U.S. patent application number 16/718054 was filed with the patent office on 2020-04-23 for gas sensor and sensor device.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Satoru MOMOSE, Ikuo SOGA, Osamu TSUBOI.
Application Number | 20200124563 16/718054 |
Document ID | / |
Family ID | 54833020 |
Filed Date | 2020-04-23 |
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United States Patent
Application |
20200124563 |
Kind Code |
A1 |
MOMOSE; Satoru ; et
al. |
April 23, 2020 |
GAS SENSOR AND SENSOR DEVICE
Abstract
A gas sensor, which includes a solid electrolyte layer including
positive charge carriers to which detection-target gas coordinates,
an electrode arranged on part of a plane of the solid electrolyte
layer, and a unit configured to accelerate movements of the
positive charge carriers.
Inventors: |
MOMOSE; Satoru; (Atsugi,
JP) ; TSUBOI; Osamu; (Kawasaki, JP) ; SOGA;
Ikuo; (Isehara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
54833020 |
Appl. No.: |
16/718054 |
Filed: |
December 17, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15353006 |
Nov 16, 2016 |
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16718054 |
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PCT/JP2014/065203 |
Jun 9, 2014 |
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15353006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 27/4065 20130101;
G01N 27/4073 20130101; G01N 27/4071 20130101 |
International
Class: |
G01N 27/407 20060101
G01N027/407 |
Claims
1-6. (canceled)
7. A gas sensor comprising: a solid electrolyte layer including
positive charge carriers to which detection-target gas is to
coordinate; a first electrode and a second electrode, both of which
are arranged on a plane of the solid electrolyte layer opposite to
the plane of the solid electrolyte layer to be in contact with the
detection-target gas; and a unit configured to accelerate movements
of the positive charge carriers, where the movements of the
positive charge carriers are movements in a plane direction of the
solid electrolyte layer and in a direction from the second
electrode to the first electrode within the solid electrolyte
layer.
8. The gas sensor according to claim 7, wherein the unit configured
to accelerate movements of the positive charge carriers is a
voltage source.
9. The gas sensor according to claim 7, wherein the unit configured
to accelerate movements of the positive charge carriers is arranged
on at least part of a plane of the solid electrolyte layer to be in
contact with the detection-target gas, and the unit is a layer
covering the solid electrolyte layer.
10. The gas sensor according to claim 9, wherein the layer covering
the solid electrolyte layer is a layer that includes a material
capable of coordinating to the positive charge carriers and allows
the detection-target gas to pass therethrough.
11. The gas sensor according to claim 10, wherein the material
capable of coordinating to the positive charge carriers is an
organic material including a carbon-carbon double bond.
12. The gas sensor according to claim 11, wherein the organic
material including a carbon-carbon double bond is polyisoprene
rubber, natural rubber, or polybutadiene rubber.
13. The gas sensor according to claim 7, wherein the positive
charge carriers are copper ions, or silver ions, or both copper
ions and silver ions.
14. The gas sensor according to claim 7, wherein the positive
charge carriers are copper ions.
15. The gas sensor according to claim 7, wherein a material of the
solid electrolyte layer is copper (I) bromide, copper (I) sulfide,
silver sulfide, silver iodide, or silver rubidium iodide.
16. The gas sensor according to claim 7, wherein a material of the
solid electrolyte layer is copper (I) bromide.
17-18. (canceled)
19. A sensor device comprising: the gas sensor according to claim
7; and a unit configured to detect a change in a potential
difference of the gas sensor, where the unit is connected to the
first electrode of the gas sensor.
20. The sensor device according to claim 19, wherein the unit
configured to detect a change in a potential difference of the gas
sensor is a field-effect transistor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of
International Application PCT/JP2014/065203 filed on Jun. 9, 2014
and designated the U.S., the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein relate to a gas sensor, and
a sensor device including the gas sensor.
BACKGROUND
[0003] As gas sensors detecting gas, such as ammonia and nitrogen
oxide, gas sensors that detect gas based on changes in electrical
resistance have been conventionally used. The gas sensors detect
the gas based on changes in electrical resistance of a
semiconductor, such as tin dioxide, due to absorption of the gas on
a surface of the semiconductor.
[0004] In the gas sensors that detect gas based on changes in
electrical resistance, electric current needs to be supplied to the
semiconductor using a constant-current power supply in order to
measure changing electrical resistance. Therefore, the gas sensors
that detect gas based on changes in electrical resistance have a
problem that power consumption of a detection circuit itself
becomes large.
[0005] Moreover, the semiconductor in the gas sensor needs to be
heated to a temperature (for example, 400.degree. C.) at which
excellent detection properties can be obtained. Therefore, the gas
sensor has a problem that a large quantity of power needs to be
used for a heater configured to heat the gas sensor.
[0006] Accordingly proposed are gas sensors, which detect gas based
on changes in potential difference due to adsorption of the gas,
not changes in electrical resistance. As such gas sensors, proposed
are gas sensors using solid electrolytes having ion conductivity,
such as oxygen ion conductivity; oxide ion conductivity, and proton
conductivity (for example, see Japanese Patent Application
Laid-Open (JP-A) Nos. 2002-031619, 2005-221428, 2007-248335, and
2009-198346).
[0007] In the proposed techniques, however, temperatures, at which
the solid electrolytes for use (e.g., zirconia) exhibit excellent
ion conductivity, are high temperature of 300.degree. C. or higher.
In the proposed techniques, moreover, a chemical reaction, such as
an oxidation reaction, of gas to be adsorbed is used for causing a
change in a potential difference in the solid electrolyte, and
therefore the gas sensor needs to be heated to a temperature at
which the chemical reaction is induced.
[0008] Accordingly the proposed techniques have a problem that a
large quantity of power needs to be used for a heater configured to
heat the gas sensor.
[0009] Moreover, proposed as a gas sensor detecting gas at room
temperature is a gas sensor, which is highly sensitive, is capable
of highly selectively detecting NH.sub.3 gas at room temperature,
and uses a CuBr film (for example, see Pascal Lauque, Marc
Bendahan, Jean-Luc Seguin, Kieu An Ngo, Philippe Knauth, Analytica
Chimica Acta, 515, (2004), 279-284). In the proposed technique, gas
is detected based on a change in electrical resistance. Accordingly
it is necessary to supply electric current to the CuBr film using a
constant-current power supply in order to measure changes in
electrical resistance, and there is a problem that power
consumption of a detection circuit itself becomes large.
[0010] Accordingly; there is currently a need for a gas sensor that
does not require a supply of electric current using a
constant-current power supply does not need to be heated, and can
be used with energy-saving efficiency and a sensor device including
such a gas sensor.
SUMMARY
[0011] According to the first aspect of the disclosed gas sensor,
the disclosed gas sensor includes: [0012] a solid electrolyte layer
including positive charge carriers to which detection-target gas is
to coordinate; [0013] a first electrode arranged on part of one
plane of the solid electrolyte layer; and [0014] a second electrode
arranged on an area of the other plane of the solid electrode
layer, the area excluding an area of the other plane that faces the
first electrode and is to be in contact with the detection-target
gas.
[0015] According to the second aspect of the disclosed gas sensor,
the disclosed gas sensor includes: [0016] a solid electrolyte layer
including positive charge carriers to which detection-target gas is
to coordinate; [0017] a first electrode and a second electrode,
both of which are arranged on a plane of the solid electrolyte
layer opposite to the plane of the solid electrolyte layer to be in
contact with the detection-target gas; and [0018] a unit configured
to accelerate movements of the positive charge carriers, where the
movements of the positive charge carriers are movements in a plane
direction of the solid electrolyte layer and in a direction from
the second electrode to the first electrode within the solid
electrolyte layer.
[0019] The disclosed sensor device includes: [0020] the disclosed
gas sensor; and [0021] a unit configured to detect a change in a
potential difference of the gas sensor, where the unit is connected
to the first electrode of the gas sensor.
[0022] The disclosed gas sensor can solve the above-described
various problems existing in the art, and can provide a gas sensor,
which does not need a supply of electric current using a
constant-current power supply does not need to be heated, and can
be used with energy-saving efficiency.
[0023] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0024] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1A is a schematic cross-sectional view illustrating one
example of the first embodiment of the disclosed gas sensor;
[0026] FIG. 1B is a schematic view illustrating one plane of one
example of the first embodiment of the disclosed gas sensor;
[0027] FIG. 1C is a schematic view illustrating the other plane of
one example of the first embodiment of the disclosed gas
sensor;
[0028] FIG. 2 is a schematic cross-sectional view illustrating
another example of the first embodiment of the disclosed gas
sensor;
[0029] FIG. 3 is a schematic cross-sectional view illustrating one
example of the second embodiment of the disclosed gas sensor;
[0030] FIG. 4A is a schematic cross-sectional view illustrating
another example of the second embodiment of the disclosed gas
sensor;
[0031] FIG. 4B is a schematic view illustrating one plane of
another example of the second embodiment of the disclosed gas
sensor;
[0032] FIG. 4C is a schematic view illustrating the other plane of
another example of the second embodiment of the disclosed gas
sensor;
[0033] FIG. 5 is a schematic cross-sectional view illustrating one
example of the disclosed sensor device;
[0034] FIG. 6A is a schematic cross-sectional view of the gas
sensor of Example 1;
[0035] FIG. 6E is a schematic view of one plane of the gas sensor
of Example 1;
[0036] FIG. 6C is a schematic view of the other plane of the gas
sensor of Example 1;
[0037] FIG. 7 is a graph presenting the result of the measurement
of the potential difference of the gas sensor of Example 1;
[0038] FIG. 8A is a schematic cross-sectional view of the gas
sensor of Example 2;
[0039] FIG. 8B is a schematic view of one plane of the gas sensor
of Example 2;
[0040] FIG. 8C is a schematic view of the other plane of the gas
sensor of Example 2;
[0041] FIG. 9 is a graph presenting the result of the measurement
of the potential difference of the gas sensor of Example 2;
[0042] FIG. 10 is a schematic cross-sectional view of the gas
sensor of Example 3;
[0043] FIG. 11 is a graph presenting the result of the measurement
of the potential difference of the gas sensor of Example 3;
[0044] FIG. 12A is a schematic cross-sectional view of the gas
sensor of Example 4;
[0045] FIG. 12B is a schematic view of one plane of the gas sensor
of Example 4;
[0046] FIG. 12C is a schematic view of the other plane of the gas
sensor of Example 4;
[0047] FIG. 13 is a graph presenting the result of the measurement
of the potential difference of the gas sensor of Example 4;
[0048] FIG. 14A is a schematic cross-sectional view of the gas
sensor of Comparative Example 1;
[0049] FIG. 14B is a schematic view of one plane of the gas sensor
of Comparative Example 1;
[0050] FIG. 14C is a schematic view of the other plane of the gas
sensor of Comparative Example 1; and
[0051] FIG. 15 is a graph presenting the result of the measurement
of the potential difference of the gas sensor of Comparative
Example 1.
DESCRIPTION OF EMBODIMENTS
(Gas Sensor)
First Embodiment
[0052] The first embodiment of the disclosed gas sensor includes at
least a solid electrolyte layer, a first electrode, and a second
electrode, and may further include other members according to the
necessity.
<<Solid Electrolyte Layer>>
[0053] The solid electrolyte layer is not particularly limited, and
may be appropriately selected depending on the intended purpose, as
long as the solid electrolyte layer includes positive charge
carriers to which detection-target gas coordinates.
[0054] The positive charge carriers are preferably movable at
normal temperature.
[0055] In the present specification, the term "normal temperature"
means a temperature of a state where the gas sensor is not heated,
and is for example 25.degree. C.
[0056] The term "movable" means that the positive charge carriers
can move to a degree that a change in a potential difference of the
gas sensor can be confirmed.
[0057] The detection-target gas is not particularly limited, and
may be appropriately selected depending on the intended purpose, as
long as the detection-target gas is gas capable of coordinating to
the positive charge carriers. Examples of the gas capable of
coordinating to the positive charge carrier include
nitrogen-including compounds, oxygen-containing compounds, and
sulfur-containing compounds. Examples of the nitrogen-including
compounds include ammonia, amine, and nitric oxide. Examples of the
sulfur-containing compound include hydrogen sulfide and sulfur
dioxide.
[0058] The positive charge carriers are not particularly limited,
and may be appropriately selected depending on the intended
purpose, as long as the positive charge carriers are carriers to
which the detection-target gas coordinates. In view of excellent
carrier mobility the positive charge carriers are preferably copper
ions, or silver ions, or both copper ions and silver ions.
[0059] A material of the solid electrolyte layer is not
particularly limited, and may be appropriately selected depending
on the intended purpose. Examples of the material include copper
(I) bromide (CuBr), copper (I) sulfide (Cu.sub.2S), silver sulfide
(Ag.sub.2S), silver iodide (AgI), and silver rubidium iodide
(RbAg.sub.4I.sub.5). Since the above-listed solid electrolytes have
sufficient mobility of the positive charge carriers even at normal
temperature (for example, 25.degree. C.), the above-listed solid
electrolytes can be used for the solid electrolyte layer. Among the
above-listed solid electrolytes, copper (I) bromide is preferable
because of excellent mobility of positive charge carriers at normal
temperature.
[0060] A shape, size, and structure of the solid electrolyte layer
are not particularly limited, and may be appropriately selected
depending on the intended purpose.
[0061] A formation method of the solid electrolyte layer is not
particularly limited, and may be appropriately selected depending
on the intended purpose. Examples of the formation method include
sputtering. In the case where a material of the solid electrolyte
layer is copper (I) bromide, examples of the formation method
include a method in which copper is immersed in a copper (II)
bromide aqueous solution to turn the copper into copper (I)
bromide.
<<First Electrode>>
[0062] The first electrode is not particularly limited, and may be
appropriately selected depending on the intended purpose, as long
as the first electrode is an electrode arranged on part of one
plane of the solid electrolyte layer.
[0063] Examples of a material of the first electrode include metals
more noble than a metal element of the positive charge
carriers.
[0064] Moreover, the material of the first electrode is preferably
the same metal to the metal element of the positive charge carrier
because potential of the solid electrolyte layer becomes stable. In
the case where the first electrode has a laminate structure, a
material of an electrode to be in contact with the solid
electrolyte layer is preferably the same metal to the metal element
of the positive charge carrier.
[0065] A shape, size, and structure of the first electrode are not
particularly limited, and may be appropriately selected depending
on the intended purpose.
[0066] The average thickness of the first electrode is not
particularly limited, so and may be appropriately selected
depending on the intended purpose. The average thickness of the
first electrode is preferably equal to or less than the average
thickness of the solid electrolyte layer.
[0067] A formation method of the first electrode is not
particularly limited, and may be appropriately selected depending
on the intended purpose. Examples of the formation method include
vacuum deposition.
<<Second Electrode>>
[0068] The second electrode is not particularly limited, and may be
appropriately selected depending on the intended purpose, as long
as the second electrode is an electrode arranged on the other plane
of the solid electrode, excluding an area of the other plane that
faces the first electrode and to be in contact with the
detection-target gas.
[0069] Examples of a material of the second electrode include
metals more noble than a metal element of the positive charge
carriers.
[0070] Moreover, the material of the second electrode is preferably
the same metal to the metal element of the positive charge carrier
because potential of the solid electrolyte layer becomes stable. In
the case where the second electrode has a laminate structure, a
material of an electrode to be in contact with the solid
electrolyte layer is preferably the same metal to the metal element
of the positive charge carrier.
[0071] A shape, size, and structure of the second electrode are not
particularly limited, and may be appropriately selected depending
on the intended purpose.
[0072] A formation method of the second electrode is not
particularly limited, and may be appropriately selected depending
on the intended purpose. Examples of the formation method include
vacuum deposition.
<<Other Units>>
[0073] The above-mentioned other units are not particularly
limited, and may be appropriately selected depending on the
intended purpose. Examples of the units include a unit configured
to accelerate movements of the positive charge carriers.
--Unit Configured to Accelerate Movements of Positive Charge
Carriers--
[0074] Examples of the unit configured to accelerate movements of
the positive charge carriers include a layer, which is arranged on
an area of the other plane of the solid electrolyte layer, where
the area faces the first electrode and is to be in contact with the
detection-target gas, includes a material capable of coordinating
to the positive charge carriers, and allows the detection-target
gas to pass therethrough. Since the gas sensor includes the unit
configured to accelerate movements of the positive charge carriers,
movements of the positive charge carriers in the solid electrolyte
layer are accelerated to increase a change in a potential
difference.
[0075] The layer that includes a material capable of coordinating
to the positive charge carriers and allows the detection-target gas
to pass through. Therefore, the layer does not interfere
coordinates of the detection-target gas to the positive charge
carriers of the solid electrolyte layer.
[0076] Examples of the material capable of coordinating to the
positive charge carrier include an organic material including a
carbon-carbon double bond. Examples of the organic material
including a carbon-carbon double bond include natural rubber
(polyisoprene), synthetic rubber, such as polyisoprene and
polybutadiene, unsaturated fatty acid, unsaturated fatty acid
ester, and unsaturated fatty acid amide. Examples of the
unsaturated fatty acid include oleic acid and linoleic acid.
[0077] Note that, the carbon-carbon double bond has an ability for
supplying electrons to atoms and ions of a transition metal to form
a coordinate bond. Accordingly, the solid electrolyte layer can be
doped with electrons when the organic material coordinates to the
positive charge carriers. As a result, bias voltage can be
introduced to the solid electrolyte layer to accelerate movements
of the positive charge carriers.
[0078] The first embodiment of the gas sensor is described with
reference to drawings here. A gas sensor, in which a material of a
solid electrolyte layer is copper (I) bromide and detection-target
gas is ammonia, is described.
[0079] The gas sensor illustrated in FIGS. 1A to 1C includes a
solid electrolyte layer 1 formed of copper (I) bromide, a first
electrode 2 that is a gold electrode, and a second electrode 3 that
is a copper electrode. The first electrode 2 is arranged on part of
one plane of the solid electrolyte layer 1. The second electrode 3
is arranged on the other plane of the solid electrolyte layer 1
excluding the gas-contacting area 4 that faces the first electrode
2 and is to be in contact with the detection-target gas.
[0080] Ammonia is adsorbed onto the gas-contacting area 4 that is a
surface of the solid electrolyte layer 1. The ammonia then
coordinates to copper ions positioned in the gas-contacting area 4.
Since the copper ions, to which the ammonia has coordinated, are
fixed in the gas-contacting area 4 of the solid electrolyte layer
1, the copper ions do not function as positive charge carriers. As
a result, a concentration of the positive charge carriers in a
region of the solid electrolyte layer 1 (the region .alpha. in FIG.
1A) between the gas-contacting area 4 and the electrode 2 facing
the gas-contacting area 4 reduces.
[0081] On the other hand, a region .beta. having a surface covered
with the second electrode 3 does not cause a reduction at the
concentration of the positive charge carriers due to the contact
with the gas.
[0082] Accordingly; a state where a concentration of the positive
charge carriers in the region .alpha. and a concentration of the
positive charge carrier in the region .beta. within the solid
electrolyte layer 1 are different is caused. The positive charge
carriers voluntarily move from the region .beta. to the region
.alpha. to level the concentration within the solid electrolyte
layer 1. As a result, the potential difference changes within the
solid electrolyte layer 1.
[0083] The number of copper ions to be fixed on the gas-contacting
area 4 per surface area is determined with adsorption equilibrium
of ammonia in the gas-contacting area 4. In the case where the
ammonia is contained at low concentration, therefore, the number of
the copper ions to be fixed on the gas-contacting area 4 per
surface area is proportional to the concentration of the ammonia in
the atmosphere. The number of the copper ions to move from the
region .beta. to the region .alpha. to the level of the
concentration of the positive charge carriers and the potential
difference generated by the movement of the copper ions are
proportional to the concentration of the ammonia. Accordingly the
concentration of the detection-target gas can be measured by
measuring the potential difference between the first electrode 2
and the second electrode 3.
[0084] Next, another example of the first embodiment of the gas
sensor is described.
[0085] FIG. 2 is a schematic cross-sectional view illustrating
another example of the first embodiment of the gas sensor.
[0086] In the gas sensor of FIG. 2, a natural rubber layer 5
serving as the unit configured to accelerate movements of the
positive charge carriers is arranged on the gas-contacting area of
the solid electrolyte layer 1. The structure other than the above
is identical to the gas sensor of FIGS. 1A to 1C. A thickness of
the natural rubber layer 5 is thin and the natural rubber layer 5
can pass through the detection-target gas.
[0087] In the gas sensor of FIG. 2, bias voltage can be introduced
to the solid electrolyte layer 1, as the carbon-carbon double bond
included in the natural rubber layer 5 supplies electrons to the
solid electrolyte layer 1 for doping. As a result, movements of the
positive charge carriers are accelerated.
Second Embodiment
[0088] The second embodiment of the disclosed gas sensor includes
at least a solid electrolyte layer, a first electrode, a second
electrode, and a unit configured to accelerate movements of
positive charge carriers, and may further include other units
according to the necessity.
<<Solid Electrolyte Layer>>
[0089] The solid electrolyte layer is not particularly limited, and
may be appropriately selected depending on the intended purpose, as
long as the solid electrolyte layer is a solid electrolyte layer
including positive charge carriers to which detection-target gas
coordinates. Examples of the solid electrolyte layer include the
solid electrolyte layer listed in the first embodiment of the gas
sensor. A preferable embodiment of the solid electrolyte layer is
also identical to the preferable embodiment of the solid
electrolyte layer listed in the first embodiment of the gas
sensor.
[0090] The detection-target gas is not particularly limited, and
may be appropriately selected depending on the intended purpose, as
long as the detection-target gas is a gas capable of coordinating
to the positive charge carriers. Examples of the detection-target
gas include nitrogen-including compounds, oxygen-containing
compounds, and sulfur-containing compounds. Examples of the
nitrogen-including compounds include ammonia, amine, and nitric
oxide. Examples of the sulfur-containing compounds include hydrogen
sulfide and sulfur dioxide.
<<First Electrode and Second Electrode>>
[0091] The first electrode and the second electrode are not
particularly limited, and may be appropriately selected depending
on the intended purpose, as long as the first electrode and the
second electrode are electrodes arranged on a plane of the solid
electrolyte layer opposite to a plane of the electrolyte layer to
be in contact with the detection-target gas. Examples of the first
electrode and the second electrode include the first electrode and
the second electrode listed in the gas sensor of the so first
embodiment. Preferable embodiments of the first electrode and the
second electrode are also respectively identical to the preferable
embodiments of the first electrode and the second electrode listed
in the first embodiment of the gas sensor.
<<Unit Configured to Accelerate Movements of Positive Charge
Carriers>>
[0092] The unit configured to accelerate movements of the positive
charge carriers is not particularly limited, and may be
appropriately selected depending on the intended purpose, as long
as the unit is a unit configured to accelerate movements of the
positive charge carriers in a plane direction of the solid
electrolyte layer and in a direction from the second electrode to
the first electrode within the solid electrolyte layer. The unit is
preferably a voltage source in view of a simple device structure,
and preferably the layer covering the solid electrolyte layer that
is arranged on at least part of a plane of the solid electrolyte
layer to be in contact with the detection-target gas in view of
energy saving.
--Voltage Source--
[0093] The voltage source is not particularly limited, and may be
appropriately selected depending on the intended purpose, as long
as the voltage source is a power source capable of applying bias
voltage, as long as the voltage source is a power source capable of
applying bias voltage in a plane direction of the solid electrolyte
layer and in a direction from the second electrode to the first
electrode within the solid electrolyte layer.
[0094] Since bias voltage is applied in the above-described
directions of the solid electrolyte layer using the voltage source,
movements of the positive charge carriers are accelerated when the
detection-target gas is brought into contact with the plane of the
solid electrolyte layer to be in contact with the detection-target
gas, and the potential difference between the first electrode and
the second electrode changes.
Layer Covering Solid Electrolyte Layer--
[0095] The layer covering the solid electrolyte layer is not
particularly limited, and may be appropriately selected depending
on the intended purpose, as long as the layer covering the solid
electrolyte layer is arranged on at least part of a plane of the
solid electrolyte layer to be in contact with the detection-target
gas, and is the above-described layer covering the solid
electrolyte layer. The layer is preferably a layer, which includes
a material capable of coordinating to the positive charge carriers
and allows the detection-target gas to pass therethrough, because
movements of the positive charge carriers within the solid
electrolyte layer are accelerated even more.
[0096] Since the layer that includes a material capable of
coordinating to the positive charge carriers and allows the
detection-target gas to pass therethrough, the layer does not
inhibit coordination of the detection-target gas to the positive
charge carriers of the solid electrolyte layer.
[0097] Examples of the material capable of coordinating to the
positive charge carrier include an organic material including a
carbon-carbon double bond. Examples of the organic material
including a carbon-carbon double bond include natural rubber
(polyisoprene), synthetic polyisoprene, polybutadiene, unsaturated
fatty acid, unsaturated fatty acid ester, and unsaturated fatty
acid amide. Examples of the unsaturated fatty acid include oleic
acid and linoleic acid.
[0098] Note that, the carbon-carbon double bond has an ability for
supplying electrons to atoms and ions of a transition metal to form
a coordinate bond. Accordingly, the solid electrolyte layer can be
doped with electrons when the organic material coordinates to the
positive charge carriers. As a result, bias voltage can be
introduced to the solid electrolyte layer to accelerate movements
of the positive charge carriers.
[0099] The thickness or density of the layer covering the solid
electrolyte is preferably changed along the direction from one
electrode to the other electrode on a plane of the solid
electrolyte layer to be in contact with the detection-target gas.
The change of the thickness of the density may be a step-by-step
change or a gradual change. In the case where the first electrode
is used as a sensing electrode and the second electrode is used as
a reference electrode in the gas sensor, the thickness or density
of the layer covering the solid electrolyte layer is preferably
thicker or denser in the part facing the second electrode than the
part facing the first electrode. Movements of the positive charge
carriers are accelerated by the above-described thickness or
density of the layer.
[0100] The second embodiment of the gas sensor is described with
reference to drawings here. A gas sensor where a material of a
solid electrolyte layer is copper w bromide and detection-target
gas is ammonia is described.
[0101] FIG. 3 is a schematic cross-sectional view illustrating one
example of the second embodiment of the gas sensor. The unit
configured to accelerate movements of the positive charge carriers
in the gas sensor illustrated in FIG. 3 is a voltage source.
[0102] The gas sensor illustrated in FIG. 3 includes a solid
electrolyte layer 11 formed of copper (I) bromide, a first
electrode 12, a second electrode 13, and a voltage source 14. The
first electrode 12 and second electrode 13 are arranged on part of
a plane of the solid electrolyte layer 11 opposite to a plane of
the solid electrolyte layer 11 to be in contact with the
detection-target gas, and with a gap between the first electrode 12
and the second electrode 13. The voltage source 14 has a structure
where a copper electrode 15, a solid electrolyte layer 16, and a
silver electrode 17 are laminated in this order.
[0103] Ammonia is adsorbed on a surface of the solid electrolyte
layer 11 The ammonia then coordinates to copper ions positioned on
the surface of the solid electrolyte layer 11. The copper ions, to
which the ammonia coordinates, are fixed on the surface of the
solid electrolyte layer 11, and therefore the copper ions do not
function as positive charge carriers. As a result, a concentration
of the positive charge carriers decreases inside the solid
electrolyte layer 11. If bias voltage is applied from a voltage
source 14 to the solid electrolyte layer 11 via the second
electrode 13 to be in contact with the solid electrolyte layer 11
at this moment, copper ions are easily moved from the area adjacent
to the second electrode 13 having a positive potential to the area
adjacent to the first electrode 12 having the lower potential. As a
result of the movements of the copper ions, the potential
difference between both electrodes changes.
[0104] The change in the potential difference depends on the
applied bias voltage and a density of positive charge carriers
inside the solid electrolyte layer (specifically, an amount of
copper ions, per surface area, fixed on the surface of the solid
electrolyte layer by ammonia). Therefore, a potential difference
corresponding to the concentration of ammonia in the atmosphere is
generated, when bias voltage is constant. Accordingly, a
concentration of the detection-target gas can be measured by
measuring a potential difference between the electrode in contact
with the solid electrolyte layer and connected to the voltage
source and the other electrode, or a potential difference in a path
from the other electrode to the voltage source.
[0105] Next, another example of the second embodiment of the gas
sensor is described.
[0106] FIGS. 4A to 4C are schematic views illustrated another
example of the second embodiment of the gas sensor.
[0107] The gas sensor of FIGS. 4A to 4C include a solid electrolyte
layer 21 formed of copper (I) bromide, a first electrode 22, a
second electrode 23, and a layer 24 covering the solid electrolyte
layer. The first electrode 22 and the second electrode 23 are
arranged on part of the plane of the solid electrolyte layer 11
opposite to the plane of the solid electrolyte layer 11 to be in
contact with the detection-target gas. The layer 24 covering the
solid electrolyte layer is formed of natural rubber, and an amount
of the natural rubber per surface area of the solid electrolyte
layer 21 is larger in the area facing the second electrode 23 than
the area facing the first electrode 22. The change in the amount is
gradual. Note that, in FIGS. 4A and 4C, the change in the amount of
the natural rubber is presented with tone of the color for visual
clearness. The darker color represents the larger amount of natural
rubber.
[0108] In the gas sensor of FIGS. 4A to 4C, the amount f the
natural rubber per surface area of the solid electrolyte layer 21
is larger in the area of the layer 24 covering the solid
electrolyte layer facing the second electrode 23 than the area
facing the first electrode 22, and therefore a doping amount of
electrons is larger at the solid electrolyte layer 21 at the side
of the second electrode 23 than at the side of the first electrode
22. The potential of the first electrode 22 is higher than the
potential of the second electrode 23 due to a difference in the
doping amount of electrons. When the detection-target gas is
brought into contact with the solid electrolyte layer 21, moreover,
the larger amount of the detection-target gas is fixed on the
region adjacent to 22, in which the amount of the natural rubber
per area covering the solid electrolyte layer 21 is smaller than
the second electrode 23. In the solid electrolyte layer 21, the
positive charge carriers are lacked more at the first electrode 22
side of a region being away from the layer 24 covering the solid
electrolyte layer than the second electrode 23 side of the region.
In the solid electrolyte layer 21, the positive charge carriers are
diffused from the side of the second electrode 23 to the side of
the first electrode 22 in order to return to a state where the
carrier concentration is leveled. As a result, the potential at the
side of the first electrode 22 becomes higher than the potential at
the side of the second electrode 23.
[0109] In FIGS. 4A to 4C, the embodiment where the amount of the
natural rubber in the layer 24 covering the solid electrolyte layer
per surface area of the solid electrolyte layer 21 is gradually
changed is illustrated, but the embodiment of the layer 24 covering
the solid electrolyte layer is not limited to the above-mentioned
embodiment. The amount may be changed step by step. Moreover, the
layer 24 covering the solid electrolyte layer may be formed on only
part of the surface of the solid electrolyte layer to be in contact
with the detection-target gas, as long as movements of the positive
charge carriers are accelerated.
[0110] The disclosed gas sensor can solve the above-described
various problems existing in the art, and can provide a gas sensor,
which does not need a supply of electric current using a
constant-current power supply, does not need to be heated, and can
be used with energy-saving efficiency.
(Sensor Device)
[0111] The disclosed sensor device includes at least the disclosed
gas sensor and a unit configured to detect a change in a potential
difference of the gas sensor, and may further include other units
according to the necessity.
<Unit Configured to Detect Change in Potential Difference of Gas
Sensor>
[0112] The unit configured to detect a change in a potential
difference of the gas sensor is not particularly limited, and may
be appropriately selected depending on the intended purpose. The
unit is preferably a field-effect transistor because the sensor
device can be down sized, and the change in the potential
difference can be amplified.
[0113] The unit configured to detect a change in a potential
difference of the gas sensor is connected to the first electrode of
the gas sensor.
<<Field-Effect Transistor>>
[0114] The field-effect transistor is not particularly limited, and
may be appropriately selected depending on the intended purpose.
Examples of the field-effect transistor include a field-effect
transistor including a gate electrode configured to apply gate
voltage, a source electrode and a drain electrode configured to
take electric current out, an active layer arranged between the
source electrode and the drain electrode, and a gate insulating
layer arranged between the gate electrode and the active layer.
Examples of a material of the active layer include silicon, and
metal oxide semiconductors.
[0115] The first electrode of the gas sensor is connected to the
gate electrode.
[0116] One example of the disclosed sensor device is described with
reference to a drawing.
[0117] FIG. 5 is a schematic cross-sectional view illustrating one
example of the sensor device.
[0118] The sensor device illustrated in FIG. 5 includes a gas
sensor and a field-effect transistor. The gas sensor includes a
solid electrolyte layer 1, a first electrode 2, and a second
electrode 3. The first electrode 2 is arranged on part of one plane
of the solid electrolyte layer 1. The second electrode 3 is
arranged on an area of the other plane of the solid electrode layer
1, where the area excludes the gas-contacting area 4 of the other
plane that faces the first electrode 2 and is to be in contact with
the detection-target gas. The field-effect transistor includes a
silicon substrate 51 also functioning as an active layer, a source
electrode 52, a drain electrode 53, a gate insulating layer 54, and
a gate electrode 55. The gate electrode 52 and the drain electrode
53 are arranged to sandwich the active layer. The gate insulating
layer 54 is arranged between the active layer and the gate
electrode 55. The first electrode 2 of the gas sensor and the gate
electrode 55 of the field-effect transistor are connected together
via the first line 56 and the second line 57. Then, the insulating
layer 58 is formed to cover the gate insulating layer 54, the gate
electrode 55, the first line 56, and the second line 57, and the
gas sensor is arranged on the insulating layer 58.
[0119] The disclosed sensor device can solve the above-described
various problems existing in the art, and can provide a sensor
device, which does not need to be heated, and can be used with
energy-saving efficiency.
EXAMPLES
[0120] Examples of the present invention are explained below, but
the present invention is not limited to the examples below in any
way.
Example 1
[0121] A gas sensor as illustrated in FIGS. 6A to 6C was produced.
Specifically the gas sensor was produced by the following
method.
<Formation of First Electrode>
[0122] A gold electrode (first electrode 2) having the width of 10
mm, the length of 25 mm, and the average thickness of 30 nm was
formed by vacuum deposition on a silicon wafer with a thermally
oxidized film having the average thickness of 1 .mu.m, where the
silicon wafer had the width of 12 mm, the length of 50 mm, and the
thickness of 0.6 mm.
<Formation of Solid Electrolyte Layer>
[0123] A copper layer having the width of 8 mm, the length of 30
mm, and the average thickness of 0.5 .mu.m was formed by vacuum
deposition to cover part of the first electrode 2. Subsequently,
copper of the copper layer was turned into copper (I) bromide using
a copper (II) bromide aqueous solution using the same method as the
method described in "2. Experimental" of the literature (Pascal
Lauque, Marc Bendahan, Jean-Luc Seguin, Kieu An Ngo, Philippe
Knauth, Analytica Chimica Acta, 515, (2004), 279-284), to thereby
obtain a solid electrolyte layer 1. The average thickness of the
obtained solid electrolyte layer was 0.5 .mu.m.
<Formation of Second Electrode>
[0124] Moreover, a copper layer having the width of 10 mm, the
length of 25 mm, and the average thickness of 60 nm was formed by
vacuum deposition in a manner that a gap G between the copper layer
and the first electrode 2 was to be 1 mm, as illustrated in FIG.
6A. A gold layer having the average thickness of 30 nm was formed
on the copper layer by vacuum deposition to thereby obtain a
laminate structure of the copper layer and the gold layer (second
electrode 3). In the manner as described, a gas sensor was
obtained.
[0125] The gap G means a gap between the edge of the projected
first electrode 2 and the edge of the second electrode 3 facing
each other, when the first electrode 2 is projected to the other
plane of the solid electrolyte layer 1 facing one plane of the
solid electrolyte layer 1 to which the first electrode 2 is
arranged.
<Evaluation on Change in Potential Difference>
[0126] 196 system DMM available from Keithley was connected to the
produced gas sensor in a manner that the first electrode 2 was to
be a sensing electrode and the second electrode 3 was to be a
reference electrode, and a potential difference between the both
electrodes was measured. A reaction of the gas sensor to ammonia
was evaluated by placing the gas sensor in a flow path of nitrogen
gas, and switching a gas source between nitrogen gas of high purity
and nitrogen gas including ammonia at the concentration of 1 ppm.
The evaluation of the reaction of the gas sensor was performed at
normal temperature without heating the gas sensor.
[0127] Note that, the nitrogen gas of high purity was used at a
flow rate of 4.0 L/min. The nitrogen gas including ammonia at the
concentration of 1 ppm was generated using a permeator (product
name: PD-1B, available from GASTEC CORPORATION), and was used by
generating under the conditions that a temperature was 30.degree.
C., and a flow rate was 2.8 L/min.
[0128] A relationship between the measured potential difference and
the lapse of time is presented in FIG. 7. Even in the state where
the nitrogen gas of high purity was to be in contact with the solid
electrolyte layer 1, the potential of the reference electrode was
higher than the potential of the sensing electrode by about 56 mV
due to equilibrium of the oxidation-reduction reaction of copper
occurred at the interface between the copper (I) bromide and the
surface of the copper electrode. When the air flow was changed from
the nitrogen gas of high purity to the nitrogen gas including
ammonia at the concentration of 1 ppm, the potential of the sensing
electrode became high, and as a result, the measured potential
difference became small by about 6 mV Accordingly, it could be
confirmed that the gas sensor of Example 1 was a gas sensor of high
sensitivity and a potential difference measuring system.
Example 2
[0129] A gas sensor as illustrated in FIGS. 8A to 8C was produced.
Specifically the gas sensor was produced by the following
method.
<Formation of First Electrode>
[0130] A gold electrode (first electrode 2) having the width of 10
mm, the length of 20 mm, and the average thickness of 60 nm was
formed by vacuum deposition on a silicon wafer with a thermally
oxidized film having the average thickness of 1 .mu.m, where the
silicon wafer had the width of 12 mm, the length of 50 mm, and the
thickness of 0.6 mm.
<Formation of Solid Electrolyte Layer>
[0131] Copper (I) bromide (solid electrolyte layer 1) having the
width of 8 mm the length of 30 mm, and the average thickness of 200
nm was formed by RF magnetron sputtering to cover part of the first
electrode 2.
[0132] The conditions for the RF magnetron sputtering were as
follows. [0133] RF power: 100 W [0134] Sputtering gas: Ar [0135]
Sputtering gas flow rate: 30 sccm [0136] Gas pressure: 0.5 Pa
<Formation of Second Electrode>
[0137] Moreover, a gold electrode (second electrode 3) having the
width of 10 mm, the length of 20 mm, and the average thickness of
60 nm was formed by vacuum deposition in a manner that the gap G
between the gold electrode and the first electrode 2 was to be 1
mm, as illustrated in FIG. 8A to thereby obtain a gas sensor.
[0138] The gap G means a gap between the edge of the projected
first electrode 2 and the edge of the second electrode 3 facing
each other, when the first electrode 2 is projected to the other
plane of the solid electrolyte layer 1 facing one plane of the
solid electrolyte layer 1 to which the first electrode 2 is
arranged.
<Covering with Natural Rubber>
[0139] The obtained gas sensor was dipped in a natural rubber
hexane solution (a concentration of the natural rubber was 0.01% by
volume) for 1 minute, and surfaces of the gas sensor was washed
with hexane. Thereafter, the gas sensor was dried through a baking
process performed in nitrogen at 100.degree. C. for 30 minutes to
fix the natural rubber layer 5 to an area of the solid electrolyte
layer 1 to be in contact with detection-target gas.
<Evaluation on Change in Potential Difference>
[0140] An evaluation of a change in potential difference was
performed in the same manner as in Example 1 by using the first
electrode 2 as a sensing electrode and the second electrode 3 as a
reference electrode, and using nitrogen gas including ammonia at
the concentration of 1 ppm. The result is presented in FIG. 9.
[0141] In the nitrogen gas of high purity, the potential at the
side of the sensing electrode was high by about 1 mV due to the
movements of the copper ions owing to the doping of electrons from
the natural rubber. This is an equivalent to bias voltage. When the
air flow was changed from the nitrogen gas of high purity to the
nitrogen gas including ammonia at the concentration of 1 ppm, the
potential of the sensing electrode became high by about 2 mV.
[0142] As described above, it was confirmed that the organic
material including a carbon-carbon double bond could be used as the
unit configured to accelerate movements of the positive charge
carriers of the solid electrolyte layer
[0143] Moreover, it was confirmed that the gas sensor of Example 2
was a gas sensor of high sensitivity and a potential difference
measuring system.
Example 3
[0144] A gas sensor as illustrated in FIG. 10 was produced.
Specifically, the gas sensor was produced by the following
method.
<Formation of First Electrode and Second Electrode>
[0145] Two gold electrodes (first electrode 12 and second electrode
13) each having the width of 10 mm, the length of 25 mm, and the
average thickness of 30 nm were formed by vacuum deposition on a
silicon wafer with a thermally oxidized film having the average
thickness of 1 .mu.m, where the silicon wafer had the width of 12
mm, the length of 55 mm, and the thickness of 0.6 mm. The two gold
electrodes were arranged with the gap of 1 mm between the edges of
the two gold electrodes facing each other.
<Formation of Solid Electrolyte Layer>
[0146] A copper layer having the width of 8 mm, the length of 30
mm, and the average thickness of 0.5 .mu.m was formed by vacuum
deposition on each of the two gold electrodes. Subsequently, copper
of the copper layers was turned into copper (I) bromide using a
copper (II) bromide aqueous solution using the same method as the
method described in "2. Experimental" of the literature (Pascal
Lauque, Marc Bendahan, Jean-Luc Seguin, Kieu An Ngo, Philippe
Knauth, Analytica Chimica Acta, 515, (2004), 279-284), to produce a
solid electrolyte layer 11 to thereby obtain a detector.
<Production of Bias Voltage Source>
[0147] On a silicon wafer with a thermally oxidized film, a copper
electrode 15 having the width of 8 mm, the length of 20 mm, and the
average thickness of 30 nm, a copper (I) bromide layer (solid
electrolyte layer 16) having the width of 8 mm, the length of 15
mm, and the average thickness of 0.5 .mu.m, and a silver electrode
17 having the width of 8 mm, the length of 15 mm, and the average
thickness of 30 nm were formed in this order in the same methods in
<Formation of first electrode and second electrode> and
<Formation of solid electrolyte layer> above. The obtained
laminate structure was used as a bias voltage source (voltage
source 14).
[0148] The silver electrode 17 of the voltage source 14 and one of
the gold electrodes (second electrode 13) of the detector were
connected together to thereby obtain a gas sensor.
[0149] A reaction to ammonia was evaluated by using a structure
where the copper electrode 15 of the voltage source 14 was used as
a reference electrode and the other gold electrode (first electrode
12) of the detection body was used as a sensing electrode, placing
the gas sensor in the flow of the nitrogen gas, and switching the
gas source between nitrogen gas of high purity and nitrogen has
including ammonia at the concentration of 1 ppm, while measuring
the potential difference between the both electrodes, in the same
manner as in Example 1. At the time of the evaluation, the voltage
from the bias voltage source was -90.+-.3 mV.
[0150] A relationship between the measured potential difference and
the lapse of time is presented in FIG. 11. Even in the state where
the nitrogen gas of high purity was to be in contact with the solid
electrolyte layer 11, the potential of the reference electrode was
higher than the potential of the sensing electrode by about 100 mV
due to equilibrium of the oxidation-reduction reaction of supper
occurred at the interface between the copper (I) bromide and the
surface of the copper electrode. When the air flow was changed from
the nitrogen gas of high purity to the nitrogen gas including
ammonia at the concentration of 1 ppm, the potential of the sensing
electrode became high, and as a result, the measured potential
difference became small by about 50 mV.
[0151] It was confirmed that a gas sensor of high sensitivity and a
potential difference measuring system could be obtained with a
structure where a plurality of the electrodes were disposed not to
inhibit contact between the surface of the solid electrolyte layer
and the atmosphere, and bias voltage is applied into the solid
electrolyte layer in the direction substantially parallel to the
plane to be in contact with the detection-target gas, and by using
one of the electrodes in contact with solid electrolyte layer as a
sensing electrode, and the electrode at the side of the bias
voltage source not connected to the solid electrolyte layer as a
reference electrode, as described above.
Example 4
[0152] A gas sensor as illustrated in FIGS. 12A to 12C was
produced. Specifically the gas sensor was produced by the following
method.
<Formation of First Electrode and Second Electrode>
[0153] Two gold electrodes (first electrode 22 and second electrode
23) each having the width of 10 mm, the length of 20 mm, and the
average thickness of 60 nm were formed by vacuum deposition on a
silicon wafer with a thermally oxidized film having the average
thickness of 1 .mu.m, where the silicon wafer had the width of 12
mm, the length of 55 mm, and the thickness of 0.6 mm. The two gold
electrodes were arranged with the gap of 1 mm between the edges of
the two gold electrodes facing each other.
<Formation of Solid Electrolyte Layer>
[0154] Copper (I) bromide (solid electrolyte layer 21) having the
width of 8 mm, the length of 30 mm, and the average thickness of
200 nm was formed by RF magnetron sputtering on the two gold
electrodes, to thereby obtain a device.
[0155] The conditions of the RF magnetron sputtering were the same
as in Example 2.
<Covering with Natural Rubber>
[0156] The obtained device was dipped in a natural rubber hexane
solution (a concentration of the natural rubber was 0.01% by
volume) for 1 minute. Thereafter, the device was dried while the
hexane solution was allowed to run down on the surface of the solid
electrolyte layer 21 in the state where a long side of the silicon
wafer was set substantially vertical. Specifically at the time of
the above-mentioned drying process, a state where an amount of the
natural rubber per unit area of the surface of the solid
electrolyte layer 21 was small at the top side and the amount was
large at the bottom side was formed, and the layer 24, which was a
natural rubber layer and covers the solid electrolyte, was
obtained. The resultant device was stored in a nitrogen flow for 24
hours at room temperature before use, to thereby obtain a gas
sensor. Note that, in FIGS. 12A and 12C, the amount of the natural
rubber per unit area of the layer 24 covering the solid electrolyte
was presented with tone of the color. Specifically the darker color
represented the larger amount of the natural rubber.
<Evaluation on Change in Potential Difference>
[0157] An evaluation of a change in potential difference was
performed by using, as a reference electrode, the gold electrode
(second electrode 23) that was at the bottom side at the time of
the drying, using, as a sensing electrode, the gold electrode
(first electrode 22) that was at the top side, and using nitrogen
gas including ammonia at the concentration of 1 ppm in the same
manner as in Example 1. The result is presented in FIG. 13.
[0158] Since the amount of electrons doped from the natural rubber
was large at the side of the reference electrode and was small at
the side of the sensing electrode, the potential was high at the
side of the sensing electrode by 51.+-.1 mV in the nitrogen gas
atmosphere. This is an equivalent to bias voltage. When the air
flow was changed from the nitrogen gas of high purity to the
nitrogen gas including ammonia at the concentration of 1 ppm, the
potential of the sensing electrode became high by about 25 mV.
[0159] As described above, it was confirmed that the gas sensor of
Example 4 was a gas sensor of high sensitivity and a potential
difference measuring system.
Comparative Example 1
[0160] A gas sensor as illustrated in FIGS. 14A to 14C was
produced. Specifically, the gas sensor was produced by the
following method.
<Formation of First Electrode and Second Electrode>
[0161] Two gold electrodes (first electrode 32 and second electrode
33) each having the width of 10 mm, the length of 20 mm, and the
average thickness of 60 nm were formed by vacuum deposition on a
silicon wafer with a thermally oxidized film having the average
thickness of 1 .mu.m, where the silicon wafer had the width of 12
mm, the length of 55 mm, and the thickness of 0.6 mm. The two gold
electrodes were arranged with the gap of 1 mm between the edges of
the two gold electrodes facing each other.
<Formation of Solid Electrolyte Layer>
[0162] Copper (I) bromide (solid electrolyte layer 31) having the
width of 8 mm, the length of 30 mm, and the average thickness of
200 nm was formed by RF magnetron sputtering on the two gold
electrodes, to thereby obtain a device.
[0163] The conditions of the RF magnetron sputtering were the same
as in Example 2.
<Covering with Natural Rubber>
[0164] The obtained gas sensor was dipped in a natural rubber
hexane solution (a concentration of the natural rubber was 0.01% by
volume) for 1 minute, and surfaces of the gas sensor was washed
with hexane. Thereafter, the gas sensor was dried through a baking
process performed in nitrogen at 100.degree. C. for 30 minutes. The
natural rubber layer 35 formed on the solid electrolyte layer 31
was uniformly formed on the solid electrolyte layer 31.
<Evaluation on Change in Potential Difference>
[0165] An evaluation was performed in the same manner as in Example
1 by using one of the two gold electrodes as a reference electrode
and the other as a sensing electrode, and using nitrogen gas
including ammonia at the concentration of 1 ppm. The result is
presented in FIG. 15.
[0166] In this case, there has hardly any potential difference
between the both electrodes, because there was not difference in
the structure between the reference electrode and the sensing
electrode. Even when the air flow was switched from the nitrogen
gas of high purity to the nitrogen gas including ammonia at the
concentration of 1 ppm, the natural rubber layer 35 did not
function as the unit configured to accelerate movements of the
positive charge carriers, and the potential difference between the
both electrodes hardly changed.
[0167] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority and
inferiority of the invention. Although the embodiments of the
present invention have been described in detail, it should be
understood that the various changes, substitutions, and alterations
could be made hereto without departing from the spirit and scope of
the invention.
* * * * *