Elastic wave device

Abstract

Provided is an elastic wave device having a wide fractional bandwidth. An elastic wave device (1) includes a high sound velocity member (3), a low sound velocity layer (4) laminated on the high sound velocity member (3), a piezoelectric layer (5) directly or indirectly laminated on the low sound velocity layer (4), and an electrode (7) provided on the piezoelectric layer (5), the low sound velocity layer (4) including a dielectric material having a lower Young's modulus than silicon oxide or a layer having the dielectric material as a main component.

Description

Technical Field

[0001] The present invention relates to an elastic wave device having a structure in which a low-sound-velocity layer and a piezoelectric layer are stacked on a high-sound-velocity component. Background Technology

[0002] Conventionally, an elastic wave device has been developed that has an IDT electrode disposed on a composite substrate having a piezoelectric layer. For example, in the elastic wave device described in Patent Document 1 below, a low-velocity layer comprising silicon oxide and a piezoelectric layer comprising LiTaO3 are stacked on a high-velocity substrate comprising a high-velocity material. An IDT electrode is disposed on this piezoelectric layer. In this configuration, elastic waves can be effectively confined within the piezoelectric layer, thereby improving the Q value.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-073331 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In elastic wave resonators used in bandpass filters and the like, a wide fractional bandwidth is sometimes required. However, in conventional elastic wave devices, it has been difficult to sufficiently widen the fractional bandwidth.

[0008] The purpose of this invention is to provide an elastic wave device with a wider fractional bandwidth.

[0009] means for solving problems

[0010] The elastic wave device of the present invention comprises: a high-velocity acoustic component; a low-velocity acoustic layer stacked on the high-velocity acoustic component; a piezoelectric layer stacked directly or indirectly on the low-velocity acoustic layer; and an electrode disposed on the piezoelectric layer, wherein the low-velocity acoustic layer comprises a dielectric material having a lower Young's modulus than silicon oxide, or a layer having the dielectric material as the main component.

[0011] Invention Effects

[0012] According to the present invention, it is possible to provide an elastic wave device with a wide fractional bandwidth. Attached Figure Description

[0013] Figure 1 This is a front sectional view showing the main parts of the elastic wave device according to the first embodiment of the present invention.

[0014] Figure 2 This is a schematic top view showing the electrode structure of the elastic wave device according to the first embodiment.

[0015] Figure 3This is a graph showing the impedance-frequency characteristics of the elastic wave resonator of the elastic wave device as Example 1 and Comparative Example 1.

[0016] Figure 4 This is a graph showing the impedance-frequency characteristics of the elastic wave resonator of the elastic wave device as Example 2 and Comparative Example 2.

[0017] Figure 5 This is a graph showing the relationship between the material of the low-velocity layer and the fractional bandwidth in an elastic wave device in which a LiTaO3 film is used as a piezoelectric layer.

[0018] Figure 6 This is a graph showing the relationship between the material of the low-velocity layer and the fractional bandwidth in an elastic wave device in which a LiNbO3 film is used as a piezoelectric layer.

[0019] Figure 7 This is a front sectional view showing the main parts of the elastic wave device according to the second embodiment of the present invention. Detailed Implementation

[0020] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0021] It should be noted that the embodiments described in this specification are illustrative, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0022] Figure 1 This is a front sectional view showing the main parts of the elastic wave device according to the first embodiment of the present invention. Figure 2 This is a schematic top view showing its electrode structure.

[0023] In the elastic wave device 1, an IDT electrode 7 is provided on the piezoelectric composite substrate 6.

[0024] The IDT electrode 7 has multiple first electrode fingers 7a and multiple second electrode fingers 7b that are interleaved with each other.

[0025] It should be noted that elastic wave device 1 is an elastic wave resonator. For example... Figure 2 As shown, reflectors 8 and 9 are provided on both sides of the elastic wave propagation direction of IDT electrode 7.

[0026] The IDT electrode 7 and reflectors 8 and 9 can be made of suitable metals or alloys. Alternatively, the IDT electrode 7 and reflectors 8 and 9 can also comprise a stack of multiple metal films.

[0027] In the piezoelectric composite substrate 6, a high-velocity acoustic component 3, a low-velocity acoustic layer 4, and a piezoelectric layer 5 are stacked on a support substrate 2. In this embodiment, the support substrate 2 comprises Si. However, the support substrate 2 can also be made of other suitable dielectrics or semiconductors. The high-velocity acoustic component 3 comprises a high-velocity acoustic material. A high-velocity acoustic material is a material in which the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric layer 5. Examples of such high-velocity acoustic materials include alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film or diamond, dielectrics mainly composed of the above materials, and dielectrics mainly composed of mixtures of the above materials. In this embodiment, the high-velocity acoustic component 3 comprises SiN as silicon nitride.

[0028] The low-velocity layer 4 comprises a low-velocity material in which the velocity of the propagating bulk wave is lower than that of the bulk wave propagating in the piezoelectric layer 5. Furthermore, the low-velocity layer 4 comprises a dielectric material with a Young's modulus lower than that of silicon oxide. There is no particular limitation on such a dielectric material, but a material selected from the group consisting of aluminum titanate, boron nitride, carbon-containing silicon oxide, and nitrogen-containing silicon carbide can be used. In this embodiment, the low-velocity layer 4 comprises AlTiO4 as aluminum titanate.

[0029] It should be noted that the Young's modulus of AlTiO4 is 13 GPa, while that of silicon oxide is 73 GPa.

[0030] The piezoelectric layer 5 comprises a piezoelectric single crystal, of which lithium tantalate (LiTaO3) is used. It should be noted that lithium niobate can also be used. It should also be noted that the piezoelectric layer 5 can be indirectly stacked on the low-velocity layer 4.

[0031] In the piezoelectric composite substrate 6, having the above-described laminated structure, elastic waves can be effectively confined within the piezoelectric layer 5. Therefore, the Q value can be improved. Furthermore, since the low-velocity layer 4 comprises a dielectric material with a Young's modulus lower than that of silicon oxide, it is clear from the experimental examples described later that the fractional bandwidth can be effectively broadened.

[0032] Furthermore, when the resonant frequency is set to fr and the anti-resonant frequency is set to fa, the fractional bandwidth in the elastic wave resonator is represented by (fa-fr) / fr.

[0033] Next, in the elastic wave device 1, by explaining the resonance characteristics of Examples 1 to 4, it becomes clear how the fractional bandwidth can be widened as described above.

[0034] (Example 1)

[0035] As an example 1, an elastic wave device with the following structure was fabricated.

[0036] As the support substrate 2, Si with a face orientation of (111) and a third Euler angle of 73° was used. As the high-velocity component 3, a SiN film with a thickness of 300 nm was used. As the low-velocity layer 4, AlTiO4 with a Young's modulus of 13 GPa was used, and the film thickness was set to 400 nm.

[0037] For piezoelectric layer 5, a 35° Y-cut X-propagated LiTaO3 film with a thickness of 300 nm was used.

[0038] In IDT electrode 7, a Ti / AlCu / Ti laminate is used. From the upper surface opposite to the piezoelectric layer 5, the film thickness is 12 nm / 100 nm / 4 nm. IDT electrode 7 has 100 pairs of electrode fingers with a cross-width of 40 μm, and the wavelength λ, determined by the distance between the electrode fingers, is 2 μm. It should be noted that the cross-width refers to the dimension along the direction extending from the first electrode finger 7a to the second electrode finger 7b, where the region overlaps when viewed from the direction of elastic wave propagation.

[0039] For comparison, the elastic wave device of Comparative Example 1 was prepared in the same manner as in Example 1, except that a silicon oxide film with a thickness of 300 nm was used in the low sound velocity layer 4.

[0040] Figure 3 This is a diagram showing the resonant characteristics of the elastic wave resonator in the elastic wave device of Example 1 and Comparative Example 1. From... Figure 3 It is clear that, compared to Comparative Example 1, according to Example 1, the resonant frequency can be shifted to the lower frequency side. Therefore, the fractional bandwidth is widened.

[0041] The reason is believed to be as follows. It is believed that when the Young's modulus of the low-velocity layer 4 is small, the acoustic impedance difference between the piezoelectric layer 5 and the low-velocity layer 4 becomes larger. As a result, the elastic wave can be more effectively confined in the piezoelectric layer 5, and the fractional bandwidth becomes larger.

[0042] (Example 2)

[0043] Next, as Example 2, an elastic wave device using boron nitride (BN) as the low-velocity layer 4 was fabricated. The Young's modulus of BN was 10 GPa, and its thickness was set to 400 nm. The IDT electrode 7 had 100 pairs of electrode fingers, a cross-width of 40 μm, and a wavelength determined by the distance between the electrode fingers of 2 μm. Other structures were the same as in Example 1. For comparison, the elastic wave device of Comparative Example 2 was prepared in the same manner as in Example 2, except that a 300 nm thick silicon oxide film was used as the low-velocity layer 4.

[0044] Figure 4This is a graph showing the impedance-frequency characteristics of the elastic wave resonator of the elastic wave device used in Embodiment 2 and Comparative Example 2. From... Figure 4 It is clear that, compared with Comparative Example 2, according to Example 2, the resonant frequency shifts to the lower frequency side and the fractional bandwidth is widened.

[0045] As can be clearly seen from the results of Examples 1 and 2 above, according to the present invention, the low-velocity layer 4 includes a dielectric material with a Young's modulus lower than that of silicon oxide, thus effectively widening the fractional bandwidth of the elastic wave device. It should be noted that the low-velocity layer 4 can include this dielectric material as the main component. That is, the low-velocity layer 4 can also be a layer with this dielectric material as the main component.

[0046] As described above, in this invention, a dielectric material with a lower Young's modulus than silicon oxide is used as the material constituting the low-velocity layer 4. Besides AlTiO4 as aluminum titanate and BN as boron nitride, suitable dielectric materials include SiOC as carbon-containing silicon oxide and SiCN as nitrogen-containing silicon carbide.

[0047] (Example 3)

[0048] In Example 3, a high-velocity acoustic component 3 comprising silicon nitride (SiN) with a thickness of 300 nm is stacked on a support substrate 2 comprising Si, and various dielectric materials of 200 nm are used as a low-velocity acoustic layer 4, thereby constituting an elastic wave device.

[0049] A 400 nm thick LiTaO3 film with a 40° Y-cut X-propagation was used in piezoelectric layer 5. The electrode stack-up structure was the same as in Example 1. It should be noted that the wavelength λ, determined by the finger spacing of the IDT electrode 7, is 2 μm, the number of finger pairs is 100, and the crossover width is 40 μm.

[0050] SiOC, AlTiO4, SiCN, and BN were used as the dielectric materials described above. For comparison, a structure consisting of SiO2 as the low-velocity layer 4 was prepared.

[0051] The characteristics of the elastic wave resonators used as these elastic wave devices were evaluated, and the fractional bandwidth was determined. Figure 5 Show the results. For example... Figure 5 As shown, compared with the case of using SiO2, the fractional bandwidth can be effectively widened when using SiOC, AlTiO4, SiCN or BN.

[0052] It should be noted that the Young's moduli of SiOC, AlTiO4, SiCN, BN and SiO2 are shown in Table 1 below.

[0053] [Table 1]

[0054] Young's modulus <![CDATA[SiO2]]> 73GPa <![CDATA[AlTiO4]]> 13GPa BN 10GPa SiOC 15GPa SiCN 40GPa

[0055] (Example 4)

[0056] Except for the piezoelectric layer 5, which includes a 400 nm thick LiNbO3 film with a 30° Y-cut X-propagation, the elastic wave device was constructed in the same manner as in Example 3, using each dielectric material as the low-velocity sound layer 4. The resonant characteristics of each elastic wave device were measured in the same manner as in Example 3, and the fractional bandwidth was determined. Figure 6 Show the results. For example... Figure 6 As shown, compared to the case where the dielectric material constituting the low-velocity layer 4 is SiO2, the fractional bandwidth can be broadened when using SiOC, AlTiO4, SiCN, or BN. Thus, in this invention, even when LiNbO3 is used as the piezoelectric layer 5, the fractional bandwidth can be effectively broadened.

[0057] Figure 7 This is a front sectional view of the elastic wave device showing the main parts of the elastic wave device according to the second embodiment of the present invention.

[0058] In the elastic wave device 21, the hypersonic component 3 is a support substrate comprising a hypersonic material. In this case, the hypersonic component, which is made of a different material than the support substrate, can be omitted. Regarding other configurations, the elastic wave device 21 and... Figure 1 The elastic wave device shown is the same as 1.

[0059] Explanation of reference numerals in the attached figures

[0060] 1, 21… elastic wave device;

[0061] 2...support base plate;

[0062] 3…high-speed components;

[0063] 4…low-speed layer

[0064] 5…piezoelectric layer;

[0065] 6…Piezoelectric composite substrate;

[0066] 7…IDT electrode;

[0067] 7a, 7b... First electrode finger, second electrode finger;

[0068] 8, 9... reflectors.

Claims

1. An elastic wave device, comprising: High-speed components; A low-velocity layer is stacked on the high-velocity component; A piezoelectric layer, which is directly or indirectly stacked on the low-sound-velocity layer; and Electrodes, which are disposed on the piezoelectric layer, The low-velocity layer comprises a dielectric material with a Young's modulus lower than that of silicon oxide, or a layer with the dielectric material as the main component, wherein the dielectric material does not include carbon-containing silicon oxide.

2. The elastic wave device according to claim 1, wherein, The dielectric material includes one material selected from the group consisting of aluminum titanate, boron nitride, and nitrogen-containing silicon carbide.

3. The elastic wave device according to claim 1 or 2, wherein, The elastic wave device also includes a support substrate. The hypersonic component is stacked on the support substrate.

4. The elastic wave device according to claim 1 or 2, wherein, The hypersonic component is a support substrate comprising hypersonic material.

5. The elastic wave device according to claim 3, wherein, The supporting substrate is a silicon substrate.

6. The elastic wave device according to claim 1 or 2, wherein, The piezoelectric layer includes lithium tantalate or lithium niobate.

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