U.S. patent application number 16/225087 was filed with the patent office on 2019-05-16 for dryness/wetness responsive sensor having first and second wires spaced 5 nm to less than 20 um apart.
This patent application is currently assigned to NATIONAL INSTITUTE FOR MATERIALS SCIENCE. The applicant listed for this patent is NATIONAL INSTITUTE FOR MATERIALS SCIENCE. Invention is credited to Toyohiro CHIKYO, Jin KAWAKITA, Toshihide NABATAME, Akihiko OHI, Tomoko OHKI, Tadashi SHINOHARA.
Application Number | 20190145920 16/225087 |
Document ID | / |
Family ID | 55163069 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190145920 |
Kind Code |
A1 |
KAWAKITA; Jin ; et
al. |
May 16, 2019 |
DRYNESS/WETNESS RESPONSIVE SENSOR HAVING FIRST AND SECOND WIRES
SPACED 5 nm TO LESS THAN 20 um APART
Abstract
The present invention improves the sensitivity and the
responsiveness of a dryness/wetness responsive sensor utilizing a
galvanic current, allowing for downsizing of the dryness/wetness
responsive sensor. Instead of the conventional structure in which
an anode electrode and a cathode electrode are stacked with an
intervening insulator, the present invention employs a structure in
which both electrodes run in juxtaposition with each other on an
insulating substrate in the form of, for example, a comb-shaped
electrode as shown in the drawing. By utilizing a semiconductor
manufacturing process or any other micro/nano-fabrication
technology, an inter-electrode distance can be extremely shortened
as compared with the conventional sensors, allowing enhancing the
sensitivity per unit footprint of the electrodes. Accordingly, a
decrease in the size of the dryness/wetness responsive sensor can
be easily achieved.
Inventors: |
KAWAKITA; Jin; (Ibaraki,
JP) ; SHINOHARA; Tadashi; (Ibaraki, JP) ;
CHIKYO; Toyohiro; (Ibaraki, JP) ; NABATAME;
Toshihide; (Ibaraki, JP) ; OHI; Akihiko;
(Ibaraki, JP) ; OHKI; Tomoko; (Ibaraki,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL INSTITUTE FOR MATERIALS SCIENCE |
Ibaraki |
|
JP |
|
|
Assignee: |
NATIONAL INSTITUTE FOR MATERIALS
SCIENCE
Ibaraki
JP
|
Family ID: |
55163069 |
Appl. No.: |
16/225087 |
Filed: |
December 19, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15327103 |
Jan 18, 2017 |
|
|
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PCT/JP2015/070692 |
Jul 21, 2015 |
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16225087 |
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Current U.S.
Class: |
324/694 |
Current CPC
Class: |
G01N 17/04 20130101;
G01N 27/045 20130101; G01N 27/121 20130101; G01N 27/048 20130101;
G01N 27/223 20130101; G01N 17/00 20130101 |
International
Class: |
G01N 27/04 20060101
G01N027/04; G01N 27/12 20060101 G01N027/12; G01N 27/22 20060101
G01N027/22; G01N 17/04 20060101 G01N017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2014 |
JP |
2014-149505 |
Claims
1-13. (canceled)
14. A dryness/wetness responsive sensor comprising a thin wire of a
first metal, a thin wire of a second metal, the second metal being
different from the first metal, and a current measurement means
electrically connected to the thin wire of the first metal and the
thin wire of the second metal, wherein the thin wire of the first
metal and the thin wire of the second metal are disposed in
juxtaposition with each other on an insulating substrate, wherein a
spacing between the first thin wire and the second thin wire is in
a range of 5 nm or more and less than 20 .mu.m. wherein a part of
the insulating substrate corresponding to the spacing between the
thin wire of the first metal and the thin wire of the second metal
has an insulating surface over the entire part.
15. The dryness/wetness responsive sensor according to claim 14,
comprising a plurality of at least one selected from the group
consisting of the thin wire of the first metal and the thin wire of
the second metal, and wherein the thin wire of the first metal
extends from a first side towards a second side that is opposite to
the first side and the thin wire of the second metal extends from
the second side towards the first side such that the thin wire of
the first metal and the thin wire of the second metal run in
parallel.
16. The dryness/wetness responsive sensor according to claim 14,
wherein the thin wire of the first metal and the thin wire of the
second metal are arranged in a double spiral.
17. The dryness/wetness responsive sensor according to claim 14,
wherein the insulating substrate is a silicon substrate with a
silicon oxide film on its surface.
18. The dryness/wetness responsive sensor according to claim 14,
wherein the first metal is selected from a group consisting of
gold, platinum, silver, titanium, an alloy thereof, and carbon.
19. The dryness/wetness responsive sensor according to claim 14,
wherein the second metal is selected from a group consisting of
silver, copper, iron, zinc, nickel, cobalt, aluminum, tin,
chromium, molybdenum, manganese, magnesium, and an alloy
thereof.
20. The dryness/wetness responsive sensor according to claim 14,
wherein a number of pairs of the thin wire of the first metal and
the thin wire of the second metal is more than 50.
21. The dryness/wetness responsive sensor according to claim 14,
further comprising a meshed member covering an area in which the
thin wire of the first metal and the thin wire of the second metal
are disposed in juxtaposition with each other.
22. The dryness/wetness responsive sensor according to claim 14,
further comprising an insulating protection film covering an area
in which the thin wire of the first metal and the thin wire of the
second metal are disposed in juxtaposition with each other, and
wherein the insulating protection film has a groove-shaped opening
that exposes at least a part of the thin wires.
23. The dryness/wetness responsive sensor according to claim 22,
wherein the groove-shape opening further exposes at least a part of
a gap between the thin wire of the first metal and the thin wire of
the second metal.
24. The dryness/wetness responsive sensor according to claim 14,
wherein the insulating substrate comprises an opening portion
passing through from one side to an opposite side of the insulating
substrate, and the opening portion is obtained by removing at least
a part of the insulating substrate corresponding to the spacing
between the thin wire of the first metal and the thin wire of the
second metal.
25. A dryness/wetness responsive sensor assembly for remote
installation comprising the dryness/wetness responsive sensor
according to claim 14 attached to an attachment member having an
attachment portion at one end for attachment to an object such that
the dryness/wetness responsive sensor is attached to the object via
the attachment member.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-speed
response/high-sensitivity dryness/wetness responsive sensor and,
more particularly, to a dryness/wetness responsive sensor that has
an appropriate structure for decreasing the size and increasing the
sensitivity and realizes a high-speed response.
BACKGROUND ART
[0002] Conventionally, as dryness/wetness responsive sensors,
humidity sensors are known which detect humidity based on a change
in the electric resistance value (impedance) or electrostatic
capacitance of a sensor element (dryness/wetness responsive part).
In a humidity sensor of an electric resistance type, as a
dryness/wetness responsive material of a sensor element, a polymer,
ceramics, or the like is generally used, and since the material is
low-cost and the structure is simple, a low cost can be achieved
through mass production. However, if the humidity sensor of the
electric resistance type gets wet with water, the sensor element
will break down, and thus, the humidity sensor of the electric
resistance type cannot be used under a condition in which dew
condensation may occur. For this reason, the measurement humidity
range is restricted to the range of 10 to 90% RH, and it is
difficult to use the humidity sensor of the electric resistance
type in a low humidity environment of 10% RH or less and in a high
humidity environment of over 90% RH. In addition, the humidity
sensor of the electric resistance type has a large aging variation,
and, since it also has high temperature dependency in many cases, a
temperature correction is required. Furthermore, the humidity
sensor of the electric resistance type also has problems of large
variation in precision (about .+-.5 to 15% RH) and a long response
time (30 seconds to several minutes or even more).
[0003] In a humidity sensor of an electrostatic capacitance type, a
polymer membrane is generally used as the dryness/wetness
responsive material of the sensor element. Accordingly, the
humidity sensor of the electrostatic capacitance type has a higher
response speed (normally, about several seconds to ten seconds) and
higher precision/reproducibility/reliability than the electric
resistance type. Though its typical measurement humidity range is 0
to 100% RH, there are occasions when the sensor element is broken
down under a dew condensation condition. In addition, the humidity
sensor of the electrostatic capacitance type also has a problem of
higher production cost than that of the humidity sensor of the
electric resistance type.
[0004] A humidity sensor of both of the electric resistance type
and the electrostatic capacitance type requires an external drive
power supply for driving the sensor. In addition, a conventional
humidity sensor cannot detect the size of water droplets attached
to the surface of the sensor element due to its sensor structure or
its detection principle.
[0005] Recently, a dryness/wetness responsive sensor based on
galvanic action has been developed and used as a corrosion
environment sensor that is used mainly for monitoring the corrosive
environment of a construction.
[0006] In a bridge and other various constructions, since its steel
members are often exposed to outside, the degree of corrosion of
used steel members has great influence on the durability
performance. The progress of corrosion of a steel member greatly
varies according to not only the properties of the steel member
itself but also use environments including the amount of a
corrosive material and electrolytes contained in the atmosphere and
rainwater, the amount of attached rainwater, and its wet time.
Thus, in order to evaluate remaining lives of constructions of this
type and appropriately maintain them by inspection, repair or the
like, it is preferable to continuously evaluate the corrosion
status for each of the constructions or, if necessary, for the
respective portions of even one construction the corrosion
environments of which are considered to be different from each
other.
[0007] However, since it is difficult and takes a cost to perform
an inspection of the degree of corrosion of a steel member itself
configuring a structure on site, technique has been developed
actually in which corrosion environment sensors are attached to
respective places for evaluating their corrosion environments and
the degree of corrosion of a steel member are estimated and
predicted based on the evaluation results For example, as
illustrated in FIG. 1, the degradation of the steel member of a
bridge or the like was predicted by attaching a sensor of this type
to the steel member and monitoring the corrosion environment at
that place.
[0008] A representative example of the corrosion environment sensor
is an atmospheric corrosion monitoring (ACM) sensor that detects a
galvanic current flowing between metals of different types due to a
contact therebetween via water. Refer to Non Patent Literatures 1
to 4 for its structure, method of evaluating measured data, and the
like. However, since the size of the conventional galvanic sensor
becomes larger for compensating for its low sensitivity, it has
problems of inconvenience of the handling and high price.
SUMMARY OF INVENTION
Technical Problem
[0009] An object of the present invention is to improve the
sensitivity and the responsiveness of a dryness/wetness responsive
sensor with the operation principle of detection of a galvanic
current, and in turn to decrease the size of the dryness/wetness
responsive sensor.
Solution to Problem
[0010] According to one aspect of the present invention, there is
provided a dryness/wetness responsive sensor comprising a thin wire
of a first metal and a thin wire of a second metal, the second
metal being different from the first metal, wherein the thin wire
of the first metal and the thin wire of the second metal are
disposed in juxtaposition with each other on an insulation
substrate, and, wherein a spacing between the first thin wire and
the second thin wire is in a range of 5 nm or more and less than 20
.mu.M.
[0011] Here, a plurality of instances is provided for at least one
of the thin wire of the first metal and the thin wire of the second
metal, and the thin wire of the first metal and the thin wire of
the second metal extend from mutually opposite sides toward the
other sides so as to run in parallel.
[0012] Further, the thin wire of the first metal and the thin wire
of the second metal may be arranged in a double spiral.
[0013] Further, the insulating substrates may be a silicon
substrate with a silicon oxide film on its surface.
[0014] Further, the first metal may be selected from a group
consisting of gold, platinum, silver, titanium, an alloy thereof,
and carbon.
[0015] Further, the second metal may be selected from a group
consisting of silver, copper, iron, zinc, nickel, cobalt, aluminum,
tin, chromium, molybdenum, manganese, magnesium, and an alloy
thereof.
[0016] Further, a meshed member covering an area in which the thin
wire of the first metal and the thin wire of the second metal may
be disposed in juxtaposition with each other.
[0017] Further, an insulating protection film covering an area in
which the thin wire of the first metal and the thin wire of the
second metal are disposed in juxtaposition with each other, wherein
the insulting protection film has a groove-shaped opening that
exposes at least a part of the thin wires.
[0018] Further, a groove-shape opening that exposes at least a part
of a gap between the thin wire of the first metal and the thin wire
of the second metal.
[0019] Further, an opening portion passing through between front
and rear sides of the insulating substrate by removing at least a
part of a position of the insulating substrate corresponding to a
gap between the thin wire of the first metal and the thin wire of
the second metal.
[0020] According to another aspect of the present invention, there
is provided a dryness/wetness responsive sensor assembly for remote
installation comprising an attachment member with an attachment
portion at one end for attachment to an object to which any of the
dryness/wetness responsive sensor described above is attached so as
to allow the dryness/wetness responsive sensor to be remotely
located.
[0021] According to yet another aspect of the present invention,
there is provided a dryness/wetness responsive sensor system
comprising a plurality of any of the dryness/wetness responsive
sensors described above, where the dryness/wetness responsive
sensor in the system in which a short circuit has occurred or which
does not generate an output current is disconnected.
[0022] Here, the disconnection of the dryness/wetness responsive
sensor may be performed by electrically disconnecting the
dryness/wetness responsive sensor or not using an output of the
dryness/wetness responsive sensor.
Advantageous Effects of Invention
[0023] According to the present invention, since a dryness/wetness
responsive sensor of high sensitivity and high-speed responsiveness
is provided that has a simple structure and needs no sensor driving
power, the dryness/wetness responsive sensor can be reduced in size
and price.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a photograph that illustrates an example of the
use of a conventional corrosion environment sensor.
[0025] FIGS. 2(a) and 2(b) are diagrams that illustrate the
structure of a conventional corrosion environment sensor based on
detection of a galvanic current. In the drawing, the dimension is
in units of mm.
[0026] FIG. 3 is a conceptual diagram for illustrating the
detection of a galvanic current.
[0027] FIG. 4 is a conceptual diagram for illustrating a structure
for improving the sensitivity of a corrosion environment sensor
based on detection of a galvanic current.
[0028] FIG. 5 is a graph for illustrating a lower limit of an
electrode gap of a conventional corrosion environment sensor based
on the detection of a galvanic current.
[0029] FIG. 6 is a diagram that illustrates an example of an
electrode arrangement structure of a dryness/wetness responsive
sensor based on detection of a galvanic current according to the
present invention.
[0030] FIG. 7A is a diagram for schematically illustrating the
former half of the manufacturing process of the dryness/wetness
responsive sensor of an embodiment of the present invention.
[0031] FIG. 7B is a diagram for schematically illustrating the
latter half of a process of manufacturing the dryness/wetness
responsive sensor of the embodiment of the present invention.
[0032] FIG. 8A is a photograph of the whole of the cathode and
anode electrodes of the dryness/wetness responsive sensor of the
embodiment of the present invention.
[0033] FIG. 8B shows photographs illustrating the major portion of
the dryness/wetness responsive sensor of the embodiment of the
present invention for the cases where an electrode gap is 10 .mu.m,
1 .mu.m, and 0.5 .mu.m.
[0034] FIG. 9A is a diagram for illustrating a temporal change of
the output of the dryness/wetness responsive sensor according to
the present invention.
[0035] FIG. 9B is a diagram for illustrating examples of the output
of the dryness/wetness responsive sensor of the embodiment of the
present invention for the cases where an inter-electrode distance
were configured to be 10 .mu.m, 1 .mu.m, and 0.5 .mu.m.
[0036] FIG. 10 is a diagram for illustrating the attenuation curves
of the current values after recording the maximum current value in
the dryness/wetness responsive sensors of the embodiment of the
present invention having inter-electrode distances of 10 .mu.m, 1
.mu.m, and 0.5 .mu.m.
[0037] FIG. 11 is a diagram for illustrating the results of output
currents measured under humidity conditions of 0% RH, 38% RH, and
100% RH by using the dryness/wetness responsive sensor of the
embodiment of the present invention having the inter-electrode
distance configured to be 1.0 .mu.m.
[0038] FIG. 12 is a diagram for illustrating examples of the output
of the dryness/wetness responsive sensor of the embodiment of the
present invention having an inter-electrode distance of 1.0 .mu.m
and the number of pairs of electrodes of 10, 50 and 200.
DESCRIPTION OF EMBODIMENTS
[0039] First, the structure of a conventional corrosion environment
sensor using detection of a galvanic current disclosed in Non
Patent Literature 3 will be described with reference to the
drawings. FIG. 2(a) is a plan view of the corrosion environment
sensor, and FIG. 2(b) is an enlarged diagram of a portion near a
center portion of a cross-sectional view taken along A-A'
represented in FIG. 2(a). In this corrosion environment sensor, for
example, by coating a metallic substrate such as carbon steel with
insulating paste (for example, SiO.sub.2, BN, or the like), an
insulating film formed using the insulating paste is formed on the
substrate. By coating the insulating film with conductive paste,
for example, a film of another metal such as silver is formed. A
vertical-striped portion having a light color inside a tire-shaped
area (sensor area) in FIG. 2(a) is a portion in which neither a
film of a metal such as silver nor insulating paste is formed but a
substrate of metal such as carbon steel is exposed. FIG. 2(b)
illustrates a cross-sectional structure of this portion. In
addition, a copper foil is attached to a portion deviating from the
sensor area on the film of a metal such as silver so as to be set
as an electrode. Also from the substrate formed using a metal such
as copper steel, the other electrode is led out (an upper left
corner in FIG. 2(a)). When this corrosion environment sensor is
used, a current meter is connected between both the electrodes and
measures a galvanic current.
[0040] In a case where this corrosion environment sensor is
installed at an outdoor place, water (hereinafter, represented by
rainwater) such as rainwater according to a rain fall is attached
thereto. Naturally, the rainwater is not pure water but dissolves
fine particles of salts floating in the atmosphere and gases
(carbon dioxide, sulfur dioxide, nitrogen oxides, and the like)
generating ions by being dissolved into water and, in addition, in
the initial period of a rainfall, dissolves a solid substance
attached to the surface of the corrosion environment sensor, and
accordingly, rainwater attached to the sensor area becomes an
electrolytic solution connecting metals (iron composing the
substrate and silver on the insulating film) of different kinds.
Accordingly, as illustrated in FIG. 2(b), a local cell formed by
iron-rainwater-gold is formed along the periphery of the
vertical-striped area of silver inside the sensor area. This local
cell is conceptually illustrated in FIG. 3. Since the cell is
formed in the sensor area in this way, in a case where the copper
foil and the substrate are connected, a galvanic current according
to the amount of the electrolyte in the rainwater flows. This
current is measured by a current meter connected thereto. It is
known that the magnitude of the galvanic current measured in this
way has a strong correlation with corrosion according to a local
cell formed on the surface of the steel member at the same place in
accordance with to the same rainwater or the like, and accordingly,
the progress of the corrosion can be evaluated by measuring the
galvanic current.
[0041] In a case where the size of the corrosion environment sensor
is decreased, the degree of freedom in the attachment position
increases, and the corrosion environment sensor is not conspicuous
for the attachment thereof, and there is less restriction in the
attachment position also from this point. In addition, generally,
since the cost is lowered due to the decrease in size,
implementation of multiple points of measurement positions can be
easily performed. In the corrosion environment sensor using a
galvanic current as illustrated in FIGS. 2(a) and 2(b), in
principle, the sensitivity is improved in a case where a distance
between two electrodes formed using different kinds of metals is
decreased as illustrated in FIG. 4. However, in the corrosion
environment sensor having the structure illustrated in FIGS. 2(a)
and 2(b), there is a restriction in the decrease in the
inter-electrode distance. FIG. 5 is quoted from Non Patent
Literature 5 and is a graph in which a result of actually measuring
a relation between an inter-electrode distance (d) of a corrosion
environment sensor of this kind and a galvanic current at that time
is plotted. As illustrated in this graph, while there is
non-uniformity, in a case where the inter-electrode distance d is
decreased, the galvanic current increases, in other words, the
sensitivity is improved. However, the inter-electrode distance is
decreased only up to about 20 .mu.m. Accordingly, it is difficult
to improve the sensitivity of the corrosion environment sensor
using the galvanic current (more specifically, the improvement of
the sensitivity of the sensor area per unit area).
[0042] The inventors of the present application have reviewed the
cause of such restriction and a solution thereof and have found
that there is a problem in a structure in which two electrodes (the
substrate and the silver film) are vertically stacked through an
insulating layer formed using the insulating paste in a
conventional corrosion environment sensor of which the structure is
illustrated in FIGS. 2(a) and 2(b). In other words, different from
a device used under a protected environment such as a common
electronic device, for the corrosion environment sensor having a
natural premise of direct exposure for a considerably long period
to an environment for which there is a risk for damaging the device
such as outer air, various weather conditions, emission of
sunlight, collisions with particles such as dusts, interferences
from animals and plants, and the like, in order not to cause the
function of a sensor to disappear due to a direct contact between
the substrate of metal and a film of a different metal even in a
case where there is a damage of some degree in the sensor area,
there is a restriction on the decrease in the inter-electrode
distance by thinning the insulating layer. In addition, the
insulating layer is produced through coating using the insulating
paste, and thus, in a case where the insulating layer is formed to
be thin exceeding a certain limit, there are cases where an
insulation defect occurs in the process of generating the sensor,
and, even in a case where there is no problem at the time of the
production, but the insulation is broken according to aging under a
severe environment as described above. Furthermore, while the edge
of the vertical-striped portion formed by the insulating layer and
the metal layer is ideally erected vertically from the substrate,
practically, as illustrated in FIG. 2(b), the edge may be easily
inclined slightly, and thus, the inter-electrode distance increases
also from this point.
[0043] For this reason, the inventors of the present application
have conceived the idea in that the problem described above can be
solved by employing a structure in which an electrode of a metal
and an electrode of another metal are closely juxtaposed laterally
on an insulating substrate instead of the conventional stacking
structure of electrodes as illustrated in FIGS. 2(a) and 2(b).
Describing this structure more specifically, portions of both
electrodes facing each other are portions that mainly function as a
cell that is locally generated, and thus, increasing a length of
the portions of both the electrodes facing each other with
approaching each other is more effective for an increase in the
capacity of the cell, in other words, an increase in the galvanic
current to be taken out than increasing the areas of such
electrodes on the substrate. Accordingly, a structure in which such
electrodes are thinned and arranged in parallel with each other
over a long distance or the like may be employed. As a
configuration for increasing a length (hereinafter, referred to as
a parallel running distance) of approached portions between thin
wires (electrodes) by arranging such thin wires in parallel with
each other, for example, a comb structure or a double
spirally-wound structure may be employed. In addition, a structure
itself for increasing a parallel running distance between two
electrodes inside a predetermined plane area as possibly as can be
is well known in the field of a semiconductor device and the like,
and thus, such a structure may be employed as is necessary. In the
present invention, "juxtaposing electrodes on a substrate" is not
for specifying mutual directions of a plurality of electrodes
placed on the substrate but represents that the electrodes are
arranged on a same plane of the substrate with being separate from
each other.
[0044] In this way, according to the present invention, by
detecting liquid droplets present on the surface of a solid object
in accordance with a phenomenon of dew condensation of water vapor
contained in the air on the surface of the solid object or a
phenomenon of adsorption of mist droplets onto the surface of the
solid object based on a current that is based on the galvanic
action between electrodes formed using different kinds of
materials, a dryness/wetness responsive sensor capable of
determining a dry/wet state at a high speed with high sensitivity
is realized.
[0045] A dryness/wetness responsive sensor according to the present
invention, compared to a conventional humidity sensor using a
system measuring a dry/wet state through a process of absorbing
moisture into a dryness/wetness responsive material, can directly
detect liquid droplets attached to the surface of the sensor from
the air and thus has high-speed responsiveness.
[0046] In addition, since there is dependency between an
inter-electrode distance of the sensor and the size of liquid
droplets, the dryness/wetness responsive sensor according to the
present invention has high sensitivity that is completely different
in nature from a conventional sensor. This point will be described
below in detail.
[0047] Here, the insulating substrate has an insulating property of
a degree not disturbing the measurement of a galvanic current
flowing from the above-described cell formed thereon, and the
material and the like thereof are not particularly limited as long
as the insulating substrate has durability that is required under
an assumed use environment. For example, in addition to a silicon
substrate in which a coating film of silicon oxide used in the
embodiment to be described hereinafter is formed, plastic, rubber,
or any other various insulating materials can be used. In addition,
as in the conventional technology described above, it should be
noted that a substrate in a form having an insulating property seen
from electrodes by forming insulating coating, insulating covering,
or the like on a substrate main body that is a conductive body of a
metal or the like also belongs the category of the "insulating
substrate" in the present application.
[0048] By employing such a structure, the dryness/wetness
responsive sensor according to the present invention can decrease
the inter-electrode distance up to about 5 nm by using a technique
of a semiconductor manufacturing process. While there is no
particular upper limit of the inter-electrode distance, the upper
limit may be 20 .mu.m or less that is shorter than the
inter-electrode distance according to the conventional technology
described above. In this way, up to the attachment of a water
droplet having an extremely small size and a fine water droplet
that is in a state immediately before dew condensation, of which
detection is difficult by using a sensor having an inter-electrode
distance of 20 .mu.um of more, which is manufactured using a
conventional machine processing technology or a conventional
printing technology, can be detected. Therefore, in the
dryness/wetness responsive sensor according to the present
invention, a correlation between a detection result acquired by the
sensor and the progress status of corrosion is improved. Here, the
inter-electrode distance may be a constant value in accordance with
the use of the dryness/wetness responsive sensor, the installation
environment, and the like, or a plurality of setting values may be
combined.
[0049] As the inter-electrode distance is decreased, conductive
fine particles such as metal powders present in the air, in the
rainwater, and the like are attached between the electrodes, and
accordingly, a possibility of forming a short circuit increases.
Regarding this problem, by setting up a countermeasure as below,
the occurrence of the problem can be prevented.
(1) By arranging a meshed body on the front face of the electrodes,
fine particles do not arrive at the electrodes. (2) An insulating
protection film of a silicon oxide or the like is arranged on the
front face of each electrode, and fine openings exposing at least a
part of the thin wire of each electrode (in addition, at least a
part of the gap between the thin wires, as needed) is formed in the
insulating protection film. With this configuring, even when
conductive fine particles are attached near the entrance of the
fine opening portion of the insulating protection film, the fine
openings prevent the particles from directly contacting the thin
wire and causing a short circuit, since the thin wire of the
electrode is positioned deep in the opening by the thickness of the
insulating protection film. (3) An approach from the aspect of the
sensor system can be employed in which, for example, though the
dryness/wetness responsive sensor itself having an ordinary
structure according to the present invention is used, a plurality
of such sensors are arranged closely to each other, and the sensor
in which a short circuit between the cathode electrode and the
anode electrode is detected or from which no output current is
detected while output currents are detected from other sensors is
excluded from the measurement system (electrically disconnected,
the measured value of the output current not used with the electric
connection unchanged, etc.).
[0050] As another modified embodiment of the sensor according to
the present application, for example, while a substrate to which a
metal is not attached is present in the gap between the cathode
electrode and the anode electrode in the sensor structure described
above, by removing the substrate of the gap portion through etching
or the like, the air may be configured to be allowed to flow
between the cathode electrode and the anode electrode while water
is not attached to the sensor. More specifically, for example, by
removing at least a part of positions corresponding to the gap
between the thin wires, an opening portion passing through the
front and rear sides of the substrate can be arranged. By
configuring as such, the sensor can be used as a sensor for
moisture contained in the air or any other component. In addition,
by completely removing the substrate of the gap portion, in a case
where the mechanical strength is decreased or in a case where an
eigenfrequency is included for which there is a risk of the
occurrence of a trouble according to resonance with a mechanical
vibration applied from the outside under a use environment, a
countermeasure such as configuring the substrate of a part of the
gap portion to remain or the like may be established.
[0051] While the sensor described until now is assumed to be
directly installed to the surface of a building such as a steel
frame and have the use for evaluating the corrosion environment of
the surface of the building, a use for evaluating not the
environment of the surface but the corrosion environment of a free
space may be considered. Also in the case of such a use, the sensor
needs to be fixed inside a space. However, for such a reason, in a
case where the sensor is directly attached to the surface of a
certain large installation target object, there are cases where a
substance attached to the object flows on the sensor in accordance
with rain or the like, or splash jumps into the sensor, or there
are cases where an airflow is different from that of the case of a
free space, and accordingly, there are cases where there is an
influence of the object on a measured value. In order to exclude
such an adverse effect, it is preferable to employ a configuration
in which the sensor is raised to a position located far from an
installation position of an installation target object. More
specifically, for example, one end of an attachment tool having a
plate shape, a rod shape, or the like to which the sensor is
attached is attached to an installation target object for
installation, and one or a plurality of sensors may be attached at
a position separate from the installation target object on an
attachment member.
[0052] In addition, the dryness/wetness responsive sensor according
to the present invention can be used as a humidity sensor. As
described above, the size of the dryness/wetness responsive sensor
according to the present invention can be decreased by
significantly decreasing the inter-electrode distance to be less
than that of a conventional sensor, and external power for driving
the sensor is unnecessary. Accordingly, in addition to the
improvement of the measurement accuracy as a humidity sensor, the
dryness/wetness responsive sensor according to the present
invention is expected to be able to manage a desired humidity
condition also for an electronic apparatus, a physical distribution
system, an industrial plant, and the like in which, conventionally,
it is difficult to install the sensor due to a large size, no
securement of external power, or the like.
EXAMPLES
[0053] Hereinafter, an embodiment will be described in which a
dryness/wetness responsive sensor of which the sensitivity per unit
area of the sensor area is improved by employing a simple structure
by arranging two electrodes in a comb shape. It is understood that
the present invention is not limited to such a specific form, and
it should be noted that the technical scope of the present
invention is defined by claims.
[0054] FIG. 6 illustrates the embodiment of a structure of the
major portion, in other words, an electrode arrangement structure
of the dryness/wetness responsive sensor in which an anode
electrode of a metal such as iron and a cathode electrode of a
metal different from the above-described metal such as silver are
arranged in a comb shape on an insulating substrate. As the
insulating substrate, for example, a silicon wafer having a silicon
oxide film can be used. As examples of a material that can be used
for the cathode electrode include gold, platinum, silver, titanium,
and an alloy thereof; and carbon and allotrope thereof. For the
anode electrode, for example, silver, copper, iron, zinc, nickel,
cobalt, aluminum, tin, chromium, molybdenum, manganese, magnesium,
or an alloy thereof can be used. However, in a case where silver
and an alloy thereof are used for the anode electrode, for the
cathode electrode, a material other than silver and the alloy
thereof among the above-described materials of the cathode
electrode may be used.
[0055] In each of the cathode electrode and the anode electrode,
while a side close to a signal lead terminal (not illustrated in
the drawing) of the dryness/wetness responsive sensor for the
outside is unified as one to be a concentrated portion (the upper
and lower sides in FIG. 6 are denoted by thick lines running in the
horizontal direction), the concentrated portion branches into a
plurality of parts near each terminal end portion. In the
embodiment illustrated in FIG. 6, ten branches of each electrode
are disposed. The branching cathode electrodes and the branching
anode electrodes extend in a parallel direction (more specifically,
an antiparallel direction; hereinafter, simply referred to as a
parallel direction) and, for most of the extended distance, run
parallel in the parallel direction with approaching each other. In
this embodiment, the concentrated portions of the cathode electrode
and the anode electrode extend in the antiparallel direction with
being separate by 1180 .mu.m, and each branching portion extends by
1090 .mu.m toward an opposing concentrated portion. Each thin wire
of the branching portion runs parallel in a direction parallel to
the thin wire of the extended portion of the opposite side over
1000 .mu.m except for 90 .mu.m of the root portion. As a gap (a
separation distance between the branching thin wire of the cathode
electrode and the branching thin wire of the anode electrode)
between both the electrodes of this parallel running portion, in
this embodiment, three distances of 0.5 .mu.um, 1 .mu.m, and 10
.mu.um were produced. In this embodiment, ten branching thin wires
of the cathode electrode and ten branching thin wires of the anode
electrode run parallel over 1000 .mu.m. Since there are 19 parallel
running sites (gaps between the branching thin wires of the cathode
electrode and the anode electrode) between the branching thin
wires, a total parallel running distance is 1000 .mu.m.times.19 =19
mm. Since a structure in which the inter-electrode distance is
significantly decreased to be less than about 20 .mu.m that is a
conventional practical limit can be manufactured easily and stably,
according to the present invention, a very narrow inter-electrode
distance and a long running distance can be realized inside a small
sensor area, and accordingly, the sensitivity per unit area in the
sensor area can be significantly improved.
[0056] FIGS. 7A and 7B illustrate an example of the process
configured by Steps (a) to (l) performed for generating a
dryness/wetness responsive sensor having the structure illustrated
in FIG. 6. FIGS. 7A and 7B correspond to a portion of the sensor in
which thin wires of the cathode electrode and the anode electrode
run parallel. A silicon wafer having a silicon oxide film on the
surface was prepared, the surface thereof is coated with a resist
(Step (a)), and a resist located at a position at which a cathode
electrode is to be disposed was removed through photolithography
(Step (b)). Next, by depositing titanium of 10 nm on the whole, an
adhesive layer used for the cathode electrode was formed at the
position at which the resist was removed (Step (c)). In addition,
gold of 150 nm was deposited on the whole (Step (d)), and, next,
titanium of 10 nm was deposited (Step (e)), whereby a main body of
the cathode electrode formed from gold was formed at this position,
and a stabilization layer formed from titanium was formed thereon.
In this way, since the formation of the cathode electrode was
completed, by lifting off the resist and the remaining metal layer,
only the cathode electrode was caused to remain on a silicon oxide
layer (Step (f)). Next, by performing a series of steps (Steps (g)
to (l): here, a layer to be deposited as a metal of the main body
of the anode electrode in Step (j) is a layer of copper having a
thickness of 150 nm) similar to that of the cathode electrode, an
anode electrode was formed at a position running parallel with the
cathode electrode.
[0057] The whole electrode portion of the dryness/wetness
responsive sensor manufactured in this way is illustrated in FIG.
8A. When FIG. 8A is seen with being positioned in a horizontally
long direction, near an upper left corner and a lower right corner,
electrode pads (signal lead terminal) connecting lead wires toward
the cathode electrode and the anode electrode are seen as square
areas of a color thinner than that of the periphery. Wires
(portions of a color that is slightly thinner than that of the
periphery) horizontally running from the electrode pads are
concentrated portions horizontally running near the upper end and
the lower end in FIG. 6. A black linear shaped portion vertically
running at the center in FIG. 8A represents the branching portions
of the cathode electrode and the anode electrode vertically running
near the center in FIG. 6. A photograph acquired by enlarging a
portion near the center of this branching portion illustrated in
FIG. 8A is illustrated in FIG. 8B. As described above, since three
kinds of dryness/wetness responsive sensors having inter-electrode
distances of 10 .mu.m, 1 .mu.m, and 0.5 .mu.m are produced,
enlarged photographs of branching portions of these three kinds are
illustrated in FIG. 8B. In order to evaluate the basic performance
of the dryness/wetness responsive sensor, in any one of these three
kinds of sensors, 10 thin wires of branching portions of each of
the cathode electrodes and the anode electrodes are prepared. In a
case where an actual dryness/wetness responsive sensor is
configured, in order to effectively use the area of the main
portion of the sensor that can be used, for covering the whole area
of the main body or almost the whole area with the thin wires of
the branching portions, as the inter-electrode distance is
decreased, the number of the thinned lines increases. Accordingly,
by decreasing the inter-electrode distance, it should be noted
that, based on both an effect of an increase in the sensitivity per
unit parallel running distance in accordance with the decrease in
the inter-electrode distance and an effect of an increase in the
parallel running distance per unit area, the sensitivity of this
sensor is remarkably increased.
[0058] By dropping down water to the dryness/wetness responsive
sensor produced in this way and measuring a change in the flowing
current, the sensitivity of the dryness/wetness responsive sensor
according to the present invention was actually measured.
Actually-measured data for the dryness/wetness responsive sensors
having inter-electrode distances of 10 .mu.m, 1 .mu.m, and 0.5
.mu.m are illustrated in FIG. 9B.
[0059] In the measurement, pure water of 1 .mu.L was dropped onto
the concentrated portion of the dryness/wetness responsive sensor
illustrated in FIG. 6, in other words, the comb-shaped electrode
portion, and the sensor was dried, and a time elapse of the current
for a while was measured. As can be understood from a graph
illustrating a temporal change of the output of the dryness/wetness
responsive sensor illustrated in FIG. 9A, when the water film
immediately after the dropping is thick, the dissolved amount of
the metal (here, copper that is the component of the anode
electrode) depends on the amount of water, and accordingly, as the
amount of water is increased, the corrosion speed becomes higher,
and the output of the sensor becomes larger. As time passes, the
water film becomes thin and narrow, the corrosion speed decreases,
and the output of the sensor also decreases. Immediately before the
sensor is dried, the water film becomes very thin, and accordingly,
oxygen can easily arrive at the surface of the gold electrode, and
oppositely, the corrosion speed increases. When the sensor is
dried, in accordance with a decrease in moisture remaining so as to
cause the electrodes to be in contact, resistance between the
electrodes increases, and accordingly, the current decreases.
[0060] When an average value of the current changing in this way
from dropping liquid droplets onto the sensor until immediately
before the sensor is dried is taken, the average value is about 400
pA in a case where the inter-electrode distance is a width of 10
.mu.m and is about 800 pA in the case of the inter-electrode
distance is a width of 1 .mu.m or 0.5 .mu.m, and the improvement of
the output value in accordance with a decrease in the width up to 1
.mu.m could be confirmed. In this embodiment, while gold and copper
are used as the metal materials of the electrodes, it is understood
that the output (current) of the sensor depends on a combination of
the metal materials of the electrodes. For example, comparing
combination of Ag/Fe with that of Au/Ag, the combination of Ag/Fe
has a higher corrosion speed per the same unit area, and
accordingly, the acquired current value is larger. Instead of that,
since Au/Ag has less consumption of electrodes and has a longer
life.
[0061] As described above, in the embodiment illustrated in FIG. 6,
while the number of each of the cathode electrodes and the anode
electrodes is 10, considering to lay electrodes as possibly as can
between a certain length (range), the laying density of the
electrodes can be estimated as below. When the width of the
electrode itself is 1 .mu.m, and the number of pairs of electrodes
is n, in an inter-electrode distance of 10 .mu.m, the laying width
is calculated as 2n30 10.times.(2n-1)=22n-10 .mu.m. Similarly, in
the inter-electrode distances of 1 .mu.m and 0.5 .mu.m, the laying
widths are respectively 4n-1 .mu.m and 3n-0.5 .mu.m. Accordingly,
when the inter-electrode distance of 10 .mu.m is used as the
reference, the ratio of the number of pairs to the same laying
width for 1 .mu.m is (22n-10)/(4n-1)=(22-10/n)/(4-1/n) and, when n
is sufficiently large (for example, 100 or more), a fraction having
the denominator of n can be regarded as zero, and thus, 22/4=5.5.
For 0.5 .mu.m, the value of this ratio is 22/3=7 through similar
calculation. In consideration of the average value of the current
acquired in the embodiment, for the same laying width, when the
inter-electrode distance of 10 .mu.m is changed to 1 .mu.m and 0.5
.mu.m, we can say the output becomes 11 times and 14 times as
large, respectively. Since the S/N ratio of 1:100 or more is
obtained even for the conventional measurement system, we can say
that the experimentally produced sensor of the above embodiment can
also perform the sensing without amplification or noise filtering.
When the width of the electrode itself is configured to be narrower
(thinner), the number of pairs for the same laying width is
increased, allowing the output to be further improved.
[0062] In relation to FIG. 9B, FIG. 10 represents attenuation
curves of current values after recording a maximum current value in
dryness/wetness responsive sensors of the present embodiment with
the inter-electrode distance of 10 .mu.m, 1 .mu.m, and 0.5 .mu.m.
As can be understood from FIG. 10, the time the current reaches the
background current (10.sup.-11 A) becomes longer as the
inter-electrode distance is reduced. This suggests that the current
can be measured until the size of liquid droplets remaining between
the electrodes is reduced to a smaller size, as the inter-electrode
distance is decreased. In other words, it is suggested that the
dryness/wetness responsive sensor according to the present
invention can determine the size of liquid droplets remaining
between the electrodes.
[0063] FIG. 11 is a result of output currents measured under
humidity conditions of 0% RH, 38% RH, and 100% RH by using the
dryness/wetness responsive sensor of the present embodiment having
an inter-electrode distance of 1.0 .mu.m. As can be understood from
FIG. 11, the dryness/wetness responsive sensor according to the
present invention can perform high-precision detection in the
humidity range of 0 to 100% RH. Each humidity condition is set as
below.
0% RH: a state in which the surface of the sensor is dried using a
drier 38% RH: a value acquired by measuring the humidity of the
measurement environment using a commercially available hygrometer
100% RH: a state in which the entire surface of the sensor is
cloudy by blowing out a breath onto the surface of the sensor
[0064] Next, by using a production method similar to the method
described above, three kinds of dryness/wetness responsive sensors
having an inter-electrode distance of 1.0 .mu.m and the number n of
pairs of electrodes of 10, 50, and 200 were produced, and the
sensitivity of each of the sensors was actually measured. The
result is illustrated in FIG. 12.
[0065] In the measurement, a breath is blown out to the surface of
the sensor (the current value increases in accordance therewith),
and, after the current value is returned to the background, an
operation of blowing out a breath is repeated again. As can be
understood from FIG. 12, by increasing the number n of pairs of
electrodes from 10 to 50 and 200, the output of the sensor was
increased respectively to 20 times and 50 times. In this way, in
the dryness/wetness responsive sensor according to the present
invention, by adjusting the number of sets of electrodes in
accordance with the laying condition and the like in addition to
the inter-electrode distance, the output of the sensor can be
improved.
[0066] In the dryness/wetness responsive sensor, when a galvanic
current flows repeatedly, the metal of the anode electrode is
ionized, and accordingly, the anode electrode is gradually
consumed. In addition, in a case where a long-term use under an
environment having high humidity and a large salt damage is
assumed, particularly, in a dryness/wetness responsive sensor
having thin electrodes for increasing the laying density, there is
a possibility that the inter-electrode distance is gradually
increased or the thin wire of the electrode is cut out in
accordance with the consumption of the anode electrode. In order to
address these problems with the laying density of the electrodes
maintained, for example, the thickness of the anode electrode may
be increased, or the width of the anode electrode may be increased
instead of the width of the cathode electrode may be decreased. In
a case where the inter-electrode distance is very short, the
influence of a slight increase in the inter-electrode distance
according to the consumption of the anode electrode on a result of
the measurement increases. In a case where such an influence
matters, for example, by using a principle that the consumption of
the metal of the anode electrode is in proportion to the time
integral of a galvanic current, a countermeasure of performing
compensation calculation for the result of the measurement as the
whole measurement system may be established.
[0067] Though the present embodiment shows an example in which the
inter-electrode distance is constant, the sensor system may combine
a plurality of sensor modules having different inter-electrode
distances according to a desired application or the like.
INDUSTRIAL APPLICABILITY
[0068] As described above, according to the present invention, a
dryness/wetness responsive sensor having a size significantly
smaller than that of a conventional case without decreasing the
sensitivity is provided and thus can be installed to various places
without being conspicuous, and contributions thereof to the
improvement of the accuracy of the evaluation or the prediction of
corrosion and degradation of a structure such as a steel frame
exposed to an corrosive environment are expected. In addition, the
dryness/wetness responsive sensor according to the present
invention can be applied not only to corrosive environment
monitoring but also to various humidity measurements such as a
dryness/wetness monitoring/tracking until physical distribution
from manufacturing/growing industrial products, foods, and the
like, a mold generation status prediction for an indoor bathroom, a
washer, or the like.
CITATION LIST
Non Patent Literature
[0069] Non Patent Literature 1: F. Mansfeld at al., Corrosion
Science, Vol. 16, pp. 111' to 122 (1976)
[0070] Non Patent Literature 2: Peter Norberg, Service Life
Prediction Methodology and Metrologies, ACS Symposium Series 805,
Jonathan W Martin and David R. Bauer, Eds., American Chemical
Society, 2002, pp 23-36
[0071] Non Patent Literature 3: T. Shinohara et al., Journal of
Metals, Materials and Minerals, Vol. 20 No. 2 pp. 23-27, 2010
[0072] Non Patent Literature 4: Shinohara. Tadashi, etc. Materials
and Environments Vol. 54, No. 8 (2005) pp. 375-382
[0073] Non Patent Literature 5: Engajiet al, Toyota Tech. rep., 40
(1987) p. 57
* * * * *