JPH0552788A - Electrical heater and detector - Google Patents

Abstract

PURPOSE:To enable the number of manufacturing processes to be reduced and at the same time mechanical strength in a reduced and at the same time mechanical strength in a retention edge of an overhanging portion to be improved and then obtain a highly reliable electrical heater and each kind of detector by constituting one portion of an electrical insulation material in one piece as the overhanging portion. CONSTITUTION:An electrical insulation substance 1 with a recessed portion is prepared. It is made of glass, crystal, etc., or acryl, polyimide, etc., which are suited for fine machining and the recessed portion is formed by the normal photoetching method. A heater lead 2 is formed on an opposite surface 1a where the recessed portion is opened. Pt is most desirable as a material for the lead 2. After pattern for the lead 2 is formed, a photoresist is coated on a surface of a side where the lead is formed and then a photoresist pattern 3 for forming a penetration hole is formed near the lead 2. Then, an electrical insulation substance is etched by wet etching, plasma etching, etc., for providing a penetration hole and then a heater lead 12 is formed at an overhanding portion 15. A catalyst layer 13 is provided on the lead 12, thus obtaining a gas sensor.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric heater suitable for heating a detection element such as a gas sensor, a humidity sensor, a hot-wire flow sensor, and various detectors using the electric heater.

[0002]

2. Description of the Related Art Generally, a gas sensor or the like requires an electric heater for heating the detection element itself or the detection element. It is desirable that the electric heater has low power consumption and a small thermal time constant, and therefore, a miniaturized electric heater having a small heat capacity has already been proposed (Japanese Patent Publication No. 62-2).
438 and JP-A-57-178149). The former electric heater has a structure in which an insulating layer made of a material different from that of the substrate is formed on a substrate and a heating element is formed thereon, and the insulating layer including the heating element has a structure floating in the air. That is, a step of forming a layer of a substance different from that of the substrate is required on the substrate, which is disadvantageous in manufacturing cost. Further, since the substrate and the insulating layer are made of different materials, there is a problem in mechanical strength at the holding end. On the other hand, the latter electric heater has a structure in which only a conductive substance is crosslinked in the air, and this also has some problems in mechanical strength. Further, since only the conductive substance used as the heating element is heated, and it is preferable that the heating element itself also serves as the detection element, the heater lead as the heating element as in the third embodiment of the present invention is used. It cannot be applied when the detection element (here, the metal oxide semiconductor layer) is different.

[0003]

[Purpose] An object of the present invention is to provide an electric heater having a simple manufacturing process and high reliability, and various detectors using the electric heater, in view of the above points.

[0004]

According to a first aspect of the present invention, a portion of an electrically insulating substance is integrally provided by projecting in the air, a heater lead made of a conductive substance is formed on the projecting portion, and a current is supplied to the heater lead. Is an electric heater, wherein the overhanging portion is used as a heat generating portion. This embodiment will be described. An electrically insulating substance 1 having a recess as shown in FIG. 1 is prepared. As a material of the electrically insulating substance, a glass, quartz, ceramics or a photo of Corning suitable for microfabrication, which is relatively heat resistant and has a selectivity that the subsequent etching process is easy and does not etch other constituent materials. Foam, photoserum, epoxy, acrylic, polyimide, etc. are preferred. In forming the recess, by a normal photo-etching method,
In the case of quartz, it can be formed by an HF-based etchant using a photoresist as a mask, and in the case of polyimide, it can be formed by an alkaline-based etchant. The heater lead 2 is formed on the opposite surface 1a on the side where the recess opens, corresponding to the position where the recess is formed (FIG. 2). As the material of the heater lead, Pt, Pd, Pt group alloy, NiCr, Ta
N ₂ , BN, SiC, Kanthal and the like can be mentioned, and of these, Pt is most preferable. As a method of forming the heater lead, a normal film forming method such as a vapor deposition method or a sputtering method is used to form, for example, Pt on the surface opposite to the side where the recess of the electrically insulating material shown in FIG. 1 is opened. After that, a photoresist is applied on Pt to form a photoresist pattern in a heater lead shape. Then, Pt is etched using this photoresist pattern as a mask. Pt
Etching is wet etching with hot aqua regia, C
A known method such as plasma etching with Cl ₄ + O ₂ or sputter etching may be used. After that, the photoresist on Pt is removed. In etching, if the etching ratio of the photoresist to Pt is relatively large, another material (such as Si) is used instead of the photoresist.
An O ₂ film or the like) may be etched in the shape of the heater lead 2 in advance, and this may be appropriately used as an etching mask for Pt. Next, a method of forming the overhanging portion 15 will be described. After the pattern formation of the heater lead 2 is completed, a photoresist is applied again to the surface of the heater lead formation side, and a photoresist pattern 3 for forming a through hole is formed near the heater lead 2 as shown in FIG. Then, if the electrically insulating material is quartz from the photoresist pattern side, the through hole 4 is formed by etching the electrically insulating material by HF-based wet etching or by a known method such as sputter etching or plasma etching. (Fig. 4).

In a second aspect of the present invention, a catalyst layer is provided on the electric heater according to claim 1, and a temperature change generated by burning the gas in the catalyst layer is caused by a change in the resistance value of the heater lead itself, or It is a gas sensor characterized by being detected by another temperature detecting element installed on the projecting portion.
An example of the gas sensor of the present invention is shown in FIG. 5A. This gas sensor is provided with a heater lead 12 and a catalyst layer 13 on an overhanging portion, an electric current is applied to the heater lead to heat the catalyst layer to about 400 to 600 ° C., and a combustible gas is burned on the surface thereof. Gas detection is performed by measuring the temperature rise due to the heat of combustion reaction. In this case, it is easy to utilize the change in the resistance value of the heater lead itself to detect the rising temperature, but a temperature detecting element such as a thermistor may be installed on the overhanging portion to detect it. The catalyst layer 13 is installed in the vicinity of the heater lead 12 so as to be effectively heated, or is installed on the heater lead 12. When it is installed on the heater lead and the catalyst layer has conductivity, SiO is formed on the heater lead as shown in FIG. 5B.
An insulating layer 14 of ₂ , Si ₃ N ₄ , MgO, Al ₂ O ₃ or the like is provided, and a catalyst layer is formed thereon. As the material of the catalyst layer, platinum group and platinum group alloys such as Pt, Pd, Ir, Ru, etc., or those supporting the platinum group or platinum group alloy on a porous carrier containing silica or alumina as a main component are preferable. The catalyst layer may be formed by a usual method such as a vapor deposition method or a sputtering method. Generally, the resistance change of the heater lead due to the combustion reaction heat of the gas is very small and is influenced by the ambient temperature. Therefore, as shown in FIG. 6, the overhanging portion 15a having no catalyst layer is provided along with the heater lead resistance. 12
a is an overhanging portion 15 having a catalyst layer as shown in FIG.
It may be used by incorporating it in a bridge circuit so as to be adjacent to the heater lead resistor 12b of b.

According to a third aspect of the present invention, a metal oxide semiconductor layer is provided on the electric heater according to claim 1, and when the metal oxide semiconductor layer is brought into contact with a gas and reacts with the gas, a gas is detected as a change in its resistance value. It is a gas sensor characterized by performing. An example of the gas sensor of the present invention is shown in FIG. Here, an example of detecting the resistance value change of the metal oxide semiconductor layer 24 and the detection lead 23 is used. However, when the detection lead may be made of the same material as the heater lead 22, both can be formed at the same time. After that, a metal oxide semiconductor layer is formed. Examples of the material of the metal oxide semiconductor include oxides of tin, indium, titanium, zinc, iron, nickel, tungsten, vanadium and the like. Examples of the method for forming the metal oxide semiconductor layer include a sputtering method and a vapor deposition method. The method of forming the pattern of the metal oxide semiconductor layer may be the same as the method of forming the Pt pattern described in the first aspect of the present invention. Then, the electrically insulating material is etched to form a through hole. Except for the metal oxide semiconductor layer and the bonding pad portion 25, the surface is covered with Si.
It is desirable to protect with an electric insulating film such as O ₂ , Si ₃ N ₄ , MgO, Ta ₂ O ₅ , and Al ₂ O ₃ .

According to a fourth aspect of the present invention, a metal oxide layer or a thin film having a temperature coefficient of resistance is provided on the electric heater according to claim 1, and the resistance value change of the metal oxide layer or the thin film having the temperature coefficient of resistance is changed. The present invention relates to a humidity sensor characterized by performing humidity detection. An example of the humidity sensor of the present invention is shown in FIG. This humidity sensor has a heater lead 32 and a metal oxide layer or a thin film 34 having a temperature coefficient of resistance on the protruding portion. Zn as a metal oxide material
_{O-Li 2 O-V 2} O 5 -Cr 2 O 3 system and MgCr ₂ O ₄ -T
The iO ₂ system and the ZrO ₂ —MgO system are typical, and when water in the air adsorbs them, the electric resistance value changes.
The detection lead 33 preferably has a structure in which the metal oxide layer is sandwiched from above and below, and examples of the material thereof include porous Au and RuO ₂ . The metal oxide layer and the detection lead can be formed by a sputtering method or the like. On the other hand, by using a substance having a temperature coefficient of resistance such as a thermistor,
Humidity can be detected. The thermal conductivity of gas is peculiar to each gas element, and the thermal conductivity differs depending on the amount of water in the air. That is, by applying a current to the heater lead, heating the thermistor to a certain temperature, and detecting the temperature change of the thermistor due to the change of the thermal conductivity of the gas by the change of the resistance value of the thermistor itself, the water content in the air Can be measured. In this case, it is preferable to use two thermistors, one of which is filled with dry air and which is used as a matching element. The substance having a temperature coefficient of resistance may be the same as the commonly used thermistor. For example, a mixture of some oxides of Ni, Mn, Co, Fe, ZrO ₂ —Y ₂ O ₃ system, BaTi.
O ₃ system and the like. The material of the detection lead is Pt, A
The material may be selected from u, Ni, Al, etc. according to the material of the thermistor. As the method of forming the thermistor and the detection lead, a usual method such as a sputtering method may be used as in the other methods. In the case of a temperature sensor, deterioration with time is caused by impurities generated by reacting with hydroxyl groups and oil components adsorbed on the surface. Therefore, it is formed on the electric heater as in this example,
Reliability can be improved by periodically heating at about 400 to 500 ° C. to remove impurities and the like.

In a fifth aspect of the present invention, two or more electric heaters according to claim 1 are provided side by side, which are installed in a fluid, and the resistance values of the heater leads 42, 43 themselves due to temperature changes of the respective electric heaters. The present invention relates to a flow rate sensor that measures a flow rate by using another temperature detecting element that is changed or installed on an overhang portion. An example of the present invention is shown in FIG. Except for the number of overhangs, the structure and manufacturing method may be the same as in claim 1.
Current is applied to both heater leads to set the electric heater to a certain temperature. When there is a flow of air or the like in the direction of the arrow in the figure, the overhanging portion 44 is cooled and the temperature thereof drops. On the other hand, the overhang portion 45 receives the heat of the overhang portion 44, so that the temperature thereof rises. The material of the heater lead may be the same as that of the first embodiment of the present invention, but a material having a relatively large temperature coefficient of resistance is preferable. Heater lead 4
A relatively large output can be obtained by using resistors 2 and 43 on two adjacent sides of the bridge circuit. In addition to the method of utilizing the change in the resistance value of the heater lead, a temperature detecting element such as a thermistor may be provided on each protruding portion to detect the change in temperature. Although the number of overhangs is two here, it may be more than this depending on the application.

Although the cross-link structure has been described above as the shape of the projecting portion, it goes without saying that a cantilever structure as shown in FIG. 11 may be used. FIG. 11 shows FIG.
Is a cantilever structure.

[0010]

[Effect] As described above, by integrally forming a part of the electrically insulating material as the projecting portion, the step of forming an electrically insulating layer made of a substance different from that of the substrate on the substrate unlike the conventional case is unnecessary. Yes, we were able to reduce the manufacturing process.
Further, since the substrate and the projecting portion are not made of different materials, the mechanical strength at the holding end of the projecting portion is improved, and a highly reliable electric heater and various detectors using the same can be realized. ..

[Brief description of drawings]

FIG. 1 is a view showing an example of a substrate used in the present invention,
A is a plan view thereof, and B is a sectional view taken along line XX '.

FIG. 2 is a plan view showing an intermediate body according to a specific example of the first present invention.

FIG. 3 is a plan view showing a state in which a photoresist layer is provided on that of FIG.

FIG. 4 is a drawing showing a specific example of the first present invention, in which A is a plan view thereof, B is a sectional view taken along the line XX ′, and C is a sectional view taken along the line YY ′.

FIG. 5 shows two specific examples of the second invention,
Shown as B. Both are sectional views.

FIG. 6 is a plan view showing another specific example of the second invention.

FIG. 7 shows a bridge circuit used in the gas sensor of FIG.

FIG. 8 is a drawing showing a specific example of the third aspect of the present invention, in which A is a plan view, B is a sectional view taken along the line XX ′, and C is a sectional view taken along the line YY ′.

FIG. 9 is a view showing a fourth aspect of the present invention, in which A is a plan view,
B is a sectional view taken along the line XX ', and C is a sectional view taken along the line YY'.

FIG. 10 is a view showing the fifth aspect of the present invention, in which A is a plan view, B is a sectional view taken along line XX ′, and C is a sectional view taken along line YY ′.

FIG. 11 is a drawing for explaining a cantilever structure that can be used for the first to fifth aspects of the present invention, where A is a plan view and B is a plan view.
Is a sectional view taken along line XX ′.

[Explanation of symbols]

 1 Electrical Insulating Material 2 Heater Lead 3 Photoresist Pattern 4 Through Hole 12 Heater Lead 12a Heater Lead on Overhanging Part without Catalyst Layer 12b Heater Lead on Overhanging Part with Catalyst Layer 13 Catalyst Layer 14 Insulating Layer 15 Overhanging Part 15a Overhang without catalyst layer 15b Overhang with catalyst layer 22 Heater lead 23 Detection lead 24 Metal oxide semiconductor layer 25 Bonding pad section 32 Heater lead 33 Detection lead 34 Metal oxide layer or thin film having temperature coefficient of resistance 42 Heater lead 43 Heater lead 44 Overhang 45 Overhang

Front Page Continuation (72) Inventor Takayuki Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) In-house Yasuhiro Sato 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Junji Manaka 1-9-17 Omorinishi, Ota-ku, Tokyo Reco Seiki Co., Ltd. (72) Inventor Shigeki Takano 1-9-17 Omorinishi, Ota-ku, Tokyo Ricoh Seiki Ware corporation

Claims (5)

[Claims] 1. A substrate made of an electrically insulating material, a part of which has a projecting portion integrally projecting into the air, and a heater lead made of a conductive material formed on the projecting portion. Electric heater to do. 2. A substrate made of an electrically insulating material, a part of which has a projecting portion integrally projecting in the air, a heater lead made of a conductive material formed on the projecting portion, the heater lead, or A gas sensor comprising a catalyst layer provided in the vicinity thereof. 3. A substrate made of an electrically insulating material, a part of which has an overhanging portion integrally protruding into the air, a heater lead made of a conductive material formed on the overhanging portion, the heater lead, or A gas sensor comprising a metal oxide semiconductor layer provided in the vicinity thereof. 4. A substrate made of an electrically insulating material, a part of which has an overhanging portion integrally protruding into the air, a heater lead made of a conductive material formed on the overhanging portion, and the heater lead or A humidity sensor in a gas, comprising a metal oxide layer or a thin film having a temperature coefficient of resistance provided in the vicinity thereof. 5. A substrate made of an electrically insulating material, a part of which has two or more overhanging portions integrally protruding into the air, and a heater lead made of a conductive material formed on each of the overhanging portions. A gas flow rate sensor characterized by: