JPH0735726A - Gas component detecting element - Google Patents

Abstract

PURPOSE:To obtain a gas component detecting element in which the accuracy and stability are enhanced and the settling time is shortened while reducing the size without requiring correction of oxygen concentration in case of heated air and which can be produced through simple steps and equipment. CONSTITUTION:The gas component detecting element comprises a first insulation layer 3, a heater layer 4, a second insulation layer 5, and a stabilized zirconia layer 6, formed sequentially on an insulating or semiconductive substrate 1, noble metal electrodes 7a, 7b connected electrically with the stabilized zirconia layer 6, and a third insulation layer 9 formed on the electrodes 7a, 7b and the stabilized zirconia layer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas component detecting element suitable for detecting oxygen and humidity of a gas.

[0002]

9 and 10 are configuration diagrams showing the principle of a limiting current type zirconia oxygen detection element, FIG. 11 is a characteristic diagram showing the relationship between voltage and current in the configurations of FIGS. 9 and 10, and FIG. FIG. 13 is a characteristic diagram showing the relationship between the applied voltage and the limiting current, FIG. 13 is a characteristic diagram showing the relationship between the applied voltage and the limiting current in moist air and dry air, and FIG. 14 is a characteristic showing the relationship between the water vapor pressure and the current. It is a figure. First, the principle of the limiting current type zirconia oxygen detection element will be described. ZrO2, which is a solid electrolyte, that is, the zirconia element 1 can allow O2-ions to pass through when heated to several hundred degrees Celsius. As shown in FIG. 9, when electrodes 7a and 7b are provided on both sides of this ZrO2 and a voltage is applied by a power source 8, O2-ions can be carried from the cathode side to the anode side. This is called the oxygen pump action.

Further, as shown in FIG. 10, a cover 12 having a small hole 11 is provided in the electrode 4 on the cathode side to limit the inflow of gas.

Then, as shown in FIG. 11, even if the applied voltage is increased, the current value reaches a equilibrium at a certain constant value and does not increase any more. This is called the limiting current. This is the first limiting current IL1. This is because the inflow of gas is restricted by the small holes 6, and this limiting current value is proportional to the O2 concentration in the atmosphere.

When this sensor is placed in an atmosphere containing water vapor and the applied voltage is further increased, a second limiting current, that is, a second limiting current IL2 as shown in FIG. 12 appears. This is because the water molecules in the air are water-decomposed on the cathode side and become O2-ions, so that the current increases. That is, H2O + 2e- → H2 + O2- on the cathode side and O2- → 1 / 2O2 + 2e- on the anode side. In this case as well, the limiting current value is proportional to the water vapor pressure of the atmosphere.

Next, a method of detecting water vapor using this detecting element will be described. That is, when the amount of water vapor increases in the characteristics of FIG. 12, the first limit current IL1 decreases and the second limit current IL2 increases, as shown in FIG. The first limit current IL1 decreases because the amount of oxygen, that is, the ratio of oxygen, decreases due to the water vapor, and the second limit current IL2 increases because the water vapor is electrolyzed. The first limit current IL1 and the second limit current I
Although the amount of water vapor can be measured in any of L2, considering the selectivity of only water vapor, it is better to use the second limiting current IL2. Furthermore, the first limiting current IL1 decreases even if other gas is mixed, and is not limited to water vapor.

FIG. 14 shows the relationship between the water vapor pressure and the first and second limiting currents IL1 and IL2. That is, both the first limiting current IL1 and the second limiting current IL2 have linearity with respect to the water vapor pressure, but the second limiting current IL2 has several times the sensitivity as compared with the first limiting current IL1 and has both selectivity and resolution. I know it's good.

This type of detection element has a characteristic that it is linear in principle with respect to the water vapor pressure of the atmosphere, and since ZrO2 ceramic having excellent heat resistance is constantly heated to several hundreds of degrees, it is used at room temperature from 100 ° C. It is suitable for measuring the amount of water vapor at the above high temperatures.

Conventionally, a gas component detecting element is constructed by detecting the second limiting current IL2, and when this is used in a burner type heating furnace or the like, it will detect the humidity contained in the air heated by the burner or the like. In that case, the proportion of oxygen in the heated air becomes smaller than that in normal air, and an error occurs in the humidity detection. The same phenomenon occurs in the case of the gas component detection element of other principle. Therefore, it is necessary to correct the oxygen concentration.

Conventionally, a gas component detection element using a limiting current type or concentration cell type zirconia cannot be miniaturized because the zirconia is manufactured from the same powder sintered body as ordinary ceramics. Therefore, it takes a long time to heat the heater, and it takes several minutes to several tens of minutes to reach a measurable state. Furthermore, the process is complicated and various equipments are required. That is, a heating and firing furnace for pulverizing and sintering zirconia, a printer and a firing furnace for attaching electrodes on zirconia and making a heater, or a cutter or wire for detaching and attaching electrode wires to each sensor element. It requires various processes such as bonding and their equipment.

[0011]

As described above, in the conventional gas component detecting element, an error occurs in the humidity detection due to the decrease of the oxygen concentration in the heated air, and when there is another gas, the oxygen concentration is However, this is a measurement error. Further, in the measurement, it takes time for the heater to be sufficiently heated, and therefore, it takes a lot of time for reaching the measurement state. Further, there is a problem that the manufacturing process of the detection element is complicated and various facilities are required.

The present invention has been made in order to solve the above-mentioned problems, and does not require correction even when the oxygen concentration is decreased as in the case of heated air, and by making the shape smaller. It is an object of the present invention to obtain an element with high accuracy and good stability, to shorten the time from the start to the stable operation, and to manufacture by a simple process and apparatus using thin film manufacturing technology.

[0013]

A gas component detecting element according to the present invention comprises a substrate made of an insulating material or a semiconductor, a first insulating layer formed on the substrate, and a first insulating layer formed on the insulating layer. Heater layer, a second insulating layer formed on the heater layer, a stabilizing zirconia layer formed on the second insulating layer, and an electrical connection between both ends of the stabilizing zirconia layer. It has a noble metal electrode connected thereto and a third insulating layer formed on the noble metal electrode and the stabilized zirconia layer.

[0014]

The gas component detecting element according to the present invention is formed by using the thin film manufacturing technique, and the element itself is thin because it has a layer shape as a whole. When a voltage of 1.4 V or less is applied to this gas component detection element, it becomes an oxygen sensor,
When a voltage of 1.4 V or higher is applied, it is used as a humidity sensor. Therefore, oxygen and humidity are simultaneously measured at the same location where two elements are arranged in parallel and two different voltages are applied to each other. When this gas component detection element is placed in oxygen or water vapor, the detection output of those gases becomes a value proportional to the concentration.

[0015]

【Example】

Example 1. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view of a gas component detecting element according to the present invention, and FIG. 2 is a plan view thereof. FIG. 8 is a plan view of a gas component detecting element in which an oxygen sensor and a humidity detecting sensor are formed on one substrate. In the figure, 1 is a substrate,
This substrate is formed of a semiconductor such as silicon. A thin portion 2 is provided on a part of the substrate 1. This thin portion 2 is for reducing the heat capacity, shortening the operation stabilization time from power-on, and increasing the speed. When the heat capacity of the substrate 1 is sufficiently small as a whole, the thin portion 2 need not be provided. Reference numeral 4 is a heater layer formed on the first insulating layer 3. The heater layer 4 is formed of a noble metal such as platinum or gold, and a sputtering method, a photolithography method, or the like is used for the manufacturing method. A second insulating layer 5 is formed on the upper surface of the heater layer 4. A stabilized zirconia layer 6 having a porous property is formed on the upper surface of the second insulating layer 5 by a semiconductor thin film forming method such as sputtering, electron beam evaporation method, or photolithography. Noble metal electrodes 7a and 7b are formed on both ends of the upper surface of the stabilized zirconia layer 6 by a method similar to the method of forming the stabilized zirconia layer 6, that is, a method such as sputtering, electron beam vapor deposition or photolithography. In addition, it is electrically connected to the stabilized zirconia layer 6. At this time, the length L1 of one electrode 7a, that is, the electrode on the cathode side is formed shorter (L1 <L2) than the length L2 of the other electrode 7b, that is, the electrode on the anode side. Or one electrode 7
The contact area S1 of the a for the stabilized zirconia layer 6 is the contact area S1 of the other electrode 7b for the stabilized zirconia layer 6.
It is set narrower than 2 (S1 <S2). Both electrodes 7a and 7b have a porous property. Also, both electrodes 7a, 7
b is connected between the power supplies 8 as shown in FIG. The electrodes 7a and 7b and the stabilized zirconia layer 6 have a third surface on the upper surface.
The insulating layer 9 is formed, and the third insulating layer 9 protects the stabilized zirconia layer 6 and the electrodes 7a and 7b from dirt, humidity, or a large amount of corrosive gas. This constitutes the gas component detection element 10.

When the gas component detection element 10 having the above structure is placed in a gas heated to several hundred degrees Celsius, the electrodes 7a and 7b are placed.
The stabilized zirconia layer 6 is permeable to oxygen ions due to its porous property. In this state, the gas component detection element 10
When a voltage of 1.4 V or less is applied to the first limit current IL1 shown in FIG. 12, the oxygen concentration in the gas is measured. The amount of oxygen gas permeated is limited by the porosity of the one electrode 7a side.

Further in this state, the gas component detecting element 10
When a voltage of 1.4 V or more is applied to the second limiting current IL2 shown in FIG. 12, the humidity in the gas is measured. This is because the water molecules in the air are decomposed on the electrodes and become oxygen ions, so that the current increases. This second limiting current value is proportional to oxygen concentration and water vapor pressure.
The amount of water vapor permeation is also limited by the porosity of the one electrode 7a side.

Example 2. Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a vertical sectional view showing a second embodiment of the present invention. In the configurations of FIGS. 1 and 2, the substrate 1 made of a semiconductor has been described. However, when the substrate 1 is made of an insulating material such as ceramic, quartz, or sapphire, the substrate 1 is not shown in FIG.
Also serves as the first insulating layer 3 shown in FIG. In this case, the heater layer 4 is directly formed on the substrate 1 as shown in FIG. Other configurations are the same as those shown in FIG. 1 and FIG. 2, and therefore description thereof will be omitted.

Example 3. Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a vertical sectional view showing a third embodiment of the present invention, and FIG. 5 is a plan view of the same. In the figure, the substrate 1, the first insulating layer 3, the heater layer 4, the second insulating layer 5, the stabilized zirconia layer 6, the noble metal electrodes 7a and 7b, and the third insulating layer 9 are both configured and manufactured. Since it is the same as that shown in FIGS. 1 and 2, its description is omitted. 4 and 5 are different from FIGS. 1 and 2 in that the second insulating layer 5 and the third insulating layer
That is, the gas introducing port 11 for communicating the stabilized zirconia layer 6 with the atmosphere is formed between the insulating layer 9 and the insulating layer 9. The gas inlet 11 is formed with high precision by using a thin film fine processing technique. For example, after forming a thin film of polysilicon or the like and forming the third insulating layer 9, sodium hydroxide (NaO
It is formed by etching with H) or the like. Further, the area of the gas inlet 11 is formed smaller than the area of the anode electrode 7a, thereby giving the same characteristics as the porous characteristics of the electrodes of the first and second embodiments and limiting the rate of gas diffusion. Thus, the diffusion rate is set to be proportional to the gas concentration.

The basic operation in FIGS. 4 and 5 is the same as that shown in FIGS. However, the difference from those shown in FIGS. 1 and 2 is that the porous properties of the electrodes 7a and 7b are not utilized. Therefore, the oxygen ions and the water-decomposed oxygen ions of the water vapor directly pass through the stabilized zirconia layer 6.

Example 4. Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a plan view showing a fourth embodiment of the gas component detecting device according to the present invention, in which only the electrode structure on the substrate 1 is shown. In the figure, one electrode 7a, that is, the electrode on the anode side is formed on a disk,
Further, the other electrode 7b, that is, the electrode on the cathode side is formed by a concentric band so as to surround one electrode,
As a result, one of the electrodes 7a is
The area S1 in contact with the stabilized zirconia layer 6 is narrower than the area S2 in contact with the stabilized zirconia layer 6 of the other electrode 7b.

Embodiment 5. Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a plan view showing a fifth embodiment of the gas component detecting device according to the present invention.
In the figure, one electrode 7a, that is, the cathode side electrode, and the other electrode 7b, that is, the anode side electrode, are both formed in a comb shape, and are arranged so that the blade portions bite into each other. In this figure, one electrode 7a is constituted by two blades, and the other electrode 7b is constituted so as to surround the periphery of the two blades, whereby, as shown in FIGS. 2 and 6, The area S1 of one electrode 7a in contact with the stabilized zirconia layer 6 is made narrower than the area S2 of the other electrode 7b in contact with the stabilized zirconia layer 6.

Example 6. Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a plan view showing a sixth embodiment of the gas component detecting device according to the present invention.
In the figure, the gas component detection element 10 is mounted on one substrate 1
Individually arranged. One gas component detection element 10a has 1.4
It is used as an oxygen sensor by being connected to one power source 8a set to V or less. The other gas component detection element 10b is the other power source 8 set to a voltage of 1.4 V or higher.
It is connected to b and used as a humidity sensor.

In FIG. 8, one gas component detecting element 1
The oxygen concentration in the gas is detected by 0a. The amount of water vapor in the gas is detected by the other gas component detection element 10b. That is, these gas component detection elements 10
a and 10b detect the oxygen concentration and the amount of water vapor of the gas in the same gas and at substantially the same point.

The present invention is appropriately implemented by the following embodiments. (1) The gas component detecting element according to claim 1 or 2, wherein a gas inlet 11 is provided between the second insulating layer 5 and the third insulating layer 9. (2) The length L1 of the one electrode 7a connected to the cathode side of the stabilized zirconia layer 6 is made shorter than the length L2 of the other electrode 7b, or the length of the stabilized zirconia layer 6 is increased. The area S1 in contact with one electrode 7a connected to the cathode side and the stabilized zirconia layer 6 is set to the other electrode 7b.
And the area S2 in contact with the stabilized zirconia layer 6,
The gas component detection element according to claim 1, which is narrowed. (3) One electrode 7a connected to the cathode side of the stabilized zirconia layer 6 and the other electrode 7b connected to the anode side of the stabilized zirconia layer 6 are formed concentrically with each other, and The gas component detecting element according to claim 1, wherein an area of the electrode 7a in contact with the stabilized zirconia layer 6 is narrower than an area S2 of contact with the other electrode 7b and the stabilized zirconia layer 6. (4) One electrode 7a connected to the cathode side of the stabilized zirconia layer 6 and the other electrode 7b connected to the anode side of the stabilized zirconia layer 6 are formed in a comb shape, and each tooth is Arranged to fit each other,
The gas component detecting element according to claim 1, wherein the area of the one electrode 7a in contact with the stabilized zirconia layer 6 is narrower than the area S2 of the other electrode 7b in contact with the stabilized zirconia layer 6.

[0026]

As described above, according to the gas component detecting element of the invention of claim 1, the semiconductor substrate, the first insulating layer formed on the substrate, and the insulating layer on the first insulating layer are formed on the substrate. The formed heater layer, the second insulating layer formed on the heater layer, the stabilized zirconia layer formed on the second insulating layer, and the electric charges formed on both ends of the stabilized zirconia layer. Since it is provided with a noble metal electrode that is electrically connected and a third insulating layer formed on this electrode and the stabilized zirconia layer, it can be configured by a semiconductor thin film technique.
Therefore, the manufacturing process is simplified and the size can be further reduced. In addition, it is possible to obtain an element with uniform characteristics, high reliability, and high yield, and to achieve mass production.

According to the gas component detecting element of the invention of claim 2, a substrate made of an insulating material, a heater layer formed on the substrate, and a first insulating layer formed on the heater layer. A stabilized zirconia layer formed on the first insulating layer, noble metal electrodes electrically connected to both ends of the stabilized zirconia layer, and a noble metal electrode formed on the electrode and the stabilized zirconia layer. Since the second insulating layer is provided, not only is it possible to obtain a device having a simple manufacturing process, uniform characteristics, high reliability, and high yield as in the first aspect of the invention, Further, it is possible to obtain a detection element having a smaller number of insulating layers.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a first embodiment of a gas component detecting element according to the present invention.

FIG. 2 is a plan view of the gas component detection element of FIG.

FIG. 3 is a vertical sectional view showing a second embodiment of the gas component detecting element according to the present invention.

FIG. 4 is a vertical sectional view showing a third embodiment of the gas component detecting element according to the present invention.

5 is a plan view of the gas component detection element of FIG. 4. FIG.

FIG. 6 is a plan view showing a fifth embodiment of the gas component detecting element according to the present invention.

FIG. 7 is a plan view showing a fifth embodiment of the gas component detecting element according to the present invention.

FIG. 8 is a plan view showing a sixth embodiment of the gas component detecting element according to the present invention.

FIG. 9 is a configuration diagram showing the principle of a limiting current type zirconia oxygen detection element.

10 is a configuration diagram of a state in which a cover is provided in the principle of the limiting current type zirconia oxygen detection element of FIG. 9.

FIG. 11 is a characteristic diagram showing a relationship between voltage and current in the configurations of FIGS. 9 and 10.

FIG. 12 is a characteristic diagram showing a relationship between an applied voltage and a limiting current.

FIG. 13 is a characteristic diagram showing a relationship between an applied voltage and a limiting current in wet air and dry air.

FIG. 14 is a characteristic diagram showing the relationship between water vapor pressure and limiting current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Thin portion 3 First insulating layer 4 Heater layer 5 Second insulating layer 6 Stabilized zirconia layer 7a, 7b Electrode 8 Power supply 9 Third insulating layer 9 10 Gas component detection element

Claims (2)

[Claims] 1. A substrate 1 made of a semiconductor, and a substrate 1 on the substrate 1.
A first insulating layer 3 formed on the insulating layer 3, a heater layer 4 formed on the insulating layer 3, a second insulating layer 5 formed on the heater layer 4, and a second insulating layer Stabilized zirconia layer 6 formed on layer 5 and noble metal electrodes 7a and 7b electrically connected to both ends of this stabilized zirconia layer 6.
And a gas component detection element including the electrodes 7a and 7b and the third insulating layer 9 formed on the stabilized zirconia layer 6. 2. A substrate 1 made of an insulating material, which substantially forms a first insulating layer 3, a heater layer 4 formed on the substrate 1, and a heater layer 4 formed on the heater layer 4. Second insulating layer 5, a stabilized zirconia layer 6 formed on the second insulating layer 5, precious metal electrodes 7a and 7b electrically connected to both ends of the stabilized zirconia layer 6, and Electrode 7
A gas component detection element comprising a and 7b and a third insulating layer 9 formed on the stabilized zirconia layer 6.