JP3132210B2 - Gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element structure of a gas sensor having a heating element.

[0002]

2. Description of the Related Art A conventional gas sensor having a heating element has a structure in which a heating element and a gas-sensitive film sandwich a support substrate and heat the support substrate, as disclosed in, for example, Japanese Patent Application Laid-Open No. 1-145561. What is necessary,
As disclosed in Japanese Patent No. 313751 or JP-A-1-167645, a heating element is mounted on a support substrate, and a gas-sensitive film is mounted on the heating element. Some did not need to be heated.

FIG. 7 shows an example of a conventional gas sensor, and this gas sensor will be described. Conventional gas sensor 10
Reference numeral 0 denotes a heating element 102 made of platinum or the like on a support substrate 101.
The heating element 102 is attached to the insulator 1 having high thermal conductivity.
03, and a pair of electrodes 105 and 106 and a gas-sensitive film 1 using a metal oxide on the insulator 103.
07.

[0004] With this configuration, the heating element 102 is heated,
When this heat is transmitted to the gas-sensitive film 107 via the insulator 103 and the like, the internal resistance of the gas-sensitive film 107 changes to a predetermined value by sensing an external gas. Therefore, this resistance value is converted to the electrodes 105 and 1 by using a voltage conversion circuit (not shown).
If the value is converted into a voltage value via the signal line 06, the gas can be detected from a predetermined voltage.

[0005]

However, in the conventional gas sensor 100, the heat generated by the heating element 102 diffuses not only into the gas-sensitive film 107 but also into the support substrate 101, so that the heat efficiency is reduced and the power consumption is reduced. Accordingly, the time required for stabilizing the gas-sensitive film 107 at a predetermined temperature (response time) was relatively long. To solve this problem, the thickness of the supporting substrate 101 may be reduced to reduce the heat capacity of the supporting substrate 101a in the heated portion S, but there is a disadvantage that the mechanical strength of the supporting substrate 101 is reduced. . Further, no measures have been taken against radiant heat leaking from the heating element 102 to portions other than the gas-sensitive film 107. Accordingly, it is an object of the present invention to provide a gas sensor that has a reduced response time, reduced power consumption, and improved mechanical strength.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a gas-sensitive film having a heater mounted on a first support substrate and having an insulator and a pair of electrodes on the heater. In the gas sensor attached, a concave portion is formed on the upper surface of the first support substrate corresponding to the attachment portion of the heating element, and a second support substrate is sandwiched between the first support substrate and the heating element. .

[0007] A through hole may be formed in the first support substrate instead of the recess.

[0008] Then, a reflecting member such as a metal is attached to the lower surface of the second support substrate which corresponds to the attaching portion of the heating element .

[0009]

The heating element diffuses into the first support substrate by forming a depression on the upper surface of the first support substrate, covering the depression with the second support substrate, and attaching the heating element on the second support substrate. And the mechanical strength of the first support substrate is improved.

By making the recess a through-hole, processing becomes relatively easy.

By attaching the reflection member to the lower surface of the second support substrate, heat generated from the heating body downward is reflected.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, a gas sensor 1 of the present invention includes a first support substrate 2 having a concave portion 2a formed on an upper surface thereof, and a relatively thin glass (for example, 20) attached on the first support substrate 2 with an adhesive 3 such as epoxy resin. Micron to 100
Micron), a metal film 5 attached to the lower surface of the second support substrate 4 facing the opening of the recess 2a, and a metal film 5 attached to the second support substrate 4. Heating body 6
And an insulator 8 covering the heating element 6 with a resin having high thermal conductivity and attached on the resin, and a pair of electrodes 9 and 10 and a gas sensitive film 11 attached on the insulator 8. It consists of.

Next, a manufacturing process of the gas sensor 1 will be described. In FIG. 2, a photoresist having an opening only at a portion corresponding to the concave portion 2a is formed on the first support substrate 2 by a photolithography method generally used for glass, and is etched with a mixed acid of hydrofluoric acid to form the concave portion 2a. To form The etching depth is about 1 to 100
Micron. The thickness of the first support substrate 2 is approximately 3
00-1100 microns.

Next, as shown in FIG. 3, the second support substrate 4 is attached to the first support substrate 2, and the lower surface of the second support substrate 4 is formed by a method such as vapor deposition or electroless plating. A metal film 5 for radiant heat reflection is attached. The metal film 5 is processed to have a size that fits into the recess 2a. Incidentally, the metal film 5 can be formed by thick film printing.
Further, it is also possible to make the entire gas sensor 1 thin by etching the entire second support substrate 4 with a mixed acid of hydrogen fluoride.

Next, as shown in FIG. 4, the heating element 6 is aligned with the area where the metal film 5 is attached, and
Attach on top. By attaching the heating element 6 above the metal film 5 in this manner, the radiant heat generated from the heating element 6 can be reflected by the metal film 5. Therefore, power consumption can be saved because radiant heat can be used effectively. The material of the heating element 6 is, for example, Si, W, Ti, Cu, Ni, Cr, Pt, Pd,
Au, Ag or an alloy thereof can be used, but a substance that is strong in electromicrography and has high specific resistance is preferable. According to these materials, the current flowing through the heating element can be relatively small, so it is almost unnecessary to consider the voltage drop of the wire itself connected to the heating element, and therefore, a relatively thin wire can be used, It is suitable for reducing cost and power consumption.

Next, as shown in FIG.
₂ , an insulator 8 made of a ceramic material such as Si ₃ N ₄ , TiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ or a resin such as glass and polyimide is attached. It is preferable to use an insulator 8 having a relatively high thermal conductivity and an insulator having a small thickness as long as the insulation can be maintained. In this embodiment, the SiO ₂ was etched by a sputtering method with a mixed acid of hydrogen fluoride except for a heated portion N to a thickness of 0.3 μm. This is to prevent heat from diffusing through the insulator 8.

Next, the pair of electrodes 9, 10 and the gas-sensitive film 11 are attached on the insulator 8. The electrode 9,
In this embodiment, Ti is formed to have a thickness of 0.3 μm, but W, Ni, Al, C are used as other materials.
u, Ag, Au, Pt, Pd, Cr, or an alloy thereof may be used. In this embodiment, SiO ₂ is used as the gas-sensitive film 11, but another metal oxide may be used.

As shown in FIG. 5, the first support substrate 2
Alternatively, a through hole 2b may be formed instead of the concave portion 2a. By forming the through holes 2b, the processing is relatively easy, and the processing cost can be reduced. In addition, the first and second
Although the adhesive 3 is used to attach the support substrates 2 and 4, the invention is not limited to the adhesive 3. For example, electrode bonding or heat bonding (not shown) may be used. Although glass is used as the first support substrate 2, the present invention is not limited to glass. For example, a Si wafer, a glass epoxy substrate, or the like may be used. Although glass is also used for the second support substrate 4, a resin such as polyimide or PET film may be used as long as it can withstand the temperature of the heating body 6.

FIG. 6 shows an example of the time-temperature characteristic of the gas sensor according to the present invention. This measurement is performed by providing a thermistor instead of the sensitive film 11. According to FIG. 6, it can be seen that the characteristic T1 of the gas sensor according to the present invention rises about 1.5 seconds earlier than the characteristic T2 of the conventional gas sensor. The temperature in the stable state is about 100 ° C., and the power consumption is 50 mW for the conventional gas sensor,
The gas sensor according to the present invention was significantly reduced to 10 mW.

[0020]

The heat capacity of the substrate is reduced because the concave portion is formed in the first support substrate. Therefore, heat transmitted from the heating body to the substrate is reduced, and the response time is shortened.

By forming a through hole in place of the concave portion, it is possible to reduce man-hours and costs.

By attaching the reflecting member to the lower surface of the second support substrate, the heat generated downward from the heating body is reflected, so that the thermal efficiency can be increased, and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view taken along line MM of a gas sensor according to the present invention.

FIG. 2 is a plan view and M of a manufacturing process of the gas sensor.
It is -M longitudinal sectional view.

FIG. 3 is a plan view and M of the gas sensor in a manufacturing process.
It is -M longitudinal sectional view.

FIG. 4 is a plan view and M of a manufacturing process of the gas sensor.
It is -M longitudinal sectional view.

FIG. 5 is a plan view and a side view of another embodiment of the first support substrate of the gas sensor.

FIG. 6 is a time-temperature characteristic of the gas sensor.

FIG. 7 is a plan view and a vertical sectional view taken along line MM of a conventional gas sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... gas sensor, 2 ... 1st support substrate, 2a ... recessed part,
2b: through-hole; 4: second support substrate; 5: metal film;
..Heating element, 8 ... insulator, 9,10 ... electrode, 11 ... gas sensitive film.

Claims (2)

(57) [Claims] 1. A gas sensor having a heating element mounted on a first support substrate and a gas-sensitive film having an insulator and a pair of electrodes mounted on the heating element. A concave portion is formed on an upper surface of the first support substrate, a second support substrate is sandwiched between the first support substrate and the heating body, and the second support hitting an attachment portion of the heating body.
A gas sensor, wherein a reflection member such as a metal is attached to a lower surface of a holding substrate . 2. The gas sensor according to claim 1, wherein a through hole is formed in the first support substrate instead of the recess.