KR102356185B1 - Gas sensor and manufacturing method thereof - Google Patents

Abstract

The present invention provides a gas-sensitive layer made of nickel oxide (NiO) to which titanium (Ti) is added; Disclosed is a gas sensor comprising a.

Description

GAS SENSOR AND MANUFACTURING METHOD THEREOF

The present invention relates to a gas sensor and a method for manufacturing the same.

The oxide semiconductor type gas sensor has advantages such as high gas sensitivity, fast response speed, economical price, and small size integration, so it is advantageous for sensor applications mounted on mobile and small devices. In addition, it can be widely used in various fields, such as explosive gas detection, industrial gas detection, driver's drunkenness measurement, a food freshness sensor of a refrigerator, and environmental gas monitoring inside a vehicle or indoors.

With the recent advancement of industry and growing interest in human health and environmental pollution, high-functional gas-sensitive materials are required to be used in indoor and outdoor environmental gas detection sensors, gas sensors for self-diagnosis of diseases, and high-performance artificial olfactory sensors that can be mounted on mobile devices. . In particular, since various indoor pollutants exist indoors, such as residential and office spaces, where many people are active for a long time in daily life, an indoor pollution measurement sensor capable of precise monitoring of these in real time is required.

Among the harmful gases that need to be detected, volatile organic compounds are harmful to the human body, and it is difficult to determine whether they exist in small amounts. VOCs such as benzene, xylene, toluene, formaldehyde, ethanol, and formaldehyde are continuously generated in furniture, paints, organic solvents, paints, leather products, and finishing materials. It can cause various fatal diseases such as , skin diseases, and cancer.

Therefore, there is a need for a sensitive material capable of detecting methylbenzene with high sensitivity and high selectivity. In addition, the need for a gas sensor capable of adjusting the sensitivity characteristics according to the needs of the application field is also increasing significantly. However, most of the oxide semiconductor type gas sensors currently used have a problem in that they show similar sensitivity to the above gases or show great sensitivity only to highly reactive gases such as alcohol and formaldehyde. A sensitive material that can be detected is required. In addition, it is a very difficult technical task to adjust the gas sensor characteristics in response to the requirements of the application field.

The present invention is a gas sensor gas sensor showing high sensitivity and selectivity to xylene and toluene while gas sensitivity to interfering gases such as ethanol, benzene, and formaldehyde by using titanium-added nickel oxide, and manufacturing thereof The purpose is to provide a method.

On the other hand, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned are clearly to those of ordinary skill in the art to which the present invention belongs from the description below. can be understood

A gas sensor according to an embodiment of the present invention includes a gas sensitive layer made of nickel oxide (NiO) to which titanium (Ti) is added; includes

In addition, the molar concentration ratio (Ti/Ni) of titanium and nickel in the gas-sensitive layer may be 0.02 to 0.3.

Also, the gas-sensitive layer may include a plurality of structures made of nickel oxide (NiO) to which titanium (Ti) is added.

In addition, the diameter of the structure may be 0.2㎛ to 5㎛.

In addition, the structure may have the shape of a multi-room hollow sphere.

In addition, the structure may have the shape of a hollow sphere.

In addition, the structure may be a solid mixture fine powder.

In addition, the thickness of the gas-sensitive layer may be 2㎛ to 40㎛.

In addition, the manufacturing method of the gas sensor according to an embodiment of the present invention comprises the steps of (A) forming a nickel oxide (NiO) structure to which titanium (Ti) is added; and (B) forming a gas-sensitive layer using the titanium (Ti)-added nickel oxide (NiO) structure.

In addition, the step (A) includes (A-1) a titanium (Ti) precursor and a nickel oxide (NiO) precursor such that the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is 0.02 to 0.3 and (A-2) forming a nickel oxide (NiO) structure to which titanium (Ti) is added with the mixed solution through ultrasonic spray pyrolysis.

In addition, the structure formed in step (A-2) may have the shape of a multi-room hollow sphere and a hollow sphere.

In addition, the diameter of the structure formed in step (A-2) may be 0.2㎛ to 5㎛.

In addition, the step (A) is (A-3) _{preparing a solid mixture by mixing the titanium oxide (TiO 2} ) powder and the molar concentration ratio (Ti/Ni) of the nickel oxide (NiO) powder to be 0.02 to 0.3; and (A-4) forming a fine powder of a nickel oxide (NiO) solid mixture to which titanium (Ti) is added through a solid-phase reaction method using the solid-phase mixture.

In addition, the diameter of the fine powder of the solid mixture formed in step (A-4) may be 0.2㎛ to 5㎛.

In addition, the thickness of the gas-sensitive layer formed in step (B) may be 2㎛ to 40㎛.

According to an embodiment of the present invention, using nickel oxide to which titanium is added, gas sensitivity to interfering gases such as ethanol, benzene, and formaldehyde is very small, and high sensitivity and selectivity to xylene and toluene can be exhibited. .

In addition, the addition of titanium realizes high sensitivity by controlling the hole concentration of nickel oxide, and increases the oxidation catalytic activity of nickel oxide to enable complete oxidation or reforming of the gas.

At this time, highly reactive gases such as ethanol and formaldehyde are decomposed into less reactive gases to lower the sensitivity, and xylene and toluene, which are relatively less reactive, are reformed with highly reactive gases to detect highly sensitive and highly selective gases. let there be In addition, the sensing characteristics of xylene and methylbenzene can be effectively controlled by adjusting the thickness of the gas-sensitive layer and the composition of the material constituting the sensitive layer.

On the other hand, the effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be able

1 and 2 are cross-sectional views schematically showing a gas sensor according to the present invention,
3 is a flowchart illustrating a gas sensor manufacturing method according to an embodiment of the present invention;
4 is a flowchart showing a gas sensor manufacturing method according to another embodiment of the present invention,
5 is an SEM and TEM image of a nickel oxide structure to which titanium is added according to an embodiment of the present invention;
6 is an elemental analysis image of a nickel oxide structure to which titanium is added according to an embodiment of the present invention;
7 is an exemplary view for explaining the structure of a nickel oxide structure to which titanium is added according to an embodiment of the present invention,
8 is a SEM image for explaining the thickness of the gas-sensitive layer according to an embodiment of the present invention,
9 and 10 are X-ray diffraction analysis results of titanium-added nickel oxide structures according to an embodiment and a comparative example of the present invention;
11 and 12 are graphs showing the comparison of gas sensitivities to 1 ppm ethanol, xylene, toluene, benzene, and formaldehyde in the gas sensors according to Examples 1, 2 and Comparative Examples of the present invention,
13 is a graph showing the gas sensitivity to xylene gas compared to Examples 1-2 and 2-2 of the present invention and the existing research results at an operating temperature of 350 degrees by comparison;
14 is a graph showing the gas response characteristic results and repetitive xylene gas (50 ppb) response characteristic results according to the xylene gas concentration (25-125 ppb) of Example 1-2 of the present invention at an operating temperature of 350 degrees. ,
15 is a graph showing the comparison of gas sensitivities to 1 ppm ethanol, xylene, toluene, benzene, and formaldehyde in the gas sensor according to Example 3-1 and Comparative Example 3-1 of the present invention at an operating temperature of 350 ° C. ,
16 is an X-ray diffraction analysis result of the titanium-added nickel oxide structure according to Example 4 and Comparative Example 4 of the present invention;
17 is a gas sensor according to Example 4-1 and Comparative Example 4-1 of the present invention at an operating temperature of 350 degrees 1 ppm ethanol, xylene, toluene, benzene of Example 4-1, Comparative Example 4-1, It is a graph showing a comparison of gas sensitivity to formaldehyde,
18 is a graph showing a comparison of gas sensitivities to 1 ppm ethanol and xylene of Example 5-1 of the present invention at an operating temperature of 350 degrees.

Hereinafter, an embodiment of the present invention will be described in more detail with reference to the accompanying drawings. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the following embodiments. This embodiment is provided to more completely explain the present invention to those of ordinary skill in the art. Accordingly, the shapes of elements in the drawings are exaggerated to emphasize a clearer description.

The configuration of the invention for clarifying the solution to the problem to be solved by the present invention will be described in detail with reference to the accompanying drawings based on a preferred embodiment of the present invention, but the same in assigning reference numbers to the components of the drawings For the components, even if they are on different drawings, the same reference numbers are given, and it is noted in advance that the components of other drawings can be cited when necessary in the description of the drawings.

A gas sensor according to the present invention is a gas sensor including a gas sensitive layer made of nickel oxide to which titanium is added. Prior to the present invention, titanium-added nickel oxide has low gas sensitivity to interfering gases such as ethanol, benzene, carbon monoxide, and formaldehyde, but has high selectivity for toxic xylene and toluene. It is unknown and this is the use and effect discovered for the first time in the present invention.

In addition, the gas sensor according to the present invention has a small gas sensitivity to interfering gases such as ethanol, benzene, and formaldehyde depending on the concentration of Ti added to pure NiO and control of the thickness of the gas sensitive layer, It is possible to design a high-sensitivity, high-selectivity oxide semiconductor-type gas sensor with high selectivity.

In addition, it shows that it can be applied to various application situations by adjusting the sensitivity to low-concentration xylene and xylene in a wide concentration range through thickness control, as well as selectivity to interfering gas.

1 and 2 are cross-sectional views schematically showing a gas sensor according to the present invention.

However, the structure of the gas sensor according to the present invention is not limited to the one presented here, and any structure of the gas sensor having a gas sensitive layer made of nickel oxide to which titanium is added corresponds to the present invention.

The gas sensor shown in FIG. 1 has a structure in which electrodes 110 and 130 are respectively provided on the lower surface and upper surface of the gas sensitive layer 120 .

In the gas sensor shown in FIG. 2 , a microheater 150 is formed on a lower surface of a substrate 140 , two electrodes 160 and 165 are formed on an upper surface of the substrate 140 , and a gas sensitive layer 170 is provided thereon. is a structure that has been The gas sensitive layers 120 and 170 in the gas sensors of FIGS. 1 and 2 are all made of nickel oxide to which titanium is added, and the amount of titanium may be adjusted as necessary.

Meanwhile, in the gas sensor according to the present invention, the thickness of the gas sensitive layers 120 and 170 is preferably formed in a range of 2 μm to 40 μm.

Here, when the thickness of the gas-sensitive layers 120 and 170 is less than 2 μm, there is a problem in that the selectivity to methylbenzene is not shown, and when the thickness of the gas-sensitive layers 120 and 170 exceeds 40 μm, the sensitivity is greatly reduced. there is a problem.

In the present invention, the gas sensitization property is improved through the electronic sensitization effect by controlling the hole concentration by replacing titanium inside the nickel oxide lattice by using the high solubility of nickel oxide to titanium.

In addition, the addition of titanium increases the oxidation catalytic activity of nickel oxide, so that the gas can be completely oxidized or reformed. At this time, highly reactive gases such as ethanol and formaldehyde are decomposed into less reactive gases to lower the sensitivity, and xylene and toluene, which are relatively less reactive, are reformed with highly reactive gases to detect highly sensitive and highly selective gases. let there be In addition, the sensing characteristics of xylene and methylbenzene can be effectively controlled by adjusting the thickness of the gas-sensitive layer and the composition of the material constituting the sensitive layer.

As a result of the experiment, the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is preferably 0.02 to 0.3. When the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is 0.02 or less and when the molar concentration ratio (Ti/Ni) is 0.3 or more, high sensitivity and high selectivity for xylene and toluene can be secured. none.

Here, when the molar concentration ratio (Ti/Ni) is 0.02 or less, it cannot be said to have high sensitivity only to xylene and toluene compared to other gases, and when the molar concentration ratio (Ti/Ni) is 0.3 or more, the resistance in air is very large. Xylene and toluene gases cannot be detected because this is impossible.

According to the present invention, the gas sensor provided with the gas sensitive layers 120 and 170 made of nickel oxide to which titanium is added is a p-type oxide semiconductor type gas sensor. When negatively charged oxygen is adsorbed on the surface of the p-type oxide semiconductor, a hole accumulation layer in which holes near the surface are gathered is generated. When the p-type oxide semiconductor is exposed to a reducing gas, the reducing gas reacts with negatively charged oxygen to inject electrons, so the concentration of holes is reduced by electron-hole recombination and the thickness of the hole accumulation layer is reduced. As a result, the resistance of the sensor increases. Conversely, when the p-type oxide semiconductor is exposed to an oxidizing gas, the thickness of the hole accumulation layer increases and the resistance of the sensor decreases.

As described above, the gas sensor according to the present invention operates by a gas-sensitive mechanism of conductivity change due to surface adsorption of gas.

Gas sensors using n-type oxide semiconductors (SnO ₂ , In ₂ O ₃ , Cr ₂ O ₃ , ZnO, etc.) reported so far have excellent gas sensitivity, but show high sensitivity to various gases at the same time, resulting in poor selectivity and low base It has a high resistance of several to tens of MΩ, so it reacts sensitively to atmospheric humidity and the base resistance changes significantly, indicating a problem of poor stability.

On the other hand, the p-type oxide semiconductor has a low base resistance of several to several tens of KΩ, so the resistance change of the sensor in air during long-term operation of the sensor is small, which shows excellent long-term stability, but the gas sensitivity is relatively lower than that of the n-type oxide semiconductor. It has a disadvantage that it is difficult to detect low-concentration gas.

Since the gas sensor according to the present invention is a p-type oxide gas sensor having excellent long-term stability and very high sensitivity, a gas sensor with high sensitivity and high reliability can be developed.

In the present invention, when titanium is added to a nickel oxide-sensitive material having various structures, it has higher stability than an n-type oxide semiconductor type gas sensor, and at the same time, the sensitivity to xylene and toluene gas is lower than that of the conventional one regardless of the structure. can be more than doubled. It also shows that good selectivity between xylene and toluene gas can be obtained.

According to the present invention, methylbenzene of a nickel oxide semiconductor type gas sensor in which a _{NiTiO 3} secondary phase exists by adding titanium to a p-type oxide semiconductor nickel oxide of various structures by adjusting the concentration, and replacing titanium into a lattice of nickel oxide It is possible to dramatically improve gas sensitivity.

On the other hand, high selectivity for reacting only with gases to xylene and toluene can be obtained. It is confirmed that the fabricated high-sensitivity p-type oxide semiconductor type gas sensor can contribute to the commercialization of gas sensors due to its excellent long-term stability and selectivity.

3 is a flowchart illustrating a method of manufacturing a gas sensor according to an embodiment of the present invention.

First, a titanium precursor, a nickel precursor, and dextrin/sucrose are added to distilled water and stirred, and then a mixed solution for spraying is prepared (step S10). The spray solution may further contain ethylene glycol.

Here, the molar concentration ratio (Ti/Ni) of Ti/Ni contained in 100 mL of distilled water is preferably 0.02 to 0.3.

Here, when the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is 0.02 or less and when the molar concentration ratio (Ti/Ni) is 0.3 or more, high sensitivity and high selectivity for xylene and toluene are secured Can not.

When the molar concentration ratio (Ti/Ni) is 0.02 or less, it cannot be said to have high sensitivity only to xylene and toluene compared to other gases. Therefore, it cannot detect xylene and toluene gas.

Next, the liquid mixture is subjected to ultrasonic spray pyrolysis (step S20).

A nanostructure is formed through a process using a mixed solution containing a titanium precursor and a nickel precursor. For example, a nickel oxide (NiO) structure to which titanium (Ti) is added can be formed by spraying the mixed solution through ultrasonic waves and pyrolyzing it to pass through a quartz tube.

Here, as shown in FIGS. 5 to 7 , the structure 10 formed in step S20 has a spherical shape, and has a multi-room hollow spherical shape and a hollow spherical shape having a plurality of spaces 1 partitioned therein. can

On the other hand, the diameter of the structure 10 formed in step S20 is preferably 0.2㎛ to 5㎛.

Here, when the diameter of the structure 10 is less than 0.2 μm, there is a possibility that the nanostructure is not well formed, and when the diameter of the structure 10 exceeds 5 μm, there is a problem in terms of application to the MEMS sensor.

In this step (step S20), a process of synthesizing and recovering the powder by generating fine droplets by spraying the mixed solution and introducing the fine droplets into the reactor may be included. The size of the micro-droplets can be controlled by the internal pressure of the spraying device, the concentration of the spraying solution, the viscosity of the spraying solution, and the like. By heating in the reactor, most of the solvent contained in the micro-droplets is volatilized, leaving the polymer precursor and the oxide and metal catalyst precursor components.

A gas sensor is manufactured by forming a gas sensitive layer using such a nanostructure (step S30).

Meanwhile, FIG. 4 is a flowchart illustrating a gas sensor manufacturing method according to another embodiment of the present invention.

First, a fine titanium powder and a fine nickel powder are prepared, respectively (step S110).

Next, after mixing fine titanium powder and fine nickel powder, a solid mixture is generated through ball milling, and this is heat-treated to synthesize a commercial fine powder solid mixture in _{which NiO and TiO 2 phases are mixed by a solid-state reaction method (} step S120).

Here, the molar concentration ratio (Ti/Ni) of Ti/Ni contained in the solid mixture is preferably 0.02 to 0.3.

Here, when the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is 0.02 or less and when the molar concentration ratio (Ti/Ni) is 0.3 or more, high sensitivity and high selectivity for xylene and toluene are secured Can not.

When the molar concentration ratio (Ti/Ni) is 0.02 or less, it cannot be said to have high sensitivity only to xylene and toluene compared to other gases. Therefore, it cannot detect xylene and toluene gas.

A solid mixture fine powder is formed through a process using a solid phase mixing method. Through this, it is possible to form a fine powder of a nickel oxide (NiO) solid mixture to which titanium (Ti) is added.

Here, when the diameter of the fine powder of the solid mixture is less than 0.2 μm, there is a possibility that the fine powders are excessively agglomerated, and when the diameter of the fine powder of the solid mixture exceeds 5 μm, there is a problem in terms of application to the MEMS sensor.

A gas sensor is manufactured by forming a gas-sensitive layer using the fine powder of the solid-state mixture (step S130).

Hereinafter, with reference to [Table 1] and FIGS. 4 to 15, the characteristics of the gas sensors according to Examples and Comparative Examples will be compared and described.

manufacturing method gas-sensitive layer thickness concentration ratio
(Ti/Ni) structure of structure Example 1-1 Ultrasonic Spray Pyrolysis 5μm 0.05 multi room Example 1-2 Ultrasonic Spray Pyrolysis 5μm 0.1 multi room Examples 1-3 Ultrasonic Spray Pyrolysis 5μm 0.2 multi room Comparative Example 1-1 Ultrasonic Spray Pyrolysis 5μm 0 (Ni 100%) multi room Example 2-1 Ultrasonic Spray Pyrolysis 12μm 0.05 multi room Example 2-2 Ultrasonic Spray Pyrolysis 12μm 0.1 multi room Example 2-3 Ultrasonic Spray Pyrolysis 12μm 0.2 multi room Comparative Example 2-1 Ultrasonic Spray Pyrolysis 12μm 0
(Ni 100%) multi room Example 3-1 Ultrasonic Spray Pyrolysis 5μm 0.1 hollow sphere Comparative Example 3-1 Ultrasonic Spray Pyrolysis 5μm 0
(Ni 100%) hollow sphere Example 4-1 solid-state reaction 5μm 0.1 fine powder Comparative Example 4-1 solid-state reaction 5μm 0
(Ni 100%) fine powder Example 5-1 Ultrasonic Spray Pyrolysis 5μm 0.1 multi room

<Example 1-1>

_{Calculate 5.82 g of nickel(II) nitrate hexahydrate [Ni(NO 3} ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 0.560 g of Ti/Ni in 200 mL of distilled water so that the concentration ratio is 0.05. Titanium (IV) bis(ammonium lactato) dihydroxide solution [(CH ₃ CH(O-)CO ₂ NH ₄ ] ₂ Ti(OH) ₂ , 50 wt% in H ₂ O, Sigma-Aldrich, USA], 3 g A spray solution was prepared by adding dextrin [(C ₆ H ₁₀ O ₅ ) _x ·nH ₂ O, Samchun, Korea] and stirring until all the reagents were dissolved.

A precursor is formed as the prepared spray solution passes through a furnace (400 degrees) connected to the spray outlet at the same time as ultrasonic spraying in nitrogen gas at a flow rate of 15 L·min-1. Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a Ti-added NiO multi-room structure. The heat-treated Ti-added NiO multi-room structure powder thus obtained is mixed with an organic binder, and a gas-sensitive layer is applied on an alumina substrate having two electrodes.

Here, application is used to include various methods such as printing, brushing, blade coating, dispensing, and micropipette dropping. Thereafter, to remove the solvent, a gas sensor was fabricated by heat treatment at 450°C for 2 hours. In this case, the thickness of the fabricated gas-sensitive layer is about 5 μm.

The manufactured gas sensor was placed inside a gas sensing chamber composed of quartz tube, and pure air or mixed gas was alternately injected to measure the change in resistance of the gas sensor in real time. After mixing the gas to an appropriate concentration through the MFC, it was rapidly injected using a 4-way valve to change the gas concentration inside the gas sensing chamber. The total flow rate inside the gas sensing chamber was fixed at 200 sccm so that the temperature of the gas sensor was maintained even with a sudden change in gas concentration.

<Example 1-2>

_{Calculate 5.29 g of nickel(II) nitrate hexahydrate [Ni(NO 3} ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 1.07 g of Ti/Ni in 200 mL of distilled water so that the concentration ratio is 0.1. Titanium (IV) bis(ammonium lactato) dihydroxide solution [(CH ₃ CH(O-)CO ₂ NH ₄ ] ₂ Ti(OH) ₂ , 50 wt% in H ₂ O, Sigma-Aldrich, USA], 3 g A spray solution was prepared by adding dextrin [(C ₆ H ₁₀ O ₅ ) _x ·nH ₂ O, Samchun, Korea] and stirring until all the reagents were dissolved.

A precursor is formed while the prepared spray solution is passed through a furnace (400 degrees) connected to the spray outlet at the same time as ultrasonic spraying in nitrogen gas at a flow rate of 15 L·min-1.

Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a Ti-added NiO multi-room structure.

Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Example 1-3>

_{Calculate 4.85 g of nickel(II) nitrate hexahydrate [Ni(NO 3} ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 1.96 g of Ti/Ni in 200 mL of distilled water so that the concentration ratio is 0.2. Titanium (IV) bis(ammonium lactato) dihydroxide solution [(CH ₃ CH(O-)CO ₂ NH ₄ ] ₂ Ti(OH) ₂ , 50 wt% in H ₂ O, Sigma-Aldrich, USA], 3 g A spray solution was prepared by adding dextrin [(C ₆ H ₁₀ O ₅ )x·nH ₂ O, Samchun, Korea] and stirring until all the reagents were dissolved.

A precursor is formed as the prepared spray solution is subjected to ^{ultrasonic spraying in nitrogen gas at a flow rate of 15 L·min -1} and a furnace (400 degrees) connected to the spray outlet at the same time. Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a Ti-added NiO multi-room structure.

Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Comparative Example 1-1>

In 200 mL of distilled water, 5.81 g of nickel(II) nitrate hexahydrate [Ni(NO ₃ ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 3 g of dextrin [(C ₆ H ₁₀ O ₅ )x ·nH ₂ O, Samchun, Korea] was added and stirred until all the reagents were dissolved to prepare a spray solution.

A precursor is formed as the prepared spray solution passes through a furnace (400 degrees) connected to the spray outlet at the same time as ultrasonic spraying in nitrogen gas at a flow rate of 15 L·min ^-1.

Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a pure NiO multi-room structure. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Example 2-1>

The synthesis method of Example 2-1 is the same as that of Example 1-1. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1, and the thickness of the prepared gas sensitive layer was about 12 μm.

<Example 2-2>

The synthesis method of Example 2-2 is the same as that of Example 1-2. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1, and the thickness of the prepared gas sensitive layer was about 12 μm.

<Example 2-3>

The synthesis method of Example 2-3 is the same as that of Example 1-3. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1, and the thickness of the prepared gas sensitive layer was about 12 μm.

<Comparative Example 2-1>

The synthesis method of Comparative Example 2-1 is the same as that of Comparative Example 1-1. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1, and the thickness of the prepared gas sensitive layer was about 12 μm.

<Example 3-1>

Calculate 2.64 g of nickel(II) nitrate hexahydrate [Ni(NO ₃ ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 0.53 g of Titanium (IV) bis(ammonium lactato) dihydroxide solution [(CH ₃ CH(O-)CO ₂ NH ₄ ] ₂ Ti(OH) ₂ , 50 wt% in H ₂ O, Sigma-Aldrich, USA], 6.84 g A spray solution was prepared by adding sucrose [C ₁₂ H ₂₂ O ₁₁ , Sigma-Aldrich, USA] and stirring until all the reagents were dissolved.

A precursor is formed as the prepared spray solution passes through a furnace (700 degrees) connected to the spray outlet at the same time as ultrasonic spraying in the air at a flow rate of 10 L·min ^-1. Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a Ti-added NiO hollow structure. Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Comparative Example 3-1>

In 200 mL of distilled water, 2.91 g of nickel(II) nitrate hexahydrate [Ni(NO ₃ ) ₂ 6H ₂ O, 99.999%, Sigma-Aldrich, USA], 6.84 g of sucrose [C ₁₂ H ₂₂ O ₁₁ , Sigma- Aldrich, USA] was added and stirred until all the reagents were dissolved to prepare a spray solution.

A precursor is formed as the prepared spray solution passes through a furnace (700 degrees) connected to the spray outlet at the same time as ultrasonic spraying in the air at a flow rate of 10 L·min ^-1. Thereafter, the formed precursor is heat-treated at 600° C. for 3 hours to form a pure NiO hollow structure.

Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Example 4-1>

Commercially fine powders, Nickel oxide [NiO, powder, Sigma-Aldrich, USA] and Titanium oxide [TiO ₂ , anatase nanopowder, Sigma-Aldrich, USA] were prepared. After mixing the fine powders in the same ratio as in Example 1-2 (Ti/Ni concentration ratio = 0.1), a mixture was made through ball-milling for 24 hours.

Thereafter, the prepared mixture was heat-treated at 600° C. for 3 hours to synthesize a commercial fine powder solid mixture in _{which NiO and TiO 2 phases were mixed by a solid-state reaction method.}

Thereafter, the sensor manufacturing method and gas sensitivity measurement were the same as in Example 1-1.

<Example 5-1>

The synthesis method of Example 5-1 is the same as that of Example 1-2. The multi-room structure thus obtained was mixed with an organic binder mixed with ethylene glycol and glycerol in a mass ratio of 1:2, coated on a MEMS substrate electrode by micro-dispensing, dried at 200 degrees for 1 hour, and then heat treated at 400 degrees for 2 hours. A gas sensor was manufactured. Thereafter, the gas sensitivity measurement is the same as in Example 1-1.

A gas sensor was manufactured using the powders synthesized by the above methods and measured at a total of five temperatures of 350, 375, 400, 425, and 450 degrees.

When the resistance of the sensor in air is constant, the atmosphere is changed to the gas to be tested (ethanol, xylene, toluene, benzene, formaldehyde, 1 ppm), and when the resistance in the gas is constant, the atmosphere is changed to air again to change the resistance was measured.

All of the synthesized sensitizing materials exhibit characteristics of a p-type oxide semiconductor with increased resistance to the reducing gas. Therefore, the gas sensitivity is R _g/ R _a ( R _g : device resistance in gas, R _a : device resistance in air).

After manufacturing the sensor using the synthesized powder, the gas sensitivity was measured and the selectivity was calculated by comparing the sensitivity with other gases.

5 is an SEM and TEM image of a nickel oxide structure to which titanium is added according to an embodiment of the present invention, and FIG. 6 is an elemental analysis image of a nickel oxide structure to which titanium is added according to an embodiment of the present invention.

5 and 6, it was confirmed that all of the manufactured structures had a spherical multi-room structure, and as a result of elemental analysis, it was confirmed that Ti is uniformly distributed throughout the structure in the NiO multi-room structure to which Ti is added. could In addition, it was confirmed that the thickness of the gas-sensitive layer of Example 1-2 and Example 2-2 was different.

7 is an exemplary view for explaining the structure of a nickel oxide structure to which titanium is added according to an embodiment of the present invention.

5 to 7 , the structure 10 formed according to Examples 1 and 2 may have a spherical shape, and may have a multi-room hollow spherical shape having a plurality of spaces 1 partitioned therein.

8 is an SEM image for explaining the thickness of the gas-sensitive layer according to an embodiment of the present invention.

Referring to FIG. 8 , it can be seen that the thickness can be adjusted differently like the gas-sensitive layer of Examples 1-2 and 2-2.

9 and 10 are X-ray diffraction analysis results of titanium-added nickel oxide structures according to an embodiment and a comparative example of the present invention.

Referring to FIG. 9 , it was confirmed that the NiO cubic phase was present in both Examples and Comparative Examples, and it was confirmed that a small amount _{of NiTiO 3 secondary phase was present in Examples 1-3.} This shows that the added Ti mostly displaced Ni and entered the lattice.

In addition, referring to FIG. 10 , the results of X-ray diffraction analysis of the hollow structures of Example 3-1 and Comparative Example 3-1 synthesized using ultrasonic spray pyrolysis can be confirmed. As a result of the analysis, it can be confirmed that the NiO cubic phase is present in both Example 3-1 and Comparative Example 3-1.

11 and 12 are graphs showing a comparison of gas sensitivities to 1 ppm ethanol, xylene, toluene, benzene, and formaldehyde in the gas sensors according to Examples 1 and 2 and Comparative Examples of the present invention.

11 and 12 , Comparative Example 1-1 and Comparative Example 2-1 showed very small sensitivity to ethanol, xylene, toluene, benzene, and formaldehyde gases, whereas Ti-doped Example 1 In the case of -1, it can be seen that the sensitivity of xylene is greatly increased.

In addition, in the case of Example 1-2, Example 1-3, Example 2-1, Example 2-2, and Example 2-3, it was confirmed that the sensitivity of methylbenzene was significantly increased. In particular, in the case of Examples 1-2 and 2-2, the sensitivity of xylene at an operating temperature of 350 °C was about 338 and 320 (Rg/Ra), respectively, which is the result of those of Comparative Examples 1-1 and 2-1, which are pure NiO. It is about 260 times higher than the xylene sensitivity of 1.3.

It is judged that when Ti having a tetravalent valence is doped into NiO, the concentration of charge carriers is reduced, resulting in electronic sensitization of the sensitizing material, and thus the sensitivity is greatly improved.

In addition, as Ti is doped, the oxidation catalytic activity of NiO increases, so that xylene and toluene gases with low reactivity are reformed into highly reactive gases as they pass through the gas-sensitive layer and reach the lower end of the gas-sensitive layer. It is judged that the sensitivity of toluene was particularly greatly increased.

That is, in the case of ethanol and formaldehyde, which are representative interfering gases and show great sensitivity in general oxide semiconductors, most of them are completely oxidized at the upper end of the gas sensitive layer due to the excellent oxidation catalytic activity of Ti-doped NiO, and thus have low reactivity. It seems that the sensitivity is low because it is converted to .

This shows that Ti doping has a very good effect on improving the sensitivity and selectivity of methylbenzene of the NiO sensor.

13 is a graph showing a comparison of gas sensitivity to xylene gas compared with Examples 1-2 and 2-2 of the present invention and the existing research results at an operating temperature of 350 degrees.

Referring to FIG. 13 , it can be seen that the results of Examples 1-2 and 2-2 have significantly higher xylene sensitivity compared to the studies conducted so far, and when changing the sensor gas sensitive layer thickness, the xylene concentration and It was confirmed that the slope of the xylene sensitivity was changed.

In particular, in the case of Example 1-2, it is determined that a large sensitivity to ppb-level xylene is shown, and in the case of Example 2-2, it is determined that a reliable large sensitivity to xylene in a wider range is exhibited. This shows that when the thickness of the gas-sensitive layer is changed using the sensitive material of the present invention, the gas sensitivity-concentration gradient that determines the resolution of the gas-sensitive characteristic and the lower limit of the gas-sensitive concentration can be adjusted.

14 is a graph showing the gas response characteristic results and repetitive xylene gas (50 ppb) response characteristic results according to the xylene gas concentration (25-125 ppb) of Example 1-2 of the present invention at an operating temperature of 350 degrees. .

Referring to FIG. 14 , it can be seen that the sensor of Example 1-2 exhibits stable xylene sensing characteristics even in multiple repeated measurements of xylene and long-term (>20 day) sensor measurements.

That is, it can be confirmed that the gas sensor according to the present invention is reliable.

15 is a graph showing the comparison of gas sensitivities to 1 ppm ethanol, xylene, toluene, benzene, and formaldehyde in the gas sensor according to Example 3-1 and Comparative Example 3-1 of the present invention at an operating temperature of 350 degrees Celsius .

15 , Example 3-1 exhibited very high sensitivity to xylene and toluene, and Comparative Example 3-1 exhibited very small sensitivity to xylene and toluene, and did not show selectivity (y-axis Change the maximum to around 50).

It is judged that when Ti is doped with NiO, the concentration of charge carriers is reduced, and accordingly, electronic sensitization of the sensitive material occurs, and thus the sensitivity is greatly improved.

In addition, as Ti is doped, the oxidation catalytic activity of NiO increases, so xylene and toluene gases with low reactivity pass through the gas-sensitive layer and are reformed into highly reactive gases to reach the lower end of the gas-sensitive layer. It is considered that the sensitivity of toluene is particularly significantly increased.

16 is an X-ray diffraction analysis result of the titanium-added nickel oxide structure according to Example 4 and Comparative Example 4 of the present invention.

Referring to FIG. 16 , in the case of Example 4-1, it _{was confirmed that NiO and TiO 2} (anatase) phases were present together.

17 is a gas sensor according to Example 4-1 and Comparative Example 4-1 of the present invention at an operating temperature of 350 degrees 1 ppm ethanol, xylene, toluene, benzene of Example 4-1, Comparative Example 4-1, It is a graph showing a comparison of gas sensitivity to formaldehyde.

Referring to FIG. 17 , Example 4-1 showed a selective detection characteristic for xylene, and Comparative Example 4-1 was not selective for xylene, and showed very little sensitivity.

It is judged that the sensitivity is greatly improved because electronic sensitization caused by replacing Ti with NiO and electrical sensitization caused by a decrease in the concentration of charge carriers of NiO at the pn junction of _{TiO 2 and NiO occur together.}

18 is a graph showing a comparison of gas sensitivities to 1 ppm ethanol and xylene of Example 5-1 of the present invention at an operating temperature of 350 degrees.

Here, in Example 5-1, the titanium-doped nickel oxide multi-room structure of Example 1-2 was applied on the electrode of the MEMS sensor by micro-dispensing.

Referring to FIG. 18 , it was confirmed that the MEMS sensor also exhibited selective detection characteristics for xylene at an operating temperature of 350°C.

Here, the thickness of the gas-sensitive layer applied in the MEMS sensor may be about 2 μm to 40 μm.

The above detailed description is illustrative of the present invention. In addition, the above description shows and describes preferred embodiments of the present invention, and the present invention can be used in various other combinations, modifications, and environments. That is, changes or modifications are possible within the scope of the concept of the invention disclosed herein, the scope equivalent to the written disclosure, and/or within the scope of skill or knowledge in the art. The written embodiment describes the best state for implementing the technical idea of the present invention, and various changes required in the specific application field and use of the present invention are possible. Therefore, the detailed description of the present invention is not intended to limit the present invention to the disclosed embodiments. Also, the appended claims should be construed as including other embodiments.

Claims (16)

a gas-sensitive layer made of nickel oxide (NiO) to which titanium (Ti) is added; including,
The gas-sensitive layer is
It includes a plurality of structures composed of nickel oxide (NiO) to which titanium (Ti) is added,
The structure is a gas sensor having the shape of a multi-room hollow sphere or the shape of a hollow sphere.
The method of claim 1,
in the gas-sensitive layer
A gas sensor having a molar concentration ratio of titanium and nickel (Ti/Ni) of 0.02 to 0.3.
delete 3. The method of claim 2,
A gas sensor having a diameter of 0.2 μm to 5 μm of the structure.
delete delete delete 5. The method of claim 4,
The thickness of the gas sensitive layer is 2㎛ to 40㎛ gas sensor.
(A) forming a nickel oxide (NiO) structure to which titanium (Ti) is added; and
(B) comprising the step of forming a gas-sensitive layer with the titanium (Ti) added nickel oxide (NiO) structure,
The step (A) is
(A-1) preparing a mixed solution containing a titanium (Ti) precursor and a nickel oxide (NiO) precursor so that the molar concentration ratio (Ti/Ni) of titanium (Ti) and nickel (Ni) is 0.02 to 0.3; and
(A-2) forming a nickel oxide (NiO) structure to which the titanium (Ti) is added with the mixed solution through ultrasonic spray pyrolysis;
containing
A method of manufacturing a gas sensor.
delete 10. The method of claim 9,
The structure formed in the step (A-2) is a method of manufacturing a gas sensor having the shape of a multi-room hollow sphere.
10. The method of claim 9
The structure formed in step (A-2) is a method of manufacturing a gas sensor having a shape of a hollow sphere.
10. The method of claim 9,
A method of manufacturing a gas sensor having a diameter of 0.2 μm to 5 μm of the structure formed in step (A-2).
delete delete 10. The method of claim 9,
In step (B)
The thickness of the formed gas-sensitive layer is 2㎛ to 40㎛ method of manufacturing a gas sensor.

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