JPH08219836A - Mass flow sensor - Google Patents

Abstract

PURPOSE: To provide a mass flow sensor which has high sensitivity even in a minute flow and is suitable for mass production by improving the detection sensitivity. CONSTITUTION: A mass flow sensor comprises a substrate 7 formed by a material having a small thermal conductivity such as glass or ceramics, and thin film thermally-sensitive elements 1a, 2a, 1b, 2b which are formed on both surfaces of the substrate 7 and paired on the respective surfaces, wherein the paired thin film thermally-sensitive elements 1a, 2a, 1b, 2b include thin film thermally-sensitive elements 1a, 1b disposed on the upstream side with respect to the flow direction B of a fluid to be detected, and thin film thermally- sensitive elements 2a, 2b disposed on the downstream side, the thin film thermally-sensitive elements 1a, 2a, 1b, 2b are heating elements and temperature measuring resistors, and the thin film thermally-sensitive elements 1a, 1b of the same upstream side and the thin film thermally-sensitive elements 2a, 2b of the same downstream side are disposed on the opposite sides of a Wheatstone bridge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a circuit configuration of a mass flow sensor for measuring the flow rate of a fluid because the resistance value of a Wheatstone bridge circuit formed by a thin film thermal sensor changes due to the passage of the fluid.

[0002]

2. Description of the Related Art A mass flow sensor detects the flow rate of a fluid by utilizing the fact that the resistance value of a resistance temperature detector heated by a heating resistor changes due to the passage of the fluid. FIG. 6 is a structural diagram of a conventional mass flow sensor. 6, in the mass flow sensor, a silicon oxide film 4A for heat insulation is provided on a silicon substrate 4, a heating resistor 3a is formed at the center of the silicon oxide film 4A, and a silicon oxide film 4A is formed on the same silicon oxide film 4A. The first resistance temperature detector 1a and the second resistance temperature sensor 2a are arranged symmetrically with respect to the heating resistor 3a.

With such a structure, when a constant current is passed through the heating resistor 3a through the electrode 6, the temperature of the temperature measuring resistors 1a and 2a rises. In this state, the fluid is caused to flow from the direction of the first resistance temperature detector 1a toward the heat generation resistance body 3a and the second resistance temperature detector 2a. Fluid is first
After the resistance temperature detector 1a is cooled and heated by the heat generation resistor 3a, the second
The resistance temperature detector 2a is further heated. In this way, the temperature of the first resistance temperature detector 1a decreases and the temperature of the second resistance temperature detector 2a increases. As shown in FIG. 6C, the two resistance temperature detectors 1a and 2a are connected in series to a bridge circuit, and an unbalanced voltage generated from a change in resistance value caused by a temperature change, The flow rate of the fluid is detected by the voltage difference from the bias voltage on the other side of the bridge circuit.

In such a mass flow sensor, a silicon oxide film 4A is formed on the surface of a silicon semiconductor substrate 4 by thermal oxidation, a Ni film is formed on the substrate surface (4A) by a sputtering method, and a first photolithographic method is used. Resistance temperature detector
Patterning of 1a, the heating element 3a, and the second resistance temperature detector 2a is performed. After that, the first RTD 1a, the heating resistor 3a, and the second RTD 2a are plasma-etched from the back surface of the substrate 4.
A cavity 4B is provided below the substrate to form a diaphragm made of a silicon oxide film 4A.

By providing the hollow portion 4B, the lower portion of the first resistance temperature detector 1a, the heating resistance resistor 3a, and the second resistance temperature detector 2a becomes only the silicon oxide film 4A, and the first resistance temperature detector 1a and the second resistance temperature detector 1a The temperature change of the resistance temperature detector 2a can be made sensitive. Now, assuming that the cavity 4B is not formed, the silicon oxide film
4A itself has low thermal conductivity and good thermal insulation, but since the silicon oxide film 4A is thin, the temperature difference detected by the first resistance temperature detector 1a and the second resistance temperature detector 2a is due to this oxidation. It flows through the silicon film 4A to the silicon semiconductor substrate 4, which has a relatively good thermal conductivity, and causes a decrease in detection sensitivity. Therefore, as described above, by providing the cavity portion 4B, the lower portion of the first resistance temperature detector 1a, the heating resistance resistor 3a, and the second resistance temperature detector 2a becomes only the silicon oxide film 4A, and the first resistance temperature detector With the decrease of the specific heat between the body 1a and the second resistance temperature detector 2a, the thermal insulation is improved,
It is possible to detect temperature changes with high sensitivity and sensitivity to minute changes in fluid.

[0006]

However, in the mass flow sensor of the prior art as described above, since the thermosensitive element composed of the resistance temperature detector is arranged on the plane of the sensor substrate, the detection of the fluid by this mass flow sensor is The surface flow flowing on the surface of the sensor substrate is detected depending on the contact state between the fluid to be measured and the heat sensitive body. Therefore, when a minute flow of the fluid to be measured is detected, the fluid and the heat sensitive body may not be sufficiently contacted with each other depending on the arrangement and position of the sensor, and sufficient sensitivity may not be obtained. Further, as a method of increasing the detection sensitivity of the fluid to be measured, a method of improving the fluid detection characteristic by using an auxiliary heating means such as a heater is performed, but in such a case, an independent heater drive circuit is required, The configuration was complicated.

The present invention has been made in view of the above points, and its purpose is to solve the above-mentioned problems, improve the detection sensitivity as a mass flow sensor, and be suitable for mass production with high sensitivity even in a minute flow. It is to provide a mass flow sensor.

[0008]

In order to achieve the above object, according to the first invention, a substrate made of glass or a material having a small thermal conductivity of ceramics, and a substrate formed on both sides of each substrate A pair of thin-film thermal sensors, the pair of thin-film thermal sensors being arranged on the upstream side with respect to the flow direction of the fluid to be detected and the thin-film thermal sensor arranged on the downstream side. And the body, the thin film thermal sensor is a heating element and a resistance temperature detector, and the thin film thermal sensors on the upstream side and the downstream side are arranged on opposite sides of the Wheatstone bridge.

According to the second aspect of the invention, the outer side end faces of the pair of thin film heat sensing elements are arranged in the vicinity of the side end face of the substrate. Further, according to the third invention, a third thin film thermal sensor is formed at an intermediate position between the paired thin film thermal sensors, and power is supplied to the third thin film thermal sensor by the paired thin film thermal sensors. The same power source as the Wheatstone bridge circuit is used.

Further, it is assumed that the Wheatstone bridge circuit formed by a pair of thin film thermal sensors and the third thin film thermal sensor are connected in series. Further, the Wheatstone bridge circuit formed by the pair of thin film thermal sensors and the third thin film thermal sensor are connected in parallel. Further, it is assumed that the individual resistance values of the pair of thin film thermal sensors and the resistance value of the third thin film thermal sensor are selected to be different values.

[0011]

With the above structure, according to the first aspect of the invention, the thin film thermal sensor is patterned on both front and back surfaces of the substrate of the mass flow sensor.
Compared to the deployed one, the fluid contact area between the measured fluid and the thin film thermal sensor can be doubled, and the output voltage when the Wheatstone bridge circuit is composed of the paired thin film thermal sensors has been increased. The size can be increased to about twice that of the technology, and the detection sensitivity can be increased.

Further, according to the second aspect of the present invention, by disposing the side end face of the thin film thermal sensor near the side end face of the substrate,
The cooling effect of the upstream edge portion of the sensor substrate can be utilized, and the temperature change of the thin film thermal sensor can be made sensitive. According to the third aspect of the invention, the third thin-film thermal sensor having a function as an auxiliary heating element is provided between the upstream thin-film thermal sensor and the downstream thin-film thermal sensor to provide the downstream thin film. The heating effect of the thermal sensor can be enhanced, and further, the power supply to the third thin film thermal sensor can be connected to the same power source as the Wheatstone bridge circuit, and the number of stabilizing power source circuits required can be reduced. .

Further, by changing the resistance value of the pair of thin film thermal sensors and the resistance value of the third thin film thermal sensor,
The optimum temperature field required for fluid detection can be formed.

[0014]

1 is a block diagram of a mass flow sensor according to the first embodiment of the present invention, FIG. 2 is a Wheatstone bridge circuit diagram of the mass flow sensor, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a block diagram of a mass flow sensor according to the invention, FIG. 4 is a block diagram of a mass flow sensor according to the third invention, and FIG. 5 is a circuit configuration diagram of the mass flow sensor according to the third invention. The same members corresponding to FIG. 6 are the same. The reference numeral is attached.

Embodiment 1 FIG. 1 is a constitutional view of a mass flow sensor of one embodiment according to the first invention. (A) of FIG. 1 is a front view and a sectional view taken along the line AA of FIG. (B) shows a side view. In FIG. 1, the mass flow sensor includes a substrate 7 made of glass or a ceramic material having a low thermal conductivity, and the substrate 7
Thin-film thermal sensor formed on both sides of the surface and paired on one side
(1a, 2a) and a pair of thin-film thermal sensors (1b, 2a) on the other surface.
b) and are formed via the electrode pattern portion 6. The pair of thin-film thermal sensors (1a, 2a), (1b, 2b) are thin-film thermal sensors (hereinafter referred to as upstream thin-film thermal sensors) arranged on the upstream side with respect to the flow direction B of the fluid to be detected. 1a and 1b) and a thin film thermal sensor (2a, 2b) arranged on the downstream side.
The thin film thermal sensors (1a, 2a), (1b, 2b) are both heating elements and resistance temperature detectors.
(1a, 1b) and the downstream thin-film thermal sensors (2a, 2b) are connected to opposite sides of the Wheatstone bridge circuit shown in FIG.

With such a structure, when a current is applied to the thin film heat sensing elements (1a, 2a), (1b, 2b), which are both heating elements and resistance temperature detectors, through the electrode pattern portion 6, the thin film heat sensing elements are detected. (1a, 2a),
Ambient temperature of (1b, 2b) rises. In this state, the fluid flows in the direction of arrow B. Due to the movement of the distribution of the high temperature fluid in the fluid passage, the fluid moves to the thin film thermal sensor (1a, 1a,
Cool 1b) and heat the downstream thin-film thermal sensor (2a, 2b). In this way, the temperature of the thin film thermal sensor (1a, 1b) decreases and the temperature of the thin film thermal sensor (2a, 2b) increases. Since the upstream and downstream thin-film thermal sensors (1a, 1b), (2a, 2b) are placed on opposite sides of the bridge circuit, an imbalance occurs in the bridge due to the above-mentioned temperature difference, and the bridge unbalance voltage is generated. The flow rate of the fluid can be detected more.

The main difference between the present mass flow sensor and the conventional mass flow sensor shown in FIG. 6 is that thin film thermal sensors are patterned on both sides of the sensor substrate. With this configuration, the area of the heat sensitive element can be doubled compared to the conventional single-sided type, and the output voltage can be approximately doubled by constructing the Wheatstone bridge as shown in Fig. 2 and the detection sensitivity can be increased. Can be increased.

Embodiment 2 FIG. 3 is a block diagram of a mass flow sensor of another embodiment according to the second invention. FIG. 3 (A) is a front view and a sectional view taken along the line AA. (B) shows a side view. FIG.
1 is different from FIG. 1 in that a part of the side surface of the substrate 7 of FIG. 1 which is orthogonal to the direction of fluid flow is removed into a trapezoidal shape 7A to form a pair of thin film thermal sensors (1a, 2a), The outer side end face of (1b, 2b) is arranged near the side end face of the substrate 7.

With this structure, the mass flow sensor is arranged at the center of the flow path of the fluid to be detected. The fluid to be detected passes through both surfaces of the substrate 7. With this configuration,
The contact between the thin film thermal sensors (1a, 2a), (1b, 2b) and the fluid to be detected is such that the side end surface of the substrate 7 shown in FIG.
a, 2a), (1b, 2b) has a tighter coupling than the structure having a distance between the outer side end faces of the a, 2a) and (1b, 2b), and the thin film heat sensing element ( The temperature change of 1a, 1b) becomes sharp, and the detection sensitivity of the mass flow sensor can be improved.

In consideration of the structure and arrangement of the electrode pattern portion 6 in the embodiment of the present invention, it is not always necessary to remove a part of the side surface of the substrate 7 into the trapezoidal shape 7A, as shown in FIG. It has a rectangular shape like a pair of thin film thermal sensors (1a, 2
The outer side end faces of a) and (1b, 2b) may be arranged near the side end face of the substrate 7. Embodiment 3 FIG. 4 is a configuration diagram of a mass flow sensor of another embodiment according to the third invention. (A) of FIG. 4 is a front view and a sectional view taken along the line AA of FIG. ) Indicates a side view. FIG.
1 and 3 is different from that of FIG. 1 in that the third thin film thermal sensor (1a, 2a), (1b, 2b) is arranged at the intermediate position of the third.
The thin film thermal sensor (3a, 3b) is formed, and the third thin film thermal sensor (3a, 3b) is formed.
3b) is supplied to this pair of thin-film thermal sensors (1a, 2a), (1
The Wheatstone bridge circuit constructed by b, 2b) is configured to be operated from the same power source. In the embodiment shown in FIG. 4, the third thin film thermal sensor (3a, 3a) is used in the embodiment of FIG.
The case where b) is formed is shown. Note that the electrode pattern portion 6 includes 61a to 61c in order to clearly show the terminal position of the connection example shown in FIG.
It was subdivided into 64a, 61b to 64b.

With such a configuration, by supplying power to the thin film thermal sensors (1a, 2a), (1b, 2b) and the third thin film thermal sensor (3a, 3b) forming the Wheatstone bridge circuit,
Thin film thermal sensor (1a, 2a), (1b, 2b) and third thin film thermal sensor
The temperature of (3a, 3b) rises. In this state, the fluid flows in the direction of arrow B. The fluid cools the thin film thermal sensor (1a, 1b) and is heated by the third thin film thermal sensor (3a, 3b) to further heat the thin film thermal sensor (2a, 2b). In this way, the temperature of the thin film thermal sensor (1a, 1b) decreases and the temperature of the thin film thermal sensor (2a, 2b) increases. The fluid to be measured heated by the third thin-film thermal sensor (3a, 3b) can increase the heating effect of the downstream thin-film thermal sensor (2a, 2b) even in a minute flow, and the downstream thin-film thermal sensor (2a, 2b) can be heated. It is possible to improve the heat-sensitive characteristics of the sensor (2a, 2b).
In the illustrated example of FIG. 4, as already described in the second embodiment, the outer side end faces of the pair of thin film thermal sensors (1a, 2a), (1b, 2b) are arranged near the side end face of the substrate 7. Therefore, the thin film thermal sensor (1a, 1b) on the upstream side due to the cooling effect of the edge portion of the substrate 7
In addition to improving the heat-sensitive characteristics of the
Along with the improvement of the heat-sensitive characteristics of the thin film thermal sensor (2a, 2b) on the downstream side by a, 3b), a synergistic effect can be exhibited, and the detection sensitivity of the mass flow sensor can be improved.

FIG. 5 shows an example of connection in which the third thin film thermal sensor (3a, 3b) is used as an auxiliary heating element to supply power from the same power source as the Wheatstone bridge circuit. FIG. 5A shows the Wheatstone bridge. Circuit and third thin film thermal sensor (3a, 3
b) is connected in series, and (B) and (C) in FIG. 5 are connected in parallel. In FIG. 5 (A), the Wheatstone bridge circuit has terminals (61a, 6a) shown in FIG.
Connect between 2b) and (61b, 62a). The connection to the stabilized power supply 8 can be made in series by connecting the terminals 64a and 64b to the power supply terminals. In this connection method, since the current flowing through the third thin film thermal sensor (3a, 3b) is twice, the resistance value of the thin film thermal sensor (1a, 2a), (1b, 2b) and the third thin film thermal sensor When the resistance values of the bodies (3a, 3b) are equal, the temperature rise of the third thin film thermal sensor (3a, 3b) is caused by the thin film thermal sensor (1a, 2a),
It is almost four times the temperature rise of (1b, 2b). By decreasing the resistance value of the third thin film thermal sensor (3a, 3b), this temperature rise rate can be reduced. That is, the thin film thermal sensor (1a,
By appropriately selecting the ratio of the resistance values of 2a), (1b, 2b) and the third thin film thermal sensor (3a, 3b), it is possible to create an optimum temperature distribution on the substrate 7 for fluid detection.

Further, FIGS. 5B and 5C show the Wheatstone bridge circuit and the third thin film thermal sensor (3a, 3b) connected in parallel. In FIGS. 5B and 5C, the Wheatstone bridge circuit connects terminals (61a, 62b) and (61b, 62a). To connect to the stabilized power supply 8, connect the terminals 63a and 63b to the power supply terminals respectively, and perform the parallel connection of Fig. 5 (B) or Fig. 5 (C) depending on the connection location of the remaining terminals 64a and 64b. You can In the connection method of FIG. 5 (B), the current flowing through each side of the Wheatstone bridge is equal to the current flowing through the third thin film thermal sensor (3a, 3b), so that each thin film thermal sensor 1a, 2a, 1b, When the resistance values of 2b, 3a and 3b are equal, the temperature rises of the thin film thermal sensors 1a, 2a, 1b, 2b, 3a and 3b are almost equal. Also, in the connection method of FIG. 5C, the temperature rise of the third thin film thermal sensor (3a, 3b) is caused by the thin film thermal sensor (1a, 2a), (1b, 2b).
It is almost four times the temperature rise. Third thin film thermal sensor (3a, 3
This temperature rise rate can be reduced by increasing the resistance of b). That is, the thin film thermal sensor (1a, 2a), (1
By appropriately selecting the ratio of the resistance values of b, 2b) and the third thin film thermal sensor (3a, 3b), an optimal temperature distribution for fluid detection can be created on the substrate 7.

[0024]

As described above, according to the first invention,
Since the thin film thermal sensor is formed on both sides of the substrate, the fluid contact area between the fluid and the thin film thermal sensor is approximately doubled as compared with the prior art in which the thin film thermal sensor is constructed and arranged on one side. It is possible to increase the output voltage when the Wheatstone bridge circuit is composed of the pair of thin film thermal sensors to about twice as much as that of the conventional technique, and to increase the detection sensitivity.

Further, according to the second aspect of the present invention, by disposing the side end face of the thin film thermal sensor near the side end face of the substrate,
The contact between the fluid and the thin film thermal sensor can be made denser than in the conventional configuration, and the temperature change of the upstream thermal sensor can be detected sensitively due to the cooling effect of the edge portion of the sensor substrate. According to the third aspect of the invention, the third thin-film thermal sensor having a function as an auxiliary heating element is provided between the upstream thin-film thermal sensor and the downstream thin-film thermal sensor to provide the downstream thin film. The heating effect of the heat sensor can be enhanced. Further, the power supply to the third thin film thermal sensor can be connected to the same power source as the Wheatstone bridge circuit, and a special circuit for driving the auxiliary heating element is unnecessary.

Further, by appropriately selecting the ratio of the resistance value of the pair of thin film thermal sensors to the resistance value of the third thin film thermal sensor, an optimum temperature distribution for fluid detection can be formed on the sensor substrate. You can

[Brief description of drawings]

FIG. 1 is a configuration diagram of a mass flow sensor according to a first invention, which is an embodiment of the present invention.

FIG. 2 is a Wheatstone bridge circuit diagram in the first or second embodiment.

FIG. 3 is a configuration diagram of a mass flow sensor according to a second embodiment.

FIG. 4 is a configuration diagram of a mass flow sensor according to a third embodiment.

FIG. 5 is a circuit configuration diagram of a mass flow sensor according to a third embodiment.

FIG. 6 is a block diagram of a conventional mass flow sensor.

[Explanation of symbols]

 1a, 2a, 1b, 2b Thin film thermal sensor 3a, 3b Third thin film thermal sensor 4 Silicon semiconductor substrate 4A Silicon oxide film 4B Cavity part 6,61a ~ 64a, 61b ~ 64b Electrode pattern part 7 Glass or ceramic substrate 8 Stable Power source B Fluid flow direction

Front page continuation (72) Inventor Shinichi Soma 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (6)

[Claims] 1. A pair of thin-film thermal sensors comprising a substrate made of glass or ceramic material having a low thermal conductivity, and thin-film thermal sensors formed on both surfaces of the substrate and forming a pair on each surface. Includes a thin-film heat sensor arranged upstream and a thin-film heat sensor arranged downstream with respect to the flow direction of the fluid to be detected. The thin film heat sensor is a heating element. A mass flow sensor, which is also a resistance temperature detector, wherein thin-film heat sensors on the upstream side and on the downstream side are provided on opposite sides of the Wheatstone bridge. 2. The mass flow sensor according to claim 1, wherein the outer side end faces of the pair of thin film thermal sensors are arranged near the side end face of the substrate. 3. The mass flow sensor according to claim 1 or 2, wherein a third thin film thermal sensor is formed at an intermediate position of a pair of thin film thermal sensors, and power is supplied to the third thin film thermal sensor. A mass flow sensor, wherein the Wheatstone bridge circuit constituted by the pair of thin-film thermal sensors is operated from the same power source. 4. The mass flow sensor according to claim 3, wherein a Wheatstone bridge circuit formed by a pair of thin film thermal sensors and a third thin film thermal sensor are connected in series. 5. The mass flow sensor according to claim 3, wherein a Wheatstone bridge circuit formed by a pair of thin film thermal sensors and a third thin film thermal sensor are connected in parallel. 6. The mass flow sensor according to claim 3, wherein the resistance value of each of the pair of thin film thermal sensors and the resistance value of the third thin film thermal sensor are set to each other. A mass flow sensor characterized in that different values are selected.