JP6198536B2 - Elastic wave device and electronic device using the same - Google Patents

Description

  The present invention relates to an acoustic wave device and an electronic device using the same.

  As shown in FIG. 7, a conventional acoustic wave element 101 includes a piezoelectric substrate 102, an IDT electrode that is formed on the piezoelectric substrate 102 and has an electrode finger 103 that excites a Rayleigh wave having a wavelength λ as a main acoustic wave, A dielectric film 104 formed so as to cover the electrode finger 103 of the IDT electrode is provided above the piezoelectric substrate 102.

  As the dielectric film 104, silicon oxide is used. Since this silicon oxide has a frequency temperature coefficient opposite to that of the frequency temperature coefficient (TCF) of the piezoelectric substrate 102, the frequency temperature characteristic of the acoustic wave device 101 can be improved.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

International Publication No. 2005/034347

  In the conventional acoustic wave device 101, the first dielectric film 104 is made of an oxide, so that, for example, when the first dielectric film 104 is formed on the electrode finger 103 of the IDT electrode, the oxidation of the electrode finger 103 on the IDT electrode is performed. Corrosion due to was an issue.

  Therefore, an object of the present invention is to suppress electrode finger corrosion in an IDT electrode.

  In order to achieve the above object, an acoustic wave device of the present invention includes a piezoelectric substrate, an IDT electrode that is formed above the piezoelectric substrate and has an electrode finger that excites a major acoustic wave, and covers the electrode finger above the piezoelectric substrate. A first dielectric film made of oxide, formed on the electrode finger, a second dielectric film made of non-oxide formed between the electrode finger and the first dielectric film, a piezoelectric substrate and an electrode And a third dielectric film formed between the fingers, and the velocity of the transverse wave propagating through the third dielectric film is faster than the velocity of the main elastic wave propagating through the piezoelectric substrate. The first dielectric film and the third dielectric film are in contact with each other.

  The acoustic wave device of the present invention suppresses oxidation of the electrode finger when the first dielectric film is formed on the electrode finger, for example, by the second dielectric film made of non-oxide formed on the electrode finger. The That is, corrosion of the electrode finger in the IDT electrode is suppressed.

  In the acoustic wave device of the present invention, the second dielectric film is formed by using the first dielectric film as a dielectric film in contact with the third dielectric film between adjacent electrode fingers of the IDT electrode. The frequency fluctuation of the main elastic wave is suppressed. As a result, it is possible to prevent variation in characteristics of the acoustic wave device due to the frequency fluctuation.

1 is a schematic cross-sectional view of an acoustic wave device according to a first embodiment of the present invention. Cross-sectional schematic diagram of comparative acoustic wave device Sectional schematic diagram of another elastic wave device according to the first embodiment of the present invention Sectional schematic diagram of still another acoustic wave device according to the first embodiment of the present invention. 1 is a block diagram of an antenna duplexer using an acoustic wave element according to Embodiment 1 of the present invention. 1 is a block diagram of an electronic device using the acoustic wave device according to the first embodiment of the present invention. Cross-sectional schematic diagram of a conventional acoustic wave device

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the acoustic wave device according to Embodiment 1 (cross-sectional schematic view perpendicular to the extending direction of the electrode fingers of the IDT electrode).

  In FIG. 1, an acoustic wave element 1 includes a piezoelectric substrate 2, an IDT electrode that is formed on the piezoelectric substrate 2 and has an electrode finger 3 that excites a surface wave such as a Rayleigh wave as a main acoustic wave, and a piezoelectric substrate 2. And a first dielectric film 4 made of an oxide formed so as to cover the electrode finger 3. Here, the pitch of the electrode fingers 3 is P. In addition, the acoustic wave device 1 includes a second dielectric film 6 made of a non-oxide formed between the electrode finger 3 and the first dielectric film 4 on the electrode finger 3. Further, the acoustic wave device 1 includes a third dielectric film 7 formed between the piezoelectric substrate 2 and the electrode finger 3. The velocity S of the transverse wave propagating through the third dielectric film 7 is faster than the velocity of the main elastic wave propagating through the piezoelectric substrate 2. Accordingly, the electromechanical coupling coefficient of the acoustic wave element 1 can be adjusted to be smaller while suppressing loss due to the third dielectric film 7, and the filter has an optimum pass bandwidth for a communication system such as a mobile phone to be used. Can be configured.

  Further, the first dielectric film 4 and the third dielectric film 7 are in contact with each other between adjacent electrode fingers 3 in the IDT electrode.

  When the first dielectric film 4 is formed on the electrode finger 3 by the second dielectric film 6 made of a non-oxide formed on the electrode finger 3, for example, the acoustic wave element 1 oxidizes the electrode finger 3. Is suppressed. That is, corrosion of the electrode finger 3 in the IDT electrode is suppressed.

  In the acoustic wave device 1, the second dielectric film 6 is formed by using the first dielectric film 4 as the dielectric film in contact with the third dielectric film between the adjacent electrode fingers 3 in the IDT electrode. The frequency fluctuation of the main elastic wave that occurs is suppressed. Thereby, the characteristic dispersion | variation in the elastic wave element 1 by this frequency fluctuation | variation can be prevented.

The piezoelectric substrate 2 is, for example, a piezoelectric substrate that propagates a Rayleigh wave as a main elastic wave, but may be a piezoelectric substrate that propagates other elastic waves such as an SH wave (Shear Horizontal wave) or a bulk wave as a main elastic wave. good. However, “the effect of suppressing the frequency fluctuation of the main elastic wave by providing the first dielectric film 4 in contact with the third dielectric film 7 between the electrode fingers 3” is that the piezoelectric substrate 2 propagates the Rayleigh wave as the main elastic wave. This is noticeable when the piezoelectric substrate is used. When the piezoelectric substrate 2 is a piezoelectric substrate that propagates Rayleigh waves as main elastic waves, the piezoelectric substrate 2 has a cut angle and a main elastic wave propagation direction represented by Euler angles (φ, θ, ψ), and (φ, θ, ψ). Lithium niobate (LiNbO ₃ ) -based substrate satisfying (ψ) = (− 10 ° ≦ φ ≦ 10 °, 33 ° ≦ θ ≦ 43 °, −10 ° ≦ ψ ≦ 10 °), or (φ, θ, φ ) = (− 1 ° ≦ φ ≦ 1 °, 113 ° ≦ θ ≦ 135 °, −5 ° ≦ ψ ≦ 5 °) or (φ, θ, ψ) = (− 7.5 ° ≦ This is a lithium tantalate (LiTaO ₃ ) -based substrate with φ ≦ 2.5 °, 111 ° ≦ θ ≦ 121 °, −2.5 ° ≦ ψ ≦ 7.5 °.

The piezoelectric substrate 2 is a quartz crystal, lithium niobate (LiNbO ₃ ) -based, lithium tantalate (LiTaO ₃ ) -based, or potassium niobate (KNbO ₃ ) -based substrate, or thin film having Euler angles other than those described above. Other piezoelectric media may be used. For example, the piezoelectric substrate 2 is a -25 ° to 25 ° rotated Y-cut lithium niobate that propagates SH waves or Love waves, or a 25 ° to 50 ° rotated Y-cut lithium tantalate that propagates SH waves or Love waves. It may be a substrate.

  The IDT electrode constitutes a resonator or the like disposed on the piezoelectric substrate 2 so that the electrode fingers 3 of the comb-shaped electrode paired when viewed from above the acoustic wave element 1 are engaged with each other. The electrode finger 3 of the IDT electrode is, for example, a single metal made of aluminum, copper, silver, gold, titanium, tungsten, molybdenum, platinum, or chromium, an alloy containing these as a main component, or a laminated structure thereof. In the case where the electrode finger 3 of the IDT electrode has a laminated structure, the electrode finger 3 of the IDT electrode is provided on the Mo electrode layer, with the Mo electrode layer mainly composed of molybdenum in order from the piezoelectric substrate 2 side as an example. And an Al electrode layer mainly composed of Al. Since the Mo electrode layer has a relatively high density, the main elastic wave can be confined on the surface of the piezoelectric substrate 2, and the electrical resistance of the electrode finger 3 of the IDT electrode can be lowered by the Al electrode layer. This Mo electrode layer may be mixed with a mixture of silicon or the like, and the Al electrode layer may be mixed with a mixture of magnesium, copper, silicon or the like. Thereby, the power durability of the electrode finger 3 of the IDT electrode can be improved.

  The total film thickness of the electrode fingers 3 of the IDT electrode is 0.05λ × b / a or more and 0.15λ × b / a or less, where the total density b of the electrode fingers 3 of the IDT electrode is a and the density of aluminum is a. It is desirable that Here, λ is a wavelength determined by twice the pitch P of the electrode fingers 3 of the IDT electrode. At this time, the main acoustic wave can be concentrated on the surface of the acoustic wave element 1.

The first dielectric film 4 is an inorganic insulating film made of an oxide. The first dielectric film 4 is, for example, a medium in which the velocity of the transverse wave propagating through the first dielectric film 4 is slower than the velocity of the main elastic wave excited by the electrode finger 3 of the IDT electrode. For example, silicon oxide (SiO ₂ ) is mainly used. It consists of a medium as a component. This silicon oxide has a frequency temperature coefficient opposite in sign to the frequency temperature coefficient (TCF: Temperature Coefficient of Frequency) of the piezoelectric substrate 2. By using this silicon oxide as the first dielectric film 4, the frequency temperature characteristics of the acoustic wave device 1 can be improved.

  When the first dielectric film 4 is silicon oxide, the film thickness is set so that the absolute value of the frequency temperature characteristic of the main elastic wave excited by the electrode finger 3 of the IDT electrode is not more than a predetermined value (40 ppm / ° C.). ing. The film thickness of the first dielectric film 4 in the present embodiment refers to the first dielectric film 4 from the boundary between the first dielectric film 4 and the third dielectric film 7 between the electrode fingers 3 of adjacent IDT electrodes. The distance H of the upper surface of The film thickness of the first dielectric film 4 made of silicon oxide satisfying the predetermined value is not less than 0.2λ and not more than 0.5λ.

  The second dielectric film 6 is an inorganic insulating film made of a non-oxide. Thereby, when the 1st dielectric film 4 is formed on the electrode finger 3, the oxidation of the electrode finger 3 is suppressed. That is, corrosion of the electrode finger 3 is suppressed. This effect is prominent when the second dielectric film 6 is an inorganic insulating film made of a nitride such as silicon nitride or a carbide such as silicon carbide. Further, the second dielectric film 6 is, for example, a medium in which the velocity of the transverse wave propagating through the medium is faster than the velocity of the main elastic wave excited by the electrode finger 3 of the IDT electrode, or the velocity of the transverse wave propagating through the first dielectric film 4. A faster medium, for example, a medium mainly composed of diamond film, silicon nitride, silicon oxynitride, aluminum nitride, or aluminum oxide.

The third dielectric film 7 is made of a medium in which the velocity of the transverse wave propagating through the third dielectric film 7 is faster than the velocity of the main elastic wave propagating through the piezoelectric substrate 2. Accordingly, the electromechanical coupling coefficient of the acoustic wave element 1 can be adjusted to be smaller while suppressing loss due to the third dielectric film 7, and the filter has an optimum pass bandwidth for a communication system such as a mobile phone to be used. Can be configured. When the piezoelectric substrate 2 is made of quartz, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or potassium niobate (KNbO ₃ ), aluminum oxide (Al ₂ ) is used as the third dielectric film 7. O ₃ ), diamond film, silicon nitride, silicon oxynitride, aluminum nitride, titanium nitride, or the like may be employed.

The third dielectric film 7 may be a medium whose dielectric constant is smaller than that of the piezoelectric substrate 2. Thereby, the electromechanical coupling coefficient of the acoustic wave element 1 can be adjusted to be smaller, and a filter having a pass band optimum for a communication system such as a mobile phone to be used can be configured. When the piezoelectric substrate 2 is lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or potassium niobate (KNbO ₃ ), aluminum oxide (Al ₂ O ₃ ) is used as the third dielectric film 7. ), Diamond film, silicon nitride, silicon oxynitride, aluminum nitride, or the like may be employed.

  FIG. 2 is a schematic cross-sectional view (cross-sectional schematic view perpendicular to the extending direction of the electrode fingers of the IDT electrode) of the acoustic wave element 60 of the comparative example. The elastic wave device 60 of the comparative example has the third dielectric film 7 on the piezoelectric substrate 2, and has the electrode finger 3 that excites the elastic wave on the third dielectric film 7, and the electrode finger 3 is formed. A first dielectric made of oxide so as to cover the second dielectric films 5, 6, having the second dielectric films 5, 6 made of non-oxide on the third dielectric film 7 and the electrode finger 3 that are not It has a membrane 4.

  The elastic wave device 1 according to the first exemplary embodiment of the present invention can prevent variations in electrical characteristics due to frequency fluctuations as compared with the elastic wave device 60 of the comparative example.

  FIG. 3 is a cross-sectional schematic diagram (cross-sectional schematic diagram perpendicular to the extending direction of the electrode finger of the IDT electrode) of another acoustic wave element 70 in the first exemplary embodiment. As shown in FIG. 3, in the other acoustic wave element 70, the second dielectric film 6 is preferably formed also on the side surface of the electrode finger 3 of the IDT electrode. Thereby, the protective effect to the electrode finger 3 by the 2nd dielectric film 6 can be heightened, and the oxidation of the electrode finger 3 is suppressed.

  Further, it is desirable that the film thickness of the second dielectric film 6 on the electrode finger 3 is larger than the film thickness of the second dielectric film 6 on the side surface of the electrode finger 3. Thereby, the protective effect to the electrode finger 3 by the 2nd dielectric film 6 can further be heightened, and while the oxidation of the electrode finger 3 is suppressed, the suppression effect of the frequency fluctuation of the main elastic wave by the 2nd dielectric film 6 is suppressed. Can be increased.

  FIG. 4 is a schematic cross-sectional view of another acoustic wave element 80 according to Embodiment 1 (cross-sectional schematic view perpendicular to the extending direction of the electrode fingers of the IDT electrode). As shown in FIG. 4, the second dielectric film 6 formed on the side surface of the electrode finger 3 of the IDT electrode is formed so as to cover a partial region of the side surface from above the side surface. May be. Thereby, the effect of suppressing the frequency fluctuation of the main elastic wave by the second dielectric film 6 can be further enhanced, and the oxidation of the electrode finger 3 can be suppressed.

  FIG. 5 is a circuit block diagram of the antenna duplexer 10 using the acoustic wave element 1 of the present embodiment. As shown in FIG. 5, the antenna duplexer 10 includes a first filter 11 having a first pass band and a second filter 12 having a second pass band higher than the first pass band.

  In FIG. 5, an antenna duplexer 10 is, for example, an antenna duplexer for band 8 of the UMTS system. And a second filter 12 which is a reception filter having a pass band (925 MHz to 960 MHz). The first filter 11 is connected between the input terminal 14 and the antenna terminal 15, receives a transmission signal from the input terminal 14, and outputs it from the antenna terminal 15. The first filter 11 is configured by connecting a series resonator 13 and a parallel resonator 17 having a resonance frequency lower than the antiresonance frequency of the series resonator 13 in a ladder shape. Further, the ground 20 side of the parallel resonator 17 is connected by a ground terminal 19, and the first filter 11 includes an inductor 18 connected between the ground terminal 19 and the ground 20.

  The second filter 12 includes, for example, a resonator 21 and a longitudinal mode coupled filter 22 connected between the antenna terminal 15 and the output terminal (balance terminal) 16, and receives a reception signal from the antenna terminal 15. Output from the output terminal 16.

  The antenna duplexer 10 also includes a phase shifter 23 connected between the first filter 11 and the second filter 12, and the phase shifter 23 makes the other pass band between the transmission and reception filters high impedance. The improvement of mutual isolation is aimed at.

  By employing the elastic wave element 1 of the first embodiment for the first filter 11 or the second filter 12, the electrode finger corrosion of the IDT electrode in the antenna duplexer 10 is suppressed, and in each of the filters 11 and 12 Variations in characteristics of the antenna duplexer 10 due to frequency fluctuations of the main elastic wave can be prevented.

  As shown in FIG. 6, the electronic device 50 such as a mobile phone according to the first embodiment includes the acoustic wave element 1, the semiconductor element 30 connected to the acoustic wave element 1, and the semiconductor element 30. A playback device 40 including a connected display unit such as a liquid crystal display and an audio playback unit such as a speaker is provided.

  As described above, by employing the acoustic wave device 1 of the first embodiment in the electronic device 50, the communication quality of the electronic device 50 can be improved.

  The acoustic wave device according to the present invention has an effect of improving the reliability and mass productivity of the acoustic wave device, and can be applied to an electronic device such as a mobile phone.

1, 70, 80 Acoustic wave element 2 Piezoelectric substrate 3 Electrode finger 4 First dielectric film 6 Second dielectric film 7 Third dielectric film 10 Antenna duplexer 11 First filter 12 Second filter

Claims (12)

A piezoelectric substrate having an upper surface;
An IDT electrode disposed above an upper surface of the piezoelectric substrate, the IDT electrode including a plurality of electrode fingers configured to excite a major acoustic wave that is a Rayleigh wave ;
A first dielectric film made of an oxide disposed over the upper surface of the piezoelectric substrate and covering the plurality of electrode fingers;
A non-oxide second dielectric film disposed on an upper surface of the plurality of electrode fingers and between the first dielectric film and each of the plurality of electrode fingers;
A third dielectric film formed between the piezoelectric substrate and the plurality of electrode fingers so as to contact the first dielectric film at a position between adjacent electrode fingers of the plurality of electrode fingers;
The contact between the first dielectric film and the third dielectric film suppresses the frequency fluctuation of the main elastic wave caused by the formation of the second dielectric film,
Velocity of transverse wave propagating through the third dielectric film is rather fast than the speed of the primary acoustic wave propagating through the piezoelectric substrate,
In the piezoelectric substrate, the cut angle and the propagation direction of the main elastic wave are represented by Euler angles (φ, θ, ψ), and (φ, θ, ψ) = (− 10 ° ≦ φ ≦ 10 °, 33 ° ≦ θ ≦ 43 °, −10 ° ≦ ψ ≦ 10 °) lithium niobate substrate, (φ, θ, φ) = (− 1 ° ≦ φ ≦ 1 °, 113 ° ≦ θ ≦ 135 °, −5 ° ≦ (φ ≦ θ °) and (φ, θ, φ) = (− 7.5 ° ≦ φ ≦ 2.5 °, 111 ° ≦ θ ≦ 121 °, −2.5 ° ≦ φ ≦ 7. 5 °) acoustic wave element selected from the group consisting of lithium tantalate substrates . 2. The acoustic wave device according to claim 1, wherein the first dielectric film has a frequency temperature coefficient having a sign opposite to that of the piezoelectric substrate. 2. The acoustic wave device according to claim 1, wherein the first dielectric film is made of silicon oxide. 2. The acoustic wave device according to claim 1, wherein the second dielectric film is made of one of nitride and carbide. The acoustic wave device according to claim 4, wherein the second dielectric film is made of silicon nitride. The acoustic wave device according to claim 1, wherein the second dielectric film is in contact with side surfaces of the plurality of electrode fingers. 7. The elastic wave according to claim 6 , wherein the film thickness of the plurality of portions of the second dielectric film on the upper surfaces of the plurality of electrode fingers is thicker than the film thickness of the plurality of portions of the second dielectric film contacting the side surfaces of the plurality of electrode fingers. element. The acoustic wave element according to claim 6 , wherein the second dielectric film covers a part of each side surface of the plurality of electrode fingers from above the plurality of electrode fingers but does not reach the upper surface of the piezoelectric substrate. The elastic wave device according to claim 1, wherein the velocity of the transverse wave propagating through the second dielectric film is faster than the velocity of the transverse wave propagating through the first dielectric film. Electronic equipment,
An acoustic wave device according to claim 1;
And an electronic device including a reproducing device connected to the acoustic wave element. A piezoelectric substrate having an upper surface;
An IDT electrode formed above the upper surface of the piezoelectric substrate, the IDT electrode including a plurality of electrode fingers configured to excite a major acoustic wave that is a Rayleigh wave ;
A first dielectric film made of an oxide disposed over the upper surface of the piezoelectric substrate and covering the plurality of electrode fingers;
A non-oxide second dielectric film disposed on an upper surface of the plurality of electrode fingers and between the first dielectric film and each of the plurality of electrode fingers;
A third dielectric film formed between the piezoelectric substrate and the plurality of electrode fingers so as to contact the first dielectric film at a position between adjacent electrode fingers of the plurality of electrode fingers;
The contact between the first dielectric film and the third dielectric film suppresses the frequency fluctuation of the main elastic wave caused by the formation of the second dielectric film,
Dielectric constant of the third dielectric layer is minor than the dielectric constant of the piezoelectric substrate,
In the piezoelectric substrate, the cut angle and the propagation direction of the main elastic wave are represented by Euler angles (φ, θ, ψ), and (φ, θ, ψ) = (− 10 ° ≦ φ ≦ 10 °, 33 ° ≦ θ ≦ 43 °, −10 ° ≦ ψ ≦ 10 °) lithium niobate substrate, (φ, θ, φ) = (− 1 ° ≦ φ ≦ 1 °, 113 ° ≦ θ ≦ 135 °, −5 ° ≦ (φ ≦ θ °) and (φ, θ, φ) = (− 7.5 ° ≦ φ ≦ 2.5 °, 111 ° ≦ θ ≦ 121 °, −2.5 ° ≦ φ ≦ 7. 5 °) acoustic wave element selected from the group consisting of lithium tantalate substrates . Electronic equipment including an elastic wave element according to claim 1 1.

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