JP2010107497A - Flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow sensor capable of enhancing detection sensitivity of fluid flow more than previously existing by making hard to escape heat generated from a heat generator. <P>SOLUTION: Each wiring pattern 81a connected to an heat generator 81 is pulled out to one edge 33d of a membranes 33, respectively. On the other hand, each wiring pattern 83a connected to each temperature detector 83 is pulled out to another edge 33c of the opposite side, respectively. Thereby, the interval between the heat generator 81 and each wiring pattern 83a and the interval between each wiring pattern 81a and each wiring pattern 83a can be enlarged. Therefore, because thermal insulation of the heat generator 81 can be enhanced, detection sensitivity of fluid flow can be enhanced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flow rate sensor that detects a flow rate of a fluid based on a change in distribution of heat from a heating element disposed on one surface of a substrate.

Conventionally, as this type of flow sensor, a flow sensor is known in which a heating element and a temperature detector are arranged on a membrane (thin film) formed on a silicon substrate. FIG. 7 is an explanatory plan view of the membrane of the conventional flow rate sensor.
On the surface of the membrane 100, there are a heating element 90, temperature detection elements 91 and 92, a wiring pattern 90a drawn from the heating element 90, and wiring patterns 91a and 92a drawn from the temperature detection elements 91 and 92, respectively. Has been placed. The wiring patterns 90 a, 91 a, and 92 a are each drawn to one end 101 of the membrane 100.

  The heating element 90, the temperature detectors 91 and 92, and the wiring patterns 90a, 91a, and 92a are each formed in a thin film shape from silicon. Each wiring pattern 90a, 91a, 92a is connected to a control circuit (not shown). Then, a current is passed from the control circuit to the heating element 90 through the wiring pattern 90a to cause the heating element 90 to generate heat, and the temperature around the heating element 90 is raised. Therefore, the change in the temperature distribution is detected by the temperature detectors 91 and 92, and the gas flow rate and the gas flowing direction are measured based on the detection result.

Japanese Patent Laying-Open No. 2003-65819 (paragraphs 46 to 56, FIG. 1).

However, in the conventional flow rate sensor described above, since the heating element 90 and the wiring patterns 91a and 92a are close to each other, the heat generated from the heating element 90 easily escapes to the wiring patterns 91a and 92a. Further, since the wiring pattern 90a and the wiring patterns 91a and 92a are close to each other, heat generated from the heating element 90 easily escapes to the wiring patterns 91a and 92a via the wiring pattern 90a.
Therefore, the conventional flow rate sensor has a problem that it is difficult to increase the detection sensitivity of the fluid flow rate because the heat generated from the heating element 90 easily escapes.

  In view of the above, an object of the present invention is to realize a flow rate sensor capable of increasing the detection sensitivity of the fluid flow rate as compared with the prior art by making it difficult for the heat generated from the heating element to escape.

  In order to achieve the above object, according to the first aspect of the present invention, in the first aspect of the present invention, the substrate (40, 50, 80) disposed in the fluid flow and the heat generation disposed on the one surface side of the substrate. A body (81) and a temperature detection body (83), at least one first wiring (81a, 82a, 84a) drawn from the heating element on one surface side of the substrate, and at least the one surface on the one surface side of the substrate And a second wiring (83a) drawn from the temperature detection body, and detects the flow rate of the fluid by the temperature detection body based on a change in the distribution of heat from the heating element due to the flow of the fluid. In the flow sensor (30) configured as described above, the technical means is used in which the first and second wirings are drawn out in opposite directions (D1, D2) on the one surface side of the substrate.

Since the first and second wirings are drawn in opposite directions on the one surface side of the substrate, the distance between the heating element and the second wiring can be increased. Further, the interval between the first and second wirings can be increased.
Therefore, it is possible to make it difficult for the heat generated from the heating element to escape, so that the detection sensitivity of the fluid flow rate can be increased.

  In the invention according to claim 2, in the flow rate sensor (30) according to claim 1, a recess (41, 42) is formed on the other surface side of the substrate (40, 50, 80), and the temperature The detection body (83) is disposed on both sides of the heating element at a distance from the heating element (81), and the heating element and each temperature detection body are on one surface side of the substrate at the bottom of the recess. The technical means of being arranged in

  By forming a thin portion by forming a recess in the substrate, and disposing a heating element and each temperature detection body on the surface of the thin portion, it is possible to improve thermal insulation and increase detection sensitivity of the fluid flow rate. In such a structure, since the heat generated from the heating element can be made difficult to escape by pulling out the first and second wirings in opposite directions on the one surface side of the substrate, detection of the fluid flow rate Sensitivity can be further increased.

  According to a third aspect of the present invention, in the flow rate sensor (30) according to the second aspect, a distance (L) from the heating element (81) to one of the temperature detection bodies (83), and from the heating element The ratio (L / Lm) to the distance (Lm) from the one temperature detector to the edge (33a) of the bottom closest to the one temperature detector is 0.19 to 0.70. The technical means is used.

  According to the experiments conducted by the inventors of this application, the distance from the heating element to one temperature detection body, and from the heating element through one temperature detection body to the bottom edge closest to the one temperature detection body. By setting the ratio to the distance of 0.19 to 0.70, the fluid flow rate detection sensitivity could be increased.

  According to a fourth aspect of the present invention, in the flow rate sensor (30) according to the third aspect, the technical means that the ratio (L / Lm) is approximately 0.4 is used. Note that “approximately 0.4” means that a value close to 0.4 is included in addition to 0.4.

  According to the experiments conducted by the inventors of this application, the distance from the heating element to one temperature detection body, and from the heating element through one temperature detection body to the bottom edge closest to the one temperature detection body. When the ratio to the distance was set to approximately 0.4, the fluid flow rate detection sensitivity could be maximized.

  According to a fifth aspect of the present invention, in the flow rate sensor (30) according to any one of the second to fourth aspects, the substrate (40, 50, 80) includes a silicon substrate (40) as a support substrate. And an SOI substrate having an insulating film (50) as a buried layer and a semiconductor layer (80) as an SOI layer, and the recess has a cavity (41) formed in the silicon substrate on one surface side of the substrate. The heating element (81), the temperature detection element (83), the first wiring (81a, 82a, 84a), and the second wiring (83a) are respectively formed by covering with the insulating film. The technical means of being formed from a semiconductor layer is used.

In the flow rate sensor, the heating element and the temperature detector are arranged on the insulating film covering the cavity of the silicon substrate, so that the heat capacity of the part where they are arranged is kept low, and the part is thermally insulated, The detection sensitivity of the fluid flow rate is increased.
In addition, by forming the heating element, the temperature detection body, the first wiring, and the second wiring from the semiconductor layers, the heat conductivity is increased.

  In the flow sensor having such a structure, the heat generated from the heating element is more easily escaped to the first and second wirings arranged in the vicinity thereof, so the heating element and the temperature detection element are arranged. It is difficult to increase the thermal insulation of the part.

However, if the technical means according to any one of claims 2 to 4 is used, in the flow rate sensor having the above structure, the thermal insulation of the portion where the heating element and the temperature detection body are arranged is improved. be able to.
Therefore, the detection sensitivity of the fluid flow rate can be increased.

  In a sixth aspect of the present invention, in the flow sensor (30) according to any one of the second to fifth aspects, the first and second wirings (81a, 82a, 84a, 83a) are: The technical means of not intersecting the corner of the bottom part and the edge of the bottom part in the vicinity thereof is used.

  According to calculations from experiments conducted by the inventors of this application, the first and second wirings have a structure that does not intersect the corners of the bottom and the bottom edges in the vicinity thereof, so that The breakdown voltage could be increased.

  In the invention according to claim 7, in the flow sensor (30) according to claim 6, when the length of the edges (33c, 33d) between the corners adjacent to each other at the bottom is 100%, The technical means that the edge of the bottom part in the vicinity is an edge existing within a length of 10% from each corner adjacent to each other is used.

  According to calculations from experiments conducted by the inventors of this application, when the length of the edge between the corners adjacent to each other at the bottom is 100%, the first and second wirings are mutually By adopting a structure that does not intersect with the edge existing within 10% from each adjacent corner, the breakdown voltage at the bottom can be further increased.

  According to an eighth aspect of the present invention, in the flow sensor (30) according to any one of the second to seventh aspects, an edge of the bottom portion where the first wirings (81a, 82a, 84a) intersect Is the first edge (33d), the line width of the first wiring is at least wider than the width of the heating element (81), and the first wiring intersects the first edge. The technical means that the first ratio (Lb / W) indicating the ratio between the width (Lb) to be measured and the width (W) of the first edge is 0.5 to 0.9 is used.

  According to the simulation performed by the inventors of this application, the first wiring has a line width that is at least larger than the width of the heating element, and the width at which the first wiring intersects the first edge; Since the resistance value of the first wiring can be reduced by setting the first ratio indicating the ratio to the width of the edge to 0.5 to 0.9, the detection sensitivity of the fluid flow rate can be increased. did it.

  According to a ninth aspect of the present invention, in the flow sensor (30) according to any one of the second to eighth aspects, an edge of the bottom portion where the second wiring (83a) intersects the second flow sensor (30). In the case of the edge (33c), the width of the second wiring is wider than the width of the temperature detector (83), and the width (La) intersects the second edge. And a second ratio (La / W) indicating a ratio of the second width (W) to 0.5 to 0.9.

  According to the simulation performed by the inventors of the present application, the second wiring has a line width wider than the width of the temperature detection body, and a width at which the second wiring intersects the second edge; By setting the second ratio, which indicates the ratio to the width of the edge, of 0.5 to 0.9, the resistance value of the second wiring can be reduced, so that the detection sensitivity of the fluid flow rate can be increased. did it.

  According to a tenth aspect of the present invention, in the flow sensor (30) according to any one of the second to seventh aspects, an edge of the bottom portion where the first wiring (81a, 82a, 84a) intersects Is the first edge (33d), and the edge of the bottom where the second wiring (83a) intersects is the second edge (33c), the first wiring is connected to the first edge. The ratio (Lb / W) of the width (Lb) that intersects the width (W) of the first edge, the width (La) that the second wiring intersects the second edge, and the second width The technical means that the ratio (La / W) to the edge width (W) is substantially equal is used. Note that “substantially equal” includes the case where the ratio is approximate, in addition to the ratio being completely equal.

  According to calculations from experiments conducted by the inventors of this application, the ratio between the width of the first wiring intersecting the first edge and the width of the first edge, and the second wiring being the second By making the ratio of the width intersecting the edge and the width of the second edge substantially equal, the stress applied to the bottom portion can be reduced, and the portion where the first wiring intersects the first edge and the second wiring second Therefore, the pressure resistance at the bottom can be increased.

  According to an eleventh aspect of the present invention, in the flow rate sensor (30) according to the tenth aspect, technical means are used in which the first and second ratios are 0.5 to 0.9, respectively.

  According to calculations from experiments conducted by the inventors of this application, the first and second ratios are each configured to be in the range of 0.5 to 0.9, thereby increasing the withstand pressure at the bottom. I was able to.

  According to a twelfth aspect of the present invention, in the flow sensor (30) according to any one of the first to eleventh aspects, the first and second wirings (81a, 82a, 84a, 83a) are: A technical means is used in which the substrate is drawn in a direction substantially perpendicular to the fluid flow direction (F1) and in the opposite directions (D1, D2) on the one surface side of the substrate.

According to a simulation performed by the inventors of this application, the first and second wirings are drawn out in a direction substantially perpendicular to the direction of fluid flow on one surface side of the substrate and in directions opposite to each other. As a result, the heat generated by the heating element is more difficult to escape, and the fluid flow rate detection sensitivity can be further increased.
In addition, since the heat generated by the heating element is more difficult to escape, the heat generation amount of the heating element can be smaller than that of the conventional one, and thus the power consumption of the flow sensor can be reduced.

  According to a thirteenth aspect of the present invention, in the flow rate sensor (30) according to any one of the first to twelfth aspects, the first wiring (81a, 82a, 84a) includes one surface of the substrate. On the side, the technical means that wirings (82a, 84a) drawn from other than the heating element (81) (82, 84) are included is used.

  As a structure of the flow sensor, when a structure composed of a heating element and a temperature detection body is used as a basic structure, a structure in which a heating element temperature control resistor for controlling the temperature of the heating element is added to the basic structure (hereinafter, And a structure in which one temperature detector is further added to the first structure to extract the midpoint output of each temperature detector (hereinafter referred to as a second structure). In these first and second structures, when the wiring drawn from other than the heating element and the temperature detection body is drawn in the same direction as the wiring drawn from the heating element, the wiring drawn from other than the heating element and the temperature detection body By using the technical means according to claims 1 to 12 as the first wiring in combination with the wiring drawn from the heating element, the same effects as when using each technical means can be achieved. .

  In addition, the code | symbol in each said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

It is perspective explanatory drawing which shows the cross section at the time of cut | disconnecting a part of flow sensor by the part of a membrane. It is a cross-sectional explanatory drawing which expands and shows the part of the membrane of the flow sensor shown in FIG. It is a plane explanatory view of a membrane. It is an enlarged view of a heat generating body and a temperature detection body. It is a graph which shows an experimental result. It is a graph which shows the relationship between a flow velocity and a sensor output voltage. It is plane explanatory drawing of the membrane of the conventional flow sensor. It is plane explanatory drawing which shows the relationship between the flow of gas and the drawing-out direction of wiring. It is plane | planar explanatory drawing of the membrane of the flow sensor used in the simulation 1, (a) is plane | planar explanatory drawing before improvement, (b) is plane | planar explanatory drawing after improvement. It is explanatory drawing which shows the result of the simulation. It is explanatory drawing which shows the result of the simulation. It is plane explanatory drawing of the membrane of the flow sensor which improved wiring. It is an enlarged view of the temperature detection body arrange | positioned at the membrane shown in FIG. It is an enlarged view of the heat generating body arrange | positioned at the membrane shown in FIG. It is a graph which shows the result of simulation 3. It is a plane explanatory view of the membrane of the flow sensor used in the experiment. It is explanatory drawing which shows the calculation result from experiment. It is explanatory drawing which shows the calculation result from experiment.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective explanatory view showing a cross section when a part of a flow sensor is cut at a membrane portion. FIG. 2 is an enlarged cross-sectional explanatory view showing a membrane portion of the flow sensor shown in FIG. FIG. 3 is an explanatory plan view of the membrane. FIG. 4 is an enlarged view of the heating element and the temperature detection body. FIG. 8 is an explanatory plan view showing the relationship between the gas flow and the wiring drawing direction. In FIGS. 1 and 2, the substrate and the film are drawn larger than the actual dimensions for easy understanding of the structure.

[Main configuration of flow sensor]
In this embodiment, the flow sensor 30 is manufactured using an SOI substrate. As shown in FIG. 2, the flow sensor 30 is formed of a silicon substrate 40, a silicon oxide film 50 formed on the surface of the silicon substrate 40, and a single crystal silicon layer formed on the surface of the silicon oxide film 50. A wiring pattern 80, a silicon oxide film 60 covering the wiring pattern 80, and a silicon nitride film 70 formed on the surface of the silicon oxide film 60 are provided.

  A cavity 41 is formed through the back surface of the silicon substrate 40, and the opening 43 (FIG. 1) on the substrate surface side of the cavity 41 has silicon oxide films 50, 60, a wiring pattern 80, and a silicon nitride film 70. It is covered with the membrane 33 which consists of. That is, the bottom 42 of the cavity 41 is formed by the membrane 33.

  In this embodiment, the thickness of the silicon substrate 40 is 500 μm. The thickness of the portion of the membrane 33 where the wiring pattern 80 is formed is about 3 μm.

  The cavity 41 is formed by performing anisotropic etching from the exposed portion of the back surface of the silicon substrate 40 using the silicon nitride film as a mask until the silicon oxide film 50 is exposed using an etchant.

  As shown in FIG. 3, the membrane 33 is formed with a sensing unit 32 for detecting the flow rate of the gas flowing on the surface of the membrane 33. The sensing unit 32 includes a heating element 81, a heating element temperature control resistor 82 formed on both sides of the heating element 81, and a temperature detection body 83 formed on both sides of the heating element temperature control resistor body 82. . The heating element temperature control resistor 82 is a resistor whose resistance value changes upon receiving heat from the heating element 81, and is used for temperature control of the heating element 81. The temperature around the heating element 81 rises due to the heat generated from the heating element 81, and the temperature distribution generated in the membrane 33 changes as the gas flows. A change in the temperature distribution is detected by each temperature detector 83 and a midpoint output unit 84 for extracting the midpoint potential of each temperature detector 83, a wiring 84a, and a wiring 83a are used. The gas flow rate is measured by detecting the midpoint potential.

  The wiring pattern 80 is made of a single crystal silicon layer and is formed in a thin film shape. The heating element 81, the heating element temperature control resistor 82, and the temperature detector 83 are each a part of the wiring pattern 80, and are formed by doping impurities into the single crystal silicon layer. The membrane 33 is formed in a rectangular shape, and has a pair of opposite edges 33a and 33b and a pair of opposite edges 33c and 33d. The heating element 81 and the heating element temperature control resistor 82 are disposed substantially at the center of the membrane 33.

  Each temperature detector 83 is formed in a double U-shape, and is arranged in parallel with the end edges 33a and 33b. In the figure, the unhatched region is a region where the wiring pattern 80 is formed (a region composed of the single crystal silicon layer, the silicon oxide films 50 and 60, and the silicon nitride film 70), and the hatched region. Is a region where the wiring pattern 80 is not formed (region consisting of the silicon oxide films 50 and 60 and the silicon nitride film 70).

  Here, the characteristic part of the flow sensor 30 will be described. A wiring pattern 81 a is electrically connected to the heating element 81, and each wiring pattern 81 a is drawn out to one end 33 d of the membrane 33. In addition, wiring patterns 83a are electrically connected to the temperature detector 83, and each wiring pattern 83a is led out to the other edge 33c opposite to the one edge 33d. Note that the wiring pattern 82 a of the heating element temperature control resistor 82 and the wiring pattern 84 a of the midpoint output portion 84 are drawn out to one end 33 d of the membrane 33. The wiring patterns 81a, 82a, 84a drawn to the edge 33d correspond to the first wiring according to claim 1 of this application, and the wiring pattern 83a drawn to the edge 33c is the second wiring. Corresponding to In the following description, the wiring patterns 81a, 82a, and 84a are also referred to as first wirings, and the wiring pattern 83a is also referred to as second wiring.

Further, as shown in FIG. 8, the first wiring is drawn out in a direction D1 substantially perpendicular to the direction F1 in which the gas that is the detection target of the flow rate flows. In addition, the second wiring is drawn in a direction opposite to the direction D1 by 180 degrees and substantially perpendicular to the gas flow direction F1.
That is, the first wiring and the second wiring are drawn out on the surface of the membrane 33 in a direction substantially perpendicular to the gas flow direction F1 and in opposite directions.

Since it is configured in this manner, the distance between the heating element 81 and each wiring pattern 83a can be increased, so that heat generated from the heating element 81 is difficult to escape to each wiring pattern 83a.
Further, since the interval between each wiring pattern 81a and each wiring pattern 83a can be increased, the heat generated from the heating element 81 is unlikely to escape to each wiring pattern 83a via each wiring pattern 81a.
Therefore, since the heat insulation of the heating element 81 can be increased, the detection sensitivity of the fluid flow rate can be increased.

  As shown in FIG. 3 and FIG. 4, a portion 83 b of the wiring pattern 83 a that is drawn from the base portion of the temperature detection body 83 and is close to the corner portion 81 b of the heating element 81 is inclined. Is formed. Further, as shown in FIG. 3, the end edge 83 c of each wiring pattern 83 a that is close to the heating element 81 has a shape recessed in the direction of the end edge 33 c of the membrane 33. By forming in this way, the space between the heating element 81 and the wiring pattern 83a can be widened, so that the thermal insulation of the heating element 81 can be enhanced, and therefore the detection sensitivity of the fluid flow rate can be further enhanced. it can.

[Experiment]
Next, the contents of the experiment conducted by the inventors of this application will be described. The inventors of this application found that the distance between the heating element 81 and the temperature detection body 83 and the distance from the heating element 81 through the temperature detection body 83 and the edge 33a of the membrane 33 closest to the temperature detection body 83 are as follows. The influence on detection sensitivity was investigated. FIG. 5 is a graph showing experimental results.

  This experiment was performed using the flow rate sensor 30 described in the above embodiment and the conventional flow rate sensor shown in FIG. As shown in FIG. 4, the distance between the outer edge of the heating element 81 and the inner edge of the temperature detector 83 is L, and the temperature detector 83 passes from the outer edge of the heater 81 to the temperature detector 83. The distance to the edge 33a of the nearest membrane 33 was Lm. And the flow rate detection sensitivity when changing the ratio (L / Lm) of the distance L and the distance Lm was measured. The ratio between the output voltage of the flow sensor and the gas flow velocity was measured as the flow rate detection sensitivity.

  As a result, the flow rate detection sensitivity in the range of the ratio (L / Lm) of 0.19 to 0.7 was higher in the flow rate sensor 30 in the above-described embodiment than in the conventional flow rate sensor. Further, as the ratio (L / Lm) increases from 0.19, the flow rate detection sensitivity becomes higher. When the ratio (L / Lm) becomes approximately 0.4, the flow rate detection sensitivity becomes the highest sensitivity. became.

  In addition, the heating element 81, each temperature detection body 83, and the membrane edges 33a, 33b are symmetrical with respect to the membrane 33 around the line connecting the middle points of the edges 33c, 33d. It was estimated that the same experimental results as described above were obtained for the relationship between the temperature detector 83 (the temperature detector 83 arranged on the left side of the heater 81 in FIG. 3) and the heater 81.

  That is, the flow rate detection sensitivity is increased by arranging the heating element 81 and each temperature detection body 83 on the surface of the membrane 33 so that the ratio (L / Lm) is in the range of 0.19 to 0.7. In particular, it was found that when the ratio (L / Lm) is arranged to be approximately 0.4, the flow rate detection sensitivity can be maximized.

  In addition, the inventors of this application examined the relationship between the flow velocity and the sensor output voltage in the above experimental results. FIG. 6 is a graph showing the results, showing the relationship between the flow velocity and the sensor output voltage. As shown in the figure, it can be seen that the flow rate sensor 30 of the above-described embodiment has a sensor output voltage larger than that of the conventional flow rate sensor in the range of the gas from a low flow rate to a high flow rate. That is, even if the output voltage of the flow sensor is high even at the same flow rate, a small change in the flow rate can be detected. Therefore, the flow rate sensor 30 of the above-described embodiment can have a higher flow rate detection sensitivity than the conventional flow rate sensor. I understood.

[Simulation 1]
Next, the inventors of this application performed a simulation to see how much the flow rate detection sensitivity is improved by improving the lead-out direction of the first and second wirings. FIG. 9 is an explanatory plan view of the membrane of the flow sensor used in this simulation 1, (a) is an explanatory plan view before improvement, and (b) is an explanatory plan view after improvement. FIG. 10 is an explanatory diagram showing the result of this simulation.

  As shown in FIG. 9A, the structure on the membrane 33 before the improvement is that the first wiring 81 a drawn from the heating element 81 and the second wiring 83 a drawn from the temperature detection body 83 are both membrane 33. It is the structure pulled out toward the end edge 33d. Further, as shown in FIG. 9B, the improved structure on the membrane 33 is such that the first wiring 81a is drawn out toward the end edge 33d, and the second wiring 83a is on the side opposite to the end edge 33d. It is pulled out toward the end edge 33c.

  Then, a current is passed through the heating element 81 to generate heat, and as shown in the figure, the gas to be detected is caused to flow perpendicularly to the drawing directions of the first and second wirings, and the flow rate is adjusted by the flow rate sensors before and after the improvement. Detected. As a result, as shown in FIG. 10, it was found that the improved flow rate sensor can improve the detection sensitivity by about 8% compared to the flow rate sensor before the improvement.

  That is, the first wiring 81a and the second wiring 83a are improved so as to be drawn out in a direction substantially perpendicular to the gas flow direction on the membrane 33 and in directions opposite to each other. It was also found that the detection sensitivity can be increased by about 8%.

[Simulation 2]
Next, the inventors of this application performed a simulation to see how much the amount of heat generated by the heating element is reduced by improving the drawing direction of the first and second wirings. FIG. 11 is an explanatory diagram showing the result of this simulation.

  In this simulation, the same flow sensor as used in the above-described simulation 1 was used. Then, a current was passed through the heating element 81 to generate heat, and the amount of heat generated when the heating element 81 should be maintained at a constant temperature when the gas was supplied from a certain direction for a certain period of time as in simulation 1 was obtained. As a result, as shown in FIG. 11, when the calorific value before the improvement was about 30 (arbitrary unit), the calorific value after the improvement was about 25, and the calorific value was smaller than that before the improvement.

That is, the heating element 81 is improved by pulling out the first wiring 81a and the second wiring 83a in a direction substantially perpendicular to the gas flow direction on the membrane 33 and in directions opposite to each other. It was found that the calorific value of can be reduced more than before the improvement.
Therefore, it has been found that since the current flowing through the heating element 81 can be reduced as compared with before the improvement, the power consumption of the flow sensor can be reduced.

[Simulation 3]
Next, the inventors of this application performed a simulation to see how much the detection sensitivity of the flow rate is improved by making the line widths of the first and second wirings wider than before. FIG. 12 is an explanatory plan view of the membrane of the flow sensor used in the simulation 3. FIG. 13 is an enlarged view of the second wiring 83a shown in FIG. 12, and FIG. 14 is an enlarged view of the first wiring 81a shown in FIG. FIG. 15 is a graph showing the results of this simulation.

  In this simulation, the flow rate sensor shown in FIG. 3 was used as the flow rate sensor before the wiring line width was increased. As shown in FIG. 12, the line having a larger line width is drawn from the heating element 81 and the line width of the second wiring 83 a drawn from each temperature detector 83 compared to that shown in FIG. 3. Further, the first wiring 81a and the wiring 82a drawn from the heating element temperature control resistor 82 are thicker.

  Specifically, in FIG. 13, the width L11 and the total length of the sensing part 83d constituting the temperature detector 83 are the same as those of the conventional one, and the line widths L5 to L10 of the second wirings 83a constituting the wiring part 83e are respectively thick. did. In addition, each second wiring 83a has a width L12 where each second wiring 83a drawn out from one temperature detection body 83 intersects the edge 33c of the membrane 33 is thicker than a width L11 of the temperature detection body 83. 83a was formed.

  In FIG. 14, the width L1 and the total length of the sensing portion 81c constituting the heating element 81 are the same as those in the conventional case, and the line width L2 at which each first wiring 81a constituting the wiring portion 81d intersects the edge 33d is defined. I made it thick. Further, the width L3 and the total length of the sensing part 82c constituting the heating element temperature control resistor 82 are the same as those in the conventional case, and the line width L4 where each wiring 82a constituting the wiring part 82d intersects the end edge 33d is increased.

  Further, in FIG. 14, each of the first wirings 81 a so that the width L <b> 2 where the first wiring 81 a drawn from the heating element 81 intersects the edge 33 d of the membrane 33 is thicker than the width L <b> 1 of the heating element 81. Formed. In addition, each width L4 where the first wiring 82a drawn from the heating element temperature control resistor 82 intersects the edge 33d of the membrane 33 is thicker than the width L3 of the heating element temperature control resistor 82. 1 wiring 82a was formed. Note that the wiring 84a led out from the midpoint output portion 84 is formed to have the same line width as the conventional one.

In FIG. 12, the ratio (La / W) between the width La of each second wiring 83a drawn out from the two temperature detectors 83 and the width W of the end edge 33c intersects the end edge 33c. Each second wiring 83a was formed so as to be within the range of 0.5 to 0.9.
Further, the ratio (Lb / W) of the width Lb at which the first wirings 81a, 82a, 84a intersect the edge 33d and the width W of the edge 33d falls within the range of 0.5 to 0.9. Thus, the first wirings 81a, 82a, 84a were formed.

  Then, a current was passed through the heating element 81 to generate heat, and the flow rate when a gas was allowed to flow from a certain direction for a certain period of time as in simulation 1 was detected. As a result, as shown in FIG. 15, it was found that the detection sensitivity can be improved by 3% or more when the line widths of the first and second wirings are increased by 20% compared to the conventional case. It was also found that the detection sensitivity can be improved by 4% or more when the line widths of the first and second wirings are increased by 30% compared to the prior art.

[Calculation from experiment 1]
Next, the inventors of this application conducted an experiment to determine whether the pressure resistance of the membrane 33 is affected by whether the first and second wirings intersect the corner of the membrane 33 or not. FIG. 16 is an explanatory plan view of the membrane of the flow sensor used in this experiment, and FIG. 17 is an explanatory diagram showing the result of calculation from this experiment.

  In this experiment, the flow sensor shown in FIG. 16 is used as a flow sensor having a structure in which the first and second wirings do not cross the corner of the membrane 33, and the flow sensor shown in FIG. The flow sensor shown in 3 was used. In the region indicated by E in FIG. 16, the first wirings 81 a, 82 a, and 84 a led out toward the edge 33 d of the membrane 33 do not intersect with the corners of the membrane 33. A distance ΔLb is placed between the outermost edge of the first wiring 84a closest to the corner and the corner.

  Further, the second wiring 83 a drawn out toward the end edge 33 c opposite to the end edge 33 d of the membrane 33 does not intersect the corner of the membrane 33. A distance ΔLa is placed between the outermost edge and the corner of the second wiring 83a.

  Then, pressure was applied to the membrane 33 of both flow sensors, and the pressure resistance of the membrane 33 was measured. As a result, as shown in FIG. 17, when the pressure resistance when the membrane 33 of the flow sensor before improvement in which the first and second wirings intersect the corners of the membrane 33 is broken is used as a reference, the first and second In the improved flow rate sensor configured such that the wiring 2 does not intersect with the corner of the membrane 33, the pressure resistance of the membrane 33 is improved by about 10% compared to before the improvement.

  Thus, the reason why the pressure resistance of the membrane 33 is improved by configuring the first and second wirings so as not to intersect the corners of the membrane 33 is that the stress applied to the membrane 33 is caused by the wiring being connected to the corners of the membrane 33. It was estimated that the configuration that does not intersect the part is smaller than the configuration that intersects.

  Further, when the total width of the end edge 33d of the membrane 33 is 100%, the distance ΔLb is 10% from the end of the end edge 33d (the corner of the membrane 33 that defines the end edge 33d). The wirings 81a, 82a, and 84a are formed, and the second wiring 83a is formed so that the distance ΔLb exceeds 10% from the end of the end edge 33c (the corner of the membrane 33 that defines the end 33c). Thus, the pressure resistance could be increased by at least about 10%.

[Calculation 2 from experiment]
Next, the inventors of this application calculated from experiments the effects of the ratios (La / W) and (Lb / W) in the simulation 3 described above on the pressure resistance of the membrane 33. FIG. 18 is a graph showing the results of this calculation.

  This calculation was performed using a flow rate sensor having the membrane structure shown in FIG. 12 so that the ratios (La / W) and (Lb / W) were substantially the same. Further, as shown in FIG. 18, the ratio (La / W) and (Lb / W) is 0.15, which is the ratio in the conventional flow sensor, and the pressure resistance of the membrane 33 at that time is 1. When the ratios (La / W) and (Lb / W) were set to 0.6, the pressure resistance of the membrane 33 was improved to 2 that is twice the conventional value. That is, when the ratios (La / W) and (Lb / W) are made larger than before, the pressure resistance of the membrane 33 is improved.

  Moreover, the pressure resistance of the membrane 33 was further improved by making the ratios (La / W) and (Lb / W) substantially the same. This is because when the ratio is substantially the same, the stress applied to the membrane 33 is applied evenly to each edge of the membrane 33, but if the ratio is different, the stress is biased to one edge and the pressure resistance decreases. It was estimated that.

  When the ratios (La / W) and (Lb / W) exceed 0.9, the outermost edges of the first and second wirings approach the corners of the membrane 33, and the improvement in pressure resistance of the membrane 33 is small. Therefore, the ratio is desirably 0.9 or less. Further, when the ratio is smaller than 0.5, the wiring area intersecting with the edge of the membrane 33 is reduced, and the rigidity of the membrane 33 is lowered. Therefore, the ratio is desirably 0.5 or more. That is, it is desirable that the ratios (La / W) and (Lb / W) are set to be approximately the same within a range of 0.5 to 0.9.

<Other embodiments>
In the above-described embodiment, the flow sensor having a configuration in which the heating element 81, the heating element temperature control resistor 82, the temperature detection body 83, the midpoint output unit 84, and the wirings 81a to 84a are arranged on the membrane 32 has been described. The invention according to this application can also be applied to a flow sensor that does not include the body temperature control resistor 82 and the wiring 82a. Further, the invention according to this application can also be applied to a flow sensor provided with only one temperature detector 83. Furthermore, the invention according to this application can be applied to a flow rate sensor that includes only one temperature detector 83 and does not include the heating element temperature control resistor 82 and the wiring 82a. Furthermore, the invention according to this application can also be applied to a flow rate sensor having a configuration in which the wiring 84a of the midpoint output portion 84 is drawn in the same direction as the wiring 83a of the temperature detector 83. In this case, the wirings 83a and 84a may be handled as the second wiring.

30 ... Flow sensor, 32 ... Sensing part, 33 ... Membrane,
40 .. Silicon substrate, 41 .. Cavity, 42 .. Bottom, 43 .. Opening,
33a to 33d .. edge (bottom edge), 80 .. wiring pattern, 81 .. heating element,
82 ... Heating element temperature control resistor, 83 ... Temperature detector, 84 ... Mid point output section,
81a-84a ... wiring.

Claims (13)

A substrate disposed in the fluid flow;
A heating element and a temperature detector disposed on one side of the substrate;
A first wiring drawn from at least the heating element on one surface side of the substrate;
A second wiring led out from at least the temperature detector on one surface side of the substrate;
A flow rate sensor that detects the flow rate of the fluid by the temperature detector based on a change in the distribution of heat from the heating element due to the flow of the fluid,
The flow sensor according to claim 1, wherein the first and second wirings are drawn in opposite directions on one surface side of the substrate. A recess is formed on the other surface side of the substrate,
The temperature detection body is disposed on both sides of the heating element at a distance from the heating element,
2. The flow sensor according to claim 1, wherein the heating element and each temperature detection body are arranged on one surface side of the substrate at the bottom of the recess.   The ratio of the distance from the heating element to one of the temperature detection bodies and the distance from the heating element through the one temperature detection body to the edge of the bottom closest to the one temperature detection body is 0 The flow rate sensor according to claim 2, wherein the flow rate sensor is 19 to 0.70.   The flow sensor according to claim 3, wherein the ratio is approximately 0.4. The substrate is
It consists of an SOI substrate with a silicon substrate as a support substrate, an insulating film as a buried layer, and a semiconductor layer as an SOI layer,
The recess is
It is formed by covering the cavity formed in the silicon substrate with the insulating film on one surface side of the substrate,
5. The flow sensor according to claim 2, wherein the heating element, the temperature detector, the first wiring, and the second wiring are each formed of the semiconductor layer. .   6. The flow sensor according to claim 2, wherein the first and second wirings do not intersect with the corner of the bottom and the edge of the bottom in the vicinity thereof.   When the length of the edge between the corners adjacent to each other at the bottom is 100%, the edge of the bottom near the edge exists within 10% from each of the corners adjacent to each other. The flow sensor according to claim 6, wherein the flow sensor is an edge.   When the edge of the bottom portion where the first wiring intersects is the first edge, the line width of the first wiring is at least wider than the width of the heating element, and the first wiring is The first ratio indicating a ratio of a width intersecting with the first edge and a width of the first edge is 0.5 to 0.9. The flow sensor as described in any one.   When the edge of the bottom where the second wiring intersects is the second edge, the line width of the second wiring is wider than the width of the temperature detection body, and the second wiring is The second ratio indicating the ratio between the width intersecting the second edge and the second width is 0.5 to 0.9, wherein the second ratio is 0.5 to 0.9. The flow sensor described in 1.   When the bottom edge at which the first wiring intersects is the first edge and the bottom edge at which the second wiring intersects is the second edge, the first wiring is the first edge. A first ratio indicating a ratio of a width intersecting the edge of the first edge and a width of the first edge; and a width of the second wiring intersecting the second edge and a width of the second edge. The flow rate sensor according to any one of claims 2 to 7, wherein the second ratio indicating the ratio is substantially equal.   The flow rate sensor according to claim 10, wherein the first and second ratios are 0.5 to 0.9, respectively.   The first and second wirings are led out in a direction substantially perpendicular to a direction in which the fluid flows on one surface side of the substrate and in directions opposite to each other. The flow sensor according to claim 11.   13. The wiring according to claim 1, wherein the first wiring includes a wiring drawn from a surface other than the heating element on one side of the substrate. Flow sensor.

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