U.S. patent application number 14/037934 was filed with the patent office on 2014-08-21 for piezoelectric generator, sensor node, and method of manufacturing piezoelectric generator.
The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Atsuya HIRABAYASHI, Yasuhiro ONO.
Application Number | 20140232242 14/037934 |
Document ID | / |
Family ID | 45933531 |
Filed Date | 2014-08-21 |
United States Patent
Application |
20140232242 |
Kind Code |
A1 |
ONO; Yasuhiro ; et
al. |
August 21, 2014 |
PIEZOELECTRIC GENERATOR, SENSOR NODE, AND METHOD OF MANUFACTURING
PIEZOELECTRIC GENERATOR
Abstract
A piezoelectric generator includes: a base body; and at least
one piezoelectric transducer disposed on the base body, and
including a first electrode, a piezoelectric body, and a second
electrode, wherein the piezoelectric transducer includes a support
section fixed to the base body, and a vibrating section disposed
apart from the base body, having one end connected to the support
section and the other end set as a free end, and vibrating due to a
vibration applied externally, and a distance between the other end
of the vibrating section and the base body is larger than a
distance between the one end of the vibrating section and the base
body.
Inventors: |
ONO; Yasuhiro;
(Matsumoto-shi, JP) ; HIRABAYASHI; Atsuya;
(Chino-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
45933531 |
Appl. No.: |
14/037934 |
Filed: |
September 26, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13238778 |
Sep 21, 2011 |
8575824 |
|
|
14037934 |
|
|
|
|
Current U.S.
Class: |
310/319 ;
29/25.35; 310/365 |
Current CPC
Class: |
H01L 41/113 20130101;
Y10T 29/42 20150115; H01L 41/1132 20130101; H01L 41/43 20130101;
H01L 41/273 20130101; H01L 41/314 20130101; H01L 41/047 20130101;
H02N 2/188 20130101 |
Class at
Publication: |
310/319 ;
29/25.35; 310/365 |
International
Class: |
H01L 41/047 20060101
H01L041/047; H01L 41/113 20060101 H01L041/113; H01L 41/273 20060101
H01L041/273 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2010 |
JP |
2010-230299 |
Claims
1. A method of manufacturing a piezoelectric generator, comprising:
forming a sacrificial layer by disposing a paste including a
material to be thermally decomposed in a partial area on a base
body layer using a droplet ejection process; disposing a first
electrode layer so as to straddle the base body layer and the
sacrificial layer using a droplet ejection process; disposing a
piezoelectric body layer in paste form including piezoelectric
particles on the first electrode layer using a droplet ejection
process; disposing a second electrode layer on the piezoelectric
body layer using a droplet ejection process; and firing the base
body layer, the sacrificial layer, the first electrode layer, the
piezoelectric body layer, and the second electrode layer.
2. The method of manufacturing piezoelectric generator according to
claim 1, further comprising: performing, prior to the firing the
base body layer, an isostatic pressing process on the base body
layer, the sacrificial layer, the first electrode layer, the
piezoelectric body layer, and the second electrode layer, wherein
in the providing the base body layer, as the base body layer, there
is prepared a ceramic sheet on which ceramics to be fired including
the same component as a component of the piezoelectric body layer
is disposed.
3. The method of manufacturing a piezoelectric generator according
to claim 1, wherein the base body layer is made of a material
including a component the same as a component of the piezoelectric
body layer.
4. The method of manufacturing a piezoelectric generator according
to claim 1, wherein a thermal contraction rate of the first
electrode layer is lower than a thermal contraction rate of the
piezoelectric body layer.
5. The method of manufacturing a piezoelectric generator according
to claim 1, wherein a thermal contraction rate of the second
electrode layer is higher than a thermal contraction rate of the
piezoelectric body layer.
6. The piezoelectric generator manufactured by the method according
to claim 1.
7. A sensor node comprising: a sensor; a circuit adapted to process
data obtained by the sensor; a communication system adapted to
communicate the data obtained by the sensor; and a power source
adapted to drive the sensor, the communication system, and the
circuit, wherein the piezoelectric generator manufactured by the
method according to claim 1 is provided as the sensor and the power
source.
Description
[0001] This is a Division of application Ser. No. 13/238,778 filed
Sep. 21, 2011. The prior applications, including the
specifications, drawings and abstract are incorporated herein by
reference in their entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a piezoelectric generator,
a sensor node, and a method of manufacturing a piezoelectric
generator.
[0004] 2. Related Art
[0005] There has been known a piezoelectric generator provided with
a cantilevered piezoelectric transducer, and generating electric
energy due to the piezoelectric effect caused by the vibration of
the piezoelectric transducer (see, e.g., JP-A-11-18445 (Document
1)). The piezoelectric generator described in Document 1 is
provided with a support member disposed under the piezoelectric
transducer (a first electrode, a piezoelectric thin film, and a
second electrode), the support member having a deformable section
deformed in accordance with the piezoelectric transducer, and a
support section for supporting the deformable section. Such a
piezoelectric generator is manufactured by depositing various
layers such as a sacrificial layer, a support layer, two electrode
layers, and a piezoelectric body layer on a silicon substrate using
a low-pressure deposition process such as a sputtering process or a
chemical vapor deposition process, and then patterning it using a
photolithography process and an etching process.
[0006] There is proposed a sensor network having a number of sensor
network terminals (hereinafter referred to as sensor nodes)
provided with a communication function installed in various places
to thereby form a network, and for collecting the data obtained by
each of the sensor nodes. The sensor node, which is provided with a
sensor, a circuit, a communication system, and a power source, is
required to be small in size and low-profile so as to be easily
installed in a variety of places, efficiently generate electricity
and operate for a long period of time, and is further required to
be provided at low price. As a power source of such a sensor node,
use of the piezoelectric generator described above has been
considered.
[0007] However, the piezoelectric generator described in Document 1
has a configuration that the support member intervenes under the
piezoelectric transducer, and the deformable section of the support
member vibrates in accordance with the piezoelectric transducer,
and therefore, there arises a problem that it is difficult to
achieve low-profiling. Since the manufacturing process of the
piezoelectric generator requires an expensive vacuum (low-pressure)
deposition device, and includes a complicated process using the
photolithography process and the etching process, there arises a
problem that cost reduction is difficult.
SUMMARY
[0008] An advantage of some aspects of the invention is to solve at
least a part of the problem described above, and the invention can
be implemented as the following forms or application examples.
Application Example 1
[0009] This application example of the invention is directed to a
piezoelectric generator including a base body, and at least one
piezoelectric transducer disposed on the base body, and including a
first electrode, a piezoelectric body, and a second electrode,
wherein the piezoelectric transducer includes a support section
fixed to the base body, and a vibrating section disposed apart from
the base body, having one end connected to the support section and
the other end set as a free end, and vibrating due to a vibration
applied externally, and a distance between the other end of the
vibrating section and the base body is larger than a distance
between the one end of the vibrating section and the base body.
[0010] According to this configuration, it becomes possible to
eliminate intervention of another layer on the lower side of the
piezoelectric transducer having the support section and the
vibrating section, the piezoelectric generator can be made
low-profile compared to the case in which another layer intervenes
on the lower side of the piezoelectric transducer. Since the other
end of the vibrating section is located further than the one end
thereof from the base body, the amplitude of the vibration of the
vibrating section excited by the external vibration can be made
larger compared to the case in which the distance from the base
body is the same between the one end and the other end. Thus, the
amount of the distortion caused in the piezoelectric transducer is
increased, and therefore, the electric energy generated by the
piezoelectric generator is increased. As a result, the
piezoelectric generator, which is low-profile and efficiently
generates electricity, can be provided.
Application Example 2
[0011] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that the base body is
made of a material including a component the same as a component of
the piezoelectric body.
[0012] According to this configuration, since the base body is made
of the material including the same component as the component of
the piezoelectric body, the piezoelectric generator can be
manufactured by disposing the piezoelectric transducer to be fired
on the base body in the non-fired state, and then firing them
together. On this occasion, the difference between the both layers
in contraction rate in the fireation process is reduced, and at the
same time, the diffusion of the impurities from the base body layer
into the piezoelectric body layer is also reduced compared to the
case in which the component of the base body and the component of
the piezoelectric body are different from each other. Thus,
generation of cracks and residual stress in the base body and the
piezoelectric body due to the large difference in contraction rate,
and deterioration in the piezoelectric characteristics of the
piezoelectric body due to the diffusion of the impurities can be
prevented. Since the base body to be fired has flexibility, and can
be formed to have an arbitrary shape, the freedom of installation
can be enhanced compared to the case in which the base body is
formed of a silicon substrate or the like.
Application Example 3
[0013] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that a thermal
contraction rate of the first electrode is lower than a thermal
contraction rate of the piezoelectric body.
[0014] According to this configuration, since the thermal
contraction rate of the first electrode located on the base body
side of the piezoelectric body is lower than the thermal
contraction rate of the piezoelectric body, the piezoelectric body
makes larger contraction than the first electrode when fired.
Therefore, in the piezoelectric transducer after the fireation,
since the other end as the free end of the vibrating section bends
to the opposite side to the base body side than the one end, the
distance between the other end of the vibrating section and the
base body can be set larger than the distance between the one end
of the vibrating section and the base body.
Application Example 4
[0015] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that a thermal
contraction rate of the second electrode is higher than a thermal
contraction rate of the piezoelectric body.
[0016] According to this configuration, since the thermal
contraction rate of the second electrode located on the opposite
side to the base body side of the piezoelectric body is higher than
the thermal contraction rate of the piezoelectric body, the second
electrode makes larger contraction than the piezoelectric body when
fired. Therefore, in the piezoelectric transducer after the
fireation, since the other end as the free end of the vibrating
section bends to the opposite side to the base body side than the
one end, the distance between the other end of the vibrating
section and the base body can be set larger than the distance
between the one end of the vibrating section and the base body.
Application Example 5
[0017] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that the piezoelectric
body is formed of a plurality of layers stacked one another.
[0018] According to this configuration, since the piezoelectric
body is composed of a plurality of layers, it becomes easier to
obtain the desired thickness of the piezoelectric body, and it
becomes possible to make the thickness of the layer more uniform
compared to the case in which the piezoelectric body is made of a
single layer. Thus, the breakage and the leakage between the first
electrode and the second electrode due to the variation in
thickness of the piezoelectric body can be prevented.
Application Example 6
[0019] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that to further provide
a weight disposed on the other end side of the vibrating
section.
[0020] According to this configuration, since the vibration of the
vibrating section excited by the external vibration is promoted by
the weight, the amplitude of the vibration of the vibrating section
can further be increased. By controlling the weight of the weight,
it is possible to control the natural frequency of the
piezoelectric generator to thereby make it easy to resonate with
the external vibration. Thus, since the current or the voltage
output from the piezoelectric generator is increased, the
piezoelectric generator efficiently generating electricity can be
provided.
Application Example 7
[0021] According to this application example of the invention, in
the piezoelectric generator according to the above application
example of the invention, it is preferable that two or more of the
piezoelectric transducers are stacked on the base body.
[0022] According to this configuration, the electric energy due to
the external vibration can be obtained from each of the plurality
of piezoelectric transducers stacked on the base body. Thus, since
the current or the voltage output from the piezoelectric generator
is increased, the piezoelectric generator efficiently generating
electricity can be provided.
Application Example 8
[0023] According to this application example of the invention,
there is provided a method of manufacturing a piezoelectric
generator including: providing a base body layer, forming a
sacrificial layer by disposing a paste including a material to be
thermally decomposed in a partial area on the base body layer using
a printing process, disposing a first electrode layer so as to
straddle the base body layer and the sacrificial layer using a
printing process, disposing a piezoelectric body layer in paste
form including piezoelectric particles on the first electrode layer
using a printing process, disposing a second electrode layer on the
piezoelectric body layer using a printing process, and firing the
base body layer, the sacrificial layer, the first electrode layer,
the piezoelectric body layer, and the second electrode layer.
[0024] According to this configuration, since each of the layers,
namely the sacrificial layer, the first electrode layer, the
piezoelectric layer, and the second electrode layer is disposed
using the printing process, the expensive vacuum (low-pressure)
deposition device is not required. Since by firing these layers,
the sacrificial layer is thermally decomposed and eliminated to
thereby form the piezoelectric transducer composed of the first
electrode, the piezoelectric body, and the second electrode to have
a cantilevered shape, the complicated process using the
photolithography process and the etching process for patterning and
elimination of the sacrificial layer can be made unnecessary. As a
result, the manufacturing man-hour and the manufacturing cost of
the piezoelectric generator can be reduced. The printing process
mentioned here includes a screen printing process and a droplet
ejection process such as an inkjet process.
Application Example 9
[0025] According to this application example of the invention, in
the method of manufacturing a piezoelectric generator according to
the above application example of the invention, it is preferable
that there is further provided the step of performing, prior to the
firing the base body layer, an isostatic pressing process on the
base body layer, the sacrificial layer, the first electrode layer,
the piezoelectric body layer, and the second electrode layer, and
in the providing the base body layer, as the base body layer, there
is prepared a ceramic sheet on which ceramics to be fired including
the same component as a component of the piezoelectric body layer
is disposed.
[0026] According to this configuration, since the ceramic sheet to
be fired is used as the base body layer, it becomes possible to
form the base body to have an arbitrary shape when fired. In the
step of performing the isostatic pressing process, since the
restriction to the part having contact with the base body layer in
the surface direction is smaller compared to the case in which the
base body layer has already been fired, the isostatic pressing
process can efficiently be performed. Thus, the density of the
piezoelectric particles in the piezoelectric body layer is raised,
and therefore, the piezoelectric characteristics can further be
improved. Since the base body layer and the piezoelectric body
layer include the same component, the difference between the both
layers in contraction rate in the fireation process becomes smaller
and the diffusion of impurities from the base body layer to the
piezoelectric body layer becomes smaller compared to the case in
which the components of the base body layer and the piezoelectric
body layer are different from each other. Thus, generation of
cracks and residual stress in the base body layer and the
piezoelectric body layer due to the large difference in contraction
rate, and deterioration in the piezoelectric characteristics of the
piezoelectric body layer due to the diffusion of the impurities can
be prevented.
Application Example 10
[0027] This application example of the invention is directed to a
sensor node including a sensor, a circuit adapted to process data
obtained by the sensor, a communication system adapted to
communicate the data obtained by the sensor, and a power source
adapted to drive the sensor, the communication system, and the
circuit, wherein one of the piezoelectric generator according to
the above application examples and the piezoelectric generator
manufactured by the method according to the above application
examples is provided as the sensor and the power source.
[0028] According to this configuration, since the piezoelectric
generator, which efficiently generates electricity due to an
external vibration, is provided as the power source, power source
replacement of the sensor node can also be made unnecessary. Since
the piezoelectric generator, which can be manufactured at low cost,
functions as not only the power source but also the sensor, the
low-price sensor node can be provided. Further, since the base body
of the piezoelectric generator can be formed to have an arbitrary
shape, the freedom of installation can be enhanced compared to the
case in which the base body is formed of a silicon substrate or the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0030] FIGS. 1A and 1B are schematic diagrams showing a schematic
configuration of a piezoelectric generator according to a first
embodiment of the invention.
[0031] FIG. 2 is a flowchart showing a method of manufacturing the
piezoelectric generator according to the first embodiment.
[0032] FIGS. 3A through 3E are schematic cross-sectional diagrams
showing the method of manufacturing the piezoelectric generator
according to the first embodiment.
[0033] FIGS. 4A through 4C are schematic cross-sectional diagrams
showing the method of manufacturing the piezoelectric generator
according to the first embodiment.
[0034] FIG. 5 is a schematic diagram showing a schematic
configuration of a sensor node according to the first
embodiment.
[0035] FIGS. 6A and 6B are schematic diagrams showing a schematic
configuration of a piezoelectric generator according to a second
embodiment of the invention.
[0036] FIGS. 7A through 7C are diagrams showing a schematic
configuration of a piezoelectric generator according to a modified
example.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0037] Some embodiments of the invention will hereinafter be
explained with reference to the accompanying drawings. In each of
the drawings referred to below, the dimensional ratio, angle, and
so on of each of the constituents is appropriately made different
from each other in order for showing the configuration in an
easy-to-understand manner.
First Embodiment
Configuration of Piezoelectric Generator
[0038] Firstly, a schematic configuration of the piezoelectric
generator according to a first embodiment of the invention will be
explained with reference to FIGS. 1A and 1B. FIGS. 1A and 1B are
schematic diagrams showing a schematic configuration of the
piezoelectric generator according to the first embodiment. For
details, FIG. 1A is a schematic plan view of the piezoelectric
generator, and FIG. 1B is a schematic cross-sectional view along
the line A-A shown in FIG. 1A.
[0039] As shown in FIGS. 1A and 1B, the piezoelectric generator 1
according to the first embodiment is provided with a base body 20,
and a piezoelectric transducer 24 including a first electrode 21, a
piezoelectric body 22, and a second electrode 23 disposed in a
stacked manner sequentially on the base body 20. The base body 20
is made of a ceramic material including the same component as the
piezoelectric body 22. In the present embodiment, the base body 20
is made of the same constituent material as that of the
piezoelectric body 22. The thickness of the base body 20 is, for
example, in a range of 0.01 mm through 1 mm.
[0040] The piezoelectric transducer 24 has a support section 30 and
a vibrating section 32. The support section 30 is a part of the
piezoelectric transducer 24, fixed to the base body 20. The
vibrating section 32 is a part of the piezoelectric transducer 24,
shaped like a cantilever and disposed apart upward from the base
body 20. The vibrating section 32 has one end 32a connected to the
support section 30, and the other end 32b as a free end, and
vibrates due to the vibration applied externally thereto. When
applying distortion to a piezoelectric material on which the
polarization process is performed, charge is generated inside the
piezoelectric material in a direction for canceling the distortion.
In FIG. 1B, the arrow indicates the polarization direction, and the
charge (+, -) denotes the charge generated when the vibrating
section 32 swings downward (toward the base body 20). In the
piezoelectric transducer 24, the vibrating section 32 bends to
cause distortion due to the vibration to thereby generate electric
energy due to the piezoelectric effect.
[0041] The distance G2 between the other end 32b of the vibrating
section 32 and the base body 20 is larger than the distance G1
between the one end 32a thereof and the base body 20 (see FIG. 1B).
In other words, the vibrating section 32 has a shape formed by
bending the part thereof on the other end 32b side upward (toward
the opposite side to the base body 20). Therefore, since the
vibrational amplitude of the vibrating section 32 excited by the
external vibration can be increased compared to the case in which
the distance from the base body 20 is the same between the one end
32a and the other end 32b, the amount of distortion caused in the
piezoelectric transducer 24 is enlarged. Thus, it becomes possible
to make the electric energy generated by the piezoelectric
transducer 24 larger.
[0042] The first electrode 21 is a part of the piezoelectric
transducer 24, disposed the nearest to the base body 20. The first
electrode 21 is made of, for example, an alloy of silver (Ag) and
palladium (Pd). The thickness of the first electrode 21 is, for
example, in a range of 1 .mu.m through 5 .mu.m.
[0043] The piezoelectric body 22 is disposed on the first electrode
21. The piezoelectric body 22 is formed to have one side of the
support section 30 smaller than that of the first electrode 21, for
example, so that an area for connecting a wire to the first
electrode 21 as the lower layer is exposed. The piezoelectric body
22 is formed of two piezoelectric body layers stacked one another
(see FIG. 3E). The piezoelectric body is made of a piezoelectric
material such as lead zirconium titanate (Pb(Zr,Ti)O.sub.3; PZT),
barium titanate (BaTiO.sub.3), potassium niobate (KNbO.sub.3),
Pb(Mg,Nb)O.sub.3--PbTiO.sub.3, Pb(Zn,Nb)O.sub.3--PbTiO.sub.3. The
thickness of the piezoelectric body 22 is, for example, in a range
of 3 .mu.m through 40 .mu.m.
[0044] The second electrode 23 is disposed on the piezoelectric
body 22. The second electrode 23 is formed to have, for example,
the three sides, namely the sides except the side of the other end
32b, one size smaller than those of the piezoelectric body 22 so as
not to cause contact or leakage with the first electrode 21 as the
lower layer across the piezoelectric body 22. The second electrode
23 is made of, for example, an alloy of silver (Ag) and palladium
(Pd). The thickness of the second electrode 23 is, for example, in
a range of 1 .mu.m through 5 .mu.m.
[0045] Although in FIG. 1B, the first electrode 21 is illustrated
so as to have a thickness different between the support section 30
and the vibrating section 32, the invention is not limited to such
a configuration. It is also possible that the thickness of the
first electrode 21 is substantially the same between the support
section 30 and the vibrating section 32, and the whole of the
piezoelectric transducer 24 bends upward at the one end 32a to
thereby form the shape of the cantilevered vibrating section
32.
Method of Manufacturing Piezoelectric Generator
[0046] Subsequently, a method of manufacturing the piezoelectric
generator according to the first embodiment will be explained with
reference to FIGS. 2, 3A through 3E, and 4A through 4C. FIG. 2 is a
flowchart showing the method of manufacturing the piezoelectric
generator according to the first embodiment. FIGS. 3A through 3E
and 4A through 4C are schematic cross-sectional diagrams showing
the method of manufacturing the piezoelectric generator according
to the first embodiment.
[0047] As shown in FIG. 2, the method of manufacturing the
piezoelectric generator according to the first embodiment is
provided with a step (step S1) of preparing the base body layer, a
step (step S2) of forming a sacrificial layer, a step (step S3) of
disposing the first electrode layer, a step (step S4) of disposing
the piezoelectric body layer, a step (step S5) of disposing the
second electrode layer, a step (step 6) of performing an isostatic
pressing process, and a fireation step (step S7).
[0048] As shown in FIG. 3A, in the step S1, a base body layer 10 is
prepared. As a material of the base body layer 10, there is
prepared a mixed solution obtained by adding powder of the
piezoelectric material such as lead zirconium titanate
(Pb(Zr,Ti)O.sub.3; PZT) to a solvent such as ethanol, butanol,
toluene, or terpineol, a binder such as polyvinyl alcohol or
polyvinyl butyral, a dispersant such as a polycarboxylate
dispersant, and a plasticizer such as dioctyl adipate. By mixing
the mixed solution and then performing cracking thereon using a
planetary ball mill or the like, a slurry (paste) with a
piezoelectric material preferably dispersed is prepared. By
applying the slurry to the surface of a film 15 and then drying it,
a ceramic sheet having the base body layer 10 to be fired disposed
on the film 15 can be obtained. The thickness of the base body
layer 10 is set, for example, in a range of 0.01 mm through 1 mm.
It is also possible to form the base body layer 10 by stacking a
plurality of layers if necessary.
[0049] As shown in FIG. 3B, in the step S2, a sacrificial layer 16
is formed in a certain area on the base body layer 10. As a
material of the sacrificial layer 16, for example, there is
prepared a mixed solution obtained by dissolving the binder such as
ethyl cellulose in the solvent of terpineol and then adding
particles of a material made of carbon to be thermally decomposed.
By dispersing and kneading the mixed solution using a three-roll
mill or the like, a paste including a material to be thermally
decomposed is prepared. By disposing the paste on the base body
layer 10 using, for example, a screen printing process, and then
drying it, the sacrificial layer 16 can be obtained. The thickness
of the sacrificial layer 16 is set, for example, in a range of 2
.mu.m through 20 .mu.m.
[0050] As shown in FIG. 3C, in the step S3, a first electrode layer
11 is formed so as to straddle the surface of the base body layer
10 and the surface of the sacrificial layer 16. As a material of
the first electrode layer 11, an electrode paste including, for
example, silver (Ag) and palladium (Pd) at a weight ratio of 7:3
through 8:2 is used, and the viscosity of the electrode paste is
controlled using a solvent such as terpineol if necessary. By
disposing the electrode paste on the surface of the base body layer
10 and the surface of the sacrificial layer 16 using, for example,
a screen printing process, and then drying it, the first electrode
layer 11 can be obtained. The thickness of the first electrode
layer 11 is appropriately adjusted so that the thickness of the
first electrode 21 after fireation becomes, for example, in a range
of 1 .mu.m through 5 .mu.m.
[0051] Although in FIG. 3C the first electrode is illustrated to
have a thickness different between the surface of the base body
layer 10 and the surface of the sacrificial layer 16, it is also
possible that the thickness of the first electrode layer 11 is
substantially the same between the surface of the base body layer
10 and the surface of the sacrificial layer 16.
[0052] As shown in FIGS. 3D and 3E, in the step S4, a piezoelectric
body layer 12 is formed on the first electrode layer 11. In the
present embodiment, a slurry made of the same material as that of
the base body layer 10 is used as the material of the piezoelectric
body layer 12. The slurry is disposed on the first electrode layer
11 using, for example, a screen printing process, and is then
dried. As shown in FIG. 3D, in the present embodiment, a
piezoelectric body layer 12a is firstly disposed on the first
electrode layer 11, and is then dried. As shown in FIG. 3E, a
piezoelectric body layer 12b is disposed on the piezoelectric body
layer 12a, and is then dried. Thus, the piezoelectric body layer 12
having the piezoelectric body layers 12a, 12b stacked one another
can be obtained. Here, the thicknesses of the piezoelectric body
layers 12a, 12b are appropriately controlled so that the thickness
of the piezoelectric body 22 after fireation becomes, for example,
in a range of 3 .mu.m through 40 .mu.m. The piezoelectric body
layer 12 is disposed so that the first electrode layer 11 as the
lower layer is exposed in one side.
[0053] It is also possible to form the piezoelectric body layer 12
with a single layer of the piezoelectric body layer 12a in the step
S4. However, by forming the piezoelectric body layer 12 with the
two layers as described above, it becomes easier to obtain the
desired thickness and it becomes possible to make the thickness of
the layer more uniform compared to the case of forming the
piezoelectric body layer 12 with a single layer. Thus, the breakage
and the leakage between the first electrode 21 and the second
electrode 23 after the fireation due to the variation in thickness
of the piezoelectric body layer 12 can be prevented. The
piezoelectric body layer 12 can also be composed of three or more
layers by further stacking the piezoelectric body layer on the
piezoelectric body layers 12a, 12b.
[0054] As shown in FIG. 4A, in the step S5, a second electrode
layer 13 is disposed on the piezoelectric body layer 12. The second
electrode layer 13 is formed by disposing the same material as that
of the first electrode layer 11 on the piezoelectric body layer 12
using, for example, a screen printing process, and then drying it.
The second electrode layer 13 is disposed in an area one size
smaller than the piezoelectric body layer 12 in, for example, three
sides thereof. The first electrode layer 11, the piezoelectric body
layer 12, and the second electrode layer 13 constitute a
piezoelectric transducer layer 14.
[0055] Here, the first electrode layer 11, the piezoelectric body
layer 12, and the second electrode layer 13 constituting the
piezoelectric transducer layer 14 are individually shrunk by the
fireation in the fireation step in the step S7 described later. In
order for providing the vibrating section 32 of the piezoelectric
transducer 24 obtained is a result of the fireation with the shape
having the portion of the other end 32b bending upward as shown in
FIG. 1B, it is preferable that the thermal contraction rate of the
first electrode layer 11 is lower than the thermal contraction rate
of the piezoelectric body layer 12, and that the thermal
contraction rate of the second electrode layer 13 is higher than
the thermal contraction rate of the piezoelectric body layer 12.
The thermal contraction rate of each of the layers of the
piezoelectric transducer layer 14 can be controlled by an amount of
resin material such as polyvinyl butyral, polyvinyl alcohol,
water-soluble polyurethane, or methyl cellulose to be added to the
material of each of the layers. In other words, the larger the
additive amount of the resin material is, the higher the thermal
contraction rate can be set. Therefore, by appropriately
controlling the amount of resin material described above to be
added to each of the layers, namely the first electrode layer 11,
the piezoelectric body layer 12, and the second electrode layer 13,
to thereby adjust the thermal contraction rate, the vibrating
section 32 (the piezoelectric transducer 24) having such a shape as
shown in FIG. 1B can be obtained.
[0056] The printing process for disposing the layers in the
respective steps, namely the step S2, the step S3, the step S4, and
the step S5 is not limited to the screen printing process. As such
a printing process, a droplet ejection process such as an inkjet
process or a dispenser process, or any other printing process can
also be adopted providing a predetermined outer shape (a pattern
shape) and a predetermined layer thickness can be obtained using
the printing process.
[0057] Subsequently, in the step S6, a cold isostatic pressing
(CIP) process, for example, is performed on the sacrificial layer
16 and the piezoelectric transducer layer 14 disposed on the base
body layer 10 as the isostatic pressing process as shown in FIG.
4B. By performing the isostatic pressing process, the density of
the particles of the piezoelectric material can be raised in the
piezoelectric body layer 12. Prior to the isostatic pressing
process in the step S6, the film 15 is exfoliated.
[0058] In the step S6, if the base body layer 10 is the ceramics
already fired, the sacrificial layer 16 and the first electrode 11
disposed on the base body layer 10 are held in the surfaces having
contact with the base body layer 10, and therefore, the isostatic
pressing in the surface direction becomes difficult to perform. In
contrast thereto, according to the present embodiment, since the
base body layer 10 is not yet fired and has flexibility, the
restriction to the surface having contact with the base body layer
10 is reduced, and therefore, preferable efficiency of the
isostatic pressing process can be obtained. Thus, the density of
the piezoelectric particles in the piezoelectric body layer 12 is
raised, and therefore, the piezoelectric characteristics of the
piezoelectric body 22 can be improved.
[0059] As the isostatic pressing process, a warm isostatic pressing
(WIP) process can also be adopted. By performing the warm isostatic
pressing process, the adhesiveness between the piezoelectric body
layer 12 and both of the first electrode layer 11 and the second
electrode layer 13 can be enhanced.
[0060] The step S7 is the fireation step of firing the base body
layer 10, the sacrificial layer 16, and the piezoelectric
transducer layer 14. In the step S7, as shown in FIG. 4C, the
material of the sacrificial layer 16 is thermally decomposed and
then removed by, for example, the fireation at the temperature no
higher than 1200.degree. C. in the atmosphere. The base body layer
10 and the respective layers of the piezoelectric transducer layer
14 are fired to thereby form the piezoelectric transducer 24, which
is composed of the first electrode 21, the piezoelectric body 22,
and the second electrode 23, and has the support section 30 and the
cantilevered vibrating section 32, on the base body 20.
[0061] In the step S7, since the ceramic sheet not yet fired is
used as the base body layer 10, it becomes possible to fire the
base body layer 10 while forming an arbitrary shape such as a
curved shape. Since the base body layer 10 and the piezoelectric
body layer 12 include the same component, the difference between
the both layers in contraction rate in the fireation process
becomes smaller and the diffusion of impurities from the base body
layer 10 to the piezoelectric body layer 12 becomes smaller
compared to the case in which the components of the base body layer
10 and the piezoelectric body layer 12 are different from each
other. Thus, generation of cracks and residual stress in the base
body 20 and the piezoelectric body 22 due to the large difference
in contraction rate, and deterioration in the piezoelectric
characteristics of the piezoelectric body 22 due to the diffusion
of the impurities can be prevented in the fireation process.
[0062] According to the steps S1 through S7 described hereinabove,
the piezoelectric generator 1 shown in FIGS. 1A and 1B is
manufactured.
Configuration of Sensor Node
[0063] Then, a configuration of a sensor node according to the
first embodiment will be explained with reference to FIG. 5. FIG. 5
is a schematic diagram showing a schematic configuration of the
sensor node according to the first embodiment.
[0064] As shown in FIG. 5, the sensor node 100 according to the
first embodiment is provided with the piezoelectric generator 1
disposed on the base body 101, a circuit 4, and a communication
system 5. The sensor node 100 is used as a terminal of a sensor
network (not shown). The sensor network is a network connecting the
sensor nodes installed in a variety of places to each other, and
makes it possible to collect data such as environmental information
obtained by the sensor nodes, and for example, determine the
circumstances in a specific area in a comprehensive manner based on
the data thus collected. The sensor node is also installed in a
place where the maintenance is difficult, and is therefore required
to be able to efficiently generate electricity and operate for a
long period of time, and have a maintenance-free power source not
requiring battery replacement. Since a number of sensor nodes are
installed in a variety of places, the sensor node is also required
to be small in size, low-profile, and low in price.
[0065] In the sensor node 100, the piezoelectric generator 1
functions as a power source for driving the circuit 4 and the
communication system 5. The piezoelectric generator 1 efficiently
generates the electric energy due to the piezoelectric effect of
the piezoelectric transducer 24, and can therefore be used
preferably as the maintenance-free power source not requiring
replacement. Since the piezoelectric generator 1 functions as a
sensor for sensing the vibration and impact due to the
piezoelectric effect of the piezoelectric transducer 24 provided
with the vibrating section 32, no additional sensor is
required.
[0066] The circuit 4 performs, for example, a process of comparing
with the standard value on the data the piezoelectric generator 1
obtains as a sensor. The communication system 5 performs
communication such as transmission of the data, which the
piezoelectric generator 1 obtains as a sensor, to the network. The
base body 101 is formed of, for example, a substrate, a film, or a
material selected in accordance with the place where the sensor
node 100 is installed.
[0067] Since the sensor node 100 according to the first embodiment
is provided with the piezoelectric generator 1, which can be
manufactured at low cost, and functions also as a sensor, a
small-sized and low-price sensor node 100 can be provided. Since
the base body 20 of the piezoelectric generator 1 can be formed to
have an arbitrary shape, the freedom of installation of the sensor
node 100 can be enhanced compared to the case in which the base
body 20 is formed of a silicon substrate or the like.
[0068] The piezoelectric generator 1 can also be used as a sensor
for sensing temperature or moisture by disposing a layer made of a
material, which shrinks in accordance with an environmental
variation other than a vibration or an impact, such as a variation
in temperature, moisture, or the like, on the piezoelectric
transducer 24. By adopting such a configuration, there can be
provided the sensor node 100 capable of coping with the data
acquisition of a variety of environmental information.
[0069] According to the configuration and the manufacturing method
of the piezoelectric generator 1 related to the first embodiment
described hereinabove, the following advantages can be
obtained.
[0070] 1. Since no other layer intervenes between the piezoelectric
transducer 24 having the support section 30 and the vibrating
section 32 and the base body 20, the piezoelectric generator 1 can
be made low-profile. Since the other end 32b side of the vibrating
section 32 bends upward, the amplitude of the vibration of the
vibrating section 32 excited by an external vibration can be
increased. Thus, the amount of the distortion caused in the
piezoelectric transducer 24 is increased, and therefore, the
electric energy generated by the piezoelectric generator 1 is
increased. As a result, the piezoelectric generator 1, which is
low-profile and efficiently generates electricity, can be
provided.
[0071] 2. Since the sacrificial layer 16 and the piezoelectric
transducer layer 14 are disposed using a printing process in the
manufacturing process, an expensive vacuum (low-pressure)
deposition device is not required. Since the sacrificial layer 16
is thermally decomposed to be removed by firing the layers thus
disposed to thereby form the piezoelectric transducer 24 to have
the cantilevered shape, there can be eliminated the complicated
process using the photolithography process and the etching process
for patterning the piezoelectric transducer 24 and removing the
sacrificial layer 16. As a result, the manufacturing man-hour and
the manufacturing cost of the piezoelectric generator 1 can be
reduced.
[0072] 3. Since the piezoelectric body 22 is formed of the two
layers, namely the piezoelectric body layers 12a, 12b, stacked one
another, it becomes easy to obtain a desired layer thickness, and
at the same time, the layer thickness can be made more uniform.
Thus, the breakage and the leakage between the first electrode 21
and the second electrode 23 due to the variation in thickness of
the piezoelectric body 22 can be prevented.
[0073] 4. Since the ceramic sheet to be fired is used as the base
body layer 10, it becomes possible to form the base body 20 so as
to have an arbitrary shape, and therefore, the freedom of
installation can be enhanced. In the step of performing the
isostatic pressing process, since the restriction to the part
having contact with the base body layer 10 in the surface direction
is small, the isostatic pressing process can efficiently be
performed. Thus, the density of the piezoelectric particles in the
piezoelectric body 22 is raised, and therefore, the piezoelectric
characteristics can be improved.
[0074] Since the base body layer 10 includes the same component as
that of the piezoelectric body layer 12, the difference between the
both layers in contraction rate in the fireation process is
reduced, and at the same time, the diffusion of the impurities from
the base body layer 10 into the piezoelectric body layer 12 is also
reduced. Thus, generation of cracks and residual stress in the base
body 20 and the piezoelectric body 22 due to the large difference
in contraction rate, and deterioration in the piezoelectric
characteristics of the piezoelectric body 22 due to the diffusion
of the impurities can be prevented. Further, since the base body
layer 10 has flexibility, it becomes possible to form the base body
20 after the fireation process so as to have an arbitrary
shape.
[0075] 6. Since the thermal contraction rate of the first electrode
layer 11 is lower than the thermal contraction rate of the
piezoelectric body layer 12, the piezoelectric body layer 12
located upward makes larger contraction than the first electrode
layer 11 due to the fireation. Therefore, in the piezoelectric
transducer 24 after the fireation, since the other end 32b side of
the vibrating section 32 bends upward, the distance between the
other end 32b of the vibrating section 32 and the base body 20 can
be made larger than the distance between the one end 32a of the
vibrating section 32 and the base body 20.
[0076] 7. Since the thermal contraction rate of the second
electrode layer 13 is higher than the thermal contraction rate of
the piezoelectric body layer 12, the second electrode layer 13
located upward makes larger contraction than the piezoelectric body
layer 12 due to the fireation. Therefore, in the piezoelectric
transducer 24 after the fireation, since the other end 32b side of
the vibrating section 32 bends upward, the distance between the
other end 32b of the vibrating section 32 and the base body 20 can
be made larger than the distance between the one end 32a of the
vibrating section 32 and the base body 20.
[0077] 8. Since the piezoelectric generator 1, which efficiently
generates electricity due to an external vibration, is provided as
the power source, power source replacement of the sensor node 100
can be made unnecessary. Since the piezoelectric generator 1, which
can be manufactured at low cost, functions as not only the power
source but also the sensor, the low-price sensor node 100 can be
provided. Further, since the base body 20 of the piezoelectric
generator 1 can be formed to have an arbitrary shape, the freedom
of installation can be enhanced compared to the case in which the
base body 20 is formed of a silicon substrate or the like.
Second Embodiment
Configuration of Piezoelectric Generator
[0078] Then, a configuration of a piezoelectric generator according
to a second embodiment will be explained with reference to FIGS. 6A
and 6B. FIGS. 6A and 6B are schematic diagrams showing a schematic
configuration of the piezoelectric generator according to the
second embodiment. For details, FIG. 6A is a schematic plan view of
the piezoelectric generator, and FIG. 6B is a schematic
cross-sectional view along the line A-A shown in FIG. 6A.
[0079] The piezoelectric generator 2 according to the second
embodiment is different from the piezoelectric generator 1
according to the first embodiment in the point that a weight 29 is
disposed on the vibrating section 32, and is substantially the same
in the rest of the configuration. Therefore, in the second
embodiment, the constituents common to the first and second
embodiments are denoted with the same reference symbols, and the
explanation therefor will be omitted.
[0080] As shown in FIGS. 6A and 6B, the piezoelectric generator 2
according to the second embodiment is provided with the base body
20, the piezoelectric transducer 24 disposed on the base body 20,
and the weight 29 disposed on the piezoelectric transducer 24. The
weight 29 is disposed on the other end 32b side of the vibrating
section 32 of the piezoelectric transducer 24. The weight 29 is
formed in such a manner that dot-like clods are stacked, for
example. Therefore, in FIGS. 6A and 6B, the weight 29 has a
rectangular planar shape with a flat surface, but is not limited to
such a shape.
[0081] By disposing the weight 29 on the vibrating section 32 (the
piezoelectric transducer 24), the vibration of the vibrating
section 32 excited by the external vibration is promoted by the
weight 29, and therefore, the amplitude of the vibration of the
vibrating section 32 can further be increased. As a result, since
the electric energy generated by the piezoelectric transducer 24
can be increased compared to the case in which the weight 29 is not
provided, the current or the voltage output from the piezoelectric
generator 2 can also be increased.
[0082] By disposing the weight 29 on the vibrating section 32, the
natural frequency of the piezoelectric generator 2 is lowered. By
controlling the weight of the weight 29, the natural frequency of
the piezoelectric generator 2 can be controlled. Since the output
of the piezoelectric generator 2 becomes the largest when the
frequency of the external vibration and the natural frequency of
the piezoelectric generator 2 are equal to each other, by
appropriately controlling the natural frequency of the
piezoelectric generator 2 to thereby make it easy to resonate with
the external vibration, it is possible to approximate the current
or the voltage output from the piezoelectric generator 2 to the
maximum.
[0083] Since the natural frequency of the piezoelectric generator 2
varies in accordance with the length and the thickness of the
vibrating section 32, the natural frequency can be controlled by
varying the length of the vibrating section 32 or the thickness of
the vibrating section 32 (the piezoelectric body 22). However, if
the natural frequency is controlled using the weight of the weight
29 as in the piezoelectric generator 2, the natural frequency can
easily be controlled without changing the dimensional setting of
the vibrating section 32, and therefore, it becomes possible to
easily cope with, for example, the installation environment with
different external vibration.
[0084] The manufacturing method of the piezoelectric generator 2
according to the second embodiment is different from the
manufacturing method of the piezoelectric generator 1 according to
the first embodiment in the point that a step of forming the weight
29 is further provided after the fireation step in the step S7. As
the material of the weight 29, there can be used either one of an
organic matter such as light curing resin, an inorganic matter such
as Si, SiO.sub.3, or ZrO.sub.2, a metal such as Au, Ag, or Cu, a
resist, and so on.
[0085] In the method of forming the weight 29, a plurality of
dot-like clods made of the material of the weight 29 is disposed on
the piezoelectric transducer 24 using, for example, an inkjet
process or a dispenser process. Thus, the weight 29 is formed, and
the weight of the weight 29 can be controlled by the number
(amount) of the dot-like clods. It is preferable that the place
where the weight 29 is disposed is set so that the amplitude of the
vibration of the vibrating section 32 becomes the largest. By
directly forming the weight 29 using the inkjet process, the
dispenser process, or the like, the complicated manufacturing
process is not required, and therefore, the productivity can be
improved.
[0086] The piezoelectric generator 2 according to the second
embodiment can be used as the sensor and the power source of the
sensor node 100 according to the first embodiment. By providing the
sensor node 100 with the piezoelectric generator 2, the current or
the voltage supplied from the piezoelectric generator 2 as a power
source can be made larger. Since the natural frequency of the
piezoelectric generator 2 can easily be controlled, it is possible
to easily cope with the installation environment of the sensor node
100.
[0087] Although the piezoelectric generator according to the
invention is hereinabove explained based on the embodiments
described above, the invention is not limited to these embodiments,
and various modifications can be made within the scope of the
invention. The following modified examples are possible.
[0088] Although the piezoelectric generator 1 according to the
first embodiment has the configuration of disposing a layer of the
piezoelectric transducer 24 (the first electrode 21, the
piezoelectric body 22, and the second electrode 23), the invention
is not limited to such a configuration. It is also possible for the
piezoelectric generator to have a configuration of stacking a
plurality of piezoelectric transducers on the base body 20. FIGS.
7A through 7C are diagrams showing a schematic configuration of a
piezoelectric generator according to a modified example. For
details, FIGS. 7A, 7B, and 7C are schematic cross-sectional
diagrams of the piezoelectric generators having the respective
configurations different from each other. The constituents common
to the embodiments described above and the modified example are
denoted with the same reference symbols, and the explanation
therefor will be omitted.
First Modified Example
[0089] A piezoelectric generator 1A shown in FIG. 7A is further
provided with a piezoelectric body 27 and a third electrode 28
stacked on the piezoelectric transducer 24 (the first electrode 21,
the piezoelectric body 22, and the second electrode 23). In the
piezoelectric generator 1A, a piezoelectric transducer 24a is
composed of the second electrode 23, the piezoelectric body 27, and
the third electrode 28. The second electrode 23 is also functions
as the electrode in the piezoelectric transducer 24a. Therefore,
the piezoelectric generator 1A is different from the piezoelectric
generator 1 according to the first embodiment in a point that the
piezoelectric transducer 24a stacked on the piezoelectric
transducer 24 is provided.
[0090] According to the piezoelectric generator 1A, the electric
energy due to the external vibration can be obtained from each of
the plurality of piezoelectric transducers 24, 24a stacked on the
base body 20. As indicated by the arrows in FIG. 7A, since the
polarization direction of the piezoelectric transducer 24 and the
polarization direction of the piezoelectric transducer 24a are the
same, the piezoelectric generator 1A is capable of increasing the
current to be output compared to the piezoelectric generator 1
according to the first embodiment. Thus, the piezoelectric
generator 1A efficiently generating electricity can be
provided.
Second Modified Example
[0091] A piezoelectric generator 1B shown in FIG. 7B has a
configuration of stacking the piezoelectric transducer 24a on the
piezoelectric transducer 24 similarly to the piezoelectric
generator 1A according to the first modified example. It should be
noted that the way of wiring is different, and the polarization
direction is reversed between the piezoelectric transducer 24 and
the piezoelectric transducer 24a. According to such a
configuration, the piezoelectric generator 1B is capable of
increasing the voltage to be output compared to the piezoelectric
generator 1.
Third Modified Example
[0092] A piezoelectric generator 1C shown in FIG. 7C is provided
with an insulating layer 25 disposed, on the piezoelectric
transducer 24 (the first electrode 21, the piezoelectric body 22,
and the second electrode 23), and is further provided with a fourth
electrode 26, a piezoelectric body 27, and a third electrode 28
sequentially stacked on the insulating layer 25. The fourth
electrode 26, the piezoelectric body 27, and the third electrode 28
constitute a piezoelectric transducer layer 24c. Therefore, the
piezoelectric generator 1C is different from the piezoelectric
generator 1 in the point that the piezoelectric transducer 24c is
stacked on the piezoelectric transducer 24 via the insulating layer
25.
[0093] In the piezoelectric generator 1C, the polarization
direction of the piezoelectric transducer 24 and the polarization
direction of the piezoelectric transducer 24c are the same, and
therefore, the configuration similar to that of the piezoelectric
generator 1A according to the first modified example is provided.
According to such a configuration, the piezoelectric generator 1C
is capable of increasing the current to be output similarly to the
piezoelectric generator 1A.
[0094] Compared to the piezoelectric generator 1A, since the
thickness of the vibrating section 32 increases as much as the
thickness of the insulating layer 25 and the fourth electrode 26 in
the piezoelectric generator 1C, the natural frequency is raised. In
other words, according to the configuration of the piezoelectric
generator 1C, the natural frequency of the piezoelectric generator
1C of the vibrating section 32 can be controlled by varying the
layer thickness or the material of the insulating layer 25.
Therefore, it is possible to control the natural frequency of the
piezoelectric generator 1C without varying the length of the
vibrating section 32 or the thickness of the piezoelectric bodies
22, 27, and so on.
[0095] As the material of the insulating layer 25, there is
preferably used the material, which is the same as the constituent
material of the piezoelectric bodies 22, 27, but in which no
polarization is caused. If a material different from the
constituent material of the piezoelectric bodies 22, 27 is used as
the material of the insulating layer 25, there is a possibility
that the component of the material of the insulating layer 25
diffuses into the piezoelectric bodies 22, 27 in the fireation
process to thereby deteriorate the piezoelectric characteristics of
the piezoelectric bodies 22, 27.
[0096] It is also possible to adopt a configuration of providing
the piezoelectric generators 1A, 1B, and 1C of the first, second,
and third modified examples with the weight 29 of the second
embodiment. By providing, the piezoelectric generators 1A, 1B, and
1C with the weight 29, the amplitude of the vibration of the
vibrating section 32 can further be enlarged, and at the same time,
the natural frequency can easily be controlled. It is also possible
to adopt a configuration of using one of the piezoelectric
generators 1A, 1B, and 1C of the first, second, and third modified
examples as the sensor and the power source of the sensor node 100
according to the first embodiment.
[0097] This application claims priority to Japanese Patent
Application No. 2010-230299, filed on Oct. 13, 2010, the entirety
of which is hereby incorporated by reference.
* * * * *