WO2023199837A1 - Dispositif à ondes élastiques - Google Patents

Dispositif à ondes élastiques Download PDF

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Publication number
WO2023199837A1
WO2023199837A1 PCT/JP2023/014216 JP2023014216W WO2023199837A1 WO 2023199837 A1 WO2023199837 A1 WO 2023199837A1 JP 2023014216 W JP2023014216 W JP 2023014216W WO 2023199837 A1 WO2023199837 A1 WO 2023199837A1
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Prior art keywords
substrate
piezoelectric layer
electrode
wave device
electrodes
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PCT/JP2023/014216
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English (en)
Japanese (ja)
Inventor
和則 井上
哲也 木村
昌和 三村
明洋 井山
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株式会社村田製作所
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Publication of WO2023199837A1 publication Critical patent/WO2023199837A1/fr

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves

Definitions

  • the present invention relates to an elastic wave device.
  • acoustic wave devices including a piezoelectric layer made of lithium niobate or lithium tantalate are known.
  • Patent Document 1 discloses a support in which a cavity is formed, a piezoelectric substrate provided on the support so as to overlap with the cavity, and a piezoelectric substrate provided on the piezoelectric substrate so as to overlap with the cavity.
  • An acoustic wave device is provided with an IDT (Interdigital Transducer) electrode provided, and a plate wave is excited by the IDT electrode, wherein an edge of the cavity portion is provided with a plate wave excited by the IDT electrode.
  • An elastic wave device is disclosed that does not include a straight portion extending parallel to the propagation direction of the wave.
  • a support substrate is made of silicon (Si)
  • the material of the support substrate and the material of the piezoelectric substrate are Since the coefficients of linear expansion are different, stress is applied to the piezoelectric layer above the cavity, and there is a risk that cracks may occur in the piezoelectric layer.
  • An object of the present invention is to provide an elastic wave device that can prevent cracks from occurring in a piezoelectric layer.
  • the elastic wave device of the present invention includes a support member having a cavity on one main surface, a piezoelectric layer provided on the one main surface of the support member so as to cover the cavity, and at least one of the piezoelectric layers.
  • a functional electrode is provided on the main surface so that at least a portion thereof overlaps with the cavity when viewed from the thickness direction of the piezoelectric layer.
  • the support member includes a first substrate and an intermediate layer provided between the first substrate and the piezoelectric layer. The support member contains the same kind of material as the piezoelectric layer.
  • an acoustic wave device that can prevent cracks from occurring in the piezoelectric layer.
  • FIG. 1 is a cross-sectional view schematically showing an example of an elastic wave device according to a first embodiment of the present invention.
  • FIG. 2 is a cross-sectional view showing a calculation model of the elastic wave device.
  • FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a broken line in FIG. 2.
  • FIG. 4 is a plan view showing the relationship between the Y direction shown in FIG. 2 and functional electrodes.
  • FIG. 5 is a graph showing the dependence of the coefficient of linear expansion in the X direction on the maximum principal stress of the portion indicated by the arrow in FIG.
  • FIG. 6 is a graph showing the dependence of the linear expansion coefficient in the X direction on the reduction rate of the relative maximum principal stress.
  • FIG. 5 is a graph showing the dependence of the coefficient of linear expansion in the X direction on the maximum principal stress of the portion indicated by the arrow in FIG.
  • FIG. 6 is a graph showing the dependence of the linear expansion coefficient in the X direction on the reduction rate of the relative maximum
  • FIG. 7 is a graph showing the relationship between the coefficient of linear expansion in the X direction and the cut angle of the piezoelectric layer.
  • FIG. 8 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate.
  • FIG. 9 is a cross-sectional view schematically showing an example of the process of forming the intermediate layer.
  • FIG. 10 is a cross-sectional view schematically showing an example of the process of bonding the first substrate to the intermediate layer.
  • FIG. 11 is a cross-sectional view schematically showing an example of a process of thinning a piezoelectric substrate.
  • FIG. 12 is a cross-sectional view schematically showing an example of the process of forming functional electrodes, busbar electrodes, and wiring electrodes.
  • FIG. 13 is a cross-sectional view schematically showing an example of the process of forming a through hole.
  • FIG. 14 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer.
  • FIG. 15 is a cross-sectional view schematically showing another example of the elastic wave device according to the first embodiment of the present invention.
  • FIG. 16 is a cross-sectional view schematically showing an example of an elastic wave device according to a second embodiment of the present invention.
  • FIG. 17 is a cross-sectional view schematically showing another example of the elastic wave device according to the second embodiment of the present invention.
  • FIG. 18 is a cross-sectional view schematically showing still another example of the elastic wave device according to the second embodiment of the present invention.
  • FIG. 19 is a sectional view schematically showing a first modification of the elastic wave device according to the first embodiment of the present invention.
  • FIG. 20 is a sectional view schematically showing a second modification of the elastic wave device according to the first embodiment of the present invention.
  • 21A to 21E are cross-sectional views schematically showing an example of a method of forming a cavity on the first substrate side of the support member.
  • FIG. 22 is a schematic perspective view showing the appearance of an example of an elastic wave device that utilizes bulk waves in thickness shear mode.
  • FIG. 23 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG.
  • FIG. 24 is a cross-sectional view of a portion taken along line AA in FIG. 22.
  • FIG. 25 is a schematic front sectional view for explaining Lamb waves propagating through the piezoelectric film of the acoustic wave device.
  • FIG. 26 is a schematic front sectional view for explaining a thickness shear mode bulk wave propagating through a piezoelectric layer of an elastic wave device.
  • FIG. 27 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode.
  • FIG. 28 is a diagram showing an example of resonance characteristics of the elastic wave device shown in FIG. 22.
  • FIG. 29 is a diagram showing the relationship between d/2p and the fractional band as a resonator of an acoustic wave device, where p is the distance between the centers of adjacent electrodes and d is the thickness of the piezoelectric layer.
  • FIG. 30 is a plan view of another example of an elastic wave device that uses thickness-shear mode bulk waves.
  • FIG. 31 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22.
  • FIG. 32 is a diagram showing the relationship between the fractional band and the amount of phase rotation of spurious impedance normalized by 180 degrees as the magnitude of spurious when a large number of elastic wave resonators are configured according to the present embodiment. It is.
  • FIG. 33 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional band.
  • FIG. 34 is a diagram showing a map of fractional bands with respect to Euler angles (0°, ⁇ , ⁇ ) of LiNbO 3 when d/p is brought as close to 0 as possible.
  • FIG. 35 is a partially cutaway perspective view for explaining an example of an elastic wave device that uses Lamb waves.
  • FIG. 36 is a cross-sectional view schematically showing an example of an elastic wave device that uses bulk waves.
  • the acoustic wave device of the present invention includes a piezoelectric layer made of lithium niobate or lithium tantalate, a first electrode and a first electrode facing each other in a direction crossing the thickness direction of the piezoelectric layer. 2 electrodes.
  • a bulk wave in a thickness shear mode such as a primary thickness shear mode is used.
  • the first electrode and the second electrode are adjacent electrodes, and when the thickness of the piezoelectric layer is d and the distance between the centers of the first electrode and the second electrode is p, d/ p is set to be 0.5 or less.
  • the Q value can be increased even when miniaturization is promoted.
  • Lamb waves are used as plate waves. Then, resonance characteristics due to the Lamb wave described above can be obtained.
  • the acoustic wave device of the present invention includes a piezoelectric layer made of lithium niobate or lithium tantalate, and an upper electrode and a lower electrode that face each other in the thickness direction of the piezoelectric layer with the piezoelectric layer in between.
  • bulk waves are utilized.
  • FIG. 1 is a cross-sectional view schematically showing an example of an elastic wave device according to a first embodiment of the present invention.
  • the elastic wave device 10 shown in FIG. 1 includes a support member 20, a piezoelectric layer 21, and a functional electrode 22.
  • the support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 1).
  • the piezoelectric layer 21 is provided on one main surface of the support member 20 so as to cover the cavity 23.
  • the piezoelectric layer 21 is made of, for example, lithium niobate (LiNbO x ) or lithium tantalate (LiTaO x ). In that case, the piezoelectric layer 21 may be composed of LiNbO 3 or LiTaO 3 .
  • the functional electrode 22 is provided on at least one main surface of the piezoelectric layer 21.
  • the functional electrode 22 is provided on one main surface (the upper main surface in FIG. 1) of the piezoelectric layer 21.
  • the functional electrode 22 is provided so that at least a portion thereof overlaps with the cavity 23 when viewed from the thickness direction of the piezoelectric layer 21 (vertical direction in FIG. 1).
  • the functional electrode 22 may be provided so that the entirety thereof overlaps with the cavity 23, or a part of the functional electrode 22 may be provided so as to overlap with the cavity 23. .
  • the functional electrode 22 is, for example, an IDT electrode provided on one main surface of the piezoelectric layer 21.
  • the functional electrode 22 is connected to a busbar electrode and wiring electrode 24, and a two-layer wiring 25.
  • the support member 20 includes a first substrate 31 and an intermediate layer (also referred to as a bonding layer or an insulating layer) 41 provided between the first substrate 31 and the piezoelectric layer 21.
  • the intermediate layer 41 is made of silicon oxide (SiO x ) such as silicon dioxide (SiO 2 ), for example.
  • the cavity 23 may or may not penetrate the support member 20 in the thickness direction (vertical direction in FIG. 1).
  • the cavity 23 may be provided so as to penetrate the intermediate layer 41 in the thickness direction, or the cavity 23 may be provided so as not to penetrate the intermediate layer 41 in the thickness direction.
  • the support member 20 contains the same kind of material as the piezoelectric layer 21.
  • the term "materials of the same kind” includes not only cases where the materials are completely the same, but also cases where the crystallinity or orientation is different, and cases where the presence or absence or concentration of additives is different. The same applies to the following.
  • the piezoelectric layer 21 on which the functional electrode 22 is provided with the support member 20 containing the same material as the piezoelectric layer 21, it is possible to reduce the difference in linear expansion coefficient between the two. can. Thereby, stress on the membrane portion 21M, which is a part of the piezoelectric layer 21, can be reduced and cracks generated in the piezoelectric layer 21 can be prevented.
  • the portion of the piezoelectric layer located in the region overlapping with the cavity when viewed from the thickness direction is also referred to as a "membrane portion.”
  • the thickness of the first substrate 31 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21.
  • the thickness of the first substrate 31 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41.
  • the first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example.
  • the first substrate 31 is preferably a piezoelectric substrate.
  • the first substrate 31 is made of, for example, lithium niobate (LiNbO x ) or lithium tantalate (LiTaO x ).
  • the first substrate 31 may be made of LiNbO 3 or LiTaO 3 .
  • the following two-dimensional model is used to evaluate the relationship between the linear expansion coefficient of the first substrate 31 and the stress that causes cracks in the membrane portion 21M. A simulation was conducted.
  • FIG. 2 is a cross-sectional view showing a calculation model of the elastic wave device.
  • FIG. 3 is an enlarged cross-sectional view of a portion surrounded by a broken line in FIG. 2.
  • FIG. FIG. 4 is a plan view showing the relationship between the Y direction shown in FIG. 2 and functional electrodes.
  • the elastic wave device 10A shown in FIG. 2 includes a support member 20, a piezoelectric layer 21, a functional electrode 22 (see FIG. 4), a single-layer electrode 24A, and a double-layer electrode 25A.
  • the support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 2).
  • the support member 20 includes a first substrate 31 and an intermediate layer 41 provided between the first substrate 31 and the piezoelectric layer 21.
  • the constituent material of the piezoelectric layer 21 is lithium niobate (LiNbO 3 ), the functional electrode 22 is an IDT electrode, and the constituent material of the intermediate layer 41 is silicon dioxide (SiO 2 ).
  • Stress generation conditions Heat to the maximum reflow temperature (270°C).
  • Material conditions (1) When the first substrate 31 is made of Si, the orientation of lithium niobate in the piezoelectric layer 21 is changed. (2) When the first substrate 31 is made of the same lithium niobate as the piezoelectric layer 21, the orientation of the lithium niobate in the piezoelectric layer 21 is changed.
  • FIG. 5 is a graph showing the dependence of the linear expansion coefficient in the X direction on the maximum principal stress in the portion indicated by the arrow in FIG.
  • the linear expansion coefficient of the piezoelectric layer 21 in the X direction is smaller than when the first substrate 31 is made of Si (Si substrate). It can be seen that the larger the value, the smaller the maximum principal stress.
  • FIG. 6 is a graph showing the dependence of the coefficient of linear expansion in the X direction on the reduction rate of the relative maximum principal stress.
  • FIG. 7 is a graph showing the relationship between the coefficient of linear expansion in the X direction and the cut angle of the piezoelectric layer.
  • the piezoelectric layer 21 is made of lithium niobate such as LiNbO 3 , if the rotational Y cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less, Since the effect of reducing the maximum principal stress by 5% or more is expected, it is considered to be effective against cracks. Therefore, it is preferable that the piezoelectric layer 21 is made of lithium niobate such as LiNbO 3 and that the rotational Y-cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less.
  • the piezoelectric layer 21 and the first substrate 31 are made of lithium niobate such as LiNbO 3 and that the rotational Y-cut angle of the piezoelectric layer 21 is in the range of 90 degrees or more and 163 degrees or less.
  • the elastic wave device of the present invention is manufactured, for example, by the following method.
  • FIG. 8 is a cross-sectional view schematically showing an example of the process of forming a sacrificial layer on a piezoelectric substrate.
  • a sacrificial layer 50 is formed on the piezoelectric substrate 30.
  • the piezoelectric substrate 30 for example, a substrate made of LiNbO 3 or LiTaO 3 is used.
  • the material for the sacrificial layer 50 an appropriate material that can be removed by etching, which will be described later, is used.
  • an appropriate material that can be removed by etching which will be described later, is used.
  • ZnO or the like is used.
  • the sacrificial layer 50 can be formed, for example, by the following method. First, a ZnO film is formed by sputtering. Thereafter, resist coating, exposure and development are performed in this order. Next, a pattern of the sacrificial layer 50 is formed by performing wet etching. Note that the sacrificial layer 50 may be formed by other methods.
  • FIG. 9 is a cross-sectional view schematically showing an example of the process of forming the intermediate layer.
  • the surface of the intermediate layer 41 is planarized.
  • the intermediate layer 41 for example, a SiO 2 film or the like is formed.
  • the intermediate layer 41 can be formed by, for example, a sputtering method.
  • the intermediate layer 41 can be planarized by, for example, chemical mechanical polishing (CMP).
  • FIG. 10 is a cross-sectional view schematically showing an example of the process of bonding the first substrate to the intermediate layer.
  • the first substrate 31 is bonded to the intermediate layer 41. Thereby, the support member 20 is formed.
  • a piezoelectric substrate made of, for example, LiNbO 3 or LiTaO 3 is used.
  • FIG. 11 is a cross-sectional view schematically showing an example of the process of thinning the piezoelectric substrate.
  • the piezoelectric substrate 30 is thinned. As a result, the piezoelectric layer 21 is formed.
  • the piezoelectric substrate 30 can be thinned by, for example, a smart cut method, polishing, or the like.
  • FIG. 12 is a cross-sectional view schematically showing an example of the process of forming functional electrodes, busbar electrodes, and wiring electrodes.
  • a functional electrode 22, a busbar electrode, and a wiring electrode 24 are formed on one main surface of the piezoelectric layer 21.
  • the functional electrode 22, the bus bar electrode, and the wiring electrode 24 can be formed by, for example, a lift-off method.
  • a two-layer wiring 25 is also formed on one main surface of the piezoelectric layer 21.
  • FIG. 13 is a cross-sectional view schematically showing an example of the step of forming a through hole.
  • through holes 51 are formed in the piezoelectric layer 21.
  • the through hole 51 is formed to reach the sacrificial layer 50.
  • the through hole 51 can be formed by, for example, a dry etching method.
  • the through hole 51 is used as an etching hole.
  • FIG. 14 is a cross-sectional view schematically showing an example of the process of removing the sacrificial layer.
  • the sacrificial layer 50 is removed using the through hole 51.
  • a cavity 23 is formed in the support member 20.
  • the elastic wave device 10 is obtained.
  • FIG. 15 is a cross-sectional view schematically showing another example of the elastic wave device according to the first embodiment of the present invention.
  • the support member 20 may further include a second substrate 32 made of Si on the opposite side of the intermediate layer 41 with the first substrate 31 in between.
  • the thickness of the second substrate 32 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31.
  • the thickness of the second substrate 32 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21.
  • the thickness of the second substrate 32 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41.
  • the outer circumferential edge of the second substrate 32 be located outside the outer circumferential edge of the first substrate 31 when viewed from the thickness direction. That is, it is preferable that the outer periphery of the first substrate 31 is located inside the outer periphery of the second substrate 32 when viewed from the thickness direction.
  • An intermediate layer 42 may be provided between the first substrate 31 and the second substrate 32.
  • the intermediate layer 42 may not be provided between the first substrate 31 and the second substrate 32. That is, the first substrate 31 and the second substrate 32 may be directly bonded.
  • the material constituting the intermediate layer 42 is preferably the same type of material as the material constituting the intermediate layer 41.
  • the thickness of the intermediate layer 42 may be the same as the thickness of the intermediate layer 41, may be greater than the thickness of the intermediate layer 41, or may be smaller than the thickness of the intermediate layer 41.
  • the thickness of the intermediate layer 42 may be the same as the thickness of the piezoelectric layer 21, may be greater than the thickness of the piezoelectric layer 21, or may be smaller than the thickness of the piezoelectric layer 21.
  • the thickness of the intermediate layer 42 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31.
  • the thickness of the intermediate layer 42 may be the same as the thickness of the second substrate 32, may be greater than the thickness of the second substrate 32, or may be smaller than the thickness of the second substrate 32.
  • the support member further includes a second substrate made of Si on the opposite side of the intermediate layer with the first substrate in between. Furthermore, a third substrate made of Si or metal is provided with a gap between the piezoelectric layer and the main surface of the piezoelectric layer opposite to the cavity, and the second substrate and the third substrate are metal-bonded. Hermetically sealed.
  • the piezoelectric layer provided with the functional electrode is held by a support member containing the same kind of material as the piezoelectric layer, so that both The difference in linear expansion coefficient can be reduced. This can reduce stress on the membrane portion, which is a part of the piezoelectric layer, and prevent cracks from occurring in the piezoelectric layer.
  • the supporting member is of the same type as the piezoelectric layer.
  • the flexural strength is weaker than that of a Si substrate which is commonly used as a support substrate.
  • the support member further includes a second substrate made of Si, and the second substrate made of Si and the third substrate made of Si or metal are hermetically sealed by metal bonding, thereby improving the grindability of the substrate. As a result, a low-profile, hermetically sealed package structure can be realized.
  • FIG. 16 is a cross-sectional view schematically showing an example of an elastic wave device according to the second embodiment of the present invention.
  • the elastic wave device 10C shown in FIG. 16 includes a support member 20, a piezoelectric layer 21, and a functional electrode 22.
  • the support member 20 has a cavity 23 on one main surface (the upper main surface in FIG. 16).
  • the piezoelectric layer 21 is provided on one main surface of the support member 20 so as to cover the cavity 23.
  • the functional electrode 22 is provided on at least one main surface of the piezoelectric layer 21.
  • the functional electrode 22 is provided on one main surface (the upper main surface in FIG. 16) of the piezoelectric layer 21.
  • the functional electrode 22 is, for example, an IDT electrode provided on one main surface of the piezoelectric layer 21.
  • the functional electrode 22 is connected to a busbar electrode and wiring electrode 24, and a two-layer wiring 25.
  • the support member 20 includes a first substrate 31 and an intermediate layer 41 provided between the first substrate 31 and the piezoelectric layer 21.
  • the support member 20 contains the same type of material as the piezoelectric layer 21.
  • the first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example.
  • the intermediate layer 41 is made of silicon oxide (SiO x ) such as silicon dioxide (SiO 2 ), for example.
  • the support member 20 further includes a second substrate 32 made of Si on the opposite side of the intermediate layer 41 with the first substrate 31 in between.
  • the intermediate layer 42 may be provided between the first substrate 31 and the second substrate 32, or the intermediate layer 42 may not be provided.
  • the elastic wave device 10C further includes a third substrate 33 made of Si or metal.
  • the third substrate 33 is provided at a distance from the piezoelectric layer 21 so as to face the main surface of the piezoelectric layer 21 on the side opposite to the cavity 23 .
  • the third substrate 33 is made of, for example, Si. In that case, the second substrate 32 and the third substrate 33 are both Si substrates.
  • the third substrate 33 is made of metal.
  • the third substrate 33 is, for example, a metal substrate made of Cu or the like.
  • the thickness of the third substrate 33 may be the same as the thickness of the first substrate 31, may be greater than the thickness of the first substrate 31, or may be smaller than the thickness of the first substrate 31. Further, the thickness of the third substrate 33 may be the same as the thickness of the second substrate 32, may be greater than the thickness of the second substrate 32, or may be smaller than the thickness of the second substrate 32.
  • the second substrate 32 and the third substrate 33 are hermetically sealed by metal bonding.
  • the metal bond is, for example, Au-Au bond or solder bond.
  • the second substrate 32 and the third substrate 33 are hermetically sealed by a metal seal 35 and a solder seal 37.
  • the elastic wave device 10C further includes a terminal electrode 45 that is electrically connected to the functional electrode 22.
  • the terminal electrode 45 is exposed on the surface of the second substrate 32 on the opposite side to the first substrate 31. That is, the terminal electrode 45 is arranged on the second substrate 32 side.
  • the terminal electrode 45 is provided so as to penetrate the support member 20 in the thickness direction.
  • Solder balls 47 are provided on the surface of the second substrate 32 on the opposite side from the first substrate 31.
  • the solder ball 47 is electrically connected to the functional electrode 22 via the terminal electrode 45, the two-layer wiring 25, and the like.
  • FIG. 17 is a cross-sectional view schematically showing another example of the elastic wave device according to the second embodiment of the present invention.
  • the cross sections of the piezoelectric layer 21, intermediate layer 41, and first substrate 31 may have a tapered shape toward the piezoelectric layer 21 side.
  • the cross section of the intermediate layer 42 may also have a tapered shape toward the piezoelectric layer 21 side.
  • the cross sections of the support member 20 and the piezoelectric layer 21 excluding the second substrate 32 may have a tapered shape toward the piezoelectric layer 21 side.
  • FIG. 18 is a cross-sectional view schematically showing still another example of the elastic wave device according to the second embodiment of the present invention.
  • the terminal electrode 45 is exposed on the surface of the third substrate 33 on the opposite side from the piezoelectric layer 21. That is, the terminal electrode 45 is arranged on the third substrate 33 side.
  • the terminal electrode 45 penetrates the third substrate 33 in the thickness direction and reaches the surface of the second substrate 32 on the first substrate 31 side.
  • a two-layer wiring 25 extending to the surface of the second substrate 32 on the first substrate 31 side is connected to the terminal electrode 45.
  • Solder balls 47 are provided on the surface of the third substrate 33 on the opposite side from the piezoelectric layer 21.
  • the solder ball 47 is electrically connected to the functional electrode 22 via the terminal electrode 45, the two-layer wiring 25, and the like.
  • the cross sections of the piezoelectric layer 21, intermediate layer 41, and first substrate 31 may have a tapered shape toward the piezoelectric layer 21 side.
  • the cross section of the intermediate layer 42 may also have a tapered shape toward the piezoelectric layer 21 side.
  • the cross sections of the support member 20 and the piezoelectric layer 21 excluding the second substrate 32 may have a tapered shape toward the piezoelectric layer 21 side.
  • the elastic wave device of the present invention is not limited to the above embodiments, and various applications and modifications can be made within the scope of the present invention regarding the configuration, manufacturing conditions, etc. of the elastic wave device.
  • the cavity is provided on the intermediate layer side of the support member, but the cavity may be provided on the first substrate side of the support member.
  • FIG. 19 is a cross-sectional view schematically showing a first modification of the elastic wave device according to the first embodiment of the present invention.
  • a cavity 23 is provided on the first substrate 31 side of the support member 20.
  • An intermediate layer 41 is provided between the piezoelectric layer 21 and the cavity 23.
  • the first substrate 31 is made of the same kind of material as the piezoelectric layer 21, for example.
  • the cavity 23 can be formed on the first substrate 31 side by diffusing various metals such as titanium (Ti) into the first substrate 31 using heat.
  • FIG. 20 is a sectional view schematically showing a second modification of the elastic wave device according to the first embodiment of the present invention.
  • a cavity 23 is provided on the first substrate 31 side of the support member 20.
  • the intermediate layer 41 may not be provided between the piezoelectric layer 21 and the cavity 23.
  • FIGS. 21A to 21E are cross-sectional views schematically showing an example of a method for forming a cavity on the first substrate side of the support member.
  • a piezoelectric substrate 30 having an intermediate layer 41 provided on its surface is prepared.
  • a first substrate 31 in which a sacrificial layer 50 is embedded is prepared.
  • the piezoelectric substrate 30 and the first substrate 31 are bonded by atomic diffusion bonding (ADB) so that the intermediate layer 41 and the sacrificial layer 50 face each other.
  • ADB atomic diffusion bonding
  • the piezoelectric substrate 30 and the first substrate 31 are bonded via a metal layer 52 such as Ti.
  • heat treatment is performed on the joined piezoelectric substrate 30 and first substrate 31. Due to the heat treatment, metal such as Ti contained in the metal layer 52 is diffused into the piezoelectric material (lithium niobate, etc.) of the first substrate 31.
  • the piezoelectric substrate 30 is thinned to form the piezoelectric layer 21, and electrodes such as the functional electrode 22 are formed.
  • the sacrificial layer 50 is removed using the through hole 51.
  • the metal layer 52 on the sacrificial layer 50 is removed together with the sacrificial layer 50.
  • a cavity 23 is formed on the first substrate 31 side of the support member 20.
  • an elastic wave device that utilizes a thickness shear mode and a plate wave will be described using as an example an elastic wave device in which the material of the support substrate corresponding to the first substrate is not limited to the same type of material as the piezoelectric layer. Note that the following description uses an example in which the functional electrode is an IDT electrode.
  • FIG. 22 is a schematic perspective view showing the appearance of an example of an elastic wave device that utilizes bulk waves in thickness shear mode.
  • FIG. 23 is a plan view showing the electrode structure on the piezoelectric layer of the acoustic wave device shown in FIG. 22.
  • FIG. 24 is a cross-sectional view of a portion taken along line AA in FIG. 22.
  • the acoustic wave device 1 has a piezoelectric layer 2 made of, for example, LiNbO 3 .
  • the piezoelectric layer 2 may be made of LiTaO 3 .
  • the cut angle of LiNbO 3 or LiTaO 3 is, for example, a Z cut, but may also be a rotational Y cut or an X cut.
  • the propagation directions of Y propagation and X propagation are ⁇ 30°.
  • the thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shear mode, it is preferably 50 nm or more and 1000 nm or less.
  • the piezoelectric layer 2 has a first main surface 2a and a second main surface 2b that face each other.
  • Electrode 3 and an electrode 4 are provided on the first main surface 2a of the piezoelectric layer 2, on the first main surface 2a of the piezoelectric layer 2, an electrode 3 and an electrode 4 are provided.
  • electrode 3 is an example of a "first electrode”
  • electrode 4 is an example of a "second electrode”.
  • the plurality of electrodes 3 are the plurality of first electrode fingers connected to the first busbar electrode 5.
  • the plurality of electrodes 4 are a plurality of second electrode fingers connected to the second busbar electrode 6.
  • the plurality of electrodes 3 and the plurality of electrodes 4 are interposed with each other. Electrode 3 and electrode 4 have a rectangular shape and have a length direction.
  • the electrode 3 and the adjacent electrode 4 face each other in a direction perpendicular to this length direction.
  • Electrodes 3 and 4 constitute an IDT (Interdigital Transducer) electrode.
  • the length direction of the electrodes 3 and 4 and the direction perpendicular to the length direction of the electrodes 3 and 4 are both directions that intersect the thickness direction of the piezoelectric layer 2. Therefore, it can be said that the electrode 3 and the adjacent electrode 4 face each other in the direction intersecting the thickness direction of the piezoelectric layer 2. Further, the length direction of the electrodes 3 and 4 may be replaced with the direction perpendicular to the length direction of the electrodes 3 and 4 shown in FIGS. 22 and 23. That is, in FIGS.
  • the electrodes 3 and 4 may be extended in the direction in which the first busbar electrode 5 and the second busbar electrode 6 are extended. In that case, the first busbar electrode 5 and the second busbar electrode 6 will extend in the direction in which the electrodes 3 and 4 extend in FIGS. 22 and 23.
  • a plurality of pairs of structures in which an electrode 3 connected to one potential and an electrode 4 connected to the other potential are adjacent to each other are provided in a direction perpendicular to the length direction of the electrodes 3 and 4.
  • the expression “electrode 3 and electrode 4 are adjacent” does not mean that electrode 3 and electrode 4 are arranged so as to be in direct contact with each other, but when electrode 3 and electrode 4 are arranged with a gap between them.
  • the center-to-center distance between the electrodes 3 and 4, that is, the pitch, is preferably in the range of 1 ⁇ m or more and 10 ⁇ m or less. Note that the center-to-center distance between the electrodes 3 and 4 refers to the center of the width dimension of the electrode 3 in the direction orthogonal to the length direction of the electrode 3, and the width dimension of the electrode 4 in the direction orthogonal to the length direction of the electrode 4.
  • the distance between the center of refers to the average value of the distance between the centers of adjacent electrodes 3 and 4 among 1.5 or more pairs of electrodes 3 and 4.
  • the width of the electrodes 3 and 4, that is, the dimension in the opposing direction of the electrodes 3 and 4 is preferably in the range of 150 nm or more and 1000 nm or less.
  • the direction perpendicular to the length direction of the electrodes 3 and 4 is the direction perpendicular to the polarization direction of the piezoelectric layer 2.
  • “orthogonal” is not limited to strictly orthogonal, but approximately orthogonal (for example, the angle between the direction orthogonal to the length direction of the electrodes 3 and 4 and the polarization direction is 90° ⁇ 10°) But that's fine.
  • a support substrate 8 is laminated on the second main surface 2b side of the piezoelectric layer 2 with an intermediate layer (also called a bonding layer) 7 interposed therebetween.
  • the intermediate layer 7 and the support substrate 8 have a frame-like shape, and have openings 7a and 8a, as shown in FIG. Thereby, a cavity 9 is formed.
  • the cavity 9 is provided so as not to hinder the vibration of the excitation region C (see FIG. 23) of the piezoelectric layer 2. Therefore, the support substrate 8 is laminated on the second main surface 2b with the intermediate layer 7 interposed therebetween at a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 are provided. Note that the intermediate layer 7 may not be provided. Therefore, the support substrate 8 can be laminated directly or indirectly on the second main surface 2b of the piezoelectric layer 2.
  • the intermediate layer 7 is made of silicon oxide, for example. However, other than silicon oxide, an appropriate insulating material such as silicon oxynitride or alumina can be used.
  • the support substrate 8 is made of Si. The plane orientation of the Si surface on the piezoelectric layer 2 side may be (100), (110), or (111). Preferably, Si has a high resistivity of 4 k ⁇ or more. However, the support substrate 8 can also be constructed using an appropriate insulating material or semiconductor material.
  • Examples of materials for the support substrate 8 include aluminum oxide, lithium tantalate, lithium niobate, piezoelectric materials such as crystal, alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, and starch.
  • Various ceramics such as tite and forsterite, dielectrics such as diamond and glass, semiconductors such as gallium nitride, etc. can be used.
  • the plurality of electrodes 3, electrodes 4, first busbar electrode 5, and second busbar electrode 6 are made of an appropriate metal or alloy such as Al or AlCu alloy.
  • the electrode 3, the electrode 4, the first busbar electrode 5, and the second busbar electrode 6 have a structure in which an Al film is laminated on a Ti film. Note that an adhesive layer other than the Ti film may be used.
  • an AC voltage is applied between the plurality of electrodes 3 and the plurality of electrodes 4. More specifically, an AC voltage is applied between the first busbar electrode 5 and the second busbar electrode 6.
  • d/p is 0. It is considered to be 5 or less. Therefore, the bulk wave in the thickness shear mode is effectively excited, and good resonance characteristics can be obtained. More preferably, d/p is 0.24 or less, in which case even better resonance characteristics can be obtained.
  • the distance p between the centers of the adjacent electrodes 3 and 4 is the average distance between the centers of the adjacent electrodes 3 and 4.
  • the elastic wave device 1 of this embodiment has the above configuration, even if the logarithm of the electrodes 3 and 4 is reduced in an attempt to achieve miniaturization, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides and has little propagation loss. Further, the reason why the reflector is not required is because the bulk wave in the thickness shear mode is used. The difference between the Lamb wave used in a conventional elastic wave device and the thickness-shear mode bulk wave will be explained with reference to FIGS. 25 and 26.
  • FIG. 25 is a schematic front sectional view for explaining Lamb waves propagating through the piezoelectric film of the acoustic wave device.
  • the piezoelectric film 201 in the elastic wave device described in Patent Document 1 (Japanese Patent Publication No. 2012-257019), waves propagate in the piezoelectric film 201 as indicated by arrows.
  • the first main surface 201a and the second main surface 201b are opposite to each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z direction. It is.
  • the X direction is the direction in which the electrode fingers of the IDT electrodes are lined up.
  • the Lamb wave the wave propagates in the X direction as shown.
  • the piezoelectric film 201 vibrates as a whole, but since the wave propagates in the X direction, reflectors are placed on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is attempted, that is, when the number of logarithms of electrode fingers is reduced, the Q value decreases.
  • FIG. 26 is a schematic front cross-sectional view for explaining a thickness-shear mode bulk wave propagating through a piezoelectric layer of an elastic wave device.
  • the waves connect the first main surface 2a and the second main surface 2b of the piezoelectric layer 2. It propagates almost in the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Since resonance characteristics are obtained by the propagation of waves in the Z direction, a reflector is not required. Therefore, no propagation loss occurs when propagating to the reflector. Therefore, even if the number of electrode pairs consisting of electrodes 3 and 4 is reduced in an attempt to promote miniaturization, the Q value is unlikely to decrease.
  • FIG. 27 is a diagram showing the amplitude direction of the bulk wave in the thickness shear mode. As shown in FIG. 27, the amplitude direction of the bulk wave in the thickness shear mode is opposite between the first region 451 included in the excitation region C of the piezoelectric layer 2 and the second region 452 included in the excitation region C.
  • FIG. 27 schematically shows a bulk wave when a voltage is applied between electrode 3 and electrode 4 such that electrode 4 has a higher potential than electrode 3.
  • the first region 451 is a region of the excitation region C between a virtual plane VP1 that is perpendicular to the thickness direction of the piezoelectric layer 2 and bisects the piezoelectric layer 2, and the first main surface 2a.
  • the second region 452 is a region of the excitation region C between the virtual plane VP1 and the second principal surface 2b.
  • the elastic wave device 1 As mentioned above, in the elastic wave device 1, at least one pair of electrodes consisting of the electrode 3 and the electrode 4 are arranged, but since the wave is not propagated in the X direction, the elastic wave device 1 is made up of the electrodes 3 and 4. There does not necessarily have to be a plurality of pairs of electrodes. That is, it is only necessary that at least one pair of electrodes be provided.
  • the electrode 3 is an electrode connected to a hot potential
  • the electrode 4 is an electrode connected to a ground potential.
  • the electrode 3 may be connected to the ground potential
  • the electrode 4 may be connected to the hot potential.
  • at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.
  • FIG. 28 is a diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22. Note that the design parameters of the elastic wave device 1 that obtained this resonance characteristic are as follows.
  • Intermediate layer 7 silicon oxide film with a thickness of 1 ⁇ m.
  • Support substrate 8 Si substrate.
  • the length of the excitation region C is a dimension along the length direction of the electrodes 3 and 4 of the excitation region C.
  • the distances between the electrode pairs made up of the electrodes 3 and 4 were all equal in multiple pairs. That is, the electrodes 3 and 4 were arranged at equal pitches.
  • d/p is preferably 0.5 or less, More preferably it is 0.24 or less. This will be explained with reference to FIG. 29.
  • FIG. 29 is a diagram showing the relationship between d/2p and the fractional band as a resonator of an acoustic wave device, where p is the distance between the centers of adjacent electrodes and d is the thickness of the piezoelectric layer.
  • the at least one pair of electrodes may be one pair, and in the case of one pair of electrodes, the above p is the distance between the centers of adjacent electrodes 3 and 4. Furthermore, in the case of 1.5 or more pairs of electrodes, the average distance between the centers of adjacent electrodes 3 and 4 may be set to p.
  • the thickness d of the piezoelectric layer if the piezoelectric layer 2 has thickness variations, a value obtained by averaging the thicknesses may be adopted.
  • FIG. 30 is a plan view of another example of an elastic wave device that utilizes bulk waves in thickness-shear mode.
  • a pair of electrodes including an electrode 3 and an electrode 4 are provided on the first main surface 2a of the piezoelectric layer 2.
  • K in FIG. 30 is the intersection width.
  • the number of pairs of electrodes may be one. Even in this case, if the above-mentioned d/p is 0.5 or less, bulk waves in the thickness shear mode can be excited effectively.
  • the metallization ratio MR of the adjacent electrodes 3 and 4 satisfies MR ⁇ 1.75(d/p)+0.075. In that case, spurious can be effectively reduced. This will be explained with reference to FIGS. 31 and 32.
  • FIG. 31 is a reference diagram showing an example of the resonance characteristics of the elastic wave device shown in FIG. 22.
  • a spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency.
  • d/p 0.08 and the Euler angles of LiNbO 3 (0°, 0°, 90°).
  • the metallization ratio MR was set to 0.35.
  • the metallization ratio MR will be explained with reference to FIG. 23.
  • the area surrounded by the dashed line C becomes the excitation region.
  • This excitation region is the region where the electrode 3 overlaps the electrode 4 when the electrode 3 and the electrode 4 are viewed in a direction perpendicular to the length direction of the electrodes 3 and 4, that is, in a direction in which they face each other. and a region between electrodes 3 and 4 where electrodes 3 and 4 overlap.
  • the area of the electrodes 3 and 4 in the excitation region C with respect to the area of this excitation region becomes the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of the metallized portion to the area of the excitation region.
  • MR may be the ratio of the metallized portion included in all the excitation regions to the total area of the excitation regions.
  • FIG. 32 is a diagram showing the relationship between the fractional band and the amount of phase rotation of spurious impedance normalized by 180 degrees as the magnitude of spurious when a large number of elastic wave resonators are configured according to the present embodiment. It is. Note that the specific band was adjusted by variously changing the thickness of the piezoelectric layer and the dimensions of the electrode. Furthermore, although FIG. 32 shows the results when a Z-cut piezoelectric layer made of LiNbO 3 is used, the same tendency occurs even when piezoelectric layers with other cut angles are used.
  • the spurious is as large as 1.0.
  • the fractional band exceeds 0.17, that is, exceeds 17%, a large spurious with a spurious level of 1 or more will affect the pass band even if the parameters constituting the fractional band are changed. Appear within. That is, as in the resonance characteristic shown in FIG. 31, a large spurious signal indicated by arrow B appears within the band. Therefore, it is preferable that the fractional band is 17% or less. In this case, by adjusting the thickness of the piezoelectric layer 2, the dimensions of the electrodes 3 and 4, etc., the spurious can be reduced.
  • FIG. 33 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional band.
  • various elastic wave devices having different d/2p and MR were constructed and the fractional bands were measured.
  • the hatched area on the right side of the broken line D in FIG. 33 is the area where the fractional band is 17% or less.
  • FIG. 34 is a diagram showing a map of fractional bands with respect to Euler angles (0°, ⁇ , ⁇ ) of LiNbO 3 when d/p is brought as close to 0 as possible.
  • the hatched areas in FIG. 34 are regions where a fractional band of at least 5% can be obtained, and the range of these regions can be approximated by the following equations (1), (2), and (3). ).
  • ...Formula (1) (0° ⁇ 10°, 20° to 80°, 0° to 60° (1-( ⁇ -50) 2 /900) 1/2 ) or (0° ⁇ 10°, 20° to 80°, [180 °-60° (1-( ⁇ -50) 2 /900) 1/2 ] ⁇ 180°)
  • ...Formula (2) (0° ⁇ 10°, [180°-30° (1-( ⁇ -90) 2 /8100) 1/2 ] ⁇ 180°, arbitrary ⁇ ) ...Formula (3) Therefore, the Euler angle range of formula (1), formula (2), or formula (3) above is preferable because the fractional band can be made sufficiently wide.
  • FIG. 35 is a partially cutaway perspective view for explaining an example of an elastic wave device that utilizes Lamb waves.
  • the elastic wave device 81 has a support substrate 82.
  • the support substrate 82 is provided with an open recess on the upper surface.
  • a piezoelectric layer 83 is laminated on the support substrate 82 . Thereby, a cavity 9 is formed.
  • An IDT electrode 84 is provided on the piezoelectric layer 83 above the cavity 9 .
  • Reflectors 85 and 86 are provided on both sides of the IDT electrode 84 in the elastic wave propagation direction. In FIG. 35, the outer periphery of the cavity 9 is shown by a broken line.
  • the IDT electrode 84 includes a first busbar electrode 84a, a second busbar electrode 84b, an electrode 84c as a plurality of first electrode fingers, and an electrode 84d as a plurality of second electrode fingers. and has.
  • the plurality of electrodes 84c are connected to the first busbar electrode 84a.
  • the plurality of electrodes 84d are connected to the second busbar electrode 84b.
  • the plurality of electrodes 84c and the plurality of electrodes 84d are interposed with each other.
  • the elastic wave device 81 by applying an alternating current electric field to the IDT electrode 84 on the cavity 9, a Lamb wave as a plate wave is excited. Since the reflectors 85 and 86 are provided on both sides, the resonance characteristic due to the Lamb wave described above can be obtained.
  • the elastic wave device of the present invention may utilize plate waves such as Lamb waves.
  • the elastic wave device of the present invention may utilize bulk waves. That is, the elastic wave device of the present invention can also be applied to a bulk acoustic wave (BAW) element.
  • the functional electrodes are an upper electrode and a lower electrode.
  • FIG. 36 is a cross-sectional view schematically showing an example of an elastic wave device that uses bulk waves.
  • the elastic wave device 90 includes a support substrate 91.
  • a cavity 93 is provided so as to penetrate the support substrate 91.
  • a piezoelectric layer 92 is laminated on a support substrate 91 .
  • An upper electrode 94 is provided on the first main surface 92a of the piezoelectric layer 92, and a lower electrode 95 is provided on the second main surface 92b of the piezoelectric layer 92.
  • an intermediate layer may be provided between the support substrate 91 and the piezoelectric layer 92.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

La présente invention concerne un dispositif à ondes élastiques (10) qui comprend : un élément de support (20) ayant une cavité (23) dans une surface principale de celui-ci ; une couche piézoélectrique (21) disposée sur la surface principale de l'élément de support (20) de façon à recouvrir la cavité (23) ; et une électrode fonctionnelle (22) disposée sur au moins l'une des surfaces principales de la couche piézoélectrique (21) de façon à chevaucher au moins partiellement la cavité (23) lorsqu'elle est vue depuis la direction de l'épaisseur de la couche piézoélectrique (21). L'élément de support (20) comprend un premier substrat (31) et une couche intermédiaire (41) disposée entre le premier substrat (31) et la couche piézoélectrique (21). L'élément de support (20) contient le même type de matériau que la couche piézoélectrique (21).
PCT/JP2023/014216 2022-04-14 2023-04-06 Dispositif à ondes élastiques WO2023199837A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013528996A (ja) * 2010-04-23 2013-07-11 テクノロジアン テュトキムスケスクス ヴェーテーテー 広帯域音響結合薄膜ｂａｗフィルタ
WO2021246447A1 (fr) * 2020-06-04 2021-12-09 株式会社村田製作所 Dispositif à ondes élastiques
WO2022054773A1 (fr) * 2020-09-09 2022-03-17 株式会社村田製作所 Dispositif à onde acoustique
JP2022044314A (ja) * 2020-09-07 2022-03-17 太陽誘電株式会社 弾性波デバイス
WO2022071605A1 (fr) * 2020-10-02 2022-04-07 株式会社村田製作所 Dispositif à ondes élastiques et son procédé de fabrication

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013528996A (ja) * 2010-04-23 2013-07-11 テクノロジアン テュトキムスケスクス ヴェーテーテー 広帯域音響結合薄膜ｂａｗフィルタ
WO2021246447A1 (fr) * 2020-06-04 2021-12-09 株式会社村田製作所 Dispositif à ondes élastiques
JP2022044314A (ja) * 2020-09-07 2022-03-17 太陽誘電株式会社 弾性波デバイス
WO2022054773A1 (fr) * 2020-09-09 2022-03-17 株式会社村田製作所 Dispositif à onde acoustique
WO2022071605A1 (fr) * 2020-10-02 2022-04-07 株式会社村田製作所 Dispositif à ondes élastiques et son procédé de fabrication

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