KR100931702B1 - Thermopile Flow Rate Sensor - Google Patents

Abstract

A thermopile flow rate sensor is provided. According to an embodiment of the present invention, a flow rate detecting device includes at least one heating thermopile using a resistance of a thermopile as a heating element, a heating unit for dissipating heat, and at least one thermopile for temperature measurement. And at least two temperature sensing units installed upstream or downstream of the heating unit, and measuring the temperature change of the measured fluid due to the heat emitted from the heating unit in the temperature sensing unit to measure the flow velocity and flow rate of the measured fluid. do.

In addition, the thermopile flow rate sensor according to an embodiment of the present invention is a main flow passage through which the working fluid flows, a measurement flow passage through which the measured fluid branched from the main flow passage flows, and a measurement fluid passage installed in the measurement flow passage. A flow rate sensor comprising a flow rate detecting element for measuring a flow rate of a gas and a control circuit for controlling a signal of the flow rate detecting element, wherein the flow rate detecting element comprises at least one heating part configured to emit heat and at least It consists of a thermopile for measuring temperature and includes at least two temperature sensing units installed upstream or downstream of the heating unit, and the temperature sensing unit measures the temperature change of the measured fluid due to heat emitted from the heating unit. Measure the flow rate and flow rate of the fluid to be measured.

 Flow rate sensor, thermopile, flow rate detection element, flow direction detection

Description

Thermopile flow sensor {Thermopile flow sensor}

The present invention relates to a thermopile flow rate sensor, and more particularly, to a thermopile flow rate sensor capable of improving responsiveness, wide flow rate measurement range, and flow rate (flow rate) measurement accuracy by newly designing a shape of a sensing unit in a gas flow rate sensor. It is about.

In general, a thermal air flow meter is composed of an upstream temperature sensor, a heating part, and a downstream temperature sensor, and the temperature of each part is a conductive heat transfer and measurement fluid in which thermal energy is diffused to a substrate by a large heat gradient caused by the heating of the heating part. It is governed by the convective heat transfer geometry that is conveyed, measuring the flow rate and flow rate by measuring the temperature or temperature difference at a given location upstream and downstream, or by measuring the power (or voltage) required to control to maintain a constant temperature difference.

The former method has a disadvantage in that the power consumption is very large to increase the sensing temperature of the sensor at high speed, and the latter method has a disadvantage in that the measurement accuracy is significantly decreased at a low speed. It can also lead to significant errors depending on the installation angle.

A support for supporting the sensor element in the measuring flow path branched from the main flow passage is required, and the temperature characteristic of the support depends largely on the intake temperature characteristic and the wall temperature characteristic. The intake temperature characteristic is caused by a change in external environmental conditions, and the measurement accuracy is lowered by temperature changes such as density, kinematic viscosity, and thermal conductivity, which are physical properties of air. In addition, the wall temperature characteristic is that when the thermal flow rate sensor is used in a severe condition such as an automobile, heat is conducted to the heat generating resistor of the thermal air flow sensor and the temperature measuring temperature measuring resistor due to an increase in the temperature of the internal combustion engine, thereby degrading the measurement accuracy. .

In addition, the basic principle of the hot wire (heat film) flowmeter is a technique known for a long time. The heating wire flowmeter is divided into constant current mode, constant temperature mode, constant temperature difference method, and constant power difference method according to the operation control method. To measure.

For example, US Pat. No. 5,533,412 (Pulsed thermal flow sensor) using a thermal pulse as a thermal marker, and using conventional convective heat transfer as disclosed in Japanese Patent Application Laid-open No. Hei 8-29226. The heat transfer phenomenon on the surface of the thin film device is used. That is, the flow rate sensor is manufactured by using a well-known semiconductor process technology in which a heating resistor made of a metal thin film and a temperature measuring resistance resistor for temperature measurement are deposited on a silicon wafer using micromachining technology or coating a thin film by sputtering or the like. It is to measure the flow rate and the flow rate.

However, the conventional flow rate sensor has the following problems.

The thermal flux sensor manufactured using the conventional semiconductor manufacturing process uses a method of adjusting the length of the resistance wire of a single line width in order to change the resistance, so that it cannot measure sufficiently the rapid temperature gradient upstream of the heating element, so it is measured at medium speed or high speed flow. There is a disadvantage of poor precision.

In addition, a relatively simple arrangement of the thin film resistance wire on the insulating film has a limitation in the measurement flow rate range, and a function as a heating resistor or a temperature resistance resistor is predetermined, and it is possible to suppress or cool the heat transfer from the surroundings to the flow rate detection element under severe use conditions. Since there is no function, heat through the flow rate sensor support affects the flow rate detecting element, which makes it difficult to accurately measure the flow rate.

Until now, a single semiconductor has gone through four stages: circuit design, wafer processing, wiring, assembly and inspection of packages. The existing assembly process involves cutting a chip from a processed wafer and then attaching and ball attaching a plastic package through a small circuit board (PCB) attachment and wire bonding process.

Of course, a protective sealing material may be applied to wire-bond the connection between the flow rate detecting element and the wiring for signal detection control and then protect it. However, in this case, there is a concern that the electrical properties are deteriorated by using a separate wire as well as the process is lengthened because wires and bonding must be wired.

The present invention is designed to improve the above problems, the technical problem to be achieved by the present invention is to enable a thermocouple connected in series by using a thermocouple in series to enable the function of a heating element or a thermometer, It is to improve the responsiveness according to the flow rate change, have a wide flow rate and flow measurement range, and improve the precision for the flow rate and flow rate measurement.

Another technical problem of the present invention is to enable the arbitrary waveform generation to adjust the heating mode and cooling heat transfer characteristics of the control circuit and improve the power consumption, thereby reducing power consumption and distinguishing the flow direction. This significantly increases the flow rate and flow rate measurement range.

Technical problem of the present invention is not limited to those mentioned above, another technical problem that is not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the flow rate detecting element according to an embodiment of the present invention is composed of at least one heating thermopile using a resistance of the thermopile (Thermopile) as a heating element and a heating unit for dissipating heat and at least one A thermopile for measuring temperature and including at least two temperature sensing unit installed on the upstream or downstream side around the heating unit, and measuring the temperature change of the measured fluid by the heat emitted from the heating unit in the temperature sensing unit To measure the flow rate and flow rate of the measured fluid.

In order to achieve the above object, the thermopile flow rate sensor according to an embodiment of the present invention is a main flow passage through which the working fluid flows, a measurement flow passage through which the measured fluid branched from the main flow passage, and the measurement flow A flow rate sensor provided in a passage and including a flow rate detecting element for measuring a flow rate of the measured fluid and a control circuit for controlling a signal of the flow rate detecting element, wherein the flow rate detecting element comprises at least one heat generating thermopile. And a heating unit for dissipating heat and at least one thermopile for measuring temperature, and including at least two temperature sensing units installed on an upstream or downstream side of the heating unit, the heat dissipating from the heating unit The temperature change of the measured fluid is measured by the temperature sensing unit to determine the flow rate and flow rate of the measured fluid. Measure

According to the thermopile flow rate sensor of the present invention as described above has one or more of the following effects.

First, by using a semiconductor manufacturing process by arranging multiple thermopile connected thermocouple in series to function as a heating element or a thermometer, it improves the response according to the flow rate change, has a wide flow rate and flow rate measurement range, Improve accuracy for flow rate and flow rate measurements.

Second, by arranging a thermopile of a multi-array on the insulating film, and by forming a cavity in the lower portion of the insulating film to suppress the conduction heat transfer to the semiconductor substrate, it is possible to increase the ratio of convective heat transfer and conduction heat transfer to improve the response.

Third, in order to adjust the heating mode and cooling heat transfer characteristics of the control circuit and improve the power consumption, it is possible to generate an arbitrary waveform generation to reduce the power consumption and distinguish the flow direction, and to measure the flow rate and flow rate. Can be increased significantly. In particular, it is possible to significantly increase the flow rate and flow rate measurement range by allowing a thermopile that functions as a heating element or a thermometer to be selected by switching depending on the application conditions.

Fourth, the detection element support and the flow rate detection element are cut into chips on the processed wafer, and then fixed to the recesses of the detection element support, and then connected to the circuit board (PCB) connection terminal and wire bonding to form a plastic package. In addition to the conventional method of covering the substrate, the photosensitive insulating material is coated on the resistive chip implemented on the semiconductor substrate, wires are combined, and the insulating material is overlaid again to reduce the procedure and greatly simplify the packaging process. You can.

The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and the general knowledge in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, the present invention will be described with reference to the drawings for describing a thermopile flow rate sensor according to embodiments of the present invention.

Figure 1a is a front view showing a thermopile flow rate sensor according to an embodiment of the present invention, Figure 1b is a longitudinal cross-sectional view showing a thermopile flow rate sensor according to an embodiment of the present invention.

The thermopile flow rate sensor 1 according to the exemplary embodiment of the present invention may include a main flow passage 100, a measurement flow passage 200, a flow rate detection element 300, and a control circuit 400.

The main flow passage 100 may provide a space in which the working fluid 10 flows. For example, the main flow passage 100 may be an intake passage of an internal combustion engine such as an automobile.

The measurement flow passage 200 provides a space through which the measured fluid 20 branched from the main flow passage 100 flows, and the flow rate detecting element 300 measuring the flow rate of the measured fluid 20 therein is provided. Can be deployed.

FIG. 2 is a diagram illustrating an embodiment of a measurement flow path in which a flow rate detection element is disposed in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the measurement flow passage 200 may include a first curved path 220 having at least two inflection points and a second curved path 230 branching from the first curved path 220. Can be. In addition, the flow rate detecting element 300 may be installed at an upper end of the second curved path 230.

A mesh 240 may be inclined at an inlet portion of the second curved path 230 branching from the first curved path 220. The mesh 240 may serve as a filter for removing foreign matters and the like contained in the measurement fluid 20 branching from the main flow passage 100.

In addition, at least one flow hole 250a, 250b, 250c, or 260 may be included in a central portion of the first curved path 220 and the second curved path 230. Preferably, at least one flow hole 250a or 250b having a different size relative to a portion where the flow of the measured fluid 20 changes rapidly by the first curved path 220 and the second curved path 230. , 250c, 260 may be formed. Accordingly, the measured fluid 20 branching from the main flow passage 100 is vented into the main flow passage through the flow holes 250a, 250b, 250c, and 260, and thus, in the measurement flow passage 200. It is possible to suppress the formation of recycle flow in the reactor. That is, according to Bernoulli's theorem, a part of the measured fluid 20 is flow holes 250a, 250b, 250c, and 260 according to the pressure difference with the working fluid 10 flowing at a high speed outside the measurement flow passage 200. By exiting into the main flow passage 100 through) it is possible to suppress the formation of vortex and recycle flow in the measurement flow passage. The position, shape and number of the flow holes 250a, 250b, 250c, and 260 can be changed by those skilled in the art.

Meanwhile, the measurement flow passage 200 may further include a flow rate detection element support (not shown) so that the flow rate detection element 300 may be installed at the upper end of the second curved path 230 therein. In addition, the flow rate detecting element support may serve to support the flow rate detecting element 300 so that the control circuit 400 can be electrically connected to the contact pad 375 of the flow rate detecting element 300. The flow rate detection element support may be molded of a resin such as polybutylene terephthalate.

Referring back to FIG. 1B, the flow rate detection element 300 serves to measure the flow rate of the measured fluid 20 and a thermal mass flow sensor for measuring the flow rate of the fluid using a heat transfer phenomenon. It can be made in the form of. The flow rate detecting element 300 will be described later in detail.

The control circuit 400 may serve to control the signal of the flow rate detecting element 300. Preferably, the control circuit 400 may include a waveform generator 401 for supplying a control signal to the heating unit 301 in a heat generating shape of an arbitrary waveform. Accordingly, the waveform generator 401 adjusts the heat pattern of the heating unit 301 to the period and duty ratio required by using the built-in program, while adjusting the heat flux to arbitrary waveforms such as triangular wave, square wave, sawtooth wave, and sine wave. Can be set. This will be described later in detail.

On the other hand, the thermopile flow rate sensor 1 supplies power to the control circuit case 410 and the flow rate detection element 300 in which the control circuit 400 is accommodated therein and has an electromagnetic shield (not shown). The apparatus may further include an electrical connector 420 for drawing out a flow rate detection signal of the flow rate detection element 300 to the outside. The control circuit case 410 and the electric connector 420 can be integrally molded using resin such as polybutylene telephthalate.

Figure 3a is a plan view showing the structure of the flow rate detection element in the thermopile flow rate sensor according to an embodiment of the present invention, Figure 3b is a structure of the flow rate detection element in the thermopile flow rate sensor according to an embodiment of the present invention It is a longitudinal cross-sectional view which shows.

The flow rate detecting element 300 of the thermopile flow rate sensor 1 according to an embodiment of the present invention is an element that senses the flow rate by using a heat transfer phenomenon, such as a thermal mass flow sensor. 301, temperature sensing units 302a and 302b, semiconductor substrate 320, insulating film 350, and pattern protection film 360. The flow rate detecting element 300 measures the flow rate and flow rate of the measured fluid 20 by measuring the temperature change of the measured fluid 20 due to the heat emitted from the heating unit 301 by the temperature sensing units 302a and 302b. Can play a role.

The heating unit 301 may serve as a heater that radiates heat toward the measurement fluid 20. Preferably, the heating unit 301 may be formed of at least one heating thermopile 310a using a resistance of the thermopile as a heating element. In FIG. 3A, a case in which one heat generating thermopile 310a is configured will be described as an example.

As illustrated in FIG. 3A, a thermopile is formed by connecting a plurality of thermocouples in series to generate electromotive force according to a temperature difference when the different metal thin films 311a and 312a or thermoelectric materials are connected (this is called a Seebeck effect). Can be formed. A contact point, that is, a hot contact point and a cold contact point 313a and 314a, which are temperature measuring points may be formed at a portion connecting the metal thin films 311a and 312a to each other. The hot junction means a contact with a relatively high temperature, and the cold junction means a contact with a relatively low temperature. Here, the contact point is a place where different metal thin films 311a and 312a are connected, and may mean a point where a line meets a line, or a contact surface where a face meets a face.

Meanwhile, each thermopile may be made of a thermoelectric material including a metal thin film such as platinum, ruthenium, tungsten, titanium, aluminum, gold, copper, chromium, nickel, or polysilicon doped with impurities.

In the thermopile flow rate sensor 1 according to the exemplary embodiment of the present invention, a thermopile is used in place of a conventional resistor in the heating unit 301 of the flow rate detecting element 300, thereby improving the responsiveness according to the flow rate change, It has a flow rate and flow rate measurement range, and can improve the precision of the flow rate and flow rate measurement.

The temperature detectors 302a and 302b may serve to measure the temperature of the measurement fluid 20. The flow rate detecting element 300 may include at least two temperature sensing units 302a and 302b installed upstream or downstream of the heating unit 301. Preferably, each of the temperature detectors 302a and 302b may be formed of at least one thermopile for temperature measurement.

In FIG. 3A, an upstream side temperature sensing unit 302a disposed at an upstream side where the measurement fluid 20 flows around the heating unit 301 and including a temperature measuring thermopile 310b and The case where it consists of the downstream temperature sensing part 302b which is arrange | positioned on the downstream side from which the measurement fluid 20 flows out, and contains one temperature measurement thermopile 310c is demonstrated, for example.

Meanwhile, as shown in FIG. 3B, the flow rate detecting element 300 is an insulating layer covering the semiconductor substrate 320 on which the cavity 330 is formed and the semiconductor substrate 320 to form a membrane 340. And may include 350. The insulating film 350 may form at least one layer. In addition, a passivation layer 360 may be formed to cover the plurality of thermopiles 310a, 310b, and 310c disposed on the insulating layer 350. The pattern protection layer 360 may form at least one layer, and may cover the thermopile to minimize internal residual stress and to significantly reduce deformation of the membrane 340.

The semiconductor substrate 320 may have an insulating film 350 on which the heating thermopile 310a of the heating unit 301 and the temperature measuring thermopile of the temperature sensing units 302a and 302b are arranged. Preferably, a silicon substrate such as a silicon wafer, a silicon-on-insulator (SOI), or the like may be used as the semiconductor substrate 320. A cavity may be formed in the semiconductor substrate 320.

Referring again to FIG. 3A, each of the thermopiles constituting the heating unit 301 and the temperature sensing units 302a and 302b has contact points that are temperature measuring points, that is, hot contacts, at portions connecting different metal thin films. junction and cold junction may be formed. For example, the heating thermopile 310a of the heating unit 301 may connect a plurality of thermocouples composed of two different metal thin films 311a and 312a in series, and the two metal thin films 311a and 312a may be connected in series. A portion to be connected may have a plurality of contacts 313a and 314a. At both ends of the heating thermopile 310a, a lead wire 370 and a contact pad 375 may be formed to connect the heating thermopile 310a with a control circuit lead of the control circuit 400 that is external. . The lead wire 370 may select one of materials constituting the heating thermopile 310a or select a third material and adjust the width to adjust the size of the resistor.

In addition, the flow rate detecting element 300 may further include temperature compensators 303a and 303b for measuring a temperature at an inlet or an outlet of the measured fluid 20 to correct a temperature change of the measured fluid 20. have. This will be described later in detail.

On the other hand, the thermopile serving as the heat generating thermopile 310a and the thermopile serving as the temperature measuring thermopile 310b and 310c are selected from among a plurality of thermopiles in the flow rate detecting element 300 according to application conditions. The contact pads 375 on the lead wires 370 may be controlled by a modular connection terminal (not shown) of the control circuit 400. For example, in FIG. 3A, the thermopile 310a positioned at the center of the semiconductor substrate 320 is used as a heating thermopile, and the thermopiles 310b and 310c located at both sides thereof are used as the thermopile for temperature measurement. have. However, the thermopile 310c located on the downstream side by connecting the modular connection terminal of the control circuit 400 to the desired contact pad 375 is a heating thermopile, and the two thermopiles 310a located on the upstream side. , 310b) may be set as a thermopile for temperature measurement.

On the other hand, the contact pads 375 on the lead wires 370 connected to the thermopile may convert the connection of the connection of the control circuit 400 including switching (conduction time) control, current or voltage control algorithms depending on the application. The modular pin shape makes it possible to increase the flexibility of the application. In addition, the circuit may be configured by connecting the contact pads 375 in series or in parallel. That is, the position, shape, connection method, etc. of the lead wire 370 and the contact pad 375 can be changed by those skilled in the art.

4A to 4B are views illustrating a flow rate measuring method according to a temperature measuring position measured by a flow rate detecting element in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

Different thermopiles may be concentrated on a portion having a relatively large temperature gradient on the semiconductor substrate 320 to improve the accuracy of temperature measurement. Therefore, the flow rate and the flow rate can be measured over a wide range.

In order to improve the accuracy of the temperature measurement, the flow rate detecting element 300 adjusts the weight of the temperature distribution according to the position by changing the position of the temperature measuring point, that is, the hot or cold junction, according to the temperature distribution on the insulating film 350. It is possible to increase the measurement sensitivity and increase the measurement accuracy.

4A is a view illustrating a flow rate measuring method according to a temperature measuring position of the flow rate detecting device according to the first embodiment of the present invention.

First, referring back to FIG. 3A, preferably, the upstream temperature measurement thermopile 310b and the downstream temperature measurement thermopile 310c are mainly centered on the heating thermopile 310a of the heating unit 301. It may be arranged symmetrically. However, the upstream temperature measurement thermopile 310b and the downstream temperature measurement thermopile 310c are asymmetrically disposed about the heat generating thermopile 310a of the heating unit 301, so that the upstream or downstream side is The weight of the temperature distribution can be adjusted according to the position of.

Meanwhile, in FIG. 3A, the cold junctions 313b and 314c of the thermomechanical thermopile are disposed on the semiconductor substrate 320 and the hot junctions 314b and 313c are disposed on the membrane 340.

In contrast, as shown in FIG. 4A, the cold junctions 313b and 314c and the hot junctions 314b and 313c of the thermomechanical thermopile are disposed on the membrane 340 to provide a temperature on the insulating film 350. By changing the position of the temperature measurement point according to the distribution it is possible to adjust the weight of the temperature according to the position.

4B is a view illustrating a flow rate measuring method according to a temperature measuring position of the flow rate detecting device according to the second embodiment of the present invention.

According to the second embodiment of the present invention, the position of the contacts of the thermomechanical thermopile 310b, 310c, that is, the hot contacts 314b, 313c or the cold contacts 313b, 314c is adjusted according to the position. The weight of the temperature distribution can be adjusted.

As shown in FIG. 4B, the contacts of the thermomechanical thermopiles 310b and 310c, that is, the hot contacts 314b and 313c or the cold contacts 313b and 314c, are arranged in an arbitrary shape, thereby measuring the temperature. By varying the magnitude of the electromotive force in the thermal thermopile (310b, 310c) according to the application conditions, the weight of the temperature distribution according to the position can be adjusted. That is, the contacts of the thermomechanical thermopiles 310b and 310c, that is, the hot contacts or the cold contacts may be arranged in any shape including a straight line or a curve such as a straight line, a circle, an ellipse, and a triangle. For example, in FIG. 4B, the on-contact points 314b and 313c of the thermomechanical thermopiles 310b and 310c are arranged in a substantially linear-elliptic mixed shape.

4C to 4E illustrate a method of compensating for a temperature measured by a flow rate detecting element in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

4C is a view illustrating a temperature compensation method of a flow rate detecting device according to a third embodiment of the present invention.

According to the third embodiment of the present invention, the flow rate detecting element 300 measures the temperature at the inlet or outlet side of the measured fluid 20 to compensate for the temperature change of the measured fluid 20. , 303b) may be further included.

As shown in FIG. 4C, the temperature compensators 303a and 303b are disposed outside the temperature measurement thermopile 310b and 310c around the heat generating thermopile 310a, and as a weight of the temperature distribution according to the position thereof. The influence of the temperature change of the fluid under measurement 20 on the flow rate measurement accuracy can be reflected. That is, since the temperature change measured by the temperature sensing units 302a and 302b may vary according to the environment for measuring the flow velocity, the measured fluid 20 may be formed at the inlet or outlet of the measured fluid 20. By measuring the temperature, the temperature change can be corrected according to the surrounding environment. The temperature compensating units 303a and 303b may be provided at least one on the upstream side or the downstream side.

Preferably, the temperature compensators 303a and 303b may use one single resistor 311a and 311b. In addition, the temperature compensators 303a and 303b may use any one of the materials 311a and 312a constituting the thermopile.

4D is a view illustrating a temperature compensation method of a flow rate detecting device according to a fourth embodiment of the present invention.

According to the fourth embodiment of the present invention, the flow rate detecting element 300 has a side surface on the membrane 340 by providing additional terminals on both sides of the heating thermopile 310a perpendicular to the flow direction of the measured fluid 20. The temperature at can be measured.

As illustrated in FIG. 4D, additional terminals, that is, lead wires 371, 372, and 373, and contact pads 376 and 377 may be additionally connected to both sides of the heating thermopile 310a. In this case, the lead wires 371, 372, and 373 may use the same material as the metal thin film 312a at the end of the heating thermopile 310a. That is, since the metal thin film 312a and the lead wires 371, 372, and 373 are made of the same material, the metal thin film 312a and the lead wires 371a, 372, and 373 may act as a single resistor. The weight of the distribution can be reflected in the flow rate measurement and the temperature compensation to improve the accuracy.

4E is a view illustrating a temperature compensation method of a flow rate detecting element according to a fifth embodiment of the present invention.

According to the fifth embodiment of the present invention, the flow rate detecting element 300 is provided on the semiconductor substrate 320 by providing additional terminals on both sides of the heating thermopile 310a perpendicular to the flow direction of the measured fluid 20. The temperature at the side can be measured.

The basic configuration is as described in FIG. 4D. However, as shown in FIG. 4E, since the metal thin film 312a at the end of the heating thermopile 310a is outside the membrane 340, the temperature at the side surface of the semiconductor substrate 320 may be measured.

5A to 5E are views illustrating various embodiments of controlling a temperature of a heating thermopile constituting a heating unit of a flow rate detection element in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

FIG. 5A is a diagram showing an example of a PWM signal for constantly controlling the temperature of the heating thermopile, and FIG. 5B is a diagram showing the temperature distribution on the semiconductor substrate when the temperature of the heating thermopile is constantly controlled.

As shown in FIG. 5A, the temperature of the heating thermopile 310a of the heating unit 301 may be maintained at a constant temperature by the control circuit 400. In the graph of FIG. 5A, the horizontal axis (x-axis) indicates the elapsed time of the flow rate measurement, and the vertical axis (y-axis) indicates a PWM control output signal (electricity, power) supplied from the control circuit 400 to the heating thermopile 310a. , Voltage or current).

FIG. 5B shows the temperature distribution on the semiconductor substrate 320, where the horizontal axis (x axis) represents the position on the semiconductor substrate 20, and the vertical axis (y axis) represents the temperature on the semiconductor substrate 20. It can mean a dimensionless coefficient.

Even when the temperature of the heat generating thermopile 310a is constantly controlled, as shown in FIG. 5B, the central portion (about X _m = 0.5 mm portion) where the heat generating thermopile 310a is located has a substantially constant temperature. However, in reality, the temperature is lower than the downstream edge (X _m = 0.55 mm) as it goes to the upstream edge (X _m = 0.45 mm), but actually, the center of the heating thermopile 310a is U-shaped. The portion tends to be lower than the edges. In addition, when there is no flow of the measured fluid 20, the temperature distribution is symmetrical, but when there is a flow, heat transfer occurs downstream by the flow, and thus appears in an asymmetrical shape distorted downstream. By measuring this temperature distribution according to the flow rate, the flow rate can be measured.

Therefore, in order to keep the temperature of the heating thermopile 310a constant, the position of the temperature measuring point of the heating thermopile 310a may be adjusted. As described in FIG. 4B, since the contacts of the temperature measurement thermopiles 310b and 310c are arranged in an arbitrary shape, detailed description thereof will be omitted.

In addition, by providing additional terminals on both sides of the heating thermopile 310a perpendicular to the flow direction of the measurement fluid 20, it is possible to measure the temperature at the side surface on the semiconductor substrate 320 or the membrane 340. It is also possible to adjust the weight of the temperature distribution according to the position. This is as described in FIGS. 4D and 4E.

In addition, the temperature sensing unit 302a, 302b may be located on the membrane 340 above the cavity 330 to measure the temperature.

5C is a view showing an example of a signal for controlling the temperature of the heating thermopile in a heat generating shape of an arbitrary waveform, and FIG. 5D is a semiconductor substrate when the temperature of the heating thermopile is controlled in a heat generating shape of one pulse waveform. It is a figure which shows the temperature distribution on a phase, and FIG. 5E is a figure which shows the example of the waveform generation source which supplies the signal to control to the heat generating shape of arbitrary waveform.

As illustrated in FIG. 5C, the heating unit 301 may adjust the temperature in a heat generating shape of an arbitrary waveform by the control circuit 400. As described above, the control circuit 400 may include a waveform generator 401 for supplying a control signal in a heat generating shape of any desired waveform to the heat generating thermopile 310a. 5E illustrates an example of the waveform generation source 401. Accordingly, the waveform generator 401 may set the heat flux to an arbitrary waveform while adjusting the heating pattern of the heating thermopile 310a to a period and duty ratio required by using a built-in program. The configuration of the waveform generator 401 can be changed by those skilled in the art.

In FIG. 5C, examples of arbitrary waveforms are shown in the form of a triangular wave, square wave, sawtooth wave, and sine wave. Here, A is a section for supplying a control signal (power, voltage or current), B is a section for stopping the supply of the control signal, C is a processing time (processing step including processing the signal from the flow rate detection element ( Processing time) may mean a period. A section including all of the A to C sections may mean a period of an arbitrary waveform, and a ratio of the section including the A to B sections to the A section may mean a duty ratio.

FIG. 5D shows the temperature distribution on the semiconductor substrate 320 over time, in the graph, the horizontal axis (x axis) refers to the position on the semiconductor substrate 20, and the vertical axis (y axis) on the semiconductor substrate 20. It may mean a dimensionless coefficient representing the temperature of.

When the temperature of the heat generating thermopile 310a is controlled to a heat generating shape of an arbitrary waveform, for example, in the case of one pulse waveform, as shown in FIG. In the case of supplying a voltage or a current), the center portion (about X _m = 0.5 mm portion) in which the heat generating thermopile 310a is positioned has the highest temperature, and the temperature gradually decreases when the current supply is stopped. In FIG. 5D, measurement results (a, b, and c) are shown at regular time intervals from the initial current supply time. In addition, since the heat transfer occurs downstream by the flow of the measured fluid 20, the movement of the center line appears in a slightly distorted form downstream.

On the other hand, while the heating thermopile 310a generates an arbitrary waveform, the contact surface of the heating or non-heating measurement fluid 20 is connected to the interface of the heating thermopile 310a by stopping the supply of electricity or current for a predetermined time. The electromotive force generated while passing through 313a and 314a may be used to detect the flow direction of the measured fluid 20.

6A to 6E are views illustrating various embodiments of the structure of the flow rate detection device according to the manufacturing method.

Preferably, the flow rate detecting element 300 includes a plurality of thermopiles of the heating unit 301 and the temperature sensing units 302a and 302b on the insulating film 350 of the semiconductor substrate 320. Thin film by deposition or sputtering It can be arranged by coating in a form and arranged. In addition, the disposed plurality of thermopiles may be coated with at least one layer of passivation layer 360 to minimize internal residual stress and to significantly reduce deformation of the membrane 340.

In addition, the heat generating thermopile and the temperature measuring thermopile of the flow rate detecting element 300 may be made of a CMOS compatible material, and may be formed using a micromachining technique on the insulating film 350 formed on the semiconductor substrate 320. Multiple arrangements can be made using a CMOS conforming process of coating 350).

6A to 6E illustrate a heating unit 310 including one heating thermopile 310a, an upstream temperature sensing unit 302a including two temperature measuring thermopiles 310b and 310c, and Downstream temperature sensing unit 302b including two temperature measuring thermopiles 310d and 310e, upstream temperature compensating unit 303a including two temperature compensating resistors 310f and 310g, and two The case of including the downstream temperature compensator 303b including the temperature compensating resistors 310h and 310i is taken as an example.

FIG. 6A is a diagram illustrating a structure of a flow rate detection device having a bridge structure that can be manufactured using surface micromachining technology according to the first embodiment of the present invention.

According to the flow rate detection device 300 according to the first embodiment of the present invention, the cavity 330 is formed inside the semiconductor substrate 320, and at least two flow paths 321 and 322 that can be connected to the outside are provided. Can be formed. Since the cavity 330 is formed in the semiconductor substrate 320, heat conduction may be suppressed to increase the ratio of convective heat transfer and conduction heat transfer. In addition, at least two flow paths 321 and 322 that can be connected to the outside are formed, so that even when there is a sudden change in the working pressure, the breakdown strength can be improved to prevent breakage of the flow rate detecting element, thereby improving responsiveness. You can.

Meanwhile, the insulating layer 365 may be formed under the semiconductor substrate 320.

FIG. 6B is a diagram illustrating a structure of a flow rate detection device having a bridge structure having a porous silicon layer that can be manufactured using a surface micromachining technique according to a second embodiment of the present invention.

According to the flow rate detecting element 300 according to the second embodiment of the present invention, by adding the porous silicon layer 380 to the structure of the flow rate detecting element of FIG. 6A, the ratio of convective heat transfer and conduction heat transfer according to the porosity is appropriately By adjusting, the dynamic measurement range can be expanded and the bending of the semiconductor substrate 320 can be prevented. In addition, due to the air layer 323 formed between the insulating film 350 and the porous silicon layer 380 may have a heat insulating effect, it is maintained in the elastic deformation region even at abnormal high pressure to prevent breakage of the flow rate detection element 300. Can be.

FIG. 6C is a diagram illustrating a structure of a flow rate detecting element of a membrane structure that can be manufactured using a bulk micromachining technique according to a third embodiment of the present invention. FIG.

According to the flow rate detecting element 300 according to the third exemplary embodiment of the present invention, in the structure of the flow rate detecting element of FIG. 330 is formed, as described above, the ratio of convective heat transfer and conduction heat transfer can be increased by suppressing heat conduction by the cavity 330.

FIG. 6D illustrates a structure of a flow rate detection device having a membrane structure having a porous silicon layer that can be manufactured using a bulk micromachining technique according to a fourth embodiment of the present invention.

According to the flow rate detection device 300 according to the fourth embodiment of the present invention, the effect of forming the porous silicon layer 380 is as described with reference to FIG. 6B. However, in addition to the porous silicon layer 380, silicon oxide (SiO 2), and silicon nitride (SiNx) formed under the insulating film 350, the photoresist (PR) and the metal powder (Metal Particle) may be mixed to form a layer. It may be formed. Even in this case, breakage of the semiconductor substrate 320, that is, the membrane 340 can be prevented, and it can also have a heat insulating effect.

FIG. 6E illustrates a structure of a flow rate detection device having a membrane structure in which a silicon layer is formed over an entire semiconductor substrate that can be manufactured using a bulk micromachining technique according to a fifth embodiment of the present invention.

According to the flow rate detecting device 300 according to the fifth embodiment of the present invention, the entire semiconductor substrate 320 is composed of a porous silicon layer, and for example, in a liquid or a high pressure fluid having a large shear force, such as a biochip. It can be used for measuring the flow velocity.

7A is a perspective view illustrating a state in which a flow rate detection element is installed in a flow rate detection element holder in a thermopile flow rate sensor according to an exemplary embodiment of the present invention, and FIG. 7B illustrates a state in which a flow rate detection element is installed in a flow rate detection element holder. Longitudinal section.

7A and 7B, the flow rate detecting element 300 may be mounted on the flow rate detecting element holder 510, and the flow rate detecting element accommodating part (7) may be formed in a yaw shape on the flow rate detecting element holder 510. The bottom surface of the 512 may be provided with a raised die bonding portion 514 to block the entire cavity on the rear surface of the flow rate detecting element 300. Therefore, one end of the flow rate detecting element 300 is fixed to the die bonding portion 514 by using a high strength adhesive, and the remaining corner portion of the flow rate detecting element 300 is simply attached to the flow rate detecting element accommodating portion 512. It may be supported or secured with a low strength adhesive. At this time, the upper surface of the installed flow rate detection element 300 may be installed so as to substantially coincide with the surface of the flow rate detection element holder (510).

As illustrated in FIG. 7B, the die bonding unit 514 may form a space 516 except for a portion where the die bonding unit 514 and the flow rate detecting element 300 contact each other. That is, a space 516 is formed between the rear surface of the flow rate detecting element 300 and the bottom surface of the flow rate detecting element accommodating part 512 so that the flow rate detecting element 300 does not contact the flow rate detecting element holder 510. Can be.

The circuit connecting line 522 may be used to connect the contact pad 375 of the flow rate detecting element 300 to the control circuit lead 520 for connecting to the control circuit 400. As the circuit connecting line 522, a gold wire having a thickness of about 25 μm may be used, and it may be protected by a sealant. In addition, the thermopile flow rate sensor 1 includes an interface connector 530 that connects the flow rate detecting element holder 510 and the control circuit 400 so that the flow rate detecting element 300 can be electrically connected to the control circuit 400. It may include.

8 is a view showing the flow of the measured fluid in the thermopile flow rate sensor according to an embodiment of the present invention. That is, it is a left side view of a center cross section in the flow velocity detection element part of FIG. 7B.

In FIG. 8, the flow of the feeder 22 branched from the measured fluid 20 flows through the space 516 formed between the rear surface of the flow rate detecting element 300 and the bottom surface of the flow rate detecting element accommodating part 512 in a dotted line. It is displaying.

In the thermopile flow rate sensor 1 according to the exemplary embodiment of the present invention, when there is a flow of the working fluid 10, the bottom surface of the flow rate detecting element accommodating part 512 and the space 516 of the surface of the flow rate detecting element 300 are 516. ) Occurs, and the periphery of the cavity 330 is blocked only on the protruding face 514. Therefore, it is possible to eliminate the heat storage effect due to the sealed cavity and to prevent the breakage of the membrane 340 due to the pressure difference, thereby improving accuracy in measuring the flow rate and flow rate.

In addition, in most cases, the flow rate detecting element holder 510 and the flow rate detecting element 300 are cut to a chip in the processed wafer, and then fixed to the main portion of the flow rate detecting element holder 510 and then connected to a circuit board (PCB). Terminals and wire bonding (wire bonding) through the wiring process to cover the plastic package. In the case of the thermopile flow rate sensor 1 according to the exemplary embodiment of the present invention, electrical contact is unnecessary on each thermopile disposed on the semiconductor substrate 320 in the connection of the flow rate detecting element 300 and the connection line 520. The packaging process can be greatly simplified by bumping the parts with photosensitive insulating material, wire bonding, and then overlying the insulating material.

9A to 9B are diagrams illustrating still another embodiment in which a flow rate detecting element is installed in a flow rate detecting element holder in a thermopile flow rate sensor.

9A illustrates a thermopile flow rate sensor having a form in which a flow rate detecting element holder 510 equipped with the flow rate detecting element 300 is detachable from an interfacing connector 530 connected to a control circuit. In addition, FIG. 9B illustrates that the flow rate detecting element 300 may be asymmetrically disposed with respect to the center line of the flow rate detecting element holder 510.

As described above, the thermopile flow rate sensor 1 according to the exemplary embodiment of the present invention may function as a heating element or a thermometer by arranging multiple thermopiles in which thermocouples are connected in series using a semiconductor manufacturing process. Therefore, it is possible to improve the responsiveness according to the flow rate change, have a wide flow rate and flow rate measurement range, and improve the accuracy of the flow rate and the flow rate measurement.

In particular, by arranging a thermopile of multiple arrays on the insulating film 350, by forming a cavity in the lower portion of the insulating film 350 to suppress the conduction heat transfer to the semiconductor substrate 320, the ratio of convective heat transfer and conduction heat transfer is increased to respond Can improve the sex.

In addition, in order to improve the heating mode and cooling heat transfer characteristics of the control circuit 400, by enabling an arbitrary waveform generation, power consumption can be reduced, flow direction can be distinguished, and the flow rate and flow rate measurement range are remarkable. Can be increased. In particular, it is possible to significantly increase the flow rate and flow rate measurement range by allowing a thermopile that functions as a heating element or a thermometer to be selected by switching depending on the application conditions.

In addition, the connection connection terminal can be sufficiently secured to change the control circuit 400 including the heating shape control, the energization time control, and the current / voltage control algorithm according to the application field, thereby increasing the flexibility of the application.

Therefore, the thermopile flow rate sensor 1 according to an embodiment of the present invention can be miniaturized by using a semiconductor manufacturing process, and can be expected to have a compact resistance line arrangement, improved response to pulsating flow, and detection of reverse flow. The measurement accuracy may be improved by reducing the influence of heat capacity of the semiconductor substrate 320 due to continuous heating.

The thermopile flow rate sensor 1 according to an embodiment of the present invention is adopted in a gas mass flow meter such as an air mass flow rate and flow meter for an automobile, an air flow meter for a combustion device, an industrial furnace, etc. Productivity can also be increased through precision. In addition, it can be applied to biotechnology, medical devices such as biochips and micro reaction systems as well as industrial.

Those skilled in the art will appreciate that the present invention can be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalent concept are included in the scope of the present invention. Should be interpreted.

Figure 1a is a front view showing a thermopile flow rate sensor according to an embodiment of the present invention.

Figure 1b is a longitudinal sectional view showing a thermopile flow rate sensor according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an embodiment of a measurement flow path in which a flow rate detection element is disposed in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

3A is a plan view illustrating a structure of a flow rate detection device in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

3B is a longitudinal cross-sectional view illustrating a structure of a flow rate detection element in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

4A is a view illustrating a flow rate measuring method according to a temperature measuring position of the flow rate detecting device according to the first embodiment of the present invention.

4B is a view illustrating a flow rate measuring method according to a temperature measuring position of the flow rate detecting device according to the second embodiment of the present invention.

4C is a view illustrating a temperature compensation method of a flow rate detecting device according to a third embodiment of the present invention.

4D is a view illustrating a temperature compensation method of a flow rate detecting device according to a fourth embodiment of the present invention.

4E is a view illustrating a temperature compensation method of a flow rate detecting element according to a fifth embodiment of the present invention.

5A is a diagram illustrating an example in which the temperature of the heating thermopile for heating is constantly controlled.

5B is a diagram showing a temperature distribution on a semiconductor substrate when the temperature of the heat generating thermopile is constantly controlled.

5C is a diagram illustrating an example in which the temperature of the heat generating thermopile is controlled to a heat generating shape of an arbitrary waveform.

5D is a diagram showing a temperature distribution on a semiconductor substrate when the temperature of the heat generating thermopile is controlled to a heat generating shape of an arbitrary waveform.

It is a figure which shows the example of the waveform generation source which supplies the signal to control to the heat generating shape of arbitrary waveform.

FIG. 6A is a diagram illustrating a structure of a flow rate detection device having a bridge structure that can be manufactured using surface micromachining technology according to the first embodiment of the present invention.

FIG. 6B is a diagram illustrating a structure of a flow rate detection device having a bridge structure having a porous silicon layer that can be manufactured using a surface micromachining technique according to a second embodiment of the present invention.

FIG. 6C is a diagram illustrating a structure of a flow rate detecting element of a membrane structure that can be manufactured using a bulk micromachining technique according to a third embodiment of the present invention. FIG.

FIG. 6D illustrates a structure of a flow rate detection device having a membrane structure having a porous silicon layer that can be manufactured using a bulk micromachining technique according to a fourth embodiment of the present invention.

FIG. 6E illustrates a structure of a flow rate detection device having a membrane structure in which a silicon layer is formed over an entire semiconductor substrate that can be manufactured using a bulk micromachining technique according to a fifth embodiment of the present invention.

7A is a perspective view illustrating a state in which a flow rate detecting element is installed in a flow rate detecting element holder in a thermopile flow rate sensor according to an exemplary embodiment of the present invention.

It is a longitudinal cross-sectional view which shows the state which installed the flow rate detecting element in the flow rate detecting element holder.

8 is a view showing the flow of the measured fluid in the thermopile flow rate sensor according to an embodiment of the present invention.

9A to 9B are diagrams illustrating still another embodiment in which a flow rate detecting element is installed in a flow rate detecting element holder in a thermopile flow rate sensor.

<Explanation of symbols for the main parts of the drawings>

1: Thermopile Flow Rate Sensor

10: working fluid 20: measured fluid

100: main flow passage 200: measurement flow passage

210: measuring flow passage support portion 220: first curved flow path

230: second curve flow path 240: mesh

250a, 250b, 250c, 260: flow hole

300: flow rate detection element

310: Thermopile for heating or temperature measurement

320: semiconductor substrate 321, 322: flow path

330: Cavity 340: Membrane

350: insulating film 360: pattern protective film

370: lead wire 375: contact pad

380: porous silicon layer

400: control circuit 401: waveform generator

410: control circuit case 420: electrical connector

510: flow rate detection element holder 512: flow rate detection element storage

514: die bonding unit 520: control circuit lead

522: circuit connecting line 530: interfacing connector

Claims (24)

A heating unit made of at least one heating thermopile using a resistance of the thermopile as a heating element and dissipating heat; And Comprising at least one temperature measurement thermopile and at least two temperature sensing unit installed on the upstream or downstream side around the heating unit, And a flow rate detecting element measuring a flow rate and a flow rate of the measured fluid by measuring a temperature change of the measured fluid due to heat emitted from the heating part. The method of claim 1, The heat generating thermopile and the temperature measuring thermopile are thermoelectric materials including a polysilicon doped with a metal thin film or impurity made of at least one of platinum, ruthenium, tungsten, titanium, aluminum, gold, copper, chromium and nickel. Flow velocity detection element. The method of claim 1, A semiconductor substrate having a cavity formed therein; And An insulating film covering the semiconductor substrate to form a membrane; The heat generating thermopile and the temperature measuring thermopile are disposed on the insulating film by using a micromachining technique or coated by sputtering, and are coated with at least one layer of pattern protection layer. . The method of claim 3, wherein The heat generating thermopile and the temperature measuring thermopile are made of a CMOS compatible material, and may be multiplexed using a CMOS suitable process of coating the insulating film on the insulating film formed on the semiconductor substrate by the micromachining technique. Arranged flow rate detection element. The method of claim 3, wherein Flow rate detection device for adjusting the weight of the temperature distribution according to the position by adjusting the position of the temperature measurement point of the temperature measurement thermopile. The method of claim 3, wherein The cold junctions of the temperature measuring thermopile are disposed on the semiconductor substrate and the hot junctions are disposed on the membrane to adjust the weight of the temperature distribution according to the position by changing the position of the temperature measurement point according to the temperature distribution on the insulating film. Flow rate detection element. The method of claim 3, wherein And a cold contact point and a hot contact point of the temperature measuring thermopile on the membrane to adjust the weight of the temperature distribution according to the position by changing the position of the temperature measurement point according to the temperature distribution on the insulating film. The method of claim 3, wherein And a temperature compensator configured to measure a temperature at an inlet or outlet of the measured fluid and correct a temperature change of the measured fluid. The method of claim 3, wherein The heating unit is a flow rate detection element capable of temperature control in the form of heat of an arbitrary waveform (arbitrary waveform). The method of claim 9, And a flow rate detecting element controlling a heating cycle and a duty ratio of the heat generating shape of the arbitrary waveform. The method of claim 9, Detects the flow direction by using a change in electromotive force generated while the interface of the measured or heated heating fluid passes through the contact point of the heating thermopile by cutting off the power supply for a predetermined time while generating the arbitrary waveform. Flow rate detection element. The method of claim 9, And an additional terminal on both sides of the heating thermopile perpendicular to the flow direction of the measured fluid to form a resistor to measure the temperature at the side surface on the membrane. The method of claim 9, And an additional terminal on both sides of the heat generating thermopile perpendicular to the flow direction of the measured fluid to form a resistor to measure the temperature at the side surface on the semiconductor substrate. The method of claim 3, wherein And the heating part is controlled at a constant temperature. The method of claim 14, And a temperature detecting element measuring temperature by placing the temperature sensing unit on the membrane above the cavity. The method of claim 14, The heating unit is a flow rate detection element is controlled to a desired temperature distribution by adjusting the position of the temperature measuring point of the heat generating thermopile. The method of claim 14, And an additional terminal on both sides of the heat generating thermopile perpendicular to the flow direction of the measured fluid, to measure the temperature at the side surface on the semiconductor substrate. A main flow passage through which the working fluid flows; A measurement flow passage through which the measured fluid branched from the main flow passage flows; A flow rate detecting element installed in the measurement flow passage and measuring a flow rate of the measured fluid; And A control circuit for controlling a signal of the flow rate detecting element, The flow rate detecting element, A heating unit made of at least one heating thermopile using the resistance of the thermopile as a heating element and dissipating heat; And Comprising at least one temperature measurement thermopile and at least two temperature sensing unit installed on the upstream or downstream side around the heating unit, Thermopile flow rate sensor for measuring the flow rate and the flow rate of the measured fluid by measuring the temperature change of the measured fluid by the heat emitted from the heating unit in the temperature sensing unit. The method of claim 18, The flow rate detecting element, A semiconductor substrate having a cavity formed therein; And An insulating film covering the semiconductor substrate to form a membrane; The thermopile flow rate sensor, wherein the heat generating thermopile and the temperature measuring thermopile are deposited on the insulating film by using micromachining or coated by sputtering, and are covered with at least one layer of a patterned protective film. The method of claim 18, The control circuit, A thermopile flow rate sensor comprising a waveform generation source for supplying a control signal in a heat generating shape of an arbitrary waveform to the heat generating thermopile. The method of claim 20, The waveform generator can set the heat flux to an arbitrary waveform such as triangular wave, square wave, sawtooth wave, sine wave, etc. while adjusting the heating pattern of the heating thermopile to a period and duty ratio required by using a built-in program. Thermopile flow rate sensor. The method of claim 18, The measuring flow passage, A first curved path having at least two inflection points, A second curve path diverging from the first curve path, The flow rate detecting element is a thermopile flow rate sensor is installed on the upper end of the second curved path. The method of claim 22, Thermopile flow rate sensor is installed inclined mesh in the inlet portion of the second curved path branching from the first curved path. The method of claim 22, And at least one flow hole in a central portion of the first curved path and the second curved path.

Images