Gas sensor and manufacturing method thereof

Abstract

The present invention relates to a gas sensor and a method for manufacturing the same. The gas sensor of the present invention includes an electrode (20), a sensing layer (30), and an anti-interference layer (40) formed on a substrate (10). The sensing layer (30) can be made of either an alkali metal or an alkaline earth metal and a metal oxide, and the anti-interference layer (40) can be made of silica impregnated with platinum. The anti-interference layer (40) can prevent, for example, ethanol, a volatile organic compound, from reacting with the sensing layer, thereby enabling formaldehyde to be detected with high sensitivity by the sensing layer.

Description

[Technical Field]

[0001] The present invention relates to a gas sensor for detecting the presence of formaldehyde gas and a method for manufacturing the same. [Background technology]

[0002] Immediately after a new building or renovation, people may experience eye irritation, headaches, allergies, and other physical problems. This is called sick building syndrome, and 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, and plywood, and is released when these materials are used indoors, causing problems. It is not possible to completely avoid the use of these materials, and when volatile organic compounds, including formaldehyde, are released, they have many adverse effects on indoor occupants.

[0004] When considering the effects of formaldehyde on the human body, an airborne concentration of around 0.04 ppm can trigger nerve tissue irritation, potentially causing atopic dermatitis in sensitive children. At 0.05-1.0 ppm, the odor can be detected. This concentration is the indoor standard in Canada and California. At an airborne concentration of around 0.2 ppm, eye irritation begins, and at 0.25-0.33 ppm, respiratory problems can occur. 0.5 ppm is the minimum level at which throat irritation begins and is the maximum level permitted by the Korean Society of Occupational Hygiene. At 2.0-3.0 ppm, eye stinging occurs, and at 4.0 ppm, tears can occur. At 10.0-20.0 ppm, intense tears occur and normal breathing becomes difficult. At 30.0 ppm or higher, acute poisoning can occur within minutes, potentially leading to death from toxic emphysema.

[0005] For reference, the indoor environmental standard set by the International Health Organization (WHO), Japan, etc. 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] The structure of Japanese Patent No. 3854358, which is Prior Document 1, is shown in Figure 1. This is a gas sensor that detects both volatile organic compounds and formaldehyde with high sensitivity. Prior Document 1's structure includes gold electrodes 4A and 4B formed on the surface of a substrate 1, with a sensing layer 6 formed between them as a sensing material. The resistance value formed between the gold electrodes 4A and 4B is detected via a lead wire 5. A heater 3 is formed on the back surface of the substrate 1 and provides heating during gas sensor operation. The heater 3 receives power from an external source via a lead wire 5' via heater lands 2A and 2B. Electrode lands 4A' and 4B' are formed on the back surface of the substrate 1 and are electrically connected to the gold electrodes 4A and 4B on the front surface of the substrate 1. Lead wires 5 are connected to these electrode lands 4A' and 4B' to exchange signals with the external source.

[0007] The sensing layer 6 is made of tin oxide (SnO2) or a tin oxide-alumina oxide mixture doped with at least one of Gd and Nd, and is also provided with a material doped with organic silica or alumina sol. Using the sensing material SnO2 doped with Pd, Gd, and organic silica, a sensitivity of 20% was achieved for 0.1 ppm of formaldehyde (calculated as a percentage of resistance change). Meanwhile, the sensitivity was also 25% for 0.1 ppm of VOCs. Thus, while both formaldehyde and VOCs are detected with high sensitivity, the selectivity for formaldehyde is relatively low.

[0008] Prior literature 2 includes "Study on a micro-gas sensor with SnO2-NiO sensitive film for indoor formaldehyde detection" (Sensors and Actuators B vol. 132, (2008) pp. 74-80), in which a formaldehyde sensor with a MEMS structure was fabricated using tin oxide-nickel oxide as the sensing material.

[0009] The sensitivity to 0.06 ppm formaldehyde is 1.6%, and the sensitivity to 1 ppm ethanol is less than 0.1%. The sensitivity ratio between formaldehyde and ethanol is large at over 10, suppressing interference from ethanol gas. However, there is a problem in that the sensitivity to formaldehyde is relatively low.

[0010] On the other hand, other volatile organic compound gases such as alcohol may exist in the atmosphere, and when sensing the concentration of formaldehyde gas, these other volatile organic compound gases may become interference gases. Therefore, a gas sensor that can sense only the concentration of formaldehyde gas without being affected by other volatile organic compound gases is required. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a gas sensor for detecting formaldehyde in volatile organic compounds.

[0012] An object of the present invention is to provide a gas sensor that provides both high sensitivity and high selectivity for formaldehyde among volatile organic compounds.

[0013] An object of the present invention is to provide a gas sensor that detects formaldehyde while suppressing the influence of interfering gases in volatile organic compounds.

[0014] An object of the present invention is to provide a method for manufacturing a gas sensor for detecting formaldehyde in volatile organic compounds.

[0015] It is an object of the present invention to provide a method for manufacturing a gas sensor that provides both high sensitivity and high selectivity to formaldehyde among volatile organic compounds.

[0016] An object of the present invention is to provide a method for manufacturing a gas sensor that detects formaldehyde while suppressing the influence of interfering gases in volatile organic compounds. [Means for solving the problem]

[0017] To achieve the above object, the present invention is provided with a sensing layer for detecting formaldehyde.

[0018] In the present invention, an interference prevention layer is provided to block the influence of interfering gases in order to selectively detect formaldehyde.

[0019] The present invention includes a heater that provides heat for selectively detecting formaldehyde.

[0020] The present invention can include a substrate, at least two electrodes provided on the substrate, a sensing layer connecting the electrodes and comprising a compound of an alkali metal or alkaline earth metal and a metal oxide, and an anti-interference layer formed on the sensing layer and made of a material including silica impregnated with a platinum-based element.

[0021] The metal oxide constituting the sensing layer may comprise (comprise; constitute; construct; set; encapsulate; include; contain; have) at least one element selected from Ti, Zn, In, and Sn.

[0022] The alkali metal element may be at least one element selected from Li, Na, K, Rb, and Cs, and the alkaline earth metal element may be at least one element selected from Be, Mg, Ca, Sr, Ba, and Ra.

[0023] The platinum group element may be at least one selected from Ru, Rh, Pd, Os, Ir, and Pt.

[0024] The content of the alkali metal element or alkaline earth metal element may be 0.01 atm % to 30 atm %.

[0025] The content of the platinum-based element constituting the interference prevention layer may be 0.01 atm % to 30 atm %.

[0026] The electrodes can be formed of gold and at least one element from the platinum group.

[0027] The anti-interference layer can be made of Pd-SiO2.

[0028] The substrate may further include a heater for providing heat.

[0029] The heater may be provided on the surface of the substrate on which the electrodes, the sensing layer, and the anti-interference layer are formed.

[0030] The heater may be provided on the surface opposite to the substrate on which the electrodes, sensing layer, and anti-interference layer are formed.

[0031] The present invention can include a substrate made of glass, alumina, or silicon; at least two electrodes provided on one surface of the substrate and having a plurality of electrode branches arranged alternately side by side; a sensing layer connecting the electrode branches and containing an alkali metal or alkaline earth metal and a metal oxide; and an anti-interference layer formed on the sensing layer and made of a material containing silica impregnated with a platinum-based element.

[0032] The platinum group element forming the interference prevention layer may be at least one selected from Ru, Rh, Pd, Os, Ir, and Pt.

[0033] The material for forming the interference prevention layer can be Pd-SiO2.

[0034] The anti-interference layer may have a thickness of 1 μm to 100 μm.

[0035] The metal oxide constituting the sensing layer may contain at least one element selected from Ti, Zn, In, and Sn.

[0036] The alkali metal element may be at least one element selected from Li, Na, K, Rb, and Cs, and the alkaline earth metal element may be at least one element selected from Be, Mg, Ca, Sr, Ba, and Ra.

[0037] The present invention provides a method for manufacturing a gas sensor having a sensing layer formed to connect electrodes formed on a substrate, which may include the steps of: forming an electrode using at least one element selected from Au or a platinum-based element; forming the sensing layer using an alkali metal oxide or a compound of an alkaline earth metal oxide and a metal oxide; and forming an anti-interference layer on the sensing layer to block reaction between the sensing layer and volatile organic compounds.

[0038] The metal oxide may contain at least one element selected from Ti, Zn, In, and Sn.

[0039] The metal oxide may be tin oxide.

[0040] The anti-interference layer can be made of a material including silica impregnated with a platinum group element.

[0041] The anti-interference layer can be made of a material including palladium (Pd)-impregnated silica (Pd-SiO2).

[0042] The Pd-SiO2 can be formed by adding tin(IV) chloride pentahydrate as a binder to an aqueous solution of palladium(II) chloride dissolved in pure water, adding fumed silica to the aqueous solution, drying it in the air at a predetermined temperature, and firing it at a predetermined temperature. [Effects of the Invention]

[0043] The gas sensor and the manufacturing method thereof according to the present invention can have at least one of the following effects.

[0044] The present invention enables the detection of formaldehyde among volatile organic compounds by using an oxide containing at least one element selected from Ti, Zn, In, and Sn as an oxide containing an alkali metal or alkaline earth metal as the material of the sensing layer.

[0045] In particular, in the present invention, an oxide of an alkali metal or alkaline earth metal containing tin oxide is used as the material of the sensing layer, which has the effect of enabling formaldehyde to be detected with higher sensitivity.

[0046] Furthermore, in the present invention, an anti-interference layer for blocking the detection of interfering gases is provided on the sensing layer made of the above material, which blocks the influence of interfering gases and allows only formaldehyde to be detected with relatively high sensitivity.

[0047] In particular, in the present invention, the anti-interference layer uses silica impregnated with a platinum-based element, which has the effect of blocking the influence of alcohol-based interfering gases including ethanol while enabling formaldehyde to be detected with high sensitivity.

[0048] The present invention also provides Pd-SiO2 as a material for forming an anti-interference layer by impregnating silica (SiO2) with a platinum-based element. The material for forming the anti-interference layer is applied to the sensing layer, followed by drying and firing processes to form the anti-interference layer. When the anti-interference layer is formed in this manner, it forms on the sensing layer without peeling, suppressing the detection of interfering gases and enabling highly sensitive detection of formaldehyde. [Brief explanation of the drawings]

[0049] [Figure 1] 1A and 1B are diagrams showing the configuration of a gas sensor according to a conventional technique, in which (a) is a perspective view showing the surface of the gas sensor, and (b) is a perspective view showing the bottom surface of the gas sensor. [Figure 2] 1 is a schematic cross-sectional side view showing the configuration of a preferred embodiment of a gas sensor according to the present invention. [Figure 3] 3 is a plan view showing the configuration of the embodiment shown in FIG. 2 with the upper surface of the substrate as a reference. [Figure 4] 3 is a bottom view showing the configuration of the embodiment shown in FIG. 2 with the bottom surface of the substrate as the reference. [Figure 5] FIG. 10 is a plan view showing another embodiment of the present invention in which both an electrode and a heater are provided on one surface side of a substrate. [Figure 6] FIG. 10 is a schematic cross-sectional view showing another embodiment of the present invention, in which a MEMS system is adopted and a heater and an electrode are provided in an area where they overlap each other. [Figure 7] FIG. 7 is a plan view showing the configuration of important parts of the embodiment shown in FIG. 6. [Figure 8] FIG. 7 is a plan view showing the configuration of the embodiment shown in FIG. 6. [Figure 9] FIG. 10 is a schematic cross-sectional view showing another embodiment of the present invention in which a MEMS system is adopted and a heater and an electrode are provided in a region where they do not overlap. [Figure 10] FIG. 10 is a plan view showing the configuration of important parts of the embodiment shown in FIG. 9. [Figure 11] FIG. 10 is a plan view showing the configuration of the embodiment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0050] Hereinafter, several embodiments of the present invention will be described in detail with reference to the accompanying drawings. When assigning reference numerals to components in each drawing, it should be noted that identical components are assigned the same numerals as much as possible, even if they are displayed in different drawings. Furthermore, when describing the embodiments of the present invention, if a detailed description of related known structures or functions is deemed to hinder understanding of the embodiments of the present invention, such detailed description will be omitted.

[0051] The configuration of an embodiment of the present invention is shown in a schematic cross-sectional view in FIG. 2. There is a substrate 10 that forms a base. The substrate 10 is a plate having a predetermined shape. In this embodiment, the substrate 10 is a glass substrate having dimensions of 10 mm wide, 12 mm long, and 0.7 mm thick. However, the dimensions of the substrate 10 can vary. The substrate 10 may be an alumina substrate or a silicon substrate.

[0052] An electrode 20 is formed on the substrate. The electrode 20 may be two electrodes 20 corresponding to each other. The electrode 20 is formed in a pattern on the substrate 10. The electrode 20 may be made of platinum (Pt), for example. However, the electrode 20 may be made of a different material depending on the required electrical conductivity. The material of the electrode 20 may be at least one selected from gold (Au) or platinum group elements such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).

[0053] In the present invention, the gas concentration can be sensed by sensing the current flowing between the two electrodes 20, sensing a change in the current flowing through the electrodes 20, or sensing a change in the electrical resistance or capacitance of the electrodes 20.

[0054] The configuration of the electrode 20 will be described in more detail. The electrode 20 has an electrode body 22, and electrode branches 23 may be provided on the electrode body 22 to extend toward the opposing electrode body 22. A plurality of the electrode branches 23 may be provided side by side. In the embodiment shown in FIG. 3, six electrode branches 23 extend from each electrode body 22. The electrode branches 23 provided on each of the two electrodes 20 may be alternately formed and extend side by side. The electrode branches 23 may be provided perpendicular to the electrode body 22.

[0055] Electrode lands 24, 24' are provided for connecting the electrode 20 to the outside. The electrode land 24 may be exposed to one side of the surface of the substrate 10. A lead wire 26 may be connected to the electrode land 24, thereby electrically connecting the electrode to the outside.

[0056] However, in the illustrated embodiment, a lead wire 26 is connected to the electrode land 24' on the back surface of the substrate 10, among the electrode lands 24, 24'. To this end, a through hole 25 is formed in the substrate 10, and the electrode land 24' is formed on the back surface of the substrate 10. The electrode lands 24, 24' can be electrically connected by plating the inner surface of the through hole 25 with an electrode material. FIG. 4 shows that the lead wire 26 is connected to the electrode land 24' formed on the back surface of the substrate 10.

[0057] When the lead wire 26 is attached to the electrode land 24' by wire bonding, the surface of the electrode land 24' may be coated with a material having better electrical conductivity than the material of the electrode land 24'.

[0058] Here, the electrode 20, more precisely the electrode branch 23, may have a width of 5 μm to 20 μm and a thickness of 10 nm to 1 μm, and the spacing between the electrode branch 23 may have a value of 2 μm to 100 μm.

[0059] The sensing layer 30 may be formed to connect the electrodes 20. The material forming the sensing layer 30 has an inherent resistance, but when it reacts with formaldehyde, its electrical properties, such as resistance, change. That is, as the sensing layer 30 and formaldehyde undergo an oxidation-reduction reaction, the sensing layer 30 can transfer electrons to the electrode 20 or receive electrons from the electrode 20. In other words, when the sensing layer 30 reacts with formaldehyde, the penetration of formaldehyde causes a change in the molecular configuration structure of the sensing layer 30, which may change the overall charge capacity.

[0060] The sensing layer 30 may be made of a material capable of sensing formaldehyde. The sensing layer 30 may also react with other volatile organic compounds in addition to formaldehyde. That is, some volatile organic compounds may have the same reactivity as formaldehyde with the material of the sensing layer 30. For this reason, the anti-interference layer 40 described below inhibits the reaction of volatile organic compounds other than formaldehyde.

[0061] The sensing layers 30 may be formed to be connected to the corresponding electrodes 20. More specifically, the sensing layers 30 may be formed to connect the electrode branches 23 to each other.

[0062] The material forming the sensing layer 30 is an oxide containing an alkali metal element or alkaline earth metal element and at least one element selected from Ti, Zn, In, and Sn, where the alkali metal can be at least one of Li, Na, K, Rb, and Cs, and the alkaline earth metal can be at least one of Be, Mg, Ca, Sr, Ba, and Ra.

[0063] In this embodiment, the sensing layer 30 is made of tin oxide (Mg-SnO2) containing Mg, an alkaline earth metal. The content of the alkali metal element and alkaline earth metal element in the sensing layer 30 is, for example, 0.01 atm% to 30 atm%. The lower limit of the sensing layer 30 is set to 0.01 atm% because a lower value makes it difficult for the sensing layer 30 to function properly. The upper limit of the sensing layer 30 is set to 30 atm% because a higher value would result in too much alkali metal or alkaline earth metal, preventing at least one element selected from Ti, Zn, In, and Sn from functioning properly. To ensure more stable operation of the sensing layer 30, the content of the alkali metal element and alkaline earth metal element can be set to 0.1 atm% to 10 atm%.

[0064] The sensing layer 30 may be applied in the form of a film and fired to connect the pair of electrodes 20, i.e., the electrode branches 23. The sensing layer 30 does not need to cover the entire electrode branches 23, and may be partially visible from the outside. The thickness of the sensing layer 30 may be 0.1 μm to 50 μm. If the thickness of the sensing layer 30 is less than 0.1 μm, the sensing layer 30 will not function properly. If the thickness of the sensing layer 30 is greater than 50 μm, the overall thickness of the sensing layer 30 will increase and the size of the sensor will increase, occupying a large amount of space without improving the performance of sensing the formaldehyde concentration.

[0065] An anti-interference layer 40 may be formed to cover the sensing layer 30. The anti-interference layer 40 is made of silica impregnated with a platinum-based element. In an embodiment of the present invention, the anti-interference layer 40 is made of silica (Pd-SiO2) impregnated with palladium (Pd). The silica is preferably fine particles. The thickness of the anti-interference layer 40 may be 1 μm to 100 μm. The reason why the lower limit of the anti-interference layer 40 is 1 μm is that if the anti-interference layer 40 is thinner than this, it will not function as an anti-interference layer 40. The reason why the upper limit of the anti-interference layer 40 is 100 μm is that if the anti-interference layer 40 is thicker than this, the function of the sensing layer 30 will be reduced due to the anti-interference layer 40.

[0066] A pattern may be formed on the rear surface of the substrate 10 to serve as a heater 50. FIG. 4 shows a patterned heater 50. The heater 50 may function to heat the electrodes 20 and the sensing layer 30.

[0067] The heater 50 has a heater body 52 formed in a predetermined region of the substrate 10. As shown in FIG. 4, the heater body 52 is provided so as to extend alternately from left to right so as to cover as wide an area as possible. The heater body 52 may have a width of 10 μm to 500 μm and a thickness of 0.1 μm to 1 μm. In the illustrated embodiment, the heater body 52 extends alternately from left to right, but may have various other shapes, such as a spiral shape.

[0068] In this embodiment, platinum (Pt) is used as the material for making the heater 50. However, any platinum group element can be used as the material for making the heater 50. Platinum group elements include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), and the material for making the heater 50 can be at least one of these platinum group elements.

[0069] An adhesive contact layer (not shown) may be present between the substrate 10 and the heater 50. For example, at least one of Ti and Cr may be used as the material for the adhesive contact layer.

[0070] Heater lands 54 for supplying power are provided on both ends of the heater body 52. ​​Lead wires 56 are connected to the heater lands 54 so that they can be connected to an external power source. In the illustrated embodiment, the heater lands 54 are rectangular, but they may have various shapes. The heater lands 54 are exposed on the back surface of the substrate 10. That is, the heater body 52 may be configured to be covered with, for example, a protective layer (not shown) with good thermal insulation properties. Of course, in FIG. 2, the heater body 52 is exposed on the back surface of the substrate 10.

[0071] When the lead wire 56 is wire-bonded to the heater land 54, the surface of the heater land 54 can be coated with a material having electrical conductivity superior to that of the material of the heater land 54. This is to improve the electrical conductivity between the heater land 54 and the lead wire 56.

[0072] Meanwhile, FIG. 5 shows another embodiment of the present invention. In this embodiment, the electrode 120, sensing layer 130, anti-interference layer 140, and heater 150 are all located on one surface of the substrate 110. In particular, the heater body 152 of the heater 150 is configured to surround the areas where the electrode 120, sensing layer 130, and anti-interference layer 140 are formed. In the illustrated embodiment, the heater body 152 forms a double rectangle in a plan view. However, the shape of the heater body 152 may be various, such as a circle.

[0073] The sensing layer 120 may be formed to cover an area where the electrode body 122 and the electrode branch portion 123 constituting the electrode 120 are arranged, and the anti-interference layer 130 may be formed to cover the sensing layer 120. In the illustrated embodiment, the sensing layer 130 and the anti-interference layer 140 do not cover the area where the heater body 122 is formed, but this is not necessarily the case, and the sensing layer 130 and the anti-interference layer 140 may cover the heater body 122.

[0074] The electrode 120 has an electrode land 124 on one surface of the substrate 110, and a lead wire 126 is connected to the electrode land 124. The heater 150 has a heater land 154 on one surface of the substrate 110, and a lead wire 156 is connected to the heater land 154. Here, the electrode land 124 and the heater land 154 are formed on the same surface of the substrate 110.

[0075] 6 to 8 show an embodiment of the MEMS type. A substrate 210 made of a silicon material can be used. A cavity 212 can be formed in the substrate 210. In this embodiment, the cavity 212 is formed to be open to the surface of the substrate 210. However, the cavity 212 may also be formed to penetrate the substrate 210 from top to bottom. Since air can be present in the cavity 212, it is possible to minimize the loss of heat generated by a heater 250 (described below) through the cavity of the substrate 210.

[0076] Meanwhile, the substrate 210 does not necessarily have to have the cavity 212. That is, instead of the cavity 212, the region of the substrate 210 corresponding to the cavity 212 may be made of a material with very low heat conductivity.

[0077] The substrate 210 may have insulating layers 214, 214' on its surface. The insulating layers 214, 214' may include a first insulating layer 214 and a second insulating layer 214'. The insulating layers 214, 214' have a base 215 located in the cavity 212 and a plurality of bridges 216 extending from the base 215. The bridges 216 extend to and are fixed to the edges of the substrate 210, thereby supporting the base 215 above the cavity 212. An electrode branch 223, a sensing layer 230, an anti-interference layer 240, and a heater 250, which will be described later, may be provided on the base 215.

[0078] The portion where the base 215 and a part of the bridge portion 216 exist is a region corresponding to the cavity 212 of the substrate 210, and is the portion remaining after forming the opening 218. Of course, the opening 218 does not have to be formed in the insulating layers 214 and 214'. In this case, the cavity 212 may be blocked by the insulating layers 214 and 214'. However, the cavity 212 may be open downward.

[0079] The insulating layers 214, 214' may be made of an electrically insulating material such as SiO2 or Si3N4, and may have a thickness of, for example, 0.5 μm to 10 μm. The insulating layers 214, 214' support the electrodes 230, the sensing layer 230, the anti-interference layer 240, the heater 250, etc., on the cavity 212 of the substrate 210.

[0080] A heater 250 may be formed on the first insulating layer 214 of the substrate 210. The heater 250 may include a heater body 252 and a heater land 254, as described in the above embodiment. The heater body 252 may be formed on a base 215 of the first insulating layer 214, extend along the bridge portion 216, and be connected to the heater land 254 as shown in FIG. 8. A lead wire 256 may be bonded to the heater land 254 to allow connection to the outside.

[0081] The second insulating layer 214' may be formed on the first insulating layer 214. The second insulating layer 214' also includes a base 215 and a bridge portion 216, but an electrode 220 is formed on the base 215. The electrode 220 has a configuration similar to that described in the above embodiment, including an electrode body 222, a plurality of electrode branches 223, and an electrode land 224. The shapes of the electrode body 222 and the electrode branches 223 are as shown in FIG. 3. However, in this embodiment, the electrode body 222 extends in different directions for connection to the electrode land 224. That is, the two electrode bodies 222 extend in different directions along the bridge portion 216 and are connected to the electrode land 224. Lead wires 226 are bonded to the electrode lands 224, allowing connection to the outside.

[0082] A sensing layer 230 may be formed on the electrode body 222 and the electrode branch portions 223. The configuration of the sensing layer 230 is the same as that described in the above embodiment. The sensing layer 230 is formed to connect the electrode branch portions 223, but does not necessarily cover the entire electrode branch portions 223.

[0083] An anti-interference layer 240 is formed on the sensing layer 230. The anti-interference layer 240 covers the sensing layer 230. The configuration of the anti-interference layer 240 is the same as that described in the above embodiment.

[0084] In this embodiment, the region where the heater body 252 of the heater 250 exists overlaps with the region where the electrode body 222 and the electrode branch portion 223 exist when the substrate 210 is viewed from above. However, in the embodiment shown in Figures 9 to 11 described below, these regions do not overlap with each other.

[0085] Another embodiment of the present invention will be described with reference to Figures 9 to 11. This embodiment is an MEMS type in which the area where the heater 350 is provided does not overlap with the areas where the electrodes 320, sensing layer 330, and anti-interference layer 340 are provided. In other words, the heater 350 is disposed surrounding the areas where the electrodes 320, sensing layer 330, and anti-interference layer 340 are provided.

[0086] The substrate 310 may be made of a silicon material. A cavity 312 may be formed in the substrate 310. Of course, the cavity 312 is not necessarily required. That is, instead of the cavity 312, the area of ​​the substrate 310 corresponding to the cavity 312 may be made of a material with very low thermal conductivity.

[0087] Furthermore, the cavity 312 may be present but the insulating layer 314 may not have the through-hole 318. In this case, the cavity 312 may be blocked by the insulating layer 314. Furthermore, the cavity 312 may be open at the bottom.

[0088] In this embodiment, the cavity 312 is formed to be open to the surface of the substrate 310. However, the cavity 312 may be formed to penetrate the substrate 310 from top to bottom. Since there may be air in the cavity 312, it is possible to minimize the loss of heat generated by a heater 350 (described below) through the substrate 310.

[0089] An insulating layer 314 is provided on the surface of the substrate 310. The insulating layer 314 includes a base 315 located at a position corresponding to the cavity 312 and a plurality of bridges 316 extending from the base 315. The bridges 316 are fixed to and extend to the edge of the substrate 310, thereby supporting the base 315 above the cavity 312. The base 315 may be provided with an electrode branch 323, a sensing layer 330, an anti-interference layer 340, and a heater 350, which will be described later. The bridges 316 are located within openings 318 formed in the insulating layer 314 at positions corresponding to the cavity 312. The base 315 and a portion of the bridges 316 are located in the region of the substrate 310 corresponding to the cavity 312, which is the remaining portion after the openings 318 are formed. The insulating layer 314 may be made of an electrically insulating substance such as SiO2 or Si3N4, and may have a thickness of, for example, 0.5 μm to 10 μm.

[0090] The electrode 320, the sensing layer 330, the anti-interference layer 340, and the heater 350 may be provided on the insulating layer 314 of the substrate 310. First, the electrode 320 is formed in the central region of the base 315. The configuration of the electrode 320 is substantially the same as that described in the above embodiment. The electrode 320 includes an electrode body 322, a plurality of electrode branches 323, and an electrode land 324. The shapes of the electrode body 322 and the electrode branches 323 are as shown in FIG. 3. However, in this embodiment, the electrode body 322 extends to connect to the electrode land 324, but may be provided by extending to one bridge portion 316. That is, two electrode bodies 222 ultimately extend in the same direction along the bridge portion 316 and connect to the electrode land 324. A lead wire 326 (see FIG. 11) is bonded to the electrode land 324, thereby enabling connection to the outside.

[0091] A sensing layer 330 may be formed on the electrode body 322 and the electrode branches 323. The configuration of the sensing layer 330 is the same as that described in the above embodiment. The sensing layer 330 is formed to connect the electrode branches 323, but does not necessarily cover the entire electrode branches 323.

[0092] An anti-interference layer 340 is formed on the sensing layer 330. The anti-interference layer 340 covers the sensing layer 330. The configuration of the anti-interference layer 340 is the same as that described in the above embodiment.

[0093] The heater 350 may be formed along the edge of the base 315. Alternatively, the heater 350 may be formed to surround the area where the electrode body 322 and the electrode branch 323 are formed, or the area where the sensing layer 330 and the anti-interference layer 340 are formed.

[0094] As described in the above embodiment, the heater 350 may include a heater body 352 and a heater land 354. The heater body 352 may be formed on a base 315 of the insulating layer 314, extend along a bridge portion 316 on one side, and be connected to the heater land 354 as shown in Fig. 11. A lead wire 356 may be bonded to the heater land 354 to allow connection to the outside.

[0095] The manufacturing method of the gas sensor of the present invention having the above-described configuration will be described in detail below. For convenience of explanation, the description will be made with reference to the embodiment shown in FIGS.

[0096] In a preferred embodiment of the gas sensor of the present invention, the substrate 10 is a glass substrate, the electrode 20 is made of a material containing platinum (Pt), the sensing layer 30 is made of tin oxide containing magnesium (Mg-SnO2), and the anti-interference layer 40 is made of Pd-SiO2.

[0097] First, we will explain how to prepare the Mg-containing tin oxide (Mg-SnO2) that forms the sensing layer 30. An aqueous solution containing 2.0 g of tin(II) chloride dihydrate and 0.02 g of magnesium sulfate is prepared. Ammonia water is added dropwise to the solution to obtain a precipitate. The precipitate is washed with pure water and then dried in the air. The dried powder is calcined at a temperature of approximately 800°C to obtain Mg-SnO2.

[0098] Next, we will explain how to prepare the Pd-SiO2 for the anti-interference layer 40. An aqueous solution is prepared by dissolving 0.005 g of palladium (II) chloride in pure water, and 0.035 g of tin (IV) chloride pentahydrate is added as a binder. 0.05 g of fumed silica is added to this aqueous solution, which is then dried in the air at around 100°C. It is then fired at around 500°C.

[0099] The manufacturing method of the gas sensor of the present invention will be described. For example, a Pt thin film is formed on a glass substrate using Ti as an adhesive layer. Here, the Pt thin film forms an electrode 20 in a comb-shaped pattern with multiple electrode branches 23. That is, multiple electrode branches 23 are arranged side by side to form a comb shape. The pattern formation can be performed by any of photolithography, sputter deposition, and lift-off processes.

[0100] The sensing layer 30 was formed by dispersing Mg-SnO2 powder in a pure water / glycerin mixed solution, applying it to the electrode branch 23, drying it at about 140°C, and then heat-treating it at a temperature of around 500°C.

[0101] The anti-interference layer 40 was formed by dispersing Pd-SiO2 powder in a toluene solution, applying it to the sensing layer 20, drying it at a temperature of around 100°C, and heating it at a temperature of around 500°C.

[0102] Next, a gas response evaluation method using such a gas sensor will be described. The gas sensor manufactured as described above was installed in a gas introduction container, and a gas with an adjusted concentration was introduced. The change in the resistance value between the electrodes 20 was detected and evaluated.

[0103] The concentration-adjusted gas was generated by a permeator using pure air as a diluent gas, and the flow rate was adjusted using a mass flow controller before being introduced into the gas inlet vessel. Humidity was generated by bubbling pure water and evaluated at 54% relative humidity. Heat was generated using the heater 50 and used for heating. Resistance was monitored by applying a voltage through lead wires 26 attached to the electrometasensor element and measuring the current.

[0104] For reference, the sensing layer 30 of the present invention specifically reacts to formaldehyde. Metal oxides change from a stoichiometric composition to a non-stoichiometric composition when metal ions and non-metal ions combine. Lattice defects, which are generated during the process of metal ions and oxygen ions changing from a stoichiometric composition to a non-stoichiometric composition, act as donors or acceptors.

[0105] In the present invention, when the sensing layer 30 is composed of a compound of an alkali metal or alkaline earth metal oxide and tin oxide, formaldehyde or a formaldehyde reactor can be introduced into the lattice structure of the sensing layer 30 .

[0106] Table 1 shows the sensitivity to formaldehyde and ethanol with and without the anti-interference layer 40. Table 1 shows the concentration and sensitivity characteristics to formaldehyde and ethanol when only Mg-SnO2 is used as the material for making the sensing layer 30, and when Pd-SiO2, the material that forms the anti-interference layer 40, is combined with the sensing layer material Mg-SnO2.

[0107] [Table 1]

[0108] In Table 1, the concentrations of formaldehyde and ethanol gas are both 0.01 ppm. When there is no anti-interference layer 40 and there is a sensing layer 30 made of Mg-SnO2, the sensitivity to formaldehyde and ethanol is 25% and 24%, respectively, which are comparable to each other.

[0109] However, when the anti-interference layer 40 made of Pd-SiO2 was combined with the sensing layer 30 made of Mg-SnO2, the sensitivity to formaldehyde was 20%, which was the same as when no anti-interference layer was used, but the sensitivity to ethanol decreased to 4%. This confirms that the presence of the anti-interference layer 40 suppresses the influence of the interfering gas ethanol and enables selective detection of formaldehyde with high sensitivity. The present invention provides a gas sensor that can suppress the influence of interfering gases and detect formaldehyde with high sensitivity.

[0110] Although all components constituting the embodiments of the present invention have been described as being combined or operating in combination, the present invention is not necessarily limited to these embodiments. That is, within the scope of the present invention, all components may be selectively combined and operate in combination. Furthermore, unless otherwise specified, the terms "comprise," "comprise," "have," and the like used above mean that the component in question may be inherent, and should be interpreted as including other components rather than excluding other components. Unless otherwise defined, all terms, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Commonly used terms, such as dictionary-defined terms, should be interpreted in accordance with the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined in the present invention.

[0111] 2, the electrode 20 is formed on the substrate 10, and the sensing layer 30 is formed to cover the electrode 20. Alternatively, for example, the sensing layer 30 may be formed on the substrate 10, and the electrode 20 may be formed on the sensing layer 30. In this case, an anti-interference layer 40 may be formed to cover the sensing layer 30 and the electrode 20 (or the electrode branch portion 23).

[0112] [Claims at the time of international application] [Claim 1] A gas sensor comprising: A substrate; At least two electrodes provided on the substrate; a sensing layer connecting the electrodes and comprising a compound of an alkali metal or alkaline earth metal and a metal oxide; an interference prevention layer formed on the sensing layer and made of a material including silica impregnated with a platinum group element. [Claim 2] 2. The gas sensor according to claim 1, wherein the metal oxide constituting the sensing layer contains at least one element selected from the group consisting of Ti, Zn, In, and Sn. [Claim 3] the alkali metal element is at least one element selected from Li, Na, K, Rb, and Cs; 2. The gas sensor according to claim 1, wherein the alkaline earth metal element is at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra. [Claim 4] 2. The gas sensor according to claim 1, wherein the platinum group element is at least one selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt. [Claim 5] 2. The gas sensor according to claim 1, wherein the content of the alkali metal element or alkaline earth metal element is 0.01 atm % to 30 atm %. [Claim 6] 2. The gas sensor according to claim 1, wherein the content of the platinum group element constituting the interference prevention layer is 0.01 atm % to 30 atm %. [Claim 7] 7. The gas sensor according to claim 6, wherein the electrodes are formed of at least one element selected from the group consisting of gold and platinum-based elements. [Claim 8] 10. The gas sensor according to claim 1, wherein the anti-interference layer is made of Pd-SiO2. [Claim 9] The gas sensor according to claim 1 , further comprising a heater for providing heat to the substrate. [Claim 10] 2. The gas sensor according to claim 1, wherein the substrate is made of one of glass, alumina, and silicon. [Claim 11] 2. The gas sensor according to claim 1, wherein the electrode has a plurality of electrode branches arranged side by side on the electrode body, and the electrode branches of a pair of electrodes are arranged alternately. [Claim 12] 1. A method for manufacturing a gas sensor having a sensing layer formed to connect electrodes formed on a substrate, comprising: forming an electrode using at least one element selected from Au or a platinum-based element; forming the sensing layer from an alkali metal oxide or an alkaline earth metal oxide and a metal oxide compound; and forming an anti-interference layer on the sensing layer to block reaction between the sensing layer and volatile organic compounds. [Claim 13] 13. The method for manufacturing a gas sensor according to claim 12, wherein the metal oxide is tin oxide. [Claim 14] 13. The method for manufacturing a gas sensor according to claim 12, wherein the anti-interference layer is made of a material including palladium (Pd)-impregnated silica (Pd-SiO2). [Claim 15] The Pd-SiO2 is Palladium(II) chloride was dissolved in pure water and tin(IV) chloride pentahydrate was added as a binder; After adding fumed silica to the aqueous solution; Dry in air at a given temperature; The method for manufacturing the gas sensor according to claim 14, wherein the gas sensor is formed by firing at a predetermined temperature.

Claims

1. A gas sensor comprising: A substrate; At least two electrodes provided on the substrate; a sensing layer connecting the electrodes and comprising a compound of an alkali metal or alkaline earth metal and a metal oxide; an interference prevention layer formed on the sensing layer and made of a material including silica impregnated with a platinum group element.

2. 2. The gas sensor according to claim 1, wherein the metal oxide constituting the sensing layer contains at least one element selected from the group consisting of Ti, Zn, In, and Sn.

3. the alkali metal element is at least one element selected from Li, Na, K, Rb, and Cs; 2. The gas sensor according to claim 1, wherein the alkaline earth metal element is at least one element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

4. 2. The gas sensor according to claim 1, wherein the platinum group element is at least one selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt.

5. 2. The gas sensor according to claim 1, wherein the content of the alkali metal element or alkaline earth metal element is 0.01 atm % to 30 atm %.

6. 2. The gas sensor according to claim 1, wherein the content of the platinum group element constituting the interference prevention layer is 0.01 atm % to 30 atm %.

7. 7. The gas sensor according to claim 6, wherein the electrodes are formed of at least one element selected from the group consisting of gold and platinum-based elements.

8. The anti-interference layer is made of Pd—SiO ２ 10. The gas sensor of claim 1, wherein the gas sensor is made of

9. The gas sensor according to claim 1 , further comprising a heater for providing heat to the substrate.

10. 2. The gas sensor according to claim 1, wherein the substrate is made of one of glass, alumina, and silicon.

11. 2. The gas sensor according to claim 1, wherein the electrode has a plurality of electrode branches arranged side by side on the electrode body, and the electrode branches of a pair of electrodes are alternately arranged.

12. 1. A method for manufacturing a gas sensor having a sensing layer formed to connect electrodes formed on a substrate, comprising: forming an electrode using at least one element selected from Au or a platinum-based element; forming the sensing layer from an alkali metal oxide or an alkaline earth metal oxide and a metal oxide compound; and forming an anti-interference layer on the sensing layer to block reaction between the sensing layer and volatile organic compounds.

13. 13. The method for manufacturing a gas sensor according to claim 12, wherein the metal oxide is tin oxide.

14. The anti-interference layer is made of palladium (Pd)-impregnated silica (Pd-SiO ２ 13. The method of claim 12, wherein the gas sensor is made of a material comprising:

15. The Pd—SiO ２ teeth, Add tin(IV) chloride pentahydrate as a binder to an aqueous solution of palladium(II) chloride dissolved in pure water; After adding fumed silica to the aqueous solution; Dry in air at a given temperature; The method for manufacturing the gas sensor according to claim 14, wherein the gas sensor is formed by firing at a predetermined temperature.

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