JP2019138780A - Heat type flow sensor - Google Patents

Abstract

A thermal flow sensor chip in which two temperature sensors having a small and simple structure with high sensitivity and high accuracy are arranged on a thin film 10 with a heater 25 for measuring the flow of a fluid to be measured, and a small size on which the thermal flow sensor chip is mounted. And an inexpensive thermal flow sensor, and the flow direction and type of the fluid to be measured can be specified.
A semiconductor thin film thermally separated from a substrate by a cavity is made into a bridge structure, a heater is arranged at the center of the thin film, and a heat resistance part is interposed on both sides in the flow direction across the heater. The thin film region A and the thin film region B are formed at symmetrical positions, and the first thermocouple 20A and the second thermocouple 20B are formed on the thin film region A and the thin film region B, respectively. The structure is connected in series, and the temperature difference signal is taken out as two terminals to the outside. The flow direction is specified from the positive and negative output voltages. A temperature variable means 250 is provided to change the temperature of the heater, and the type of fluid is specified by comparison with data prepared in advance regarding fluids having various thermal conductivities.
[Selection] Figure 1

Description

The present invention relates to a thermal type flow sensor that measures a flow such as a flow rate and a flow rate of a fluid that is a gas or a liquid. A thermal flow sensor chip that has a thin film thermocouple temperature sensor in the direction of flow on both sides of the heater, and a heater on the center of the thin film thermally separated from the substrate. Provided is a thermal flow sensor that is small, has a simple structure, is highly sensitive, and is inexpensive, and that can determine the direction and type of fluid.

Conventionally, it is a bridge structure that bridges the cavity formed in the substrate, and three thin film bridges suspended in the air thermally separated from this substrate are formed symmetrically along the groove, each of which is formed with a platinum thin film, There has been a gas flow sensor as a heat conduction type sensor using a thin film bridge in the center as a heater and thin film bridges on both sides as a temperature sensor (Patent Documents 1 and 2). This is because when there is no gas flow along the flow path, the temperatures of the thin film bridges on both sides that are symmetrical about the central heater are equal, but when there is a gas flow, As the cold gas flows, it cools, and on the downstream side, the temperature rises by receiving heat from the central heater thin film bridge. In this way, the gas flow causes a temperature difference between the thin film bridges on both sides of the heater, and this is a method for measuring the gas flow using this. However, since a resistance temperature sensor such as a platinum thin film is an absolute temperature sensor, the resistance itself corresponds to the absolute temperature. Therefore, in order to measure the temperature difference, it is necessary to prepare two absolute temperature sensors, and to obtain the difference between these outputs, and because the characteristics vary due to subtle differences in the shape of the resistance temperature sensor, the minute temperature The difference measurement was unsuitable for the large error.

Further, in the conventional thermal type flow sensor, in many cases, a platinum thin film is used as a heater and an absolute temperature sensor. Therefore, since a platinum film with a positive resistance temperature coefficient of a thin thin film is used as a heater, the temperature tends to concentrate at a location where the resistance is high, the wire is easily disconnected, and the change over time is large. Since the influence of the temperature is reflected as it is, it is difficult to correct the ambient temperature. In order to achieve this, many sensors and a temperature control system based on the sensors are required, and the flow sensor must be an expensive flow sensor.

In general, when a thin film suspended in the air for thermal separation from the substrate is used, the heated thin film is subjected to Newton's cooling law when the heating is stopped. It is cooled by releasing heat in proportion to the temperature difference (T-Tr) between the ambient temperature and the temperature T of the heated thin film, and finally becomes equal to the temperature of the substrate. In this way, the temperature of the heated object conducts heat to the surrounding medium, and the temperature rises or falls in relation to the heat transfer coefficient of the surrounding medium. In a heat conduction sensor used to measure a temperature change of a temperature sensor and measure a physical state of the surrounding medium, for example, a flow rate, a flow rate, a vacuum degree, an atmospheric pressure, etc., the substrate temperature that can be considered as the ambient temperature Tr The temperature difference from the temperature T of the heated thin film is more important than the absolute temperature. In this way, the temperature difference is measured by a thermocouple or thermopile, which is a small temperature difference sensor that outputs only the temperature difference, rather than the absolute temperature sensor such as a platinum resistor or thermistor. It is preferable because it can be measured with almost no exposure.

The inventor previously invented a gas flow sensor and an impurity concentration sensor using a thermocouple which is a temperature difference sensor (Patent Document 3). In addition, a sensing unit and a thermal flow sensor equipped with the sensing unit were invented as a temperature sensor that can measure only the temperature difference of the thermocouple (Patent Document 4). In these thermal type flow sensors, the heater has a cavity extending in the fluid flow direction, but the temperature sensor and the SOI thin film that protrudes like a cantilever using the side surface of the substrate along the flow direction of the cavity as a support portion. A heater was formed. And the cantilever-like thin film of the heater is arranged in the center, and the thermocouple is formed on both sides of the cantilever-like thin film that is formed on the upstream side and the downstream side of the flow. Since the cantilever-like thin film and the thin film on which the temperature sensor is formed are not connected except for the support portion, the heat from the cantilever-like heater (where a thermocouple can also be used as a heater) The thin film having temperature sensors arranged on the upstream side and the downstream side on both sides of the heater is heated only through an ambient fluid such as a gas to be measured. For this reason, the cantilevered thin film with the temperature sensor on the upstream side is cooled by the flow of the fluid, and the cantilevered thin film with the temperature sensor on the downstream side rises in temperature by receiving heat from the heater. It was possible to measure the flow of fluid with high sensitivity only by temperature. However, when the temperature of the surrounding fluid changes, the heat transfer coefficient of the fluid changes, and even if a thermocouple that is a temperature difference sensor is provided as a temperature sensor, due to the temperature dependence of the heat transfer coefficient of the fluid, Even if the heater is heated with the same power or heated to control the temperature difference from the same substrate, the temperature difference output varies depending on the temperature fluctuation of the fluid itself, and the temperature correction becomes complicated. was there. Of course, when the type of fluid is changed, the heat transfer coefficient differs, so that there is a problem that the influence of the type of fluid is large.

Conventionally, in order to measure the temperature difference before and after the heater due to the flow of fluid, in order to measure only the temperature difference, the thermopile is applied to the same thin film formed in the same cavity, and the heater is connected to the upstream side and the downstream side. There is a flow sensor in which the temperature dependence of the heat transfer coefficient of the fluid is reduced as a result (Patent Document 5). However, in these examples, since the thermopile was used to amplify the temperature difference output, the area of the sensor part had to be large, and in order to form many cold junctions, a diaphragm structure was used. As a result, it has been necessary to increase the bonding area with the substrate, so that the heat from the broken heater flows to the substrate side, resulting in a temperature drop and a temperature distribution in the temperature sensor region. there were.

Conventionally, in a thermal flow sensor, it is necessary to know in advance the type of fluid to be measured when measuring the flow velocity or flow rate of the fluid to be measured. In that case, a thermal flow sensor displayed using basic data such as a specific standard fluid to be measured (standard gas), for example, heat transfer coefficient of nitrogen gas at 20 ° C. and 1 atm in the case of gas. If the type of fluid to be measured is changed from the standard gas, the output values such as the flow velocity and flow rate of the sensor are changed using the known basic data such as the heat transfer coefficient at the temperature and pressure of the fluid to be measured. The output values such as flow velocity and flow rate of the thermal flow sensor were calibrated. In the measurement of the flow rate (for example, mass flow rate) of helium gas or hydrogen gas having a high heat transfer coefficient, the display is greatly deviated from the nitrogen gas as the standard gas, and it is necessary to calibrate it. This situation is the same for the thermal pressure sensor as a heat conduction sensor.Because the heat transfer coefficient of the fluid to be measured is involved in the measurement, know the type of gas of the fluid to be measured in advance and determine the output value. There was a need to calibrate. Thus, a heat conduction type sensor that can automatically calibrate without knowing in advance the type of gas of the fluid to be measured has been desired.

US004478077 Special Table 2004-514153 JP 2009-128254 A JP 2010-230601 A JP 2001-165731 A

The present invention has been made to solve the above-described problems, and is a thin film in which a heater (25) is arranged in measuring the flow (mainly the flow velocity or flow rate) of a fluid to be measured such as a gas or a liquid. (10) is equipped with a thermal flow sensor chip that has two small and simple temperature sensors with high sensitivity and high accuracy, and a thermal flow sensor chip with high sensitivity, small size, simple structure, and low cost. An object of the present invention is to provide a sensor and to specify the flow direction and type of a fluid to be measured.

In order to achieve the above object, in the thermal type flow sensor chip according to claim 1 of the present invention, the thin film 10 mainly composed of a semiconductor thin film thermally separated from the substrate 1 by the cavity 40 has a crosslinked structure. In addition, there is a heater 25 at the center of the thin film 10, and the same thin film 10 is passed from the heater 25 via the thermal resistance portion 45 on both sides of the flow of the fluid to be measured across the heater 25. The thin film region A and the thin film region B are formed at symmetrical positions, and the first thermocouple 20A and the second thermocouple 20A that use the thin film 10 as a common thermoelectric material in the thin film region A and the thin film region B. Each of the hot junctions 81A and the hot junctions 81B of the thermocouple 20B has a structure in which heat is received from the heater 25 and heated, and the first thermocouple 20A and the second thermocouple 20B are These temperatures There are connected in series so as to be able to detect, that they were taken out as external to the two-terminal, and is characterized in.

In the thermal type flow sensor chip of the present invention, a crosslinked structure is used as the thin film 10 that is thermally separated from the substrate 1. This is because if the thin film 10 is formed of a diaphragm, the heat conduction from the heater 25 to the substrate 1 is large, and the temperature of the thin film 10 is difficult to rise. If the cantilever type is used, the fluid to be measured is liquid. This is because even if it is a gas, if the flow rate is high, it is easily destroyed. On the other hand, the thin film 10 having a bridge structure allows heat to escape from the narrow support part mainly to the substrate 1 only slightly, but the heater temperature tends to rise, so that power consumption is small and both ends are supported. This is because the mechanical strength is also larger than that of cantilever.

A thin film region A and a thin film region B are formed in the same thin film 10 via a thermal resistance portion 45 at spatially symmetrical positions along the flow of the fluid to be measured with the heater 25 interposed therebetween. In the thin film region A, the hot junction 81A of the first thermocouple 20A is formed, and in the thin film region B, the hot contact 81B of the second thermocouple 20B is formed similarly. For example, when the Joule heater 25 is heated to about 50 ° C. and there is no flow of the fluid to be measured, the hot junction 81A and the hot junction 81B on both sides are heated equally through the thin film 10, so The contact 81A and the warm contact 81B originally reach the same temperature. Therefore, in such a case, for example, the first thermocouple 20A and the second thermocouple 20B formed in the base portion of the substrate 1 (the region excluding the cross-linking structure portion of the substrate 1) are common. The differential output of the first thermocouple 20A and the second thermocouple 20B to the cold junction 82 should be zero. Even if there is no flow of the fluid to be measured, if there is a structural shift in the position of the hot junction 81A and the hot junction 81B, the differential between the first thermocouple 20A and the second thermocouple 20B Since the output does not become zero, it is preferable to correct the output electronically.

For example, when an SOI (Silicon on Insulator) substrate is used as the substrate 1, a thin film 10 thermally separated from the substrate 1 made of an SOI layer, which is a single crystal silicon (Si) thin film, is converted into a known MEMS (Micro Electro Mechanical Systems) technology. Therefore, it can be formed easily. Since the SOI layer is a single crystal semiconductor of Si, this layer is preferably used as a main constituent film of the thin film 10.

The single crystal semiconductor of Si depends on its conductivity type (n-type or p-type) and its resistivity, but has a large Seebeck coefficient α as a thermoelectric material, for example, n-type, resistivity: 0.1 Ω · cm Then, it has a very large Seebeck coefficient α of about 1 mV / K. Therefore, rather than combining a thermocouple made of two metals as a thermoelectric material to form a thermopile, a single thermocouple using a single crystal semiconductor thin film of Si as one thermoelectric material is small and has high sensitivity. Therefore, an extremely small high-sensitivity temperature sensitive part can be formed.

In the first thermocouple 20A and the second thermocouple 20B, for example, a common SOI layer may be formed as one thermoelectric material in the same thin film 10 using the above-described SOI layer as a main material. it can. The same metal as the other thermoelectric material from the hot junction 81A and the hot junction 81B of the first thermocouple 20A and the second thermocouple 20B formed in the thin film region A and the thin film region B, respectively. For example, a nichrome (Ni—Cr) thin film is drawn out in ohmic contact with the SOI layer, and wired to the two electrode pads formed in the base region of the substrate 1 described above, and two terminals are externally provided. Can be taken out as. If it does in this way, the output voltage between each two electrode pads as two terminals will correspond to the temperature difference of the 1st thermocouple 20A and the 2nd thermocouple 20B.

The thermal type flow sensor chip according to claim 2 of the present invention is a case where an absolute temperature sensor is formed on the substrate 1.

For example, when the common cold junction 82 of the first thermocouple 20A and the second thermocouple 20B is formed in the base region of the substrate 1, the first thermocouple 20A and the second thermocouple 20B are formed. These outputs are outputs corresponding to only the temperature differences between the hot junction 81A and the hot junction 81B based on the temperature of the base region. For this reason, the heater temperature when the heater is heated and the absolute temperature of the hot junction 81A and the hot junction 81B cannot be measured. Thus, generally, when using a thermocouple, in order to know the absolute temperature of a hot junction, it is necessary to measure the absolute temperature of a cold junction, for example. Therefore, in the present invention, an absolute temperature sensor is formed on the substrate 1 (for example, the base portion). In this way, the absolute temperatures of the hot junction 81A and the hot junction 81B of the first thermocouple 20A and the second thermocouple 20B can be measured. Of course, if the thermocouple hot junction 81H is formed in the thin film 10 where the heater 25 is formed, the absolute temperature at the position of the heater 25 can be measured in the same manner. As an absolute temperature sensor, a pn junction diode, a thermistor, a platinum resistance temperature detector, or the like may be formed. The ambient temperature can be corrected by using the output of the absolute temperature sensor.

A thermal type flow sensor according to a third aspect of the present invention includes the thermal type flow sensor chip according to the first or second aspect, and the first flow generated by the flow of the fluid to be measured based on the heating of the heater 25. The temperature difference between the thermocouple 20A and the second thermocouple 20B is measured, and the flow of the fluid to be measured is measured using calibration data prepared in advance. It is.

The temperature of the thin film 10 floating in the air heated by the heater (thermally separated from the substrate 1 by the same cavity 40) varies in heat transfer coefficient depending on the temperature of the fluid to be measured and the type of the fluid. If the thermal properties of the fluid are not known in advance, a large error will occur in the flow velocity and flow rate, which are physical states of the fluid to be measured. Therefore, the temperature difference between the first thermocouple 20A and the second thermocouple 20B is previously tested using the fluid to be measured, and the thermal properties of the fluid to be measured, particularly the heat transfer coefficient at the temperature and pressure, are determined. It is necessary to prepare calibration data that can be calibrated on the basis of the data so that a correct measurement value can be obtained. This is calibration data prepared in advance. By obtaining calibration data using the thermal flow sensor of the same structure of the present invention, various effects that are theoretically difficult to predict are included in this calibration data, so it is important to use calibration data It is. Accordingly, it is preferable to incorporate calibration data including information such as a flow rate including the temperature dependence of the heat transfer coefficient of the fluid to be measured in the memory, and to incorporate calibration means 200 that calculates and displays using the measurement data. . If the flow rate of the fluid to be measured is measured with respect to the flow velocity, the flow rate can be calculated from the cross-sectional area of the flow path.

According to a fourth aspect of the present invention, there is provided a thermal type flow sensor, wherein, in the output voltage from the two terminals according to the first aspect, the output voltage in the state where the fluid to be measured does not flow is zero, and positive and negative. This is a case where the flow direction of the fluid to be measured is determined from the sign of the output voltage, and the flow velocity can be measured from the magnitude of the output voltage.

As described above, the first thermocouple 20A and the second thermocouple 20B are formed on the same thin film on both sides of the direction of the fluid to be measured with the heater 25 interposed between the heater 25 and the thermal resistance unit 45. 10, a thin film region A and a thin film region B are formed at symmetrical positions. The thin film region A should have a warm contact point 81A and the thin film region B should have a warm contact point 81B at a symmetric position from the heater 25. Even if there is no flow of the fluid to be measured, a slight temperature difference may occur, and the output voltage may not become zero. In such a case, it is preferable to provide a correction circuit that sets the output voltage to zero in a state where there is no flow of the fluid to be measured so that the output voltage is forcibly set to zero.

Since there are the hot junction 81A and the hot junction 81B at symmetrical positions on both sides of the flow direction of the fluid to be measured across the heater 25, the upstream hot junction is cooled with respect to the heater 25, and the downstream hot junction is Be warmed up. Thus, for example, when the hot junction 81A is arranged on the upstream side and the hot junction 81B is arranged on the downstream side, the hot junction 81A is cooled and the hot junction 81B is heated, so that the common thin film The difference in output voltage as two terminals of the first thermocouple 20A and the second thermocouple 20B using 10 SOI layers as one thermocouple material (from the output voltage of the first thermocouple 20A to the second thermocouple The output voltage of 20B is subtracted when the thin film 10 is an n-type SOI layer. Conversely, when the flow direction is changed, the difference in output voltage between the two terminals in the above configuration is as follows. , Become positive. In this way, the direction (orientation) of the flow of the fluid to be measured can be checked based on the sign of the difference between the output voltages at the two terminals.

According to a fifth aspect of the present invention, there is provided a thermal type flow sensor, wherein the output voltage from the two terminals according to the first aspect is connected to a non-inverting input terminal of an operational amplifier, and a variable resistor is connected to the inverting input terminal of the operational amplifier. This is a case in which the measurement range of the flow velocity of the fluid to be measured can be expanded by connecting and switching the variable resistor to a predetermined resistance value.

I would like to expand the measurement range of the flow velocity as the flow of the fluid to be measured using one thermal flow sensor. One of them is switching of the amplification factor in the signal amplification circuit. In order to measure an extremely small flow velocity, amplification with high sensitivity and a high S / N ratio is necessary, and it is better to obtain a predetermined amplification factor that does not depend on the internal resistance of the thermal flow sensor. In the present invention, when an operational amplifier having a high input impedance is used and the output voltage from the two terminals is inserted between the ground E of the amplifier circuit and the non-inverting input terminal of the operational amplifier, the operational amplifier is connected between the input terminals. Is equivalently equipotential, the output voltage from the two terminals is directly applied to the variable resistor r connected to the inverting input terminal of the operational amplifier, and the current flowing through the variable resistor r is the variable resistor r. It is determined only by r and the output voltage from the two terminals. Therefore, under the same feedback resistor Rf of the operational amplifier, the gain of the signal amplifier circuit is changed by changing the value of the variable resistor r, and this variable resistor is switched, for example, by one digit. In this case, the amplification factor changes by one digit. For example, when the feedback resistor Rf is 10 kΩ and the variable resistor r is 100Ω, the amplification factor A of the amplifier circuit is Rf / r = 100, and the output voltage from the two terminals is amplified 100 times. Become.

The thermal type flow sensor according to claim 6 of the present invention is provided with temperature variable means 250 for changing the heating temperature of the heater 25, and the heater 25 is heated while the flow of the fluid to be measured is stopped. The temperature can be changed to various predetermined temperatures using the temperature variable means 250, the output voltages at the various predetermined temperatures of the first thermocouple 20A and the second thermocouple 20B, and the predetermined temperature. The type of the fluid to be measured can be specified by using data prepared in advance regarding the thermal conductivity of each of a plurality of predetermined fluids corresponding to the above.

In general, the thermal conductivity k of a fluid is a function of temperature and increases with increasing temperature. If there is no flow of the fluid to be measured, the heat transfer coefficient h is determined as a function of the type of fluid to be measured, its temperature and pressure (eg, atmospheric pressure). Further, the temperature rise of the micro thin film provided with the temperature sensor is such that if the distance between the heater 25 and the temperature sensor is fixed, the temperature of the heater, the heat conduction through the thin film 10, and the temperature of the fluid to be measured And the heat transfer coefficient at pressure. However, the heat transfer coefficient is a function of the velocity of the fluid, but it has been found that when the velocity is zero, it is simplified and proportional to the thermal conductivity, an inherent property of the fluid. Therefore, if the distance between the heater and the temperature sensor is fixed, the temperature and pressure of the fluid to be measured are known, and if the heater temperature is measured by some method, the temperature rise of the temperature sensor is calculated. By measuring in the absence of flow, the thermal conductivity of the fluid under measurement at that time is determined. In this way, the data prepared experimentally in advance and the measurement data of the unknown fluid to be measured are compared, and from the situation of coincidence with the data of the known fluid having the same temperature dependence, The type of fluid to be measured such as gas can be identified (specified).

For the same heater supply power at the same ambient temperature, information on the thermal conductivity of the fluid under measurement at that ambient temperature can be easily obtained. However, the thermal conductivity of the fluid to be measured is temperature-dependent, and if the ambient temperature changes, the thermal conductivity changes accordingly. Although the ambient environment temperature can be adjusted with an external heater, in the present invention, the temperature of the fluid to be measured in the vicinity of the heater 25 is changed by changing the heating temperature using the temperature variable means of the heater 25 without using the external heater. Also change. At this time, the temperature of the thin film 10 heated by the heater 25 is measured by the temperature sensor 20H formed therein, the temperature dependency of the thermal conductivity of the fluid to be measured is obtained, and the temperature dependency is utilized. Thus, the type of fluid to be measured can be specified.

Since the thermal flow sensor chip of the present invention is the thin film 10 having a bridge structure that is thermally separated from the substrate 1 by the same cavity 40, the strength of the cantilever type with respect to the flow of the fluid to be measured is large. In addition, the temperature detection has an advantage of higher sensitivity than the diaphragm type.

Since the thermal type flow sensor chip of the present invention uses a thermocouple, the temperature sensitive part only needs to be a hot junction, so an extremely small sensor chip can be achieved with respect to the thermopile type of similar temperature difference detection. A highly accurate and inexpensive sensor can be provided.

Since the thermal flow sensor chip of the present invention can use a semiconductor thin film as a main constituent film as the thin film 10, the value of the Seebeck coefficient α is an order of magnitude larger than that of a metal, which is one of the thermocouples common to the thermocouple. A thermal type flow sensor chip that can be used as a material, is small, has high sensitivity and high accuracy, and is inexpensive can be provided.

In the thermal type flow sensor chip of the present invention, the first thermocouple 20A and the second thermocouple 20B are connected in series so that the temperature difference between them can be detected. Since the output voltage difference related to the temperature difference at the position of each of the hot junction 81A and the hot junction 81B of the thermocouple 20B is taken out as two terminals to the outside, a differential output voltage based on the temperature difference between the hot junction 81A and the hot junction 81B is obtained. There is an advantage that it can be directly input to the amplifier and has a very simple configuration.

Since the thermal flow sensor chip of the present invention forms an absolute temperature sensor on the substrate 1, each thermocouple 20A, second thermocouple 20B, etc., which are thermocouples for measuring flow velocity, are combined with each other. The absolute temperature can be measured. Moreover, since the board | substrate 1 can also be regarded as substantially ambient temperature, ambient temperature can also be measured.

In the thermal type flow sensor of the present invention, as described above, the hot junction 81A and the hot junction 81B are symmetrically arranged on both sides in the flow direction of the fluid to be measured with respect to the position of the heater 25 at the center. There is an advantage that the direction of the flow of the fluid to be measured can be detected by the positive / negative sign of the two-terminal output as the output voltage difference with respect to the temperature difference at the position.

The thermal type flow sensor of the present invention has an advantage that a variable resistance is connected to the inverting input terminal of the operational amplifier and the size thereof is adjusted, so that the measurement range of the flow velocity of the fluid to be measured can be easily expanded. Garage.

Since the thermal type flow sensor of the present invention includes the temperature variable means 250 that changes the heating temperature of the heater 25, data prepared in advance regarding the thermal conductivity of each of a plurality of predetermined fluids corresponding to the predetermined temperature. This is advantageous in that it is possible to specify the type of unknown fluid to be measured.

It is the plane schematic of one Example of the heat flow sensor chip | tip of this invention. Example 1 It is the cross-sectional schematic in the XX line of FIG. Example 1 It is the plane schematic of another Example of the heat flow sensor chip | tip of this invention. (Example 2) It is the plane schematic of another Example of the heat flow sensor chip | tip of this invention. (Example 3) It is a block diagram of a composition outline of one example of a thermal type flow sensor of the present invention. (Example 1), (Example 3), (Example 4) It is the schematic of one Example of the operational amplifier circuit containing the mode of the input of the output voltage taken out from the heat flow sensor chip of this invention outside. Example 1

  The thermal flow sensor chip of the present invention can be formed on a silicon (Si) substrate that can also create an integrated circuit (IC) using mature semiconductor integration technology and MEMS technology. The thermal flow sensor chip is manufactured using an SOI substrate, which is a silicon (Si) substrate, and a thermal flow sensor on which the thermal flow sensor chip is mounted will be described in detail below based on an embodiment with reference to the drawings.

FIG. 1 is a schematic plan view showing an embodiment of the thermal flow sensor chip of the present invention, and FIG. 2 is a schematic cross-sectional view taken along the line XX. In this embodiment, an n-type SOI substrate (thickness: 500 μm, SOI layer 12 thickness: about 10 μm, BOX layer 13 thickness: about 1 μm) is used as the semiconductor silicon substrate 1 as the thermal flow sensor chip of the present invention. This is the case. This SOI layer 12 is formed into a thin film 10 having a crosslinked structure 14 thermally separated from the substrate 1, and a heater 25 made of a nichrome (Ni—Cr) film is provided at the center of the thin film 10 of the crosslinked structure 14. It extends to the end of the heat flow sensor chip along the length direction. For example, the cross-linked structure 14 has a length of about 2 mm and a thickness of about 10 μm, and a narrow width of about 0.5 mm. Near the end of the base portion of the substrate 1 (the base portion of the substrate 1), electrode pads 70a and 70b for heating the heater 25 are formed by photolithography. Further, in the vicinity of the center of the bridging structure 14 of the thin film 10, symmetrical positions in the same thin film 10 from the heater 25 through the thermal resistance portion 45 on both sides of the flow of the fluid to be measured with the heater 25 interposed therebetween. A thin film region A48 and a thin film region B49 are formed. And in these thin film area | region A48 and thin film area | region B49, each hot junction 81A of the 1st thermocouple 20A and the 2nd thermocouple 20B which are temperature difference sensors which used the SOI layer of the thin film 10 as a common thermoelectric material, The hot junctions 81B are arranged at symmetrical positions, and the hot junctions 81A and 81B, together with the thin film region A48 and the thin film region B49, receive heat from the heated heater 25 and are heated. ing. The first thermocouple 20A and the second thermocouple 20B are composed of the common cold junction 82, the hot junction 81A, and the hot junction 81B, respectively, as one thermoelectric material 120a, and the SOI layer of the thin film 10. 12 and the other thermoelectric material 120b are configured to use a nichrome (Ni—Cr) film which is a material of the heater 25. The other ends of the thermoelectric materials 120b of the first thermocouple 20A and the second thermocouple 20B are heated so as to have the same temperature as the electrode pad 72c of the common cold junction 82 as the electrode pad 71a and the electrode pad 71b, respectively. The base portions of the substrate 1 of the flow sensor chip are arranged close to each other. In this embodiment, the absolute temperature sensor 21 is formed on the base portion of the substrate 1, and in this embodiment, a pn junction diode is formed.

In general, when differential amplification is performed using two thermocouples, the respective thermocouples are connected in series, and the connection point connected in series is connected to the ground E of the differential amplifier circuit. The remaining terminals at the ends are connected to the two input terminals of the differential amplifier circuit for differential amplification. In the heat flow sensor chip of the present invention, the SOI layer 12 of the common thin film 10 is in series as one common thermoelectric material 120a of the first thermocouple 20A and the second thermocouple 20B, which are two thermocouples. In order to perform differential amplification, it is not necessary to connect this point to the ground E of the differential amplifier circuit, and each of the remaining two other thermocouple materials via the thermoelectric material 120b of the above two thermocouples. One of the features is that only the electrode pad 71a and the electrode pad 71b, which are the terminals, are taken out as two terminals to the outside.

The heat flow sensor chip of the present invention is formed as follows, for example. Since the SOI substrate 12 as the substrate 1 has a BOX layer 51 as a buried insulating layer below the SOI layer 12, for example, in an aqueous solution of hydrazine, which is an alkaline etchant, an SOI layer made of single crystal silicon. 12 and the underlying substrate 2 are dissolved (etched), but the BOX layer 51 is not etched, so that a crosslinked structure 14 is formed which is a thin film structure composed of a thin film 10 suspended in the air that is easily thermally separated from the substrate 1. it can. By utilizing this technique, the SOI layer 12 of the thin film 10 on which the first thermocouple 20A and the second thermocouple 20B, which are one heater 25 and the temperature sensor 20, are formed is used as a main constituent material. Further, the slit 41 is formed by anisotropic etching from the SOI layer 12 side, and the cavity 40 is formed by anisotropic etching from the back surface of the substrate 1. At this time, the thin film 10 as a protected region surrounded by the silicon oxide film 50 and the BOX layer 51 is formed as a thin film floating in the air, and the bridge structure 14 having support portions on the substrate 1 on both opposite sides of the cavity 40 is formed. It is formed with.

The heater 25, the thermoelectric material 120b, and the electrode pads 70, 71, 72, etc. are made of a nichrome (Ni—Cr) film that is difficult to be thermally oxidized, is stable and has a high resistivity, and is formed by a sputtering method with high adhesion strength. ing. In addition, the nichrome thin film is advantageous because it can withstand the alkaline etchant of the thermoelectric materials 120a, 120b and the electrode pads 70, 71, 72, etc. Of course, without using an alkaline etchant, the cross-linked structure 14, the slit 41, the cavity 40, and the like can be formed by known dry etching. At that time, if it is covered as a mask with a photoresist or the like, the material selection of the thermoelectric material and the electrode pad becomes easy. The manufacturing process related to the patterning of the heat flow sensor chip described above can be performed by a well-known MEMS technology using photolithography.

In this embodiment, two thin film regions A48 and B49 are formed at symmetrical positions from the heater 25 disposed in the center of the thin film 10 so that the thermal resistance portion 45 is formed by the slit 41. The heat from the heater 25 is equally transmitted to the two thin film regions A48 and B49, and the positions of the hot junction 81A and the hot junction 81B formed in these are also formed at symmetrical positions from the heater 25. Therefore, when there is no flow of the fluid to be measured, the hot junction 81A and the hot junction 81B are heated to the same temperature. Therefore, in the state where there is no flow of the fluid to be measured, the thermoelectromotive forces of the two first thermocouples 20A and the second thermocouple 20B are equal, and the output voltage difference between them is essentially zero. The output voltage between the two terminals of the electrode pad 71a and the electrode pad 71b for extracting the difference between these output voltages becomes zero.

The operation of the heat flow sensor of the present invention will be described as follows with reference to FIGS. 1 and 2 of this embodiment of the heat flow sensor chip. An electric current is passed through the heater 25 provided in the thin film 10 to heat in a measured fluid, for example, a known gas such as air, under no flow, at room temperature (for example, 20 ° C.), and at atmospheric pressure (1 atm). Expose the mold flow sensor chip. When the heater 25 is driven at a predetermined power, for example, 30 [mW], the temperature of the heater 25 rises. The temperature rise at that time is the first thermocouple 20A shown in FIG. Using either one of the two thermocouples 20B, it is possible to know roughly. For example, by measuring the potential difference between the electrode pad 71a which is an external output terminal of the first thermocouple 20A and the common electrode pad 72c, the same thermoelectric as the SOI layer 12 of the thin film 10 which has been experimentally prepared in advance. The substrate 1 of the thermal type flow sensor chip based on the calibration data of the relationship between the thermoelectromotive force and the temperature using the thermocouple composed of the thermoelectric material 120b of the same nichrome (Ni—Cr) film as the material 120a. And the temperature difference ΔTa (the temperature rise from the substrate 1) between the first thermocouple 20A and the hot junction 81A can be obtained. Further, since the substrate 1 uses a pn junction diode as the absolute temperature sensor 21, the absolute temperature sensor 21 also has a temperature dependence of the forward voltage Vf under a predetermined forward current obtained experimentally in advance. The temperature Ts of the base portion of the substrate 1 can be known from the calibration data. In this way, the absolute temperature Ta of the hot junction 81A is represented by the sum of the temperature Ts of the substrate 1 and the above temperature difference ΔTa due to heater heating. For example, since the temperature difference ΔTa is about 50 ° C. due to the heater heating of the 30 [mW] heater 25, for example, if the room temperature Tr is set to 20 ° C., the room temperature Tr is substantially equal to the temperature Ts. If this is the case, the absolute temperature Ta of the hot junction 81A is about 70 ° C., and if expressed in absolute temperature, it is about 343K.

As shown in FIG. 1, when the first thermocouple 20A side is the upstream side of the fluid to be measured with respect to the heater 25 of the thermal type flow sensor chip 100, the heater-heated thin film region A48 on the upstream side. The thin film region A49 heated by the heater on the downstream side is somewhat cooled by the flow of the fluid to be measured, but is exposed to the fluid to be measured warmed by the heater 25, so that it is exposed to the thin film region A48 on the upstream side. In comparison, the temperature is increased. Since this phenomenon is caused by the flow of the fluid to be measured, when the flow velocity V of the fluid to be measured is zero, the temperature between the hot junction 81A and the hot junction 81B formed in the thin film region A48 and the thin film region A49. The difference ΔTab increases almost linearly from zero with the flow velocity V of the fluid to be measured. However, it becomes saturated as the flow velocity V increases. This can also be derived from King's law that the amount of heat Q _f taken away from a heated object in a flowing fluid is proportional to the fluid's velocity V to the half power. Therefore, in the thermal type flow sensor of the present invention, as shown in FIG. 1, the thermal type flow sensor chip 100 is directly exposed to the flow velocity V of the fluid to be measured so that the thin film region A48 is on the upstream side. The electrode pad 71a and the electrode pad 71b are connected between a non-inverting input terminal of a differential amplifier circuit such as an operational amplifier (OP amplifier) and the ground E, and amplified with a desired amplification factor. The output voltage may be taken out, for example, calculated using calibration data prepared experimentally in advance and displayed as a flow velocity or a flow rate. The heater heating may be always driven with a predetermined constant power consumption such as 30 mW. For example, regardless of the flow velocity V of the fluid to be measured, the temperature of the upstream thin film region A48 is set to a predetermined temperature, for example, 50 The heater 25 is driven by the control circuit such as maintaining a constant value such as ° C, or maintaining the temperature difference ΔTa between the substrate 1 and the thin film region A48, for example, a constant value of 30 ° C. You can also. In this case, the output voltage of the first thermocouple 20A (the output voltage between the electrode pad 71a and the electrode pad 72c) is extracted and amplified.

In FIG. 5, the block diagram of the structure outline | summary of the thermal type flow sensor of this invention is shown. As shown in the block diagram, for example, the room temperature Tr is 20 ° C., and the control circuit shown in FIG. 5 enables control of a predetermined temperature rise of the heater 25, predetermined power supply control, and heating temperature control of the heater. However, here, for example, a case where the heater 25 is driven at a constant power consumption of 30 mW is shown. When the flow rate V of the air as the fluid to be measured is zero, the thin film region A48 and the thin film region A49 are heated at a flow rate V = 5 (sccm) when the temperature of the thin film region A48 and the thin film region A49 is increased by ΔTa = 50 ° C. The temperature of the contact 81A is lowered by about 0.5 ° C., and the hot contact 81B is raised by about 0.5 ° C. Therefore, the temperature difference ΔTab between the hot junction 81A and the hot junction 81B is about 1 ° C., and the difference output voltage between the first thermocouple 20A and the second thermocouple 20B based on this is the thermal flow. An output voltage is output to the outside from the electrode pad 71a and the electrode pad 71b which are two terminals of the output of the sensor chip 100. This output voltage is input to the amplifier circuit shown in FIG. 5, and the calibration data prepared in advance as described above is taken in, and the arithmetic circuit corrects the influence of the type of fluid to be measured and the influence of the temperature (calibration). ), And the true values of the gas flow velocity and flow rate are sent to the display unit for display. What is necessary is just to adjust the amplification factor of an amplifier circuit so that the output voltage of a desired magnitude | size can be obtained with a variable resistance circuit. 6 shows the variable resistance circuit 150, the electrode pad 71a that is the two terminals of the output of the thermal type flow sensor chip 100, and the state of input of the output voltage from the electrode pad 71b to the outside. A schematic diagram of an operational amplifier circuit as an example is shown. The output from the two terminals of the output of the thermal type flow sensor chip 100 is input to the non-inverting input terminal of the operational amplifier circuit, and the variable resistance circuit 150 is connected to the inverting input terminal. The plurality of variable resistors r1, r2,... Rk of the variable resistor circuit 150 are switched by the changeover switch 310. For example, when r1 is selected, the amplification factor A = (feedback resistor Rf) of the operational amplifier circuit / (Variable resistance r1), so that when the feedback resistance Rf = 100 kΩ and r1 = 100Ω, the amplification factor A = 1000, and the temperature difference signal is output from the two terminals of the output of the thermal type flow sensor chip 100 described above. The voltage is amplified 1000 times. Of course, in addition to the operational amplifier circuit, an amplifier circuit at the subsequent stage may be provided to amplify the signal voltage necessary for driving a liquid crystal display or the like.

FIG. 3 is a schematic plan view showing another embodiment of the thermal flow sensor chip of the present invention, and the operation and effect are substantially the same as those of FIG. The major difference between FIG. 1 of the embodiment and FIG. 3 of the present embodiment is that the thin film region A48 and the thin film region A49 in FIG. 1 of the embodiment are near the center of the bridging structure 14 of the thin film 10 and the thermal resistance by the slit 41. This is the case where the structure protrudes outward in the shape of a cantilever through the portion 45. For this purpose, the electrode pad 71a and the electrode which are two terminals of the output from the hot junction 81A and the hot junction 81B of the thermal type flow sensor chip 100 are used. Two thermoelectric materials 120b extending to the pad 71b are formed through a region where the bridge structure 14 of the thin film 10 is narrow. On the other hand, in the thermal flow sensor chip shown in FIG. 3 of the second embodiment, the thin film region A48 and the thin film region A49 are also formed into the bridge structure 14, and the new thin film region A48 and the thin film region A49 Two thermoelectric materials 120b extending from the hot junction 81A and the hot junction 81B to the electrode pad 71a and the electrode pad 71b are formed through the bridging structure 14 portion. Since the thin film region A48 and the thin film region A49 in FIG. 1 of the embodiment are in a cantilever shape, if the cantilever shape is bent so as to be slightly bent, the resistance increases as the flow velocity V of the fluid to be measured increases. Although the thin film region A48 and the thin film region A49 are easily broken, the thin film region A48 and the thin film region A49 are further provided with support portions by forming the thin film region A48 and the thin film region A49 in the crosslinked structure 14 as in the second embodiment. At the same time, warping becomes difficult, so it is difficult to be destroyed. However, since the heat easily escapes to the substrate 1 accordingly, the heat from the heater 25 easily escapes, the thin film region A48 and the thin film region A49 are difficult to increase in temperature, and the power consumption increases. Depending on the type and the measurement range of the flow velocity V, the shape shown in FIG. 1 of the first embodiment or the shape shown in FIG. 3 of the second embodiment may be determined.

As the heat flow sensor of the present invention, the heat flow sensor chip of the present invention as shown in FIG. 3 is used in the same manner as described in the first embodiment. Is omitted.

FIG. 4 is a schematic plan view showing another embodiment of the thermal flow sensor chip according to the present invention, which is the same as FIG. 3 in the second embodiment, but is different from the second embodiment in FIG. In FIG. 3 of Example 2, since the thermocouple for measuring the temperature near the center of the bridge structure 14 of the thin film 10 is not arranged, the temperature measurement near the heater 25 near the center of the bridge structure 14 cannot be directly measured. The thermometer 100 and the heater 25 are formed using the hot junction 81A and the hot junction 81B respectively formed in the thin film region A48 and the thin film region A49 formed from the vicinity of the center of the bridging structure 14 via the thermal resistance portion 45. The temperature was controlled. On the other hand, in the embodiment of FIG. 4 shown in the third embodiment, the thermocouple 20H of the heater portion is also provided in the vicinity of the heater 25 near the center of the bridging structure 14, so that The biggest difference from FIG. 3 of the second embodiment is that the temperature in the vicinity of the center of the bridge structure 14 that becomes high can be directly measured. The temperature measurement in the vicinity of the heater 25 near the center of the bridge structure 14 is exactly the same as the temperature measurement in the thin film region A48 and the thin film region A49 by the first thermocouple 20A and the second thermocouple 20B. Temperature measurement of the thin film region A48 and the thin film region A49 from the output voltage between the electrode pad 71h for extracting the output voltage of the thermocouple 20H and the electrode pad 72c of the common cold junction 82 formed on the substrate 1. Similarly, the temperature at the location of the hot junction 81H of the thermocouple 20H of the heater portion can be measured using calibration data for thermocouple prepared in advance. Then, using the thermocouple 20H of the heater unit, for example, the heater 25 is driven at a constant power consumption of 30 mW or the temperature in the vicinity of the heater 25 is combined with the control circuit shown in FIG. It is also possible to drive the heater 25 so that the temperature at the contact 81H is maintained at a desired constant value, for example, 55 ° C.

Another difference between FIG. 3 of the second embodiment and FIG. 4 of the third embodiment is that in FIG. 4, the calibration circuit means 200 not depicted in FIG. 3 of the second embodiment is replaced with the thermal flow sensor chip of the present invention. It is a case where it is mounted on. It is not always necessary to mount the calibration circuit means 200 on the thermal type flow sensor chip, and the thermal type flow sensor may be configured by attaching it to the outside. However, here, since the substrate 1 has the SOI layer 12, an IC manufacturing technique is incorporated for compactness and mounted on the same thermal type flow sensor chip. Of course, this calibration circuit means 200 can also be mounted in FIGS. 1 and 3 of the above embodiment. The calibration circuit means 200 includes an amplifier circuit 210, an arithmetic circuit 220, and a control circuit 230. The amplifier circuit, arithmetic circuit, and control circuit shown in FIG. 5 are the thermal type shown in FIG. It can be considered that it is mounted on the flow sensor chip. In the calibration circuit means 200, the output voltage related to the flow rate and flow rate of the fluid to be measured from the electrode pad 71a and the electrode pad 71b, which are two terminals of the output from the hot junction 81A and the hot junction 81B, is supplied to the amplifier circuit 210 and the arithmetic circuit 220. A signal, an output signal relating to the temperature of the hot junction 81H of the thermocouple 20H of the heater part, an output signal from the absolute temperature sensor 21 relating to the temperature of the substrate 1, etc. are sent out and processed, and the influence of the type of fluid to be measured, temperature Correct (calibrate) the effects of. In the control circuit 230, control for a predetermined temperature rise of the heater 25, predetermined power supply control, and heater heating temperature control can be performed. Since the operation of the thermal type flow sensor is the same as that of the above embodiment, its detailed description is omitted.

The heat flow sensor of the present invention has been found to have a simple composition such as air, nitrogen gas, hydrogen gas, oxygen gas, argon gas, etc., but even if it does not know which gas is flowing, the fluid to be measured As the gas, the absolute temperature measurement, the type of the fluid to be measured can be specified using the thermal type flow sensor chip in the first to third embodiments in the state where there is no flow of the fluid to be measured. . For example, nitrogen gas is used as the standard gas. The gas of the fluid to be measured is different from the standard nitrogen gas in that the thermal conductivity λ is different, and the temperature dependence of the thermal conductivity λ of the gas to be detected, which is the fluid to be measured, is also different. The amount of heat transfer per unit area, unit temperature, and unit time is called the heat transfer coefficient h, and the heat transfer amount Q [W] from the object with the surface temperature Tw to the fluid temperature Ta is the surface temperature Tw and the fluid temperature Ta. Is expressed by Newton's law of cooling, which is proportional to the temperature difference between and the heat transfer coefficient h. The heat transfer coefficient h becomes simple when there is no gas flow, and is proportional to the thermal conductivity λ of the gas of the fluid to be measured. Therefore, the temperature of the gas to be detected is measured by the absolute temperature sensor 21 mounted on the thermal type flow sensor chip, and the temperature of the gas to be detected is a schematic diagram of the configuration of the thermal type flow sensor shown in the first embodiment. 5 is combined with the temperature variable means 250 and the control circuit 230, and by heating the heater 25, for example, the temperature in the vicinity of the heater 25 is changed from a room temperature Tr to about 100 ° C. The temperature, for example, the temperature measurement data of the thin film region A48 of the first thermocouple 20A at a temperature from 20 ° C. at room temperature Tr to about 100 ° C. at intervals of 5 ° C. Compared with acquired data on the same multiple temperatures, such as air, nitrogen gas, hydrogen gas, oxygen gas, argon gas, etc., including standard gases, gases that show the same temperature dependence pattern In Succoth, it is possible to identify the unknown of the detected gas. Then, the flow velocity V and the flow rate value of the specified gas to be detected can be calibrated by comparison with calibration data prepared in advance using the standard gas nitrogen gas of the fluid to be measured.

In the above description, the temperature in the vicinity of the heater 25 is the data for measuring the temperature of the thin film region A48 of the first thermocouple 20A at each of a plurality of predetermined temperatures from room temperature Tr to about 100 ° C. Then, the temperature may be measured when it is considered that temperature saturation has occurred, or the heating of the heater 25 is stopped, and the thin film region A48 where the first thermocouple 20A is arranged in the unknown gas to be detected is provided. It is also possible to identify an unknown gas to be detected (a known gas, a gas whose thermal characteristics are known) by comparing the pattern shape of the temperature characteristics over time in the cooling process when cooling. A gas having a large thermal conductivity λ such as hydrogen gas has a small thermal time constant τ and is quickly cooled. However, a gas having a small thermal conductivity λ such as argon gas has a large thermal time constant τ and has a similar exponent. It is functional but cools slowly. In the above description, the temperature measurement with the first thermocouple 20A is taken as an example, but the second thermocouple 20B may be used, and depending on the case, the temperature measurement in the vicinity of the heater 25 may be performed with the thermocouple 20H of the heater unit. Further, in the above description, the fluid to be measured is limited to gas, but the liquid to be detected is also unknown by using data such as the standard liquid setting and the temperature dependence of the thermal conductivity λ of the known liquid. This can be handled in the same manner as in the case of gas.

The thermal type flow sensor chip and the thermal type flow sensor of the present invention are not limited to this embodiment, and naturally, various modifications can be made while the gist, operation and effect of the present invention are the same.

Since the thermal type flow sensor chip of the present invention can be formed by the MEMS technology by photolithography, it has an ultra-small sensing unit using a semiconductor thermocouple, and has a uniform shape and high productivity. A thermocouple whose thermoelectromotive force is determined only by the Seebeck coefficient α of the thermoelectric material is used for the temperature sensor, and a semiconductor thermocouple is used. Since it is possible to increase sensitivity, it is not necessary to use a thermopile, and the temperature sensing unit can use a thermocouple that is only a hot junction, so that the temperature sensor is extremely compact, highly sensitive, and highly accurate. Since the temperature can be output from the two terminals from the hot junction 81A and the hot junction 81B where a temperature difference occurs due to the presence of the velocity V of the fluid to be measured, a simple circuit configuration is obtained, and further, the direction of the flow is determined by the sign of the output voltage. Since it can be detected, it is also suitable as a thermal flow sensor for measuring the velocity V and flow rate of a fluid to be measured such as a flow path having a reciprocating flow. When the velocity V or flow rate of the fluid to be measured is large, a bypass is provided in the flow path, and the thermal flow sensor chip of the present invention is formed in the bypass region, so that the velocity V of the fluid to be measured is obtained. And the measurement range of flow rate can be expanded. The thermal type flow sensor of the present invention can be applied not only to a gas but also to a liquid to be measured.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Base substrate 10 Thin film 12 SOI layer 13 BOX layer 14 Crosslinking structure 20 Temperature sensor 20A First thermocouple 20B Second thermocouple 20H Heater thermocouple 21 Absolute temperature sensor 25 Heater 40 Cavity 41 Slit 45 Thermal resistance Part 48 Thin film region A
49 Thin film region B
50 Silicon oxide films 70a, 70b Electrode pads 71a, 71b, 71h Electrode pads 72c Electrode pads 81A, 81B, 81H Hot junction 82 Cold junction 100 Thermal flow sensor chips 120, 120a, 120b Thermoelectric material 150 Variable resistance circuit 200 Calibration circuit means 210 Amplifier 220 Arithmetic circuit 230 Control circuit 250 Temperature varying means 310 Changeover switch

Claims (6)

The thin film (10) mainly composed of a semiconductor thin film thermally separated from the substrate (1) by the cavity (40) has a crosslinked structure, and the central portion of the thin film (10) in the direction of the flow of the fluid to be measured. Has a heater (25), and the same thin film (from the heater (25) through the thermal resistance portion (45) on both sides of the flow of the fluid to be measured across the heater (25). 10) that the thin film region A and the thin film region B are formed at symmetrical positions, and the thin film region A and the thin film region B have the first thermoelectric material using the thin film (10) as a common thermoelectric material. Each of the hot junction (81A) and the hot junction (81B) of the pair (20A) and the second thermocouple (20B) is disposed, and is configured to receive heat from the heater (25) and be heated, First thermocouple (20A) and second thermocouple (20B) Was converted, these connected in series so that the temperature difference can be detected, a thermal flow sensor chip that they were taken out as external to the two-terminal, characterized by. The thermal type flow sensor chip according to claim 1, wherein an absolute temperature sensor is formed on the substrate (1). The thermal type flow sensor chip according to claim 1 or 2 is mounted, and the first thermocouple (20A) and the second thermocouple generated by the flow of the fluid to be measured based on the heating of the heater (25). A thermal type flow sensor characterized in that a temperature difference from (20B) is measured and the flow of the fluid to be measured is measured using calibration data prepared in advance. The output voltage from the two terminals according to claim 1, wherein the output voltage in a state where there is no flow of the fluid to be measured is zero, and the flow direction of the fluid to be measured is determined from the signs of the positive and negative output voltages. The thermal type flow sensor according to claim 3, wherein the thermal flow sensor is capable of determining and measuring the flow speed from the magnitude of the output voltage. The output voltage from the two terminals according to claim 1 is connected to a non-inverting input terminal of an operational amplifier, a variable resistor is connected to the inverting input terminal of the operational amplifier, and the variable resistor is switched to a predetermined resistance value. The thermal flow sensor according to claim 3, wherein the measurement range of the flow velocity of the fluid to be measured can be expanded. A temperature variable means (250) for changing the heating temperature of the heater (25) is provided, and the heating temperature of the heater (25) is set to various predetermined temperatures while the flow of the fluid to be measured is stopped. The temperature can be changed using the temperature variable means (250), the output voltages of the first thermocouple (20A) and the second thermocouple (20B) at various predetermined temperatures, and the predetermined temperature. 6. The method according to claim 3, wherein the type of the fluid to be measured can be specified by using data prepared in advance regarding the thermal conductivity of each of the plurality of predetermined fluids. Thermal type flow sensor according to crab.

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