Flow sensor

Abstract

Reduces variations in the offset voltage of the flow sensor. [Solution] This flow sensor has a substrate (1) having a peripheral portion (11) and a membrane portion (12) that is thinner than the peripheral portion (11), a heater (2) disposed on the membrane portion (12), and a plurality of thermopiles (3) that are symmetrically arranged with respect to the heater (2), wherein the plurality of thermopiles (3) have a first wiring (31) and a second wiring (32), and the first wiring (31) and the second wiring (32) are connected to the membrane portion (1 2) is connected on the membrane portion (12) and on the peripheral portion (11), the first wiring (31) has a first portion (311) and a second portion (312) which is thicker than the first portion (311), and the second wiring (32) has a third portion (321) and a fourth portion (322) which is thicker than the third portion (321), and the second portion (312) and the fourth portion (322) are arranged to straddle the membrane portion (12) and the peripheral portion (11).

Description

Technical Field

[0006] ,

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

Background Art

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

[0003] For example, Patent Document 1 discloses a configuration in which at least two heat conduction regions on the chip surface are arranged at the same distance with respect to temperature sensors arranged symmetrically with respect to a heating element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a flow sensor, it is important to suppress variations in offset voltage.

[0006] An object of the present invention is to reduce variations in the offset voltage of a flow sensor.

Means for Solving the Problems

[0007] This flow sensor has a substrate (1) having a peripheral portion (11) and a membrane portion (12) that is thinner than the peripheral portion (11), a heater (2) disposed on the membrane portion (12), and a plurality of thermopiles (3) arranged symmetrically with respect to the heater (2), wherein the plurality of thermopiles (3) have a first wiring (31) and a second wiring (32), and the first wiring (31) and the second wiring (32) are above the membrane portion (12) The first wiring (31) is connected and connected on the peripheral portion (11), and the first wiring (32) has a first portion (311) and a second portion (312) that is thicker than the first portion (311), and the second wiring (32) has a third portion (321) and a fourth portion (322) that is thicker than the third portion (321), and the second portion (312) and the fourth portion (322) are arranged to straddle the membrane portion (12) and the peripheral portion (11).

[0008] The reference symbols in parentheses above are provided for ease of understanding and are merely examples; they do not limit the possible configurations shown in the illustrations. [Effects of the Invention]

[0009] According to the present invention, variations in the offset voltage of the flow sensor can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] This is an example of a schematic top view showing the overall configuration of the flow sensor according to the first embodiment. [Figure 2] This is an example of a schematic cross-sectional view of line II-II in Figure 1. [Figure 3] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the first embodiment. [Figure 4] This is an example of a schematic top view showing an enlarged view of the thermopile of a flow sensor according to a modification of the first embodiment. [Figure 5] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the second embodiment. [Figure 6] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the third embodiment. [Figure 7] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the fourth embodiment. [Figure 8] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the fifth embodiment. [Figure 9] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the sixth embodiment. [Figure 10] This is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor according to the seventh embodiment. [Figure 11] This is an example of a top view showing a flow sensor according to an embodiment. [Modes for carrying out the invention]

[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 Y direction corresponds to the first direction in which the first wiring and the second wiring of the thermopile included in the flow sensor according to the embodiment extend. The X direction corresponds to the second direction intersecting the first direction. The Z direction corresponds to the third direction which is the direction of viewing the plane of the membrane portion included in the flow sensor according to the embodiment from above. In this specification, they are denoted as the first direction Y, the second direction X, and the third direction Z. Also, viewing an object from the third direction Z may be referred to as a top view.

[0014] The terms indicating the above specific directions and positions are merely used to make the relative directions and positions in the referenced drawings easier to understand. These terms do not limit the direction of the embodiment, and the orientation during the use of the flow sensor according to the embodiment is arbitrary. Also, in this specification, "arrange" is not limited to the case of direct contact, and includes the case of arranging indirectly, for example, via other members.

[0015] [First Embodiment] <Configuration of the Flow Sensor According to the First Embodiment> Referring to FIGS. 1 to 3, the configuration of the flow sensor according to the first embodiment will be described. FIG. 1 is an example of a schematic top view showing the overall configuration of the flow sensor 100 according to the first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a schematic top view showing an enlarged view of the thermopile 3 included in the flow sensor 100.

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

[0017] In the example shown in FIG. 1, the flow sensor 100 has a substantially rectangular outer shape in a top view. The size of the flow sensor 100 in a top view is, as an example, 1.6 mm × 1.6 mm. However, the outer shape of the substrate 1 in a top view may be substantially circular, substantially elliptical, or substantially polygonal, etc. Also, the size of the flow sensor 100 is not limited to the above. The flow sensor 100 is formed by a semiconductor process or the like.

[0018] As shown in FIG. 1, the flow sensor 100 includes a substrate 1 having a peripheral portion 11 and a membrane portion 12 thinner than the peripheral portion 11, a heater 2 disposed on the membrane portion 12, and a plurality of thermopiles 3 symmetrically disposed with respect to the heater 2. The plurality of thermopiles 3 have a first wiring 31 and a second wiring 32. The connected first wiring 31 and second wiring 32 can be referred to as a thermocouple as a set. One ends of the first wiring 31 and the second wiring 32 of the substrate 1 are connected above the membrane portion 12, and the other ends are connected above the peripheral portion 11.

[0019] In the example shown in FIG. 1, the heater 2 extends in the second direction X. The heater 2 is connected to heater pads 21 disposed at both ends in the second direction X. In the first direction Y, eight thermopiles 3 are arranged side by side in the second direction X at regular intervals symmetrically with respect to the heater 2. The membrane length LM in FIG. 1 is the length of the membrane portion 12 in the first direction Y.

[0020] In the example shown in FIG. 1, the flow sensor 100 has two thermopiles 3. A thermopile 3A disposed on the +Y side of the heater 2 and a thermopile 3B disposed on the -Y side of the heater 2 are mirror-symmetrical with respect to the heater 2 and form a pair. Note that the thermopile 3 can be referred to as a thermopile, and it can be said that a plurality of thermocouples are connected to form the thermopile 3.

[0021] The flow sensor 100 outputs the detection signal obtained by the thermopile 3 through four sensor pads 10 (10A-1, 10A-2, 10B-1, 10B-2) located near the four corners of the substrate 1. Sensor pads 10A-1 and 10A-2 are connected to both ends of thermopile 3A, and sensor pads 10B-1 and 10B-2 are connected to both ends of thermopile 3B. Thermopile 3A converts the temperature difference between the first point 33 and the second point 34 of the multiple thermocouples into a voltage difference and outputs that voltage difference to sensor pads 10A-1 and 10A-2. Thermopile 3B converts the temperature difference between the first point 33 and the second point 34 of the multiple thermocouples into a voltage difference and outputs that voltage difference to sensor pads 10B-1 and 10B-2.

[0022] In the example shown in Figure 1, the first wiring 31 and the second wiring 32 are connected at the first point 33 by the first contact plug 330. The first wiring 31 and the second wiring 32 are connected at the second point 34 by the second contact plug 340. Here, the first contact plug 330 is the first point 33, and the second contact plug 340 is the second point 34. Therefore, in Figure 1, the reference numerals for the first contact plug 330 and the first point 33 are shown together, and the reference numerals for the second contact plug 340 and the second point 34 are also shown together. Note that the first point 33 may be the center of the first contact plug 330, and the second point 34 may be the center of the second contact plug 340.

[0023] In the example shown in Figure 1, thermopiles 3A and 3B each have eight first wirings 31 and eight second wirings 32. The first wirings 31 and second wirings 32 are numbered 1, 2, ..., n, ..., and 8 from the smallest second direction X. If n is an integer greater than or equal to 1, then in the membrane portion 12, the nth second wiring 32n and the nth first wiring 31n are connected at the first point 33. Also, in the peripheral portion 11, the nth second wiring 32n and the (n+1)th first wiring 31n+1 are connected at the second point 34.

[0024] In the example shown in Figure 2, the flow sensor 100 has a substrate 1, an insulating film 113 placed on the substrate 1 in the third direction Z, and a protective film 13 placed on the insulating film 113. The peripheral portion 11 has a support portion 111 made of the substrate 1. The 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 membrane portion 12 is approximately 2 μm. The second wiring 32 is located above the first wiring 31 in the third direction Z, for example, on the +Z side. The first wiring 31 and the second wiring 32 are connected at a first point 33 on the membrane portion 12 and at a second point 34 on the peripheral portion 11. The first point 33 is the hot junction of the two contacts of the thermopile 3, used for temperature measurement. The second point 34 is the cold junction other than the hot junction of the two contacts of the thermopile 3.

[0025] 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 membrane portion 12 and functions as a heat sink. The heater 2 is a heat-generating resistor composed of platinum, nichrome, polysilicon, etc., which generates heat in response to the current or voltage supplied via the heater pad 21.

[0026] The first wiring 31 of the thermopile 3 is a polysilicon wiring composed of, for example, a polysilicon film. The second wiring 32 of the thermopile 3 is an aluminum wiring composed of, for example, an aluminum film. The first wiring 31 and the second wiring 32 each extend in the first direction Y. The thermopile 3 has a repeating structure in which the polysilicon film of the first wiring 31 and the aluminum film of the second wiring 32 are connected in series.

[0027] As shown in Figure 3, in this embodiment, the first wiring 31 has a first portion 311 and a second portion 312 which is thicker than the first portion 311. The second wiring 32 has a third portion 321 and a fourth portion 322 which is thicker than the third portion 321. The second portion 312 and the fourth portion 322 are arranged to straddle the membrane portion 12 and the peripheral portion 11. In the example shown in Figure 3, the second portion 312 and the fourth portion 322 are arranged to straddle the membrane portion 12 and the peripheral portion 11 via the boundary 120 between the membrane portion 12 and the peripheral portion 11.

[0028] Furthermore, in this embodiment, at the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, the second wiring 32 is included within the first wiring 31 in both the first direction Y and the second direction X. From another viewpoint, in the vicinity of the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, the second wiring 32 is included within the first wiring 31 in both the first direction Y and the second direction X.

[0029] <Effects of the flow sensor 100 according to the first embodiment> In the flow sensor 100, fluid flows from the negative (-Y direction) to the positive (+Y direction) of the first direction Y. When detecting the fluid flow rate or velocity, the flow sensor 100 energizes the heater 2, creating a roughly symmetrical temperature distribution around the heater 2. When a fluid flow occurs in the space on the +Z side of the flow sensor 100 while a roughly symmetrical temperature distribution has been formed with respect to the heater 2, the symmetry of the temperature distribution formed by the heater 2 is disrupted. As a result of this disruption of temperature distribution symmetry, the difference in electromotive force between the paired thermopile 3A (downstream side) and thermopile 3B (upstream side) corresponds to the flow rate or velocity. The flow sensor 100 outputs a voltage signal corresponding to this difference in electromotive force as a detection signal for the fluid flow rate or velocity.

[0030] For example, the membrane portion 12 of the substrate 1 is formed by deep dry etching to deeply engrave the substrate 1, or by crystal anisotropic etching using a chemical solution such as tetramethylammonium hydroxide (TMAH). These deep dry etching and crystal anisotropic etching processes do not have high processing accuracy. Therefore, due to processing errors in the membrane portion 12, the position of the boundary 120 between the membrane portion 12 and the peripheral portion 11, as shown in Figures 2 and 3, may be shifted in the first direction Y from the desired position. Due to the displacement of the boundary 120, the distance (distance AL in Figure 3) from the first point 33 of the thermopile 3A and thermopile 3B, which are arranged with the heater 2 in the first direction Y, to the boundary between the peripheral portion 11 and the membrane portion 12 will be different. In other words, the symmetry of the heat sink function of thermopile 3A and thermopile 3B is disrupted. As a result, a difference in temperature sensing characteristics between thermopile 3A and thermopile 3B occurs, creating an offset voltage that prevents the detection signal of the flow sensor 100 from becoming zero, even in windless conditions where there is no fluid flow rate or velocity. This variation in offset voltage causes variations in the detection value by the flow sensor 100, reducing the detection accuracy of the flow sensor 100.

[0031] In this embodiment, the second portion 312 of the first wiring 31 and the fourth portion 322 of the second wiring 32 are arranged to straddle the membrane portion 12 and the peripheral portion 11. The second portion 312 is formed thicker than the first portion 311, resulting in a larger heat capacity compared to the first portion 311 and lower thermal resistance with the peripheral portion 11 of the substrate 1, thus providing a heat sink function. The fourth portion 322 is formed thicker than the third portion 321, resulting in a larger heat capacity compared to the third portion 321, thus providing a heat sink function. Here, the first wiring 31 and the second wiring 32 need to have high processing accuracy in order to accurately detect temperature. The processing accuracy for the first wiring 31 and the second wiring 32 is higher compared to deep dry etching or crystal anisotropy etching on a silicon substrate. Therefore, by increasing the positional accuracy of the second portion 312 and the fourth portion 322, the dimensional accuracy of distance BL (distance AL minus length PL) is higher than that of distance AL.

[0032] In Figure 3, the end of the fourth portion 322 of the second wiring 32 located on the membrane portion 12 is defined as the heat sink end 350 of the heat sink portion 35. If the heat dissipation efficiency of the first wiring 31 is higher than that of the second wiring 32, the heat sink end 350 will be the end of the third portion 321 of the first wiring 31 located on the membrane portion 12. If the heat dissipation efficiency of the first wiring 31 and the second wiring 32 are the same, the heat sink end 350 will be the end of the membrane portion 12 closer to the heater 2 between the third portion 321 and the fourth portion 322. The high dimensional accuracy of the heat sink length LH improves the symmetry of the heat sink function of thermopile 3A and thermopile 3B. That is, the variation in the length LI-A from the heat sink end 350 of thermopile 3A to the heater 2 and the length LI-B from the heat sink end 350 of thermopile 3B to the heater 2, as shown in Figure 1, is reduced. By improving the symmetry of the heat sink function, variations in the offset voltage of the flow sensor 100 can be reduced in this embodiment. Furthermore, by reducing variations in the offset voltage, the detection accuracy of the flow sensor 100 can be increased in this embodiment.

[0033] The second portion 312 and the fourth portion 322 are portions that contribute little to the detection sensitivity of the fluid flow rate or velocity by the flow sensor 100. Therefore, it is preferable to make the second portion 312 and the fourth portion 322 thicker to lower their resistance. From another viewpoint, in this embodiment, it is preferable that the resistance of the second portion 312 is lower than the resistance of the first portion 311. When the resistance of the second portion 312 is lower than the resistance of the first portion 311, noise in the detection signal is reduced, and the SNR (Signal Noise Ratio) of the flow sensor 100 is increased. When the SNR of the flow sensor 100 is increased, the detection accuracy of the flow sensor 100 is increased.

[0034] Furthermore, because the first portion 311 located in the membrane portion 12 is thinner than the second portion 312, and the third portion 321 located in the membrane portion 12 is thinner than the fourth portion 322, the detection sensitivity of the fluid flow rate or velocity by the flow sensor 100 is increased. This increased detection sensitivity of the fluid flow rate or velocity leads to increased detection accuracy of the flow sensor 100.

[0035] In this embodiment, the second wiring 32 is positioned above the first wiring 31 in the third direction Z, for example, on the +Z side. Also, at the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, the second wiring 32 is included within the first wiring 31 in both the first direction Y and the second direction X. For example, at the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, if the ends of the first wiring 31 and the second wiring 32 overlap in both the first direction Y and the second direction X, a misalignment of the first wiring 31 and the second wiring 32 when viewed from the third direction Z may result in unfinished processing of the second wiring 32 on the side surface of the first wiring 31. If unfinished processing occurs, an unintended wiring short may occur. At the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, the second wiring 32 is included in the first wiring 31 in both the first direction Y and the second direction X, thereby reducing the generation of aluminum processing residue in the second wiring 32 (fourth portion 322).

[0036] In Figure 3, the length PL of the heat sink end 350 of the heat sink portion 35, which protrudes toward the +Y side from the boundary 120 between the membrane portion 12 and the peripheral portion 11, is preferably 1 μm or more and less than or equal to 1 / 4 of the membrane length LM. This improves the detection accuracy of the flow sensor 100.

[0037] Here, Figure 4 is an example of a schematic top view showing an enlarged view of the thermopile of the flow sensor 100 according to a modification of the first embodiment. For example, in Figure 4, most of the heat sink portion 35 is thermally grounded to the peripheral portion 11, and there is no temperature difference with respect to the peripheral portion 11. Therefore, the heat sink portion 35 does not contribute to the electromotive force of the flow sensor 100 and is only a region that generates parasitic resistance. Therefore, by injecting impurities into the polysilicon film of the heat sink portion 35-1 in the thermopile 3, the resistance of the heat sink portion 35-1 can be lowered. From another point of view, in this embodiment, the impurity concentration of the second portion 312 is higher than that of the first portion 311. By lowering the resistance of the heat sink portion 35, thermal noise is reduced and the SNR of the flow sensor 100 is increased. Furthermore, from the perspective of lowering the impurity concentration and increasing the thermopile sensitivity, it is preferable that the impurity concentration in the portion of the thermopile 3 closer to the membrane portion 12 than in the heatsink portion 35 be lower than in the heatsink portion 35.

[0038] [Second Embodiment] Next, a flow sensor according to the second embodiment will be described. Note that names and reference numerals identical to those used 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.

[0039] Figure 5 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the second embodiment.

[0040] In this embodiment of the flow sensor, the boundary 120 between the membrane portion 12 and the peripheral portion 11 differs from the flow sensor 100 according to the first embodiment in that, when viewed from the third direction Z, the entirety of the second portion 312 and the fourth portion 322 in the second direction X overlap at the boundary 120 between the membrane portion 12 and the peripheral portion 11.

[0041] The overlap of the second portion 312 and the fourth portion 322 in the second direction X maximizes the area of ​​each portion of the heat sink 35. This maximizes the heat dissipation efficiency of the heat sink 35. However, the configuration in which the second portion 312 and the fourth portion 322 in the second direction X completely overlap when viewed from the third direction Z is not limited to this configuration; at least a portion may overlap.

[0042] Other effects of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

[0043] [Third Embodiment] Next, a flow sensor according to the third embodiment will be described.

[0044] Figure 6 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the third embodiment.

[0045] In this embodiment, the flow sensor differs from the flow sensor 100 according to the first embodiment in that, at the boundary 120 between the membrane portion 12 and the peripheral portion 11, the second wiring 32 is positioned such that, when viewed from the third direction Z, it is offset from the first wiring 31 in the first direction Y and the second direction X, respectively.

[0046] At the boundary 120 between the membrane portion 12 and the peripheral portion 11, when viewed from the third direction Z, the thickness of the second wiring 32 and the first wiring 31 are the same in the first direction Y, and the second wiring 32 is positioned offset from the first wiring 31 in both the first direction Y and the second direction X. As a result, the ends of the first wiring 31 and the second wiring 32 do not overlap, reducing the possibility of residual aluminum in the fourth portion 322 of the second wiring 32. This eliminates the need to thin the second wiring 32, thus maintaining the effectiveness of the heat sink and suppressing a decrease in machining accuracy in the heat sink portion 35. Note that the configuration of the second wiring 32 is not limited to being offset from the first wiring 31 in both the first direction Y and the second direction X; it is sufficient if it is offset from the first wiring 31 in at least the second direction X.

[0047] Other effects of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

[0048] [Fourth Embodiment] Next, we will describe the flow sensor according to the fourth embodiment.

[0049] Figure 7 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the fourth embodiment.

[0050] In this embodiment of the flow sensor, the second wiring 32 has a fifth portion 323 that is thinner than the fourth portion 322 between the boundary 120 between the membrane portion 12 and the peripheral portion 11 and the second point 34. In addition, in this embodiment of the flow sensor, the first wiring 31 has a sixth portion 313 that is thinner than the second portion 312 between the boundary 120 between the membrane portion 12 and the peripheral portion 11 and the second point 34.

[0051] For example, if the spacing between adjacent second wirings 32 is narrow, the risk of the second wirings 32 short-circuiting may increase. The second wiring 32 has a fifth portion 323 that is narrower than the fourth portion 322 between the boundary 120 of the membrane portion 12 and the peripheral portion 11 and the second point 34. Specifically, the fifth portion 323 is placed in the part where the second wiring 32 bends, straddling the first wiring 31n and the first wiring 31n+1. The wiring width becomes wider in the part where the wiring bends due to processing. Here, compared to the case where the second wiring 32 does not have a fifth portion 323 in the part where the second wiring 32 bends, the second spacing d2 between adjacent second wirings 32 becomes wider. This reduces the possibility of the second wirings 32 short-circuiting each other.

[0052] Furthermore, for example, if the spacing between adjacent first wirings 31 is narrow, the coverage of the first wirings 31 by the second wiring 32 decreases, which may increase the risk of disconnection. The first wiring 31 has a sixth portion 313 that is thinner than the second portion 312 between the boundary 120 of the membrane portion 12 and the peripheral portion 11 and the second point 34. Specifically, the sixth portion 313 is positioned in the portion where the second wiring 32 straddles the first wiring 31n and the first wiring 31n+1. In this case, the first spacing d1 between adjacent first wirings 31 becomes wider compared to the case where the first wiring 31 does not have the sixth portion 313. For example, when the second wiring 32 is formed by physical vapor deposition (PVD), if the spacing between the first wirings 31 is narrow, the raw material molecules may not reach between adjacent first wirings 31. As a result, the coverage of the second wiring 32 between the first wirings 31 decreases, potentially causing the second wiring 32 to break. In this embodiment, by widening the first spacing d1 between adjacent first wirings 31, raw material molecules can more easily reach between adjacent first wirings 31. As a result, the risk of the second wiring 32 breaking is reduced.

[0053] Other effects of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

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

[0055] Figure 7 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the fifth embodiment.

[0056] In this embodiment of the flow sensor, the first wiring 31 is a polysilicon wiring of the first conductivity type, and the second wiring 32 is a polysilicon wiring of the second conductivity type, which is opposite to the first conductivity type, which is the difference between the two.

[0057] As shown in Figure 8, in the third direction Z, the end of the first wiring 31 in the first direction Y on the membrane portion 12 is exposed from the second wiring 32. In the portion where the first wiring 31 is exposed, the first wiring 31 is connected to the first contact plug 330 and is connected to the second wiring 32 via the upper wiring 36 and contact plug 361. The upper wiring 36 is positioned above the second wiring 32 in the third direction Z. Also in the third direction Z, the end of the first wiring 31 in the first direction Y on the peripheral portion 11 is exposed from the second wiring 32. In the portion where the first wiring 31 is exposed, the first wiring 31 is connected to the second contact plug 340 and is connected to the second wiring 32 via the upper wiring 37 and contact plug 371.

[0058] In the example shown in Figure 8, 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. The second wiring 32 includes a seventh portion 324 connected to the first wiring 31 by the first contact plug 330. The upper layer wirings 36 and 37 are made of, for example, aluminum. The upper layer wirings 36 and 37 may also be formed in the same layer. The contact plugs 361 and 671 may be made of the same material as the upper layer wirings 36 and 37, for example, aluminum. Alternatively, they may be made of a different material from the upper layer wirings 36 and 37, for example, a metal such as tungsten.

[0059] As described above, even when the first wiring 31 and the second wiring 32 are made of conductive polysilicon, the same effects and advantages as those of the flow sensor 100 according to the first embodiment can be obtained.

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

[0061] Figure 9 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the sixth embodiment.

[0062] The flow sensor according to this embodiment differs from the flow sensor 100 according to the first embodiment in that it has a member 4 that is arranged to span the membrane portion 12 and the peripheral portion 11.

[0063] In the second direction X, component 4 is electrically independent from the first wiring 31 and the second wiring 32, and in the first direction Y, the position of the end portion 40 on the membrane portion 12 is the same as the position of the heat sink end portion 350.

[0064] In the example shown in Figure 9, member 4 has a first layer 41 arranged in the same layer as the first wiring 31, and a second layer 42 arranged in the same layer as the second wiring 32. The first layer 41 is composed of, for example, a polysilicon film. The second layer 42 is composed of, for example, an aluminum film. The external shape of member 4 in a top view is approximately rectangular. However, the external shape of member 4 in a top view may be approximately circular, approximately elliptical, approximately polygonal, etc. The end 40 is the end on the membrane portion 12 of the second layer 42. If the heat dissipation efficiency of the first layer 41 is higher than that of the second layer 42, the end 40 will be the end on the membrane portion 12 of the first layer 41. If the heat dissipation efficiency of the first layer 41 and the second wiring 32 are the same, the end 40 will be the end on the membrane portion 12 of the first layer 41 or the second layer 42 that is closer to the heater 2.

[0065] The second layer 42 is contained within the first layer 41 in both the first direction Y and the second direction X when viewed from the third direction Z, near the boundary 120 between the membrane portion 12 and the peripheral portion 11. However, the positional relationship between the first layer 41 and the second layer 42 when viewed from the third direction Z is not limited to the above; it is sufficient that at least a portion of them overlaps when viewed from the third direction Z.

[0066] Component 4 functions as a heat sink. The first layer 41 of component 4 is formed using the same process as the first wiring 31. The second layer 42 of component 4 is formed using the same process as the second wiring 32. In other words, the machining accuracy of component 4 is higher than that of the peripheral portion 11. In the flow sensor according to the sixth embodiment, the symmetry of the heat sink function is improved due to the high machining accuracy of component 4. As a result, the variation in offset voltage is further reduced.

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

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

[0069] Figure 10 is a schematic top view showing an enlarged view of the thermopile 3 of the flow sensor according to the seventh embodiment.

[0070] The flow sensor according to this embodiment differs from the flow sensor according to the sixth embodiment in that member 4 has a slit 43 that exposes the boundary 120 between the membrane portion 12 and the peripheral portion 11.

[0071] In the example shown in Figure 10, the member 4 has a roughly rectangular shape in top view, with its longitudinal side in the first direction Y, and has two slits 43 aligned in the second direction X. However, the arrangement, number, and shape of the slits 43 in top view can be changed as appropriate, as long as the boundary 120 between the membrane portion 12 and the peripheral portion 11 can be exposed.

[0072] The first layer 41 has a plurality of first layer portions 411 arranged at predetermined intervals in the second direction X. In the example shown in Figure 10, the shape of the first layer portion 411 in a top view is approximately rectangular with the first direction Y as its longest side. The first layer 41 has three first layer portions 411 arranged in the second direction X. However, the arrangement, number, and shape of the first layer portions 411 in a top view can be changed as appropriate.

[0073] The second layer 42 has a plurality of second layer portions 421 arranged at predetermined intervals in the second direction X, and a plurality of connecting portions 422 connecting the first layer portion 411 and the second layer portion 421. The shape of the second layer portion 421 in a top view is a substantially rectangular shape with the first direction Y as its longitudinal side.

[0074] In the example shown in Figure 10, the second layer 42 has three second layer portions 421 aligned in the second direction X. The connecting portion 422 extends in the second direction X and connects the first layer portion 411 and the second layer portion 421. The second layer 42 has four connecting portions 422. However, the arrangement, number, and shape of the second layer portions 421 and connecting portions 422 in a top view can be changed as appropriate.

[0075] In this embodiment, the slit 43 is formed by the overlap of the spacing between adjacent first layer portions 411 and the spacing between adjacent second layer portions 421 in the third direction Z.

[0076] In this embodiment, member 4 has a slit 43. This relieves the stress on the polysilicon film of the first layer 41 and the aluminum film of the second layer 42, reducing the risk of delamination or fracture of the polysilicon film and the aluminum film. In addition, the boundary 120 is exposed by the slit 43. This allows the position of the boundary 120 to be detected through the slit 43, making it easier to control the manufacturing process of the flow sensor.

[0077] Furthermore, in this embodiment, the first layer 41 has a plurality of first layer portions 411, and the second layer 42 has a plurality of second layer portions 421 and a plurality of connecting portions 422. As a result, the stress on the polysilicon film of the first layer 41 and the aluminum film of the second layer 42 is relieved, reducing the risk of peeling or fracture of the polysilicon film and the aluminum film. In addition, the boundary 120 is exposed by the spacing between adjacent first layer portions 411 and the spacing between adjacent second layer portions 421. As a result, the position of the boundary 120 can be detected, making it easier to control the manufacturing process of the flow sensor.

[0078] Other effects of the flow sensor according to this embodiment are the same as those of the flow sensor 100 according to the first embodiment.

[0079] [Examples] Figure 11 is a top view showing a flow sensor 100 according to an embodiment. Figure 11 shows an example of a specific layout of the flow sensor 100 according to an embodiment. However, the embodiment is not limited to the embodiment shown.

[0080] As shown in Figure 11, the flow sensor 100 according to the embodiment includes a substrate 1 having a peripheral portion 11 and a membrane portion 12 that is thinner than the peripheral portion 11, and a heater 2 disposed on the membrane portion 12. The flow sensor 100 also includes a plurality of thermopiles 3 arranged symmetrically with respect to the heater 2, and a member 4 that, in a top view, is disposed outside the plurality of thermopiles 3 in the second direction X.

[0081] Multiple thermopiles 3 include a heat sink section 35. The heat sink section 35 is positioned to span the membrane section 12 and the peripheral section 11. The higher machining precision of the heat sink section 35 compared to the machining precision of the peripheral section 11 improves the symmetry of the heat sink function and reduces variations in the offset voltage of the flow sensor 100.

[0082] Component 4 is a component having a heat sink function, constructed using parts other than the thermopile 3. Component 4 is composed of, for example, a polysilicon film and an aluminum film. Four components 4 are arranged adjacent to the thermopile 3 in the second direction X. The higher machining accuracy of component 4 compared to the machining accuracy of the peripheral portion 11 further improves the symmetry of the heat sink function and further reduces the variation in the offset voltage of the flow sensor 100.

[0083] 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.

[0084] Examples of the present invention are as follows: <1> The flow sensor comprises a substrate having a peripheral portion and a membrane portion thinner than the peripheral portion, a heater disposed on the membrane portion, and a plurality of thermopiles symmetrically arranged with respect to the heater, wherein the plurality of thermopiles have a first wiring and a second wiring, the first wiring and the second wiring are connected on the membrane portion and on the peripheral portion, the first wiring has a first portion and a second portion thicker than the first portion, the second wiring has a third portion and a fourth portion thicker than the third portion, and the second portion and the fourth portion are arranged to straddle the membrane portion and the peripheral portion. <2> The first and second wirings extend in a first direction, with the direction intersecting the first direction being the second direction, the membrane portion has a plane, with the direction of viewing the plane from above being the third direction, and at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, at least a portion of the second portion and the fourth portion in the second direction overlap. <1> This is the flow sensor described in [reference]. <3> The first and second wirings extend in a first direction, the direction intersecting the first direction is the second direction, the membrane portion has a plane, the direction in which the plane is viewed from above is the third direction, in the third direction the second wiring is located above the first wiring, and at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, the second wiring is included in the first wiring in both the first and second directions, respectively. <1> or the above <2> This is the flow sensor described in [reference]. <4> The first and second wirings extend in a first direction, with the direction intersecting the first direction being the second direction, the membrane portion has a plane, with the direction of viewing the plane from above being the third direction, and at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, the second wiring is arranged to be offset from the first wiring in at least the second direction, <1> or the above <2> This is the flow sensor described in [reference]. <5> The ends of the first wiring and the second wiring do not overlap, <5> This is the flow sensor described in [reference]. <6> Let n be an integer of 1 or more, the first and second wirings extend in a first direction, multiple first and second wirings are arranged at regular intervals in a second direction intersecting the first direction, the membrane portion has a plane, the direction in which the plane is viewed from above is the third direction, in the third direction the second wiring is located above the first wiring, in the membrane portion the nth second wiring and the nth first wiring are connected at a first point, and in the peripheral portion the nth second wiring and the (n+1)th first wiring are connected at a second point, <1> From the above <5> It is a flow sensor described in one of the following documents. <7> The second wiring has a fifth portion that is thinner than the fourth portion between the boundary between the membrane portion and the peripheral portion and the second point. <6> This is the flow sensor described in [reference]. <8> The first wiring has a sixth portion that is thinner than the second portion between the boundary between the membrane portion and the peripheral portion and the second point. <7> This is the flow sensor described in [reference]. <9> The first wiring is a polysilicon wiring of a first conductivity type, the second wiring is a polysilicon wiring of a second conductivity type opposite to the first conductivity type, in the third direction, the first wiring is exposed from the second wiring at the first point, and in the portion where the first wiring is exposed, the first wiring is connected to a first contact plug and is connected to the second wiring via a third wiring through a second contact plug, in the third direction, the first wiring is exposed from the second wiring at the second point, and in the portion where the first wiring is exposed, the first wiring is connected to a third contact plug and is connected to the second wiring via a fourth wiring through a fourth contact plug, <6> This is the flow sensor described in [reference]. <10> The resistance of the second part is lower than the resistance of the first part. <1> From the above <9> It is a flow sensor described in one of the following documents. <11> The impurity concentration of the second portion is higher than the impurity concentration of the first portion. <1> From the above <10> It is a flow sensor described in one of the following documents. <12> The first and second wirings extend in a first direction, with the direction intersecting the first direction being the second direction, and in the second direction having a member that is electrically independent from the first and second wirings, and in the first direction having an end on the membrane at the same position as the end of the second or fourth portion, the member being arranged to straddle the membrane portion and the peripheral portion, <1> From the above <11> It is a flow sensor described in one of the following documents. <13> The member has a first layer arranged in the same layer as the first wiring and a second layer arranged in the same layer as the second wiring. <12> This is the flow sensor described in [reference]. <14> The member has a slit that exposes the boundary between the membrane portion and the peripheral portion, <12> This is the flow sensor described in [reference]. <15> The membrane portion has a plane, and the direction in which the plane is viewed from above is the third direction, the first layer has a plurality of first layer portions arranged at predetermined intervals in the second direction, the second layer has a plurality of second layer portions arranged at predetermined intervals in the second direction, and a plurality of connecting portions connecting the first layer portions and the second layer portions, and the spacing between adjacent first layer portions and the spacing between adjacent second layer portions overlap in the third direction to form a slit, <13> This is the flow sensor described in [reference]. [Explanation of symbols]

[0085] 1...Substrate, 2...Heater, 3...Thermopile, 4...Component, 10...Sensor pad, 11...Peripheral part, 12...Membrane part, 13...Protective film, 21...Heater pad, 31, 31n, 31n+1...First wiring, 32, 32n...Second wiring, 33...First point, 34...Second point, 35, 35-1...Heat sink part, 40...End, 41...First layer, 42...Second layer, 43...Slit, 100...Flow sensor, 110...Top surface, 111...Support part, 112... ...Top, 120...Boundary, 311...First part, 312...Second part, 313...Sixth part, 321...Third part, 322...Fourth part, 323...Fifth part, 324...Seventh part, 330...First contact plug, 340...Second contact plug, 350...Heat sink end, 411...First layer section, 421...Second layer section, 422...Connection section, d1...First spacing, d2...Second spacing, LH...Heat sink length, LM...Membrane length, PL...Length

Claims

1. A substrate having a peripheral portion and a membrane portion that is thinner than the peripheral portion, A heater is placed in the membrane portion, The heater comprises a plurality of thermopiles arranged symmetrically with respect to the heater, The plurality of thermopiles each have a first wiring and a second wiring, The first wiring and the second wiring are connected on the membrane portion and on the peripheral portion. The first wiring has a first portion and a second portion that is thicker than the first portion. The second wiring has a third portion and a fourth portion which is thicker than the third portion. The second and fourth portions are flow sensors arranged to span the membrane portion and the peripheral portion.

2. The first wiring and the second wiring extend in the first direction, The direction intersecting the first direction is defined as the second direction. The membrane portion has a flat surface, and the direction in which the flat surface is viewed from above is defined as the third direction. The flow sensor according to claim 1, wherein at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, at least a portion of the second portion and the fourth portion in the second direction overlap.

3. The first wiring and the second wiring extend in the first direction, The direction intersecting the first direction is defined as the second direction. The membrane portion has a flat surface, and the direction in which the flat surface is viewed from above is defined as the third direction. In the third direction, the second wiring is located above the first wiring. The flow sensor according to claim 1, wherein, at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, the second wiring is included in the first wiring in both the first and second directions.

4. The first wiring and the second wiring extend in the first direction, The direction intersecting the first direction is defined as the second direction. The membrane portion has a flat surface, and the direction in which the flat surface is viewed from above is defined as the third direction. The flow sensor according to claim 1, wherein, at the boundary between the membrane portion and the peripheral portion, when viewed from the third direction, the second wiring is arranged to be offset from the first wiring in at least the second direction.

5. The ends of the first wiring and the second wiring do not overlap. The flow sensor according to claim 4.

6. Let n be an integer greater than or equal to 1. The first wiring and the second wiring extend in the first direction, The first and second wirings are arranged in multiples at regular intervals in a second direction intersecting the first direction. The membrane portion has a flat surface, and the direction in which the flat surface is viewed from above is defined as the third direction. In the third direction, the second wiring is located above the first wiring. In the membrane portion, the nth second wiring and the nth first wiring are connected at the first point. The flow sensor according to claim 1, wherein the nth second wiring and the (n+1)th first wiring are connected at a second point in the peripheral portion.

7. The flow sensor according to claim 6, wherein the second wiring has a fifth portion that is thinner than the fourth portion between the boundary between the membrane portion and the peripheral portion and the second point.

8. The flow sensor according to claim 7, wherein the first wiring has a sixth portion that is thinner than the second portion between the boundary between the membrane portion and the peripheral portion and the second point.

9. The first wiring is a first-conductivity type polysilicon wiring, The second wiring is a polysilicon wiring of a second conductivity type opposite to that of the first conductivity type. In the third direction, the first wiring is exposed from the second wiring at the first point, In the portion where the first wiring is exposed, the first wiring is connected to the first contact plug and is connected to the second wiring via the third wiring through the second contact plug. In the third direction, the first wiring is exposed from the second wiring at the second point, The flow sensor according to claim 6, wherein in the portion where the first wiring is exposed, the first wiring is connected to a third contact plug and is connected to the second wiring via a fourth wiring through the fourth contact plug.

10. The flow sensor according to claim 1, wherein the resistance of the second portion is lower than the resistance of the first portion.

11. The flow sensor according to claim 1, wherein the impurity concentration of the second portion is higher than the impurity concentration of the first portion.

12. The first wiring and the second wiring extend in the first direction, The direction intersecting the first direction is defined as the second direction. In the second direction, the present invention has a member that is electrically independent of the first and second wiring, and in the first direction, the position of its end on the membrane is the same as the position of the end of the second or fourth portion. The flow sensor according to claim 1, wherein the member is arranged to span the membrane portion and the peripheral portion.

13. The flow sensor according to claim 12, wherein the member comprises a first layer disposed in the same layer as the first wiring and a second layer disposed in the same layer as the second wiring.

14. The flow sensor according to claim 12, wherein the member has a slit that exposes the boundary between the membrane portion and the peripheral portion.

15. The membrane portion has a flat surface, and the direction in which the flat surface is viewed from above is defined as the third direction. The first layer has a plurality of first layer portions arranged at predetermined intervals in the second direction, The second layer comprises a plurality of second layer portions arranged at predetermined intervals in the second direction, and a plurality of connecting portions connecting the first layer portion and the second layer portion. The flow sensor according to claim 13, wherein the spacing between adjacent first layer portions and the spacing between adjacent second layer portions overlap in the third direction to form a slit.

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