JPH04343023A - Flowrate sensor - Google Patents

Abstract

PURPOSE:To improve the thermal response characteristic of a sensor and to reduce the heat loss of a heater thereby to save power consumption. CONSTITUTION:A heater 3, a temperature sensitive resistance body 4 at the upperstream side and a temperature sensitive resistance body 5 at the downstream side are coated with a lower insulating film 2 and an upper insulating film 6. The lower insulating film 2 is formed of material of small thermal conductivity, so that the heat loss of the heater 3 is decreased and the consuming power is reduced. Moreover, since the upper insulating film 6 is made of material of large thermal conductivity, the movement of the heat of a fluid to be measured is accurately detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate sensor, and more particularly to a flow rate sensor suitable for use in measuring extremely small amounts of fluid flow.

0002

2. Description of the Related Art Conventionally, as a flow rate sensor for measuring the flow rate of a small amount of fluid, the one described in, for example, Japanese Patent Application Laid-open No. 142268/1983 has been proposed. The flow rate sensor described in this publication has a structure in which the upper and lower surfaces of the main part that measures the flow rate, which includes a heater, a heat sensing sensor, etc., are covered with a thin insulating film made of the same material.

0003

However, the above-mentioned prior art has the following problems. In other words, the insulating films covering both the upper and lower surfaces of the flow rate measuring section of the flow rate sensor are made of the same material, but if a material with high thermal conductivity is used as both insulating films, for example, the flow of the fluid will be affected. The temperature of the corresponding fluid cannot be detected accurately, and as a result, a problem arises in that the flow rate of the fluid cannot be accurately measured. On the other hand, if a material with low thermal conductivity is used for both insulating films, for example, a problem occurs in that heat loss in the heater increases and power consumption increases.

The present invention solves the above problems by using materials with different thermal conductivities as the insulating films covering the upper and lower surfaces of the flow rate measuring section, thereby improving the thermal response and reducing the heat generated by the heater. The object of the present invention is to provide a flow sensor that achieves reduced loss and reduced power consumption.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a substrate, a heating means provided on the upper surface of the substrate for heating a fluid to be measured, and a heating means provided on the upper surface of the substrate. a temperature sensing means for detecting the temperature of a heated fluid to be measured as a resistance value; an upper insulating film covering an upper part of the heating means and the temperature sensing means; and a lower part of the heating means and the temperature sensing means. A flow rate sensor comprising a lower insulating film is characterized in that the upper insulating film and the lower insulating film are made of materials having different thermal conductivities.

[0006]

According to the present invention, since the upper insulating film and the lower insulating film are made of materials having different thermal conductivities, it is possible to reduce heat loss of the heating means and reduce power consumption. Furthermore, since the thermal response in the temperature sensing means can be made faster, the heat transfer of the fluid to be measured can be accurately detected. This makes it possible to significantly improve the performance of the flow sensor.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. 1 and 2 are configuration diagrams of the flow rate sensor of this embodiment, in which a lower insulating film 2 with a thickness of, for example, 400 nm is provided at the center of the upper surface of a semiconductor substrate 1 with a thickness of, for example, 200 to 400 μm. is formed on the upper surface of the lower insulating film 2, and the thickness for heating the fluid to be measured is, for example, 80 nm.
The heater 3 is arranged on one side (the upstream side in the fluid flow direction indicated by the arrow in FIG. 1) and has a thickness of, for example, 8.
An upstream temperature-sensitive resistor 4 with a thickness of 0 nm, and a downstream temperature-sensitive resistor with a thickness of, for example, 80 nm, which is disposed on the other side of the heater 3 (downstream in the fluid flow direction indicated by the arrow in FIG. 1). 5 is formed. That is, the heater 3, the upstream temperature-sensitive resistor 4, and the downstream temperature-sensitive resistor 5 are covered with the lower insulating film 2 and the upper insulating film 6. Furthermore, the heater 3, the upstream temperature sensitive resistor 4, and the downstream temperature sensitive resistor 5
An upper insulating film 6 having a thickness of, for example, 400 nm is formed on the upper surface. Furthermore, a space 7 is formed in the center of the substrate 1 below the flow rate measurement section composed of the heater 3, the upstream temperature-sensitive resistor 4, and the downstream temperature-sensitive resistor 5.

The lower insulating film 2 is made of a material with low thermal conductivity, such as silicon oxide (in this embodiment, the thermal conductivity is 1.4 W/m·K, for example). (It is not limited to this numerical value), thereby reducing the heat loss of the heater 3 and reducing the power consumption of the heater 3. Further, the upper insulating film 6
is made of a material with high thermal conductivity, such as silicon nitride (in this example, the thermal conductivity is 19W, for example).
/m·K, but is not limited to this value), thereby making it possible to accurately detect the heat transfer of the fluid to be measured. In this case, when processing the semiconductor substrate 1 using etching technology, the lower insulating film 2 made of silicon oxide or the like is removed using an etching solution (
For example, because it is slightly immersed in potassium hydroxide aqueous solution, etc.
In order to prevent the problem of the lower insulating film 2 being removed when the lower insulating film 2 is exposed to an etching solution for a long period of time, the lower layer of the lower insulating film 2 is coated with an etching solution that is more likely to be attacked than silicon oxide. It is also possible to further form silicon nitride, which is difficult to form.

Next, the operation of the flow rate sensor of this embodiment having the above configuration will be explained. When the flow rate sensor measures the flow rate of the fluid to be measured, an external circuit (not shown) supplies electricity to the heater 3 to heat it, and controls the heater 3 to have a temperature higher than the ambient temperature by a predetermined value. do. When there is no fluid flow, the temperature distribution in the flow sensor is centered around the heater 3 and the upstream temperature sensing resistor 4.
and the downstream temperature-sensitive resistor 5 side. On the other hand, when fluid flows in the direction shown by the arrow in FIG. 1, the upstream temperature-sensitive resistor 4 is cooled, while the fluid flows in the downstream temperature-sensitive resistor 5 from the direction of the arrow in FIG. Since heat conduction from the heater 3 is promoted using the fluid as a medium and the temperature rises, a temperature difference occurs between the upstream temperature sensitive resistor 4 and the downstream temperature sensitive resistor 5. Therefore, by connecting the upstream temperature-sensitive resistor 4 and the downstream temperature-sensitive resistor 5 to, for example, a Wheatstone bridge circuit, the temperature difference between the two temperature-sensitive resistors 4 and 5 is converted into voltage, and the voltage is adjusted according to the flow rate. By extracting the voltage output, the flow rate of the fluid can be measured.

In this case, the flow rate measuring section composed of the heater 3, the upstream temperature-sensitive resistor 4, and the downstream temperature-sensitive resistor 5 consists of a lower insulating film 2 and an upper insulating film having a very thin film thickness of, for example, 400 nm. covered with a membrane 6, and
It is thermally insulated by a space 7 formed in the substrate 1 below the flow rate measuring section, and furthermore, the lower insulating film 2 is made of a material with low thermal conductivity, such as silicon oxide. , heat loss can be reduced, and as a result, the power supplied to the heater 3 can be reduced. Further, since the upper insulating film 6 is formed of a material with high thermal conductivity such as silicon nitride, it is possible to accurately detect the heat transfer of the fluid to be measured, and the upstream temperature-sensitive resistor 4 - It is possible to speed up the thermal response in the downstream temperature-sensitive resistor 5. This makes it possible to significantly improve the performance of the flow sensor.

[0011]

[Effects of the Invention] As explained above, according to the present invention, there is provided a substrate, a heating means provided on the upper surface of the substrate for heating the fluid to be measured, and a fluid heated by the heating means provided on the upper surface of the substrate. a temperature sensing means for detecting the temperature of the fluid to be measured as a resistance value; an upper insulating film covering the upper part of the heating means and the temperature sensing means; and a lower insulating film covering the lower part of the heating means and the temperature sensing means. In the flow rate sensor comprising the above, since the upper insulating film and the lower insulating film are made of materials having mutually different thermal conductivities, the following effects can be achieved. ■The upper insulating film that covers the upper part of the heating means/temperature-sensing means and the lower insulating film that covers the lower part are made of materials with different thermal conductivities, reducing heat loss in the heating means and power consumption. can be reduced. Furthermore, since the thermal response in the temperature sensing means can be made faster, the heat transfer of the fluid to be measured can be accurately detected. This makes it possible to significantly improve the performance of the flow sensor. ■Due to the above,
When a material with high thermal conductivity is used as the upper and lower insulating films made of the same material as in the past, there are problems such as the inability to accurately detect the temperature of the fluid according to the flow, and the problem that the upper and lower insulating films have high thermal conductivity. It is possible to solve the problem that heat loss in the heating means becomes large and power consumption increases when a substance with a small value is used.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a flow sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line A-A in FIG. 1 of this embodiment.

[Explanation of symbols]

1 Semiconductor substrate 2 Lower insulating film 3 Heater (heating means) 4 Upstream temperature sensing resistor (temperature sensing means) 5 Downstream temperature sensing resistor (temperature sensing means) 6 Upper insulating film 7 Space section

Claims (1)

[Claims] 1. A substrate, a heating means provided on the upper surface of the substrate to heat a fluid to be measured, and a temperature of the fluid to be measured heated by the heating means provided on the upper surface of the substrate to be detected as a resistance value. A flow rate sensor comprising a temperature sensing means, an upper insulating film covering an upper part of the heating means and the temperature sensing means, and a lower insulating film covering a lower part of the heating means and the temperature sensing means, A flow rate sensor characterized in that the upper insulating film and the lower insulating film are made of materials having different thermal conductivities.