JP7634595B2 - Gas sensor for sensing volatile organic compounds and method for manufacturing said gas sensor - Google Patents

Description

The present invention relates to a gas sensor that detects volatile organic compounds, and more specifically to a gas sensor that can specifically detect formaldehyde among volatile organic compounds, and a method for manufacturing the gas sensor.

Newly built or renovated homes can cause physical problems such as sore eyes, headaches, and allergies. This is called "stolen house syndrome," and it is said to be caused by volatile organic compounds (VOCs), such as formaldehyde.

Among volatile organic compounds, formaldehyde is contained in various adhesives, flooring materials, particle boards, and plywood, and is released when these are used indoors, causing problems. It is not possible to completely avoid using these substances, and when volatile organic compounds containing formaldehyde are generated, they have many adverse effects on indoor occupants.

When it comes to the effects of formaldehyde on the human body, when the concentration of formaldehyde in the air reaches about 0.04 ppm, it starts to irritate the nervous tissue, and sensitive children may develop atopic dermatitis. When the concentration of formaldehyde in the air is between 0.05 and 1.0, the odor can be detected, and this concentration is the indoor standard value in Canada and California. When the concentration of formaldehyde in the air is around 0.2 ppm, eye irritation starts, and when the concentration is between 0.25 and 0.33 ppm, respiratory problems may occur. A concentration of 0.5 ppm in the air is the minimum value at which throat irritation starts, and is the maximum value permitted by the Korean Society of Industrial Hygiene. When the concentration of formaldehyde in the air is between 2.0 and 3.0, it causes a stinging pain in the eyes, and when the concentration is 4.0, it can cause tears. If the concentration of formaldehyde in the air is between 10.0 and 20.0 ppm, it can cause intense tearing and difficulty in breathing normally, and if it is 30.0 ppm or higher, it can cause acute poisoning within minutes and even death from toxic emphysema.

Incidentally, the indoor environmental standard set by the World Health Organization (WHO), Japan, and other countries is a formaldehyde concentration of 0.08 ppm in the air. In accordance with this standard, it is necessary to use a gas sensor to detect the formaldehyde concentration in the air.

However, when formaldehyde is generated, other volatile organic compound (VOC) gases such as alcohol may be present. However, since general volatile organic compounds and formaldehyde have different effects on the human body, selective sensitivity specific to formaldehyde is required.

A typical gas sensor shows similar sensitivity to most volatile organic compounds, and an example of such a sensor is disclosed in Japanese Patent No. 3854358. In this sensor, gold (Au) electrodes are formed on a substrate, and tin oxide ( _SnO2 ) doped with one or more elements selected from Ga, Y, La, Nd, etc. is used as a sensing material between the electrodes.

However, this type of conventional gas sensor shows similar sensitivity to most volatile organic compounds. For example, when a sensing material in which Pd or Gd is added to _SiO2 is used, the sensitivity S is 20% for 0.1 ppm of formaldehyde, but is also 25% for 1 ppm of volatile organic compounds. The above sensitivity is obtained by converting the percentage of resistance change. Thus, conventional gas sensors can detect both formaldehyde and volatile organic compounds with high sensitivity, but cannot selectively detect only formaldehyde.

Figure 1 shows the reactivity of a conventional gas sensor. This is disclosed in the paper "Study on a micro-gas sensor with SnO ₂ -NiO sensitive film for indoor formaldehyde detection" (Sensors and Actuators B vol. 132, (2008) pp. 74-80). The gas sensor in this case has a MEMS structure that uses tin oxide-nickel oxide as the sensing material and Pt for the electrodes, and detects formaldehyde.

However, the gas sensor disclosed in this paper has a sensitivity S of 1.6% at 0.06 ppm of formaldehyde, and a sensitivity S of less than 0.1% at 1 ppm of ethanol. Furthermore, the sensitivity ratio between formaldehyde and ethanol is large, at over 10, and interference from ethanol gas is suppressed. However, the sensitivity S of formaldehyde is very low at 1.6%.

In other words, the gas sensor is more sensitive to formaldehyde than to volatile organic compounds, including alcohol, but has a fundamental limitation in that it cannot selectively sense formaldehyde.

Therefore, while conventional gas sensors can detect the presence of volatile organic compounds, they have the problem of being unable to provide information about whether the volatile organic compounds contain formaldehyde and, if so, how much.

The objective of the present invention is to provide a gas sensor that is most sensitive to formaldehyde, a volatile organic compound.

The object of the present invention is to provide a gas sensor capable of detecting the presence or concentration of formaldehyde in volatile organic compounds.

The object of the present invention is to provide a gas sensor that maintains both high sensitivity and high selectivity.

One Aspect of the Present Invention The present invention can propose the following as one aspect thereof.
[1]
A gas sensor for sensing a volatile organic compound, comprising:
A substrate constructed of a non-conductive material;
an electrode made of a conductive material on the substrate;
a sensing layer in contact with or overlying at least a portion of the electrodes, the sensing layer being reactive with gas;
A gas sensor for sensing volatile organic compounds, wherein the sensing layer comprises a compound of an alkali metal oxide or an alkaline earth metal oxide and tin oxide.
[2]
The gas sensor for sensing a volatile organic compound according to claim 1, wherein the alkali metal oxide contains at least one element selected from the group consisting of Li, Na, K, Rb, Cs, and Fr.
[3]
The gas sensor for sensing a volatile organic compound according to claim 1, wherein the alkaline earth metal oxide contains at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.
[4]
The gas sensor for sensing a volatile organic compound according to claim 1, wherein the electrodes are made of indium tin oxide (ITO).
[5]
The electrode is
A first electrode formed on the substrate;
a second electrode formed on the substrate and spaced apart from the first electrode;
The gas sensor for sensing a volatile organic compound according to claim 1, wherein the sensing layer is arranged to connect the first electrode and the second electrode.
[6]
The gas sensor for sensing a volatile organic compound according to claim 5, wherein the sensing layer is configured such that at least a portion of the first electrode and at least a portion of the second electrode are exposed to air.
[7]
the substrate further comprising a heater;
The gas sensor for sensing a volatile organic compound according to claim 1, wherein the heater is located on a surface of the substrate on which the electrodes are located, or on a surface opposite to the surface of the substrate on which the electrodes are located.
[8]
A gas sensor for sensing a volatile organic compound, comprising:
A substrate constructed of a non-conductive material;
a sensing layer disposed on the substrate;
an electrode made of a conductive material for sensing electron transfer and capacitance in the sensing layer;
The electrodes include a first electrode made of a conductive material;
a second electrode that supplies a current to the first electrode or receives a current from the first electrode;
A gas sensor for sensing a volatile organic compound, wherein the sensing layer connects the first electrode and the second electrode, and is configured such that at least a portion of the first electrode and at least a portion of the second electrode are exposed to the atmosphere.
[9]
The gas sensor for sensing a volatile organic compound according to claim 8, wherein the sensing layer is disposed between the substrate and the electrode.
[10]
The gas sensor for sensing volatile organic compounds according to claim 9, wherein the first electrode and the second electrode are provided on an outer surface of the sensing layer.
[11]
The gas sensor for sensing a volatile organic compound according to claim 8, wherein the sensing layer shields at least a portion of the first electrode and at least a portion of the second electrode.
[12]
the substrate further comprising a heater;
The gas sensor for sensing a volatile organic compound according to claim 8, wherein the heater is located on a surface of the substrate on which the electrodes are located, or on a surface opposite to the surface of the substrate on which the electrodes are located.
[13]
A method for manufacturing a gas sensor in which a sensing layer is formed and electrodes formed on a substrate are connected to each other, comprising the steps of:
forming an electrode using indium tin oxide (ITO);
forming said sensing layer using a compound of an alkali metal oxide or an alkaline earth metal oxide and tin oxide.
[14]
The alkali metal oxide contains at least one element selected from Li, Na, K, Rb, Cs, and Fr, or
The method for producing a gas sensor for sensing a volatile organic compound according to claim 13, wherein the alkaline earth metal oxide contains at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.
[15]
The method for manufacturing a gas sensor for sensing a volatile organic compound described in [14], wherein the sensing layer is formed by applying a mixed solution of pure water and glycerin in which Mg-SnO2 is dispersed, and heating the mixture at a predetermined temperature.

The present invention provides a gas sensor with a novel combination of sensing materials containing alkali metal elements or alkaline earth metal elements, and provides a sensor with high sensitivity and high selectivity.

The present invention can detect formaldehyde by using tin oxide together with an alkali metal oxide or an alkaline earth metal oxide to create a compound to form a sensing layer.

When constructing a gas sensor, the present invention provides electrodes made of indium tin oxide (ITO).

The present invention includes a substrate made of a non-conductive material, electrodes formed on the substrate of a conductive material, and a sensing layer formed to contact or cover at least a portion of the electrodes and react with a gas, the sensing layer may include a compound of an alkali metal oxide or an alkaline earth metal oxide and tin oxide.

The alkali metal oxide may contain at least one element selected from Li, Na, K, Rb, Cs, and Fr.

The alkaline earth metal oxide may contain at least one element selected from Be, Mg, Ca, Sr, Ba, and Ra.

The electrodes can be made of indium tin oxide (ITO).

The electrodes may include a first electrode formed on the substrate and a second electrode formed on the substrate at a distance from the first electrode, and the sensing layer may be disposed to connect the first electrode and the second electrode.

The sensing layer can be formed so that at least a portion of the first electrode and the second electrode are exposed to air.

The substrate is further provided with a heater, which may be located on the surface of the substrate on which the electrodes are located or on the surface opposite the surface of the substrate on which the electrodes are located.

The present invention may include a substrate made of a non-conductive material, a sensing layer located on the substrate, and electrodes made of a conductive material for sensing electron movement and capacitance in the sensing layer, the electrodes may include a first electrode formed of a conductive material and a second electrode for supplying current to the first electrode or receiving current from the first electrode, the sensing layer connects the first electrode and the second electrode, and may be formed such that at least a portion of the first electrode and the second electrode are exposed to the atmosphere.

The sensing layer can be disposed between the substrate and the electrode.

The first electrode and the second electrode may be provided on the outer surface of the sensing layer.

The sensing layer can shield a portion of the first electrode and a portion of the second electrode.

The substrate may further include a heater, which may be located on the surface of the substrate on which the electrodes are located or on the surface opposite the surface of the substrate on which the electrodes are located.

The present invention relates to a method for manufacturing a gas sensor in which a sensing layer is formed to connect electrodes formed on a substrate, and can include the steps of forming the electrodes using indium tin oxide (ITO) and forming the sensing layer using an alkali metal oxide or a compound of an alkaline earth metal oxide and tin oxide.

The alkali metal oxide may contain at least one element selected from Li, Na, K, Rb, Cs, and Fr, and the alkaline earth metal oxide may contain at least one element selected from Be, Mg, Ca, Sr, Ba, and Ra.

The sensing layer can be formed by dispersing Mg-- _SnO2 in a mixed solution of pure water and glycerin, applying the solution, and heating the solution at a predetermined temperature.

The gas sensor according to the present invention can have at least one of the following effects:

The present invention has the effect of being able to detect formaldehyde gas at concentrations as low as 10 ppb.

The present invention has the advantage of being able to avoid interference between formaldehyde and other gases. Therefore, it is possible to effectively detect only formaldehyde.

In the gas sensor of the present invention, 1 ppm of ethanol gas, a typical volatile organic compound, has a sensitivity equivalent to 10 ppb or less of formaldehyde. Therefore, the gas sensor of the present invention can detect formaldehyde better than other volatile organic compounds, and has high selectivity for formaldehyde.

1 is a graph showing that the selectivity of a conventional gas sensor for formaldehyde is lower than that for ethanol. 1 is a schematic cross-sectional view showing a structure of a gas sensor according to the present invention. 4 is a graph showing the sensitivity of the gas sensor according to the present invention to formaldehyde, ethanol, and toluene. 1 is an explanatory diagram for explaining how gas is sensed in a gas sensor according to the present invention; FIG. FIG. 4 is a schematic cross-sectional view showing another embodiment of a gas sensor according to the present invention. FIG. 4 is a schematic cross-sectional view showing another embodiment of a gas sensor according to the present invention. FIG. 3 is a schematic cross-sectional view showing a gas sensor in which a heater is added to the embodiment shown in FIG. 2 .

Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the attached drawings. In this specification, the same or similar reference numbers are used for the same or similar configurations even in different embodiments, and the description thereof replaces the initial description. As used in this specification, singular expressions include plural expressions unless otherwise clearly indicated in the context. In addition, when describing the embodiments disclosed in this specification, if it is determined that a specific description of related publicly known technology may obscure the gist of the embodiments disclosed in this specification, the detailed description will be omitted. In addition, it should be noted that the attached drawings are merely intended to facilitate an understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification should not be construed as being limited by the attached drawings.

Figure 2 shows a schematic structure of a gas sensor according to an embodiment of the present invention. The gas sensor 10 according to the embodiment of the present invention has a substrate 100 that forms a skeleton. Electrodes 200 are provided on the substrate 100. A sensing layer 300 is provided to connect the electrodes 200 to each other.

The substrate 100 is made of a non-conductive material such as silicon dioxide ( _SiO2 ). The substrate 100 is made of a resin-based material and serves to support the electrode 200 and the sensing layer 300. The substrate 100 may be a plate having a predetermined shape. The substrate 100 may be a glass substrate, an alumina substrate, or the like.

The electrode 200 may be composed of at least one pair of a first electrode 210 and a second electrode 220. The first electrode 210 and the second electrode 220 may be electrically connected to the outside. The first electrode 210 and the second electrode 220 are formed on the substrate 100 at a predetermined interval, and a current can be transmitted between the first electrode 210 and the second electrode 220 via the sensing layer 300.

The gas sensor 10 of the present invention can sense formaldehyde by sensing the current flowing between the first electrode 210 and the second electrode 220, by sensing a change in the current, or by sensing a change in the electrical resistance or capacitance of the electrode 200.

The sensing layer 300 can be formed to cover the first electrode 210 and the second electrode 220. The sensing layer 300 can change the strength of the current flowing between the first electrode 210 and the second electrode 220, or the capacitance or electrical resistance of the electrode 200. That is, the material forming the sensing layer 300 has an inherent resistance, but when it comes into contact with or combines with formaldehyde, its electrical properties can change.

For example, when the material forming the sensing layer 300 comes into contact with or combines with the formaldehyde, it can transfer electrons to the electrode 200 or receive electrons from the electrode 200 while undergoing an oxidation-reduction reaction with the formaldehyde. Alternatively, when the material forming the sensing layer 300 comes into contact with or combines with the formaldehyde, the penetration of the formaldehyde can change the molecular arrangement structure of the sensing layer 300, thereby changing the overall charge capacity.

However, the sensing layer 300 may not react with any other volatile organic compounds other than formaldehyde, or may have a very low reactivity compared to formaldehyde.

Due to these characteristics, the gas sensor 10 of the present invention can specifically detect formaldehyde. This is because even if formaldehyde is present in the atmosphere or indoors together with volatile organic compounds, the sensing layer 300 does not react with other volatile organic compounds other than formaldehyde, or has very low reactivity with them.

The following describes the characteristics of the gas sensor 10 of the present invention, which reacts specifically to formaldehyde and detects formaldehyde, but does not react to other volatile organic compounds and therefore does not detect other volatile organic compounds or has reduced sensitivity to other volatile organic compounds.

In the gas sensor 10 of the present invention, the materials of the electrode 200 and the sensing layer 300 are specified. That is, the materials of the electrode 200 and the sensing layer 300 are specified to have a characteristic that reacts specifically to formaldehyde or has a significantly higher sensitivity to formaldehyde than to other volatile organic compounds.

Through research, the present invention has found that when the material of the sensing layer 300 is a compound of an oxide of an alkali metal element or an oxide of an alkaline earth metal element and tin oxide ( _SnO2 ), its sensitivity to formaldehyde is significantly greater than its sensitivity to other volatile organic compounds, or it reacts specifically with only formaldehyde.

Therefore, a compound of an oxide of an alkali metal element or an oxide of an alkaline earth metal element and tin oxide (SnO ₂ ) is selected as the material for forming the sensing layer 300 of the gas sensor 10 of the present invention.

The alkali metal element may include at least one element selected from Li, Na, K, Rb, Cs, and Fr. The alkaline earth metal element may include at least one element selected from Be, Mg, Ca, Sr, Ba, and Ra.

When Mg- _SnO2 is used as the material of the sensing layer 300 of the present invention, the sensitivity to ethanol, toluene, and formaldehyde is shown as a graph in Figure 3. Referring to Figure 3, it can be seen that the sensitivity to formaldehyde A is higher than that to ethanol B and toluene C, which react most competitively with formaldehyde A among volatile organic compounds.

That is, the gas sensor 10 of the present invention has a sensitivity to formaldehyde A between 20% and 70%, while most concentrations of ethanol (B) and toluene (C) are less than 10% or just exceed 10%.

It can also be seen that the gas sensor 10 of the present invention exhibits a sensitivity of 20% or more even when the concentration of formaldehyde A is less than 100 ppb, but exhibits a sensitivity of not more than 20% even when the concentrations of ethanol B and toluene C are 1000 ppb or more.

When the sensing layer 300 was made of Mg-- _SnO.sub.2 and the electrode 200 was made of ITO as described below, the sensitivity of the gas sensor 10 at formaldehyde A concentrations of 0.03 ppm to 0.30 ppm was 20 to 60%.

However, the sensitivity of the gas sensor 10 of the present invention was very low at 2.3% for a concentration of ethanol B of 1 ppm. This sensitivity corresponds to a sensitivity of 0.01 ppm or less when converted to formaldehyde.

For toluene C, the sensitivity of the gas sensor 10 of the present invention was measured to be 6.8% at a concentration of 1.5 ppm, which corresponds to a formaldehyde concentration of 0.01 ppm or less.

As a result, the gas sensor 10 of the present invention can detect formaldehyde A at a concentration of about 0.08 ppm, which is the environmental standard value set by the International Health Organization, with high sensitivity. In addition, the gas sensor 10 of the present invention can measure volatile organic compounds including ethanol B and toluene C with a sensitivity of 0.01 ppm or less based on formaldehyde, confirming that it has selectivity for formaldehyde.

The gas sensor 10 of the present invention is capable of specifically sensing formaldehyde A by making the sensing layer 300 from an oxide of an alkali metal element or an oxide of an alkaline earth metal element and a compound of tin oxide.

On the other hand, the gas sensor 10 of the present invention does not require the application of other metal elements to the sensing layer 300. Conventional gas sensors have applied various other metal elements as the sensing material. This is because it is a well-known fact that these conventional gas sensors do not derive a specific effect on formaldehyde, but only detect the presence or concentration of most volatile organic compounds as a whole.

In addition, when metals other than alkali metals and alkaline earth metals were used as materials for the sensing layer 300 in experiments, they reacted specifically only to formaldehyde as shown in Figure 3, or the sensitivity to formaldehyde was not higher than that to ethanol and toluene.

In addition, the gas sensor 10 of the present invention can exclude nickel and nickel oxide from the alkali metal elements. The conventional gas sensor used in FIG. 1 uses a compound of nickel oxide and tin oxide as the material of the sensing layer. Specifically, in the conventional gas sensor, _SnO2 -NiO is used as the material of the sensing layer, and gold (Au) is used as the electrode. When formaldehyde is 0.03 ppm to 0.20 ppm as shown in FIG. 1, the sensitivity of the conventional gas sensor is 26 to 61%. However, the sensitivity of the conventional gas sensor to ethanol at a concentration of 1 ppm is 68%, which is even greater than the sensitivity to formaldehyde.

As a result, it can be seen that in conventional sensors, when the sensing material contains a nickel compound, the response or sensitivity to ethanol is even greater, so that when formaldehyde and ethanol are present together in the air or indoors, it is not possible to distinguish between them. This can be understood as being because in the case of nickel, the molecular structure of the oxide and the diameter of the atoms do not react specifically to only formaldehyde, but react more strongly to gases made of organic compounds with other functional groups.

That is, nickel reacts more easily, strongly, and quickly to ethanol and the like than to formaldehyde. Therefore, in the gas sensor 10 of the present invention, when an oxide of an alkali metal element or an oxide of an alkaline earth metal element is used for the sensing layer 300, nickel and nickel oxide can be excluded.

Figure 4 explains the mechanism by which the gas sensor 10 of the present invention reacts specifically to formaldehyde. In metal oxides, metal ions and nonmetal ions combine to form a non-stoichiometric composition from a stoichiometric composition. Lattice defects that are created in the process in which metal ions and oxygen ions change from a stoichiometric composition to a non-stoichiometric composition act as donors or acceptors.

When the material constituting the sensing layer 300 of the gas sensor 10 of the present invention is composed of an oxide of an alkali metal or alkaline earth metal excluding nickel and a compound of tin oxide, the formaldehyde or formaldehyde reactive group can be introduced into the lattice structure of the sensing layer 300.

The following description will be given with reference to (a) of FIG. 4. Volatile organic compounds including formaldehyde A may be present indoors or in the air, and for example, formaldehyde A and ethanol B may be present together indoors or in the air.

FIG. 4(b) shows that formaldehyde A is accommodated in the lattice structure of the sensing layer 300. When formaldehyde A is accommodated in the lattice structure of the sensing layer 300 in this manner, the capacitance or electrical resistance of the entire sensing layer 300 can be changed.

In addition, the formaldehyde A contained in the sensing layer 300 can generate a large amount of electron transfer while strongly generating an oxidation-reduction reaction with an alkali metal or an alkaline earth metal. Therefore, the large amount of electron transfer generated inside the sensing layer 300 can be amplified and transmitted to the electrode unit 200, and the capacitance or electrical resistance of the electrode 200 can be changed.

As a result, the gas sensor 10 of the present invention can detect even small amounts of formaldehyde A with high sensitivity. However, other than formaldehyde A, volatile organic compounds such as ethanol B and toluene C, which have large molecular structures or other functional groups, cannot be introduced into the lattice structure of the sensing layer 300.

In other words, ethanol B can come into contact with the sensing layer 300, but cannot be introduced into the lattice structure inside the sensing layer 300. Furthermore, ethanol B cannot undergo a strong oxidation-reduction reaction with the sensing layer 300.

Therefore, volatile organic compounds such as ethanol B cannot generate a large amount of electron transfer in the sensing layer 300 and cannot change the capacitance or electrical resistance of the sensing layer 300.

As a result, the gas sensor 10 of the present invention may not react to volatile organic compounds other than formaldehyde, or may have very low sensitivity. Therefore, the gas sensor 10 of the present invention can ensure high sensitivity and sensing specificity for formaldehyde A.

Meanwhile, experimental results show that the gas sensor 10 of the present invention exhibits or is enhanced when the electrode 200 is made of indium tin oxide (ITO). This means that if the electrode 200 is made of a general gold (Au) or platinum (Pt) compound, there is a risk of a decrease in the reception sensitivity of the specific capacitance change and electron transfer that occurs in the sensing layer 300.

Specifically, the electrode 200 may be made of a metal oxide containing at least one of the elements Ti, Zn, In, and Sn, and may not contain gold (Au) or platinum (Pt).

The sensing layer 300 can be configured to completely cover the electrode 200. This ensures that the first electrode 210 and the second electrode 220 are connected by the sensing layer 300.

In addition, the area of the sensing layer 300 exposed to the atmosphere or indoor air can be maximized to further improve formaldehyde sensing performance.

Figure 5 shows another embodiment of the gas sensor 10' according to the present invention. In the gas sensor 10' of this embodiment, the sensing layer 300 has a property of reacting specifically with formaldehyde, so there are cases where it is not necessary to cover the entire electrode 200.

Therefore, in the gas sensor 10' of this embodiment, a portion of the surface area of the electrode 200, region I, can be exposed, and the remaining region II can be covered by the sensing layer 300. The exposed portion of the electrode 200 is called the exposed region I, and the region covered by the sensing layer 300 is called the blocked region II.

This embodiment takes into consideration that the sensing layer 300 can function normally if it can contact formaldehyde in the atmosphere or indoors while connecting the first electrode 210 and the second electrode 220. In this way, the sensing layer 300 can be formed in a relatively narrow area, thereby minimizing the amount of material used to form the sensing layer 300.

By providing the exposed region I, it is easy to check whether the electrode 200 is installed correctly or whether the electrode 200 is operating normally. For reference, by providing the exposed region I on the electrode 200 as in this embodiment, the exposed region I can also be used as a portion to which a lead wire for connection to the outside is connected, so that the size of the gas sensor 10' can be reduced.

Figure 6 shows another embodiment of the gas sensor 10" of the present invention. The gas sensor 10" of this embodiment has a sensing layer 300 that reacts specifically with formaldehyde A, so as long as the electrode section 200 can be connected by the sensing layer 300, it can function normally no matter where the sensing layer 300 is located.

In this embodiment, a sensing layer 300 is formed on a substrate 100, and an electrode 200 is formed on the sensing layer 300. The electrode 200 is formed by pairing a first electrode 210 and a second electrode 220 with a predetermined distance between them. Here, the first electrode 210 and the second electrode 220 may each be connected to the outside via a separate lead wire (not shown).

The electrode 200 itself does not react with formaldehyde A or volatile organic compounds, so it can be exposed indoors or in the air. In light of this, the electrode 200 is formed on the sensing layer 300.

In this embodiment, the sensing layer 300 is first formed on the substrate 100, and the electrode 200 is formed on the sensing layer 300. That is, the sensing layer 300 is interposed between the substrate 100 and the electrode 200, and the first electrode 210 and the second electrode 220 can be formed on the surface of the sensing layer 300. In this manner, by forming the first electrode 210 and the second electrode 220 on the sensing layer 300, it is possible to ensure that the first electrode 210 and the second electrode 220 are connected by the sensing layer 300.

In this embodiment, all of the outer surfaces of the first electrode 210 and the second electrode 220 are exposed to the outside except for the surfaces where the first electrode 210 and the second electrode 220 are attached to the sensing layer 300. Therefore, it may be easier to connect lead wires for electrical connection to the outside. In particular, it may be relatively easy to form the first electrode 210 and the second electrode 220 during the manufacturing process, and maintenance after manufacturing may be relatively easy.

Next, FIG. 7 shows that a heater 400 has been added to the embodiment shown in FIG. 2. For ease of explanation, the same reference numerals as in the embodiment shown in FIG. 2 are used here, and the heater 400 has been added.

The heater 400 provides heat to enable the gas sensor 10 to operate at a particular temperature. The heater 400 can be made of gold or platinum. The heater 400 can be on the surface of the substrate 100 opposite the surface on which the electrode 200 is located, as shown in FIG. 7. However, the heater 400 may also be located on the surface on which the electrode 200 is located, surrounding the electrode 200.

Below, an embodiment of a method for manufacturing the gas sensor 10 of the present invention will be described. For convenience of explanation, the gas sensor 10 shown in FIG. 2 will be referred to for explanation.

In the gas sensor 10 of the present invention, indium tin oxide (ITO) is used as the material of the electrode 200. As the material of the sensing layer 300, Mg-containing tin oxide (Mg-SnO ₂ ) is used.

The production of Mg- _SnO2 will be explained. Tin chloride ( _SnCl2 ) and an aqueous solution of magnesium sulfate are reacted. Here, the content of Sn and Mg can be set to a molar ratio of Sn:Mg=20:1. A precipitate can be obtained by dropping ammonia water into this aqueous solution.

The precipitate is washed with distilled water and then dried. Drying can be performed in air. The dried powder can be calcined at 600-800°C to obtain Mg- _SnO2 .

An electrode 200 made of indium tin oxide (ITO) may be formed on the surface of the substrate 100. After the first electrode 210 and the second electrode 220 of the electrode 200 are formed on the substrate 100, a sensing layer 300 is formed. The sensing layer 300 is made of the above-mentioned Mg- _SnO2 . The sensing layer 300 may be formed by dispersing Mg- _SnO2 in a mixed solution of pure water and glycerin and applying the solution to connect the first electrode 210 and the second electrode 220.

After forming the sensing layer 300, it can be heat treated at 500°C.

The following describes how to measure gas response using the gas sensor 10 of the present invention. The gas sensor 10 is placed in a gas introduction container and exposed to a gas with an adjusted concentration. In this state, the change in resistance between the first electrode 210 and the second electrode 220 can be detected to measure the sensitivity, etc.

The gas with adjusted concentration can be generated in a gas generator (Permeator) using pure air as a dilution gas, and the flow rate can be adjusted using a mass flow controller and introduced into the gas introduction vessel. Humidity can be generated by bubbling distilled water. The relative humidity obtained from the results in Figure 3 can be set to 54%.

The resistance value of the gas sensor 10 was obtained by applying a voltage through wiring installed in the electrometer sensor element and measuring the current.

The gas sensor 10 of the present invention can be used in a variety of home appliances. For example, it can be installed in air conditioners, air purifiers, washing machines, dryers, and clothing management machines to detect whether formaldehyde is being generated and perform the necessary operations accordingly.

The present invention can be modified and embodied in various forms, but the scope of the rights is not limited to the above-mentioned embodiment. Therefore, if a modified embodiment includes elements of the claims of the present invention, it should be understood that it falls within the scope of the rights of the present invention.

10, 10', 10" Gas sensor 100 Substrate 200 Electrode 210 First electrode 220 Second electrode 300 Sensing layer 400 Heater

Claims (4)

A gas sensor for sensing a volatile organic compound, comprising:
A substrate constructed of a non-conductive material;
a sensing layer disposed on the substrate;
an electrode made of a conductive material for sensing electron transfer and capacitance in the sensing layer;
The electrodes include a first electrode made of a conductive material;
a second electrode that supplies a current to the first electrode or receives a current from the first electrode;
the sensing layer is configured to connect the first electrode and the second electrode, and at least a portion of the first electrode and at least a portion of the second electrode are exposed to the atmosphere;
The electrodes are made of indium tin oxide (ITO),
The sensing layer is made of Mg - _SnO2 ,
The sensing layer is disposed between the substrate and the electrode . 2. The gas sensor for sensing volatile organic compounds as claimed in claim 1 , wherein the first electrode and the second electrode are provided on an outer surface of the sensing layer. the substrate further comprising a heater;
2. The gas sensor for sensing volatile organic compounds according to claim 1 , wherein the heater is located on a surface of the substrate on which the electrodes are located or on a surface opposite to the surface on which the electrodes are located. A method for manufacturing a gas sensor in which a sensing layer is formed and electrodes formed on a substrate are connected to each other by the sensing layer, comprising the steps of:
forming an electrode using indium tin oxide (ITO);
forming the sensing layer using Mg - _SnO2 ;
The sensing layer is formed by applying a mixed solution of pure water and glycerin in which Mg--SnO2 _is dispersed, and heating it at a predetermined temperature .