KR20060111296A - Hydrogen sensor and manufacturing method thereof - Google Patents

Abstract

A hydrogen sensor and a manufacturing method thereof are provided to be easily manufactured in mass production with a stable structure by measuring a concentration of the hydrogen by sensing a static electricity change between a fixed electrode and a relative electrode. In a hydrogen sensor, a variable electrode unit includes a driving electrode(240) having elasticity and varied in a position thereof by a partial pressure of hydrogen and a Pd reactive-film. Both side surfaces of the variable electrode unit are fixed with being separated from the fixed electrode. And, the external structure exposes the Pd reactive-film of the variable electrode unit to an external environment with supporting or protecting the fixed electrode and the variable electrode unit.

Description

Hydrogen sensor and its manufacturing method {HYDROGEN SENSOR AND MANUFACTURING METHOD THEREOF}

1 is a conceptual diagram showing the structure and operation of the fuel cell.

2 is a recommended performance of the hydrogen sensor.

3 is a type of a typical commercial hydrogen sensor.

Figure 4 is a graph showing the stress and light transmittance characteristics of the Pd thin film according to the hydrogen partial pressure.

5 is a conceptual view and application example of the operation of the hydrogen sensor using a micro cantilever.

6 is a conceptual diagram illustrating an example of an optical hydrogen sensor.

7 is a conceptual diagram and application example of the resistance-type hydrogen sensor.

8 is a schematic conceptual view and application example of the FET-type hydrogen sensor.

9 is a sectional view showing a structure of an embodiment of the present invention.

10 is a cross-sectional view showing a structure of another embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100: outer case 110: lower substrate

120: fixed electrode 130: counter electrode

140: diaphragm 150: reaction film

200: outer case 210: lower substrate

220: fixed electrode 230: upper substrate

240: upper electrode 250: membrane layer

260: reaction membrane

The present invention relates to a hydrogen sensor and a method of manufacturing the same, and in particular, by using a physical volume change of the Pd reaction membrane to vary the distance between the electrodes by mass production of a hydrogen sensor for measuring the concentration of hydrogen in a simple and easy structure and process The present invention relates to a hydrogen sensor and a manufacturing method thereof.

With the rapid industrialization, energy consumption has soared, and the depletion of the fossil fuels we are using now is tangible. In 2003, British refinery British Petroleum (BP) estimated that fossil fuel reserves remained 40 years of crude oil, 62 years of natural gas and 216 years of coal. It is expected to be shorter than this by appearance. As the development of energy to replace fossil fuels is rapidly progressing, interest in hydrogen that can generate electricity through high explosiveness or by combining with oxygen is increasing.

FIG. 1 is a conceptual diagram showing a basic structure and a method of operation of a fuel cell in which many studies are conducted as a means for using hydrogen. As shown in FIG. 1, electricity is generated through a chemical reaction between hydrogen and oxygen. However, since hydrogen has an explosion range of 4 to 75% and is ignited with only 0.02mJ of energy in the atmosphere, the explosion risk is a big problem in using fuel cells. In addition, the diffusion coefficient is very high (0.61 cm2 / s in air) and it is very difficult to easily diffuse through most materials and to be locked in a specific container. As a result, hydrogen-related devices or related accessories require attention to hydrogen leakage. Therefore, in order to use a fuel cell, a hydrogen leak sensor that can detect a hydrogen concentration of approximately 1000 ppm to 4% must be installed. There is also a need for a hydrogen sensor that can identify the quality of hydrogen entering the fuel cell. The concentration of hydrogen can vary from 40 to 99.9%, depending on the design of the fuel cell system. The exact specifications of the hydrogen sensor have not yet been unified, but the US Department of Energy (DOE) provides the specifications shown in Figure 2.

In other words, it has a wide measurement range and a temperature range of use, fast measurement speed is required, and it can be seen that the use time is also set very long for safety.

Figure 3 shows some of the current commercially available hydrogen sensors, there are contact combustion (a), semiconductor (b), electrochemical (c) sensor. However, the contact combustion sensor (a) cannot be used as a hydrogen leakage sensor because it reacts with most combustible gases in principle, and cannot be used even in a fuel cell system without oxygen gas because oxygen gas is required for combustion. The semiconductor sensor (b) also lacks hydrogen selectivity in principle, and since oxygen gas is required, this is also difficult to use as a leak sensor and a sensor applied in the system. Electrochemical sensor (c) is very good hydrogen selectivity can detect even a small amount of hydrogen gas, but the life is short, the sensor should be replaced every six months, there is a disadvantage that high concentration hydrogen is difficult to detect. In addition, since it is based on the reaction with oxygen in principle, it can be used only in the atmosphere.

Therefore, the current commercially available hydrogen sensor is difficult to use as a leak sensor for applying to a fuel cell, so the development of a hydrogen sensor that can be used in a fuel cell has been mainly studied using Pd (palladium). When Pd is exposed to hydrogen gas, hydrogen gas dissociates from the surface of Pd and is absorbed into Pd. Pd can dissolve hydrogen up to 600 times in volume ratio, and the absorbed hydrogen reacts with Pd to form hydrogen compounds of PdHx. x is determined by the partial pressure of hydrogen, and thus the mechanical, optical and electrical properties of PdHx change according to the partial pressure of hydrogen. Therefore, it is possible to measure the concentration of hydrogen by measuring the change in the electrical, mechanical and optical properties of the Pd hydrogen compound, and also to measure the concentration of hydrogen alone without being affected by other gases, and vacuum or oxygen-free atmosphere. There is also an advantage that can be used.

4 is a graph showing the change in stress and light transmittance of the Pd thin film according to the partial pressure of hydrogen. As the partial pressure of hydrogen increases, the Pd thin film forms a hydrogen compound and the volume expands, thereby rapidly causing mechanical stress. Various sensors capable of measuring the concentration of hydrogen using these characteristics have been developed and studied for use in the fuel cell described above.

FIG. 5 shows a micro-cantilever-type hydrogen sensor constructed by paying attention to the fact that the Pd film formed on a specific substrate expands in volume with hydrogen partial pressure, thereby increasing stress and causing deformation in the substrate. It uses microelectromechanical system (MEMS) technology to make microcantilevers and to coat Pd thin films on the cantilevers. The coated Pd absorbs hydrogen gas and causes deformation, and when the cantilever is deformed, the capacitance of the hydrogen sensor changes. Therefore, the concentration of hydrogen can be measured by measuring the capacitance.

The hydrogen sensor has the advantages of excellent sensitivity and very low power consumption, but the manufacturing process is very complicated, and since the structure of fixing the support layer floating in the air on only one side is difficult to level, the initial offset of individual devices increases. As a result, the measurement deviation of individual devices according to the concentration is also very large. In other words, the low reproducibility is extremely vulnerable to mass production, and the reliability of the measurement is also very low because the measurement value varies depending on the individual devices and the measurement value can vary according to the accumulation of physical fatigue.

FIG. 6 illustrates the concept of an optical hydrogen sensor based on the fact that the hydrogen compound formed by the reaction between Pd and hydrogen has a characteristic that the transmittance of light varies according to the partial pressure of hydrogen gas (FIG. 4). As shown, Pd is coated on one end of the optical fiber, and light is generated (using a laser diode) on the other end. Light passing through the optical fiber is reflected back from Pd, and the ratio of the amount of reflected light and the amount transmitted is determined by the partial pressure of hydrogen gas. Therefore, the concentration of hydrogen can be measured by detecting the amount of reflected light. However, although the sensor using the optical fiber shows excellent sensing characteristics, commercialization is difficult due to the need for an optical packaging technology having a very expensive and complicated structure.

Hydrogen compounds formed by the reaction of Pd with hydrogen show different electrical property changes according to hydrogen concentration, and some sensors use such electrical property changes. The resistive hydrogen sensor of FIG. 7 and the field effect transistor of FET 8 of FIG. Hydrogen sensors are typical. The resistive hydrogen sensor is currently being studied (US Pat. No. 5,338,708) by coating a thick film of Pd on a substrate to calculate the hydrogen concentration by measuring the electrical resistance change of the Pd hydrogen compound. In addition, the hydrogen sensor for measuring the threshold voltage of the FET is formed of a gate electrode having a general metal insulator semiconductor FET (MISFET) structure of Pd alloy. When hydrogen gas is present in the atmosphere, the hydrogen sensor reacts with Pd to change electrical characteristics of the gate metal. The threshold voltage of the transistor changes greatly, and it works on the principle that the concentration of hydrogen gas can be known by measuring it. It is simply a MIS (Metal Insulator Semiconductor) structure that can be used as a hydrogen sensor by measuring the capacitance change of the insulator caused by the change in the electrical properties of the Pd metal.

Among the various hydrogen sensors described above, there is a microcantilever type in which a volume increase of a hydrogen compound generated as the Pd reaction layer is combined with hydrogen is a sensor that changes significantly with the concentration of hydrogen. As described above, the sensitivity is excellent because it is sensitive to the physical change caused by the increase of hydrogen, and the power consumption is very low because there is almost no current consumed for the measurement, but the currently developed structure is due to structural factors. Problems had to occur. That is, since only one side of the operation part is fixed on the substrate, manufacturing is difficult, reproducibility is extremely low, and the characteristic difference between the devices is also severely generated, so that the measured values of hydrogen of the same concentration appear differently. In addition, the degree of change in the measured value according to the change in hydrogen concentration is also different for each individual element, and even in the same element, the measured value fluctuations due to the accumulation of fatigue tend to occur. In addition, since it has a limited cantilever structure, the area that can be measured is inevitably narrowed, and it is difficult to deform into various forms, thereby limiting a measurement target to be applied.

As described above, the cantilever structure sensor, which has a small influence on the external environment, high hydrogen selectivity, and which can be miniaturized, changes in volume when the Pd reaction membrane is combined with hydrogen, has a sensitivity and power consumption. Although it has excellent characteristics, it is structurally fragile, difficult to manufacture, and there is a large variation in each device, which not only complicates the means for correcting it, but also makes it difficult to mass-produce, which is expensive, and only a limited amount of Pd reaction film can be formed only on the limited cantilever. There was a problem that the concentration region was narrow. That is, the conventional sensor for measuring the concentration of hydrogen by the change in capacity due to physical electrode displacement has a problem that all of productivity, cost, ease of measurement, reproducibility, and changeability are very weak.

In view of the above problems, the present invention includes a fixed electrode, a solid support structure on top thereof, and a Pd whose volume varies depending on the counter electrode, the diaphragm, and the hydrogen concentration so that the distance to the fixed electrode can be varied. After the reaction film is installed to form a capacitor, the hydrogen concentration can be measured by detecting the change in capacitance between the fixed electrode and the counter electrode by the elastic diaphragm deformed by the volume change of the Pd reaction film according to the hydrogen concentration. It is an object of the present invention to provide a hydrogen sensor and a method for producing the same, which are structurally stable and greatly improve the ease of processing.

In order to achieve the above object, the present invention is fixed fixed electrode; A variable electrode part spaced apart from the fixed electrode and fixed at least on both sides thereof, the variable electrode part including an elastic driving electrode and a Pd reaction film whose position is changed by partial pressure of hydrogen; And an external structure that exposes the Pd reaction film of the variable electrode part to an external environment while supporting or protecting the fixed electrode and the variable electrode part.

The fixed electrode is formed to have a predetermined area on the substrate mounted on one side of the external structure, characterized in that the variable electrode having a predetermined area on the fixed electrode is located opposite.

The variable electrode part is fixed to at least both sides by the external structure, and is spaced apart from the fixed electrode through this, and has a diaphragm structure in which a distance from the fixed electrode is varied by physical deformation of the Pd reaction film.

In addition, the present invention comprises the steps of forming a fixed electrode on the substrate; Forming a driving electrode including an elastic portion having a predetermined tensile stress; Forming a reaction layer on one surface of the driving electrode to react with hydrogen to change a volume; Fixing at least two side surfaces of the driving electrode with each of the electrodes facing each other by separating the driving electrode and the reaction layer from the fixed electrode by a predetermined distance; Packaging the structure into an external structure having a predetermined passage so that the structure can be exposed to an external hydrogen environment while protecting the structure.

The driving electrode and the reaction layer including the elastic part sequentially form the driving electrode on a substrate, and form a membrane layer having a diaphragm function using a material having a tensile stress thereon, and then reacting the Pd on the membrane layer. And forming the film into a pattern having an area of a predetermined size.

When described in detail with reference to the accompanying drawings, the present invention as follows.

9 is a cross-sectional view showing a structure of an embodiment of the present invention, a lower structure consisting of a lower substrate 110 on which a fixed electrode 120 is formed, a driving electrode 130, a diaphragm 130, and a Pd reaction. It consists of an upper structure composed of the membrane 150 and an outer case 100 which physically supports it and protects it from the external pollution environment and enables the flow of hydrogen.

Here, at least both side surfaces of the upper structure including the driving electrode 130, the diaphragm 130, and the Pd reaction film 150 may be fixed by the outer case 100, or may be separated from the lower structure by a separate support. It must be fixed in the spaced apart position. That is, the upper structure including the driving electrode 130 is formed as a kind of diaphragm structure in which both sides or the entire boundary surface may be fixed in terms of physical stability and ease of manufacture. Here, the diaphragm 130 is a film having a predetermined tensile stress, and when the Pd reaction film 150 formed on one side is combined with hydrogen to change volume, the position of the driving electrode 130 is changed and the hydrogen concentration is lowered. When the volume is reduced, it means a layer that functions to return the position of the driving electrode 130 to its original position. This is preferably formed of a material having excellent elasticity of a ceramic-based or polymer-based material such as SiNx, SiO ₂ / SiNx / SiO ₂ .

Accordingly, in the structure, the sensor unit has a diaphragm-type capacitor structure having a predetermined area, and depends on a distance between the driving electrode 130 and the fixed fixed electrode 120 moving according to the volume change of the Pd reaction film 150. The changing capacitance can be measured by the concentration of hydrogen. In addition, the measurement power is extremely weak since only the capacitance between the electrodes 120 and 130 needs to be obtained for the measurement.

FIG. 10 shows another embodiment of the present invention. The basic principle is the same as that of FIG. 9, but the semiconductor process is used to facilitate the manufacturing process and to be suitable for mass production.

As shown, after separately manufacturing a structure in which the fixed electrode 220 is formed on the lower substrate 210, the upper substrate 230, the driving electrode 240, and the diaphragm operation are performed by using a general thick film bulk etching. A structure consisting of the membrane layer 250 and the Pd reaction film 260 is formed. And, while protecting this in an external environment, the hydrogen is protected by an outer case 200 in which a plurality of holes are formed to enable access.

That is, in detail, in the manufacturing process of the upper portion, the driving electrode 240, the membrane layer 250, and the Pd reaction film 260 are sequentially formed on the single crystal silicon substrate 230, and then the single crystal silicon substrate 230 is formed. Bulk etching the back of the) to expose a portion of the driving electrode 240. Of course, a different type of substrate may be used instead of the single-nose silicon substrate 230, and the vertical etching may be performed to form a structure having the same function. It is recommended to use the same rear bulk etching technique.

The membrane layer 250 may be formed of a material having excellent elasticity of a ceramic-based or polymer-based material such as SiNx, SiO ₂ / SiNx / SiO _2, and is increased according to a volume change of the Pd reaction layer 260. Other kinds of materials may also be used which may have a suitable tensile stress that is restored to a circular state again.

These structures are fairly easy to implement, and mass production can be simplified, resulting in significant cost savings. In addition, many improvements have been made to the film-forming process in the semiconductor process, so the highly accurate electrode, the diaphragm structure providing elasticity, and the reproducibility of the thickness and area of the Pd thin film can be produced in large quantities to produce sensors without variation in desired performance. have.

The hydrogen sensor having the structure of the present invention as described above provides various advantages, first of all, it is easy to adjust the area of each electrode, and it is easy to integrate the same structure in a single outer case 100 to adjust the area and number It is easy to design sensors that can be used for many purposes, such as sensitive sensors at high hydrogen concentrations or sensitive sensors at low hydrogen concentrations. In addition, the diaphragm structure configured to move the driving electrode may be fixed to both sides in a state spaced apart from the fixed electrode to increase physical strength, and the diaphragm structure may be stressed even when the reaction membrane is suddenly changed in volume due to hydrogen reaction. Since the driving electrodes are hardly peeled off, the device reliability and lifespan can be improved. In addition, since the present invention measures the hydrogen concentration by the change in capacitance, no separate power is consumed for driving the sensor.

As described above, the hydrogen sensor of the present invention and the method of manufacturing the same have a fixed electrode, and have a solid support structure on the top thereof, and have a volume according to the counter electrode, the diaphragm, and the hydrogen concentration so that the distance to the fixed electrode can be varied. After the variable Pd reaction film is installed to form a capacitor, the hydrogen concentration is measured by detecting the change in capacitance between the fixed electrode and the counter electrode by the elastic diaphragm deformed by the volume change of the Pd reaction film according to the hydrogen concentration. In this way, it is possible to easily manufacture large quantities of structurally stable and undeviated sensor structures, and to adjust the area of each electrode in order to design a sensor suitable for a desired application environment. To provide hydrogen sensors with superior reliability and precision There.

Claims (9)

A fixed fixed electrode; A variable electrode part spaced apart from the fixed electrode and fixed at least on both sides thereof, the variable electrode part including an elastic driving electrode and a Pd reaction film whose position is changed by partial pressure of hydrogen; And an external structure for exposing the Pd reaction film of the variable electrode part to an external environment while supporting or protecting the fixed electrode and the variable electrode part. The fixed electrode of claim 1, wherein the fixed electrode is formed to have a predetermined area on a substrate mounted on one side of the external structure, and the variable electrode part having a predetermined area on the fixed electrode is disposed to face each other. Hydrogen sensor. The diaphragm structure according to claim 1, wherein the variable electrode part is fixed at least on both sides by the external structure, and is spaced apart from the fixed electrode through the external structure, and has a diaphragm structure in which a distance from the fixed electrode is changed by physical deformation of the Pd reaction film. Hydrogen sensor characterized by having. 2. The fixed electrode of claim 1, wherein the variable electrode part is formed on an upper portion of the substrate from which a predetermined region is removed, and a substrate for removing the predetermined region to expose the driving electrode of the variable electrode portion is disposed on the fixed electrode. A hydrogen sensor having a structure to secure the separation distance between the electrodes. The hydrogen sensor according to claim 1, wherein the elastic driving electrode is formed by a combination of an elastic diaphragm and a conductive layer. 6. The hydrogen sensor according to claim 5, wherein the material constituting the diaphragm is a ceramic-based or polymer-based high elastic material including SiNx, SiO ₂ / SiNx / SiO ₂ . Forming a fixed electrode on the substrate; Forming a driving electrode including an elastic portion having a predetermined tensile stress; Forming a reaction layer on one surface of the driving electrode to react with hydrogen to change a volume; Fixing at least two side surfaces of the driving electrode with each of the electrodes facing each other by separating the driving electrode and the reaction layer from the fixed electrode by a predetermined distance; Packaging the structure into an external structure having a predetermined passage so that the structure can be exposed to an external hydrogen environment while protecting the structure. The method of claim 7, wherein the driving electrode and the reaction layer including the elastic part sequentially form a driving electrode on a substrate, and a membrane layer having a diaphragm function is formed of a material having a tensile stress on the substrate. Forming a Pd reaction film in a pattern having an area having a predetermined size on the membrane layer. The method of claim 8, further comprising etching the rear surface of the substrate to expose the driving electrode, and then disposing the structure on the substrate on which the fixed electrode is formed.

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