阅读说明：本技术 弹性波装置 (Elastic wave device ) 是由 岩本英树 山根毅 谷口康政 大门克也 于 2019-10-17 设计创作，主要内容包括：提供一种不易产生Q的劣化的弹性波装置。弹性波装置(1)具备：压电体(5),具有相互对置的一个主面以及另一个主面；IDT电极(6),设置在压电体(5)的一个主面上,具有多根电极指(11、12)；高声速构件(3),配置在压电体(5)的另一个主面侧,传播的体波的声速比在压电体(5)传播的弹性波的声速高；以及第1电介质膜(13),设置在电极指(11、12)的上表面,在IDT电极(6)的电极指(11、12)间有不存在电介质的部分。(Provided is an elastic wave device in which Q is not easily deteriorated. An elastic wave device (1) is provided with: a piezoelectric body (5) having one main surface and the other main surface that face each other; an IDT electrode (6) which is provided on one main surface of the piezoelectric body (5) and has a plurality of electrode fingers (11, 12); a high acoustic velocity member (3) which is arranged on the other principal surface side of the piezoelectric body (5) and which has a higher acoustic velocity of a bulk wave propagating than an acoustic wave propagating through the piezoelectric body (5); and a1 st dielectric film (13) provided on the upper surfaces of the electrode fingers (11, 12), wherein there is a portion where no dielectric exists between the electrode fingers (11, 12) of the IDT electrode (6).)

1. An elastic wave device is provided with:

a piezoelectric body having one main surface and the other main surface that are opposed to each other;

an IDT electrode provided on the one main surface of the piezoelectric body and having a plurality of electrode fingers;

a high sound velocity member disposed on the other principal surface side of the piezoelectric body, the sound velocity of a bulk wave propagating being higher than the sound velocity of an elastic wave propagating through the piezoelectric body; and

a1 st dielectric film disposed on upper surfaces of the electrode fingers,

there is a portion where no dielectric exists between the electrode fingers of the IDT electrode.

2. An elastic wave device is provided with:

a piezoelectric body having one main surface and the other main surface that are opposed to each other;

an IDT electrode provided on the one main surface of the piezoelectric body and having a plurality of electrode fingers;

a high sound velocity member disposed on the other principal surface side of the piezoelectric body; and

a1 st dielectric film disposed on upper surfaces of the electrode fingers,

the high acoustic velocity member contains a medium containing at least one material or a mixture of at least one material as a main component of aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesium oxide, a DLC film, that is, a diamond-like carbon film, or diamond,

there is a portion where no dielectric exists between the electrode fingers of the IDT electrode.

3. The elastic wave device according to claim 1 or 2,

the 1 st dielectric film is not present in the entire region between the electrode fingers.

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

the film thickness of the 1 st dielectric film is 4% or less of a wavelength λ determined by an electrode finger pitch of the IDT electrode.

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

a fillet containing the dielectric is disposed between at least one electrode finger,

the rounded corner extends from a side surface of the electrode finger in the IDT electrode, passes through a boundary between the electrode finger and the one main surface of the piezoelectric body, and further reaches a part of the one main surface between the electrode fingers,

in a cross section in a direction orthogonal to a direction in which the electrode finger extends, the rounded outer surface is a curved line that is recessed toward a corner portion that is a boundary between the side surface of the electrode finger and the one principal surface of the piezoelectric body in the cross section.

6. The elastic wave device according to any one of claims 1 to 5,

grooves are provided in the one main surface of the piezoelectric body between the electrode fingers.

7. The elastic wave device according to any one of claims 1 to 6,

the electrode fingers have a forward tapered shape.

8. The elastic wave device according to any one of claims 1 to 7,

the 1 st dielectric film has a forward tapered shape, and a taper angle θ 1 of the forward tapered shape is 88 ° or less.

9. The elastic wave device according to claim 8,

the taper angle θ 1 is 50 ° or more.

10. The elastic wave device according to claim 8 or 9,

the taper angle θ 1 is 60 ° or more and 80 ° or less.

11. The elastic wave device according to any one of claims 1 to 10,

further provided with: and a 2 nd dielectric film disposed between the piezoelectric body and the electrode fingers.

12. The elastic wave device according to claim 11,

the 2 nd dielectric film is not present in the entire region between the electrode fingers of the IDT electrode.

13. The elastic wave device according to claim 11 or 12,

the 1 st dielectric film and the 2 nd dielectric film each have a forward tapered shape,

when the taper angle of the forward taper shape of the 1 st dielectric film is represented by θ 1 and the taper angle of the forward taper shape of the 2 nd dielectric film is represented by θ 2, θ 1 > θ 2.

14. The elastic wave device according to claim 11 or 12,

the 1 st dielectric film and the 2 nd dielectric film each have a forward tapered shape,

when the taper angle of the forward taper shape of the 1 st dielectric film is represented by θ 1 and the taper angle of the forward taper shape of the 2 nd dielectric film is represented by θ 2, θ 1 < θ 2.

15. The elastic wave device according to any one of claims 11 to 14,

when the density of the 1 st dielectric film is D1 and the density of the 2 nd dielectric film is D2, D2 > D1.

16. The elastic wave device according to claim 1,

the high sound velocity member is a high sound velocity support substrate mainly made of a high sound velocity material.

17. The elastic wave device according to claim 1,

further provided with: and a low sound velocity film disposed between the high sound velocity member and the piezoelectric body, the low sound velocity film being configured to propagate a bulk wave having a sound velocity lower than that of the bulk wave propagating through the piezoelectric body.

18. The elastic wave device according to any one of claims 1 to 17,

the 1 st dielectric film is a silicon oxide film.

Technical Field

The present invention relates to an elastic wave device having a structure in which a piezoelectric body is directly or indirectly laminated on a high-sound-velocity member, and an elastic wave filter, a composite filter device, a high-frequency front-end circuit, and a communication device using the elastic wave device.

Background

Patent document 1 below discloses an elastic wave device having a structure in which a piezoelectric body is directly or indirectly laminated on a high-sound-velocity member. In patent document 1, an IDT electrode is provided on a piezoelectric body. In patent document 1, a dielectric film is provided so as to cover the IDT electrode on the piezoelectric body.

Prior art documents

Patent document

Patent document 1: WO2012/086639 publication

Disclosure of Invention

Problems to be solved by the invention

In the elastic wave device described in patent document 1, a piezoelectric body is directly or indirectly laminated on a high sound velocity member. In this configuration, the Q value can be improved.

However, the inventors of the present application have found that if a dielectric film is provided so as to cover the IDT electrode including the inter-electrode-finger region of the IDT electrode, the Q value may be deteriorated due to the influence of the dielectric film. Therefore, the advantage of the elastic wave device having a high Q value is often impaired.

The invention aims to provide an elastic wave device which is not easy to generate Q value deterioration. Another object of the present invention is to provide an elastic wave filter, a composite filter device, a high-frequency front-end circuit, and a communication device, each of which includes the elastic wave device of the present invention.

Means for solving the problems

An elastic wave device according to the present invention is an elastic wave device including: a piezoelectric body having one main surface and the other main surface that are opposed to each other; an IDT electrode provided on the one main surface of the piezoelectric body and having a plurality of electrode fingers; a high sound velocity member disposed on the other main surface side of the piezoelectric body, the sound velocity of a bulk wave (bulk wave) propagating being higher than the sound velocity of an elastic wave propagating through the piezoelectric body; and a1 st dielectric film provided on the upper surfaces of the electrode fingers, and having a portion between the electrode fingers of the IDT electrode where no dielectric exists.

The elastic wave filter according to the present invention includes the elastic wave device according to the present invention.

The composite filter device according to the present invention includes a plurality of bandpass filters having one ends commonly connected to each other, and at least one of the bandpass filters is an elastic wave filter configured according to the present invention.

The high-frequency front-end circuit according to the present invention includes an elastic wave device and a power amplifier configured according to the present invention.

The communication device according to the present invention includes a high-frequency front-end circuit and an RF signal processing circuit configured according to the present invention.

Effects of the invention

According to the elastic wave device of the present invention, deterioration of the Q value can be suppressed.

Drawings

Fig. 1 (a) is a front cross-sectional view of an elastic wave device according to embodiment 1 of the present invention, and fig. 1 (b) is a partially enlarged front cross-sectional view in which a main portion thereof is enlarged.

Fig. 2 is a schematic plan view showing an electrode structure of an elastic wave device according to embodiment 1 of the present invention.

Fig. 3 is a circuit diagram of an elastic wave filter according to embodiment 2 of the present invention.

Fig. 4 is a circuit diagram of a composite filter device according to embodiment 3 of the present invention.

Fig. 5 is a diagram showing resonance characteristics of the acoustic wave device according to example 1 of embodiment 1 and the acoustic wave devices according to comparative examples 1 and 2.

Fig. 6 is a graph showing Q characteristics of the elastic wave devices of example 1 and comparative examples 1 and 2.

FIG. 7 shows SiO as the No. 1 dielectric film₂Film thicknesses (. lamda.) and Q_maxA graph of the relationship of (1).

Fig. 8 (a) is a partially enlarged front sectional view for explaining an elastic wave device according to embodiment 4 of the present invention, and fig. 8 (b) is a partially enlarged front sectional view for explaining an elastic wave device according to embodiment 5.

Fig. 9 is an enlarged view of a portion provided with rounded corners in an elastic wave device according to embodiment 5 of the present invention.

Fig. 10 is a graph showing a relationship between the size of the fillet and the mesas stress.

Fig. 11 is a partially enlarged cross-sectional front view for explaining an elastic wave device according to embodiment 6 of the present invention, and is a view for explaining a taper angle θ 1 formed by the 1 st side surface of the 1 st dielectric film and the lower surface of the 1 st dielectric film and an angle α formed by the side surface of the electrode finger and the upper surface of the piezoelectric body.

Fig. 12 is a diagram showing a relationship between the taper angle θ 1 and the phase of the higher-order mode closest to the main mode in the elastic wave device according to embodiment 1.

Fig. 13 is a diagram showing a relationship between the taper angle θ 1 and the phase of a higher-order mode in the vicinity of a frequency 2 times the resonance frequency of the main mode in the elastic wave device according to embodiment 1.

Fig. 14 is a front cross-sectional view of an elastic wave device according to embodiment 7 of the present invention.

Fig. 15 is a front cross-sectional view of an elastic wave device according to embodiment 8 of the present invention.

Fig. 16 is a graph showing the Q characteristics of example 3 relating to the elastic wave device shown in fig. 15 and example 4 in which no groove is provided on the upper surface of the piezoelectric body.

Fig. 17 is a partially enlarged front cross-sectional view for explaining an elastic wave device according to embodiment 9 of the present invention.

Fig. 18 is a diagram showing a relationship between the taper angle θ 2 of the side surface of the 2 nd dielectric film and the phase of the higher-order mode closest to the main mode in the case where the taper angle θ 1 of the side surface of the 1 st dielectric film is 40 °.

Fig. 19 is a partially enlarged front cross-sectional view for explaining an elastic wave device according to embodiment 10 of the present invention.

Fig. 20 is a diagram showing a relationship between the taper angle θ 2 of the side surface of the 2 nd dielectric film and the phase of the rayleigh wave in the case where the taper angle θ 1 of the side surface of the 1 st dielectric film is 40 °.

Fig. 21 is a graph showing the relationship between the density ratio of the density D2 of the 2 nd dielectric film/the density D1 of the 1 st dielectric film and the phase of the higher-order mode closest to the main mode.

Fig. 22 is a front cross-sectional view of an elastic wave device according to embodiment 11 of the present invention.

Fig. 23 is a front cross-sectional view of an elastic wave device according to embodiment 12 of the present invention.

Fig. 24 is a circuit diagram for explaining a high-frequency front-end circuit and a communication device according to an embodiment of the present invention.

Detailed Description

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

Note that the embodiments described in the present specification are exemplary, and partial replacement or combination of the structures may be performed between different embodiments.

Fig. 1 (a) is a front cross-sectional view of an elastic wave device according to embodiment 1 of the present invention, and fig. 1 (b) is a partially enlarged front cross-sectional view in which a main portion thereof is enlarged. Fig. 2 is a schematic plan view showing an electrode structure of an elastic wave device according to embodiment 1.

A high acoustic velocity member 3 and a low acoustic velocity film 4 are laminated on the support substrate 2. A piezoelectric body 5 is laminated on the low sound velocity membrane 4. An IDT electrode 6 and reflectors 7 and 8 are provided on the upper surface 5a of the piezoelectric body 5. Acoustic wave device 1 is a single-port type acoustic wave resonator.

The IDT electrode 6 has a plurality of 1 st electrode fingers 11 and a plurality of 2 nd electrode fingers 12. As shown in fig. 1 (b) in an enlarged manner, the 1 st dielectric film 13 is laminated on the 1 st electrode finger 11 and the 2 nd electrode finger 12. The 1 st dielectric film 13 is not provided in the entire region of the gap between the 1 st electrode finger 11 and the 2 nd electrode finger 12.

As described later, in the present invention, a dielectric may be present in a region between electrode fingers. That is, a region where no dielectric exists between electrode fingers may be provided. The "dielectric" not present between the electrode fingers includes all dielectrics including the 1 st dielectric film 13. In other words, the "region between the electrode fingers where no dielectric exists" refers to a case where the 1 st dielectric film 13 is not present between the electrode fingers and the dielectric film other than the 1 st dielectric film 13 is not present. In addition, a region where no dielectric exists may be present between all electrode fingers of the IDT electrode, or a portion where no dielectric exists may be present between at least some electrode fingers.

In embodiment 1, since no dielectric is present between the electrode fingers, deterioration of the Q value is less likely to occur. This point will be described in detail with reference to example 1, comparative example 1, and comparative example 2, which will be described later.

Returning to fig. 1 (a), in the present embodiment, the support substrate 2 is a silicon substrate. However, the material of the support substrate 2 is not particularly limited, and various ceramics such as alumina, diamond, sapphire, lithium tantalate, lithium niobate, quartz, alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, and the like, dielectrics such as glass, semiconductors such as gallium nitride, and resins can be used.

The high acoustic velocity member 3 includes a high acoustic velocity material having a higher acoustic velocity of a bulk wave propagating than that of an elastic wave propagating through the piezoelectric body 5. In the present embodiment, the high sound velocity member 3 includes aluminum nitride. However, as long as the elastic wave can be confined, various materials such as alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a DLC (diamond-like carbon) film or diamond, a medium containing the above materials as a main component, and a medium containing a mixture of the above materials as a main component can be used as the high acoustic velocity material. In order to confine the elastic wave to the portion where the piezoelectric body 5 and the low acoustic velocity film 4 are laminated, the thickness of the high acoustic velocity member 3 is preferably as thick as possible, and is preferably 0.5 times or more, and more preferably 1.5 times or more, the wavelength λ of the elastic wave.

In the present specification, the main component means a component exceeding 50% by weight of the material.

The low acoustic velocity film 4 is made of an appropriate material having a lower acoustic velocity of a bulk wave propagating through the piezoelectric body 5. In the present embodiment, the low acoustic velocity film 4 contains silicon oxide. However, as a material constituting the low acoustic velocity film, silicon oxynitride, tantalum carbide, glass, or the like can be used in addition to silicon oxide. Further, a medium containing these elements as main components, such as a compound obtained by adding fluorine, carbon, boron, or the like to these materials, may also be used.

Piezoelectric body 5 contains LiTaO₃. However, LiNbO may be used for the piezoelectric body 5₃And ZnO, etc.

The IDT electrode 6 and the reflectors 7 and 8 are made of appropriate metals. Such a metal is not particularly limited. Further, a laminated metal film in which a plurality of metal films are laminated may be used.

The 1 st dielectric film 13 contains silicon oxide. However, the material of the 1 st dielectric film 13 is not limited to this. Other dielectric materials such as silicon oxynitride, alumina, etc. may also be used. The 1 st dielectric film 13 may contain a mixed material containing these dielectrics as a main component.

The 1 st dielectric film 13 has a forward tapered shape. The 1 st dielectric film 13 has a lower surface 13a, an upper surface 13b, a1 st side surface 13c, and a 2 nd side surface 13 d. The lower surface 13a is a portion laminated on the 1 st electrode finger 11. The upper surface 13b faces the lower surface 13a in the thickness direction of the 1 st dielectric film 13. The 1 st side surface 13c and the 2 nd side surface 13d face each other in the width direction of the 1 st electrode finger 11. As shown in fig. 1 (b), the 1 st dielectric film 13 is provided with a forward tapered shape such that its width dimension decreases from the lower surface 13a toward the upper surface 13 b. Here, the width direction dimension means a dimension along the width direction of the 1 st electrode finger 11.

Therefore, the 1 st side surface 13c and the 2 nd side surface 13d are inclined so as to approach each other as they face upward. Here, the angle formed by the 1 st side surface 13c and the lower surface 13a is defined as a taper angle θ 1. The 2 nd side surface 13d is also tapered at an angle θ 1 with respect to the lower surface 13 a. Similarly, the 1 st dielectric film 13 is provided with a forward tapered shape on the 2 nd electrode finger 12.

Next, the improvement of the Q value in elastic wave device 1 will be described based on a specific experimental example.

An elastic wave device according to example 1 below was prepared.

λ is a wavelength determined by the electrode finger pitch of the IDT electrode. λ 2 μm.

The number of pairs of electrode fingers of the IDT electrode 6 is 67 pairs.

The duty ratio of the IDT electrode 6 is 0.45.

The 1 st electrode finger 11 and the 2 nd electrode finger 12 have a width dimension of 0.45 μm.

The cross width was 90 μm.

The number of electrode fingers of the reflectors 7 and 8 is 41 each.

Materials of IDT electrode 6 and reflectors 7 and 8: A1. the thickness is 145 nm.

1 st dielectric film 13: the silicon oxide film has a thickness of 35nm and a taper angle θ 1 of 55 °.

The width-directional dimension of the lower surface 13a is 0.385 μm.

The width-directional dimension of the upper surface 13b is 0.338 μm.

The thickness of the 1 st dielectric film 13 is 0.025 λ, that is, 2.5% of the wavelength.

As comparative example 1, an elastic wave device was prepared in the same manner as in example 1, except that a silicon oxide film was provided in a thickness of 0.025 λ over the entire region of the gap between the electrode fingers.

An acoustic wave device having the same configuration as that of example 1, except that the first dielectric film 13 was not provided, was prepared as the acoustic wave device of comparative example 2.

Fig. 5 is a diagram showing resonance characteristics of the acoustic wave device of example 1 and the acoustic wave devices of comparative examples 1 and 2, and fig. 6 is a diagram showing Q characteristics. In fig. 5 and 6, the solid line shows the results of example 1, the broken line shows the results of comparative example 1, and the alternate long and short dash line shows the results of comparative example 2.

As is clear from fig. 5, in example 1, the peak-to-valley ratio in the resonance characteristics of the main mode is larger than in comparative examples 1 and 2. In example 1, the response of the higher-order mode shown by the arrow X is also smaller than those of comparative examples 1 and 2.

As shown in fig. 6, the Q value was good in comparative example 2 in which the 1 st dielectric film was not provided, whereas the Q characteristic was considerably poor in comparative example 1 in which the 1 st dielectric film was present between the electrode fingers. On the other hand, example 1 shows the same Q characteristics as comparative example 1.

Therefore, it is understood that according to embodiment 1, a good resonance characteristic can be obtained without deteriorating a good Q characteristic in an elastic wave device in which the piezoelectric body 5 is directly or indirectly laminated on the high sound velocity member.

In the acoustic wave device having the same structure as in example 1, the thickness of the 1 st dielectric film 13 was changed. FIG. 7 shows thickness and Q of the 1 st dielectric film 13_maxA graph of the relationship of (1). As is clear from fig. 7, if the thickness of the 1 st dielectric film 13 is increased, particularly, if it exceeds 0.04 λ, Q is increased_maxAnd drops sharply. Therefore, the film thickness of the 1 st dielectric film 13 is preferably 0.04 λ or less, that is, 4% or less of the wavelength λ.

Fig. 3 is a circuit diagram of an elastic wave filter according to embodiment 2 of the present invention. Elastic wave filter 21 is a ladder filter having a plurality of elastic wave resonators. The plurality of series-arm resonators S1 to S4 and the plurality of parallel-arm resonators P1 to P3 are elastic wave resonators. At least one of the elastic wave resonators is formed by the elastic wave device 1.

The elastic wave filter of the present invention is not limited to an elastic wave filter having a ladder circuit. Any elastic wave filter may be used as long as it has the elastic wave device of the present invention.

Fig. 4 is a circuit diagram of a composite filter device according to embodiment 3 of the present invention. In the composite filter device 30, one ends of a plurality of band-pass filters 31 to 34 are commonly connected. The composite filter device 30 can be suitably used for a CA (carrier aggregation) system. That is, the composite filter device 30 can be suitably used for simultaneously transmitting and receiving reception signals, transmission signals, and the like in a plurality of frequency bands. In this case, at least one of the plurality of band-pass filters 31 to 34 may be formed of an elastic wave filter according to the present invention. In this case, the Q value of the acoustic wave device can be reduced, and thus good filter characteristics can be obtained.

Fig. 8 (a) is a partially enlarged front sectional view for explaining an elastic wave device according to embodiment 4 of the present invention, and fig. 8 (b) is a partially enlarged front sectional view for explaining an elastic wave device according to embodiment 5.

In elastic wave device 41 shown in fig. 8 (a), the 1 st electrode finger 11 and the 2 nd electrode finger 12 are provided with a forward tapered shape. The 1 st electrode finger 11 is typically described, and the 1 st electrode finger 11 has a lower surface 11a, an upper surface 11b, and a pair of side surfaces 11c and 11 d. The 1 st electrode finger 11 is provided with a forward taper shape such that the side surface 11c and the side surface 11d approach each other in the width direction of the electrode finger as going upward from the upper surface 5a of the piezoelectric body 5. In this manner, the 1 st electrode finger 11 may be provided with a forward taper shape.

In elastic wave device 41 according to embodiment 4, rounded corners 42 including a dielectric are provided in a region of a part of the gap between the 1 st electrode finger 11 and the 2 nd electrode finger 12. As described above, the present invention is not limited to a structure in which no dielectric is provided in the entire region between the electrode fingers. That is, a dielectric such as the rounded corners 42 may be present in a part of the region between the electrode fingers.

Similarly, as in the elastic wave device 43 according to embodiment 5 shown in fig. 8 (b), the rounded corners 42 may be provided in the gaps between the 1 st and 2 nd electrode fingers 11 and 12 not provided with the regular tapered shape. By providing such rounded corners 42, in the elastic wave devices according to embodiments 4 and 5, stress applied to the boundaries between the 1 st electrode finger 11 and the 2 nd electrode finger 12 and the piezoelectric body 5 and the boundaries and the vicinity thereof can be reduced. This can improve thermal shock resistance and improve IMD characteristics. This is explained with reference to fig. 9.

Fig. 9 is an enlarged view of a portion of elastic wave device 43 according to embodiment 5 where rounded corners 42 are provided. When thermal shock is applied or heat is generated during driving, a large stress is applied to the hatched region in the vicinity of the boundary Y between the 1 st electrode finger 11 and the upper surface 5a of the piezoelectric body 5. The rounded corners 42 can suppress strain due to the stress and can alleviate stress concentration. This can improve thermal shock resistance and IMD characteristics.

The rounded corners 42 include a dielectric, and extend from the side surfaces 11d of the first electrode fingers 11 through the boundary Y to reach a part of the region of the gap on the upper surface 5a of the piezoelectric body 5 in order to achieve the above-described effects. Here, the upper end of the rounded corner may be the upper end of the side surface 11d of the 1 st electrode finger 11. That is, the upper end of the rounded corner 42 may reach the upper end edge of the side surface 11d, not limited to the inside of the side surface 11 d. Fig. 9 shows a cross section in a direction orthogonal to the longitudinal direction of the 1 st electrode finger 11. In a cross section orthogonal to the longitudinal direction, the outer surface of the round corner 42 has a curved shape recessed toward the corner portion as the boundary Y.

Here, the height H and the length L of the fillet 42 are defined as follows.

The height H is the dimension between the boundary Y and the upper end of the rounded corner 42 on the side 11 d. The length L is a dimension between the boundary Y and the farthest end of the rounded corner 42 on the upper surface 5a of the piezoelectric body 5. Here, a relationship between the round size L and the misses stress is shown in fig. 10. FIG. 10 is a graph showing the size and application of rounded corners to a LiTaO-containing substrate₃A graph of the relationship between the missles stress of the piezoelectric body 5 and the 1 st electrode finger 11. In addition, in fig. 10, results regarding the 4 configurations a) to d) are shown.

a) In LiTaO₃And an electrode finger including Al is laminated thereon.

This condition isMoreover LiTaO₃The stress on the upper surface side of (b) is denoted as LT @ LT. Further, stress on the electrode finger side containing Al is represented by Al @ LT.

b) In LiNbO₃And an electrode finger including Al is laminated thereon.

In FIG. 10, LN @ LN shows LiNbO in this configuration₃Lateral stress. Al @ LN shows the stress on the electrode finger side containing Al in this configuration.

c) A structure in which Al is laminated on an Si substrate.

In this case, Si @ Si shows the stress of the Si substrate side. Al @ Si shows the stress on the electrode finger side containing Al in this configuration.

d) A structure in which a high sound velocity member, a low sound velocity membrane, and a piezoelectric body are laminated as in embodiment 1.

The stress on the piezoelectric side in this configuration is shown with PECT @ PECT. The stress on the electrode finger side containing Al in this configuration is shown by Al @ PECT.

In fig. 10, as described above, the fillet size dependency of the two types of stresses is shown for each of the structures a) to d). However, in fig. 10, Al @ LT, Al @ LN, and Al @ PECT are substantially the same values and are repeated, and thus are shown by a dashed line. Similarly, LT @ LT and PECT @ PECT also substantially overlap and are therefore shown by a solid line.

As is clear from fig. 10, in any of the structures a) to d), stress can be effectively relieved as long as the fillet size L is 1.0nm or more.

As is clear from fig. 10, in the range of 1000nm or less, the fillet dimension L can reduce stress as compared with the case of less than 1.0 nm.

As in embodiment 4 shown in fig. 8 (a), the 1 st electrode finger 11 and the 2 nd electrode finger 12 may be provided with a regular tapered shape. This can further relieve the stress.

Fig. 11 is a partially enlarged front cross-sectional view for explaining an elastic wave device according to embodiment 6 of the present invention. In elastic wave device 51 according to embodiment 6, 1 st electrode finger 11 has a forward tapered shape, and 1 st dielectric film 13 also has a forward tapered shape. Although not particularly shown, the 2 nd electrode finger 12 side is also configured similarly. Here, in acoustic wave device 51, taper angle θ 1 of 1 st side surface 13c and 2 nd side surface 13d of 1 st dielectric film 13 is set to 50 ° or more and 88 ° or less. This can effectively suppress a higher-order mode closest to the main mode. This is explained with reference to fig. 12.

Fig. 12 is a diagram showing a relationship between the taper angle θ 1 and the phase of the higher-order mode closest to the main mode shown by an arrow X in fig. 5. As is clear from fig. 12, the phase of the higher-order mode is smaller if the taper angle θ 1 is 50 ° or more and 88 ° or less, as compared with the case where the taper angle θ 1 is 90 °, that is, no taper is provided. It is also found that if the phase is in the range of 90 ° to 100 °, the phase of the high-order mode is saturated and does not become small.

Therefore, in the elastic wave device 51, since the taper angle θ 1 is 50 ° or more and 88 ° or less, the influence of the high-order mode can be effectively suppressed. In particular, the taper angle θ 1 is more preferably 80 ° or less.

When elastic wave device 1 is used in a bandpass filter of composite filter device 30 shown in fig. 4, for example, if the above-described higher-order mode occurs, there is a possibility that the filter characteristics of other bandpass filters are adversely affected. That is, if the frequency of occurrence of the high-order mode is within the pass band of another bandpass filter, the filter characteristics of the other bandpass filter are also deteriorated. Therefore, it is preferable to suppress a higher-order mode other than the main mode used. In the present embodiment, since the taper angle θ 1 is 88 ° or less, the high-order mode can be effectively suppressed.

In addition, although not shown in fig. 5, not only the higher-order mode closest to the above-described main mode but also the higher-order mode occurs at a position near a frequency 2 times the resonance frequency of the main mode.

Fig. 13 is a diagram showing a relationship between the taper angle θ 1 and the phase of the higher-order mode in the vicinity of a frequency 2 times the resonance frequency. As is clear from fig. 13, if the taper angle θ 1 is 60 ° or more and 80 ° or less, the high-order mode can be effectively suppressed. Therefore, the taper angle θ 1 is more preferably 60 ° or more and 80 ° or less.

In fig. 11, the inclination angle α is an angle formed by the side surface 11c and the lower surface 11a in the forward tapered structure of the 1 st electrode finger 11.

Fig. 14 is a front cross-sectional view of an elastic wave device according to embodiment 7 of the present invention. Elastic wave device 61 according to embodiment 7 is configured in the same manner as elastic wave device 1 according to embodiment 1, except that 1 st electrode finger 11 and 2 nd electrode finger 12 have a forward tapered shape and are provided with 2 nd dielectric film 62 in the same manner as in embodiment 6. The 2 nd dielectric film 62 is laminated between the upper surface 5a of the piezoelectric body 5 and the 1 st and 2 nd electrode fingers 11 and 12. In this embodiment, the 2 nd dielectric film 62 is a silicon oxide film. The dielectric constituting the 2 nd dielectric film 62 is not limited thereto. An appropriate dielectric such as silicon oxynitride, alumina, tantalum oxide, or the like can be used. Further, a material containing these dielectrics as a main component and other dielectrics or elements added thereto may be used.

The 2 nd dielectric film 62 does not reach the entire region of the gap between the 1 st electrode finger 11 and the 2 nd electrode finger 12. Here, the gap does not mean the entire region between the lower ends of the 1 st electrode finger 11 and the 2 nd electrode finger 12, but means the exposed region between the upper surfaces 5a of the piezoelectric bodies 5 between the 2 nd dielectric films 62 and 62 integrated with the 1 st electrode finger 11 and the 2 nd electrode finger 12. Therefore, in elastic wave device 61 according to embodiment 7, there is no dielectric medium in the entire region of the gap. However, the elastic wave device 61 according to embodiment 7 may be provided with the above-described rounded corners. In the gap, a dielectric may be present in a partial region.

The material of the 2 nd dielectric film 62 is not necessarily the same as the material of the 1 st dielectric film 13, and may be different.

The side surface of the 1 st electrode finger 11 of the IDT electrode 6 and the upper surface 5a of the piezoelectric body 5 in the gap between the electrode fingers are not covered with a dielectric. Therefore, the surface acoustic wave propagates efficiently in the piezoelectric body 5. Therefore, since the viscosity loss (viscous loss) of the piezoelectric body is smaller than that of the dielectric body, deterioration of the Q value can be effectively suppressed.

Therefore, in elastic wave device 61, since no dielectric is present in a portion between electrode finger 1 and electrode finger 212, deterioration of the Q value can be suppressed as in embodiment 1.

Further, by providing the 2 nd dielectric film 62, the frequency can be adjusted in a direction of narrowing the relative bandwidth. Further, the frequency can be easily adjusted by adjusting the thickness and material of the upper 1 st dielectric film 13.

Fig. 15 is a front cross-sectional view of an elastic wave device according to embodiment 8. In elastic wave device 71 according to embodiment 8, groove 5b is provided on upper surface 5a of piezoelectric body 5 in the gap between first electrode finger 11 and second electrode finger 12. The acoustic wave device 71 is configured similarly to the acoustic wave device 61 except that the groove 5b is provided. Since the groove 5b is provided, the bottom surface 5b1 of the groove 5b is located at a position lower than the upper surface 5a of the piezoelectric body 5.

Since the groove 5b is provided in the acoustic wave device 71, the Q value can be further increased. This is explained with reference to fig. 16.

As an example of acoustic wave device 71, the elastic wave device of example 3 below was prepared without providing the 2 nd dielectric film 62 and omitting the 2 nd dielectric film 62.

Parameters of example 3.

Orientation of the support substrate containing Si: (111) and (5) kneading.

The high sonic speed member 3: silicon nitride film, thickness 300 nm.

Low acoustic velocity membrane 4: silicon oxide film, 225nm thick.

Piezoelectric body 5: 50 degree Y cut LiTaO₃And the thickness is 300 nm.

The wavelength λ determined by the electrode finger pitch of the IDT electrode 6 is 2 μm.

The number of pairs of electrode fingers of the IDT electrode 6 is 100 pairs, and the duty ratio is 0.5.

The 1 st electrode finger 11 and the 2 nd electrode finger 12 have a width dimension of 30 μm.

The electrode structure of the IDT electrode 6 and reflectors 7 and 8 is a stacked structure of Ti film/Al film/Ti film from below. The thickness of the film was 16nm, 120nm and 4nm, respectively.

1 st dielectric film 13: the silicon oxide film has a thickness of 35nm and a taper angle θ 1 of 78 °.

The definition of the 2 nd taper angle θ 2 will be described later.

Example 3 having the above design parameters and example 4 having the same configuration as that of elastic wave device 71 except that groove 5b was not provided were prepared.

Fig. 16 is a graph showing the Q characteristics of the elastic wave devices of example 3 and example 4. The solid line shows the results of example 3 and the dashed line shows the results of example 4. As is clear from fig. 16, in example 3 in which the groove 5b is provided, the Q characteristic can be more effectively improved.

Fig. 17 is a partially enlarged front cross-sectional view for explaining an elastic wave device according to embodiment 9 of the present invention. Elastic wave device 81 is configured in the same manner as elastic wave device 61. However, the taper angle θ 2 > the taper angle θ 1 shown in fig. 17 are set. Here, the taper angle θ 2 is an inclination angle of the 3 rd side surface 62c and the 4 th side surface 62d in the 2 nd dielectric film 62. The 2 nd dielectric film 62 has a lower surface 62a, an upper surface 62b, and a 3 rd side surface 62c and a 4 th side surface 62 d. As described previously, the 2 nd dielectric film 62 has a forward tapered shape. Therefore, the 3 rd side surface 62c and the lower surface 62a, that is, the upper surface 5a of the piezoelectric body 5 are tapered at an angle θ 2.

The present embodiment is characterized in that θ 2 > θ 1, and thus, the high-order mode can be effectively suppressed. This is explained with reference to fig. 18. The taper angle θ 1 of the side surface of the 1 st dielectric film 13 is fixed to 40 °, and the taper angle θ 2 of the side surface of the 2 nd dielectric film 62 is changed. Fig. 18 is a diagram showing a relationship between the taper angle θ 2 and the phase of the higher-order mode closest to the main mode. Other design parameters are the same as those in embodiment 4 described above. That is, in the piezoelectric body, no groove is provided in the gap between the electrode fingers.

As is clear from fig. 18, if the taper angle θ 2 of the 2 nd dielectric film 62 exceeds 40 °, the phase of the higher-order mode becomes extremely small. Therefore, θ 2 > θ 1 is preferable, whereby the high-order mode can be effectively suppressed.

Fig. 19 is a partially enlarged front cross-sectional view for explaining an elastic wave device according to embodiment 10. In elastic wave device 91, in contrast to elastic wave device 81, taper angle θ 1 > taper angle θ 2. With respect to the other structures, elastic wave device 91 is similar to elastic wave device 81. Fig. 20 is a diagram showing a change in the phase of the rayleigh wave when the taper angle θ 1 of the side surface of the 1 st dielectric film 13 is fixed to 40 ° and the taper angle θ 2 of the side surface of the 2 nd dielectric film 62 is changed. As is clear from fig. 20, if the taper angle θ 2 is smaller than 40 °, the phase of the rayleigh wave can be reduced. Therefore, the rayleigh wave as a stray can be effectively suppressed.

Fig. 21 is a diagram showing a relationship between the density ratio (density D2 of the 2 nd dielectric film 62/density D1 of the 1 st dielectric film 13) and the phase of the higher-order mode closest to the master mode. The design parameters of the elastic wave device were the same as those in example 4. Here, the 1 st dielectric film 13 is made of silicon oxide, and the density of the 2 nd dielectric film 62 is changed by changing the material of the 2 nd dielectric film 62. Further, the density of silicon oxide was 2.2X 10³kg/m³。

As is clear from fig. 21, the phase of the higher-order mode becomes smaller as the density ratio becomes larger beyond 1. Therefore, D2 > D1 is preferred.

Fig. 22 is a front cross-sectional view of an elastic wave device according to embodiment 11. Elastic wave device 101 does not have high acoustic velocity member 3. The support substrate 2 is a high-sound-velocity support substrate 2A including a high-sound-velocity material. As described above, the high-speed support substrate 2A may be used as the high-speed member.

Fig. 23 is a front cross-sectional view of an elastic wave device according to embodiment 12 of the present invention. In elastic wave device 111, low acoustic velocity film 4 in elastic wave device 101 is removed. With respect to the other structures, elastic wave device 111 is the same as elastic wave device 101. As described above, the high acoustic velocity support substrate 2A may be directly laminated as a high acoustic velocity member on the surface of the piezoelectric body 5 opposite to the side on which the IDT electrode 6 is provided.

The acoustic wave device according to each of the above embodiments can be used as a duplexer of a high-frequency front-end circuit or the like. This example will be explained below.

Fig. 24 is a block diagram of a communication device and a high-frequency front-end circuit. In the figure, the components connected to the high-frequency front-end circuit 230, for example, the antenna element 202 and the RF signal processing circuit (RFIC)203, are also shown. The high-frequency front-end circuit 230 and the RF signal processing circuit 203 constitute a communication device 240. The communication device 240 may include a power supply, a CPU, and a display.

The high-frequency front-end circuit 230 includes a switch 225, duplexers 201A and 201B, filters 231 and 232, low-noise amplifier circuits 214 and 224, and power amplifier circuits 234a, 234B, 244a, and 244B. The high-frequency front-end circuit 230 and the communication device 240 in fig. 24 are examples of a high-frequency front-end circuit and a communication device, and are not limited to this configuration.

The duplexer 201A has filters 211, 212. The duplexer 201B includes filters 221 and 222. The duplexers 201A and 201B are connected to the antenna element 202 via a switch 225. The elastic wave devices may be duplexers 201A and 201B, or may be filters 211, 212, 221, and 222.

Further, the elastic wave device can be applied to a multiplexer including 3 or more filters, such as a triplexer in which antenna terminals of 3 filters are shared and a hexaplexer in which antenna terminals of 6 filters are shared.

That is, the acoustic wave device includes an acoustic wave resonator, a filter, a duplexer, and a multiplexer including 3 or more filters. The multiplexer is not limited to the configuration including both the transmission filter and the reception filter, and may be a configuration including only the transmission filter or only the reception filter.

The switch 225 connects the antenna element 202 to a signal path corresponding to a predetermined frequency band in accordance with a control signal from a control unit (not shown), and is formed of, for example, a switch of SPDT (Single Pole Double Throw) type. The number of signal paths connected to the antenna element 202 is not limited to one, and may be plural. That is, the high frequency front end circuit 230 may also handle carrier aggregation.

The low noise amplifier circuit 214 is a reception amplifier circuit that amplifies the high frequency signal (here, a high frequency reception signal) having passed through the antenna element 202, the switch 225, and the duplexer 201A, and outputs the amplified signal to the RF signal processing circuit 203. The low noise amplifier circuit 224 is a reception amplifier circuit that amplifies the high frequency signal (here, a high frequency reception signal) having passed through the antenna element 202, the switch 225, and the duplexer 201B, and outputs the amplified signal to the RF signal processing circuit 203.

The power amplifier circuits 234a and 234b are transmission amplifier circuits that amplify the high-frequency signal (here, a high-frequency transmission signal) output from the RF signal processing circuit 203 and output the amplified signal to the antenna element 202 via the duplexer 201A and the switch 225. The power amplifier circuits 244a and 244B are transmission amplifier circuits that amplify the high-frequency signal (here, a high-frequency transmission signal) output from the RF signal processing circuit 203 and output the amplified signal to the antenna element 202 via the duplexer 201B and the switch 225.

The RF signal processing circuit 203 performs signal processing on the high-frequency reception signal input from the antenna element 202 via the reception signal path by down-conversion or the like, and outputs the reception signal generated by performing the signal processing. The RF signal processing circuit 203 performs signal processing on the input transmission signal by up-conversion or the like, and outputs a high-frequency transmission signal generated by the signal processing to the power amplifier circuits 234a, 234b, 244a, and 244 b. The RF signal processing circuit 203 is, for example, an RFIC. The communication device may include a BB (baseband) IC. In this case, the BBIC performs signal processing on the reception signal processed by the RFIC. Further, the BBIC performs signal processing on the transmission signal and outputs the signal to the RFIC. The received signal processed by the BBIC and the transmitted signal before the BBIC performs signal processing are, for example, an image signal and an audio signal.

The high-frequency front-end circuit 230 may include a duplexer according to a modification of the duplexers 201A and 201B, instead of the duplexers 201A and 201B.

On the other hand, the filters 231 and 232 in the communication device 240 are connected between the RF signal processing circuit 203 and the switch 225 without passing through the low noise amplifier circuits 214 and 224 and the power amplifier circuits 234a, 234b, 244a, and 244 b. The filters 231 and 232 are also connected to the antenna element 202 via the switch 225, similarly to the duplexers 201A and 201B.

While the elastic wave device, the elastic wave filter, the composite filter device, the high-frequency front-end circuit, and the communication device according to the embodiments of the present invention have been described above by referring to the embodiments and modifications thereof, other embodiments are also encompassed by the present invention, in which arbitrary constituent elements in the above-described embodiments and modifications are combined, modifications are obtained by implementing various modifications that can be conceived by those skilled in the art to the above-described embodiments within a range that does not depart from the gist of the present invention, and various devices incorporating the high-frequency front-end circuit and the communication device according to the present invention are also encompassed by the present invention.

The present invention is widely applicable to communication devices such as mobile phones as elastic wave resonators, filters, duplexers, multiplexers applicable to multiband systems, front-end circuits, and communication devices.

Description of the reference numerals

1: an elastic wave device;

2: a support substrate;

2A: a high acoustic velocity support substrate;

3: a high sound velocity member;

4: a low acoustic velocity membrane;

5: a piezoelectric body;

5 a: an upper surface;

5 b: a groove;

5b 1: a bottom surface;

6: an IDT electrode;

7. 8: a reflector;

11: the 1 st electrode finger;

11 a: a lower surface;

11 b: an upper surface;

11 c: a side surface;

11 d: a side surface;

12: the 2 nd electrode finger;

13: 1 st dielectric film;

13 a: a lower surface;

13 b: an upper surface;

13 c: the 1 st side;

13 d: a 2 nd side;

21: an elastic wave filter;

30: a composite filter device;

31-34: a band-pass filter;

41: an elastic wave device;

42: round corners;

43: an elastic wave device;

51: an elastic wave device;

61: an elastic wave device;

62: a 2 nd dielectric film;

62 a: a lower surface;

62 b: an upper surface;

62c, the ratio of: a 3 rd side;

62 d: a 4 th side;

71: an elastic wave device;

81: an elastic wave device;

91: an elastic wave device;

101: an elastic wave device;

111: an elastic wave device;

201A, 201B: a duplexer;

202: an antenna element;

203: an RF signal processing circuit;

211. 212, and (3): a filter;

214: a low noise amplifier circuit;

221. 222: a filter;

224: a low noise amplifier circuit;

225: a switch;

230: a high-frequency front-end circuit;

231. 232: a filter;

234a, 234 b: a power amplifier circuit;

240: a communication device;

244a, 244 b: a power amplifier circuit;

P1-P3: a parallel arm resonator;

S1-S4: a series arm resonator.