JP2005260909A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element which can easily bring an antiresonant frequency close to a resonant frequency. <P>SOLUTION: By forming a layer of insulating material made of silicon oxide between interdigital electrode sections 12 and 14 and a piezoelectric substrate 11, electromechanical coupling factor k<SP>2</SP>of the element becomes small, and the antiresonant frequency approaches the resonant frequency. Therefore, a frequency outside the passband can be decreased rapidly and sufficiently. As a difference between the antiresonant frequency and the resonant frequency of the surface acoustic element can be reduced without adding an external coil or capacitor to the element, the device can be miniaturized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave device used as a resonator, and more particularly to a surface acoustic wave device that can easily bring an antiresonance frequency and a resonance frequency close to each other.

  FIG. 18 shows a bandpass filter F1 formed using a conventional surface acoustic wave element. The band-pass filter F1 is formed by connecting a resonator S1 and a resonator S2 that are surface acoustic wave elements.

  The resonators S1 and S2 are formed on the piezoelectric substrate 1 by forming a comb-like electrode portion 2 and a comb-like electrode portion 3 using a sputtering method, a plating method, or the like. The comb-tooth-shaped electrode portions 2 and the comb-tooth-shaped electrode portions 3 are arranged alternately at a predetermined interval.

  Further, the connection portion 4 is electrically connected to the comb-like electrode portion 2 and the comb-like electrode portion 3, and the resonator S <b> 1 and the resonator S <b> 2 are connected via the connection portion 4.

  One end A of the resonator S1 is connected to the input terminal in of the bandpass filter F1, and the other end B is connected to the output terminal out. One end A of the resonator 2 is connected to one end A of the resonator S1, and the other end B of the resonator S2 is connected to the ground potential via the terminal GND.

FIG. 19 shows an equivalent circuit diagram of the bandpass filter F1 shown in FIG. The resonators S1 and S2 are equivalent to a resonator circuit including capacitors C1 and C2 and an inductor L1.
20 is a cross-sectional view of the resonator S1 shown in FIG. 18 taken along the alternate long and short dash line DD and viewed from the direction of the arrows. As shown in FIG. 20, the comb-like electrode portions 2 and 3 are directly laminated on the piezoelectric substrate 1.

  In addition, reflectors 5 and 5 for reflecting surface waves generated on the surface of the piezoelectric substrate 1 are provided on both sides of the comb-like electrode portions 2 and 3.

  The operating principle of the bandpass filter F1 shown in FIG. 18 will be described. FIG. 21A is a graph showing the frequency characteristics of the resonators S1 and S2. In FIG. 21A, the vertical axis represents the reactance X, and the horizontal axis represents the frequency f. The anti-resonance frequency far of the resonator S1 is higher than the anti-resonance frequency far of the resonator S2, and the resonance frequency fr of the resonator S1 and the anti-resonance frequency far of the resonator S2 overlap. Therefore, the frequency characteristic of the band-pass filter F1 formed by connecting the resonator S1 and the resonator S2 as shown in FIG. 18 is shown by the graph in FIG. The resonance frequency fr of the resonator S1, that is, the antiresonance frequency far of the resonator S2, becomes the center frequency of the pass band of the bandpass filter F1. Further, the attenuation of the bandpass filter F1 increases near the resonance frequency fr of the resonator S2 and at the antiresonance frequency far of the resonator S1, and is less than the resonance frequency fr of the resonator 2 and above the antiresonance frequency far of the resonator 1. The band is an attenuation band.

  In order to steeply and sufficiently attenuate the frequency outside the pass band of the high frequency filter formed by combining the resonators, it is necessary to bring the antiresonance frequency and the resonance frequency of the resonator close to each other.

Patent Document 1 discloses a configuration in which an anti-resonance frequency and a resonance frequency of a resonator are made closer by connecting an external capacitor and coil to a resonator made of a surface acoustic wave element.
JP-A-9-321573 JP-A-9-83282 (page 3, FIG. 1)

  However, in the configuration in which an external capacitor and coil are connected to the surface acoustic wave element as in the bandpass filter disclosed in Patent Document 1, the volume of the bandpass filter F1 is increased.

Patent Document 2 describes a surface acoustic wave element in which an insulating layer made of SiO ₂ is interposed between a comb-like electrode portion and a piezoelectric substrate. However, the insulating layer of the surface acoustic wave element described in Patent Document 2 is for compensating temperature characteristics of the surface acoustic wave element and reducing electromigration. For this reason, in the surface acoustic wave element described in Patent Document 2, the thickness of the insulating layer is as large as 1000 mm.

  An object of the present invention is to provide a surface acoustic wave device that can easily bring the antiresonance frequency and the resonance frequency close to each other without adding external parts.

The present invention relates to a surface acoustic wave device having a piezoelectric substrate and an electrode portion formed in a thin film on the piezoelectric substrate.
The electrode part has a comb-like electrode part and a connection part connected to the comb-like electrode part, and an insulating material layer is provided between the comb-like electrode part and the piezoelectric substrate. It is a feature.

  When the insulating material layer is interposed between the comb-like electrode portion and the piezoelectric substrate as in the present invention, the elastic surface in which the comb-like electrode portion is directly laminated on the piezoelectric substrate Compared to the wave element, the antiresonance frequency approaches the resonance frequency. In addition, in the present invention, since the difference between the anti-resonance frequency and the resonance frequency of the surface acoustic wave element can be reduced without adding an external coil or capacitor to the surface acoustic wave element, downsizing of the apparatus can be promoted.

In the surface acoustic wave device according to the present invention, the antiresonance frequency approaches the resonance frequency because the insulating material layer is interposed between the comb-shaped electrode portion and the piezoelectric substrate. presumably because the coefficient k ² becomes small.

  In the present invention, a reflector for reflecting surface waves generated on the surface of the piezoelectric substrate is provided on the piezoelectric substrate on the side of the comb-shaped electrode portion, and between the reflector and the piezoelectric substrate. It is preferable that an insulating material layer is provided.

In the present invention, the insulating material layer, for example, silicon oxide _(SiO 2), alumina _{(Al 2 O} 3), can be formed by any one or more of silicon nitride (Si ₃ N _4).

In the present invention, the thickness of the insulating material layer is preferably 5 nm or more and 20 nm or less.
Further, when the inter-center distance (pitch width) of the comb-tooth portion of the comb-shaped electrode portion is λ nm and the film thickness of the insulating material layer is Hnm, the normalized film thickness H / λ of the insulating material layer Is preferably 0.0025 or more and 0.01 or less.

  Furthermore, in the present invention, in order to prevent diffusion of oxygen contained in the piezoelectric substrate into the comb-shaped electrode portion and the reflector, either one or both of the comb-shaped electrode portion and the reflector are provided. It is preferable to have a base layer made of TiN.

  In the present invention, since the insulating material layer is interposed between the comb-like electrode portion and the piezoelectric substrate, the surface acoustic wave in which the comb-like electrode portion is directly laminated on the piezoelectric substrate. Compared to the element, the antiresonance frequency approaches the resonance frequency.

  In addition, in the present invention, since the difference between the anti-resonance frequency and the resonance frequency of the surface acoustic wave element can be reduced without adding an external coil or capacitor to the surface acoustic wave element, downsizing of the apparatus can be promoted.

  FIG. 1 is a plan view showing a resonator according to a first embodiment of the present invention and a high-frequency filter formed using the resonator. The resonator S11 and the resonator S12 are surface acoustic wave elements, and are connected as shown in FIG. 1 so that only a signal in a specific frequency band is output to the output port among the high-frequency signals input to the input port. A band pass filter F11 is configured.

  The resonators S11 and S12 are formed on the piezoelectric substrate 11 by forming a comb-like electrode portion 12 and a comb-like electrode portion 13 using a sputtering method, a plating method, or the like. The comb-like electrode portions 12 and the comb-like electrode portions 13 are alternately arranged with a predetermined interval in the X direction shown in the drawing.

  Further, a connection portion 14 is electrically connected to the comb-tooth electrode portion 12 and the comb-tooth electrode portion 13, and the resonator S <b> 11 and the resonator S <b> 12 are connected via the connection portion 14.

  One end A of the resonator S11 is connected to the input terminal in of the bandpass filter F11, and the other end B is connected to the output terminal out. One end A of the resonator 12 is connected to one end A of the resonator S11, and the other end B of the resonator S12 is connected to the ground potential via the terminal GND. In the present embodiment, the resonator S11 constitutes the first resonator group of the present invention, and the resonator S12 corresponds to the second resonator group of the present invention.

2 is a cross-sectional view of the resonator S11 shown in FIG. 1 taken along the alternate long and short dash line D1-D1 and viewed from the direction of the arrow. As shown in FIG. 2, an insulating material layer 16 is formed between the comb-like electrode portions 12 and 13 and the piezoelectric substrate 11. The dielectric constant of the insulating material layer 16 is 4 to 5. The insulating material layer 16 is made of, for example, silicon oxide (SiO ₂ ) (relative dielectric constant: 3.8), alumina (Al ₂ O ₃ ) (relative dielectric constant: 9.4), or silicon nitride (Si ₃ N ₄ ). It can form by 1 type (s) or 2 or more types.

  In the present embodiment, the comb-like electrode portions 12 and 13 and the reflectors 15 and 15 have a two-layer structure of a base layer 17 and a metal layer 18 laminated on the base layer 17. The underlayer 17 is made of, for example, titanium nitride (TiN). The metal layer 18 is formed of an Al alloy such as Al or AlSc alloy, or a Cu alloy such as Cu or AlCu alloy.

  When the underlayer 17 is provided between the metal layer 18 and the piezoelectric substrate 11 or the insulating material layer 16, the diffusion of oxygen or the like contained in the piezoelectric substrate 11 or the insulating material layer 16 is prevented and the metal layer 18 is deteriorated. Can be suppressed.

Further, a protective layer made of TiN or the like may be provided on the metal layer 18.
In addition, reflectors 15 and 15 for reflecting surface waves generated on the surface of the piezoelectric substrate 11 are provided on both sides of the comb-like electrode portions 12 and 13. In FIG. 1, the ends of the electrodes constituting the reflector 15 are opened. However, the ends of the electrodes constituting the reflector 15 may be short-circuited.

  When a high frequency signal is applied to the comb-like electrode portion 12 and the comb-like electrode portion 13, a surface acoustic wave is generated on the surface of the piezoelectric element 11, and this surface wave travels in the X direction shown in the figure and in a direction parallel to the X direction shown in the figure. To do. The surface wave is reflected by the reflectors 15 and 15 and returns to the comb-like electrode portions 12 and 13. The resonator (surface acoustic wave element) S11 and the resonator (surface acoustic wave element S12) have a resonance frequency and an antiresonance frequency, and the impedance is highest at the antiresonance frequency.

  The connection part 14 and the reflectors 15 and 15 may be formed with the same material as the comb-tooth shaped electrode parts 12 and 13, and may be formed with other electroconductive materials, such as Au.

  In the embodiment shown in FIGS. 1 and 2, the comb tooth portion 12a of the comb-like electrode portion 12 and the comb tooth portion 13a of the comb-like electrode portion 13 have the same width dimension W1, and the interval width P1 is also set. It is a constant value. Moreover, the comb tooth part 12a and the comb tooth part 13a cross | intersect with the length dimension of L1. The width dimension W1 is 0.3 μm or more and 1.5 μm or less, the interval width P1 is 0.6 μm or more and 1.5 μm or less, and the length dimension L1 is 16 μm or more and 200 μm or less. Further, the inter-center distance (pitch width) λ of the comb tooth portion 12a of the resonator (surface acoustic wave element) S11 is the same as the inter-center distance (pitch width) λ of the comb tooth portion 13a, and λ is 1.2 μm or more. 0 μm or less. The center distance (pitch width) λ is equal to the wavelength of the surface wave of the resonator (surface acoustic wave element). The comb-like electrode portions 12 and 13, the connection portion 14, and the reflectors 15 and 15 are formed by a thin film formation process such as a sputtering method or a vapor deposition method and a pattern formation by resist photolithography.

  FIG. 3 shows an equivalent circuit diagram of the bandpass filter F11 shown in FIG. The resonator S11 is equivalent to a resonator circuit including a capacitor C11, an inductor L11, a capacitor C13, and a capacitor C14. The series connection of the capacitor C11 and the inductor L11 reflects the electromechanical coupling of the surface acoustic wave element, and the resonance frequency of the resonator S11 is defined by the capacitance of the capacitor C11 and the inductance value of the inductor L11. A capacitor C13 connected in parallel to the capacitor C11 and the inductor L11 reflects the capacitance between the comb teeth of the comb-shaped electrode portion. Furthermore, the capacitor 14 connected in series with the capacitor C13 reflects the additional capacitance due to the insulating material layer 16 which is a feature of the present invention.

  On the other hand, the resonator S12 in which the comb-like electrode portions 12 and 13 are directly laminated on the piezoelectric substrate is equivalent to a resonator circuit including a capacitor C21, an inductor L21, and a capacitor C22. That is, the equivalent circuit of the resonator S12 is the same as the equivalent circuit of the conventional resonator.

  When the insulating material layer 16 is interposed between the comb-like electrode portions 12 and 13 of the resonator S11 and the piezoelectric substrate 11, the comb-like electrode portions 12 and 13 are directly laminated on the piezoelectric substrate 11. The antiresonance frequency approaches the resonance frequency as compared with the surface acoustic wave element. In addition, in the present invention, since the difference between the anti-resonance frequency and the resonance frequency of the surface acoustic wave element can be reduced without adding an external coil or capacitor to the surface acoustic wave element, downsizing of the apparatus can be promoted.

In the surface acoustic wave device of the present invention, the anti-resonance frequency approaches the resonance frequency because the insulating material layer 16 is interposed between the comb-like electrode portions 12 and 13 and the piezoelectric substrate 11. presumably because the electromechanical coupling coefficient k ² becomes small.

  Note that the capacitance between the comb-like electrode portions 12 and 13 via the piezoelectric substrate 11 of the resonator S11 (the combined capacitance of C13 and C14 in FIG. 3) is via the piezoelectric substrate 11 of the resonator S12. It is smaller than the electrostatic capacity (C22 in FIG. 3) between the comb-like electrode portions 12 and 13.

  In FIG. 1, an insulating material layer 16 is also provided between the reflectors 15 and 15 and the piezoelectric substrate 11. However, the piezoelectric substrate 11 may be directly laminated on the reflectors 15 and 15 without providing the insulating material layer 16 between the reflectors 15 and 15 and the piezoelectric substrate 11.

  In the present invention, the thickness of the insulating material layer 16 is preferably 5 nm or more and 20 nm or less. Further, when the inter-center distance (pitch width) of the comb-tooth portions 12a and 13a of the comb-tooth electrode portions 12 and 13 is λ nm and the film thickness of the insulating material layer 16 is Hnm, the insulating material layer 16 is normalized. The film thickness H / λ is preferably 0.0025 or more and 0.01 or less.

  The operation principle of the bandpass filter F11 will be described. FIG. 4A is a graph showing the frequency characteristics of the resonators S11 and S12. In FIG. 4A, the vertical axis represents the reactance X, and the horizontal axis represents the frequency f. The anti-resonance frequency far2 of the resonator S11 is larger than the anti-resonance frequency far1 of the resonator S12, and the resonance frequency fr2 of the resonator S11 and the anti-resonance frequency far1 of the resonator S12 overlap.

  For reference, the frequency characteristic of the resonator S1 mounted on the conventional bandpass filter shown in FIG. 18 is indicated by a dotted line. When the insulating material layer 16 is interposed between the comb-like electrode portions 12 and 13 of the resonator S11 and the piezoelectric substrate 11 (embodiment), the comb-like electrode portions 12 and 12 are disposed on the piezoelectric substrate 11. Compared to the surface acoustic wave element (conventional example) in which 13 is directly laminated, the antiresonance frequency far2 approaches the resonance frequency fr2. The resonance frequency fr2 is not changed from that of the conventional example. The resonance frequency fr1 and antiresonance frequency far1 of the resonator S12 are the same as those of the resonator S2 of the conventional bandpass filter F1.

  The frequency characteristic of the bandpass filter F11 formed by connecting the resonator S11 and the resonator S12 as shown in the figure is shown by the graph in FIG. 4B. The resonance frequency fr2 of the resonator S11, that is, the anti-resonance frequency far1 of the resonator S12 becomes the center frequency of the pass band of the bandpass filter F11. In addition, the attenuation of the bandpass filter F11 increases near the resonance frequency fr1 of the resonator S12 and the antiresonance frequency far2 of the resonator S11, and is below the resonance frequency fr1 of the resonator S12 and above the antiresonance frequency far2 of the resonator S11. Is the attenuation band.

  Since the bandpass filter F11 of the present embodiment can bring the antiresonance frequency far2 and the resonance frequency fr2 of the resonator S11 close to each other, the frequency outside the passband can be steeply and sufficiently attenuated.

  FIG. 5 is a plan view showing a band-pass filter as a high-frequency filter according to the second embodiment of the present invention.

  This bandpass filter F12 is also formed by connecting a resonator S21, a resonator S22, and a resonator S23, which are surface acoustic wave elements, like the bandpass filter F11 shown in FIG. The resonator S21, which is a surface acoustic wave element, has the same configuration as the resonator S11 in FIG. 1, and the resonator S22 and the resonator S23 have the same configuration as the resonator S12 in FIG. Therefore, in FIG. 5, the resonator S21 is the resonator of the present invention, and the comb-like electrode portion 12 and the comb-like electrode portion 13 of the resonator S21 and the reflectors 15 and 15 and the piezoelectric substrate 11 are insulated. A material layer 16 is provided.

  The resonators S21, S22, and S23 are also formed on the piezoelectric substrate 11 by forming the comb-like electrode portion 12 and the comb-like electrode portion 13 using a sputtering method, a plating method, or the like. The comb-like electrode portions 12 and the comb-like electrode portions 13 are alternately arranged with a predetermined interval in the X direction shown in the drawing. The sectional view of the resonator S21 taken along line D1-D1 and viewed from the direction of the arrow is the same as the sectional view shown in FIG.

  Further, the comb-like electrode portion 13 of the resonator S21 and the comb-like electrode portion 12 of the resonator S22 are electrically connected via the connection portion 14, and resonate with the comb-like electrode portion 12 of the resonator S21. The comb-like electrode portion 12 of the vessel S23 is electrically connected via the connection portion 20.

  One end A of the resonator S21 is connected to the input terminal in of the bandpass filter F12, and the other end B is connected to the output terminal out. One end A of the resonator S22 is connected to one end A of the resonator S21, and the other end B of the resonator S22 is connected to the ground potential via the terminal GND. One end A of the resonator S23 is connected to the other end A of the resonator S21, and the other end B of the resonator S23 is connected to the ground potential via the terminal GND. In the present embodiment, the resonator S21 constitutes the first resonator group of the present invention, and the resonator S22 and the resonator S23 constitute the second resonator group of the present invention.

  Of the high-frequency signal input to the input port side consisting of the terminal in and the terminal GND of the bandpass filter F12, only a signal in a specific frequency band is output to the output port consisting of the terminal out and the terminal GND.

  FIG. 6 shows an equivalent circuit diagram of the bandpass filter F12 shown in FIG. The bandpass filter F12 is a so-called π-type bandpass filter.

  The resonator S21 is equivalent to a resonator circuit including a capacitor C11, an inductor L11, a capacitor C13, and a capacitor C14. The capacitor 14 connected in series with the capacitor 13 reflects the additional capacitance due to the insulating material layer 16 which is a feature of the present invention.

  On the other hand, the resonator S22 and the resonator S23 in which the comb-like electrode portions 12 and 13 are directly laminated on the piezoelectric substrate are a resonator circuit including a capacitor C21, an inductor L21 and a capacitor C22, a capacitor C31, and an inductor L31, respectively. And a resonator circuit composed of the capacitor C32. That is, the equivalent circuit of the resonators S22 and S23 is the same as the equivalent circuit of the conventional resonator.

  Also in the present embodiment, the bandpass filter F12 of the present embodiment can bring the anti-resonance frequency far and the resonance frequency fr of the resonator S21 close to each other, so that the frequency outside the passband can be attenuated steeply and sufficiently.

  FIG. 7 is a plan view showing a band-pass filter as a high-frequency filter according to the third embodiment of the present invention.

  The bandpass filter F13 is also formed by connecting a resonator S31, a resonator S32, and a resonator S33, which are surface acoustic wave elements. The resonators S31 and S33, which are surface acoustic wave elements, have the same configuration as the resonator S11 in FIG. 1, and the resonator S32 has the same configuration as the resonator S12 in FIG. Therefore, in FIG. 5, the resonators S31 and S33 are the resonators of the present invention, and the comb-like electrode portions 12 and the comb-like electrode portions 13 of the resonators S31 and S33 and the reflectors 15 and 15 and the piezoelectric substrate 11 are provided. An insulating material layer 16 is provided therebetween.

  The resonators S31, S32, and S33 are also formed on the piezoelectric substrate 11 by forming the comb-like electrode portion 12 and the comb-like electrode portion 13 using a sputtering method, a plating method, or the like. The comb-like electrode portions 12 and the comb-like electrode portions 13 are alternately arranged with a predetermined interval in the X direction shown in the drawing. The sectional view of the resonator S31 and the resonator S32 taken along the line D1-D1 and viewed from the direction of the arrow is the same as the sectional view shown in FIG.

  The comb-like electrode part 12 of the resonator S31, the comb-like electrode part 12 of the resonator S32, and the comb-like electrode part 13 of the resonator S33 are electrically connected via the connection part 14.

  One end A of the resonator S31 is connected to the input terminal in of the bandpass filter F13, and the other end B is connected to one end A of the resonator S33. The other end B of the resonator S33 is connected to the output terminal out. One end A of the resonator S32 is connected to the other end B of the resonator S31 and one end A of the resonator S33, and the other end B of the resonator S32 is connected to the ground potential via the terminal GND. In the present embodiment, the resonator S31 and the resonator S33 constitute a first resonator group of the present invention, and the resonator S32 corresponds to a second resonator group of the present invention.

  Of the high-frequency signal input to the input port P1 side composed of the terminal in and the terminal GND of the bandpass filter F13, only a signal in a specific frequency band is output to the output port P2 composed of the terminal out and the terminal GND.

  FIG. 8 shows an equivalent circuit diagram of the bandpass filter F13 shown in FIG. This bandpass filter F13 is a so-called T-type bandpass filter.

  The resonator S31 is equivalent to a resonator circuit composed of a capacitor C41, an inductor L41, a capacitor C43 and a capacitor C44, and the resonator S33 is equivalent to a resonator circuit composed of a capacitor C61, an inductor L61, a capacitor C63 and a capacitor C64. The capacitor C44 connected in series to the capacitor C43 and the capacitor C64 connected in series to the capacitor C63 reflect the additional capacitance due to the insulating material layer 16 that is a feature of the present invention.

  On the other hand, the resonator S32 in which the comb-like electrode portions 12 and 13 are directly laminated on the piezoelectric substrate is equivalent to a resonator circuit including a capacitor C51, an inductor L51, and a capacitor C52. That is, the equivalent circuit of the resonator S32 is the same as the equivalent circuit of the conventional resonator.

  Also in this embodiment, the bandpass filter F13 of this embodiment can bring the resonance frequency fr of the resonator S31 and the resonator S33 close to the anti-resonance frequency far, so that the frequency outside the passband is steeply and sufficiently attenuated. Can do.

  Further, by changing the capacitance between the comb-like electrode portions 12 and 13 by changing the film thickness of the insulating material layer 16 of the resonator S31 and the insulating material layer 16 of the resonator S32, it is shown in FIG. A bandpass filter having such a frequency characteristic can also be configured.

  FIG. 10 is a plan view showing a band-pass filter as a high-frequency filter according to the fourth embodiment of the present invention.

  This band pass filter F14 is also formed by connecting the resonator S41, the resonator S42, the resonator S43, and the resonator S44. The resonators S41 and S43, which are surface acoustic wave elements, have the same configuration as the resonator 11 in FIG. 1, and the resonator S42 and the resonator S44 have the same configuration as the resonator S12 in FIG. Therefore, in FIG. 5, the resonators S41 and S43 are the resonators of the present invention, and the comb-like electrode portions 12 and comb-like electrode portions 13 of the resonators S41 and S43 and the reflectors 15 and 15 and the piezoelectric substrate 11 are provided. An insulating material layer 16 is provided therebetween.

  The resonators S41, S42, S43, and S44 are formed by forming the comb-like electrode portion 12 and the comb-like electrode portion 13 on the piezoelectric substrate 11 using a sputtering method, a plating method, or the like. Yes. The comb-like electrode portions 12 and the comb-like electrode portions 13 are alternately arranged with a predetermined interval in the X direction shown in the drawing. The sectional view of the resonator S41 and the resonator S43 taken along the line D1-D1 and viewed from the arrow direction is the same as the sectional view shown in FIG.

  The comb-like electrode part 12 of the resonator S41, the comb-like electrode part 12 of the resonator S42, and the comb-like electrode part 13 of the resonator S43 are electrically connected via the connection part 14. The comb-like electrode portion 12 of the resonator S43 and the comb-like electrode portion 12 of the resonator S44 are electrically connected via the connection portion 21.

  One end A of the resonator S41 is connected to the input terminal in of the bandpass filter F14, and the other end B is connected to one end A of the resonator S43 and one end A of the resonator S42. The other end B of the resonator S43 is connected to the output terminal out. The other end B of the resonator S42 is connected to the ground potential via the terminal GND. One end A of the resonator S44 is connected to the other end B of the resonator S43, and the other end B is connected to the ground potential via the terminal GND.

  In the present embodiment, the resonator S41 and the resonator S43 constitute a first resonator group of the present invention, and the resonator S42 and the resonator S44 constitute a second resonator group of the present invention.

  Of the high-frequency signal input to the input port P1 side composed of the terminal in and the terminal GND of the bandpass filter F14, only a signal in a specific frequency band is output to the output port P2 composed of the terminal out and the terminal GND.

  FIG. 11 is a plan view showing a resonator according to the fifth embodiment of the present invention and a high-frequency filter formed using the resonator. The bandpass filter F15 is formed by connecting a resonator S51 and a resonator S52, which are surface acoustic wave elements.

  The resonators S51 and S52 are formed on the piezoelectric substrate 11 by forming the comb-like electrode portion 12 and the comb-like electrode portion 13 using a sputtering method, a plating method, or the like. The comb-like electrode portions 12 and the comb-like electrode portions 13 are alternately arranged with a predetermined interval in the X direction shown in the drawing.

  A connecting portion 14 is electrically connected to the comb-shaped electrode portion 12 and the comb-shaped electrode portion 13, and the resonator S 51 and the resonator S 52 are connected via the connecting portion 14.

  One end A of the resonator S51 is connected to the input terminal in of the bandpass filter F15, and the other end B is connected to the output terminal out. The other end B of the resonator S51 is connected to one end A of the resonator S52, and the other end B of the resonator S52 is connected to the ground potential via the terminal GND. In the present embodiment, the resonator S51 constitutes the first resonator group of the present invention, and the resonator S52 corresponds to the second resonator group of the present invention. FIG. 12 shows an equivalent circuit diagram of the bandpass filter F15 shown in FIG.

  Also in this embodiment, the bandpass filter F15 can bring the resonance frequency fr and the antiresonance frequency far of the resonator S51 close to each other, so that the frequency outside the passband can be attenuated steeply and sufficiently.

  In the resonator (surface acoustic wave element) according to the embodiment of the present invention described above, the insulating material layer 16 is also provided between the reflectors 15 and 15 and the piezoelectric substrate 11. However, the piezoelectric substrate 11 may be directly laminated on the reflectors 15 and 15 without providing the insulating material layer 16 between the reflectors 15 and 15 and the piezoelectric substrate 11.

The film thickness of the insulating material layer of the surface acoustic wave element (resonator) of the present invention in which an insulating material layer is provided between the piezoelectric substrate and the comb-like electrode portion, the capacitance Co of the resonator, and the electric machine The relationship between the coupling coefficient k ² and the difference between the antiresonance frequency far and the resonance frequency fr was examined.

First, an insulating material layer made of silicon oxide (SiO ₂ ) is formed on a piezoelectric substrate by a sputtering method, and a comb-like electrode portion and a reflective electrode are formed on the insulating material layer using a conductive material. To form a vessel.

  The surface acoustic wave element (resonator) of this example has the same shape as the resonator S11 shown in FIG. The measurement was performed on one surface acoustic wave element (resonator). Each dimension of the comb-like electrode part and the reflector is shown below.

The width dimension W1 of the comb tooth portion of the comb-like electrode part and the width dimension W2 of each strip of the reflector: W1 = W2 = 0.4 μm to 0.545 μm

Interdigital dimension P1 of the comb-like electrode part and the standard dimension P2 of each strip of the reflector: P1 = P2 = 0.4 μm to 0.545 μm

Intersection length dimension L1 of comb tooth part 13a and comb tooth part 14a
: L1 = 33 × (wavelength λ of surface acoustic wave) = 40 × 2 × (W1 + P1)

The film thickness of the comb-like electrode part and the film thickness of each strip of the reflector: H1 = 0.095 μm
Number of comb teeth of comb-like electrode part: 200 Number of strips of reflector: 50

Distance L2 between comb-like electrode portion and reflector: L2 = P1 = P2 = 0.4 μm to 0.545 μm

The material of the piezoelectric substrate is LiTaO _3. In this embodiment, the frequency is set to 1.7 GHz to 2.1 GHz. Further, the comb-like electrode portion and the reflector are formed of a Cu _97.0 Ag _3.0 alloy (subscript is a mass%).

FIG. 13 is a graph showing the relationship between the thickness of the insulating material layer (SiO ₂ thickness) and the electromechanical coupling coefficient k ² of the surface acoustic wave element.

The graph of FIG. 14 shows the relationship between the normalized film thickness (H (SiO ₂ ) / λ) of the insulating material layer and the electromechanical coupling coefficient k ² of the surface acoustic wave element. The normalized film thickness H / λ of the insulating material layer is obtained by dividing the film thickness Hnm of the insulating material layer 16 of the comb-shaped electrode portions 12 and 13 by the center-to-center distance (pitch width) λnm of the comb-tooth portions. Value. The inter-center distance (pitch width) λ of the comb teeth is equal to the wavelength of the surface acoustic wave propagating on the surface of the piezoelectric substrate.

From the results of FIG. 13, it is understood that the electromechanical coefficient k ² of about SAW device film thickness provided the insulating layer is increased between the interdigital transducer electrode portions and the piezoelectric substrate becomes linearly smaller .

The results of FIG. 14 shows that the insulating electromechanical coupling of surface acoustic wave device as standardized thickness H / lambda becomes large material layer coefficient k ² becomes linearly smaller.

FIG. 15 is a graph showing the relationship between the film thickness of the insulating material layer (SiO ₂ film thickness) and the capacitance Co between the comb-like electrode portions. FIG. 16 is a graph showing the relationship between the normalized film thickness H / λ of the insulating material layer and the capacitance Co between the comb-shaped electrode portions.

  The capacitance Co between the comb-like electrode portions is the total capacitance between the comb-like electrode portions 12 and 13 via the piezoelectric substrate 11 and the insulating material layer 16 in FIG. 2 (C13 in FIG. 3). And the combined capacitance of C14).

  From the result of FIG. 15, as the film thickness of the insulating material layer provided between the comb-shaped electrode portion and the piezoelectric substrate increases, the capacitance Co between the surface acoustic wave element and the comb-shaped electrode portion becomes linear. It turns out that it becomes small automatically. Also, the result of FIG. 16 shows that the capacitance Co between the surface acoustic wave element and the comb-like electrode portion linearly decreases as the normalized film thickness H / λ of the insulating material layer increases. .

The graph of FIG. 17 is a value obtained by dividing the difference between the normalized film thickness (H (SiO ₂ ) / λ) of the insulating material layer and the antiresonance frequency far and the resonance frequency fr of the surface acoustic wave element (resonator) by the resonance frequency. It is a graph which shows the relationship with (DELTA) f / fr.

  From the results of FIG. 17, it can be seen that Δf / fr decreases linearly as the normalized film thickness H / λ of the insulating material layer increases.

  By reducing Δf / fr of the resonator, the frequency outside the pass band of the bandpass filter formed using this resonator can be sharply attenuated.

As the normalized film thickness H / λ of the insulating material layer increases, Δf / fr decreases linearly, as shown in FIGS. 13 and 14, the electromechanical coupling coefficient k ^{2 of the} surface acoustic wave device. This is considered to be because of the decrease.

  As shown in FIGS. 15 and 16, by providing an insulating material layer between the comb-like electrode portion and the piezoelectric substrate, Δf / fr of the surface acoustic wave element (resonator) is reduced and elastic at the same time. Capacitance Co between the surface wave element and the comb-like electrode portion can be reduced.

The present invention is characterized in that Δf / fr of the surface acoustic wave element (resonator) is reduced.
However, if the thickness of the insulating material layer between the comb-like electrode portion and the piezoelectric substrate and the normalized thickness are too large, the efficiency of exciting the surface acoustic wave on the surface of the piezoelectric substrate decreases. For this reason, in the present invention, the upper limit of the thickness of the insulating material layer is preferably 20 nm or less, and the upper limit of the normalized film thickness is preferably 0.01 or less.

The top view which shows 1st Embodiment of the resonator (surface acoustic wave element) of this invention and the band pass filter formed using this resonator, FIG. 1 is a partial cross-sectional view of the surface acoustic wave element of FIG. 1 is an equivalent circuit diagram of the bandpass filter shown in FIG. The figure which shows the frequency characteristic of the resonator shown by FIG. The figure which shows the frequency characteristic of the band pass filter shown by FIG. The top view which shows 2nd Embodiment of the resonator (surface acoustic wave element) of this invention and the band pass filter formed using this resonator, FIG. 5 is an equivalent circuit diagram of the bandpass filter shown in FIG. The top view which shows 3rd Embodiment of the resonator (surface acoustic wave element) of this invention and the band pass filter formed using this resonator, FIG. 7 is an equivalent circuit diagram of the bandpass filter shown in FIG. The figure which shows an example of the frequency characteristic of the band pass filter shown by FIG. The top view which shows 4th Embodiment of the resonator (surface acoustic wave element) of this invention and the band pass filter formed using this resonator, The top view which shows 5th Embodiment of the resonator (surface acoustic wave element) of this invention and the band pass filter formed using this resonator, FIG. 11 is an equivalent circuit diagram of the bandpass filter shown in FIG. A graph showing the relationship between the film thickness of the insulating material layer (SiO ₂ film thickness) and the electromechanical coupling coefficient k ² of the surface acoustic wave element; A graph showing the relationship between the normalized film thickness (H (SiO ₂ ) / λ) of the insulating material layer and the electromechanical coupling coefficient k ² of the surface acoustic wave element; A graph showing the relationship between the film thickness of the insulating material layer (SiO ₂ film thickness) and the capacitance Co between the comb-like electrode portions; A graph showing the relationship between the normalized film thickness H / λ of the insulating material layer and the capacitance Co between the comb-like electrode portions; The normalized thickness of the insulating material layer (H (SiO ₂ ) / λ) and the value Δf / fr obtained by dividing the difference between the anti-resonance frequency far and the resonance frequency fr of the surface acoustic wave element (resonator) by the resonance frequency A graph showing the relationship, Plan view of a conventional resonator (surface acoustic wave element) and a bandpass filter formed using this resonator, FIG. 18 is an equivalent circuit diagram of the bandpass filter shown in FIG. FIG. 18 is a partial cross-sectional view of the surface acoustic wave element of FIG. The figure which shows the frequency characteristic of the resonator shown by FIG. The figure which shows the frequency characteristic of the band pass filter shown by FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Piezoelectric substrate 12, 13 Comb-tooth shaped electrode part 14 Connection electrode part 15 Reflector 16 Insulating material layer S11, S12 Resonator (surface acoustic wave element)
F11 bandpass filter

Claims (6)

In a surface acoustic wave device having a piezoelectric substrate and an electrode portion formed in a thin film on the piezoelectric substrate,
The electrode part has a comb-like electrode part and a connection part connected to the comb-like electrode part, and an insulating material layer is provided between the comb-like electrode part and the piezoelectric substrate. A surface acoustic wave device.   A reflector for reflecting surface waves generated on the surface of the piezoelectric substrate is provided on the piezoelectric substrate on the side of the comb-like electrode portion, and an insulating material is provided between the reflector and the piezoelectric substrate. The surface acoustic wave device according to claim 1, further comprising a layer. The insulating material layer is formed of one or more of silicon oxide (SiO ₂ ), alumina (Al ₂ O ₃ ), and silicon nitride (Si ₃ N ₄ ). Surface acoustic wave element.   The surface acoustic wave device according to any one of claims 1 to 3, wherein the insulating material layer has a thickness of 5 nm to 20 nm.   When the inter-center distance (pitch width) of the comb teeth of the comb-like electrode portion is λ nm and the thickness of the insulating material layer is Hnm, the normalized thickness H / λ of the insulating material layer is 0. 5. The surface acoustic wave element according to claim 1, wherein the surface acoustic wave element is not less than 0.01 and not more than 0.01.   6. The surface acoustic wave device according to claim 1, wherein either one or both of the comb-like electrode portion and the reflector have a base layer made of TiN.

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