JPH0688802A - Ambient gas sensor - Google Patents

Abstract

PURPOSE:To obtain an ambient gas sensor which has high sensitivity and stable detection characteristics by easily forming an air hole communicating a chamber for detection with the outside air with high accuracy and inexpensively suppressing characteristic variation. CONSTITUTION:A chamber 14 for reference and chamber 15 for detection having the same recessed shape are formed on a silicon substrate 10 by anisotropic etching and, at the same time, an air vent groove 16 extended to the surface of the substrate 10 is formed in the chamber 15. The groove 16 communicates the chamber 15 with the outside air except an opening 16a while the groove 16 is partially closed by a cover 18 jointed to the substrate 10 above the chamber 15. Heating resistors in the chambers 14 and 15 formed in the form of thin wires on a thin film insulator 11 supported by the bridging supporting section of the insulator 11 above the recessed sections.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a structure of an atmosphere sensor, and more particularly to a structure of an atmosphere sensor such as a temperature sensor and a gas sensor for detecting an atmosphere gas.

[0002]

2. Description of the Related Art Conventionally, as a gas sensor, a metal oxide semiconductor has a built-in electrode and a heater also serving as an electrode, and when the metal oxide semiconductor is heated by the heater, the resistance value of the metal oxide semiconductor is the metal. There is proposed an oxide semiconductor which utilizes the fact that gas is adsorbed on the surface of the oxide semiconductor to lower it, but there is a problem that it consumes a large amount of power and is not suitable for driving a dry battery. In order to improve this point, a bridge that extends in the air, such as a bridge structure or a cantilever structure, is provided, and a metal oxide semiconductor is formed on this bridge, so that the heat capacity can be increased. Attempts have been made to reduce the power consumption by reducing the power consumption by increasing the response characteristics.

On the other hand, in the gas sensor, two detectors having the same structure are provided, and one of the detectors is brought into contact with the ambient atmosphere to be used for gas detection, and the other detector is not brought into contact with the ambient atmosphere. Then, the temperature of the surroundings is detected by this detector having a sealed structure to perform temperature compensation.

3 (a) and 3 (b) show Japanese Patent Application Laid-Open No. 3-927.
In a plan view and a cross-sectional view showing an example of the absolute humidity sensor disclosed in Japanese Patent Publication No. 54-54, as shown in the figure, a recess 6 for mounting a detection element 3 made of a thin film resistance heating element on a first substrate 1 made of silicon. , 7 are formed, an insulating protective film is formed on the surface of the substrate 1, and the detection element 3 formed of a thin-film resistance heating element is installed so as to be bridge-supported in the recess.

With the above structure, the heat of the detecting element 3 having a small heat capacity is prevented from being directly conducted to the substrate, and the thermal equilibrium is maintained by the heat conduction of the gas in the space constituted by the substrate, It aims to reduce power consumption and speed up response.

Further, the second substrate 2 is also provided with recesses 6 and 7 for forming a space for the detection element 3 at a position corresponding to the substrate 1.
And a cutout portion for exposing the pad portion 9 of the detection element 3 is formed. Further, the low melting point glass paste 5 for bonding is screen-printed on the substrate 2 in a pattern shown by diagonal lines in the figure, and The solvent in the paste is evaporated by calcination,
Subsequently, in a dry air or an air atmosphere having a constant known humidity to be enclosed in the space of the reference element, the substrates 1 and 2 are opposed to each other, and the recesses surround the detection element 3 of the thin-film heating element as shown in the drawing. Then, the low melting glass is melted by heating and the substrates are joined.

By the above-mentioned joining, the space 6 on the reference side is shielded from the outside air and always kept in a constant atmosphere. The atmosphere to be hermetically sealed does not necessarily have to be atmospheric pressure. At this time, the space 7 on the detection side formed at the same time has a vent hole 8 formed at a position facing each other with a gap between the joints.

When the humidity sensor configured as described above is supplied with constant energy by electric power to the two detection elements 3 to cause them to self-heat, the amount of water vapor in the reference space 6 and the detection space 7, respectively, that is, , It radiates heat according to the thermal conductivity of the space corresponding to absolute humidity, and it becomes a constant temperature, and each has a constant resistance value, so the difference is detected as the output of the non-balanced potential of the bridge circuit and the absolute humidity is detected. It can be measured.

In the conventional atmosphere sensor described above, the space 6 on the reference side and the space 7 on the detection side are the recesses 6 between the substrate 1 and the substrate 2.
And 7 and their internal volumes are equal and small.
Since the space 6 on the reference side is hermetically sealed and the heat of the thin film heating element 3 is not easily released to the outside, the inner wall surface is heated by heat radiation and is transferred to the space 7 on the detection side. The temperature influences the space 6 on the side. The closer the distance between the space 7 on the detection side and the space 6 on the reference side is, the larger the influence is. The temperature equilibrium is unlikely to occur even if the atmosphere is constant, and the balance easily shifts with the passage of time. Moreover, since the heat capacity of the substrate 2 is large, there is a change over time in which the balance is gradually lost.

Further, the vent hole 8 melts the low melting point glass,
The cross-sectional area of the vent hole 8 at the joined portion depending on the glass thickness,
Since the volumes of the space 6 on the detection side and the space 7 for reference are defined, the variation in the characteristics becomes large due to the change in the glass thickness. There is also another method of providing the vent holes 8 in the substrate 2 in the space 7 on the detection side, but since the hole diameter of the vent holes 8 at this time is smaller than the plate thickness, the accuracy cannot be improved by the hole processing by a simple etching process. If you try to improve the accuracy, the cost will increase.

FIG. 4 is a view showing another ventilation hole in the conventional space on the detection side. A dimensional difference is given to the concave shape of the substrate 1 and the substrate 2 in the space 6 on the detection side, and the dimensional difference is determined. The size of the vent hole 8 is used. However, the substrate 2 has a space 6 on the detection side.
Since it serves as a cover for the thin film heating element 3 in
The size of the vent hole 8 must be kept to a minimum, and it is expensive to manufacture such a vent hole 8 with high accuracy.

[0012]

[Purpose] The present invention has been made in view of the above-mentioned circumstances, and (1) a ventilation hole communicating from the detection chamber to the outside air is processed with high accuracy and at a low cost to reduce variations in product characteristics. Further, (2) an object of the present invention is to provide an atmosphere sensor having high sensitivity and long-term stable characteristics.

[0013]

In order to achieve the above object, the present invention provides (1)
A substrate having concave portions of the same shape, a thin film insulator cross-linked and supported on each concave portion of the substrate, a heat-generating resistor formed on each thin film insulator and having the same resistance, and a cover covering the concave portion. And the one recess is hermetically sealed as a reference chamber, and the other recess is used as a detection chamber that conducts to the outside air, based on the difference in the heat radiation amount of the heating resistor between the reference chamber and the detection chamber. In the atmosphere sensor for detecting the atmosphere, the conduction from the recess of the detection chamber to the outside air is performed through the vent hole groove extending from the bottom surface of the board recess to the surface, and the vent groove is formed on the wall surface of the board recess, and the cover is formed. Open to the outside,
(2) In (1) above, the heating resistor is provided on a substantially square heating part thin film insulator having a side larger than a bridge support part bridged in the reference chamber and the detection chamber. It is characterized by. Hereinafter, description will be given based on examples of the present invention.

1 (a) and 1 (b) are views for explaining an atmosphere sensor according to the present invention. FIG. 1 (a) is a plan view taken along the line BB of FIG. 1 (b), and FIG. FIG. 4A is a cross-sectional view taken along the line AA of FIG. 7A, in which 10 is a substrate, 11 is a thin film insulator,
12 and 13 are heating resistors, 14 is a reference chamber, 15 is a detection chamber, 16 is a vent hole groove, 16a is an opening, and 17 and 18 are covers.

The substrate 10 shown in the figure is a flat plate of silicon (Si) having a crystal plane of (100) and a thin film insulator 1 of SiO _{2 on} the upper surface.
1 is formed, and a metal thin film is further formed by a method such as vapor deposition, CVD and sputtering. Metal thin film is a heating resistor 1
Metals such as platinum, which are stable to oxidation, are used to form the layers 2 and 13. After that, by photolithography, anisotropic etching, etc., the concave reference chamber 14 and
The heating resistor 12 is formed on the thin film insulator 11 which is cross-linked on the recess. At the same time, the detection chamber 15 having the same concave shape as the reference chamber 14 and the thin-film insulator 11 bridging over the concave portion
A heating resistor 13 having the same resistance as the heating resistor 12 is formed on the top.

The detection chamber 15 is provided with a vent hole groove 16 extending from the bottom surface of the recess to the upper surface of the substrate 10 on the wall surface of the recess. The vent groove 16 is formed at the same time when the concave shape is anisotropically etched. If the side wall surface of the vent hole groove 16 is selected to be the (111) plane, the vent hole groove 16 having the same rectangular cross section and the same depth parallel to the concave surface is formed.

Next, a cover 17 having a concave portion is attached to the upper portion of the reference chamber 14 so as to cover and adhere to the substrate 10 through the thin film insulator 11, and similarly to the upper portion of the detection chamber 15, the same cover 17 is used. A cover 18 having a shape is covered and fixed on the substrate 10.
At this time, the cover 17 of the detection chamber 15 is fixed with a low-melting glass or the like with an opening 16a in a part of the vent hole groove 16. Since the glass layer on the fixing surface has a thickness in the axial direction of the vent hole groove 16, even if there are many variations in the thickness of the glass layer, the area of the opening 16a does not change. If the air vent grooves 16 are evenly provided at symmetrical positions on the inner circumference of the detection chamber 15, the depth of the grooves is processed to be constant, so that even if the fixing position of the cover 17 is slightly displaced, the total opening 16a is The area is constant.

FIG. 2 is a detailed plan view of the detection chamber 15.
In the figure, 19 is a heat generating part thin film insulator, and 20 and 21 are bridging support parts. In the figure, parts having the same functions as in FIG. 1 are denoted by the same reference numerals as in FIG.

The substrate 10 is formed with a concave detection chamber 15 and a vent groove 16. The thin film insulator 11 has a heating element thin film insulator 19 having a substantially square shape above the detection chamber 15. The portions of the bridge supporting portions 20 and 21 for bridge-supporting the heat generating portion thin film insulator 19 on the outer peripheral surface of the detection chamber 15 are left. The width of the bridge supporting portions 20 and 21 is narrower than one side of the heat generating portion thin film insulator 19. On the other hand, the heat generating resistor 13 is formed on the heat generating portion thin film insulator 19 in an area slightly smaller than this, and is connected to the lead portion 13b on the bridge supporting portion 21 and the pad portion 13a on the substrate 10 which face each other. .

Since the heating resistor 13 forms a thin resistance wire continuous in, for example, a zigzag pattern, the resistance value can be increased and the sensitivity can be increased. Further, since the heating resistor 13 is separated from the substrate 10 by the length of the bridge supporting portion 21, heat transfer to the substrate 10 is small even if the heating resistor 13 is heated, and the entire heating resistor 13 is covered. It is heated uniformly and has a constant heat generation distribution. As a result, compared with the conventional heating resistor 3 linearly arranged on the upper symmetry axis of the detection chamber 15 shown in FIG. 3, it is possible to measure the ambient gas with high sensitivity and with high accuracy.

[0021]

As is apparent from the above description, according to the present invention, (1) the vent hole of the detection chamber is anisotropically etched and simultaneously processed to form the recess of the detection chamber. Therefore, the number of processing steps is small, and the accuracy of the opening area of the ventilation hole can be increased, so that the atmosphere sensor having uniform quality can be manufactured at low cost.
(2) Since the heat generating resistor is provided on the heat generating portion thin film insulator which is separated from the substrate and bridged, it is possible to provide a highly sensitive atmosphere sensor having a small thermal interference and a uniform temperature distribution.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an atmosphere sensor according to the present invention.

2 is a detailed plan view of the detection chamber 15. FIG.

FIG. 3 is a plan view and a cross-sectional view showing an example of a conventional absolute humidity sensor.

FIG. 4 is a view showing another conventional ventilation hole in the space on the detection side.

[Explanation of symbols]

10 ... Substrate, 11 ... Thin film insulator, 12, 13 ... Heating resistor, 14 ... Reference chamber, 15 ... Detection chamber, 16 ... Vent groove, 16a ... Opening, 17, 18 ... Cover.

Claims (2)

[Claims] 1. A substrate having a concave portion of the same shape, a thin film insulator cross-linked and supported on each concave portion of the substrate, a heating resistor having an equal resistance formed on each thin film insulator, and the concave portion. A cover for covering one of the recesses to form a reference chamber, and the other recess to serve as a detection chamber that communicates with the outside air. In an atmosphere sensor for detecting an atmosphere based on a difference in heat quantity, conduction from the recess of the detection chamber to the outside air is performed through a vent hole groove extending from the bottom surface of the board recess to the surface, and the vent groove is formed on the wall surface of the board recess. An atmosphere sensor, which is formed on the cover and opened to the outside of the cover. 2. The heating resistor is provided on a substantially square heating portion thin film insulator having a side larger than a bridge support portion bridged in the reference chamber and the detection chamber. The atmosphere sensor according to claim 1.