JPH04160790A - Heater substrate - Google Patents

Abstract

PURPOSE:To enable mounting a plurality of small-sized and lightweight gas sensor portions by causing local variations in disposition density of the heater disposed over the whole surface of a ceramics substrate. CONSTITUTION:A heater 2 of different disposition densities is formed on a single ceramics substrate 1. For this reason, the amount of heat transferred from the heater 2 to an insulation layer 3 per unit area thereof differs for each corresponding region, whereby the regions having different surface temperatures are formed inside the substrate. And a gas sensor layer is disposed the reactivity of which becomes peculiarly high at the temperature of each corresponding region. This makes it possible to detect two different types of gases by the two gas sensor layers 7a, 7b disposed with respect to the one substrate. This enables the easy formation of a composite sensor simple in structure, small in size and light in weight.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a heater substrate in which a heater is formed on a ceramic substrate, and particularly relates to a heater substrate in which a heater is formed on a ceramic substrate. Regarding possible heater substrates.

(Prior Art) A heater substrate, in which a heater is formed by printing a linear resistor on a ceramic substrate, is widely used as a surface heating element or a gas sensor.

For example, as a type of gas sensor, a semiconductor gas sensor that detects the transfer of charge between a semiconductor and gas molecules adsorbed on the semiconductor as a change in electrical conductivity has been put into practical use, and has been used as a gas leak alarm for toxic gases. It is used as a gas leak alarm for city gas made of hydrocarbons, etc.

As such a semiconductor gas sensor, a resistance type sensor using a ceramic substrate has been developed. This gas sensor is configured, for example, by forming an electrode, a gas detection layer and a catalyst layer for contacting gas on one side (front side) of a ceramic substrate, and forming a heater on the other side (back side). Ru.

The gas sensing layer is composed of, for example, a semiconductor film (thick film) having gas-sensitive characteristics and a catalyst layer formed over the semiconductor film. In this gas sensor, when gas comes into contact with the detection layer and the catalyst layer, the electrical conductivity, or resistance value, of the electrode changes due to the transfer of charge between the gas molecules and the catalyst layer, and the value of the current flowing through the electrode changes. to detect the presence of gas.

In the gas sensor configured in this way, the catalyst layer is heated to a predetermined temperature by energizing the heater, and the redox reaction of the gas is smoothly carried out on the surface of the catalyst layer, thereby increasing the sensitivity and responsiveness of the semiconductor film. , removing dirt from the catalyst layer.

(Problem to be Solved by the Invention) By the way, the sensitivity and responsiveness of a gas sensor differ depending on the type and temperature of the semiconductor or catalyst, and in order to maintain the detection sensitivity at the optimum value for a specific detection target gas, it is necessary to It is necessary to select a semiconductor with excellent gas-sensitive characteristics and to maintain a constant sensor temperature.

Therefore, the above-mentioned gas sensor uses a heater substrate in which the heater pattern formed on the ceramic substrate is planar or linear heaters are routed over the entire surface of the substrate in order to make the temperature distribution on the substrate surface uniform. As a result, S having gas-sensitive properties constitutes the gas detection layer of the sensor.
The sensitivity distribution of semiconductor films such as n02 is kept constant.In this way, conventional gas sensors have been designed to detect only one specific type of gas by providing one type of gas detection layer on one heater substrate. Common. In order to form a composite sensor that detects two or more types of gases with different characteristics,
A plurality of heater substrates with different catalyst types or sensor temperatures were created and then combined.

However, a composite sensor formed by combining multiple heater substrates has a large capacity, and it is necessary to adjust the heater resistance and applied voltage for each substrate.
There were problems in that the wiring and power supply configuration were complicated and it was difficult to make the configuration compact.

In recent years, the miniaturization of devices that use sensors has progressed rapidly.
In order to meet this demand, there is a need for a sensor heater substrate that is small and lightweight and capable of detecting multiple gases with high precision.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a heater substrate that can be made smaller and lighter, and on which a plurality of gas detection sections can be attached.

[Structure of the invention]

(Means and effects for solving the problem) In order to achieve the above object, the heater board according to the present invention has the following features:
A heater substrate having a ceramic substrate, a heater arranged over the entire surface of the ceramic substrate, and an insulating layer formed over the heater, characterized in that the arrangement density of the heaters is partially changed. shall be.

The ceramic substrate used in the heater substrate according to the present invention preferably has a relatively low thermal conductivity, such as alumina with a thermal conductivity of about 10 to 20 W/m-, or alumina with a thermal conductivity of 15 to 20 W/m. Silicon nitride and the like can be mentioned.

Further, as the conductor (resistor) used in the heater, one whose main component is a high melting point metal (tungsten type, molybdenum type) is used, and among them, a tungsten-platinum type alloy is preferable because it has excellent oxidation resistance.

Further, as an insulating layer, an insulating paste containing alumina, silicon nitride, glass paste, or the like as a main component is formed so as to overlap the heater. In particular, by using the same material as the ceramic substrate, the coefficient of thermal expansion of the insulating layer and the ceramic substrate can be made equal, and peeling due to the difference in thermal expansion between the two can be prevented, resulting in a highly durable heater substrate. can be formed.

The method for manufacturing a heater substrate according to the present invention is to first add a sintering aid to ceramic raw material powder such as alumina or silicon nitride, and then add an organic binder, a solvent, etc. to prepare a uniform mixture. The mixture is injected into a plate shape using a doctor blade method or the like to form a green sheet.

Next, a wiring pattern is printed on the obtained green sheet by screen printing or the like using a conductor (resistor) paste containing tungsten or molybdenum powder as a main component to form a heater.

On a screen plate used in screen printing, portions where heaters are arranged sparsely and portions where heaters are densely arranged are formed in advance.

Further, an insulating layer is formed by printing an insulating paste whose main component is the same material as the ceramic substrate, such as alumina, over the entire surface of the substrate by screen printing so as to overlap the top surface of the heater.

Note that the insulating layer is provided with through holes for guiding the ends of the heaters to the outside of the insulating layer, and each through hole is filled with a conductive paste to form a lead pad.

Then, the obtained heater substrate laminate is degreased and baked in an inert atmosphere such as N2, and then integrated to obtain a heater substrate of a predetermined shape. By integrally forming the ceramic substrate, the heater, and the insulating layer by co-firing in this manner, the adhesion between the respective constituent materials is improved, and in particular, changes in heater resistance over time are effectively prevented.

According to the heater substrate according to the present invention, since the arrangement density of the heaters formed on one ceramic substrate is different, the amount of heat transferred from the heater is different for each region of the ceramic substrate, and the surface temperature is different. A region is formed within a single substrate. By arranging gas detection layers with different detection characteristics for each region, it is possible to detect different types of gas with multiple gas detection layers arranged on one substrate, resulting in a simple structure. A compact and lightweight composite sensor can be easily formed.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings. FIGS. 1(a) and 1(b) are a plan view and a sectional view, respectively, of a heater substrate A according to this embodiment.

Linear heaters 2 are formed in a meandering manner so as to be distributed over the entire surface of an alumina substrate 1 serving as a ceramic substrate.

However, the arrangement density of the heaters 2 is the same as the alumina substrate 1 in the figure.
It is set to be dense in the left half of the image, while sparse in the right half.

An insulating layer 3 is formed on top of the heater 2, and heater electrode pads 4 are formed at diagonal corners of the insulating layer 3. It is connected to the end of the heater 2 through through holes 5 formed at diagonal corners of the insulating layer 3, respectively.

The above heater substrate is mass-produced, for example, through the following steps. First, 10 parts by weight of polyvinyl butyral (PVB) was added as a binder to a powder mainly composed of alumina with an average particle size of 1 to 2 μm, and then a plasticizer and a solvent were added to form a slurry. As shown in the figure, the length is 60 m, the width is 90 m, and the thickness is 0. A 4+am alumina green sheet was prepared.

Next, as shown in FIG. 1(a), platinum paste is applied so that the meandering width W is 3 mm and the meandering interval Ll in the left half of the substrate is 0.
．． 2 ma, meandering interval L2 on the right half of the board is 0.
Identical conductor (heater pattern) meandering at 5mm
is printed by a screen plate, and 1 is printed as shown in Figure 4.
00 substrate bodies were formed.

Next, an insulating paste prepared by adding a binder and a solvent to a powder having the same composition as that used for the alumina-based green sheet is used, and it is printed on the substrate using the same screen printing method to cover the entire surface of the heater. An insulating layer was printed. At this time, printing was performed so that through holes 5 were formed in predetermined portions of the insulating layer as shown in FIG.

Next, while filling the through holes with platinum paste, slit lines 6 are formed using a cutter knife or the like so as to partition each heater substrate A molded body.

Next, as shown in FIG.
Co-fire at 540°C. Then, it is divided along the slit line 6 to form a structure as shown in FIGS. 1(a) and 1(b).
A large number of heater substrates A having heaters with different arrangement densities are manufactured.

When power was applied to the heater power supply pads 4, 4 of the thus obtained heater board A and the surface temperature on both left and right sides of the insulating layer 3 was measured, it was found that in the area on the left side in the figure where the heaters were densely arranged, the temperature was 500. ℃, and in the region where the heaters are sparsely arranged on the right side, the heat generation amount of the heater is small, so the temperature is 460°C, and the temperature difference is 40°C.

In addition, as in the above manufacturing method, a heater substrate manufactured by simultaneously firing a heater substrate formed by screen-printing a heater pattern and an insulating layer on a green sheet has a high bonding strength between the ceramic substrate, the heater, and the insulating layer. is extremely strong, and since the heater is covered with an insulating layer, there is little change in heater resistance over time, ensuring high reliability over a long period of time, especially when used as a heater substrate for a gas sensor.

FIGS. 2(a) and 2(b) are a plan view and a sectional view, respectively, showing a gas sensor using the heater substrate A according to the present invention. The heater board A used in this gas sensor is the first
It is the same as that shown in Figures (a) and (b), and the same parts are given the same reference numerals.

That is, a heater 2 is formed in a meandering manner on an alumina substrate 1, and an insulating layer 3 is further formed to cover the heater 2. The arrangement density of the heaters 2 is set to be dense in the left half of the figure, and sparse in the right half. Heater power supply pads 4.4 connected to each end of the heater 2 are formed at diagonal corners of the insulating layer 3.

Further, gas detection layers 7a and 7b are formed on the surface of the insulating layer 3 corresponding to the sparse and dense portions of the heater 2, respectively. Each gas detection layer 7a, 7b is constructed by laminating a Pt-Rh based catalyst layer on the surface of an SnO2 based semiconductor film. The gas detection layers 7a and 7b are connected to a pair of high-temperature part counter electrodes 8.8 and a pair of low-temperature part counter electrodes 9.9 formed on both edges of the insulating layer 3a corresponding to the dense and dense parts of the heater 2, respectively. be done.

The above gas sensor can be mass-produced by the following steps in accordance with the manufacturing method of the heater substrate.

That is, after baking a sheet-shaped heater substrate as shown in FIG. 4, screen-printing a counter electrode for sensor detection with gold (Au)-based paste and baking, and then applying semiconductor (S n O2-based) paste. , catalyst (Pt-Rh system)
The paste is sequentially printed on the surface of the insulating layer 3 of the heater substrate A by a screen printing method, and then fired to form a gas sensing portion.

A specific gas in the atmosphere is detected by the gas detection layer 7a of the gas sensor.
, 7b, a gas redox reaction occurs depending on the selectivity and temperature of the catalyst, and the resistance value of the gas detection layers 7a, 7b changes due to the exchange of electrons, and the signal current changes depending on the gas concentration. , a detection circuit detects the presence of gas.

In the gas sensor obtained in this way, when the surface temperature of the high-temperature part counter electrode 8.8 side of the insulating layer 3 in which the heaters 2 are arranged densely is set to 500°C, the heaters 2 are arranged sparsely. The surface temperature of the low temperature part counter electrode 9.9 of the insulating layer 3 is 46
The temperature was 0° C., and while the gas detection layer 7a located in the high temperature region could specifically detect ethanol, the gas detection layer 7b located in the low temperature region could detect hydrogen with high sensitivity.

FIG. 3 is a perspective view of the detection section of a composite gas sensor formed by mounting the gas sensor in which the gas detection layers 7a and 7b are formed on the upper surface of the heater substrate A as described above on a minute stem 10 with a diameter of approximately 1 mm. . Six connector pins 11 pass through the stem 10 in the axial direction, and the high temperature section counter electrode 8, the low temperature section counter electrode 9, and the heater electrode pad 4 are connected to the connector pins by lead wires 12 soldered with silver. 1
Connected to 1.

As described above, according to the gas sensor using the heater substrate according to this embodiment, since the arrangement density of the heaters 2 formed on one ceramic substrate 1 is different, The amount of heat transferred from the substrate 2 differs from region to region, and regions having different surface temperatures are formed within one substrate. By arranging a gas detection layer whose reactivity is specifically high at the temperature of each region, two gas detection layers 7a in which two different types of gas are arranged on one substrate are formed.
, 7b, it is possible to easily form a composite sensor that has a simple structure, is small in size, and is lightweight.

In the above embodiments, the same type of semiconductor film and catalyst layer were formed on the surfaces of two insulating layers having different surface temperatures, which were formed by changing the arrangement density of heaters, but the present invention The present invention is not limited to these examples. For example, by differentiating the catalyst species applied to the gas detection layers 7a and 7b into W-Cu type and Pt-Rh type, or by further changing the arrangement density of the heaters into three or more levels, the heater temperature distribution can be adjusted. Furthermore, by making various changes to match the conditions that maximize the reactivity of the gas to be detected, it becomes possible to detect other types of gases at the same time.

〔Effect of the invention〕

As described above, according to the heater substrate according to the present invention, since the arrangement density of the heaters arranged on one ceramic substrate is different, the amount of heat transferred from the heater is different for each region of the ceramic substrate. Regions with different surface temperatures are formed within one substrate.

By arranging gas detection layers with different detection characteristics for each region, it is possible to detect different types of gas with multiple gas detection layers arranged on one substrate, resulting in a simple structure. A compact and lightweight composite sensor can be easily formed.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a plan view and a sectional view showing an embodiment of the heater substrate according to the present invention, respectively, and FIG.
a) and (b) are respectively a plan view and a sectional view of a gas sensor using a heater substrate according to the present invention, FIG. 3 is a perspective view showing an example of mounting a composite gas sensor using a heater substrate according to the present invention, and FIG. The figure is a plan view of a green sheet when a large number of heater substrates are simultaneously manufactured by printing heaters and the like. 1... Alumina substrate (ceramic substrate), 2...
Heater, 3... Insulating layer, 4... Power supply pad for heater, 5... Through hole, 6... Slit line, 7
a. 7b... Gas detection layer, 8... High temperature part counter electrode, 9...
...low-temperature part counter electrode, 10... stem, 11... connector pin, 12... lead wire. Applicant's agent Hisashi Hatano 1st I! ! 2nd m

Claims (1)

[Claims] A heater substrate having a ceramic substrate, a heater arranged over the entire surface of the ceramic substrate, and an insulating layer formed over the heater, characterized in that the arrangement density of the heaters is partially changed. heater board.