JP2008039588A - Flow sensor and mass flow controller - Google Patents

Abstract

The effect of an external heat source such as a valve is reduced.
A mass flow controller has a flow sensor 4a disposed in a flow path 6a and a valve 5a for controlling the flow rate of fluid. The flow sensor 4a includes a temperature sensor disposed on the upstream side of the fluid and a temperature sensor disposed on the downstream side. The temperature sensor on the upstream side and the temperature sensor on the downstream side are arranged at an equal distance from the valve 5a that is an external heat source.
[Selection] Figure 1

Description

  The present invention relates to a thermal flow sensor that measures the flow rate or flow rate of a fluid, and a mass flow controller that controls the flow rate of a fluid using the flow sensor.

Conventionally, thermal flow sensors that measure the flow rate or flow rate of fluid have been proposed (see, for example, Patent Document 1 and Patent Document 2), and a mass flow controller that controls the flow rate of fluid by combining a flow sensor and a valve has been proposed. It has been commercialized.
FIG. 11A is a plan view showing a configuration of a conventional mass flow controller, and FIG. 11B is a cross-sectional view of the mass flow controller of FIG. 11A and 11B, 1 is a main body block, 2 is a sensor package, 3 is a head portion of the sensor package 2, 4 is a flow sensor, 5 is a valve, and 6 is formed inside the main body block 1. The flow path 7 is an opening on the inlet side of the flow path 6, and 8 is an opening on the outlet side of the flow path 6.

The fluid flows into the flow path 6 from the opening 7, passes through the valve 5, and is discharged from the opening 8. At this time, the flow sensor 4 measures the flow velocity or flow rate of the fluid.
12A is a plan view showing the configuration of the flow sensor 4, and FIG. 12B is a cross-sectional view of the flow sensor 4 in FIG. 12A and 12B, reference numeral 40 denotes a silicon chip as a base, 41 denotes a diaphragm made of, for example, silicon nitride formed in a thin shape by providing a space 42 on the upper surface of the silicon chip 40, and 43 denotes A metal thin film heating element (heater) formed on the diaphragm 41, 44 is a metal thin film thermal resistor (temperature sensor) formed on the upstream side of the heater 43 on the diaphragm 41, and 45 is a heater on the diaphragm 41. A temperature sensor formed on the downstream side of 43, 46 is an ambient temperature sensor (a metal thin film thermal resistor), 47 is a slit that penetrates the diaphragm 41, and P1 to P6 are electrode pads.

The heater 43 and the temperature sensors 44 to 46 are covered with a thin insulating layer 48 made of, for example, silicon nitride. The ambient temperature sensor 46 is disposed where the temperature of the fluid can be detected without being affected by the heat from the heater 43. When the ambient temperature, that is, the temperature of the fluid changes, the ambient temperature sensor 46 is used to compensate for the change.
The flow sensor 4 is mounted on the header portion 3 of the sensor package 2 with the surface shown in FIG. 12A facing down, and is mounted on the main body block 1 so as to be exposed to the fluid to be measured.

  The principle of flow measurement by the flow sensor 4 will be described. The heater 43 is driven so as to be a constant temperature higher than the ambient temperature, and the temperature sensors 44 and 45 are driven with a constant current or a constant voltage. When the flow velocity of the fluid to be measured is zero, the temperatures of the temperature sensors 44 and 45 are the same, and there is no difference between the resistance values of the temperature sensors 44 and 45. When there is a fluid flow to be measured, the temperature sensor 44 located upstream is cooled because heat is carried away by the fluid flow toward the heater 43. On the other hand, the temperature sensor 45 located downstream is heated by the flow of fluid from the direction of the heater 43. As a result, a difference occurs between the resistance values of the temperature sensors 44 and 45, and by detecting the difference between the resistance values as a voltage difference, an output corresponding to the flow rate or flow rate of the fluid to be measured is obtained. Therefore, if the relationship between the flow path cross-section average flow velocity or flow rate and the voltage difference detected by the sensor output circuit is calibrated in advance, the actual flow cross-section average flow velocity or flow rate is measured from the voltage difference detected by the sensor output circuit. can do.

  A control circuit (not shown) of the mass flow controller obtains the flow rate of the fluid from the voltage output of the flow sensor 4, compares the flow rate value with a preset value, and outputs a drive current to the valve 5 based on the comparison result. To do. Thus, by driving the valve 5, the flow rate of the fluid is controlled to coincide with the set value.

JP-A-5-99722 JP 2002-340646 A

  In the conventional mass flow controller shown in FIGS. 11A and 11B, the upstream temperature sensor 44, the downstream temperature sensor 45, and the valve 5 are arranged on a straight line. In such an arrangement structure, particularly when the valve 5 is a solenoid valve, the temperature distribution formed by the flow sensor 4 is distorted by the heat generated when the valve 5 is driven. There was a problem that an error occurred in the flow measurement.

  That is, the temperature sensor 45 is near the valve 5, and the temperature sensor 44 is farther from the valve 5 than the temperature sensor 45. For this reason, the influence of the heat generated from the valve 5 on the temperature sensors 44 and 45 is not the same, and the temperature sensor 45 close to the valve 5 is more susceptible. When there is no influence of the heat generated from the valve 5, the temperature difference between the temperature sensors 44 and 45 is proportional to the flow rate (flow velocity) of the fluid, but when there is an influence of the heat generated from the valve 5, the temperature sensor Since the temperature difference between 44 and 45 does not reflect only the flow rate, an error occurs in the flow rate measurement.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a flow sensor and a mass flow controller that can reduce the influence from an external heat source such as a valve.

The present invention provides a flow sensor for measuring the flow velocity or flow rate of the fluid by obtaining a temperature difference between two points or a difference in the amount of heat deprived due to heat transfer due to the flow of the fluid. A temperature sensor disposed on the upstream side of the fluid; and a temperature sensor disposed on the downstream side of the fluid; and the upstream temperature sensor and the downstream temperature sensor are disposed at an equal distance from an external heat source. It is a thing.
Further, the mass flow controller of the present invention includes the flow sensor, a valve that is the external heat source that controls the flow rate of the fluid, a temperature difference between the upstream temperature sensor and the downstream temperature sensor. And a control circuit for determining the flow rate and driving the valve based on the value of the flow rate.

  According to the present invention, since the upstream temperature sensor and the downstream temperature sensor are arranged at the same distance from the external heat source, the influence of the heat of the external heat source on the two temperature sensors becomes almost the same. The influence of the heat of the heat source on the sensor characteristics can be reduced, and the fluid flow rate can be correctly measured.

[First Embodiment]
Embodiments of the present invention will be described below with reference to the drawings. 1A is a plan view showing the configuration of the mass flow controller according to the first embodiment of the present invention, FIG. 1B is a cross-sectional view taken along the line I-I of the mass flow controller of FIG. (C) is the II-II sectional view taken on the line of the mass flow controller of Drawing 1 (A). In FIG. 1, 1a is a main body block, 2a is a sensor package, 3a is a head portion of the sensor package 2a, 4a is a flow sensor, 5a is a valve, 6a is a flow path formed inside the main body block 1a, and 7a is a flow path. 6a is an opening on the inlet side, and 8a is an opening on the outlet side of the flow path 6a.

The fluid flows into the flow path 6a from the opening 7a, passes through the valve 5a, and is discharged from the opening 8a. As will be described later, the valve 5a controls the flow rate of the fluid.
The configuration of the flow sensor 4a is the same as that of the flow sensor 4 shown in FIGS. 12 (A) and 12 (B). The flow sensor 4a is mounted on the header portion 3a of the sensor package 2a so that the surface shown in FIG. The sensor package 2a on which the flow sensor 4a is mounted is mounted on the main body block 1a. At this time, the flow sensor 4a is disposed so as to protrude into the flow path 6a so as to be exposed to the fluid to be measured.

  FIG. 2 is a circuit diagram of a constant temperature difference circuit of the flow sensor 4a. The heater 43, the ambient temperature sensor 46, and the three fixed resistors R1, R2, and R3 form a bridge circuit, and the bridge circuit, the resistor R4, the capacitor C1, and the operational amplifier OP1 form a constant temperature difference circuit. The operational amplifier OP1 uses the midpoint voltage of the resistor R1 of the bridge circuit and the heater 43 as an inverting input and the midpoint voltage of the resistors R2 and R3 as a non-inverting input. The output of the operational amplifier OP1 is commonly connected to one ends of the resistors R1 and R2. The resistance values of the resistors R1, R2, and R3 are set so that the heater 43 is always higher than the ambient temperature sensor 46 by a constant temperature.

  FIG. 3 is a circuit diagram of a sensor output circuit of the flow sensor 4a. The two temperature sensors 44 and 45 and the two fixed resistors R5 and R6 constitute a bridge circuit, and the bridge circuit and the operational amplifier OP2 constitute a sensor output circuit. Note that the positions of the temperature sensor 44 and the fixed resistor R6 may be interchanged.

  1A, FIG. 1B, FIG. 12A when the heater 43 is heated to a certain higher temperature than the ambient temperature by energizing the bridge circuit of the constant temperature difference circuit shown in FIG. ), When flowing in the direction of the arrow in FIG. 12B, the diaphragm 41 is deprived of heat in proportion to its flow rate by the fluid, so the heater 43 is also deprived of heat and the resistance value decreases. For this reason, although the equilibrium state of the bridge circuit of the constant temperature difference circuit is broken, the output voltage corresponding to the voltage generated between the inverting input and the non-inverting input is applied to the bridge circuit by the operational amplifier OP1, and therefore the heat deprived by the fluid The amount of heat generated by the heater 43 increases so as to compensate for the above. As a result, when the resistance value of the heater 43 increases, the bridge circuit of the constant temperature difference circuit returns to the equilibrium state. Therefore, a voltage corresponding to the flow velocity is applied to the bridge circuit in an equilibrium state.

  When the temperature distribution in the vicinity of the heater 43 collapses due to the flow of fluid, a temperature difference occurs between the temperature sensor 44 located upstream of the heater 43 and the temperature sensor 45 located downstream, so that the temperature sensors 44 and 45 A difference occurs in the resistance value. The sensor output circuit shown in FIG. 3 detects this difference in resistance value as a voltage difference. The temperature difference between the two temperature sensors 44 and 45 is proportional to the fluid flow rate. Therefore, if the relationship between the flow path cross-section average flow velocity or flow rate and the voltage difference detected by the sensor output circuit is calibrated in advance, the actual flow cross-section average flow velocity or flow rate is measured from the voltage difference detected by the sensor output circuit. can do.

  The control circuit 9 of the mass flow controller shown in FIG. 3 obtains the flow rate of the fluid as described above from the voltage output of the sensor output circuit of the flow sensor 4a, compares this flow rate value with a preset value, Based on the result, the drive current to the valve 5a is output. Thus, by driving the valve 5a, the flow rate of the fluid is controlled to coincide with the set value.

  As described above, also in the present embodiment, the configuration of the flow sensor 4 a is the same as that of the conventional flow sensor 4. However, the present embodiment differs from the prior art in that the temperature sensors 44 and 45 of the flow sensor 4a are arranged at an equal distance from the valve 5a that is an external heat source. According to such an arrangement, the flow path 6a has a so-called crank shape such that it bends 90 degrees before reaching the flow sensor 4a and bends 90 degrees again after passing through the flow sensor 4a. Accordingly, the temperature sensor 44 is disposed on the upstream side, and the temperature sensor 45 is disposed on the downstream side. That is, in the conventional mass flow controller shown in FIGS. 12A and 12B and the mass flow controller of the present embodiment shown in FIGS. 1A and 1B, the sensor package 2a is arranged. The angle differs by 90 degrees, and in FIG. 1A, the temperature sensor 44 is disposed on the upper side and the temperature sensor 45 is disposed on the lower side.

In the present embodiment, since the temperature sensors 44 and 45 are arranged at an equal distance from the valve 5a, even if heat is generated when the valve 5a is driven, the influence of the heat on the temperature sensors 44 and 45 is almost the same. . Accordingly, since the temperature difference between the temperature sensors 44 and 45 reflects only the flow rate of the fluid, the influence of the heat generated from the valve 5a on the sensor characteristics can be reduced, and the flow rate of the fluid can be measured correctly. Can be controlled.
In the present embodiment, the thermal resistor is used as the temperature sensor, but a thermopile may be used.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. 4A is a plan view showing the configuration of the flow sensor 4a according to the second embodiment of the present invention, and FIG. 4B is a cross-sectional view of the flow sensor 4a in FIG. is there. 4A and 4B, reference numeral 50 denotes a silicon chip as a base, 51 denotes a diaphragm made of, for example, silicon nitride formed in a thin shape by providing a space 52 on the upper surface of the silicon chip 50, 53, 54 is a metal thin film heating element formed on the diaphragm 51, 55 and 56 are ambient temperature sensors, 57 is a slit that penetrates the diaphragm 51, and P1 to P6 are electrode pads. The heating elements 53 and 54 serve as a heater and a temperature sensor.

  The present embodiment shows another example of the flow sensor 4a used in the first embodiment. The arrangement of the flow sensor 4a is as described in the first embodiment. Accordingly, the heating element 53 is disposed on the upstream side, and the heating element 54 is disposed on the downstream side. That is, in the case of FIG. 1A, the heating element 53 is arranged on the upper side and the heating element 54 is arranged on the lower side.

  FIG. 5 is a circuit diagram of the constant temperature difference circuit and sensor output circuit of the flow sensor 4a of FIG. The heating element 53, the ambient temperature sensor 55, and the fixed resistors R7, R8, and R9 constitute a bridge circuit, and the bridge circuit, the resistor R10, the capacitor C2, and the operational amplifier OP3 constitute a constant temperature difference circuit. The operational amplifier OP3 uses the midpoint voltage of the resistor R7 and the heating element 53 of the bridge circuit as an inverting input and the midpoint voltage of the resistors R8 and R9 as a non-inverting input. The output of the operational amplifier OP3 is commonly connected to one ends of the resistors R7 and R8. The resistance values of the resistors R7, R8, and R9 are set so that the heating element 53 is always higher than the ambient temperature sensor 55 by a certain temperature.

  Similarly, the heating element 54, the ambient temperature sensor 56, and the fixed resistors R11, R12, and R13 form a bridge circuit, and the bridge circuit, the resistor R14, the capacitor C3, and the operational amplifier OP4 form a constant temperature difference circuit. . The operational amplifier OP4 uses the midpoint voltage of the resistor R11 and the heating element 54 of the bridge circuit as an inverting input and the midpoint voltage of the resistors R12 and R13 as a non-inverting input. The output of the operational amplifier OP4 is commonly connected to one ends of the resistors R11 and R12. The resistance values of the resistors R11, R12, and R13 are set so that the heating element 54 is always higher than the ambient temperature sensor 56 by a certain temperature.

  The operational amplifier OP5 constitutes a sensor output circuit. The operational amplifier OP5 uses the midpoint voltage of the resistor R7 and the heating element 53 as a non-inverting input, and uses the midpoint voltage of the resistor R11 and the heating element 54 as an inverting input.

  When the fluid is passed in the direction of the arrows in FIGS. 4A and 4B with the heating elements 53 and 54 heated to a certain higher temperature than the ambient temperature by energizing the two bridge circuits, the heating elements 53 is deprived of heat by the fluid, the resistance value of the heating element 53 decreases, and the equilibrium state of the bridge circuit comprising the heating element 53, the ambient temperature sensor 55, and the fixed resistors R7, R8, R9 is lost, but the output of the operational amplifier OP3 When the voltage is applied to the bridge circuit, the heat generation amount of the heating element 53 is increased so as to compensate for the heat taken away by the fluid. As a result, the resistance value of the heating element 53 increases and the bridge circuit returns to the equilibrium state. Therefore, a voltage corresponding to the flow velocity is applied to the bridge circuit in an equilibrium state. The same applies to a bridge circuit including the heating element 54, the ambient temperature sensor 56, and the fixed resistors R11, R12, and R13.

  Thus, by detecting the voltage difference between the upstream heating element 53 and the downstream heating element 54 with a circuit as shown in FIG. 5, the flow velocity or flow rate of the fluid and the direction of the flow can be measured. In the circuit shown in FIG. 5, two constant temperature difference circuits are used, and a voltage difference between terminals of the heat generating element 53 and the heat generating element 54 is amplified by the operational amplifier OP5 to obtain a voltage output. The flow rate can be determined by the magnitude of the voltage output, and the direction can be determined by the polarity.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 6 is a cross-sectional view showing the configuration of the flow rate measurement unit of the mass flow controller according to the third embodiment of the present invention, and FIG. 7 is a plan view showing the configuration of the flow sensor according to the third embodiment of the present invention. . In FIG. 7, the outer shape of the valve 5a is schematically drawn in order to explain the positional relationship between the flow sensor 21 and the valve 5a.
The mass flow controller of the present embodiment includes a flow sensor 21, a flow path forming member 22 that forms a flow path 30 of fluid together with the flow sensor 21, a valve 5a, and a control circuit (not shown).

  The flow sensor 21 includes a substrate 24 and flow velocity detection means (a heater 43, temperature sensors 44 and 45, an ambient temperature sensor 46, and electrode pads P1 to P6) formed on the surface of the substrate 24. This flow sensor 21 is obtained by forming the constituent elements of the flow sensor shown in FIGS. 12A and 12B on the surface of a substrate 24. Therefore, the constant temperature difference circuit and the sensor output circuit of the flow sensor 21 are as shown in FIGS. 2 and 3, respectively. The heating elements 53 and 54, the ambient temperature sensors 55 and 56, and the electrode pads P1 to P6 shown in FIGS. 4A and 4B may be formed on the surface of the substrate 24 as flow velocity detection means. In this case, the constant temperature difference circuit and the sensor output circuit are as shown in FIG.

  The substrate 24 is formed in a rectangular plate shape, the outer peripheral edge portion forms a thick fixing portion 24 </ b> A, and is bonded to the surface of the flow path forming member 22. The central portion of the substrate 24 forms a thin portion 24B by forming an oval concave portion 26 on the back side. The thin part 24B has a film thickness of about 50 to 150 μm and forms a sensor part having a diaphragm structure. As the material of the substrate 24, a material having a low thermal conductivity compared to silicon and having high heat resistance, corrosion resistance and rigidity, such as stainless steel, sapphire, or ceramics, is used. In the present embodiment, an example is shown in which the substrate 24 is formed of a stainless steel thin plate having a thickness of about 0.5 to 3 mm. When the substrate 24 is made of stainless steel, when the thickness is 150 μm or more, the heat conduction efficiency between the thickness direction of the substrate 24, that is, between the fluid 2 and the flow velocity detection means is decreased, and the substrate 24 is parallel to the surface of the substrate 24. Since the amount of heat transfer in the direction (heat loss) increases, it is not preferable.

  The surface of the substrate 24 is mirror-polished, and the electrical insulating film 13 is formed over the entire surface. On the surface of the electrical insulating film 13, a flow velocity detecting means including a heater 43, temperature sensors 44 and 45, an ambient temperature sensor 46, and electrode pads P1 to P6 is formed. Examples of the electrical insulating film 13 include a thin silicon oxide film, a silicon nitride film, an alumina film, and a polyimide film having a thickness of about several thousand angstroms to several microns.

  The flow path forming member 22 is made of an elongated metal plate made of stainless steel, like the substrate 24, and has a convex portion 22 </ b> A whose outer shape protrudes from the center of the surface and is substantially equal to the substrate 24, and two through holes 40, 41. The fixing portion 24A of the substrate 24 is joined to the upper surface of the convex portion 22A, and the through holes 40 and 41 and the concave portion 26 of the substrate 24 communicate with each other to form a fluid flow path 30. When such a flow path forming member 22 is formed of stainless steel, which is the same material as the substrate 24, both members can be welded without using different metals by YAG laser welding or the like. The flow path forming member 22 may be aluminum, ceramics, or the like. In this case, the O-ring and bolts are used for joining. Of course, even when the flow path forming member 22 is made of stainless steel, it may be joined using an O-ring and a bolt.

The fluid flows into the flow path 30 from the through hole 40 and is discharged from the through hole 41. If the fluid exiting the through hole 41 is guided to the valve 5a and the control circuit 9 shown in FIG. 3 or 5 controls the opening degree of the valve 5a based on the voltage output of the sensor output circuit of the flow sensor 21, A mass flow controller equivalent to that of the first embodiment can be realized.
Also in the present embodiment, by arranging the temperature sensors 44 and 45 at an equal distance from the valve 5a as shown in FIG. 7, the influence of heat generated from the valve 5a on the sensor characteristics can be reduced. It is possible to correctly measure and control the flow rate. As described above, even in a mass flow controller in which the flow sensor 21 does not come into contact with the fluid, the same effect as that of the first embodiment can be obtained.

  In the present embodiment, since the flow sensor is longer in the fluid flow direction and the contact area with the flow path forming member 22 is larger than that in the first embodiment, the temperature difference between the temperature sensors 44 and 45 is caused by an external heat source. It becomes more susceptible to In the present embodiment, since the substrate 24 is not made of silicon having high thermal conductivity, but is made of a material having low thermal conductivity such as stainless steel, sapphire, ceramics, etc., the temperature difference in the plane of the substrate 24 is reduced. Easy to do. Therefore, the effect of arranging the upstream temperature sensor 44 and the downstream temperature sensor 45 at an equal distance from the external heat source becomes more prominent in the present embodiment.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 8 is a perspective view showing a configuration of a flow rate measuring unit of a mass flow controller according to a fourth embodiment of the present invention, and FIG. 9 is a plan view showing the configuration of a sensor chip according to the fourth embodiment of the present invention. 10 is a cross-sectional view of the sensor chip of FIG. 9 along the line BB. In FIG. 9, the outer shape of the valve 5a is schematically drawn in order to explain the positional relationship between the sensor chip and the valve 5a.

  The mass flow controller of the present embodiment includes a sensor chip 102, a glass chip 103 as a cover member whose lower surface is bonded to the upper surface of the sensor chip 102, a flow rate detection unit 110 formed on the upper surface of the sensor chip 102, It has a valve 5a and a control circuit (not shown). The glass chip 103 is made of transparent glass, and the inside is seen through. Therefore, the flow rate detection unit 110 is also drawn through. Moreover, the glass chip 103 and the flow path 6a formed in the main body block 1a of the mass flow controller shown in FIG. 1 are connected via a sealing material such as an O-ring or packing. Alternatively, the glass chip 103 is hermetically bonded to the main body block 1a shown in FIG. 1 with a low melting point glass or a resin adhesive sheet, and is connected to the flow path 6a formed inside.

  As shown in FIG. 9, in the sensor chip 102, an insulating film 105 of silicon nitride or silicon dioxide is formed in the center of the upper surface 104a of the silicon substrate 104 over the entire width in the width direction. A heater 43, temperature sensors 44 and 45, and an ambient temperature sensor 46 are formed. This sensor chip 102 is obtained by forming the constituent elements of the flow sensor shown in FIGS. 12A and 12B on the surface of the insulating film 105. Therefore, the constant temperature difference circuit and the sensor output circuit of the flow sensor 21 are as shown in FIGS. 2 and 3, respectively. The heating elements 53 and 54 and the ambient temperature sensors 55 and 56 shown in FIGS. 4A and 4B may be formed on the surface of the insulating film 105. In this case, the constant temperature difference circuit and The sensor output circuit is as shown in FIG.

The heater 43, the temperature sensors 44 and 45, and the ambient temperature sensor 46 are entirely covered with an insulating film 109 of silicon nitride or silicon dioxide as shown in FIGS. The heater 43, the temperature sensors 44 and 45, and the ambient temperature sensor 46 form a flow rate detection unit 110.
A recess 104b is formed on the upper surface 104a of the silicon substrate 104 at a position below the heater 43 and the temperature sensors 44 and 45, and a portion covering the recess 104b of the insulating film 105 is a diaphragm. Thereby, the heater 43, the temperature sensors 44 and 45, and the silicon substrate 104 are thermally shut off.

  The glass chip 103 is formed of transparent glass, for example, borosilicate glass, which is approximately the same size as the silicon substrate 104, and allows fluid to flow on the flow rate detection unit 110 along the longitudinal direction in the center of the lower surface as shown in FIG. The flow path 111 is formed. The flow path 111 has both end portions 111a and 111b opened on the upper surface of the glass chip 103, and allows fluid to flow on the flow rate detection unit 110 formed on the sensor chip 102 from the temperature sensor 44 side to the temperature sensor 45 side. It is supposed to flow. Therefore, the glass chip 103 has a function as a flow path forming member for flowing a fluid.

The flow path 111 may be processed by, for example, melt molding, hydrofluoric acid etching, an end mill, sandblasting, or the like.
The glass used for the glass chip 103 is preferably one having a thermal expansion coefficient close to that of the substrate (silicon) of the sensor chip 102, for example, borosilicate glass.
In order to join the sensor chip 102 and the glass chip 103, the glass chip 103 is disposed so that the flow path 111 is above the flow rate detection unit 110 and along the arrangement direction of the heater 43 and the temperature sensors 44 and 45. A low melting point glass called frit glass is disposed between the lower surface of the glass chip 103 and the upper surface 104a of the silicon substrate 104 and bonded.

Other bonding methods include anodic bonding or combined use of anodic bonding and low-melting glass. In order to join the sensor chip 102 and the glass chip 103 by the combined use of anodic bonding and low-melting glass, the flow path 111 is located above the flow rate detection unit 110 and along the arrangement direction of the heater 43 and the temperature sensors 44 and 45. The glass chip 103 is disposed on the upper surface 104 a of the silicon substrate 104.
Subsequently, the lower surface of the glass chip 103 and the upper surface 104a of the silicon substrate 104 are bonded by anodic bonding. A groove to be escaped is formed in advance on the lower surface portion of the glass chip 103 facing the insulating films 105 and 109 and the flow rate detection unit 110, and low melting glass is applied to the groove and pre-baked. That's fine. Due to the thin film wiring pattern from the insulating films 105 and 109 and the flow rate detection unit 110 between the groove of the glass chip 103 and the upper surface 104a of the silicon substrate 104, the low melting point glass is melted by heat applied during anodic bonding. Fill in the unevenness to ensure close contact. In order to perform anodic bonding, the glass chip 103 needs to have ion conductivity, and for example, borosilicate glass is suitable.

The fluid flows into the flow path 111 of the glass chip 103 from the end 111a and is discharged from the end 111b. If the fluid flowing out from the end 111b is guided to the valve 5a and the control circuit 9 shown in FIG. 3 or 5 controls the opening degree of the valve 5a based on the voltage output of the sensor output circuit of the sensor chip 102, A mass flow controller equivalent to that of the first embodiment can be realized.
Also in the present embodiment, by arranging the temperature sensors 44 and 45 at an equal distance from the valve 5a as shown in FIG. 9, the influence of heat generated from the valve 5a on the sensor characteristics can be reduced. The flow rate can be correctly measured and controlled, and the same effect as in the first embodiment can be obtained.

  The present invention can be applied to a mass flow controller.

It is the top view and sectional drawing which show the structure of the mass flow controller which concerns on the 1st Embodiment of this invention. It is a circuit diagram of the constant temperature difference circuit of the flow sensor in the 1st Embodiment of this invention. It is a circuit diagram of the sensor output circuit of the flow sensor in the 1st embodiment of the present invention. It is the top view and sectional drawing which show the structure of the flow sensor which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of the constant temperature difference circuit and sensor output circuit of the flow sensor in the 2nd Embodiment of this invention. It is sectional drawing which shows the flow volume measurement part structure of the massflow controller which concerns on the 3rd Embodiment of this invention. It is a top view which shows the structure of the flow sensor which concerns on the 3rd Embodiment of this invention. It is a perspective view which shows the flow volume measurement part structure of the massflow controller which concerns on the 4th Embodiment of this invention. It is a top view which shows the structure of the sensor chip based on the 4th Embodiment of this invention. It is sectional drawing of the sensor chip of FIG. It is the top view and sectional drawing which show the structure of the conventional mass flow controller. It is the top view and sectional drawing which show the structure of the conventional flow sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a ... Main body block, 2a ... Sensor package, 3a ... Head part, 4a, 21 ... Flow sensor, 5a ... Valve, 6a ... Flow path, 7a, 8a ... Opening, 9 ... Control circuit, 40, 50 ... Silicon chip, 41 , 51 ... Diaphragm, 43, 53, 54 ... Heater, 44, 45 ... Temperature sensor, 46, 55, 56 ... Ambient temperature sensor.

Claims (2)

In a flow sensor that has a heating means and measures the flow velocity or flow rate of the fluid by determining the temperature difference between two points due to the transfer of heat due to the flow of the fluid or the difference in the amount of heat lost,
A temperature sensor disposed upstream of the fluid;
A temperature sensor disposed downstream of the fluid;
The flow sensor, wherein the upstream temperature sensor and the downstream temperature sensor are arranged at an equal distance from an external heat source. A flow sensor according to claim 1;
A valve that is the external heat source for controlling the flow rate of the fluid;
A mass flow controller comprising: a control circuit that obtains a flow rate of the fluid from a temperature difference between the upstream temperature sensor and the downstream temperature sensor and drives the valve based on a value of the flow rate.

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