Elastic wave device

文档序号：1866518 发布日期：2021-11-19 浏览：18次中文

阅读说明：本技术 弹性波装置 (Elastic wave device ) 是由大门克也于 2020-04-03 设计创作，主要内容包括：一种弹性波装置,能够有效地抑制高次模式。本发明的弹性波装置(1)具备作为硅基板的支承基板(4)、设置在支承基板(4)上的氮化硅膜(5)、设置在氮化硅膜(5)上的氧化硅膜(6)、设置在氧化硅膜(6)上且使用了Y切割X传播的钽酸锂的压电体层(7)及设置在压电体层(7)上且具有多个电极指的IDT电极(3)。将由IDT电极(3)的电极指间距规定的波长设为λ时,压电体层(7)的膜厚为1λ以下,压电体层(7)的欧拉角为(0±5°的范围内,θ,0±5°的范围内)或(0±5°的范围内,θ,180±5°的范围内),压电体层(7)的欧拉角中的θ为相互等效的95.5°≤θ＜117.5°或-84.5°≤θ＜-62.5°,压电体层(7)的欧拉角中的θ与氮化硅膜(5)的膜厚的关系为表1或表2所示的组合。(An elastic wave device capable of effectively suppressing higher-order modes. An elastic wave device (1) is provided with a support substrate (4) as a silicon substrate, a silicon nitride film (5) provided on the support substrate (4), a silicon oxide film (6) provided on the silicon nitride film (5), a piezoelectric layer (7) provided on the silicon oxide film (6) and using Y-cut X-propagated lithium tantalate, and an IDT electrode (3) provided on the piezoelectric layer (7) and having a plurality of electrode fingers. When λ is a wavelength defined by the electrode finger pitch of the IDT electrode (3), the film thickness of the piezoelectric layer (7) is 1 λ or less, the Euler angle of the piezoelectric layer (7) is (in the range of 0 + -5 °, θ, in the range of 0 + -5 °), or (in the range of 0 + -5 °, θ, in the range of 180 + -5 °), θ in the Euler angle of the piezoelectric layer (7) is 95.5 ° < θ < 117.5 ° or-84.5 ° < θ < 62.5 ° which are equivalent to each other, and the relationship between θ in the Euler angle of the piezoelectric layer (7) and the film thickness of the silicon nitride film (5) is a combination shown in Table 1 or Table 2.)

1. An elastic wave device is provided with:

a support substrate as a silicon substrate;

a silicon nitride film provided on the support substrate;

a silicon oxide film provided on the silicon nitride film;

a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and

an IDT electrode disposed directly or indirectly on the piezoelectric layer and having a plurality of electrode fingers,

wherein the thickness of the piezoelectric layer is 1 λ or less when λ is a wavelength defined by an electrode finger pitch of the IDT electrode,

the Euler angle of the piezoelectric layer is (in the range of 0 + -5 DEG, theta, in the range of 0 + -5 DEG) or (in the range of 0 + -5 DEG, theta, in the range of 180 + -5 DEG), theta in the Euler angle of the piezoelectric layer is 95.5 DEG or more and 117.5 DEG or-84.5 DEG or more and theta is less than-62.5 DEG which are equivalent to each other,

the relation between theta in the Euler angle of the piezoelectric layer and the film thickness of the silicon nitride film is a combination shown in the following Table 1 or Table 2,

[ Table 1]

[ Table 2]

2. The elastic wave device according to claim 1,

the film thickness of the silicon nitride film is 0.5 lambda or less,

the plane orientation of the support substrate is Si (111), the propagation angle of the support substrate is psi, and n is an arbitrary integer 0, + -1, + -2. -,

in the case where the euler angle of the piezoelectric layer is (in the range of 0 ± 5 °, θ, in the range of 0 ± 5 °), the propagation angle ψ of the support substrate is in the range of 60 ° ± 50 ° +120 ° × n,

in the case where the euler angle of the piezoelectric layer is (in the range of 0 ± 5 °, θ, in the range of 180 ± 5 °), the propagation angle ψ of the support substrate is in the range of 0 ° ± 50 ° +120 ° × n.

3. The elastic wave device according to claim 2,

in the case where the euler angle of the piezoelectric layer is (in the range of 0 ± 5 °, θ, in the range of 0 ± 5 °), the propagation angle ψ of the support substrate is in the range of 60 ° ± 34 ° +120 ° × n,

4. The elastic wave device according to any one of claims 1 to 3,

a dielectric layer is provided between the piezoelectric layer and the IDT electrode,

the acoustic velocity of a bulk wave propagating through the dielectric layer is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric layer.

5. The elastic wave device according to claim 4,

the dielectric layer is a layer of SiN,

the thickness of the SiN layer and θ in the Euler angle of the piezoelectric layer are an angle and a thickness of the film in a range in which the phase of a Rayleigh wave derived from the following formula 1 is-70 DEG or less,

[ numerical formula 1]

The rayleigh wave has a phase (-81.6949045454545) + (-0.67490613636364) x (θ -110) + (-189.247997265892) x (("SiN film thickness [ λ ]") -0.05) +0.111730638111889 x ((θ -110) x (θ -110) -40) +36.1595358851675 x (((θ -110) x (("SiN film thickness [ λ ]") -0.05)) +5258.22469396632 x (((((("SiN film thickness [ λ ]") -0.05) x (("SiN film thickness [ λ ]") -0.05) -0.00083125)

… formula 1.

6. The elastic wave device according to claim 4,

the dielectric layer is Al₂O₃A layer of a material selected from the group consisting of,

theta and Al in Euler angle of the piezoelectric layer₂O₃The film thickness of the layer is an angle and film thickness in a range where the phase of Rayleigh waves derived from the following formula 2 is-70 DEG or less,

[ numerical formula 2]

The rayleigh wave phase (-80.1333863636364) + (-0.554522499999998) x (θ -110) + (-173.463554340396) x (("Al 2O3 thickness [ λ ]") -0.05) +0.149698033216783 x (((θ -110) x (θ -110) -40) +41.1703301435407 x (((θ -110) ("Al 2O3 thickness [ λ ]") -0.05)) +4990.83763126825 x ((((("Al 2O3 thickness [ λ ]") -0.05) × ("Al 2O3 thickness [ λ ]") -0.05) -0.00083125)

… formula 2.

7. The elastic wave device according to claim 4,

the dielectric layer is an AlN layer,

theta in the Euler angle of the piezoelectric layer and the film thickness of the AlN layer are an angle and a film thickness in a range in which the phase of the Rayleigh wave derived from the following formula 3 is-70 DEG or less,

[ numerical formula 3]

The rayleigh wave has a phase (-87.3504136363636) + (-0.270137500000004) x (θ -110) + (-97.7367464114832) x (("AIN film thickness [ λ ]") -0.05) +0.0257423222610727 x ((θ -110) x (θ -110) -40) +14.0575563909775 x (((θ -110) x (("AIN β [ λ ]") -0.05)) +3335.40856272914 x (((((("AIN film thickness [ λ ]") -0.05))) x ((("AIN film thickness [ λ ]") -0.05) -0.00083125)

… formula 3.

8. An elastic wave device is provided with:

a support substrate as a silicon substrate;

a silicon nitride film provided on the support substrate;

a silicon oxide film provided on the silicon nitride film;

a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and

an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers,

wherein the thickness of the piezoelectric layer is 1 λ or less when λ is a wavelength defined by an electrode finger pitch of the IDT electrode,

the Euler angle of the piezoelectric layer is (0 + -5 degree, theta, 0 + -5 degree), theta in the Euler angle of the piezoelectric layer is 117.5 DEG-theta < 129.5 DEG,

the relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the silicon nitride film is a combination shown in table 3 below,

[ Table 3]

9. An elastic wave device is provided with:

a support substrate as a silicon substrate;

a silicon nitride film provided on the support substrate;

a silicon oxide film provided on the silicon nitride film;

a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and

an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers,

wherein the thickness of the piezoelectric layer is 1 λ or less when λ is a wavelength defined by an electrode finger pitch of the IDT electrode,

the Euler angle of the piezoelectric layer is (0 + -5 degree, theta, 0 + -5 degree), theta in the Euler angle of the piezoelectric layer is more than or equal to 85.5 degrees and less than 95.5 degrees,

the relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the silicon nitride film is a combination shown in table 4 below,

[ Table 4]

10. The elastic wave device according to claim 1,

the elastic wave device further includes a protective film provided on the piezoelectric layer so as to cover the IDT electrode,

the protective film is a SiN protective film made of SiN,

the thickness of the SiN protective film and θ in the Euler angle of the piezoelectric layer are an angle and a thickness in a range in which the phase of a Rayleigh wave derived from the following expression 4 is-70 DEG or less and the phase of a higher-order mode derived from the following expression 5 is-70 DEG or less,

[ numerical formula 4]

Rayleigh (-51.52545) +1.78434436363636 x (θ -127.5) +551.57103030303 x (("SiN protective film [ λ ]") -0.0275) +0.102490363636364 x ((θ -127.5) × (θ -127.5) -206.25) +60.3989730027549 x ((θ -127.5) × ((("SiN protective film [ λ ]") -0.0275))

… formula 4

[ numerical formula 5]

High-order mode (-26.58444) +2.61766496969697 x (θ -127.5) +1545.84533333333 x (("SiN protective film [ λ ]") -0.0275) + (-0.0379121515151515) × ((θ -127.5) × (θ -127.5) -206.25) +56.9468179981635 × ((θ -127.5) × ((("SiN protective film [ λ ]") -0.0275))

… formula 5.

11. The elastic wave device according to claim 1,

the elastic wave device further includes a protective film provided on the piezoelectric layer so as to cover the IDT electrode,

the protective film is made of Al₂O₃Al of (2)₂O₃A protective film is arranged on the surface of the substrate,

theta and Al in Euler angle of the piezoelectric layer₂O₃The film thickness of the protective film is an angle and a film thickness in a range in which the phase of a Rayleigh wave derived from the following expression 6 is-70 DEG or less and the phase of a higher-order mode derived from the following expression 7 is-70 DEG or less,

[ numerical formula 6]

Rayleigh wave (-40.9578496399338) +2.25601530917004 x (θ -127.272727272727) +964.821146439353 x (("Al 2O3 protective film [ λ ]") -0.0274747474747475) +0.100000607678288 x (((θ -127.272727272727) × (θ -127.272727272727) -203.168044077135) +74.7099873794682 x (((θ -127.272727272727) × (("Al 2O3 protective film [ λ ]") -0.0274747474747475))

… formula 6

[ number formula 7]

High-order mode (-21.0375184962657) +2.73177575694271 x (θ -127.272727272727) +1701.65880601573 x (("Al 2O3 protective film [ λ ]") -0.0274747474747475) + ("0.0499273041403373) × ((θ -127.272727272727) × (θ -127.272727272727) -203.168044077135) +53.1637721066764 x (((θ -127.272727272727) × ((((" Al2O3 protective film [ λ ] ") -0.0274747474747475)) + (" 34811.3628963409) × ((((((("Al 2O3 protective film [ λ ]") -0.0274747474747475) × ("Al 2O3 protective film [ λ ]") -0.0274747474747475) -0.00020826956433017)

… formula 7.

12. The elastic wave device according to claim 1,

the elastic wave device further includes a protective film provided on the piezoelectric layer so as to cover the IDT electrode,

the protective film is an AlN protective film made of AlN,

the thickness of the AlN protective film and theta at the Euler angle of the piezoelectric layer are an angle and a thickness in a range in which the phase of a Rayleigh wave derived from the following expression 8 is-70 DEG or less and the phase of a higher-order mode derived from the following expression 9 is-70 DEG or less,

[ number formula 8]

Rayleigh (-46.4003800000001) +1.94268775757576 x (θ -127.5) +755.618424242424 x (("AIN protective film [ λ ]") -0.0275) +0.109821151515152 x ((θ -127.5) × (θ -127.5) -206.25) +69.3031610651975 x ((θ -127.5) × ((("AlN protective film [ λ ]") -0.0275))

… formula 8

[ numerical formula 9]

High-order mode (-24.10841) +2.65936036363636 x (θ -127.5) +1560.34145454545 x (("AIN protective film [ λ ]") -0.0275) + (-0.0415194696969697) × ((θ -127.5) × (θ -127.5) -206.25) +54.3834578512397 x (((θ -127.5) × (((("AIN protective film [ λ ]") -0.0275))

… formula 9.

Technical Field

The present invention relates to an elastic wave device.

Background

Conventionally, elastic wave devices have been widely used in filters of cellular phones and the like. Patent document 1 listed below discloses an example of an elastic wave device. In this acoustic wave device, a support substrate, a high acoustic velocity film, a low acoustic velocity film, and a piezoelectric film are sequentially stacked, and an IDT (Inter Digital Transducer) electrode is provided on the piezoelectric film. The Q value is improved by providing the above-described laminated structure.

Prior art documents

Patent document

Patent document 1: international publication No. 2012/086639

Disclosure of Invention

Problems to be solved by the invention

However, in the above-described elastic wave device, when the surface orientation of the supporting substrate used is, for example, Si (111), the higher-order mode may not be sufficiently suppressed.

The present invention aims to provide an elastic wave device capable of effectively suppressing higher-order modes.

Means for solving the problems

In one broad aspect, an elastic wave device according to the present invention includes: a support substrate as a silicon substrate; a silicon nitride film provided on the support substrate; a silicon oxide film provided on the silicon nitride film; a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and an IDT electrode which is provided directly or indirectly on the piezoelectric layer and has a plurality of electrode fingers, wherein when a wavelength specified by an electrode finger pitch of the IDT electrode is represented by λ, a film thickness of the piezoelectric layer is 1 λ or less, an Euler angle of the piezoelectric layer is (in a range of 0 ± 5 °, θ, in a range of 0 ± 5 °), or (in a range of 0 ± 5 °, θ, in a range of 180 ± 5 °), θ in the Euler angles of the piezoelectric layer is 95.5 ° ≦ θ < 117.5 ° or-84.5 ° ≦ θ < -62.5 ° which are equivalent to each other, and a relationship between θ in the Euler angles of the piezoelectric layer and a film thickness of the silicon nitride film is a combination shown in the following Table 1 or Table 2.

[ Table 1]

[ Table 2]

In another broad aspect of the elastic wave device according to the present invention, the elastic wave device includes: a support substrate as a silicon substrate; a silicon nitride film provided on the support substrate; a silicon oxide film provided on the silicon nitride film; a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, wherein when λ is a wavelength defined by an electrode finger pitch of the IDT electrode, a film thickness of the piezoelectric layer is 1 λ or less, an euler angle of the piezoelectric layer is (in a range of 0 ± 5 ° and θ, in a range of 0 ± 5 °), θ in the euler angle of the piezoelectric layer is 117.5 ° or less and θ < 129.5 °, and a relationship between θ in the euler angle of the piezoelectric layer and a film thickness of the silicon nitride film is a combination shown in table 3 below.

[ Table 3]

In another broad aspect of the elastic wave device according to the present invention, the elastic wave device includes: a support substrate as a silicon substrate; a silicon nitride film provided on the support substrate; a silicon oxide film provided on the silicon nitride film; a piezoelectric layer provided on the silicon oxide film and using Y-cut X-propagated lithium tantalate; and an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, wherein when λ is a wavelength defined by an electrode finger pitch of the IDT electrode, a film thickness of the piezoelectric layer is 1 λ or less, an euler angle of the piezoelectric layer is (in a range of 0 ± 5 ° and θ, in a range of 0 ± 5 °), θ in the euler angle of the piezoelectric layer is 85.5 ° or more and θ <95.5 °, and a relationship between θ in the euler angle of the piezoelectric layer and a film thickness of the silicon nitride film is a combination shown in table 4 below.

[ Table 4]

Effects of the invention

According to the elastic wave device of the present invention, higher-order modes can be effectively suppressed.

Drawings

Fig. 1 is a plan view of an elastic wave device according to a first embodiment of the present invention.

Fig. 2 is a front cross-sectional view taken along line I-I in fig. 1 and showing the vicinity of a pair of electrode fingers in an IDT electrode of an acoustic wave device according to a first embodiment of the present invention.

Fig. 3 is a schematic diagram for explaining the (111) plane of the silicon substrate.

FIG. 5 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 97 ° ≦ θ ≦ 103 ° in the Euler angle of the piezoelectric layer.

FIG. 6 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 104 ° ≦ θ ≦ 110 ° in the Euler angle of the piezoelectric layer.

Fig. 7 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 111 ° ≦ θ ≦ 117 ° in the euler angle of the piezoelectric layer.

Fig. 8 is a diagram showing a relationship between the propagation angle ψ of the support substrate and the phase of the higher-order mode.

Fig. 9 is an enlarged view of fig. 8.

Fig. 10 is a diagram showing a relationship between the propagation angle ψ of the support substrate and the phase of the higher-order mode.

Fig. 11 is a front cross-sectional view showing the vicinity of a pair of electrode fingers in an IDT electrode of an acoustic wave device according to a second embodiment of the present invention.

Fig. 12 is a diagram showing phase characteristics of elastic wave devices according to the first and second embodiments of the present invention.

Fig. 13 is an enlarged view of fig. 12.

Fig. 14 is a graph showing a relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the silicon nitride layer and the phase of the rayleigh wave.

Fig. 15 is a graph showing a relationship between θ and the film thickness of the aluminum oxide layer and the phase of the rayleigh wave in the euler angle of the piezoelectric layer.

Fig. 16 is a graph showing a relationship between θ and the film thickness of the aluminum nitride layer and the phase of the rayleigh wave in the euler angle of the piezoelectric layer.

FIG. 18 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 119 ° ≦ θ ≦ 122 ° in the Euler angle of the piezoelectric layer.

Fig. 19 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 123 ° ≦ θ ≦ 126 ° in the euler angle of the piezoelectric layer.

FIG. 20 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 127 ° ≦ θ ≦ 129 ° in the Euler angle of the piezoelectric layer.

Fig. 21 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 130 ° in the euler angle of the piezoelectric body layer.

Fig. 23 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 86 ° ≦ θ ≦ 88 ° in the euler angle of the piezoelectric layer.

FIG. 24 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 89 ° ≦ θ ≦ 95 ° in the Euler angle of the piezoelectric layer.

Fig. 25 is a front cross-sectional view showing the vicinity of a pair of electrode fingers in an IDT electrode of an acoustic wave device according to a fifth embodiment of the present invention.

Fig. 26 is a diagram showing a relationship between θ and the film thickness of the SiN protective film in the euler angle of the piezoelectric layer, and the phase of the rayleigh wave and the higher-order mode.

FIG. 27 shows theta and Al in Euler angles of piezoelectric layers₂O₃A graph of the relationship between the protective film and the phases of the Rayleigh wave and the higher-order mode.

Fig. 28 is a diagram showing a relationship between θ and the AlN protective film thickness at the euler angle of the piezoelectric layer, and the phase of the rayleigh wave and the higher-order mode.

Detailed Description

The present invention will be made clear by the following description of specific embodiments thereof with reference to the accompanying drawings.

It should be noted that the embodiments described in the present specification are exemplary, and it is pointed out in advance that partial substitutions or combinations of the structures can be made between different embodiments.

Fig. 1 is a plan view of an elastic wave device according to a first embodiment of the present invention.

Elastic wave device 1 includes piezoelectric substrate 2. An IDT electrode 3 is provided on the piezoelectric substrate 2. The elastic wave is excited by applying an ac voltage to the IDT electrode 3. A pair of reflectors 8A and 8B are provided on the piezoelectric substrate 2 on both sides of the IDT electrode 3 in the elastic wave propagation direction. Elastic wave device 1 of the present embodiment is an elastic wave resonator. However, acoustic wave device 1 of the present invention is not limited to the acoustic wave resonator, and may be a filter device having a plurality of acoustic wave resonators, a multiplexer including the filter device, or the like.

The IDT electrode 3 includes a first bus bar 16 and a second bus bar 17 facing each other. The IDT electrode 3 has a plurality of first electrode fingers 18 each having one end connected to the first bus bar 16. The IDT electrode 3 has a plurality of second electrode fingers 19 each having one end connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are alternately inserted into each other.

The IDT electrode 3 includes a laminated metal film in which a Ti layer, an Al layer, and a Ti layer are laminated in this order from the piezoelectric substrate 2 side. The material of the reflectors 8A and 8B is also the same as that of the IDT electrode 3. The materials of the IDT electrode 3, the reflectors 8A and the reflectors 8B are not limited to the above. Alternatively, the IDT electrode 3, the reflectors 8A and 8B may include a single metal film.

Fig. 2 is a front cross-sectional view taken along line I-I in fig. 1 and showing the vicinity of a pair of electrode fingers in IDT electrode 3 of the acoustic wave device according to the first embodiment.

Piezoelectric substrate 2 of elastic wave device 1 includes support substrate 4, silicon nitride film 5 provided on support substrate 4, silicon oxide film 6 provided on silicon nitride film 5, and piezoelectric layer 7 provided on silicon oxide film 6. The IDT electrode 3, the reflector 8A, and the reflector 8B are provided on the piezoelectric layer 7.

The support substrate 4 of the present embodiment is a silicon substrate. The plane orientation of the support substrate 4 is Si (111). Here, the plane orientation of the support substrate 4 means the plane orientation of the support substrate 4 on the piezoelectric layer 7 side. Si (111) represents a substrate obtained by cutting in a (111) plane orthogonal to a crystal axis represented by miller index [111] in a crystal structure of silicon having a diamond structure. The (111) plane is the plane shown in fig. 3. However, other crystallographically equivalent facets are also included. In the present embodiment, the euler angle of the (111) plane of the support substrate 4 is (-45 °, -54.7 °, ψ). Here, ψ among euler angles of the support substrate 4 is a propagation angle of the support substrate 4. The propagation angle of the support substrate 4 is an angle formed by the elastic wave propagation direction and the crystal axis [1-10] of silicon in the (111) plane. The crystal symmetry is expressed as psi +120 °.

In the elastic wave device 1, the silicon nitride constituting the silicon nitride film 5 is SiN, and the silicon oxide constituting the silicon oxide film 6 is SiO₂. However, nitrogenThe ratio of nitrogen in the silicon oxide film 5 and the ratio of oxygen in the silicon oxide film 6 are not limited to the above.

The piezoelectric layer 7 is a lithium tantalate layer. More specifically, for the piezoelectric layer 7, LiTaO propagating Y cut X is used₃. Here, when λ is a wavelength defined by the electrode finger pitch of the IDT electrode 3, the thickness of the piezoelectric layer 7 is 1 λ or less. The "film thickness" of a certain layer (film) is the size of the layer in the thickness direction, and is the size of the support substrate 4, the silicon nitride film 5, the silicon oxide film 6, and the piezoelectric layer 7 in the direction in which the layers are stacked. The euler angle of the piezoelectric layer 7 is (in the range of 0 ± 5 °, θ, in the range of 0 ± 5 °) or (in the range of 0 ± 5 °, θ, in the range of 180 ± 5 °). Theta in the Euler angles of the piezoelectric layers 7 is 95.5 DEG-117.5 DEG or-84.5 DEG-62.5 DEG equivalent to each other.

The present embodiment is characterized by having the following configuration. 1) The piezoelectric substrate 2 includes a laminated body in which a support substrate 4 as a silicon substrate, a silicon nitride film 5, a silicon oxide film 6, and a piezoelectric layer 7 using lithium tantalate which is Y-cut X-propagated are laminated in this order. 2) The thickness of the piezoelectric layer 7 is 1 λ or less. 3) The relationship between θ in the euler angle of piezoelectric layer 7 and the film thickness of silicon nitride film 5 is a combination shown in table 5 or table 6 below. This can suppress the high-order mode. The details thereof are explained below. After the description of the case shown in table 5, the case shown in table 6 will be described.

[ Table 5]

[ Table 6]

In an elastic wave device having the same laminated structure as that of the first embodiment, the relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer and the phase of the higher-order mode was determined. Table 5 shows that the high-order mode is-70 ° or less, and θ and the film thickness of the silicon nitride film in the high-order mode can be effectively suppressed. Here, the conditions of the elastic wave device are as follows.

A support substrate: silicon (Si), plane orientation,. Si (111), euler angle in (111) plane, (-45 °, -54.7 °, 46 °)

Silicon nitride film: film thickness of 0.0005 lambda or more and 1.5 lambda or less

Silicon oxide film: film thickness 0.15 lambda

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (96 DEG to 117 DEG inclusive) and 0 DEG

IDT electrode: the material was, in order from the piezoelectric substrate side, Ti/Al/Ti, and the film thickness of each layer was, in order from the piezoelectric substrate side, 0.006 λ/0.05 λ/0.002 λ

Wavelength λ of IDT electrode: 2 μm

Fig. 4 to 7 show the results obtained when θ in the euler angles of the piezoelectric layers was changed in the range of 96 ° ≦ θ ≦ 117 °. For example, θ is θ₁When the effect of suppressing spurious in higher-order mode or the like is exhibited, it is found that if θ is set₁Within the range of about + -0.5 deg., the same effect can be obtained. Therefore, Table 5 shows the range from 95.5. ltoreq. theta.less than 96.5 degrees to 116.5. ltoreq. theta.less than 117.5 degrees. Similarly, tables other than table 5 may be described as ranges within θ ± 0.5 °.

Fig. 4 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 96 ° in the euler angle of the piezoelectric body layer. FIG. 5 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 97 ° ≦ θ ≦ 103 ° in the Euler angle of the piezoelectric layer. FIG. 6 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 104 ° ≦ θ ≦ 110 ° in the Euler angle of the piezoelectric layer. Fig. 7 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 111 ° ≦ θ ≦ 117 ° in the euler angle of the piezoelectric layer.

As shown in fig. 4, when θ is 96 °, the phase of the high-order mode becomes-70 ° or less when the film thickness of the silicon nitride film is in the range of 0.0005 λ or more and 0.746 λ or less. Table 5 shows the results. Similarly, as shown in fig. 5 to 7, table 5 shows the range of the film thickness of the silicon nitride film in which the phase of the higher-order mode is equal to or less than-70 ° when θ in the euler angle of the piezoelectric layer is changed from 97 ° to 117 ° at once. As described above, it is understood that the relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer can effectively suppress the higher-order mode in the present embodiment as the combination shown in table 5. The reason why the high-order mode can be suppressed in this manner is considered to be as follows.

For example, a high-order mode near twice the resonance frequency is a rayleigh system mode, and has a propagation direction component and a depth direction component. The coupling coefficient of the rayleigh wave decreases within a certain fixed range of the cut angle of the piezoelectric body constituting the piezoelectric layer. Similarly, the cut angle of the piezoelectric body is also considered to affect the higher-order mode. In addition, it is considered that the plane orientation of silicon constituting the support substrate also affects the higher-order mode. Therefore, it is considered that the higher-order mode can be suppressed by setting the film thickness of the silicon nitride film to such a degree that the wave reaches the support substrate.

Even in the case where-84.5 ° ≦ θ ≦ -62.5 ° equivalent to the case where θ in the euler angle of the piezoelectric layer 7 is 95.5 ° ≦ θ < 117.5 °, the higher order mode can be suppressed in the same manner as described above. Therefore, even when the relationship between θ and the film thickness of the silicon nitride film 5 is the combination shown in table 6, the higher-order mode can be suppressed.

However, in the above, the case where the propagation angle ψ in the (111) plane of the support substrate is 46 ° is shown, but is not limited thereto. With the structure described below, when θ in the euler angle of the piezoelectric layer is 95.5 ° ≦ θ < 117.5 ° or-84.5 ° ≦ θ < -62.5 °, the higher-order mode can be further suppressed. 1) The silicon nitride film has a film thickness of 0.5 lambda or less, and the surface orientation of the support substrate is Si (111). 2a) The Euler angle of the piezoelectric layer is (0 + -5 DEG, theta, 0 + -5 DEG), and when n is an arbitrary integer (0, + -1, + -2) and theta in the Euler angle of the piezoelectric layer is 95.5 DEG-theta < 117.5 DEG or-84.5 DEG-theta < 62.5 DEG, the propagation angle psi of the support substrate is in the range of 60 DEG + -50 DEG +120 DEG x n. 2b) The Euler angle of the piezoelectric layer is (0 + -5 DEG, theta, 180 + -5 DEG), and when n is an arbitrary integer (0, + -1, + -2) and theta in the Euler angle of the piezoelectric layer is 95.5 DEG-theta < 117.5 DEG or-84.5 DEG-theta < 62.5 DEG, the propagation angle psi of the support substrate is in the range of 0 DEG + -50 DEG +120 DEG x n. The details thereof are explained. The case of 2b) will be described after the case of 2a) is described.

In an elastic wave device having the same laminated structure as that of the first embodiment, the relationship between θ in the euler angle of the piezoelectric layer, the film thickness of the silicon nitride film, the propagation angle ψ of the support substrate, and the phase of the higher-order mode was obtained. The conditions of the elastic wave device are as follows.

A support substrate: silicon (Si), plane orientation, euler angle in Si (111), (111) plane (-45 °, -54.7 °, 0 ° < ψ < 360 °)

Silicon nitride film: film thickness of 0.5 lambda or less

Silicon oxide film: film thickness 0.15 lambda

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (96 DEG to 117 DEG inclusive) and 0 DEG

Wavelength λ of IDT electrode: 2 μm

Fig. 8 shows a relationship between the propagation angle ψ of the support substrate and the phase of the higher-order mode. Fig. 9 is an enlarged view of fig. 8. Here, ψ +120 ° indicates a case where ψ is 0 ° to 120 °.

As shown in fig. 8, regardless of the magnitude of the propagation angle ψ, the phase of the high-order mode is smaller than-77 °, and the high-order mode is sufficiently suppressed. In particular, as shown in fig. 9, it is found that when ψ is 10 ° or more, the value of the phase of the high-order mode becomes further smaller. Similarly, when ψ is 110 ° or less, the value of the phase of the high-order mode becomes further smaller. It is found that when ψ is in the range of 60 ° ± 50 ° +120 ° × n, the higher-order mode can be further suppressed.

As shown in fig. 8, the propagation angle ψ of the support substrate becomes larger as it approaches 26 °, the value of the phase of the high-order mode becomes smaller rapidly, and when 26 ° ≦ ψ ≦ 60 °, the phase of the high-order mode is further suppressed. Similarly, the value of the phase of the high-order mode becomes smaller as ψ becomes smaller as it approaches 94 °, and the high-order mode is further suppressed in the case of 60 ° ≦ ψ ≦ 94 °. Therefore, when ψ is in the range of 60 ° ± 34 ° +120 ° × n, the high-order mode can be further suppressed. The same applies to (0 °, -84 ° ≦ θ ≦ -63 °, 0 °).

Next, based on the conditions of the elastic wave device in the case of obtaining the relationship shown in fig. 8, (i) only the euler angles of the piezoelectric layers are set to (θ, ψ) was obtained as a relationship between ψ, the film thickness of the silicon nitride film, the propagation angle ψ of the support substrate, and the phase of the higher-order mode.

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is (0 degrees, theta is more than or equal to 96 degrees and less than or equal to 117 degrees and 180 degrees)

Fig. 10 is a diagram showing a relationship between the propagation angle ψ of the support substrate and the phase of the higher-order mode.

As shown in fig. 10, regardless of the magnitude of the propagation angle ψ, the phase of the high-order mode is smaller than-77 °, and the high-order mode is sufficiently suppressed. In particular, it is found that when ψ is-50 ° or more, the phase value of the higher-order mode becomes further smaller. Similarly, when ψ is 50 ° or less, the value of the high-order mode becomes further smaller. It is found that when ψ is in the range of 0 ° ± 50 ° +120 ° × n, the higher-order mode can be further suppressed.

Further, as shown in FIG. 10, the value of the phase of the high-order mode becomes smaller as the propagation angle ψ becomes larger as closer to-34 °, and the phase of the high-order mode is suppressed even more in the case of-34 ° ≦ ψ ≦ 0 °. Similarly, the value of the phase of the high-order mode becomes smaller as ψ becomes closer to 34 °, and the high-order mode is further suppressed in the case of 0 ° ≦ ψ ≦ 34 °. Therefore, when ψ is in the range of 0 ° ± 34 ° +120 ° × n, the high-order mode can be further suppressed.

Fig. 11 is a front cross-sectional view showing the vicinity of a pair of electrode fingers in an IDT electrode of an acoustic wave device according to a second embodiment.

The present embodiment differs from the first embodiment in that a dielectric layer 28 is provided between the piezoelectric layer 7 and the IDT electrode 3. In the first embodiment, the IDT electrode 3 is directly provided on the piezoelectric layer 7, but the IDT electrode 3 may be indirectly provided on the piezoelectric layer 7 via the dielectric layer 28 as in the present embodiment.

The acoustic velocity of the bulk wave propagating through the dielectric layer 28 is higher than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 7. In this embodiment, the dielectric layer 28 is a silicon nitride layer. The dielectric layer 28 is not limited to a silicon nitride layer, as long as it has a relatively high acoustic velocity.

Here, the phase characteristics of the elastic wave device having the structure of the second embodiment and the elastic wave device having the structure of the first embodiment are shown below. The conditions of each elastic wave device are as follows.

A support substrate: silicon (Si), plane orientation,. Si (111), euler angle in (111) plane, (-45 °, -54.7 °, 47 °)

Silicon nitride film: film thickness 0.15 lambda

Silicon oxide film: film thickness 0.15 lambda

Piezoelectric layer: y-cut X-propagated LiTaO₃Film thickness 0.2 λ, euler angle (0 °, 110 °, 0 °)

Wavelength λ of IDT electrode: 2 μm

Fig. 12 is a diagram showing phase characteristics of the elastic wave devices according to the first and second embodiments. Fig. 13 is an enlarged view of fig. 12. In fig. 12 and 13, the solid line indicates the result of the second embodiment, and the broken line indicates the result of the first embodiment.

As shown in fig. 12 and 13, in the first and second embodiments, the high-order mode can be effectively suppressed. In particular, in the second embodiment, it is found that the higher-order mode can be further suppressed. In the second embodiment, a dielectric layer having a high acoustic velocity is provided, and the acoustic velocity of the higher-order mode becomes high. This allows the high-order mode to leak in the body direction, and thus, the high-order mode on the high frequency side can be further suppressed.

Here, for example, when SH waves or the like are used as the main mode, rayleigh waves are stray waves. When the dielectric layer 28 is an SiN layer, stray rayleigh waves can be suppressed by having a structure described later. The details thereof are explained.

The relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the dielectric layer and the phase of the rayleigh wave in the elastic wave device having the structure of the second embodiment was obtained. The conditions of the elastic wave device are as follows.

A support substrate: silicon (Si), plane orientation,. Si (111), euler angle in (111) plane, (-45 °, -54.7 °, 47 °)

Silicon nitride film: film thickness 0.15 lambda

Silicon oxide film: film thickness 0.15 lambda

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (96 DEG to 117 DEG inclusive) and 0 DEG

Wavelength λ of IDT electrode: 2 μm

Dielectric layer: SiN in a film thickness of 0.0025 lambda to 0.0975 lambda

Fig. 14 is a diagram showing a relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the silicon nitride layer and the phase of the rayleigh wave in the case where the dielectric layer is a silicon nitride layer.

The range outside the range shown by hatching in fig. 14 is a range in which the phase of the rayleigh wave is-70 ° or less. Here, the relationship shown in fig. 14 is shown by the following equation 1. In formula 1, the thickness of the silicon nitride layer is referred to as SiN thickness.

[ numerical formula 1]

… formula 1

The thickness of θ and the silicon nitride layer in the euler angle of the piezoelectric layer is preferably an angle and a thickness in a range in which the phase of the rayleigh wave derived from equation 1 is-70 ° or less. In this case, the rayleigh wave can be effectively suppressed in addition to the high-order mode.

As described above, the dielectric layer is not limited to the silicon nitride layer. For example, even when the dielectric layer is an aluminum oxide layer or an aluminum nitride layer, rayleigh waves can be effectively suppressed in addition to the high-order mode. These cases are shown below.

The relationship between θ in the euler angle of the piezoelectric layer, the film thickness of the alumina layer, and the phase of the rayleigh wave was obtained. On the other hand, the relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the aluminum nitride layer and the phase of the rayleigh wave was obtained. The elastic wave device is provided under the condition that the dielectric layer is made of Al₂O₃Or AlN, the conditions for obtaining the relationship of fig. 14 are the same.

Fig. 15 is a graph showing a relationship between θ in the euler angle of the piezoelectric layer and the film thickness of the alumina layer and the phase of the rayleigh wave in the case where the dielectric layer is the alumina layer.

The range outside the range shown by hatching in fig. 15 is a range in which the phase of the rayleigh wave is-70 ° or less. Here, the following equation 2 shows the structure shown in FIG. 15And (4) relationship. In formula 2, the thickness of the alumina layer is expressed as Al₂O₃And (5) film thickness.

[ numerical formula 2]

The rayleigh wave phase (-80.1333863636364) + (-0.554522499999998) x (θ -110) + (-173.463554340396) x (("AI 203 film thickness [ λ ]") -0.05) +0.149698033216783 x ((θ -110) x (θ -110) -40) +41.1703301435407 x (((θ -110) (("AI 203 film thickness [ λ ]") -0.05)) +4990.83763126825 x (((((("Al 203 film thickness [ λ ]") -0.05) × (("Al 203 film thickness [ λ ]") -0.05)) -0.00083125)

… formula 2

The thickness of the alumina layer and θ in the euler angle of the piezoelectric layer are preferably an angle and a thickness in a range in which the phase of the rayleigh wave derived from equation 2 is-70 ° or less. In this case, the rayleigh wave can be effectively suppressed in addition to the high-order mode.

Fig. 16 is a diagram showing a relationship between θ in the euler angle of the piezoelectric body layer and the film thickness of the aluminum nitride layer and the phase of the rayleigh wave in the case where the dielectric layer is the aluminum nitride layer.

The range outside the range shown by hatching in fig. 16 is a range in which the phase of the rayleigh wave is-70 ° or less. Here, the relationship shown in fig. 16 is shown by the following equation 3. In formula 3, the thickness of the aluminum nitride layer is expressed as AlN thickness or AlN β.

[ numerical formula 3]

The rayleigh wave has a phase (-87.3504136363636) + (-0.270137500000004) x (θ -110) + (-97.7367464114832) x (("AIN film thickness [ λ ]") -0.05) +0.0257423222610727 x ((θ -110) x (θ -110) -40) +14.0575563909775 x (((θ -110) x ((("AIN β [ λ ]") -005)) +3335.40856272914 x (((((("AIN film thickness [ λ ]") -0.05) x) ("AIN film thickness [ λ ]") -0.05) -0.00083125)

… formula 3

The thickness of θ and the aluminum nitride layer in the euler angle of the piezoelectric layer is preferably an angle and a thickness in a range in which the phase of the rayleigh wave derived from equation 3 is-70 ° or less. In this case, the rayleigh wave can be effectively suppressed in addition to the high-order mode.

However, in the first and second embodiments, the case where θ in the euler angles of the piezoelectric layers is 95.5 ≦ θ < 117.5 ° is shown. Hereinafter, a configuration is shown in which the high order mode can be suppressed even in the case of 117.5 ° ≦ θ < 129.5 ° or 85.5 ° ≦ θ <95.5 °. The third embodiment having the same configuration as the first embodiment except for 117.5 ° ≦ θ < 129.5 ° will be described in detail with reference to fig. 17 to 21. A detailed description of a fourth embodiment having the same configuration as the first embodiment, except that the angle θ is 85.5 ° ≦ θ <95.5 °, will be described with reference to fig. 22 to 24.

The elastic wave device according to the third embodiment has the following configuration, and can suppress higher-order modes. 1) The piezoelectric substrate includes a laminated body in which a support substrate as a silicon substrate, a silicon nitride film, a silicon oxide film, and a piezoelectric layer using lithium tantalate are laminated in this order. 2) The thickness of the piezoelectric layer is 1 lambda or less. 3) The relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer is a combination shown in table 7 below.

[ Table 7]

From the conditions of the elastic wave device when the relationships in fig. 4 to 7 were obtained, the relationship between θ and the film thickness of the silicon nitride film and the phase of the higher-order mode was obtained by only making the condition of θ different in the euler angle of the piezoelectric layer.

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (00 DEG, theta is more than or equal to 118 DEG and less than or equal to 129 DEG and 0 DEG)

Fig. 17 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 118 ° in the euler angle of the piezoelectric body layer. FIG. 18 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 119 ° ≦ θ ≦ 122 ° in the Euler angle of the piezoelectric layer. Fig. 19 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 123 ° ≦ θ ≦ 126 ° in the euler angle of the piezoelectric layer. FIG. 20 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 127 ° ≦ θ ≦ 129 ° in the Euler angle of the piezoelectric layer. Fig. 21 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 130 ° in the euler angle of the piezoelectric body layer.

As shown in fig. 17, when θ is 118 °, the phase of the high-order mode is-70 ° or less in the range where the film thickness of the silicon nitride film is 0.0005 λ or more and 0.092 λ or less or in the range where 0.166 λ or more and 0.597 λ or less. Table 7 shows the results. Similarly, as shown in fig. 18 to 20, table 7 shows the range of the film thickness of the silicon nitride film in which the phase of the higher-order mode is equal to or less than-70 ° when θ in the euler angle of the piezoelectric layer is changed from 119 ° to 129 ° at a time.

On the other hand, as shown in fig. 21, when θ is 130 °, the phase of the high-order mode exceeds-70 ° in the range where the film thickness of the silicon nitride film is 1.5 λ or less, and it is difficult to sufficiently suppress the phase of the high-order mode. As described above, it is understood that the higher-order mode can be effectively suppressed when the relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer is the combination shown in table 7.

The elastic wave device according to the fourth embodiment has the following configuration, and can suppress higher-order modes. 1) The piezoelectric substrate includes a laminated body in which a support substrate as a silicon substrate, a silicon nitride film, a silicon oxide film, and a piezoelectric layer using lithium tantalate are laminated in this order. 2) The thickness of the piezoelectric layer is 1 lambda or less. 3) The relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer is a combination shown in table 8 below.

[ Table 8]

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (00 DEG, theta is more than or equal to 86 DEG and less than or equal to 95 DEG and 0 DEG)

FIG. 22 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 75 ° ≦ θ ≦ 85 ° in the Euler angle of the piezoelectric layer. Fig. 23 is a diagram showing a relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 86 ° ≦ θ ≦ 88 ° in the euler angle of the piezoelectric layer. FIG. 24 is a graph showing the relationship between the film thickness of the silicon nitride film and the phase of the higher-order mode when θ is 89 ° ≦ θ ≦ 95 ° in the Euler angle of the piezoelectric layer.

As shown in fig. 22, when θ is 75 ° ≦ θ ≦ 85 °, the phase of the high-order mode exceeds-70 ° in the range of the film thickness of the silicon nitride film of 1.5 λ or less, and it is difficult to sufficiently suppress the phase of the high-order mode.

On the other hand, as shown in fig. 23, when θ is 86 °, the phase of the higher-order mode becomes-70 ° or less in the range where the film thickness of the silicon nitride film is 0.0005 λ or more and 0.03 λ or less, or in the range where the film thickness is 0.43 λ or more and 0.46 λ or less. Table 8 shows the results. Similarly, as shown in fig. 23 and 24, table 8 shows the range of the film thickness of the silicon nitride film in which the phase of the higher-order mode is equal to or less than-70 ° when θ in the euler angle of the piezoelectric layer is changed from 87 ° to 95 ° at once. As described above, it is understood that the higher-order mode can be effectively suppressed when the relationship between θ and the film thickness of the silicon nitride film in the euler angle of the piezoelectric layer is the combination shown in table 8.

Fig. 25 is a front cross-sectional view showing the vicinity of a pair of electrode fingers in an IDT electrode of an acoustic wave device according to a fifth embodiment.

The present embodiment differs from the first embodiment in that a protective film 39 is provided on the piezoelectric layer 7 so as to cover the IDT electrode 3. The material of the protective film 39 of this embodiment is silicon nitride. More specifically, the protective film 39 is a SiN protective film made of SiN. The ratio of nitrogen in the silicon nitride constituting the protective film 39 is not limited to the above. Alternatively, the material of the protective film 39 is not limited to silicon nitride, and may be aluminum nitride or aluminum oxide, for example.

The elastic wave device of the present embodiment can suppress a higher-order mode and also suppress a stray rayleigh wave by having a configuration described later. The details are explained.

The relationship between θ in the euler angle of the piezoelectric layer and the relationship between the film thickness of the protective film and the phase of the rayleigh wave in the elastic wave device having the structure of the fifth embodiment was obtained. The conditions of the elastic wave device are as follows.

A support substrate: silicon (Si), plane orientation,. Si (111), euler angle in (111) plane, (-45 °, -54.7 °, 46 °)

Silicon nitride film: film thickness 0.15 lambda

Silicon oxide film: film thickness 0.15 lambda

Piezoelectric layer: y-cut X-propagated LiTaO₃The film thickness is 0.2 lambda, and the Euler angle is 0 DEG (96 DEG to 117 DEG inclusive) and 0 DEG

Wavelength λ of IDT electrode: 2 μm

Protecting the film: SiN in a film thickness of 0.005 lambda or more and 0.05 lambda or less

The range outside the range shown by hatching in fig. 26 is a range in which the phase of the higher-order mode is-70 ° or less and the phase of the rayleigh wave is-70 ° or less. Here, the relationship between θ in the euler angle of the piezoelectric body layer shown in fig. 26, the film thickness of the SiN protective film, and the phase of the rayleigh wave is shown by the following equation 4. Similarly, the relationship between θ and the film thickness of the SiN protective film and the phase of the higher-order mode is shown by the following equation 5. In equations 4 and 5, the thickness of the SiN protective film is described as the SiN protective film.

[ numerical formula 4]

Rayleigh (-51.52545) +1.78434436363636 x (θ -1275) +551.57103030303 x (("SiN protective film [ λ ]") -0.0275) +0.102490363636364 x ((θ -127.5) × (θ -127.5) -206.25) +60.3989730027549 x ((θ -127.5) × (((("SiN protective film [ λ ]") -0.0275))

… formula 4

[ numerical formula 5]

High-order mode (-26.58444) +2.61766496969697 x (θ -127.5) +1545.84533333333 x (("SiN protective film [ λ ]") -0.0275) + ("0.0379121515151515) × ((θ -127.5) × (θ -1275) -206.25) +56.9468179981635 × ((θ -127.5) × (((" SiN protective film [ λ ] ") -0.0275))

… formula 5

In the present embodiment, the film thicknesses of the θ and SiN protective films at the euler angle of the piezoelectric layer are an angle and a film thickness in a range in which the phase of the rayleigh wave derived from equation 4 is-70 ° or less and the phase of the higher-order mode derived from equation 5 is-70 ° or less. This can suppress the higher-order mode and also effectively suppress the rayleigh wave.

The lower limit of the phase of the rayleigh wave derived from equation 4 is preferably-90 °. This makes it possible to more reliably and effectively suppress the rayleigh wave. The lower limit of the phase of the higher-order mode derived from equation 5 is preferably-90 °. This makes it possible to suppress the higher-order mode more reliably and effectively. The same applies to expressions 6 and 8 and expressions 7 and 9 described later.

Here, the protective film is not limited to the SiN protective film. For example, even when the material of the protective film is alumina or aluminum nitride, rayleigh waves can be effectively suppressed in addition to the high-order mode. These cases are shown below as a first modification and a second modification of the fifth embodiment. In the first modification, the protective film is made of Al₂O₃Al of (2)₂O₃And (5) protecting the film. In the second modification, the protective film is an AlN protective film made of AlN. However, the ratio of oxygen or nitrogen in the aluminum oxide or aluminum nitride constituting the protective film is not limited to the above.

Find out the pressureTheta and Al in Euler angle of electric layer₂O₃The film thickness of the protective film, and the phase of the Rayleigh wave and the higher-order mode. In the condition of the elastic wave device, the material other than the protective film is Al₂O₃Except for this point, the same conditions as those for obtaining the relationship of fig. 26 are used.

Protecting the film: al material₂O₃A film thickness of 0.005 lambda or more and 0.05 lambda or less

FIG. 27 shows theta and Al in Euler angles of piezoelectric layers₂O₃A graph of the relationship between the protective film and the phases of the Rayleigh wave and the higher-order mode.

The range outside the range shown by hatching in fig. 27 is a range in which the phase of the higher-order mode is-70 ° or less and the phase of the rayleigh wave is-70 ° or less. Here, θ and Al in the euler angle of the piezoelectric layer shown in fig. 27 are shown by the following equation 6₂O₃The relationship between the film thickness of the protective film and the phase of the rayleigh wave. Similarly, the following formula 7 shows θ and Al₂O₃The relationship between the film thickness of the protective film and the phase of the higher-order mode. In the formulas 6 and 7, Al is added₂O₃The thickness of the protective film is described as Al only₂O₃And (5) protecting the film.

[ numerical formula 6]

Rayleigh wave (-40.9578496399338) +2.25601530917004 x (θ -127.272727272727) +964.821146439353 x (("Al 203 protective film [ λ ]") -0.0274747474747475) +0.100000607678288 x ((θ -127.272727272727) × (θ -127.272727272727) -203.168044077135) +74.7099873794682 x ((θ -127.272727272727) × (("AI 203 protective film [ λ ]") -0.0274747474747475))

… formula 6

[ number formula 7]

High-order mode (-21.0375184962657) +2.73177575694271 x (θ -127.272727272727) +1701.65880601573 x ((("AI 203 protective film [ λ ]") -0.0274747474747475) + ("0.0499273041403373) × ((θ -127.272727272727) × (θ -127.272727272727) -203.168044077135) +53.1637721066764 x (((θ -127.272727272727) × ((((" AI203 protective film [ λ ] ") -0.0274747474747475)) + (" 34811.3628963409) × ((((((("AI 203 protective film [ λ ]") -0.0274747474747475) × (((("AI 203 protective film [ λ ]") -0.0274747474747475) -0.00020826956433017)

… formula 7

In the first modification, θ and Al in the euler angle of the piezoelectric layer₂O₃The film thickness of the protective film is an angle and a film thickness in a range in which the phase of the rayleigh wave derived from equation 6 is-70 ° or less and the phase of the higher-order mode derived from equation 7 is-70 ° or less. This can suppress the higher-order mode and also effectively suppress the rayleigh wave.

On the other hand, the relationship between θ and the AlN protective film thickness at the euler angle of the piezoelectric layer, and the phase of the rayleigh wave and the higher-order mode was obtained. The conditions of the elastic wave device are the same as those for obtaining the relationship in fig. 26, except that the material of the protective film is AlN.

Protecting the film: AlN, and a film thickness of 0.005 lambda to 0.05 lambda

The range outside the range shown by hatching in fig. 28 is a range in which the phase of the rayleigh wave is-70 ° or less. Here, the relationship between θ in the euler angle of the piezoelectric layer shown in fig. 28, the film thickness of the AlN protective film, and the phase of the rayleigh wave is shown by the following equation 8. Similarly, the relationship between θ and the AlN protective film thickness and the phase of the higher-order mode is shown by the following equation 9. In equations 8 and 9, the film thickness of the AlN protection film is described as the AlN protection film.

[ number formula 8]

Rayleigh (-46.4003800000001) +1.94268775757576 x (θ -1275) +755.618424242424 x (("AIN protective film [ λ ]") -0.0275) +0.109821151515152 x ((θ -127.5) × (θ -127.5) -206.25) +69.3031610651975 x ((θ -127.5) × ((("AIN protective film [ λ ]") -0.0275))

… formula 8

[ numerical formula 9]

High-order mode (-24.10841) +2.65936036363636 x (θ -127.5) +1560.34145454545 x (("AIN protective film [ λ ]") -0.0275) + ("0.0415194696969697) × ((θ -127.5) × (θ -127.5) -206.25) +54.3834578512397 x (((θ -127.5) (" AIN protective film [ λ ] ") -0.0275))

… formula 9

In the second modification, the θ and the AlN protective film thickness at the euler angle of the piezoelectric layer are an angle and a film thickness in a range in which the phase of the rayleigh wave derived from equation 8 is-70 ° or less and the phase of the higher-order mode derived from equation 9 is-70 ° or less. This can suppress the higher-order mode and also effectively suppress the rayleigh wave.

Description of the reference numerals

An elastic wave device;

a piezoelectric substrate;

an IDT electrode;

supporting a substrate;

a silicon nitride film;

a silicon oxide film;

a piezoelectric layer;

a reflector;

16. a first bus bar, a second bus bar;

18. a first electrode finger, a second electrode finger;

a dielectric layer;

a protective film.

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Elastic wave device

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