Surface acoustic wave device with improved q

Abstract

A surface acoustic wave (SAW) device having improved Q performance and high reliability of a bonding unit and a method of manufacturing the same are provided. The surface acoustic wave device includes: a support substrate; a high acoustic velocity layer formed on the support substrate; a first low sound velocity layer formed on the high sound velocity layer; a second low sound velocity layer formed on the first low sound velocity layer; a piezoelectric plate formed on the second low acoustic velocity layer; and a plurality of I DT electrode fingers formed on the piezoelectric plate, and the sound velocity of the first low sound velocity layer and the sound velocity of the second low sound velocity layer are different from each other.

Description

Technical Field

[0001] The present invention relates to a surface acoustic wave (SAW) device with improved Q performance and a method for manufacturing the same, and more particularly, to a surface acoustic wave (SAW) device configured with a plurality of low acoustic velocity layers and a method for manufacturing the same. Background Art

[0002] Surface acoustic wave (SAW) refers to a wave that propagates along the surface of an elastic solid. The energy of the surface acoustic wave is concentrated near the surface and propagates, which is equivalent to a mechanical wave. A surface acoustic wave device is an electromechanical device that uses the interaction between surface acoustic waves and conduction electrons and uses surface acoustic waves transmitted to the surface of a piezoelectric crystal. Surface acoustic wave devices can be used in a very wide range of industrial applications including sensors, oscillators, filters, etc., and can be miniaturized and lightweight, with many advantages such as robustness, stability, sensitivity, low cost, and real-time performance.

[0003] As a surface acoustic wave device requiring high performance, in order to obtain a high Q value, such as Figure 1 As shown, a structure in which the high acoustic velocity layer 110 and the low acoustic velocity layer 120 are stacked between the piezoelectric plate 130 and the support substrate 100 has been adopted.

[0004] Non-patent document 0001 discloses the use of Figure 1 The result shown is that a high acoustic velocity layer and a low acoustic velocity layer limit the SAW energy to within 2 Lambda from the surface. Patent document 0001 discloses a surface acoustic wave device consisting of a piezoelectric body, a low acoustic velocity layer, a high acoustic velocity layer and a supporting substrate, and by reducing the thickness of the piezoelectric body to 1.5 Lambda or less, the surface acoustic wave energy can be captured in the low acoustic velocity layer and the piezoelectric body.

[0005] Reference Figure 1 According to the prior art, a surface acoustic wave device is configured by forming a high acoustic velocity layer 110 and a low acoustic velocity layer 120 on a supporting substrate 100, and bonding the low acoustic velocity layer 120 and a piezoelectric plate 130. At this time, the supporting substrate 100 is made of single crystal silicon or sapphire, the high acoustic velocity layer 110 is made of aSi, PolySi, SiN or AlN, the low acoustic velocity layer 120 is made of SiO2, and the piezoelectric plate 130 is made by bonding single crystal LiTaO3 (LT) and then thinning it. In this structure, the surface acoustic wave energy is concentrated on the piezoelectric plate 130 made of LT and the low acoustic velocity layer 120 made of SiO2, and the energy leaking to the high acoustic velocity layer 110 or the supporting substrate 100 can be ignored.

[0006] Generally, it is difficult to change the viscosity of the single crystal LiTaO3 constituting the piezoelectric plate 130. In addition, SiO2 is used for the low acoustic velocity layer 120, and it is usually manufactured by a chemical vapor deposition (CVD) device, is amorphous, has various crystal structures and porosities, and has various viscosities according to the conditions at the time of deposition. When the low acoustic velocity layer 120 is manufactured by a physical vapor deposition (PVD) device, the viscosity is greater. There is a problem in the high viscosity distribution of the low acoustic velocity layer 120 in the existing structure, that is, it will deteriorate the Q performance of the surface acoustic wave device.

[0007] Current technical literature

[0008] (Patent Document 0001) JP5910763B2

[0009] (Non-Patent Document 0001) Incredibly High-Performance SAW Resonators on a Novel Multilayer Substrate (2016 IEEE International Ultrasound Symposium (I US)) Summary of the invention

[0010] Therefore, the present invention is proposed based on the above problems, and its object is to provide a surface acoustic wave device and a manufacturing method thereof that can stably achieve a high Q value.

[0011] The technical problems of the present invention are not limited to the above technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

[0012] In order to achieve the above object, according to one aspect of the present invention, a surface acoustic wave device is provided.

[0013] The invention comprises: a supporting substrate; a first low acoustic velocity layer formed directly or indirectly on the supporting substrate; at least one second low acoustic velocity layer formed on the first low acoustic velocity layer; a piezoelectric plate formed on the second low acoustic velocity layer; and a plurality of IDT electrode fingers formed on the piezoelectric plate, wherein the acoustic velocity of the first low acoustic velocity layer and the acoustic velocity of the second low acoustic velocity layer are different.

[0014] In some embodiments of the present invention, the first low acoustic velocity layer and the second low acoustic velocity layer may include the same material.

[0015] In some embodiments of the present invention, the first low acoustic velocity layer and the second low acoustic velocity layer may include SiO 2 material.

[0016] In some embodiments of the present invention, the sound velocity of the second low sound velocity layer may be higher than the sound velocity of the first low sound velocity layer.

[0017] In some embodiments of the present invention, the density of the second low sound velocity layer may be higher than the density of the first low sound velocity layer.

[0018] In some embodiments of the present invention, the stiffness of the second low sound velocity layer may be higher than the stiffness of the first low sound velocity layer.

[0019] In some embodiments of the present invention, the oxygen content of the second low acoustic velocity layer may be higher than the oxygen content of the first low acoustic velocity layer.

[0020] In some embodiments of the present invention, the resonant frequency of the surface acoustic wave may be determined by a wavelength λ defined by the IDT electrode finger pitch.

[0021] In some embodiments of the present invention, the thickness of the piezoelectric plate may be 1.5 times the wavelength or less.

[0022] In some embodiments of the present invention, the first low acoustic velocity layer may be formed by chemical vapor deposition (CVD), and the second low acoustic velocity layer may be formed by physical vapor deposition (PVD).

[0023] In some embodiments of the present invention, the surface acoustic wave device may further include one or more low acoustic velocity layers between the first low acoustic velocity layer and the second low acoustic velocity layer.

[0024] According to the surface acoustic wave filter device with improved structure and the manufacturing method thereof of the present invention, the deterioration of Q performance caused by the high viscosity of the low acoustic velocity layer in the existing structure can be improved by low viscosity of the low acoustic velocity layer (second low acoustic velocity layer).

[0025] The effects of the present invention are not limited to the above-mentioned effects, and other unmentioned effects will be clearly understood by those skilled in the art from the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a diagram showing a surface acoustic wave device including a high acoustic velocity layer and a low acoustic velocity layer according to the prior art.

[0027] Figure 2a and 2b is a diagram showing a surface acoustic wave device including two or more low acoustic velocity layers according to an embodiment of the present invention.

[0028] Figure 3a and 3b : is a diagram for explaining the effect of the surface acoustic wave device according to the embodiment of the present invention.

[0029] Figures 4 to 9 is a diagram for explaining a method of manufacturing a surface acoustic wave device including two or more low acoustic velocity layers according to an embodiment of the present invention.

[0030] Description of symbols

[0031] 100: Support substrate

[0032] 110: High sound velocity layer

[0033] 120: Low sound velocity layer

[0034] 121: The first low sound velocity layer

[0035] 122: The second lowest sound velocity layer

[0036] 130: Piezoelectric plate

[0037] 150: IDT electrode finger DETAILED DESCRIPTION

[0038] The advantages and features of the present invention and the methods for achieving these advantages and features will be clearly demonstrated by the embodiments described in detail below and the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. These embodiments are only used to make the disclosure of the present invention complete and fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0039] "And / or" includes each and every item mentioned and all combinations of one or more of the mentioned items.

[0040] The terms used in this specification are intended to describe embodiments rather than to limit the present invention. In this specification, singular forms also include plural forms unless otherwise specified in the article. The terms "include" and / or "comprising..." used in this specification mean that the components, steps, operations and / or elements mentioned do not exclude the existence or addition of one or more other components, steps, operations and / or elements.

[0041] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used as the meanings commonly understood by those skilled in the art. In addition, unless clearly and specifically defined, terms defined in commonly used dictionaries will not be idealized or over-interpreted.

[0042] Figure 2a and 2b is a diagram showing the structure of a surface acoustic wave device according to an embodiment of the present invention.

[0043] First, refer to Figure 2a The surface acoustic wave device according to the embodiment of the present invention includes a high acoustic velocity layer 110 , a first low acoustic velocity layer 121 , a second low acoustic velocity layer 122 , a piezoelectric plate 130 , and a plurality of IDT electrode fingers 150 formed on a support substrate 100 .

[0044] Reference Figure 2bThe surface acoustic wave device according to the embodiment of the present invention includes a first low acoustic velocity layer 121 , a second low acoustic velocity layer 122 , a piezoelectric plate 130 , and a plurality of IDT electrode fingers 150 formed on the piezoelectric plate 130 , which are directly or indirectly formed on a support substrate 100 .

[0045] The transverse wave speed of the support substrate 100 may be higher than that of the piezoelectric plate 130 , and the transverse wave speed of the high acoustic velocity layer 110 may also be higher than that of the piezoelectric plate 130 .

[0046] The support substrate 100 may include, for example, a silicon substrate, a sapphire substrate, a silicon carbide (SiC) substrate, a quartz substrate, a glass substrate, or the like.

[0047] The high acoustic velocity layer 110 may be formed on the support substrate 100. The high acoustic velocity layer 110 may include, for example, amorphous silicon (a-Si), polycrystalline silicon (PolySi), silicon nitride (SiN), silicon oxynitride (SiON), aluminum nitride (AlN), boron nitride (BN), diamond, or the like.

[0048] The first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 may be formed on the support substrate 100 or the high acoustic velocity layer 110. The acoustic velocity of the shear wave propagating through the first low acoustic velocity layer 121 may be different from the acoustic velocity of the shear wave propagating through the second low acoustic velocity layer 122.

[0049] Specifically, the sound velocity of the second low sound velocity layer 122 may be higher than the sound velocity of the first low sound velocity layer 121 .

[0050] The transverse wave sound velocity of the second low acoustic velocity layer 122 may be lower than the transverse wave sound velocity of the piezoelectric plate 130, and the sound velocity of the first low acoustic velocity layer 121 may be different from the sound velocity of the second low acoustic velocity layer 122. In order to make the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 have different sound velocities, for example, the density of the second low acoustic velocity layer 122 may be higher than the density of the first low acoustic velocity layer 121. Alternatively, the stiffness of the second low acoustic velocity layer 122 may be higher than the stiffness of the first low acoustic velocity layer 121.

[0051] Meanwhile, the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 may include the same material. For example, although both include the same SiO2, the acoustic velocity of the second low acoustic velocity layer 122 may be further increased by increasing the oxygen O content of the second low acoustic velocity layer 122. In some embodiments of the present invention, the second low acoustic velocity layer 122 may also include argon Ar.

[0052] In some embodiments of the present invention, the deposition of the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 can be performed in different processes. Specifically, the first low acoustic velocity layer 121 can be deposited by chemical vapor deposition (CVD), and the second low acoustic velocity layer 122 can be deposited by PVD. When the second low acoustic velocity layer 122 is deposited by physical vapor deposition (PVD), its acoustic velocity and density may be higher, and its viscosity may be lower, compared to the first low acoustic velocity layer 121 deposited by CVD. In this way, a second low acoustic velocity layer 122 having a higher acoustic velocity than the first low acoustic velocity layer 121 can be formed.

[0053] The piezoelectric plate 130 may include a piezoelectric element and generate elastic waves from a signal applied to the IDT electrode finger 150, and may include a material such as LiTaO3 (LT) and LiNbO3 (LN).

[0054] The resonance frequency of the surface acoustic wave may be determined by a wavelength λ defined by the pitch of the IDT electrode fingers 150. At this time, the piezoelectric plate 130 may be manufactured to have a thickness equal to or less than the wavelength λ.

[0055] Figure 3a and 3b : is a diagram for explaining the effect of the surface acoustic wave device according to the embodiment of the present invention.

[0056] Reference Figure 3a , a graph is shown, comparing the admittance and Q characteristics of a surface acoustic wave device in which a single layer of low acoustic velocity layer is deposited using a CVD device according to the prior art, and the admittance and Q characteristics of a surface acoustic wave device in which a single layer of low acoustic velocity layer is deposited using a PVD device. The red graph shows the admittance and Q characteristics of a surface acoustic wave device including a low acoustic velocity layer deposited by CVD, and the black graph shows the admittance and Q characteristics of a surface acoustic wave device in which a low acoustic velocity layer is deposited using a PVD device. In the comparative example, LiTaO3 is used for the piezoelectric plate, SiO2 is used for the low acoustic velocity layer, polycrystalline silicon is used for the high acoustic velocity layer, and Si is used for the supporting substrate. When the thickness of each layer is standardized to the power of the IDT electrode of the surface acoustic wave device, the piezoelectric plate is 0.3l ambda, the low acoustic velocity layer is 0.2lambda, and the high acoustic velocity layer is 0.2l ambda.

[0057] Since the acoustic velocity of the low acoustic velocity layer deposited using the PVD equipment is higher than that of the low acoustic velocity layer deposited using the CVD equipment, the resonant frequency of the surface acoustic wave device including the low acoustic velocity layer deposited using the PVD equipment is higher than that of the surface acoustic wave device including the low acoustic velocity layer deposited using the CVD equipment. In addition, since the low acoustic velocity layer deposited by PVD has a high density and some defects, the Q characteristics may also be improved. However, the PVD equipment has a defect of generating particles when SiO2 attached to the film deposition chamber is peeled off due to its structure, and although it is managed by cleaning the chamber, the generation of about 1,000 particles with a size of 0.2 μm is the actual lower limit. The particles generated during the deposition process are included in the stacked structure of the device and generate void defects or wafer bonding defects, which are likely to increase in reliability tests involving heating.

[0058] Furthermore, since it is necessary to release the vacuum of the vacuum equipment for cleaning, then open the chamber and physically remove the deposited SiO 2 , it is preferable to minimize the operating frequency during mass production to reduce manufacturing costs.

[0059] On the other hand, CVD equipment can use gas to clean the inside of the chamber after each deposition is completed, greatly reducing the frequency of defects caused by particles or wafer bonding defects. However, due to the low density of the low acoustic velocity layer deposited by CVD, there may be defects with low acoustic velocity and high loss.

[0060] Therefore, in order to solve the defect problem, the surface acoustic wave device according to the embodiment of the present invention may form a second low acoustic velocity layer 122 near the piezoelectric plate 130, which has a relatively higher density and acoustic velocity than the first low acoustic velocity layer 121, and the admittance characteristics and Q characteristics measured from the device of the present invention are as follows: Figure 3b shown.

[0061] Reference Figure 3b The admittance and Q characteristics measured from the surface acoustic wave device of the present invention including the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 are shown in red graphs, and the black graphs show Figure 3a Also shown are the characteristics of the case where a single low acoustic velocity layer deposited by CVD is included. Figure 3b The device in specifically includes a first low acoustic velocity layer 121 deposited by CVD and a second low acoustic velocity layer 122 deposited by PVD and having a velocity relatively higher than that of the first low acoustic velocity layer 121, in this way, an increase in resonance frequency and an improvement in Q value can be confirmed.

[0062] In addition to the above-mentioned effects of improving the resonant frequency and the Q value, due to the double-layer low acoustic velocity layer structure (especially containing SiO2) of the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122, the bonding strength can be improved and the reliability of the surface acoustic wave device can be enhanced by adopting the bonding structure of the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122, rather than the bonding structure between the LiTaO3 of the piezoelectric plate 130 having low bonding strength and the SiO2 of the low acoustic velocity layer.

[0063] Figures 4 to 9 FIG. 1 is a diagram for explaining a method for manufacturing a surface acoustic wave device including two or more low acoustic velocity layers according to an embodiment of the present invention, and explains the improved effect compared with the conventional structure.

[0064] Reference Figure 4 , prepare a support substrate 100 made of Si. The support substrate 100 may include a silicon substrate, or may include a sapphire or quartz substrate.

[0065] Reference Figure 5 , a high acoustic velocity layer 110 is deposited on the support substrate 100. Depositing the high acoustic velocity layer 110 may include, for example, forming polysilicon using a CVD device, etc. In some embodiments, in addition to polysilicon, the high acoustic velocity layer 110 may also be made of amorphous silicon (aSi), SiN, AlN, BN, diamond, etc.

[0066] Reference Figure 6 , forming a first low acoustic velocity layer 121 on the high acoustic velocity layer 110. Forming the first low acoustic velocity layer 121 may include, for example, depositing SiO2 using a CVD device. Figure 3b As shown, when the high acoustic velocity layer 110 is not deposited, the first low acoustic velocity layer 121 is formed on the support substrate 100 .

[0067] CVD equipment can increase deposition rate and reduce wafer manufacturing costs more easily than sputtering equipment.

[0068] In some embodiments of the present invention, the surface of the first low acoustic velocity layer 121 may be polished using chemical mechanical polishing (CMP), ion milling, etc. to reduce surface roughness and facilitate wafer bonding.

[0069] Reference Figure 7 , prepare a piezoelectric plate 130 containing single crystal LT or LN.

[0070] Reference Figure 8, a second low acoustic velocity layer 122 is formed on one side of the piezoelectric plate 130. Forming the second low acoustic velocity layer 122 may include, for example, depositing a thin film using the same SiO2 as the first low acoustic velocity layer 121 using a sputtering device. Of course, here, the second low acoustic velocity layer 122 may be formed, as described above, to have different physical properties from the first low acoustic velocity layer 121 so as to have a different acoustic velocity from the first low acoustic velocity layer 121.

[0071] Meanwhile, in some embodiments of the present invention, the second low acoustic velocity layer 122 may be formed by depositing SiO2 on one side of the piezoelectric plate 130 through a sputtering process. Due to the thermoelectricity and Curie temperature of LiTaO3, it is difficult to perform CVD deposition at high temperatures, and the deposition is mainly performed at a temperature of about 250°C to 400°C. In the case of low temperature deposition, the productivity is high, and the density of SiO2 is low and the viscosity is high. Therefore, when the CVD device deposits the second low acoustic velocity layer 122, it is preferred to deposit the second low acoustic velocity layer 122 thinly.

[0072] In addition, the acoustic velocity of the second low acoustic velocity layer 122 deposited using a sputtering device may be higher than the acoustic velocity of the first low acoustic velocity layer 121 deposited using a CVD device, and the viscosity may be lower. Figure 1 In the prior art structure, since the low acoustic velocity layer 120 is formed using a CVD device, the low viscosity of the second low acoustic velocity layer in this embodiment can prevent the Q performance from being deteriorated compared to the case of having a high viscosity.

[0073] At the same time, although the case of two low acoustic velocity layers such as the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 is described in the surface acoustic wave device in the embodiment of the present invention, the effect may be the same even if three or more low acoustic velocity layers are included, that is, one or more low acoustic velocity layers are included between the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122.

[0074] In some embodiments of the present invention, the surface of the second low acoustic velocity layer 122 may be polished using CMP, ion milling, etc. to reduce surface roughness and facilitate wafer bonding.

[0075] Reference Fig. 9 , the first low acoustic velocity layer 121 and the second low acoustic velocity layer 122 are bonded. In some embodiments of the present invention, the thickness of the piezoelectric plate 130 after the bonding process may be set to 1.5 wavelengths or less of the surface acoustic waves propagating to the piezoelectric plate.

[0076] Although the embodiments of the present invention are described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or basic features. Therefore, the embodiments described above should be understood to be illustrative in all aspects and not restrictive.

Claims

1. A surface acoustic wave device, characterized in that: include: A supporting substrate; A first low acoustic velocity layer formed directly or indirectly on a supporting substrate; at least one second low sound velocity layer formed on the first low sound velocity layer; a piezoelectric plate formed on the second low acoustic velocity layer; and A plurality of IDT electrode fingers are formed on the piezoelectric plate, The sound velocity of the first low sound velocity layer and the sound velocity of the second low sound velocity layer are different.

2. The surface acoustic wave device according to claim 1, characterized in that The first low sound velocity layer and the second low sound velocity layer include the same material.

3. The surface acoustic wave device according to claim 2, characterized in that: The first low acoustic velocity layer and the second low acoustic velocity layer include SiO2 material.

4. The surface acoustic wave device according to claim 1, characterized in that The sound velocity of the second low sound velocity layer is higher than the sound velocity of the first low sound velocity layer.

5. The surface acoustic wave device according to claim 1, characterized in that: The density of the second low sound velocity layer is higher than the density of the first low sound velocity layer.

6. The surface acoustic wave device according to claim 1, characterized in that The second low sound velocity layer has a higher stiffness than the first low sound velocity layer.

7. The surface acoustic wave device according to claim 1, characterized in that: The oxygen content of the second low sound velocity layer is higher than the oxygen content of the first low sound velocity layer.

8. The surface acoustic wave device according to claim 1, characterized in that The resonant frequency of the surface acoustic wave is determined by the wavelength λ defined by the IDT electrode finger pitch.

9. The surface acoustic wave device according to claim 8, characterized in that: The thickness of the piezoelectric plate is 1.5 times the wavelength or less.

10. The surface acoustic wave device according to claim 1, characterized in that The first low acoustic velocity layer is formed by chemical vapor deposition (CVD), and the second low acoustic velocity layer is formed by physical vapor deposition (PVD).

11. The surface acoustic wave device according to claim 1, characterized in that: One or more low sound velocity layers are further included between the first low sound velocity layer and the second low sound velocity layer.

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