Flow sensor

Abstract

Provided is a flow sensor capable of reducing the effect of any change in output due to the difference in the position of a thermopile in the longitudinal direction of a heater. This flow sensor comprises: a substrate having a peripheral part and a first membrane part; and a first measurement unit having a first heater disposed on the first membrane part and extending in a first direction, a plurality of first thermopiles disposed side by side in the first direction and having a first thermocouple that has a first hot contact on the first membrane part, and a plurality of second thermopiles disposed side by side in the first direction and having a second thermocouple that has a second hot contact on the first membrane part. The first thermocouples and the second thermocouples are disposed in alternating fashion in the first direction, and a first distance from the first heater to the first hot contact in a second direction intersecting the first direction is greater than a second distance from the first heater to the second hot contact in the second direction.

Description

Flow sensor

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

[0002] Conventionally, flow sensors for detecting the flow rate, flow velocity, or thermal conductivity of fluids such as gases or liquids are known.

[0003] For example, Patent Document 1 discloses a technique for changing the distance from a heater to a thermopile in order to increase the measurement range of flow rate measurement.

[0004] Japanese Unexamined Patent Application Publication No. 2018 - 141664

[0005] However, Patent Document 1 does not suggest the influence of output changes due to differences in the position of the thermopile in the longitudinal direction of the heater.

[0006] An object of the present invention is to provide a flow sensor capable of reducing the influence of output changes due to differences in the position of the thermopile in the longitudinal direction of the heater.

[0007] The present flow sensor includes a substrate (1) having a peripheral portion (11) and a first membrane portion (12), a first heater (2) disposed on the first membrane portion (12) and extending in a first direction (X), a first thermopile (3) having a plurality of first thermocouples (31) arranged side by side in the first direction (X) and having a first hot junction (32) on the first membrane portion (12), and a second thermopile (4) having a plurality of second thermocouples (41) arranged side by side in the first direction (X) and having a second hot junction (42) on the first membrane portion (12), and a first measurement unit (110). In the first direction (X), the first thermocouple (31) and the second thermocouple (41) are alternately arranged, and in a second direction (Y) intersecting the first direction (X), a first distance (L1) from the first heater (2) to the first hot junction (32) is longer than a second distance (L2) from the first heater (2) to the second hot junction (42).

[0008] The reference numerals in the parentheses above are for ease of understanding and are merely examples and are not limited to the illustrated embodiments.

[0009] According to the present invention, it is possible to provide a flow sensor that can reduce the influence of output changes due to differences in the position of thermopiles in the longitudinal direction of the heater.

[0010] This is an example of a schematic top view showing the overall configuration of the flow sensor according to the first embodiment. This is an example of a schematic cross-sectional view along line II-II in Figure 1. This is an example of a schematic top view showing an enlarged view of the first thermopile and the second thermopile of the flow sensor according to the first embodiment. This is an example of a schematic top view showing the overall configuration of the flow sensor according to the second embodiment. This is an example of a schematic top view showing an enlarged view of the first thermopile and the second thermopile of the flow sensor according to the third embodiment. This is an example of a schematic top view showing an enlarged view of the first thermopile and the second thermopile of the flow sensor according to the fourth embodiment. This is an example of a schematic top view showing the first thermopile and the second thermopile of the flow sensor according to the fifth embodiment. This is an example of a schematic top view showing the first thermopile and the second thermopile of the flow sensor according to the sixth embodiment. This is an example of a schematic top view showing the first thermopile and the second thermopile of the flow sensor according to the seventh embodiment.

[0011] 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. However, the embodiments shown below are illustrative of flow sensors for realizing the technical concept of this disclosure and are not limited thereto. Note that the size, positional relationships, etc., of the components shown in each drawing may be exaggerated for clarity of explanation.

[0012] 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 approximately orthogonal to each other. The direction pointed to by the X-axis arrow is denoted as the +X direction or +X side, and the opposite direction is denoted as the -X direction or -X side. The direction pointed to by the Y-axis arrow is denoted as the +Y direction or +Y side, and the opposite direction is denoted as the -Y direction or -Y side. The direction pointed to by the Z-axis arrow is denoted as the +Z direction or +Z side, and the opposite direction is denoted as the -Z direction or -Z side.

[0013] The X direction corresponds to the first direction, which is the longitudinal direction of the heater in the flow sensor according to the embodiment. The Y direction corresponds to the second direction, which intersects the first direction. The Z direction corresponds to the third direction, which is the direction in which the plane of the first membrane portion of the flow sensor according to the embodiment is viewed from above. In this specification, these are referred to as the first direction X, the second direction Y, and the third direction Z. Viewing an object from the third direction Z is sometimes referred to as a top view.

[0014] The terms used above to indicate specific directions and positions are merely for the purpose of clarifying the relative directions and positions in the referenced drawings. These terms do not limit the orientation of the embodiments, and the orientation of the flow sensor when using the embodiments is arbitrary. Furthermore, in this specification, "place" is not limited to direct contact, but also includes indirect placement, for example, via other components.

[0015] [First Embodiment] <Configuration of the flow sensor according to the first embodiment> The configuration of the flow sensor according to the first embodiment will be described with reference to Figures 1 to 3. Figure 1 is an example of a schematic top view showing the overall configuration of the flow sensor 100 according to the first embodiment. Figure 2 is a schematic cross-sectional view taken along line II-II in Figure 1. Figure 3 is a schematic top view showing an enlarged view of the first thermopile 3 and the second thermopile 4 of the flow sensor 100.

[0016] The flow sensor 100 is a thermal sensor that detects the thermal conductivity of a fluid such as a gas or liquid. The flow sensor 100 outputs a detection signal corresponding to the thermal conductivity of the fluid.

[0017] In the example shown in Figure 1, the flow sensor 100 has a roughly rectangular shape when viewed from above. The size of the flow sensor 100 when viewed from above is, for example, 1.6 mm × 1.6 mm. However, the outer shape of the substrate 1 when viewed from above may be roughly circular, roughly elliptical, or roughly polygonal, etc. Furthermore, the size and thickness of the flow sensor 100 are not limited to those described above. The flow sensor 100 is formed by a semiconductor process or the like.

[0018] As shown in Figure 1, the flow sensor 100 includes a substrate 1 having a peripheral portion 11 and a first membrane portion 12. The flow sensor 100 also includes a first measuring unit 110. The first measuring unit 110 includes a first heater 2 arranged on the first membrane portion 12 and extending in a first direction X, and a first thermopile 3 arranged in a plurality along the first direction X, each having a first thermocouple 31 with a first hot junction 32 on the first membrane portion 12. The first measuring unit 110 also includes a second thermopile 4 arranged in a plurality along the first direction X, each having a second thermocouple 41 with a second hot junction 42 on the first membrane portion 12. In Figure 1, to indicate that the first measuring unit 110 has a first heater 2, a first thermopile 3, and a second thermopile 4, the reference numerals for the first heater 2, the first thermopile 3, and the second thermopile 4 are shown together with the reference numeral for the first measuring unit 110. Reference numerals may be shown together for similar purposes in subsequent diagrams.

[0019] In the example shown in Figure 1, the first heater 2 is connected to first heater pads 21 located at both ends in the first direction X. In the second direction Y, seven first thermocouples 31 and six second thermocouples 41 are arranged symmetrically with respect to the first heater 2, aligned in the first direction X at approximately constant intervals.

[0020] In the example shown in Figure 1, the flow sensor 100 has two first thermopiles 3 and two second thermopiles 4. The first thermopile 3A, located on the +Y side of the first heater 2, and the first thermopile 3B, located on the -Y side of the first heater 2, are mirror-symmetric with respect to the first heater 2 and form a pair. Similarly, the second thermopile 4A, located on the +Y side of the first heater 2, and the second thermopile 4B, located on the -Y side of the first heater 2, are mirror-symmetric with respect to the first heater 2 and form a pair. The first thermopiles 3 are referred to as thermoelectric piles, and it can be said that multiple thermocouples are connected to form the first thermopile 3. The second thermopiles 4 are also referred to as thermoelectric piles, and it can be said that multiple thermocouples are connected to form the second thermopile 4.

[0021] In this embodiment, the first thermocouple 31 and the second thermocouple 41 are arranged alternately in the first direction X. Also, in the second direction Y which intersects the first direction X, the first distance L1 from the first heater 2 to the first hot junction 32 is longer than the second distance L2 from the first heater 2 to the second hot junction 42. In the first measurement unit 110, the fluid to be detected flows in the first direction X. In this embodiment, the first measurement unit 110 calculates the thermal conductivity of the fluid based on the output difference between the first thermopile 3 and the second thermopile 4, which corresponds to the difference between the first distance L1 and the second distance L2.

[0022] In the example shown in Figure 2, the flow sensor 100 has a substrate 1, an insulating film 113 disposed on the substrate 1 in a third direction Z, and a protective film 13 disposed on the insulating film 113. The peripheral portion 11 has a support portion 111 made of the substrate 1. The first membrane portion 12 does not have a support portion 111. In the third direction Z, the thickness of the peripheral portion 11 is approximately 400 μm, and the thickness of the first membrane portion 12 is approximately 2 μm. The second wiring 312 is located above the first wiring 311 in the third direction Z, for example, on the +Z side. The first wiring 311 and the second wiring 312 are connected at a first hot junction 32 on the first membrane portion 12 and at a first cold junction 33 on the peripheral portion 11. The first hot junction 32 is the contact of the first thermocouple 31 that is used for temperature measurement. The first cold junction 33 is the junction other than the hot junction among the two junctions of the first thermocouple 31.

[0023] The first thermocouple 31 has a first wiring 311 and a second wiring 312 positioned above the first wiring 311, i.e., on the +Z side. The first wiring 311 and the second wiring 312 are located inside the protective film 13. The connected first wiring 311 and the second wiring 312 can be referred to as a thermocouple as a set. One end of the first wiring 311 and the second wiring 312 on the substrate 1 is connected on the first membrane portion 12, and the other end is connected on the peripheral portion 11.

[0024] The protective film 13 is a laminated structure in which multiple insulating films are stacked. The support portion 111 of the peripheral portion 11 is the substrate 1, which is a material composed of, for example, silicon. The peripheral portion 11 has higher heat dissipation efficiency compared to the first membrane portion 12 and functions as a heat sink. The first heater 2 is a heat-generating resistor composed of platinum, nichrome, polysilicon, etc., and generates heat in accordance with the current or voltage supplied via the first heater pad 21.

[0025] The first wiring 311 of the first thermocouple 31 is a polysilicon wiring composed of, for example, a polysilicon film. The second wiring 312 of the first thermocouple 31 is an aluminum wiring composed of, for example, an aluminum film. The first wiring 311 and the second wiring 312 each extend in the second direction Y. The first thermocouple 31 has a repeating structure in which the polysilicon film of the first wiring 311 and the aluminum film of the second wiring 312 are connected in series.

[0026] As shown in Figure 3, in this embodiment, when n is an integer of 1 or more, the nth first wiring 311n and the nth second wiring 312n are connected at the first hot junction 32 by a contact plug 322 in the first membrane portion 12. Also, the (n+1)th first wiring 311n+1 and the nth second wiring 312n are connected at the first cold junction 33 in the peripheral portion 11. The second wiring 312 extends in the Y direction, passes over the conductive film 81 in the Z direction, crosses the adjacent second thermocouple 41 in the X direction, and is connected to the contact plug 331. The contact plug 331 is electrically connected to the (n+1)th first wiring in the peripheral portion 11.

[0027] The second thermocouple 41 of the second thermopile 4 has a third wire 411 and a fourth wire 412 positioned above the third wire 411, i.e., on the +Z side. The third wire 411 and the fourth wire 412 are also positioned inside the protective film 13, similar to the first wire 311 and the second wire 312 shown in Figure 2.

[0028] The third wiring 411 and the fourth wiring 412 are connected at the second hot junction 42, which is a third point on the first membrane portion 12. Furthermore, the third wiring 411 and the fourth wiring 412 are connected at the peripheral portion 11 via a connection portion 34.

[0029] In this embodiment, when m is an integer of 1 or more, the mth third wiring 411m and the mth fourth wiring 412m are connected at the second hot junction 42 by the contact plug 422 in the first membrane portion 12. The third wiring 411m is connected to the contact plug 342, and the contact plug 342 is connected to the conductive film 81. The conductive film 81 passes under 312n and 312n+1 and is connected to the contact plug 343. The contact plug 343 is connected to the contact plug 341 via the wiring 344. The contact plug 341 is connected to the (m+1)th third wiring 411m+1. The mth third wiring 411m is connected to the contact plug 342. The third wiring 411m+1 is connected to the third wiring 411m via the contact plug 342, the contact plug 343 and the wiring 344.

[0030] The first wiring 311 of the first thermopile 3 and the third wiring 411 of the second thermopile 4 are polysilicon wirings, for example, that include a polysilicon film. The second wiring 312 of the first thermopile 3 and the fourth wiring 412 of the second thermopile 4 are aluminum wirings, for example, that include an aluminum film. The first wiring 311, the second wiring 312, the third wiring 411, and the fourth wiring 412 each extend in the second direction Y. The first thermopile 3 has a repeating structure in which the polysilicon film of the first wiring 311 and the aluminum film of the second wiring 312 are connected in series. The second thermopile 4 has a repeating structure in which the polysilicon film of the third wiring 411 and the aluminum film of the fourth wiring 412 are connected in series.

[0031] In the example shown in Figure 3, the flow sensor 100 includes a conductive film 81 and a contact plug 82 disposed on the conductive film 81. The conductive film 81 is composed of, for example, polysilicon or another layer of aluminum. The contact plug 82 may be composed of, for example, aluminum, or tungsten or the like.

[0032] <Effects of the flow sensor 100 according to the first embodiment> When the flow sensor 100 detects the thermal conductivity of a fluid, the first heater 2 is energized and heated, causing the temperature of the space around the first heater 2 to rise. Depending on the difference between the first distance L1 and the second distance L2, a temperature difference ΔT is generated between the temperature at the location of the first thermopile 3 and the temperature at the location of the second thermopile 4. The flow sensor 100 calculates the thermal conductivity of the fluid based on the temperature difference ΔT corresponding to the output difference between the first thermopile 3 and the second thermopile 4, which is determined by the difference between the first distance L1 and the second distance L2.

[0033] Here, the temperature difference ΔT depends on the thermal conductivity of the fluid being detected, as well as the thermal conductivity and thermal resistance of the flow sensor 100 itself. In order to detect the thermal conductivity of the fluid using the flow sensor 100, it is preferable to minimize the influence of the thermal conductivity or thermal resistance of the flow sensor 100 itself.

[0034] For example, if the center of the first heater pad 21 is taken as 0 in the first direction X, a large difference between the average value of the positions of the first hot junctions 32 of the multiple first thermocouples 31 and the average value of the positions of the second hot junctions 42 of the multiple second thermocouples 41 will result in a large difference between the temperature at the positions of the multiple first thermocouples 31 and the temperature at the positions of the multiple second thermocouples 41. More specifically, for example, if, in the first direction X, multiple first thermocouples 31 are collectively located on the -X side and multiple second thermocouples 41 are collectively located on the +X side, the difference between the average value of the positions of the first thermocouples 31 and the average value of the positions of the second thermocouples 41 will be large. As a result, the temperature difference detected by the multiple first thermocouples 31 and the multiple second thermocouples 41 will contain a large component of temperature difference corresponding to the difference in position in the first direction X. As the component of the temperature difference corresponding to the difference in position becomes larger, the temperature difference ΔT corresponding to the thermal conductivity of the fluid, that is, the output difference between the first thermocouple 31 and the second thermocouple 41 corresponding to the thermal conductivity of the fluid, becomes less accurately detected. As a result, the accuracy of thermal conductivity detection by the flow sensor may decrease.

[0035] On the other hand, it is conceivable to correct for detection errors by calculation, which are caused by the difference between the positions of the multiple first thermocouples 31 and the multiple second thermocouples 41. However, such correction increases the computational load on the flow sensor. Furthermore, some degree of correction error is unavoidable, so there are limits to how much detection accuracy can be improved through correction.

[0036] In this embodiment, the first thermocouple 31 and the second thermocouple 41 are arranged alternately in the first direction X. This reduces the difference between the average value of the positions of the multiple first thermocouples 31 and the average value of the positions of the multiple second thermocouples 41 in the first direction X. By reducing the difference in the average values, the influence of output changes due to the difference in the positions of the first thermocouples 31 and the second thermocouples 41 in the first direction X is reduced. In other words, in this embodiment, a flow sensor 100 can be provided that can reduce the influence of output changes due to the difference in the positions of thermocouples in the longitudinal direction of the first heater 2. Furthermore, by reducing the influence of output changes due to the difference in the positions of the thermopile, the detection accuracy of the thermal conductivity based on the output difference of the thermocouples is improved.

[0037] Furthermore, in this embodiment, the fluid to be detected flows from the negative (-X direction) to the positive (+X direction) of the first direction X in the first measuring unit 110. As a result, the first measuring unit 110 can detect the thermal conductivity of the fluid.

[0038] In this embodiment, the nth first wire 311n and the nth second wire 312n are connected at a first hot junction 32 in the first membrane portion 12, and the (n+1)th first wire 311n+1 and the nth second wire 312n are connected at a first cold junction 33 in the peripheral portion 11. In addition, the mth third wire 411m and the mth fourth wire 412m are connected at a third point in the first membrane portion 12, and the (m+1)th third wire 411m+1 and the mth fourth wire 412m are connected at a connection portion 34 in the peripheral portion 11. With this configuration, the first wires 311 and second wires 312 constituting the first thermocouple 31 and the third wires 411 and fourth wires 412 constituting the second thermocouple 41 can be crossed. As a result, the flow sensor 100 can alternately arrange multiple first thermocouples 31 and multiple second thermocouples 41.

[0039] [Second Embodiment] Next, a flow sensor according to the second embodiment will be described. Note that names and reference numerals identical to those in the previously described embodiments indicate the same or identical components or configurations, and detailed explanations will be omitted as appropriate. This also applies to the embodiments described later.

[0040] Figure 4 is an example of a schematic top view showing the overall configuration of the flow sensor according to the second embodiment.

[0041] The flow sensor according to this embodiment differs from the flow sensor 100 according to the first embodiment in that it further comprises a second measuring unit 120. The second measuring unit 120 includes a second membrane portion 14 formed on the substrate 1, a second heater 6, and a third thermopile 7 arranged in a plurality in a second direction Y, including a third thermocouple 71 having a third hot junction 72 on the second membrane portion 14.

[0042] In this embodiment, in the second measurement unit 120, the fluid flows from the minus side (-X direction) to the plus side (+X direction) in the first direction X. The second heater 6 is connected to second heater pads 61 arranged at both ends in the second direction Y.

[0043] The second measurement unit 120 outputs a detection signal corresponding to the flow rate or flow velocity of the fluid. For example, when detecting the flow rate or flow velocity of the fluid by the second measurement unit 120, the second heater 6 is energized and heated, thereby forming a substantially symmetric temperature distribution centered on the second heater 6. In a state where a substantially symmetric temperature distribution is formed with respect to the second heater 6, when a fluid flow in the first direction X occurs in the +Z side space of the second measurement unit 120, the symmetry of the temperature distribution formed by the second heater 6 is disrupted. By disrupting the symmetry of the temperature distribution, the difference in electromotive force between the paired third thermopiles 7 becomes corresponding to the flow rate or flow velocity or the like. The flow rate or flow velocity of the fluid is calculated from the voltage signal corresponding to the difference in electromotive force detected by the second measurement unit 120.

[0044] The flow sensor according to this embodiment detects the thermal conductivity of the fluid by the first measurement unit 110 and also detects the flow rate or flow velocity of the fluid by the second measurement unit 120. Thereby, the flow sensor according to this embodiment can simultaneously detect the thermal conductivity of the fluid and the flow rate or flow velocity. [[ID=)7]]

[0045] The effects other than those described above in the flow sensor according to this embodiment are the same as those of the flow sensor according to the first embodiment. Also, the first measurement unit 110 included in the flow sensor according to this embodiment is not limited to the first measurement unit 110 included in the flow sensor 100 according to the first embodiment. For example, the first measurement unit 110 included in the flow sensor according to this embodiment may be the first measurement unit 110 included in the flow sensor 100 according to the third to seventh embodiments shown below.

[0046] [Third Embodiment] Next, the flow sensor according to the third embodiment will be described.

[0047] FIG. 5 is an example of a schematic top view showing an enlargement of the first thermopile 3 and the second thermopile 4 included in the flow sensor according to the third embodiment.

[0048] In the flow sensor according to the present embodiment, the first thermopile 3 is composed of a plurality of first thermocouples 31. The first thermocouple 31 has a first wiring 311 which is a polysilicon wiring of the first conductivity type, and a second wiring 312 which is arranged above the first wiring 311 and is a polysilicon wiring of the second conductivity type opposite to the first conductivity type. The second thermopile 4 is composed of a plurality of second thermocouples 41. The second thermocouple 41 has a third wiring 411 which is a polysilicon wiring of the first conductivity type, and a fourth wiring 412 which is a polysilicon wiring of the second conductivity type. In the flow sensor according to the present embodiment, these points are different from the flow sensor 100 according to the first embodiment.

[0049] Further, the contact plug 323 located at the first hot junction 32 is formed so as to be continuous with the first wiring 311 and the second wiring 312. As a result, the first wiring 311 and the second wiring 312 can be connected without using an upper layer wiring connected to the contact plug 323. Further, the contact plug 324 located at the second hot junction 42 is formed so as to be continuous with the third wiring 411 and the fourth wiring 412. As a result, the third wiring 411 and the fourth wiring 412 can be connected without using an upper layer wiring connected to the contact plug 324.

[0050] Also, the n-th second wiring 312n is connected to the first cold junction 33 by a contact plug 350 in the peripheral portion 11. The contact plug 350 is connected to a wiring 351. The wiring 351 passes above the conductive film 81, straddles the second thermocouple 41n, and is connected to a contact plug 331. The contact plug 331 is electrically connected to the (n + 1)-th first wiring 331n+1 in the peripheral portion 11.

[0051] The third wire 411m is connected to contact plug 342, and contact plug 342 is connected to conductive film 81. Conductive film 81 passes under 312n and 312n+1 and is connected to contact plug 343. Contact plug 343 is connected to contact plug 341 via wire 344. Contact plug 341 is connected to the (m+1)th third wire 411m+1. The mth third wire 411m is connected to contact plug 342. The third wire 411m+1 is connected to the third wire 411m via contact plug 342, contact plug 343 and wire 344.

[0052] In the example shown in Figure 5, the first conductivity type is P-type and the second conductivity type is N-type. However, the first conductivity type may be N-type and the second conductivity type may be P-type.

[0053] As described above, even when the first wiring 311 and the second wiring 312, and the third wiring 411 and the fourth wiring 412 are each made of conductive polysilicon, the same effects and advantages as those of the flow sensor 100 according to the first embodiment can be obtained.

[0054] [Fourth Embodiment] Next, a flow sensor according to the fourth embodiment will be described.

[0055] Figure 6 is an example of a schematic top view showing an enlarged view of the first thermopile 3 and the second thermopile 4 of the flow sensor according to the fourth embodiment.

[0056] In the flow sensor according to this embodiment, the connections of the first hot junction 32, the first cold junction 33, and the second hot junction 42 are the same as in the flow sensor according to the third embodiment. On the other hand, the (m+1)th third wiring 411m+1 extends in the Y direction and is connected to the conductive film 811. Here, the third wiring 411m+1 and the conductive film 811 are integrated, formed in the same process, and made of the same material. This is the point in which the flow sensor according to this embodiment differs from the flow sensor according to the third embodiment.

[0057] The third wiring 411m is connected to the contact plug 343, and the contact plug 343 is connected to the wiring 344. The contact plug 341 is connected to the contact plug 343 via the wiring 344.

[0058] With the above configuration, when the first thermopile 3 and the second thermopile 4 are composed of two types of polysilicon, N-type and P-type, and aluminum, the first wiring 311 and the second wiring 312 constituting the first thermopile 3 and the third wiring 411 and the fourth wiring 412 constituting the second thermopile 4 can be crossed. As a result, in the flow sensor according to this embodiment, a plurality of first thermopiles 3 and a plurality of second thermopiles 4 can be arranged alternately.

[0059] Other effects and benefits of the flow sensor according to this embodiment are the same as those of the flow sensor according to the third embodiment.

[0060] [Fifth Embodiment] Next, a flow sensor according to the fifth embodiment will be described.

[0061] Figure 7 is an example of a schematic top view showing the first thermopile 3 and the second thermopile 4 of the flow sensor according to the fifth embodiment.

[0062] In this embodiment of the flow sensor, the first thermopile 3 consists of n first thermocouples 31, and the second thermopile 4 consists of n second thermocouples 41, which is different from the flow sensor 100 according to the first embodiment. In other words, the number of first thermocouples 31 is equal to the number of second thermocouples 41. In the example shown in Figure 7, six first thermocouples 31 and six second thermocouples 41 are arranged in a first direction X at approximately constant intervals.

[0063] Furthermore, in the example shown in Figure 7, if n is an even number, the first thermocouple 31, the second thermocouple 41, and the electrically independent fourth thermocouple 5 are arranged between the n / 2th and n / 2+1th thermopile 3. The fourth thermocouple 5 has a fifth wire 51 and a sixth wire 52 positioned above the fifth wire 51. One end 521 of the sixth wire 52 of the fourth thermocouple 5 is connected to the fifth wire 51, and the other end 522 of the sixth wire 52 is terminated. In other words, the fourth thermocouple 5 is electrically independent and can be called a dummy thermocouple. A contact plug 347 may be placed on the fifth wire 51. The contact plug 347 is not connected to the wire and is electrically independent.

[0064] In this embodiment, the number of first thermocouples 31 in the first thermopile 3 is equal to the number of second thermocouples 41 in the second thermopile 4. This reduces the difference between the average value of the positions of the multiple first thermopiles 3 and the average value of the positions of the multiple second thermopiles 4, compared to the case where the number of first thermocouples 31 and the number of second thermocouples 41 are not equal. As a result, the flow sensor according to this embodiment is less affected by output changes due to differences in thermopile positions, and the detection accuracy of thermal conductivity based on the output difference of the thermopiles is improved.

[0065] In this embodiment, a fourth thermocouple 5 is placed, and the wiring of the first thermocouples 31 at both ends of it, and the multiple second thermocouples 41 are connected to it. The arrangement of the first thermocouples 31 and the second thermocouples 41 can be symmetrical in the X direction with respect to the fourth thermocouple 5. With this configuration, the first thermopile 3 and the second thermopile 4 become electrically balanced. As a result, in the flow sensor according to this embodiment, the influence of output changes due to differences in the position of the thermopiles is reduced, and the detection accuracy of thermal conductivity based on the output difference of the thermopiles is improved.

[0066] The fourth thermocouple 5 is positioned at the center of the first thermocouple 31 in the first direction X. As a result, the number of first thermocouples 31 and second thermocouples 41 are symmetrical in the first direction X, the average values ​​of the positions of the first thermocouple 31 and the second thermocouple 41 become equal, and the accuracy of detecting the thermal conductivity based on the output difference of the thermopile is improved.

[0067] Other effects and benefits of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

[0068] [Sixth Embodiment] Next, a flow sensor according to the sixth embodiment will be described.

[0069] Figure 8 is an example of a schematic top view showing the first thermopile 3 and the second thermopile 4 of the flow sensor according to the sixth embodiment.

[0070] In the flow sensor according to this embodiment, the n / 2 first thermocouple 31 and the n / 2+1 first thermocouple 31 are connected by connection parts 348 and 349. The connection parts 348 and 349 are arranged on the same layer as the second wiring 312, and the material of the connection parts 348 and 349 can be the same as that of the second wiring 312.

[0071] Specifically, the second wiring 312n / 2 of the n / 2th first thermocouple 31 is connected to a connection portion 348 formed on the fifth wiring 51 of the fourth thermocouple 5. The connection portion 348 is connected to a connection portion 349. The connection portion 349 is connected to the first wiring 311n+1 of the n / 2+1th first thermocouple 31. Furthermore, the connection portion 349 has the same shape as the second wiring 312 that connects the first thermocouples 31 (specifically, the conductive film 81 and the second wiring 312 located in the -Y direction relative to the conductive film 81). These points differ from the flow sensor according to the fourth embodiment. Also, the sixth wiring 52 is terminated, so that the fourth thermocouple 5 is electrically independent from the first thermocouple 31. In addition, the contact plug 347 can be omitted.

[0072] With the above configuration, the wiring layout connecting the first thermocouples 31 is repeated, which improves the processing accuracy of the flow sensor. As a result, this embodiment provides a flow sensor with high detection accuracy.

[0073] Other effects and benefits of the flow sensor according to this embodiment are the same as those of the flow sensor according to the fifth embodiment.

[0074] [Seventh Embodiment] Next, a flow sensor according to the seventh embodiment will be described.

[0075] Figure 9 is an example of a schematic top view showing the first thermopile 3 and the second thermopile 4 of the flow sensor according to the seventh embodiment.

[0076] In the flow sensor according to this embodiment, the first wiring 311 of the first thermocouple 31 and the third wiring 411 of the second thermocouple 41 have the same shape. Also, the second wiring 312 of the first thermocouple 31 and the fourth wiring 412 of the second thermocouple 41 have the same shape. These points differ from the flow sensor 100 according to the first embodiment. From another viewpoint, the first wiring 311 of the first thermocouple 31 and the third wiring 411 of the second thermocouple 41 have the same shape when viewed from above. Also, the second wiring 312 of the first thermocouple 31 and the fourth wiring 412 of the second thermocouple 41 have the same shape when viewed from above.

[0077] In the example shown in Figure 9, the first thermocouple 31 includes a first dummy section 37. The first dummy section 37 is a location where the first wiring 311 of the first thermocouple 31 is provided to have the same shape as the third wiring 411 of the second thermocouple 41. On the other hand, the first hot junction 32 is a location where the first wiring 311 and the second wiring 312 are connected by a contact plug. In the first dummy section 37, the first wiring 311 and the second wiring 312 are not connected by a contact plug, so the first dummy section 37 is not a hot junction.

[0078] Furthermore, the second thermocouple 41 includes a second dummy section 47. The second dummy section 47 is a location where the third wiring 411 of the second thermocouple 41 is provided to have the same shape as the first wiring 311 of the first thermocouple 31. On the other hand, the second hot junction 42 is a location where the third wiring 411 and the fourth wiring 412 are connected by a contact. In the second dummy section 47, the third wiring 411 and the fourth wiring 412 are not connected by a contact plug, so the second dummy section 47 is not a hot junction.

[0079] The first distance L1 from the first heater 2 to the first hot junction 32 is longer than the second distance L2 from the first heater 2 to the second hot junction 42, similar to the flow sensor 100 according to the first embodiment.

[0080] For example, the first wiring 311 and the third wiring 411 have the same shape. Also, the second wiring 312 and the fourth wiring 412 have the same shape. As a result, the difference in thermal conductivity between the first thermopile 3 and the second thermopile 4 is further reduced. These features make it easier to derive the thermal conductivity of the fluid from the outputs of the first thermopile 3 and the second thermopile 4 in this embodiment. Furthermore, the detection accuracy of the thermal conductivity of the fluid is improved in this embodiment.

[0081] In this embodiment, the first thermocouple 31 includes a first dummy portion 37, and the second thermocouple 41 includes a second dummy portion 47. This allows the first wiring 311 and the third wiring 411 to have the same shape, and the third wiring 411 and the fourth wiring 412 to have the same shape, while making the first distance L1 longer than the second distance L2. As a result, in this embodiment, the process of deriving the thermal conductivity of the fluid from the outputs of the first thermopile 3 and the second thermopile 4 becomes easier. Furthermore, in this embodiment, the detection accuracy of the thermal conductivity of the fluid is improved.

[0082] Other effects and benefits of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

[0083] In this embodiment, by arranging the first thermopile 3 and the second thermopile 4 alternately in the first direction X, the difference between the average value of the positions of the multiple first thermopiles 3 and the average value of the positions of the multiple second thermopiles 4 is reduced. By reducing the difference in the average values, the influence of output changes due to the difference in the positions of the first thermopiles 3 and the second thermopiles 4 in the first direction X is reduced. In other words, this embodiment provides a flow sensor 100 that can reduce the influence of output changes due to the difference in the positions of the thermopiles in the longitudinal direction of the first heater 2. Furthermore, by reducing the influence of output changes due to the difference in the positions of the thermopiles, the detection accuracy of the thermal conductivity based on the output difference of the thermopiles is improved.

[0084] Furthermore, in Figures 3, 5 to 9, the wiring connections on the peripheral portion 11 may be reversed, with the first thermocouple and the second thermocouple being reversed.

[0085] 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.

[0086] Aspects of the present invention are as follows, for example: <1> A flow sensor comprising: a substrate having a peripheral portion and a first membrane portion; a first heater disposed on the first membrane portion and extending in a first direction; a first thermopile arranged in a plurality in the first direction and having a first thermocouple having a first hot junction on the first membrane portion; and a second thermopile arranged in a plurality in the first direction and having a second thermocouple having a second hot junction on the first membrane portion, wherein in the first direction, the first thermocouple and the second thermocouple are arranged alternately, and in a second direction intersecting the first direction, the first distance from the first heater to the first hot junction is longer than the distance from the first heater to the second hot junction. <2> The flow sensor according to <1>, wherein in the first measurement portion, the fluid to be detected flows in the first direction. <3> The flow sensor described in <2> further comprises a second measuring unit having a second membrane portion formed on the substrate, a second heater, and a third thermopile including a third thermocouple having a third hot junction on the second membrane portion, wherein in the second measuring unit, the fluid flows in the first direction. <4> The flow sensor according to any one of <1> to <3> above, wherein m and n are each integers of 2 or more, the first thermopile consists of a plurality of first thermocouples, each first thermocouple has a first wire and a second wire positioned above the first wire, the nth first wire and the nth second wire are connected at a first hot junction in the first membrane portion, the (n+1)th first wire and the nth second wire are connected at a first cold junction in the peripheral portion, the second thermopile consists of a plurality of second thermocouples, each second thermocouple has a third wire and a fourth wire positioned above the third wire, the mth third wire and the mth fourth wire are connected at a third point in the first membrane portion, and the (m+1)th third wire and the mth fourth wire are connected at the peripheral portion via a connection portion.<5> The flow sensor according to any one of <1> to <4>, wherein the first thermopile consists of a plurality of first thermocouples, and the first thermocouple has a first wiring which is a polysilicon wiring of a first conductivity type and a second wiring which is a polysilicon wiring of a second conductivity type opposite to that of the first wiring, and the second thermopile consists of a plurality of second thermocouples, and the second thermocouple has a third wiring which is a polysilicon wiring of a first conductivity type and a fourth wiring which is a polysilicon wiring of a second conductivity type. <6> The flow sensor according to <5>, wherein m and n are integers of 1 or more, the nth first wire and the nth second wire are connected at a first point in the first membrane portion, the (n+1)th first wire and the nth second wire are connected in the peripheral portion via a first connection portion, the mth third wire and the mth fourth wire are connected at a third point in the first membrane portion, and the (m+1)th third wire and the mth fourth wire are connected in the peripheral portion via a second connection portion. <7> The flow sensor according to any one of <1> to <6>, wherein n is an integer of 2 or more, the first thermopile consists of n first thermocouples, and the second thermopile consists of n second thermocouples. <8> The flow sensor according to <7>, wherein n is an even number, and the first thermocouple and the fourth thermocouple, which is electrically independent of the second thermocouple, are arranged between the n / 2th and n / 2+1th thermopile of the first thermopile. <9> The flow sensor according to <8>, wherein the first thermocouple has a first wire and a second wire positioned above the first wire, the fourth thermocouple has a fifth wire and a sixth wire positioned above the fifth wire, one end of the sixth wire is connected to the fifth wire, the other end of the sixth wire is terminated, and the n / 2nd second wire is connected to the n / 2+1th first wire via a connection positioned above the fifth wire.<10> The flow sensor according to any one of <1> to <9> above, wherein m and n are each integers of 2 or more, the first thermopile consists of n first thermocouples, the first thermocouple has a first wire and a second wire positioned above the first wire, the second thermopile consists of m second thermocouples, the second thermocouple has a third wire and a fourth wire, the first wire and the third wire have the same shape, and the second wire and the fourth wire have the same shape. <11> The flow sensor according to <10> above, wherein the first hot junction is the location where the first wire and the second wire are connected by a contact plug, and the second hot junction is the location where the third wire and the fourth wire are connected by a contact plug.

[0087] This application claims priority based on Japanese Patent Application No. 2024-188477, filed with the Japan Patent Office on 25 October 2024, and includes the entire contents of that Japanese Patent Application.

[0088] 1...Substrate, 2...First heater, 3...First thermopile, 4...Second thermopile, 5...Fourth thermocouple, 6...Second heater, 7...Third thermopile, 11...Peripheral part, 12...First membrane part, 13...Protective film, 14...Second membrane part, 21...First heater pad, 31...First thermocouple, 32...First hot junction, 33...First cold junction, 34...Connection part, 35...First connection part, 36...Second connection part, 37...First dummy part, 41...Second thermocouple, 42...Second hot junction, 47...Second dummy part, 51...Fifth wiring, 52...Second 6 wiring, 61...Second heater pad, 71...Third thermocouple, 72...Third hot junction, 81...Conductive film, 82...Contact plug, 100...Flow sensor, 110...First measuring section, 120...Second measuring section, 130...Top surface, 311, 311n, 311n / 2+1...First wiring, 312, 312n, 312n+1, 312n / 2...Second wiring, 411, 411m, 411m+1...Third wiring, 412, 412m...Fourth wiring, 521...One end, 522...Other end, L1...First distance, L2...Second distance, X...First direction, Y...Second direction, Z...Third direction

Claims

1. A flow sensor comprising: a substrate having a peripheral portion and a first membrane portion; a first heater disposed on the first membrane portion and extending in a first direction; a first thermopile arranged in a plurality in the first direction and having a first thermocouple having a first hot junction on the first membrane portion; and a second thermopile arranged in a plurality in the first direction and having a second thermocouple having a second hot junction on the first membrane portion, wherein in the first direction, the first thermocouple and the second thermocouple are arranged alternately, and in a second direction intersecting the first direction, the first distance from the first heater to the first hot junction is longer than the second distance from the first heater to the second hot junction.

2. The flow sensor according to claim 1, wherein in the first measuring unit, the fluid to be detected flows in the first direction.

3. The flow sensor according to claim 2, further comprising: a second membrane portion formed on the substrate; a second heater; and a third thermopile, which is arranged in a plurality in the second direction and includes a third thermocouple having a third hot junction on the second membrane portion, wherein in the second measuring portion, the fluid flows in the first direction.

4. A flow sensor according to any one of claims 1 to 3, wherein m and n are each integers of 2 or more, the first thermopile consists of a plurality of first thermocouples, each first thermocouple has a first wire and a second wire positioned above the first wire, the nth first wire and the nth second wire are connected at the first hot junction in the first membrane portion, the (n+1)th first wire and the nth second wire are connected at the first cold junction in the peripheral portion, the second thermopile consists of a plurality of second thermocouples, each second thermocouple has a third wire and a fourth wire positioned above the third wire, the mth third wire and the mth fourth wire are connected at the third point in the first membrane portion, and the (m+1)th third wire and the mth fourth wire are connected via a connection portion in the peripheral portion.

5. The flow sensor according to any one of claims 1 to 4, wherein the first thermopile comprises a plurality of first thermocouples, each first thermocouple having a first wiring which is a polysilicon wiring of a first conductivity type and a second wiring which is a polysilicon wiring of a second conductivity type opposite to that of the first wiring, and the second thermopile comprises a plurality of second thermocouples, each second thermocouple having a third wiring which is a polysilicon wiring of a first conductivity type and a fourth wiring which is a polysilicon wiring of a second conductivity type.

6. The flow sensor according to claim 5, wherein m and n are each integers of 1 or more, the nth first wire and the nth second wire are connected at a first point in the first membrane portion, the (n+1)th first wire and the nth second wire are connected via a first connection portion in the peripheral portion, the mth third wire and the mth fourth wire are connected at a third point in the first membrane portion, and the (m+1)th third wire and the mth fourth wire are connected via a second connection portion in the peripheral portion.

7. The flow sensor according to any one of claims 1 to 6, wherein n is an integer of 2 or more, the first thermopile consists of n first thermocouples, and the second thermopile consists of n second thermocouples.

8. The flow sensor according to claim 7, wherein n is an even number, and the first thermocouple and the fourth thermocouple, which is electrically independent of the second thermocouple, are arranged between the n / 2th and n / 2+1th elements of the first thermopile.

9. The flow sensor according to claim 8, wherein the first thermocouple has a first wire and a second wire positioned above the first wire, the fourth thermocouple has a fifth wire and a sixth wire positioned above the fifth wire, one end of the sixth wire is connected to the fifth wire, the other end of the sixth wire is terminated, and the n / 2 second wire is connected to the n / 2+1 first wire via a connection positioned above the fifth wire.

10. A flow sensor according to any one of claims 1 to 9, wherein m and n are each integers of 2 or more, the first thermopile consists of n first thermocouples, the first thermocouple has a first wire and a second wire positioned above the first wire, the second thermopile consists of m second thermocouples, the second thermocouple has a third wire and a fourth wire, the first wire and the third wire have the same shape, and the second wire and the fourth wire have the same shape.

11. The flow sensor according to claim 10, wherein the first hot junction is the location where the first wiring and the second wiring are connected by a contact plug, and the second hot junction is the location where the third wiring and the fourth wiring are connected by a contact plug.

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