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DESCRIPTION JP2006191304

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DESCRIPTION JP2006191304
The present invention makes it possible to use a piezoelectric film having high crystallinity and
excellent flatness in a piezoelectric resonator using an acoustic mirror, and to realize a
piezoelectric resonator having a small insertion loss and high frequency selectivity. Do. A first
acoustic mirror material 12 made of silicon oxide and a second acoustic mirror material 13 made
of tungsten are alternately laminated six cycles on a substrate 11 to form an acoustic mirror 14.
ing. A lower electrode 16 composed of a first adhesive layer 31 and a second adhesive layer 32
made of gold is formed on the acoustic mirror 14, and the first adhesive layer 31 and the second
adhesive layer 32 are formed. An adhesive surface 19 is formed between them. A piezoelectric
film 23 made of aluminum nitride is formed on the lower electrode 16, and an upper electrode
24 made of molybdenum is formed on the piezoelectric film 23. [Selected figure] Figure 1
Piezoelectric resonator and method of manufacturing the same
[0001]
The present invention relates to a resonator that can be used for a high frequency filter or the
like in an electronic circuit and a method of manufacturing the same, and more particularly to an
acoustic resonator that utilizes the resonance of a piezoelectric material.
[0002]
In recent years, with the widespread use of mobile phones worldwide, the number of mobile
phones in use has increased at an accelerating pace, and along with this, there has been a
demand for higher performance of mobile phones.
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1
In a mobile phone, the frequency of a high frequency signal used for communication between a
terminal and a base station is defined for each communication system. Also, in each
communication scheme, the frequency of the high frequency signal transmitted from the base
station to the terminal (this is called a downstream frequency) and the frequency of the high
frequency signal transmitted from the terminal to the base station (this is referred to as the
upstream frequency It is different from calling). In addition, at the time of signal processing in
the terminal, the frequency is also temporarily converted to a frequency (this is called an
intermediate frequency) lower than the high frequency signal to be transmitted / received. Thus,
in a mobile phone, it is necessary to process a plurality of high frequency signals of different
frequencies.
[0003]
In processing each of these high frequency signals, it is generally necessary to remove high
frequency signals of frequencies other than the target frequency. For example, in a terminal
called a front end which receives a high frequency signal transmitted from a base station, it is
always necessary to remove high frequency signals of frequencies other than the downlink
frequency. Further, also in the circuit for converting the downstream frequency to the
intermediate frequency, it is necessary to remove high frequency signals of frequencies other
than the intermediate frequency. A component called a filter is generally used to remove high
frequency signals of unnecessary frequencies and pass only high frequency signals of desired
frequencies as described above.
[0004]
One of the components constituting such a filter is a resonator. In recent years, in order to
miniaturize the filter and improve its performance, it has been attempted to form the filter by a
SAW resonator using surface acoustic waves, a piezoelectric resonator using bulk elastic waves,
or the like. The operating principle of a piezoelectric resonator using bulk acoustic waves will be
described below with reference to the drawings.
[0005]
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2
FIG. 9 shows a cross-sectional structure of a conventional general bulk acoustic wave-based
piezoelectric resonator (see, for example, Patent Document 1). A piezoelectric resonator having a
resonant frequency of about 2 GHz using a general bulk elastic wave has a polygonal or circular
planar shape with a side of 100 μm to 200 μm. Further, as shown in FIG. 9, as a cross-sectional
structure, a piezoelectric film 201 made of aluminum nitride (AlN) having a thickness of about
500 nm is formed on a substrate 204 in which an opening 205 is formed. Upper and lower
electrodes 202 and 203 made of molybdenum (Mo) and having a thickness of 300 nm are
formed on the upper and lower surfaces of the piezoelectric film 201, respectively.
[0006]
When high frequency power is applied to the upper electrode 202 and the lower electrode 203, a
high frequency electric field is induced in the piezoelectric film 201, and the piezoelectric
property of the piezoelectric film 201 generates an ultrasonic wave of the same frequency as the
electric field. The induced ultrasound is usually attenuated inside the piezoelectric film 201, the
upper electrode 202, the lower electrode 202 and the substrate 204. However, if the thickness of
the piezoelectric film 201 is sufficiently larger than the thickness of the upper electrode 202 and
the thickness of the lower electrode 203, the ultrasonic wave of the frequency f represented by
the equation (1) has a thickness of the piezoelectric film 201 It becomes a standing wave formed
in the longitudinal direction and does not attenuate.
[0007]
f = nV / 2d (1) where n is an integer of 1 or more, V is the velocity of sound in the thickness
direction of the piezoelectric film 201, d is the thickness of the piezoelectric film 201, and the
thickness of the upper electrode 202, and It is the sum of the thickness of the lower electrode
203.
[0008]
The ultrasonic wave of the frequency f induces an electric field of the frequency f by the
piezoelectricity of the piezoelectric film 201. Therefore, unlike the other frequencies, only the
high frequency of the frequency f easily passes between the upper electrode 202 and the lower
electrode 203. be able to.
This frequency f is called a resonant frequency. The impedance between the upper electrode 202
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and the lower electrode 203 has a peak that is minimized at the resonance frequency f.
[0009]
In a piezoelectric resonator using a bulk elastic wave, the portion that induces ultrasonic waves
in the thickness direction (hereinafter referred to as the cavity portion) vibrates in the
longitudinal direction, so the substrate and the sealing material vibrate in the longitudinal
direction. It is necessary not to attenuate. Therefore, it is necessary to form a structure in which
the upper and lower parts of the cavity are not in contact with anything.
[0010]
As shown in FIG. 9, in the general piezoelectric resonator, the upper electrode 202 in the cavity
portion has a structure in which nothing is in contact with the upper portion. In addition, an
opening 205 is formed below the lower electrode in the cavity, and the substrate 204 is
configured to suppress the attenuation of the vibration in the vertical direction.
[0011]
However, forming the opening 205 in the substrate 204 is generally not easy. Although etching
is generally performed from the lower side of the substrate 204, the etching takes a lot of time
because the substrate 204 is usually 100 μm or more. Furthermore, although it is ideal for the
opening 205 to have a constant opening diameter, the lower opening diameter is actually larger
than the upper opening diameter. As a method of solving such a defect, there is also a method of
forming the cavity on the lower surface of the lower electrode 203 by scraping the upper surface
of the substrate 204 only in the cavity portion.
[0012]
Common to these shapes is that the cavity portion is structured so as to be supported only on the
periphery of the cavity portion and to float in the air. For this reason, the cavity portion is
mechanically very fragile, and when a downward force is applied from the upper portion of the
cavity portion, the cavity portion is easily depressed downward. Therefore, it is necessary to take
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care not to damage the cavity portion in the manufacturing process, and there is a problem that
the process becomes complicated.
[0013]
In order to solve the defect that the cavity portion is mechanically fragile, a piezoelectric
resonator using the following acoustic mirror is disclosed (see, for example, Patent Document 2).
FIG. 10 shows the cross-sectional structure of a conventional piezoelectric resonator using an
acoustic mirror.
[0014]
As shown in FIG. 10, the piezoelectric film 301 on which the upper electrode 302 and the lower
electrode 303 are formed is formed on the acoustic mirror 306. The acoustic mirror 306 has a
structure in which a first acoustic mirror material 304 and a second acoustic mirror material 305
are alternately stacked several times on a substrate 307.
[0015]
The first acoustic mirror material 304 and the second acoustic mirror material 305 are selected
by combining materials whose acoustic impedances are largely different from each other. Then,
reflection of the acoustic wave occurs at the interface between the first acoustic mirror material
304 and the second acoustic mirror material 305. At this time, the frequency of the sound wave
reflected by the acoustic mirror 306 is determined by the characteristics of the acoustic mirror
306 determined by the thickness of the acoustic mirror material 304 and the thickness of the
second acoustic mirror material 305. If this frequency is designed to coincide with the resonant
frequency of the piezoelectric resonator, the same effect as in the case where a cavity or opening
is provided in the lower part of the cavity of the piezoelectric resonator can be obtained. That is,
energy can be confined in the cavity without diffusing the acoustic energy generated in the
piezoelectric resonator downward.
[0016]
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FIG. 11 shows a method of manufacturing a conventional piezoelectric resonator using an
acoustic mirror in the order of steps. First, as shown in FIG. 11A, a substrate 307 is prepared. On
top of the substrate 307, a first acoustic mirror material 304 is deposited, followed by laminating
a second acoustic mirror material 305. This is repeated about six cycles to form an acoustic
mirror 306 in which the first acoustic mirror material 304 and the second acoustic mirror
material 305 are alternately stacked.
[0017]
Next, as shown in FIG. 11B, the lower electrode 303 made of Mo is formed on the acoustic mirror
306. Next, as shown in FIG. 11C, a piezoelectric film 301 made of AlN is deposited on the lower
electrode 303. Next, as shown in FIG. 11D, the upper electrode 302 is formed on the
piezoelectric film 301.
[0018]
The characteristics of the piezoelectric resonator largely depend on the piezoelectric film. If the
crystallinity of the piezoelectric film is poor, it is considered that many crystal defects and crystal
boundaries exist in the piezoelectric film. Therefore, it is considered that ultrasonic waves
generated in the piezoelectric film are attenuated at crystal defects or crystal boundaries, and
energy is lost. This causes an increase in the insertion loss of the piezoelectric resonator and
causes the characteristic to deteriorate. In addition, when the film thickness of the piezoelectric
film is not uniform, a distribution occurs in the resonant frequency of the piezoelectric resonator,
which causes the frequency selectivity of the piezoelectric resonator to deteriorate. Therefore, it
is desirable to form the piezoelectric film on a substrate excellent in flatness and crystallinity. JPA-6-295181 "Journal of Material Science", 1993, Vol. 28, p. 5088-5091
[0019]
However, in a piezoelectric resonator using a conventional acoustic mirror, the piezoelectric film
301 must be deposited on the acoustic mirror 306. Since the acoustic mirror 306 has to
repeatedly laminate the first acoustic mirror material 304 and the second acoustic mirror
material 305 for at least six cycles, it is very difficult to ensure the flatness of the top surface of
the acoustic mirror 306 It is. In addition, the acoustic mirror 306 is easily warped due to the
thermal expansion coefficient of the first acoustic mirror material 304 and the thermal expansion
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coefficient of the second acoustic mirror material 305 being different from each other.
[0020]
Since the lower electrode 303 is formed on the acoustic mirror having poor flatness and the
piezoelectric film 301 is formed thereon, the film thickness of the piezoelectric film 301 becomes
nonuniform. In addition, since the piezoelectric film 301 is formed on an uneven surface where
warpage has occurred, the crystallinity of the piezoelectric film 301 is degraded. As a result, the
conventional piezoelectric resonator using an acoustic mirror has a problem that the insertion
loss increases and a problem that the frequency selectivity is degraded.
[0021]
Furthermore, even in a piezoelectric resonator using an acoustic mirror, when the substrate on
which the piezoelectric resonator is formed is mounted on a package, in order to prevent vertical
vibration from being attenuated in the upper portion of the cavity, It is necessary to ensure that
nothing comes in contact with the top. However, in the resin-sealed package which is an
inexpensive mounting means, since the resin comes in contact with the upper portion of the
cavity portion, the resin-sealed package can not be used for the mounting of the piezoelectric
resonator. On the other hand, since the performance of the piezoelectric resonator is deteriorated
due to external moisture and the like, this needs to be prevented, and the piezoelectric resonator
must be mounted in an airtight package. For this reason, there is also a problem that the
piezoelectric resonator must be mounted in a structure in which nothing comes in contact with
the upper portion of the cavity portion using an expensive hermetically sealed package or the
like.
[0022]
The present invention solves the above-mentioned conventional problems, and enables the use of
a piezoelectric film having high crystallinity and excellent flatness in a piezoelectric resonator
using an acoustic mirror, with a small insertion loss and frequency selectivity. An object of the
present invention is to realize a high piezoelectric resonator and a method of manufacturing the
same.
[0023]
In order to achieve the above object, the present invention provides a piezoelectric resonator in
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which a piezoelectric film formed on another substrate is bonded onto an acoustic mirror.
[0024]
Specifically, the piezoelectric resonator according to the present invention is provided on a
substrate, on a substrate, a first acoustic mirror material, and a second acoustic mirror material
having a high acoustic impedance compared to the first acoustic mirror material. And a
piezoelectric film provided on the acoustic mirror, an upper electrode provided on the
piezoelectric film, and a lower electrode provided below the piezoelectric film. An adhesive
surface in which metal films are bonded to each other is formed between the substrate and the
piezoelectric film.
[0025]
In the piezoelectric resonator according to the present invention, since the first bonding surface
in which the metals are bonded to each other is formed between the substrate and the
piezoelectric film, the crystallinity and the flatness formed on the forming substrate are obtained.
Since the acoustic mirror can be disposed under the excellent piezoelectric film, the flatness of
the acoustic mirror does not matter.
As a result, it is possible to easily realize a piezoelectric resonator having a small insertion loss
and high frequency selectivity.
[0026]
In the piezoelectric resonator of the present invention, the first acoustic mirror material is
preferably any one of silicon oxide, aluminum, titanium and gallium nitride.
Preferably, the second acoustic mirror material is any one of tungsten, iridium, aluminum nitride
and molybdenum.
With such a configuration, an acoustic mirror can be reliably obtained.
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[0027]
The piezoelectric resonator according to the present invention preferably further comprises an
adhesive layer made of metal provided between the substrate and the acoustic mirror, and the
adhesive surface is preferably formed on the adhesive layer. In addition, the bonding surface may
be formed on the lower electrode. With such a configuration, it is possible to use a piezoelectric
film having excellent crystallinity and flatness for a piezoelectric resonator provided with an
acoustic mirror.
[0028]
In the piezoelectric resonator of the present invention, the metal forming the first adhesive
surface is preferably gold and gold, gold and tin, gold and germanium, or lead and tin. With such
a configuration, the adhesive surface can be formed with certainty.
[0029]
The piezoelectric resonator of the present invention preferably further includes a first barrier
metal layer for preventing mutual diffusion between the lower electrode and the acoustic mirror,
between the lower electrode and the acoustic mirror. The first barrier metal layer is preferably
made of nickel or platinum. With such a configuration, mutual diffusion does not occur between
the lower electrode and the acoustic mirror, so that changes in the composition and structure of
the lower electrode and the acoustic mirror can be reliably prevented.
[0030]
The piezoelectric resonator according to the present invention preferably further includes an
upper acoustic mirror having a laminated structure in which a first acoustic mirror material and
a second acoustic mirror material are alternately laminated on the upper electrode. . With such a
configuration, it is not necessary to have a structure in which nothing is in contact with the upper
side of the piezoelectric resonator, so that the piezoelectric resonator can be sealed in a resin
package or the like. Further, the upper electrode preferably has a structure in which metal films
are bonded to each other. In this way, the upper acoustic mirror can be formed by bonding.
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[0031]
In the piezoelectric resonator of the present invention, preferably, a second barrier metal layer
for preventing mutual diffusion between the upper electrode and the acoustic mirror is further
provided between the upper electrode and the upper acoustic mirror. The second barrier metal
layer is preferably made of nickel or platinum.
[0032]
In a first method of manufacturing a piezoelectric resonator according to the present invention, a
first acoustic mirror material on a first substrate, and a second acoustic mirror material having a
high acoustic impedance as compared to the first acoustic mirror. Forming an acoustic mirror by
alternately laminating the first and second electrodes, and forming a piezoelectric film on the
second substrate; Forming a second lower electrode forming layer on the film (b), and forming a
first lower electrode forming layer on the first substrate and a second forming on the second
substrate And a step (d) of removing the second substrate from the piezoelectric film by bonding
the lower electrode to the lower electrode forming layer.
[0033]
According to the first method of manufacturing a piezoelectric resonator, the first lower
electrode formation layer formed on the lower first substrate and the second lower electrode
formation layer formed on the second substrate And the step of forming the lower electrode by
bonding, there is no need to form a piezoelectric film on the acoustic mirror, and there is no need
to consider the flatness of the acoustic mirror, so the insertion loss is very easy. It is possible to
manufacture a piezoelectric resonator having a low frequency and excellent frequency selectivity.
[0034]
In the first method for manufacturing a piezoelectric resonator, the first lower electrode
formation layer and the second lower electrode formation layer are both made of gold, and in the
step (c), the first lower electrode formation is performed by a thermocompression bonding
method. It is preferable to be a step of bonding the layer and the second lower electrode
formation layer.
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In addition, the first lower electrode formation layer and the second lower electrode formation
layer are made of a combination of gold and tin, gold and germanium, or lead and tin, and the
step (c) is performed by the eutectic bonding method. It may be a step of bonding the electrode
formation layer and the second lower electrode formation layer.
With such a configuration, the first lower electrode formation layer and the second lower
electrode formation layer can be reliably bonded.
[0035]
In the first method of manufacturing a piezoelectric resonator, the process step (a) includes a
first barrier metal layer for preventing mutual diffusion between an acoustic mirror and a lower
electrode, an acoustic mirror and a first lower electrode forming layer. It is preferable to include
the process of forming between them. The first barrier metal layer is preferably nickel or
platinum. With such a configuration, mutual diffusion does not occur between the lower
electrode and the acoustic mirror, so that changes in the composition and structure of the lower
electrode and the acoustic mirror can be reliably prevented.
[0036]
The method of manufacturing the first piezoelectric resonator comprises the steps of: (e) forming
an upper electrode on the piezoelectric film from which the second substrate has been removed;
and (e) after the step (d); Preferably, the method further comprises the step (f) of forming an
upper acoustic mirror by alternately laminating the acoustic mirror material of 1 and the second
acoustic mirror material. With such a configuration, it is not necessary to have a structure in
which nothing is in contact with the upper side of the piezoelectric resonator, so that the
piezoelectric resonator can be sealed in a resin package or the like.
[0037]
In the method of manufacturing the first piezoelectric resonator, after the step (d), the step (g) of
forming a first upper electrode forming layer on the piezoelectric film from which the second
substrate has been removed; The upper acoustic mirror is formed by alternately laminating the
first acoustic mirror material and the second acoustic mirror material on the substrate of (b), and
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then the second upper electrode forming layer is formed on the upper acoustic mirror Step (h),
forming an upper electrode by bonding the first upper electrode forming layer and the second
upper electrode forming layer, and (i) removing the third substrate from the upper acoustic
mirror And (j) may be included. With such a configuration, the upper acoustic mirror can be
reliably formed.
[0038]
In this case, the first upper electrode formation layer and the second upper electrode formation
layer are both made of gold, and in the step (i), the first upper electrode formation layer and the
second upper electrode are formed by thermocompression bonding. It is preferable that it is the
process of adhering with a formation layer. In addition, the first upper electrode forming layer
and the second upper electrode forming layer are made of a combination of gold and tin, gold
and germanium, or lead and tin, and in the step (i), the first upper portion is formed by eutectic
bonding. It may be a step of bonding the electrode formation layer and the second upper
electrode formation layer.
[0039]
In the step (h), a second barrier metal layer for preventing mutual diffusion between the upper
acoustic mirror and the upper electrode is formed between the upper acoustic mirror and the
second upper electrode forming layer. It is preferable to contain. In this case, the second barrier
metal layer is preferably nickel or platinum.
[0040]
In a second method of manufacturing a piezoelectric resonator according to the present
invention, a step (a) of forming a first adhesive layer on a first substrate, a piezoelectric film on a
second substrate, and a lower electrode A step of sequentially forming an acoustic mirror in
which a first acoustic mirror material and a second acoustic mirror material having a higher
acoustic impedance than the first acoustic mirror are alternately stacked, and a second adhesive
layer (b Bonding the first adhesive layer formed on the first substrate and the second adhesive
layer formed on the second substrate (c); And (d) removing the substrate.
[0041]
According to the second method of manufacturing a piezoelectric resonator, since the step of
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forming the second adhesive layer on the acoustic mirror is provided, the lower electrode does
not need to be formed of a material that can be adhered, so the lower electrode It is possible to
freely select the material of
[0042]
In the second method of manufacturing a piezoelectric resonator, the first adhesive layer and the
second adhesive layer are both made of gold, and in the step (c), the first adhesive layer and the
second adhesive layer are bonded by a thermocompression bonding method. It is preferable that
it is the process of adhering with a layer.
Also, the first adhesive layer and the second adhesive layer consist of a combination of gold and
tin, gold and germanium, or lead and tin, and the step (c) is carried out by a eutectic bonding
method to form the first adhesive layer and the second adhesive layer. It may be a step of
bonding with an adhesive layer of
[0043]
In the second method for manufacturing a piezoelectric resonator, after the step (d), a step (i) of
forming an upper electrode on the piezoelectric film, a first acoustic mirror material on the upper
electrode, and Preferably, the method further comprises the step (j) of forming an upper acoustic
mirror by alternately laminating 2 acoustic mirror materials.
[0044]
According to the present invention, it is possible to use a piezoelectric film having high
crystallinity and excellent flatness in a piezoelectric resonator using an acoustic mirror, and a
piezoelectric resonator having a small insertion loss and high frequency selectivity, and the same
The manufacturing method can be realized.
[0045]
First Embodiment FIG. 1 shows a cross-sectional configuration of a piezoelectric resonator
according to a first embodiment of the present invention.
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13
As shown in FIG. 1, the piezoelectric resonator of the present embodiment is a piezoelectric
resonator provided with an acoustic mirror.
[0046]
On the substrate 11 made of silicon (Si), a first acoustic mirror material 12 made of silicon oxide
(SiO 2) and a second acoustic mirror material 13 made of tungsten (W) are alternately laminated
in four cycles. The acoustic mirror 14 is formed.
The thickness of each of the first acoustic mirror material 12 and the second acoustic mirror
material 13 is set to be 1⁄4 wavelength of the resonance frequency, and is, for example, 200 nm
to 500 nm when the resonance frequency is 2 GHz. .
[0047]
A lower electrode 16 composed of a first adhesive layer 31 and a second adhesive layer 32 of
gold (Au) each having a thickness of about 150 nm is formed on the acoustic mirror 14, and the
first adhesive is formed. An adhesive surface 19 is formed between the layer 31 and the second
adhesive layer 32.
[0048]
A piezoelectric film 23 made of aluminum nitride (AlN) and having a thickness of about 500 nm
is formed on the lower electrode 16, and an upper electrode 24 made of molybdenum (Mo)
having a thickness of about 300 nm is formed on the piezoelectric film 23. Is formed.
The thicknesses of the upper electrode 24, the piezoelectric film 23, the lower electrode 16, and
the acoustic mirror 14 are set in accordance with the resonant frequency of the resonator.
[0049]
The acoustic mirror 14 may be formed by alternately laminating a material having a small
acoustic impedance and a material having a large acoustic impedance for 4 to 8 cycles, and
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aluminum (Al), titanium (Ti) or nitrided may be used as the first acoustic mirror material 12 in
addition to SiO2. Any of gallium (GaN) or the like can be used, and for the second acoustic mirror
material 13, any of iridium (Ir), aluminum nitride (AlN), molybdenum (Mo), etc. in addition to W
can be used. Can be used.
Also, the first acoustic mirror material 12 and the second acoustic mirror material 13 may be
alternately arranged, and the stacking order may be reversed.
[0050]
Hereinafter, a method of manufacturing the piezoelectric resonator according to the present
embodiment will be described. FIG. 2 shows the state of the cross section in each step of the
method of manufacturing the piezoelectric resonator of the present embodiment in the order of
steps. First, as shown in FIG. 2A, on a substrate 11 made of silicon, a first acoustic mirror
material 12 made of SiO 2 with a thickness of 300 nm and a second acoustic mirror made of W
with a thickness of 300 nm The acoustic mirror 14 is formed by alternately laminating the
material 13 for six cycles. Subsequently, Au of 150 nm in thickness is deposited on the acoustic
mirror 14 to form a first adhesive layer 31.
[0051]
On the other hand, as shown in FIG. 2B, a buffer layer 22 of GaN having a thickness of 100 nm is
formed on a forming substrate 21 of sapphire, and AlN is epitaxially grown on the buffer layer
22. A piezoelectric film 23 of 500 nm is formed. Subsequently, Au having a thickness of 150 nm
is deposited on the piezoelectric film 23 to form a second adhesive layer 32.
[0052]
Next, as shown in FIG. 2C, the substrate 11 and the formation substrate 21 are vertically pressed
at a pressure of 1 to 3 MPa so that the first adhesive layer 31 and the second adhesive layer 32
are in close contact with each other. Pressurize. By heating for 10 minutes at a temperature of
350 ° C. in this state, the first adhesive layer 31 and the second adhesive layer 32 are bonded
by a thermocompression bonding method to form the lower electrode 16.
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15
[0053]
Next, as shown in FIG. 2D, the formation substrate 21 is removed by a laser lift-off method in
which the buffer layer 22 is irradiated with laser light from the side of the formation substrate
21.
[0054]
Next, as shown in FIG. 2E, the upper electrode 24 made of Mo and having a thickness of 300 nm
is formed on the piezoelectric film 23.
[0055]
In order to obtain an excellent resonator having a small insertion loss, it is necessary to form a
piezoelectric film 23 excellent in crystallinity and flatness.
According to the method of manufacturing the piezoelectric resonator of the present
embodiment, after the piezoelectric film is formed on the sapphire substrate by epitaxial growth,
it is bonded to the acoustic mirror 14.
Therefore, the piezoelectric film 23 excellent in film quality can be obtained regardless of the
flatness and crystallinity of the acoustic mirror 14 and the lower electrode 16, so that a
piezoelectric resonator having a small insertion loss and high frequency selectivity can be easily
manufactured. It is possible.
[0056]
Note that instead of the epitaxial growth method, after forming a metal layer such as Mo with
good flatness by sputtering on a substrate made of Si, the piezoelectric film 23 is formed by
depositing AlN on the metal layer by sputtering or the like. You may
[0057]
Further, the first adhesive layer 31 or the second adhesive layer 32 is formed of tin (Sn), and the
first adhesive layer 31 and the second adhesive layer 32 are adhered by a gold-tin eutectic
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bonding method. You may
Similarly, eutectic bonding is also possible using lead (Pb) and tin (Sn) or the like.
[0058]
Further, as the substrate 11, a GaAs substrate or a sapphire substrate may be used instead of the
Si substrate.
[0059]
(Modification of First Embodiment) FIG. 3 shows the state of the cross section of a piezoelectric
resonator according to a modification of the first embodiment.
The description of the components shown in FIG. 3 that are the same as those shown in FIG. 1
will be omitted by retaining the same reference numerals.
[0060]
As shown in FIG. 3, a third adhesive layer 33 and a fourth adhesive layer 34 made of gold are
formed on the substrate 11. On the fourth adhesive layer 34, an acoustic mirror 14 is formed in
which the first acoustic mirror material 12 made of SiO 2 and the second acoustic mirror
material 13 made of W are alternately laminated in six cycles. . A lower electrode 16 made of Mo
having a thickness of 300 nm is formed on the acoustic mirror 14, and a piezoelectric film 23
made of AlN and an upper electrode 24 made of Mo are formed on the lower electrode 16. There
is.
[0061]
FIG. 4 shows the state of the cross section in each manufacturing process of the piezoelectric
resonator of this modification in order of processes. First, as shown in FIG. 4A, a third adhesive
layer 33 made of Au and having a thickness of 150 nm is formed on a substrate 11 made of Si.
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17
[0062]
Next, as shown in FIG. 4B, the buffer layer 22 made of GaN, the piezoelectric film 23 made of
AlN, and the lower electrode 16 made of Mo are sequentially formed on the formation substrate
21 made of sapphire. Subsequently, the acoustic mirror 14 is formed by alternately laminating
the first acoustic mirror material 12 made of SiO 2 and the second acoustic mirror material made
of W on the upper electrode 24 for 6 cycles, and then the thickness is A fourth adhesion layer 34
of 150 nm Au is formed.
[0063]
Next, as shown in FIG. 4C, the substrate 11 and the formation substrate 21 are pressed from
above and below so that the third adhesive layer 33 and the fourth adhesive layer 34 adhere to
each other, and the temperature is 350 ° C. Heating at a temperature of 10 minutes to bond the
third adhesive layer 33 and the fourth adhesive layer 34.
[0064]
Next, as shown in FIG. 4D, the formation substrate 21 is peeled off by a laser lift-off method, and
then the upper electrode 24 made of Mo is formed on the piezoelectric film 23.
[0065]
In the piezoelectric resonator of this modification, since the lower electrode and the adhesive
layer are separately provided, the material of the lower electrode can be freely selected.
In this modification, Mo having high hardness is used for the lower electrode, but by using
tungsten (W) or iridium (Ir) excellent in acoustic impedance, the selectivity (Q value) of the
resonator can be improved. .
[0066]
Second Embodiment Hereinafter, a piezoelectric resonator according to a second embodiment of
the present invention will be described with reference to the drawings.
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FIG. 5 shows the cross-sectional structure of the piezoelectric resonator of the present
embodiment. The description of the components shown in FIG. 5 which are the same as those
shown in FIG. 1 will be omitted by retaining the same reference numerals.
[0067]
As shown in FIG. 5, in the piezoelectric resonator of the present embodiment, the upper acoustic
mirror 15 is formed on the upper electrode 24 of the piezoelectric resonator of the first
embodiment. The upper electrode 24 formed on the piezoelectric film 23 is composed of a fifth
adhesive layer 35 and a sixth adhesive layer 36 of Au each having a thickness of 150 nm, and
the fifth adhesive layer 35 and the sixth adhesive are formed. A bonding surface 35 is formed
between the layers 36. An upper acoustic mirror 15 in which the first acoustic mirror material
12 and the second acoustic mirror material 13 are alternately stacked six cycles is formed on the
upper electrode 24.
[0068]
In the piezoelectric resonator of the present embodiment, since the upper acoustic mirror 15 is
further formed on the upper electrode 24, there is no need to have a structure in which nothing
is in contact with the upper side of the piezoelectric resonator. Therefore, it is possible to seal the
piezoelectric resonator in an inexpensive resin package.
[0069]
FIG. 6 shows the state of the cross section in each manufacturing process of the piezoelectric
resonator of the present embodiment in the order of processes. The process until the formation
substrate 21 is peeled off by the laser lift-off method is the same as that of the first embodiment,
and thus the description thereof is omitted.
[0070]
As shown in FIG. 6A, a fifth adhesive layer 35 of Au having a thickness of 150 nm is formed on
the piezoelectric film 23 from which the formation substrate 21 has been peeled off by the laser
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lift-off method.
[0071]
Next, as shown in FIG. 6B, the first acoustic mirror material 12 made of SiO 2 having a thickness
of 300 nm and W having a thickness of 300 nm are formed on a substrate 41 for forming an
upper acoustic mirror made of Si. The upper acoustic mirror 15 is formed by alternately
laminating the second acoustic mirror material 13 of six cycles for six cycles.
Subsequently, a sixth adhesive layer 36 made of Au and having a thickness of 150 nm is formed
on the upper acoustic mirror 15.
[0072]
Next, as shown in FIG. 6C, the substrate 11 and the substrate 41 are vertically pressed so that the
fifth adhesive layer 35 and the sixth adhesive layer 36 are in close contact with each other. In
this state, by heating at a temperature of 350 ° C. for 10 minutes, the fifth adhesive layer 35
and the sixth adhesive layer 36 are bonded to form the upper electrode 24.
[0073]
Next, as shown in FIG. 6D, the substrate 41 is removed by polishing or the like.
[0074]
In the present embodiment, the first adhesive layer 31 and the second adhesive layer 32, and the
fifth adhesive layer 35 and the sixth adhesive layer 36 are all made of Au, and the first adhesive
layer 31 and the second adhesive layer 36 are formed. Although the example which adhere |
attaches the contact bonding layer 32 and the 5th contact bonding layer 35 and the 6th contact
bonding layer 36 by the thermocompression bonding method was shown, you may adhere |
attach by the eutectic bonding method.
In that case, gold-germanium (Au-Ge, eutectic point: about 360 ° C.) is used for the first
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adhesive layer 31 and the second adhesive layer 32, and the fifth adhesive layer 35 and the sixth
adhesive layer When gold-tin (Au-Sn, with a eutectic point of about 280 ° C.) having a melting
point (eutectic point) lower than that of Au-Ge is used for bonding the upper acoustic mirror 44,
the first adhesive layer 31 And the adhesive surface of the second adhesive layer 32 is not
affected.
[0075]
Further, after forming the upper electrode made of Mo in the same manner as in the first
embodiment, the first acoustic mirror material 12 made of SiO 2 and the second acoustic mirror
material 13 made of W are formed directly on the upper electrode. May be deposited alternately
to form the upper acoustic mirror 15.
[0076]
In the present embodiment, the upper acoustic mirror is formed on the piezoelectric resonator of
the first embodiment, but the upper acoustic mirror is formed on the piezoelectric resonator
shown in a modification of the first embodiment. You may form.
[0077]
Third Embodiment Hereinafter, a piezoelectric resonator according to a third embodiment of the
present invention will be described with reference to the drawings.
FIG. 7 shows the state of the cross section of the piezoelectric resonator of the present
embodiment.
The description of the components shown in FIG. 7 which are the same as those shown in FIG. 1
will be omitted by retaining the same reference numerals.
[0078]
As shown in FIG. 7, the piezoelectric resonator of the present embodiment has a barrier metal 51
made of nickel (Ni) and having a thickness of 50 nm between the acoustic mirror 14 and the
lower electrode 16.
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[0079]
In general, when one metal is in contact with another metal, a phenomenon occurs in which the
two metals mutually diffuse.
The ease of occurrence of this interdiffusion largely varies depending on the type of metal in
contact, temperature conditions and the like. For example, it is known that considerable
interdiffusion occurs between Ti and Au (see, for example, Non-Patent Document 1). When Ti and
Au are laminated and then heated at a temperature of 250 ° C., the interface between Ti and Au
becomes unclear, and further a phenomenon that irregularities are generated on the surface is
recognized, and the composition of Ti and Au and mutual diffusion A change occurs in the
structure such as film thickness.
[0080]
Therefore, when Au is used for the lower electrode 16 and Ti is used for the first acoustic mirror
material 12 of the uppermost layer of the acoustic mirror 14, mutual diffusion occurs between
the lower electrode 16 and the first acoustic mirror material 12. As a result, the composition, film
thickness, and the like of the lower electrode 16 and the first acoustic mirror material 12 change.
As a result, the resonant frequency of the piezoelectric resonator changes, so that the frequency
characteristic of the piezoelectric resonator is significantly degraded.
[0081]
In the present embodiment, a barrier metal layer 51 made of Ni is provided between the lower
electrode 16 and the first acoustic mirror material 12 made of Ti formed in the uppermost layer
of the acoustic mirror 14. The interdiffusion between Au and Ni and Ti and Ni is very small
compared to the interdiffusion between Au and Ti. Therefore, almost no change occurs in the
composition, film thickness, and the like of the lower electrode 16 and the first acoustic mirror
material 12, and deterioration of the frequency characteristics of the piezoelectric resonator can
be prevented.
[0082]
In the present embodiment, the material and thickness of the barrier metal layer 51 need to be
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changed according to the materials of the lower electrode 16 and the first acoustic mirror
material 12, but the lower electrode 16 and the first acoustic mirror material When 12 is Au and
Ti, respectively, platinum (Pt) may be used for the barrier metal layer 51.
[0083]
Further, in the present embodiment, an example in which the uppermost layer of the acoustic
mirror 14 is the first acoustic mirror material 12 is shown, but in the case where the uppermost
layer of the acoustic mirror 14 is the second acoustic mirror 13 It is possible to prevent
interdiffusion between the lower electrode 16 and the second acoustic mirror material 13 in a
similar manner.
[0084]
(Modification of Third Embodiment) FIG. 8 shows the state of the cross section of a piezoelectric
resonator according to a modification of the third embodiment.
The description of the components shown in FIG. 8 that are the same as those shown in FIG. 7
will be omitted by retaining the same reference numerals.
[0085]
As shown in FIG. 8, in the present modification, the barrier metal layer 52 is formed on the upper
electrode 24, and the upper acoustic mirror 15 is formed on the barrier metal layer 52.
[0086]
According to the piezoelectric resonator of this modification, mutual diffusion between the upper
electrode 24 and the first acoustic mirror material forming the upper acoustic mirror 15 can be
prevented.
[0087]
The piezoelectric resonator according to the present invention and the method for manufacturing
the same make it possible to use a piezoelectric film having high crystallinity and excellent
flatness in a piezoelectric resonator using an acoustic mirror, with small insertion loss and
frequency selectivity. Since a high piezoelectric resonator and a method of manufacturing the
same can be realized, it is useful as a resonator that can be used for a high frequency filter or the
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like in an electronic circuit, a method of manufacturing the same, and the like.
[0088]
FIG. 1 is a cross-sectional view showing a piezoelectric resonator according to a first embodiment
of the present invention.
FIG. 5A is a cross-sectional view showing the manufacturing process of the piezoelectric
resonator according to the first embodiment of the present invention in order of processes.
FIG. 6 is a cross-sectional view showing a piezoelectric resonator according to a modification of
the first embodiment of the present invention.
FIG. 7A is a cross-sectional view showing a manufacturing process of a piezoelectric resonator
according to a modification of the first embodiment of the present invention in order of
processes.
FIG. 7 is a cross-sectional view showing a piezoelectric resonator according to a second
embodiment of the present invention. It is sectional drawing which shows the manufacturing
process of the piezoelectric resonator concerning the 2nd Embodiment of this invention to
process order. It is sectional drawing which shows the piezoelectric resonator concerning the 3rd
Embodiment of this invention. FIG. 14 is a cross-sectional view showing a piezoelectric resonator
according to a modification of the third embodiment of the present invention. It is sectional
drawing which shows the conventional common piezoelectric resonator. It is sectional drawing
which shows the piezoelectric resonator using the conventional acoustic mirror. FIG. 14 is a
cross-sectional view showing a manufacturing process of a piezoelectric resonator using a
conventional acoustic mirror in order of processes.
Explanation of sign
[0089]
Reference Signs List 11 substrate (first substrate) 12 first acoustic mirror material 13 second
acoustic mirror material 14 acoustic mirror 15 upper acoustic mirror 16 lower electrode 19
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junction surface 21 formation substrate (second substrate) 22 buffer layer 23 piezoelectric Film
24 upper electrode 31 first adhesive layer 32 second adhesive layer 33 third adhesive layer 34
fourth adhesive layer 35 fifth adhesive layer 36 sixth adhesive layer 41 substrate (third
substrate) 51 barrier Metal layer 52 Barrier metal layer
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