KR20060036576A - Semiconductor type thick film gas sensor device, and apparatus for measuring performance of a gas sensor device - Google Patents

Abstract

In the semiconductor thick film gas sensor device according to the present invention, two or more sensors including an electrode and a sensing film are formed on the front of the substrate to form a sensor array, and a heater is formed on the back of the substrate, and the sensing material constituting the sensing film is oxidized. Include comments. Moreover, the performance measuring apparatus of the gas sensor element by this invention contains a 4-way valve and a mini reactor.

The semiconductor thick film gas sensor element has excellent selectivity against various gases, particularly chemical agents used in chemical terrorism. In addition, the performance measuring device of the gas sensor element minimizes the reaction time of the gas sensor element and the measurement gas.

Semiconductor thick film gas sensor, sensor array, tin oxide, alumina, indium oxide, zinc oxide, zirconium oxide, 4-way valve, mini reactor

Description

Semiconductor type thick film gas sensor device, and apparatus for measuring performance of a gas sensor device

1A to 1C are photographs of the front side, the back side, and the front side after being screened, respectively, of the single sensor element.

2 is a schematic diagram of a measuring device capable of measuring the performance of a sensor element.

3A-3D are graphs of sensitivity for each of the four chemical agents of the fabricated single sensor device.

4A-4C are photographs of the front, back, and front of the screen before the screen of the sensor array combined with the four sensing materials.

5A to 5D are graphs of sensitivity changes according to operating temperatures (250, 300, 350, and 400 ° C., respectively) of the sensor array of FIGS. 4A to 4C.

6A and 6B are graphs of principal component analysis results for classification of four chemical agents.

Figure 7a is a photograph of the performance measurement device of the sensor element used to reduce the reaction time to a minimum.

FIG. 7B schematically illustrates FIG. 7A.

FIG. 7C schematically illustrates a state in which the four-way valve is rotated 90 ° in FIG. 7A.

8 is a photograph of a printed circuit board (PCB) on which a sensor array is bonded.

<Description of Symbols for Main Parts of Drawings>

1: sensor element 10: 4-way valve

12: first passage 14: second passage

20: reference gas line 30: measurement gas line

40: measuring line 50: vent line

70: chamber

The present invention relates to a semiconductor thick film gas sensor element used for detection of a chemical agent or the like, and an apparatus for measuring the performance of a gas sensor element.

Chemical agents are not only toxic but also colorless, which is very dangerous and deadly. Therefore, to protect human life, chemical agents must be able to be detected quickly and accurately. Chemical agents are divided into four categories: nerves, blisters, choking, and blood agents.

In general, semiconductor gas sensors have several advantages. The manufacturing cost is low, stable to environmental changes, and high sensitivity even at low concentrations. Many sensors have a problem with selectivity because they exhibit similar responses to various gases.

Currently, various methods have been studied such as adding a catalyst, using a sensor array, or a combination of the two to classify various gases. The method using a catalyst requires a long time because many experiments are required. However, the sensor array uses neural networks and statistics, which can save a lot of time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas sensor having excellent selectivity that can accurately prevent the chemical agent during chemical terrorism to prevent human injury.

In order to achieve the above object, in the semiconductor thick film gas sensor device according to the present invention, two or more sensors including an electrode and a sensing film are formed on the front of the substrate to form a sensor array, and a heater is formed on the back of the substrate. The constituent sensing material comprises tin oxide.

In order to achieve the above object, the performance measuring apparatus of the gas sensor element according to the present invention has four openings, and two pairs of two adjacent openings are respectively connected by passages to form a first and second passages; A reference gas line for introducing a reference gas into the four-way valve; A measurement gas line for introducing a measurement gas into the four-way valve; A measurement line for introducing the reference gas or the measurement gas into the reactor from the four-way valve; A vent line for discharging the reference gas or the measurement gas to the outside from the four-way valve; An exhaust line for discharging the reference gas or the measurement gas from the reactor to the outside; A reaction tank in which a reaction between a gas sensor element and the measurement gas occurs; And a measurement unit connected to the gas sensor element,

During stabilization, the reference gas passes sequentially through the reference gas line, the first passage, and the measurement line, and the measurement gas passes sequentially through the measurement gas line, the second passage, and the vent line. Positioning the four-way valve,

In the measurement, the measurement gas passes sequentially through the measurement gas line, the first passage, and the measurement line, and the reference gas passes sequentially through the reference gas line, the second passage, and the vent line. Place the four-way valve.

Hereinafter, the present invention will be described in detail.

The present inventors first fabricated a semiconductor thick film sensor element having a single sensor using the materials shown in Table 1 below, and then changed the measurement temperature and the gas concentration for the similar gases of the four chemical agents shown in Table 2, and then showed the characteristics thereof. I looked at it.

Materials used to fabricate sensor elements Parent material Additive material Addition amount (% by weight) Manufacturing method SnO ₂ SnO ₂ α-Al2O3 4, 12, 20 Physical mixing SnO ₂ In ₂ O ₃ WO ₃ 1, 2, 3 Physical mixing SnO ₂ Pt Pd 1, 2, 3 Impregnation method SnO ₂ ZnO 1 2 3 4 5 Copulation SnO ₂ ZrO ₂ 1, 3, 5 Copulation SnO ₂ SiO ₂ TiO ₂ 3, 5, 10 Physical mixing

Chemical Agents and Similar Gases Classification of chemical agents Chemical agent Quasi-gas Blood agonists HCN Acetonitrile Nerve agent Tabun Dimethyl methyl phosphonate Choking agent Phosgene Dichloromethane Blister Mustard gas Dipropylene glycol methyl ether

In order to precisely control the concentration of the measurement gas used, acetonitrile (acetonitrile, CH ₃ CN) and dichloromethane (CH ₂ Cl ₂ ) was calculated by applying the antoine formula of the following equation, Dimethyl methyl phosphonate (hereinafter referred to as "DMMP") is represented by the following equation (2), dipropylene glycol methyl ether (hereinafter referred to as "DPGME") using a specific value for the vapor pressure The concentration was obtained.

DPGME has vapor pressures of 0.3mmHg and 0.5mmHg at 20 ° C and 25 ° C, respectively. Here, P (mmHg) means vapor pressure and constants A, B and C are specific values. And T (K) represents the saturation temperature. As can be seen in Equations 1 and 2, the desired gas concentration can be adjusted by changing the saturation temperature. Table 3 below shows constant values for the antoin formula (Equation 1). Here, the use temperature range means the range of temperatures that can be actually used in this formula.

Constant Value of Equation 1 Acetonitrile Dichloromethane Operating temperature range (K) 280 to 300 -40 to 40 A 5.93296 4.53691 B 2345.829 1327.016 C 43.815 -20.474

From the measurement results for the analogous gases of the four chemical agents, four materials were selected to construct a sensor array. As described above, although a sensor array having four sensors is preferable, the present invention is not limited thereto, and a sensor array having two or more sensors is also possible.

The fabricated sensor array was measured by operating temperature and by type of measurement gas. Excellent sensitivity, stability, and selectivity were obtained through the sensor array. Sensor arrays were classified using principal component analysis statistical methods.

Sensitivity was calculated using the following equation. Where R _a is the resistance of the sensor in the air, and R _g is the resistance of the sensor in the presence of the measurement gas. In other words, the ratio between the absence and the measurement gas is defined as the sensitivity.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail.

As shown in Table 1 above, only the tin oxide was used as a sensing material, or a sensing material was prepared by adding a catalyst to the tin oxide. There are three types of manufacturing methods.

First, tin oxide (SnO ₂ ) is prepared by using an impregnation method using platinum (Pt) and / or palladium (Pd) as a catalyst. At this time, the addition amount of the catalyst was 4, 12, 20% by weight, but not limited to this, it is preferable that it is about 1 to 20% by weight.

Second, in the group consisting of alumina (Al ₂ O ₃ ), indium oxide (In ₂ O ₃ ), tungsten oxide (WO ₃ ), silica (SiO ₂ ), and titanium oxide (TiO ₂ ) At least one selected as a catalyst was prepared by mixing by a physical mixing method (ball-milling method). When using alumina as a catalyst, the addition amount is preferably 1 to 20% by weight, of which 4, 12, 20% by weight were selected. In the case of using indium oxide or tungsten oxide as the catalyst, the addition amount is preferably 1 to 3% by weight, of which 1, 2, and 3% by weight were selected. In the case of using silica or titanium oxide as a catalyst, the addition amount is preferably 3 to 10% by weight, of which 3, 5, and 10% by weight are selected.

Finally, zinc oxide (ZnO) and / or zirconium oxide (ZrO ₂ ) was used as a catalyst to prepare tin oxide and coprecipitation. At this time, in the case of using zinc oxide as a catalyst, the addition amount is preferably 1 to 5% by weight, of which 1, 2, 3, 4, 5% by weight was selected. When using zirconium oxide as a catalyst, the addition amount is preferably 0.5 to 5% by weight, of which 1, 3, 5% by weight were selected.

The sensing material (powder) thus prepared was sequentially dried, calcined, calculated, screen printed, and heat treated to form a sensing film. To describe a preferred process for this, first the sensing material was dried at 110 ℃ for one hour, and then calcined for one hour at 600 ℃ using an electric furnace. Using the powder thus prepared, a sensing film was formed on the alumina substrate by screen-printing, and heat-treated at 700 ° C. for 1 hour.

1A-1C are actual photographs of sensor elements fabricated in the above manner. FIG. 1A is a front side of a sensor element coated with a platinum (Pt) electrode for reading a sense resistor, FIG. 1B is a rear side of a sensor element with a heater for adjusting the operating temperature of the sensor element, and FIG. 1C is similar to a chemical agent. It is the front surface of the sensor element coated with a sensing material to detect gas.

The platinum electrode on the front surface of the alumina substrate was formed to have a thickness of 1000 직류 using a DC sputter, and the heater on the rear side formed a thick film by screen-printing using platinum paste. Thereafter, curing was performed at 850 ° C. for 10 minutes in an electric furnace. The resistance of the heater was set to 10Ω as a fixed resistance, and the electrode was designed in an inter-digit (IDT) structure. All sensor elements were measured after stabilization time at 400 ° C. for 3 days. The overall sensor element size was 7mm x 10mm x 0.6mm, and the size of the sensing film was 6mm x 4mm.

The schematic diagram of the measuring apparatus for detecting a chemical agent is shown in FIG. The amount of gas was controlled using mass flow controllers 22 and 32. The measurement gas concentration in the reactor 70 was obtained by adjusting the amount of the reaction gas 34 and the amount of the reference gas. The total amount of flowing gas was kept constant at 1000 ml per minute. The temperature controller (circulator) (33) was used to constantly adjust the saturation temperature. The change of the sensor resistance to the reaction of the measurement gas was stored in real time using a data acquisition board (model NI E6024, model 80). The data acquisition board is a device that can simultaneously accept analog signals through sampling of 500,000 per second on 16 channels. Reference numeral 1 denotes a sensor element, 20 reference gas line, 24 air tank, 30 measurement gas line, 31 saturator, 40 measurement line, 60 exhaust line, 62 hood , 90 represents a power supply.

Results of response characteristics of the four sensor gases of the fabricated sensor element are shown in FIGS. 3A to 3D. FIG. 3a is the result of reaction for DMMP, FIG. 3b is the result for DPGME, FIG. 3c is the result for acetonitrile, and FIG. 3d is the result for dichloromethane. Response characteristics for the four gases were tested for different measurement temperatures and gas concentrations. 3A to 3D show the results obtained by fixing the operating temperature of the sensor element at 300 ppm and the concentration of each measurement gas at 0.5 ppm. The humidity of the mixed gas (measurement gas) at the time of measurement was 40%. Most sensor elements exhibited a high sensitivity of 50% or higher for chemical agents. In the repeatability experiments, a good result showing an error within 3% was obtained. Of all the data for each sensor element, only data having an important meaning is shown in FIGS. 3A to 3D. Here, the abbreviations P, C, and I after weight percent on the x-axis of each figure mean physical mixing, coprecipitation, and impregnation, respectively.

As shown in FIGS. 3A to 3D, the case where the metal or the metal oxide was added to the tin oxide showed higher sensitivity than when the tin oxide was used alone as the sensing material. This is the result of a lot of adsorption, with the catalyst (metal or metal oxide) creating even more active sites on the surface of the sensor. DMMP and DPGME showed high sensitivity to most of four materials: alumina (Al ₂ O ₃ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), and zinc oxide (ZrO ₂ ). Acetonitrile and dichloromethane showed good sensitivity to zinc oxide (ZnO) and zirconium oxide (ZrO ₂ ). However, the reaction was not good for alumina (Al ₂ O ₃ ) and indium oxide (In ₂ O ₃ ). From the above results, four materials to be used as the sensor array were selected. Materials selected are 4% by weight alumina, 2% by weight indium oxide, 2% by weight zinc oxide, 1% by weight zirconium oxide.

4A is a front view of a sensor element coated with a platinum (Pt) electrode for reading a sense resistor, FIG. 4B is a rear view of a sensor element installed with a heater for adjusting an operating temperature of the sensor element, and FIG. 4C is a gas similar to that of a chemical agent. A photograph of the front surface of a sensor element coated with a sensing material to be detected. Four pairs of electrodes are formed on the front side of the sensor array, and a heater having a resistance of 10Ω is formed on the back side. The overall size of the fabricated sensor element was 10mm × 10mm × 0.25mm and the size of the sensing film was 2mm × 2mm. The total power consumption was 2W at an operating temperature of 300 ° C., and the power consumption for the individual sensor was approximately 500mW.

5A to 5D are graphs of sensitivity of four measurement gases according to operating temperatures (250, 300, 350, and 400 ° C, respectively) of the fabricated sensor array. The gas injection concentration was constant at 0.5 ppm. It can be seen that the reaction graph changes according to the change in operating temperature.

6A and 6B show a result of performing principal component analysis for classification of four measurement gases using data measured by a sensor array. The methods used for data classification are neural network method and statistical method. Principal component analysis belongs to the statistical method. There are many types of data that can be collected through the sensor array. For example, there are many data such as data on reaction time, data on reaction gas (measuring gas) type, data on sensing substances, data on reaction gas (measuring gas) concentration, and data on operating temperature. If you draw a graph using all of this data, you will draw a graph with many dimensions, so it is not easy to organize the data at a glance. Principal component analysis is a statistical method that easily classifies through pictures by drawing two or three data with the most significant meaning in order to get the desired result among multiple meaningful data to be. Principal component analysis is known as a suitable method for the classification of chemical agents.

For the sensor element according to an embodiment of the present invention, as shown in FIGS. 6A and 6B, a graph is plotted in two dimensions by performing principal component analysis using data such as the type and concentration of the measurement gas, the type of the sensing substance, and the operating temperature. saw. 6A shows the classification of various measurement gases. The measurement gases used were four chemical agents, toxic gases carbon monoxide (CO), volatile gases methane (CH ₄ ), butane (C ₄ H ₁₀ ), and hydrogen (H ₂ ). The result of this graph is the result of three repeated experiments, whereby three display portions on the graph for each measurement gas are shown. 6B shows the classification results for only four chemical agents. 6A and 6B, the next number after the measurement gas name means the concentration of the measurement gas, and the very large value of the first principal component means that the content of the x-axis is greater than the content of the y-axis. Indicates to display. As can be seen in Figure 6a, by using the sensor array it can be seen that not only four chemical agents but also other gases can be classified.

FIG. 7A is a photograph of a performance measuring device of a gas sensor element used to reduce a reaction time according to an embodiment of the present invention. FIG. 7B schematically illustrates FIG. 7A, and FIG. 7C is FIG. 7A. Figure 4 schematically shows a state in which the four-way valve 10 rotated by 90 °.

Two air mass flow controllers (22, 32) are used to flow the same amount, that is, 1000 cc of reference gas per minute. The air mass flow meters 22 and 32 above adjust the flow rate of the reference gas used for the initial stabilization of the sensor element. The lower air mass flow meter 32 is a carrier flow meter that is input to adjust the concentration of the measurement gas. The concentration of the measurement gas is controlled using an air mass flow meter 32 at the bottom and a chemical working agent mass flow controller 37 at the middle.

The experiment is carried out as follows. First, in order to stabilize the sensor element, the upper air mass flow meter 22, the reference gas (air) line 20, the first passage 12 of the four-way valve 10, and the measurement line 40 are sequentially passed. Therefore, only air (reference gas) flows into the reaction tank 70 and is discharged through the exhaust line 60 (see FIG. 7B). The four-way valve 10 has four openings, two openings are where the gas is introduced, the other two openings are where the gas is flowing, and two pairs of two adjacent openings are each connected by a passage. It forms the first and second passages 12, 14. Accordingly, when stabilizing, only air flows into the reaction tank 70 through the upper air mass flow meter 22, and the measurement gas whose measured concentration is adjusted is the second passage of the measurement gas line 30 and the four-way valve 10. 14 and the vent line 50 sequentially pass outward through the reactor 70 (see FIG. 7B).

After waiting for stabilization in this manner, when the four-way valve 10 is rotated by 90 ° at the time of measurement, the measurement gas whose measurement concentration is adjusted is introduced into the reactor 70 through the measurement line 40 (see FIG. 7C). In contrast, air entering through the upper air mass flow meter 22 flows outward through the vent line 50. Then, after the response to the measurement gas has been made, that is, the response of the measurement gas reaches saturation, the four-way valve 10 is rotated 90 ° again to introduce only air through the upper air mass flow meter 22. You can go back to step

By using the four-way valve 10 can be expected very fast reaction speed. In order to increase the reaction rate, the time for introducing the measurement gas should be reduced, and the capacity of the reaction tank 70 should be reduced to the minimum (about 70 to 90 cc). In this experiment, the reaction time of less than 20 seconds was obtained by using a four-way valve 10 and specially manufacturing an 80cc reactor.

The apparatus for measuring the performance of the gas sensor element described above can be applied not only to the semiconductor thick film gas sensor element according to the present invention but also to other gas sensor elements for collecting data by the reaction of the gas and the gas sensor element in the reactor.

8 is a bonded photograph of an actual fabricated sensor array according to an embodiment of the present invention. This sensor array was placed in a mini reactor and the experiments described above were performed.

The present inventors fabricated a sensor element capable of real-time monitoring of chemical agents that may occur during chemical terrorism using tin oxide as a parent material. In order to solve the selectivity problem, which is a disadvantage of the semiconductor gas sensor device having a single sensor, a sensing material sensitive to each chemical agent is selected and configured as a sensor array, and the similar sensor of each chemical agent is measured using the configured sensor array. The resistance of the sensing film was measured by gas, by operating temperature, and by the amount of the added substance. Based on the data obtained thereafter, each chemical agent was classified through principal component analysis. As a result, it was manufactured with a thick film and showed high sensitivity, and solved the selectivity problem which is a disadvantage of the semiconductor gas sensor.

By establishing a gas detection system using the fabricated sensor array and principal component analysis method, it is possible to quickly and quantitatively detect the types of chemical agents used in terrorism and their specific substances, and to take actions corresponding to those substances, thereby preventing human injury. This can be reduced to a minimum. In particular, sensors may be placed in important terror-producing areas in advance, and real-time remote monitoring will prevent damage caused by terrorism in advance, further securing safety from the threat of chemical terrorism.

The semiconductor thick film gas sensor element according to the present invention has excellent selectivity against various gases, especially chemical agents used in chemical terrorism.

The performance measuring device of the gas sensor element according to the present invention minimizes the reaction time between the gas sensor element and the measurement gas.

Although the present invention described above has been described in detail only with respect to the specific examples described, it will be apparent to those skilled in the art that various modifications and changes are possible within the technical spirit of the present invention, and such modifications and modifications belong to the appended claims. will be.

Claims (14)

At least two sensors consisting of an electrode and a sensing film formed on the front surface of the substrate to form a sensor array, a heater is formed on the back of the substrate, And a sensing material constituting the sensing film comprises tin oxide. The method of claim 1, The sensing material further comprises at least one selected from the group consisting of alumina, indium oxide, tungsten oxide, platinum, palladium, zinc oxide, zirconium oxide, silica, and titanium oxide. The method of claim 2, The content of the sensing material is 1 to 20% by weight of alumina, 1 to 3% by weight of indium oxide and / or tungsten oxide, 1 to 3% by weight of platinum and / or palladium, and content of zinc oxide. A semiconductor thick film gas sensor device, characterized in that 1 to 5% by weight, the content of zirconium oxide is 0.5 to 5% by weight, and the content of silica and / or titanium oxide is 3 to 10% by weight. The method of claim 2, And four sensors, and four sensing films each include alumina, indium oxide, zinc oxide, and zirconium oxide. The method of claim 4, wherein The semiconductor thick film gas sensor device, characterized in that the content of the alumina is 4% by weight, the content of indium oxide is 2% by weight, the content of zinc oxide is 2% by weight, the content of zirconium oxide is 1% by weight. . The method of claim 1, A semiconductor thick film gas sensor element, characterized in that the resistance of the heater is 10Ω. The method of claim 2, If the sensing material comprises tin oxide, platinum and / or palladium, the sensing material is manufactured by an impregnation method. The method of claim 2, If the sensing material comprises tin oxide and at least one selected from the group consisting of alumina, indium oxide, tungsten oxide, silica, and titanium oxide, the sensing material is a semiconductor formula, characterized in that the manufacturing by physical mixing Thick film gas sensor element. The method of claim 2, If the sensing material comprises tin oxide, zinc oxide and / or zirconium oxide, the sensing material is manufactured by a coprecipitation method. The method according to any one of claims 7 to 9, And forming the sensing film by sequentially drying, calcining, screen-printing, and heat-treating the manufactured sensing material. A four-way valve having four openings, two pairs of two adjacent openings each connected by a passage to form a first and a second passage; A reference gas line for introducing a reference gas into the four-way valve; A measurement gas line for introducing a measurement gas into the four-way valve; A measurement line for introducing the reference gas or the measurement gas into the reactor from the four-way valve; A vent line for discharging the reference gas or the measurement gas to the outside from the four-way valve; An exhaust line for discharging the reference gas or the measurement gas from the reactor to the outside; A reaction tank in which a reaction between a gas sensor element and the measurement gas occurs; And A measuring unit connected to the gas sensor element; Including; During stabilization, the reference gas passes sequentially through the reference gas line, the first passage, and the measurement line, and the measurement gas passes sequentially through the measurement gas line, the second passage, and the vent line. Positioning the four-way valve, In the measurement, the measurement gas passes sequentially through the measurement gas line, the first passage, and the measurement line, and the reference gas passes sequentially through the reference gas line, the second passage, and the vent line. Performance measuring device of the gas sensor element for positioning the four-way valve. The method of claim 11, Performance measurement of the gas sensor element is a performance measurement device of the gas sensor element, characterized in that for measuring the resistance of the sensing film to the reaction of the measurement gas. The method of claim 12, The gas sensor element is a performance measuring device of the gas sensor element, characterized in that the semiconductor thick film gas sensor element. The method according to any one of claims 11 to 13, The capacity of the reactor is 80cc performance measurement apparatus of the gas sensor element.

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