WO2022269721A1 - Surface acoustic wave device - Google Patents

Surface acoustic wave device Download PDF

Info

Publication number
WO2022269721A1
WO2022269721A1 PCT/JP2021/023478 JP2021023478W WO2022269721A1 WO 2022269721 A1 WO2022269721 A1 WO 2022269721A1 JP 2021023478 W JP2021023478 W JP 2021023478W WO 2022269721 A1 WO2022269721 A1 WO 2022269721A1
Authority
WO
WIPO (PCT)
Prior art keywords
substrate
thickness
acoustic wave
surface acoustic
wave device
Prior art date
Application number
PCT/JP2021/023478
Other languages
French (fr)
Japanese (ja)
Inventor
道雄 門田
秀治 田中
Original Assignee
国立大学法人東北大学
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 国立大学法人東北大学 filed Critical 国立大学法人東北大学
Priority to PCT/JP2021/023478 priority Critical patent/WO2022269721A1/en
Priority to JP2023530404A priority patent/JPWO2022270406A1/ja
Priority to PCT/JP2022/024130 priority patent/WO2022270406A1/en
Publication of WO2022269721A1 publication Critical patent/WO2022269721A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • 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 surface acoustic wave devices.
  • BAW Bulk Acoustic Wave
  • SAW surface acoustic wave
  • the vibration mode of the bulk wave used is only the thickness longitudinal vibration of the longitudinal wave.
  • the sound velocity of this longitudinal wave is expressed by (c33 D /density) 1/2 (c33 D is the elastic stiffness constant), and the resonance frequency is basically determined by sound velocity/(2 ⁇ film thickness).
  • c33 D is the elastic stiffness constant
  • the thickness of the piezoelectric thin film must be increased while the longitudinal wave is used.
  • the underlying Si substrate is greatly warped or cracked, and the electrode size increases in proportion to the thickness of the piezoelectric thin film. For this reason, in the BAW device, the size of the filter in the low frequency region becomes extremely large, making its realization difficult.
  • the filter requires a bandwidth of 5% to 30% depending on the application.
  • the bandwidth of the filter is approximately twice the bandwidth of the resonator, and the specific bandwidth of the resonator is approximately given by the square of the coupling coefficient/2.
  • LN substrates and LT substrates having coupling coefficients required for the band of the filter have been conventionally used.
  • the higher the impedance ratio the better.
  • the impedance ratio is 20 ⁇ log(Za/Zr), where Zr is the impedance at the resonance frequency fr and Za is the impedance at the antiresonance frequency fa. Also, the bandwidth is (fa-fr)/fr.
  • the speed of propagating surface acoustic waves can be reduced to about 3000 m/s. In order to utilize surface waves, there is a problem that the speed of sound needs to be further reduced.
  • the present invention has been made in view of such problems, and provides a surface acoustic wave device capable of further reducing the speed of sound of propagating surface acoustic waves and achieving miniaturization and low frequency. for the purpose.
  • a surface acoustic wave device includes a piezoelectric substrate made of a LiNbO 3 or LiTaO 3 single crystal, and a piezoelectric substrate provided on one surface of the piezoelectric substrate and having a density of 8100 kg/m 3 or more. and an underlying substrate made of an isotropic material or crystal with respect to the propagation of elastic waves and provided on the other surface of the piezoelectric substrate, the underlying substrate being the sound velocity of the propagating longitudinal wave. is lower than 8431 m/s, or the sound speed of propagating transverse waves is lower than 5341 m/s, or the density is lower than the density of the piezoelectric substrate.
  • the surface acoustic wave device uses high-density interdigital transducers whose density is at least three times the density of Al (2700 kg/m 3 ), that is, at least 8100 kg/m 3 . is slower than 8431 m/s, or the propagating transverse wave has a sound velocity slower than 5341 m/s, or the density is lower than that of the piezoelectric substrate. It is possible to further reduce the speed of sound of the surface acoustic wave. By using an isotropic glass substrate or quartz substrate as the underlying substrate with respect to acoustic wave propagation, the sound velocity of the excited and propagating surface acoustic waves can be reduced to 3000 m/s or less.
  • the resonant frequency of the propagating surface acoustic wave can also be lowered, and the frequency can be lowered.
  • the speed of sound can be reduced without changing the wavelength of the propagating surface acoustic waves. Therefore, it is possible to reduce the size of the device without increasing the size of the device.
  • the interdigital transducer may be made of any material as long as it has a density of 8100 kg/m 3 or more. It may consist of a metal film or the like.
  • the piezoelectric substrate is made of a single crystal of LiNbO 3 and has Euler angles of ( ⁇ 5° to 35°, 69° to 123°, 0° ⁇ 5°). It is preferably (0° ⁇ 5°, 69° to 123°, 0° ⁇ 5°). In this case, a relatively high impedance ratio is obtained. Also, in order to suppress spurious, the Euler angles are preferably (0° ⁇ 5°, 90° to 115°, 0° ⁇ 5°).
  • the Euler angles of the piezoelectric substrate are (0° ⁇ 5°, 69° to 117°, 0° ⁇ 5° or 90° ⁇ 5° ), more preferably (0° ⁇ 5°, 78° to 110°, 0° ⁇ 5° or 90° ⁇ 5°), (0° ⁇ 5°, 80° to 104 °, 0° ⁇ 5° or 90° ⁇ 5°).
  • the Euler angles of the piezoelectric substrate are preferably (0° ⁇ 5°, 81° to 123°, 0° ⁇ 5°) in order to obtain a higher impedance ratio.
  • (0 ° ⁇ 5 °, 83 ° to 120 °, 0 ° ⁇ 5 °) is more preferable, and (0 ° ⁇ 5 °, 87 ° to 114 °, 0 ° ⁇ 5 °) More preferred.
  • the piezoelectric substrate is made of a single crystal of LiTaO 3 and has Euler angles of ( ⁇ 5° to 35°, 80° to 126°, 0° ⁇ 5°). It is preferably (0° ⁇ 5°, 80° to 126°, 0° ⁇ 5°). In this case, a relatively high impedance ratio can be obtained. In order to obtain a higher impedance ratio, the Euler angles of the piezoelectric substrate are preferably (0° ⁇ 5°, 90° to 118°, 0° ⁇ 5°).
  • the interdigital transducer is made of Cu and has a thickness of 0.077 ⁇ 0.5/MR to 0.4 ⁇ where ⁇ is the wavelength and MR is the metallization ratio. It is preferably 0.5/MR.
  • the acoustic velocity of the excited and propagating surface acoustic waves can be reduced to 3000 m/s or less.
  • the thickness of the interdigital transducer is preferably 0.08 ⁇ 0.5/MR or more, more preferably 0.115 ⁇ 0.5/MR or more. is more preferable, and 0.123 ⁇ 0.5/MR or more is even more preferable.
  • the interdigital transducer is made of a material other than Cu, and has a thickness of 0.077 ⁇ 8930 where ⁇ is the wavelength, MR is the metallization ratio, and ⁇ ave is the average density. ⁇ 0.5/(MR ⁇ ave ) to 0.4 ⁇ 8930 ⁇ 0.5/(MR ⁇ ave ). In this case, the sound velocity of propagating surface acoustic waves can be reduced to 3000 m/s or less.
  • the thickness of the interdigital transducer is preferably 0.08 ⁇ 8930 ⁇ 0.5/(MR ⁇ ave ) or more, and more preferably 0.115 ⁇ 8930 It is more preferably 0.5/(MR ⁇ ave ) or more, and more preferably 0.123 ⁇ 8930 ⁇ 0.5/(MR ⁇ ave ) or more.
  • the thickness of the piezoelectric substrate is preferably 0.14 ⁇ to 5 ⁇ , where ⁇ is the wavelength of the interdigital transducer. In this case, it is possible to suppress the occurrence of ripples and obtain a relatively high impedance ratio.
  • the interdigital transducer is composed of a Cu electrode, and the underlying substrate is composed of a quartz substrate.
  • the thickness t is When 0.06 ⁇ h ⁇ 0.16 ⁇ , t ⁇ 11.2 ⁇ 125.3 ⁇ h+228 ⁇ h 2 +796.5 ⁇ h 3 When 0.16 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 2 ⁇ 21.7 ⁇ h+84.1 ⁇ h 2 ⁇ 108.1 ⁇ h 3 is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
  • the interdigital electrode is made of a material other than Cu
  • the base substrate is made of a crystal substrate
  • the thickness of the interdigital electrode is h
  • the wavelength is ⁇
  • the thickness t of the piezoelectric substrate is When 0.06 ⁇ H ⁇ 0.16 ⁇ , t ⁇ 11.2 ⁇ 125.3 ⁇ H+228 ⁇ H 2 +796.5 ⁇ H 3
  • 0.16 ⁇ H ⁇ 0.4 ⁇ , t ⁇ 2 ⁇ 21.7 ⁇ H+84.1 ⁇ H 2 ⁇ 108.1 ⁇ H 3 is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
  • the interdigital transducer is composed of a Cu electrode, and the underlying substrate is composed of a glass substrate.
  • the thickness t is (I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 , When 0.06 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 5.1 ⁇ 60.9 ⁇ h+257.7 ⁇ h 2 ⁇ 361.3 ⁇ h 3 (II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 , When 0.06 ⁇ h ⁇ 0.13 ⁇ , t ⁇ 1.956 ⁇ 28 ⁇ h+311 ⁇ h 2 ⁇ 1376.8 ⁇ h 3 When 0.13 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 3.5 ⁇ 40.5 ⁇ h+163.4 ⁇ h 2 ⁇ 218.2 ⁇ h 3 (III) When the base substrate has a density of 2100 kg/m 3 to 2225 kg/m 3 , When 0.06 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 5.07 ⁇ 62.3 ⁇ h+265.7 ⁇ h
  • the interdigital electrode is made of a material other than Cu
  • the base substrate is made of a glass substrate
  • the thickness of the interdigital electrode is h
  • the wavelength is ⁇
  • the thickness t of the piezoelectric substrate is (I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 , When 0.06 ⁇ H ⁇ 0.4 ⁇ , t ⁇ 5.1 ⁇ 60.9 ⁇ H+257.7 ⁇ H 2 ⁇ 361.3 ⁇ H 3 (II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 , When 0.06 ⁇ H ⁇ 0.13 ⁇ , t ⁇ 1.956 ⁇ 28 ⁇ H+311 ⁇ H 2 ⁇ 1376.8 ⁇ H 3 When 0.13 ⁇ H ⁇ 0.4 ⁇ , t ⁇ 3.5 ⁇ 40.5 ⁇ H+163.4
  • the base substrate preferably has a coefficient of linear expansion of 4.0 ⁇ 10 ⁇ 6 (1/° C.) or less, and the ratio of the thickness of the base substrate to the thickness of the piezoelectric substrate is It is preferably 15 or more.
  • the influence of temperature change can be suppressed.
  • the underlying substrate in order to further suppress the influence of temperature change, preferably has a coefficient of linear expansion of 0.5 ⁇ 10 ⁇ 6 (1/° C.) or less. It is preferable that the thickness ratio is 10 or more.
  • the piezoelectric substrate is made of a single crystal of LiNbO 3 , is bonded to the base substrate on the plus side, and has a thickness of 0.06 ⁇ to 0.06 ⁇ , where ⁇ is the wavelength of the interdigital transducer. 2 ⁇ , and the underlying substrate is preferably made of a crystal substrate. In this case, the impedance ratio can be increased.
  • the Euler angles ( ⁇ , ⁇ , ⁇ ) are right-handed and represent the cut surface of the piezoelectric substrate and the propagation direction of the elastic wave. That is, with respect to the crystal axes X, Y, and Z of LT or LN forming the piezoelectric substrate, the X axis is rotated counterclockwise by ⁇ with the Z axis as the rotation axis to obtain the X′ axis. Next, the Z-axis is rotated counterclockwise by .theta. with the X'-axis as the rotation axis to obtain the Z'-axis.
  • the Z'-axis is the normal line, and the plane including the X'-axis is the cutting plane of the piezoelectric substrate. Also, the direction obtained by rotating the X'-axis counterclockwise by ⁇ with the Z'-axis as the rotation axis is defined as the propagation direction of the elastic wave. An axis perpendicular to the X'-axis and the Z'-axis obtained by moving the Y-axis by these rotations is defined as the Y'-axis.
  • a 40° rotated Y-plate X-direction propagation is expressed in Euler angles as (0°, ⁇ 50°, 0°) and a 40° rotated Y-plate 90° X-direction Propagation is expressed in Euler angles as (0°, -50°, 90°).
  • an error of about ⁇ 0.5° at the maximum may occur with respect to each component of the Euler angles.
  • the characteristics of elastic waves there is almost no characteristic difference due to a deviation of about ⁇ 5° for ⁇ and ⁇ among the Euler angles ( ⁇ , ⁇ , ⁇ ).
  • (0°, ⁇ +360°, 0°) is a plane equivalent to the Euler angles (0°, ⁇ , 0°).
  • (0°, ⁇ +180°, 0°) is not a plane equivalent to (0°, ⁇ , 0°) in terms of Euler angles, but it is the front and back of the substrate.
  • the orientations of the front and back sides of the substrates here are equivalent planes except for the bonded substrates under certain conditions, for example, as shown in FIG. 15 below.
  • a surface acoustic wave device capable of further reducing the speed of sound of propagating surface acoustic waves and achieving miniaturization and low frequency.
  • FIG. 1 is a side view showing a surface acoustic wave device according to an embodiment of the invention
  • FIG. Conventional (a) Al electrode (thickness 0.08 ⁇ ) / (0 °, 38 °, 0 °) LN structure, (b) Al electrode (thickness 0.08 ⁇ ) / (0 °, 97 °, 0 °) LN 4 is a graph showing frequency characteristics of the surface acoustic wave device of the structure; Cu electrode (thickness 0.18 ⁇ ) / (0°, 97°, 0°) LN (thickness 0.6 ⁇ ) / (0°, 132° 45', 0°) of the embodiment of the present invention made of crystal 4 is a graph showing frequency characteristics of a surface acoustic wave device; Cu electrode (thickness 0.18 ⁇ ) / (0°, 120°, 0°) LN (thickness 0.6 ⁇ ) / (0°, 132° 45', 0°) of the embodiment of the present invention made of crystal 4
  • Cu electrode (thickness 0.12 ⁇ )/(0°, ⁇ , 0°) LT (thickness 0.8 ⁇ )/ZE glass and Cu electrode (thickness 0.12 ⁇ )/(0°) of the embodiment of the present invention °, ⁇ , 0°) LT (thickness 1.0 ⁇ )/ZE shows the relationship between the Euler angle ⁇ of the LT substrate and the impedance ratio (Impedance ratio) of the resonant sound velocity on the low speed side in a surface acoustic wave device made of ZE glass. graph.
  • Cu electrodes (thickness 0.10 ⁇ , 0.13 ⁇ , 0.20 ⁇ )/(0°, 101°, 0°) LN substrate of surface acoustic wave device made of LN/ZE glass according to the embodiment of the present invention 4 is a graph showing the relationship between thickness and impedance ratio.
  • (b) Cu electrode (thickness 0.14 ⁇ )/(0°, 101°, 0°) LN (thickness 1.0 ⁇ )/(0°, 160°, 90°) frequency characteristics of a crystal surface acoustic wave device is a graph showing Thickness h of Cu electrode and LN substrate of surface acoustic wave device composed of Cu electrode/(0°, 101°, 0°) LN/(0°, 160°, 90°) crystal according to the embodiment of the present invention 3 is a graph showing the relationship between the thickness t of .
  • the density of the underlying substrate is (a) group I (3100 kg/m 3 to 8015 kg). /m 3 ), (b) Group II (2225 kg/m 3 to 3100 kg/m 3 ), (c) Group III (2100 kg/m 3 to 2225 kg/m 3 ), thickness h of Cu electrode and LN substrate 3 is a graph showing the relationship between the thickness t of .
  • a Cu electrode (thickness 0.12 ⁇ ) is formed on the surface of the LN substrate, (a) the positive surface of the LN substrate and the 70 ° Y 90 ° X crystal substrate, (b) the negative surface of the LN substrate 4 is a graph showing the relationship between the thickness of the LN substrate and the impedance ratio of a surface acoustic wave device in which a 70°Y90°X crystal substrate is bonded to a 70°Y90°X crystal substrate.
  • FIG. 5 is a graph showing frequency characteristics of a surface acoustic wave device comprising a Cu electrode (thickness of 0.08 ⁇ )/11° YXLN (thickness of 0.7 ⁇ )/single crystal Si according to an embodiment of the present invention.
  • FIG. 1 to 16 show surface acoustic wave (SAW) devices according to embodiments of the present invention.
  • a surface acoustic wave device 10 has a piezoelectric substrate 11, an interdigital transducer (IDT) 12, and a base substrate 13.
  • IDT interdigital transducer
  • the piezoelectric substrate 11 is made of single crystal LiNbO 3 (LN) or single crystal LiTaO 3 (LT).
  • the piezoelectric substrate 11 preferably has a thickness of 0.14 ⁇ to 0.5 ⁇ , where ⁇ is the period (wavelength) of the electrode fingers of the interdigital transducer 12 .
  • the interdigital transducer 12 is made of a material whose density is at least three times the density of Al (2700 kg/m 3 ), that is, at least 8100 kg/m 3 , and is formed on one surface of the piezoelectric substrate 11 by a photolithography process or the like. there is
  • the interdigital transducer 12 is made of, for example, a Cu electrode, Mo electrode, Pt electrode, alloy, multilayer metal film, or the like.
  • the underlying substrate 13 is made of a material isotropic with respect to acoustic wave propagation or crystal.
  • the base substrate 13 is made of a material in which the sound velocity of propagating longitudinal waves is lower than 8431 m/s, or a material in which the sound velocity of propagating transverse waves is lower than 5341 m/s, or a material whose density is that of the piezoelectric substrate 11. It consists of a material that is less dense than it is.
  • the base substrate 13 is provided on the other surface of the piezoelectric substrate 11 , that is, on the surface opposite to the interdigital transducer 12 . Further, the base substrate 13 preferably has a coefficient of linear expansion of 4.0 ⁇ 10 ⁇ 6 (1/° C.) or less.
  • the underlying substrate 13 is made of, for example, a crystal substrate or a glass substrate.
  • the surface acoustic wave device 10 uses a high-density interdigital transducer 12 with a density of 8100 kg/m 3 or more, and an underlying substrate in which the sound velocity of the acoustic wave propagating is lower than that of the acoustic wave propagating through the piezoelectric substrate 11.
  • the speed of sound of the propagating surface acoustic wave can be further reduced.
  • the resonant frequency of the propagating surface acoustic wave can also be lowered, and the frequency can be lowered.
  • the speed of sound can be reduced without changing the wavelength of the propagating surface acoustic waves. Therefore, it is possible to reduce the size of the device without increasing the size of the device.
  • Examples and comparative examples of the surface acoustic wave device 10 are shown below. (in the case of a comparative example).
  • FIG. 2A shows the frequency characteristics of a SAW resonator having an Al electrode (thickness 0.08 ⁇ )/(0°, 38°, 0°) LN structure, which is currently in practical use.
  • ⁇ is the period (wavelength) of the electrode fingers of the interdigital transducer (same below).
  • the horizontal axis represents the speed of sound obtained by multiplying the wavelength ⁇ of the IDT by the frequency.
  • the resonant sound velocity was 3810 m/s and the anti-resonant sound velocity was 3960 m/s.
  • the bandwidth (BW) was 3.8% and the impedance ratio was 50 dB.
  • the frequency characteristics of a SAW resonator with an Al electrode (thickness 0.08 ⁇ )/(0°, 97°, 0°) LN structure were obtained and shown in FIG. 2(b).
  • the horizontal axis also represents the speed of sound obtained by multiplying the wavelength ⁇ of the IDT by the frequency.
  • the resonance speed of sound was 3790 m/s and the anti-resonance speed of sound was 4460 m/s.
  • the bandwidth (BW) was 17.7% and the impedance ratio was 62 dB. Since the piezoelectric substrate with this azimuth angle has a large leakage component, many ripples are generated in the band, and it is considered that it cannot be used as it is.
  • Example of the present invention The same LN substrate as in FIG. .6 ⁇ )/(0°, 132° 45′, 0°)
  • the frequency characteristics of a SAW resonator made of crystal were determined and shown in FIG.
  • the metallization ratio (MR) of the interdigital transducer is 0.5 (same below).
  • the resonance speed of sound was 2020 m/s and the anti-resonance speed of sound was 2310 m/s.
  • the bandwidth (BW) was 14.5% and the impedance ratio was 80 dB.
  • FIG. 6B also shows the relationship between the Euler angle ⁇ and the impedance ratio when the base substrate is changed from a crystal substrate to a glass substrate made of Pyrex (registered trademark) glass.
  • the temperature-frequency characteristic which indicates the deviation of the frequency with respect to the temperature change per 1°C, shows a negative value regardless of the azimuth angle for the LN substrate and the LT substrate, but for the quartz substrate, there are also azimuth angles that show a positive TCF. exist. Therefore, the TCF can be improved by combining an LN substrate or LT substrate exhibiting a negative TCF with a crystal substrate exhibiting a positive TCF at an azimuth angle.
  • the crystal substrate preferably has an Euler angle ⁇ indicating that the TCF of the Rayleigh wave is positive, such as (0° ⁇ 5°, 0° to 132°, 0° ⁇ 5°), (0° ⁇ 5° , 0°-45°, 90° ⁇ 5°) or (0° ⁇ 5°, 172°-180°, 90° ⁇ 5°).
  • the quartz substrate may have Euler angles ⁇ at which the TCF of the leaky SAW (LSAW) is positive, such as (0° ⁇ 5°, 0° to 17°, 0° ⁇ 5°), (0 ° ⁇ 5°, 25° ⁇ 65°, 0° ⁇ 5°), (0° ⁇ 5°, 132° ⁇ 180°, 0° ⁇ 5°), (0° ⁇ 5°, 0° ⁇ 42° , 90° ⁇ 5°) or (0° ⁇ 5°, 125°-180°, 90° ⁇ 5°).
  • ZE glass has a density of 2500 kg/m 3 , a longitudinal wave speed of 6498 m/s, a transverse wave speed of 3979 m/s, a Young's modulus of 95 GPa, and a Poisson's ratio of 0.2.
  • the thickness of the Cu electrode and the resonant sound velocity (The relationship between the sound velocity Vr at the resonance frequency fr and the sound velocity Va) at the anti-resonance frequency fa is determined and shown in FIG. 9(a).
  • the thickness of the Cu electrode is 0.06 ⁇ or more and 3300 m/s or less, 0.08 ⁇ or more and 3000 m/s or less, and 0.123 ⁇ or more and 2500 m/s or less. It was confirmed that the speed of sound was obtained.
  • BI glass has a density of 5630 kg/m 3 , a longitudinal wave speed of 4373 m/s, a transverse wave speed of 2491 m/s, a Young's modulus of 90 GPa, and a Poisson's ratio of 0.26. As shown in FIG. 9(b), it was confirmed that there was almost no difference in sound velocity depending on the type of glass.
  • the resonant sound velocity Vr is 3000 m/s or less when the thickness of the Cu electrode is 0.077 ⁇ or more and 2500 m/s or less when the Cu electrode thickness is 0.115 ⁇ or more. In both cases of FIGS. 9A and 9B, the thicker the Cu electrode, the lower the resonance sound velocity.
  • FIGS. 9(a) and (b) are for when the metallization ratio of the Cu electrode is 0.5, and the resonant sound velocity is inversely proportional to the metallization ratio. Therefore, if the metallization ratio of the Cu electrode is MR, the thickness of the Cu electrode that can obtain a certain resonant sound velocity is the value obtained by multiplying the thickness when the metallization ratio is 0.5 by 0.5/MR. becomes.
  • the thickness of the electrode that can obtain the same resonant sound velocity is 8930 ⁇ the thickness of the Cu electrode with a metallization ratio of 0.5. It is a value multiplied by 0.5/(MR ⁇ ave ).
  • the relationship between the thickness of the LN substrate and the impedance ratio of the SAW resonator made of Cu electrode (thickness 0.10 ⁇ , 0.13 ⁇ , 0.20 ⁇ )/(0°, 101°, 0°) LN/ZE glass A relationship was determined and shown in FIG. As shown in FIG. 10, it was confirmed that the same tendency was exhibited regardless of the thickness of the Cu electrode, and that an impedance ratio of 70 dB or more was obtained when the thickness of the LN substrate was 0.17 ⁇ to 5 ⁇ . It was also confirmed that ripples occur when the thickness of LN is 0.15 ⁇ or less.
  • the thickness of the Cu electrode and the thickness of the LN substrate are varied to obtain A range in which ripples do not occur was determined.
  • the results are shown in FIG. It was confirmed that the range above the curve shown in FIG. 12 is the range in which ripples do not occur, and that ripples occur when the LN thickness is less than 0.14 ⁇ . It has been confirmed that the same results as in FIG. 12 are obtained with the azimuth angles of the LN substrate and the crystal substrate shown in FIGS. Also, the metallization ratio of the Cu electrode is 0.5.
  • the range in which ripples do not occur can be expressed as follows from the approximation curve of the curve shown in FIG. When 0.06 ⁇ h ⁇ 0.16 ⁇ , t ⁇ 11.2 ⁇ 125.3 ⁇ h+228 ⁇ h 2 +796.5 ⁇ h 3 When 0.16 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 2 ⁇ 21.7 ⁇ h+84.1 ⁇ h 2 ⁇ 108.1 ⁇ h 3
  • the thickness of the LN substrate when the thickness of the Cu electrode is 0.4 ⁇ is substantially the same as when the thickness of the Cu electrode is 0.3 ⁇ . Also, the same impedance ratio is shown up to a thickness of 5 ⁇ of the LN substrate.
  • the film thickness h of the electrode can be calculated
  • required by (1) Formula. Therefore, if h Cu in the formula (1) is H and the thickness of LN is t, the range in which ripples do not occur can be expressed as follows. When 0.06 ⁇ H ⁇ 0.16 ⁇ , t ⁇ 11.2 ⁇ 125.3 ⁇ H+228 ⁇ H 2 +796.5 ⁇ H 3 When 0.16 ⁇ H ⁇ 0.4 ⁇ , t ⁇ 2 ⁇ 21.7 ⁇ H+84.1 ⁇ H 2 ⁇ 108.1 ⁇ H 3 where H h*MR*[rho] ave /(8930*0.5).
  • the base substrate is not a crystal substrate but an isotropic substrate such as a glass substrate
  • the range in which ripples do not occur varies depending on the density of the substrate.
  • the SAW resonator consisting of Cu electrode/(0°, 101°, 0°) LN/underlying substrate
  • the material of the underlying substrate was classified into group I (3100 kg/m 3 to 8015 kg/m 3 ) and group II ( 2225 kg/m 3 to 3100 kg/m 3 ) and Group III (2100 kg/m 3 to 2225 kg/m 3 ), and the range in which ripples do not occur was determined for each group.
  • the results are shown in FIGS. 13(a) to 13(c), respectively.
  • Table 1 shows examples of glass substrates and the like included in each group. For reference, Table 1 also shows the densities of crystal, LN, LT, single-crystal Si, and polycrystalline Si, longitudinal wave sonic velocity, and transverse wave sonic velocity.
  • the range in which ripples do not occur can be expressed as follows from the approximation curves of the curves shown in each figure.
  • the groove I shown in FIG. 13(a) When 0.06 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 5.1 ⁇ 60.9 ⁇ h+257.7 ⁇ h 2 ⁇ 361.3 ⁇ h 3
  • the groove II shown in FIG. 13(b) When 0.06 ⁇ h ⁇ 0.13 ⁇ , t ⁇ 1.956 ⁇ 28 ⁇ h+311 ⁇ h 2 ⁇ 1376.8 ⁇ h 3
  • 0.13 ⁇ h ⁇ 0.4 ⁇ t ⁇ 3.5 ⁇ 40.5 ⁇ h+163.4 ⁇ h 2 ⁇ 218.2 ⁇ h 3
  • the groove III shown in FIG. 13(c) When 0.06 ⁇ h ⁇ 0.4 ⁇ , t ⁇ 5.07 ⁇ 62.3 ⁇ h+265.7 ⁇ h 2 ⁇ 373 ⁇ h 3 is.
  • the upper limit of the thickness of the LN substrate is 5 ⁇ .
  • the film thickness h of the electrode can be calculated
  • the piezoelectric substrate is an LN substrate
  • the relationship with the temperature coefficient (TCF) was determined and shown in FIG. 14(a).
  • the underlying substrate having a linear expansion coefficient of 0.5 ⁇ 10 ⁇ 6 (1/° C.) or less has a particularly small TCF absolute value and a thickness ratio of 10 or more. was confirmed to be 20 ppm/°C or less.
  • the base substrate has a coefficient of linear expansion of 4.0 ⁇ 10 ⁇ 6 (1/° C.) or less and the thickness ratio is 15 or more
  • the absolute value of TCF is 30 ppm/° C. or less. Therefore, in order to suppress the influence of temperature change, for example, a base substrate having a coefficient of linear expansion of 4.0 ⁇ 10 ⁇ 6 (1/° C.) or less is used, and the ratio of the thickness of the base substrate to the thickness of the LN substrate is It can be said that the thickness of the base substrate and the LN substrate should be determined so that the thickness is 15 or more.
  • the piezoelectric substrate is an LT substrate
  • TCF temperature coefficient
  • the base substrate having a linear expansion coefficient of 0.5 ⁇ 10 ⁇ 6 (1/° C.) or less has a particularly small TCF absolute value and a thickness ratio of 10 or more. was confirmed to be 10 ppm/°C or less.
  • the absolute value of TCF is 15 ppm/° C. or less. It was also confirmed that when the base substrate had a coefficient of linear expansion of 8.4 ⁇ 10 ⁇ 6 (1/° C.) or less and the thickness ratio was 15 or more, the absolute value of TCF was 20 ppm/° C. or less.
  • a base substrate having a coefficient of linear expansion of 4.0 ⁇ 10 ⁇ 6 (1/° C.) or less is used, and the ratio of the thickness of the base substrate to the thickness of the LT substrate is It can be said that the thickness of the base substrate and the LT substrate should be determined so that the thickness is 15 or more.
  • Table 2 shows examples of linear expansion coefficients of various materials that can constitute the substrate.
  • an interdigital electrode made of Cu (thickness 0.12 ⁇ ) is formed on the surface of the LN substrate, and the positive side of the LN substrate, that is, equivalent to (0°, ⁇ 90° to +90°, 0°) in Euler angles and a crystal substrate of 70°Y90°X, and a Cu interdigital electrode (thickness 0.12 ⁇ ) is formed on the surface of the LN substrate.
  • the relationship between the thickness of the LN substrate and the impedance ratio of a SAW resonator in which a plane equivalent to (0°, +90° to +270°, 0°) in Euler angles and a crystal substrate of 70°Y90°X are joined. is shown in FIG. As shown in FIG.
  • the thickness of the LN substrate is 0.06 ⁇ to 2 ⁇
  • the case where the positive side of the LN substrate and the crystal substrate are bonded is better than the case where the negative side of the LN substrate is bonded to the crystal substrate.
  • the impedance ratio increased by 0.3 to 3.5 dB.
  • the underlying substrate is a glass substrate, there is no difference between the positive and negative bonding surfaces of the LN substrate.

Abstract

[Problem] To provide a surface acoustic wave device that can further reduce the sound velocity of a propagating surface acoustic wave, and that can be made more compact and have a lower frequency. [Solution] A piezoelectric substrate 11 is formed from a single crystal of LiNbO3 or LiTaO3. An interdigital electrode 12 is provided on one surface of the piezoelectric substrate 11 and has a density of 8,100 kg/m3 or more. A base substrate 13 is provided on the other surface of the piezoelectric substrate 11 and comprises a material or a crystal that is isotropic with respect to the propagation of elastic waves. The base substrate 13 is such that the sound velocity of a propagating longitudinal wave is lower than 8,431 m/s, the sound velocity of a propagating transverse wave is lower than 5,341 m/s, or the density is lower than that of the piezoelectric substrate 11.

Description

弾性表面波デバイスsurface acoustic wave device
　本発明は、弾性表面波デバイスに関する。 The present invention relates to surface acoustic wave devices.
　スマートフォン等で主に使用されている７００ＭＨｚから３ＧＨｚの周波数帯には、８０近くのバンドがあり、非常に混雑している。これらの帯域のうち、７００ＭＨｚから１．３ＧＨｚの低周波数の帯域が、電波障害が最も少なく、周波数を最も有効利用することができる。このため、スマートフォン等で利用される低周波帯のデュプレクサ（Duplexer）などのフィルタには、近年のスマートフォン等の高機能化により、小型化が要求されている。 There are nearly 80 bands in the frequency band from 700 MHz to 3 GHz, which is mainly used for smartphones, etc., and it is extremely crowded. Among these bands, the low frequency band from 700 MHz to 1.3 GHz has the least radio interference and allows the most efficient use of frequencies. For this reason, filters such as low-frequency-band duplexers used in smartphones and the like are required to be smaller due to the recent sophistication of smartphones and the like.
　従来、デュプレクサなどのフィルタには、ＡｌＮやＳｃＡｌＮなどの圧電薄膜を用いたバルク弾性波（ＢＡＷ；Bulk Acoustic Wave）デバイスや、ＬｉＮｂＯ３（ＬＮ）やＬｉＴａＯ３（ＬＴ）を用いた弾性表面波（ＳＡＷ）デバイスが用いられている。ＢＡＷデバイスでは、用いられるＡｌＮ膜やＳｃＡｌＮ膜などがｃ軸配向の多結晶膜であるため、用いるバルク波の振動モードは、縦波の厚み縦振動のみとなる。この縦波の音速は、（ｃ３３Ｄ／密度）１／２で表され（ｃ３３Ｄは弾性スティッフネス定数）、共振周波数は、基本的に音速／（２×膜厚）で決定される。ｃ軸配向では、縦波の半分の音速を有する横波は励振できないため、共振周波数を低くするためには、縦波を用いたまま、その圧電薄膜を厚くしなければならないが、厚い圧電薄膜を成膜すると下地のＳｉ基板が大きく反ったり割れたりし、また、圧電薄膜の厚みに比例して電極サイズも大きくなる。このため、ＢＡＷデバイスでは、低周波数領域でのフィルタのサイズが極端に大きくなり、その実現が困難であった。 Bulk Acoustic Wave (BAW) devices using piezoelectric thin films such as AlN and ScAlN , and surface acoustic wave ( SAW) devices are used. In the BAW device, since the AlN film, the ScAlN film, or the like used is a polycrystalline film with c-axis orientation, the vibration mode of the bulk wave used is only the thickness longitudinal vibration of the longitudinal wave. The sound velocity of this longitudinal wave is expressed by (c33 D /density) 1/2 (c33 D is the elastic stiffness constant), and the resonance frequency is basically determined by sound velocity/(2×film thickness). In the c-axis orientation, a transverse wave having half the sound velocity of a longitudinal wave cannot be excited. Therefore, in order to lower the resonance frequency, the thickness of the piezoelectric thin film must be increased while the longitudinal wave is used. When the film is formed, the underlying Si substrate is greatly warped or cracked, and the electrode size increases in proportion to the thickness of the piezoelectric thin film. For this reason, in the BAW device, the size of the filter in the low frequency region becomes extremely large, making its realization difficult.
　一方、ＬＮやＬＴを用いたＳＡＷデバイスでは、その共振周波数ｆは、基板の音速をＶ、すだれ状電極（ＩＤＴ）の周期（波長）をλとすると、ｆ＝Ｖ／λで決まる。このため、共振周波数を低くするためには、λを大きくするか、Ｖを小さくすればよい。しかし、波長λを大きくすると、素子サイズが大きくなってしまうため、小型化の要求に対応することができない。そこで、Ｖが小さい低音速の基板を用いて、低周波数化を図る試みが行われている。例えば、一般的に使用されているＬＮやＬＴの音速は、３８００ｍ／ｓであるが、すだれ状電極として高密度電極を用いることにより、基板の音速を低下させたものがある（例えば、非特許文献１参照）。このときの音速の低下量は１８％であり、実際の音速は、３０２６ｍ／ｓである。また、そのときのインピーダンス比は、６６ｄＢである。 On the other hand, in a SAW device using LN or LT, its resonance frequency f is determined by f=V/λ, where V is the sound velocity of the substrate and λ is the period (wavelength) of the interdigital transducer (IDT). Therefore, in order to lower the resonance frequency, λ should be increased or V should be decreased. However, if the wavelength λ is increased, the element size is increased, and thus the demand for miniaturization cannot be met. Therefore, attempts have been made to lower the frequency by using a substrate with a low V and a low sound velocity. For example, LN and LT, which are generally used, have a sound velocity of 3800 m/s. Reference 1). The amount of reduction in sound speed at this time is 18%, and the actual sound speed is 3026 m/s. Moreover, the impedance ratio at that time is 66 dB.
　なお、フィルタでは、用途に応じ、５％～３０％の帯域が要求される。そのフィルタの帯域は、共振子の帯域の約２倍となり、共振子の比帯域は、おおよそ結合係数の自乗／２で与えられる。このように、帯域が結合係数に依存しているため、従来、フィルタの帯域に必要な結合係数を有するＬＮ基板やＬＴ基板が使用されてきた。一方、インピーダンス比は高ければ高いほうがよく、一応の目安として、６５ｄＢ以上であることが望ましいとされている。 It should be noted that the filter requires a bandwidth of 5% to 30% depending on the application. The bandwidth of the filter is approximately twice the bandwidth of the resonator, and the specific bandwidth of the resonator is approximately given by the square of the coupling coefficient/2. Thus, since the band depends on the coupling coefficient, LN substrates and LT substrates having coupling coefficients required for the band of the filter have been conventionally used. On the other hand, the higher the impedance ratio, the better.
　ここで、インピーダンス比（Impedance ratio）は、共振周波数ｆｒにおけるインピーダンスをＺｒ、反共振周波数ｆａにおけるインピーダンスをＺａとすると、２０×ｌｏｇ（Ｚａ／Ｚｒ）である。また、帯域（Bandwidth）は、（ｆａ－ｆｒ）／ｆｒである。 Here, the impedance ratio is 20×log(Za/Zr), where Zr is the impedance at the resonance frequency fr and Za is the impedance at the antiresonance frequency fa. Also, the bandwidth is (fa-fr)/fr.
　非特許文献１に記載の、すだれ状電極として高密度電極を用いた弾性表面波デバイスでは、伝搬する弾性表面波の音速を約３０００ｍ／ｓ程度まで低下させることができるが、より低い周波数の弾性表面波を利用するためには、音速をさらに低下させる必要があるという課題があった。 In the surface acoustic wave device using high-density electrodes as interdigital electrodes described in Non-Patent Document 1, the speed of propagating surface acoustic waves can be reduced to about 3000 m/s. In order to utilize surface waves, there is a problem that the speed of sound needs to be further reduced.
　本発明は、このような課題に着目してなされたもので、伝搬する弾性表面波の音速をさらに低下させることができ、小型化および低周波数化を図ることができる弾性表面波デバイスを提供することを目的とする。 SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and provides a surface acoustic wave device capable of further reducing the speed of sound of propagating surface acoustic waves and achieving miniaturization and low frequency. for the purpose.
　上記目的を達成するために、本発明に係る弾性表面波デバイスは、ＬｉＮｂＯ３またはＬｉＴａＯ３の単結晶から成る圧電基板と、前記圧電基板の一方の表面に設けられ、密度が８１００ｋｇ／ｍ３以上のすだれ状電極と、弾性波の伝搬に関して等方性の材料または水晶から成り、前記圧電基板の他方の表面に設けられた下地基板とを有し、前記下地基板は、伝搬する縦波の音速が８４３１ｍ／ｓよりも低速である、または、伝搬する横波の音速が５３４１ｍ／ｓよりも低速である、または、密度が前記圧電基板の密度よりも小さいことを特徴とする。 To achieve the above object, a surface acoustic wave device according to the present invention includes a piezoelectric substrate made of a LiNbO 3 or LiTaO 3 single crystal, and a piezoelectric substrate provided on one surface of the piezoelectric substrate and having a density of 8100 kg/m 3 or more. and an underlying substrate made of an isotropic material or crystal with respect to the propagation of elastic waves and provided on the other surface of the piezoelectric substrate, the underlying substrate being the sound velocity of the propagating longitudinal wave. is lower than 8431 m/s, or the sound speed of propagating transverse waves is lower than 5341 m/s, or the density is lower than the density of the piezoelectric substrate.
　本発明に係る弾性表面波デバイスは、密度が、Ａｌの密度（２７００ｋｇ／ｍ３）の３倍以上、すなわち８１００ｋｇ／ｍ３以上の高密度のすだれ状電極を用いると共に、伝搬する縦波の音速が８４３１ｍ／ｓよりも低速である下地基板、または、伝搬する横波の音速が５３４１ｍ／ｓよりも低速である下地基板、または、密度が圧電基板の密度よりも小さい下地基板を用いることにより、伝搬する弾性表面波の音速をさらに低下させることができる。下地基板として、弾性波の伝搬に関して等方性のガラス基板や、水晶基板を用いることにより、励振され伝搬する弾性表面波の音速を３０００ｍ／ｓ以下にまで低下させることができる。これにより、伝搬する弾性表面波の共振周波数も低下させることができ、低周波数化を図ることができる。また、伝搬する弾性表面波の波長を変えることなく、その音速を低下させることができる。このため、素子サイズを大きくする必要がなく、小型化を図ることができる。 The surface acoustic wave device according to the present invention uses high-density interdigital transducers whose density is at least three times the density of Al (2700 kg/m 3 ), that is, at least 8100 kg/m 3 . is slower than 8431 m/s, or the propagating transverse wave has a sound velocity slower than 5341 m/s, or the density is lower than that of the piezoelectric substrate. It is possible to further reduce the speed of sound of the surface acoustic wave. By using an isotropic glass substrate or quartz substrate as the underlying substrate with respect to acoustic wave propagation, the sound velocity of the excited and propagating surface acoustic waves can be reduced to 3000 m/s or less. As a result, the resonant frequency of the propagating surface acoustic wave can also be lowered, and the frequency can be lowered. In addition, the speed of sound can be reduced without changing the wavelength of the propagating surface acoustic waves. Therefore, it is possible to reduce the size of the device without increasing the size of the device.
　本発明に係る弾性表面波デバイスで、すだれ状電極は、密度が８１００ｋｇ／ｍ３以上であれば、いかなる材料から成っていてもよく、例えば、Ｃｕ電極や、Ｍｏ電極、Ｐｔ電極、合金、多層金属膜などから成っていてもよい。 In the surface acoustic wave device according to the present invention, the interdigital transducer may be made of any material as long as it has a density of 8100 kg/m 3 or more. It may consist of a metal film or the like.
　本発明に係る弾性表面波デバイスで、前記圧電基板は、ＬｉＮｂＯ３の単結晶から成り、オイラー角が（－５°～３５°，６９°～１２３°，０°±５°）であることが好ましく、（０°±５°，６９°～１２３°，０°±５°）であることがより好ましい。この場合、比較的高いインピーダンス比が得られる。また、スプリアスを抑えるために、オイラー角が（０°±５°，９０°～１１５°，０°±５°）であることが好ましい。また、下地基板が水晶基板から成るとき、より高いインピーダンス比を得るために、圧電基板のオイラー角が（０°±５°，６９°～１１７°，０°±５°または９０°±５°）であることが好ましく、（０°±５°，７８°～１１０°，０°±５°または９０°±５°）であることがより好ましく、（０°±５°，８０°～１０４°，０°±５°または９０°±５°）であることがさらに好ましい。また、下地基板がガラス基板から成るとき、より高いインピーダンス比を得るために、圧電基板のオイラー角が（０°±５°，８１°～１２３°，０°±５°）であることが好ましく、（０°±５°，８３°～１２０°，０°±５°）であることがより好ましく、（０°±５°，８７°～１１４°，０°±５°）であることがさらに好ましい。 In the surface acoustic wave device according to the present invention, the piezoelectric substrate is made of a single crystal of LiNbO 3 and has Euler angles of (−5° to 35°, 69° to 123°, 0°±5°). It is preferably (0°±5°, 69° to 123°, 0°±5°). In this case, a relatively high impedance ratio is obtained. Also, in order to suppress spurious, the Euler angles are preferably (0°±5°, 90° to 115°, 0°±5°). In addition, when the base substrate is made of a quartz substrate, the Euler angles of the piezoelectric substrate are (0°±5°, 69° to 117°, 0°±5° or 90°±5° ), more preferably (0° ± 5°, 78° to 110°, 0° ± 5° or 90° ± 5°), (0° ± 5°, 80° to 104 °, 0°±5° or 90°±5°). Further, when the underlying substrate is made of a glass substrate, the Euler angles of the piezoelectric substrate are preferably (0°±5°, 81° to 123°, 0°±5°) in order to obtain a higher impedance ratio. , (0 ° ± 5 °, 83 ° to 120 °, 0 ° ± 5 °) is more preferable, and (0 ° ± 5 °, 87 ° to 114 °, 0 ° ± 5 °) More preferred.
　本発明に係る弾性表面波デバイスで、前記圧電基板は、ＬｉＴａＯ３の単結晶から成り、オイラー角が（－５°～３５°，８０°～１２６°，０°±５°）であることが好ましく、（０°±５°，８０°～１２６°，０°±５°）であることがより好ましい。この場合、比較的高いインピーダンス比を得ることができる。また、より高いインピーダンス比を得るために、圧電基板のオイラー角が（０°±５°，９０°～１１８°，０°±５°）であることが好ましい。 In the surface acoustic wave device according to the present invention, the piezoelectric substrate is made of a single crystal of LiTaO 3 and has Euler angles of (−5° to 35°, 80° to 126°, 0°±5°). It is preferably (0°±5°, 80° to 126°, 0°±5°). In this case, a relatively high impedance ratio can be obtained. In order to obtain a higher impedance ratio, the Euler angles of the piezoelectric substrate are preferably (0°±5°, 90° to 118°, 0°±5°).
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ電極から成り、その波長をλ、メタライゼーション比をＭＲとすると、厚みが０．０７７λ×０．５／ＭＲ～０．４λ×０．５／ＭＲであることが好ましい。この場合、励振され伝搬する弾性表面波の音速を、３０００ｍ／ｓ以下にまで低下させることができる。また、伝搬する弾性表面波の音速をさらに低下させるために、すだれ状電極の厚みが０．０８λ×０．５／ＭＲ以上であることが好ましく、０．１１５λ×０．５／ＭＲ以上であることがより好ましく、０．１２３λ×０．５／ＭＲ以上であることがさらに好ましい。 In the surface acoustic wave device according to the present invention, the interdigital transducer is made of Cu and has a thickness of 0.077λ×0.5/MR to 0.4λ× where λ is the wavelength and MR is the metallization ratio. It is preferably 0.5/MR. In this case, the acoustic velocity of the excited and propagating surface acoustic waves can be reduced to 3000 m/s or less. In order to further reduce the acoustic velocity of propagating surface acoustic waves, the thickness of the interdigital transducer is preferably 0.08λ×0.5/MR or more, more preferably 0.115λ×0.5/MR or more. is more preferable, and 0.123λ×0.5/MR or more is even more preferable.
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ以外の材料から成り、その波長をλ、メタライゼーション比をＭＲとし、平均密度をρａｖｅとすると、厚みが０．０７７λ×８９３０×０．５／（ＭＲ×ρａｖｅ）～０．４λ×８９３０×０．５／（ＭＲ×ρａｖｅ）であることが好ましい。この場合、伝搬する弾性表面波の音速を、３０００ｍ／ｓ以下にまで低下させることができる。また、伝搬する弾性表面波の音速をさらに低下させるために、すだれ状電極の厚みが０．０８λ×８９３０×０．５／（ＭＲ×ρａｖｅ）以上であることが好ましく、０．１１５λ×８９３０×０．５／（ＭＲ×ρａｖｅ）以上であることがより好ましく、０．１２３λ×８９３０×０．５／（ＭＲ×ρａｖｅ）以上であることがさらに好ましい。 In the surface acoustic wave device according to the present invention, the interdigital transducer is made of a material other than Cu, and has a thickness of 0.077λ×8930 where λ is the wavelength, MR is the metallization ratio, and ρave is the average density. ×0.5/(MR×ρ ave ) to 0.4λ×8930×0.5/(MR×ρ ave ). In this case, the sound velocity of propagating surface acoustic waves can be reduced to 3000 m/s or less. In order to further reduce the acoustic velocity of propagating surface acoustic waves, the thickness of the interdigital transducer is preferably 0.08λ×8930×0.5/(MR×ρ ave ) or more, and more preferably 0.115λ×8930 It is more preferably 0.5/(MR×ρ ave ) or more, and more preferably 0.123λ×8930×0.5/(MR×ρ ave ) or more.
　本発明に係る弾性表面波デバイスは、前記すだれ状電極の波長をλとすると、前記圧電基板の厚みが、０．１４λ～５λであることが好ましい。この場合、リップルの発生を抑えて、比較的高いインピーダンス比を得ることができる。 In the surface acoustic wave device according to the present invention, the thickness of the piezoelectric substrate is preferably 0.14λ to 5λ, where λ is the wavelength of the interdigital transducer. In this case, it is possible to suppress the occurrence of ripples and obtain a relatively high impedance ratio.
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ電極から成り、前記下地基板は、水晶基板から成り、前記すだれ状電極の厚みをｈ、波長をλとすると、前記圧電基板の厚みｔは、
　　０．０６λ≦ｈ＜０．１６λのとき、
　　　　ｔ≧１１．２－１２５．３×ｈ＋２２８×ｈ２＋７９６．５×ｈ３
　　０．１６λ≦ｈ≦０．４λのとき、
　　　　ｔ≧２－２１．７×ｈ＋８４．１×ｈ２－１０８．１×ｈ３
であることが好ましい。この場合にも、リップルの発生を抑え、高いインピーダンス比を得ることができる。 In the surface acoustic wave device according to the present invention, the interdigital transducer is composed of a Cu electrode, and the underlying substrate is composed of a quartz substrate. The thickness t is
When 0.06λ≤h<0.16λ,
t≧11.2−125.3×h+228×h 2 +796.5×h 3
When 0.16λ≤h≤0.4λ,
t≧2−21.7×h+84.1×h 2 −108.1×h 3
is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ以外の材料から成り、前記下地基板は、水晶基板から成り、前記すだれ状電極の厚みをｈ、波長をλ、メタライゼーション比をＭＲ、平均密度をρａｖｅとし、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）とすると、前記圧電基板の厚みｔは、
　　０．０６λ≦Ｈ＜０．１６λのとき、
　　　　ｔ≧１１．２－１２５．３×Ｈ＋２２８×Ｈ２＋７９６．５×Ｈ３
　　０．１６λ≦Ｈ≦０．４λのとき、
　　　　ｔ≧２－２１．７×Ｈ＋８４．１×Ｈ２－１０８．１×Ｈ３
であることが好ましい。この場合にも、リップルの発生を抑え、高いインピーダンス比を得ることができる。 In the surface acoustic wave device according to the present invention, the interdigital electrode is made of a material other than Cu, the base substrate is made of a crystal substrate, the thickness of the interdigital electrode is h, the wavelength is λ, and the metallization ratio is Assuming that MR and average density are ρ ave and H=h×MR×ρ ave /(8930×0.5), the thickness t of the piezoelectric substrate is
When 0.06λ≤H<0.16λ,
t≧11.2−125.3×H+228×H 2 +796.5×H 3
When 0.16λ≤H≤0.4λ,
t≧2−21.7×H+84.1×H 2 −108.1×H 3
is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ電極から成り、前記下地基板は、ガラス基板から成り、前記すだれ状電極の厚みをｈ、波長をλとすると、前記圧電基板の厚みｔは、
　（Ｉ）前記下地基板の密度が３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３では、
　　　０．０６λ≦ｈ＜０．４λのとき、
　　　　ｔ≧５．１－６０．９×ｈ＋２５７．７×ｈ２－３６１．３×ｈ３
　（ＩＩ）前記下地基板の密度が２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３では、
　　　０．０６λ≦ｈ＜０．１３λのとき、
　　　　ｔ≧１．９５６－２８×ｈ＋３１１×ｈ２－１３７６．８×ｈ３
　　　０．１３λ≦ｈ＜０．４λのとき、
　　　　ｔ≧３．５－４０．５×ｈ＋１６３．４×ｈ２－２１８．２×ｈ３
　（ＩＩＩ）前記下地基板の密度が２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３では、
　　　０．０６λ≦ｈ＜０．４λのとき、
　　　　ｔ≧５．０７－６２．３×ｈ＋２６５．７×ｈ２－３７３×ｈ３
であることが好ましい。この場合にも、リップルの発生を抑え、高いインピーダンス比を得ることができる。 In the surface acoustic wave device according to the present invention, the interdigital transducer is composed of a Cu electrode, and the underlying substrate is composed of a glass substrate. The thickness t is
(I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 ,
When 0.06λ≤h<0.4λ,
t≧5.1−60.9×h+257.7×h 2 −361.3×h 3
(II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 ,
When 0.06λ≤h<0.13λ,
t≧1.956−28×h+311×h 2 −1376.8×h 3
When 0.13λ≤h<0.4λ,
t≧3.5−40.5×h+163.4×h 2 −218.2×h 3
(III) When the base substrate has a density of 2100 kg/m 3 to 2225 kg/m 3 ,
When 0.06λ≤h<0.4λ,
t≧5.07−62.3×h+265.7×h 2 −373×h 3
is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
　本発明に係る弾性表面波デバイスで、前記すだれ状電極は、Ｃｕ以外の材料から成り、前記下地基板は、ガラス基板から成り、前記すだれ状電極の厚みをｈ、波長をλ、メタライゼーション比をＭＲ、平均密度をρａｖｅとし、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）とすると、前記圧電基板の厚みｔは、
　（Ｉ）前記下地基板の密度が３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３では、
　　　０．０６λ≦Ｈ＜０．４λのとき、
　　　　ｔ≧５．１－６０．９×Ｈ＋２５７．７×Ｈ２－３６１．３×Ｈ３
　（ＩＩ）前記下地基板の密度が２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３では、
　　　０．０６λ≦Ｈ＜０．１３λのとき、
　　　　ｔ≧１．９５６－２８×Ｈ＋３１１×Ｈ２－１３７６．８×Ｈ３
　　　０．１３λ≦Ｈ＜０．４λのとき、
　　　　ｔ≧３．５－４０．５×Ｈ＋１６３．４×Ｈ２－２１８．２×Ｈ３
　（ＩＩＩ）前記下地基板の密度が２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３では、
　　　０．０６λ≦Ｈ＜０．４λのとき、
　　　　ｔ≧５．０７－６２．３×Ｈ＋２６５．７×Ｈ２－３７３×Ｈ３
であることが好ましい。この場合にも、リップルの発生を抑え、高いインピーダンス比を得ることができる。 In the surface acoustic wave device according to the present invention, the interdigital electrode is made of a material other than Cu, the base substrate is made of a glass substrate, the thickness of the interdigital electrode is h, the wavelength is λ, and the metallization ratio is Assuming that MR and average density are ρ ave and H=h×MR×ρ ave /(8930×0.5), the thickness t of the piezoelectric substrate is
(I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 ,
When 0.06λ≤H<0.4λ,
t≧5.1−60.9×H+257.7×H 2 −361.3×H 3
(II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 ,
When 0.06λ≤H<0.13λ,
t≧1.956−28×H+311×H 2 −1376.8×H 3
When 0.13λ≤H<0.4λ,
t≧3.5−40.5×H+163.4×H 2 −218.2×H 3
(III) When the base substrate has a density of 2100 kg/m 3 to 2225 kg/m 3 ,
When 0.06λ≤H<0.4λ,
t≧5.07−62.3×H+265.7×H 2 −373×H 3
is preferably Also in this case, it is possible to suppress the occurrence of ripples and obtain a high impedance ratio.
　本発明に係る弾性表面波デバイスで、前記下地基板は、線膨張係数が４．０×１０－６（１／℃）以下であることが好ましく、下地基板の厚みと圧電基板の厚みの比が１５以上であることが好ましい。この場合、温度変化による影響を抑えることができる。また、この場合、温度変化による影響をさらに抑えるために、下地基板は、線膨張係数が０．５×１０－６（１／℃）以下であることが好ましく、下地基板の厚みと圧電基板の厚みの比が１０以上であることが好ましい。 In the surface acoustic wave device according to the present invention, the base substrate preferably has a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less, and the ratio of the thickness of the base substrate to the thickness of the piezoelectric substrate is It is preferably 15 or more. In this case, the influence of temperature change can be suppressed. In this case, in order to further suppress the influence of temperature change, the underlying substrate preferably has a coefficient of linear expansion of 0.5×10 −6 (1/° C.) or less. It is preferable that the thickness ratio is 10 or more.
　本発明に係る弾性表面波デバイスで、前記圧電基板は、ＬｉＮｂＯ３の単結晶から成り、プラス面で前記下地基板と接合され、前記すだれ状電極の波長をλとすると、厚みが０．０６λ～２λであり、前記下地基板は、水晶基板から成ることが好ましい。この場合、インピーダンス比を高めることができる。 In the surface acoustic wave device according to the present invention, the piezoelectric substrate is made of a single crystal of LiNbO 3 , is bonded to the base substrate on the plus side, and has a thickness of 0.06λ to 0.06λ, where λ is the wavelength of the interdigital transducer. 2λ, and the underlying substrate is preferably made of a crystal substrate. In this case, the impedance ratio can be increased.
　ここで、オイラー角（φ、θ、ψ）は、右手系であり、圧電基板の切断面と、弾性波の伝搬方向とを表現するものである。すなわち、圧電基板を構成するＬＴまたはＬＮの結晶軸Ｘ、Ｙ、Ｚに対し、Ｚ軸を回転軸としてＸ軸を反時計廻りにφ回転し、Ｘ’軸を得る。次に、そのＸ’軸を回転軸としてＺ軸を反時計廻りにθ回転しＺ’軸を得る。このとき、Ｚ’軸を法線とし、Ｘ’軸を含む面を、圧電基板の切断面とする。また、Ｚ’軸を回転軸としてＸ’軸を反時計廻りにψ回転した方向を、弾性波の伝搬方向とする。また、これらの回転によりＹ軸が移動して得られる、Ｘ’軸およびＺ’軸と垂直な軸を、Ｙ′軸とする。 Here, the Euler angles (φ, θ, ψ) are right-handed and represent the cut surface of the piezoelectric substrate and the propagation direction of the elastic wave. That is, with respect to the crystal axes X, Y, and Z of LT or LN forming the piezoelectric substrate, the X axis is rotated counterclockwise by φ with the Z axis as the rotation axis to obtain the X′ axis. Next, the Z-axis is rotated counterclockwise by .theta. with the X'-axis as the rotation axis to obtain the Z'-axis. At this time, the Z'-axis is the normal line, and the plane including the X'-axis is the cutting plane of the piezoelectric substrate. Also, the direction obtained by rotating the X'-axis counterclockwise by ψ with the Z'-axis as the rotation axis is defined as the propagation direction of the elastic wave. An axis perpendicular to the X'-axis and the Z'-axis obtained by moving the Y-axis by these rotations is defined as the Y'-axis.
　オイラー角をこのように定義することにより、例えば、４０°回転Ｙ板Ｘ方向伝搬は、オイラー角で（０°、－５０°、０°）と表され、４０°回転Ｙ板９０°Ｘ方向伝搬は、オイラー角で（０°、－５０°、９０°）と表される。なお、圧電基板を所望のオイラー角で切り出す際には、オイラー角の各成分に対して、最大で±０．５°程度の誤差が発生する可能性がある。弾性波の特性に関しては、（φ、θ、ψ）のオイラー角のうち、φ、ψに関しては、±５°程度のずれによる特性差はほとんどない。また、オイラー角（０°、θ、０°）に対し、（０°、θ＋３６０°、０°）は、オイラー角で等価な面である。一方、（０°、θ＋１８０°、０°）は、（０°、θ、０°）とはオイラー角で等価な面ではないが、基板の表裏の関係にある。しかし、弾性波デバイスでは、表と裏でも同じ特性を示すため、ここでは、基板の表裏の関係の方位も、例えば下記の図１５に示すような、ある条件の接合基板以外は、等価な面とみなす。 By defining the Euler angles in this way, for example, a 40° rotated Y-plate X-direction propagation is expressed in Euler angles as (0°, −50°, 0°) and a 40° rotated Y-plate 90° X-direction Propagation is expressed in Euler angles as (0°, -50°, 90°). Note that when the piezoelectric substrate is cut out at desired Euler angles, there is a possibility that an error of about ±0.5° at the maximum may occur with respect to each component of the Euler angles. Regarding the characteristics of elastic waves, there is almost no characteristic difference due to a deviation of about ±5° for φ and ψ among the Euler angles (φ, θ, ψ). Further, (0°, θ+360°, 0°) is a plane equivalent to the Euler angles (0°, θ, 0°). On the other hand, (0°, θ+180°, 0°) is not a plane equivalent to (0°, θ, 0°) in terms of Euler angles, but it is the front and back of the substrate. However, since acoustic wave devices exhibit the same characteristics on the front and back sides, the orientations of the front and back sides of the substrates here are equivalent planes except for the bonded substrates under certain conditions, for example, as shown in FIG. 15 below. Consider.
　また、すだれ状電極（ＩＤＴ）のメタライゼーション比（ＭＲ）は、弾性表面波の伝搬方向に沿って、すだれ状電極の電極指の幅Ｆを、電極指の周期（λ）の半分（電極指の幅Ｆと電極指間の隙間Ｇとの和）で除した比率であり、ＭＲ＝Ｆ／（Ｆ＋Ｇ）＝２×Ｆ／λである。 In addition, the metallization ratio (MR) of the interdigital transducer (IDT) is such that the width F of the electrode fingers of the interdigital transducer is half the period (λ) of the electrode fingers (electrode finger MR=F/(F+G)=2×F/λ.
　本発明によれば、伝搬する弾性表面波の音速をさらに低下させることができ、小型化および低周波数化を図ることができる弾性表面波デバイスを提供することができる。 According to the present invention, it is possible to provide a surface acoustic wave device capable of further reducing the speed of sound of propagating surface acoustic waves and achieving miniaturization and low frequency.
本発明の実施の形態の弾性表面波デバイスを示す側面図である。1 is a side view showing a surface acoustic wave device according to an embodiment of the invention; FIG. 従来の（ａ）Ａｌ電極（厚み０．０８λ）／（０°，３８°，０°）ＬＮ構造、（ｂ）Ａｌ電極（厚み０．０８λ）／（０°，９７°，０°）ＬＮ構造の、弾性表面波デバイスの周波数特性を示すグラフである。Conventional (a) Al electrode (thickness 0.08λ) / (0 °, 38 °, 0 °) LN structure, (b) Al electrode (thickness 0.08 λ) / (0 °, 97 °, 0 °) LN 4 is a graph showing frequency characteristics of the surface acoustic wave device of the structure; 本発明の実施の形態の、Ｃｕ電極（厚み０．１８λ）／（０°，９７°，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶から成る弾性表面波デバイスの周波数特性を示すグラフである。Cu electrode (thickness 0.18λ) / (0°, 97°, 0°) LN (thickness 0.6λ) / (0°, 132° 45', 0°) of the embodiment of the present invention made of crystal 4 is a graph showing frequency characteristics of a surface acoustic wave device; 本発明の実施の形態の、Ｃｕ電極（厚み０．１８λ）／（０°，１２０°，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶から成る弾性表面波デバイスの周波数特性を示すグラフである。Cu electrode (thickness 0.18λ) / (0°, 120°, 0°) LN (thickness 0.6λ) / (0°, 132° 45', 0°) of the embodiment of the present invention made of crystal 4 is a graph showing frequency characteristics of a surface acoustic wave device; 本発明の実施の形態の、Ｃｕ電極（厚み０．１８λ）／（０°，θ，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶、および、Ｃｕ電極（厚み０．１８λ）／（０°，θ，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，９０°）水晶から成る弾性表面波デバイスの、ＬＮ基板のオイラー角θと共振音速（Phase velocity）との関係を示すグラフである。Cu electrode (thickness 0.18λ) / (0°, θ, 0°) LN (thickness 0.6λ) / (0°, 132° 45', 0°) crystal of the embodiment of the present invention, and Cu electrode (thickness 0.18λ) / (0°, θ, 0°) LN (thickness 0.6λ) / (0°, 132° 45', 90°) LN substrate of surface acoustic wave device made of crystal 4 is a graph showing the relationship between Euler angle θ and resonance sound velocity (Phase velocity). 図５に示す弾性波デバイスの、（ａ）ＬＮ基板のオイラー角θと帯域（Bandwidth）との関係、（ｂ）ＬＮ基板のオイラー角θとインピーダンス比（Impedance ratio）との関係を示すグラフである。A graph showing the relationship between (a) the Euler angle θ of the LN substrate and the bandwidth, and (b) the relationship between the Euler angle θ of the LN substrate and the impedance ratio of the acoustic wave device shown in FIG. be. 本発明の実施の形態の、Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．５λ）／（０°，θ，０°）水晶、および、Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．５λ）／（０°，θ，９０°）水晶から成る弾性表面波デバイスの、水晶基板（Quartz）のオイラー角θとインピーダンス比（Impedance ratio）との関係を示すグラフである。Cu electrode (thickness 0.14λ)/(0°, 101°, 0°) LN (thickness 1.5λ)/(0°, θ, 0°) crystal and Cu electrode of the embodiment of the present invention (Thickness 0.14λ)/(0°, 101°, 0°) LN (Thickness 1.5λ)/(0°, θ, 90°) Euler of crystal substrate (Quartz) of surface acoustic wave device made of crystal 4 is a graph showing the relationship between angle θ and impedance ratio. 本発明の実施の形態の、Ｃｕ電極（厚み０．１２λ）／（０°，θ，０°）ＬＴ（厚み０．８λ）／ＺＥガラス、および、Ｃｕ電極（厚み０．１２λ）／（０°，θ，０°）ＬＴ（厚み１．０λ）／ＺＥガラスから成る弾性表面波デバイスの、ＬＴ基板のオイラー角θと、低速側の共振音速のインピーダンス比（Impedance ratio）との関係を示すグラフである。Cu electrode (thickness 0.12λ)/(0°, θ, 0°) LT (thickness 0.8λ)/ZE glass and Cu electrode (thickness 0.12λ)/(0°) of the embodiment of the present invention °, θ, 0°) LT (thickness 1.0λ)/ZE shows the relationship between the Euler angle θ of the LT substrate and the impedance ratio (Impedance ratio) of the resonant sound velocity on the low speed side in a surface acoustic wave device made of ZE glass. graph. 本発明の実施の形態の、（ａ）Ｃｕ電極／（０°，１０１°，０°）ＬＮ（厚み１λ）／（０°，１３２°４５’，０°）水晶、（ｂ）Ｃｕ電極／（０°，１０１°，０°）ＬＮ（厚み１λ）／ガラス（ＢＩガラス、ＺＥガラス、石英ガラス）から成る弾性表面波デバイスの、Ｃｕ電極の厚みと共振音速（共振周波数ｆｒのときの音速Ｖｒ、および、反共振周波数ｆａのときの音速Ｖａ）との関係を示すグラフである。(a) Cu electrode/(0°, 101°, 0°) LN (thickness 1λ)/(0°, 132°45′, 0°) crystal, (b) Cu electrode/ (0°, 101°, 0°) LN (thickness 1λ)/glass (BI glass, ZE glass, quartz glass) Cu electrode thickness and resonance sound velocity (sound velocity at resonance frequency fr 5 is a graph showing the relationship between Vr and sound velocity Va) at anti-resonance frequency fa. 本発明の実施の形態の、Ｃｕ電極（厚み０．１０λ、０．１３λ、０．２０λ）／（０°，１０１°，０°）ＬＮ／ＺＥガラスから成る弾性表面波デバイスの、ＬＮ基板の厚みとインピーダンス比（Impedance ratio）との関係を示すグラフである。Cu electrodes (thickness 0.10λ, 0.13λ, 0.20λ)/(0°, 101°, 0°) LN substrate of surface acoustic wave device made of LN/ZE glass according to the embodiment of the present invention 4 is a graph showing the relationship between thickness and impedance ratio. 本発明の実施の形態の、（ａ）Ｃｕ電極（厚み０．０５λ）／（０°，１０１°，０°）ＬＮ（厚み０．４λ）／（０°，１６０°，９０°）水晶、（ｂ）Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．０λ）／（０°，１６０°，９０°）水晶から成る弾性表面波デバイスの周波数特性を示すグラフである。(a) Cu electrode (thickness 0.05λ)/(0°, 101°, 0°) LN (thickness 0.4λ)/(0°, 160°, 90°) crystal of the embodiment of the present invention, (b) Cu electrode (thickness 0.14λ)/(0°, 101°, 0°) LN (thickness 1.0λ)/(0°, 160°, 90°) frequency characteristics of a crystal surface acoustic wave device is a graph showing 本発明の実施の形態の、Ｃｕ電極／（０°，１０１°，０°）ＬＮ／（０°，１６０°，９０°）水晶から成る弾性表面波デバイスの、Ｃｕ電極の厚みｈとＬＮ基板の厚みｔとの関係を示すグラフである。Thickness h of Cu electrode and LN substrate of surface acoustic wave device composed of Cu electrode/(0°, 101°, 0°) LN/(0°, 160°, 90°) crystal according to the embodiment of the present invention 3 is a graph showing the relationship between the thickness t of . 本発明の実施の形態の、Ｃｕ電極／（０°，１０１°，０°）ＬＮ／下地基板から成る弾性表面波デバイスの、下地基板の密度が（ａ）グループＩ（３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３）、（ｂ）グループＩＩ（２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３）、（ｃ）グループＩＩＩ（２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３）のときの、Ｃｕ電極の厚みｈとＬＮ基板の厚みｔとの関係を示すグラフである。In the surface acoustic wave device comprising Cu electrode/(0°, 101°, 0°) LN/underlying substrate according to the embodiment of the present invention, the density of the underlying substrate is (a) group I (3100 kg/m 3 to 8015 kg). /m 3 ), (b) Group II (2225 kg/m 3 to 3100 kg/m 3 ), (c) Group III (2100 kg/m 3 to 2225 kg/m 3 ), thickness h of Cu electrode and LN substrate 3 is a graph showing the relationship between the thickness t of . 本発明の実施の形態の弾性表面波デバイスの、（ａ）下地基板の厚みとＬＮ基板の厚みとの比、（ｂ）下地基板の厚みとＬＴ基板の厚みとの比と、周波数温度係数（ＴＣＦ）との関係を示すグラフである。In the surface acoustic wave device of the embodiment of the present invention, (a) the ratio of the thickness of the base substrate to the thickness of the LN substrate, (b) the ratio of the thickness of the base substrate to the thickness of the LT substrate, and the frequency temperature coefficient ( It is a graph showing the relationship with TCF). 本発明の実施の形態の、ＬＮ基板の表面にＣｕ電極（厚み０．１２λ）を形成し、（ａ）ＬＮ基板のプラス面と７０°Ｙ９０°Ｘ水晶基板、（ｂ）ＬＮ基板のマイナス面と７０°Ｙ９０°Ｘ水晶基板とを接合した弾性表面波デバイスの、ＬＮ基板の厚みとインピーダンス比（Impedance ratio）との関係を示すグラフである。In the embodiment of the present invention, a Cu electrode (thickness 0.12λ) is formed on the surface of the LN substrate, (a) the positive surface of the LN substrate and the 70 ° Y 90 ° X crystal substrate, (b) the negative surface of the LN substrate 4 is a graph showing the relationship between the thickness of the LN substrate and the impedance ratio of a surface acoustic wave device in which a 70°Y90°X crystal substrate is bonded to a 70°Y90°X crystal substrate. 本発明に関する実施の形態の、Ｃｕ電極（厚み０．０８λ）／１１°ＹＸＬＮ（厚み０．７λ）／単結晶Ｓｉから成る弾性表面波デバイスの周波数特性を示すグラフである。5 is a graph showing frequency characteristics of a surface acoustic wave device comprising a Cu electrode (thickness of 0.08λ)/11° YXLN (thickness of 0.7λ)/single crystal Si according to an embodiment of the present invention.
　以下、図面および実施例に基づいて、本発明の実施の形態について説明する。
　図１乃至図１６は、本発明の実施の形態の弾性表面波（ＳＡＷ）デバイスを示している。
　図１に示すように、弾性表面波デバイス１０は、圧電基板１１とすだれ状電極（ＩＤＴ）１２と下地基板１３とを有している。 BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described based on drawings and examples.
1 to 16 show surface acoustic wave (SAW) devices according to embodiments of the present invention.
As shown in FIG. 1, a surface acoustic wave device 10 has a piezoelectric substrate 11, an interdigital transducer (IDT) 12, and a base substrate 13. As shown in FIG.
　圧電基板１１は、ＬｉＮｂＯ３の単結晶（ＬＮ）またはＬｉＴａＯ３の単結晶（ＬＴ）から成っている。圧電基板１１は、すだれ状電極１２の電極指の周期（波長）をλとすると、厚みが、０．１４λ～０．５λであることが好ましい。すだれ状電極１２は、密度が、Ａｌの密度（２７００ｋｇ／ｍ３）の３倍以上、すなわち８１００ｋｇ／ｍ３以上の材料から成り、圧電基板１１の一方の表面にフォトリソグラフィー工程等により形成されている。すだれ状電極１２は、例えば、Ｃｕ電極や、Ｍｏ電極、Ｐｔ電極、合金、多層金属膜などから成っている。 The piezoelectric substrate 11 is made of single crystal LiNbO 3 (LN) or single crystal LiTaO 3 (LT). The piezoelectric substrate 11 preferably has a thickness of 0.14λ to 0.5λ, where λ is the period (wavelength) of the electrode fingers of the interdigital transducer 12 . The interdigital transducer 12 is made of a material whose density is at least three times the density of Al (2700 kg/m 3 ), that is, at least 8100 kg/m 3 , and is formed on one surface of the piezoelectric substrate 11 by a photolithography process or the like. there is The interdigital transducer 12 is made of, for example, a Cu electrode, Mo electrode, Pt electrode, alloy, multilayer metal film, or the like.
　下地基板１３は、弾性波の伝搬に関して等方性の材料や、水晶から成っている。また、下地基板１３は、伝搬する縦波の音速が８４３１ｍ／ｓよりも低速である材料、または、伝搬する横波の音速が５３４１ｍ／ｓよりも低速である材料、または、密度が圧電基板１１の密度よりも小さい材料から成っている。下地基板１３は、圧電基板１１の他方の表面、すなわち、すだれ状電極１２とは反対側の表面に設けられている。また、下地基板１３は、線膨張係数が４．０×１０－６（１／℃）以下であることが好ましい。下地基板１３は、例えば、水晶基板やガラス基板から成っている。 The underlying substrate 13 is made of a material isotropic with respect to acoustic wave propagation or crystal. In addition, the base substrate 13 is made of a material in which the sound velocity of propagating longitudinal waves is lower than 8431 m/s, or a material in which the sound velocity of propagating transverse waves is lower than 5341 m/s, or a material whose density is that of the piezoelectric substrate 11. It consists of a material that is less dense than it is. The base substrate 13 is provided on the other surface of the piezoelectric substrate 11 , that is, on the surface opposite to the interdigital transducer 12 . Further, the base substrate 13 preferably has a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less. The underlying substrate 13 is made of, for example, a crystal substrate or a glass substrate.
　次に、作用について説明する。
　弾性表面波デバイス１０は、密度が８１００ｋｇ／ｍ３以上の高密度のすだれ状電極１２を用いると共に、伝搬する弾性波の音速が、圧電基板１１を伝搬する弾性波の音速よりも低速の下地基板１３を用いることにより、伝搬する弾性表面波の音速をさらに低下させることができる。これにより、伝搬する弾性表面波の共振周波数も低下させることができ、低周波数化を図ることができる。また、伝搬する弾性表面波の波長を変えることなく、その音速を低下させることができる。このため、素子サイズを大きくする必要がなく、小型化を図ることができる。 Next, the action will be described.
The surface acoustic wave device 10 uses a high-density interdigital transducer 12 with a density of 8100 kg/m 3 or more, and an underlying substrate in which the sound velocity of the acoustic wave propagating is lower than that of the acoustic wave propagating through the piezoelectric substrate 11. By using 13, the speed of sound of the propagating surface acoustic wave can be further reduced. As a result, the resonant frequency of the propagating surface acoustic wave can also be lowered, and the frequency can be lowered. In addition, the speed of sound can be reduced without changing the wavelength of the propagating surface acoustic waves. Therefore, it is possible to reduce the size of the device without increasing the size of the device.
　以下に、弾性表面波デバイス１０の実施例および比較例を示すが、それらの構造を、「すだれ状電極（ＩＤＴ）／圧電基板／下地基板」や、「すだれ状電極（ＩＤＴ）／圧電基板」（比較例の場合）のように記載する。 Examples and comparative examples of the surface acoustic wave device 10 are shown below. (in the case of a comparative example).
［従来の弾性表面波デバイス］
　現在、実用化されている、Ａｌ電極（厚み０．０８λ）／（０°，３８°，０°）ＬＮ構造のＳＡＷ共振子の周波数特性を求め、図２（ａ）に示す。ここで、λは、すだれ状電極の電極指の周期（波長）である（以下同じ）。図２（ａ）では、横軸を、ＩＤＴの波長λと周波数とを乗じた音速表示で示す。図２（ａ）に示すように、共振音速は３８１０ｍ／ｓ、反共振音速は３９６０ｍ／ｓであった。また、帯域（ＢＷ）は３．８％、インピーダンス比は５０ｄＢであった。 [Conventional surface acoustic wave device]
FIG. 2A shows the frequency characteristics of a SAW resonator having an Al electrode (thickness 0.08λ)/(0°, 38°, 0°) LN structure, which is currently in practical use. Here, λ is the period (wavelength) of the electrode fingers of the interdigital transducer (same below). In FIG. 2(a), the horizontal axis represents the speed of sound obtained by multiplying the wavelength λ of the IDT by the frequency. As shown in FIG. 2(a), the resonant sound velocity was 3810 m/s and the anti-resonant sound velocity was 3960 m/s. Also, the bandwidth (BW) was 3.8% and the impedance ratio was 50 dB.
　同様に、Ａｌ電極（厚み０．０８λ）／（０°，９７°，０°）ＬＮ構造のＳＡＷ共振子の周波数特性を求め、図２（ｂ）に示す。図２（ｂ）でも、横軸を、ＩＤＴの波長λと周波数とを乗じた音速表示で示す。図２（ｂ）に示すように、共振音速は３７９０ｍ／ｓ、反共振音速は４４６０ｍ／ｓであった。また、帯域（ＢＷ）は１７．７％、インピーダンス比は６２ｄＢであった。この方位角の圧電基板では漏洩成分が大きいため、帯域内に多くのリップルが生じており、このままでは使用できないと考えられる。 Similarly, the frequency characteristics of a SAW resonator with an Al electrode (thickness 0.08λ)/(0°, 97°, 0°) LN structure were obtained and shown in FIG. 2(b). In FIG. 2(b), the horizontal axis also represents the speed of sound obtained by multiplying the wavelength λ of the IDT by the frequency. As shown in FIG. 2(b), the resonance speed of sound was 3790 m/s and the anti-resonance speed of sound was 4460 m/s. Also, the bandwidth (BW) was 17.7% and the impedance ratio was 62 dB. Since the piezoelectric substrate with this azimuth angle has a large leakage component, many ripples are generated in the band, and it is considered that it cannot be used as it is.
［本発明の実施例］
　図２（ｂ）と同じＬＮ基板に、高密度電極から成るすだれ状電極、および水晶基板を組み合わせた、Ｃｕ電極（厚み０．１８λ）／（０°，９７°，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶から成るＳＡＷ共振子の周波数特性を求め、図３に示す。なお、すだれ状電極のメタライゼーション比（ＭＲ）は、０．５である（以下、同じ）。図３に示すように、共振音速は２０２０ｍ／ｓ、反共振音速は２３１０ｍ／ｓであった。また、帯域（ＢＷ）は１４．５％、インピーダンス比は８０ｄＢであった。 [Example of the present invention]
The same LN substrate as in FIG. .6λ)/(0°, 132° 45′, 0°) The frequency characteristics of a SAW resonator made of crystal were determined and shown in FIG. The metallization ratio (MR) of the interdigital transducer is 0.5 (same below). As shown in FIG. 3, the resonance speed of sound was 2020 m/s and the anti-resonance speed of sound was 2310 m/s. Also, the bandwidth (BW) was 14.5% and the impedance ratio was 80 dB.
　図３に示すように、図２（ａ）に示す従来のＳＡＷ共振子と比較すると、共振音速が４７％減、インピーダンス比が３０ｄＢ上昇していることが確認された。また、図２（ｂ）に示す従来のＳＡＷ共振子と比較すると、共振音速が４７％減、インピーダンス比が１８ｄＢ上昇しており、さらにリップルがなく、漏洩成分がなくなっていることが確認された。このことから、図３に示す弾性表面波デバイスは、非常に良好な特性を有しているといえる。 As shown in FIG. 3, it was confirmed that the resonance sound velocity was reduced by 47% and the impedance ratio was increased by 30 dB compared to the conventional SAW resonator shown in FIG. 2(a). Moreover, compared with the conventional SAW resonator shown in FIG. 2(b), the resonance sound velocity was reduced by 47% and the impedance ratio was increased by 18 dB. . From this, it can be said that the surface acoustic wave device shown in FIG. 3 has very good characteristics.
　次に、Ｃｕ電極（厚み０．１８λ）／（０°，１２０°，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶から成るＳＡＷ共振子の周波数特性を求め、図４に示す。なお、このＳＡＷ共振子は、図３のものとは、ＬＮ基板の方位角のみが異なっているものである。図４に示すように、この場合でも、広帯域かつ高インピーダンス比が得られているが、高速度域に大きなスプリアスが生じていることが確認された。図３および図４に示す結果から、ＬＮ基板やＬＴ基板では、スプリアスの生じない最適な方位角が存在すると考えられる。 Next, Cu electrode (thickness 0.18λ)/(0°, 120°, 0°) LN (thickness 0.6λ)/(0°, 132°45′, 0°) frequency of SAW resonator made of crystal The properties were determined and shown in FIG. This SAW resonator differs from that of FIG. 3 only in the azimuth angle of the LN substrate. As shown in FIG. 4, even in this case, a wide band and a high impedance ratio were obtained, but it was confirmed that large spurious emissions occurred in the high-speed region. From the results shown in FIGS. 3 and 4, it is considered that the LN substrate and the LT substrate have an optimum azimuth angle at which no spurious occurs.
　次に、Ｃｕ電極（厚み０．１８λ）／（０°，θ，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，０°）水晶、および、Ｃｕ電極（厚み０．１８λ）／（０°，θ，０°）ＬＮ（厚み０．６λ）／（０°，１３２°４５’，９０°）水晶から成るＳＡＷ共振子の、ＬＮ基板のオイラー角θと共振音速（Phase velocity）、帯域（Bandwidth）およびインピーダンス比（Impedance ratio）との関係を求め、それぞれ図５、図６（ａ）および（ｂ）に示す。また、図６（ｂ）には、下地基板を、水晶基板からパイレックス（Ｐｙｒｅｘ；登録商標）ガラスから成るガラス基板に変えたときの、オイラー角θとインピーダンス比との関係も示している。 Next, Cu electrode (thickness 0.18λ) / (0 °, θ, 0 °) LN (thickness 0.6 λ) / (0 °, 132 ° 45', 0 °) crystal, and Cu electrode (thickness 0 .18λ)/(0°, θ, 0°) LN (thickness 0.6λ)/(0°, 132°45', 90°) Eulerian angle θ of LN substrate and resonance sound velocity of SAW resonator made of crystal (Phase velocity), bandwidth (Bandwidth) and impedance ratio (Impedance ratio) are obtained and shown in FIGS. 5, 6(a) and (b), respectively. FIG. 6B also shows the relationship between the Euler angle θ and the impedance ratio when the base substrate is changed from a crystal substrate to a glass substrate made of Pyrex (registered trademark) glass.
　図４に示すように、スプリアスにより２つの共振特性が認められることがあり、図５および図６中の○、▲、＊はそれぞれ、（０°，１３２°４５’，０°）および（０°１３２°４５’，９０°）の水晶基板を用いたときの低速側の共振音速を示し、図５および図６中の□、▼、×はそれぞれ、（０°，１３２°４５’，０°）および（０°１３２°４５’，９０°）の水晶基板を用いたときの高速側の共振音速を示している。図５に示すように、水晶基板の方位角の違いによる共振特性の差は、ほとんどないことが確認された。また、オイラー角θが９０°～１１５°の範囲で、高速側の共振音速が認められず、スプリアスが生じていないことが確認された。なお、オイラー角（φ、θ、ψ）のφが－５°～３５°の範囲では、φ＝０°のときとほぼ同じ値を示す。 As shown in FIG. 4, two resonance characteristics may be recognized due to spurious, and ○, ▲, and * in FIGS. ° 132° 45', 90°) shows the resonance sound velocity on the low speed side when using a crystal substrate, and □, ▼, and × in Figs. °) and (0° 132° 45', 90°), the resonant sound velocity on the high speed side when using a crystal substrate. As shown in FIG. 5, it was confirmed that there was almost no difference in resonance characteristics due to the difference in the azimuth angle of the crystal substrate. Moreover, it was confirmed that no resonance sound velocity on the high-speed side was observed when the Euler angle .theta. It should be noted that when φ of the Euler angles (φ, θ, ψ) is in the range of −5° to 35°, the values are almost the same as when φ=0°.
　図６（ａ）に示すように、低速側の共振音速で、θ＝５８°～１２５°で６％以上、７０°～１１７°で１０％以上の帯域が得られることが確認された。また、図６（ｂ）に示すように、水晶基板のとき、低速側の共振音速で、θ＝６９°～１１７°で７０ｄＢ以上、θ＝７８°～１１０°で７５ｄＢ以上、θ＝８０°～１０４°で７５ｄＢ以上のインピーダンス比が得られることが確認された。また、ガラス基板のとき、低速側の共振音速で、θ＝８１°～１２３°で６６ｄＢ以上、θ＝８３°～１２０°で６８ｄＢ以上、θ＝８７°～１１４°で７０ｄＢ以上のインピーダンス比が得られることが確認された。 As shown in FIG. 6(a), it was confirmed that a band of 6% or more was obtained at θ = 58° to 125° and a band of 10% or more was obtained at 70° to 117° at the resonance speed of sound on the low speed side. Further, as shown in FIG. 6(b), in the case of a crystal substrate, the resonance sound velocity on the low speed side is 70 dB or more at θ = 69° to 117°, 75 dB or more at θ = 78° to 110°, and θ = 80°. It was confirmed that an impedance ratio of 75 dB or more was obtained at ~104°. In the case of a glass substrate, the impedance ratio is 66 dB or more at θ = 81° to 123°, 68 dB or more at θ = 83° to 120°, and 70 dB or more at θ = 87° to 114° at the resonance sound velocity on the low speed side. confirmed to be obtained.
　次に、Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．５λ）／（０°，θ，０°）水晶、および、Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．５λ）／（０°，θ，９０°）水晶から成るＳＡＷ共振子の、水晶のオイラー角θとインピーダンス比との関係を求め、図７に示す。図７に示すように、水晶基板のオイラー角によらず、インピーダンス比は一定であることが確認された。 Next, Cu electrodes (thickness 0.14λ) / (0°, 101°, 0°) LN (thickness 1.5λ) / (0°, θ, 0°) crystal, and Cu electrodes (thickness 0.14λ )/(0°, 101°, 0°) LN (thickness 1.5λ)/(0°, θ, 90°) Find the relationship between the Euler angle θ of the crystal and the impedance ratio of the SAW resonator made of crystal. , as shown in FIG. As shown in FIG. 7, it was confirmed that the impedance ratio was constant regardless of the Euler angle of the quartz substrate.
　１℃当たりの温度変化に対する周波数のズレを表す周波数温度特性（ＴＣＦ）は、ＬＮ基板やＬＴ基板では、その方位角にかかわらずマイナスを示すが、水晶基板では、プラスのＴＣＦを示す方位角も存在する。このため、マイナスのＴＣＦを示すＬＮ基板やＬＴ基板と、プラスのＴＣＦを示す方位角の水晶基板とを組み合わせることにより、ＴＣＦは改善される。このため、水晶基板は、レイリー波のＴＣＦがプラスを示すオイラー角θを有することが好ましく、（０°±５°、０°～１３２°、０°±５°）、（０°±５°、０°～４５°、９０°±５°）、または（０°±５°、１７２°～１８０°、９０°±５°）であることが好ましい。また、水晶基板は、漏洩ＳＡＷ（ＬＳＡＷ）のＴＣＦがプラスを示すオイラー角θを有していてもよく、（０°±５°、０°～１７°、０°±５°）、（０°±５°、２５°～６５°、０°±５°）、（０°±５°、１３２°～１８０°、０°±５°）、（０°±５°、０°～４２°、９０°±５°）、または（０°±５°、１２５°～１８０°、９０°±５°）であることが好ましい。なお、オイラー角（φ、θ、ψ）のφが－５°～３５°の範囲では、φ＝０°±５°のときとほぼ同じ値を示す。 The temperature-frequency characteristic (TCF), which indicates the deviation of the frequency with respect to the temperature change per 1°C, shows a negative value regardless of the azimuth angle for the LN substrate and the LT substrate, but for the quartz substrate, there are also azimuth angles that show a positive TCF. exist. Therefore, the TCF can be improved by combining an LN substrate or LT substrate exhibiting a negative TCF with a crystal substrate exhibiting a positive TCF at an azimuth angle. For this reason, the crystal substrate preferably has an Euler angle θ indicating that the TCF of the Rayleigh wave is positive, such as (0°±5°, 0° to 132°, 0°±5°), (0°±5° , 0°-45°, 90°±5°) or (0°±5°, 172°-180°, 90°±5°). Also, the quartz substrate may have Euler angles θ at which the TCF of the leaky SAW (LSAW) is positive, such as (0°±5°, 0° to 17°, 0°±5°), (0 °±5°, 25°~65°, 0°±5°), (0°±5°, 132°~180°, 0°±5°), (0°±5°, 0°~42° , 90°±5°) or (0°±5°, 125°-180°, 90°±5°). It should be noted that when φ of the Euler angles (φ, θ, ψ) is in the range of −5° to 35°, the values are almost the same as when φ=0°±5°.
　次に、Ｃｕ電極（厚み０．１２λ）／（０°，θ，０°）ＬＴ（厚み０．８λ）／ＺＥガラス、および、Ｃｕ電極（厚み０．１２λ）／（０°，θ，０°）ＬＴ（厚み１．０λ）／ＺＥガラスから成るＳＡＷ共振子の、ＬＴ基板のオイラー角θと、低速側の共振音速のインピーダンス比との関係を求め、図８に示す。なお、ＺＥガラスは、密度が２５００ｋｇ／ｍ３、縦波音速が６４９８ｍ／ｓ、横波音速が３９７９ｍ／ｓ、ヤング率が９５ＧＰａ、ポアソン比が０．２のガラスである。図８に示すように、ＬＴ基板の厚みによらず、ほぼ同じ関係が得られることが確認された。また、θ＝８０°～１２６°で６６ｄＢ以上、９０°～１１８°で７０ｄＢ以上のインピーダンス比が得られることが確認された。 Next, Cu electrode (thickness 0.12λ)/(0°, θ, 0°) LT (thickness 0.8λ)/ZE glass, and Cu electrode (thickness 0.12λ)/(0°, θ, 0 °) The relationship between the Euler angle θ of the LT substrate and the impedance ratio of the resonance sound velocity on the low speed side of the SAW resonator made of LT (thickness 1.0λ)/ZE glass was obtained and shown in FIG. ZE glass has a density of 2500 kg/m 3 , a longitudinal wave speed of 6498 m/s, a transverse wave speed of 3979 m/s, a Young's modulus of 95 GPa, and a Poisson's ratio of 0.2. As shown in FIG. 8, it was confirmed that substantially the same relationship was obtained regardless of the thickness of the LT substrate. It was also confirmed that an impedance ratio of 66 dB or more was obtained at θ=80° to 126° and an impedance ratio of 70 dB or more was obtained at 90° to 118°.
　次に、Ｃｕ電極／（０°，１０１°，０°）ＬＮ（厚み１λ）／（０°，１３２°４５’，０°）水晶から成るＳＡＷ共振子の、Ｃｕ電極の厚みと共振音速（共振周波数ｆｒのときの音速Ｖｒ、および、反共振周波数ｆａのときの音速Ｖａ）との関係を求め、図９（ａ）に示す。図９（ａ）に示すように、音速Ｖｒでは、Ｃｕ電極の厚みが０．０６λ以上で３３００ｍ／ｓ以下、０．０８λ以上で３０００ｍ／ｓ以下、０．１２３λ以上で２５００ｍ／ｓ以下の共振音速が得られることが確認された。 Next, the thickness of the Cu electrode and the resonant sound velocity ( The relationship between the sound velocity Vr at the resonance frequency fr and the sound velocity Va) at the anti-resonance frequency fa is determined and shown in FIG. 9(a). As shown in FIG. 9A, at the sound velocity Vr, the thickness of the Cu electrode is 0.06λ or more and 3300 m/s or less, 0.08λ or more and 3000 m/s or less, and 0.123λ or more and 2500 m/s or less. It was confirmed that the speed of sound was obtained.
　次に、Ｃｕ電極／（０°，１０１°，０°）ＬＮ（厚み１λ）／ガラス（ＢＩガラス、ＺＥガラス、石英ガラス）から成るＳＡＷ共振子の、Ｃｕ電極の厚みと共振音速（共振周波数ｆｒのときの音速Ｖｒ、および、反共振周波数ｆａのときの音速Ｖａ）との関係を求め、図９（ｂ）に示す。なお、ＢＩガラスは、密度が５６３０ｋｇ／ｍ３、縦波音速が４３７３ｍ／ｓ、横波音速が２４９１ｍ／ｓ、ヤング率が９０ＧＰａ、ポアソン比が０．２６のガラスである。図９（ｂ）に示すように、ガラスの種類による音速の差は、ほとんどないことが確認された。また、音速Ｖｒでは、Ｃｕ電極の厚みが０．０７７λ以上で３０００ｍ／ｓ以下、０．１１５λ以上で２５００ｍ／ｓ以下の共振音速が得られることが確認された。なお、図９（ａ）および（ｂ）のいずれの場合も、Ｃｕ電極を厚くすればするほど共振音速は低下するが、現在の露光技術では、電極厚は０．４λが限界である。 Next, the thickness of the Cu electrode and the resonance sound velocity (resonance frequency The relationship between the sound velocity Vr at fr and the sound velocity Va at antiresonance frequency fa) is obtained and shown in FIG. 9(b). BI glass has a density of 5630 kg/m 3 , a longitudinal wave speed of 4373 m/s, a transverse wave speed of 2491 m/s, a Young's modulus of 90 GPa, and a Poisson's ratio of 0.26. As shown in FIG. 9(b), it was confirmed that there was almost no difference in sound velocity depending on the type of glass. In addition, it was confirmed that the resonant sound velocity Vr is 3000 m/s or less when the thickness of the Cu electrode is 0.077λ or more and 2500 m/s or less when the Cu electrode thickness is 0.115λ or more. In both cases of FIGS. 9A and 9B, the thicker the Cu electrode, the lower the resonance sound velocity.
　なお、図９（ａ）および（ｂ）は、Ｃｕ電極のメタライゼーション比が０．５のときのものであり、共振音速はメタライゼーション比に反比例する。このため、Ｃｕ電極のメタライゼーション比をＭＲとすると、ある共振音速を得ることができるＣｕ電極の厚みは、メタライゼーション比が０．５のときの厚みに、０．５／ＭＲを掛けた値となる。 Note that FIGS. 9(a) and (b) are for when the metallization ratio of the Cu electrode is 0.5, and the resonant sound velocity is inversely proportional to the metallization ratio. Therefore, if the metallization ratio of the Cu electrode is MR, the thickness of the Cu electrode that can obtain a certain resonant sound velocity is the value obtained by multiplying the thickness when the metallization ratio is 0.5 by 0.5/MR. becomes.
　また、共振音速は、メタライゼーション比だけでなく、すだれ状電極の電極密度およびその膜厚にも反比例する。このため、Ｃｕ電極以外の、Ｍｏ電極、Ｐｔ電極、合金、多層金属膜などを使用する場合、その電極のメタライゼーション比をＭＲ、平均密度をρａｖｅとすると、所定の共振音速での膜厚ｈは、その共振音速が得られるＣｕ電極（メタライゼーション比０．５）の膜厚をｈＣｕ、密度をρＣｕ（８９３０ｋｇ／ｍ３）として、次の（１）式により求めることができる。
　　　ｈ＝ｈＣｕ×ρＣｕ×０．５／（ＭＲ×ρａｖｅ）　　　　　　　　（１） Further, the resonant sound velocity is inversely proportional not only to the metallization ratio but also to the electrode density of the interdigital transducer and its film thickness. For this reason, when using a Mo electrode, a Pt electrode, an alloy, a multilayer metal film, etc. other than a Cu electrode, if the metallization ratio of the electrode is MR and the average density is ρ ave , the film thickness at a predetermined resonant sound velocity is h can be obtained by the following equation (1), where h Cu is the film thickness of the Cu electrode (metallization ratio 0.5) and ρ Cu (8930 kg/m 3 ) is the density of the Cu electrode (metallization ratio 0.5) at which the resonant sound velocity is obtained.
h= hCu × ρCu ×0.5/(MR× ρave ) (1)
　この（１）式を利用すると、すだれ状電極がＣｕ以外の電極から成るとき、同じ共振音速を得ることができる電極の厚みは、メタライゼーション比が０．５のＣｕ電極の厚みに、８９３０×０．５／（ＭＲ×ρａｖｅ）を掛けた値となる。 Using this formula (1), when the interdigital transducer is made of an electrode other than Cu, the thickness of the electrode that can obtain the same resonant sound velocity is 8930× the thickness of the Cu electrode with a metallization ratio of 0.5. It is a value multiplied by 0.5/(MR×ρ ave ).
　次に、Ｃｕ電極（厚み０．１０λ、０．１３λ、０．２０λ）／（０°，１０１°，０°）ＬＮ／ＺＥガラスから成るＳＡＷ共振子の、ＬＮ基板の厚みとインピーダンス比との関係を求め、図１０に示す。図１０に示すように、Ｃｕ電極がいずれの厚みであっても同様の傾向を示し、ＬＮ基板の厚みが０．１７λ～５λのとき、７０ｄＢ以上のインピーダンス比が得られることが確認された。また、ＬＮの厚みが０．１５λ以下のときには、リップルが発生することが確認された。 Next, the relationship between the thickness of the LN substrate and the impedance ratio of the SAW resonator made of Cu electrode (thickness 0.10λ, 0.13λ, 0.20λ)/(0°, 101°, 0°) LN/ZE glass A relationship was determined and shown in FIG. As shown in FIG. 10, it was confirmed that the same tendency was exhibited regardless of the thickness of the Cu electrode, and that an impedance ratio of 70 dB or more was obtained when the thickness of the LN substrate was 0.17λ to 5λ. It was also confirmed that ripples occur when the thickness of LN is 0.15λ or less.
　次に、Ｃｕ電極（厚み０．０５λ）／（０°，１０１°，０°）ＬＮ（厚み０．４λ）／（０°，１６０°，９０°）水晶、および、Ｃｕ電極（厚み０．１４λ）／（０°，１０１°，０°）ＬＮ（厚み１．０λ）／（０°，１６０°，９０°）水晶から成るＳＡＷ共振子の、周波数特性を求め、それぞれ図１１（ａ）および（ｂ）に示す。図１１に示すように、（ａ）では２．８ＧＨｚ付近にリップルが発生しており、（ｂ）ではリップルが発生していないことが確認された。このことから、すだれ状電極の電極厚と圧電基板の厚みとの関係には、リップルが発生しない最適な範囲が存在していると考えられる。 Next, a Cu electrode (thickness 0.05λ)/(0°, 101°, 0°) LN (thickness 0.4λ)/(0°, 160°, 90°) crystal and a Cu electrode (thickness 0.0. 14λ)/(0°, 101°, 0°) LN (thickness 1.0λ)/(0°, 160°, 90°) The frequency characteristics of the SAW resonator made of crystal were obtained, and the frequency characteristics are shown in FIG. and (b). As shown in FIG. 11, it was confirmed that ripples occurred near 2.8 GHz in (a) and no ripples occurred in (b). From this, it is considered that there exists an optimum range in which ripples do not occur in the relationship between the electrode thickness of the interdigital transducer and the thickness of the piezoelectric substrate.
　そこで、Ｃｕ電極／（０°，１０１°，０°）ＬＮ／（０°，１６０°，９０°）水晶から成るＳＡＷ共振子において、Ｃｕ電極の厚みとＬＮ基板の厚みとを変化させて、リップルが発生しない範囲を求めた。その結果を、図１２に示す。図１２に示す曲線より上の範囲が、リップルが発生しない範囲であり、ＬＮの厚みが０．１４λより小さいときには、リップルが発生することが確認された。なお、図５～図８に示すＬＮ基板および水晶基板の方位角では、図１２と同じ結果が得られることを確認している。また、Ｃｕ電極のメタライゼーション比は、０．５である。 Therefore, in a SAW resonator composed of Cu electrode/(0°, 101°, 0°) LN/(0°, 160°, 90°) crystal, the thickness of the Cu electrode and the thickness of the LN substrate are varied to obtain A range in which ripples do not occur was determined. The results are shown in FIG. It was confirmed that the range above the curve shown in FIG. 12 is the range in which ripples do not occur, and that ripples occur when the LN thickness is less than 0.14λ. It has been confirmed that the same results as in FIG. 12 are obtained with the azimuth angles of the LN substrate and the crystal substrate shown in FIGS. Also, the metallization ratio of the Cu electrode is 0.5.
　Ｃｕ電極の厚みをｈ、ＬＮ基板の厚みをｔとすると、リップルが発生しない範囲を、図１２に示す曲線の近似曲線から、以下のように表すことができる。
　　０．０６λ≦ｈ＜０．１６λのとき、
　　　　ｔ≧１１．２－１２５．３×ｈ＋２２８×ｈ２＋７９６．５×ｈ３
　　０．１６λ≦ｈ≦０．４λのとき、
　　　　ｔ≧２－２１．７×ｈ＋８４．１×ｈ２－１０８．１×ｈ３
　なお、図１２には図示していないが、Ｃｕ電極の厚みが０．４λのときのＬＮ基板の厚みは、Ｃｕ電極の厚みが０．３λのときとほぼ同じである。また、ＬＮ基板の厚みが５λまでは、同じインピーダンス比を示している。 Assuming that the thickness of the Cu electrode is h and the thickness of the LN substrate is t, the range in which ripples do not occur can be expressed as follows from the approximation curve of the curve shown in FIG.
When 0.06λ≤h<0.16λ,
t≧11.2−125.3×h+228×h 2 +796.5×h 3
When 0.16λ≤h≤0.4λ,
t≧2−21.7×h+84.1×h 2 −108.1×h 3
Although not shown in FIG. 12, the thickness of the LN substrate when the thickness of the Cu electrode is 0.4λ is substantially the same as when the thickness of the Cu electrode is 0.3λ. Also, the same impedance ratio is shown up to a thickness of 5λ of the LN substrate.
　また、Ｃｕ電極以外の電極を使用する場合、その電極の膜厚ｈは、（１）式により求めることができる。このため、（１）式のｈＣｕをＨとし、ＬＮの厚みをｔとすると、リップルが発生しない範囲を、以下のように表すことができる。
　　０．０６λ≦Ｈ＜０．１６λのとき、
　　　　ｔ≧１１．２－１２５．３×Ｈ＋２２８×Ｈ２＋７９６．５×Ｈ３
　　０．１６λ≦Ｈ≦０．４λのとき、
　　　　ｔ≧２－２１．７×Ｈ＋８４．１×Ｈ２－１０８．１×Ｈ３
　ここで、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）である。 Moreover, when using electrodes other than a Cu electrode, the film thickness h of the electrode can be calculated|required by (1) Formula. Therefore, if h Cu in the formula (1) is H and the thickness of LN is t, the range in which ripples do not occur can be expressed as follows.
When 0.06λ≤H<0.16λ,
t≧11.2−125.3×H+228×H 2 +796.5×H 3
When 0.16λ≤H≤0.4λ,
t≧2−21.7×H+84.1×H 2 −108.1×H 3
where H=h*MR*[rho] ave /(8930*0.5).
　また、下地基板が水晶基板ではなく、ガラス基板などの等方体基板の場合には、基板の密度によりリップルが発生しない範囲が異なる。Ｃｕ電極／（０°，１０１°，０°）ＬＮ／下地基板から成るＳＡＷ共振子において、下地基板の材料を、密度により、グループＩ（３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３）、グループＩＩ（２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３）、グループＩＩＩ（２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３）の３つに分けて、それぞれのグループについてリップルが発生しない範囲を求めた。その結果を、それぞれ図１３（ａ）～（ｃ）に示す。各図中に示す曲線より上の範囲が、リップルが発生しない範囲であり、ＬＮの厚みが０．１７λより小さいときには、リップルが発生することが確認された。また、各グループに含まれるガラス基板等の例を、表１に示す。なお、表１には、参考として、水晶、ＬＮ、ＬＴ、単結晶Ｓｉ、多結晶Ｓｉの密度、縦波音速、横波音速も示している。 Further, when the base substrate is not a crystal substrate but an isotropic substrate such as a glass substrate, the range in which ripples do not occur varies depending on the density of the substrate. In the SAW resonator consisting of Cu electrode/(0°, 101°, 0°) LN/underlying substrate, the material of the underlying substrate was classified into group I (3100 kg/m 3 to 8015 kg/m 3 ) and group II ( 2225 kg/m 3 to 3100 kg/m 3 ) and Group III (2100 kg/m 3 to 2225 kg/m 3 ), and the range in which ripples do not occur was determined for each group. The results are shown in FIGS. 13(a) to 13(c), respectively. The range above the curve shown in each figure is the range in which ripples do not occur, and it was confirmed that ripples occur when the LN thickness is less than 0.17λ. Table 1 shows examples of glass substrates and the like included in each group. For reference, Table 1 also shows the densities of crystal, LN, LT, single-crystal Si, and polycrystalline Si, longitudinal wave sonic velocity, and transverse wave sonic velocity.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　Ｃｕ電極の厚みをｈ、ＬＮ基板の厚みをｔとすると、リップルが発生しない範囲を、各図に示す曲線の近似曲線から、以下のように表すことができる。
　図１３（ａ）に示すグルーブＩでは、
　　０．０６λ≦ｈ≦０．４λのとき、
　　　　ｔ≧５．１－６０．９×ｈ＋２５７．７×ｈ２－３６１．３×ｈ３
　図１３（ｂ）に示すグルーブＩＩでは、
　　０．０６λ≦ｈ＜０．１３λのとき、
　　　　ｔ≧１．９５６－２８×ｈ＋３１１×ｈ２－１３７６．８×ｈ３
　　０．１３λ≦ｈ≦０．４λのとき、
　　　　ｔ≧３．５－４０．５×ｈ＋１６３．４×ｈ２－２１８．２×ｈ３
　図１３（ｃ）に示すグルーブＩＩＩでは、
　　０．０６λ≦ｈ≦０．４λのとき、
　　　　ｔ≧５．０７－６２．３×ｈ＋２６５．７×ｈ２－３７３×ｈ３
　である。なお、図示していないが、ＬＮ基板の厚みの上限は、５λである。 Assuming that the thickness of the Cu electrode is h and the thickness of the LN substrate is t, the range in which ripples do not occur can be expressed as follows from the approximation curves of the curves shown in each figure.
In the groove I shown in FIG. 13(a),
When 0.06λ≤h≤0.4λ,
t≧5.1−60.9×h+257.7×h 2 −361.3×h 3
In the groove II shown in FIG. 13(b),
When 0.06λ≤h<0.13λ,
t≧1.956−28×h+311×h 2 −1376.8×h 3
When 0.13λ≤h≤0.4λ,
t≧3.5−40.5×h+163.4×h 2 −218.2×h 3
In the groove III shown in FIG. 13(c),
When 0.06λ≤h≤0.4λ,
t≧5.07−62.3×h+265.7×h 2 −373×h 3
is. Although not shown, the upper limit of the thickness of the LN substrate is 5λ.
　また、Ｃｕ電極以外の電極を使用する場合、その電極の膜厚ｈは、（１）式により求めることができる。このため、（１）式のｈＣｕをＨとし、ＬＮ基板の厚みをｔとすると、リップルが発生しない範囲を、以下のように表すことができる。
　図１３（ａ）に示すグルーブＩでは、
　　０．０６λ≦Ｈ≦０．４λのとき、
　　　　ｔ≧５．１－６０．９×Ｈ＋２５７．７×Ｈ２－３６１．３×Ｈ３
　図１３（ｂ）に示すグルーブＩＩでは、
　　０．０６λ≦Ｈ＜０．１３λのとき、
　　　　ｔ≧１．９５６－２８×Ｈ＋３１１×Ｈ２－１３７６．８×Ｈ３
　　０．１３λ≦Ｈ≦０．４λのとき、
　　　　ｔ≧３．５－４０．５×Ｈ＋１６３．４×Ｈ２－２１８．２×Ｈ３
　図１３（ｃ）に示すグルーブＩＩＩでは、
　　０．０６λ≦Ｈ≦０．４λのとき、
　　　　ｔ≧５．０７－６２．３×Ｈ＋２６５．７×Ｈ２－３７３×Ｈ３
　である。ここで、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）である。 Moreover, when using electrodes other than a Cu electrode, the film thickness h of the electrode can be calculated|required by (1) Formula. Therefore, when h 2 Cu in equation (1) is H and the thickness of the LN substrate is t, the range in which ripples do not occur can be expressed as follows.
In the groove I shown in FIG. 13(a),
When 0.06λ≤H≤0.4λ,
t≧5.1−60.9×H+257.7×H 2 −361.3×H 3
In the groove II shown in FIG. 13(b),
When 0.06λ≤H<0.13λ,
t≧1.956−28×H+311×H 2 −1376.8×H 3
When 0.13λ≤H≤0.4λ,
t≧3.5−40.5×H+163.4×H 2 −218.2×H 3
In the groove III shown in FIG. 13(c),
When 0.06λ≤H≤0.4λ,
t≧5.07−62.3×H+265.7×H 2 −373×H 3
is. where H=h*MR*[rho] ave /(8930*0.5).
　次に、圧電基板がＬＮ基板から成るとき、様々な線膨張係数を有する下地基板について、下地基板の厚みとＬＮ基板の厚みとの比と、１℃当たりの温度変化に対する周波数のズレを表す周波数温度係数（ＴＣＦ）との関係を求め、図１４（ａ）に示す。図１４（ａ）に示すように、線膨張係数が０．５×１０－６（１／℃）以下の下地基板が、特にＴＣＦの絶対値が小さく、厚みの比が１０以上のとき、ＴＣＦの絶対値が２０ｐｐｍ／℃以下になることが確認された。また、線膨張係数が４．０×１０－６（１／℃）以下の下地基板で、厚みの比が１５以上のとき、ＴＣＦの絶対値が３０ｐｐｍ／℃以下になることが確認された。このため、温度変化による影響を抑えるためには、例えば、線膨張係数が４．０×１０－６（１／℃）以下の下地基板を用い、下地基板の厚みとＬＮ基板の厚みの比が１５以上になるよう、下地基板およびＬＮ基板の厚みを決定すればよいといえる。 Next, when the piezoelectric substrate is an LN substrate, for base substrates having various coefficients of linear expansion, the ratio of the thickness of the base substrate to the thickness of the LN substrate and the frequency representing the deviation of the frequency with respect to the temperature change per 1 ° C. The relationship with the temperature coefficient (TCF) was determined and shown in FIG. 14(a). As shown in FIG. 14(a), the underlying substrate having a linear expansion coefficient of 0.5×10 −6 (1/° C.) or less has a particularly small TCF absolute value and a thickness ratio of 10 or more. was confirmed to be 20 ppm/°C or less. It was also confirmed that when the base substrate has a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less and the thickness ratio is 15 or more, the absolute value of TCF is 30 ppm/° C. or less. Therefore, in order to suppress the influence of temperature change, for example, a base substrate having a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less is used, and the ratio of the thickness of the base substrate to the thickness of the LN substrate is It can be said that the thickness of the base substrate and the LN substrate should be determined so that the thickness is 15 or more.
　同様に、圧電基板がＬＴ基板から成るとき、様々な線膨張係数を有する下地基板について、下地基板の厚みとＬＴ基板の厚みとの比と、１℃当たりの温度変化に対する周波数のズレを表す周波数温度係数（ＴＣＦ）との関係を求め、図１４（ｂ）に示す。図１４（ｂ）に示すように、線膨張係数が０．５×１０－６（１／℃）以下の下地基板が、特にＴＣＦの絶対値が小さく、厚みの比が１０以上のとき、ＴＣＦの絶対値が１０ｐｐｍ／℃以下になることが確認された。また、線膨張係数が４．０×１０－６（１／℃）以下の下地基板で、厚みの比が１５以上のとき、ＴＣＦの絶対値が１５ｐｐｍ／℃以下になることが確認された。また、線膨張係数が８．４×１０－６（１／℃）以下の下地基板で、厚みの比が１５以上のとき、ＴＣＦの絶対値が２０ｐｐｍ／℃以下になることが確認された。このため、温度変化による影響を抑えるためには、例えば、線膨張係数が４．０×１０－６（１／℃）以下の下地基板を用い、下地基板の厚みとＬＴ基板の厚みの比が１５以上になるよう、下地基板およびＬＴ基板の厚みを決定すればよいといえる。ここで、基板を構成可能な各種材料の線膨張係数の例を、表２に示す。 Similarly, when the piezoelectric substrate is an LT substrate, for base substrates having various coefficients of linear expansion, the ratio of the thickness of the base substrate to the thickness of the LT substrate, and the frequency that represents the deviation of the frequency with respect to the temperature change per 1 ° C. The relationship with the temperature coefficient (TCF) was determined and shown in FIG. 14(b). As shown in FIG. 14(b), the base substrate having a linear expansion coefficient of 0.5×10 −6 (1/° C.) or less has a particularly small TCF absolute value and a thickness ratio of 10 or more. was confirmed to be 10 ppm/°C or less. It was also confirmed that when the base substrate has a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less and the thickness ratio is 15 or more, the absolute value of TCF is 15 ppm/° C. or less. It was also confirmed that when the base substrate had a coefficient of linear expansion of 8.4×10 −6 (1/° C.) or less and the thickness ratio was 15 or more, the absolute value of TCF was 20 ppm/° C. or less. Therefore, in order to suppress the influence of temperature change, for example, a base substrate having a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less is used, and the ratio of the thickness of the base substrate to the thickness of the LT substrate is It can be said that the thickness of the base substrate and the LT substrate should be determined so that the thickness is 15 or more. Here, Table 2 shows examples of linear expansion coefficients of various materials that can constitute the substrate.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　次に、ＬＮ基板の表面にＣｕから成るすだれ状電極（厚み０．１２λ）を形成し、ＬＮ基板のプラス面、すなわちオイラー角で(０°，－９０°～＋９０°,０°)と等価な面と、７０°Ｙ９０°Ｘの水晶基板とを接合したＳＡＷ共振子、および、ＬＮ基板の表面にＣｕから成るすだれ状電極（厚み０．１２λ）を形成し、ＬＮ基板のマイナス面、すなわちオイラー角で(０°，＋９０°～＋２７０°,０°)と等価な面と、７０°Ｙ９０°Ｘの水晶基板とを接合したＳＡＷ共振子の、ＬＮ基板の厚みとインピーダンス比との関係を求め、図１５に示す。図１５に示すように、ＬＮ基板の厚みが０．０６λ～２λのとき、ＬＮ基板のプラス面と水晶基板とを接合したものの方が、ＬＮ基板のマイナス面で水晶基板と接合したものに比べて、インピーダンス比が０．３～３．５ｄＢ大きくなっていることが確認された。なお、下地基板がガラス基板の場合には、ＬＮ基板の接合面のプラス、マイナスでの差は認められないことも確認された。 Next, an interdigital electrode made of Cu (thickness 0.12λ) is formed on the surface of the LN substrate, and the positive side of the LN substrate, that is, equivalent to (0°, −90° to +90°, 0°) in Euler angles and a crystal substrate of 70°Y90°X, and a Cu interdigital electrode (thickness 0.12λ) is formed on the surface of the LN substrate. The relationship between the thickness of the LN substrate and the impedance ratio of a SAW resonator in which a plane equivalent to (0°, +90° to +270°, 0°) in Euler angles and a crystal substrate of 70°Y90°X are joined. , and is shown in FIG. As shown in FIG. 15, when the thickness of the LN substrate is 0.06λ to 2λ, the case where the positive side of the LN substrate and the crystal substrate are bonded is better than the case where the negative side of the LN substrate is bonded to the crystal substrate. It was confirmed that the impedance ratio increased by 0.3 to 3.5 dB. It was also confirmed that when the underlying substrate is a glass substrate, there is no difference between the positive and negative bonding surfaces of the LN substrate.
　次に、Ｃｕ電極（厚み０．０８λ）／１１°ＹＸＬＮ（厚み０．７λ）／単結晶Ｓｉ（縦波音速８４３１ｍ／ｓ、横波音速５８４４ｍ／ｓ）から成るＳＡＷ共振子の周波数特性を求め、図１６に示す。図１６に示すように、下地基板として、高音速の単結晶Ｓｉ基板を用いているため、音速が大きくなっていることが確認された。また、共振音速の約１．４倍の音速を有する高次モードで、大きなスプリアスが励振されており、良好な特性は得られないことが確認された。また、下地基板として、縦波音速８９４５ｍ／ｓ、横波音速５３４１ｍ／ｓの多結晶Ｓｉを用いたときも、同様に大きなスプリアスの励振が確認された。また、下地基板として、縦波音速６３６０ｍ／ｓ、横波音速４６７６ｍ／ｓの水晶を用いたときには、スプリアスがない良好な特性を示すことが確認された。このことから、縦波音速が８４３１ｍ／ｓよりも低速である下地基板、または、横波音速が５３４１ｍ／ｓよりも低速である下地基板を使用するのが望ましいといえる。 Next, the frequency characteristics of a SAW resonator composed of a Cu electrode (thickness 0.08λ)/11° YXLN (thickness 0.7λ)/single crystal Si (longitudinal wave speed 8431 m/s, transverse wave speed 5844 m/s) were determined, It is shown in FIG. As shown in FIG. 16, it was confirmed that the sound velocity was increased because a single-crystal Si substrate with a high sound velocity was used as the underlying substrate. In addition, it was confirmed that a high-order mode having a speed of sound about 1.4 times as high as the speed of resonance was excited, and good characteristics were not obtained. Also, when polycrystalline Si with a longitudinal wave speed of 8945 m/s and a transverse wave speed of 5341 m/s was used as the underlying substrate, a large spurious excitation was similarly confirmed. It was also confirmed that good characteristics with no spurious were exhibited when crystal with a longitudinal wave speed of 6360 m/s and a transverse wave speed of 4676 m/s was used as the underlying substrate. From this, it can be said that it is desirable to use a base substrate having a longitudinal wave speed of sound lower than 8431 m/s or a base substrate having a transverse wave speed of sound lower than 5341 m/s.
　１０　弾性表面波デバイス
　１１　圧電基板
　１２　すだれ状電極
　１３　下地基板
  REFERENCE SIGNS LIST 10 surface acoustic wave device 11 piezoelectric substrate 12 interdigital transducer 13 underlying substrate

Claims (13)

  1. 　ＬｉＮｂＯ３またはＬｉＴａＯ３の単結晶から成る圧電基板と、
    　前記圧電基板の一方の表面に設けられ、密度が８１００ｋｇ／ｍ３以上のすだれ状電極と、
    　弾性波の伝搬に関して等方性の材料または水晶から成り、前記圧電基板の他方の表面に設けられた下地基板とを有し、
    　前記下地基板は、伝搬する縦波の音速が８４３１ｍ／ｓよりも低速である、または、伝搬する横波の音速が５３４１ｍ／ｓよりも低速である、または、密度が前記圧電基板の密度よりも小さいことを
    　特徴とする弾性表面波デバイス。     a piezoelectric substrate made of a single crystal of LiNbO 3 or LiTaO 3 ;
    an interdigital electrode provided on one surface of the piezoelectric substrate and having a density of 8100 kg/m 3 or more;
    an underlying substrate made of an isotropic material or crystal with respect to elastic wave propagation and provided on the other surface of the piezoelectric substrate;
    The underlying substrate has a longitudinal wave propagating sound velocity lower than 8431 m/s, a transverse wave propagating sound speed lower than 5341 m/s, or a density lower than that of the piezoelectric substrate. A surface acoustic wave device characterized by:
  2. 　励振され伝搬する弾性表面波の音速が３０００ｍ／ｓ以下であることを特徴とする請求項１記載の弾性表面波デバイス。 The surface acoustic wave device according to claim 1, characterized in that the surface acoustic wave that is excited and propagates has a sound velocity of 3000 m/s or less.
  3. 　前記圧電基板は、ＬｉＮｂＯ３の単結晶から成り、オイラー角が（－５°～３５°，６９°～１２３°，０°±５°）であることを特徴とする請求項１または２に記載の弾性表面波デバイス。 3. The piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is made of a single crystal of LiNbO 3 and has Euler angles of (−5° to 35°, 69° to 123°, 0°±5°). surface acoustic wave device.
  4. 　前記圧電基板は、ＬｉＴａＯ３の単結晶から成り、オイラー角が（－５°～３５°，８０°～１２６°，０°±５°）であることを特徴とする請求項１または２に記載の弾性表面波デバイス。 3. The piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is made of a single crystal of LiTaO 3 and has Euler angles of (−5° to 35°, 80° to 126°, 0°±5°). surface acoustic wave device.
  5. 　前記すだれ状電極は、Ｃｕ電極から成り、その波長をλ、メタライゼーション比をＭＲとすると、厚みが０．０７７λ×０．５／ＭＲ～０．４λ×０．５／ＭＲであることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。 The interdigital transducer is made of Cu and has a thickness of 0.077λ×0.5/MR to 0.4λ×0.5/MR, where λ is the wavelength and MR is the metallization ratio. 5. The surface acoustic wave device according to any one of claims 1 to 4.
  6. 　前記すだれ状電極は、Ｃｕ以外の材料から成り、その波長をλ、メタライゼーション比をＭＲとし、平均密度をρａｖｅとすると、厚みが０．０７７λ×８９３０×０．５／（ＭＲ×ρａｖｅ）～０．４λ×８９３０×０．５／（ＭＲ×ρａｖｅ）であることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。 The interdigital transducer is made of a material other than Cu and has a thickness of 0.077λ ×8930×0.5/(MR× ρave ) to 0.4λ×8930×0.5/(MR×ρ ave ).
  7. 　前記すだれ状電極の波長をλとすると、前記圧電基板の厚みが、０．１４λ～５λであることを特徴とする請求項１乃至６のいずかれ１項に記載の弾性表面波デバイス。 The surface acoustic wave device according to any one of claims 1 to 6, wherein the piezoelectric substrate has a thickness of 0.14λ to 5λ, where λ is the wavelength of the interdigital transducer.
  8. 　前記すだれ状電極は、Ｃｕ電極から成り、
    　前記下地基板は、水晶基板から成り、
    　前記すだれ状電極の厚みをｈ、波長をλとすると、前記圧電基板の厚みｔは、
    　　０．０６λ≦ｈ＜０．１６λのとき、
    　　　　ｔ≧１１．２－１２５．３×ｈ＋２２８×ｈ２＋７９６．５×ｈ３
    　　０．１６λ≦ｈ≦０．４λのとき、
    　　　　ｔ≧２－２１．７×ｈ＋８４．１×ｈ２－１０８．１×ｈ３
    であることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。     The interdigital electrodes are made of Cu electrodes,
    The base substrate is made of a quartz substrate,
    Assuming that the thickness of the interdigital transducer is h and the wavelength is λ, the thickness t of the piezoelectric substrate is
    When 0.06λ≤h<0.16λ,
    t≧11.2−125.3×h+228×h 2 +796.5×h 3
    When 0.16λ≤h≤0.4λ,
    t≧2−21.7×h+84.1×h 2 −108.1×h 3
    5. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that:
  9. 　前記すだれ状電極は、Ｃｕ以外の材料から成り、
    　前記下地基板は、水晶基板から成り、
    　前記すだれ状電極の厚みをｈ、波長をλ、メタライゼーション比をＭＲ、平均密度をρａｖｅとし、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）とすると、前記圧電基板の厚みｔは、
    　　０．０６λ≦Ｈ＜０．１６λのとき、
    　　　　ｔ≧１１．２－１２５．３×Ｈ＋２２８×Ｈ２＋７９６．５×Ｈ３
    　　０．１６λ≦Ｈ≦０．４λのとき、
    　　　　ｔ≧２－２１．７×Ｈ＋８４．１×Ｈ２－１０８．１×Ｈ３
    であることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。     the interdigital transducer is made of a material other than Cu,
    The base substrate is made of a quartz substrate,
    Let h be the thickness of the interdigital transducer, λ be the wavelength, MR be the metallization ratio, and ρ ave be the average density . t is
    When 0.06λ≤H<0.16λ,
    t≧11.2−125.3×H+228×H 2 +796.5×H 3
    When 0.16λ≤H≤0.4λ,
    t≧2−21.7×H+84.1×H 2 −108.1×H 3
    5. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that:
  10. 　前記すだれ状電極は、Ｃｕ電極から成り、
    　前記下地基板は、ガラス基板から成り、
    　前記すだれ状電極の厚みをｈ、波長をλとすると、前記圧電基板の厚みｔは、
    　　（Ｉ）前記下地基板の密度が３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３では、
    　　　０．０６λ≦ｈ＜０．４λのとき、
    　　　　ｔ≧５．１－６０．９×ｈ＋２５７．７×ｈ２－３６１．３×ｈ３
    　　（ＩＩ）前記下地基板の密度が２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３では、
    　　　０．０６λ≦ｈ＜０．１３λのとき、
    　　　　ｔ≧１．９５６－２８×ｈ＋３１１×ｈ２－１３７６．８×ｈ３
    　　　０．１３λ≦ｈ＜０．４λのとき、
    　　　　ｔ≧３．５－４０．５×ｈ＋１６３．４×ｈ２－２１８．２×ｈ３
    　　（ＩＩＩ）前記下地基板の密度が２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３では、
    　　　０．０６λ≦ｈ＜０．４λのとき、
    　　　　ｔ≧５．０７－６２．３×ｈ＋２６５．７×ｈ２－３７３×ｈ３
    であることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。     The interdigital electrodes are made of Cu electrodes,
    The base substrate is made of a glass substrate,
    Assuming that the thickness of the interdigital transducer is h and the wavelength is λ, the thickness t of the piezoelectric substrate is
    (I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 ,
    When 0.06λ≤h<0.4λ,
    t≧5.1−60.9×h+257.7×h 2 −361.3×h 3
    (II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 ,
    When 0.06λ≤h<0.13λ,
    t≧1.956−28×h+311×h 2 −1376.8×h 3
    When 0.13λ≤h<0.4λ,
    t≧3.5−40.5×h+163.4×h 2 −218.2×h 3
    (III) When the base substrate has a density of 2100 kg/m 3 to 2225 kg/m 3 ,
    When 0.06λ≤h<0.4λ,
    t≧5.07−62.3×h+265.7×h 2 −373×h 3
    5. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that:
  11. 　前記すだれ状電極は、Ｃｕ以外の材料から成り、
    　前記下地基板は、ガラス基板から成り、
    　前記すだれ状電極の厚みをｈ、波長をλ、メタライゼーション比をＭＲ、平均密度をρａｖｅとし、Ｈ＝ｈ×ＭＲ×ρａｖｅ／（８９３０×０．５）とすると、前記圧電基板の厚みｔは、
    　　（Ｉ）前記下地基板の密度が３１００ｋｇ／ｍ３～８０１５ｋｇ／ｍ３では、
    　　　０．０６λ≦Ｈ＜０．４λのとき、
    　　　　ｔ≧５．１－６０．９×Ｈ＋２５７．７×Ｈ２－３６１．３×Ｈ３
    　　（ＩＩ）前記下地基板の密度が２２２５ｋｇ／ｍ３～３１００ｋｇ／ｍ３では、
    　　　０．０６λ≦Ｈ＜０．１３λのとき、
    　　　　ｔ≧１．９５６－２８×Ｈ＋３１１×Ｈ２－１３７６．８×Ｈ３
    　　　０．１３λ≦Ｈ＜０．４λのとき、
    　　　　ｔ≧３．５－４０．５×Ｈ＋１６３．４×Ｈ２－２１８．２×Ｈ３
    　　（ＩＩＩ）前記下地基板の密度が２１００ｋｇ／ｍ３～２２２５ｋｇ／ｍ３では、
    　　　０．０６λ≦Ｈ＜０．４λのとき、
    　　　　ｔ≧５．０７－６２．３×Ｈ＋２６５．７×Ｈ２－３７３×Ｈ３
    であることを特徴とする請求項１乃至４のいずかれ１項に記載の弾性表面波デバイス。     the interdigital transducer is made of a material other than Cu,
    The base substrate is made of a glass substrate,
    Let h be the thickness of the interdigital transducer, λ be the wavelength, MR be the metallization ratio, and ρ ave be the average density . t is
    (I) When the base substrate has a density of 3100 kg/m 3 to 8015 kg/m 3 ,
    When 0.06λ≤H<0.4λ,
    t≧5.1−60.9×H+257.7×H 2 −361.3×H 3
    (II) When the base substrate has a density of 2225 kg/m 3 to 3100 kg/m 3 ,
    When 0.06λ≤H<0.13λ,
    t≧1.956−28×H+311×H 2 −1376.8×H 3
    When 0.13λ≤H<0.4λ,
    t≧3.5−40.5×H+163.4×H 2 −218.2×H 3
    (III) When the base substrate has a density of 2100 kg/m 3 to 2225 kg/m 3 ,
    When 0.06λ≤H<0.4λ,
    t≧5.07−62.3×H+265.7×H 2 −373×H 3
    5. The surface acoustic wave device according to any one of claims 1 to 4, characterized in that:
  12. 　前記下地基板は、線膨張係数が４．０×１０－６（１／℃）以下であることを特徴とする請求項１乃至１１のいずかれ１項に記載の弾性波デバイス。 12. The acoustic wave device according to claim 1, wherein the base substrate has a coefficient of linear expansion of 4.0×10 −6 (1/° C.) or less.
  13. 　前記圧電基板は、ＬｉＮｂＯ３の単結晶から成り、プラス面で前記下地基板と接合され、前記すだれ状電極の波長をλとすると、厚みが０．０６λ～２λであり、
    　前記下地基板は、水晶基板から成ることを
    　特徴とする請求項１乃至３のいずかれ１項に記載の弾性表面波デバイス。
          The piezoelectric substrate is made of a LiNbO 3 single crystal, is bonded to the base substrate on the plus side, and has a thickness of 0.06λ to 2λ where λ is the wavelength of the interdigital electrode,
    4. The surface acoustic wave device according to any one of claims 1 to 3, wherein the base substrate is made of a crystal substrate.
PCT/JP2021/023478 2021-06-21 2021-06-21 Surface acoustic wave device WO2022269721A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
PCT/JP2021/023478 WO2022269721A1 (en) 2021-06-21 2021-06-21 Surface acoustic wave device
JP2023530404A JPWO2022270406A1 (en) 2021-06-21 2022-06-16
PCT/JP2022/024130 WO2022270406A1 (en) 2021-06-21 2022-06-16 Surface acoustic device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2021/023478 WO2022269721A1 (en) 2021-06-21 2021-06-21 Surface acoustic wave device

Publications (1)

Publication Number Publication Date
WO2022269721A1 true WO2022269721A1 (en) 2022-12-29

Family

ID=84544337

Family Applications (2)

Application Number Title Priority Date Filing Date
PCT/JP2021/023478 WO2022269721A1 (en) 2021-06-21 2021-06-21 Surface acoustic wave device
PCT/JP2022/024130 WO2022270406A1 (en) 2021-06-21 2022-06-16 Surface acoustic device

Family Applications After (1)

Application Number Title Priority Date Filing Date
PCT/JP2022/024130 WO2022270406A1 (en) 2021-06-21 2022-06-16 Surface acoustic device

Country Status (2)

Country Link
JP (1) JPWO2022270406A1 (en)
WO (2) WO2022269721A1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015012005A1 (en) * 2013-07-25 2015-01-29 日本碍子株式会社 Composite board and method for making same
WO2018097016A1 (en) * 2016-11-25 2018-05-31 国立大学法人東北大学 Elastic wave device
US20200119710A1 (en) * 2018-10-16 2020-04-16 Tohoku University Acoustic wave devices

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190074819A1 (en) * 2017-08-18 2019-03-07 Skyworks Solutions, Inc. Filter with surface acoustic wave device for carrier aggregation system
JP7199195B2 (en) * 2018-10-17 2023-01-05 太陽誘電株式会社 Acoustic wave devices and composite substrates

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015012005A1 (en) * 2013-07-25 2015-01-29 日本碍子株式会社 Composite board and method for making same
WO2018097016A1 (en) * 2016-11-25 2018-05-31 国立大学法人東北大学 Elastic wave device
US20200119710A1 (en) * 2018-10-16 2020-04-16 Tohoku University Acoustic wave devices

Also Published As

Publication number Publication date
WO2022270406A1 (en) 2022-12-29
JPWO2022270406A1 (en) 2022-12-29

Similar Documents

Publication Publication Date Title
US6661313B2 (en) Surface acoustic wave devices using optimized cuts of lithium niobate (LiNbO3)
EP2744107B1 (en) Elastic wave device
US6833774B2 (en) Surface acoustic wave filter
JP4419961B2 (en) Boundary acoustic wave device
US11611324B2 (en) Acoustic wave device, high frequency front end circuit, and communication apparatus
US7323803B2 (en) Boundary acoustic wave device
JPWO2004070946A1 (en) Boundary acoustic wave device
WO2020204045A1 (en) High-order mode surface acoustic wave device
US20020067227A1 (en) Surface acoustic wave devices using optimized cuts of a piezoelectric substrate
KR102294196B1 (en) Acoustic wave devices, high-frequency front-end circuits and communication devices
WO2020184621A1 (en) Elastic wave device
JP7433873B2 (en) Acoustic wave resonators, filters, and multiplexers
JP2023060058A (en) Acoustic wave resonator, filter and multiplexer
JP2023036845A (en) Acoustic wave device
US6865786B2 (en) Method for manufacturing a surface acoustic wave device using a shear horizontal type surface acoustic wave
WO2022269721A1 (en) Surface acoustic wave device
JP2004236285A (en) Surface wave device
WO2021090861A1 (en) Elastic wave device
CN114641932A (en) Thin film surface acoustic wave device using Rayleigh mode
WO2021172032A1 (en) Acoustic wave device
WO2022168798A1 (en) Elastic wave device
WO2022224470A1 (en) Resonator
WO2022168799A1 (en) Elastic wave device
WO2022168796A1 (en) Elastic wave device
Owaki et al. Excellent frequency stability and high-Q and small SH-type quartz SAW resonators

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 21947010

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE