average thickness of the comb-teeth electrode and λ represents the wavelength of the transverse wave type surface acoustic wave) is 0.03 to 0.14. Item 7. The surface acoustic wave device according to Item 6. 8. The surface acoustic wave device according to claim 6, wherein the normalized film thickness H / λ of the comb-tooth electrode and the cut angle θ are set so as to satisfy a relationship A shown below.
[Relationship A]
θmin ≦ θ ≦ θmax
θmax = 3344.8 (H / λ) ² −143.65 (H / λ) +129.098
θmin = 2560.4 (H / λ) ² −147.18 (H / λ) +122.8 A pair of reflectors provided via the comb-teeth electrodes, comprising a plurality of reflectors;
The reflectors are arranged such that an angle ψ formed by the propagation direction of the surface acoustic wave and the X axis of the quartz crystal substrate is 90 ± 10 °.
The surface acoustic wave device according to claim 1, wherein the insulating film is further provided on at least a surface of each reflector opposite to the quartz substrate.   The surface acoustic wave device according to claim 9, wherein each of the reflectors is made of Al as a main material.   The surface acoustic wave device according to claim 10, wherein the normalized film thickness of each reflector is 0.03 to 0.14.   The surface acoustic wave device according to claim 10 or 11, wherein the normalized film thickness of each reflector and the cut angle θ are set so as to satisfy the relationship A.   An electronic apparatus comprising the surface acoustic wave device according to claim 1.

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