JP6432299B2 - Surface acoustic wave device - Google Patents

Description

  The present invention relates to a surface acoustic wave device in which a comb-tooth electrode for exciting a surface acoustic wave (hereinafter abbreviated as SAW) is provided on the surface of a piezoelectric film, and in particular, a scandium-containing aluminum nitride as a piezoelectric film. (Hereinafter abbreviated as ScAlN).

Conventionally, as this type of SAW element, a surface acoustic wave member made of, for example, LiTaO ₃ (hereinafter abbreviated as “LT”) as a piezoelectric body, and a surface acoustic wave is excited on the surface acoustic wave member. The thing provided with the comb-tooth electrode to be made is proposed (refer patent document 1).

  Examples of such SAW elements include transversal filter type and reflection type delay type SAW elements, and resonance type SAW elements. These SAW elements are applied to various uses such as communication and sensors. Yes.

JP2013-240105A

  By the way, in the SAW element, it is desired to improve the piezoelectric characteristics, that is, to increase the electromechanical coupling coefficient. The electromechanical coupling coefficient is a coefficient representing the conversion capability between electrical and mechanical, and is one of the quantities representing the magnitude of the piezoelectric effect. In the above-mentioned patent document 1, it is said that the piezoelectric characteristics can be improved by specifying the film thickness of the comb-tooth electrode in a configuration using LT as a piezoelectric body.

  In contrast, the present inventor has studied a configuration using a ScAlN film as a piezoelectric film, that is, a configuration including a surface acoustic wave member in which a ScAlN film is formed on the surface of a substrate. In recent years, ScAlN has been applied as a SAW element that has a higher electromechanical coupling coefficient than other piezoelectric films.

  However, even in the case of the SAW element using the ScAlN film, further improvement of the electromechanical coupling coefficient is desired. In this case, the present inventor has obtained the relationship between the film thickness of the comb electrode and the electromechanical coupling coefficient. We decided to investigate the relationship.

  The present invention has been made in view of the above circumstances, and in a SAW element using a ScAlN film, by specifying the film thickness of the comb electrode, a large electromechanical coupling coefficient can be appropriately realized. With the goal.

  In the case of a SAW element using a ScAlN film, the present inventor investigated the relationship between the thickness of the comb electrode and the electromechanical coupling coefficient, and the electrode film thickness was the SAW (surface acoustic wave) wavelength λ. The standardized film thickness was adopted and the following points were taken into consideration.

  The comb electrode is typically formed by a lift-off process. However, since the thinner electrode is easier to make, the comb electrode has a thickness of 0.05λ (SAW wavelength λ at most). Less than 0.05 times).

  For example, the line width and the electrode spacing (Line and Space) of the comb electrode are 0.25λ and 0.25λ. In this case, the resist thickness is about 0.15λ for good exposure. . For the lift-off, the thickness of the comb electrode is preferably less than 0.05λ at the maximum, so there has been no particular reason for setting the thickness of the comb electrode to 0.05λ or more.

  In consideration of this point, as a result of intensive studies, the present inventor has made electromechanical coupling by increasing the thickness of the comb electrode at 0.05λ or more in the case of the SAW element using the ScAlN film. We have found that the coefficient can be greatly increased.

  Then, when the thickness of the comb electrode is set to 0.05λ or more, a calculation can be made as to whether a large electromechanical coupling coefficient equal to or higher than that of the conventional can be realized no matter how much the thickness is increased. The experiment was conducted.

  Further, a diamond substrate, a Si substrate, and a sapphire substrate that are typical for SAW elements were used as the substrate, and copper and aluminum that were also typical for the comb-teeth electrode were used. And the said experiment was done about the combination of each material.

For each combination, the range of the film thickness that can realize a large electromechanical coupling coefficient equal to or greater than that of the conventional one at a film thickness of the comb electrode of 0.05λ or more can be obtained from the experiment by the above calculation. (See FIGS. 4 to 9 described later). The inventions described in claims 1 to 4 have been created as a result of such experimental studies.

In the first aspect of the present invention, the substrate (11) made of diamond and the surface acoustic wave member (10) having the ScAlN film (12) formed on the surface of the substrate and the surface of the ScAlN film are formed and elastic. A comb-like electrode (20) made of copper for exciting the surface acoustic wave on the surface wave member, and when the wavelength of the surface acoustic wave is λ, the thickness of the comb-like electrode is 0.05 of the wavelength λ. 0.20 times der less than doubled Ri, ScAlN film, Sc concentration when the 100 atomic% of the sum of Sc and Al are 43at%, the thickness of ScAlN membrane wavelength λ of the surface acoustic wave 0 A surface acoustic wave device characterized in that the surface acoustic wave device is .6 times is provided.

  By specifying the thickness of the comb electrode as 0.05λ or more and 0.20λ or less as in the present invention, a large electromechanical coupling coefficient can be appropriately realized in the SAW element using the ScAlN film.

In the invention according to claim 2 , the surface acoustic wave member (10) having the substrate (11) made of sapphire and the ScAlN film (12) formed on the surface of the substrate, and formed on the surface of the ScAlN film is elastic. A comb-like electrode (20) made of copper for exciting the surface acoustic wave on the surface wave member, and when the wavelength of the surface acoustic wave is λ, the thickness of the comb-like electrode is 0.05 of the wavelength λ. 0.35 times der less than doubled Ri, ScAlN film, Sc concentration when the 100 atomic% of the sum of Sc and Al are 43at%, the thickness of ScAlN membrane wavelength λ of the surface acoustic wave 0 A surface acoustic wave device characterized in that the surface acoustic wave device is .6 times is provided.

  By specifying the thickness of the comb electrode as 0.05λ or more and 0.35λ or less as in the present invention, a large electromechanical coupling coefficient can be appropriately realized in the SAW device using the ScAlN film.

In the invention described in claim 3 , a surface acoustic wave member (10) having a substrate (11) made of diamond and a ScAlN film (12) formed on the surface of the substrate, and an elastic surface wave member (10) formed on the surface of the ScAlN film. And a comb-like electrode (20) made of aluminum for exciting the surface acoustic wave on the surface wave member. When the wavelength of the surface acoustic wave is λ, the thickness of the comb-like electrode is 0.05 of the wavelength λ. 0.25 times der less than doubled Ri, ScAlN film, Sc concentration when the 100 atomic% of the sum of Sc and Al are 43at%, the thickness of ScAlN membrane wavelength λ of the surface acoustic wave 0 A surface acoustic wave device characterized in that the surface acoustic wave device is .6 times is provided.

  By specifying the thickness of the comb electrode as 0.05λ or more and 0.25λ or less as in the present invention, a large electromechanical coupling coefficient can be appropriately realized in the SAW device using the ScAlN film.

In the invention according to claim 4 , the surface acoustic wave member (10) having the substrate (11) made of sapphire and the ScAlN film (12) formed on the surface of the substrate, and formed on the surface of the ScAlN film, is elastic. And a comb-like electrode (20) made of aluminum for exciting the surface acoustic wave on the surface wave member. When the wavelength of the surface acoustic wave is λ, the thickness of the comb-like electrode is 0.05 of the wavelength λ. 0.42 der less than doubled Ri, ScAlN film, Sc concentration when the 100 atomic% of the sum of Sc and Al are 43at%, the thickness of ScAlN membrane wavelength λ of the surface acoustic wave 0 A surface acoustic wave device characterized in that the surface acoustic wave device is .6 times is provided.

  By specifying the thickness of the comb electrode as 0.05λ or more and 0.42λ or less as in the present invention, a large electromechanical coupling coefficient can be appropriately realized in the SAW device using the ScAlN film.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a perspective view showing a SAW element according to a first embodiment of the present invention. It is a schematic sectional drawing in alignment with the dashed-dotted line AA in FIG. It is a graph which shows each characteristic of the ScAlN film | membrane used for the simulation for calculating | requiring the relationship between the film thickness of the comb-tooth electrode concerning 1st Embodiment, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb electrode concerning 1st Embodiment, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb electrode concerning 2nd Embodiment of this invention, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb-tooth electrode concerning 3rd Embodiment of this invention, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb electrode concerning 4th Embodiment of this invention, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb-tooth electrode concerning 5th Embodiment of this invention, and an electromechanical coupling coefficient. It is a graph which shows the relationship between the film thickness of the comb-tooth electrode concerning 6th Embodiment of this invention, and an electromechanical coupling coefficient.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
A SAW element (surface acoustic wave element) 1 according to a first embodiment of the present invention will be described with reference to FIG. This SAW element is applied as a physical quantity sensor for detecting a pressure (for example, engine combustion pressure) or a load as a physical quantity.

  As shown in FIG. 1, the SAW element 1 includes a chip-shaped surface acoustic wave member (hereinafter referred to as a SAW member) 10 and electrodes 20 and 30 formed on the SAW member 10.

  The electrodes formed on the SAW member 10 are a comb electrode 20 that excites SAW (surface acoustic wave) in the SAW member 10 and a reflector 30 that reflects the SAW propagated from the comb electrode 20. A region between the comb electrode 20 and the reflector 30 on the surface of the SAW member 10 constitutes a propagation path 40 through which the SAW propagates. The comb electrode 20, the reflector 30, and the propagation path 40 constitute a reflection delay type SAW element 1.

  The comb-tooth electrode 20 is composed of a pair of electrodes having a plurality of comb-tooth portions 21 extending in parallel with each other. The reflector 30 has a plurality of linear electrodes arranged in parallel to each other and in parallel to the comb teeth portion 21.

  When the high frequency signal (burst signal) corresponding to the resonance frequency of the comb electrode 20 is applied to the comb electrode 20, the comb electrode 20 is driven. Then, SAW is excited in the SAW member 10 by driving the comb electrode 20, and the SAW propagates in a direction perpendicular to the comb tooth portion 21 of the comb electrode 20. The arrow direction D1 in FIG. 1 indicates the SAW propagation direction, and the arrow D2 indicates the direction perpendicular to the SAW propagation direction.

  The comb electrode 20 and the reflector 30 are collectively formed by a lift-off process, and both are made of copper. Here, the copper constituting the comb electrode 20 and the reflector 30 includes, in addition to pure Cu, copper containing a small amount of impurities or an alloy containing Cu as a main component. It is a waste.

  Note that SAW in this specification means a Rayleigh wave type surface acoustic wave, and among the modes of the Rayleigh wave type surface acoustic wave, the first order mode which is the lowest order mode is the Rayleigh wave, and the second order mode is Sezawa wave. In the present embodiment, Sezawa waves whose Rayleigh wave type surface acoustic wave mode is a secondary mode are used as SAWs. That is, the comb electrode 20 is configured to excite the Sezawa wave.

  As shown in FIG. 2, the SAW member 10 includes a substrate 11 made of diamond as the non-piezoelectric substrate 11 (hereinafter referred to as diamond substrate 11), and a piezoelectric film directly formed on the surface of the diamond substrate 11. And a ScAlN (scandium-containing aluminum nitride) film 12 having a ScAlN / diamond structure.

  As the diamond substrate 11, one having a plane orientation (001) and a SAW propagation direction <100> is used. Under these conditions, the SAW characteristics are improved.

  The ScAlN film 12 is a film obtained by adding Sc to AlN, and is formed by sputtering or the like. The Sc concentration of the ScAlN film 12 is preferably 40 to 50 at% when the total of Sc and Al is 100 atomic% (at%). In this case, the piezoelectric constant can be maximized. In the present embodiment, the electrodes 20 and 30 are formed on the surface 12a (upper surface 12a in FIG. 2) of the ScAlN film 12 opposite to the diamond substrate 11 side.

  The SAW element 1 of the present embodiment detects pressure or load as follows.

  By driving the comb electrode 20, SAW is excited on the surface of the SAW member 10, and the SAW reflected by the reflector 30 is received by the comb electrode 20. At this time, when the SAW member 10 receives an external pressure or load, the SAW member 10 warps and deforms. That is, the SAW member 10 is distorted by pressure and load.

  Thereby, since the length of the propagation path 40 of the SAW member 10 changes, the phase of the SAW excited by the comb electrode 20 and reflected by the reflector 30 and received by the comb electrode 20 changes according to the pressure. To do. Therefore, this phase change amount is detected, and the pressure or load is calculated based on the detected phase change amount and the relationship between the phase change amount and the pressure or load. Note that the phase of the SAW is detected by a phase detection circuit (not shown), and the calculation of the phase change amount and the calculation of the pressure and load from the phase change amount are executed by a calculation unit (not shown).

  In such a SAW element 1, in this embodiment, when the wavelength of SAW is λ, the film thickness D3 of the comb electrode 20 is 0.05 times or more and 0.20 times or less of the wavelength λ. . The film thickness D3 of the comb-tooth electrode 20 is the thickness dimension of the comb-tooth portion 21 along the thickness direction of the ScAlN film 12, as shown in FIG.

  The grounds for specifying the film thickness D3 of the comb electrode 20 in the range of 0.05λ to 0.20λ will be described. The reflector 30 is formed at the same time as the comb electrode 20 and therefore has the same film thickness as the comb electrode 20.

  In order to improve the piezoelectric characteristics in the SAW element 1 of the present embodiment using the ScAlN film 12, the present inventor uses the film thickness D3 of the comb electrode 20 and the SAW member 10 to excite SAW. The relationship with electromechanical coupling coefficient was investigated by simulation. The comb electrode 20 has a thickness D3 normalized by the SAW wavelength λ (standardized thickness) and does not depend on the wavelength λ.

  Here, the ScAlN film 12 used in the simulation for obtaining the electromechanical coupling coefficient has an Sc concentration of 43 at% when the total of Sc and Al is 100 at%, and a film thickness of 0.6λ (with SAW wavelength). 0.6 times). Each characteristic of the ScAlN film 12, that is, the elastic constant, the piezoelectric e constant, and the dielectric constant is described in the table shown in FIG.

  The characteristics of the diamond substrate 11 and the comb-shaped electrode 20 made of copper used in the simulation, that is, the elastic constant and dielectric constant of the substrate 11 and the elastic constant and dielectric constant of the comb-shaped electrode 20 are generally Typical values were used.

  FIG. 4 shows the result of this simulation. Here, the Sezawa wave, which is the second-order mode of the SAW having the highest electromechanical coupling coefficient, is shown. As shown in FIG. 4, regarding the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient is Once it increased, it tended to decrease. In FIG. 4, the peak of the increase is when the film thickness D3 is about 0.12λ.

  Here, as described above, since the film thickness D3 of the conventional comb-teeth electrode 20 is less than 0.05λ, the reference value for increasing the electromechanical coupling coefficient to be equal to or larger than the conventional one is shown in FIG. In this graph, the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0 was used.

  When the film thickness D3 of the comb electrode 20 is 0.20λ, the electromechanical coupling coefficient is equal to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. Accordingly, it can be seen from FIG. 4 that if the thickness D3 of the comb electrode 20 is in the range of 0.05λ or more and 0.20λ or less, a large electromechanical coupling coefficient equal to or greater than the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  Then, as in this embodiment, in the SAW element 1 using the ScAlN film 12, by specifying the film thickness D3 of the comb electrode 20 as 0.05λ or more and 0.20λ or less, it is equal to or more than the conventional one. A large electromechanical coupling coefficient can be appropriately realized.

  Increasing the thickness D3 of the comb electrode 20 to 0.20λ can be realized by a lift-off process. In addition, by increasing the film thickness D3 of the comb electrode 20 to 0.20λ in this way, it is possible to expect the effects of reducing the wiring resistance and increasing the reflection coefficient.

(Second Embodiment)
A SAW element according to a second embodiment of the present invention will be described. The SAW element of this embodiment is the same as the SAW element 1 of the first embodiment, except that the substrate 11 of the SAW member 10 is a substrate 11 made of Si (hereinafter referred to as Si substrate 11). The difference is. In the present embodiment, this difference will be mainly described.

  Thus, in the SAW element of this embodiment, the SAW member 10 has a ScAlN / Si structure. As this Si substrate 11, a substrate using a plane orientation (001) and a SAW propagation direction <100> is used.

  In the present embodiment, the thickness D3 of the comb electrode 20 is 0.05 times or more and 0.40 times or less the SAW wavelength λ.

  The basis of the range of the film thickness D3 of the comb electrode 20 in this embodiment will be described. Also for the SAW element of this embodiment, the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient was examined by simulation in the same manner as in the first embodiment.

  The ScAlN film 12 used in this simulation has the same Sc concentration, film thickness, and characteristics (see FIG. 3) as those in the first embodiment, and the Si substrate 11 and the comb made of copper used in the simulation. For each characteristic (elastic constant and dielectric constant) of the tooth electrode 20, general values were used.

  FIG. 5 shows the result of this simulation, and here also shows the Sezawa wave, which is the second-order mode of the SAW having the highest electromechanical coupling coefficient. As shown in FIG. 5, also in this embodiment, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient tends to decrease after increasing once. It was.

  As in the first embodiment, in the range where the thickness D3 of the comb electrode 20 is 0.05λ or more, a guideline value for making the electromechanical coupling coefficient equal to or larger than the conventional one is shown in FIG. In the graph, the value of the electromechanical coupling coefficient when extrapolated to film thickness D3 = 0 was used.

  According to FIG. 5, when the film thickness D3 of the comb electrode 20 is 0.40λ, the electromechanical coupling coefficient is equivalent to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. . From this, it can be seen from FIG. 5 that if the film thickness D3 of the comb electrode 20 is in the range of 0.05λ or more and 0.40λ or less, a large electromechanical coupling coefficient equal to or greater than the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  Then, in the SAW element using the ScAlN film 12 as in the present embodiment, by specifying the film thickness D3 of the comb electrode 20 as 0.05λ or more and 0.40λ or less, it is equal to or larger than the conventional one. The electromechanical coupling coefficient can be appropriately realized.

  Also in this embodiment, increasing the film thickness D3 of the comb electrode 20 to 0.40λ can be realized by a lift-off process. In addition, by increasing the film thickness D3 of the comb electrode 20 to 0.40λ in this way, it is possible to expect the effects of decreasing the wiring resistance and increasing the reflection coefficient.

(Third embodiment)
A SAW element according to a third embodiment of the present invention will be described. The SAW element of the present embodiment is the same as the SAW element 1 of the first embodiment, except that the substrate 11 of the SAW member 10 is a substrate 11 made of sapphire (hereinafter referred to as sapphire substrate 11). The difference is. In the present embodiment, this difference will be mainly described.

  Thus, in the SAW element of this embodiment, the SAW member 10 has a ScAlN / sapphire structure. As this sapphire substrate 11, for example, a substrate whose surface orientation is the C plane and the SAW propagation direction is the direction in the a plane or the direction rotated by 60 ° from this direction is used. Under these conditions, the SAW characteristics are improved.

  In the present embodiment, the film thickness D3 of the comb electrode 20 is 0.05 times or more and 0.35 times or less of the SAW wavelength λ.

  The basis of the range of the film thickness D3 of the comb electrode 20 in this embodiment will be described. Also for the SAW element of this embodiment, the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient was examined by simulation in the same manner as in the first embodiment.

  The Sc concentration, film thickness, and characteristics (see FIG. 3) of the ScAlN film 12 used in the simulation are the same as those in the first embodiment, and the sapphire substrate 11 and the comb made of copper used in the simulation. For each characteristic (elastic constant and dielectric constant) of the tooth electrode 20, general values were used.

  FIG. 6 shows the result of this simulation, and here also shows the Sezawa wave as described above. As shown in FIG. 6, also in this embodiment, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient tends to decrease after increasing once. It was.

  As in the first embodiment, in the range where the thickness D3 of the comb electrode 20 is 0.05λ or more, a reference value for making the electromechanical coupling coefficient equal to or larger than the conventional one is shown in FIG. In the graph, the value of the electromechanical coupling coefficient when extrapolated to film thickness D3 = 0 was used.

  According to FIG. 6, when the film thickness D3 of the comb electrode 20 is 0.35λ, the electromechanical coupling coefficient is equal to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. . Thereby, it can be seen from FIG. 6 that if the film thickness D3 of the comb electrode 20 is in the range of 0.05λ or more and 0.40λ or less, a large electromechanical coupling coefficient equal to or greater than the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  Then, in the SAW element using the ScAlN film 12 as in this embodiment, the comb-teeth electrode 20 has a film thickness D3 of 0.05λ or more and 0.35λ or less, which is equal to or larger than the conventional one. The electromechanical coupling coefficient can be appropriately realized.

  Also in this embodiment, increasing the film thickness D3 of the comb electrode 20 to 0.35λ can be realized by a lift-off process. In addition, by increasing the film thickness D3 of the comb electrode 20 to 0.35λ in this way, it is possible to expect the effects of reducing the wiring resistance and increasing the reflection coefficient.

(Fourth embodiment)
A SAW device according to a fourth embodiment of the present invention will be described. The SAW element of this embodiment is different from the SAW element 1 of the first embodiment in that the material of the comb electrode 20 is changed from copper to aluminum. In the present embodiment, this difference will be mainly described.

  That is, in the SAW element of the present embodiment, both the comb-tooth electrode 20 and the reflector 30 formed collectively are made of aluminum. Here, the aluminum constituting the comb electrode 20 and the reflector 30 includes, in addition to pure Al, those containing a small amount of impurities containing Al as a main component, or alloys containing Al as a main component. It is a waste.

  In the present embodiment, the thickness D3 of the comb electrode 20 is 0.05 times or more and 0.25 times or less the SAW wavelength λ. The range of the film thickness D3 in this embodiment is also based on the result of examining the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient by simulation in the same manner as in the first embodiment. Is.

  The Sc concentration, film thickness, and characteristics (see FIG. 3) of the ScAlN film 12 used in this simulation are the same as those in the first embodiment, and the diamond substrate 11 and the comb made of aluminum used in the simulation are used. For each characteristic (elastic constant and dielectric constant) of the tooth electrode 20, general values were used.

  FIG. 7 shows the result of this simulation, and here also shows the Sezawa wave, as described above. As shown in FIG. 7, also in this embodiment, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient tends to decrease after increasing once. It was.

  As in the first embodiment, when the film thickness D3 of the comb electrode 20 is in the range of 0.05λ or more, the reference value for making the electromechanical coupling coefficient as large as the same as or higher than the conventional one is shown in FIG. In the graph, the value of the electromechanical coupling coefficient when extrapolated to film thickness D3 = 0 was used.

  According to FIG. 7, when the film thickness D3 of the comb electrode 20 is 0.25λ, the electromechanical coupling coefficient is equal to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. . Accordingly, it can be seen from FIG. 7 that if the thickness D3 of the comb electrode 20 is in the range of 0.05λ or more and 0.25λ or less, a large electromechanical coupling coefficient equal to or greater than that of the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  Then, in the SAW element using the ScAlN film 12 as in the present embodiment, by specifying the film thickness D3 of the comb electrode 20 as 0.05λ or more and 0.25λ or less, it is equal to or larger than the conventional one. The electromechanical coupling coefficient can be appropriately realized.

  Also in this embodiment, increasing the film thickness D3 of the comb electrode 20 to 0.25λ can be realized by a lift-off process. Then, by increasing the film thickness D3 of the comb electrode 20 to 0.25λ in this way, it is possible to expect the effect of reducing the wiring resistance or increasing the reflection coefficient.

(Fifth embodiment)
A SAW element according to a fifth embodiment of the present invention will be described. The SAW element of this embodiment is different from the SAW element 1 of the ScAlN / Si structure in the SAW member 10 shown in the second embodiment in that the material of the comb electrode 20 is changed from copper to aluminum. In the present embodiment, this difference will be mainly described.

  In other words, in the SAW element of the present embodiment, the SAW member 10 has a ScAlN / Si structure, and the comb electrode 20 and the reflector 30 formed in a lump on it are both made of aluminum. Here, the aluminum which comprises the comb-tooth electrode 20 and the reflector 30 is the same as that of the said 4th Embodiment.

  In the present embodiment, the thickness D3 of the comb electrode 20 is set to be 0.05 times or more and 0.55 times or less of the SAW wavelength λ. The range of the film thickness D3 in this embodiment is also based on the result of examining the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient by simulation in the same manner as in the first embodiment. Is.

  The ScAlN film 12 used in this simulation has the same Sc concentration, film thickness, and characteristics (see FIG. 3) as in the first embodiment, and the Si substrate 11 used in the simulation and a comb made of aluminum. For each characteristic (elastic constant and dielectric constant) of the tooth electrode 20, general values were used.

  FIG. 8 shows the result of this simulation, and here also shows the Sezawa wave as described above. As shown in FIG. 8, also in this embodiment, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient tends to decrease after increasing once. It was.

  As in the first embodiment, when the film thickness D3 of the comb electrode 20 is in the range of 0.05λ or more, the reference value for making the electromechanical coupling coefficient as large as the same as or higher than the conventional one is shown in FIG. In the graph, the value of the electromechanical coupling coefficient when extrapolated to film thickness D3 = 0 was used.

  According to FIG. 8, when the film thickness D3 of the comb electrode 20 is 0.55λ, the electromechanical coupling coefficient is equal to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. . Accordingly, it can be seen from FIG. 8 that if the film thickness D3 of the comb electrode 20 is in the range of 0.05λ to 0.55λ, a large electromechanical coupling coefficient equal to or greater than that of the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  Then, in the SAW element using the ScAlN film 12 as in the present embodiment, by specifying the film thickness D3 of the comb electrode 20 as 0.05λ or more and 0.55λ or less, it is equal to or larger than the conventional one. The electromechanical coupling coefficient can be appropriately realized.

  Also in this embodiment, increasing the film thickness D3 of the comb electrode 20 to 0.55λ can be realized by a lift-off process. In addition, by increasing the film thickness D3 of the comb electrode 20 to 0.55λ in this way, it is possible to expect the effect of reducing the wiring resistance or increasing the reflection coefficient.

(Sixth embodiment)
A SAW device according to a sixth embodiment of the present invention will be described. The SAW element of the present embodiment is different from the SAW element 1 of the ScAlN / sapphire structure shown in the third embodiment in that the material of the comb electrode 20 is changed from copper to aluminum. In the present embodiment, this difference will be mainly described.

  In other words, in the SAW element of the present embodiment, the SAW member 10 has a ScAlN / sapphire structure, and the comb electrode 20 and the reflector 30 formed in a lump on it are both made of aluminum. Here, the aluminum which comprises the comb-tooth electrode 20 and the reflector 30 is the same as that of the said 4th Embodiment.

  In the present embodiment, the thickness D3 of the comb electrode 20 is 0.05 times or more and 0.42 times or less of the SAW wavelength λ. The range of the film thickness D3 in this embodiment is also based on the result of examining the relationship between the film thickness D3 of the comb electrode 20 and the electromechanical coupling coefficient by simulation in the same manner as in the first embodiment. Is.

  The ScAlN film 12 used in this simulation has the same Sc concentration, film thickness, and characteristics (see FIG. 3) as in the first embodiment, and the sapphire substrate 11 used in the simulation and a comb made of aluminum. For each characteristic (elastic constant and dielectric constant) of the tooth electrode 20, general values were used.

  FIG. 9 shows the result of this simulation, and here also shows the Sezawa wave, as described above. As shown in FIG. 9, also in this embodiment, as the film thickness D3 of the comb electrode 20 increases from 0, the electromechanical coupling coefficient tends to decrease after increasing once. It was.

  As in the first embodiment, in the range where the thickness D3 of the comb electrode 20 is 0.05λ or more, the reference value for making the electromechanical coupling coefficient as large as the same as or higher than the conventional one is shown in FIG. In the graph, the value of the electromechanical coupling coefficient when extrapolated to film thickness D3 = 0 was used.

  According to FIG. 9, when the film thickness D3 of the comb electrode 20 is 0.42λ, the electromechanical coupling coefficient is equal to the value of the electromechanical coupling coefficient when extrapolated to the film thickness D3 = 0. . Accordingly, it can be seen from FIG. 9 that if the film thickness D3 of the comb electrode 20 is in the range of 0.05λ to 0.42λ, a large electromechanical coupling coefficient equal to or greater than that of the conventional one can be realized. The above is the basis for specifying the range of the film thickness D3 of the comb electrode 20 in the present embodiment.

  And, in the SAW element using the ScAlN film 12 as in this embodiment, the film thickness D3 of the comb electrode 20 is specified as 0.05λ or more and 0.42λ or less, so that it is equal to or larger than the conventional one. The electromechanical coupling coefficient can be appropriately realized.

  Also in this embodiment, increasing the film thickness D3 of the comb electrode 20 to 0.42λ can be realized by a lift-off process. Then, by increasing the film thickness D3 of the comb electrode 20 to 0.42λ in this way, it is possible to expect the effect of reducing the wiring resistance or increasing the reflection coefficient.

(Other embodiments)
In FIGS. 1 and 2, the reflection delay type SAW element is shown, but a transversal filter type SAW element, a resonance type SAW element, or the like may also be used. In addition to the sensor, the SAW element can be used for various purposes such as communication.

  Further, the present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope described in the claims. Moreover, each said embodiment is not limited to said example of illustration. In each of the above-described embodiments, it is needless to say that elements constituting the embodiment are not necessarily essential unless explicitly stated as essential and clearly considered essential in principle. Yes. Further, in each of the above embodiments, when numerical values such as the number, numerical value, quantity, range, etc. of the constituent elements of the embodiment are mentioned, it is clearly limited to a specific number when clearly indicated as essential and in principle. The number is not limited to the specific number except for the case. Further, in each of the above embodiments, when referring to the shape, positional relationship, etc. of the component, etc., the shape, unless otherwise specified and in principle limited to a specific shape, positional relationship, etc. It is not limited to the positional relationship or the like.

10 Surface acoustic wave member (SAW member)
11 Substrate 12 ScAlN film 20 Comb electrode

Claims (4)

A surface acoustic wave member (10) having a substrate (11) made of diamond and a ScAlN film (12) formed on the surface of the substrate;
A comb-tooth electrode (20) formed on the surface of the ScAlN film and made of copper for exciting the surface acoustic wave member with a surface acoustic wave;
Wherein when the wavelength of the surface acoustic wave is lambda, the thickness of the comb electrodes, Ri 0.20 times der 0.05 times or more of the wavelength lambda,
The ScAlN film has a Sc concentration of 43 at% when the total of Sc and Al is 100 at%, and the film thickness of the ScAlN film is 0.6 times the wavelength λ of the surface acoustic wave. A surface acoustic wave device. A surface acoustic wave member (10) having a substrate (11) made of sapphire and a ScAlN film (12) formed on the surface of the substrate;
A comb-tooth electrode (20) formed on the surface of the ScAlN film and made of copper for exciting the surface acoustic wave member with a surface acoustic wave;
Wherein when the wavelength of the surface acoustic wave is lambda, the thickness of the comb electrodes, Ri 0.35 times der 0.05 times or more of the wavelength lambda,
The ScAlN film has a Sc concentration of 43 at% when the total of Sc and Al is 100 at%, and the film thickness of the ScAlN film is 0.6 times the wavelength λ of the surface acoustic wave. A surface acoustic wave device. A surface acoustic wave member (10) having a substrate (11) made of diamond and a ScAlN film (12) formed on the surface of the substrate;
A comb-tooth electrode (20) formed on the surface of the ScAlN film and made of aluminum for exciting the surface acoustic wave member with a surface acoustic wave;
When the wavelength of the surface acoustic wave lambda, the thickness of the comb electrodes, Ri 0.25 times der 0.05 times or more of the wavelength lambda,
The ScAlN film has a Sc concentration of 43 at% when the total of Sc and Al is 100 at%, and the film thickness of the ScAlN film is 0.6 times the wavelength λ of the surface acoustic wave. A surface acoustic wave device. A surface acoustic wave member (10) having a substrate (11) made of sapphire and a ScAlN film (12) formed on the surface of the substrate;
A comb-tooth electrode (20) formed on the surface of the ScAlN film and made of aluminum for exciting the surface acoustic wave member with a surface acoustic wave;
Wherein when the wavelength of the surface acoustic wave is lambda, the thickness of the comb electrodes, Ri 0.42 der 0.05 times or more of the wavelength lambda,
The ScAlN film has a Sc concentration of 43 at% when the total of Sc and Al is 100 at%, and the film thickness of the ScAlN film is 0.6 times the wavelength λ of the surface acoustic wave. A surface acoustic wave device.

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