JPH02221856A - Ceramics heater and oxygen sensor element having the same - Google Patents

Abstract

PURPOSE:To prevent the diffusion and evaporation of the platinum used for a circuit without allowing a heater to be disconnected by handling by coating the heater for heating on a ceramics substrate with a protective layer made of glass. CONSTITUTION:The heater 2 for heating formed on the ceramics substrate 1 is coated with the protective layer 5 made of the glass, by which the calcination of this protective layer 5 at the temp. below 1,000 to 1,400 deg.C calcination temp. is enabled. The diffusion of the platinum which is a heater material at the time of the calcination is, therefore, obviated. The change in resistance value by the evaporation of the platinum is consequently obviated and the disconnection of lead wires by handling, etc., is prevented. Further, the sharp softening point is obtd. from the properties of a crystallized glass material and the stable and excellent mechanical and electrical characteristics are obtd. in the service region if the above-mentioned material is used for the protective layer 5.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applied to electronic equipment and general-purpose equipment, such as heaters for oxygen sensors, and is used to heat components and elements that require heating using a heater formed on a ceramic substrate. The present invention relates to a ceramic heater for heating an oxygen sensor element having the heater.

[Problems to be solved by conventional techniques and inventions] Conventionally,
In order to protect this type of ceramic heater, a protective layer is formed using alumina, which has excellent electrical insulation, by means such as plasma spraying or screen printing. Usually 140
It must be fired at a high temperature of 0°C or higher. For this reason,
Platinum, which is commonly used as a heater material, has the problem of diffusing from the ceramic substrate and changing the properties of the ceramic substrate material.

In addition, if the protective layer described above is not coated, the heater may break due to handling during the manufacturing process, or the platinum may evaporate due to direct exposure to air, causing the heater to break during use. There was a problem that the resistance value changed.

Furthermore, when a ceramic heater such as the one described above is applied to an oxygen sensor element, there is a problem that variations occur in temperature characteristics and responsiveness, resulting in a significant decrease in reliability.

Therefore, the present invention has been made in consideration of the above circumstances.
To provide a ceramic heater which can be used in a printing process by protecting the heater itself so that it does not break due to handling and preventing diffusion and evaporation of platinum used in the heater circuit. The purpose of this invention is to improve the reliability of the oxygen sensor element by using the heater in the oxygen sensor element, for example.

[Means to solve the problem]

In order to achieve the above object, the ceramic heater of the present invention is characterized in that a glass protective layer is coated on the heater formed on the ceramic substrate.

Further, it is desirable that the protective layer is made of a crystallized glass material.

Furthermore, the ceramic heater described above may be applied to an oxygen sensor element.

[For production]

In the present invention having the above configuration, a glass protective layer is coated on the heating heater formed on the ceramic substrate, so that the firing temperature of this protective layer is 10.
It becomes possible to perform firing at temperatures below 00 to 1400°C. Therefore, platinum, which is the heater material, does not diffuse during this firing. Therefore, the resistance value did not change due to evaporation of platinum, and breakage of the lead wire due to handling or the like could be prevented.

Further, it is preferable to use a crystallized glass material for the protective layer because the softening point is sharp due to the properties of this crystallized glass material, and the mechanical and electrical properties are stable and excellent in the operating temperature range.

Furthermore, if the ceramic heater described above is applied to an oxygen sensor element, temperature characteristics and responsiveness can be stably maintained, and reliability can be significantly improved.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure is a cross-sectional view showing one embodiment of the ceramic heater according to the present invention. In the figure, 1 is a ceramic substrate made of alumina (A1203) or mullite (3A12032 SiO2), which have excellent electrical insulation properties. A heating heater 2 is formed on this ceramic substrate 1 .

The heating heater 2 is made of platinum (PT) or platinum-palladium (
Pd) etc. are baked by applying paste printing at a temperature below 1000 to 1400°C. As shown in FIG. 2, a lead wire attachment portion 3 extends in the outer circumferential direction from the heater 2, and lead wires 4, 4 are connected to the lead wire attachment portion 3, respectively.

Further, a protective layer 5 made of glass is coated on the heater 2, and in particular, the protective layer 5 is formed of a crystallized glass material such as Ba-based alkali glass by a printing method. In this case, if alumina paste is used as a protective layer, poor dispersion of alumina in the paint will occur during the printing process, and printing unevenness will occur frequently.

Here, the reason why a crystallized glass material is used as the glass of the protective layer 5 is as follows. In other words, ordinary amorphous glass does not sinter even when fired at elevated temperatures and has a softening point unique to glass, but in the case of crystallized glass, sintering occurs during firing, and the glass phase and glass This is because it is composed of a crystalline phase precipitated from glass, has a resharpening softening point different from amorphous glass, and has excellent mechanical and electrical properties.

The firing temperature of the crystallized glass material of the protective layer 5 is 10
Since the temperature is around 00°C, which is not so high, damage caused by heat diffusion and the like due to firing of the heater pattern is reduced. That is, platinum (PT), which is the material of the heating heater 2, has a temperature of 1400°C.
Diffusion occurs gradually. Therefore, the firing temperature is 100
It is best to carry out at a temperature of 0 to less than 1400°C, preferably 100°C.
A temperature of about 0 to 1°100°C is good. No thermal diffusion of platinum is observed in this temperature range.

Furthermore, in order to prevent the heater 2 from peeling off from the ceramic substrate 1, it is desirable to use a crystallized glass whose linear expansion coefficient is relatively close to that of platinum, 100×10 7°C. Therefore, it is desirable that the linear expansion coefficient of the crystallized glass of the protective layer 5 is 50 to 120X10/'C, and if it is within this range, it has been experimentally shown that there is no problem at all with platinum patterns formed on alumina substrates. It is clear that

Further, it is desirable that the alkali metal content of the crystallized glass of the protective layer 5 is 0.1% by weight or less. Incidentally, if the alkali metal content is 0.1% by weight or less, when the heater 2 is heated to a high temperature, alkali ions in the glass will move and prevent heater current leakage, but if the alkali metal content is This is because if it exceeds 0.1% by weight, this will become unavoidable.

Furthermore, since the heating heater 2 is normally used at a high temperature of 200°C or higher, it is required to have a certain level of heat resistance.
It is desirable to have heat resistance of 0°C or higher.

The operation of this embodiment in the above configuration will be explained.

By coating and printing a glass protective layer 5 on the heater 2 formed on the ceramic substrate 1,
The protective layer 5 can now be fired at a temperature below 1000 to 1400°C. Therefore, platinum, which is the heater material, does not diffuse during firing, prevents disconnection of the heater due to handling, etc. during the manufacturing process, and does not change the resistance value due to evaporation of platinum.

In particular, it is preferable to use a crystallized glass material for the protective layer 5 because the softening point is sharp due to the properties of this crystallized glass material, and the mechanical and electrical properties are stable and excellent in the operating temperature range. .

FIG. 3 shows an embodiment of an oxygen sensor element to which a ceramic heater according to the present invention is applied, and the same parts as in FIG. 1 are given the same reference numerals and will be described. In Figure 3,
The oxygen sensor element 10 is made of solid electrolyte pellets [
For example, it is made of stabilized zirconia in which a metal oxide (for example, YO, CaO, etc.) is dissolved in zirconium oxide (ZrO: zirconia).] Platinum electrodes 12 are formed on both sides of 11, and gas diffusion holes 13 are formed. A cap 14 made of ceramic is bonded to one side of the cap. This cap 14 corresponds to the ceramic substrate 1 shown in FIG. Furthermore, a heater 2 is formed on the cap 14 as in FIG. 1, and a protective layer 5 made of glass is coated on the heater 2.

Then, by applying a voltage between both platinum electrodes 12, a current using oxygen ions as carriers flows due to the oxygen bombing effect of the pellet 11 under heating, and the gas diffusion hole 1
Oxygen molecules that have entered the gas reaction chamber in the cap 14 through the pellet 11 are discharged through the pellet 11.

Therefore, since the flat region of the current that appears in the voltage region of the voltage-current characteristic at this time, that is, the limiting current value and the oxygen concentration have a one-to-one relationship (a linear relationship when taken logarithmically), A constant voltage is applied to the electrode, and the oxygen concentration is detected from the limiting current value at that time.

By the way, the limiting current characteristics of the oxygen sensor vary greatly depending on the temperature, and if the temperature of the sensor becomes too low, the flat area will no longer be observed and the sensor will no longer function. On the other hand, it has been found that the responsiveness of the sensor is temperature dependent, with the higher the temperature of the sensor, the faster the response time.

Therefore, the oxygen sensor element 10 shown in FIG.
Since the heater 2 is coated with the protective layer 5 made of glass, the resistance value of the heater does not change, and the temperature characteristics and responsiveness can be stably maintained.

The present invention is not limited to the above-mentioned embodiments, and various modifications are possible.

Although the above embodiment describes an example in which the present invention is applied to an oxygen sensor element, it can also be applied to other electronic equipment or general-purpose equipment, for example.

〔Effect of the invention〕

As described above, according to the ceramic heater of the present invention, the heater is coated with a protective layer made of glass, so that the heater does not break due to handling, and the platinum of the heater is prevented from diffusing and evaporating due to heat. As a result, the resistance value of the heater does not change and can always be maintained at a constant value.

Additionally, by using glass instead of alumina as a protective layer, the printing process became smoother and work efficiency was significantly improved.

Furthermore, since the protective layer is made of a crystallized glass material, the softening point is sharp due to the properties of this crystallized glass material, and the mechanical and electrical properties are stable and excellent in the operating temperature range.

Furthermore, since the oxygen sensor element includes the ceramic heater, the temperature characteristics and responsiveness are stably maintained, and the reliability of the oxygen sensor element can be significantly improved.

2 is a plan view showing the ceramic heater shown in FIG. 1 with the protective layer removed. FIG.

FIG. 3 is an explanatory diagram showing an embodiment of an oxygen sensor element to which the ceramic heater shown in FIG. 1 is applied.

1... Ceramic substrate, 2... Heating heater 3
...Lead wire attachment part, 5...Protective layer 10...
Oxygen sensor element.

Claims (1)

[Scope of Claims] 1. A ceramic heater characterized in that a glass protective layer is coated on a heater formed on a ceramic substrate. 2. The ceramic heater according to claim 1, wherein the protective layer is made of a crystallized glass material. 3. An oxygen sensor element comprising the ceramic heater according to claim 1.