Gas sensor for sensing volatile organic compounds and method for manufacturing said gas sensor

Abstract

To provide a gas sensor for sensing a volatile organic compound and a method for manufacturing the gas sensor.SOLUTION: In the present invention, a sensing layer (300) is formed using a sensing material containing an alkali metal or alkaline earth metal so as to specifically react to formaldehyde among volatile organic compounds. When the sensing layer (300) connects between electrodes (200) and senses formaldehyde, a change in physical quantity is confirmed, thereby making it possible to detect formaldehyde.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas sensor for sensing a volatile organic compound, and more particularly to a gas sensor capable of specifically sensing formaldehyde among volatile organic compounds, and a method for manufacturing the gas sensor. [Background technology]

[0002] In newly built or remodeled houses, physical disorders such as sore eyes, headaches, and allergies can occur. This condition is called "stolen house syndrome," and it is said to be caused by volatile organic compounds (VOCs), such as formaldehyde.

[0003] Among volatile organic compounds, formaldehyde is contained in various adhesives, flooring materials, particle boards, plywood, etc., and is released when these are used indoors, causing problems. It is not possible to completely avoid using these materials, and when volatile organic compounds including formaldehyde are generated, they have many adverse effects on indoor residents.

[0004] When we look at the effects of formaldehyde on the human body, when the concentration of formaldehyde in the air reaches about 0.04 ppm, it starts irritating the nervous system, and sensitive children may develop atopic dermatitis. When the concentration of formaldehyde in the air is 0.05-1.0, the odor can be sensed, and this concentration is the indoor standard value in Canada and California. When the concentration of formaldehyde in the air is about 0.2 ppm, eye irritation starts, and when the concentration of formaldehyde in the air is 0.25-0.33 ppm, respiratory problems may occur. When the concentration of formaldehyde in the air is 0.5 ppm, it is the minimum value at which throat irritation starts, and the maximum value allowed by the Korean Society of Industrial Hygiene. When the concentration of formaldehyde in the air is 2.0-3.0, it causes a stinging pain in the eyes, and when the concentration of formaldehyde in the air is 4.0, it may 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 a few minutes and even death from toxic emphysema.

[0005] 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 order to comply with this standard, it is necessary to use a gas sensor to detect the formaldehyde concentration in the air.

[0006] 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.

[0007] A typical gas sensor shows similar sensitivity to most volatile organic compounds, and one such example is disclosed in Japanese Patent No. 3854358. Here, 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 the sensing material between them.

[0008] 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.

[0009] Figure 1 shows the reactivity of a conventional gas sensor. This is disclosed in the paper "Study on a micro-gas sensor with SnO2-NiO sensitive film for indoor formaldehyde detection" (Sensors and Actuators B vol132, (2008) p74-80). The gas sensor here has a MEMS structure using tin oxide-nickel oxide as the sensing material and Pt for the electrodes, and detects formaldehyde.

[0010] 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 of formaldehyde to 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%.

[0011] In other words, although the gas sensor is more sensitive to formaldehyde than to volatile organic compounds including alcohol, it has a fundamental limitation in that it cannot selectively sense formaldehyde.

[0012] Therefore, although conventional gas sensors can detect the presence of volatile organic compounds, they have the problem of being unable to provide information regarding whether the volatile organic compounds contain formaldehyde and, if so, how much of it is contained. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide a gas sensor having the highest sensitivity to formaldehyde among volatile organic compounds.

[0014] It is an object of the present invention to provide a gas sensor capable of sensing the presence or concentration of formaldehyde in volatile organic compounds.

[0015] It is an object of the present invention to provide a gas sensor which maintains both high sensitivity and high selectivity. [Means for solving the problem]

[0016] 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 [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 [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 volatile organic compounds described in [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 volatile organic compounds described in [1], wherein the sensing layer is arranged to connect the first electrode and the second electrode. [6] The gas sensor for sensing volatile organic compounds described in [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 volatile organic compounds described in [1], wherein the heater is located on the surface of the substrate on which the electrode is located or on the surface opposite to the surface of the substrate on which the electrode is 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 volatile organic compounds, the gas sensor being configured such that the sensing layer connects 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. [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 described in [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 the surface of the substrate on which the electrodes are located or on the 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 the 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

[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 volatile organic compounds 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 it at a predetermined temperature.

[0017] The present invention provides a gas sensor with a novel combination of sensing materials containing an alkali metal element or an alkaline earth metal element, and provides a sensor with high sensitivity and high selectivity.

[0018] The present invention is capable of detecting formaldehyde by making a compound using tin oxide together with an alkali metal oxide or an alkaline earth metal oxide to form a sensing layer.

[0019] In the present invention, when constructing a gas sensor, an electrode made of indium tin oxide (ITO) is provided.

[0020] 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 gas, the sensing layer may include a compound of an alkali metal oxide or an alkaline earth metal oxide and tin oxide.

[0021] The alkali metal oxide may contain at least one element selected from the group consisting of Li, Na, K, Rb, Cs and Fr.

[0022] The alkaline earth metal oxide may contain at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

[0023] The electrodes may be formed of indium tin oxide (ITO).

[0024] 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.

[0025] The sensing layer may be formed such that at least a portion of the first electrode and the second electrode are exposed to air.

[0026] The substrate may further include a heater, which may be located on the surface of the substrate where the electrodes are located, or on the surface opposite the surface of the substrate where the electrodes are located.

[0027] 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 and 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 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.

[0028] The sensing layer may be disposed between the substrate and the electrode.

[0029] The first electrode and the second electrode may be provided on an outer surface of the sensing layer.

[0030] The sensing layer may shield a portion of the first electrode and a portion of the second electrode.

[0031] The substrate may further include a heater, which may be located on the surface of the substrate where the electrodes are located or on a surface opposite the surface of the substrate where the electrodes are located.

[0032] The present invention provides a method for manufacturing a gas sensor having a sensing layer formed to connect electrodes formed on a substrate, the method including the steps of forming the electrodes using indium tin oxide (ITO) and forming the sensing layer using a compound of an alkali metal oxide or an alkaline earth metal oxide and tin oxide.

[0033] 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.

[0034] 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. Effect of the Invention

[0035] The gas sensor according to the present invention can have at least one of the following effects.

[0036] The present invention has the advantage of being able to detect formaldehyde gas at concentrations as low as 10 ppb.

[0037] The present invention has an advantage that it is possible to avoid interference between formaldehyde and other gases, and therefore it is possible to effectively detect only formaldehyde.

[0038] 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. [Brief description of the drawings]

[0039] [Figure 1] 1 is a graph showing that the selectivity of a conventional gas sensor for formaldehyde is lower than that for ethanol. [Diagram 2] 1 is a schematic cross-sectional view showing a structure of a gas sensor according to the present invention. [Diagram 3] 4 is a graph showing the sensitivity of the gas sensor according to the present invention to formaldehyde, ethanol, and toluene. [Figure 4] 1 is an explanatory diagram for explaining how gas is sensed in a gas sensor according to the present invention; FIG. [Diagram 5] FIG. 4 is a schematic cross-sectional view showing another embodiment of a gas sensor according to the present invention. [Figure 6] FIG. 4 is a schematic cross-sectional view showing another embodiment of a gas sensor according to the present invention. [Figure 7] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying 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. The singular expressions used in this specification include the 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 known technology may make the gist of the embodiments disclosed in this specification unclear, the detailed description will be omitted. In addition, it should be noted that the accompanying drawings are merely intended to make the embodiments disclosed in this specification easily understandable, and the technical ideas disclosed in this specification should not be construed as being limited by the accompanying drawings.

[0041] 2 is a schematic diagram showing the 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 forming a skeleton. An electrode 200 is provided on the substrate 100. A sensing layer 300 is provided to connect the electrodes 200 to each other.

[0042] 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.

[0043] The electrode 200 may include 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.

[0044] 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.

[0045] The sensing layer 300 may be formed to cover the first electrode 210 and the second electrode 220. The sensing layer 300 may change the strength of a 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 may have a change in electrical property when in contact with or combined with formaldehyde.

[0046] For example, when the material forming the sensing layer 300 comes into contact with or is bonded to the formaldehyde, it may transfer electrons to the electrode 200 while undergoing an oxidation-reduction reaction with the formaldehyde, or may receive electrons from the electrode 200. Alternatively, when the material forming the sensing layer 300 comes into contact with or is bonded to the formaldehyde, the penetration of the formaldehyde may cause a change in the molecular configuration structure of the sensing layer 300, thereby changing the overall charge capacity.

[0047] However, the sensing layer 300 may not react at all with other volatile organic compounds other than formaldehyde, or may have a much lower reactivity with other volatile organic compounds than formaldehyde.

[0048] Due to these characteristics, the gas sensor 10 of the present invention can specifically sense formaldehyde because the sensing layer 300 does not react with or has very low reactivity to other volatile organic compounds other than formaldehyde even if formaldehyde is present in the atmosphere or indoors together with volatile organic compounds.

[0049] 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.

[0050] In the gas sensor 10 of the present invention, the materials of the electrode 200 and the sensing layer 300 are specified so that they react specifically to formaldehyde or have a significantly higher sensitivity to formaldehyde than to other volatile organic compounds.

[0051] 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.

[0052] Therefore, the material for forming the sensing layer 300 of the gas sensor 10 of the present invention is selected to be a compound of an oxide of an alkali metal element or an oxide of an alkaline earth metal element and tin oxide (SnO2).

[0053] The alkali metal element may include at least one element selected from the group consisting of Li, Na, K, Rb, Cs, and Fr. The alkaline earth metal element may include at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

[0054] 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.

[0055] That is, it is found that the gas sensor 10 of the present invention has a sensitivity to formaldehyde A between 20% and 70%, while most of the concentrations of ethanol (B) and toluene (C) are less than 10% or barely exceed 10%.

[0056] 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.

[0057] When the sensing layer 300 is made of Mg--SnO2 and the electrode 200 is made of ITO, which will be described later, the sensitivity of the gas sensor 10 at formaldehyde A concentrations of 0.03 ppm to 0.30 ppm is 20 to 60%.

[0058] However, the sensitivity of the gas sensor 10 of the present invention was very low at 2.3% for a concentration of 1 ppm of ethanol B. This sensitivity corresponds to a sensitivity of 0.01 ppm or less when converted into formaldehyde.

[0059] 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.

[0060] As a result, the gas sensor 10 of the present invention can detect, for example, 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. Also, 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 the gas sensor 10 of the present invention has selectivity for formaldehyde.

[0061] The gas sensor 10 of the present invention can specifically sense formaldehyde A by making the sensing layer 300 from an oxide of an alkali metal element or a compound of an oxide of an alkaline earth metal element and tin oxide.

[0062] Meanwhile, the gas sensor 10 of the present invention does not need to apply other metal elements to the sensing layer 300. Conventional gas sensors apply various other metal elements as the sensing material, 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.

[0063] In addition, when metals other than alkali metals and alkaline earth metals were used as the material for the sensing layer 300, experimental results showed that the material reacted specifically only to formaldehyde as shown in FIG. 3, or the sensitivity to formaldehyde was higher than that to ethanol and toluene.

[0064] In addition, the gas sensor 10 of the present invention can exclude nickel and nickel oxide from the alkali metal elements. The conventional 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 sensor, SnO2-NiO is used as the material of the sensing layer, and gold (Au) is used as the electrode. When the formaldehyde concentration is 0.03 ppm to 0.20 ppm as shown in FIG. 1, the sensitivity of the conventional sensor is 26 to 61%. However, the sensitivity of the conventional sensor to ethanol at a concentration of 1 ppm is 68%, which is even greater than the sensitivity to formaldehyde.

[0065] As a result, in the conventional sensor, when the sensing material contains a nickel compound, the response or sensitivity to ethanol is greater, so that when formaldehyde and ethanol are present together in the air or indoors, the sensor cannot distinguish between formaldehyde and ethanol. 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 formaldehyde, but react more strongly to gases made of organic compounds having other functional groups.

[0066] That is, nickel reacts more easily, strongly and quickly to ethanol 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 omitted.

[0067] 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 generated in the process of metal ions and oxygen ions forming a non-stoichiometric composition from a stoichiometric composition act as donors or acceptors.

[0068] 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 incorporated into the lattice structure of the sensing layer 300.

[0069] 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.

[0070] 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.

[0071] In addition, the formaldehyde A contained in the sensing layer 300 may 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 in the sensing layer 300 may be amplified and transferred to the electrode unit 200, and the capacitance or electrical resistance of the electrode 200 may be changed.

[0072] As a result, the gas sensor 10 of the present invention can detect even a small amount 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.

[0073] In other words, ethanol B can contact the sensing layer 300, but cannot enter the lattice structure inside the sensing layer 300. Furthermore, ethanol B cannot undergo a strong redox reaction with the sensing layer 300.

[0074] Therefore, a volatile organic compound 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 .

[0075] 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.

[0076] Meanwhile, experimental results show that the above-mentioned effects are exhibited or enhanced when the electrode 200 of the gas sensor 10 of the present invention is made of indium tin oxide (ITO). This means that when the electrode 200 is made of a general gold (Au) or platinum (Pt) compound, there is a risk that the reception sensitivity of the specific capacitance change and electron transfer occurring in the sensing layer 300 may decrease.

[0077] Specifically, the electrode 200 may be made of a metal oxide containing at least one element selected from the group consisting of Ti, Zn, In, and Sn, and may not contain gold (Au) or platinum (Pt).

[0078] The sensing layer 300 may 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.

[0079] In addition, the area of ​​the sensing layer 300 exposed to the atmosphere or indoor air can be maximized, thereby further improving the formaldehyde sensing performance.

[0080] 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 specifically reacting with formaldehyde, so that it may not be necessary to cover the entire electrode 200.

[0081] 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 with the sensing layer 300. The exposed portion of the electrode 200 is called the exposed region I, and the region covered with the sensing layer 300 is called the blocked region II.

[0082] 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 for forming the sensing layer 300.

[0083] Furthermore, by providing the exposed region I, it is possible to easily check whether the electrode 200 is correctly installed and whether the electrode 200 operates 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.

[0084] FIG. 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. Therefore, as long as the electrode unit 200 can be connected by the sensing layer 300, the gas sensor 10″ can function normally regardless of the position of the sensing layer 300.

[0085] 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 includes a first electrode 210 and a second electrode 220 that are paired and spaced apart from each other by a predetermined distance. Here, the first electrode 210 and the second electrode 220 may be connected to the outside via separate lead wires (not shown).

[0086] In addition, the electrode 200 itself does not react with formaldehyde A or volatile organic compounds, so it may be exposed to indoors or the atmosphere. In consideration of this, the electrode 200 is formed on the sensing layer 300.

[0087] 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 may be formed on the surface of the sensing layer 300. As the first electrode 210 and the second electrode 220 are formed on the sensing layer 300 in this manner, it is possible to ensure that the first electrode 210 and the second electrode 220 are connected to each other by the sensing layer 300.

[0088] In this embodiment, the entire outer surface of the first electrode 210 and the second electrode 220 is exposed to the outside except for the surface where the first electrode 210 and the second electrode 220 are attached to the sensing layer 300. Therefore, it may be easier to connect a lead wire 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 a manufacturing process, and it may be relatively easy to perform maintenance after manufacturing.

[0089] Next, Fig. 7 shows that a heater 400 is added to the embodiment shown in Fig. 2. Here, for convenience of explanation, the same reference numerals as those in the embodiment shown in Fig. 2 are used, and the heater 400 is added.

[0090] 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 to the surface on which the electrode 200 is located, as shown in FIG. 7. However, the heater 400 may be located on the surface on which the electrode 200 is located, surrounding the electrode 200.

[0091] An embodiment of a method for manufacturing the gas sensor 10 of the present invention will be described below. For convenience of explanation, the gas sensor 10 shown in FIG.

[0092] 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-SnO2) is used.

[0093] The production of Mg-SnO2 is explained. Tin chloride (SnCl2) and an aqueous solution of magnesium sulfate are reacted. Here, the content of Sn and Mg can be set to Sn:Mg=20:1 in molar ratio. A precipitate can be obtained by dropping ammonia water into this aqueous solution.

[0094] 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.

[0095] 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.

[0096] After the sensing layer 300 is formed, it can be heat treated at 500°C.

[0097] Measurement of gas response using the gas sensor 10 of the present invention will be described. 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.

[0098] 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%.

[0099] The resistance value of the gas sensor 10 was obtained by applying a voltage via wiring installed in the electrometer sensor element and measuring the current.

[0100] The gas sensor 10 of the present invention can be used in various 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 generated and perform the necessary operations accordingly.

[0101] The present invention can be implemented in various forms, but the scope of the invention is not limited to the above-described embodiments. Therefore, if the modified embodiments include elements of the claims of the present invention, they should be understood to fall within the scope of the present invention. [Explanation of symbols]

[0102] 10, 10', 10" Gas Sensor 100 Substrates 200 electrodes 210 1st electrode 220 2nd electrode 300 sensing layer 400 Heater

Claims

1. 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—SnO ２ It is composed of The sensing layer is disposed between the substrate and the electrode.

2. 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.

3. 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.

4. 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); Mg-SnO ２ forming the sensing layer using The sensing layer is formed by applying a mixed solution of pure water and glycerin in which Mg--SnO 2 is dispersed, and heating the mixture at a predetermined temperature.

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