JP2023110111A - Thermal flow rate sensor - Google Patents

Abstract

To provide a thermal flow rate sensor that can enhance resistance to contamination and damage while arranging temperature detection elements symmetrically in relation to a heat-generating resistor.SOLUTION: A thermal flow rate sensor 300 comprises a diaphragm 310, a heat-generating resistor 303, and a pair of temperature detection elements 304. The diaphragm 310 is disposed along a flow direction Df of a gas 2 to be measured of which a flow rate is measured. The heat-generating resistor 303 is disposed in an intermediate portion of the diaphragm 310 in the flow direction Df. The pair of temperature detection elements 304 is disposed at both ends of the diaphragm 310 in the flow direction Df. The diaphragm 310 has an expanded portion 312 that is expanded so as to protrude, in an intersecting direction Di that intersects with the flow direction Df, from at least one lateral edge 311 from among the two lateral edges 311, 311 along the flow direction Df. At least one part of the expanded portion 312 faces a temperature detection element 304 in the intersecting direction Di.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to thermal flow sensors.

An invention related to an air mass meter has been known for some time (see Patent Document 1 below). The air mass meter described in Patent Document 1 has a sensor element formed in a micromachining type structural form. The sensor element has a heating element, a first temperature sensor element is arranged upstream of the heating element, and a second temperature sensor element is arranged downstream of the heating element. The first temperature sensor element has a first width and a first length and the second temperature sensor element has a second width and a second length. This air mass meter is dimensioned such that the first width of the first temperature sensor element is greater than the second width of the second temperature sensor element (ibid., Abstract, Claim 1, Fig. 9). etc.).

Japanese translation of PCT publication No. 2015-532439

In the above conventional air mass meter, the first temperature sensor element and the second temperature sensor element are asymmetrical with respect to the axis of symmetry formed by the heating element (ibid., paragraph 0029, FIG. 9, etc.). ). Therefore, it is necessary to correct the steady-state and non-steady-state characteristics of the air mass meter based on this asymmetry.

The present disclosure provides a thermal flow sensor capable of improving contamination resistance while arranging temperature detection elements symmetrically with respect to a heating resistor.

One aspect of the present disclosure includes a diaphragm arranged along the flow direction of the gas to be measured, a heating resistor arranged in an intermediate portion of the diaphragm in the flow direction, and at both ends of the diaphragm in the flow direction and a pair of temperature detection elements arranged, wherein the diaphragm is expanded to protrude from at least one side edge of both side edges along the flow direction in a cross direction crossing the flow direction. At least part of the extended portion and the temperature detection element are opposed to each other in the cross direction.

According to the present disclosure, it is possible to provide a thermal flow sensor capable of improving contamination resistance while arranging the temperature detection element symmetrically with respect to the heating resistor.

1 is a system diagram showing an example of an internal combustion engine control system; FIG. FIG. 2 is a rear view of the physical quantity detection device shown in FIG. 1 with a cover removed; FIG. 3 is a cross-sectional view of the chip package taken along line III-III in FIG. 2; The front view which shows an example of the thermal type flow sensor of FIG. The front view which shows an example of the thermal type flow sensor of FIG. The front view which shows the modification of the thermal type flow sensor of FIG. The front view which shows the modification of the diaphragm of the thermal type flow sensor of FIG. The front view which shows the modification of the diaphragm of the thermal type flow sensor of FIG. The front view which shows the modification of the diaphragm of the thermal type flow sensor of FIG. The front view which shows the modification of the diaphragm of the thermal type flow sensor of FIG. 1 is a front view showing an embodiment of a thermal flow sensor of the present disclosure; FIG. The front view which shows the comparative example with respect to the thermal type flow sensor of FIG. 8A. 8B is a graph showing the temperature gradient of the diaphragm for the embodiment of FIG. 8A; 8B is a graph showing the temperature gradient of the diaphragm of the comparative example of FIG. 8B; 4 is a graph showing the relationship between the aspect ratio of the extended portion and the number of carbon deposits; 5 is a graph showing the relationship between the aspect ratio of the extension and the temperature gradient;

Hereinafter, embodiments of a thermal flow sensor according to the present disclosure will be described with reference to the drawings.

FIG. 1 is a system diagram showing an example of an internal combustion engine control system 1 of an electronic fuel injection system. In the internal combustion engine control system 1 , intake air is drawn from an air cleaner 21 based on the operation of an internal combustion engine 10 having an engine cylinder 11 and an engine piston 12 . Intake air is led to the combustion chamber of the engine cylinder 11 through the main passage 22 , which is the intake body, the throttle body 23 , and the intake manifold 24 .

A physical quantity detector 20 installed in the main passage 22 measures the physical quantity of the intake air. That is, the measured gas 2 of the physical quantity detection device 20 is, for example, intake air flowing through the main passage 22 . Further, based on the physical quantity of the intake air measured by the physical quantity detection device 20, fuel is supplied from the fuel injection valve 14 and introduced into the combustion chamber together with the intake air in the form of an air-fuel mixture.

In the example shown in FIG. 1, the fuel injection valve 14 is provided in the intake port of the internal combustion engine 10, the fuel injected into the intake port is mixed with the intake air, and the mixture of the fuel and the intake air is injected into the intake valve 15. to the combustion chamber via The air-fuel mixture led to the combustion chamber is explosively combusted by spark ignition of the ignition plug 13 to generate mechanical energy.

The physical quantity detection device 20 measures physical quantities such as the flow rate, temperature, humidity, and pressure of the intake air as the measured gas 2 that is taken in through the air cleaner 21 and flows through the main passage 22 . The physical quantity detection device 20 outputs an electrical signal corresponding to the physical quantity of the intake air. An output signal from the physical quantity detection device 20 is input to the control device 4 .

Also, the output of a throttle angle sensor 26 that measures the opening of the throttle valve 25 is input to the control device 4 . In addition, the output of the rotation angle sensor 17 is input to the control device 4 in order to measure the positions and states of the engine piston 12, the intake valve 15, and the exhaust valve 16 of the internal combustion engine 10, and the rotational speed of the internal combustion engine 10. . The output of the oxygen sensor 28 is input to the control device 4 in order to measure the state of the mixture ratio between the amount of fuel and the amount of air from the state of the exhaust gas 3 .

The control device 4 calculates the fuel injection amount and ignition timing based on the physical quantity of the intake air, which is the output of the physical quantity detection device 20, and the rotation speed of the internal combustion engine 10 measured based on the output of the rotation angle sensor 17. . Based on these calculation results, the amount of fuel supplied from the fuel injection valve 14 and the ignition timing by the spark plug 13 are controlled. Further, the fuel supply amount and ignition timing are further based on the temperature measured by the physical quantity detection device 20, the change state of the throttle angle, the change state of the engine rotation speed, the air-fuel ratio state measured by the oxygen sensor 28, and the like. , is finely controlled.

The control device 4 further controls the amount of air bypassing the throttle valve 25 when the internal combustion engine 10 is idling, using an idle air control valve 27, thereby controlling the rotation speed of the internal combustion engine 10 when the engine is idling. The fuel supply amount and ignition timing, which are the main control variables of the internal combustion engine 10, are both calculated using the output of the physical quantity detection device 20 as a main parameter. Therefore, improving the accuracy of the physical quantity detection device 20, suppressing changes over time, and improving reliability are important for improving control accuracy and ensuring reliability of the vehicle.

In particular, in recent years, there has been an extremely high demand for fuel efficiency of vehicles, and an extremely high demand for purification of exhaust gas. In order to meet these demands, it is extremely important to improve the measurement accuracy of the physical quantity of the intake air, which is the measured gas 2 measured by the physical quantity detection device 20 . It is also important that the physical quantity detection device 20 maintains high reliability.

FIG. 2 is a rear view of the physical quantity detection device 20 shown in FIG. 1 with the cover removed. The physical quantity detection device 20 includes a housing 201 and a cover (not shown) attached to the housing 201 . The cover is made of, for example, a plate-like member made of a conductive material such as an aluminum alloy, or an injection-molded synthetic resin material.

Housing 201 is made of, for example, an injection-molded synthetic resin material. The housing 201 has a flange 201f, a connector 201c, and a measuring section 201m.

The flange 201f is fixed to the intake body, which is the main passage 22. As shown in FIG. The flange 201f has, for example, a substantially rectangular shape in a plan view with a predetermined plate thickness, and has through holes at the corners. The flange 201f is fixed to the main passage 22 by, for example, inserting a fixing screw through the through hole at the corner and screwing it into the screw hole of the main passage 22 .

The connector 201c protrudes from the flange 201f and is exposed outside from the intake body for electrical connection with external equipment. The connector 201c has, for example, four external terminals and a correction terminal provided therein. The external terminals are terminals for outputting physical quantities such as flow rate and temperature, which are measurement results of the physical quantity detection device 20, and power supply terminals for supplying DC power for operating the physical quantity detection device 20. The correction terminal is a terminal used to measure the manufactured physical quantity detection device 20, obtain a correction value for each physical quantity detection device 20, and store the correction value in the memory inside the physical quantity detection device 20. .

The measuring portion 201m extends so as to project toward the center of the main passage 22 from the flange 201f. The measuring portion 201m has a thin and long plate-like shape extending from the flange 201f toward the center of the main passage 22, and has a wide front surface and a rear surface, and a pair of narrow side surfaces, namely an upstream end surface 223 and a downstream end surface. 224. In addition, the X axis parallel to the central axis 22a of the main passage 22 and the short direction of the measuring portion 201m shown in FIG. 1, the Y axis parallel to the thickness direction of the measuring portion 201m, and the longitudinal direction of the measuring portion 201m. A three-dimensional Cartesian coordinate system consisting of a Z-axis is displayed in each figure.

With the physical quantity detection device 20 attached to the main passage 22, the measuring unit 201m protrudes from the inner wall of the main passage 22 toward the central axis 22a of the main passage 22, and has a front surface and a rear surface along the central axis 22a of the main passage 22. are arranged parallel to each other. The measurement portion 201m is arranged such that the upstream end surface 223 on one side in the width direction of the measurement portion 201m faces the upstream side of the main passage 22 between the upstream end surface 223 and the downstream end surface 224 having narrow widths. The downstream end surface 224 on the other hand direction side is arranged to face the downstream side of the main passage 22 .

The measurement part 201m has an upstream end surface 223 of the tip part 201t on the side opposite to the flange 201f provided at the base end part to take part of the gas 2 to be measured such as intake air into the secondary passage 234 in the measurement part 201m. An inlet 231 is provided openly. Moreover, the measurement part 201m has a first outlet 232 for returning the gas to be measured 2 taken into the sub-passage 234 in the measurement part 201m back to the main passage 22 on the downstream end face 224 opposite to the upstream end face 223 of the tip part 201t. and a second outlet 233 are provided.

In the physical quantity detection device 20, the inlet 231 of the secondary passage 234 is provided at the distal end portion 201t of the measuring portion 201m extending toward the center of the main passage 22 from the flange 201f. Therefore, the physical quantity detection device 20 can take the gas not near the inner wall surface of the main passage 22 but near the central portion away from the inner wall surface into the sub-passage. As a result, the physical quantity detection device 20 can measure the flow rate of the gas in the portion distant from the inner wall surface of the main passage 22, and can suppress a decrease in accuracy due to the influence of heat or the like.

A sub-passage groove 250 for forming a sub-passage 234 and a circuit chamber 235 for accommodating the circuit board 207 are provided in the measuring portion 201m. The circuit chamber 235 and the sub-passage groove 250 are provided in a concave shape on one surface of the plate-like measuring portion 201m in the thickness direction of the measuring portion 201m.

The circuit chamber 235 is arranged upstream in the main passage 22 in the flow direction of the gas to be measured 2 , and the sub passage 234 is arranged in the main passage 22 downstream of the circuit chamber 235 in the flow direction of the gas to be measured 2 . placed in position. The secondary passageway groove 250 forms the secondary passageway 234 with the cover. The sub-passage groove 250 has a first sub-passage groove 251 and a second sub-passage groove 252 branching in the middle of the first sub-passage groove 251 .

The first sub-passage groove 251 extends between an inlet 231 opening at an upstream end surface 223 of the measuring portion 201m and a first outlet 232 opening at a downstream end surface 224 of the measuring portion 201m. is formed to extend along the The first sub-passage groove 251 forms a first sub-passage 234 a extending from the inlet 231 along the central axis 22 a of the main passage 22 to the first outlet 232 with the cover. The first auxiliary passage 234 a takes in the measured gas 2 flowing in the main passage 22 from the inlet 231 and returns the taken-in measured gas 2 from the first outlet 232 to the main passage 22 . The first sub-passage 234 a has a branched portion between the inlet 231 and the first outlet 232 .

The second sub-passage groove 252 forms a second sub-passage 234b that branches from the first sub-passage 234a toward the flange 201f and reaches the second outlet 233 between itself and the cover. The second outlet 233 is open so as to face the downstream side in the flow direction of the gas 2 to be measured in the main passage 22 . The second outlet 233 has an opening area larger than that of the first outlet 232, and is formed closer to the proximal end in the longitudinal direction of the measuring section 201m than the first outlet 232 is. The second sub-passage 234b has, for example, a linear upstream portion 237, an arcuate or U-shaped curved portion 238, and a linear downstream portion 239, and reciprocates along the longitudinal direction of the measuring portion 201m. have a route to

More specifically, the second sub-passage groove 252 that forms the second sub-passage 234b branches, for example, from the first sub-passage groove 251 toward the flange 201f in the longitudinal direction of the measurement portion 201m. It extends in a direction substantially orthogonal to the central axis 22a. Further, the second sub-passage groove 252, for example, bends in a U-shape or arcuately toward the distal end portion 201t near the flange 201f of the measurement portion 201m and turns back to extend in the longitudinal direction of the measurement portion 201m, that is, the main passage 22. extends in a direction orthogonal to the central axis 22a of the . Furthermore, the second sub-passage groove 252 is connected to the second outlet 233 by bending in an arc shape toward the downstream end face 224 of the measuring portion 201m, for example.

The gas 2 to be measured flowing through the main passage 22 shown in FIG. In addition, the gas to be measured 2 flowing in the first sub-passage 234a flows into the second sub-passage 234b from the branch portion of the first sub-passage 234a during the forward flow. The measured gas 2 branched from the first sub-passage 234 a and flowed into the second sub-passage 234 b passes through the second sub-passage 234 b and returns to the main passage 22 from the second outlet 233 .

The physical quantity detection device 20 includes, for example, a thermal flow sensor 300 arranged in the upstream portion 237 of the second sub-passage 234b as a detection element that detects a physical quantity. More specifically, in the upstream portion 237 of the second sub-passage 234b, the thermal flow sensor 300 is arranged between the first sub-passage 234a and the curved portion 238. As shown in FIG. Since the second sub-passage 234b has the curved shape as described above, it is possible to ensure a longer passage length. The influence on the sensor 300 can be reduced.

The circuit board 207 is housed in a circuit chamber 235 provided on one side in the short direction of the measuring section 201m. The circuit board 207, for example, extends along the longitudinal direction of the measuring section 201m, and extends along the lateral direction of the measuring section 201m at the end of the measuring section 201m on the flange 201f side, and is generally L-shaped. has the shape of

An intake air temperature sensor 203 , a pressure sensor 204 , a humidity sensor 206 , and a chip package 208 having a thermal flow sensor 300 are mounted on the surface of the circuit board 207 . That is, the physical quantity detection device 20 includes, for example, an intake air temperature sensor 203, a pressure sensor 204, a thermal flow sensor 300, and a humidity sensor as elements for detecting physical quantities such as temperature, pressure, flow rate, and humidity. 206.

The intake air temperature sensor 203 is arranged, for example, in the temperature detection passage, and measures the temperature of the measured gas 2 flowing through the temperature detection passage. The temperature detection passage has an entrance, for example, near an entrance 231 that opens to the upstream end face 223 of the measurement section 201m, and has exits at both the front and rear covers 202 of the measurement section 201m.

The pressure sensor 204 measures the pressure of the gas 2 to be measured within the circuit chamber 235 , and the humidity sensor 206 measures the humidity of the gas 2 to be measured within the circuit chamber 235 . The circuit chamber 235 is defined between the housing 201 and the cover 202, communicates with the second sub-passage 234b through the pressure introduction flow path, and flows from the second sub-passage 234b through the pressure introduction flow path. flows in.

FIG. 3 is a cross-sectional view of the chip package 208 taken along line III--III in FIG. Chip package 208 includes, for example, thermal flow sensor 300, lead frame 208f, sealing portion 208r, and electronic component 208e.

Thermal flow sensor 300 is a semiconductor device mounted on lead frame 208f. Bonding wires, for example, connect between the thermal flow sensor 300 and the lead frame 208f, between the electronic component 208e and the lead frame 208f, and between the thermal flow sensor 300 and the electronic component 208e. Electronic component 208 e is, for example, an LSI including a control circuit, and operates thermal flow sensor 300 . Note that the electronic component 208 e may be arranged outside the chip package 208 , such as being mounted on the circuit board 207 .

The sealing portion 208r is, for example, a resin portion formed by insert-molding a lead frame 208f on which the thermal flow sensor 300 and the electronic component 208e are mounted, with a resin material, and the thermal flow sensor 300 is arranged. It has a groove. This concave groove has a constricted shape in which the width gradually narrows from both ends toward the center in the flow direction of the gas to be measured 2 flowing in the upstream portion 237 of the second sub-passage 234b, and the width is narrowest at the center. A thermal flow sensor 300 is arranged. Due to the constricted shape of the groove, the measured gas 2 flowing through the second sub-passage 234b is rectified, and the influence of noise on the thermal flow sensor 300 can be reduced.

Thermal flow sensor 300 includes, for example, semiconductor substrate 301 , cavity 302 , and diaphragm 310 . The semiconductor substrate 301 is made of a semiconductor such as single crystal silicon (Si) and formed into a rectangular plate shape, and has a laminated portion formed by laminating an insulating film and a wiring film on the surface. The hollow portion 302 is formed in a concave shape on the back surface side of the semiconductor substrate 301 opposite to the laminated portion on the front surface by removing a portion of the semiconductor substrate 301 by wet etching, dry etching, or the like. Cavity 302 communicates with the outside of chip package 208, for example, via a ventilation passage provided in lead frame 208f.

Diaphragm 310 is composed of a thin portion of semiconductor substrate 301 . More specifically, diaphragm 310 is part of a laminate formed on the surface of semiconductor substrate 301 and closes one end of cavity 302 . For example, the diaphragm 310 is formed by removing a part of the semiconductor substrate 301 by wet etching or dry etching from the back surface side of the semiconductor substrate 301 opposite to the front surface side of the semiconductor substrate 301 having the laminated portion, thereby forming a recessed cavity portion 302 . is provided by forming That is, by forming a cavity portion 302 from the back side of the semiconductor substrate 301 and exposing the laminated portion including the SiO ₂ layer, the SiN layer, the wiring layer, etc. on the front side of the semiconductor substrate 301 to the cavity portion 302 as a thin portion. , a diaphragm 310 is formed.

The thickness of diaphragm 310 is, for example, 2 [μm] or more and 10 [μm] or less, more specifically, for example, about 4 [μm]. The thickness of the semiconductor substrate 301 is, for example, 300 [μm] or more and 1 [mm] or less, more specifically, for example, about 400 [μm]. That is, the thickness of diaphragm 310 is, for example, about 1/100 of the thickness of semiconductor substrate 301 .

The thermal flow sensor 300 measures, for example, the flow rate of the measured gas 2 flowing through the channel between the groove of the chip package 208 and the circuit board 207 . More specifically, the gas to be measured 2 flows through, for example, a flow path between the groove of the chip package 208 and the circuit board 207 and a flow path between the second sub-passage groove 252 of the housing 201 and the circuit board 207. and the channel between the chip package 208 and the cover. Then, the flow rate, which is one of the physical quantities of the gas 2 to be measured flowing through the channel between the groove of the chip package 208 and the circuit board 207, is detected by the thermal flow sensor 300 according to this embodiment.

FIG. 4 is a front view of the thermal flow sensor 300 shown in FIG. 3 as seen in the positive direction of the Y-axis. In addition, in FIG. 4, the outer shape of the diaphragm 310 is represented by a dashed line. Thermal flow sensor 300 includes, for example, diaphragm 310 , heating resistor 303 , and a pair of temperature detection elements 304 .

The diaphragm 310 is arranged, for example, along the flow direction Df of the gas 2 to be measured, which is the gas whose flow rate is measured by the thermal flow sensor 300 . In the example shown in FIG. 4, the flow direction Df of the gas 2 to be measured is parallel to the Z axis, for example. The flow direction Df of the gas 2 to be measured may be, for example, a direction substantially parallel to the Z-axis or a direction along the Z-axis.

The diaphragm 310 has an extended portion 312 extending from at least one side edge 311 of both side edges 311, 311 along the flow direction Df so as to protrude in the cross direction Di crossing the flow direction Df. At least a portion of the extension 312 and the temperature sensing element 304 face each other in the cross direction Di. In the example shown in FIG. 4, for example, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more of the extended portion 312 in the flow direction Df is the temperature detection element in the cross direction Di. 304 is facing.

In the example shown in FIG. 4, the diaphragm 310 has extensions 312 on both side edges 311, 311 along the flow direction Df. The diaphragm 310 also has, for example, a pair of extensions 312 on each side edge 311 along the flow direction Df. In the example shown in FIG. 4, both side edges 311, 311 along the flow direction Df of the diaphragm 310 are provided with a pair of extended portions 312 symmetrically with respect to the center line 303a along the intersecting direction Di of the heating resistor 303. It is

Furthermore, in the example shown in FIG. 4, a pair of extension portions 312 are provided on both side edges 311, 311 of the diaphragm 310 along the flow direction Df, symmetrically about the center line 310a of the diaphragm 310 along the flow direction Df. . The diaphragm 310 has, for example, a rectangular main portion 313 whose longitudinal direction is the flow direction Df. The area of the extended portion 312 is smaller than the area of the main portion 313, for example.

The extended portion 312 has a rectangular shape whose longitudinal direction is the flow direction Df, and protrudes in the cross direction Di from the side edge 311 which is the long side of the rectangular main portion 313 . A pair of extensions 312 are provided on each side edge 311 of the diaphragm 310 at intervals in the flow direction Df. The distance D between the pair of extended portions 312 facing each other with the heating resistor 303 interposed therebetween in the flow direction Df is wider than the width W of the heating resistor 303 in the flow direction Df. With such a configuration, the diaphragm 310 has a generally H-shaped shape.

The heating resistor 303 is arranged, for example, in the middle portion of the diaphragm 310 in the flow direction Df. The heating resistor 303 is a micro heater made of, for example, polysilicon, single crystal silicon, molybdenum, platinum, or the like. The heat generating resistor 303 can be configured by a wiring having a width of about 1 [μm] to 150 [μm], for example. Heating resistor 303 may be formed by, for example, folding a wire a plurality of times. The heating resistor 303 is formed, for example, in an intermediate layer of the lamination section including a SiO ₂ layer, a SiN layer, or the like.

The pair of temperature detection elements 304 are arranged, for example, at both ends of the diaphragm 310 in the flow direction Df. The temperature detection element 304 can be made of the same material as the heating resistor 303, for example. The temperature detection element 304 can be configured by a wiring with a width of about 0.5 [μm] to 100 [μm], for example. The temperature detection element 304 may be formed by, for example, folding a wiring several times. The temperature detection element 304 is formed, for example, in an intermediate layer of a laminated portion including a _SiO2 layer, a SiN layer, and the like.

In the example shown in FIG. 4, the pair of temperature detection elements 304 are arranged symmetrically with respect to the center line 303a of the heating resistor 303 along the intersecting direction Di. Also, the pair of temperature detection elements 304 are, for example, thermocouples. The temperature detecting element 304 has, for example, one or more temperature measuring contacts 304j on one side edge facing the heat generating resistor 303 . The temperature measuring junction 304j is a junction of two metals. The temperature detection element 304, which is a thermocouple, generates a voltage according to the temperature difference between the temperature measuring junction 304j and the reference junction on the opposite side thereof by the Seebeck effect. Note that the pair of temperature detection elements 304 are not limited to thermocouples.

FIG. 5 is a modification of the thermal flow sensor 300 of FIG. In the example shown in FIG. 5, the pair of temperature detection elements 304 are, for example, resistor wiring. That is, the pair of temperature detection elements 304 can be configured by, for example, resistor wiring or thermocouples, as shown in FIG. 4 or FIG.

Although illustration is omitted, the thermal flow sensor 300 may have a pair of temperature measuring resistors on both sides of the diaphragm 310 in the flow direction Df, for example. The resistance temperature detector measures the temperature of the gas 2 to be measured outside the diaphragm 310 . The temperature measuring resistor can be made of the same material as the heating resistor 303, for example. The resistance temperature detector can be configured, for example, by wiring with a width of about 0.5 [μm] to 10 [μm]. The resistance temperature detector may be formed, for example, by folding the wiring several times. The temperature detection element 304 is formed in an intermediate layer of the lamination section including, for example, a _SiO2 layer and a SiN layer.

Although not shown, the thermal flow sensor 300 has, for example, a heat generating resistor 303, a temperature detecting element 304, and a temperature measuring resistor on the semiconductor substrate 301 outside the diaphragm 310, which are connected to the electronic component 208e. has a terminal for The configurations and film structures of the heating resistor 303, the temperature detecting element 304, and the temperature sensing resistor can be changed as appropriate according to the temperature measurement method.

Measurement of the flow rate of the measured gas 2 by the thermal flow sensor 300 is performed as follows. When the heating resistor 303 is energized, the air in the vicinity of the heating resistor 303 is warmed, and the temperature is detected by a pair of temperature detection elements 304 arranged on both sides of the heating resistor 303 in the flow direction Df of the gas 2 to be measured. Measured. If the flow rate in the flow direction Df is zero, the temperatures measured by the pair of temperature detection elements 304 are approximately equal.

As shown in FIG. 4, for example, when the gas 2 to be measured flows in the flow direction Df, which is the positive direction of the Z axis, the gas warmed by the heating resistor 303 moves from the upstream side to the downstream side in the flow direction Df. As a result, the temperature of the temperature detection element 304 on the upstream side in the flow direction Df decreases and the temperature of the temperature detection element 304 on the downstream side in the flow direction Df rises compared to when the flow rate of the gas 2 to be measured is zero. do. The flow rate of the gas 2 to be measured is measured by the resistance change caused by the temperature difference between the pair of temperature detection elements 304 .

The operation of the thermal flow sensor 300 of this embodiment will be described below.

The measured gas 2 whose flow rate is to be measured by the thermal flow sensor 300 contains, for example, particles such as oil carbon. The thermal flow sensor 300 is required to have improved contamination resistance to suppress contamination due to particles contained in the gas 2 to be measured without lowering responsiveness.

As described above, the thermal flow sensor 300 of this embodiment includes the diaphragm 310 arranged along the flow direction Df of the gas to be measured 2, and the heating resistor arranged in the middle portion of the diaphragm 310 in the flow direction Df. It includes a body 303 and a pair of temperature detection elements 304 arranged at both ends of the diaphragm 310 in the flow direction Df. The diaphragm 310 has an extended portion 312 extending from at least one side edge 311 of the side edges 311, 311 along the flow direction Df so as to protrude in the cross direction Di crossing the flow direction Df. there is At least part of the extended portion 312 and the temperature detection element 304 face each other in the cross direction Di.

With such a configuration, the temperature detecting element 304 is arranged symmetrically with respect to the heating resistor 303 without degrading the responsiveness of the thermal flow sensor 300, thereby improving the contamination resistance of the thermal flow sensor 300. be able to. More specifically, the thickness of extension 312 is less than the thickness of semiconductor substrate 301 outside diaphragm 310 , and the heat capacity of extension 312 is smaller than the heat capacity of semiconductor substrate 301 outside diaphragm 310 . Therefore, the temperature of the diaphragm 310 around the temperature detection element 304 can be increased compared to the case where the extension part 312 is not provided, and the temperature of the diaphragm 310 can be increased from the temperature detection element 304 toward the side edge 311 of the diaphragm 310 in the cross direction Di. , the temperature gradient of the diaphragm 310 is relaxed.

As a result, the thermophoretic force acting on the particles contained in the gas 2 to be measured is reduced, and adhesion of the particles to the diaphragm 310 of the thermal flow sensor 300 is suppressed. Further, when the area of the diaphragm 310 increases, the responsiveness of the thermal flow sensor 300 tends to decrease. No need. Therefore, according to the thermal flow sensor 300 of the present embodiment, the temperature detecting element 304 can be arranged symmetrically with respect to the heating resistor 303 without degrading the responsiveness, thereby improving the contamination resistance. .

In addition, in the thermal flow sensor 300 of this embodiment, the pair of temperature detection elements 304 are arranged symmetrically with respect to the center line 303a of the heating resistor 303 along the intersecting direction Di, as described above. With such a configuration, it is possible to provide the thermal flow sensor 300 capable of symmetrically arranging the temperature detecting element 304 with respect to the heating resistor 303 and improving the contamination resistance. Therefore, unlike the conventional air mass meter described in Patent Document 1, there is no need to correct the stationary and unsteady characteristics of the air mass meter based on asymmetry.

Further, in the thermal flow sensor 300 of the present embodiment, as described above, a pair of extensions 312 are provided on at least one side edge 311 of the diaphragm 310 symmetrically with respect to the center line 303 a of the heating resistor 303 . there is With such a configuration, the symmetry of diaphragm 310 can be improved.

Further, in the thermal flow sensor 300 of the present embodiment, as described above, a pair of extension portions 312 are provided on both side edges 311, 311 of the diaphragm 310 symmetrically about the center line 310a along the flow direction Df of the diaphragm 310. is provided. With such a configuration, the symmetry of diaphragm 310 can be further improved.

Further, in the thermal flow sensor 300 of the present embodiment, as described above, the distance D between the pair of extended portions 312 facing each other across the heating resistor 303 in the flow direction Df is the distance between the heating resistor 303 in the flow direction Df. Wider than width W. With such a configuration, an increase in the area of diaphragm 310 can be suppressed while relaxing the temperature gradient around temperature detection element 304 .

Further, the thermal flow sensor 300 of this embodiment includes the semiconductor substrate 301 as described above. Diaphragm 310 is composed of a thin portion of semiconductor substrate 301 . With such a configuration, the diaphragm 310 can be easily formed by etching the semiconductor substrate 301 .

Further, in the thermal flow sensor 300 of this embodiment, the temperature detection element 304 is composed of resistor wiring or a thermocouple. With such a configuration, the temperature detection element 304 can be easily formed on the diaphragm 310 .

As described above, according to the present embodiment, it is possible to provide the thermal flow sensor 300 capable of improving the contamination resistance while arranging the temperature detecting element 304 symmetrically with respect to the heating resistor 303. can be done. Note that the configuration of the thermal flow sensor of the present disclosure is not limited to the configuration of the thermal flow sensor 300 of the above-described embodiment. Several modifications of the thermal flow sensor 300 according to the above embodiment will be described below with reference to FIGS. 6 to 7D.

FIG. 6 is a front view showing a modification of the thermal flow sensor 300 of FIG. In the example shown in FIG. 6, the extension 312 of the thermal flow sensor 300 has a stress relief 314 connected to the side edge 311 of the diaphragm 310 . An included angle θ1 between the outer edge of the stress relaxation portion 314 and the side edge 311 of the diaphragm 310 is an obtuse angle.

More specifically, the stress relief portion 314 is provided, for example, in the diaphragm 310 between the side edge 311 of the main portion 313 along the flow direction Df and the side edge of the extension portion 312 along the cross direction Di. It is a triangular part. The included angle θ2 between the outer edge of the stress relief portion 314 and the side edge of the expanded portion 312 along the cross direction Di is also an obtuse angle.

With such a configuration, according to the thermal flow sensor 300 shown in FIG. can be done.

7A to 7D are front views showing modifications of the diaphragm 310 in the thermal flow sensor 300 of FIG. 4. FIG. In the example shown in FIG. 7A, the diaphragm 310 has an extended portion 312 extending from one side edge 311 of the side edges 311, 311 along the flow direction Df so as to protrude in the cross direction Di crossing the flow direction Df. have. In the example shown in FIG. 7A, a pair of extensions 312 are provided on one side edge 311 of the diaphragm 310 symmetrically with respect to the center line 303a of the heating resistor 303 .

In the example shown in FIG. 7B, the diaphragm 310 has extended portions 312 extending from both side edges 311, 311 along the flow direction Df so as to protrude in the cross direction Di crossing the flow direction Df. In the example shown in FIG. 7B, each of the side edges 311, 311 of the diaphragm 310 is provided with one extended portion 312 symmetrically with respect to the center line 310a of the diaphragm 310 along the flow direction Df.

In the example shown in FIG. 7C, the diaphragm 310 has stress relief portions 314, similar to the thermal flow sensor 300 shown in FIG. In the example shown in FIG. 7C, the stress relief portion 314 has a curved outer edge, providing a smooth connection between the tip of the extension 312 and the side edge 311 of the diaphragm 310 . With such a configuration, the stress acting between the extension portion 312 and the side edge 311 of the diaphragm 310 can be more effectively relieved.

In the example shown in FIG. 7D, the diaphragm 310 has extensions 312 extending from both side edges 311, 311 along the flow direction Df in the cross direction Di intersecting the flow direction Df. A pair of extended portions 312 are provided on both side edges 311, 311 of the diaphragm 310, symmetrically with respect to a center line 310a of the diaphragm 310 along the flow direction Df. However, in the example shown in FIG. 7D, the pair of extensions 312 formed on each side edge 311 of the diaphragm 310 are asymmetrical with respect to the centerline 303a of the heating resistor 303. As shown in FIG. With such a configuration, it is possible to adjust the temperature gradient around the temperature detection element 304 between the upstream side and the downstream side in the flow direction Df according to the purpose.

The embodiment of the thermal flow sensor according to the present disclosure has been described in detail above with reference to the drawings, but the specific configuration is not limited to this embodiment, and the design within the scope of the present disclosure All such modifications are intended to be included in this disclosure.

[Example]
Examples of the thermal flow sensor according to the present disclosure will be described below in comparison with comparative examples.

8A is a front view of an example thermal flow sensor of the present disclosure corresponding to the embodiment of FIG. 4; FIG. FIG. 8B is a front view showing a thermal flow sensor 300C according to a comparative example to which the thermal flow sensor 300 of the embodiment of FIG. 8A is compared. In addition, in FIG. 8A and FIG. 8B, the same components as those of the thermal flow sensor 300 according to the above-described embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

A thermocouple was used as the temperature detection element 304 in the thermal flow sensor 300 of the example shown in FIG. 8A and the thermal flow sensor 300C of the comparative example shown in FIG. 8B. In addition, in the flow direction Df of the gas 2 to be measured, the length L1 of the diaphragm 310 according to the example and the length L1 of the diaphragm 310C according to the comparative example are each set to 500 [μm]. In addition, in the cross direction Di orthogonal to the flow direction Df, the width W1 between the side edges 311, 311 of the diaphragm 310 according to the example and the width W1 between the side edges 311C, 311C of the diaphragm 310C according to the comparative example were set to 300 [μm], respectively.

Also, an extension 312 was formed in the diaphragm 310 according to the embodiment of FIG. 8A. The extended portion 312 has a length L2 of 155 [μm] in the flow direction Df of the gas 2 to be measured, and a width W2 of 50 [μm] in the cross direction Di perpendicular to the flow direction Df. On the other hand, the diaphragm 310C according to the comparative example in FIG. 8B does not have the extended portion 312.

The surface temperature was measured toward a point A′ separated in the cross direction Di direction from the temperature measuring junction A of the temperature detecting element 304 located on the center line 310a of each of the diaphragms 310 and 310C according to the embodiment and the comparative example. to obtain the temperature gradient. In FIGS. 8A and 8B, point P is a point on side edges 311 and 311C of diaphragms 310 and 310C of the example and comparative example, respectively, and point A′ is an expanded portion of diaphragm 310 of the example. This is the point corresponding to the tip position of 312 .

FIG. 9A is a graph showing the temperature gradient of diaphragm 310 according to the embodiment of FIG. 8A. FIG. 9B is a graph showing the temperature gradient of diaphragm 310C according to the comparative example of FIG. 8B. As shown in FIG. 9A, in the thermal flow sensor 300 according to the example, the temperature at the point P of the diaphragm 310 was 28 [° C.] and the temperature gradient was 0.48 [° C./μm]. On the other hand, as shown in FIG. 9B, the thermal flow sensor 300C according to the comparative example had a temperature of 24 [° C.] and a temperature gradient of 0.87 [° C./μm] at the point P of the diaphragm 310C. .

That is, in the thermal flow sensor 300 according to the embodiment, the diaphragm 310 has the extension part 312, so that the temperature detection element 304 is larger than that of the thermal flow sensor 300C according to the comparative example in which the diaphragm 310C does not have the extension part 312. The temperature gradient around the was relaxed. Therefore, the thermal flow sensor 300 according to the embodiment can suppress attachment of contaminants due to the thermophoresis effect compared to the thermal flow sensor 300C according to the comparative example. Further, it was confirmed that the thermal flow sensor 300 according to the example and the thermal flow sensor 300C according to the comparative example have the same responsiveness in flow measurement.

Next, in the thermal flow sensor 300 according to the example shown in FIG. 8A, the aspect ratio (length L2/width W2) of the extended portion 312 was varied, and the number of attached particles was obtained by simulation. Also, in the thermal flow sensor 300C according to the comparative example shown in FIG. 8B, the number of adhered particles was obtained by a similar simulation. The results are shown in Table 1 below and in FIGS. 10 and 11. FIG. 10 is a graph showing the relationship between the aspect ratio of extension 312 and the number of particles adhered to diaphragms 310 and 310C. FIG. 11 is a graph showing the relationship between the aspect ratio of the extension 312 and the temperature gradient at point P. FIG.

As shown in FIG. 10, the number of adhered particles to the thermal flow sensor 300C according to the comparative example was 3084, while the number of adhered particles to the thermal flow sensor 300 according to the example is shown in Table 1. The length L2 and width W2 of the extension 312 shown decreased for all combinations.

Further, among the diaphragms 310 according to the examples, the one having the extended portion 312 with the length L2 of 155 [μm] and the width W2 of 75 [μm] has the smallest number of adhered particles, and the diaphragm 310C of the comparative example has the smallest number of adhered particles. It was about 51% of the number of adhered particles. Therefore, it is preferable that the aspect ratio of the extended portion 312 is approximately two. The temperature gradient at the point P of the thermal flow sensor 300 according to this embodiment is 0.46 [° C./μm] as shown in FIG. It decreased significantly from 0.87 [°C/μm].

Further, among the diaphragms 310 according to the example, the diaphragm 310C of the comparative example having the extended portion 312 with the length L2 of 185 [μm] and the width W2 of 50 [μm] has the next smallest number of adhered particles. It was about 54 [%] of the number of particles adhered to. Therefore, the aspect ratio of the extended portion 312 is preferably 3.5 or more and 4 or less, more specifically about 3.7. The temperature gradient at the point P of the thermal flow sensor 300 according to this embodiment is 0.51 [° C./μm] as shown in FIG. It decreased significantly from 0.87 [°C/μm].

In addition, among the diaphragms 310 according to the examples, those having an extended portion 312 with a length L2 of 155 [μm] and a width W2 of 50 [μm] or 100 [μm] have the next smallest number of adhered particles, The number of particles adhering to the diaphragm 310C of the comparative example was about 59%. Therefore, the aspect ratio of the extended portion 312 is preferably around 3.1 or about 1.55. The temperature gradient at the point P of the thermal flow sensor 300 according to this embodiment is 0.48 [° C./μm] or 0.59 [° C./μm] as shown in FIG. The temperature gradient at point P of the flow rate sensor 300C was significantly reduced from 0.87 [°C/μm].

Further, in the diaphragm 310 according to the embodiment, the extended portion 312 having a length L2 of 125 [μm] and a width W2 of 50 [μm], or a length L2 of 155 [μm] and a width W2 of 25 [μm]. , the number of adhered particles was the second smallest, and was about 67% of the number of adhered particles to the diaphragm 310C of the comparative example. Therefore, the aspect ratio of the extended portion 312 is preferably about 2.5 or about 6.2. The temperature gradient at the point P of the thermal flow sensor 300 according to this embodiment is 0.53 [° C./μm] or 0.50 [° C./μm] as shown in FIG. The temperature gradient at point P of the flow rate sensor 300C was significantly reduced from 0.87 [°C/μm].

As described above, in the diaphragms 310 according to all the examples in Table 1, which have the extended portions 312 with aspect ratios of 1.55 or more and 6.2 or less, the temperature gradient is reduced more than the diaphragm 310C according to the comparative example. The number of adhered particles was reduced, and the antifouling property was improved.

2 Gas to be measured 300 Thermal flow sensor 301 Semiconductor substrate 303 Heating resistor 303a Center line 304 Temperature detection element 310 Diaphragm 310a Center line 311 Side edge 312 Extended portion 314 Stress relief portion D Spacing Df Flow direction Di Cross direction W Width θ1 Included angle

Claims (8)

a diaphragm arranged along the flow direction of the gas to be measured;
a heating resistor disposed in an intermediate portion of the diaphragm in the flow direction;
a pair of temperature detection elements arranged at both ends of the diaphragm in the flow direction;
with
The diaphragm has an expanded portion extending from at least one side edge of both side edges along the flow direction in a cross direction crossing the flow direction,
A thermal flow sensor, wherein at least part of the extended portion and the temperature detection element face each other in the cross direction. 2. The thermal flow sensor according to claim 1, wherein the pair of temperature detection elements are arranged symmetrically about a center line along the intersecting direction of the heating resistor. 3. The thermal flow sensor according to claim 2, wherein a pair of said extensions are provided on at least one side edge of said diaphragm symmetrically with respect to said center line of said heating resistor. 4. The thermal flow sensor according to claim 3, wherein a pair of said extension portions are provided on said both side edges of said diaphragm symmetrically with respect to a center line along said flow direction of said diaphragm. 5. The thermal flow sensor according to claim 4, wherein the pair of extension portions facing each other across the heat generating resistor in the flow direction is wider than the width of the heat generating resistor in the flow direction. . the extension has a stress relief connected to the side edge of the diaphragm;
6. The thermal flow sensor according to claim 5, wherein an included angle between an outer edge of said stress relief portion and said side edge of said diaphragm is an obtuse angle. further comprising a semiconductor substrate,
2. The thermal flow sensor according to claim 1, wherein said diaphragm is formed by a thin portion of said semiconductor substrate. 2. A thermal flow sensor according to claim 1, wherein said temperature detection element is composed of a resistor wire or a thermocouple.

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