JPS61147154A - Thin-film oxygen sensor - Google Patents

Abstract

PURPOSE:To utilize an oxygen pumping phenomenon in operation at an ordinary temp. and to determine the concentration of oxygen in a gas by laminating the 1st electrode film, a solid electrolyte film and the 2nd electrode film on an electrical insulating substrate. CONSTITUTION:When an electric power source 8 is driven against the 2nd electrode film 14 installed through the 1st electrode film 2 and the solid electrolyte film 3 on the electrical insulating substrate 1, oxygen ions pass through the electrolyte film 3 and flow from the electrod film 2 side to the electrode film 4 side toward the reverse direction against that of the electric current, and so-called pumping phenomenon occurs. Accordingly, when the volume of a chamber consisting of an opening part 5 and a resistor 6 for diffusing oxygen and the impessed current are kept constant, the discharging time of oxygen present in the chamber to the outside corresponds to the concentration of oxygen in an atmosphere to be determined. The oxygen present in the resistor 6 is discharged by increasing gradually the voltage impressed to the electrolyte film 3, and at this point of time the current is saturated, the phenomenon of limiting current is obtained and this limiting current corresponds to the concentration of oxygen in the atmosphere to be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to the measurement of oxygen concentration in gas using a solid electrolyte.

2. Description of the Related Art Conventionally, this type of sensor has been disclosed, for example, in Japanese Patent Application Laid-Open No. 52-7
No. 2286, - JP-A-59-192953, and the oxygen pump phenomenon as disclosed in the limiting current type oxygen sensor, low-temperature operation type zirconia oxygen sensor, etc. of the "Fundamentals and Applications of Senna" Symposium (4th). It is known that it is used.

However, these cells are made of sintered zirconia, which forms the solid electrolyte, and are thick film types with a thickness of approximately 0.3 to 2 mm, so the operating temperature as a sensor is 30°C.
It was designed to be used at temperatures as high as 0 to 800'C.

Problems to be Solved by the Invention However, with the above configuration, a heating source is required to be installed in the combustion exhaust gas to increase the operating temperature, or to control the temperature by fully using the heater. It had a problem of poor durability due to its use.

The present invention solves such conventional problems and operates at room temperature (
An object of the present invention is to provide a sensor that measures oxygen concentration in a gas by utilizing the oxygen pump phenomenon at temperatures ranging from room temperature to around 200°C.

Means for Solving the Problems In order to solve the above problems, the present invention forms a first electrode film, a solid electrolyte film, and a second electrode film in layers on an insulating substrate. In this structure, at least a portion of the solid electrolyte membrane formed on the solid substrate is removed, and an oxygen diffusion resistor is provided to cover the removed portion.

Effect of the present invention With the above-described configuration, when electricity is applied to the electrodes on both sides of the solid electrolyte membrane and a voltage is applied to the solid electrolyte membrane, oxygen molecules flow in from the oxygen diffusion resistor side (the first electrode is the cathode). Oxygen molecules begin to be released from the anode side of the opposite second electrode, and the current increases proportionally as the voltage increases 75S
It saturates at a certain current, which becomes the limiting current, and takes a value proportional to the oxygen concentration. This is because the oxygen diffusion resistor prevents the oxygen molecules from flowing into the first electrode side, resulting in diffusion rate limiting. Here, since the solid electrolyte membrane is formed into a thin film, oxygen ion conductivity is improved even at low temperatures, and the operating temperature can be lowered.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of the thin film oxygen sensor of the present invention. A first electrode film 2 is formed by full vapor deposition or sputtering on a part of the surface of an insulating substrate 1 made of a flat glass plate, quartz plate, silicon plate, etc., except for a part. Zirconium oxide (ZrOz) and yttrium oxide (Y2O
2), calcium oxide (CaO), magnesium oxide (MgO), etc., was used as a solid solution in target i, and sputtering was performed at a temperature of 400°C or higher to form a solid electrolyte film 3 with a thickness of 1 to 20 μm. . Next, a second electrode film 4 is deposited on the remaining surface of the insulating substrate 1 on which the first electrode 2 is formed by vapor deposition or sputtering through the solid electrolyte film 3 so as not to contact the first electrode film 2. was formed.

The first electrode film 2 and the second electrode film 4 are PT.

A thin film electrode film such as Zr is used.

The first electrode film 2. Solid electrolyte membrane 3. Second electrode film 4
After forming, a part of the back surface of the flat insulating substrate 1 is covered with HF.
It is chemically dissolved and removed by methods such as methods. At this point, a part of the surface of the first electrode film 2 is exposed to form an opening 5.

An oxygen diffusion resistor 6 is attached to the opening 6 side to form a capillary tube 7.

Said first electrode film 2. A circuit is constructed using a power source 8 configured to apply a voltage between the second electrode film 4, an ammeter 9 arranged to measure the total current flowing between both electrodes, and a voltmeter 10 arranged similarly to measure the voltage. It consists of In these power source configurations, since the oxygen diffusion resistor is on the opposite side, there is no damage to the membrane when the electrode lead is taken out, and a simple configuration can be obtained.

Next, the operation of the configuration of this embodiment will be explained.

When the power source 8 is driven and a current is applied to the second electrode film 4 provided between the first electrode film 2 and the solid electrolyte film 3'ft formed on the insulating substrate 1, the second electrode film 2 and the solid electrolyte film 3' are formed on the insulating substrate 1. 1 electrode 2
Oxygen ions flow from the side through the solid electrolyte membrane 3 to the second electrode membrane 4 side. A so-called oxygen bombing phenomenon occurs. Therefore, if the volume of the chamber made up of the opening 5 and the oxygen diffusion resistor 6 and the applied current are constant, the time it takes for oxygen in the chamber to be released to the outside corresponds to the oxygen concentration in the atmosphere A to be measured. come. By gradually increasing the voltage applied to the solid electrolyte membrane 3, it is possible to obtain a phenomenon in which the current saturates at a constant level at the point when the oxygen in the chamber in the oxygen diffusion resistor θ is released, and reaches the limit current. Current is measured in atmosphere A
Obtained according to the oxygen concentration inside. This is Figure 2 and Figure 3.
This is a graph shown in the figure. In detail, when a voltage is applied to the solid electrolyte 3 with the first electrode film as a cathode and the second electrode film as an anode, the capillary 7 of the oxygen diffusion resistor 6
The oxygen concentration in the chamber inside the oxygen diffusion resistor θ becomes lower than the concentration in the outside air entering the atmosphere to be measured due to diffusion control.

Here, the conventional original model using a solid electrolyte had the disadvantage that the internal resistance and oxygen ion conductivity did not improve unless it was heated to a high temperature of at least 300°C, but the present invention By forming a solid electrolyte 1-20μm=r which is 1-20μm thinner than the conventional method, the oxygen ion conductivity is sufficiently improved even from room temperature to 200"C or less, and the operating temperature can be reduced. Furthermore, as mentioned above, this solid electrolyte membrane 3 is made of zirconium oxide (Zr
By performing sputtering using a target material containing yttrium oxide (Y2O5) etc. as a solid solution in solid electrolyte membrane 3 and keeping the solid electrolyte forming surface at a temperature of 400"C or higher, the crystal structure of the solid electrolyte membrane 3 becomes completely stabilized zirconia. A cubic crystal structure is obtained, and the difference in ionic valence between zirconia and yttria inside creates oxygen ion vacancies, which increases the conductivity of oxygen ions at room temperature and contributes to a reduction in operating temperature. be.

Effects of the Invention The present invention provides the following effects by laminating a first electrode film, a solid electrolyte film, and a second electrode film on an insulating substrate.

(2) By making the solid electrolyte membrane thinner to a thickness of 1 to 20 μm, the operating temperature was lowered, the possibility of use at room temperature was discovered, and reliability and durability were improved.

■ A thin film with a cubic structure that improves oxygen ion conductivity was obtained by using a solid electrolyte membrane at room temperature.

■ We have developed a strong sensor structure that maintains a thin film by chemically removing part of the bottom surface of the sensor film stacked on top of a flat insulating substrate.

■ The oxygen diffusion resistor can be mounted on the opposite side of the flat insulating substrate from the thin film formation surface, making it easier to damage the film and remove the electrode leads.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thin film oxygen sensor according to an embodiment of the present invention;
Figure 2 shows the oxygen concentration and limiting current characteristics, and the third electrogram shows the voltage and limiting current characteristics. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... First electrode, 3... Solid electrolyte membrane, 4... Second electrode, 6... ...Opening, 6...Oxygen diffusion resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
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Claims (3)

[Claims] (1) Form a first electrode film on an insulating substrate, and
forming a solid electrolyte membrane so as to be at least partially in contact with the electrode membrane, and forming a second electrode membrane at least partially facing the first electrode membrane via the solid electrolyte membrane;
A thin film oxygen sensor, wherein at least a portion of the solid electrolyte membrane of the insulating substrate is removed, and an oxygen diffusion resistor is provided to cover the removed portion. (2) The thin film oxygen sensor according to claim 1, wherein the solid electrolyte membrane is thinned to a thickness of 1 to 20 μm. (3) The solid electrolyte membrane is made of zirconium oxide (ZrO_2
) with yttrium oxide (Y_2O_5), calcium oxide (CaO), magnesium oxide (MgO), etc. as a solid solution, and formed into a thin film by sputtering at a temperature of 400°C or higher. sensor.