Flow sensor

Abstract

To provide a flow sensor that improves detection accuracy. [Solution] The flow sensor comprises a substrate, a heater disposed on the substrate and extending in a second direction that intersects a first direction, which is the direction of fluid flow, in a plan view, a detection unit including a first temperature detection unit and a second temperature detection unit, each disposed on the substrate and positioned to sandwich the heater in the first direction, a first wiring connected to one end of the heater, and a second wiring connected to the other end of the heater, wherein the first wiring has a first portion located next to the first temperature detection unit and a second portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater and the first portion, and the second wiring has a third portion located next to the first temperature detection unit and a fourth portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater and the third portion.

Description

Technical Field

[0006] , , , ,

[0001] The present invention relates to a flow sensor.

Background Art

[0002] Flow sensors for detecting the flow rate or flow velocity of fluids such as gases or liquids are known. For example, Patent Document 1 discloses a thermal flow sensor having a thin film portion including a heating element and an insulating film covering the heating element, and a heat conductive member having higher thermal conductivity than the insulating film provided as a dummy pattern through which no current flows.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When there is no fluid flow in the flow path, if there is a bias in the temperature distribution in the flow path and on the flow sensor due to the heat generated by the heater, the detection accuracy of the fluid flow rate or flow velocity may decrease.

[0005] The present invention provides a flow sensor that improves detection accuracy.

Means for Solving the Problems

[0006] The flow sensor comprises a substrate, a heater disposed on the substrate and extending in a second direction intersecting a first direction which is the direction of fluid flow in a plan view, a detection unit including a first temperature detection unit and a second temperature detection unit, each disposed on the substrate and positioned to sandwich the heater in the first direction, a first wiring connected to one end of the heater, and a second wiring connected to the other end of the heater, wherein the first wiring has a first portion located next to the first temperature detection unit and a second portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater and the first portion, and the second wiring has a third portion located next to the first temperature detection unit and a fourth portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater and the third portion. [Effects of the Invention]

[0007] According to the present invention, the detection accuracy of fluid flow rate or velocity can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic top view showing an example of a flow sensor according to the first embodiment. [Figure 2] Figure 1 shows an example of a cross-sectional view of a flow sensor, schematically illustrating the cross-section obtained by cutting along the line II-II. [Figure 3A] This is a cross-sectional view of a flow sensor showing an example of the temperature distribution inside the flow path and on the flow sensor when no fluid flow is occurring. [Figure 3B] This is a cross-sectional view of a flow sensor showing an example of the temperature distribution within the flow path and on the flow sensor when fluid flow is occurring. [Figure 4] This is a schematic top view showing an example of a flow sensor in a comparative example. [Figure 5] This is a schematic top view showing an example of a flow sensor according to the second embodiment. [Figure 6] Figure 5 shows an example of a cross-sectional view of a flow sensor, schematically illustrating the cross-section obtained by cutting along the line VI-VI. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and redundant explanations are omitted as appropriate.

[0010] In each drawing, a Cartesian coordinate system with X, Y, and Z axes is used to represent direction. The X, Y, and Z axes are orthogonal to each other. In the X-axis direction, the direction the arrow points is denoted as the +X direction or +X side, and the opposite direction is denoted as the -X direction or -X side. In the Y-axis direction, the direction the arrow points is denoted as the +Y direction or +Y side, and the opposite direction is denoted as the -Y direction or -Y side. In the Z-axis direction, the direction the arrow points is denoted as the +Z direction or +Z side, and the opposite direction is denoted as the -Z direction or -Z side.

[0011] In this specification, the fluid to be detected is assumed to flow in the Y-axis direction. Hereinafter, the Y-axis direction will be referred to as the "first direction Y". The first direction Y corresponds to the direction of fluid flow. The direction of fluid flow from the -Y side to the +Y side will be referred to as the "forward direction". The direction of fluid flow from the +Y side to the -Y side will be referred to as the "reverse direction". The X-axis direction is the direction that intersects the first direction Y when viewed from the Z-axis direction. Hereinafter, the X-axis direction will be referred to as the "second direction X". The Z-axis direction corresponds to the height direction of the flow sensor according to the embodiment. Hereinafter, the Z-axis direction will be referred to as the "third direction Z". Viewing the object from the third direction Z will be referred to as the "planar view".

[0012] In this specification, "along the direction" includes cases where the two axes or directions do not intersect, as well as cases where the angle between the two axes or directions is ±5 degrees or less. Furthermore, "orthogonal" includes cases where the angle with respect to any direction is within the range of 90 degrees ± 5 degrees. However, these directional expressions do not limit the direction of the embodiment. The orientation when using the flow sensor according to the embodiment is arbitrary. In this embodiment, as an example of the temperature detection unit (the first temperature detection unit 31 and the second temperature detection unit 32 described later), a thermopile is used, which connects two different conductors and detects temperature by the electromotive force generated between a hot junction and a cold junction. Note that a platinum resistance thermometer or a bolometer using vanadium oxide can also be used as the temperature detection unit.

[0013] [First Embodiment] <Example of overall structure> Referring to Figures 1 to 4, an example of the overall configuration of the flow sensor 1 according to the first embodiment will be described. Figure 1 is a schematic top view showing an example of the flow sensor 1 according to the first embodiment. Figure 2 is a schematic cross-sectional view of the flow sensor 1 showing a cross section cut along the line II-II shown in Figure 1. Figure 3A is a cross-sectional view of the flow sensor 1 showing an example of the temperature distribution in the flow path and on the flow sensor 1 when no fluid flow is occurring (hereinafter referred to as "windless conditions"). Figure 3B is a cross-sectional view of the flow sensor 1 showing an example of the temperature distribution in the flow path and on the flow sensor 1 when fluid flow is occurring. Figure 4 is a schematic top view showing an example of the flow sensor 1R of a comparative example. For the sake of explanation, the protective film 13 on the substrate 10 of the flow sensor 1 is omitted in Figure 1. The cross sections of the flow sensor 1 shown in Figures 3A and 3B correspond to the cross sections cut along the line II-II shown in Figure 1.

[0014] The flow sensor 1 is a thermal flow sensor that detects the flow rate or velocity of a fluid such as a gas or liquid. As shown in Figure 1, the flow sensor 1 comprises a substrate 10, a heater 20, a detection unit 30, a first wiring 40, and a second wiring 50. In the example shown in Figure 1, the flow sensor 1 further comprises terminals 61a, 61b, 61c, 61d, 61e, 61f, a third wiring 70a, 70b, a fourth wiring 75a, 75b, and other wiring 77. The flow sensor 1 may further comprise other components. The detection unit 30 includes a first temperature detection unit 31 and a second temperature detection unit 32. As an example of the first temperature detection unit 31, a thermopile can be mentioned above. Hereinafter, the first temperature detection unit 31 will be described as the "first thermopile 31". However, the first temperature detection unit 31 is not limited to a thermopile. Furthermore, a thermopile can be cited as an example of the second temperature detection unit 32. Hereinafter, the second temperature detection unit 32 will be described as the "second thermopile 32". The second temperature detection unit 32 is not limited to a thermopile. As mentioned above, other examples of the first temperature detection unit 31 and the second temperature detection unit 32 include a platinum resistance thermometer and a bolometer using vanadium oxide.

[0015] Terminals 61a and 61b are connected to an external power source, which is the power source for heating the heater 20. As shown in Figure 1, terminal 61a is connected to one end 21 of the heater 20 via the first wiring 40. Terminal 61b is connected to the other end 22 of the heater 20 via wiring 77. In other words, the heater 20 is connected to an external power source via terminals 61a and 61b. In this specification, "connection" is not limited to cases where multiple objects are physically connected, but also includes cases where they are electrically connected.

[0016] Each of the terminals 61c, 61d, 61e, and 61f is a terminal connected to an external signal processing circuit via a connection member such as a bonding wire. The terminal 61c is connected to the first thermopile 31 included in the detection unit 30 via the third wiring 70a. The terminal 61d is connected via the fourth wiring 75a. That is, the first thermopile 31 is connected to an external signal processing circuit via the terminals 61c and 61d. The detection signal from the first thermopile 31 is output to the external signal processing circuit via 61c and 61d. Note that the detection signal from the first thermopile 31 is an example of the "detection signal from the detection unit 30".

[0017] The terminal 61e is connected to the second thermopile 32 included in the detection unit 30 via the third wiring 70b. The terminal 61f is connected to the third conductor portion 321 via the fourth wiring 75b. That is, the second thermopile 32 is connected to an external signal processing circuit via the terminals 61e and 61f. The detection signal from the second thermopile 32 is output to the external signal processing circuit via the terminals 61e and 61f. Note that the detection signal from the second thermopile 32 is an example of the "detection signal from the detection unit 30".

[0018] <Substrate 10> The substrate 10 has a support portion 11 that supports each component of the flow sensor 1. The fluid to be detected flows above the substrate 10. That is, in the flow sensor 1, the space above the substrate 10 (+Z side) corresponds to the fluid flow path.

[0019] As shown in FIGS. 1 and 2, the substrate 10 has, in addition to the support portion 11, an insulating film 12 and a protective film 13. The support portion 11 is made of a semiconductor material such as silicon (Si), for example. An opening 10S is formed inside the support portion 11 by removing a part of the substrate 10. The support portion 11 is a frame-shaped portion disposed around the opening 10S that is recessed upward from the lower surface of the substrate 10.

[0020] The insulating film 12 is made of an insulating material such as silicon oxide (SiO2). As shown in Figure 2, the insulating film 12 is placed on the support portion 11 and closes the opening 10S. On the insulating film 12, for example, a heater 20, a first thermopile 31, a second thermopile 32, a first wiring 40, a second wiring 50, a third wiring 70a, 70b, and a fourth wiring 75a, 75b are arranged.

[0021] The protective film 13 is a laminated structure in which multiple insulating films, such as an SiO2 film and a silicon nitride (SiN) film, are stacked. The protective film 13 is placed on the insulating film 12 and covers the heater 20, the first thermopile 31, the second thermopile 32, the first wiring 40, the second wiring 50, the third wiring 70a, 70b, and the fourth wiring 75a, 75b together.

[0022] Of the insulating film 12 and protective film 13, the portion inside the support portion 11 in a plan view is hereinafter referred to as the "thin film portion 111". Also, the support portion 11, and the outer portions of the insulating film 12 and protective film 13 that overlap with the support portion 11 in a plan view are hereinafter referred to as the "peripheral portion 112". In other words, the substrate 10 has a thin film portion 111 and a peripheral portion 112. The thin film portion 111 overlaps with the opening 10S in the Z-axis direction. The peripheral portion 112 is arranged to surround the thin film portion 111 in a plan view. As shown in Figure 2, the thickness of the thin film portion 111 is thinner than the thickness of the peripheral portion 112.

[0023] In the example shown in Figure 1, the substrate 10 has a roughly rectangular shape in plan view. However, the outer shape of the substrate 10 in plan view is not limited to a roughly rectangular shape. The outer shape of the substrate 10 in plan view may be roughly circular, roughly elliptical, or a roughly polygonal shape other than a rectangle.

[0024] <Heater 20> The heater 20 is placed on the substrate 10. The heater 20 includes a conductor that generates heat in response to a voltage or current supplied from an external power source via terminals 61a and 61b. The heat generated by the heater 20 is transferred through the substrate 10 to a flow path formed above the heater 20. This creates a temperature distribution in the flow path originating from the heat generated by the heater 20. Preferably, the heater 20 is made of a conductor with a relatively high thermal resistance, such as a heat-generating resistor. For example, the heater 20 is made of polysilicon. However, the material constituting the heater 20 is not limited to polysilicon.

[0025] As shown in Figure 1, the heater 20 extends in the second direction X. One end 21 of the heater 20 is located on the -X side. The other end 22 of the heater 20 is located on the +X side. The region between the one end 21 and the other end 22 of the heater 20 is located on the thin film portion 111 of the substrate 10. In the example shown in Figure 1, each of the one end 21 and the other end 22 of the heater 20 is located on the peripheral portion 112 of the substrate 10. However, each of the one end 21 and the other end 22 of the heater 20 may be located on the thin film portion 111 of the substrate 10.

[0026] <Detection unit 30> In the illustrated example, the detection unit 30 includes a first thermopile 31 and a second thermopile 32. The detection unit 30 detects the temperature in the flow path and on the flow sensor 1 through the first thermopile 31 and the second thermopile 32. Specifically, the first thermopile (first temperature detection unit) 31 detects the temperature of the space on the first thermopile (first temperature detection unit) 31 within the space forming the flow path. The second thermopile (second temperature detection unit) 32 detects the temperature of the space on the second thermopile (second temperature detection unit) 32 within the space forming the flow path.

[0027] The first thermopile 31 and the second thermopile 32 are each placed on the substrate 10. As shown in Figure 1, the first thermopile 31 and the second thermopile 32 are arranged so as to sandwich the heater 20 in the first direction Y. In the example shown in Figure 1, the first thermopile 31, the heater 20, and the second thermopile 32 are arranged in order from the +Y side to the -Y side. However, the second thermopile 32, the heater 20, and the first thermopile 31 may be arranged in order from the +Y side to the -Y side.

[0028] The first thermopile 31 is composed of a plurality of thermocouples connected in series. The plurality of thermocouples constituting the first thermopile 31 are arranged, for example, in a second direction X. Each of the plurality of thermocouples constituting the first thermopile 31 includes a first conducting portion 311 and a second conducting portion 312, which are made of different conducting materials. The conducting material constituting the first conducting portion 311 is, for example, polysilicon. The conducting material constituting the second conducting portion 312 is, for example, aluminum. However, the conducting materials constituting the first conducting portion 311 and the conducting materials constituting the second conducting portion 312 are not limited to these.

[0029] In the example shown in Figure 1, the first thermopile 31 has eight thermocouples. That is, in the example shown in Figure 1, the first thermopile 31 has eight first conductor sections 311 and eight second conductor sections 312. However, the number of thermocouples in the first thermopile 31 (i.e., the number of first conductor sections 311 and the number of second conductor sections 312) is not limited to this. In the example shown in Figure 2, the second conductor sections 312 are arranged on the first conductor sections 311. However, the first conductor sections 311 may be arranged on the second conductor sections 312.

[0030] The first thermopile 31 has a plurality of hot junctions 313 located near the heater 20 and a plurality of cold junctions 314 located further away from the heater 20 than the hot junctions 313. In the example shown in Figures 1 and 2, each of the plurality of hot junctions 313 corresponds to the contact point between the first conductor portion 311 and the second conductor portion 312 of the same thermocouple. As shown in Figure 1, each of the plurality of hot junctions 313 is aligned in the second direction X and is located on the thin film portion 111 of the substrate 10.

[0031] In the examples shown in Figures 1 and 2, each of the multiple cold junctions 314 is the contact point between a first conductor portion 311 of one of two adjacent thermocouples and a second conductor portion 312 of the other. As shown in Figure 1, each of the multiple cold junctions 314 is arranged in a line in the second direction X. Of the multiple cold junctions 314, the cold junction 314 located furthest to the -X side is connected to terminal 61d via a fourth wiring 75a. In the example shown in Figure 1, each of the multiple cold junctions 314 is located on the peripheral portion 112 of the substrate 10.

[0032] The second thermopile 32 is composed of a plurality of thermocouples connected in series. The plurality of thermocouples constituting the second thermopile 32 are arranged, for example, in a second direction X. Each of the plurality of thermocouples constituting the second thermopile 32 includes a third conducting portion 321 and a fourth conducting portion 322, which are composed of different conducting materials. The conducting material constituting the third conducting portion 321 is, for example, polysilicon. The conducting material constituting the fourth conducting portion 322 is, for example, aluminum. However, the conducting materials constituting the third conducting portion 321 and the fourth conducting portion 322 are not limited to these.

[0033] In the example shown in Figure 1, the second thermopile 32 has eight thermocouples. That is, in the example shown in Figure 1, the second thermopile 32 has eight third conductor sections 321 and eight fourth conductor sections 322. However, the number of thermocouples in the second thermopile 32 (i.e., the number of third conductor sections 321 and the number of fourth conductor sections 322) is not limited to this. In the example shown in Figure 2, the fourth conductor section 322 is arranged on the third conductor section 321. However, the third conductor section 321 may be arranged on the fourth conductor section 322.

[0034] The second thermopile 32 has a plurality of hot junctions 323 located near the heater 20 and a plurality of cold junctions 324 located further away from the heater 20 than the hot junctions 323. In the example shown in Figures 1 and 2, each of the plurality of hot junctions 323 corresponds to the contact between the third conductor portion 321 and the fourth conductor portion 322 of the same thermocouple. Each of the plurality of hot junctions 323 is arranged in the second direction X and is located on the thin film portion 111 of the substrate 10.

[0035] In the examples shown in Figures 1 and 2, each of the multiple cold junctions 324 is the contact point between the third conductor portion 321 of one of two adjacent thermocouples and the fourth conductor portion 322 of the other. Each of the multiple cold junctions 324 is arranged in a line in the second direction X. In the example shown in Figure 1, each of the multiple cold junctions 324 is located on the peripheral portion 112 of the substrate 10.

[0036] Referring to Figures 3A and 3B, an example of the detection principle of fluid flow rate or velocity based on the detection signal output from the detection unit 30 will be explained. As shown in Figure 3A, the heat generated by the heater 20 is transmitted approximately isotropically to the space above the substrate 10, that is, to the flow path and flow sensor 1, which are the space above the heater 20. As a result, in the absence of wind, an approximately symmetrical temperature distribution centered on the heater 20 is formed in the flow path and on the flow sensor 1. On the other hand, when fluid flow occurs in the flow path, the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 in the absence of wind is disrupted. For example, as shown in Figure 3B, when the fluid flow direction is forward, the temperature distribution in the flow path and on the flow sensor 1 is biased such that the temperature on the +Y side of the space in the flow path and on the flow sensor 1 is higher than the temperature on the -Y side. Also, when the fluid flow direction is reverse, the temperature distribution in the flow path and on the flow sensor 1 is biased such that the temperature on the -Y side of the space in the flow path and on the flow sensor 1 is higher than the temperature on the +Y side. Thus, in both the forward and reverse directions of fluid flow, a temperature difference occurs between the space above the first thermopile 31 and the space above the second thermopile 32 within the flow path and the space above the flow sensor 1. As a result, a voltage difference is generated between the voltage value of the detection signal output from the first thermopile 31 and the voltage value of the detection signal output from the second thermopile 32. This voltage difference can be considered to correspond to the fluid flow rate or velocity. This allows the detection unit 30 to detect the fluid flow rate or velocity. The external signal processing circuit calculates the fluid flow rate or velocity based on the voltage difference output from the detection unit 30. For example, the external signal processing circuit calculates the fluid flow rate or velocity by multiplying the voltage difference output from the detection unit 30 by a predetermined coefficient.

[0037] Incidentally, from the viewpoint of improving the detection accuracy of fluid flow rate or velocity, it is preferable that the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 is ensured when there is no wind. That is, it is preferable that the differential voltage output from the first thermopile 31 and the second thermopile 32 is zero when there is no wind. On the other hand, the substrate 10 is provided with various wirings, such as wiring for supplying power from an external power source to the heater 20 or wiring for outputting a detection signal from the detection unit 30 to the outside. Here, since the wiring has low thermal resistance, the temperature near the wiring is lowered due to the heat sink effect of the wiring provided on the substrate 10. At this time, if the geometric symmetry of the wiring layout is low, a bias may occur in the distribution of heat dissipation within the plane of the flow sensor 1. Therefore, even when there is no wind, the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 may be disrupted. As a result, an offset voltage in which the differential voltage is not zero is output from the detection unit 30 when there is no wind. As a result, when fluid flow occurs, the correspondence between the differential voltage output from the detection unit 30 and the flow rate or flow velocity changes depending on the direction of fluid flow (forward or reverse), which can lead to a decrease in the detection accuracy of the fluid flow rate or flow velocity.

[0038] Using the comparative example flow sensor 1R shown in Figure 4, an example of a bias in the distribution of heat dissipation within the plane of the flow sensor 1R will be explained. As shown in Figure 4, the wiring 40R connecting one end 21 of the heater 20 and terminal 61a of the comparative example flow sensor 1R is located only on the +Y side with respect to the heater 20. Furthermore, the substrate 10 of the flow sensor 1R does not have any other wiring that has a portion symmetrically positioned with respect to at least a part of the wiring 40R on the +X side with respect to the heater 20. Therefore, in the conventional flow sensor 1R, a bias in the distribution of heat dissipation within the plane may occur. On the other hand, the flow sensor 1 according to this embodiment can improve the geometric symmetry of the wiring layout provided on the substrate 10 by including the first wiring 40 and the second wiring 50, which will be described separately, and can reduce the bias in the distribution of heat dissipation within the plane. The first wiring 40 and the second wiring 50 will be described in detail below. In this specification, unless otherwise specified, "symmetry" means that two objects are positioned symmetrically with respect to a predetermined reference such as the heater 20. Furthermore, "high symmetry" or "improving symmetry" means that the positional relationship between multiple objects approaches line symmetry.

[0039] <1st wiring 40> The first wiring 40 is connected to one end 21 of the heater 20. In a cross-sectional view, the first wiring 40 is located above the heater 20, for example. The first wiring 40 may be connected to one end 21 of the heater 20 via a connecting member extending in the Z-axis direction, such as a contact plug. In the example shown in Figure 1, the first wiring 40 connects one end 21 of the heater 20 to terminal 61a and is for supplying voltage or current to the heater 20 from an external power source. However, the first wiring 40 is not limited to the wiring that connects one end 21 of the heater 20 to terminal 61a. The thermal resistance of the first wiring 40 is smaller than the thermal resistance of the heater 20. The first wiring 40 is made of a metal material such as aluminum, for example.

[0040] As shown in Figure 1, the first wiring 40 has a first portion 41 and a second portion 42. The first wiring 40 also has another portion 43 positioned between the first portion 41 and terminal 61a. However, the first wiring 40 may consist only of the first portion 41 and the second portion 42, or it may have a portion different from the other portion 43.

[0041] The first part 41 is located next to the first thermopile 31. Specifically, the first part 41 is positioned in the second direction X, aligned with the first conductor section 311 and the second conductor section 312, which are located on the -X side of the first thermopile 31. Furthermore, the first part 41 is positioned in the second direction X, aligned with the hot junction 313, which is located on the -X side of the first thermopile 31. Note that it is possible to avoid placing wiring between the first part 41 and the first thermopile 31. As a result, the heat sink effect of the first part 41 contributes most to temperature control of the first thermopile 31.

[0042] The second part 42 is located next to the second thermopile 32. Specifically, the second part 42 is positioned in the second direction X, aligned with the third conductor section 321 and the fourth conductor section 322, which are located on the -X side of the second thermopile 32. It is possible to avoid placing wiring between the second part 42 and the second thermopile 32. As a result, the heat sink effect of the second part 42 contributes most to temperature control of the second thermopile 32. Furthermore, the second part 42 is positioned in the second direction X, aligned with the hot junction 323, which is located on the -X side of the second thermopile 32. As a result, the positional symmetry of the first part 41 and the second part 42 at the hot junction 323, which is important for maintaining the symmetry of the temperature distribution, can be ensured.

[0043] The second portion 42 is a portion of the first wiring 40 that is continuous with the first portion 41 and is positioned symmetrically with respect to the heater 20. The first wiring 40 has a portion that extends to the +Y side from one end 21 of the heater 20 (first portion 41) and a portion that extends to the -Y side from one end 21 of the heater 20 (second portion 42). In this specification, "symmetrically positioned with respect to the heater 20" means that the two objects are positioned symmetrically with respect to a reference line CL that extends in the second direction X so as to overlap with the heater 20.

[0044] The first wiring 40 has a first portion 41 and a second portion 42 that are symmetrically positioned with respect to the heater 20, allowing the temperature reduction region resulting from the heat sink effect of the first wiring 40 to be distributed symmetrically on the +Y and -Y sides of the heater 20. As a result, compared to the flow sensor 1R shown in Figure 4, the bias in the distribution of heat dissipation within the plane can be reduced, and the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 can be ensured in the absence of wind. Therefore, the detection accuracy of the fluid flow rate or velocity can be improved.

[0045] In the example shown in Figure 1, the first portion 41 and the second portion 42 are located on the peripheral portion 112 of the substrate 10 and near the boundary 120 between the thin film portion 111 and the peripheral portion 112. By positioning the first portion 41 and the second portion 42 near the boundary 120 between the thin film portion 111 and the peripheral portion 112, the first portion 41 and the second portion 42 can be brought closer to the thin film portion 111, which is composed of an insulating film 12 and a protective film 13 made of insulating material and has a weak heat sink effect. As a result, the symmetry of the temperature distribution can be improved. Note that "near the boundary 120 between the thin film portion 111 and the peripheral portion 112" means that the distance between the object, such as the first portion 41 and the second portion 42, and the boundary 120 in the second direction X is 10% or less of the distance of the thin film portion 111 in the second direction X. The same applies to other objects different from the first portion 41 and the second portion 42 (for example, the third portion 51 and the fourth portion 52 of the second wiring 50 which will be described separately).

[0046] It is preferable that each of the first portion 41 and the second portion 42 extends in the first direction Y. That is, it is preferable that the first portion 41 and the second portion 42 are arranged on the same straight line along the first direction Y. By each of the first portion 41 and the second portion 42 extending in the first direction Y, the first portion 41 and the second portion 42 can be easily formed, and the first portion 41 and the second portion 42 can be arranged symmetrically with respect to the heater 20.

[0047] <2nd wiring 50> The second wiring 50 is connected to the other end 22 of the heater 20. In a cross-sectional view, the second wiring 50 is located, for example, above the heater 20. The second wiring 50 may also be connected to the other end 22 of the heater 20 via a connecting member extending in the Z-axis direction, such as a contact plug. The thermal resistance of the second wiring 50 is smaller than the thermal resistance of the heater 20. That is, the thermal resistance of the first wiring 40 and the thermal resistance of the second wiring 50 are smaller than the thermal resistance of the heater 20. The second wiring 50 is made of a metallic material such as aluminum. As a result, the temperature distribution can be controlled by effectively lowering the temperature around the first wiring 40 and the second wiring 50.

[0048] As shown in Figure 1, the second wiring 50 has a third portion 51 and a fourth portion 52. In the example shown in Figure 1, the second wiring 50 consists only of the third portion 51 and the fourth portion 52. However, the second wiring 50 may have further portions different from the third portion 51 and the fourth portion 52.

[0049] The third part 51 is located next to the first thermopile 31. Specifically, the third part 51 is positioned in the second direction X, aligned with the first conductor section 311 and the second conductor section 312, which are located on the +X side of the first thermopile 31. Furthermore, the third part 51 is positioned in the second direction X, aligned with the hot junction 313, which is located on the +X side of the first thermopile 31. Note that it is possible to avoid placing wiring between the third part 51 and the first thermopile 31. As a result, the heat sink effect of the third part 51 contributes most to temperature control of the first thermopile 31.

[0050] As shown in Figure 1, it is preferable that the first portion 41 of the first wiring 40 and the third portion 51 of the second wiring 50 are positioned symmetrically with respect to the center point 20CP of the heater 20 in the second direction X. That is, it is preferable that the first portion 41 of the first wiring 40 and the third portion 51 of the second wiring 50 are positioned symmetrically with respect to the first thermopile 31, with respect to the first thermopile 31. This allows the temperature reduction regions resulting from the heat sink effect of the first wiring 40 and the second wiring 50 to be distributed symmetrically on the +X and -X sides of the center point 20CP of the heater 20. As a result, the bias in the distribution of heat dissipation in the plane can be further reduced, and the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 can be ensured in the absence of wind. Therefore, the detection accuracy of the fluid flow rate or flow velocity can be further improved. In this specification, "two objects are positioned symmetrically with respect to the central point 20CP of the heater 20 in the second direction X" means that the two objects are positioned symmetrically with respect to a reference line extending in the first direction Y so as to coincide with the central point 20CP.

[0051] The first portion 41 of the first wiring 40 and the third portion 51 of the second wiring 50 preferably extend parallel to the first direction Y. By having the first portion 41 of the first wiring 40 and the third portion 51 of the second wiring 50 extend parallel to the first direction Y, the symmetry between the first wiring 40 and the second wiring 50 with respect to the center point 20CP of the heater 20 can be further improved. This makes it possible to further reduce the uneven distribution of heat dissipation in the plane.

[0052] The fourth section 52 is located next to the second thermopile 32. Specifically, the fourth section 52 is positioned in the second direction X, aligned with the third conductor section 321 and the fourth conductor section 322, which are located on the +X side of the second thermopile 32. It is possible to avoid placing wiring between the fourth section 52 and the second thermopile 32. As a result, the heat sink effect of the fourth section 52 contributes most to temperature control of the second thermopile 32. Furthermore, the fourth section 52 is positioned in the second direction X, aligned with the hot junction 323, which is located on the +X side of the second thermopile 32. As a result, the positional symmetry of the third section 51 and the fourth section 52 at the hot junction 323, which is important for maintaining the symmetry of the temperature distribution, can be ensured.

[0053] The fourth portion 52 is a portion of the second wiring 50 that is continuous with the third portion 51 and is positioned symmetrically with respect to the heater 20. The second wiring 50 has a portion that extends to the +Y side from the other end 22 of the heater 20 (third portion 51) and a portion that extends to the -Y side from the other end 22 of the heater 20 (fourth portion 52).

[0054] The second wiring 50 has a third portion 51 and a fourth portion 52 that are symmetrically positioned with respect to the heater 20, allowing the temperature reduction region resulting from the heat sink effect of the second wiring 50 to be distributed symmetrically on the +Y and -Y sides of the heater 20. As a result, the bias in the distribution of heat dissipation within the plane can be further reduced, and the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 can be ensured in the absence of wind. Therefore, the detection accuracy of the fluid flow rate or velocity can be further improved.

[0055] In the example shown in Figure 1, the third portion 51 and the fourth portion 52 of the second wiring 50 are located on the peripheral portion 112 of the substrate 10 and near the boundary 120 between the thin film portion 111 and the peripheral portion 112. By positioning the third portion 51 and the fourth portion 52 near the boundary 120 between the thin film portion 111 and the peripheral portion 112, the third portion 51 and the fourth portion 52 can be brought closer to the thin film portion 111, which is composed of an insulating film 12 and a protective film 13 made of insulating material and has a weak heat sink effect. As a result, the symmetry of the temperature distribution can be improved.

[0056] It is preferable that each of the third portion 51 and the fourth portion 52 extends in the first direction Y. That is, it is preferable that the third portion 51 and the fourth portion 52 are arranged on the same straight line along the first direction Y. By each of the third portion 51 and the fourth portion 52 extending in the first direction Y, the third portion 51 and the fourth portion 52 can be easily formed, and the third portion 51 and the fourth portion 52 can be arranged symmetrically with respect to the heater 20.

[0057] As shown in Figure 1, it is preferable that the second portion 42 of the first wiring 40 and the fourth portion 52 of the second wiring 50 are positioned symmetrically with respect to the center point 20CP of the heater 20 in the second direction X. That is, it is preferable that the second portion 42 of the first wiring 40 and the fourth portion 52 of the second wiring 50 are positioned symmetrically with respect to the second thermopile 32 in the second direction X, with respect to the second thermopile 32. This allows the temperature reduction region resulting from the heat sink effect of the first wiring 40 and the second wiring 50 to be distributed symmetrically on the +X and -X sides of the center point 20CP of the heater 20. As a result, the bias in the distribution of heat dissipation in the plane can be further reduced, and the symmetry of the temperature distribution formed in the flow path and on the flow sensor 1 can be ensured in the absence of wind. Therefore, the detection accuracy of the fluid flow rate or flow velocity can be further improved.

[0058] The second portion 42 of the first wiring 40 and the fourth portion 52 of the second wiring 50 preferably extend parallel to the first direction Y. By having the second portion 42 of the first wiring 40 and the fourth portion 52 of the second wiring 50 extend parallel to the first direction Y, the symmetry between the first wiring 40 and the second wiring 50 with respect to the center point 20CP of the heater 20 can be further improved. This further reduces the uneven distribution of heat dissipation in the plane.

[0059] In the example shown in Figure 1, the end 42T of the first wiring 40 on the second portion 42 side and the end 52T of the second wiring 50 on the fourth portion 52 side are both terminated. Also, in the example shown in Figure 1, the end 42T of the first wiring 40 on the second portion 42 side and the end 52T of the second wiring 50 on the fourth portion 52 side are at the same position in the first direction Y. Because the end 42T of the first wiring 40 on the second portion 42 side and the end 52T of the second wiring 50 on the fourth portion 52 side are both terminated and at the same position in the first direction Y, the symmetry between the first wiring 40 and the second wiring 50 with respect to the center point 20CP of the heater 20 can be further improved. This can further reduce the bias in the distribution of heat dissipation in the plane.

[0060] <Third wiring 70a, 70b, fourth wiring 75a, 75b> As shown in Figure 1, the third wire 70a connects the second conductor section 312, located furthest to the +X side of the first thermopile 31, to terminal 61c. The third wire 70b connects the fourth conductor section 322, located furthest to the +X side of the second thermopile 32, to terminal 61e. The fourth wire 75a connects the first conductor section 311, located furthest to the -X side of the first thermopile 31, to terminal 61d. The fourth wire 75b connects the third conductor section 321, located furthest to the -X side of the second thermopile 32, to terminal 61f. In the example shown in Figure 1, the third wire 70a and the fourth wire 75a are wires for outputting the detection signal from the first thermopile 31 to the outside. The third wire 70b and the fourth wire 75b are wires for outputting the detection signal from the second thermopile 32 to the outside.

[0061] The third wiring 70a and the third wiring 70b are positioned symmetrically with respect to the heater 20. The thermal resistance values ​​of the third wiring 70a and the third wiring 70b are smaller than the thermal resistance value of the heater 20. Each of the third wiring 70a and the third wiring 70b is made of, for example, aluminum. However, the material constituting each of the third wiring 70a and the third wiring 70b is not limited to aluminum.

[0062] The fourth wiring 75a and the fourth wiring 75b are positioned symmetrically with respect to the heater 20. The thermal resistance values ​​of the fourth wiring 75a and the fourth wiring 75b are smaller than the thermal resistance value of the heater 20. Each of the fourth wiring 75a and the fourth wiring 75b is made of, for example, aluminum. However, the material constituting each of the fourth wiring 75a and the fourth wiring 75b is not limited to aluminum.

[0063] The widths of the first part 41 and the second part 42 of the first wiring 40, and the third part 51 and the fourth part 52 of the second wiring can be made the same. This further reduces the uneven distribution of heat dissipation within the plane.

[0064] [Second Embodiment] Next, an example of the configuration of the flow sensor 1A according to the second embodiment will be described with reference to Figures 5 and 6. Figure 5 is a schematic top view showing an example of the flow sensor 1A according to the second embodiment. Figure 6 is an example of a schematic cross-sectional view of the flow sensor 1A showing a cross section cut along the line VI-VI shown in Figure 5. In the second embodiment, the same reference numerals are used for components similar to those in the first embodiment, and their descriptions are omitted as appropriate.

[0065] As shown in Figure 5, a wiring 78 is provided to connect one end 21a of the heater 20A to terminal 61a. As shown in Figure 6, one end 21a of the heater 20 and the wiring 78 are electrically connected by a contact plug 80. In the second embodiment, the wiring 78 corresponds to the wiring that supplies voltage or current from an external power source to the heater 20A. In contrast to the first embodiment, the first wiring 40A is located on the same layer as the heater 20A. In the example shown in Figure 5, the first wiring 40A consists only of a first part 41A and a second part 42.

[0066] As shown in Figure 6, the positions of the first wiring 40A and the second wiring 50A in the height direction are the same as the positions of the heater 20A in the height direction. That is, the first wiring 40A is continuous with one end 21a of the heater 20A, and the second wiring 50A is continuous with the other end 22a of the heater 20A.

[0067] The materials constituting the first wiring 40A and the second wiring 50A may be the same as the materials constituting the heater 20A. In other words, the thermal resistance values ​​of the first wiring 40A and the second wiring 50A may be the same as the thermal resistance value of the heater 20A. The heater 20A, the first wiring 40A, and the second wiring 50A are each made of, for example, polysilicon.

[0068] By aligning the heater 20A, the first wiring 40A, and the second wiring 50A in the same height direction, and by constructing them from the same material, each can be formed in the same process. This reduces the cost of forming the heater 20A, the first wiring 40A, and the second wiring 50A.

[0069] As shown in Figure 5, the end 41T on the first portion 41A side and the end 42T on the second portion 42 side of the first wiring 40A are terminated. Similarly, the end 51T on the third portion 51A side and the end 52T on the fourth portion 52A side of the second wiring 50A are terminated. In the example shown in Figure 5, the first wiring 40A and the second wiring 50A extend parallel to the first direction Y.

[0070] The length 40L of the first wiring 40A in the first direction Y is the same as the length 50L of the second wiring 50A in the first direction Y. This equality between the length 40L of the first wiring 40A and the length 50L of the second wiring 50A improves the symmetry between the first wiring 40A and the second wiring 50A with respect to the center point 20CP of the heater 20A. This further reduces the uneven distribution of heat dissipation within the plane.

[0071] The flow sensor 1A, like the first embodiment, includes a plurality of terminals 61c, 61d, 61e, and 61f that are connected to a signal processing circuit that processes the detection signal output from the detection unit 30. The third wiring 70a is connected to terminal 61c. The third wiring 70a is also connected to the hot junction 313a that is closest to the second wiring 50A among the plurality of hot junctions 313 of the first thermopile 31. In other words, the third wiring 70a connects terminal 61c and hot junction 313a. The third wiring 70b is connected to terminal 61e. The third wiring 70b is also connected to the hot junction 323a that is closest to the second wiring 50A among the plurality of hot junctions 323 of the second thermopile 32. In other words, the third wiring 70b connects terminal 61e and hot junction 323a.

[0072] As shown in Figure 6, the third wiring 70a is positioned above the heater 20A, the first wiring 40A, and the second wiring 50A. The third wiring 70a is separated from the heater 20A, the first wiring 40A, and the second wiring 50A in the Z-axis direction via another insulating film 14 located between the insulating film 12 and the protective film 13. Similarly, the third wiring 70b is positioned above the heater 20A, the first wiring 40A, and the second wiring 50A, and is separated from the heater 20A, the first wiring 40A, and the second wiring 50A via the insulating film 14. Furthermore, as shown in Figure 5, in a plan view, the third wiring 70a overlaps with the third portion 51A, which is part of the second wiring 50A. In a plan view, the third wiring 70b overlaps with the fourth portion 52A, which is part of the second wiring 50A. This prevents short circuits between the third wires 70a and 70b connected to terminals 61c and 61e, respectively, and the second wire 50A, while improving the flexibility of the wiring layout on the circuit board 10. Furthermore, the flow sensor 1A can be miniaturized. In the example shown in Figure 5, each of the third wires 70a and 70b overlaps with a portion of the second wire 50A in a plan view; however, only one of the third wires 70a or 70b may overlap with a portion of the second wire 50A in a plan view.

[0073] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the present invention.

[0074] Examples of the present invention are as follows: <1> circuit board and A heater is placed on the substrate and extends in a second direction that intersects with the first direction, which is the direction of fluid flow, in a plan view. A detection unit including a first temperature detection unit and a second temperature detection unit, each arranged on the substrate and positioned to sandwich the heater in the first direction, A first wiring harness connected to one end of the heater, A second wiring harness connected to the other end of the heater, Equipped with, The first wiring comprises a first portion located next to the first temperature detection unit and a second portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater. The second wiring has a third portion located next to the first temperature detection unit, and a fourth portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater. Flow sensor. <2> The first and third parts are positioned symmetrically with respect to the center point of the heater in the second direction. The aforementioned <1> The flow sensor described above. <3> The first and third parts extend parallel to the first direction, The aforementioned <1> or the above <2> The flow sensor described above. <4> The second and fourth parts are positioned symmetrically with respect to the center point of the heater in the second direction. The aforementioned <1> from the above <3> A flow sensor as described in one of the following documents. <5> The second and fourth parts extend parallel to the first direction, The aforementioned <4> The flow sensor described above. <6> The end of the first wiring on the second portion side and the end of the second wiring on the fourth portion side are each terminated and are in the same position in the first direction. The aforementioned <5> The flow sensor described above. <7> The first temperature detection unit and the second temperature detection unit are thermopiles having a hot junction. The first portion of the first wiring and the third portion of the second wiring are aligned with the hot junction of the first temperature detection unit in the second direction. The second portion of the first wiring and the fourth portion of the second wiring are aligned with the hot junction of the second temperature detection unit in the second direction. The aforementioned <1> from the above <6> A flow sensor as described in one of the following documents. <8> The thermal resistance values ​​of the first wiring and the second wiring are smaller than the thermal resistance value of the heater. The aforementioned <1> from the above <7> A flow sensor as described in one of the following documents. <9> The positions of the first and second wiring in the height direction are the same as the positions of the heater in the height direction. The end of the first portion and the end of the second portion of the first wiring are terminated, The end of the second wiring on the third portion side and the end on the fourth portion side are terminated, The length of the first wiring in the first direction is the same as the length of the second wiring in the first direction. The aforementioned <1> from the above <8> A flow sensor as described in one of the following documents. <10> The first temperature detection unit and the second temperature detection unit are thermopiles having a plurality of hot junctions. The aforementioned flow sensor is Multiple terminals connected to a signal processing circuit that processes the detection signal output from the detection unit, A third wiring is positioned above the heater, the first wiring, and the second wiring, and is connected to the hot junction that is closest to the second wiring among the plurality of hot junctions that have at least one of the first temperature detection unit and the second temperature detection unit, Furthermore, The third wiring connects at least one of the plurality of terminals to the hot junction located closest to the second wiring, and overlaps with a portion of the second wiring in a plan view. The aforementioned <9> The flow sensor described above. <11> The substrate has a thin film portion and a peripheral portion that surrounds the thin film portion in a plan view. The first and second portions of the first wiring, and the third and fourth portions of the second wiring, are each located on the peripheral portion and near the boundary between the thin film portion and the peripheral portion. The aforementioned <1> from the above <10> A flow sensor as described in one of the following documents. [Explanation of Symbols]

[0075] 1,1A...Flow sensor, 10...Substrate, 111...Thin film section, 112...Peripheral section, 20,20A...Heater, 20CP...Center point, 21,21a...One end of heater, 22,22a...Other end of heater, 30...Detection section, 31...First thermopile, 313...Hot junction of the first thermopile, 314...Cold junction of the first thermopile, 32...Second thermopile, 323...Hot junction of the second thermopile, 324... ...Cold junction of the second thermopile, 40, 40A...First wiring, 41, 41A...First section, 41T...End on the first section side, 42...Second section, 42T...End on the second section side, 50, 50A...Second wiring, 51, 51A...Third section, 51T...End on the third section side, 52, 52A...Fourth section, 52T...End on the fourth section side, 61a~61f...Terminals, 70a, 70b...Third wiring, 75a, 75b...Fourth wiring

Claims

1. circuit board and A heater is placed on the substrate and extends in a second direction that intersects with a first direction, which is the direction of fluid flow, in a plan view. A detection unit including a first temperature detection unit and a second temperature detection unit, each arranged on the substrate and positioned to sandwich the heater in the first direction, A first wiring harness connected to one end of the heater, A second wiring harness connected to the other end of the heater, Equipped with, The first wiring comprises a first portion located next to the first temperature detection unit and a second portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater. The second wiring has a third portion located next to the first temperature detection unit, and a fourth portion located next to the second temperature detection unit and symmetrically positioned with respect to the heater. Flow sensor.

2. The first and third parts are positioned symmetrically with respect to the center point of the heater in the second direction. The flow sensor according to claim 1.

3. The first and third portions extend parallel to the first direction, The flow sensor according to claim 1 or claim 2.

4. The second and fourth parts are positioned symmetrically with respect to the center point of the heater in the second direction. The flow sensor according to claim 1 or claim 2.

5. The second and fourth portions extend parallel to the first direction, The flow sensor according to claim 4.

6. The end of the first wiring on the second portion side and the end of the second wiring on the fourth portion side are each terminated and are in the same position in the first direction. The flow sensor according to claim 5.

7. The first temperature detection unit and the second temperature detection unit are thermopiles having a hot junction. The first portion of the first wiring and the third portion of the second wiring are aligned with the hot junction of the first temperature detection unit in the second direction. The second portion of the first wiring and the fourth portion of the second wiring are aligned with the hot junction of the second temperature detection unit in the second direction. The flow sensor according to claim 1 or claim 2.

8. The thermal resistance values ​​of the first wiring and the second wiring are smaller than the thermal resistance value of the heater. The flow sensor according to claim 1 or claim 2.

9. The positions of the first and second wiring in the height direction are the same as the positions of the heater in the height direction. The end of the first portion and the end of the second portion of the first wiring are terminated, The end of the second wiring on the third portion side and the end of the fourth portion side are terminated, The length of the first wiring in the first direction is the same as the length of the second wiring in the first direction. The flow sensor according to claim 1 or claim 2.

10. The first temperature detection unit and the second temperature detection unit are thermopiles having a plurality of hot junctions. The aforementioned flow sensor is Multiple terminals connected to a signal processing circuit that processes the detection signal output from the detection unit, A third wiring is positioned above the heater, the first wiring, and the second wiring, and is connected to the hot junction that is closest to the second wiring among the plurality of hot junctions that have at least one of the first temperature detection unit and the second temperature detection unit, Furthermore, The third wiring connects at least one of the plurality of terminals to the hot junction located closest to the second wiring, and overlaps with a portion of the second wiring in a plan view. The flow sensor according to claim 9.

11. The substrate has a thin film portion and a peripheral portion that is arranged to surround the thin film portion in a plan view. The first portion and the second portion of the first wiring, and the third portion and the fourth portion of the second wiring, are each located on the peripheral portion and near the boundary between the thin film portion and the peripheral portion. The flow sensor according to claim 1 or claim 2.

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