JP6842622B2 - Flow sensor and its manufacturing method - Google Patents

Description

The present invention relates to a flow sensor and a method for manufacturing the same.

A gas sensor that detects, for example, a gas as a fluid has characteristics that vary depending on the flow rate of the gas, so it is necessary to monitor the flow rate. For example, a flow sensor is used to monitor the flow rate. Since there are various types of gases detected by the flow sensor, such as acid gas, alkaline gas, and combustible gas, the gas sensor is required to have high corrosion resistance. Further, the handy type flow sensor is required to have low power consumption in order to enable long-term battery operation.

As such a flow sensor, one that measures the flow rate and the direction of flow of a fluid by including a heating body and a temperature measuring body that measures the temperature difference of the fluid generated by the heating body is disclosed (for example,). , Patent Document 1).

Further, the microheater as a heating body supports the support film having a plurality of irregularities, the heating body provided on one surface of the support film, and the periphery of the support film, and the portion facing the heating body is removed. Those including a substrate are disclosed (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2014-016237 Japanese Unexamined Patent Publication No. 2013-003020

However, in the case of the above patent document, there is a problem that it is difficult to efficiently transfer the heat of the microheater to the fluid. That is, in the case of Patent Document 1, since the heated body cannot be said to be in a position close to the gas, the fluid in contact with the heated body is limited.

Further, in the case of Patent Document 2, since the heating body is provided on the support film, the fluid passes only above the heating body and cannot pass below the heating body. Further, there is a problem that the heat generated by the microheater escapes to the support film.

Therefore, an object of the present invention is to provide a flow sensor capable of heating a fluid more efficiently and a method for manufacturing the same.

The flow sensor according to the present invention is a flow sensor including a substrate on which a heating element and a resistance temperature detector arranged on both sides of the heating element are formed on the surface, and the heating element and the resistance temperature detector are wired. A resistor having a portion and a connecting portion formed at an end portion of the wiring portion is included, the resistor is fixed to the substrate at the connecting portion, and the central portion of the wiring portion is the substrate. It is characterized by having a mountain shape that is convex from the surface.

The method for manufacturing a flow sensor according to the present invention includes a step of depositing a metal film on a surface layer by using a sputtering method, and selectively removing the surface layer around the metal film, and the central portion is formed by film stress. It is characterized by comprising a step of forming the resistor having a mountain shape that is convex from the surface of the substrate.

According to the present invention, since the central portion of the wiring portion has a mountain shape that is convex from the surface of the substrate, the wiring portion can be closer to the gas, so that the flow sensor can efficiently use the gas in the flow path. Can be heated.

It is a top view which shows typically the structure of the flow sensor which concerns on this embodiment. It is an AA end view in FIG. 1 which shows the structure of the resistor which concerns on this embodiment. It is a vertical cross-sectional view which shows the manufacturing method of the flow sensor which concerns on this Embodiment stepwise, FIG. 3A is the stage which prepared the substrate, FIG. 3D is a diagram showing a stage in which the photoresist is removed, and FIG. 3E is a diagram showing a stage in which a part of the substrate is removed. It is a micrograph of a flow sensor actually manufactured. It is a vertical cross-sectional view which shows the manufacturing method of the flow sensor which concerns on a modification step by step, FIG. FIG. 5D shows a stage of forming, FIG. 5D shows a stage of removing a part of the substrate, and FIG. 5F shows a stage of heating at a temperature equal to or higher than the curing temperature. It is a vertical cross-sectional view which shows the manufacturing method of the flow sensor which concerns on another modification step by step. FIG. 6A is a stage where a convex portion is formed on a substrate, and FIG. 6B is a stage where a surface layer having a mountain-shaped portion is formed. FIG. 6C is a stage in which a photoresist is formed, FIG. 6D is a stage in which a metal film is formed, FIG. 6E is a stage in which the photoresist is removed, and FIG. 6F is a diagram showing a stage in which a part of the substrate is removed. FIG. 7A is an enlarged plan view of the vicinity of the connection portion of the flow sensor of the modified example, FIG. 7A is a diagram showing the flow sensor of the modified example (1), and FIG. 7B is a diagram showing the flow sensor of the modified example (2). It is a top view which shows the modification of the wiring part, FIG. 8A is a figure which shows the modification (1), and FIG. 8B is a figure which shows the wiring part of the modification (2). It is sectional drawing which shows the structure of the modification (3) of the wiring part.

1. 1. Embodiment (overall configuration)
The flow sensor according to the embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the flow sensor 10 has a heating element 14 and a first temperature measuring element 16 and a second temperature measuring element 18 as temperature measuring elements arranged on both sides of the heating element 14 on the surface thereof. The formed substrate 12 is provided. The flow sensor 10 is provided so as to arrange the first resistance temperature detector 16 on the downstream side and the second resistance temperature detector 18 on the upstream side in the flow path 28 (FIG. 2) through which the gas as a fluid flows. The substrate 12 can be formed of an insulator such as Si, Al ₂ O ₃ , resin, or the like. In the case of the present embodiment, the substrate 12 is composed of a SiO ₂ substrate having a rectangular shape in a plan view and a surface layer 13 provided on the _{SiO 2 substrate.} The surface layer 13 is preferably formed of a material having corrosion resistance, for example, a thermosetting resin such as polyimide, or ceramics.

The heating element 14, the first resistance temperature detector 16 and the second resistance temperature detector 18 are formed in layers. Since the heating element 14, the first resistance temperature measuring element 16 and the second resistance temperature measuring element 18 have the same configuration, the heating element 14 will be described below in order to omit the description. In the case of the present embodiment, the heating element 14 is formed of a heating element material whose electric resistance value changes with temperature, for example, a metal film such as gold or platinum, and is formed between the pair of electrodes 21 and the electrodes 21. Has 20 and. One electrode 21 is formed on each side of the substrate 12 (two electrodes in total).

The resistor 20 is arranged substantially in the center of the substrate 12. The resistor 20 includes a wiring portion 22 and a connecting portion 24 formed at an end portion of the wiring portion 22. In a plan view, the wiring portion 22 is formed in a linear shape, and the connecting portion 24 is formed in a rectangular shape. Specifically, in a plan view, the wiring portion 22 has a linear shape having a uniform thickness from one end to the other end, and the connecting portion 24 has a square shape.

The wiring portion 22 is formed to have a narrower line width than the connection portion 24 so that the electrical resistance is larger than that of the connection portion 24. A plurality of wiring portions 22 (five in the case of this figure) are arranged in parallel so as to be parallel to each other, and are connected to other wiring portions 22 adjacent to each other via a connecting portion 24 at an end portion in a zigzag manner. It is formed in a shape. Two wiring portions 22 are connected to the connection portion 24. A short-circuit portion 26 for electrically connecting the wiring portions 22 to each other is formed in a ladder shape between the wiring portion 22 and the connection portion 24. The ends of the wiring portions 22 arranged at both ends constituting the resistor 20 are connected to the electrodes 21 via the connecting portions 24. A short-circuit portion 26 for electrically connecting the wiring portions 22 to each other is also formed in a ladder shape between the connection portion 24 and the electrode 21.

As shown in FIG. 2, the wiring portion 22 has a mountain shape in which the central portion is convex from the surface of the substrate 12. The substrate 12 is formed with a support portion 30 projecting from the surface. The connecting portion 24 of the resistor 20 is fixed to the supporting portion 30. The height of the support portion 30 is not particularly limited, but can be, for example, about 10 μm. Since both ends of the wiring portion 22 are supported by the connecting portion 24, the wiring portion 22 has a double-sided beam structure. The height of the top portion of the wiring portion 22 from the support portion 30 is not particularly limited, but can be, for example, about 10 to 50 μm.

(Manufacturing method of wiring part)
Next, a method of manufacturing the wiring unit 22 will be described with reference to FIG. For convenience of explanation, a case where one wiring portion 22 is manufactured will be described. First, _{a substrate having a surface layer 13A on the SiO 2} substrate 31 is prepared (FIG. 3A). Then, as shown in FIG. 3B, the photoresist 32 is selectively formed. Then, as shown in FIG. 3C, the metal film 34 is formed by a sputtering method. Then, the photoresist 32 is removed using an organic solvent such as acetone. At the same time, the metal film 34 formed on the photoresist 32 is also removed by lift-off (FIG. 3D). Finally, the surface layer 13 of the formed opening 36 is removed by etching with hydrofluoric acid, for example, to form a groove 38 (FIG. 3E). Then, due to the film stress, a wiring portion 22 having a mountain shape in which the central portion is convex from the surface of the substrate 12 and having a double-sided beam structure can be obtained.

(Action and effect)
In the flow sensor 10 configured as described above, when electric power is supplied between the electrodes 21 of the heating element 14, the resistor 20 of the heating element 14 is heated by the electric resistance. The resistor 20 is formed so that the wiring portion 22 has a larger electric resistance than the connecting portion 24, and is further connected to the connecting portion 24 via the short-circuit portion 26. As a result, the temperature of the resistor 20 rises around the central portion.

When heated in this way, the temperature of the gas around the heating element 14 rises. When there is no flow in the surrounding gas, the temperature distribution around the heating element 14 is symmetrical, so that the temperatures of the first resistance thermometer 16 and the second resistance temperature detector 18 are equal.

On the other hand, when a flow occurs in the surrounding gas, the temperature distribution around the heating element 14 is not symmetrical, and one becomes higher. For example, when gas is flowing from the upstream side to the downstream side, the temperature of the second resistance temperature detector 18 decreases and the temperature of the first resistance temperature detector 16 increases. The flow sensor 10 can obtain an electric output according to the flow rate by detecting the difference between the resistance values of the first resistance temperature detector 16 and the second resistance temperature detector 18 with a bridge circuit (not shown).

In the case of the present embodiment, the wiring portion 22 has a mountain shape in which the central portion is convex from the surface of the substrate 12, so that the wiring portion 22 can be closer to the gas in the flow path 28, and moreover, between the wiring portion 22 and the substrate 12. The gas can be easily circulated. Further, since the wiring portion 22 can be held at a position away from the surface of the substrate 12, it is possible to prevent the heat generated in the wiring portion 22 from escaping to the substrate 12. Therefore, the flow sensor 10 can efficiently heat the gas in the flow path 28.

Since the resistor 20 is configured to be connected to the connecting portion 24 via the short-circuit portion 26, the wiring portion 22 can be heated more efficiently.

Since the wiring portion 22 has a double-sided beam structure in which both ends are connected to the connecting portion 24 fixed to the substrate 12, deformation due to thermal expansion can be suppressed. Therefore, the flow sensor 10 can reduce the influence of thermal expansion on the gas flow, so that the measurement accuracy can be improved. Further, since the central portion of the wiring portion 22 has a mountain shape that is convex from the surface of the substrate 12, the thermal stress generated by thermal expansion can be relaxed.

In the above embodiment, the case where the substrate 12 is formed of the SiO ₂ substrate 31 and the surface layer 13 has been described, but the present invention is not limited to this, and the substrate 12 is formed of the Si substrate provided with an oxide film and the surface layer 13. It may be formed only with a resin.

FIG. 4 shows a micrograph of the heating element 14 and the resistance temperature detector 16 actually manufactured according to the procedure shown in the above “(Method for manufacturing the wiring portion)”. A substrate 12 having a surface layer 13 made of polyimide formed on a Si substrate was used. The metal film 34 was formed by forming a Pt film having a film thickness of 300 nm by a sputtering method. The wiring portion 22 was obtained by removing the polyether 32 by dipping it in acetone and forming a groove 38 by dry etching. As a result, it was possible to manufacture a heating element 14 and a temperature measuring element 16 having a wiring portion 22 having a line width of 6 μm, a thickness of 0.4 μm, and a height of 30 μm from the support portion.

2. Modifications The present invention is not limited to the above embodiment, and can be appropriately modified within the scope of the gist of the present invention. In the case of the above embodiment, the case where the wiring portion 22 having a mountain shape whose central portion is convex from the surface of the substrate 12 is formed by the film stress has been described, but the present invention is not limited to this.

A method of manufacturing the wiring portion 22 according to the modified example will be described with reference to FIG. First, a _{thermosetting resin is applied onto the SiO 2} substrate 31 and heated at a temporary curing temperature lower than the thermosetting temperature to form a temporary curing resin layer 13B (FIG. 5A). Then, as shown in FIG. 5B, the photoresist 32 is selectively formed. Then, as shown in FIG. 5C, the metal film 34 is formed by a sputtering method. Then, the photoresist 32 is removed using an organic solvent such as acetone. At the same time, the metal film 34 formed on the photoresist 32 is also removed by lift-off (FIG. 5D). The temporarily cured surface layer 13C is obtained by removing the temporarily cured resin layer 13B of the formed opening 36 by, for example, etching with hydrofluoric acid to form a groove 38 (FIG. 5E). Finally, it is heated at the main curing temperature higher than the thermosetting temperature. Then, the temporarily cured surface layer 13C is cured, so that the surface layer 13 is obtained. At the same time, due to heat shrinkage when the temporarily cured surface layer 13C is cured, a wiring portion 22 having a mountain shape in which the central portion is convex from the surface of the substrate 12 and having a double-sided beam structure can be obtained (FIG. 5F).

A method of manufacturing the wiring portion 22 according to another modification will be described with reference to FIG. First, the _{convex portion 40 is formed on the SiO 2} substrate 31 with a thermosetting resin (FIG. 6A). Next, a surface layer 13D having a mountain-shaped portion 41 is formed of a thermosetting resin so as to cover the _{SiO 2} substrate 31 including the convex portion 40 (FIG. 6B). Then, as shown in FIG. 6C, the photoresist 32 is selectively formed. Then, as shown in FIG. 6D, the metal film 34 is formed by a sputtering method. Then, the photoresist 32 is removed using an organic solvent such as acetone. At the same time, the metal film 34 formed on the photoresist 32 is also removed by lift-off (FIG. 6E). Finally, the surface layer 13D of the formed opening 36 is removed by etching with hydrofluoric acid, for example, to form a groove 38 (FIG. 6F). Then, a wiring portion 22 having a double-sided beam structure having a mountain shape in which the central portion is convex from the surface of the substrate 12 along the convex portion can be obtained.

The above-described embodiment, modified example, and manufacturing method according to another modified example may be appropriately combined. For example, the wiring portion 22 may be manufactured by combining the embodiment and another modified example, and the modified example and another modified example.

As described above, the flow sensor 10 has a mountain shape in which the central portion of the wiring portion 22 included in the resistor 20 is convex from the surface of the substrate 12, so that the gas in the flow path (FIG. 2, reference numeral 28) can be removed. The effect of being able to heat efficiently can be obtained. The connection portion 24, the short-circuit portion 26, and the wiring portion 22 included in the resistor 20 can be appropriately changed so that the central portion of the wiring portion 22 is more reliably formed into a mountain shape and the desired effect is sufficiently exhibited. ..

For example, as in the flow sensor 10A shown in the modified example (1) of FIG. 7A, a trapezoidal connecting portion 24A and a wide wiring portion 26A on the connecting portion 24A side can be provided on the substrate 12A. The connecting portion 24A has an isosceles trapezoidal shape with the electrode 21 side as the lower base. The wiring portion 26A includes a straight portion 26Aa and a widening portion 26Ab. The widening portion 26Ab is gradually widened toward the connecting portion 24A side between the straight portion 26Aa and the connecting portion 24A by inclining one side. Thus, the width of the wiring portion 26A, the connection portion 24 A side is the largest, is constant after gradually decreased.

In the flow sensor 10A, a trapezoidal connecting portion 24A and a wide wiring portion 26A on the connecting portion 24A side are provided on the substrate 12A . A tapered shape toward the connecting section 24A on the center part of the wiring portion. As a result, the central portion of the wiring portion is easily bent, and a mountain shape in which the central portion of the wiring portion is convex from the surface of the substrate 12A can be obtained more reliably.

As in the flow sensor 10B shown in the modified example (2) of FIG. 7B, the wiring portion 26B including the straight portion 26Ba and the widening portion 26Bb can be provided. The widening portion 26Bb is gradually widened between the straight portion 26Ba and the connecting portion 24 toward the connecting portion 24 side. Two similar widening portions 26Bb may be arranged between the ladder-shaped short-circuit portion 26 and the connection portion 24 to form the short-circuit portion 26C. Three straight portions 26Ba may be provided between the connecting portion 24 and the electrode 21 to form the short-circuit portion 26D.

In the flow sensor 10B, a wide wiring portion 26B and a short-circuit portion 26C on the connection portion 24 side are provided on the substrate 12B. Since a wiring portion (not shown) is connected to the short-circuit portion 26C, the shape is tapered from the connection portion 24 toward the central portion of the wiring portion. As a result, the central portion of the wiring portion can be easily bent, and a mountain shape in which the central portion of the wiring portion is convex from the surface of the substrate 12B can be obtained more reliably. The fact that the short-circuit portion 26D including the three straight portions 26Ba is provided between the electrode 21 and the connection portion 24 also promotes the central portion of the wiring portion to have a mountain shape.

The thickness of the wiring portion 22 does not have to be uniform from one end to the other end when viewed from above. Like the wiring portion 22A of the modified example (1) shown in FIG. 8A, the shape may be a medium-thin shape in which the width decreases from both ends 22Aa to the central region 22Ab. Further, as in the wiring portion 22B of the modified example (2) shown in FIG. 8B, a medium-thick shape may be formed in which the width increases from both ends 22Ba to the central region 22Bb.

Since the widths of the wiring portions 22A and 22B are different between the both end portions 22Aa and 22Ba and the central regions 22Ab and 22Bb, the force applied to the wiring portions 22A and 22B is concentrated on the narrow portion. In the wiring portion 22A, the central region 22Ab is easily bent, and in the wiring portion 22B, both ends 22Ba are easily bent. As a result, the wiring portions 22A and 22B can more reliably obtain a mountain shape in which the central portion is convex from the substrate (not shown).

As in the wiring portion 22C of the modified example (3) shown in FIG. 9, a two-layer film laminated structure may be used. The wiring portion 22C includes two layers of films 22Ca and 22Cb having different stresses acting on the inside. Specifically, in the wiring portion 22C, a second film 22Cb on which tensile stress acts is laminated on the first film 22Ca on which compressive stress acts. The first film 22Ca and the second film 22Cb can be formed by appropriately combining materials. _{For example, when SiO 2} is used as the first film 22Ca, Pt can be used for the second film 22Cb.

As shown by arrows A1 and A2, compressive stress from both ends to the inside acts on the first layer 22Ca constituting the lower layer of the wiring portion 22C. On the other hand, tensile stress acts from the inside toward both ends as shown by arrows B1 and B2 on the second layer 22Cb forming the upper layer of the wiring portion 22C. Since compressive stress acts on the lower layer and tensile stress acts on the upper layer of the wiring portion 22C, it is possible to more reliably obtain a mountain shape in which the central portion is convex from the substrate (not shown).

The trapezoidal connecting portion 24A shown in the flow sensor 10A can be combined with any of the short-circuited portions 26C and 26D shown in the flow sensor 10B. Wiring portions (wiring portion 22A or wiring portion 22B) having varying widths may be connected to the short-circuit portions 26C and 26D. In this case, the wiring portion may be formed by laminating a second film 22Cb on which tensile stress acts on the first film 22Ca on which compressive stress acts, as in the wiring portion 22C.

10 Flow sensor 12 Substrate 13 Surface layer 13B Temporarily cured resin layer 14 Heating element 16 First resistance temperature detector (resistance temperature detector)
18 Second resistance temperature detector (resistance temperature detector)
20 Resistor 22 Wiring part 24 Connection part 26 Short circuit part 41 Mountain-shaped part

Claims (10)

In a flow sensor including a substrate on which a heating element and a temperature measuring element arranged on both sides of the heating element are formed on the surface thereof.
Each of the heating element and the temperature measuring element has a plurality of wiring portions arranged in parallel, a connection portion for connecting one ends of two adjacent wiring portions among the plurality of wiring portions, and the connection portion. Includes a resistor that is provided adjacent to and has a ladder-shaped short circuit that electrically connects the two adjacent wiring portions.
The resistor is fixed to the substrate at the connection portion, and is fixed to the substrate.
A flow sensor characterized in that each of the plurality of wiring portions has a mountain shape in which a central portion thereof is convex from the surface of the substrate. The flow sensor according to claim 1, wherein the short-circuit portion is formed between the two adjacent wiring portions and the connection portion. The flow sensor according to claim 1 or 2, wherein the substrate is provided with a surface layer formed of a corrosion-resistant material on the surface thereof. The flow sensor according to any one of claims 1 to 3, wherein the connecting portion has a trapezoidal shape. The flow sensor according to any one of claims 2 to 4, wherein the short-circuited portion has a wide width on the connecting portion side. The flow sensor according to any one of claims 1 to 5, wherein each of the plurality of wiring portions has a medium-thin shape. The flow sensor according to any one of claims 1 to 5, wherein each of the plurality of wiring portions has a medium-thick shape. Each of the plurality of wiring portions includes a first film on which compressive stress acts and a second film on which tensile stress acts, which is laminated on the first film. The flow sensor according to any one of 1 to 7. In the method for manufacturing a flow sensor in which a resistor is formed on the surface layer of a substrate,
The step of forming the surface layer having a mountain-shaped portion and
A step of depositing a metal film on the surface layer using a sputtering method, and
The present invention includes a step of selectively removing the surface layer around the metal film to form the resistor formed of the metal film having a mountain shape in which the central portion is convex from the surface of the substrate. A method for manufacturing a flow sensor. In the method for manufacturing a flow sensor in which a resistor is formed on the surface layer of a substrate,
The process of applying a thermosetting resin and heating it at a temporary curing temperature lower than the thermosetting temperature to form a temporary curing resin layer, and
A step of depositing a metal film on the temporarily cured resin layer using a sputtering method, and
A step of obtaining a temporarily cured surface layer by selectively removing the temporarily cured resin layer around the metal film, and
The surface layer is obtained by curing the temporarily cured surface layer by heating at a main curing temperature higher than the thermosetting temperature, and the central portion is the surface of the substrate due to heat shrinkage when the temporarily cured surface layer is cured. A method for manufacturing a flow sensor, which comprises a step of forming the resistor having a chevron shape and formed of the metal film.

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