JP2005172445A - Flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow sensor in which miniaturization can be realized without receiving limitation in installation attitude, without causing convection flow even using a shunt structure. <P>SOLUTION: The flow sensor is constituted in such a manner that a flat surface section of top face of silicon substrate 11, and an inverse U groove of upper case 2, form the inverse U shape sensing flow path 10, and on a flat part of upstream side of the mutually parallel sensing flow path 10 in an inverse U shape on the silicon substrate 11 thin film resistors 6a, and 6b are provided, and on the flat part of downstream side on the silicon substrate 11 the thin film resistor 7a, and 7b are provided. Then, the thin film resistors 6a, and 7a, and the thin film resistors 6b, and 7b are serially connected respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermal type flow sensor for measuring a flow rate of a fluid.

  A flow sensor using heat is provided with one heating resistance element or a plurality of heat generation and / or temperature measurement resistance elements arranged in the flow path to electrically detect heat flow of the heating resistance element due to the flow, Measure. In order to ensure the accuracy of output especially when the flow is zero, heaters are arranged on the upstream side and downstream side of the flow path, maintaining thermal equilibrium without flow on the upstream side and downstream side, and thermal equilibrium is achieved by the flow. When it breaks down, there is one that detects this and measures the flow rate. In this type of flow sensor, conventionally, two heaters made of a metal film patterned on a silicon substrate are formed, and a gas flow path for flowing gas from one heater to the other heater is formed. Is known (for example, see Patent Document 1).

  Also disclosed is a flow sensor formed by patterning a heating resistor and a resistance temperature detector on a silicon substrate (see, for example, Patent Document 2).

  In addition, it is also known that a measurement chip on which heat rays are formed is mounted on a substrate, a sensor flow path is formed as a groove between the measurement chip and the substrate, and a heat line is bridged in the sensor flow path separately from the main flow path. (For example, see Patent Document 3).

In addition, a flow sensor having a good thermal conductivity in the flow path, generally a method of winding a heat-sensitive resistance wire around a thin tube made of a metal material, makes the narrow tube in an inverted U shape, and the first and second portions are formed in one vertical portion. It is known that a thermal resistance wire is wound and third and fourth thermal resistance wires are wound around other vertical portions (for example, see Patent Document 4).
JP 2002-340646 A Japanese Patent Application Laid-Open No. 2000-146652 JP 2002-168669 A JP-A-7-27582

  In the flow sensor described in Patent Document 1 described above, as shown in FIG. 20A, when the upstream heater 30a and the downstream heater 30b are placed horizontally, the heat distribution is balanced without flow, When a flow occurs, as shown in FIG. 20 (b), the heat distribution collapses and the flow rate can be detected by a bridge circuit. However, as shown in FIG. However, there is a problem that heat distribution collapses due to convection. The flow sensor described in Patent Document 2 has the same problem.

  In Patent Document 1, as a method for solving this problem, the temperature is kept uniform by leaving silicon below the heater without leaving a cavity, and the influence of disturbance is avoided. However, this is because the thermal conductivity of silicon, which brings about the smoothness of heat distribution, requires a considerable amount of power to raise the heater temperature, and the power saving characteristic of this type of sensor cannot be realized.

  Further, such a flow sensor is applied to a sensor flow path arranged in parallel with the main flow path, or in the flow sensor described in Patent Document 3, as shown in FIG. When there is no sensor, the heat distribution is balanced, but as shown in FIG. 19 (b), when it is placed vertically, the warmed fluid around the detector moves vertically upward, the heat distribution collapses, and the sensor A circulation flow by convection occurs between the channel 32 and the main channel 31. Therefore, in the case where the upstream and downstream thermal resistors are arranged horizontally, there is a problem that the installation posture is limited.

  In addition, in the technique of Patent Document 4, there is no need to restrict the posture, but the inverted U-shaped flow path uses a thin tube made of a highly heat-conductive material in principle. In addition, since the resistor is a winding, the processing of the resistor lead wire becomes practically complicated, power consumption is large, and there is a problem in downsizing such as installation space.

  In order to solve the above problems, the inventors of the present invention form a flow path from the surface of the flow path base, from the front surface to the back surface and the back surface, and to either the front surface or the back surface of the flow path base. Created a flow sensor in which a thin film resistor for upstream is arranged, and a thin film resistor for downstream is arranged in the other flow path with respect to either the front or back surface of the flow path base. (Japanese Patent Application 2003-002729).

  The flow sensor according to this application is not limited by the mounting posture, and a flow dividing structure that does not cause convection and can achieve downsizing is obtained. However, the flow sensor is a flow path base. It has a structure of forming a flow path and a thin film resistor on both front and back sides of a silicon substrate, or joining a structure in which a flow path and a thin film resistor are formed on one surface of a silicon substrate. There was still a way to turn.

  The present invention has been made paying attention to the above-mentioned problems, and is intended to provide a flow sensor that can be reduced in size without being restricted by the mounting posture, without causing convection even as a shunt structure. It is aimed.

  In the flow sensor of the present invention, one or a plurality of combinations of thin film resistors for detection formed on a thin film substrate are installed in a detection flow path to detect a thermal action of a fluid on the thin film resistor. The detection flow path is formed in a U shape including the flat portion of the thin film substrate in the flow path, and a pair of thin film resistors is provided on the flat portions of the U-shaped parallel flow path portions. The body is installed.

  In the flow sensor of the present invention, the combination of the two thin film resistors installed in the parallel portion makes the heat generation form equal to each other. For example, the shape of the corresponding thin film resistors may be the same.

  In the flow sensor of the present invention, both detection outputs are added to each other.

  In the flow sensor of the present invention, the thin film resistor is for detection as a heater and may be of a self-heating type.

  In the flow sensor of the present invention, the thin film resistor may be an indirectly heated type including a detector and a heater.

  In this indirectly heated flow sensor, the thin film resistor for the heater may be disposed between a pair of thin film resistors for detection in the respective flow path portions on the upstream side and the downstream side.

  According to the present invention, a pair of heat generation type thin film resistors are arranged in the U-shaped parallel portion of the flow path, respectively, so that the fluid heated in the vicinity of the detection unit even in the case of no vertical flow. Therefore, even if a flow path such as a bypass is provided in parallel with the sensor flow path, a circulation flow due to convection does not occur. Further, in the above posture, by adding the detection outputs of the combination of the thin film resistors in both the parallel portions, the flow sensitivity of both is doubled, and the output error due to both convections is canceled out.

  Furthermore, by forming the thin film resistor in the upstream flow channel and the thin film resistor in the downstream flow channel on one flat surface, it can be simplified and the formation position can be overwhelmingly reduced, resulting in further downsizing. it can.

  Hereinafter, the present invention will be described in more detail with reference to embodiments.

  1, 2, and 3 are diagrams showing a schematic configuration of a flow sensor 1 according to an embodiment of the present invention. FIG. 1 is a front view of the flow sensor 1 according to the embodiment, and FIG. FIG. 3 and FIG. 3 are sectional views cut along XX ′ in FIG. In the flow sensor 1 of this embodiment, an upper housing 2 and a lower housing 3 are joined.

  The lower housing 3 is provided with a silicon substrate (sensor chip) 11 on the surface and through holes 20 that serve as inlets and outlets of the detection flow path 10. On the other hand, a slot 10 having a U-shaped portion in plan view is formed in the upper casing 2, and the formation surface of the slot 10 of the upper casing 2 and the silicon substrate 11 of the lower casing 3 are formed. And a U-shaped flow path 10 is formed. Both ends of the U-shaped flow path 10 communicate with the through hole 20 of the lower housing 3. Accordingly, the through hole 20 constitutes an inlet and an outlet for the fluid of the flow sensor 1. The U-shaped flow path 10 and the silicon substrate 11 constituting the main part of the flow sensor 1 of this embodiment are indicated by broken lines in FIG.

  The upper housing 2 has a through hole 13 that communicates from the outside to the silicon substrate 11. A lead wire for connecting to the electrode 9 is inserted through the through hole 13, and the through hole 13 is sealed with a conductive adhesive or the like. 4 is a surface view of the silicon substrate 11 of the flow sensor 1 of the embodiment, and FIG. 5 is a partial cross-sectional view of the upper housing 2 of the flow sensor 1 of the embodiment cut in parallel to the surface of the silicon substrate 11. As shown in FIGS. 4 and 5, upstream thin film resistors 6 a and 6 b and downstream thin film resistors 7 a and 7 b are formed and arranged on the upper surface (surface) of the silicon substrate 11.

  The upper housing 2 has a U-shaped portion 10a and a groove 10 having an inlet 10b and an outlet 10c directed outward at the U-shaped tip, and the groove 10 of the upper housing 2 is formed in the silicon substrate 11. When facing each other and joining, a U-shaped detection flow path 10 is formed as shown in FIGS. The upper housing 2 is made of resin, glass, semiconductor, metal material, or the like, and is machined or molded by a mold, or a semiconductor substrate is manufactured by micromachine technology. The lower housing 3 in which the silicon substrate 11 is placed and buried is also made of the same material. The thin film resistors 6 a and 6 b of the silicon substrate 11 are disposed on the upstream side of the detection flow path 10, and the thin film resistors 7 a and 7 b are disposed on the downstream side of the detection flow path 10. These thin film resistors 6a, 6b, 7a and 7b are used both for heaters and for detection. The thin film formation on the silicon substrate 11 is manufactured by a well-known micromachine technique. In the vicinity of the thin film resistors 6a, 6b and 7a, 7b, holes for anisotropic etching (shaded portions in FIG. 4) for forming cavities are formed in the lower portions. The hole 8 is formed by removing the protective film and the insulating film by, for example, wet etching or RIE. Thereafter, by performing anisotropic etching of silicon using, for example, a TMAH etchant, the long hole (cavity) 12 shown in FIGS. 6 and 7 can be formed. Thin film resistors 6a, 7b, 7a, 7b sandwiched between an insulating film and a protective film are formed above the elongated hole 12. By providing the cavity 12 in the silicon substrate 11, the thermal insulation of the thin film portion having the thin film resistors 6a, 7b, 7a, 7b can be ensured.

  As shown in FIG. 4, the thin film resistors 6a, 6b, 7a, and 7b are connected in series with the thin film resistor 6a on the upstream side of the upstream channel and the thin film resistor 7a on the upstream side of the downstream channel. Further, the thin film resistor 6b on the downstream side of the upstream channel and the thin film resistor 7b on the downstream side of the downstream channel are connected in series. This is a basic example of a method of adding the detection outputs of both thin film resistors to each other, and is an effective means that can reduce and simplify the detection circuit. However, the surface view of FIG. 4 depicts a simplified wiring from the thin film resistor to the thin film resistor and from the thin film resistor to the electrode. Actually, this part of the wiring is a part not directly related to detection, and because of the electrical connection function, the wiring pattern is formed so that the resistance value is as small as possible and the resistance difference between upstream and downstream is small. .

  The thin film resistors 6a, 6b, 7a, and 7b in this embodiment can use FIG. 8B as a bridge circuit connection. In this circuit, a series circuit of thin film resistors 6a and 7a and a series circuit of thin film resistors 6b and 7b are directly connected at one end. Of course, the thin film resistors 6a and 7a are connected in series and the thin film resistors 6b and 7b are connected in series so as not to directly form a bridge circuit, as shown in FIG. The heater drive / temperature difference detection circuit may be configured individually. Further, as shown in FIG. 8A, the thin film resistors 6a and 6b constitute a bridge circuit of the upstream flow path, and the bridge circuit of the downstream flow path is configured as 6a of the circuit shown in FIG. Another circuit in which 6b is replaced with 7a and 7b may be used.

  As described above, the upstream thin film resistor of the upstream flow channel and the upstream thin film resistor of the downstream flow channel are connected in series, and the downstream thin film resistor of the upstream flow channel and the downstream thin film of the downstream flow channel By connecting the resistors in series, the power consumption is slightly higher than in the case of not connecting them in series, but the sensitivity is doubled.

  In the flow sensor 1 of this embodiment, FIG. 18 shows the shape of a conventional flow sensor that has no restriction on the installation posture. However, when applied to the flow sensor 1 of this embodiment, 6a and 6b are shown in 30a and 7a in 30b. 7b, the thin film resistors 6a and 7a are upstream, and the thin film resistors 6b and 7b are downstream resistors. Here, as shown in 18 (b), there is no problem in (b) in the case where the U-shaped flow path is arranged horizontally. When the U-shaped channel is installed so as to be vertical as shown in FIG. 18A, the surrounding fluid heated by the thin film resistors 6a, 6b and 7a, 7b has a higher temperature in the vertical upper part due to convection. However, the ambient detection output shifts to the plus side in the thin film resistors 6a and 6b, and cystes to the minus side in the thin film resistors 7a and 7b. Since each pair of thin film resistors has the same shape and the same heat generation state, adding this output cancels the shift of the entire detection output.

  In order to compare the flow sensor of this embodiment with the flow sensor [FIG. 16 (b)] created by the present inventor for comparison, the sensitivity characteristic and the response characteristic were measured with the gas lines shown in FIG. FIG. 13 shows a case where a test fluid is supplied to a sample flow sensor (measured flow sensor) 43 via an MFC (mass flow controller) 41 and a pipe 42 to perform characteristic measurement. The measurement result shows that the response characteristics are almost the same as shown in FIG. 12 (a: the flow sensor of the present embodiment, b: the flow sensor for comparison), but the sensitivity characteristics are as shown in FIG. 11 (characteristic a ), The flow sensor of this embodiment gave a higher sensitivity result.

  In addition, when comparing the sensitivity characteristics of the conventional flow sensor having the shape of FIG. 18 shown in FIG. 14 that does not restrict the installation posture with the sensitivity characteristics of FIG. 11, the sensitivity in the low flow velocity region is low in FIG. On the other hand, in the flow sensor of this embodiment, the sensitivity in the low flow velocity region is very high. This is because it is difficult for a conventional flow sensor that has no restrictions on the installation posture to form a pair of thin film resistors close to each other in shape. This is due to cooling before being transmitted to the thin film resistor on the downstream side. However, since the flow sensor of this embodiment can be formed close to a pair of thin film resistors, it can sufficiently transfer heat even in a low flow rate region, and has high sensitivity. This is very advantageous for improving the accuracy in the low flow velocity region.

  FIG. 15 is a diagram showing another embodiment of the present invention. FIG. 15 corresponds to FIG. 5 of the embodiment flow sensor of FIGS. 1 to 3 described above, and is a cross-sectional view in which the upper housing 2 is cut parallel to the silicon substrate 11 of the embodiment flow sensor 1. . In this embodiment, the flow sensor 1 includes a silicon substrate 11 (embedded in the upper surface of the lower housing 3) and an upper housing 2, and the upper housing 2 has a U-shaped portion 10a. FIG. 4 and FIG. 5 show that the groove 10 of the inlet 10b and the outlet 10c directed outward at the tip end and the groove 10 of the upper housing 2 are joined to face the surface of the silicon substrate 11. This is the same as the flow sensor shown.

  In the flow sensor of this embodiment, unlike the flow sensors shown in FIGS. 4 and 5, the thin film resistors 6a, 6b, 6c are provided upstream of the detection flow path 10 on the upper surface of the silicon substrate 11, and the thin film resistors are provided downstream. That is, the bodies 7a, 7b and 7c are formed. The heater thin film resistors 6c and 7c are arranged at the center on the upstream side and the downstream side, respectively, and the temperature detecting thin film resistors 6a, 6b, 7a and 7b are arranged on the upper and lower sides of the thin film. Yes. For the thin film resistors 6a, 6b, 6c and 7a, 7b, 7c of the flow sensor of this embodiment, for example, a detection and drive circuit shown in FIG. 10 may be used.

  As a result, the heat distribution can be kept in balance regardless of the vertical and horizontal orientation of the installation posture. Moreover, the drive circuit can be simplified by connecting the thin film resistors 6a and 7a upstream to each other, the thin film resistors 6b and 7b downstream from each other, and the thin film resistors 6c and 7c between heaters in series.

  Here, in order to compare the influence of the installation flow sensor of the embodiment and the conventional flow sensor, the embodiment flow sensor shown in FIG. 16A and the comparison flow sensor shown in FIG. Is also used. Fluid SF6 (sulfur hexafluoride) in which the influence of inclination appears greatly is used, and the enclosure pressures are 0.1 MPa and 0.2 MPa, and attention is paid to sides A, B, C, and D in FIG. , (1) C front-A back [horizontal, standard posture], (2) B top-D bottom [vertical], (3) D top-B bottom [vertical], (4) A top-C bottom [vertical] When the influences were investigated in the four postures, the results shown in FIG. 17 were obtained.

  As a result, there is no effect in the case where the reference posture, C front-A back, is 0, and A up-C down, but in the case of B up-D down, B down-D, Assuming that the influence of the conventional case of 16 (b) is 1, in the embodiment of the present invention of FIG. 16 (a), −0.16 and 0.16, the flow sensor of the embodiment has an installation posture. It was confirmed that the impact was small.

It is a front view which shows schematic structure of the flow sensor which is one Embodiment of this invention. It is a reverse view of the same embodiment flow sensor. It is sectional drawing cut | disconnected by X-X 'shown in FIG. 1 of the same embodiment flow sensor. It is a top view of the silicon substrate of the same embodiment flow sensor. It is the cross-sectional view which cut | disconnected the housing | casing part parallel to the silicon substrate of the same embodiment flow sensor. It is sectional drawing which cut | disconnected the flow-path part of the same embodiment flow sensor in parallel with the flow-path direction. It is sectional drawing which cut | disconnected the flow-path part of the same embodiment flow sensor in the direction orthogonal to a flow path. It is a circuit diagram which shows the example of a connection circuit of the thin film resistor of the same embodiment flow sensor. It is a circuit diagram which shows the other connection circuit example of the thin film resistor of the same embodiment flow sensor. It is a circuit diagram which shows the further another connection circuit example of the thin film resistor of the same embodiment flow sensor. It is a figure which shows the sensitivity characteristic of a prior art example and the flow sensor of this invention. It is a figure which shows the response characteristic of the conventional example and the flow sensor of this invention. It is a figure explaining the characteristic feature of the flow sensor of a prior art example and this invention. It is a figure which shows the sensitivity characteristic of the flow sensor which does not have a restriction | limiting in the conventional installation attitude | position. It is the cross-sectional view which cut | disconnected the housing | casing part in equilibrium with the silicon substrate of the flow sensor of other embodiment of this invention. It is a figure for demonstrating the installation attitude | position evaluation of a prior art example and the flow sensor of this invention. It is a figure which shows the comparison of the influence of the installation attitude | position of the flow sensor of the conventional example and this invention. It is a figure explaining the case where the installation attitude | position of the flow sensor which does not have a restriction | limiting in the conventional installation attitude | position is changed. It is a figure explaining the problem at the time of changing the installation attitude | position of the conventional flow sensor. It is a figure explaining the problem at the time of changing the installation attitude | position of the other conventional flow sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow sensor 2 Upper housing | casing 3 Lower housing | casing 4 Fixing hole 6, 7 A pair of thin film resistor 6a, 6b, 6c, 7a, 7b, 7c Thin film resistor 8 Etching hole 9 Electrode 10 Channel 11 Silicon substrate 12 Cavity Part 20 Channel inlet / outlet through hole 22 Sealing material

Claims (2)

In a flow sensor for detecting a thermal action of a fluid on a thin film resistor by installing one or more combinations of thin film resistors for detection formed on a thin film substrate in a detection flow path,
The detection flow path is formed in a U shape including the flat surface portion of the thin film substrate in the flow path, and a pair of thin film resistors are provided on the flat surface portions of the U-shaped parallel flow path portions. A flow sensor characterized by installation.   The two sets of thin film resistors installed in the parallel part of the U-shaped flow path are formed so that their shapes or heat generation are thermally equal, and their detection outputs are added to each other. 1. The flow sensor according to 1.

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