JP2002286519A - Thermal flow velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal flow velocity sensor with enhanced measurement accuracy by making it possible to obtain, over a wide flow velocity range, a signal sharply changing with changes in flow velocity, thereby improving linearity. SOLUTION: This thermal flow velocity sensor is equipped with thermal elements 13 having heat-sensing parts for sensing temperature and generating electrical signals according to temperatures sensed by the heat-sensing parts and Peltier elements 14 having exothermic parts 4A and endothermic parts 4B. The exothermic parts and endothermic parts of the Peltier elements are parallelized with the heat-sensing parts 3A and 3B of the thermal elements, respectively, and they are arranged along the flowing direction of a fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow sensor for detecting a change in heat transfer in a fluid that changes according to the flow of a fluid such as a gas and generating a signal corresponding to the speed of the fluid. It is.

[0002]

2. Description of the Related Art Conventionally, this type of sensor is composed of a heat-sensitive element for sensing heat, a heater, and a substrate for holding and floating these elements, and two heat-sensitive elements are opposed to one side of one heater. It is known that a semiconductor device such as silicon is used for a substrate, and the whole is manufactured using a semiconductor process technology.

According to the principle of detecting the flow velocity of the flow velocity sensor having the above-described structure, the heater is heated to a constant temperature higher than the temperature of the substrate by a predetermined value. On the other hand, the temperature of the substrate is almost the same as the temperature of the flowing fluid, and most of the heat conduction from the heater is performed through the fluid, and when there is no fluid flow,
A heat-sensitive element composed of a heat-sensitive resistor whose resistance value changes in accordance with the temperature provided at the symmetrical position on the upstream side and the downstream side of the heater is heated to the same temperature lower by a predetermined value than the heating temperature of the heater, No difference occurs in the resistance values.

On the other hand, when a fluid has a flow,
The heat-sensitive element located on the upstream side is cooled because heat is carried away by the flow of fluid toward the heater, and the heat-sensing element located on the downstream side is heated by the flow of fluid from the heater. The resulting difference in resistance between the heat sensitive elements results in a difference in voltage, and the flow velocity is measured.

As a thermal element, an element using a thermopile element instead of a thermal resistor or a temperature measuring resistor is known. In this thermopile element, the hot junctions of a pair of thermopile elements are arranged adjacent to the heater in the flow direction of the fluid, and the hot junctions of the upstream and downstream thermopile elements generate the fluid by the heat generated by the heater. Is to be heated through. As a result, the temperature of the hot junction of both thermopile elements differs due to the flow of the fluid, and the temperature difference between the cold junction and the hot junction, which is usually at the temperature of the fluid, changes in the opposite direction. This temperature difference causes a difference in the output voltage of the thermopile element, and the flow velocity is measured.

[0006]

In any of the conventional thermal flow sensors described above, the temperature sensed by the heat-sensitive elements arranged upstream and downstream across the heater varies from zero to the maximum flow velocity of the fluid. Then, in principle, attention is paid to the fact that the temperature changes to the gas temperature and the heater temperature, respectively. For this reason, a signal having a magnitude corresponding to the difference between the gas temperature and the heater temperature is obtained at the maximum, and the variation width of the signal according to the flow velocity does not become larger. As a result, when trying to detect a wide range of flow velocity changes from a small flow velocity to a large flow velocity, the linearity of the signal deteriorates and the measurement accuracy cannot be obtained. In some cases, the flow velocity in the high flow velocity area could not be detected.

Therefore, in view of the above-mentioned conventional problems, the present invention improves the linearity by obtaining a signal that changes greatly due to a change in flow velocity over a wide flow velocity range, and improves the measurement accuracy. It is an object to provide a flow rate sensor.

[0008]

According to a first aspect of the present invention, there is provided a method for detecting a change in heat transfer in a fluid, which changes in accordance with the flow of a fluid such as a gas. A thermal type flow sensor that generates a signal according to a speed has a heat-sensitive part that detects a temperature, and has a heat-sensitive element that generates an electric signal according to the temperature detected by the heat-sensitive part, and a heat-generating part and a heat-absorbing part. A thermal flow sensor comprising a Peltier element, wherein a heat-generating part and a heat-absorbing part of the Peltier element and a heat-sensitive part of the heat-sensitive element are arranged in correspondence with a flow direction of a fluid.

In the above configuration, the heat-generating portion and the heat-absorbing portion of the Peltier element and the heat-sensitive portion of the heat-sensitive element are arranged along the flow direction of the fluid so as to correspond to each other. The degree to which the corresponding heat-sensitive part is heated and the degree to which the heat-absorbing part cools the corresponding heat-sensitive part are changed. Therefore, the temperature of both heat-sensitive portions changes in opposite directions according to the flow of the fluid, and a large change in temperature difference appears between the heat-sensitive portions of the heat-sensitive element according to the change in the flow of the fluid. In addition, finally, a temperature difference depending on the difference between the temperature of the heat generating portion and the temperature of the heat absorbing portion of the Peltier element appears between the two heat-sensitive portions regardless of the temperature of the fluid.

[0010] The present invention has been made to solve the above-mentioned problems.
According to a preferred embodiment of the present invention, in the thermal flow sensor according to claim 1, a heat-generating portion and a heat-absorbing portion of the Peltier element are located upstream of the heat-sensitive portion of the heat-sensitive element. Exists.

In the above configuration, since the heat-generating portion and the heat-absorbing portion of the Peltier element are located on the upstream side of the heat-sensitive portion of the heat-sensitive element, the heat-generating portion heats the corresponding heat-sensitive portion in accordance with the flow of the fluid, and The corresponding heat sensitive part will be cooled. Therefore, the temperature of both heat-sensitive portions changes in the opposite direction according to the flow of the fluid, and a large change in the temperature difference appears between the heat-sensitive portions of the heat-sensitive element according to the change in the flow of the fluid.

A third aspect of the present invention has been made to solve the above problems.
According to a preferred embodiment of the present invention, in the thermal type flow rate sensor according to claim 1 or 2, the heat-generating part and the heat-absorbing part of the Peltier element and the heat-sensitive part of the heat-sensitive element are electrically and thermally formed on a semiconductor substrate. A thermal flow sensor characterized by being disposed on an insulating thin film portion.

In the above structure, the heat-generating portion and the heat-absorbing portion of the Peltier element and the heat-sensitive portion of the heat-sensitive element are arranged on the thin film portion having electrical and thermal insulation formed on the semiconductor substrate. The heat-sensitive portion of the Peltier element is less susceptible to heat transmitted through portions other than the fluid, and its temperature changes due to heat generated by the heat-generating portion and the heat-absorbing portion of the Peltier element and transmitted through the fluid. .

A fourth aspect of the present invention has been made to solve the above problem.
The invention described in the thermal flow sensor according to any one of claims 1 to 3, wherein the heat-sensitive element has a hot junction and a cold junction as the heat-sensitive portion, and a temperature between the hot junction and the cold junction. A thermopile element that generates an electric signal of a magnitude corresponding to the difference, and the heat generating part and the heat absorbing part of the Peltier element are arranged along the flow direction of the fluid in correspondence with the hot junction and the cold junction of the thermopile element, respectively. The present invention is directed to a thermal type flow velocity sensor.

In the above structure, the thermosensitive element includes a thermopile element having a hot junction and a cold junction as a heat sensitive part, and a thermopile element for generating an electric signal having a magnitude corresponding to a temperature difference between the hot junction and the cold junction. The heat generating portion and the heat absorbing portion of the thermopile element are arranged along the flow direction of the fluid in correspondence with the hot junction and the cold junction of the thermopile element, so that the heat generating portion heats the hot junction according to the flow of the fluid. As a result, the degree to which the heat absorbing portion cools the cold junction changes. Therefore, both the temperature of the hot junction and the temperature of the cold junction both change in the opposite direction according to the flow of the fluid, and the temperature difference between the hot junction and the cold junction of the thermopile element greatly changes according to the flow velocity change. And finally, a temperature difference corresponding to the difference between the temperature of the heat generating portion and the temperature of the heat absorbing portion of the Peltier element appears between the hot junction and the cold junction of the thermopile element regardless of the temperature of the fluid. As a result, it is possible to generate an electric signal that changes greatly according to a change in the flow velocity in a wide range.

A fifth aspect of the present invention has been made to solve the above problems.
The described invention is the thermal type flow rate sensor according to any one of claims 1 to 3, wherein each of the thermal elements has a resistor whose resistance value changes according to the sensed temperature by sensing the temperature. A pair of heat-sensitive resistance elements that generate an electric signal of a magnitude corresponding to the resistance value of the resistor, and correspond to the heat-generating portion and the heat-absorbing portion of the Peltier element and the resistors of the pair of heat-sensitive resistance elements, respectively. The thermal flow velocity sensor is arranged along the flow direction of the fluid.

In the above configuration, each of the heat-sensitive elements has a resistor that senses the temperature and changes the resistance according to the sensed temperature, and generates an electric signal having a magnitude corresponding to the resistance of the resistor. It consists of a pair of heat-sensitive resistance elements, and the heat-generating part and heat-absorbing part of the Peltier element and the respective resistors of the pair of heat-sensitive resistance elements are arranged along the flow direction of the fluid so as to correspond to each other. In response, the temperatures of the resistors of both thermosensitive resistance elements both change in the opposite direction,
The temperature difference between the resistors of the two thermosensitive resistance elements greatly changes according to the flow velocity change, and finally, the temperature of the heat generating part and the temperature of the heat absorbing part of the Peltier element do not depend on the temperature of the fluid. Of the thermopile element appears between the hot junction and the cold junction of the thermopile element, so that an electric signal that changes greatly in accordance with a wide range of flow velocity change can be generated.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 show an embodiment of a thermal flow sensor according to the present invention. FIG. 1 is a cross-sectional view of a thermal flow sensor. In FIG.
A Si substrate 11 as a semiconductor substrate made of, SiO ₂
12 as a thin film portion having an electrical and thermal insulating layer composed of a layer and a Si ₃ N ₄ layer, and a thermopile element as a thermal element incorporated in the diaphragm 12 to form a part of the diaphragm 12 13 and
It has a thermopile element 13 and a Peltier element 14 which forms a part of the diaphragm 12 as well.

The thermopile element 13 has a configuration in which a plurality of thermocouples that generate a voltage corresponding to a temperature difference between connection points of different kinds of metals are connected in series. Specifically, each thermocouple is formed on a lower surface of an insulating layer 13a made of a SiO ₂ layer.
^++- Si13A and Al13B formed on the upper surface are interconnected, and as shown in the plan view of the thermal type flow sensor shown in FIG.
a plurality of p ⁺⁺ -Si formed on the lower surface and the upper surface of
And Al are connected in a zigzag shape to form a thermopile element 13. The outermost A
1 is also used as the power supply electrode 13C.

Then, among the interconnection points, the connection point which is set to a relatively high temperature is the hot junction 3A as one heat sensitive portion.
The connection point set at a low temperature is the cold junction 3B as the other heat sensitive portion. In the illustrated example, the hot junction 3A
Although the cold junction 3B is located on the upstream side of the fluid flow and the cold junction 3B is located on the downstream side, the order may be reversed if the cold junction 3B is located along the fluid flow direction. Further, the number of thermocouples can be set to an arbitrary number.

As shown in FIG. 3, the Peltier element 14 is formed on an insulating layer 13a made of a SiO ₂ layer and an insulating layer 13b made of an Si ₃ N ₄ layer formed so as to cover Al on the upper surface thereof. P-type semiconductor layer 14a and N-type semiconductor layer 1
4b, these semiconductor layers are interconnected by a conductive electrode 14c on the upstream side of the flow, and a power supply electrode 14d is connected to each downstream layer. In the case of the arrangement shown in the drawing, the current i is caused to flow in the direction of the arrow shown in the drawing, whereby
b and the conductive electrode 14c become a heat generating portion 4A that emits heat to the outside, and a connecting portion between the P-type semiconductor layer 14a and the N-type semiconductor layer 14b and the power supply electrode 14d absorbs surrounding heat. Becomes

As shown in FIG. 2, the Peltier element 14 disposed above the thermopile element 13 via the insulating layer 13b composed of a Si ₃ N ₄ layer has a heat-generating part 4A and a heat-absorbing part 4B. Are located upstream of the hot junction 3A and the cold junction 3B, respectively. With this arrangement, when a current is temporarily passed through the Peltier element 14, the heat generating portion 4A generates heat to heat the surrounding fluid while the current is flowing, and the heat absorbing portion 4B absorbs the heat to cause the surrounding fluid to flow. To cool. When there is no flow of the fluid, there is no movement of the heated or cooled fluid, so that a constant temperature distribution is generated around the heat generating portion 4A and the heat absorbing portion 4B, and the hot junction 3A and the cold junction 3B of the thermopile element 13 It is heated and cooled to a temperature corresponding to the temperature distribution at that position, and as a result, a certain temperature difference occurs between the hot junction 3A and the cold junction 3B.

In the above-described embodiment, the hot junction 3A and the cold junction 3B of the thermopile element 13 are arranged so as to be located within the temperature distribution around the heat generating portion 4A and the heat absorbing portion 4B when no fluid flows. However, by arranging each contact at the outermost position of the temperature distribution when there is no fluid flow, each contact can be adjusted from the gas temperature when the flow velocity is 0 to almost the peak temperature of the temperature distribution when the flow velocity is the maximum. This makes it possible to generate an electric signal corresponding to a larger flow velocity change, that is, a wide flow velocity range.

On the other hand, when there is a flow of fluid, the heated or cooled fluid moves and the temperature distribution shifts downstream, so that the hot junction 3A is heated to a higher temperature and the cold junction 3B
Will be cooled to a lower temperature, the degree of which will increase as the flow increases. In such a situation, the peaks of the temperature distribution are the hot junction 3A and the cold junction 3B.
The temperature difference between the hot junction 3A and the cold junction 3B continues to increase in accordance with the flow rate of the fluid in this range.
From C, a temperature difference signal that changes according to the flow velocity of the fluid can be extracted.

As described above, when there is a flow in the fluid, a phenomenon occurs in which the temperature of the hot junction 3A rises and the temperature of the cold junction 3B falls simultaneously in accordance with the change in the flow velocity of the fluid, and the temperature difference increases. Since the temperature difference signal is changed, the change per unit change in the flow rate of the temperature difference signal is increased, and the change in the flow rate can be measured more accurately by the change in the temperature difference signal.

The formation of the thermopile element is based on
Oxidation and photolithography from both surfaces of the Si substrate 11
Selective etching such as luffing and impurity diffusion
This is done by And of the thermopile element
After formation, the surface_ThreeN _FourInsulation layer by layer deposition
Is formed, and a P-type semiconductor layer, an N-type semiconductor layer, and gold are formed thereon.
Peltier by depositing and etching metal layers
D) An element is formed.

In the above-described embodiment, the heat-generating portion and the heat-absorbing portion of the Peltier element are located on the upstream side of the hot junction and the cold junction of the thermopile element, but may be located on the downstream side or directly above. Good. However, as in the embodiment, the arrangement on the upstream side is advantageous in that a larger temperature difference is generated by positively utilizing the heat of the heat generating unit and the cooling unit.

Further, in the embodiment, the heat generating portion and the heat absorbing portion of the Peltier element and the hot junction and the cold junction of the thermopile element are arranged on a thin film portion having electrical and thermal insulation formed on the semiconductor substrate. However, other configurations may be used as long as the heat of the heat generating portion and the heat absorbing portion can be transmitted to the hot junction and the cold junction of the thermopile element through a fluid. By forming it on the thin film part having the property, it is possible to prevent the heat of the heat generating part and the heat absorbing part from being transmitted to the hot junction and the cold junction of the thermopile element through a part other than the fluid with a simple configuration. Is advantageous.

Furthermore, in the embodiment, a thermopile element is used as the heat-sensitive element. However, other than the thermopile element, for example, there is provided a resistor that senses temperature and changes the resistance value according to the sensed temperature. However, it is also possible to use a pair of heat-sensitive resistance elements that generate an electric signal having a magnitude corresponding to the resistance value of the resistor. In this case, the heat-generating portion and the heat-absorbing portion of the Peltier element and the respective resistors of the pair of heat-sensitive resistance elements are arranged corresponding to each other along the flow direction of the fluid. Specifically, each resistor of a pair of thermal resistance elements is arranged at a position corresponding to a hot junction and a cold junction of a thermopile element, respectively.

In the case where the above-described thermosensitive element is used, similarly to the case where the thermopile element is used, when there is a flow in the fluid, the resistance of one of the thermosensitive elements is changed according to the change in the flow velocity of the fluid. At the same time, the temperature of the resistor of the other heat-sensitive resistance element decreases, causing the temperature of both resistors to change in the opposite direction, causing a large difference in the resistance value exhibited by both resistors. Therefore, a large difference occurs in the magnitude of the electric signal generated by each thermal resistance element. Therefore, a signal corresponding to a temperature difference signal generated by the thermopile element can be obtained by inputting both electric signals to, for example, a differential amplifier and obtaining a signal corresponding to the difference therebetween as an output. This signal, like the temperature difference signal generated by the thermopile element, has a large change per unit change in the flow rate, and the change in the flow rate can be more accurately measured by the change in the temperature difference signal.

In the case where a heat-sensitive resistance element is used,
Although a pair of elements will be provided, the number of terminals will be increased as compared to a thermopile element which may be a single element, but each element only has a heat-sensitive portion made of a resistor, and the structure is compared with a thermopile element. Since the sensor is simple, the structure as a sensor is simplified, and the manufacturing process is simplified, the sensor is inexpensive. However, a differential amplifier is separately required to obtain a temperature difference signal. Therefore, it is effective to use the thermopile element properly depending on the situation.

[0032]

As described above, according to the first aspect of the present invention, the degree of heating of the corresponding heat-sensitive part by the heat-generating part and the heat-sensitive part by the heat-absorbing part correspond to the flow of the fluid. As the degree of cooling changes, the temperature of both thermosensitive parts changes in opposite directions according to the flow of the fluid, and a large temperature difference between the thermosensitive parts of the thermosensitive element according to the change in the flow of the fluid. A change appears, and finally, a temperature difference depending on the difference between the temperature of the heat generating portion and the temperature of the heat absorbing portion of the Peltier element appears between the two heat sensitive portions regardless of the temperature of the fluid. Therefore, it is possible to obtain a thermal type flow rate sensor in which a signal which largely changes due to a change in flow rate can be obtained over a wide flow rate range to improve linearity and improve measurement accuracy.

According to the present invention described in claim 2, according to the invention described in claim 1, the heat-generating portion heats the corresponding heat-sensitive portion in accordance with the flow of the fluid, and the heat-absorbing portion heats the corresponding heat-sensitive portion. So that the temperature of both heat-sensitive parts changes in the opposite direction according to the flow of the fluid, so that a large change in temperature difference appears between the heat-sensitive parts of the heat-sensitive element according to the change in the flow of the fluid. Therefore, it is possible to obtain a thermal type flow velocity sensor having higher measurement accuracy.

According to the third aspect of the present invention, in the first or second aspect, the heat-sensitive portion of the heat-sensitive element is further affected by heat transmitted through a portion other than the fluid. It becomes difficult, and the temperature is changed by the heat generated by the heat-generating part and the heat-absorbing part of the Peltier element and transmitted through the fluid, so that the thermal flow velocity can be measured more accurately with a simple configuration. A sensor can be obtained.

According to the present invention described in claim 4, the invention according to any one of claims 1 to 3 further comprises:
Depending on the flow of the fluid, the degree to which the heating part heats the hot junction,
The degree to which the heat absorbing part cools the cold junction changes,
In accordance with the flow of the fluid, both the temperature of the hot junction and the temperature of the cold junction both change in the opposite direction, so that the temperature difference between the hot junction and the cold junction of the thermopile element greatly changes according to the flow velocity change. And finally, a temperature difference according to the difference between the temperature of the heat generating portion and the temperature of the heat absorbing portion of the Peltier element, which does not depend on the temperature of the fluid, appears between the hot junction and the cold junction of the thermopile element. As a result, it is possible to generate an electric signal that changes greatly in response to a wide range of flow rate changes, so that the use of a single thermopile element enables a signal that changes greatly due to a change in flow rate to be obtained over a wide flow rate range. As a result, it is possible to obtain a small thermal flow sensor capable of improving linearity and improving measurement accuracy.

According to the present invention described in claim 5, according to the invention described in any one of claims 1 to 3,
In accordance with the flow of the fluid, the temperature of the resistors of both thermal resistance elements both changes in the opposite direction, so that the temperature difference between the resistors of both thermal resistance elements greatly changes according to the flow velocity change. In the end, a temperature difference depending on the difference between the temperature of the heat generating portion and the temperature of the heat absorbing portion of the Peltier element appears between the hot junction and the cold junction of the thermopile element regardless of the temperature of the fluid. Therefore, it is possible to generate an electric signal that changes greatly in accordance with a wide range of flow velocity changes, so that a signal that largely changes due to a change in flow velocity can be obtained over a wide flow velocity range by using a heat-sensitive resistance element having a simple structure. Thus, an inexpensive thermal flow sensor that can improve linearity and improve measurement accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a thermal flow sensor according to the present invention.

FIG. 2 is a top view in which a part of the thermal type flow sensor of FIG. 1 is omitted.

FIG. 3 is a plan view showing a Peltier element omitted in FIG. 2;

[Description of Signs] 11 Semiconductor substrate 12 Thin film section 13 Thermopile element (Thermal element) 3A Hot junction (Thermal section) 3B Cold junction (Thermal section) 14 Peltier element 4A Heating section 4B Heat absorbing section

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Minoru Seto, Tokyo Gas Co., Ltd., 1-5-20, Kaigan, Minato-ku, Tokyo (72) Yasuhiro Okamoto 1500 Onjuku 1500, Susono-shi, Shizuoka Prefecture F-term Yazaki Sogyo Co., Ltd. (Reference) 2F035 EA02 EA08

Claims (5)

[Claims] A thermal type flow rate sensor for detecting and measuring a change in heat transfer in a fluid, which varies in accordance with the flow of the fluid, has a heat-sensitive portion for sensing a temperature. A heat-sensing element that generates an electric signal according to the temperature sensed by the unit; and a Peltier element having a heat-generating part and a heat-absorbing part. The heat-generating part and heat-absorbing part of the Peltier element and the heat-sensitive part of the heat-sensitive element are respectively A thermal type flow velocity sensor, which is arranged along the flow direction of a fluid in a corresponding manner. 2. The thermal type flow sensor according to claim 1, wherein the heat generating portion and the heat absorbing portion of the Peltier element are located on the upstream side of the heat sensitive portion of the heat sensitive element. 3. A heat-generating part and a heat-absorbing part of the Peltier element and a heat-sensitive part of the heat-sensitive element are arranged on a thin film part having electrical and thermal insulation formed on a semiconductor substrate. Item 3. A thermal flow sensor according to item 1 or 2. 4. The thermosensitive element comprises a thermopile element having a hot junction and a cold junction as the heat sensitive portion, and generating a signal having a magnitude corresponding to a temperature difference between the hot junction and the cold junction, 2. The heat generating part and the heat absorbing part of the Peltier element and the hot junction and the cold junction of the thermopile element are respectively arranged along the flow direction of the fluid in correspondence with each other.
4. A thermal flow sensor according to any one of claims 1 to 3. 5. Each of the thermal elements has a resistor that senses a temperature and changes a resistance value according to the sensed temperature, and generates an electric signal having a magnitude corresponding to the resistance value of the resistor. The heat-generating part and the heat-absorbing part of the Peltier element are arranged along the flow direction of the fluid in such a manner as to correspond to each of the resistors of the pair of thermal resistance elements. The thermal flow sensor according to any one of claims 1 to 3.