JP5367612B2 - Lamb wave device - Google Patents

Description

  The present invention relates to a Lamb wave device that excites Lamb waves in a piezoelectric thin film.

  Patent Document 1 discloses a bulk acoustic wave device that excites a longitudinal wave in a thickness direction on a piezoelectric thin film obtained by removing a piezoelectric substrate. In such a bulk acoustic wave device, since the frequency is inversely proportional to the film thickness of the piezoelectric thin film, the film thickness of the piezoelectric thin film must be reduced in order to increase the frequency. For example, in order to set the frequency to several GHz, although depending on the piezoelectric material constituting the piezoelectric thin film, the thickness of the piezoelectric thin film must be several hundred nm.

  However, when the film thickness of the piezoelectric thin film is reduced to several 100 nm, there arises a problem that the film thickness variation caused by the processing variation causes a large frequency variation. There is also a problem that the mechanical strength of the piezoelectric thin film is insufficient.

On the other hand, Patent Document 2 discloses a Lamb wave device for exciting an A ₁ mode Lamb wave in a piezoelectric thin film. In such a Lamb wave device, the thickness of the piezoelectric thin film becomes thicker than in the case of a bulk acoustic wave device that excites a longitudinal wave in the thickness direction. For this reason, the problem that the mechanical strength of the piezoelectric thin film is insufficient is alleviated.

JP 2007-228319 A International Publication No. 2007-046236 Pamphlet

However, even in the Lamb wave device of Patent Document 2, the influence of the variation in the film thickness on the variation in the resonance frequency is not negligible. This is because the sound speed of the higher order mode Lamb wave such as the A ₁ mode has a great dispersibility with respect to the film thickness of the piezoelectric thin film. The present invention has been made to solve this problem, and an object of the present invention is to provide a Lamb wave device with small frequency variation.

  In order to solve the above problems, the Lamb wave device according to claim 1 supports a piezoelectric thin film, an IDT electrode provided on a main surface of the piezoelectric thin film, and a laminate of the piezoelectric thin film and the IDT electrode. A support structure, and the support structure includes a support substrate, and a support film formed with a cavity that joins the support substrate and the laminate and separates the excitation unit of the laminate from the support substrate. Wherein the piezoelectric thin film thickness and the finger pitch of the IDT electrode are selected such that a high-order mode Lamb wave having a sound velocity of 5000 m / s or more is excited at a target frequency. The etching rate at 65 ° C. with respect to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride on the main surface on the support structure side of the thin film is 1 / of the main surface on the support substrate side of the support film. The orientation of the piezoelectric thin film is selected to be less.

  The Lamb wave device according to claim 2 is the Lamb wave device according to claim 1, wherein the main surface of the piezoelectric thin film on the side of the support structure is 65 ° C. with respect to a solution containing hydrogen fluoride or a gas containing hydrogen fluoride. The orientation of the piezoelectric thin film is selected so that the etching rate at is less than 1/20 of the main surface of the support film on the support substrate side.

  The Lamb wave device according to claim 3 includes a piezoelectric thin film, an IDT electrode provided on a main surface of the piezoelectric thin film, and a support structure that supports a stacked body of the piezoelectric thin film and the IDT electrode. The support structure comprises a support substrate, and the film thickness of the piezoelectric thin film and the finger of the IDT electrode so that a high-order mode Lamb wave having a sound speed of 5000 m / s or more at a target frequency is excited. The etching rate at 65 ° C. with respect to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride on the main surface of the piezoelectric thin film on the side of the support structure is selected at a pitch of 65 ° C. The orientation of the piezoelectric thin film is selected so that it is ½ or less of the main surface on the side opposite to the side.

  A Lamb wave device according to a fourth aspect is the Lamb wave device according to the third aspect, wherein the main surface of the piezoelectric thin film on the side of the support structure is against a solution containing hydrogen fluoride or a gas containing hydrogen fluoride. The orientation of the piezoelectric thin film is selected so that the etching rate at 0 ° C. is 1/20 or less of the main surface on the side opposite to the piezoelectric thin film side of the support substrate.

  According to the first to fourth aspects of the invention, since the piezoelectric thin film is suppressed from being etched when the cavity is formed in the support structure, the frequency variation is reduced.

It is a disassembled perspective view of the Lamb wave device of a 1st embodiment. It is sectional drawing of the Lamb wave apparatus of 1st Embodiment. The piezoelectric material is a dispersion curve of A ₁ mode when a lithium niobate. The piezoelectric material is a dispersion curve of A ₁ mode when a lithium niobate. It is a dispersion curve of A ₁ mode when the piezoelectric material is lithium tantalate. It is a figure which shows the relationship between an etching rate ratio and frequency variation. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 1st Embodiment. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 1st Embodiment. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 1st Embodiment. It is sectional drawing of the Lamb wave apparatus of 2nd Embodiment. It is a figure which shows the relationship between an etching rate ratio and frequency variation. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 2nd Embodiment. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 2nd Embodiment. It is sectional drawing explaining the manufacturing method of the Lamb wave apparatus of 2nd Embodiment. It is sectional drawing of the laminated body of 3rd Embodiment. It is sectional drawing of the laminated body of 4th Embodiment. It is a figure which shows the change of the frequency by the film thickness of a piezoelectric material thin film.

<1 First Embodiment>
<1-1 Configuration of Lamb Wave Device 102>
FIG.1 and FIG.2 is a schematic diagram of the Lamb wave apparatus 102 of 1st Embodiment. 1 is an exploded perspective view of the Lamb wave device 102, and FIG. 2 is a cross-sectional view of the Lamb wave device 102.

  As shown in FIGS. 1 and 2, the Lamb wave device 102 has a structure in which the laminated body 104 is supported by a support structure 122. The laminated body 104 includes a piezoelectric thin film 106 and an IDT electrode 108 that excites Lamb waves in the piezoelectric thin film 106. The support structure 122 includes a support substrate 124 and a support film 126 that joins the support substrate 124 and the stacked body 104. In the support film 126, a cavity 180 that separates the excitation unit of the stacked body 104 from the support substrate 124 is formed. The IDT electrode 108 is provided inside a region where the cavity 180 is formed (hereinafter referred to as “cavity region”).

{Thickness h of piezoelectric thin film 106 and pitch p of fingers 110 of IDT electrode 108}
As for the film thickness h of the piezoelectric thin film 106 and the pitch p of the fingers 110 of the IDT electrode 108, a Lamb wave having a sound velocity of 5000 m / s or more is excited at a target frequency (design frequency; design resonance frequency in the case of a resonator). It is desirable to be selected. Thereby, the film thickness h of the piezoelectric thin film 106 becomes thicker than the case where the longitudinal wave in the thickness direction is excited.

For sound velocity to excite Lamb waves to be 5000 m / s or more, S _n mode (n following a higher order mode other than S ₀ mode (0-order symmetric mode) and A ₀ mode (0-order anti-symmetric mode) It is desirable to excite Lamb waves in a symmetric mode (n is a natural number of 1 or more) or an _An mode (n-order antisymmetric mode; n is a natural number of 1 or more). First, if the film thickness of the piezoelectric thin film 106 is the same, the sound speed of the Lamb wave is higher in the higher order mode than in the S ₀ mode and the A ₀ mode. Secondly, the sound speed of the Lamb wave in the S ₀ mode increases as the film thickness h decreases, but the increase gradually decreases, and the sound speed of the Lamb wave in the A ₀ mode decreases as the film thickness h decreases. The speed of the Lamb wave in the higher-order mode monotonically increases as the film thickness h decreases, whereas it is difficult to set the speed to 5000 m / s. By being easy.

3 and 4 are A ₁ mode dispersion curves when the piezoelectric material constituting the piezoelectric thin film is a single crystal of lithium niobate (LiNbO ₃ ). FIGS. 3 and 4 show changes in the sound velocity v depending on the ratio h / λ of the film thickness h to the wavelength λ in the piezoelectric thin film obtained by thinning the 128 ° Y plate and the 90 ° Y plate, respectively. FIG. 5 is an A ₁ mode dispersion curve when the piezoelectric material constituting the piezoelectric thin film is a single crystal of lithium tantalate (LiTaO ₃ ). FIG. 5 shows the change in the sound velocity v depending on the ratio h / λ of the film thickness h to the wavelength λ in the piezoelectric thin film obtained by thinning the 90 ° Y plate.

As shown in FIGS. 3 to 5, in the range where the excitation condition h / λ ≦ 1 of the Lamb wave is satisfied, the sound velocity v is 5000 m / s or more, although there is a slight difference depending on the azimuth angle. Depending on the piezoelectric material constituting the piezoelectric thin film 106, the sound velocity v may be less than 5000 m / s when the ratio h / λ approaches the upper limit of the excitation condition h / λ ≦ 1 of the Lamb wave, but as described above. acoustic velocity v of the Lamb waves a ₁ mode, since the film thickness h is monotonically faster as thinner, by slightly reducing the thickness h, the acoustic velocity v of the Lamb waves of a ₁ mode above 5000 m / s It's easy to do. The same applies to higher-order modes other than the A ₁ mode.

{Significance of making the speed of sound over 5000 m / s}
Among general steppers using a mercury lamp as a light source, the i-line stepper having the highest resolution is an i-line stepper having an i-line having a wavelength of 365 nm and a minimum line width of 0.365 μm. When the IDT electrode 108 is patterned by this i-line stepper, the shortest wavelength λ of the Lamb wave excited by the IDT electrode 108 is 0.365 × 4 = 1.46 μm. Therefore, if the speed of sound is 5000 m / s or more, the frequency is about 3.4 GHz or more even when the IDT electrode 108 is patterned by a general i-line stepper, and a Lamb wave device that can be used for many high frequency applications is realized. The However, if the line width is narrowed to the limit value of 0.365 μm, the power resistance of the IDT electrode 108 may be deteriorated or the Q value may be reduced due to ohmic loss. Therefore, the sound speed should be 8000 m / s or more. Is more desirable.

{Piezoelectric thin film 106}
The piezoelectric material constituting the piezoelectric thin film 106 is not particularly limited, but quartz (SiO ₂ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), lithium tetraborate (Li ₂ B ₄ O ₇ ) It is desirable to select from single crystals such as zinc oxide (ZnO), potassium niobate (KNbO ₃ ), langasite (La ₃ Ga ₃ SiO ₁₄ ), aluminum nitride (AlN), and gallium nitride (GaN). This is because if the piezoelectric material is selected from a single crystal, the electromechanical coupling coefficient and mechanical quality factor of the piezoelectric thin film 106 can be improved.

  The crystal orientation of the piezoelectric thin film 106 is such that the etching rate at 65 ° C. with respect to hydrofluoric acid of the lower surface 1062 on the support structure 122 side of the piezoelectric thin film 106 is higher than that of the lower surface 1262 of the support film 126 on the support substrate 124 side. It is desirable to select it so that it is sufficiently slow, and it is more desirable to select the etching rate for hydrofluoric acid to be 1/2 or less, and to select the etching rate for hydrofluoric acid to be 1/20 or less. Is particularly desirable. The same can be said for etching with a solution containing hydrogen fluoride other than hydrofluoric acid, such as buffered hydrofluoric acid or hydrofluoric nitric acid. The same applies to dry etching with a gas containing hydrogen fluoride. As a result, when the cavity 180 is formed, a piezoelectric substrate (to be described later) that will eventually become the piezoelectric thin film 106 is hardly etched, so that variations in film thickness of the piezoelectric thin film 106 are reduced, and variations in resonance frequency are small. Become. For example, if the piezoelectric thin film 106 is a thin film of a lithium niobate θ ° Y plate, θ = 0 to 45 ° or 128 to 180 ° is desirable.

  FIG. 6 is a diagram showing the relationship between the ratio of the etching rate of the piezoelectric substrate to be the piezoelectric thin film to the etching rate of the support film (hereinafter referred to as “etching rate ratio”) and the frequency variation. FIG. 6 also shows an insulating material constituting the support film and a piezoelectric material constituting the piezoelectric substrate (piezoelectric material constituting the piezoelectric thin film). “LN36”, “LN45” and “LN90” shown in FIG. 6 mean a single crystal 36 ° Y plate, 45 ° Y plate and 90 ° Y plate of lithium niobate (LN), respectively. FIG. 6 shows the relationship when a support film is formed on the −Z surface of the piezoelectric substrate.

  The piezoelectric thin film 106 covers the entire surface of the support substrate 124.

{IDT electrode 108}
The conductive material constituting the IDT electrode 108 is not particularly limited, but aluminum (Al), molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), silver (Ag), copper (Cu), Titanium (Ti), Chromium (Cr), Ruthenium (Ru), Vanadium (V), Niobium (Nb), Tantalum (Ta), Rhodium (Rh), Iridium (Ir), Zirconium (Zr), Hafnium (Hf), It is desirable to select from palladium (Pd) or an alloy based on these, and it is particularly desirable to select from aluminum or an alloy based on aluminum.

  The IDT electrode 108 is provided on the upper surface of the piezoelectric thin film 106. The IDT electrode 108 may be provided on the lower surface of the piezoelectric thin film 106.

  The IDT electrode 108 includes a finger 110 that applies an electric field to the piezoelectric thin film 106 and collects surface charges generated on the surface of the piezoelectric thin film 106, and a bus bar 116 that connects the fingers 110. The fingers 110 extend in a direction perpendicular to the propagation direction of the Lamb wave, and are arranged at equal intervals in the propagation direction of the Lamb wave. The bus bar 116 extends in the propagation direction of the Lamb wave. The finger 110 has a first finger 112 connected to the first bus bar 118 at one end and a second finger 114 connected to the second bus bar 120 at the other end. Yes, the first fingers 112 and the second fingers 114 are arranged alternately. As a result, the IDT electrode 108 transmits a Lamb wave corresponding to the signal input between the first bus bar 116 and the second bus bar 116, and transmits a signal corresponding to the received Lamb wave to the first bus bar. It outputs between 116 and the 2nd bus-bar 116.

  The two-phase IDT electrode 108 in which the alternately arranged first fingers 112 and second fingers 114 are in different phases has the strongest Lamb wave having a wavelength λ that is twice the pitch p of the fingers 110. Excited.

  The Lamb wave excited by the IDT electrode 108 is reflected by the end face of the cavity region, and the Lamb wave device 102 functions as a resonator. The IDT electrode 108 may be sandwiched between reflector electrodes from both sides in the Lamb wave propagation direction. Further, the Lamb wave device 102 may be configured as a filter / duplexer or the like in which a plurality of resonators are combined, or the Lamb wave device 102 may be configured as a sensor or the like. Generally speaking, the “Lamb wave device” means all electronic components that excite a Lamb wave in a piezoelectric thin film and use an electrical response of the Lamb wave. “Lamb wave” is composed of both longitudinal wave (L wave: Longitudinai wave) and transverse wave (SV wave: Shear Virtical wave) having a displacement component in the propagation plane. It is a wave that propagates in combination with a transverse wave.

{Support substrate 124}
The insulating material constituting the support substrate 124 is not particularly limited, but is a single element of IV element such as silicon (Si) / germanium (Ge), sapphire (Al ₂ O ₃ ), magnesium oxide (MgO), zinc oxide (ZnO).・ Simple oxides such as silicon dioxide (SiO ₂ ), borides such as zirconium boride (ZrB ₂ ), lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), lithium aluminate (LiAlO ₂ ), gallium Complex oxides such as lithium oxide (LiGaO ₂ ), spinel (MgAl ₂ O ₄ ), lanthanum strontium lithium tantalate aluminate ((LaSr) (AlTa) O ₃ ), neodymium gallate (NdGaO ₃ ), silicon germanium (SiG It is desirable to select group IV-IV compounds such as gallium arsenide (GaAs), aluminum nitride (AlN), gallium nitride (GaN), and aluminum gallium nitride (AlGaN).

{Support membrane 126}
The insulating material constituting the support film 126 is not particularly limited, but it is desirable to select silicon dioxide. The support film 126 is generally provided outside the cavity region, its lower surface is in contact with the upper surface of the support substrate 124, and its upper surface is in contact with the lower surface 1062 of the piezoelectric thin film 106. The support film 126 serves as a spacer that separates the stacked body 104 from the support substrate 124 in the cavity region.

{Design example}
The material and size of each component of the Lamb wave device 102 is selected to perform its function, but according to a typical design example, it is as follows. However, this design example does not limit the present invention.

IDT electrode 108: Aluminum (film thickness 0.1 μm, pitch 0.73 μm)
Piezoelectric thin film 106: thinned 128 ° Y plate of lithium niobate (film thickness 1 μm)
Support film 126: silicon dioxide (film thickness 0.5 μm)
Support substrate 124: 128 ° Y plate of lithium niobate (plate thickness 500 μm)

<1-2 Manufacturing Method of Lamb Wave Device 102>
7 to 9 are schematic views for explaining a method for manufacturing the Lamb wave device 102. 7-9 is sectional drawing of the work-in-process in the middle of manufacture.

{Production of plate-like structure 130}
In manufacturing the Lamb wave device 102, first, as shown in FIG. 7, the plate-like structure 130 in which the support film 126 is formed on the lower surface of the piezoelectric substrate 132 is manufactured. The support film 126 is formed by forming a film of an insulating material constituting the support film 126 on the entire lower surface of the piezoelectric substrate 132 and removing unnecessary portions of the film by etching with hydrofluoric acid. At this time, the etching rate with respect to hydrofluoric acid of the piezoelectric substrate 132 that finally becomes the piezoelectric thin film 106 is sufficiently slower than that of the support film 126. Therefore, when the cavity 180 is formed with hydrofluoric acid, the piezoelectric substrate 132 is almost etched. Not. Etching is performed by immersing an in-process product in which a film of an insulating material constituting the support film 126 is formed on the entire lower surface of the piezoelectric substrate 132 in hydrofluoric acid having a hydrogen fluoride concentration of 50% adjusted to a temperature of 65 ° C. went. The temperature of the hydrofluoric acid was adjusted by heating the hydrofluoric acid contained in the fluororesin beaker inside the thermostatic water tank. The work-in-process was immersed in hydrofluoric acid after the hydrofluoric acid temperature was stabilized. The depth of the cavity was measured with a contact level meter. Note that the temperature at which the etching is performed is not necessarily “65 ° C.” if the temperature is maintained constant, but if it is “65 ° C.”, the etching rate is increased and the time required for etching is shortened.

{Junction of plate-like structure 130 and support substrate 124}
After the plate-like structure 130 is produced, the lower surface of the plate-like structure 130 and the upper surface of the support substrate 124 are joined as shown in FIG. The bonding between the plate-like structure 130 and the support substrate 124 is not particularly limited, and is performed, for example, by surface activated bonding, adhesive bonding, thermocompression bonding, anodic bonding, eutectic bonding, or the like.

{Removal processing of piezoelectric substrate 132}
After the plate-like structure 130 and the support substrate 124 are joined, as shown in FIG. 9, the piezoelectric substrate 132 is removed while maintaining the state where the plate-like structure 130 and the support substrate 124 are joined. The piezoelectric substrate 132 having a thickness that can withstand its own weight (for example, 50 μm or more) is reduced to a thickness that cannot withstand its own weight (for example, 10 μm or less). As a result, the piezoelectric thin film 106 covering the entire upper surface of the support substrate 124 is formed.

  The removal processing of the piezoelectric substrate 132 is performed by mechanical processing such as cutting, grinding, polishing, or chemical processing such as etching. Here, by combining a plurality of removal processing methods and removing the piezoelectric substrate 132 while switching the removal processing method from a removal processing method with a high processing speed to a removal processing method with small processing alteration that occurs in the processing target, it is high. While maintaining the productivity, the quality of the piezoelectric thin film 106 can be improved and the characteristics of the Lamb wave device 102 can be improved. For example, after performing grinding in which the piezoelectric substrate 132 is brought into contact with fixed abrasive grains and polishing in which the piezoelectric substrate 132 is brought into contact with loose abrasive grains are sequentially performed, a work-affected layer generated on the piezoelectric substrate 132 by the polishing. Is preferably removed by finish polishing.

{Formation of IDT electrode 108}
After removing the piezoelectric substrate 132, the IDT electrode 108 is formed on the upper surface of the piezoelectric thin film 106, and the Lamb wave device 102 shown in FIGS. 1 and 2 is completed. The IDT electrode 108 is formed by forming a conductive material film covering the entire upper surface of the piezoelectric thin film 106 and removing unnecessary portions of the conductive material film by etching.

  According to the method of manufacturing the Lamb wave device 102, unlike the case where the piezoelectric thin film 106 is formed by sputtering or the like, the piezoelectric material constituting the piezoelectric thin film 106 and the crystal orientation of the piezoelectric thin film 106 are subject to the restrictions of the base. Therefore, the degree of freedom in selecting the crystal orientation of the piezoelectric material and the piezoelectric thin film 106 constituting the piezoelectric thin film 106 is high. Therefore, the Lamb wave device 102 can easily achieve desired characteristics.

{Others}
When providing the IDT electrode on the lower surface of the piezoelectric thin film 106, the IDT electrode may be formed on the lower surface of the piezoelectric substrate 132 prior to the formation of the support film 126.

<2 Second Embodiment>
<2-1 Configuration of Lamb Wave Device 202>
The second embodiment replaces the support structure 122 of the first embodiment with a support structure 222 that supports the laminate 204 including the piezoelectric thin film 206 and the IDT electrode 208 as in the first embodiment. About. FIG. 10 is a schematic diagram of the Lamb wave device 202 of the second embodiment. FIG. 10 is a cross-sectional view of the Lamb wave device 202.

  As shown in FIG. 10, the support structure 222 includes a support substrate 224, but does not include a support film. In the support substrate 224, a cavity 280 that separates the excitation unit of the multilayer body 204 from the support substrate 224 is formed. Unlike the cavity 280 of the Lamb wave device 202, the cavity 280 of the Lamb wave device 202 penetrates the upper surface and the lower surface of the support substrate 224.

  The crystal orientation of the piezoelectric thin film 206 is such that the etching rate at 65 ° C. with respect to hydrofluoric acid of the lower surface 2062 on the support structure 222 side of the piezoelectric thin film 206 is opposite to the piezoelectric thin film 206 side of the support substrate 224. It is desirable to select it so that it is sufficiently slower than 2242. It is more desirable to select the etching rate for hydrofluoric acid to be 1/2 or less, and the etching rate for hydrofluoric acid is 1/20 or less. It is particularly desirable to choose. The same can be said for etching with a solution containing hydrogen fluoride other than hydrofluoric acid, such as buffered hydrofluoric acid or hydrofluoric nitric acid. The same applies to dry etching with a gas containing hydrogen fluoride. Accordingly, since the piezoelectric thin film 206 is hardly etched when the cavity 280 is formed, the variation in the film thickness of the piezoelectric thin film 206 is reduced, and the variation in the resonance frequency is reduced. For example, if the piezoelectric thin film 206 is a thin film of a lithium niobate θ ° Y plate, θ = 0 to 45 ° or 128 to 180 ° is desirable.

  FIG. 11 is a diagram showing the relationship between the ratio of the etching rate of the piezoelectric thin film to the etching rate of the material substrate to be the support substrate later (hereinafter referred to as “etching rate ratio”) and the frequency variation. FIG. 12 also shows an insulating material constituting the support substrate (an insulating material constituting the material substrate) and a piezoelectric material constituting the piezoelectric thin film. “LN36” and “LN90” shown in FIG. 11 mean single crystal 36 ° Y plate and 90 ° Y plate of lithium niobate (LN), and “LT36” and “LT90” are lithium tantalate ( LT) single crystal 36 ° Y plate and 90 ° Y plate. FIG. 7 shows the relationship when the −Z plane of the piezoelectric thin film and the + Z plane of the material substrate are joined. Etching procedures and conditions are the same as in the first embodiment.

The material of the support substrate 224 is lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), which is easily etched by a solution containing hydrogen fluoride or a gas containing hydrogen fluoride to form the through-hole cavity 280 It is desirable to use silicon dioxide (SiO ₂ ), silicon (Si), or the like.

  The material and size of each component of the Lamb wave device 202 is selected to perform its function, but according to a typical design example, it is as follows. However, this design example does not limit the present invention.

IDT electrode 108: Aluminum (film thickness 0.1 μm, pitch 0.73 μm)
Piezoelectric thin film 106: thinned 128 ° Y plate of lithium niobate (film thickness 1 μm)
Support substrate 124: 128 ° Y plate of lithium niobate (plate thickness 500 μm)

<2-2 Manufacturing Method of Lamb Wave Device 202>
12 to 14 are schematic views for explaining a method for manufacturing the Lamb wave device 202. 12-14 is sectional drawing of the work in process in the middle of manufacture.

{Junction of piezoelectric substrate 232 and material substrate 230}
In manufacturing the Lamb wave device 202, first, as shown in FIG. 12, the lower surface of the piezoelectric substrate 232 and the upper surface of the material substrate 230 that finally becomes the support substrate 224 are bonded. Bonding of the piezoelectric substrate 232 and the material substrate 230 is performed in the same manner as in the first embodiment.

{Removal processing of piezoelectric substrate 232}
After joining the piezoelectric substrate 232 and the material substrate 230, as shown in FIG. 13, the piezoelectric substrate 232 is removed while maintaining the state where the piezoelectric substrate 232 and the material substrate 230 are joined, and the piezoelectric thin film is obtained. 206 is obtained. The removal processing of the piezoelectric substrate 232 is performed in the same manner as in the first embodiment.

{Production of support substrate 224}
After removing the piezoelectric substrate 232, as shown in FIG. 14, the material substrate 230 is etched from the lower surface side to produce the support substrate 224 in which the cavity 280 is formed. Since the etching rate of the piezoelectric thin film 206 with respect to hydrofluoric acid is sufficiently slower than that of the material substrate 230, the piezoelectric thin film 206 is hardly etched when the cavity 280 is formed with hydrofluoric acid. Note that the cavity 280 may be formed after the IDT electrode 208 is formed.

{Formation of IDT electrode 208}
After producing the support substrate 224, the IDT electrode 208 is formed on the upper surface of the piezoelectric thin film 206, and the Lamb wave device 202 shown in FIG. 10 is completed. The IDT electrode 208 is formed in the same manner as in the first embodiment.

  According to the method of manufacturing the Lamb wave device 202, unlike the case where the piezoelectric thin film 206 is formed by sputtering or the like, the piezoelectric material constituting the piezoelectric thin film 206 and the crystal orientation of the piezoelectric thin film 206 are subject to the restrictions of the base. Therefore, the degree of freedom in selecting the piezoelectric material constituting the piezoelectric thin film 206 and the crystal orientation of the piezoelectric thin film 206 is high. Therefore, the Lamb wave device 202 can easily achieve desired characteristics.

<3 Third Embodiment>
The third embodiment relates to a laminate 304 that can be used instead of the laminate 104 of the first embodiment and the laminate 204 of the second embodiment. FIG. 15 is a schematic diagram of the laminated body 304 of the third embodiment. FIG. 15 is a cross-sectional view of the laminate 304.

  As shown in FIG. 15, the laminated body 304 includes an IDT electrode 309 in addition to the piezoelectric thin film 306 and the IDT electrode 308 similar to the piezoelectric thin film 106 and the IDT electrode 108 of the first embodiment. The IDT electrode 309 is provided on the lower surface of the piezoelectric thin film 306. The IDT electrode 309 has the same planar shape as the IDT electrode 308 and is provided at a position facing the IDT electrode 308. Opposing IDT electrode 308 finger 310 and IDT electrode 309 finger 311 are in phase.

  Even when such IDT electrodes 308 and 309 are employed, a Lamb wave having a wavelength λ that is twice the pitch p of the fingers 310 and 311 is most strongly excited.

<4 Fourth Embodiment>
The third embodiment relates to a laminate 404 that can be employed instead of the laminate 104 of the first embodiment and the laminate 204 of the second embodiment. FIG. 16 is a schematic diagram of a stacked body 404 of the fourth embodiment.

  As shown in FIG. 16, the laminated body 404 includes a surface electrode 409 in addition to the piezoelectric thin film 406 and the IDT electrode 408 similar to the piezoelectric thin film 106 and the IDT electrode 108 of the first embodiment. The surface electrode 409 is provided on the lower surface of the piezoelectric thin film 406. The surface electrode 409 is provided at a position facing the IDT electrode 408. The surface electrode 409 may be grounded or may be electrically floating without being connected anywhere.

  Even when such an IDT electrode 408 is employed, a Lamb wave having a wavelength λ that is twice the pitch p of the fingers 410 is most strongly excited.

<5 Advantages of exciting Lamb waves in higher order mode>
FIG. 17 is a diagram showing changes in the frequency of the resonator depending on the film thickness of the piezoelectric thin film when the A ₁ mode and S ₀ mode Lamb waves and the longitudinal wave in the thickness direction are excited.

As shown in FIG. 17, by exciting Lamb waves of A ₁ mode, allows high frequency than in the case of exciting the thickness direction longitudinal waves, achieved in case of exciting Lamb waves of S ₀ mode obtained High frequency is also possible.

In Table 1, the case of forming a large number of resonator for exciting a Lamb wave and the thickness direction longitudinal wave A ₁ mode structure having a structure in which a three-inch wafer is supported a piezoelectric thin film obtained by thinning the support structure The measured results of frequency fluctuations are compared. All design frequencies are 3 GHz. The piezoelectric thin film is formed by thinning a 128 ° Y plate of lithium niobate to 1.0 μm when exciting the A ₁ mode, and a 36 ° Y plate of lithium niobate when exciting the longitudinal wave in the thickness direction. Is thinned to 0.5 μm. As shown in Table 1, when the A ₁ mode ram is excited, the frequency variation is half that when the thickness direction longitudinal wave is excited.

<6 Others>
Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention. In particular, it is naturally planned to combine what has been described in the first to fifth embodiments.

102, 202 Lamb wave device 104, 204, 304, 404 Laminate 106, 206, 306, 406 Piezoelectric thin film 108, 208, 308, 309, 408 IDT electrode 110, 310 Finger 116 Bus bar 122, 222 Support structure 124, 224 Support substrate 180,280 Cavity

Claims (4)

A Lamb wave device,
A piezoelectric thin film;
IDT electrodes provided on the main surface of the piezoelectric thin film;
A support structure for supporting a laminate of the piezoelectric thin film and the IDT electrode;
With
The support structure is
A support substrate;
A support film formed with a cavity for bonding the support substrate and the laminate and separating the excitation portion of the laminate from the support substrate;
With
The film thickness of the piezoelectric thin film and the pitch of the fingers of the IDT electrode are selected so that a high-order mode Lamb wave with a sound velocity of 5000 m / s or more is excited at a target frequency.
The etching rate at 65 ° C. with respect to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride of the main surface on the support structure side of the piezoelectric thin film is higher than that of the main surface on the support substrate side of the support film. A Lamb wave device in which the orientation of the piezoelectric thin film is selected so as to be 1/2 or less. The lamb wave device of claim 1,
The etching rate at 65 ° C. with respect to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride of the main surface on the support structure side of the piezoelectric thin film is higher than that of the main surface on the support substrate side of the support film. A Lamb wave device in which the orientation of the piezoelectric thin film is selected to be 1/20 or less. A Lamb wave device,
A piezoelectric thin film;
IDT electrodes provided on the main surface of the piezoelectric thin film;
A support structure for supporting a laminate of the piezoelectric thin film and the IDT electrode;
With
The support structure is
Support substrate,
With
The film thickness of the piezoelectric thin film and the pitch of the fingers of the IDT electrode are selected so that a high-order mode Lamb wave having a sound speed of 5000 m / s or more at the target frequency is excited.
The etching rate at 65 ° C. with respect to a solution containing hydrogen fluoride or a gas containing hydrogen fluoride on the main surface on the support structure side of the piezoelectric thin film is opposite to that on the piezoelectric thin film side of the support substrate. A Lamb wave device in which the orientation of the piezoelectric thin film is selected so that it is ½ or less of the principal surface on the side. The Lamb wave device of claim 3,
The etching rate at 65 ° C. with respect to a solution containing hydrogen fluoride or a gas containing hydrogen fluoride on the main surface on the support structure side of the piezoelectric thin film is opposite to that on the piezoelectric thin film side of the support substrate. A Lamb wave device in which the orientation of the piezoelectric thin film is selected so that it is 1/20 or less of the main surface on the side of the surface.

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