Flow Sensor

Abstract

A flow rate sensor according to the present disclosure comprises a flow rate detecting unit 151 that detects the flow rate of a gas 2 to be measured. The flow rate detecting unit 151 includes: a semiconductor substrate 151a that has a cavity section 151b; a thin-film structure 151d provided adjacent to the cavity section 151b of the semiconductor substrate 151a; a heater element 151e and a pair of temperature measuring elements 151f that are provided to the thin-film structure 151d; and a metallic heat dissipation pattern 151g that is provided in the flow rate detecting unit 151 while being electrically insulated from the heater element 151e and the pair of temperature measuring elements 151f.

Description

[Technical Field]

[0001] The present disclosure relates to a flow sensor. [Background technology]

[0002] There have been known inventions relating to flow sensors that measure flow rates using heaters. For example, a flow measurement element as an example of a flow sensor described in Patent Document 1 has an electrically insulating layer formed on a single crystal silicon substrate, on which a heater, upstream and downstream temperature sensors, etc. are formed, and on which a protective layer is further formed.

[0003] Furthermore, by forming a cavity on the surface of the single crystal silicon substrate opposite to the surface on which the electrical insulating layer etc. is formed, and exposing the electrical insulating layer, a thin film structure including a heater and upstream and downstream temperature sensors is formed in the region where the cavity is formed (Patent Document 1, paragraphs 0025-0026, Figure 1, etc.).

[0004] When air flows from the upstream temperature sensor to the downstream temperature sensor along the surface of the thin-film structure opposite the cavity, the air heated by the heater located between the upstream and downstream temperature sensors moves above the downstream temperature sensor. As a result, a temperature difference occurs between the upstream and downstream temperature sensors, causing a change in their resistance values, and the potential difference generated in the bridge circuit is detected as a flow rate signal corresponding to the flow rate (Patent Document 1, paragraphs 0030-0034, Figures 2 and 9, etc.).

[0005] On the other hand, the thermal flow velocity / flow rate sensor described in Patent Document 2 below has a pair of heater elements mounted on the front and back of the substrate part at the tip of an elongated support part attached to a substrate such as a printed circuit board, and a temperature measuring element mounted adjacent to the heater elements, forming a flow velocity detection part (paragraphs 0069-0072, Figure 1).

[0006] When a thermal flow velocity / flow rate sensor with this configuration is placed in a fluid, the heat of the heater element changes depending on the flow velocity of the fluid. This heat is conducted to the temperature measuring element via the board where the board part is mounted, and the flow velocity and flow rate are calculated from the temperature measured by the temperature measuring element based on the operating principle of the thermal flow velocity / flow rate sensor (Patent Document 2, paragraph 0075, etc.).

[0007] The thermal flow velocity / flow rate sensor of Patent Document 2 has the following configuration as Example 7. A temperature measuring element, a heat dissipation pattern, and a heater element are mounted on one side and the other side of the substrate, respectively. Furthermore, the heater element, the temperature measuring element, and the heat dissipation pattern are thermally connected by a member with high thermal conductivity, and the heater element and the heat dissipation pattern are thermally connected via a through-hole and a heater element circuit pattern, improving heat transfer (paragraph 0119, Figure 8). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2004-257870 A [Patent Document 1] JP 2015-210196 A Summary of the Invention [Problem to be solved by the invention]

[0009] In a flow sensor in which a heater and a temperature sensor are provided in a thin film structure adjacent to a cavity in a single crystal silicon substrate, such as the flow sensor in Patent Document 1, further improvement in detection accuracy when pulsation occurs in the gas to be measured is required. To improve the detection accuracy of such a flow sensor, improvement in the heat dissipation property of the thin film structure is required.

[0010] In Example 7 of the thermal flow velocity / flow rate sensor in Patent Document 2, by providing a heat dissipation pattern, it is possible to reduce the difference in the amount of heat dissipated into the fluid and improve the directional characteristics so that the detection sensitivity of the flow velocity detection unit becomes omnidirectional. Also, by providing a heat dissipation pattern, it is possible to reduce the number of heater elements, thereby reducing the power consumption required for heat dissipation (Patent Document 2, paragraph 0120, etc.).

[0011] However, the thermal flow velocity / flow rate sensor of Patent Document 2 has a different configuration and measurement principle from the flow rate sensor of Patent Document 1. Therefore, the heat dissipation pattern described in Patent Document 2 cannot be applied to the thin film structure of the flow rate sensor described in Patent Document 1. Even if the heat dissipation pattern of Patent Document 2 could be applied to the flow rate sensor of Patent Document 1, it would be difficult to improve the heat dissipation performance of the thin film structure because the heater element and the heat dissipation pattern are connected via a through hole.

[0012] The present disclosure provides a flow sensor that can improve the heat dissipation of a thin film structure that includes a heater element and a temperature measuring element and is provided adjacent to a cavity in a semiconductor substrate. [Means for solving the problem]

[0013] One aspect of the present disclosure is a flow sensor including a flow rate detection unit that detects the flow rate of a gas to be measured, wherein the flow rate detection unit includes a semiconductor substrate having a cavity, a thin film structure provided adjacent to the cavity of the semiconductor substrate, a heater element and a pair of temperature measuring elements provided in the thin film structure, and a metallic heat dissipation pattern provided in the thin film structure and electrically insulated from the heater element and the pair of temperature measuring elements. [Effects of the Invention]

[0014] According to the above aspect of the present disclosure, it is possible to provide a flow sensor that can improve the heat dissipation properties of a thin film structure that includes a heater element and a temperature measuring element and is arranged adjacent to a cavity portion of a semiconductor substrate. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of a control system illustrating an embodiment of a flow sensor according to the present disclosure. [Figure 2] FIG. 2 is a front view of a physical quantity detection device used in the control system of FIG. 1. [Figure 3] FIG. 3 is a right side view of the physical quantity detection device of FIG. 2. [Figure 4] FIG. 3 is a rear view of the physical quantity detection device of FIG. 2 with the cover removed. [Figure 5] FIG. 5 is a front view of a circuit board of the physical quantity detection device of FIG. 4. [Figure 6] 6 is a cross-sectional view of the circuit board and the flow sensor taken along line VI-VI in FIG. 5. [Figure 7] FIG. 7 is a plan view of the flow rate detecting portion of the flow rate sensor of FIG. 6. [Figure 8] 8 is a plan view showing a modified example of the flow rate detecting portion of the flow rate sensor of FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of a flow sensor according to the present disclosure will be described with reference to the drawings.

[0017] 1 is a schematic diagram of an internal combustion engine control system 1 illustrating an embodiment of a flow sensor according to the present disclosure. The internal combustion engine control system 1 includes, for example, an internal combustion engine 10, a physical quantity detection device 100, a throttle valve 25, a throttle angle sensor 26, an idle air control valve 27, an oxygen sensor 28, and a control device 4.

[0018] Although details will be described later, the flow rate sensor 150 (see FIG. 4) of this embodiment constitutes a part of a physical quantity detection device 100 used, for example, in an internal combustion engine control system 1. The physical quantity detection device 100 is inserted into the main passage 22 through a mounting hole provided in the passage wall of the intake body, which is the main passage 22, and is used in a state where it is fixed to the passage wall of the main passage 22.

[0019] The physical quantity detection device 100 detects a physical quantity of intake air, which is the measurement target gas 2 that is taken in through the air cleaner 21 and flows through the main passage 22, and outputs the detected physical quantity to the control device 4. The physical quantity detection device 100 protrudes in the radial direction of the main passage 22 from the passage wall of the main passage 22 toward a center line 22a of the main passage 22 that is along the main flow direction of the measurement target gas 2 that flows through the main passage 22. That is, the protruding direction of the physical quantity detection device 100 in the main passage 22 is, for example, a direction perpendicular to the center line 22a of the main passage 22.

[0020] 1, a three-dimensional Cartesian coordinate system is shown, which is made up of an X axis parallel to the protruding direction of the physical quantity detection device 100 in the main passage 22, a Y axis parallel to the center line 22a of the main passage 22, and a Z axis parallel to the thickness direction of the physical quantity detection device 100. In the following description, it is assumed that the measurement gas 2 flows along the center line 22a (Y axis) of the main passage 22.

[0021] The throttle valve 25 is built into a throttle body 23 that is disposed, for example, on the upstream side of the intake manifold 24 in the flow direction of the measurement target gas 2. The control device 4 changes the opening of the throttle valve 25 based on, for example, the operation amount of an accelerator pedal, to control the flow rate of intake air, which serves as the measurement target gas 2, flowing into the combustion chamber in the cylinder 11 of the internal combustion engine 10. A throttle angle sensor 26 measures the opening of the throttle valve 25 and outputs the result to the control device 4. An idle air control valve 27 controls the amount of air bypassing the throttle valve 25.

[0022] The internal combustion engine 10 includes, for example, a cylinder 11, a piston 12, a spark plug 13, a fuel injection valve 14, an intake valve 15, an exhaust valve 16, and a rotation angle sensor 17. Intake air is taken in through an air cleaner 21 based on the movement of the piston 12 of the internal combustion engine 10, flows through a main passage 22, and the flow rate is controlled by a throttle valve 25 in a throttle body 23. The intake air that passes through the throttle body 23 passes through an intake manifold 24, and further passes through a fuel injection valve 14 provided in an intake port, and flows into the combustion chamber in the cylinder 11 via the intake valve 15.

[0023] The control device 4 controls the fuel injection valve 14 based on the physical quantity of the intake air as the measurement target gas 2 input from the physical quantity detection device 100, to inject fuel into the intake air. As a result, the intake air that has passed through the intake manifold 24 is mixed with the fuel injected from the fuel injection valve 14, and the air-fuel mixture is introduced into the combustion chamber. The control device 4 explosively combusts the air-fuel mixture in the combustion chamber by spark ignition from the spark plug 13, causing the internal combustion engine 10 to generate mechanical energy.

[0024] The rotation angle sensor 17 detects information relating to the positions and states of the piston 12, intake valve 15, and exhaust valve 16, as well as the rotation speed of the internal combustion engine 10, and outputs the information to the control device 4. Gas generated by combustion is discharged from the combustion chamber of the cylinder 11 through the exhaust valve 16 into the exhaust pipe, and is then discharged from the exhaust pipe to the outside of the vehicle as exhaust gas 3. The oxygen sensor 28 is provided in the exhaust pipe, and measures the oxygen concentration of the exhaust gas 3 flowing through the exhaust pipe, and outputs the result to the control device 4.

[0025] The control device 4 controls each part of the control system 1 for the internal combustion engine based on the physical quantities, such as the flow rate, temperature, humidity, and pressure, of the intake air as the measurement target gas 2 flowing through the main passage 22, detected by the physical quantity detection device 100. Specifically, when the control device 4 controls the opening degree of the throttle valve 25 based on the operation amount of the accelerator pedal, the flow rate of the intake air as the measurement target gas 2 flowing through the main passage 22 changes. For example, the control device 4 controls the supply amount of fuel injected from the fuel injection valve 14 based on the flow rate of the measurement target gas 2 detected by the physical quantity detection device 100. In this way, the mechanical energy generated by the internal combustion engine 10 is controlled.

[0026] 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 100, 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 control device 4 controls the fuel injection amount by the fuel injection valve 14 and the ignition timing of the spark plug 13. In reality, the control device 4 also finely controls the fuel supply amount and ignition timing based on the temperature of the measurement target gas 2, the change in the opening of the throttle valve 25, the change in the rotation speed of the internal combustion engine 10, and the air-fuel ratio of the exhaust gas 3.

[0027] The control device 4 further controls the amount of air bypassing the throttle valve 25 by using an idle air control valve 27 when the internal combustion engine 10 is idling, thereby controlling the rotation speed of the internal combustion engine 10 when the internal combustion engine 10 is idling. The amount of fuel supply 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 100 as a main parameter. Therefore, improving the measurement accuracy of the physical quantity detection device 100, suppressing changes over time, and improving reliability are important for improving vehicle control accuracy and ensuring reliability.

[0028] In particular, in recent years, there has been a very strong demand for fuel efficiency in vehicles and for exhaust gas purification. To meet these demands, it is extremely important to improve the detection accuracy of the physical quantity of intake air detected by the physical quantity detection device 100. It is also important that the physical quantity detection device 100 maintains high reliability. Vehicles equipped with the physical quantity detection device 100 are used in environments with large changes in temperature and humidity. It is desirable that the physical quantity detection device 100 be designed to adapt to changes in temperature and humidity in the usage environment, as well as to adapt to dust, pollutants, and the like.

[0029] Furthermore, the physical quantity detection device 100 is attached to an intake pipe that is affected by heat generated by the internal combustion engine 10. Therefore, the heat generated by the internal combustion engine 10 is transmitted to the physical quantity detection device 100 through the intake pipe. Since the physical quantity detection device 100 detects the flow rate of the measurement target gas 2 by transferring heat to the measurement target gas 2, it is important to suppress the influence of external heat as much as possible.

[0030] The physical quantity detection device 100 of this embodiment will be described in more detail below with reference to Fig. 2 to Fig. 7. Fig. 2 to Fig. 4 are a front view, a right side view, and a rear view with a cover 120 removed, respectively, of the physical quantity detection device 100 used in the control system 1 for the internal combustion engine of Fig. 1. The physical quantity detection device 100 includes, for example, a housing 110 and a cover 120.

[0031] The housing 110 is manufactured by, for example, injection molding a synthetic resin material. The cover 120 is, for example, a plate-shaped member made of metal or synthetic resin. For example, a molded product made of synthetic resin material can be used for the cover 120. The housing 110 and the cover 120 form a housing for the physical quantity detection device 100 that is placed in the main passage 22. The housing 110 has, for example, a flange 111, a connector 112, and a measuring unit 113.

[0032] The flange 111 has a generally rectangular plate-like shape in a plan view in which the physical quantity detection device 100 protrudes (in the X-axis direction), and has a pair of fixing portions 111a at diagonally opposite corners. The fixing portion 111a has a cylindrical through-hole in the center that penetrates the flange 111 and through which a fixing screw is inserted. To fix the physical quantity detection device 100 to the main passage 22, the measuring unit 113 is inserted into an attachment hole provided in the main passage 22. Then, the fixing screw inserted into the through-hole of the flange 111 is screwed into the threaded hole of the main passage 22 and fastened, thereby fixing the flange 111 to the passage wall of the main passage 22. In this way, the physical quantity detection device 100 is fixed to the main passage 22, which is an intake body, and the housing 110 is set in the main passage 22.

[0033] The connector 112 protrudes from the flange 111, is disposed outside the main passage 22, which is the intake body, and is connected to an external device. As shown in Fig. 3, a plurality of external terminals 112a and correction terminals 112b are provided inside the connector 112. The external terminals 112a include, for example, output terminals for physical quantities such as flow rate and temperature, which are measurement results of the physical quantity detection device 100, and power supply terminals for supplying DC power to operate the physical quantity detection device 100.

[0034] The correction terminal 112b is used to measure a physical quantity after the physical quantity detection device 100 is manufactured, to find a correction value for each physical quantity detection device 100, and to store the correction value in a memory inside the physical quantity detection device 100. In subsequent measurements of physical quantities by the physical quantity detection device 100, correction data based on the correction value stored in the memory is used, and the correction terminal 112b is not used.

[0035] The measuring part 113 extends from the flange 111 fixed to the passage wall of the main passage 22 toward the center line 22a of the main passage 22 so as to protrude in the radial direction of the main passage 22 perpendicular to the center line 22a. The measuring part 113 has a generally rectangular parallelepiped flattened angular shape. The measuring part 113 has a length in the protruding direction (X-axis direction) of the measuring part 113 in the main passage 22 and a width in the main flow direction (Y-axis direction) of the measurement target gas 2 in the main passage 22. The measuring part 113 also has a thickness in the direction (Z-axis direction) perpendicular to the protruding direction (X-axis direction) and the main flow direction (Y-axis direction) of the measurement target gas 2. As described above, the measuring part 113 has a flattened shape along the main flow direction of the measurement target gas 2, thereby reducing the fluid resistance to the measurement target gas 2.

[0036] The measurement unit 113 has a front surface 113a, a back surface 113b, an upstream side surface 113c, a downstream side surface 113d, and a bottom surface 113e. The front surface 113a and the back surface 113b have larger areas than the other surfaces of the measurement unit 113 and are generally parallel to the protruding direction of the measurement unit 113 (X-axis direction) and the center line 22a of the main passage 22 (Y-axis direction). The upstream side surface 113c and the downstream side surface 113d have elongated shapes with smaller areas than the front surface 113a and the back surface 113b and are generally perpendicular to the center line 22a of the main passage 22 (Y-axis direction). The bottom surface 113e has a smaller area than the other surfaces of the measurement unit 113 and is generally parallel to the center line 22a of the main passage 22 (Y-axis direction) and generally perpendicular to the protruding direction of the measurement unit 113 (X-axis direction).

[0037] The measuring unit 113 has a bypass passage inlet 114 on an upstream side surface 113c, and a first outlet 115 and a second outlet 116 on a downstream side surface 113d. The bypass passage inlet 114, the first outlet 115, and the second outlet 116 are provided at the tip of the measuring unit 113 closer to the tip than the center in the protruding direction (X-axis direction) of the measuring unit 113. This allows the measurement target gas 2 near the center of the main passage 22, which is away from the inner wall surface of the main passage 22, to be taken in through the bypass passage inlet 114. Therefore, the physical quantity detecting device 100 can suppress a decrease in measurement accuracy due to the influence of heat from the internal combustion engine 10.

[0038] As shown in Fig. 4, the housing 110 has a concave bypass passage groove 117 and a concave circuit chamber 118 on the rear surface 113b side of the measuring unit 113. The circuit chamber 118 accommodates a circuit board 140. The opening of the bypass passage groove 117 is closed by the cover 120, thereby forming a bypass passage 130 together with the cover 120. The bypass passage 130 takes in and bypasses part of the measurement target gas 2 flowing through the main passage 22. The part of the measurement target gas 2 flowing through the main passage 22 is taken into the bypass passage 130 from a bypass passage inlet 114 that opens on a side surface 113c on the upstream side of the measuring unit 113, for example.

[0039] The bypass passage groove 117 has, for example, a first bypass passage groove 117a and a second bypass passage groove 117b. The first bypass passage groove 117a extends along the center line 22a (Y-axis direction) of the main passage 22 from a bypass passage inlet 114 opening on an upstream side surface 113c of the measuring section 113 to a first outlet 115 opening on a downstream side surface 113d of the measuring section 113. For example, as shown in FIG. 3 , the first bypass passage groove 117a forms a first bypass passage 131 between itself and the cover 120. The first bypass passage 131 returns the measurement target gas 2 taken in from the bypass passage inlet 114 to the main passage 22 from the first outlet 115.

[0040] 4, the second by-passage groove 117b branches off midway from the first by-passage groove 117a and extends along the protruding direction (X-axis direction) of the measurement section 113 toward the flange 111. Furthermore, the second by-passage groove 117b curves in a U-shape so as to turn back in the opposite direction, and extends along the protruding direction (X-axis direction) of the measurement section 113 toward the tip of the measurement section 113.

[0041] The second by-passage groove 117b curves in a direction along the center line 22a (Y-axis direction) of the main passage 22 at the tip of the measurement section 113, and is connected to a second outlet 116 that opens into a downstream side surface 113d of the measurement section 113. For example, as shown in FIG. 3, the opening of the second by-passage groove 117b is closed by a cover 120, thereby forming a second by-passage 132 between the cover 120 and the second by-passage groove 117b. The by-passage 130 includes a first by-passage 131 and a second by-passage 132.

[0042] The circuit chamber 118 is recessed and provided on the rear surface 113b side of the measuring part 113 of the housing 110, on the base end side of the measuring part 113 connected to the flange 111, and accommodates the circuit board 140. The circuit chamber 118 is provided closer to the base end side of the measuring part 113 than the first by-passage groove 117a of the by-passage groove 117, and adjacent to the upstream side of the second by-passage groove 117b in the main flow direction (Y-axis direction) of the measurement target gas 2 flowing through the main passage 22.

[0043] Fig. 5 is a front view of the circuit board 140 of the physical quantity detection device 100 of Fig. 4. On the circuit board 140, for example, a flow rate sensor 150, a temperature sensor 160, a pressure sensor 170, and a humidity sensor 180 are mounted.

[0044] The temperature sensor 160 is, for example, a chip-type temperature sensor mounted on the circuit board 140. For example, as shown in Fig. 5, the temperature sensor 160 is disposed at the tip of the extension part 140c of the circuit board 140 extending toward the tip of the measurement part 113 in the protruding direction (X-axis direction) of the measurement part 113. The temperature sensor 160 is disposed in the temperature measurement passage 190 of the measurement part 113 shown in Figs. 2 and 4, and measures the temperature of the measurement target gas 2 taken into the temperature measurement passage 190 from the main passage 22.

[0045] 4 and 5, the pressure sensor 170 is mounted on the surface of the circuit board 140 and disposed in the circuit chamber 118. The circuit chamber 118 is connected to the folded portion of the second bypass passage groove 117b that curves in a U-shape near the flange 111, i.e., the folded portion of the second bypass passage 132. This makes it possible to measure the pressure of the measurement target gas 2 taken into the bypass passage 130 by the pressure sensor 170 disposed in the circuit chamber 118.

[0046] 4 and 5, the humidity sensor 180 is mounted on the surface of the circuit board 140 and disposed in a partitioned area closer to the tip end of the measuring unit 113 than the circuit chamber 118. This partitioned area is in communication with, for example, the second sub-passage 132 of the sub-passage 130. In this way, the humidity sensor 180 detects the humidity of the measurement target gas 2 taken into the sub-passage 130.

[0047] Fig. 6 is a cross-sectional view of the circuit board 140 and the flow sensor 150 taken along line VI-VI in Fig. 5. The flow sensor 150 is, for example, a chip package mounted on the surface of the circuit board 140. The flow sensor 150 has a first resin part 150a and a second resin part 150b.

[0048] The first resin portion 150a and the second resin portion 150b are resin sealing portions integrally molded by, for example, transfer molding of a thermosetting resin. As shown in Fig. 4, the first resin portion 150a is disposed in a second bypass passage groove 117b that forms a bypass passage in the housing 110, and the second resin portion 150b is disposed in a circuit chamber 118 of the housing 110.

[0049] 6, the flow sensor 150 has a flow rate detection part 151. The flow rate detection part 151 is provided in the first resin part 150a and detects the flow rate of the measurement target gas 2 flowing through the sub-passage 130. The flow rate sensor 150 is, for example, a thermal flow rate sensor, and the flow rate detection part 151 has a semiconductor substrate 151a having a cavity 151b and a thin film structure 151d provided adjacent to the cavity 151b of the semiconductor substrate 151a.

[0050] The semiconductor substrate 151a is, for example, a single-crystal silicon substrate. The cavity 151b and the thin-film structure 151d can be fabricated, for example, using semiconductor manufacturing technology as follows: First, a silicon dioxide layer is formed as an electrically insulating layer on the single-crystal silicon substrate by thermal oxidation, chemical vapor deposition (CVD), or the like. Then, a polycrystalline silicon layer is formed on top of that by CVD or the like, and is then doped with an impurity such as phosphorus (P) to obtain a polycrystalline silicon layer with the desired resistance value.

[0051] Thereafter, the polycrystalline silicon layer on the electrical insulating layer formed on the surface of the semiconductor substrate 151a is patterned, which allows the heater element and pair of temperature measuring elements, the heater wiring and temperature measuring wiring respectively connected to these elements, the heater temperature measuring element, the reference temperature measuring element and pair of resistance elements, etc., to be formed on the electrical insulating layer.

[0052] The above elements and wiring may be fabricated by forming a metal layer of platinum (Pt), molybdenum (Mo), or the like on an electrical insulating layer by CVD or the like and then patterning it. Next, a silicon nitride layer or silicon dioxide layer is formed as a protective layer by CVD or the like on the electrical insulating layer on which the above elements and wiring are formed. The protective layer is then patterned and removed from the portions where electrode pads will be formed.

[0053] Next, a metal layer is formed by CVD or the like and patterned to form electrode pads, a heat dissipation pattern (described later), etc. Then, to form cavity 151b in semiconductor substrate 151a, a silicon nitride layer serving as a mask is formed by CVD or the like on the surface of semiconductor substrate 151a on which no electrical insulating layer or elements are formed, and then patterned. Thereafter, cavity 151b is formed in semiconductor substrate 151a by anisotropic etching.

[0054] By hollowing out the semiconductor substrate 151a in this way, the region including the elements and wiring of the electrical insulating layer and protective layer formed on the semiconductor substrate 151a is adjacent to the cavity 151b and becomes a thin film structure 151d that is thermally insulated from the semiconductor substrate 151a. Finally, the semiconductor substrate 151a is diced into a plurality of flow rate detecting units 151. Each flow rate detecting unit 151 is, for example, a rectangular plate with long sides of about 5 mm and short sides of about 2.5 mm.

[0055] Fig. 7 is a plan view of the flow rate detecting unit 151 of the flow rate sensor 150 of Fig. 6. Fig. 7 is a plan view of the thin film structure 151d of the semiconductor substrate 151a as viewed from the opposite side of the cavity 151b in the thickness direction (Z-axis direction) of the circuit board 140 shown in Fig. 6. Note that Fig. 7 does not show a protective layer that covers elements and wiring on the electrical insulating layer 151c formed on the surface of the semiconductor substrate 151a.

[0056] As described above, the flow rate detecting unit 151 includes the semiconductor substrate 151a having the cavity 151b and the thin film structure 151d provided adjacent to the cavity 151b of the semiconductor substrate 151a. The flow rate detecting unit 151 also includes the heater element 151e and a pair of temperature measuring elements 151f provided on the thin film structure 151d. The heater element 151e is provided, for example, at the center in the length direction Dl of the thin film structure 151d along the flow direction (X-axis direction) of the measurement target gas 2 and in the width direction Dw of the thin film structure 151d perpendicular to the length direction Dl.

[0057] The heater element 151e is connected to a pair of heater wires 151h. The heater element 151e generates heat when power is supplied via the heater wires 151h, and heats the measurement target gas 2 flowing along the thin film structure 151d. Furthermore, the heat generated by the heater element 151e generates a temperature distribution in the thin film structure 151d. The material of the heater element 151e and the heater wires 151h is, for example, molybdenum (Mo) having a thermal conductivity of approximately 142 [W / mK].

[0058] The pair of temperature measuring elements 151f are arranged on both sides of the heater element 151e in the length direction Dl of the thin film structure 151d along the flow direction (X-axis direction) of the measurement target gas 2. That is, the heater element 151e is arranged between the pair of temperature measuring elements 151f in the length direction Dl of the thin film structure 151d. Each heater element 151e has, for example, two resistance wires that extend parallel to each other and are repeatedly bent and meandering. Each temperature measuring element 151f has one end and the other end of each resistance wire connected to a temperature measuring wire 151i.

[0059] The pair of temperature measuring elements 151f detects a temperature difference occurring between the upstream side and downstream side of the heater element 151e in the flow direction (X-axis direction) of the measurement target gas 2. This temperature difference between the upstream side and downstream side of the heater element 151e occurs when the measurement target gas 2 heated by the heater element 151e flows along the length direction Dl of the thin film structure 151d. The material of the temperature measuring elements 151f and the temperature measuring wiring 151i is, for example, a metal such as molybdenum (Mo) like the heater element 151e.

[0060] The flow rate detecting unit 151 also has a metal heat dissipation pattern 151g provided in the thin film structure 151d so as to be electrically insulated from the heater element 151e and the pair of temperature measuring elements 151f. More specifically, in this embodiment, two pairs of heat dissipation patterns 151g are arranged on both sides of the pair of temperature measuring elements 151f in the width direction Dw orthogonal to the length direction Dl of the thin film structure 151d.

[0061] These four heat dissipation patterns 151g are spaced apart from surrounding elements and wiring, including, for example, heater element 151e, temperature measuring element 151f, heater wiring 151h, and temperature measuring wiring 151i, and are electrically insulated from these surrounding elements and wiring. Each heat dissipation pattern 151g may be connected to a ground wiring or a ground pattern.

[0062] Each heat dissipation pattern 151g has, for example, a triangular shape, and the dimension in the width direction Dw of the thin film structure 151d decreases as it moves away from the heater element 151e in the length direction Dl of the thin film structure 151d. The heat dissipation pattern 151g, the heater element 151e, and the pair of temperature measuring elements 151f are formed of the same metal material, for example, molybdenum (Mo).

[0063] The flow rate detection unit 151 further includes, for example, a heater temperature measuring element 151j, a reference temperature temperature measuring element 151m, and a pair of resistance elements 151n. The heater temperature measuring element 151j is provided, for example, in the thin film structure 151d, between the heater element 151e and the pair of temperature measuring elements 151f, and detects the temperature of the heater element 151e. The heater temperature measuring element 151j includes, for example, a resistance wire bent so as to surround three sides of the heater element 151e, with one end and the other end of the resistance wire each connected to the heater temperature measuring wiring 151k.

[0064] The reference temperature measuring element 151m is provided, for example, outside the thin film structure 151d on the semiconductor substrate 151a near the thin film structure 151d, and measures a reference temperature. The reference temperature is, for example, the temperature of the semiconductor substrate 151a that is not affected by the heater element 151e outside the thin film structure 151d adjacent to the cavity 151b. The reference temperature measuring element 151m is provided midway along the heater temperature measuring wire 151k that is connected to one end of the heater temperature measuring element 151j, and is connected in series to one end of the heater temperature measuring element 151j via the heater temperature measuring wire 151k.

[0065] The pair of resistor elements 151n are provided, for example, near a plurality of electrode pads 151p provided on one side of the semiconductor substrate 151a spaced apart from the thin film structure 151d, and are connected in series with each other. One end of the pair of resistor elements 151n is connected to the common electrode pad 151p, and the other ends of the pair of resistor elements 151n are connected to different electrode pads 151p.

[0066] In the flow rate detection unit 151, a heater temperature measuring element 151j and a reference temperature measuring element 151m connected in series are connected in parallel to a pair of resistor elements 151n connected in series to form a bridge circuit for temperature control. Each electrode pad 151p connected to the pair of resistor elements 151n is connected to, for example, the power supply or ground of the bridge circuit.

[0067] 6, the flow rate detection unit 151 measures the flow rate of the measurement target gas 2 flowing through a measurement flow path 132a formed between the circuit board 140 and the recessed groove 150c of the flow sensor 150. For example, as shown in FIG. 4, the measurement flow path 132a is formed in the second by-passage groove 117b of the by-passage groove 117, i.e., in the second by-passage 132 of the by-passage 130.

[0068] 6, the flow sensor 150 has, for example, an electronic component 152 and a lead frame 153. The electronic component 152 is mounted on the lead frame 153 together with a flow detection unit 151. The electronic component 152 is, for example, an LSI, and is connected to the flow detection unit 151 via bonding wires to drive the flow detection unit 151. The flow sensor 150 detects the flow rate of the measurement target gas 2 by, for example, detecting the temperature difference between a pair of temperature measuring elements 151f of the flow detection unit 151.

[0069] The operation of the flow sensor 150 of this embodiment will be described below.

[0070] As described above, the flow sensor 150 of this embodiment includes a flow rate detection unit 151 that detects the flow rate of the measurement target gas 2. The flow rate detection unit 151 includes a semiconductor substrate 151a having a cavity 151b, a thin film structure 151d provided adjacent to the cavity 151b of the semiconductor substrate 151a, and a heater element 151e and a pair of temperature measuring elements 151f provided on the thin film structure 151d. Furthermore, the flow rate detection unit 151 includes a metal heat dissipation pattern 151g provided on the thin film structure 151d so as to be electrically insulated from the heater element 151e and the pair of temperature measuring elements 151f.

[0071] With this configuration, the flow sensor 150 of this embodiment can dissipate heat from the thin film structure 151d heated by the heater element 151e by conducting it to the metal heat dissipation pattern 151g, which has low thermal resistance. Here, the heat dissipation pattern 151g is electrically insulated from the heater element 151e and the pair of temperature measuring elements 151f, and is provided independently from the surrounding elements and wiring. This further improves the heat dissipation performance of the thin film structure 151d.

[0072] Furthermore, the degree of freedom in the layout of the heat dissipation pattern 151g is improved, and the area of ​​the heat dissipation pattern 151g can be increased, thereby further improving the heat dissipation performance of the thin film structure 151d. Furthermore, the improved heat dissipation performance of the thin film structure 151d improves the responsiveness of flow rate detection of the flow sensor 150 that detects the flow rate of the measurement target gas 2 based on the temperature difference between the pair of temperature measuring elements 151f. Therefore, according to the flow sensor 150 of this embodiment, it is possible to improve the accuracy of flow rate detection when pulsation occurs in the measurement target gas 2.

[0073] Furthermore, in the flow sensor 150 of this embodiment, a heater element 151e is arranged between a pair of temperature measuring elements 151f in a length direction Dl of the thin film structure 151d along the flow direction (X-axis direction) of the measurement target gas 2. Then, two pairs of heat dissipation patterns 151g are arranged on both sides of the pair of temperature measuring elements 151f in a width direction Dw orthogonal to the length direction Dl of the thin film structure 151d.

[0074] With this configuration, the flow sensor 150 of this embodiment can further improve the heat dissipation performance of the thin film structure 151d heated by the heater element 151e. More specifically, in the width direction Dw of the thin film structure 151d that is approximately perpendicular to the flow direction of the measurement target gas 2, the heat dissipation patterns 151g are arranged on both sides of each temperature measuring element 151f, and the area is enlarged compared to when the heat dissipation patterns 151g are arranged on only one side.

[0075] Therefore, the heat generated by the heater elements 151e is conducted to the heat dissipation patterns 151g, the areas of which are enlarged on both sides of each temperature measuring element 151f, in the width direction Dw of the thin film structure 151d, and is further conducted to the semiconductor substrate 151a outside the thin film structure 151d and dissipated. Therefore, the heat dissipation performance of the thin film structure 151d can be further improved.

[0076] In the flow sensor 150 of this embodiment, the dimension of the heat dissipation pattern 151g in the width direction Dw of the thin film structure 151d decreases as it gets farther away from the heater element 151e in the length direction Dl of the thin film structure 151d.

[0077] With this configuration, according to the flow sensor 150 of this embodiment, the closer the heat dissipation pattern 151g is to the heater element 151e in the length direction Dl of the thin film structure 151d, the more improved the heat dissipation performance in the width direction Dw of the flow detection unit 151 by the heat dissipation pattern 151g. Also, the influence of the heat dissipation pattern 151g on the pair of temperature measuring elements 151f that are distant from the heater element 151e in the length direction Dl of the thin film structure 151d can be reduced, thereby suppressing a decrease in the sensitivity of flow rate detection by the flow sensor 150. Therefore, it is possible to suppress a decrease in the sensitivity of flow rate detection while improving the responsiveness of flow rate detection by the flow sensor 150.

[0078] In the flow sensor 150 of this embodiment, the heat dissipation pattern 151g, the heater element 151e, and the pair of temperature measuring elements 151f are made of the same metal material.

[0079] With this configuration, according to the flow sensor 150 of this embodiment, the heat dissipation pattern 151g, heater element 151e, and pair of temperature measuring elements 151f of the flow detection unit 151 can be simultaneously manufactured using the semiconductor manufacturing technology described above. Therefore, the structure of the flow detection unit 151 of the flow sensor 150 can be simplified and productivity can be improved.

[0080] Furthermore, in the flow sensor 150 of this embodiment, the flow detection unit 151 has a bridge circuit including a heater temperature measuring element 151j, a reference temperature temperature measuring element 151m, and a pair of resistance elements 151n. The heater temperature measuring element 151j is provided between the heater element 151e and the pair of temperature measuring elements 151f in the thin film structure 151d. The reference temperature temperature measuring element 151m and the pair of resistance elements 151n are provided on the semiconductor substrate 151a outside the thin film structure 151d.

[0081] With this configuration, the flow sensor 150 of this embodiment can control the temperature of the heater element 151e using a bridge circuit including the heater temperature measuring element 151j, the reference temperature temperature measuring element 151m, and a pair of resistance elements 151n.

[0082] As described above, according to this embodiment, a flow sensor 150 can be provided that includes a heater element 151e and a temperature measuring element 151f and that can improve the heat dissipation properties of a flow detection unit 151 that is provided adjacent to a cavity 151b in a semiconductor substrate 151a.

[0083] Fig. 8 is a plan view showing a modified example of the flow rate detection unit 151 of the flow sensor 150 shown in Fig. 7. In the flow rate detection unit 151 of the flow sensor 150 according to this modified example, a heat dissipation pattern 151g provided on only one side of the heater element 151e and the pair of temperature measuring elements 151f in the width direction Dw of the thin film structure 151d extends to the outside of the thin film structure 151d. Other configurations of the flow rate detection unit 151 of the physical quantity detection device 100 according to this modified example are similar to those of the flow rate detection unit 151 of the flow sensor 150 according to the above-described embodiment shown in Fig. 7, and therefore similar parts are denoted by the same reference numerals and description thereof will be omitted.

[0084] In the flow detection unit 151 of the flow sensor 150 of this modified example, the heat dissipation pattern 151g extends from near the heater element 151e of the thin film structure 151d to above the semiconductor substrate 151a outside the thin film structure 151d. With this configuration, the heat of the thin film structure 151d heated by the heater element 151e can be dissipated to the semiconductor substrate 151a outside the thin film structure 151d via the heat dissipation pattern 151g.

[0085] Therefore, in the flow sensor 150 according to this modification, the heat dissipation property of the thin film structure 151d can be improved, similarly to the flow sensor 150 according to the above embodiment. As a result, the responsiveness of the flow sensor 150 in flow rate detection can be improved, and the detection accuracy of the flow rate when pulsation occurs in the measurement gas 2 can be improved.

[0086] The above describes embodiments of the flow sensor according to the present disclosure and variations thereof, but the flow sensor according to the present disclosure is not limited to the above embodiments, and additions, omissions, substitutions, and other modifications to the configuration are possible within the scope of the spirit of the present invention. [Explanation of symbols]

[0087] 2. Gas to be measured 150 Flow Sensor 151 Flow rate detection unit 151a Semiconductor substrate 151b Cavity 151d thin film structure 151e Heater element 151f Temperature measuring element 151g heat dissipation pattern 151h Heater wiring 151i Temperature measurement wiring 151j Heater temperature sensor element 151m Reference temperature sensor element 151n resistor element Dl Lengthwise Dw width direction

Claims

1. A flow rate sensor including a flow rate detection unit that detects the flow rate of a measurement target gas, the flow rate detection unit includes a semiconductor substrate having a cavity, a thin film structure provided adjacent to the cavity of the semiconductor substrate, a heater element and a pair of temperature measuring elements provided in the thin film structure, and a metal heat dissipation pattern provided in the thin film structure so as to be electrically insulated from the heater element and the pair of temperature measuring elements; the heater element is disposed between the pair of temperature measuring elements in a length direction of the thin film structure along a flow direction of the measurement target gas, two pairs of the heat dissipation patterns are arranged on both sides of the pair of temperature measuring elements in a width direction perpendicular to the length direction of the thin film structure, The dimension of the heat dissipation pattern in the width direction of the thin film structure decreases as it moves away from the heater element in the length direction of the thin film structure. A flow sensor characterized by:

2. 2. The flow sensor according to claim 1, wherein the heat dissipation pattern, the heater element, and the pair of temperature measuring elements are made of the same metal material.

3. The flow sensor according to claim 1, characterized in that the flow detection unit has a bridge circuit including a heater temperature measuring element provided between the heater element and the pair of temperature measuring elements in the thin film structure, and a reference temperature temperature measuring element and a pair of resistance elements provided on the semiconductor substrate outside the thin film structure.

Images