JP2005142629A - Surface acoustic wave element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element for increasing reliability and frequency accuracy with respect to an environment temperature change and attaining an improvement in yield, and to provide a manufacturing method thereof. <P>SOLUTION: In the surface acoustic wave element wherein interdigital electrodes 12 each stimulating a surface acoustic wave on a piezoelectric substrate 11 and an insulation protection film for protecting the interdigital electrodes 12 are arranged, the insulation protection film is configured of a plurality of layers of insulation films 13, 14 with different densities. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave element (SAW device), which is one of key devices in the communication field such as a mobile phone, and a manufacturing method thereof.

A surface acoustic wave element (SAW device) uses a phenomenon in which a specific frequency is selected in the process of converting a high-frequency signal into a surface acoustic wave and converting the surface acoustic wave into a high-frequency signal again using a piezoelectric material. It is an element and an essential device for all communication devices. A general configuration of such a surface acoustic wave element is that a comb-shaped electrode (Inter-Digital Transducer: IDT) for exciting a surface acoustic wave is disposed on a piezoelectric substrate, and the comb-shaped electrode and piezoelectric element are arranged. In this structure, an insulating film is arranged as a single layer film on a substrate. This structure protects the comb-shaped electrode from fine dust, moisture, and the like, can prevent a short circuit between the electrodes, and plays an important role in ensuring device reliability.
In mobile communication devices such as mobile phones, demands for the frequency characteristics and temperature characteristics of surface acoustic wave elements have become more and more stringent with the increase in frequency and functionality.

  The film quality of the insulating film is desirably high density. For example, a porous film has a phenomenon in which water molecules and other substances are adsorbed in the film, which causes a decrease in insulating properties. Moreover, it becomes a factor which fluctuates an oscillation frequency by the effect by mass increase. Further, when there are minute defects such as atomic vacancies, these are taken into the vacancies in order to come into contact with various atoms and molecules during the processing in the manufacturing process, and the frequency variation is similarly generated. These are problems that require measures to reduce reliability and manufacturing yield.

On the other hand, it is possible to perform so-called temperature compensation, which improves the temperature characteristics of the entire device by placing a film having an appropriate temperature characteristic on a piezoelectric material having a certain temperature characteristic. It has become. The temperature characteristic here means that the oscillation frequency fluctuates in conjunction with the fluctuation of the material constant such as the Young's modulus of the material with respect to the environmental temperature change. In general, there is a demand for an element having a small oscillation frequency fluctuation with respect to a change in environmental temperature, in other words, a high frequency accuracy.
The two functions described above can be realized with the same film. By appropriately setting the temperature characteristics of the insulating film, the yield and reliability are ensured, and the frequency accuracy is ensured. Is possible.

  However, increasing the density of the material tends to increase the amount of fluctuation of the oscillation frequency with respect to the temperature change. If the density of the insulating film disposed on the comb-shaped electrode is increased excessively, the temperature compensation property is lost. Therefore, the frequency accuracy is deteriorated.

On the other hand, as a conventional example of a surface acoustic wave element, an insulating film disposed on a comb-shaped electrode has a two-layer structure of an insulating protective film having a smaller linear expansion coefficient than a piezoelectric substrate and a frequency adjusting film disposed thereon. The thing is proposed (for example, refer patent document 1).
However, although the document describes the thickness of the insulating film, there is no description about the density of the insulating film. The upper frequency adjustment film is provided to adjust to the standard frequency by adjusting the film thickness. More generally, there is no correlation between insulator linear expansion coefficient and density.
JP 2001-44787 A

  An object of the present invention is to provide a surface acoustic wave device and a method for manufacturing the same that achieves an improvement in reliability and frequency accuracy with respect to environmental temperature changes and an improvement in yield, focusing on the density of an insulating film.

  According to the surface acoustic wave device of the present invention, a comb-shaped electrode for exciting a surface acoustic wave on a piezoelectric substrate and an insulating protective film for protecting the comb-shaped electrode are provided on a piezoelectric substrate. In the surface acoustic wave element to be arranged, the insulating protective film is formed of a plurality of insulating films having different densities.

  In the first aspect of the present invention, focusing on the density of the insulating film, a single-layer structure of the insulating film is provided by providing a density difference between the lower insulating film and the upper insulating film (the meaning of the surface insulating film, the same shall apply hereinafter). Thus, it is possible to simultaneously satisfy both requirements of reliability and frequency accuracy (that is, temperature characteristics and frequency characteristics) that cannot be realized. Therefore, frequency deviation between chips is reduced, and manufacturing yield is improved.

  According to another aspect of the present invention, a surface acoustic wave device includes a comb-shaped electrode for exciting a surface acoustic wave on a piezoelectric substrate and an insulating protective film for protecting the comb-shaped electrode. The insulating protective film is formed of a plurality of insulating films having different densities and thicknesses, and the upper insulating film is denser and thinner than the lower insulating film. .

  According to the invention of claim 2, not only the density difference between the lower insulating film and the upper insulating film, but also a film thickness difference is provided at the same time, and the upper insulating film is made denser and thinner than the lower insulating film, The same effect as that of the invention of claim 1 can be obtained.

  In the surface acoustic wave device of the present invention, the lower insulating film constituting the insulating protective film is a temperature compensating film, and the upper insulating film has a higher density than the temperature compensating film. That is, temperature compensation is performed by the lower insulating film. The upper insulating film only needs to have a high density so as not to lose the temperature compensation of the lower insulating film.

As for the density of the insulating film, the density of the lower insulating film is preferably 0.1 to 30 g / cm ³ .
If the density is less than 0.1 g / cm ³ , the mechanical strength of the lower insulating film is greatly reduced, and the deterioration of the insulation and temperature compensation is increased. If the density exceeds 30 g / cm ³ , This is because the density difference from the upper insulating film is reduced, so that the temperature compensation is lost due to the mass effect and the frequency fluctuation is increased. Further, the frequency shift between chips becomes large, and the yield deteriorates.

The density of the upper insulating film is preferably 0.5 to 40 g / cm ³ . This is because if the density is less than 0.5 g / cm ³ , the mechanical strength of the upper insulating film is greatly reduced, and if it exceeds 40 g / cm ³ , the frequency fluctuation increases due to the mass effect and the frequency accuracy decreases. . Further, the frequency shift between chips becomes large, and the yield deteriorates.

  Regarding the film thickness of the insulating film, it is necessary that the lower insulating film has a temperature compensation function. For this purpose, the film thickness is preferably 30 nm or more.

  Regarding the film thickness of the upper insulating film, the upper insulating film may be of a thickness that does not lose the insulating property. For this purpose, the film thickness is preferably 5 nm or more.

Regarding the material of the insulating film, the lower insulating film and the upper insulating film are silicon monoxide, silicon dioxide, silicon nitride, titanium oxide, tantalum oxide, aluminum oxide, zirconium oxide, strontium oxide, zinc oxide, tungsten oxide, chromium oxide, It is made of one or more materials selected from potassium tantalate, lithium tantalate, and potassium niobate.
The material of the lower insulating film and the upper insulating film can be the same or different materials selected from these materials.

The piezoelectric substrate is made of a bulk material or a substrate in which a piezoelectric thin film having piezoelectricity is formed on a substrate.
Here, the bulk material or the substrate is made of one or more materials selected from silicon, lithium tantalate, lithium niobate, potassium niobate, crystal, and diamond.
The piezoelectric thin film is made of one or more materials selected from zinc oxide, aluminum nitride, lithium tantalate, lithium niobate, and potassium niobate.

According to a surface acoustic wave device manufacturing method of the present invention, a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate and the comb-shaped electrode is protected. When the insulating film is disposed, the insulating film is laminated in a plurality of layers, and the upper insulating film is formed at a higher density than the lower insulating film.
By this manufacturing method, a surface acoustic wave device having excellent temperature characteristics and frequency characteristics can be efficiently manufactured.

According to another aspect of the present invention, there is provided a method for manufacturing a surface acoustic wave device, wherein a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate, and the comb-shaped electrode is protected. When the insulating film is arranged, the insulating film is laminated in a plurality of layers, and the upper insulating film is formed in a thin film with a higher density than the lower insulating film.
According to this manufacturing method, a surface acoustic wave device excellent in temperature characteristics and frequency characteristics can be efficiently manufactured as in the invention of claim 13.

  According to another aspect of the present invention, there is provided a method for manufacturing a surface acoustic wave device, wherein a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate and the comb-shaped electrode is protected. When the insulating film made of the same material is formed by sputtering, the insulating film is continuously formed into a plurality of layers while changing the flow rate ratio between the sputtering gas and the introduced gas containing one of the constituent components of the insulating film. In addition, the upper insulating film is formed at a higher density than the lower insulating film.

  According to this manufacturing method, since the same insulating material is continuously used for the lower and upper insulating films by the sputtering method, more efficient manufacturing is possible.

According to the surface acoustic wave device manufacturing method of the present invention, a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate, and the comb-shaped electrode is protected. When the insulating film made of the same material is formed by sputtering, the insulating film is continuously formed into a plurality of layers while changing the flow rate ratio between the sputtering gas and the introduced gas containing one of the constituent components of the insulating film. The upper insulating film is formed in a thin film with a higher density and a lower density than the lower insulating film.
This manufacturing method has the same effect as that of the invention described in claim 14.

  In particular, in the manufacturing method according to claim 14 or claim 15, when the sputtering gas is argon and the introduction gas is oxygen, the flow ratio of argon to oxygen may be in the range of 50:50 to 70:30. preferable. If it is in the range of this flow ratio, the frequency accuracy can be ensured with high accuracy.

  In each of the above manufacturing methods, the film thickness of the upper insulating film is decreased by reactive ion etching and adjusted to the standard frequency. Thereby, the frequency shift between chips can be reduced as much as possible, and the frequency of the surface acoustic wave element can be adjusted to the standard frequency.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the basic structure of a surface acoustic wave device according to the present invention.
In the surface acoustic wave element 10 of the present invention, a comb-teeth electrode (IDT) 12 for exciting a surface acoustic wave is disposed on a piezoelectric substrate 11, and insulation is provided on the comb-teeth electrode 12 and the piezoelectric substrate 11. In this structure, the films 13 and 14 are stacked in two layers. The lower insulating film 13 is a film for the purpose of temperature compensation, and can be an element having better frequency accuracy than an element constituted by a single layer of only the insulating film 13 that is a temperature compensating film. Further, the upper layer (surface layer) insulating film 14 is a film having a higher density than the lower layer insulating film 13, and is superior in reliability and yield to an element constituted by a single layer of only the insulating film 14 being a high density film. Element. In other words, requirements that are difficult to realize with a single-layer structure of an insulating film are complemented by forming two layers with films having different densities. Note that the insulating film is not particularly limited as long as films having different functions are stacked in a plurality of layers. Moreover, there is no limitation in particular also about the film thickness of each layer.

  Here, the density of the insulating film will be described. The insulating film mainly has an amorphous structure. When a silicon oxide film is taken as an example, there are four bonds in Si atoms, and oxygen atoms are bonded thereto. A network is formed through this Si—O—Si bond, and the state is not ordered. There is a gap between the networks, and a film having a small gap can be called a high-density film. Also, four oxygen atoms are not necessarily bonded to Si bonds, but there are bonds (dangling bonds) that are not bonded to any atom, and those with few bonds are high-density films. Can do. Accordingly, whether or not the density of the insulating film is high depends on the gap (for example, the degree of porosity) or the number of dangling bonds.

In the present invention, the lower insulating film (temperature compensation film) 13 is a film having a lower density than the upper insulating film (high density film) 14, and the density of the lower insulating film 13 is suitably 0.1 to 30 g / cm ^3. ing. This is because if the density is less than 0.1 g / cm ³ , the mechanical strength of the film is weak, and the protection function (insulation function) and temperature compensation function of the comb-shaped electrode 12 cannot be performed. On the other hand, if it exceeds 30 g / cm ³ , the density difference from the upper insulating film (high-density film) 14 becomes small, the temperature compensation is lost due to the mass effect, and the frequency accuracy deteriorates. Further, the frequency shift between chips becomes large, and the yield deteriorates.

The upper insulating film (high-density film) 14 is a film having a higher density than the lower insulating film (temperature compensation film) 13. In this case, the density of the upper insulating film 14 is suitably 0.5 to 40 g / cm ³ . This is because when the density is less than 0.5 g / cm ³ , the mechanical strength of the film decreases, and when it exceeds 40 g / cm ³ , the amount of oscillation frequency fluctuation increases due to the mass effect and the frequency accuracy decreases. Further, the frequency shift between chips becomes large, and the yield deteriorates.

Usually, the same material is used for the lower and upper insulating films 13 and 14, but different materials may be used. Even if the same material is used, films having different densities can be formed. For example, in the case of a sputtering film forming method, the density can be varied mainly by changing the flow ratio of oxygen and argon.
As the insulating material to be applied, a commonly used material can be used. Specific examples include silicon dioxide, silicon monoxide, silicon nitride, titanium oxide, tantalum oxide, aluminum oxide, zirconium oxide, strontium oxide, zinc oxide, tungsten oxide, chromium oxide, potassium tantalate, and potassium niobate. In the present invention, one or two materials selected from these materials are used.

Regarding the film thickness, the lower insulating film 13 should have a film thickness of at least 30 nm in order to have a temperature compensation function. The upper insulating film 14 is preferably at least 5 nm thick so as not to lose the insulating property.
Further, as a method for forming the insulating films 13 and 14, a sputtering method, a vacuum evaporation method, a CVD method, or the like can be used.

The piezoelectric substrate 11 may be a bulk material or a substrate in which a piezoelectric thin film is formed. Specific examples of the bulk material or the substrate material include silicon, lithium tantalate, lithium niobate, potassium niobate, crystal, and diamond, and one or more of them are used.
Examples of the material for the piezoelectric thin film include zinc oxide, aluminum nitride, lithium tantalate, lithium niobate, and potassium niobate, and one or more of them are used. By making full use of semiconductor technology, for example, SAW filters can be multilayered.
Further, as a method for forming the piezoelectric thin film, a sputtering method, a vacuum deposition method, a CVD method, a sol-gel method, or the like can be used.

Next, examples of the present invention will be described. FIG. 2 is a plan view of the surface acoustic wave element according to the embodiment, and FIG. 3 is an enlarged sectional view showing a part of the electrode portion.
The surface acoustic wave element 10 is configured as a transversal SAW filter. Each has an input-side IDT 121 and an output-side IDT 122 made of comb-shaped electrodes arranged in a pair of opposed states. Further, electrode terminals 123 and 124 are connected to the IDTs 121 and 122, respectively, via lead portions. The IDTs 121 and 122 including the electrode terminals 123 and 124 are made of, for example, an aluminum thin film, and are formed on the zinc oxide piezoelectric thin film 112 formed on the silicon substrate 111 by sputtering. As the lower insulating film 13, for example, a silicon oxide film is formed by a sputtering method, and the same silicon oxide film is formed thereon as an upper insulating film 14 by a sputtering method. The difference in density between the insulating films 13 and 14 is realized by changing the flow ratio of argon and oxygen during sputtering.

Furthermore, the manufacturing method of the present embodiment will be specifically described with reference to FIGS.
(1) A zinc oxide film 112 having piezoelectricity is formed on a silicon substrate 111 with a film thickness of 500 nm by RF magnetron sputtering.

(2) An aluminum film having a thickness of 100 nm is formed on the zinc oxide film 112 by DC magnetron sputtering (of course, RF magnetron sputtering may be used), and then an electrode having a comb-teeth shape is formed by photolithography. Pattern. Both the line width of the electrode fingers and the space between the electrode fingers are 2 μm. Further, the above-described IDTs 121 and 122 are manufactured by etching the aluminum film provided with the photoresist pattern by a reactive ion etching (RIE) method using carbon tetrafluoride gas.

(3) Next, a silicon oxide film having a thickness of 300 nm is formed on the zinc oxide film 112 and the IDTs 121 and 122 by RF magnetron sputtering. At this time, first, silicon oxide corresponding to the lower insulating film 13 is continuously formed to a thickness of 250 nm, and then silicon oxide corresponding to the upper insulating film 14 is continuously formed to a thickness of 50 nm.
In addition, when forming silicon oxide, a mixed gas of argon as a sputtering gas and oxygen as an insulating film component is introduced into the vacuum chamber, and silicon oxide that hits the lower insulating film 13 has a flow ratio of argon and oxygen. 90:10, and the silicon oxide corresponding to the upper insulating film 14 is 60:40. Thus, the silicon oxide that hits the lower insulating film 13 becomes a film having a higher density than the silicon oxide that hits the upper insulating film 14.
FIG. 4 shows the relationship between the flow rate ratio of argon / (argon + oxygen) and the frequency variation (ppm). From this graph, it can be seen that when the flow ratio of argon to oxygen is 60:40, the amount of frequency fluctuation is a minimum value. The flow rate ratio between argon and oxygen is preferably in the range of 50:50 to 70:30.

(4) The silicon oxide film (the lower insulating film 13 and the upper insulating film 14) is removed only at the electrode terminal window using the photolithography method and the RIE method. The gas used at this time is carbon tetrafluoride.

(5) Next, aluminum is formed by DC magnetron sputtering with a film thickness of 300 nm, and only the electrode terminal portion is removed by photolithography and RIE. The main gas used at this time is chlorine.

(6) The wafer is cut into chips by dicing.
(7) As frequency adjustment, silicon oxide corresponding to the upper insulating film 14 is removed by about several nanometers by RIE method, and adjusted to the standard frequency. The gas used at this time is carbon tetrafluoride. Note that the frequency adjustment is performed on a chip having a frequency lower than the standard frequency, and a thickness corresponding to the frequency difference is removed. At the same time, the frequency is monitored by a network analyzer.
(8) Finally, die bonding and wire bonding of the chip are performed, and sealing is performed with a package.
As described above, the surface acoustic wave element 10 having desired performance (temperature characteristics and frequency characteristics) can be obtained.

(9) Durability test In order to compare and evaluate the performance of this example, a durability test was performed under the condition of applying 5 mW at a temperature of 150 ° C. The results are shown in FIGS. Fig. 5 is a graph showing the results of the durability test as a relationship between time (H) and frequency variation (ppm), and Fig. 6 shows the temperature characteristics of the device as a relationship between temperature (° C) and frequency variation (ppm). It is a graph. In FIG. 5, as a comparative example, an element having a single-layer structure including only the lower insulating layer (temperature compensation film) 13 was manufactured and compared with the element of the example according to the present invention. In FIG. 6, as a comparative example, an element having a single layer structure including only the upper insulating film (high-density film) 14 was manufactured and compared with the element of the example according to the present invention. The material of the insulating films 13 and 14 are the same SiO _2, the density, in both Comparative Examples and Examples, the lower insulating layer 13 is 1.5 g / cm ^3, the upper insulating film 14 was 5 g / cm ³ .

As shown in FIG. 5, in the case of an element having a single layer structure composed only of the lower insulating layer 13 of the comparative example, it can be seen that a frequency variation of 10 ppm or more occurs in 100 hours after the start of the test, and the reliability is inferior. On the other hand, in the element of the two-layer structure of the example (structure in which the upper and lower films are provided with a density difference, the same applies hereinafter), the fluctuation range is within 10 ppm even after 2000 hours.
This is because, in the case of the comparative example, the lower insulating film 13 adsorbs a considerable amount of moisture, foreign molecules, etc. inside the film during the processing steps (4) to (8) above, due to the high temperature during the durability test. It is considered that the adsorbate is desorbed. On the other hand, in the case of the example, since the upper layer high-density film 14 prevents moisture and different molecules from entering as much as possible and there are few adsorbed substances inside the film, the frequency fluctuation during the test is suppressed to a small level.

With respect to the temperature characteristics, as shown in FIG. 6, in the case of a single layer structure element composed of only the upper insulating film 14 of the comparative example, the insulating layer 14 made of SiO ₂ has a high density, so that the frequency variation with respect to the temperature change increases. It can be seen that the frequency accuracy is lacking. On the other hand, in the element of the two-layer structure of the example, the frequency variation with respect to the temperature change is within about 0 to −100 ppm and is small, and it can be seen that it has high frequency accuracy.

Next, another embodiment in which the insulating material is changed will be described. In this embodiment, SiO ₂ (silicon dioxide) is used for the lower insulating film (temperature compensation film) 13 and Al ₂ O ₃ (aluminum oxide) is used for the upper insulating film (high density film) 14. Table 1 shows the configuration.

FIG. 7 is a graph showing the results of the durability test. This example also shows that the frequency fluctuation is much smaller and the reliability is higher than that of the comparative example (element having a SiO ₂ single layer structure).

The above description is about a transversal SAW filter, but the present invention is not limited to this. For example, the present invention can be similarly applied to a ladder-type or resonant-type surface acoustic wave element. An application example of the resonance type surface acoustic wave element is shown in FIG.
This example is a 1-port SAW resonator, and has a configuration in which resonators 125 and 126 are arranged on the left and right with the input side IDT 121 and the output side 122 in the center.
In such a SAW resonator, the lower insulating film 13 (temperature compensation film) and the upper insulating film (high-density film) 14 are formed on the entire surface of the piezoelectric substrate 11 except for the electrode terminals 123 and 124 in a two-layer structure. By arranging, the effects as described above can be obtained.

1 is a schematic cross-sectional view showing a basic structure of a surface acoustic wave element of the present invention. The top view of the surface acoustic wave element in an Example. The expanded sectional view which shows a part of electrode part of an Example. The graph which shows the relationship between the flow rate ratio of argon / (argon + oxygen), and the amount of frequency fluctuations. The graph which shows the durability test result of an Example. Graph of temperature characteristic measurement results. The graph which shows the durability test result of another Example. The schematic plan view which shows other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Surface acoustic wave element, 11 Piezoelectric substrate, 12 Comb-shaped electrode, 13 Lower insulating film (temperature compensation film), 14 Upper insulating film (high-density film), 111 Silicon substrate, 112 Piezoelectric thin film (zinc oxide film), 121 Input side IDT, 122 Output side IDT, 123 Electrode terminal, 124 Electrode terminal, 125 Resonator, 126 Resonator

Claims (17)

In a surface acoustic wave element in which a comb-shaped electrode for exciting a surface acoustic wave on a piezoelectric substrate and an insulating protective film for protecting the comb-shaped electrode are arranged,
A surface acoustic wave device, wherein the insulating protective film is composed of a plurality of insulating films having different densities. In a surface acoustic wave element in which a comb-shaped electrode for exciting a surface acoustic wave on a piezoelectric substrate and an insulating protective film for protecting the comb-shaped electrode are arranged,
A surface acoustic wave device comprising: a plurality of insulating films having different densities and film thicknesses; and an upper insulating film having a higher density and a lower thickness than a lower insulating film.   3. The surface acoustic wave device according to claim 1, wherein the lower insulating film constituting the insulating protective film is a temperature compensating film, and the upper insulating film has a higher density than the temperature compensating film. 4. The surface acoustic wave device according to claim 1, wherein the density of the lower insulating film is 0.1 to 30 g / cm < ³ >. 5. The surface acoustic wave device according to claim 1, wherein a density of the upper insulating film is 0.5 to 40 g / cm ³ .   6. The surface acoustic wave element according to claim 1, wherein the lower insulating film has a thickness of 30 nm or more.   The surface acoustic wave device according to claim 1, wherein the upper insulating film has a thickness of 5 nm or more.   The lower insulating film and the upper insulating film are silicon monoxide, silicon dioxide, silicon nitride, titanium oxide, tantalum oxide, aluminum oxide, zirconium oxide, strontium oxide, zinc oxide, tungsten oxide, chromium oxide, potassium tantalate, tantalate 8. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is made of one or more materials selected from lithium and potassium niobate.   9. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of a bulk material or a piezoelectric thin film formed on a substrate.   10. The bulk material or the substrate is made of one or more materials selected from silicon, lithium tantalate, lithium niobate, potassium niobate, crystal, and diamond. Surface acoustic wave device.   The piezoelectric thin film is made of one or more materials selected from zinc oxide, aluminum nitride, lithium tantalate, lithium niobate, and potassium niobate. Surface acoustic wave device.   When a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate and an insulating film for protecting the comb-shaped electrode is disposed, the insulating film is laminated in a plurality of layers and an upper layer insulating layer is formed. A method of manufacturing a surface acoustic wave device, wherein a film is formed at a higher density than a lower insulating film.   When a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate and an insulating film for protecting the comb-shaped electrode is disposed, the insulating film is laminated in a plurality of layers and an upper layer insulating layer is formed. A method of manufacturing a surface acoustic wave device, wherein a film is formed in a thin film with a higher density than a lower insulating film.   When a comb-shaped electrode for exciting surface acoustic waves is formed on a piezoelectric substrate and an insulating film made of the same material for protecting the comb-shaped electrode is formed by sputtering, the sputtering gas and the insulation are The insulating film is continuously laminated in a plurality of layers while changing the flow rate ratio with the introduced gas containing one of the constituent components of the film, and the upper insulating film is formed at a higher density than the lower insulating film. A method of manufacturing a surface acoustic wave device.   When a comb-shaped electrode for exciting surface acoustic waves is formed on a piezoelectric substrate and an insulating film made of the same material for protecting the comb-shaped electrode is formed by sputtering, the sputtering gas and the insulation are The insulating film is continuously laminated in a plurality of layers while changing the flow rate ratio with the introduced gas containing one of the constituent components of the film, and the upper insulating film is formed in a thin film with a higher density than the lower insulating film. A method for manufacturing a surface acoustic wave device.   16. The method for manufacturing a surface acoustic wave device according to claim 14, wherein when the sputtering gas is argon and the introduction gas is oxygen, the flow ratio of argon to oxygen is in the range of 50:50 to 70:30. . 17. The method for manufacturing a surface acoustic wave device according to claim 12, wherein the thickness of the upper insulating film is adjusted to a standard frequency by reducing the thickness by reactive ion etching.

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