JPS6127704B2 - - Google Patents

Description

Detailed Description of the Invention Generally, in a catalytic combustion type gas detector or a semiconductor gas detector, an electric heater is used for the gas detection element. A small one is desirable, and for that purpose, it is necessary to downsize the electric heater and reduce its heat capacity.

In response to the above-mentioned requests, the applicant has previously
We have proposed an electric heater having a bridge-like heating section as shown in Figures 3 to 3.

In Figures 1 to 3, Figure 1 is a plan view;
Figure 2 is a sectional view taken from the - line in Figure 1;
The figure is a sectional view taken from the - line in Figure 1.
1 is a silicon (Si) wafer, 10 is a Si wafer
A silicon thermal oxide (SiO ₂ ) film formed on 1 ,
This SiO ₂ film 10 is highly heat resistant and electrically insulating, has relatively strong mechanical strength, and uses a different etching solution from that of the Si wafer 1 . 2 is a cavity provided in the Si wafer 1; 10a and 10b are cavities provided in the Si wafer 1 ;
With the slits provided in the SiO ₂ film 10 , these cavities and slits can be made, for example, as follows. First, the surface of the Si wafer 1 was thermally oxidized in a steam atmosphere at 1100°C for several hours to a thickness of 1.0
A SiO ₂ layer 10 of about μm is grown. Next, the SiO ₂ layer 10 is etched by a known photoetching method using a photoresist pattern, for example, using ammonium fluoride, and then the Si wafer 1 is etched in the crystal direction using a silver glycol etching solution or the like. A groove of an appropriate depth is created by etching using an etching solution whose etching speed does not change much depending on the etching process. After that, both sides of the groove are actively etched using an etching liquid such as an ethylenediamine aqueous solution, which is a different etching liquid for Si and hardly attacks SiO ₂ , and an undercut is made between both grooves. Penetrate cavity 2
Then, slits 10a and 10b are formed to form a bridge 10c of SiO ₂ film. On the substrate formed in this manner, a substance that has a catalytic effect on the gas to be detected, such as Pt, or a resistor with a large temperature coefficient of resistance is coated with Pt.
A conductor layer 13 is formed by sputtering a substance mixed with Pd, Pd, etc., and lead wires 15a, 15b are provided on this conductor layer 13.
When a current is passed between b, the bridge portion 13a generates heat, and if flammable gas is present around it, it burns in the bridge portion 13a, changing its electrical resistance. Therefore, by detecting this change in electrical resistance, the presence of combustible gas can be detected. The conductor layer 13 may be made of a gas-sensitive material that is sensitive to carbon monoxide, chlorine, etc. and whose electrical resistance changes due to adsorption or adhesion of these substances, such as gas-sensitive material such as carbon dioxide (SiO ₂ ). The body can also be used to detect gases other than flammable.

If a gas adsorbing material such as a porous membrane is applied to the heat generating part of a bridge structure heat generating element having a bridge heat generating part as described above, the amount of gas adsorbed can be increased and the detection sensitivity can be increased. As the thickness increases, the heat capacity increases and the response speed decreases, and the membrane becomes more likely to peel off due to thermal expansion of the membrane due to the temperature distribution in the thickness direction of the membrane. Therefore, it is necessary to make the thickness of the gas adsorption film applied to the heat generating part, for example, about 1 μm to prevent the above-mentioned defects from appearing. However, if the thickness is made thinner, the amount of gas adsorption decreases and the detection sensitivity decreases. Resulting in.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an electric heater in which a film is formed on both the upper and lower surfaces of the heat generating part to reduce the thickness of the gas adsorbing material film without reducing the amount of gas adsorbed. However, conventional thin film forming methods such as sputtering, vapor deposition, or printing cannot form both sides of the heat generating portion. Therefore, in the present invention, a substrate forming a bridge structure heating element manufactured as described above with reference to FIGS. is applied by rotating a spinner, and by adjusting the viscosity of the film-forming material and the rotational speed of the spinner, the heat-generating part can be coated while maintaining the heat-generating part in a bridge shape, that is, leaving a cavity at the bottom of the heat-generating part. This allows a film to be formed on the surface.

When the cross-linked heating element of the present invention is used as a gas detector, for example, fine alumina powder, water, and a small amount of a binder (such as water glass) are used as film-forming substances. The mixture is mixed to form a liquid, and this is applied using a spinner to the bridge structure heating element shown in FIGS. 1 to 3. In that case, the film thickness is adjusted by adjusting the viscosity of the film-forming substance, the spinner rotation speed, the spinner rotation time, etc., so that the cross-linked structure is maintained. After forming a membrane in this manner, it is dried at about 100°C, then immersed in a chloroplatinic acid solution (H ₂ PtCl ₆ ), and reduced in hydrogen or formalin gas at 400 to 500°C to transform the platinum black into porous alumina. disperse inside. 4 to 6 are diagrams showing an example of a bridge structure heating element in which a film is formed as described above. FIG. 4 is a plan view, and FIG.
FIG. 6 is a cross-sectional view taken along the - line in FIG .
They correspond to the reference numbers given in the figures.

[Brief explanation of the drawing]

FIG. 1 is a plan view for explaining an example of a bridge structure heating element to which the present invention is applied, and FIG.
FIG. 3 is a sectional view taken along the line - in FIG. 1, FIG. 4 is a plan view showing an example of the bridge structure heating element according to the present invention, and FIG. Figure 6 is a cross-sectional view taken along the line - in the figure.
FIG. 4 is a sectional view taken along the line - in FIG. 4; 1 ...Si wafer, 2...cavity, 10 ...SiO ₂
Membrane, 13a... Heat generating part, 20 ... Membrane.

Claims (1)

[Scope of Claims] 1. A substrate having a cavity in a part of its surface, a bridge portion bridging the cavity portion, a conductive heating element in the bridge portion, and an electrically conductive heating element energized. An electric heater that heats and uses the bridge portion as a heat generating portion, characterized in that the electric heater has films on both upper and lower surfaces of the bridge portion. 2. A method of forming a film on both sides of the bridge-like heat generating element of a bridge-like heat generating element having a bridge-like heat generating element, the substrate forming the bridge-like heat generating element being placed on a spinner, and forming the film. 1. A method for manufacturing an electric heater, characterized in that a liquid substance for heating is applied by rotation to both surfaces of the bridge structure heating section using the spinner.