JP2011166567A - Surface acoustic wave device, oscillator, and module apparatus - Google Patents

Abstract

A surface acoustic wave device having good temperature characteristics and a sufficient electromechanical coupling coefficient is realized.
A surface acoustic wave device includes a sapphire substrate having a C-plane as a main surface, an aluminum nitride film formed on a main surface of the sapphire substrate, and an elastic surface formed on the surface of the aluminum nitride film. Comb electrodes 21 and 22 for exciting surface waves, and a silicon dioxide film 40 covering the surfaces of the comb electrodes 21 and 22 and the aluminum nitride film 30, and the surface acoustic wave has a secondary mode of Sezawa waves. Used. Necessary for good temperature characteristics and excitation by setting the relationship between the normalized film thickness KH-AlN of the aluminum nitride film 30 and the normalized film thickness KH-SiO _{2 of the} silicon dioxide film 40 within an appropriate range. The surface acoustic wave device 1 having a sufficient electromechanical coupling coefficient K ² and a high sound speed can be realized.
[Selection] Figure 2

Description

  The present invention relates to a surface acoustic wave device, an oscillator, and a module device using a C-plane sapphire substrate.

A surface acoustic wave device that uses surface acoustic waves propagating on the surface of a piezoelectric film has a unique resonance frequency and transmission characteristics, and can be miniaturized and has a small number of components. And is applied to resonators as a reference clock. When a surface acoustic wave device is used for a filter or a resonator, the delay time temperature coefficient (TCD) representing temperature dependence and the electromechanical coupling coefficient (K ² ) representing electromechanical conversion performance may be good. Desired.

  Therefore, there is provided a surface acoustic wave device in which a comb electrode (IDT) is formed on an insulating substrate such as glass, a piezoelectric film covering the surface of the comb electrode, and a protective film is formed so as to cover the piezoelectric film. It has been proposed (see, for example, Patent Document 1).

  Further, surface acoustic wave devices have been proposed in which comb-shaped electrodes are formed on a C-plane sapphire substrate and a piezoelectric film is formed to cover the surface of the comb-shaped electrodes (see, for example, Patent Document 2 and Patent Document 3). ).

JP-A-10-178330 JP-A-10-135773 JP-A-8-130435

  In Patent Document 1, an insulating substrate such as glass is used as a substrate, and a comb-like electrode, a piezoelectric film, and a protective film are formed on the substrate in layers to prevent moisture and foreign matter from entering. The object is to prevent the deterioration and alteration of the piezoelectric film due to the atmosphere. However, unless the material and film thickness of the protective film are fully taken into account, the sound speed, electromechanical coupling coefficient, and temperature characteristics of the surface acoustic wave fluctuate, and these good characteristics cannot be obtained.

  Moreover, in patent document 2 and patent document 3, a comb-tooth electrode made of an aluminum-based alloy is formed on a C-plane sapphire substrate, and a zinc oxide (ZnO) film is formed so as to cover the comb-tooth electrode. Trying to improve migration tolerance. Even in such a configuration, if the thickness of the zinc oxide film is not fully taken into account, the sound velocity, electromechanical coupling coefficient, and temperature characteristics of the propagated surface acoustic wave will fluctuate. Has a problem that cannot be obtained.

  In addition, when zinc oxide is used as a piezoelectric film on a C-plane sapphire substrate, there is a problem that the difference between the sound speed of the sapphire substrate and the sound speed of zinc oxide is large, and this sound speed difference may affect the frequency fluctuation. .

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A surface acoustic wave device according to this application example is formed on a sapphire substrate having a C-plane as a main surface, an aluminum nitride film formed on the main surface of the sapphire substrate, and a surface of the aluminum nitride film. A comb-tooth electrode for exciting a surface acoustic wave; and a silicon dioxide film covering the surfaces of the comb-tooth electrode and the aluminum nitride film, wherein the surface acoustic wave is a secondary mode of Sezawa waves. And

  According to this application example, since a sapphire substrate having a C-plane as a main surface (hereinafter, sometimes referred to as a C-plane sapphire substrate) is used as the substrate, the substrate is higher than the case of using crystal, glass, or the like. You can get the speed of sound. That is, a high frequency device can be realized.

  In addition, by setting the aluminum nitride film and the silicon dioxide film to have a delay time temperature coefficient (TCD) with opposite signs, it is possible to obtain a favorable frequency temperature characteristic.

Aluminum nitride has a larger electromechanical coupling coefficient (K ² ) than that of the sapphire substrate, and when aluminum nitride is formed on the sapphire substrate, the crystallinity of aluminum nitride is good, so that the electromechanical coupling coefficient can be further increased. It is possible to increase the excitation efficiency of the surface acoustic wave.

  Moreover, since the sound speed of the C-plane sapphire substrate and the sound speed of aluminum nitride are substantially the same, frequency fluctuations caused by the sound speed difference can be suppressed.

  Furthermore, the secondary mode of the Sezawa wave is likely to occur when the film thickness of the aluminum nitride film is thicker than when the primary mode of the Sezawa wave is used. And has a characteristic that a higher sound speed can be obtained.

Application Example 2 In the surface acoustic wave device according to the application example, the aluminum nitride film thickness ta, the silicon dioxide film thickness ts, and the surface acoustic wave wavelength λ are standardized. Coordinates the relationship of each normalized film thickness given by KH-AlN = (2π / λ) · ta and the normalized film thickness of the silicon dioxide film as KH-SiO ₂ = (2π / λ) · ts. When displayed,
Coordinate 1 (KH—SiO ₂ , KH—AlN) = (4.50, 1.00)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.00,1.00)
Coordinate 3 (KH—SiO ₂ , KH—AlN) = (5.41, 1.17)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.57,6.75)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.57,7.38)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.63,8.63)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.66,10.00)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (4.50,10.00)
It is desirable to connect these coordinates in the order of coordinates 1 to 13 and use the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 13 and the coordinates 1.

Within this region, an electromechanical coupling coefficient K ² required for exciting the surface acoustic wave can be as high as 0.1% or higher and 5650 m / s or higher.

Application Example 3 In the surface acoustic wave device according to the application example, the aluminum nitride film thickness ta, the silicon dioxide film thickness ts, and the surface acoustic wave wavelength λ are standardized. Coordinates the relationship of each normalized film thickness given by KH-AlN = (2π / λ) · ta and the normalized film thickness of the silicon dioxide film as KH-SiO ₂ = (2π / λ) · ts. When displayed,
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,2.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.77,1.83)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.00,1.54)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.21,1.08)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.41,1.17)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 7 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.52,6.00)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.39,6.67)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (5.39,7.08)
Coordinates _{14 (KH-SiO 2, KH} -AlN) = (5.15,7.83)
Coordinate 15 (KH—SiO ₂ , KH—AlN) = (4.91, 10.00)
Coordinate 16 (KH-SiO ₂ , KH-AlN) = (4.50, 10.00)
It is desirable to connect these coordinates in the order of coordinates 1 to 16 and use the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 16 and the coordinates 1.

Within this region, the delay time temperature coefficient (TCD) can satisfy both −20 ppm / ° C. to +20 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more.
Further, a high sound speed of 5650 m / s or more can be realized, which is suitable for a high frequency band oscillator.

Application Example 4 In the surface acoustic wave device according to the application example, the aluminum nitride film thickness ta, the silicon dioxide film thickness ts, and the surface acoustic wave wavelength λ are standardized. Coordinates the relationship of each normalized film thickness given by KH-AlN = (2π / λ) · ta and the normalized film thickness of the silicon dioxide film as KH-SiO ₂ = (2π / λ) · ts. When displayed,
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.84,2.71)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.65,1.48)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.00,4.42)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (4.66,5.17)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (4.50,5.38)
It is desirable to connect these coordinates in the order of coordinates 1 to 10 and use the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 10 and the coordinates 1.

Within this region, the delay time temperature coefficient (TCD) can satisfy both −10 ppm / ° C. to +10 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more.
Further, a high sound speed of 5650 m / s or more can be realized, which is suitable for a high frequency band oscillator.

Application Example 5 In the surface acoustic wave device according to the application example, the aluminum nitride film thickness ta, the silicon dioxide film thickness ts, and the surface acoustic wave wavelength λ are standardized. Coordinates the relationship of each normalized film thickness given by KH-AlN = (2π / λ) · ta and the normalized film thickness of the silicon dioxide film as KH-SiO ₂ = (2π / λ) · ts. When displayed,
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.75)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.10,2.75)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.72,1.79)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.00,3.83)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (4.50,4.75)
It is desirable to connect these coordinates in the order of coordinates 1 to 6, and to use the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 6 and the coordinates 1.

Within this region, the delay time temperature coefficient (TCD) can satisfy both of −5 ppm / ° C. to +5 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more, and a high sound velocity of 5650 m / s or more. In addition, a surface acoustic wave device suitable for a high-frequency band oscillator that requires highly accurate temperature characteristics can be realized.

  Application Example 6 An oscillator according to this application example uses the surface acoustic wave device according to any one of the application examples described above.

  By combining the surface acoustic wave device described above with an SAW filter or an integrated circuit element as an oscillator, an oscillator having high sound speed and good frequency temperature characteristics can be realized.

  Application Example 7 A module apparatus according to this application example uses the surface acoustic wave device according to any one of the application examples described above.

  By sealing the surface acoustic wave device described above using a package, it is possible to further improve reliability by protecting the external surface environment such as moisture and dust.

FIG. 2 is a top view of the surface acoustic wave device according to the first embodiment. Sectional drawing which shows the AA cut surface in FIG. 3 is a graph showing the relationship between the normalized film thickness (KH—AlN) of an aluminum nitride film and the normalized film thickness (KH—SiO ₂ ) of a silicon dioxide film and the speed of sound in the surface acoustic wave device according to the first embodiment. 3 is a graph showing the relationship between KH—AlN, KH—SiO _2, and electromechanical coupling coefficient K ^{2 according} to the first embodiment. And KH-AlN and KH-SiO ₂ according to the first embodiment, a graph showing the relationship between the electromechanical coupling factor K ^2. And KH-AlN and KH-SiO ₂ according to the second embodiment, a graph showing the relationship between the temperature coefficient of delay time (TCD). Graph showing the relationship between the electromechanical coupling coefficient (K ^2). 10 is a graph showing the relationship between KH—AlN, KH—SiO ₂ , and delay time temperature coefficient (TCD) according to Example 3; Graph showing the relationship between the electromechanical coupling factor K ^2. And KH-AlN and KH-SiO ₂ according to the fourth embodiment, a graph showing the relationship between the temperature coefficient of delay time (TCD). Graph showing the relationship between the electromechanical coupling factor K ^2.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)

  FIG. 1 is a top view of the surface acoustic wave device according to the first embodiment, and FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1 and 2 are schematic views in which the vertical and horizontal scales of vertical and horizontal members or portions are different from actual ones for convenience of illustration.

1 and 2, a surface acoustic wave device 1 is a single crystal hexagonal system, and is formed on a sapphire substrate 10 having a C plane of a plane orientation as a main surface and the entire main surface 11 of the sapphire substrate 10. The aluminum nitride (AlN) film 30, the interdigital electrodes (IDT) 21 and 22 formed on the surface of the aluminum nitride (AlN) film 30, the surfaces of the comb electrodes 21 and 22 and the aluminum nitride film 30 are formed. A silicon dioxide (SiO ₂ ) film 40 is formed as a silicon dioxide film formed so as to cover it. Note that the C-plane is (0001) in terms of Miller index. The aluminum nitride (AlN) film 30 is a piezoelectric film.

  The comb electrodes 21 and 22 are made of aluminum or an aluminum alloy, and are configured by interposing interdigitated electrodes. One end of the comb electrode 21 is an electrode pad 21 a, and one end of the comb electrode 22 is an electrode. A pad 22a is formed. These electrode pads 21 a and 22 a penetrate the aluminum nitride film 30 and the silicon dioxide film 40 and are exposed on the surface of the silicon dioxide film 40.

  The configuration of the comb electrodes 21 and 22 shown in FIGS. 1 and 2 is one example, and the configuration of the comb electrodes and the number of cross finger electrodes are illustrated in a simplified manner. Moreover, the material of the comb-tooth electrodes 21 and 22 will not be specifically limited if it has electroconductivity.

  Next, the main steps of the method for manufacturing the surface acoustic wave device 1 will be described with reference to FIG. First, the aluminum nitride film 30 is formed on the surface of the main surface 11 of the sapphire substrate 10 by sputtering. Then, an aluminum film (or an aluminum alloy film) is formed on the surface of the aluminum nitride film 30 by a vapor deposition method. Then, a photoresist is applied to the aluminum film, exposed using a stepper, and development processing, etching, and resist stripping processing are performed to form comb electrodes 21 and 22.

Subsequently, a silicon dioxide film 40 is formed by a sputtering method. Next, an opening that penetrates the silicon dioxide film 40 is opened by photolithography. For etching the silicon dioxide film 40, CF ₄ is used as an etching gas, and the silicon dioxide film 40 in the opening is removed by a dry etching method. Thereafter, aluminum (or an aluminum alloy) is formed by vapor deposition, and electrode pads 21a and 22a are formed by photolithography.

  Next, driving of the surface acoustic wave device 1 formed in this way will be described. The comb-tooth electrode 21 and the comb-tooth electrode 22 correspond to an input-side electrode and an output-side electrode, and AC power applied to the input-side electrode is converted into mechanical energy on the surface of the aluminum nitride film 30 as a piezoelectric film. However, since the electrode has a comb-teeth shape, the aluminum nitride film 30 becomes dense and becomes elastic waves, propagates through the surface of the aluminum nitride film 30 and reaches the output-side electrode. Then, the surface acoustic wave that has reached is again converted into electrical energy by the output side electrode and output. Here, the generated elastic wave is a Sezawa wave that is a higher-order mode of a Rayleigh wave, and in the present embodiment, a secondary mode of the Sezawa wave is used.

  The surface acoustic wave device 1 formed in this way is driven, impedance characteristics are measured using a network analyzer, and the measurement results are shown in FIG.

FIG. 3 shows a normalized film thickness (hereinafter referred to as KH-AlN: vertical axis) of the aluminum nitride film 30 and a normalized film thickness (hereinafter referred to as KH−) of the silicon dioxide film 40 in the surface acoustic wave device according to the present embodiment. expressed as SiO _2: the horizontal axis) represents the relationship between the Rayleigh wave speed of sound propagating through the sapphire substrate 10 [m / s], FIG. 4 is a graph representing the temperature coefficient of delay time (TCD). In this figure, when the thickness of the aluminum nitride film 30 is ta, the thickness of the silicon dioxide film 40 is ts, and the wavelength of the surface acoustic wave is λ, the normalized film thickness of the aluminum nitride film 30 is KH-AlN = (2π / Λ) · ta, the normalized thickness of the silicon dioxide film 40 is KH-SiO ₂ = (2π / λ) · ts, the vertical axis is KH-AlN, and the horizontal axis is KH-SiO _2. Is shown.

As shown in FIG. 3, it can be seen that a sufficiently high sound speed of 5450 m / s or higher can be obtained in the measurement range of KH—SiO ₂ of 4.5 to 7.

Further, as shown in FIG. 4, it can be seen that there is a range in which the delay time temperature coefficient (TCD) is suppressed to −20 ppm / ° C. to +20 ppm / ° C. in the measurement range of KH—SiO ₂ of 4.5 to 7.

  According to this embodiment, a C-plane sapphire substrate is used as the substrate. The sapphire substrate has a sound speed of 4500 m / s or higher compared to the limit of the sound speed of the Rayleigh wave propagating on the crystal substrate, which is about 3100 m / s. can get. That is, a high frequency device can be realized.

Aluminum nitride has a sound speed of about 5600 m / s and is close to the sound speed of the C-plane sapphire substrate, so that it is possible to suppress frequency fluctuations caused by the sound speed difference. On the other hand, when a zinc oxide (ZnO) film is used as the piezoelectric film as in the prior art, the sound speed of the zinc oxide (ZnO) film is about 3100 m / s, which is lower than the sound speed of the C-plane sapphire substrate. There is a disadvantage that the difference from the sound speed of the C-plane sapphire substrate becomes large, and the frequency fluctuation due to the sound speed difference becomes large.
However, since the sound speed of the C-plane sapphire substrate and the sound speed of aluminum nitride are close to each other, it is possible to suppress the frequency fluctuation caused by the sound speed difference as compared with the case of using a zinc oxide (ZnO) film.

  Further, since silicon dioxide and aluminum nitride have a delay time temperature coefficient (TCD) with opposite signs, it is possible to have good frequency temperature characteristics.

  In this embodiment, the Sezawa wave secondary mode is used. The secondary mode of the Sezawa wave is likely to occur when the thickness of the aluminum nitride film is thicker than when the primary mode is used, and therefore, the stability against variations in film thickness is high. It has a characteristic that a higher sound speed can be obtained.

  The material of the comb electrodes 21 and 22 is not particularly limited as long as it has conductivity. However, when the film is formed on the sapphire substrate, aluminum having good crystallinity with respect to the crystal system with the sapphire substrate or More preferably, an aluminum alloy is used.

The surface acoustic wave device 1 has a unique resonance frequency and transmission characteristics, and can be miniaturized and has a small number of components. Therefore, the surface acoustic wave device 1 is applied to a resonator or the like as a band-pass filter or a reference clock for communication equipment. The When a surface acoustic wave device is used for a filter or a resonator, a frequency temperature coefficient (TCF) or a delay time temperature coefficient (TCD) representing temperature dependence, and an electromechanical coupling coefficient K ² representing electromechanical conversion performance are obtained. It is required to be good.
(Embodiment 1) Claim 2

Therefore, a specific example of this embodiment will be described.
FIG. 5 is a graph showing the relationship between KH—AlN and KH—SiO ₂ and the electromechanical coupling coefficient K ^{2 according} to Example 1. The numbers described on the contour lines in FIG. 5 are electromechanical coupling coefficients K ² (%). For example, when KH—SiO ₂ = 5 and KH—AlN = 3, the electromechanical coupling coefficient K ² is 0.14% or more. Here, assuming that the thickness ta of the aluminum nitride film 30, the thickness ts of the silicon dioxide film 40, and the wavelength λ of the surface acoustic wave, the normalized film thickness of the aluminum nitride film 30 is KH-AlN = (2π / The normalized film thickness of the silicon dioxide film 40 is given by KH-SiO ₂ = (2π / λ) · ts. In the mathematical expressions of the present application, the symbol “•” represents multiplication, and the symbol “/” represents division. When the relationship between these standardized film thicknesses is displayed as coordinates, an appropriate region can be represented by the following coordinates. In FIG. 5, coordinate 1, coordinate 2, coordinate 3... Are represented as Z1, Z2, Z3.

Coordinate 1 (KH—SiO ₂ , KH—AlN) = (4.50, 1.00)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.00,1.00)
Coordinate 3 (KH—SiO ₂ , KH—AlN) = (5.41, 1.17)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.57,6.75)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.57,7.38)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.63,8.63)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.66,10.00)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (4.50,10.00)
These coordinates are connected in the order of coordinates 1 to 13 and the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 13 and the coordinates 1 are used.

In this region, the electromechanical coupling coefficient K ² required for exciting the surface acoustic wave can be 0.1% or more, and high excitation efficiency can be obtained.
Further, when the area connected by the coordinate systems shown in FIGS. 3 and 5 is synthesized and determined, it can be seen that a speed of sound of 5650 m / s or more can be obtained in this area.
(Embodiment 2) Claim 3

Next, Example 2 will be described. Example 2 expresses a range in which an excellent delay time temperature coefficient (TCD) can be obtained.
6 is a graph showing the relationship between KH-AlN and KH-SiO _{2 according} to Example 2 and the delay time temperature coefficient (TCD), and FIG. 7 is a graph showing the relationship between the electromechanical coupling coefficient (K ² ). It is. The numbers described on the contour lines in FIG. 6 are delay time temperature coefficients (ppm / ° C.). For example, when KH—SiO ₂ = 6 and KH—AlN = 3, the delay time temperature coefficient is −15 to −10 ppm / ° C.

Here, assuming that the thickness ta of the aluminum nitride film 30, the thickness ts of the silicon dioxide film 40, and the wavelength λ of the surface acoustic wave, the normalized film thickness of the aluminum nitride film 30 is KH-AlN = (2π / The normalized film thickness of the silicon dioxide film 40 is given by KH-SiO ₂ = (2π / λ) · ts. When the relationship between these standardized film thicknesses is displayed as coordinates, an appropriate region can be represented by the following coordinates. 6 and 7, the coordinate 1, the coordinate 2, the coordinate 3... Are represented as Z1, Z2, Z3.

Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,2.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.77,1.83)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.00,1.54)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.21,1.08)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.41,1.17)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 7 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.52,6.00)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.39,6.67)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (5.39,7.08)
Coordinates _{14 (KH-SiO 2, KH} -AlN) = (5.15,7.83)
Coordinate 15 (KH—SiO ₂ , KH—AlN) = (4.91, 10.00)
Coordinate 16 (KH-SiO ₂ , KH-AlN) = (4.50, 10.00)
These coordinates are connected in the order of coordinates 1 to 16, and the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 16 and the coordinates 1 are used.

Within this region, the delay time temperature coefficient (TCD) can satisfy both −20 ppm / ° C. to +20 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more.
Moreover, when the area | region connected by each coordinate system of FIG. 3 and FIG. 6 is synthesize | combined and it judges, in this area | region, it turns out that the sound speed 5650 m / s or more is obtained.
(Embodiment 3) Claim 4

Next, Example 3 will be described. When a surface acoustic wave device is used as a resonator for an oscillator, it is required that the delay time temperature coefficient (TCD) be set to a smaller range while ensuring an electromechanical coupling coefficient K ² of 0.1% or more. Therefore, in the third embodiment, the electromechanical coupling coefficient K ² is maintained at 0.1% or more as compared with the second embodiment, and the delay time temperature coefficient (TCD) is expressed in a smaller range.

FIG. 8 is a graph showing the relationship between KH—AlN and KH—SiO _{2 according} to Example 3 and the delay time temperature coefficient (TCD), and FIG. 9 is a graph showing the relationship between the electromechanical coupling coefficient K ^2. . The numbers described on the contour lines in FIG. 8 are delay time temperature coefficients (ppm / ° C.). Moreover, the number described on the contour line of FIG. 9 is an electromechanical coupling coefficient K ² (%). Here, assuming that the thickness ta of the aluminum nitride film 30, the thickness ts of the silicon dioxide film 40, and the wavelength λ of the surface acoustic wave, the normalized film thickness of the aluminum nitride film 30 is KH-AlN = (2π / The normalized film thickness of the silicon dioxide film 40 is given by KH-SiO ₂ = (2π / λ) · ts. When the relationship between these standardized film thicknesses is displayed as coordinates, an appropriate region can be represented by the following coordinates. 8 and 9, the coordinates 1, 2, 3,... Are represented as Z 1, Z 2, Z 3.

Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.84,2.71)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.65,1.48)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.00,4.42)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (4.66,5.17)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (4.50,5.38)
These coordinates are connected in the order of coordinates 1 to 10, and the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 10 and the coordinates 1 are used.

Within this region, the delay time temperature coefficient (TCD) can satisfy both −10 ppm / ° C. to +10 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more.
3 and FIG. 8 are combined to determine the region connected by each coordinate system, a high acoustic velocity of 5650 m / s or higher can be realized in this region, and a surface acoustic wave device suitable for a high-frequency band oscillator can be obtained. It can be seen that it can be realized.
(Embodiment 4) Claim 5

Next, Example 4 will be described. When a surface acoustic wave device is used as a resonator of an oscillator for a communication device, the delay time temperature coefficient (TCD) should be further reduced while ensuring an electromechanical coupling coefficient K ² of 0.1% or more. Desired. Thus, in the fourth embodiment, the electromechanical coupling coefficient K ² is maintained at 0.1% or more, and the delay time temperature coefficient (TCD) is expressed in a smaller range than the third embodiment described above.

FIG. 10 is a graph showing the relationship between KH—AlN and KH—SiO ₂ and the delay time temperature coefficient (TCD) according to Example 4, and FIG. 11 is a graph showing the relationship between the electromechanical coupling coefficient K ^2. . The numbers described on the contour lines in FIG. 10 are delay time temperature coefficients (ppm / ° C.). The numbers described on the contour lines in FIG. 11 are the electromechanical coupling coefficient K ² (%). Here, assuming that the thickness ta of the aluminum nitride film 30, the thickness ts of the silicon dioxide film 40, and the wavelength λ of the surface acoustic wave, the normalized film thickness of the aluminum nitride film 30 is KH-AlN = (2π / The normalized film thickness of the silicon dioxide film 40 is given by KH-SiO ₂ = (2π / λ) · ts. When the relationship between these standardized film thicknesses is displayed as coordinates, an appropriate region can be represented by the following coordinates. 10 and 11, the coordinate 1, the coordinate 2, the coordinate 3... Are represented as Z1, Z2, Z3.

Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.75)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.10,2.75)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.72,1.79)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.00,3.83)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (4.50,4.75)
These coordinates are connected in the order of coordinates 1 to 6, and the KH-AlN and the KH-SiO ₂ included in the region connecting the coordinates 6 and the coordinates 1 are used.

In this region, the delay time temperature coefficient (TCD) can satisfy both −5 ppm / ° C. to +5 ppm / ° C. and the electromechanical coupling coefficient K ² of 0.1% or more.
3 and FIG. 10 are combined to determine the area connected by each coordinate system, a high acoustic velocity of 5650 m / s or higher can be realized in this area, and a surface acoustic wave device suitable for a high-frequency band oscillator can be realized. It can be seen that it can be realized.

Claims 6 and 7
In addition, by sealing the surface acoustic wave device 1 described above with a package, it is possible to further improve the reliability by protecting the external surface environment such as moisture and dust. In the above description, only the one-port resonator as shown in FIG. 1 has been mentioned, but the present invention can also be applied to a two-port resonator, an oscillator formed in combination with a filter or an integrated circuit element, and a module device. .

  DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave device, 10 ... Sapphire substrate, 11 ... Main surface of sapphire substrate, 21, 22 ... Interdigital electrode (IDT), 21a, 22a ... Electrode pad, 30 ... Aluminum nitride film, 40 ... Silicon dioxide film.

Claims (7)

A sapphire substrate having a C-plane as a main surface;
An aluminum nitride film formed on the main surface of the sapphire substrate;
A comb-like electrode formed on the surface of the aluminum nitride film to excite a surface acoustic wave;
A silicon dioxide film covering a surface of the comb electrode and the aluminum nitride film,
2. A surface acoustic wave device, wherein the surface acoustic wave is a second-order mode of a Sezawa wave. The thickness ta of the aluminum nitride film, the thickness ts of the silicon dioxide film, and the wavelength λ of the surface acoustic wave,
The normalized film thickness of the aluminum nitride film is KH-AlN = (2π / λ) · ta,
The normalized thickness of the silicon dioxide film is KH-SiO ₂ = (2π / λ) · ts,
When the coordinates of each normalized film thickness given by
Coordinate 1 (KH—SiO ₂ , KH—AlN) = (4.50, 1.00)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.00,1.00)
Coordinate 3 (KH—SiO ₂ , KH—AlN) = (5.41, 1.17)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.57,6.75)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.57,7.38)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.63,8.63)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.66,10.00)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (4.50,10.00)
The coordinates are connected in the order of coordinates 1 to 13, and the KH-AlN and the KH-SiO ₂ included in a region connecting the coordinates 13 and the coordinates 1 are used. The surface acoustic wave device as described. The thickness ta of the aluminum nitride film, the thickness ts of the silicon dioxide film, and the wavelength λ of the surface acoustic wave,
The normalized film thickness of the aluminum nitride film is KH-AlN = (2π / λ) · ta,
The normalized thickness of the silicon dioxide film is KH-SiO ₂ = (2π / λ) · ts,
When the coordinates of each normalized film thickness given by
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,2.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.77,1.83)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.00,1.54)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.21,1.08)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.41,1.17)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 7 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (5.44,4.54)
Coordinates _{11 (KH-SiO 2, KH} -AlN) = (5.52,6.00)
Coordinates _{12 (KH-SiO 2, KH} -AlN) = (5.39,6.67)
Coordinates _{13 (KH-SiO 2, KH} -AlN) = (5.39,7.08)
Coordinates _{14 (KH-SiO 2, KH} -AlN) = (5.15,7.83)
Coordinate 15 (KH—SiO ₂ , KH—AlN) = (4.91, 10.00)
Coordinate 16 (KH-SiO ₂ , KH-AlN) = (4.50, 10.00)
The coordinates are connected in the order of coordinates 1 to 16, and the KH-AlN and the KH-SiO ₂ included in a region connecting the coordinates 16 and the coordinates 1 are used. The surface acoustic wave device as described. The thickness ta of the aluminum nitride film, the thickness ts of the silicon dioxide film, and the wavelength λ of the surface acoustic wave,
The normalized film thickness of the aluminum nitride film is KH-AlN = (2π / λ) · ta,
The normalized thickness of the silicon dioxide film is KH-SiO ₂ = (2π / λ) · ts,
When the coordinates of each normalized film thickness given by
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.33)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (4.84,2.71)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.65,1.48)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.72,1.50)
Coordinate 5 (KH—SiO ₂ , KH—AlN) = (5.72, 1.79)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{7 (KH-SiO 2, KH} -AlN) = (5.44,3.67)
Coordinate _{8 (KH-SiO 2, KH} -AlN) = (5.00,4.42)
Coordinates _{9 (KH-SiO 2, KH} -AlN) = (4.66,5.17)
Coordinates _{10 (KH-SiO 2, KH} -AlN) = (4.50,5.38)
The coordinates are connected in the order of coordinates 1 to 10, and the KH-AlN and the KH-SiO ₂ included in a region connecting the coordinates 10 and the coordinates 1 are used. The surface acoustic wave device as described. The thickness ta of the aluminum nitride film, the thickness ts of the silicon dioxide film, and the wavelength λ of the surface acoustic wave,
The normalized film thickness of the aluminum nitride film is KH-AlN = (2π / λ) · ta,
The normalized thickness of the silicon dioxide film is KH-SiO ₂ = (2π / λ) · ts,
When the coordinates of each normalized film thickness given by
Coordinates _{1 (KH-SiO 2, KH} -AlN) = (4.50,3.75)
Coordinate _{2 (KH-SiO 2, KH} -AlN) = (5.10,2.75)
Coordinates _{3 (KH-SiO 2, KH} -AlN) = (5.72,1.79)
Coordinates _{4 (KH-SiO 2, KH} -AlN) = (5.50,3.00)
Coordinate _{5 (KH-SiO 2, KH} -AlN) = (5.00,3.83)
Coordinates _{6 (KH-SiO 2, KH} -AlN) = (4.50,4.75)
The coordinates are connected in the order of coordinates 1 to 6, and the KH-AlN and the KH-SiO ₂ included in a region connecting the coordinates 6 and the coordinates 1 are used. The surface acoustic wave device as described.   An oscillator using the surface acoustic wave device according to any one of claims 1 to 5.   A module apparatus using the surface acoustic wave device according to claim 1.

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