U.S. patent application number 15/957977 was filed with the patent office on 2018-11-01 for gas sensor device, gas measuring device, and method of manufacturing gas sensor device.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Kazuaki Karasawa, Satoru Momose, Osamu Tsuboi, Michio USHIGOME.
Application Number | 20180313776 15/957977 |
Document ID | / |
Family ID | 63917164 |
Filed Date | 2018-11-01 |
United States Patent
Application |
20180313776 |
Kind Code |
A1 |
Momose; Satoru ; et
al. |
November 1, 2018 |
GAS SENSOR DEVICE, GAS MEASURING DEVICE, AND METHOD OF
MANUFACTURING GAS SENSOR DEVICE
Abstract
A gas sensor device includes a first electrode, a second
electrode, and a polythiophene film which is formed between the
first and second electrodes to be electrically coupled to the first
and second electrodes, and to which cuprous bromide is
adsorbed.
Inventors: |
Momose; Satoru; (Atsugi,
JP) ; USHIGOME; Michio; (Atsugi, JP) ;
Karasawa; Kazuaki; (Hadano, JP) ; Tsuboi; Osamu;
(Kawasaki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
63917164 |
Appl. No.: |
15/957977 |
Filed: |
April 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2033/4975 20130101;
G01N 33/497 20130101; G01N 27/125 20130101; G01N 33/84
20130101 |
International
Class: |
G01N 27/12 20060101
G01N027/12; G01N 33/497 20060101 G01N033/497; G01N 33/84 20060101
G01N033/84 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2017 |
JP |
2017-090084 |
Claims
1. A gas sensor device comprising: a first electrode; a second
electrode; and a polythiophene film which is formed between the
first and second electrodes to be electrically coupled to the first
and second electrodes, and to which cuprous bromide is
adsorbed.
2. The gas sensor device according to claim 1, wherein the
polythiophene film contains a polythiophene molecule, and the
cuprous bromide is bonded to a sulfur atom contained in the
polythiophene molecule.
3. The gas sensor device according to claim 2, wherein the
polythiophene film has a stacking structure in which a plurality of
polythiophene molecules are stacked on each other in a direction
from the first electrode to the second electrode.
4. The gas sensor device according to claim 1, wherein the
polythiophene film has poly(3-thiophene).
5. A gas measuring device comprising: a gas sensor device; and a
measurement circuit coupled to the gas sensor device, wherein the
gas sensor device includes a first electrode; a second electrode;
and a polythiophene film which is formed between the first and
second electrodes to be electrically coupled to the first and
second electrodes, and to which cuprous bromide is adsorbed,
wherein the measurement circuit measures an electrical property of
the polythiophene film at a predetermined interval.
6. The gas measuring device according to claim 5, wherein the
measurement circuit calculates a change of the electric property of
the polythiophene film at the predetermined interval.
7. A method of manufacturing a gas sensor device, the method
comprising: forming a first electrode and a second electrode on a
substrate; and forming a polythiophene film on the substrate
between the first and second electrodes to be electrically coupled
to the first and second electrodes, and to which cuprous bromide is
adsorbed.
8. The method of manufacturing a gas sensor device according to
claim 7, wherein the forming a polythiophene film absorbed cuprous
bromide is performed by contacting the polythiophene film and a
cupric bromide.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2017-090084,
filed on Apr. 28, 2017, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein are related to a gas sensor
device, a gas measuring device, and a method of manufacturing a gas
sensor device.
BACKGROUND
[0003] Research and development are being conducted to discover a
disease at an early stage before a self-perceived symptom is
manifested, by detecting a specific chemical substance contained in
the exhaled breath of a person. There has been known a gas sensor
device which detects a detection target gas, by using the
phenomenon that when a contacting portion of a semiconductor formed
on an electrode is exposed to a measurement target gas, the
electric resistance value of the contacting portion changes due to
the contact of the detection target gas. By using the gas sensor
device, a simple examination may be performed to detect a gas
indicating an occurrence of a disease from gases contained in the
exhaled breath.
[0004] In order to detect a specific detection target gas from the
measurement target gas in which a plurality of gases is mixed with
each other, a gas sensor device exhibiting a high gas species
selectivity is used. For example, the gas sensor device may exhibit
a response by a change of an electric resistance value with respect
to the detection target gas at a rate of about 100 or more times
over another gas (other than the detection target gas) contained in
the measurement target gas. For example, a gas sensor device using
cuprous bromide is known as a gas sensor device exhibiting a high
ammonia gas selectivity.
[0005] Related technologies are disclosed in, for example,
Analytica Chimica Acta Vol. 515 (2004), p. 279-284.
SUMMARY
[0006] According to an aspect of the embodiments, a gas sensor
device includes a first electrode, a second electrode, and a
polythiophene film which is formed between the first and second
electrodes to be electrically coupled to the first and second
electrodes, and to which cuprous bromide is adsorbed.
[0007] The object and advantages of the disclosure will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims. It is to be understood that both the
foregoing general description and the following detailed
description are exemplary and explanatory and are not restirctive
of the disclosure, as claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a sectional view of a gas sensor device according
to a first embodiment;
[0009] FIG. 2 is a top view of the gas sensor device according to
the first embodiment;
[0010] FIG. 3 is a view illustrating a polythiophene plane of the
gas sensor device according to the first embodiment;
[0011] FIG. 4 is a view illustrating a stacking structure of
polythiophene in the gas sensor device according to the first
embodiment;
[0012] FIG. 5 is a view illustrating a molecular structure of a
contacting portion of the gas sensor device according to the first
embodiment;
[0013] FIG. 6 is a view illustrating an estimated equilibrium state
of molecules in the contacting portion when the contacting portion
comes into contact with a gas, in the gas sensor device according
to the first embodiment;
[0014] FIG. 7 is a view illustrating a process of a method of
manufacturing the gas sensor device according to the first
embodiment;
[0015] FIG. 8 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment;
[0016] FIG. 9 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment;
[0017] FIG. 10 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment;
[0018] FIG. 11 is an X-ray diffraction profile obtained by
measuring the gas sensor device manufactured by the method of
manufacturing the gas sensor device according to the first
embodiment;
[0019] FIG. 12 illustrates an exemplary of a scanning transmission
electron microscopic image of the gas sensor device manufactured by
the method of manufacturing the gas sensor device according to the
first embodiment;
[0020] FIG. 13 is a view illustrating a gas measuring device
according to a second embodiment;
[0021] FIG. 14 is a response profile of the gas sensor device
according to the second embodiment to ammonia gas and hydrogen
sulfide gas each having a concentration of 1 ppm in the air;
[0022] FIG. 15 is an enlarged view illustrating an initial response
for 30 seconds from a start of an exposure to a target gas in the
response profile illustrated in FIG. 14;
[0023] FIG. 16 is a view illustrating an exhaled breath measuring
device according to a third embodiment;
[0024] FIG. 17 is a response profile of a gas sensor device
according to a comparative example to ammonia gas and hydrogen
sulfide gas each having a concentration of 1 ppm in the air;
[0025] FIG. 18 is an enlarged view illustrating an initial response
for 60 seconds from a start of an exposure to a target gas, in the
response profile illustrated in FIG. 17;
[0026] FIG. 19 is a view illustrating a modification of the gas
sensor device according to the first embodiment; and
[0027] FIG. 20 is a view illustrating another modification of the
gas sensor device according to the first embodiment.
DESCRIPTION OF EMBODIMENTS
[0028] Among the non-detecting gases contained in the measurement
target gas, there is a gas which comes into contact with the
contacting portion like the detection target gas and changes an
electric resistance value of the contacting portion although the
change is small as compared with the detection target gas. Due to
the non-detecting gases contacting the contacting portion to change
the electric resistance value, the detection target gas selectivity
of the gas sensor device decreases, and thus, an accurate
quantification of the detection target gas may not be
performed.
[0029] Hereinafter, a gas sensor device, a gas measuring device,
and a method of manufacturing the gas sensor device according to
embodiments of the present disclosure will be described with
reference to FIGS. 1 to 20. The scope of the technology of the
present disclosure is not limited to the embodiments and includes
the matters defined in the claims and equivalents thereto. Further,
components corresponding to each other in different drawings will
be denoted by the same reference numeral, and overlapping
descriptions thereof will be omitted.
[0030] Hereinafter, a gas sensor device according to a first
embodiment will be described with reference to FIGS. 1 to 6. The
gas sensor device according to the first embodiment exhibits a
response by a change of an electric resistance value with respect
to a contact of a detection target gas contained in a measurement
target gas. In the gas sensor device according to the first
embodiment, the measurement target gas is, for example, the exhaled
breath of a person, and the detection target gas is ammonia
gas.
[0031] FIG. 1 is a sectional view of the gas sensor device
according to the first embodiment. FIG. 2 is a top view of the gas
sensor device according to the first embodiment. As illustrated in
FIGS. 1 and 2, a gas sensor device 10 includes a substrate 11, two
electrodes 12a and 12b, and a contacting portion 13.
[0032] The substrate 11 is, for example, a silicon wafer with a
thermal oxide film formed thereon (e.g., the length of the thermal
oxide film is 100 nm) and having a side of 15 mm.
[0033] The two electrodes 12a and 12b are provided as a first
electrode 12a and a second electrode 12b on the substrate 11. For
example, each of the two electrodes 12a and 12b has a width of 5
mm, a length of 6 mm, and a film thickness of 60 nm. The two
electrodes 12a and 12b are arranged at a predetermined interval
therebetween, for example, an interval of 1 mm.
[0034] The contacting portion 13 is electrically coupled to the two
electrodes 12a and 12b, and is a polythiophene film 14 with cuprous
bromide adsorbed thereto. The contacting portion 13 has, for
example, a rectangular shape having a film thickness of 60 nm and a
side of 5 mm.
[0035] The polythiophene film 14 is composed of a plurality of
polythiophene molecules and may have a stacking structure in which
thiophene rings of the plurality of polythiophene molecules are
stacked in the direction from the first electrode 12a toward the
second electrode 12b, in view of detecting the detection target gas
with a high response sensitivity when detecting the detection
target gas by using the gas sensor device 10. The plurality of
respective polythiophene molecules may be stacked in a state of
being inclined with respect to the direction from the first
electrode 12a toward the second electrode 12b.
[0036] The polythiophene film 14 may have polythiophene with a high
conductivity as a p-type semiconductor, in view of detecting the
detection target gas with a high response sensitivity when
detecting the detection target gas by using the gas sensor device
10. A specific material for the polythiophene of the polythiophene
film 14 is, for example, poly(3-hexylthiophene) (PH3T).
[0037] For example, cuprous bromide may be physically adsorbed to
the polythiophene film 14 and be present in a distance in which
exchange of electrons with the polythiophene molecules of the
polythiophene film 14 may be performed. For example, cuprous
bromide may be chemically adsorbed to the polythiophene film 14
through a coordination bond formation and form coordination bonds
with the polythiophene molecules of the polythiophene film 14. The
cuprous bromide has copper (I) ions and bromide ions.
[0038] FIG. 3 is a view illustrating a polythiophene plane of the
gas sensor device according to the first embodiment. As illustrated
in FIG. 3, the polythiophene film 14 has repeating units of
polythiophene which include thiophene rings. The atoms constituting
the thiophene rings included in the repeating units of
polythiophene are present on the same plane 14A (a polythiophene
plane 14A).
[0039] FIG. 4 is a view illustrating a stacking structure of
polythiophene in the gas sensor device according to the first
embodiment. As illustrated in FIG. 4, the polythiophene film 14 may
have a plurality of polythiophene molecules having a stacking
structure in which the polythiophene plane 14A and other
polythiophene planes including a polythiophene plane 14B are
superimposed on each other. The plurality of polythiophene
molecules become stable in the stacking structure by a
interaction.
[0040] The cuprous bromide is adsorbed to the lateral portions of
the polythiophene in the stacking structure. When the cuprous
bromide is adsorbed to the lateral portions of the polythiophene in
the stacking structure, the cuprous bromide is exposed to the
vicinity of the surface of the contacting portion 13. Since the
detection target gas easily comes into contact with the cuprous
bromide, the gas sensor device 10 exhibits a high response
sensitivity to the detection target gas.
[0041] As described above, the gas sensor device 10 includes the
contacting portion 13 which is the polythiophene film 14 with
cuprous bromide adsorbed thereto, so that the gas sensor device 10
exhibits a response by a change of an electric resistance value
with respect to a contact of the ammonia gas which is the detection
target gas with a high sensitivity, and exhibits a response by a
change of an electric resistance value with respect to a contact of
the hydrogen sulfide gas which is a gas other than the detection
target gas with a low sensitivity. Thus, the gas sensor device 10
exhibits a high ammonia gas selectivity.
[0042] Hereinafter, an estimated operation principle of the gas
sensor device according to the first embodiment will be described
with reference to FIGS. 5 and 6.
[0043] FIG. 5 is a view illustrating a molecular structure of the
contacting portion of the gas sensor device according to the first
embodiment. The cuprous bromide and the polythiophene form a
coordination bond in the manner that a sulfur atom of a thiophene
ring included in the polythiophene donates an electron to the
cuprous bromide.
[0044] FIG. 6 is a view illustrating an estimated equilibrium state
of molecules in the contacting portion when the contacting portion
comes into contact with a gas, in the gas sensor device according
to the first embodiment. When ammonia which is the detection target
gas approaches and comes into contact with the contacting portion
13, the ammonia forms a coordination bond by donating an electron
to the cuprous bromide. When the coordination bond between the
ammonia and the cuprous bromide is formed, the coordination bond
between the polythiophene and the cuprous bromide is decoupled.
[0045] When the coordination bond between the polythiophene and the
cuprous bromide is decoupled, the electron that has been donated to
the cuprous bromide is returned to the polythiopnene film 14. Since
the concentration of a p-type carrier of the poythiophene film 14
decreases, the electric resistance value of the contacting portion
13 increases.
[0046] When the concentration of the ammonia in the measurement
target gas exposed to the contacting portion 13 increases, the
coordination bond between the ammonia and the cuprous bromide is
formed as indicated by the rightward arrow in FIG. 6. To the
contrary, when the concentration of the ammonia in the measurement
target gas exposed to the contacting portion 13 decreases, the
coordination bond between the polythiophene and the cuprous bromide
is formed as indicated by the leftward arrow in FIG. 6.
[0047] Depending on the concentration of ammonia in the measurement
target gas to be exposed, a reaction shifts from the equilibrium
state of molecules to the formation of the coordination bond on the
contacting portion 13, thereby changing the rate of the formation
of the coordination bond between the ammonia and the cuprous
bromide, so that the gas sensor device 10 exhibits a response by
the change of the electric resistance value.
[0048] Since the ability of ammonia to form a coordination bond
with the cuprous bromide is much higher than the ability of
polythiophene to form a coordination bond with the cuprous bromide,
the coordination bond between the polythiophene and the cuprous
bromide is immediately decoupled, and the coordination bond between
the ammonia and the cuprous bromide is formed, on the contacting
portion 13 exposed to the ammonia gas. Since the speed for forming
the coordination bond between the ammonia and the cuprous bromide
immediately increases in the gas sensor device 10 exposed to the
ammonia gas, the gas sensor device 10 exhibits the response by the
change of the electric resistance value with a high
sensitivity.
[0049] Meanwhile, since the ability of hydrogen sulfide to form a
coordination bond with cuprous bromide is equal to the ability of
polythiophene to form a coordination bond with cuprous bromide, it
takes longer to disconnect the coordination bond between the
polythiophene and the cuprous bromide on the contacting portion 13
exposed to the hydrogen sulfide gas, than decoupling the
coordination bond between the polythiophene and the cuprous bromide
on the contacting portion 13 exposed to the ammonia gas. Since the
speed for forming the coordination bond between the hydrogen
sulfide and the cuprous bromide hardly increases due to the
hindrance by the coordination bond between the polythiophene and
the cuprous bromide, the gas sensor device 10 exposed to the
hydrogen sulfide exhibits the response by the change of the
electric resistance value with a low sensitivity.
[0050] Hereinafter, a method of manufacturing the gas sensor device
according to the first embodiment will be described with reference
to FIGS. 7 to 10.
[0051] The method of manufacturing the gas sensor device according
to the first embodiment forms the first and second electrodes on
the substrate, forms the polythiophene film to be electrically
coupled to the first and second electrodes, and brings cupric
bromide into contact with the polythiophene film so as to form the
contacting portion which is the polythiophene film with cuprous
bromide adsorbed thereto.
[0052] FIG. 7 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment. As illustrated in FIG. 7, the two electrodes 12a and
12b are formed on the substrate 11. The substrate 11 is, for
example, a silicon wafer with a thermal oxide film formed thereon
(e.g., the length of the thermal oxide film is 100 nm) and having a
side of 15 mm. The two electrodes 12a and 12b are gold electrodes
each having a width of 5 mm, a length of 6 mm, and a film thickness
of 60 nm, and are formed at an interval of 1 mm therebetween by
using vacuum deposition.
[0053] FIG. 8 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment. The polythiophene film 14 is formed to be electrically
coupled to the two electrodes 12a and 12b. The polythiophene film
14 may be formed by, for example, a method of applying 1 .mu.L of
P3HT solution dissolved in o-dichlorobenzene at a concentration of
1% by weight into a rectangular shape having a side of 5 mm, and
performing a natural drying, in view of increasing the yield of the
polythiophene film 14 having the high conductivity and obtaining
the gas sensor device capable of detecting the detection target gas
with a high response sensitivity.
[0054] FIG. 9 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment. Cupric bromide is brought into contact with the
polythiophene film 14. In order to bring the cupric bromide into
contact with the polythiophene film 14, for example, a methanol
solution in which the concentration of the cupric bromide is 0.1
mol/L is dropped and left standing for 5 minutes, and then, washing
with pure methanol and natural drying are performed.
[0055] Copper (II) ions contained in the cupric bromide oxidize the
polythiophene film 14 to receive the electrons of the polythiophene
film 14 and be reduced into copper (I) ions. Cuprous bromide is
formed by the oxidation-reduction reaction and adsorbed to the
polythiophene film 14.
[0056] FIG. 10 is a view illustrating a process of the method of
manufacturing the gas sensor device according to the first
embodiment. As illustrated in FIG. 10, the contacting portion 13
which is the polythiophene film 14 with cuprous bromide adsorbed
thereto is formed so that the gas sensor device 10 is
manufactured.
[0057] As described above, the method of manufacturing the gas
sensor device forms the contacting portion 13 electrically coupled
to the first electrode 12a and the second electrode 12b and
corresponding to the polythiophene film 14 with cuprous bromide
adsorbed thereto, so that the gas sensor device 10 having an
improved ammonia gas selectivity may be manufactured.
[0058] An element analysis by the X-ray photoelectron spectroscopy
(XPS) is performed on the gas sensor device 10 manufactured by the
method of manufacturing the gas sensor device according to the
first embodiment. When an element composition ratio analysis by the
XPS is performed on the surface of the polythiophene film 14 with
cuprous bromide adsorbed thereto in an analyte depth of about 5 nm,
the ratio of the number of copper atoms, the number of bromine
atoms, the number of sulfur atoms, and the number of carbon atoms
is about 1:1:13:130.
[0059] The analyte depth is about 5 nm with respect to the 60 nm
film thickness of the polythiophene film 14, and in view of the
ratio of the number of the carbon atoms and the number of the
sulfur atoms, the surface of the polythiophene film 14 contains one
copper atom per 13 thiophene rings. In addition, the observed
copper atoms are in the ionic state, and it is estimated that the
ratio between monovalent ions and divalent ions is about 10:1.
Thus, most of the copper compounds adsorbed to the polythiophene
film 14 are cuprous bromide.
[0060] FIG. 11 is an X-ray diffraction profile obtained by
measuring the gas sensor device 10 manufactured by the method of
manufacturing the gas sensor device according to the first
embodiment. As illustrated in FIG. 11, only the peak derived from
the stacking structure of P3HT which is the material of the
polythiophene film 14 is observed. Since no peak representing
cuprous bromide is observed, it is estimated that a cuprous bromide
crystal in a size of at least several nm has not been formed.
[0061] FIG. 12 illustrates an exemplary of a scanning transmission
electron microscopic image of the gas sensor device 10 manufactured
by the method of manufacturing the gas sensor device according to
the first embodiment. FIG. 12 is a schematic view of a scanning
transmission electron microscopic image of the gas sensor device 10
manufactured by the method of manufacturing the gas sensor device
according to the first embodiment. No crystal structure of cuprous
bromide is observed.
[0062] From the analysis result, it is estimated that the gas
sensor device 10 manufactured by the method of manufacturing the
gas sensor device according to the first embodiment mainly contains
P3HT which is the material of the polythiophene film 14 and has a
structure in which cuprous bromide is discretely present without
growing as a crystal, on the surface of P3HT.
[0063] Hereinafter, a gas measuring device according to a second
embodiment will be described with reference to FIG. 13. The gas
measuring device according to the second embodiment detects a
detection target gas in a measurement target gas. In the gas
measuring device according to the second embodiment, the
measurement target gas is, for example, the exhaled breath of a
person, and the detection target gas is ammonia gas.
[0064] FIG. 13 is a view illustrating the gas measuring device
according to the second embodiment. As illustrated in FIG. 13, the
gas measuring device 20 includes the gas sensor device 10 and a
measuring circuit including a measurement circuit 21 and a
calculation circuit 22.
[0065] The measurement circuit 21 is electrically coupled to the
two electrodes 12a and 12b of the gas sensor device 10, and
measures an electrical characteristic of the contacting portion 13
of the gas sensor device 10. The measurement circuit 21 is a
measurement circuit such as, for example, an electrometer. For
example, the measurement circuit 21 measures an electric resistance
value of the contacting portion 13 by applying a constant potential
to both ends of the contacting portion 13 and a resistance which
are coupled to each other in a series and measuring a potential of
the contact point between the contacting portion 13 and the
resistance. Further, the measurement circuit 21 applies a constant
potential to both ends of the contacting portion 13 and measures a
current value of the contact point in the contact portion.
[0066] The calculation circuit 22 calculates a change in the
electrical characteristic of the contacting portion 13 of the gas
sensor device 10. The calculation circuit 22 is electrically
coupled to the measurement circuit 21 and receives the measurement
value of the electric characteristic of the gas sensor device 10
which is measured by the measurement circuit 21, to calculate the
change of the electric characteristic. The calculation circuit 22
is, for example, a control device such as a computer. The change of
the electric characteristic is, for example, a ratio or a
difference between the initial electric resistance value R.sub.0 of
the contacting portion 13 and the electric resistance value R after
elapse of a certain time period. In addition, the change of the
electric characteristic is, for example, a ratio or a difference
between an initial current value of the contacting portion 13 and a
current value after elapse of a certain time period. The
calculation circuit 22 may calculate the concentration of the
detection target gas based on the calculated change of the electric
characteristic.
[0067] For example, the calculation circuit 22 may record the
electric resistance value of the contacting portion 13 which is
measured by the measurement circuit 21 once every second, and set
the electric resistance value measured before the exposure to the
measurement target gas as the initial electric resistance value
R.sub.0. Then, the calculation circuit 22 may calculate a change of
the electric resistance value R per unit time with respect to the
initial electric resistance value R.sub.0 after elapse of a certain
time period (e.g., 10 seconds) from the start of the exposure to
the measurement target gas.
[0068] The calculation circuit 22 may calculate the concentration
of the detection target gas by creating and recording a profile of
a change of the electrical characteristic of the contacting portion
13 per unit time, e.g., a change profile of the electric resistance
value of the contacting portion 13 per unit time when a detection
target gas having a known concentration is exposed to the gas
sensor device 10, and by comparing a calculated change of the
electric resistance value per unit time and the recorded profile
with each other.
[0069] The calculation circuit 22 may calculate the concentration
of the gas based on a change of the electrical characteristic for a
certain time period from a time point when the measurement target
gas is exposed to the gas sensor device 10, e.g., a change of the
electric resistance value per unit time for a time period until a
response to hydrogen sulfur is started.
[0070] As described above, the gas measuring device 20 includes the
gas sensor device 10, the measurement circuit 21, and the
calculation circuit 22, and may perform an accurate quantification
of ammonia by including the gas sensor device 10 exhibiting a high
ammonia gas selectivity.
[0071] Hereinafter, descriptions will be made on the response of
the gas measuring device according to the second embodiment to
ammonia and hydrogen sulfur each having a concentration of 1 ppm
with reference to FIGS. 14 and 15.
[0072] The gas sensor device 10 is provided in the air flow, and
alternately exposed to the clean air and ammonia having a
concentration of 1 ppm, to measure an electric resistance value of
the gas sensor device 10 per unit time with respect to the ammonia.
Similarly, the gas sensor device 10 is provided in the air flow,
and alternately exposed to the clean air and hydrogen sulfide
having a concentration of 1 ppm, to measure an electric resistance
value of the gas sensor device 10 per unit time with respect to the
hydrogen sulfide.
[0073] FIG. 14 is a profile of a response of the gas sensor device
according to the second embodiment with respect to the ammonia gas
and the hydrogen sulfide gas each having a concentration of 1 ppm
in the air. The horizontal axis represents time, and the vertical
axis represents relative response intensity. The relative response
intensity refers to a ratio between the initial electrical
resistance value R.sub.0 of the gas sensor device 10 under the
clean air and the electrical resistance value R measured every
second. The gas sensor device 10 exhibits the response by the
electric resistance value with a high sensitivity with respect to
the gas to the extent that the relative response intensity largely
changes per unit time.
[0074] As illustrated in FIG. 14, the relative response intensity
per unit time largely changes by the contact of the gas sensor
device 10 with ammonia. Meanwhile, in the contact of the gas sensor
device 10 with hydrogen sulfide, the relative response intensity
does not largely change for 300 seconds from a time point when the
exposure is started. From the result that the gas sensor device 10
responds to ammonia with a high sensitivity and responds to
hydrogen sulfide with a low sensitivity, the gas sensor device 10
exhibits a high ammonia gas selectivity.
[0075] FIG. 15 is an enlarged view illustrating the initial
response for 30 seconds from the start of the exposure to the
target gas in the response profile illustrated FIG. 14. As
illustrated in FIG. 15, the response of the gas sensor device 10
with respect to hydrogen sulfide exhibits no significant change in
the relative response intensity for 30 seconds from the time point
when the exposure is started. This is because the formation of the
coordination bond between the hydrogen sulfide and the cuprous
bromide is hindered by the coordination bond between the
polythiophene and the cuprous bromide, and thus, the start of the
response of the gas sensor device 10 by the electric resistance
value to the hydrogen sulfide is delayed.
[0076] From the phenomenon that the start of the response of the
gas sensor device 10 to the hydrogen sulfide is delayed, an
accurate quantification of ammonia may be performed without being
affected by the hydrogen sulfide, by using the electric resistance
value, as quantification, for a time period from the start of the
exposure to the measurement target gas until the start of the
response to the hydrogen sulfide. This is obvious because the start
of the response of the gas sensor device 10 to the hydrogen sulfide
is delayed, as compared with a comparative example to be described
later.
[0077] Hereinafter, an exhaled gas measuring device according to a
third embodiment will be described with reference to FIG. 16. The
exhaled gas measuring device according to the third embodiment
detects ammonia gas in the exhaled breath of a person. The ammonia
gas contained in the exhaled breath is known as a marker gas
indicating pylori bacterium infection related to a stomach cancer
and a heart disease. A simple examination for early detecting
diseases such as cancers may be performed by using the exhaled gas
measuring device according to the third embodiment.
[0078] FIG. 16 is a view illustrating the exhaled gas measuring
device according to the third embodiment. As illustrated in FIG.
16, the exhaled gas measuring device 30 includes a sensor 31 having
the gas sensor device 10, the measurement circuit 21, and a
transmission circuit 33, and a monitor having a reception circuit
34, the calculation circuit 22, and an output circuit 35.
[0079] The sensor 31 is a housing accommodating the gas sensor
device 10 and has a blow-in port and an exhaust port such that the
exhaled breath exposed to the gas sensor device 10 may be
introduced into the sensor 31. The sensor 31 may have, for example,
a sensor for measuring a temperature, humidity, and an atmospheric
pressure, or another gas sensor device for detecting a gas other
than ammonia gas as a detection target gas.
[0080] A person to be measured blows his/her exhaled breath into
the housing of the sensor 31 through the blow-in port for a certain
time period from a starting time of the measurement. The time for
blowing the exhaled breath into the sensor 31 is, for example, 15
seconds.
[0081] The transmission circuit 33 transmits the electrical
characteristic of the gas sensor device 10 which is measured by the
measurement circuit 21 from the starting time of the measurement,
once per second to the monitor 32 having the reception circuit 34
via a wireless communication.
[0082] The calculation circuit 22 calculates the electrical
characteristic for a certain time period such as, for example, a
change in the electrical resistance value of the contacting portion
13 of the gas sensor device 10 per unit time for a time period from
4 to 13 seconds after the starting time of the measurement. Based
on the calculated change of the electric resistance value per unit
time, the calculation circuit 22 calculates the concentration of
the ammonia gas and obtains the concentration as a calculation
result. The calculation circuit 22 may save a calibration curve
which is created in advance and represents a change of the electric
resistance value of the gas sensor device 10 in response to a
concentration of the ammonia gas, and calculate a concentration of
the ammonia gas by comparing the calculated change of the electric
resistance value per unit time with the calibration curve.
[0083] The output circuit 35 outputs the calculation result
obtained by the calculation circuit 22. The output circuit 35 is,
for example, a display or a speaker.
[0084] As described above, the exhaled gas measuring device
includes the sensor 31 having the gas sensor device 10, the
measurement circuit 21, and the transmission circuit 33, and the
monitor 32 having the reception circuit 34, the calculation circuit
22, and the output circuit 35, and may accurately and easily
measure the concentration of the ammonia gas in the exhaled
gas.
[0085] Hereinafter, a gas sensor device according to a comparative
example will be described. Descriptions of similar components to
those in the first embodiment will be omitted.
[0086] The gas sensor device according to the comparative example
includes a contacting portion of cuprous bromide, instead of the
contacting portion of the first embodiment which is the
polythiophene film with cuprous bromide adsorbed thereto.
[0087] Hereinafter, an operation principle of the gas sensor device
according to the comparative example will be described.
[0088] When the detection target gas, ammonia, comes into contact
with the contacting portion 13, the ammonia donates an electron to
the cuprous bromide so as to form a coordination bond. When the
electron is donated from the ammonia to the cuprous bromide, the
concentration of the p-type carrier in the cuprous bromide
decreases, and thus, the electric resistance value of the
contacting portion 13 decreases.
[0089] Hereinafter, descriptions will be made on the response of
the gas sensor device of the comparative example by the change of
the electric resistance value to ammonia and hydrogen sulfide each
having a concentration of 1 ppm, with reference to FIGS. 17 and 18.
The change of the electric resistance value of the gas sensor
device according to the comparative example will be measured per
time by using the similar method to that used for the gas measuring
device according to the second embodiment.
[0090] FIG. 17 is a response profile of the gas sensor device
according to the comparative example with respect to the ammonia
gas and the hydrogen sulfide gas each having a concentration of 1
ppm in the air. FIG. 18 is an enlarged view illustrating the
initial response for 60 seconds from the start of the exposure to
the target gas in the response profile illustrated in FIG. 17. The
response intensity of the gas sensor device 10 to hydrogen sulfide
increases at a rate of about 1/10 of the response to ammonia. The
start of the response of the gas sensor device 10 to hydrogen
sulfide is concurrent with the start of the response to
ammonia.
[0091] Hereinafter, a method of manufacturing the gas sensor device
according to the comparative example will be described.
Descriptions of similar portions to those in the first embodiment
will be omitted.
[0092] In the method of manufacturing the gas sensor device
according to the comparative example, a copper film is formed to be
electrically coupled to the first and second electrodes, instead of
forming the polythiophene film in the first embodiment, and cupric
bromide is brought into contact with the copper film so as to form
the contacting portion of cuprous bromide.
[0093] Instead of the polythiophene film 14 of the first
embodiment, a copper film having a side of 5 mm and a film
thickness of 60 nm is formed by using a mask at the position
electrically coupled to the two electrodes 12a and 12b on the
substrate 11 of the gas sensor device 10 in FIG. 8.
[0094] A cupric bromide solution is brought into contact with the
formed copper film. The cupric bromide solution is washed out with
pure methanol after 0.1 mol/L of an aqueous solution is dropped and
immersion is performed for one minute.
[0095] Instead of the contacting portion 13 of the first embodiment
which is the polythiophene film 14 with cuprous bromide adsorbed
thereto in FIG. 10, the contacting portion 13 of cuprous bromide is
formed so that the gas sensor device 10 is manufactured.
[0096] The gas detecting method by the gas sensor device and the
gas measuring device according to the embodiments of the present
disclosure is merely an example, and an optimum method may be
selected depending on a detection target gas or an environment
condition to be used.
[0097] FIG. 19 is a view illustrating a modification of the gas
sensor device according to the first embodiment. For example, the
contacting portion 13 may be formed in contact with only the
lateral surfaces of the two electrodes 12a and 12b as illustrated
in FIG. 19.
[0098] FIG. 20 is a view illustrating a modification of the gas
sensor device according to the first embodiment. The contacting
portion 13 may have any shape as long as the contacting portion 13
is electrically coupled to the two electrodes 12a and 12b. For
example, the contacting portion 13 may have a circular shape as
illustrated in FIG. 20.
[0099] The polythiophene film in the first embodiment may be formed
of a single polythiophene molecule.
[0100] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the disclosure 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 disclosure. Although the embodiment(s) of the
present disclosure has (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 disclosure.
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