JP2018141664A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow sensor showing sensitivity even under high flow rate.SOLUTION: The flow sensor includes a heater 5 wired in one direction and a thermopile 6a which has a plurality of hot junctions 613 and is provided on both sides of the heater 5. The plurality of hot junctions 613 are arranged at a plurality of points at different distances from the heater 5 in a direction perpendicular to the wiring direction of the heater 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flow sensor for measuring a flow rate.

  2. Description of the Related Art Conventionally, a MEMS (Micro Electro Mechanical Systems) flow sensor (hereinafter referred to as a flow sensor) using a thermopile is known as a sensor for measuring a flow rate of a measurement target (gas or the like) (see, for example, Patent Document 1). . In this flow sensor, a cavity is formed in a semiconductor substrate by MEMS processing, and a heater and a plurality of hot junctions of the thermopile are arranged in parallel above the cavity.

US Patent Application Publication No. 2010/0089118

  In a conventional flow sensor, a plurality of hot junctions are arranged in parallel to the heater. However, in this case, since the output of the flow sensor is saturated when the flow rate to be measured is large, there is a problem that the flow range in which the flow sensor has sensitivity is limited. That is, as shown in FIG. 8, as the flow rate of the measurement object increases, the output saturates, the slope becomes smaller, and the linearity is lost.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a flow sensor having sensitivity even when the flow rate is large.

  The flow sensor according to the present invention includes a heater wired in one direction and a plurality of hot contacts, and a thermopile wired on both sides across the heater, and the plurality of hot contacts are arranged in the wiring direction of the heater. It is characterized in that it is arranged at a plurality of points at different distances from the heater in a direction perpendicular to the heater.

  According to this invention, since it comprised as mentioned above, it can have a sensitivity even if the flow volume is large.

It is a figure which shows the structural example of the flow sensor which concerns on Embodiment 1 of this invention. 2A to 2D are diagrams for explaining the effect of the flow sensor according to the first embodiment of the present invention. FIGS. 2A and 2B are diagrams showing a case of a conventional flow sensor, and FIG. 2D is a diagram illustrating the case of the flow sensor according to Embodiment 1. FIG. It is a figure which shows another structural example of the flow sensor which concerns on Embodiment 1 of this invention. It is a figure which shows another structural example of the flow sensor which concerns on Embodiment 1 of this invention. It is a figure which shows another structural example of the flow sensor which concerns on Embodiment 1 of this invention. It is a figure which shows another structural example of the flow sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the flow sensor which concerns on Embodiment 2 of this invention. It is a figure which shows the characteristic of the conventional flow sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a flow sensor according to Embodiment 1 of the present invention.
The flow sensor is a sensor that measures the flow rate of a measurement target (gas or the like). In this flow sensor, as shown in FIG. 1, a cavity 2 is formed on a semiconductor substrate 1 by MEMS processing. A thin insulating layer 3 is provided on the semiconductor substrate 1. Thereby, the region (bridge portion 4) of the insulating layer 3 facing the cavity 2 is thermally insulated from the semiconductor substrate 1 by the cavity 2.

  On the bridge portion 4, a heater 5 wired in one direction is provided at the center portion. Further, temperature sensors 6 are provided on both sides (upstream side and downstream side) of the heater 5, respectively. The temperature sensors 6 on both sides are preferably symmetric with respect to the heater 5. In the flow sensor according to the first embodiment, a thermopile 6 a is used as the temperature sensor 6.

The thermopile 6a is configured by connecting a plurality of thermocouples 61 in series. The thermocouple 61 is configured by connecting first and second thin wires 611 and 612 made of different materials. The material of the first and second thin wires 611 and 612 is preferably a combination of materials that can be handled in a semiconductor process and has a large electromotive force, such as a combination of polysilicon and aluminum. In the plurality of thermocouples 61, the first and second thin wires 611 and 612 are wired alternately and in parallel (including a substantially parallel meaning) so as to cross the edge of the bridge portion 4 and are connected in series. The number of the first and second thin wires 611 and 612 is appropriately designed according to the area of the bridge portion 4 and the semiconductor process.
A hot junction 613 is formed by a connection point between the first thin wire 611 and the second thin wire 612 in the bridge portion 4, and a connection point between the first thin wire 611 and the second thin wire 612 outside the bridge portion 4. Thus, the cold junction 614 is configured. The plurality of hot junctions 613 included in the thermopile 6 a are arranged at a plurality of points at different distances from the heater 5 in a direction perpendicular to the wiring direction of the heater 5. In the example of FIG. 1, the plurality of hot junctions 613 are arranged linearly.

  Here, since the cold junction 614 is disposed on the semiconductor substrate 1, the heat capacity is large, and the temperature hardly changes even when the measurement object comes into contact. On the other hand, since the hot junction 613 is disposed on the bridge portion 4 thermally insulated from the semiconductor substrate 1, the heat capacity is small and the temperature is likely to change when the measurement object comes into contact. The thermocouple 61 detects the temperature difference between the hot junction 613 and the cold junction 614 as a voltage. In thermopile 6a, since a plurality of thermocouples 61 are connected in series, an integrated value of the voltage detected by each thermocouple 61 is obtained.

  Here, when heat is generated by the heater 5 so as to increase the predetermined temperature, when there is no flow to be measured, the temperature distribution on both sides of the heater 5 becomes symmetric, and the temperature sensor 6 arranged on the upstream side and the downstream side The temperatures detected by the temperature sensor 6 arranged in the are equal. On the other hand, when the flow of the measurement object occurs, the symmetry of the temperature distribution on both sides of the heater 5 is lost, the temperature detected by the temperature sensor 6 arranged on the upstream side is lowered, and the temperature sensor 6 arranged on the downstream side. The temperature detected at rises. Therefore, in the flow sensor, by detecting this temperature difference, an electrical output corresponding to the flow can be obtained, and the flow rate of the measurement target can be measured.

Next, the effect of the flow sensor according to Embodiment 1 will be described with reference to FIG.
In the conventional flow sensor, a plurality of hot junctions 613 are arranged in parallel to the wiring direction of the heater 5. Therefore, as shown in FIG. 2A and FIG. 2B, each temperature sensor 6 has one measurement point in the flow direction of the measurement target (direction perpendicular to the wiring direction of the heater 5). In this case, as shown in FIG. 2B, when the flow rate of the measurement object increases, the temperature sensor 6 arranged on the upstream side hardly contributes to the measurement object heated by the heater 5, and conversely the temperature arranged on the downstream side. The sensor 6 is uniformly covered with the measurement target heated by the heater 5. Therefore, measurement cannot be performed at a high flow rate, and the flow range is limited.
On the other hand, in the flow sensor according to the first embodiment, the plurality of hot junctions 613 are arranged at a plurality of points at different distances from the heater 5 in the direction perpendicular to the wiring direction of the heater 5. Therefore, as shown in FIGS. 2C and 2D, there are a plurality of measurement points of each temperature sensor 6 in the flow direction of the measurement target. As described above, when the plurality of hot junctions 613 are arranged so as to extend in the flow direction of the measurement target, subtle changes in the temperature distribution in the flow direction can be captured, so even if the flow rate of the measurement target is large. It becomes possible to measure. Therefore, it is possible to provide sensitivity regardless of the flow rate of the measurement target.

  In addition, when the temperature sensor 6 is wired symmetrically with respect to the heater 5, the electromotive force can be made zero when there is no flow to be measured.

Moreover, in FIG. 1, the case where the some hot junction 613 was arrange | positioned linearly was shown. However, the present invention is not limited to this, and the plurality of hot junctions 613 may be disposed at a plurality of points at different distances from the heater 5 in a direction perpendicular to the wiring direction of the heater 5.
For example, as shown in FIG. 3, the plurality of hot junctions 613 may be arranged obliquely with respect to the wiring direction of the heater 5. Moreover, as shown in FIG. 4, you may arrange | position the several hot junction 613 in a zigzag. The configuration shown in FIGS. 3 and 4 can achieve the same effect as the configuration shown in FIG.

Further, as shown in FIG. 5, two thermopile 6a may be provided. Thereby, electromotive force can be increased with respect to the structure shown in FIG.
Further, as shown in FIG. 6, a plurality of hot junctions 613 may be arranged at unequal intervals in a direction perpendicular to the wiring direction of the heater 5. At this time, the plurality of hot junctions 613 are arranged at intervals such that the linearity of the output with respect to the flow rate to be measured is good. Thereby, the linearity of the output with respect to the flow rate to be measured is maintained, and a high-accuracy output can be obtained even with a large flow rate.
Moreover, you may combine the arrangement | positioning shown in FIGS.

  As described above, according to the first embodiment, the heater 5 wired in one direction and the thermopile 6a having a plurality of hot junctions 613 and wired on both sides of the heater 5 are provided. Since the hot junctions 613 are arranged at a plurality of points at different distances from the heater 5 in the direction perpendicular to the wiring direction of the heater 5, they can have sensitivity even if the flow rate is large.

Embodiment 2. FIG.
In Embodiment 1, the case where the thermopile 6a was used as the temperature sensor 6 was shown. In contrast, Embodiment 2 shows a case where a resistance sensor 6 b is used as the temperature sensor 6.
FIG. 7 is a diagram showing a configuration example of a flow sensor according to Embodiment 2 of the present invention. In the flow sensor according to the second embodiment shown in FIG. 7, the thermopile 6a of the flow sensor according to the first embodiment shown in FIG. 1 is changed to a resistance sensor 6b. Other configurations are the same, and only the different parts are described with the same reference numerals.

The resistance sensors 6b are provided on both sides with the heater 5 interposed therebetween. The resistance sensors 6b on both sides are preferably symmetric with respect to the heater 5. The resistance sensor 6 b is wired in the bridge portion 4 so that the gauge length direction extends in a direction perpendicular to the wiring direction of the heater 5. An example of the material of the resistance sensor 6b is platinum.
The resistance value of the resistance sensor 6b varies depending on the temperature. Therefore, when the resistance sensor 6b is used as the temperature sensor 6, the flow rate of the measurement object can be measured from the ratio of the resistance values of the resistance sensor 6b arranged on the upstream side and the resistance sensor 6b arranged on the downstream side. is there.

  Thus, even when the resistance sensor 6b is used as the temperature sensor 6, the same effect as in the first embodiment can be obtained by taking the gauge length direction of the resistance sensor 6b widely in the gas flow direction.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Cavity 3 Insulating layer 4 Bridge part 5 Heater 6 Temperature sensor 6a Thermopile 6b Resistance sensor 61 Thermocouple 611 1st thin wire 612 2nd thin wire 613 Hot junction 614 Cold junction

Claims (8)

A heater wired in one direction;
A thermopile having a plurality of hot junctions and wired on both sides across the heater,
The plurality of hot junctions are arranged at a plurality of points at different distances from the heater in a direction perpendicular to the wiring direction of the heater. The flow sensor according to claim 1, wherein the plurality of hot junctions are arranged linearly. The flow sensor according to claim 1, wherein the plurality of hot junctions are arranged obliquely with respect to a wiring direction of the heater. The flow sensor according to claim 1, wherein the plurality of hot junctions are arranged in a zigzag manner. The flow sensor according to any one of claims 1 to 4, wherein the thermopile is provided in two stages. The flow sensor according to any one of claims 1 to 5, wherein the plurality of hot junctions are arranged at unequal intervals in a direction perpendicular to a wiring direction of the heater. . The flow sensor according to any one of claims 1 to 6, wherein the thermopile is wired symmetrically with respect to the heater. A heater wired in one direction;
A resistance sensor wired on both sides of the heater,
The flow sensor is characterized in that the gauge length direction of the resistance sensor is wired extending in a direction perpendicular to the wiring direction of the heater.

Images