KR20080050951A - Electrochemical gas sensor chip and method for preparing the same - Google Patents

Abstract

An electrochemical gas sensor chip adapted to a portable terminal and a method for preparing the sensor chip to make a compact sensor without using a liquid such as liquid electrolyte are provided. An electrochemical gas sensor chip(100) includes a substrate(101), an electrode, a solid electrolyte layer(106), and a hydrophobic micro-porous membrane(107). The electrode is patterned on the substrate. The solid electrolyte layer having proton conductivity is formed on the substrate with the patterned electrode. The hydrophobic micro-porous membrane is formed on the solid electrolyte layer. The substrate is formed of one selected from a group consisting of silicon, polycarbonate, quartz, GaAs, InP, and glass. In the patterned electrode, a working electrode(103), a counter electrode(104), and a reference electrode(105) are formed on the same surface of the substrate.

Description

Electrochemical Gas Sensor Chip and Method for Preparing the Same

1 is a diagram of an electrochemical gas sensor using a conventional liquid electrolyte.

2 is a plan view of an electrochemical gas sensor chip using a solid electrolyte according to an embodiment of the present invention.

3 is a cross-sectional view of an electrochemical gas sensor chip using a solid electrolyte according to an embodiment of the present invention.

4 is a cross-sectional view of an electrochemical gas sensor chip using a solid electrolyte according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... gas sensor 11 ... porous membrane

12 ... reaction electrode 13 ... membrane

14 ... reference electrode 15 ... counter electrode

16 ... liquid electrolyte 100 ... gas sensor chip

101 ... substrate 102 ... insulating layer

103 ... reaction electrode 104 ... counter electrode

105 ... reference electrode 106 ... solid electrolyte membrane

107 ... Hydrophobic Microporous Membrane

The present invention relates to an electrochemical gas sensor chip and a method for manufacturing the same, and more particularly, to an electrochemical gas sensor chip using a solid electrolyte and a method for manufacturing the same.

Gas sensors are required in various fields such as the automotive industry, the environmental industry, the food and beverage industry, and the robotics industry, and various technologies have been studied for their applications.

The semiconductor gas sensor using the change of conductivity of oxide semiconductor through contact with oxidizing gas or reducing gas is now commercially available, but it requires a heater because the operating temperature of oxide semiconductor for gas detection is high. If it is large, there is still a limitation of technology to use as a portable device.

The optical gas sensor that discriminates the type of gas through the change of the infrared spectrum passing through the sensing gas is now commercially available, but the limit of miniaturization of the infrared light source or the sensor, the excessive power consumption problem, and the improvement of the detection performance Due to the problems of miniaturization due to the long light path required, it is not suitable for portable use.

The gas sensor using another method is an electrochemical gas sensor. In the electrochemical gas sensor 10 of FIG. 1, which is currently commercialized, the gas diffused through the gas inlet is introduced through the porous membrane 11, and again. The introduced gases form proton ions and electrons in the catalytic electrode material of the reaction electrode 12 formed on the porous membrane by reactions such as the following Schemes 1 to 4 for each toxic gas.

Ozone (O ₃ ) Gas Sensor

Reaction electrode _{(Working Electrode) O 3 + 2e} - + 2H + → O 2 + H 2 O

Counter Electrode 2H ₂ O → O ₂ ⁺ 4H + + 4e ^-

Carbon Monoxide (CO) Gas Sensor

Reaction electrode CO + H ₂ O → CO ₂ + 2H ⁺ + 2e

A counter electrode ^{2H + + 2e - + 1 /} 2O 2 → H 2 O

Nitrogen Dioxide (NO ₂ ) Gas Sensor

Reaction electrode _{^{NO 2 + 2H + + 2e -}} → NO + H 2 O

A counter electrode ^{_{H 2 O → 2H + + 2e}} - + 1 / 2O 2

Sulfur dioxide (SO ₂ ) gas sensor

Electrode reaction _{SO 2 + H 2 O → SO} 4 2 - + 4H + + 2e -

A counter electrode ^{2H + + 2e - + 1 /} 2O 2 → H 2 O

The formed electrons are moved to the counter electrode through the current collector, and the proton ions are transferred to the counter electrode through the electrolyte to form water by forming the water by the reaction scheme as described above. At this time, since the current formed is proportional to the concentration of the gas present in the outside, the gas concentration is determined by detecting the current. The porous membrane below the inlet serves to prevent gas from entering the inside of the sensor from outside and leaks out of the electrolyte, and determines the amount of gas coming from outside. In addition, the porous membrane is a precious metal electrode material having excellent catalytic properties and is also used as a substrate for forming a reaction electrode. There is a separator under the reaction electrode, which is sufficiently wetted in the electrolyte, and the reaction electrode serves to ensure that current flows only through the counter electrode or the reference electrode and the ions below.

The counter electrode formed below serves to react between the proton ions formed in the reaction electrode and the electrons moving from the reaction electrode to the counter electrode through an external circuit, and the reference electrode is a constant potential. Serves to help maintain. The electrolyte filled inside the sensor uses an acid / base solution having excellent ion conductivity in a liquid state.

For selective sensing characteristics of each gas, it is necessary to change the type of electrode and electrolyte and to change the voltage applied between the reference electrode and the reaction electrode.

As such, the conventional electrochemical gas sensor uses a room temperature operation method and does not require a light source, compared to a semiconductor or optical type, and thus consumes less power. The liquid electrolyte has a strong acid, so there are problems such as safety, so that it is difficult in size and safety to be mounted in a portable device such as a mobile phone.

Accordingly, many attempts have been made to use solid electrolytes instead of liquid electrolytes.

US Pat. No. 4,718,991 to Yamazoe et al. Has proposed a structure in which a reaction electrode is formed on one side and a counter electrode and a reference electrode are formed on one side using a polymer membrane having excellent proton conductivity as an electrolyte. However, in the case of such a structure, electrodes are formed on both sides of a polymer film having excellent proton conductivity, and although it is possible to miniaturize to some extent, there is a difficulty in integrating the chip into a driving circuit.

In the case of an electrochemical gas sensor, data on its own characteristics, such as the response to gases (e.g. the output at several ppm concentrations) and the sensor's response to environmental changes such as external temperature and humidity, may be used. In order to operate, it must be embedded in the connected microprocessor to be able to operate normally. Therefore, in the case of practically all electrochemical gas sensor devices, a microprocessor is built in such a way that the characteristics of the sensor can be input and operate normally. However, current gas sensors cannot be integrated into one board together with components necessary for driving in structure, and a chip-type sensor must be developed to solve such a problem.

In US Pat. No. 6,896,781 to Shen et al., A hydrophobic membrane is attached to the top and bottom in the above structure, and a structure in which ions do not pass but only gas or moisture passes. However, in the case of such a structure, the proton conductivity of the electrolyte varies depending on the concentration of the surrounding moisture due to the characteristics of the gas sensor of the electrochemical method, which may act as an error in the actual concentration of the detected gas.

Therefore, the present inventors proceeded to study the electrochemical gas sensor in the form of a chip, to implement the electrochemical gas sensor using a semiconductor process on the substrate to manufacture in the form of a chip, using a hydrophobic microporous membrane The present invention has been accomplished by discovering that it can enable microminiature structures and large area processes.

Accordingly, the first technical problem of the present invention is to provide an electrochemical gas sensor chip capable of a very small structure and a large area process.

In addition, another technical problem of the present invention is to provide a method for manufacturing an electrochemical gas sensor chip capable of a very compact structure and a large area process.

In order to achieve the first technical problem, the present invention

Board;

An electrode patterned on the substrate;

A solid electrolyte membrane having a proton conductivity formed on a substrate including the patterned electrode; And

It provides an electrochemical gas sensor chip comprising a hydrophobic microporous membrane on the solid electrolyte membrane.

In order to achieve the above another technical problem, the present invention

Preparing a substrate;

Patterning and forming an electrode on the substrate;

Forming a solid electrolyte membrane having proton conductivity on a substrate including the patterned electrode; And

It provides a method for producing an electrochemical gas sensor chip comprising the step of forming a hydrophobic microporous membrane on the solid electrolyte membrane.

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

2 is a plan view of an electrochemical gas sensor chip using a solid electrolyte according to an embodiment of the present invention, Figure 3 is a cross-sectional view of the electrochemical gas sensor chip using a solid electrolyte according to an embodiment of the present invention, Figure 4 Is a cross-sectional view of an electrochemical gas sensor chip using a solid electrolyte according to another embodiment of the present invention.

2 to 3, the electrochemical gas sensor chip 100 according to an embodiment of the present invention is a pattern on the substrate 101, the insulating film 102 formed on the substrate 101, the insulating film 102 And a reaction electrode 103, a counter electrode 104 and a reference electrode 105, and a solid electrolyte membrane 106 and a hydrophobic microporous membrane 107 formed on the patterned electrode.

The substrate 101 is a base on which an electrochemical gas sensor is formed to make a gas sensor in the form of a chip and to integrate with the driving circuit. The substrate 101 may be selected from materials selected from silicon, polycarbonate, quartz, GaAs, InP, and glass, preferably a silicon substrate. The thickness of the substrate may be determined according to the size and thickness of the electrochemical gas sensor, it is preferably determined within the range of 0.3 to 1mm.

Although an electrode may be formed directly on the substrate 101, it is preferable to form an insulating film 102 to buffer the substrate 101 and the electrode before forming the electrode. As the insulating film 102, a silicon oxide film is preferable. The insulating layer 102 is preferably formed through a thermal process. The thickness of the insulating layer 102 may be determined by those skilled in the art in consideration of the thicknesses of the substrate and the electrode, and may be variously applied in the range of several tens to thousands of nanometers.

In the absence of the insulating film 102 or the insulating film 102, the reaction electrode 103, the counter electrode 104, and the reference electrode 105 are patterned on the same surface of the substrate 101.

As the electrode material, a noble metal material having excellent catalytic property may be used. Preferably, silver, gold, platinum, rhodium, iridium, ruthenium, palladium, or an oxide having conductivity may be used. Most preferably, platinum is a reaction electrode. The 103, the counter electrode 104, and the reference electrode 105 may be formed of the same material, or may be formed of different materials.

The electrode may be formed through a dry method used in a general semiconductor process, for example, sputtering or vacuum deposition, or the electrodes may be formed by chemical vapor deposition.

In addition, the patterning of the electrode is a mask or lift off method or etching used in a general semiconductor process when the reaction electrode 103, the counter electrode 104 and the reference electrode 105 are formed of the same material. It can be formed through a single process using a method, and if the reaction electrode 103, counter electrode 104 and reference electrode 105 are each used with different materials, such as a mask or lift off method or an etching method Can be formed through a multi-step process.

An example of a pattern in which the reaction electrode 103, the counter electrode 104, and the reference electrode 105 are formed on the insulating layer 102 can be seen through FIG. 2. The reaction electrode 103 is formed in the shape of a circle at the center of the insulating film 102, the counter electrode 104 is formed in the shape of a circle around the reference electrode, and finally the reference electrode 105 is formed in the shape of a rod on both sides. do.

The counter electrode 104 and the reference electrode 105 may be connected to each other so as to be electrically contacted.

The thickness of the reaction electrode 103, the counter electrode 104 and the reference electrode 105 may be the same or different, and may be variously applied within a range of several tens to tens of thousands of nanometers as necessary.

The solid electrolyte membrane 106 formed on the patterned electrode is formed through a wet process such as spin coating or screen printing after solution of a polymer having excellent proton conductivity. As the polymer having excellent proton conductivity, a general one in this field may be used, and preferably, 5 to 20 wt% of Nafion sold by DuPont may be used.

The thickness of the solid electrolyte membrane 106 may be determined according to the size of the sensor, the thickness of the substrate and the electrode, and may be variously applied within the range of several to several thousand micrometers.

Meanwhile, after the solid electrolyte membrane 106 having excellent proton conductivity is formed, it is preferable to perform chemical treatment in order to maximize proton conductivity. For example, Nafion membrane is treated for 1 to 4 hours under boiling 1-5M sulfuric acid solution.

The hydrophobic microporous membrane 107 formed on the solid electrolyte membrane 106 is to minimize the influence of the solid electrolyte membrane on environmental changes such as external temperature and humidity.

The hydrophobic microporous membrane 107 is preferably hydrophobic and has micro pores through which sensing gas passes but not ions or moisture. Specifically, PTFE (polytetrafluoroethylene), silica gel, and the like may be used. have.

Referring to FIG. 4, the electrochemical gas sensor chip 100 according to another embodiment of the present invention may include a substrate 101, an insulating film 102 formed on the substrate 101, and a relative electrode formed on the insulating film 102. And a reference electrode 105, a solid electrolyte membrane 106 formed on the electrode, a reaction electrode 103 formed on the solid electrolyte membrane 106, and a hydrophobic microporous membrane 107.

The substrate 101, the insulating film 102, the reaction electrode 103, the counter electrode 104, the reference electrode 105, the solid electrolyte membrane 106, and the hydrophobic microporous constituting the chip 100 shown in FIG. 4. Description of the membrane 107 is the same as configuring the chip 100 shown in FIGS.

4, the counter electrode 104 and the reference electrode 105 are formed on the same surface of the substrate 101 when the insulating film 102 or the insulating film 102 is not present. Is formed on the solid electrolyte membrane 106.

In the electrochemical gas sensor chip according to the present invention, the selectivity of the sensing gas may be imparted by the type of voltage and electrode applied between the counter electrode and the reference electrode for each gas.

The electrochemical gas sensor chip and its manufacturing method according to the present invention has the following advantages.

First, since the gas sensor according to the present invention has a chip structure, the gas sensor can be easily integrated with the driving circuit.

Second, mass production is possible because the semiconductor process can be used to implement the gas sensor according to the present invention on a substrate.

Third, the gas sensor according to the present invention can suppress the evaporation of water molecules in the solid electrolyte membrane by using a hydrophobic microporous membrane on the solid electrolyte membrane to maintain humidity by using a separate water reservoir. It can be used for a long time without it.

Fourth, the gas sensor according to the present invention can be miniaturized by not using a liquid material such as a liquid electrolyte can be mounted in a portable terminal device such as a mobile phone.

Fifth, the gas sensor according to the present invention can be manufactured by integrating with a circuit required for driving the sensor through a semiconductor process. (Development of sensor chip with all driving circuits possible)

Claims (13)

Board; An electrode patterned on the substrate; A solid electrolyte membrane having a proton conductivity formed on a substrate including the patterned electrode; And An electrochemical gas sensor chip comprising a hydrophobic microporous membrane on the solid electrolyte membrane. The electrochemical gas sensor chip of claim 1, wherein the substrate is selected from silicon, polycarbonate, quartz, GaAs, InP, or glass. The electrochemical gas sensor chip of claim 1, wherein the patterned electrode has a reaction electrode, a counter electrode, and a reference electrode formed on the same surface on a substrate. The electrochemical gas sensor chip of claim 1, wherein the patterned electrode has a counter electrode and a reference electrode formed on the same surface on a substrate, and a reaction electrode is formed on the solid electrolyte membrane. The electrochemical gas sensor chip of claim 3 or 4, wherein the reference electrode and the counter electrode are connected to each other. The method of claim 1, wherein the electrode is formed of silver, gold, platinum, rhodium, iridium, ruthenium, palladium, or a conductive oxide. Electrochemical gas sensor chip, the material of choice. The electrochemical gas sensor chip of claim 1, wherein the solid electrolyte membrane having proton conductivity is a Nafion ™ membrane. The electrochemical gas sensor chip of claim 1, wherein the hydrophobic microporous membrane has micropores that allow gas to pass but cannot pass ions or moisture. Preparing a substrate; Patterning and forming an electrode on the substrate; Forming a solid electrolyte membrane having proton conductivity on a substrate including the patterned electrode; And A method of manufacturing an electrochemical gas sensor chip comprising forming a hydrophobic microporous membrane on the solid electrolyte membrane. The method of claim 9, wherein the electrode is formed through a sputtering process, a vacuum deposition process, or a chemical deposition process. The method of claim 9, wherein the solid electrolyte membrane is formed through a wet process. The method of claim 9, wherein the patterned electrode is formed with a reaction electrode, a counter electrode, and a reference electrode on the same surface on a substrate. 10. The method of claim 9, wherein the patterned electrode is formed with the counter electrode and the reference electrode together on the same surface on the substrate, and the reaction electrode is formed on the solid electrolyte membrane.

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