U.S. patent application number 10/338707 was filed with the patent office on 2003-07-10 for electronic component, manufacturing method for the same, and filter, duplexer, and electronic communication apparatus using the same.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kawamura, Hideki, Takeuchi, Masaki, Yamada, Hajime, Yoshino, Yukio.
Application Number | 20030127946 10/338707 |
Document ID | / |
Family ID | 26625474 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030127946 |
Kind Code |
A1 |
Yamada, Hajime ; et
al. |
July 10, 2003 |
Electronic component, manufacturing method for the same, and
filter, duplexer, and electronic communication apparatus using the
same
Abstract
A manufacturing method for an electronic component includes a
process of forming a lower electrode and a dummy electrode, which
are electrically connected to each other, on a substrate, and a
process of forming a piezoelectric thin film on the dummy electrode
and the lower electrode while a predetermined bias potential is
applied to the lower electrode via the dummy electrode. In this
method, the piezoelectric thin film is formed on the lower
electrode by stabilizing the potential of the lower electrode,
thereby decreasing the surface roughness of the piezoelectric thin
film. It is thus possible to manufacture an electric component that
exhibits excellent piezoelectric characteristics, in which the
electromechanical coupling coefficient and the quality of a
resonator are increased.
Inventors: |
Yamada, Hajime; (Otsu-shi,
JP) ; Takeuchi, Masaki; (Otsu-shi, JP) ;
Kawamura, Hideki; (Shiga-ken, JP) ; Yoshino,
Yukio; (Otsu-shi, JP) |
Correspondence
Address: |
Keating & Bennett LLP
Suite 312
10400 Eaton Place
Fairfax
VA
22030
US
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
Nagaokakyo-shi
JP
|
Family ID: |
26625474 |
Appl. No.: |
10/338707 |
Filed: |
January 9, 2003 |
Current U.S.
Class: |
310/324 |
Current CPC
Class: |
Y10T 29/42 20150115;
Y10T 29/49156 20150115; H03H 9/173 20130101; H01L 41/316 20130101;
H03H 3/04 20130101; H03H 9/132 20130101; H03H 9/174 20130101 |
Class at
Publication: |
310/324 |
International
Class: |
H01L 041/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2002 |
JP |
2002-003304 |
Nov 11, 2002 |
JP |
2002-327253 |
Claims
What is claimed is:
1. An electronic component comprising: a substrate; an electrode
disposed on the substrate; and a piezoelectric thin film disposed
on the electrode; wherein a surface roughness of the piezoelectric
thin film is about 10 nm or smaller.
2. An electronic component according to claim 1, wherein the
piezoelectric thin film is formed while a predetermined bias
potential is applied to the electrode.
3. An electronic component comprising a resonator, said resonator
comprising: a substrate; and a vibrator disposed on the substrate,
the vibrator including a thin-film portion having at least one
layer of a piezoelectric thin film which is interposed by opposing
at least one pair of an upper electrode and a lower electrode on
first surface and a second surface of the thin-film portion;
wherein the piezoelectric thin film is formed while a predetermined
bias potential is applied to the lower electrode, and the surface
roughness of the piezoelectric thin film is about 10 nm or
smaller.
4. An electronic component according to claim 3, wherein the
substrate has one of an opening and a recessed portion, and the
vibrator is disposed on said one of the opening and the recessed
portion.
5. An electronic component according to claim 1, wherein the
piezoelectric thin film includes one element selected from the
group consisting of ZnO and AlN.
6. An electronic component according to claim 2, wherein the bias
potential ranges from about +50 V to about +300 V.
7. A filter comprising a circuit and a plurality of the electronic
components according to claim 1, wherein the electrodes of the
electronic components are connected to the circuit of the
filter.
8. A filter comprising a plurality of the electronic components
according to claim 1, the plurality of the electronic components
arranged in a ladder configuration.
9. A duplexer comprising the filter according to claim 7.
10. A duplexer comprising the filter according to claim 8.
11. An electronic communication apparatus comprising at least one
of the electronic component according to claim 1, and said at least
one electronic component is used for an electronic communication
operation.
12. A method for manufacturing an electronic component, comprising
the steps of: forming an electrode on a substrate; and forming a
piezoelectric thin film on the electrode while a predetermined bias
potential is applied to the electrode.
13. A method for manufacturing an electronic component according to
claim 12, wherein the bias potential ranges from about +50 V to
about +300 V.
14. A method for manufacturing an electronic component according to
claim 12, wherein the piezoelectric thin film includes one element
selected from the group consisting of ZnO and AlN.
15. A method for manufacturing an electronic component according to
claim 12, wherein the piezoelectric thin film is formed by using
one of ion and plasma.
16. A method for manufacturing an electronic component according to
claim 12, wherein the piezoelectric thin film is formed by one of a
chemical vapor deposition method and a sputtering method.
17. A method for manufacturing an electronic component, comprising
the steps of: forming a dummy electrode together with a lower
electrode on a substrate such that the dummy electrode surrounds a
periphery of the lower electrode and that the dummy electrode is
electrically connected to the lower electrode; forming a
piezoelectric thin film on the lower electrode and the dummy
electrode while a predetermined bias potential is applied to the
lower electrode and the dummy electrode; removing the dummy
electrode together with a peripheral portion of the piezoelectric
thin film; and forming an upper electrode on the piezoelectric thin
film such that a portion of the upper electrode and a portion of
the lower electrode define a pair of vertically opposing excitation
electrodes with the piezoelectric thin film therebetween.
18. A method for manufacturing an electronic component according to
claim 17, wherein the bias potential ranges from about +50 V to
about +300 V.
19. A method for manufacturing an electronic component according to
claim 17, wherein the piezoelectric thin film includes one element
selected from the group consisting of ZnO and AlN.
20. A method for manufacturing an electronic component according to
claim 17, wherein the piezoelectric thin film is formed by using
one of ion and plasma.
21. A method for manufacturing an electronic component according to
claim 17, wherein the piezoelectric thin film is formed by one of a
chemical vapor deposition method and a sputtering method.
22. A method for manufacturing an electronic component, comprising
the steps of: forming an insulating thin film on a substrate;
forming a dummy electrode together with a lower electrode on the
insulating thin film such that the dummy electrode surrounds a
periphery of the lower electrode and that the dummy electrode is
electrically connected to the lower electrode; forming a
piezoelectric thin film on the insulating thin film, the dummy
electrode, and the lower electrode while a predetermined bias
potential is applied to the dummy electrode and the lower
electrode; removing the dummy electrode together with a peripheral
portion of the piezoelectric thin film; and forming an upper
electrode on the piezoelectric thin film such that a portion of the
upper electrode and a portion of the lower electrode define a pair
of vertically opposing excitation electrodes with the piezoelectric
thin film disposed therebetween.
23. A method for manufacturing an electronic component according to
claim 22, wherein the bias potential ranges from about +50 V to
about +300 V.
24. A method for manufacturing an electronic component according to
claim 22, wherein the piezoelectric thin film includes one element
selected from the group consisting of ZnO and AlN.
25. A method for manufacturing an electronic component according to
claim 22, wherein the piezoelectric thin film is formed by using
one of ion and plasma.
26. A method for manufacturing an electronic component according to
claim 22, wherein the piezoelectric thin film is formed by one of a
chemical vapor deposition method and a sputtering method.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electronic component
including a piezoelectric thin film, such as a piezoelectric
thin-film resonator, and to a manufacturing method for such an
electronic component. The present invention also relates to a
filter, a duplexer, and an electronic communication apparatus
including such an electronic component.
[0003] 2. Description of the Related Art
[0004] The resonant frequency of a piezoelectric resonator
utilizing a thickness-extensional-vibration mode of a piezoelectric
substrate is inversely proportional to the thickness of the
piezoelectric substrate, and therefore, the piezoelectric substrate
must be processed to be very thin for use in the ultrahigh
frequency range. In practice, however, in terms of decreasing the
thickness of the piezoelectric substrate, a few hundred megahertz
is the limit of high frequency in the fundamental mode due to
limitations of the mechanical strength or the handling conditions,
or other factors. In order to overcome this drawback, the following
known piezoelectric thin-film resonator having better
high-frequency characteristics has been proposed.
[0005] In the piezoelectric thin-film resonator shown in FIG. 10,
by partially etching a Si substrate 90 by a micro-processing
technique, a thin-film support portion 91 having a thickness of a
few microns or smaller is formed in a portion of the Si substrate
90, and a ZnO piezoelectric thin film 94 having a pair of
excitation electrodes 92 and 93 is disposed on the thin-film
support portion 91 (see, for example, Patent Document 1, Japanese
Unexamined Patent Application Publication No. 2001-168674, page 3
and FIG. 3). In the piezoelectric thin-film resonator shown in FIG.
10, since the thickness of the thin-film support portion 91 can be
decreased by using a micro-processing technique, and the thickness
of the ZnO piezoelectric thin film 94 can also be decreased by, for
example, sputtering, the frequency characteristics can be increased
to a few hundred megahertz or a few thousand megahertz. In this
resonator, however, the temperature characteristics of the resonant
frequency are decreased because the temperature coefficients of the
Young's modulus of both the ZnO piezoelectric thin film 94 and the
Si substrate 90 are negative values
[0006] To solve the problem of a decrease in the temperature
characteristics of the resonant frequency, a piezoelectric
thin-film resonator shown in FIG. 11 has been proposed. In this
resonator, a SiO.sub.2 thin film is formed on the surface of a Si
substrate 100 by, for example, thermal oxidation, and a thin-film
support portion 101 is formed by using the SiO.sub.2 thin film by
partially etching the Si substrate 100. A ZnO piezoelectric thin
film 104 having excitation electrodes 102 and 103 on the upper and
lower surfaces is disposed on the thin-film support portion 101. In
the piezoelectric thin-film resonator shown in FIG. 11, the
temperature coefficient of the Young's modulus of the thin-film
support portion 101 is a positive value, unlike that of the ZnO
piezoelectric thin film 104. Accordingly, by setting the ratio of
the thickness of the ZnO piezoelectric thin film 104 to the
thickness of the SiO.sub.2 thin-film support portion 101 to a
suitable value, the temperature characteristics of the resonant
frequency can be made stable (see, for example, Patent Document 2,
Japanese Unexamined Patent Application Publication No. 58-121817,
all pages and all figures). However, in this resonator, the ZnO
piezoelectric thin film 104 cannot be symmetrically located with
respect to the vibration node of the fundamental thickness
extensional vibration. Accordingly, not only the odd-order higher
harmonics, such as third and fifth harmonics, but also even-order
higher harmonics, disadvantageously generate spurious
responses.
[0007] A piezoelectric thin-film resonator that can solve this
problem is shown in FIG. 12. In this resonator, SiO.sub.2 thin
films 204 and 205 are symmetrically arranged on a substrate 200
with respect to a ZnO piezoelectric thin film 203 that is provided
between electrodes 201 and 202. With this arrangement, the
vibration node is positioned at the central portion of the ZnO
piezoelectric thin film 203, thereby preventing the generation of
spurious responses of even-order higher harmonics (see, for
example, Patent Document 3, Japanese Unexamined Patent Application
Publication No. 58-137317, all pages and all figures).
[0008] In any of the piezoelectric thin-film resonators shown in
FIGS. 10 through 12, as shown in FIG. 13, a lower electrode 303
(which is equivalent to the lower electrodes 92, 102, and 201 in
FIGS. 10, 11, and 12, respectively) is patterned on a thin-film
support portion 302 (which is equivalent to the thin-film support
portions 91, 101, and 204 in FIGS. 10, 11, and 12, respectively)
formed on a Si substrate 301 (equivalent to the Si substrates 90,
100, and 200 in FIGS. 10, 11, and 12, respectively). On the
patterned lower electrode 303, a ZnO piezoelectric thin film (which
is equivalent to the piezoelectric thin films 94, 104, and 203 in
FIGS. 10, 11, and 12, respectively) is formed. When forming a ZnO
piezoelectric thin film by, for example, sputtering, the lower
electrode 303 is isolated and becomes electrically floating,
thereby having an unstable potential. Accordingly, the surface
roughness (Ra) of the ZnO piezoelectric thin film formed on the
lower electrode 303 having an unstable potential becomes greater
than 10 nm, and the electromechanical coupling coefficient of a
resonator produced by using this film becomes 1.5%, resulting in
poor piezoelectric characteristics.
SUMMARY OF THE INVENTION
[0009] In order to solve the above-described problems, preferred
embodiments of the present invention provide an electronic
component, such as a piezoelectric thin-film resonator, including a
piezoelectric thin film that exhibits excellent piezoelectric
characteristics.
[0010] A method of manufacturing an electronic component according
to a preferred embodiment of the present invention includes the
steps of forming an electrode on a substrate, and forming a
piezoelectric thin film on the electrode while a predetermined bias
potential is applied to the electrode. According to a preferred
embodiment of the present invention, the electrode can be
stabilized without becoming electrically floating during the
formation of the piezoelectric thin film. Thus, the surface
roughness of the piezoelectric thin film formed on the electrode
having a stable potential is greatly decreased, and the gradient of
the C axis of the ZnO piezoelectric thin film with respect to the
normal of the substrate is minimized. It is thus possible to
manufacture an electronic component including a piezoelectric thin
film that exhibits excellent piezoelectric characteristics, in
which the electromechanical coupling coefficient and the quality
factor are increased.
[0011] Other features, elements, steps, characteristics and
advantages of the present invention will become more apparent from
the following detailed description of preferred embodiments of the
present invention with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1A and 1B illustrate a piezoelectric thin-film
resonator according to a preferred embodiment of the present
invention, wherein FIG. 1A is a sectional view taken along line
(1)-(1) of FIG. 1B, and FIG. 1B is a plan view of the piezoelectric
thin-film resonator;
[0013] FIG. 2A illustrates an impedance characteristic and a phase
characteristic of the piezoelectric thin-film resonator of this
preferred embodiment of the present invention;
[0014] FIG. 2B illustrates an impedance characteristic and a phase
characteristic of a known piezoelectric thin-film resonator;
[0015] FIGS. 3A and 3B illustrate a first process of a
manufacturing method for the piezoelectric thin-film resonator of
this preferred embodiment of the present invention where FIG. 3A is
a sectional view taken along line (3)-(3) of FIG. 3B, and FIG. 3B
is a plan view of the piezoelectric thin-film resonator to be
manufactured;
[0016] FIGS. 4A and 4B illustrate a second process of the
manufacturing method for the piezoelectric thin-film resonator of
this preferred embodiment of the present invention, where FIG. 4A
is a sectional view taken along line (4)-(4) of FIG. 4B, and FIG.
4B is a plan view of the piezoelectric thin-film resonator to be
manufactured;
[0017] FIGS. 5A and 5B illustrate a third process of the
manufacturing method for the piezoelectric thin-film resonator of
this preferred embodiment of the present invention, where FIG. 5A
is a sectional view taken along line (5)-(5) of FIG. 5B, and FIG.
5B is a plan view of the piezoelectric thin-film resonator to be
manufactured;
[0018] FIGS. 6A and 6B illustrate a fourth process of the
manufacturing method for the piezoelectric thin-film resonator of
this preferred embodiment of the present invention, where FIG. 6A
is a sectional view taken along line (6)-(6) of FIG. 6B, and FIG.
6B is a plan view of the piezoelectric thin-film resonator to be
manufactured;
[0019] FIGS. 7A, 7B, and 7C are circuit diagrams of filters
including the piezoelectric thin-film resonator of this preferred
embodiment of the present invention;
[0020] FIG. 8 is a circuit diagram of a duplexer including the
piezoelectric thin-film resonator of this preferred embodiment of
the present invention;
[0021] FIG. 9 is a side sectional view illustrating a modification
made to the piezoelectric thin-film resonator of preferred
embodiments of the present invention;
[0022] FIG. 10 is a side sectional view illustrating a known
piezoelectric thin-film resonator;
[0023] FIG. 11 is a side sectional view illustrating another known
piezoelectric thin-film resonator;
[0024] FIG. 12 is a side sectional view illustrating still another
known piezoelectric thin-film resonator; and
[0025] FIG. 13 is a side sectional view illustrating a further
known piezoelectric thin-film resonator.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] The present invention is described in detail below with
reference to the accompanying drawings through illustration of
preferred embodiments. Preferred embodiments of the present
invention are applicable to all types of electronic components
provided with a piezoelectric film, such as a surface acoustic wave
(SAW) filter and a duplexer. Preferred embodiments are described
below in the context of a piezoelectric thin-film resonator as an
example of the electronic components. Although this piezoelectric
thin-film resonator preferably uses the
thickness-extensional-vibration n-order mode, the present invention
is applicable to other types of vibration modes, such as a
thickness-shear-vibration n-order mode. The sectional views of the
piezoelectric thin-film resonator constructed in accordance with
this preferred embodiment of the present invention are shown in
FIGS. 1A and 1B. FIG. 1A is a side sectional view of the
piezoelectric thin-film resonator, and FIG. 1B is a plan view
illustrating the piezoelectric thin-film resonator. FIG. 1A is a
cross sectional view taken along line (1)-(1) of FIG. 1B. The
piezoelectric thin-film resonator shown in FIGS. 1A and 1B
preferably includes a substrate 10, a thin-film support portion 12,
a lower electrode 14, a piezoelectric thin film 16, and an upper
electrode 18. The substrate 10 has a cavity 20. Accordingly, by the
provision of this cavity 20, the substrate 10 has an opening or a
recessed portion. The thin-film support portion 12 is provided as
an insulating thin film such that it covers the opening formed by
the cavity 20. The piezoelectric thin film 16 is disposed on the
thin-film support portion 12 such that it is sandwiched between the
lower electrode 14 and the upper electrode 18, which define a
laminated body. A portion of the lower electrode 14 and a portion
of the upper electrode 18 are used as excitation electrodes such
that they oppose each other across the piezoelectric thin film 16.
As the materials of the piezoelectric thin-film resonator
configured as described above, the substrate 10 is preferably
formed of Si, the thin-film support portion 12 is preferably formed
of SiO.sub.2, and the piezoelectric thin film 16 is preferably
essentially formed of ZnO. The signs of the temperature
coefficients of the elastic constants are opposite between
SiO.sub.2 and ZnO. Accordingly, by setting the ratio of the
thickness of SiO.sub.2 and that of ZnO to a suitable value, the
temperature coefficient of the resonant frequency in the
fundamental mode can be decreased, and the temperature
characteristics of the resonant frequency can be stabilized. In
this case, the temperature coefficient of SiO.sub.2 is preferably
about +100 ppm/.degree. C., and that of ZnO is preferably about -70
ppm/.degree. C. The materials of the thin-film support portion 12
and the piezoelectric thin film 16 are not restricted to SiO.sub.2
and ZnO, respectively, as long as the above-described temperature
coefficient can be achieved. For example, the piezoelectric thin
film 16 may be essentially formed of AlN or other components. The
material of the substrate 10 is not restricted to Si, and may be
another material, such as a liquid crystal or glass. The lower
electrode 14 and the upper electrode 18 may be formed of any
conductive metal, but more preferably, Al, Au, Pt, Nb, Mo, Ta, W,
Ni, Cu, or Ag.
[0027] In this preferred embodiment, since the piezoelectric thin
film 16 is formed by applying a predetermined bias potential, the
lower electrode 14 does not become electrically floating.
Accordingly, the piezoelectric thin-film resonator exhibits
excellent electromechanical coupling coefficient (k.sup.2) and
quality factor (Q) than a known piezoelectric thin-film resonator
in which the provision of a piezoelectric thin film causes a lower
electrode to become electrically floating.
[0028] In the piezoelectric thin-film resonator of this preferred
embodiment, the substrate 10 is formed of Si, and the cavity 20 is
formed by a certain etching technique, for example, anisotropic
etching or reactive ion etching. The thin-film support portion 12
is preferably formed of SiO.sub.2, and the piezoelectric thin film
16 is preferably formed of ZnO. The lower electrode 14 and the
upper electrode 18 are preferably formed by a certain film-forming
technique, such as liftoff deposition. The piezoelectric thin film
16 is formed by a certain film-forming technique, such as reactive
sputtering, by applying a bias potential of about +50 V to about
+300 V to the lower electrode 14. The present invention is not
limited to these film-forming techniques, and any technique may be
used to form the piezoelectric thin film 16 as long as particles of
the film 16 become ionized while a bias potential is applied to the
lower electrode 14. Such film-forming techniques include, not only
reactive sputtering, but also plasma CVD, RF sputtering, DC
sputtering, and ECR sputtering, and other suitable methods.
[0029] For comparison, the impedance characteristic and the phase
characteristic of the above-configured piezoelectric thin-film
resonator of this preferred embodiment are shown in FIG. 2A, and
the impedance characteristic and the phase characteristic of a
known piezoelectric thin-film resonator are shown in FIG. 2B. In
FIGS. 2A and 2B, the horizontal axis represents the frequency f
(Hz), and the vertical axis on the left side indicates the
impedance .vertline.Z.vertline. (.OMEGA.), and the vertical axis on
the right side indicates the phase Z(.degree.). A and B in FIGS. 2A
and 2B indicate the impedance characteristic plotting and the phase
characteristic plotting, respectively. The impedance characteristic
and the phase characteristic shown in FIG. 2A were measured when
the piezoelectric thin film 16 was formed while a bias potential of
about +90 V was applied to the electrode. The impedance
characteristic and the phase characteristic shown in FIG. 2B were
measured when a piezoelectric thin film was formed without applying
a bias potential. The surface roughness (Ra) of the piezoelectric
thin film 16 of this embodiment is about 5.7 nm, and the gradient
of the C axis of the piezoelectric thin film 16 with respect to the
normal of the substrate is about 0.2.degree. or smaller. FIG. 2A
shows that the resonator using the piezoelectric thin film 16
exhibits the following characteristics: the maximum phase angle is
about 86.degree.; the resonance resistance is about 70 .OMEGA.; the
quality factor is about 1300; and the electromechanical coupling
coefficient of the main vibration is about 2.6%. In contrast, the
surface roughness (Ra) of the piezoelectric thin film of the known
piezoelectric thin-film resonator is about 10.3 nm, and the
gradient of the C axis of the piezoelectric thin film with respect
to the normal of the substrate is about 1.degree. or greater. FIG.
2B shows that the resonator using this piezoelectric thin film
exhibits the following characteristics: the maximum phase angle is
about 73.degree.; the resonance resistance is about 210 .OMEGA.;
the quality factor is about 800; and the electromechanical coupling
coefficient of the main vibration is about 1.5%.
[0030] In this embodiment, the surface roughness (Ra) is about 5.7
nm, and this is not a limitation for the present invention.
According to the experiments carried out by the present inventor,
sufficient characteristics were not obtained if the surface
roughness (Ra) of the piezoelectric thin film was about 10.3 nm,
and thus, the surface roughness (Ra) must be about 10 nm or smaller
to obtain sufficient characteristics.
[0031] As discussed above, it is seen that the piezoelectric
thin-film resonator of this preferred embodiment exhibits more
excellent resonance characteristics than the known piezoelectric
thin-film resonator. FIG. 2A is an example only, and by applying a
positive bias potential to the lower electrode 14 within a range
from about +50 V to about +300 V, the electromechanical coupling
coefficient of the piezoelectric resonator results in a range from
about 2.6% to about 9%, and the quality factor results in a range
from about 200 to about 2000. Within the above-described range of a
positive bias applied to the lower electrode 14, the piezoelectric
thin-film resonator of preferred embodiments of the present
invention exhibits more excellent resonance characteristics than a
known piezoelectric thin-film resonator.
[0032] By applying a positive bias potential, the C-axis
orientation of ZnO becomes higher. If the bias potential exceeds
about +300 V, a tensile stress is generated in the piezoelectric
thin film 16, which may lead to a burst of the piezoelectric thin
film 16. A bias potential of lower than about +50 V is
insufficient, producing the piezoelectric thin film having a
surface roughness (Ra) of about 9 nm to about 10 nm. On the other
hand, with the application of a bias potential in a range from
about +90 V to about +200 V, stable and excellent resonance
characteristics are obtained. Accordingly, in order to obtain
stable resonance characteristics and to prevent a film burst, the
positive bias potential to be applied is, as stated above,
preferably from about +50 V to about +300 V, and more preferably,
from about +90 V to about +200 V.
[0033] A manufacturing method for the piezoelectric thin-film
resonator shown in FIGS. 1A and 1B is described below with
reference to FIG. 3A through FIG. 6B.
[0034] A first process of the manufacturing method is discussed
below with reference to FIGS. 3A and 3B. FIG. 3A is a side
sectional view of the piezoelectric thin-film resonator to be
manufactured, and FIG. 3B is a plan view thereof. FIG. 3A is a
sectional view taken along line (3)-(3) of FIG. 3B.
[0035] In the first process, the Si substrate 10 formed into the
shape of a substantially planar square when viewed from above and
having a predetermined thickness is prepared. The surface of the
substrate 10 is thermally oxidized to form the thin-film support
portion 12, which is a SiO.sub.2 insulating thin film. In this
case, the thin-film support portion 12 may be deposited on the
surface of the substrate 10 by sputtering CVD. The cavity 20 having
the shape of a trapezoid when viewed from the side is formed from
the lower surface of the substrate 10. The outer lines of the
cavity 20 on the upper surface of the substrate 10 are indicated by
20a. The cavity 20 may be formed by a known technique, and the
present invention is not restricted to any of such known
techniques. If an etching technique is used for forming the cavity
20, either wet etching or dry etching can be used. Dry etching
includes plasma, ion beam, and ion milling, and by combining plasma
etching and sputtering (reactive sputter etching or reactive ion
etching), anisotropic etching can be performed. As the etching
mode, anisotropic etching is preferable.
[0036] Subsequently, an electrode unit 22 is formed on the
thin-film support portion 12 by using Al, Au, Pt, Nb, Mo, Ta, W,
Ni, Cu, or Ag as the material for liftoff deposition, for example.
The electrode unit 22 is formed of the lower electrode 14 and a
peripheral dummy electrode 24. The lower electrode 14 includes an
input/output electrode 14a which generally has the shape of a
square when viewed from above and which is located at an
approximately central portion of the left edge of the thin-film
support portion 12, and a lead-out electrode 14b extending from the
input/output electrode 14a to the right side of FIG. 3B and
generally having the shape of a narrowed rectangle when viewed from
the top. The right edge of the lead-out electrode 14b defines the
lower excitation electrode portion. The dummy electrode 24 is
disposed around the thin-film support portion 12 such that it
surrounds the entire periphery of the lower electrode 14. The dummy
electrode 24 is electrically connected to the input/output
electrode 14a of the lower electrode 14.
[0037] A second process is discussed below with reference to FIGS.
4A and 4B. FIG. 4A is a side view of the piezoelectric thin-film
resonator to be manufactured, and FIG. 4B is a plan view thereof.
FIG. 4A is a sectional view taken along line (4)-(4) of FIG.
4B.
[0038] In the second process, the piezoelectric thin-film 16 mainly
including ZnO is preferably formed by reactive sputtering. When
forming the piezoelectric thin film 16, a bias potential of about
+90 V is applied to the dummy electrode 24 by a potential applying
device (not shown). By the application of a positive bias
potential, the lower electrode 14 can be prevented from becoming
electrically floating. The C axis of the piezoelectric thin film 16
has a high orientation with respect to the substrate 10, and is
positively or negatively polarized in order, free from a mixture of
the positive polarity and the negative polarity, which suffers from
a known piezoelectric thin film.
[0039] According to a film-forming technique, such as reactive
sputtering, plasma CVD, RF sputtering, DC sputtering, or ECR
sputtering, that allows particles of a film to be ionized, it is
not essential that a bias be applied during film formation. It is
known, however, that the application of a bias results in a highly
orientated film. If a bias is applied to the substrate 10 in the
process of forming the piezoelectric thin film 16, the lower
electrode 14 becomes electrically floating. That is, the
piezoelectric thin film 16, which plays an important role in the
piezoelectric resonator, cannot be formed on the lower electrode 14
while applying a bias. Then, by the provision of the dummy
electrode 24, a bias can be applied to the lower electrode 14,
resulting in the formation of the highly orientated piezoelectric
film 16.
[0040] As a result, the surface roughness (Ra) of the piezoelectric
thin film 16 is improved to about 5.7 nm over a known piezoelectric
thin film (10 nm). The piezoelectric characteristics of the
piezoelectric thin film 16 are also greatly improved: the
electromechanical coupling coefficient is about 2.6%; and the
quality factor is about 1300 in contrast to those of a known
piezoelectric thin film (the electromechanical coupling coefficient
is about 1.5% and the quality factor is about 800).
[0041] A third process is discussed below with reference to FIGS.
5A and 5B. FIG. 5A is a side sectional view of the piezoelectric
thin-film resonator to be manufactured, and FIG. 5B is a plan view
thereof. FIG. 5A is a sectional view taken along line (5)-(5) of
FIG. 5B.
[0042] In the third process, the outer periphery of the
piezoelectric thin film 16 and the dummy electrode 24 are removed
by reactive ion etching or wet etching, and also, the input/output
electrode 14a of the lower electrode 14 is exposed.
[0043] A fourth process is described below with reference to FIGS.
6A and 6B. FIG. 6A is a side view of the piezoelectric tin-film
resonator to be manufactured, and FIG. 6B is a sectional view
thereof. FIG. 6A is a sectional view taken along line (6)-(6) of
FIG. 6B.
[0044] In the fourth process, the upper electrode 18 is formed by,
for example, liftoff deposition. The upper electrode 18 includes an
input/output electrode 18a which generally has the shape of a
square when viewed from above and which is located at an
approximately central portion of the right edge of the
piezoelectric thin film 16, and a lead-out electrode 18b extending
from the input/output electrode 18a to the left side of FIG. 6B and
generally having the shape of a narrowed rectangle when viewed from
above. The left edge of the lead-out electrode 18b defines the
upper excitation electrode.
[0045] The piezoelectric thin-film resonator of this preferred
embodiment shown in FIGS. 1A and 1B can be manufactured, as
described above.
[0046] The piezoelectric thin-film resonator of this preferred
embodiment can be integrated into a .pi.-type ladder filter shown
in FIG. 7A, a T-type filter shown in FIG. 7B, or an L-type filter
shown in FIG. 7C. A filter integrating the piezoelectric thin-film
resonator of this preferred embodiment exhibits stable filtering
characteristics. To form such a filter having stable operating
characteristics, a plurality of the above-described piezoelectric
thin-film resonators are disposed on a substrate, and the
electrodes of the resonators are connected to the wiring
arrangement shown in FIGS. 7A, 7B, or 7C.
[0047] The piezoelectric thin-film resonator of this preferred
embodiment can be included in a duplexer 50 for switching an
antenna input/output ANT between the transmission side and the
reception side, such as that shown in FIG. 8.
[0048] The piezoelectric thin-film resonator of this preferred
embodiment or the filter shown in FIGS. 7A, 7B, or 7C can be
included in cellular telephones, wireless LANs, and other
electronic communication apparatuses, thereby enabling the
electronic communication operation of such electronic communication
apparatus to be stable.
[0049] As a modification to the electronic component of preferred
embodiments of the present invention, a piezoelectric thin-film
resonator 60 is shown in FIG. 9. A recessed portion 62 having a
desired shape may be formed on the top surface of a substrate 61,
and a thin-film support portion 63, a lower electrode 64, a
piezoelectric thin film 65, and an upper electrode 66 may
sequentially be formed on the recessed portion 62. In this case,
the recessed portion 62 has a bottom rather than vertically passing
through the substrate 61, and the recessed portion 62 is covered by
the thin-film support portion 63 so as to form a cavity.
[0050] It should be understood that the foregoing description is
only illustrative of the present invention. Various alternatives
and modifications can be devised by those skilled in the art
without departing from the present invention. Accordingly, the
present invention is intended to embrace all such alternatives,
modifications and variances which fall within the scope of the
appended claims.
* * * * *