JP2562076B2 - Flow sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flow velocity sensor for measuring the flow velocity of gas, and more particularly to a flow velocity sensor having a diaphragm structure.

[Prior Art] Generally, flow velocity sensors of various structures have been proposed for measuring the flow velocity of gas, and one of them is disclosed in, for example, JP-A-60-14.
Japanese Patent No. 2268 proposes a thermal type flow velocity sensor manufactured by using semiconductor manufacturing technology. This thermal type flow sensor has a semiconductor substrate 1 as shown in FIG.
A thin film-shaped bridge portion 3 is formed through a void portion 2 that is thermally insulated from the semiconductor substrate 1, and a heater element 4 and both sides of the heater element 4 are formed in the center portion of the surface on the bridge portion 3. The temperature-measuring resistance elements 5 and 6 for heat detection are formed in the structure. In addition, 7 is an opening communicating with the void 2.

The flow velocity sensor configured in this way heats the heater element 4 by applying an electric current, and when the gas is moved from the direction of the arrow 8 when placed in the gas flow, the temperature measuring resistance element 5 on the upstream side is gas The temperature of the temperature measuring resistance element 6 on the downstream side rises. As a result, a temperature difference occurs between the temperature measuring resistance element 5 on the upstream side and the temperature measuring resistance element 6 on the downstream side, and the resistance value changes. Therefore, by incorporating the upstream temperature measuring resistance element 5 and the downstream temperature measuring resistance element 6 into the Wheatstone bridge circuit and converting the change in the resistance value thereof into a voltage, a voltage output according to the flow velocity of the gas is obtained. As a result, the flow velocity of the gas can be detected.

[Problems to be Solved by the Invention] However, in the conventional flow velocity sensor, when the temperature measuring resistance elements 5 and 6 are arranged on both sides of the heater element 4 on the surface of the bridge portion 3, the entire shape of the resistor pattern is changed. Since it is formed to have a rectangular shape that is almost the same as the heater element 4, for example, 2 cm / sec from the direction of arrow 8
There has been a problem that it is not possible to effectively detect a change in arc-shaped temperature distribution centered on the heater element 4 that occurs with respect to a gas flow having a low flow velocity. Further, the temperature measuring resistance elements 5, 6 arranged near the heater element 4
The heat from the heater element 4 is largely conducted, and the initial temperature of the resistance temperature detector elements 5 and 6 becomes unnecessarily high.
There is a problem that it is easily affected by the detection error due to the adhesion of dust and the temperature coefficient (TCR) mismatch drift between the upstream side temperature measuring resistance element 5 and the downstream side temperature measuring resistance element 6.

[Means for Solving the Problem] In order to solve such a problem, a first flow velocity sensor according to the present invention includes a base and a diaphragm formed in a thin shape by providing a space in a part of the base. In a flow velocity sensor including a portion, a heating element formed on the diaphragm portion, and a resistance temperature detector formed on both sides of the heating element, a diaphragm on a longitudinal extension of the resistance temperature detector A contour line is formed in a direction perpendicular to the longitudinal direction of the resistance temperature detector, and the resistance temperature detector is formed by successively shortening the resistance pattern length as it goes away from the heating element.

The second flow measuring sensor according to the present invention is formed such that the portion of the resistance temperature detector close to the heating element is recessed so as to avoid the central portion of the heating element.

The third flow velocity sensor according to the present invention has a thin film pattern formed on the periphery of the resistance temperature detector to assist the heat dissipation of the resistance temperature detector.

A fourth flow velocity sensor according to the present invention is the third flow velocity sensor, wherein the thin film pattern is formed of the same material as the resistance temperature detector.

[Operation] In the first flow velocity sensor according to the present invention, the upstream temperature-measuring resistor and the downstream temperature-measuring resistor are concentrated only on the portion where the temperature distribution generated by the heating element largely changes due to the gas flow. Will be placed.

In the second flow velocity sensor according to the present invention, the upstream temperature-measuring resistor and the downstream temperature-measuring resistor do not receive heat conduction due to the heat generation of the heating element more than necessary, thereby lowering the initial temperature.

In the third and fourth flow velocity sensors according to the present invention, the temperature change caused by the gas flow between the upstream temperature-measuring resistance element and the downstream temperature-measuring resistance element becomes large.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view showing the outline of the overall configuration for explaining an embodiment of the flow velocity sensor according to the present invention. The same or corresponding parts as those in the above-mentioned drawings are designated by the same reference numerals and the description thereof will be omitted. In the figure, a thin film diaphragm portion 3a that is thermally insulated from the semiconductor substrate 1 through a gap 2 is formed in the central portion of the surface of the semiconductor substrate 1. A heater element 4 is formed in the central portion, and independent temperature measuring resistance elements 5 and 6 are formed on both sides of the heater element 4, respectively. In addition, these resistance temperature elements 5, 6
Specifically, as shown in an enlarged plan view in FIG. 2 described later, the resistor pattern is formed by concentrating only on the portion where the temperature distribution generated by the resistor pattern of the heater element 4 changes due to the gas flow. It is configured to be. Further, a large number of slits 11 for etching the semiconductor substrate 1 are formed on the surface of the semiconductor substrate 1, and the heater element 4 and the temperature measuring resistance element 5,
By performing anisotropic etching, for example, on the peripheral portion of 6 through a large number of fine slits 11 formed in the surface of the semiconductor substrate 1, a void 2 having an inverted trapezoidal air space is formed inside. ing. As a result, the upper portion of the void 2 is spatially separated from the semiconductor substrate 1 in a diaphragm shape, and the heater element 4 and the temperature measuring resistance elements 5 and 6 on both sides are thermally insulated and supported from the semiconductor substrate 1. The structure is such that the diaphragm part 3a is formed. In addition, 11 ₁ , 11 ₂ , 11, ₃ and 11 ₄ are diaphragm parts 3
In a, a slit portion is continuously opened from the windward side to the leeward side in front of and behind the arrangement of the temperature measuring resistance element 5, the heater element 4, and the temperature measuring resistance element 6 in communication with the void portion 2. Further, as shown in the enlarged plan view of the main part in FIG. 2, the temperature measuring resistance element 5 on the upstream side provided in the diaphragm portion 3a has a resistance pattern length in the longitudinal direction intersecting with the arrow direction 8 in which the gas flows. The temperature-measuring resistance element 6 on the downstream side is formed such that the length of the resistor pattern in the longitudinal direction becomes shorter from the windward side toward the leeward direction. Is formed. That is, the outer shape of the temperature measuring resistance element 5 on the upstream side and the temperature measuring resistance element 6 on the downstream side are formed to have a semicircle or a trapezoidal shape with the heater element 4 as the center. Furthermore, in the temperature measuring resistance element 5 and the temperature measuring resistance element 6, the resistor pattern is not formed in the central portion of the resistor pattern on the side close to the harter element 4, and the resistor pattern is the heater element. It is formed so as to be separated from the No. 4 by a certain distance. That is, the upstream side temperature measuring resistance element 5 is formed and arranged close to the windward side, and the downstream side temperature measuring resistance element 6 is formed and arranged close to the leeward side, and both sides of the heater element 4 are relatively wide curved planes. Region 12 is formed. In this case, the temperature measuring resistance elements 5 and 6 are, for example, the semiconductor substrate 1 having a size of 1400 μm square and a diaphragm portion.
When the square of 3a is 500 μm, the heater element 4
It is preferable that the length from the edge of is formed within the range of 80 to 300 μm.

With this configuration, the resistance temperature detector elements 5, 6
Since the outer shape is formed in a semicircle or trapezoidal shape, the outer shape is effectively arranged only in the portion where the temperature change due to the gas flow from the arrow direction 8 is large, and the useless portion is eliminated. Can be significantly improved. Further, in addition to the outer shape of the temperature measuring resistance elements 5 and 6, the heater element 4 is provided with the relatively wide curved planar area 12 in the peripheral portion thereof.
Since the heat generated by the sensor is not conducted to the resistance temperature detector elements 5 and 6 more than necessary and the initial temperature is further lowered, the detection sensitivity in the low flow velocity region can be further improved and the influence of detection error due to dust adhesion and It is less likely to be affected by temperature coefficient (TCR) mismatch drift between the upstream side temperature measuring resistance element 5 and the downstream side temperature measuring resistance element 6. Further, by providing slits 11 ₂ and 11 ₃ between the heater element 4 and the temperature measuring resistance elements 5 and 6 along the length direction of the resistor pattern, the above effect can be further improved.

FIG. 3 is a plan view of an essential part showing the structure of another embodiment of the flow velocity sensor according to the present invention. The same or corresponding parts as those in the above-mentioned drawings are designated by the same reference numerals, and the description thereof will be omitted. In the figure, the difference from FIG. 2 is that the resistances composed of an assembly of a plurality of rod-shaped patterns are provided at both ends in the length direction of the heater element 4 of the upstream side temperature measuring resistance element 5 and the downstream side temperature measuring resistance element 6. A body pattern 13 is formed and arranged. These resistor patterns 13 are temperature measuring resistance elements.
It is formed of, for example, permalloy or platinum in the same step as the formation of 5, 6.

With this configuration, the resistance temperature detector elements 5, 6
Is formed and arranged only in a portion where the temperature change caused by the gas flow on the diaphragm portion 3a is large, and the resistance change rate is large, and further, the resistor pattern 13 is arranged in the surrounding portion where there is a certain temperature change. As a result, the heat dissipation function as a cooling fin is obtained, and the temperature measuring resistance elements 5, 6
The change in temperature becomes even better. Further, by disposing the resistor pattern 13 on the ends of the temperature measuring resistance elements 5 and 6 on both sides, the initial temperature of the temperature measuring resistance elements 5 and 6 can be further lowered, so that detection due to dust adhesion It is even less susceptible to the effects of errors and the temperature coefficient (TCR) mismatch drift between the upstream temperature measuring resistance element 5 and the downstream temperature measuring resistance element 6.

It should be noted that one end of each rod-shaped resistor pattern 13 may be formed by being connected to the temperature measuring resistance elements 5 and 6. According to this configuration, the resistor pattern 13 and the temperature measuring resistance element are formed.
Since the heat conduction between the temperature measuring resistors 5 and 6 is improved, the above-mentioned effect can be further enhanced without substantially affecting the resistance values of the temperature measuring resistors 5 and 6.

FIG. 4 is a plan view of an essential part showing a configuration of a flow velocity sensor according to still another embodiment of the present invention. The same or corresponding parts as those in the above-mentioned drawings are designated by the same reference numerals and the description thereof will be omitted.
In the figure, the difference from FIG. 3 is that the upstream side temperature measuring resistance element 5 is located on the windward side and the downstream side temperature measuring resistance element 6 is arranged.
A resistor pattern 14 having the same structure as the resistor pattern 13 is formed and disposed on the leeward side.

With such a configuration, the same effect as that of the flow velocity sensor shown in FIG. 3 can be further enhanced and the mechanical strength of the diaphragm portion 3a can be reinforced. In addition, even if the plate-shaped resistor pattern 15 is formed as shown in FIG. 5, the same operation and effect as described above can be obtained. In the above-described embodiment, the semiconductor substrate is provided with a void portion. The case where the thin film portion structure is a diaphragm structure has been described, but it goes without saying that the present invention is not limited to this, and even if it is applied to a microbridge structure, almost the same effect as described above can be obtained.

Further, in the above-described embodiments, the case where the semiconductor substrate is used as the base has been described, but the present invention is not limited to this, and for example, a metal substrate such as aluminum or stainless steel is used, and the diaphragm portion is made of SiO 2. ₂ , Si ₃
Needless to say, the same effect as described above can be obtained by forming the insulating film such as N ₄ .

Further, in the above-described embodiments, the case where anisotropic etching is used for forming the diaphragm portion has been described, but the same applies even if an etching method such as isotropic etching with a mixed solution of hydrofluoric acid and nitric acid is used. Of course, it can be formed.

Further, the method of forming the diaphragm portion is not limited to etching, and it can be formed by processing with an end mill laser or the like, or the substrate and the diaphragm portion can be manufactured separately and then the same can be formed. Of course.

[Advantages of the Invention] As described above, according to the flow velocity sensor of the present invention, the contour line of the diaphragm on the extension of the resistance temperature detector in the longitudinal direction is in the direction perpendicular to the longitudinal direction of the resistance temperature detector. Since the resistance temperature detectors are formed by gradually shortening the resistance pattern length as they move away from the heating element, both resistance temperature detectors are concentrated only in the part where the temperature change caused by the gas flow is large. As a result, the rate of change in resistance increases, and the detection sensitivity can be greatly improved.
Further, the resistance temperature detectors formed on both sides of the heating element are formed so that the portions close to the heating element are recessed so as to avoid the central portion of the heating element, so that the heat of the heating element is conducted more than necessary. This reduces the initial temperature of the resistance temperature detectors on both sides, reduces the influence of dust and TCR mismatch drift, and further improves the detection sensitivity. Furthermore, by placing the resistance temperature detectors formed on both sides of the heating element away from the heating element,
The effect is remarkably obtained. In addition, by providing a thin film pattern around the resistance temperature detectors on both sides to assist the heat dissipation of the resistance temperature detectors, the temperature change between the resistance temperature detectors can be obtained more efficiently and the initial temperature can be further improved. An extremely excellent effect such as further reduction can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of an embodiment of a flow velocity sensor according to the present invention, FIG. 2 is an enlarged plan view of an essential part of FIG. 1, and FIG.
FIG. 4 is a plan view showing the structure of a flow velocity sensor according to another embodiment of the present invention, FIG. 4 is a plan view showing the structure of a flow velocity sensor according to another embodiment of the present invention, and FIG. 5 is a flow velocity sensor according to the present invention. The top view which shows the structure by the other Example of this.
FIG. 6 is a plan view of relevant parts showing the structure of a conventional flow velocity sensor. 1 ... Semiconductor substrate, 2 ... Air gap, 3a ... Diaphragm, 4 ... Heater element, 5 ... Upstream temperature measuring resistance element, 6 ... Downstream temperature measuring resistance element, 8 ... Arrow direction, 11 …… Slit, 11 ₁ , 11 ₂ , 11 ₃ , 11 ₄ …… Slit part, 12 …… Plane area, 13,14,15 …… Resistor pattern.

Claims (4)

(57) [Claims] 1. A base, a diaphragm portion formed in a thin shape with a space provided in a part of the base, a heating element formed on the diaphragm portion, and formed on both sides of the heating element. In a flow velocity sensor including a resistance temperature detector, the shape of the outer contour of the resistance temperature detector on the side not facing the heating element is formed according to the shape of the temperature distribution created by the heating element. Flow rate sensor characterized by. 2. A base, a diaphragm portion formed in a thin shape with a space provided in a part of the base, a heating element formed on the diaphragm portion, and formed on both sides of the heating element. In a flow velocity sensor including a resistance temperature detector, a resistor pattern near a central portion of a side of the resistance temperature detector facing the heating element is formed farther from the heating element than other portions. A characteristic flow velocity sensor. 3. A base, a diaphragm portion thinly formed with a space provided in a part of the base, a heating element formed on the diaphragm portion, and formed on both sides of the heating element. A flow velocity sensor including a resistance temperature detector, wherein a thin film pattern for assisting heat dissipation of the resistance temperature detector is formed in a peripheral portion of the resistance temperature detector. 4. The thin film pattern according to claim 3,
A flow velocity sensor formed of the same material as the resistance temperature detector.