JP2002374145A - Piezoelectric thin-film resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric thin-film resonator where electromechanical coupling coefficient is large, an acoustic quality coefficient (Q-value) and frequency/temperature characteristics are superior or its performance is superior in characteristics, such as bandwidth, insertion loss and gain. SOLUTION: The resonator is provided with a substrate 12 and a piezoelectric laminated structure body 14, formed on the substrate 12 via an insulator layer 13. A vibration part 21 is constituted of the insulator layer 13 and a part of the piezoelectric laminated structure body 14, which is formed by laminating a lower part electrode 15, a piezoelectric film 16 and an upper electrode 17. In the substrate 12, an air gap 20 which allows vibration of the vibration part 21, is formed in a region corresponding to the vibration part 21. The piezoelectric film 16 is an orientated crystal film, composed of solid solution of aluminum nitride and gallium nitride which is represented by general formula Al1-x Gax N (where 0<x<1) or a solid solution of aluminum nitride and indium nitride which is represented by general formula Al1-y Iny N (where 0<y<1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric device used in a wide range of fields, such as a thin film resonator used in a mobile communication device, a thin film VCO (voltage controlled oscillator), a thin film filter, a transmission / reception switching device and various sensors. The present invention relates to an element using a body thin film.

[0002]

2. Description of the Related Art Devices utilizing the piezoelectric phenomenon are used in a wide range of fields. As mobile devices such as mobile phones have become smaller and have lower power consumption, surface acoustic waves (Sulfac) have been used as RF and IF filters for such devices.
The use of e Acoustic Wave (SAW) devices is expanding. This SAW filter has responded to the strict requirements of the user by improving the design and production technology. However, as the frequency of use has become higher, the limit of the characteristic improvement has been approached. Both sides require great technological innovation.

On the other hand, a thin-film bulk acoustic resonator utilizing the thickness vibration of a piezoelectric thin film (FilmBulk Acousse).
Tic Resonator (FBAR) is formed by forming a thin film mainly composed of a piezoelectric material and an electrode for driving the thin film on a thin supporting film provided on a substrate, and is capable of fundamental resonance in a gigahertz band. . If the filter is composed of FBAR or SBAR, it can be remarkably miniaturized, low loss and wide band operation is possible, and it can be integrated with the semiconductor integrated circuit. Have been.

A piezoelectric thin film element applied to a resonator, a filter, and the like utilizing such an elastic wave is manufactured as follows. Semiconductor single crystal substrates such as silicon,
A dielectric thin film, a conductive thin film, or a thin film of these materials may be formed on a surface of a substrate formed by forming a polycrystalline diamond film on a silicon wafer or the like or a substrate formed of a constant elastic metal such as Elinvar by various thin film forming methods. A base film made of a laminated film is formed. A piezoelectric thin film is formed on this underlayer,
Further, an upper structure is formed as needed. After each film is formed or after all the films are formed, each film is subjected to physical processing or chemical processing to perform fine processing or patterning. After forming a floating structure in which a portion of the piezoelectric thin film located below the vibrating portion is removed from the substrate by anisotropic etching, the piezoelectric thin film device is separated for each element unit to obtain a piezoelectric thin film device.

For example, a piezoelectric thin film element described in Japanese Patent Application Laid-Open No. Sho 60-142607 has a structure in which a base film, a lower electrode, a piezoelectric thin film, and an upper electrode are formed on the upper surface of a substrate and then vibrated from the lower surface of the substrate. It is manufactured by removing a substrate portion below a portion to be a part and forming a via hole.

As a piezoelectric material for a piezoelectric thin film element,
Aluminum nitride (AlN), zinc oxide (ZnO), sulfur
Cadmium (CdS), lead titanate [PT] (PbT
iO _Three ), Lead zirconate titanate [PZT] (Pb (Z
r, Ti) O_Three ) Is used. In particular, AlN
Has a high elastic wave propagation speed and operates in a high frequency band.
Used in piezoelectric thin film resonators for membrane resonators and thin film filters
It is suitable as a piezoelectric material.

[0007]

Various studies have hitherto been made to apply an AlN thin film to an FBAR or SBAR. However, a thin film resonator or a thin film filter exhibiting sufficient performance in the gigahertz band has not yet been obtained, and the acoustic quality factor (Q
Value), frequency temperature coefficient and insertion loss are desired. A thin film piezoelectric element which is excellent in all of acoustic quality factor (Q value), wide band operation and frequency temperature characteristics and has high performance resonance characteristics has not been proposed. The electromechanical coupling coefficient is an important parameter that affects the performance of a resonator or a filter when it is configured, and greatly depends on the film quality of a piezoelectric thin film used. By improving the electromechanical coupling coefficient,
The acoustic quality factor (Q value) can also be improved.

Therefore, the present invention takes advantage of the characteristics of an AlN thin film that the propagation speed of an elastic wave is high, and has a large electromechanical coupling coefficient, an excellent acoustic quality coefficient (Q value), excellent frequency temperature characteristics, or a bandwidth. It is an object of the present invention to provide a piezoelectric thin-film resonator having significantly higher performance than conventional ones in terms of characteristics such as insertion loss and gain.

[0009]

SUMMARY OF THE INVENTION The present inventors have developed an FBA having an AlN thin film as a piezoelectric thin film on a substrate such as Si.
The resonance characteristics of R or SBAR greatly depend on the state of lattice matching at the interface between the metal thin film serving as an electrode and the AlN thin film, and gallium nitride (GaN) having the same wurtzite crystal structure with respect to AlN Alternatively, it has been found that by adding indium nitride (InN) to control the a-axis length of the crystal lattice, the resonance characteristics thereof are significantly improved, and the present invention has been achieved.

That is, the a-axis length of the GaN crystal is 0.319 n
m, and the a-axis length of the InN crystal is 0.353 n
m, which are the values of the a-axis length (0.
(Values around 311 nm).
Solid solution of GaN or InN in the crystal lattice of Example 1 to increase the a-axis length, improve the degree of coincidence with the lattice length of a specific orientation of the metal crystal constituting the lower electrode, and realize a good lattice matching relationship. be able to.

That is, according to the present invention, as a means for achieving the above object, a vibrating portion is constituted including a part of a piezoelectric laminated structure including a piezoelectric film and electrodes formed on both surfaces thereof. Wherein the piezoelectric film is a solid solution of aluminum nitride and gallium nitride represented by the general formula Al _1-x Ga _x N (where 0 <x <1) or the general formula Al _{1 -x} a piezoelectric thin-film resonator characterized in that it is an oriented crystal film made of a solid solution of aluminum nitride and indium nitride represented by _y In _y N (where 0 <y <1);
Is provided.

In one embodiment of the present invention, the piezoelectric laminated structure includes a plurality of piezoelectric films and electrodes formed on both surfaces of each of the plurality of piezoelectric films. In one aspect of the present invention, the peripheral portion of the piezoelectric laminated structure is supported by a substrate, and the central portion constitutes the vibrating portion.

According to the present invention, in order to achieve the above object, there is provided a substrate, and a piezoelectric laminated structure formed on the substrate, and a part of the piezoelectric laminated structure is provided. And a vibrating section is configured, wherein the piezoelectric laminated structure includes a structure in which a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order from the substrate side, and the substrate includes the vibrating section. And a void that allows the vibrating portion to vibrate in a region corresponding to the piezoelectric thin film resonator, wherein the piezoelectric film has a general formula of Al _1-x Ga _x N (where 0 <x <
1) a solid solution of aluminum nitride and gallium nitride or a general formula Al _1-y In _y N (where 0 <y <
A piezoelectric thin-film resonator characterized in that it is an oriented crystal film made of a solid solution of aluminum nitride and indium nitride represented by 1).

In one embodiment of the present invention, the upper electrode includes a first electrode portion and a second electrode portion formed apart from each other.

Further, according to the present invention, in order to achieve the above object, there is provided a substrate and a piezoelectric laminated structure formed on the substrate, and a part of the piezoelectric laminated structure is provided. A vibrating part is configured, and the piezoelectric laminated structure is formed by laminating a lower electrode, a first piezoelectric film, an internal electrode, a second piezoelectric film, and an upper electrode in this order from the substrate side. Wherein the substrate is a piezoelectric thin-film resonator forming an air gap allowing vibration of the vibrating portion in a region corresponding to the vibrating portion, wherein the first piezoelectric film and the second Each of the piezoelectric films has a general formula of Al _1-x Ga _x N (where 0
<X <1), a solid solution of aluminum nitride and gallium nitride or a general formula Al _1-y In _y N (where 0 <
A piezoelectric thin-film resonator characterized by being an oriented crystal film made of a solid solution of aluminum nitride and indium nitride represented by y <1).

In one embodiment of the present invention as described above,
An insulator layer is formed between the substrate and the piezoelectric laminated structure, and the vibrating section is configured to include a part of the insulator layer. In one embodiment of the present invention, the insulator layer is a dielectric film containing silicon oxide (SiO ₂ ) as a main component, a dielectric film containing silicon nitride (SiN _x ) as a main component, or containing silicon oxide as a main component. It is a laminated film of a dielectric film and a dielectric film containing silicon nitride as a main component. This improves the frequency-temperature characteristics while maintaining the high electromechanical coupling coefficient of the AlN-based piezoelectric thin-film resonator,
Performance can be stabilized.

In one embodiment of the present invention, the substrate is made of a semiconductor or an insulator. In one embodiment of the present invention, the substrate is made of silicon single crystal.

In one embodiment of the present invention, the piezoelectric film or the first piezoelectric film and the second piezoelectric film are:
It shows C-axis orientation, and the rocking curve half width of the X-ray diffraction peak on the (0002) plane is 3.0 ° or less.

In the present invention, a solid solution thin film of aluminum nitride and gallium nitride or a solid solution thin film of aluminum nitride and indium nitride is used as the piezoelectric film, and lattice matching between the piezoelectric film and the metal crystal of the electrode layer is performed. Thereby, the orientation and crystallinity of the piezoelectric film are improved, and a piezoelectric film having a large electromechanical coupling coefficient and a high Q value can be obtained. By manufacturing an FBAR or SBAR using such a highly oriented and highly crystalline piezoelectric thin film, the FBAR or the SBAR has low loss, high gain, excellent bandwidth, excellent frequency temperature characteristics (for example, 2.0 to 2.0). The electromechanical coupling coefficient K _t ² obtained from the measured values of the resonance frequency and the anti-resonance frequency in the range of 3.0 GHz is 4.5% or more.) High performance FBAR or S
BAR can be realized.

[0020]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a schematic plan view showing an embodiment of a piezoelectric thin film resonator according to the present invention, and FIG. 2 is a sectional view taken along line XX of FIG. In these figures, a piezoelectric thin film resonator 11 includes a substrate 12 and an insulator layer 1 formed on the upper surface of the substrate 12.
3 and a piezoelectric laminated structure 14 formed on the upper surface of the insulator layer 13. The piezoelectric laminated structure 14 is composed of the insulating layer 1
3, a lower electrode 15 formed on the upper surface of
The piezoelectric film 16 is formed on the upper surface of the insulator layer 13 so as to cover a part of the piezoelectric film 16 and the upper electrode 17 formed on the upper surface of the piezoelectric film 16. Via holes 20 are formed in the substrate 12 to form voids. Insulator layer 13
Are exposed toward the via hole 20. The exposed portion of the insulator layer 13 and the corresponding portion of the piezoelectric laminated structure 14 constitute a vibrating portion (vibrating diaphragm) 21. In addition, the lower electrode 15 and the upper electrode 17 are connected to the main portions 15a, 1 formed in a region corresponding to the vibrating portion 21.
7a and terminals 15b and 17b for connecting the main parts 15a and 17a to an external circuit. Terminal portion 15b,
17b is located outside the area corresponding to the vibration part 21.

As the substrate 12, a single crystal such as a Si (100) single crystal, or a substrate in which a silicon, diamond or other polycrystalline film is formed on the surface of a substrate such as a Si single crystal can be used. As the substrate 12, other semiconductors or even insulators can be used. Substrate 1
An example of a method of forming the second via hole 20 is an anisotropic etching method from the lower surface side of the substrate. Note that the gap formed in the substrate 12 is not limited to the one formed by the via hole 20 and may be any that allows the vibration of the vibrating part 21, and may be a recess formed in the substrate upper surface area corresponding to the vibrating part 21. There may be.

As the insulator layer 13, for example, a dielectric film mainly containing silicon oxide (SiO ₂ ), a dielectric film mainly containing silicon nitride (SiN _x ), and a dielectric film mainly containing silicon oxide A stacked film of a film and a dielectric film containing silicon nitride as a main component can be used. With respect to the material of the insulating layer 13, the main component refers to a component whose content in the dielectric film is 50 atomic% or more. The dielectric film may be composed of a single layer, or may be composed of a plurality of layers to which a layer or the like for improving adhesion is added. The thickness of the insulator layer 13 is, for example, 0.2 to 2.0 μm.
It is. Examples of a method for forming the insulator layer 13 include a thermal oxidation method and a CVD method on the surface of the substrate 12 made of silicon.

As the lower electrode 15 and the upper electrode 17,
Molybdenum (Mo), tungsten (W), platinum (P
t) and a laminated film (Pt / Ti) of titanium (Ti), aluminum (Al), a laminated film (Au / Cr) of gold (Au) and chromium (Cr), and gold (Au) and titanium (Ti) And the like (Au / Ti). Mo is preferred because of its low thermoelastic loss. For example, M
The thermoelastic loss of o is about 1/56 of Al. Not only Mo alone, but also a Mo alloy or a Mo electrode formed on a suitable adhesion layer can be used. The thickness of the lower electrode 15 and the upper electrode 17 is, for example, 50 to 200 nm. Examples of a method for forming the lower electrode 15 and the upper electrode 17 include a sputtering method and a vapor deposition method, and a photolithography technique is used for patterning into a required shape as needed.

When the main portion 15a of the lower electrode 15 is extended into two sides of the rectangular opening of the via hole 20 on the upper surface of the substrate 12, the vibrating portion 21 is held by the lower electrode 15. Therefore, the insulator layer 13 can be omitted.

The piezoelectric film 16 is made of a solid solution of AlN and GaN or a solid solution of AlN and InN, and has a thickness of, for example, 0.3 to 3.0 μm. As a method for forming the piezoelectric film 16, a reactive sputtering method is exemplified, and a photolithography technique is used for patterning into a required shape as needed.

In general, the piezoelectric properties of a piezoelectric material depend on the polarization of the crystal.
And the arrangement of the polarization axes. Piezoelectric of the present invention
The piezoelectricity of a piezoelectric film of a thin-film resonator
Domain structure, orientation and crystallinity of the constituent crystals
It is considered to depend on the crystal properties. In this specification,
A mono-oriented film has a target crystal plane aligned parallel to the substrate surface.
Means a crystallized film. For example, (000
1) The (0001) plane grows in parallel with the film plane of the single alignment film
Means a film that has Specifically, the diffractomer
When an X-ray diffraction measurement is performed by the
_1-x Ga_x N (where 0 <x <1) and AlN
Crystal of solid solution with GaN or general formula Al _1-y In_y N
(However, the solid state of AlN and InN represented by 0 <y <1)
Reflection peaks other than the target diffraction plane due to the crystal of the solution
It means that the mark can hardly be detected. For example,
The (000L) single alignment film, that is, the C-axis single alignment film has θ
Reflection other than (000L) plane in X-ray diffraction measurement at -2θ rotation
The intensity is less than 5% of the maximum peak intensity of (000L) surface reflection.
Full, preferably less than 2%, more preferably below the detection limit
The one below. The (000L) plane is (0001)
Series planes, that is, (0001) plane, (0002) plane and
This is a generic name of equivalent surfaces such as (0004) surface.

The present inventors have studied how the resonance characteristics of the FBAR having the structure shown in FIGS. 1 and 2 depend on the composition and crystallinity of the AlN-based thin film.
As a result, the FB having a piezoelectric film composed of an AlN-based thin film
It has been found that the resonance characteristics of the AR greatly depend on the composition and crystallinity of the AlN-based thin film. That is, as the piezoelectric film, a solid solution of aluminum nitride and gallium nitride represented by the general formula Al _1-x Ga _x N (where 0 <x <1) or A
The use of a solid solution of aluminum nitride and indium nitride represented by l _1-y In _y N (where 0 <y <1) to improve the lattice matching with the metal crystal of the electrode layer is a piezoelectric thin film. This is effective for improving the performance of a resonator and a piezoelectric thin film filter using the same. To improve this performance,
It is preferable that 0 <x <0.5 and 0 <y <0.3,
More preferably, 0.03 <x <0.35, 0.01 <y
<0.15.

Among the above-mentioned electrode materials, a crystal of Mo or W belongs to a body-centered cubic lattice represented by a space group _Im-3m.
The t or Au crystal belongs to a face-centered cubic lattice represented by the space group F _m-3m . The crystal of Mo or W of the body-centered cubic lattice formed by the sputtering method or the vapor deposition method shows the (110) orientation, and the (110) plane grows in parallel with the film surface. on the other hand,
The crystal of Pt or Au of the face-centered cubic lattice formed by the sputter method or the vapor deposition method shows the (111) orientation, and the (111) plane grows in parallel with the film surface. The lattice constant (a-axis length) of the Mo crystal is about 0.3147 nm, the (110) plane spacing is about 0.2225 nm, and the lattice constant (a-axis length) of the W crystal is about 0.3165 nm, (110) The plane spacing is a value around 0.2238 nm. The lattice constant (a-axis length) of the Pt crystal is a value around 0.3923 nm, the (110) plane interval on the (111) plane is a value around 0.2774 nm, and the lattice constant (a-axis length) of the Au crystal is 0.10 nm. 4079
The (110) plane interval on the (111) plane is around 0.2884 nm.

In the present invention, the metal used for the electrode layer
Is a body-centered cubic Mo crystal or W crystal
Is the lattice constant of these crystals (ie, (100) plane spacing)
And the lattice constant (a-axis length) L of the electrode metal crystal_M100When
Al_1-x Ga_x N (however, 0 <x <1) solid solution
Crystal or Al_1-y In_y N (however, 0 <y <1)
A-axis length L of solution crystal_PZa The mismatch of the lattice length with
00 * (L_M100-L_PZa) / L_M100Param [%]
Data. On the other hand, if the metal used for the electrode layer is
In the case of a lattice Pt crystal or Au crystal,
Note the spacing between (110) planes on the (111) plane of the crystal
(11) on the (111) plane of the electrode metal crystal.
0) Spacing L_M110And the above Al_1-x Ga_x N (however, 0
<X <1) system solid solution crystal or Al_1-y In_y N (however
And (10-10) plane spacing of 0 <y <1) system solid solution crystal
L_PZ1 100 * (L_M110−
L_PZ1 ) / L_M110It is represented by the parameter [%]. body
(110) plane of Mo crystal or W crystal with center cubic lattice
Arrangement in Al and Al_1-x Ga_x N (however, 0 <x <
1) system solid solution crystal or Al_1-y In_y N (however, 0 <
Atomic arrangement on (0001) plane of y <1) system solid solution crystal
Since the consistency with the row is not so good, the Mo crystal or W
Crystals and Al_1-x Ga_x N (however, 0 <x <1)
Solution crystal or Al _1-y In_y N (however, 0 <y <1)
100 * (L) mismatch of lattice length with system solid solution crystal_M100
-L_PZa ) / L_M100[%] Should be less than 1.0%
preferable. In contrast, a face-centered cubic Pt crystal or
Is the atomic arrangement on the (111) plane of Au crystal etc. and Al
_1-x Ga_x N (where 0 <x <1) solid solution crystal or
Al_{1- y} In_y N (where 0 <y <1) based solid solution crystal
Consistency with the atomic arrangement on the (0001) plane is relatively good
Pt crystal or Au crystal etc. and Al_1-x
Ga_x N (however, 0 <x <1) system solid solution crystal or Al
_1-y In_y N (however, 0 <y <1) type solid solution crystal
Child length mismatch 100 * (L_M110-L_PZ1 ) / L_M110
Is preferably 2.6% or less. Mo crystal and W connection
Length mismatch 10 for body-centered cubic lattice such as crystal
0 * (L_M100-L_PZa ) / L_M100Exceeds 1.0%
And these metal crystals and Al_1-x Ga_x N (however, 0 <
x <1) system solid solution or Al_1-y In_y N (however, 0 <
y <1) The lattice matching with the solid solution deteriorates.
AlN-GaN or AlN-InN piezoelectric thin film
Orientation and crystallinity deteriorate, resulting in electromechanical
Coefficient k_t ^TwoAnd the acoustic quality factor (Q value) becomes smaller,
Deterioration of performance as a piezoelectric thin film resonator or thin film filter
Tend to be. Similarly, the face center of Pt crystal, Au crystal, etc.
Lattice mismatch 100 * (L_M110
-L_PZ1 ) / L_M110Exceeds 2.6%, these gold
Genus crystals and Al_1-x Ga_x N (however, 0 <x <1) solid solution
Body or Al_1-yIn_y N (However, 0 <y <1) solid solution
The lattice matching with the body deteriorates, and these AlN-GaN
Orientation and crystal of AlN-based or AlN-InN-based piezoelectric thin film
And the electromechanical coupling coefficient k_t ^TwoAnd sound
Acoustic quality factor (Q value) becomes smaller,
The performance as a thin film filter tends to deteriorate.

Al _1-x Ga _x N (0 <x <1) based solid solution thin film or Al _1-y In _y N (0 <y <
1) The system solid solution thin film exhibits c-axis orientation, and the rocking curve half width (FWHM) of the diffraction peak of the (0002) plane measured by the X-ray diffraction method is preferably 3.0 ° or less. Rocking curve half width (FWHM) is 3.0
When the angle exceeds °, the electromechanical coupling coefficient k _t ² decreases, and the resonance characteristics tend to deteriorate. Further, when the rocking curve half width (FWHM) is excessively large, current leakage tends to easily occur between the lower electrode terminal 15b and the upper electrode terminal 17b.

FIG. 3 is a schematic plan view showing still another embodiment of the piezoelectric thin film resonator according to the present invention, and FIG.
It is -X sectional drawing. In these drawings, members having the same functions as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In the present embodiment, the lower electrode 15 has a substantially rectangular shape, and the upper electrode 17 is
7A and a second electrode portion 17B. These electrode parts 1
7A and 17B have main parts 17Aa and 17Ba and terminal parts 17Ab and 17Bb, respectively. The main part 17Aa,
17Ba is located in a region corresponding to the vibrating portion 21, and the terminal portions 17Ab and 17Bb are located outside a region corresponding to the vibrating portion 21.

In the present embodiment, an input voltage is applied between one of the upper electrodes 17 (for example, the second electrode portion 17B) and the lower electrode 15, and the other of the upper electrodes 17 (for example, the first electrode portion 17B). Since a voltage between the electrode portion 17A) and the lower electrode 15 can be taken out as an output voltage, the voltage itself can be used as a filter. By using the filter having such a configuration as a component of the pass band filter, the attenuation characteristics of the stop band are improved, and the frequency response performance of the filter is improved.

FIG. 5 is a schematic plan view showing still another embodiment of the piezoelectric thin film resonator according to the present invention, and FIG.
It is -X sectional drawing. In these drawings, members having the same functions as those in FIGS. 1 to 4 are denoted by the same reference numerals.

The present embodiment is directed to a laminated thin film bulk acoustic resonator (Stacked Th) having a piezoelectric laminated structure corresponding to a laminate of two piezoelectric laminated structures of the above embodiment.
inFilm Bulk Acoustic Reso
nators). That is, the lower electrode 15, the first piezoelectric film 16-1, the internal electrode 17 ', the second piezoelectric film 16-2, and the upper electrode 18 are laminated on the insulator layer 13 in this order. The internal electrode 17 ′ is the first piezoelectric film 1.
It has a function as an upper electrode for 6-1 and a function as a lower electrode for the second piezoelectric film 16-2.

In this embodiment, an input voltage is applied between the lower electrode 15 and the internal electrode 17 ', and a voltage between the internal electrode 17' and the upper electrode 18 can be taken out as an output voltage. This can itself be used as a multipole filter. By using this multipole filter as a component of the pass band filter, the attenuation characteristics of the stop band are improved, and the frequency response performance of the filter is improved.

[0038] In the piezoelectric thin-film resonator as described above, between the resonance frequency f _r and the antiresonance frequency f _a and the electromechanical coupling coefficient k _t ² in the impedance characteristic measured by using a microwave prober, or less a relationship ^{_{k t 2 = φ r / Tan}} (φ r) φ r = (π / 2) (f r / f a) is.

For simplicity, as the electromechanical coupling coefficient k _t ² , the one calculated from the following equation: k _t ² = 4.8 (f _a −f _r ) / (f _a + f _r ) can be used. In the statement,
Figures electromechanical coupling coefficient k _t ² is used as calculated using this equation.

In the FBAR or SBAR having the configuration shown in FIGS. 1, 2, 3, 4 and 5, 6, 2.0 to 3.
Electromechanical coupling coefficient k _t ² obtained from the measured value of the resonance frequency and anti-resonance frequency in the range of 0GHz is 4.5 to 6.
Preferably it is 5%. ^{3. The} electromechanical coupling coefficient k _t ² is 4.
If it is less than 5%, the bandwidth of the manufactured FBAR becomes small, and it tends to be difficult to put the FBAR to practical use in a high frequency range.

[0041]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples.

Example 1 In this example, a piezoelectric thin film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, after a SiO ₂ layer having a thickness of 1.1 μm is formed on the upper and lower surfaces of a (100) Si substrate 12 having a thickness of 350 μm by thermal oxidation, only the SiO ₂ layer on the upper surface is etched. The thickness of the upper SiO ₂ layer is 0.28 μm
To form an insulator layer 13 made of SiO ₂ . A Pt electrode layer (including a Ti adhesion layer) having a thickness of 110 nm was formed on the upper surface of the insulator layer 13 by a DC magnetron sputtering method, and was patterned by photolithography to form a Pt / Ti lower electrode 15. Lower electrode 15
The main portion 15a of this example has a shape close to a rectangle having a plane size of 140 × 160 μm. It was confirmed by X-ray diffraction measurement that the lower electrode 15 was a (111) oriented film, that is, a single oriented film. On this Pt / Ti lower electrode 15, using an Al—In alloy having an appropriate composition as a target by a reactive RF magnetron sputtering method under the conditions shown in Table 1,
An Al _1-y In _y N-based solid solution thin film (piezoelectric film) having the composition shown in the same table was formed. The Al _{1 -y} In _y N-based solid solution thin film was patterned into a predetermined shape by wet etching using hot phosphoric acid to form the piezoelectric film 16. Thereafter, using a DC magnetron sputtering method and a lift-off method, the main body 17a has a plane size of 140 × 160 with a thickness of 110 nm.
A Pt / Ti upper electrode 17 having a shape close to a rectangular shape of μm was formed. The main portion 17a of the upper electrode 17 was arranged at a position corresponding to the lower electrode main portion 15a. Next, the side on which the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 of the structure obtained as described above are formed is covered with protect wax, and the thickness formed on the lower surface of the Si substrate 12 is formed. 1.1
Using a mask formed by patterning a μm SiO ₂ layer, a portion of the Si substrate 12
The via hole 20 serving as a void was formed by etching and removing with an OH aqueous solution.

The thin-film piezoelectric resonator (FBAR) manufactured by the above-described steps was subjected to XPS
The composition analysis of the _1-y In _y N-based solid solution thin film is performed, and the lattice constant is measured by the diffractometer method and the rocking curve of the (0002) diffraction peak is measured using a multifunctional X-ray diffractometer for evaluating the surface structure. The value range (FWHM) was measured. Table 1 shows the evaluation results of the composition and crystallinity of the Al _1-y In _y N-based solid solution thin film.

Further, using manufactured by Cascade Microtech Inc. microwave prober and a network analyzer, the electrode terminal 15b of the thin film piezoelectric resonator, the measured impedance characteristic between 17b, the resonance frequency f _r
From the measured values of the anti-resonance frequency f _{a and} the electromechanical coupling coefficient k _t ² , the frequency temperature characteristic τ _f and the acoustic quality coefficient Q were determined. Fundamental frequency of the thickness vibration of the obtained piezoelectric thin film resonator, the electromechanical coupling coefficient k _t ^2, the frequency-temperature characteristic tau _f and acoustic quality factor Q shown in Table 2.

Embodiment 2 In this embodiment, a piezoelectric thin-film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, after a SiO ₂ layer having a thickness of 1.1 μm is formed on both upper and lower surfaces of a (100) Si substrate 12 having a thickness of 350 μm by a thermal oxidation method, only the SiO ₂ layer on the upper surface side is etched. The thickness of the SiO ₂ layer on the upper surface was adjusted to the value shown in Table 2 to form the insulator layer 13 made of SiO ₂ .
A Pt electrode layer (including a Ti adhesion layer) having a thickness shown in Table 1 is formed on the upper surface of the insulator layer 13 by DC magnetron sputtering, and is patterned by photolithography to form a Pt / Ti lower electrode 15. did. The main portion 15a of the lower electrode 15 has a shape close to a rectangle having a plane dimension of 140 × 160 μm. It was confirmed by X-ray diffraction measurement that the lower electrode 15 was a (111) oriented film, that is, a single oriented film. On this Pt / Ti lower electrode 15, a reactive R
An Al _1-x Ga _x N-based solid solution thin film (piezoelectric film) having the composition shown in Table 1 was formed by F magnetron sputtering under the conditions shown in Table ₁ . The piezoelectric film 16 was formed by patterning the Al _1-x Ga _x N-based solid solution thin film into a predetermined shape by wet etching using hot phosphoric acid. afterwards,
Using the DC magnetron sputtering method and the lift-off method, the plane size 140 of the main portion 17a is formed at the thickness shown in Table 1.
Pt / Ti upper electrode 1 with a shape close to a rectangle of × 160 μm
7 was formed. The main portion 17a of the upper electrode 17 was arranged at a position corresponding to the lower electrode main portion 15a. Next, the side on which the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 of the structure obtained as described above are formed is covered with protect wax, and the thickness formed on the lower surface of the Si substrate 12 is formed. Using a mask formed by patterning an SiO ₂ layer having a thickness of 1.1 μm, portions of the Si substrate 12 corresponding to the vibrating portions 21 were removed by etching with a KOH aqueous solution to form via holes 20 serving as voids.

The thin-film piezoelectric resonator (FBAR) manufactured by the above-described process was subjected to XPS
The composition analysis of the _1-x Ga _x N-based solid solution thin film (piezoelectric film) was performed, and the lattice constant was measured by a diffractometer method using a multifunctional X-ray diffractometer for surface structure evaluation.
002) Rocking curve half width (FW) of diffraction peak
HM) measurements were taken. Table 1 shows the evaluation results of the composition and crystallinity of the Al _1-x Ga _x N-based solid solution thin film.

[0049] Further, using manufactured by Cascade Microtech Inc. microwave prober and a network analyzer, the electrode terminal 15b of the thin film piezoelectric resonator, the measured impedance characteristic between 17b, the resonance frequency f _r
From the measured values of the anti-resonance frequency f _{a and} the electromechanical coupling coefficient k _t ² , the frequency temperature characteristic τ _f and the acoustic quality coefficient Q were determined. Fundamental frequency of the thickness vibration of the obtained piezoelectric thin film resonator, the electromechanical coupling coefficient k _t ^2, the frequency-temperature characteristic tau _f and acoustic quality factor Q shown in Table 2.

Example 3 In this example, a piezoelectric thin film resonator having the structure shown in FIGS. 3 and 4 was manufactured as follows.

That is, the lower electrode 15 has a plane size of 120 × 280 extending so as to include a region corresponding to the vibrating portion 21.
μm, and the upper electrode 17 has a main portion 17A having a plane size of 65 × 85 μm and a shape close to a rectangle.
a and 17Ba are arranged at intervals of 20 μm, and furthermore, the insulator layer 13, the lower electrode 15, the upper electrode 17
And the thickness, material and composition of the piezoelectric film 16 are shown in Tables 1 and 2.
The same steps as in Example 2 were performed, except as shown in Table 2.

In the same manner as in Example 2, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

Further, using a microwave prober manufactured by Cascade Microtech, the terminal portion of the lower electrode 15 of the thin film piezoelectric resonator (the exposed portion on the left side in FIGS. 3 and 4) is connected to the ground electrode, and the upper electrode is connected to the upper electrode. A signal was input from the terminal portion 17Ab of the upper electrode 17A, an output signal was taken out from the terminal portion 17Bb of the upper electrode 17B, and the signal intensity and waveform were analyzed by a network analyzer. From the measured values of the resonance frequency f _r and the antiresonance frequency f _a, the electromechanical coupling coefficient k _t ^2, determine the frequency-temperature characteristic tau _f and the acoustic quality factor Q. Fundamental frequency of the thickness vibration of the obtained piezoelectric thin film resonator, the electromechanical coupling coefficient k _t ^2, the frequency-temperature characteristic tau _f and acoustic quality factor Q shown in Table 2.

Embodiment 4 In this embodiment, a piezoelectric thin film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, the thickness, material, and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 2 were performed, except as shown in Table 2. Here, the formation of the SiN _x layer for the insulator layer 13 was performed by a low pressure CVD method.

In the same manner as in Example 2, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0057] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 2 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Example 5 In this example, a piezoelectric thin film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, the thickness, material, and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 4 were performed except as shown in Table 2.

In the same manner as in Example 4, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0061] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 4 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Embodiment 6 In this embodiment, a piezoelectric thin-film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, the thickness, material and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 2 were performed, except as shown in Table 2.

In the same manner as in Example 2, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0065] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 2 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Embodiment 7 In this embodiment, a piezoelectric thin film resonator having the structure shown in FIGS. 3 and 4 was manufactured as follows.

That is, the thickness, material, and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 3 were performed except as shown in Table 2.

In the same manner as in Example 3, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0069] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 3 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Example 8 In this example, a piezoelectric thin-film resonator having the structure shown in FIGS. 3 and 4 was manufactured as follows.

That is, the thickness, material, and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 3 were performed except as shown in Table 2.

In the same manner as in Example 3, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0073] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 3 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Embodiment 9 In this embodiment, a piezoelectric thin-film resonator having the structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, the thickness, material and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 4 were performed except as shown in Table 2.

In the same manner as in Example 4, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0077] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a which obtained in the same manner as in Example 4 to obtain the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

Embodiment 10 In this embodiment, a piezoelectric thin film resonator having the structure shown in FIGS. 3 and 4 was manufactured as follows.

That is, the thickness, material and composition of the insulator layer 13, the lower electrode 15, the upper electrode 17, and the piezoelectric film 16 are shown in Table 1.
And the same steps as in Example 8 were performed, except as shown in Table 2.

In the same manner as in Example 8, the obtained solid solution thin film (piezoelectric film) was subjected to composition analysis and X-ray diffraction measurement. Table 1 shows the evaluation results of the composition and crystallinity of the solid solution thin film.

[0081] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a obtained in the same manner as in Example 8, determine the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality factor Q Was. Fundamental frequency of thickness vibration of the obtained piezoelectric thin film resonator, electromechanical coupling coefficient k _t ² , frequency temperature characteristic τ _f
Table 2 shows the acoustic quality factor Q.

[Comparative Examples 1 and 2] In this comparative example, a piezoelectric thin film resonator having the structure shown in FIG.

That is, instead of the Al _1-x Ga _x N-based solid solution thin film or the Al _1-y In _y N-based solid solution thin film, an AlN thin film is formed by a reactive RF magnetron sputtering method, and the insulator layer 13 and the lower electrode 15 are formed. The same processes as in Example 1 or Example 8 were performed, except that the shape, thickness and material of the upper electrode 17 and the piezoelectric film 16 were as shown in Tables 1 and 2.

The thin film piezoelectric resonator (FBAR) manufactured by the above-described process was subjected to AlN by XPS spectroscopy.
Performs composition analysis of thin films and evaluates multi-function X for surface structure evaluation
Measurement of lattice constant by diffractometer method and locking of (0002) diffraction peak using X-ray diffractometer
Curve half width (FWHM) measurement was performed. The oxygen content of the AlN thin film measured by XPS spectroscopy was as shown in Table 1. The analysis and evaluation were performed by the same operation as in Example 1 or Example 8. However, because the quality of the AlN thin film was poor, there was a possibility that the film was oxidized before the XPS analysis and the oxygen content increased. Table 1 shows the evaluation results of the crystallinity of the AlN thin film.

[0085] Also, from the measured values of the resonance frequency f _r and the antiresonance frequency f _a obtained in the same manner as in Example 1 or Example 8, the electromechanical coupling coefficient k _t ^2, the frequency temperature characteristic tau _f and the acoustic quality The coefficient Q was determined. Fundamental frequency of the thickness vibration of the obtained piezoelectric thin film resonator, the electromechanical coupling coefficient k _t ^2, the frequency-temperature characteristic tau _f and acoustic quality factor Q shown in Table 2.

From the above results, it is clear that FBARs and SBARs using a thin film made of a solid solution of aluminum nitride and gallium nitride or a thin film made of a solid solution of aluminum nitride and indium nitride as a piezoelectric film exhibit unprecedented high characteristics. Became clear. This is presumably because the use of such a piezoelectric film enhances the lattice matching with the metal crystal used for the electrode. As a result, the orientation and crystallinity of the piezoelectric film are improved, and when this piezoelectric film is applied to a resonator, a filter, or the like, performance such as an acoustic quality factor (Q value) and frequency temperature characteristics is improved. Can be done.

[0087]

[Table 1]

[0088]

[Table 2]

[0089]

As described above, according to the piezoelectric thin film resonator of the present invention, a thin film made of a solid solution of aluminum nitride and gallium nitride or a thin film made of a solid solution of aluminum nitride and indium nitride is used as the piezoelectric film. Electromechanical coupling coefficient, acoustic quality coefficient (Q value)
In addition, it is possible to improve performance such as frequency temperature characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator according to the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator according to the present invention.

FIG. 4 is a sectional view taken along line XX of FIG. 3;

FIG. 5 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator according to the present invention.

FIG. 6 is a sectional view taken along line XX of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Thin-film piezoelectric resonator 12 Substrate 13 Insulator layer 14 Piezoelectric laminated structure 15 Lower electrode 15a Lower electrode main part 15b Lower electrode terminal part 16 Piezoelectric film 16-1 First piezoelectric film 16-2 Second piezoelectric material Film 17 Upper electrode 17 'Internal electrode 17a Upper electrode main part 17b Upper electrode terminal part 17A First electrode part of upper electrode 17Aa Main part of first electrode part 17Ab Terminal part of first electrode part 17B Second electrode part of upper electrode 17Ba Main portion of second electrode portion 17Bb Terminal portion of second electrode portion 18 Upper electrode 20 Via hole 21 Vibrating portion

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keigo Nagao 5F, 1978 Kogushi, Ube-shi, Ube-shi, Yamaguchi F-term in the Ube Research Laboratory, Ube Industries, Ltd. 5J108 AA04 BB08 CC04 CC11 EE03

Claims (11)

[Claims] 1. A piezoelectric thin-film resonator comprising a vibrating part including a part of a piezoelectric laminated structure including a piezoelectric film and electrodes formed on both surfaces thereof, wherein the piezoelectric film is generally Formula Al _1-x Ga _x N (where 0 <x
<1) A solid solution of aluminum nitride and gallium nitride represented by <1) or a general formula Al _1-y In _y N (where 0 <y <
A piezoelectric thin film resonator characterized in that it is an oriented crystal film made of a solid solution of aluminum nitride and indium nitride represented by 1). 2. The piezoelectric laminate structure according to claim 1, wherein the piezoelectric laminated structure includes a plurality of piezoelectric films and electrodes formed on both surfaces of each of the plurality of piezoelectric films. Piezoelectric thin film resonator. 3. The piezoelectric thin film according to claim 1, wherein a peripheral part of the piezoelectric laminated structure is supported by a substrate, and a central part constitutes the vibrating part. Resonator. 4. A piezoelectric laminated structure, comprising: a substrate; and a piezoelectric laminated structure formed on the substrate, wherein a vibrating portion includes a part of the piezoelectric laminated structure. Comprises a structure in which a lower electrode, a piezoelectric film, and an upper electrode are stacked in this order from the side of the substrate, and the substrate has a gap that allows vibration of the vibrating portion in a region corresponding to the vibrating portion. Wherein the piezoelectric film has a general formula Al _1-x Ga _x N (where 0 <x
<1) A solid solution of aluminum nitride and gallium nitride represented by <1) or a general formula Al _1-y In _y N (where 0 <y <
A piezoelectric thin film resonator characterized in that it is an oriented crystal film made of a solid solution of aluminum nitride and indium nitride represented by 1). 5. The piezoelectric thin-film resonator according to claim 4, wherein the upper electrode comprises a first electrode portion and a second electrode portion formed apart from each other. 6. A piezoelectric laminated structure, comprising: a substrate; and a piezoelectric laminated structure formed on the substrate, wherein a vibrating portion includes a part of the piezoelectric laminated structure. Is formed by laminating a lower electrode, a first piezoelectric film, an internal electrode, a second piezoelectric film, and an upper electrode in this order from the substrate side, and the substrate is located in a region corresponding to the vibrating portion. Wherein the first piezoelectric film and the second piezoelectric film each have a general formula Al _1-x Ga _x N (However, a solid solution of aluminum nitride and gallium nitride represented by 0 <x <1) or aluminum nitride and indium nitride represented by a general formula Al _1-y In _y N (where 0 <y <1) A piezoelectric thin film resonator characterized in that it is an oriented crystal film made of a solid solution of the above. 7. An insulating layer is formed between the substrate and the piezoelectric laminated structure, and the vibrating portion is configured to include a part of the insulating layer. Do
A piezoelectric thin-film resonator according to any one of claims 3 to 6. 8. The insulator layer mainly comprises a silicon oxide-based dielectric film, a silicon nitride-based dielectric film, or a silicon oxide-based dielectric film and silicon nitride. The piezoelectric thin-film resonator according to claim 7, wherein the piezoelectric thin-film resonator is a laminated film with a dielectric film. 9. The piezoelectric thin film resonator according to claim 3, wherein the substrate is made of a semiconductor or an insulator. 10. The piezoelectric thin-film resonator according to claim 9, wherein the substrate is made of silicon single crystal. 11. The piezoelectric film or the first piezoelectric film and the second piezoelectric film exhibit a C-axis orientation, and (00
The rocking curve half width of the X-ray diffraction peak of the (02) plane is 3.0 ° or less.
0. The piezoelectric thin-film resonator according to any one of 0 to 0.