KR20160125245A - Limiting current type oxygen sensor and Method of manufacturing the same - Google Patents

Abstract

Disclosed are a limiting current-type oxygen sensor and a manufacturing method thereof. According to the present invention, the limiting current-type oxygen sensor comprises: a solid electrolyte to pump oxygen ions; an anode electrode and a cathode electrode formed on an upper surface and a lower surface of the solid electrolyte, respectively; and a sensor substrate attached to a side of the cathode electrode in a surface-to-surface manner. An entrance of a linear pin hole is opened on one side wall exposing an interface between the solid electrolyte and the sensor substrate and extended and penetrated to a point where at least a portion of the cathode electrode is exposed. According to the present invention, manufacturing costs of the limiting current-type oxygen sensor can be reduced by a light weight and a small size of the sensor and a simplified process.

Description

TECHNICAL FIELD The present invention relates to a limiting current type oxygen sensor and a manufacturing method thereof,

TECHNICAL FIELD The present invention relates to a limiting current type oxygen sensor used for measurement of oxygen concentration and a manufacturing method thereof.

Oxygen sensors are used extensively for the purpose of measuring air pollution, improving fuel efficiency and thermal efficiency in combustion devices such as automobiles and boilers, reducing hazardous components in exhaust gases, and controlling the oxygen concentration in production facilities requiring oxygen.

The oxygen sensor is divided into a concentration cell type, an oxide semiconductor type, and a limiting current type according to the principle of the sensing.

The limit current type oxygen sensor has a merit that the oxygen concentration can be measured over a wide range as compared with the all-terrain type or oxide semiconductor type, the reference electrode is unnecessary, and it can be used at a relatively low temperature. In addition, it is possible to fabricate a sensor having a simple structure and a small element type, and is inexpensive in mass production and excellent in reproducibility, and is widely used among various types of oxygen sensors.

Conventionally, a limit current type oxygen sensor using a solid electrolyte made of Yttria Stabilized Zirconia (YSZ) containing yttria (Y ₂ O ₃ ) as an additive is known.

In a limiting current type oxygen sensor, when a cathode electrode and an anode electrode are attached to both surfaces of a solid electrolyte having conductivity with respect to oxygen ions (O ^2- ) and a voltage (hereinafter referred to as a pumping voltage) is applied to both electrodes, The surrounding oxygen is converted into oxygen ions (O ^2- ) by obtaining electrons from the cathode electrode. Further, the oxygen ions move toward the anode electrode through the solid electrolyte, and electrons are converted to oxygen molecules by giving electrons to the anode electrode. The above process is called electrochemical ion pumping, and the movement of oxygen ions through ion pumping causes a current to flow in the circuit connecting the cathode electrode and the anode electrode.

Ion pumping through the solid electrolyte reaches equilibrium in a short time, and the current magnitude thereafter is limited to a constant magnitude even as the magnitude of the pumping voltage changes. The magnitude of such a limiting current varies depending on the amount of oxygen supplied to the cathode electrode, that is, the partial pressure of oxygen and the temperature of the solid electrolyte. Therefore, if the size of the limiting current is measured under the condition that the temperature of the solid electrolyte is fixed, the oxygen concentration in the space where the cathode electrode is exposed can be accurately measured.

1 is a schematic diagram showing the structure of a limiting current type oxygen sensor widely used in the past.

1, a conventional limiting current type oxygen sensor 10 includes a solid electrolyte 11, an anode electrode 12 and a cathode electrode 13 made of a porous material for applying a pumping voltage to both sides thereof, .

In order to measure the limiting current in the limiting current type oxygen sensor 10, in order to control the amount of oxygen supplied to the cathode electrode 13 to be dependent on the oxygen concentration, a diffusion barrier barrier.

The limiting current type oxygen sensor 10 illustrated in FIG. 1 includes a cap structure 16 on the cathode electrode 13 side as an example of a diffusion barrier. The cap structure 16 is formed with a predetermined diffusion space A under the cathode electrode 13 and a gas diffusion hole 14 through which a gas to be measured for oxygen concentration is introduced into the diffusion space A .

The cap structure 16 includes a side wall portion 17 extending downward from a position spaced a predetermined distance from the edge of the cathode electrode 13 and a lower portion of the side wall portion 17 toward a center portion of the oxygen sensor 10 And a bottom portion 18 that is vertically bent and extends to the gas diffusion bore 14.

The gas diffusion bore 14 has a diameter and a length capable of ensuring Knudsen-type gas diffusion. Here, the nucin-type gas diffusion occurs when the pore size is smaller or smaller than the mean free path of the gas. In the case of gas diffusion, the partial pressure of oxygen increases linearly with the magnitude of the limiting current.

On the other hand, the solid electrolyte 11 of the limiting current type oxygen sensor 10 needs to be heated to a temperature capable of causing ion pumping (hereinafter referred to as reaction temperature), for example, several hundreds degrees.

To this end, a thin film heater 17 is provided below the bottom portion 18 of the cap structure 16. The thin film heater 17 receives electric power from a separate DC power source 19 through a lead wire 18 and generates resistance heat to a temperature of several hundreds degrees. Then, heat is conducted to the side of the solid electrolyte 11, and the temperature of the solid electrolyte 11 rises to a temperature at which ion pumping can occur.

The conventional limiting current type oxygen sensor 10 including the cap structure 16 as a diffusion barrier has a complicated process for forming the cap structure 6 and thus has a high manufacturing cost and a limitation in miniaturization of the sensor.

For example, in order to form the diffusion space A and the gas diffusion bore 14 by using the cap structure 6 inside the sensor, a groove is formed in the sheet base material constituting the cap structure 16, And then forming the bottom portion 18 and then punching the gas diffusion bore 14 in the central portion of the bottom portion 18.

Alternatively, a bottom portion 18 in which a gas diffusion hole 14 is formed in the central portion and a spacer-shaped side wall portion 17 to be attached in the vicinity of the cathode electrode 13 are independently fabricated, It is necessary to carry out a process of vertically stacking the layers.

In order to overcome the above problems of the cap structure 16, a technique of replacing the diffusion barrier with a porous insulating film has been commercialized. For example, a technique of coating a porous film in which alumina (Al ₂ O ₃ ) and YSZ are mixed on a particle basis is coated on the surface of the cathode electrode 13.

However, when the porous film is coated, the resolution of the sensor is deteriorated in a specific range of oxygen concentration, and the reproducibility of the sensor is deteriorated due to minute changes in porosity. Further, in order to form a porous film, a process of synthesizing a raw material powder in paste form and coating, drying, and firing must be performed. Therefore, there is a limit in reducing the manufacturing cost of the sensor by simplifying the process.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a limiting current type oxygen sensor including a diffusion barrier structure capable of spreading in a wide range of oxygen concentration, There is a purpose.

According to an aspect of the present invention, there is provided a limiting current type oxygen sensor comprising: a solid electrolyte capable of pumping oxygen ions; An anode electrode and a cathode electrode respectively formed on the upper and lower surfaces of the solid electrolyte; And a sensor substrate attached to the cathode electrode side in a face-to-face manner. A line-shaped pinhole is formed at an interface between the solid electrolyte and the sensor substrate so as to extend to a position exposing at least a part of the cathode electrode. The inlet of the line-shaped pinhole is connected to a side wall And is opened.

Preferably, the inner end of the line-shaped pinhole extends so as to overlap the inner region of the cathode electrode across the rim of the cathode electrode.

Preferably, the line-shaped pinhole remains as a trace while the combustible wire is burned.

According to an aspect of the present invention, a grain boundary of crystals constituting the solid electrolyte and the sensor substrate may be exposed through an inner wall of the line-shaped pinhole.

According to another aspect, a combustion by-product of the combustible wire may exist in an extremely small amount on the inner wall of the line-shaped pin hole.

In one example, the solid electrolyte and the sensor substrate may be made of stabilized zirconia (YSZ) to which yttria is added.

According to another aspect of the present invention, there is provided a limiting current type oxygen sensor according to the present invention, which is interposed between the solid electrolyte and the sensor substrate so as to overlap with the cathode electrode, at least a part of which is exposed to the outside along the upper surface of the sensor substrate And may further include a cathode lead wire pad. The cathode lead line may further include a cathode lead line connected to the cathode lead line pad and an anode lead line connected to the anode electrode.

According to another aspect, the cathode electrode may include a portion exposed to the outside along the lower surface of the solid electrolyte. In this case, the limiting current type oxygen sensor according to the present invention may further include a cathode lead wire connected to the exposed portion and an anode lead wire connected to the anode electrode.

According to another aspect of the present invention, the limiting current type oxygen sensor according to the present invention may further include a heater substrate attached to a lower side of the sensor substrate, and a thin film line heater formed on a lower surface of the heater substrate.

According to an aspect of the present invention, there is provided a method of manufacturing a limiting current type oxygen sensor, comprising: (a) forming an anode electrode and a cathode electrode on an upper surface and a lower surface of a green sheet for a solid electrolyte; (b) preparing a green sheet for a sensor substrate; (c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure; And (d) simultaneously firing the laminated structure to simultaneously sinter the green sheet for a solid electrolyte and the green sheet for a sensor substrate, and burning the combustible wire to form a line-shaped pinhole.

Preferably, the combustible wire may be a synthetic resin yarn, a paper yarn, a carbon fiber, or an animal fiber yarn.

Preferably, the present invention may further include a step of pressing the laminated structure using a hot isostatic press before the step (d).

Preferably, the green sheet for a solid electrolyte and the green sheet for a sensor substrate may include stabilized zirconia particles to which yttria is added.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: (b) forming a cathode lead wire pad, one end of which overlaps with the cathode electrode, To the upper surface of the green sheet for the sensor substrate. The method may further include connecting the cathode lead line and the anode lead line to the exposed portion of the cathode lead line pad and the anode electrode, respectively.

According to another aspect, the step (a) may include forming the cathode electrode such that a part of the cathode electrode is exposed to the outside along the lower surface of the green sheet for solid electrolyte. In this case, the present invention may further include connecting the cathode lead wire and the anode lead wire to the exposed portion of the cathode electrode and the anode electrode, respectively.

According to another aspect of the present invention, the method may further include preparing a heater substrate having a thin film line heater formed on a lower surface thereof, and fixing the stacked structure having the line-shaped pinhole to the heater substrate.

According to another aspect of the present invention, there is provided a method of manufacturing a limiting current type oxygen sensor, comprising: (a) forming an anode electrode and a cathode electrode on a top surface and a bottom surface of a green sheet for a solid electrolyte; (b) preparing a green sheet for a sensor substrate; (c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure; (d) fixing the laminated structure on a green sheet for a heater substrate on which a thin film line heater is formed; (e) simultaneously firing the green sheet for a heater substrate to which the laminated structure is fixed, simultaneously sintering the green sheet for a solid electrolyte, the green sheet for a sensor substrate and the green sheet for a heater substrate, burning the combustible wire And forming a line-shaped pinhole in place of the pinhole.

According to another aspect of the present invention, there is provided a method of manufacturing a limiting current type oxygen sensor, comprising: (a) forming an anode electrode and a cathode electrode on a top surface and a bottom surface of a green sheet for a solid electrolyte, ; (b) preparing a green sheet for a sensor substrate in which a cathode lead pad having one end overlapped with the cathode electrode and the other end exposed to the outside is formed on an upper surface; (c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure; (d) fixing the laminated structure on a green sheet for a heater substrate on which a thin film line heater is formed; (e) simultaneously firing the green sheet for a heater substrate to which the laminated structure is fixed, simultaneously sintering the green sheet for a solid electrolyte, the green sheet for a sensor substrate and the green sheet for a heater substrate, burning the combustible wire And forming a line-shaped pinhole in place of the pinhole.

According to an aspect of the present invention, the diffusion barrier structure of the limiting current type oxygen sensor can be formed by a simple process. Also, since the space occupied by the diffusion barrier structure is minimized, it is possible to reduce the thickness of the oxygen sensor. In addition, the manufacturing cost of the oxygen sensor can be reduced by simplifying the process. In addition, it is possible to manufacture a limiting current type oxygen sensor in which the oxygen concentration exhibits a linear dependence on the magnitude of the limiting current over a wide range of oxygen concentration.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention, And should not be construed as interpretation.
1 is a schematic diagram showing the structure of a limiting current type oxygen sensor widely used in the past.
2 is a cross-sectional view illustrating the structure of a limiting current type oxygen sensor according to an embodiment of the present invention.
FIG. 3 is a top plan view showing only the line-shaped pinhole and the cathode in the limiting current type oxygen sensor of FIG. 1; FIG.
4 is a cross-sectional view illustrating a structure of a limiting current type oxygen sensor according to another embodiment of the present invention.
FIG. 5 is a top plan view showing only the line-shaped pinhole, the cathode electrode, and the cathode lead pad in the limiting current type oxygen sensor disclosed in FIG.
FIG. 6 is a process flow chart sequentially showing the method of manufacturing the limiting current type oxygen sensor disclosed in FIG. 2. FIG.
FIG. 7 is a process flow chart sequentially showing the manufacturing method of the limiting current type oxygen sensor disclosed in FIG.
FIG. 8 is a graph showing the results of measurement of oxygen concentration using the limiting current type oxygen sensor manufactured by the process shown in FIG.
FIGS. 9 and 10 are photographs taken at 1000 times magnification and 2000 times magnification, respectively, of the line-shaped pinhole structure of the limiting current type oxygen sensor manufactured as an experimental example using an electron microscope.

Hereinafter, a limiting current type oxygen sensor according to the present invention will be described in detail with reference to the accompanying drawings. The following drawings are provided by way of example so that the idea of the present invention can be sufficiently transmitted. Therefore, the present invention is not limited to the following drawings, but may be embodied in other forms. Also, like reference numerals designate like elements throughout the specification.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the following description and the accompanying drawings, descriptions of well-known functions and constructions that may unnecessarily obscure the gist of the present invention will be omitted.

2 is a cross-sectional view illustrating the structure of a limiting current type oxygen sensor according to an embodiment of the present invention.

2, the limiting current type oxygen sensor 20 according to an embodiment of the present invention includes a solid electrolyte 21 capable of transporting oxygen ions through ion pumping, An anode lead 22a and a cathode lead wire 23a connected to the respective electrodes 22 and 23 and an anode electrode 22 and a cathode electrode 23 in the form of a porous thin film respectively formed on the surface and the lower surface, And the other side is exposed to the outside air through which the oxygen concentration is to be measured through the interface between the solid electrolyte 21 and the sensor substrate 24 and the other side is exposed to the solid electrolyte And a line-shaped pinhole 25 extending to an area of the cathode electrode 23, for example, a point B along the interface between the sensor substrate 24 and the sensor substrate 24.

The solid electrolyte 21 is not particularly limited as long as it is a material capable of pumping oxygen ions, and may be made of a YSZ material widely used as a solid electrolyte of an oxygen sensor.

The thickness of the solid electrolyte 21 is determined by the dimension of the sensor, and may be appropriately selected in the range of 50-300 .mu.m, for example.

The anode electrode 22 and the cathode electrode 23 are not particularly limited as far as they are porous conductive materials. The anode electrode 22 and the cathode electrode 23 may be made of a porous thin film made of a noble metal such as platinum (Pt) or gold (Au)

Alternatively, the anode electrode 22 and the cathode electrode 23 may be made of a composite material in which at least one of glass particles and YSZ particles is mixed using a noble metal as a matrix.

The thickness of the anode electrode 22 and the cathode electrode 23 is determined by the dimension of the sensor. For example, the thickness of the anode electrode 22 and the cathode electrode 23 may be appropriately selected in the range of 5-40um.

Meanwhile, although not essential, a portion 23 'of the cathode electrode 23 may be exposed to the outside, and a cathode lead 23a may be connected to the exposed portion 23'. The surface of the exposed portion 23 'may be completely covered with an insulating material such as glass so that the ionization reaction of the oxygen gas does not occur in the exposed portion 23' while the limiting current type oxygen sensor 20 is operated. .

The anode lead wire 22a and the cathode lead wire 23a may be made of a noble metal wire such as platinum (Pt) or gold (Au), as long as the anode lead wire 22a and the cathode lead wire 23a are made of a metal having low resistance and electrical conductivity.

The sensor substrate 24 may be made of the same material as the solid electrolyte 21, for example, a YSZ material, as long as the sensor substrate 24 is insulating and has the same or similar thermal expansion coefficient as the solid electrolyte 21.

The sensor substrate 24 is preferably thicker than the solid electrolyte 21 because it functions to mechanically support the upper structure. As an example, the thickness of the sensor substrate 24 may be suitably selected in the range of 200-800um.

The limiting current type oxygen sensor 20 includes a heater substrate 27 attached to the lower surface of the sensor substrate 24 and a thin film type line heater 28 attached to the lower surface of the heater substrate 27. [ As shown in FIG.

The thin film type line heater 28 is connected to the DC power source DC1 through the heater lead line 29 to generate resistance heat and the generated heat is transmitted to the solid electrolyte 21 side. Then, the temperature of the solid electrolyte 21 rises to a temperature at which oxygen ions can be pumped (hereinafter referred to as a reaction temperature). Here, the reaction temperature varies depending on the kind of the solid electrolyte, for example, about 400-700 degrees Celsius.

The specifications of the DC power source DC1 and the material, thickness, length, etc. of the thin film type line heater 28 can be appropriately selected so that the solid electrolyte 21 can be heated to a temperature of 400-700 degrees.

For example, the DC power source DC1 may have an operating voltage of about 3-7V. The thin film type line heater 28 may be made of platinum (Pt).

The anode lead line 22a and the cathode lead line 23a may be connected to a DC power source DC2 that applies a pumping voltage of several volts to pump the oxygen ions through the solid electrolyte 21. [ Here, the pumping voltage varies depending on the type of the solid electrolyte 21 and the reaction temperature at which ion pumping occurs. For example, the pumping voltage may be appropriately selected in the range of 1-5 V.

When the solid electrolyte 21 is heated to the reaction temperature and an appropriate level of pumping voltage is applied to the anode electrode 22 and the cathode electrode 23, an electrochemical reaction condition is established in which ion pumping occurs. In this case, the oxygen which is diffused through the line-shaped pinhole 25 and is in contact with the cathode electrode 23 is converted into oxygen ions by the reduction reaction and then pumped to the anode electrode 21 side via the solid electrolyte 21. The oxygen ions reaching the anode electrode 22 lose electrons by the oxidation reaction and are again converted into oxygen gas and released to the outside air.

When such oxygen ions are pumped, a current flows through the closed loop circuit in which the anode lead wire 22a and the cathode lead wire 23a are connected. When the ion pumping reaches a parallel state within a short time, the magnitude of the current is also constantly limited. When the magnitude of the limiting current is measured through the shunt resistor (R), the oxygen concentration of the outside air can be accurately measured.

Since the principle of measurement of oxygen concentration is well known in the art of limiting current type oxygen sensor, detailed description will be omitted.

FIG. 3 is a top plan view showing only the line-shaped pinhole 25 and the cathode electrode 23 in the limiting current type oxygen sensor 20 of FIG.

3, an end portion of the line-shaped pinhole 25, which is located inside the oxygen sensor 20, overlaps with an inner region of the electrode across the edge of the cathode electrode 23. As shown in FIG. 3, a central portion C of the lower edge T (hereinafter, referred to as a reaction region) is exposed to the outside air through which the oxygen concentration is to be measured through the line-shaped pinhole 25 . Therefore, the oxygen contained in the outside air diffuses into the oxygen sensor 20 through the line-shaped pinhole 25, reaches the reaction region C of the cathode electrode 23, and is converted to oxygen ions. The width of the reaction region C may be determined in consideration of the sensitivity and resolution of the sensor, and may be suitably selected in the range of several to several tens of μm, for example.

3 shows only one line-shaped pinhole 25, but it is apparent that the number of the line-shaped pinholes 25 may be two or more, depending on the specification of the sensor.

In addition, the line-shaped pinhole 25 is not limited to be formed to overlap with the entire surface of the cathode electrode 23. In this case, the reaction region (C) may extend to a length corresponding to the width of the cathode electrode (23). In addition, the line-shaped pinhole 25 is not limited to the case where the right end extends further and passes through the right side surface of the oxygen sensor.

Preferably, the line-shaped pinhole 25 is formed so that the combustible wire interposed at the interface between the solid electrolyte 21 and the sensor substrate 24 during the manufacturing process of the oxygen sensor 20 is subjected to a co- It is a trail.

Accordingly, the line-shaped pinhole 25 has a cylindrical inner wall structure corresponding to the shape of the combustible wire. The boundary of the ceramic crystal grains constituting the solid electrolyte 21 and the sensor substrate 24 may be exposed on the cylindrical inner wall. Also, although not essential, there may be a trace amount of carbon in the cylindrical inner wall that is not visible to the naked eye. The trace amount of carbon may be derived from the combustion of a combustible wire.

The combustible wire is not particularly limited as long as it can be burned in the co-firing process. For example, a polyolefin-based synthetic resin such as polyethylene (PE) or polypropylene (PP) Paper yarn or animal fiber yarn or carbon fiber.

The diameter and length of the line-shaped pinhole 25 may be determined so that the line-shaped pinhole 25 can function as a diffusion barrier. As an example, the line-shaped pinhole 25 has a diameter of several to several tens of um.

3, an unillustrated reference numeral 23 'denotes a portion to which the cathode lead 23a is connected, exposed to the outside of the cathode electrode 23. The lead wire connecting portion can be completely covered with an insulating material such as glass after the cathode lead wire 23a is connected.

In the limiting current type oxygen sensor 20 shown in FIGS. 2 and 3, since the diffusion barrier is formed by the line-shaped pinhole 25, the thickness of the conventional oxygen sensor is considerably thinner. Therefore, it is possible to reduce the thickness of the limit current type oxygen sensor. Also, since the line-shaped pinhole 25 is formed by the burning of the combustible wire, the manufacturing process is very simple. Therefore, the structure of the limiting current type oxygen sensor is advantageous in reducing the manufacturing cost.

4 is a cross-sectional view showing the structure of a limiting current type oxygen sensor 20 'according to another embodiment of the present invention, and FIG. 5 is a sectional view showing a structure of a line type pinhole 25, a cathode electrode 23 and a cathode lead line pad 30).

The limiting current type oxygen sensor 20 'disclosed in FIGS. 4 and 5 is constructed such that the cathode lead wire pad 30 is sandwiched between the sensor substrate 24 and the solid electrolyte 21 to cover at least a part of the area of the cathode electrode 23 And the remaining configuration is the same as the above-described embodiment.

The cathode lead wire pad 30 is an intermediate connecting member used for electrically connecting the cathode lead wire 23a to the cathode electrode 23 hidden inside the oxygen sensor 20 '. Accordingly, at least a portion 30 'of the cathode lead wire pad 30 is exposed to the outside, and the cathode lead wire 23a is connected to the exposed portion. At this time, it is preferable that the exposed portion is covered with an insulating material such as glass.

If the cathode lead wire 30 is a material having a good electrical conductivity, there is no particular limitation on the type and thickness of the material, and preferably the same material and thickness as the cathode electrode 23. As an example, the cathode lead wire pad 30 may be formed of a porous thin film made of platinum (Pt).

2, the cathode lead wire 23a is connected to the lower surface of the solid electrolyte 23, but in this embodiment, the cathode lead wire 23a is connected to the upper surface of the sensor substrate 27 . Therefore, the limiting current type oxygen sensor 20 'according to the present embodiment has a structure in which the process of connecting the cathode lead 23a is easier.

Hereinafter, a method for manufacturing the limiting current type oxygen sensor 20 shown in FIG. 2 including a line-shaped pinhole as a diffusion path of oxygen gas will be described in detail.

FIG. 6 is a process flow chart sequentially showing a manufacturing method of the limiting current type oxygen sensor 20 shown in FIG.

Referring to Fig. 6, first, a green sheet 30 for a solid electrolyte is prepared (process 1). The green sheet for a solid electrolyte 30 is prepared by finely pulverizing a mixture containing a raw material powder, a binder, a plasticizer and a solvent, which are made of a solid electrolyte, with a ball miller to obtain a slurry for tape casting on a suspension, To form a sheet and then drying it.

Preferably, the solid electrolyte powder may be a YSZ powder. Of course, the above-mentioned solid electrolyte green sheet 30 may be used by purchasing a commercially available product. The solid electrolyte green sheet 30 has a thickness of about 50-300 um.

The above green sheet forming method is disclosed in detail in the following reference documents, and the disclosure of that document can be incorporated as a part of this specification.

[Reference literature]

YJ. Oh and DYLee, "Fabrication and Characteristics of Limit-Current Type Oxygen Sensor with Monolith Aperture Structure ", J. K. Sens.Soc., Vol. 17, no. 4, pp. 273-280, 2008.

Next, the electrode paste is screen-printed on the upper and lower surfaces of the green sheet 30 for solid electrolyte and then dried to form the anode electrode 31 and the cathode electrode 32 in the form of a porous thin film ②).

Preferably, the anode electrode 31 and the cathode electrode 32 are formed to a thickness of 5-40 um. In one aspect, a portion of the cathode electrode 32 must be exposed to the outside, so that the size of the cathode electrode 32 is made larger than the size of the anode electrode 31.

The anode electrode 31 and the cathode electrode 32 may be formed by an inkjet printing method or a spraying method widely used in the electrode process of the limiting current type oxygen sensor in addition to the screen printing method.

Preferably, the electrode paste may be a platinum (Pt) paste.

In the next step, a green sheet 33 for a sensor substrate is prepared and a combustible wire 34 is placed at a point where a line-shaped pinhole to be used as a diffusion barrier of oxygen gas is to be formed, and then a solid electrolyte The green sheet 30 for the sensor substrate is laminated on the green sheet 33 for the sensor substrate to form a laminated structure (step 3).

When the line-shaped pinhole is formed so as to cross the surface of the cathode electrode 32, the right end of the combustible wire 34 passes through the right edge of the cathode electrode 32, 33).

When the line-shaped pinhole is formed so as to extend to the right side wall of the oxygen sensor, both ends may be exposed to the outside air when the combustible wire 34 is placed on the green sheet 33 for the sensor substrate.

Preferably, the combustible wire may be a synthetic resin source such as polyethylene or polypropylene or a paper yarn or an animal fiber yarn or carbon fiber processed into a wire form. And, the diameter of the combustible wire can be suitably selected to a value that can guarantee the nucin-type gas diffusion in the range of 10-50um.

Preferably, the laminated structure may be pressed into a Warm Isostatic Press at a temperature of 50-75 degrees and a pressure of 50-300 bar for 1-10 minutes. Then, the interfaces of the elements constituting the laminated structure can be tightly bonded together.

The forming method of the green sheet 33 for sensor substrate is substantially the same as that described above. However, the kind of the ceramic powder to be included in the green sheet can be changed.

Preferably, the green sheet 33 for the sensor substrate may be made of the same material as the green sheet for a solid electrolyte. In this case, cracks can be prevented from occurring at the interface because the mutual bonding green sheets have the same thermal expansion coefficient. However, the green sheet 33 for the sensor substrate may be thicker than the green sheet 30 for solid electrolyte in order to secure the mechanical rigidity of the sensor. Preferably, the green sheet 33 for the sensor substrate may have a thickness of approximately 200-800 um. However, the present invention is not limited by the material and the thickness of the green sheet 33 for a sensor substrate.

In the next step, the laminated structure obtained in the step (3) is loaded into the firing chamber, and co-firing is performed for 1 to 6 hours under an atmospheric atmosphere and a temperature condition of 1400 to 1600 degrees (step (4)). In the co-firing process, the solid electrolyte green sheet 30 and the sensor substrate green sheet 33 are sintered together, and the combustible wire 34 is burnt and the line-shaped pinhole 34 '). One end of the line-shaped pinhole 34 'is opened toward the outside air to which the oxygen concentration is to be measured, and the other end is extended to overlap with a part of the area of the cathode electrode 32 (see FIG. 3).

In the next step, a heater substrate 36 made of a ceramic material with a thin film type line heater 35 is prepared, and the resultant product obtained in the step (4) is bonded thereon with a ceramic adhesive (step (5)).

Preferably, the heater substrate 36 may be made of alumina (Al ₂ O ₃ ), and the thin film line heater 35 may be made of platinum (Pt). The thin film type line heater 35 can be formed by printing and drying a metal paste by a screen printing method. The heater substrate 36 has a thickness of 200-800 um. However, the present invention is not limited by the material and the thickness of the thin film type line heater 35 and the heater substrate 36.

In the last step, the lead wires 37, 38, 39, and 40 are connected to the anode electrode 31 and the cathode electrode 32 attached to the upper and lower surfaces of the solid electrolyte 31 and the thin film type line heater 35 . Preferably, the lead wires 37, 38, 39, 40 may be made of platinum (Pt).

On the other hand, among the above-described processes, the processes (5) and (6) can be omitted by the manufacturer because they can be performed by a manufacturer who modularizes the limiting current type oxygen sensor.

As a modification of the above process, a green sheet for a heater substrate is prepared, a thin film line heater is screen-printed on the lower surface, and a green sheet for a heater substrate is formed on the lower part of the laminated structure obtained in the step And the sensor structure obtained in step (5) can be formed at one time by performing the simultaneous firing process. This modified embodiment has the advantage of simplifying the manufacturing process of the limiting current type oxygen sensor.

FIG. 7 is a process flow chart sequentially showing a manufacturing method of the limiting current type oxygen sensor 20 'disclosed in FIG.

Referring to FIG. 7, step (1) 'is substantially the same as step (1) of FIG. 6 in the step of preparing a green sheet for a solid electrolyte. The step 2 'is substantially the same as the step 2 of FIG. 6 except that the size of the cathode electrode 32 is adjusted to almost the same size as that of the anode electrode 31.

 Process (3) 'is a process that differs from process (3) in FIG. First, a green sheet 33 for a sensor substrate is prepared, and then an electrode paste is coated on the upper surface by a screen printing method and dried to form a cathode lead wire pad 41. Preferably, platinum (Pt) paste may be used as the electrode paste. The cathode lead line pad 41 is formed to have a size that can be at least overlapped with the cathode electrode 32. Then, the flammable wire 34 is placed at the point where the line-shaped pinhole is to be formed in the surface area of the green sheet 33 for the sensor substrate on which the cathode lead wire pad 41 is formed. At this time, the right end of the combustible wire 34 must pass at least the left edge of the cathode electrode 32, and the right edge of the cathode electrode 32, and further the right edge of the green sheet 33 for sensor substrate Do not limit passing. Then, the green sheet 30 for a solid electrolyte to which the electrodes 31 and 32 are attached is laminated on the green sheet 33 for the sensor substrate to form a laminated structure.

Preferably, in order to improve the interfacial bonding property of the laminated structure, the laminated structure may be pressed as described in step (3) of FIG. 6 by using a hot isostatic press.

6 ', the line-shaped pinhole 34' is bonded to the solid electrolyte 30 and the sensor substrate 33 at the completion of the process, As shown in FIG.

Processes (5) and (6) are substantially the same as the processes (5) and (6) in FIG. 6, and correspond to the heater structure forming process and the lead wire wiring process, respectively.

On the other hand, in the process (6 '), the wiring of the cathode lead wire (38) is performed through the cathode lead wire pad (41) exposed to the outside toward the top, so that the wiring process is easier than in the above embodiment.

Also, in the manufacturing method described with reference to FIG. 7, steps (5) and (6) can be omitted because they can be performed by the manufacturer who modularizes the limiting current type oxygen sensor.

Also, before proceeding with the simultaneous firing process of step (4 '), a green sheet for a heater substrate in which a thin film type line heater 35 is formed on the lower surface can be attached to the lower surface of the green sheet 33 for sensor substrate. At this time, the interfacial adhesion property can be improved by pressing the laminated structure using a hot isostatic press. Then, the entire structure of the limiting current type oxygen sensor except the lead wire in the step (4 ') can be formed by one simultaneous firing process.

Experimental Example

FIG. 8 is a graph showing the results of measurement of oxygen concentration using the limiting current type oxygen sensor manufactured by the process shown in FIG.

In the oxygen sensor manufactured in this experiment, the diameter of the line-shaped pinhole was measured in the range of 5-10 μm along the longitudinal direction of the pinhole. A polyethylene yarn was used as a combustible wire to form a line-shaped pinhole. The effective area of the anode electrode and the cathode electrode was adjusted to 3 * 3 mm ² . The material of the solid electrolyte and the sensor substrate was unified with YSZ, and the material of the anode electrode, the cathode electrode, and the lead wire was selected as platinum (Pt) material. A dc voltage source of 1.25V was used as the pumping voltage, and a dc voltage source of 5.3V was used as the voltage source of the heater. The shunt resistor for measuring the limiting current was a resistance element having a resistance value of 1 kΩ.

In the present experimental example, the limit current type oxygen sensor is loaded in a chamber capable of precisely controlling the oxygen concentration, the heater substrate is connected to a DC voltage source for the heater power supply, and the cathode electrode and the anode electrode of the limit current type oxygen sensor are connected to a DC voltage source Respectively. Then, the magnitude of the voltage applied across the shunt resistor was measured while adjusting the oxygen concentration in the chamber. The voltage measured through the shunt resistor can be converted to the magnitude of the limiting current by Ohm's law.

Referring to FIG. 9, it can be seen that the voltage measured through the shunt resistor shows a good linear change characteristic according to the change of the oxygen concentration. Therefore, it can be confirmed that the line-shaped pinhole formed inside the limiting current type oxygen sensor functions as a diffusion barrier for ensuring the leak-tight gas diffusion.

In addition, the experimental results obtained through the graph of FIG. 8 can be used as a look-up table to measure the oxygen concentration. That is, by using the look-up table, it is possible to map the oxygen concentration corresponding to an arbitrary voltage measured using the limiting current type oxygen sensor.

Alternatively, a linear function indicating the relationship between the oxygen concentration and the voltage may be obtained from the graph of FIG. 8, and then the corresponding linear function may be utilized for measuring the oxygen concentration. That is, the oxygen concentration corresponding to an arbitrary voltage measured by using the limiting current type oxygen sensor can be calculated using the above-mentioned linear function.

Figs. 9 and 10 are photographs taken at 1000 times magnification and 2000 times magnification, respectively, of the structure of the line-shaped pinhole using an electron microscope.

Referring to FIG. 9, it can be seen that the boundaries of the green sheets completely disappeared as crystal grains were grown near the interface in the process of simultaneously firing the green sheet for a solid electrolyte and the green sheet for a sensor substrate. Also, it can be confirmed that the line-shaped pinhole is well opened in the outside direction, and it can be confirmed that the inner wall of the cylindrical structure is well developed toward the inside of the oxygen sensor.

Also, referring to FIG. 10, it can be seen that the boundaries of the crystal grains are exposed toward the outside air on the inner walls of the line-shaped pin holes.

As seen in the above embodiments, the present invention can form the diffusion barrier structure of the limiting current type oxygen sensor by a simple process. Also, since the space occupied by the diffusion barrier structure is minimized, it is possible to reduce the thickness of the oxygen sensor. In addition, the manufacturing cost of the oxygen sensor can be reduced by simplifying the process. In addition, it is possible to manufacture a limiting current type oxygen sensor in which the oxygen concentration exhibits a linear dependence on the magnitude of the limiting current over a wide range of oxygen concentration.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Various changes and modifications will be possible.

20, 20 ': limiting current type oxygen sensor 21, 30: solid electrolyte
22, 31: anode electrode 23, 32: cathode electrode
24, 33: sensor substrate 27, 36: heater substrate
28, 35: thin-film heaters 22a, 37: anode leads
23a, 38: cathode lead wire 25, 34 ': line-shaped pinhole
34: combustible wire 30, 41: cathode lead wire pad

Claims (21)

A solid electrolyte capable of pumping oxygen ions;
An anode electrode and a cathode electrode respectively formed on the upper and lower surfaces of the solid electrolyte; And
And a sensor substrate attached to the cathode electrode side in a face-
A line-shaped pinhole extending through a portion extending to a point at which at least a part of the cathode electrode is exposed is formed at an interface between the solid electrolyte and the sensor substrate, and an inlet of the line-shaped pinhole is opened through one sidewall on which the interface is exposed Wherein the limit current type oxygen sensor comprises:
The method according to claim 1,
And the inner end of the line-shaped pinhole extends so as to overlap the inner region of the cathode electrode across the rim of the cathode electrode.
The method according to claim 1,
Wherein the line-shaped pinhole is left as a trace while the combustible wire is burned.
The method according to claim 1,
And a grain boundary of crystals constituting the solid electrolyte and the sensor substrate is exposed through an inner wall of the line-shaped pinhole.
The method of claim 3,
Wherein a combustion by-product of the combustible wire is present in an extremely small amount on the inner wall of the line-shaped pin hole.
The method according to claim 1,
Wherein the solid electrolyte and the sensor substrate are made of stabilized zirconia (YSZ) to which yttria is added.
The method according to claim 1,
Further comprising a cathode lead pad interposed between the solid electrolyte and the sensor substrate so as to overlap with the cathode electrode and at least a part of which is exposed to the outside along an upper surface of the sensor substrate.
8. The method of claim 7,
Further comprising a cathode lead line connected to the cathode lead line pad and an anode lead line connected to the anode electrode.
The method according to claim 1,
Wherein the cathode electrode includes a portion exposed to the outside along a lower surface of the solid electrolyte,
Further comprising a cathode lead connected to the exposed portion and an anode lead connected to the anode electrode.
The method according to claim 1,
A heater substrate attached to a lower side of the sensor substrate; and a thin film line heater formed on a lower surface of the heater substrate.
(a) forming an anode electrode and a cathode electrode on a top surface and a bottom surface of a green sheet for a solid electrolyte;
(b) preparing a green sheet for a sensor substrate;
(c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure; And
(d) co-firing the laminated structure to simultaneously sinter the green sheet for a solid electrolyte and the green sheet for a sensor substrate, and burning the combustible wire to form a line-shaped pinhole in its place Method of manufacturing a limiting current type oxygen sensor.
12. The method of claim 11,
Wherein the combustible wire is a synthetic resin yarn, a paper yarn, a carbon fiber, or an animal fiber yarn.
12. The method of claim 11, wherein before step (d)
And pressing the stacked structure using a hot isostatic press. ≪ RTI ID = 0.0 > 21. < / RTI >
12. The method of claim 11,
Wherein the green sheet for a solid electrolyte and the green sheet for a sensor substrate comprise stabilized zirconia particles to which yttria is added.
12. The method of claim 11, further comprising, between step (b) and step (c)
And forming a cathode lead line pad on the upper surface of the green sheet for the sensor substrate, one end of which overlaps with the cathode electrode and the other end is exposed to the outside along the surface of the green sheet for the sensor substrate. A method of manufacturing a current type oxygen sensor.
16. The method of claim 15,
And connecting the cathode lead and the anode lead to the exposed portion of the cathode lead line pad and the anode electrode, respectively.
12. The method of claim 11, wherein in step (a)
Wherein the cathode electrode is formed such that a part of the cathode electrode is exposed to the outside along the lower surface of the green sheet for solid electrolyte.
18. The method of claim 17,
Further comprising the steps of: connecting a cathode lead line and an anode lead line to the exposed portion of the cathode electrode and the anode electrode, respectively.
12. The method of claim 11,
Preparing a heater substrate having a thin film line heater formed on a lower surface thereof; And
Further comprising the step of fixing the laminated structure having the line-shaped pinhole to the heater substrate.
(a) forming an anode electrode and a cathode electrode on a top surface and a bottom surface of a green sheet for a solid electrolyte, respectively;
(b) preparing a green sheet for a sensor substrate;
(c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure;
(d) fixing the laminated structure on a green sheet for a heater substrate on which a thin film line heater is formed; And
(e) simultaneously firing the green sheet for a heater substrate to which the laminated structure is fixed, simultaneously sintering the green sheet for a solid electrolyte, the green sheet for a sensor substrate and the green sheet for a heater substrate, burning the combustible wire And forming a line-shaped pinhole in the hole.
(a) forming an anode electrode and a cathode electrode on a top surface and a bottom surface of a green sheet for a solid electrolyte, respectively;
(b) preparing a green sheet for a sensor substrate in which a cathode lead pad having one end overlapped with the cathode electrode and the other end exposed to the outside is formed on an upper surface;
(c) stacking the green sheet for a solid electrolyte so that the cathode electrode faces the upper surface of the green sheet for a sensor substrate, wherein one end of the green sheet overlaps the edge of the cathode and the other end is exposed to the outside air Inserting a flammable wire of the laminated structure into a lamination interface to prepare a laminated structure;
(d) fixing the laminated structure on a green sheet for a heater substrate on which a thin film line heater is formed; And
(e) simultaneously firing the green sheet for a heater substrate to which the laminated structure is fixed, simultaneously sintering the green sheet for a solid electrolyte, the green sheet for a sensor substrate and the green sheet for a heater substrate, burning the combustible wire And forming a line-shaped pinhole in the hole.

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