JP2013024822A - Thermal type flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal type flowmeter having improved measurement accuracy.SOLUTION: The thermal type flowmeter includes: a substrate arranged so as to be exposed to flow of a fluid to be measured; a thin film part formed by removing a part of the substrate like a rectangle; heating means provided in the thin film part; at least first to fourth temperature detectors provided in the thin film part; and first to fourth wires to which the first to fourth temperature detectors are connected respectively. In the thermal type flowmeter, variations of a temperature distribution on the thin film part due to the flow of a fluid to be measured are detected by the first to fourth temperature detectors to detect a flow rate of the fluid to be measured. The first to fourth temperature detectors are connected to the first to fourth wires in the thin film part, and the first to fourth wires are drawn out of the thin film part through sides along the flow of the fluid to be measured, out of four sides in end parts of the thin film part, and the first to fourth wires are connected in a region interposed between two lines passing sides crossing the flow of the fluid to be measured, out of four sides in the end parts of the thin film part, to form a bridge circuit.

Description

  The present invention relates to a thermal type flow meter for measuring a flow rate in a fluid to be measured, and more particularly to a thermal type flow meter suitable for measuring an intake air flow rate and an exhaust gas flow rate of an internal combustion engine of an automobile.

  As an air flow meter for detecting an intake air amount of an internal combustion engine such as an automobile, a thermal air flow meter capable of directly measuring a mass flow rate has become mainstream.

  In recent years, it has been proposed to manufacture a sensor element of a thermal flow meter on a semiconductor substrate such as silicon (Si) using MEMS technology. In such a semiconductor type sensor element, a cavity is formed by removing a part of a semiconductor substrate in a rectangular shape, and a heating resistor is formed on an electrical insulating film of several microns formed in the cavity. A pair of temperature sensors (temperature sensitive resistors) are formed on the upstream and downstream sides in the vicinity of the heating resistor, and the flow rate is detected from the temperature difference between the upstream and downstream sides of the heating resistor that is generated when air flows. can do. Further, according to this method, it is possible to distinguish between forward flow and reverse flow. Furthermore, since the size of the heating resistor is as small as several hundred micrometers and is formed in a thin film shape, the heat capacity is small, and high-speed response, low power consumption, and downsizing are possible.

  As conventional techniques related to the sensor element, there are those described in Patent Document 1 and Patent Document 2. In Patent Document 1, a semiconductor sensor element, a control circuit chip, and a terminal material are integrated by molding, thereby reducing the number of parts and reducing the cost. In Patent Document 2, the flow rate detection sensitivity is improved by drawing out the wiring pattern of the thin film portion.

JP-A-11-6752 JP 2010-107497 A

  The sensor element of the thermal type flow meter disclosed in Patent Document 1 has a structure that is covered with a molding material by integrally forming a control circuit, a lead, and the like by injection molding. An epoxy resin or the like is used as the molding material. However, if the sensor element is covered with a molding material, a large stress is applied to the sensor element due to stress during molding or thermal expansion and contraction of the molding material when the temperature of the environment where the thermal flow meter is installed changes. . In Patent Document 1, approximately half of the sensor element is covered with a molding material. From the viewpoint of reducing manufacturing errors when assembling the thermal flow meter, it is effective to cover a wide area of the sensor element with a molding material. However, covering the wide area of the sensor element with the molding material further increases the stress due to the molding material.

  Further, in order to reduce the component cost of the sensor element, it is necessary to reduce the size of the sensor element. The injection molding technique is effective as a method for mounting a miniaturized sensor element because of its excellent manufacturing accuracy and easy mass production. However, when the size of the sensor element is reduced, the area of the cavity of the sensor element with respect to the entire area of the sensor element becomes relatively large, and the deformation of the sensor element with respect to stress increases.

  Further, when stress is applied to the sensor element, stress is applied to the wiring formed on the sensor element, and the resistance value of the wiring fluctuates. In particular, the wiring connected to the temperature detection element gives a large error in temperature detection accuracy due to a minute change in resistance. In particular, the measurement accuracy of the low flow rate of the thermal flow meter is deteriorated.

  In the thermal type flow meter described in Patent Document 2, the pressure resistance of the thin film portion is improved by pulling out the wiring of the temperature detection body formed on the thin film portion of the sensor element so as not to cross the corner of the thin film portion. However, Patent Document 2 describes the pressure resistance of the thin film portion, but the stress applied to the wiring is not studied, and the measurement accuracy due to the fluctuation of the resistance value of the wiring due to the stress is applied. No consideration has been given to the deterioration.

  An object of the present invention is to provide a thermal flow meter with improved measurement accuracy.

  In order to achieve the above object, a thermal flow meter of the present invention includes a substrate disposed so as to be exposed to the flow of a fluid to be measured, and a thin film formed by removing a part of the substrate into a rectangular shape. The first to fourth temperature detectors connected to each other, the heating means provided in the thin film portion, at least the first to fourth temperature detectors provided in the thin film portion, respectively. Heat for detecting the flow rate of the fluid to be measured by detecting a change in the temperature distribution on the thin film portion due to the flow of the fluid to be measured by the first to fourth temperature detectors. In the flow meter, the first to fourth temperature detectors are connected to the first to fourth wires in the thin film portion, and the first to fourth wires are connected to the end of the thin film portion. Out of the thin film portion through the side along the flow of the fluid to be measured among the four sides of the portion A bridge formed by connecting the first to fourth wirings in a region sandwiched by two lines passing through a side intersecting the fluid flow among the four sides of the end of the thin film portion. A circuit is formed.

  According to the present invention, a thermal flow meter with improved measurement accuracy can be provided.

It is a top view which shows the sensor element in a 1st Example. It is sectional drawing which shows the sensor element in a 1st Example. It is a circuit diagram which shows the drive / detection circuit of a sensor element. It is a detailed view of the periphery of the thin film portion in the first embodiment. It is detail drawing of the bridge circuit which consists of an upstream temperature sensor and a downstream temperature sensor. It is the schematic of the analysis result of the stress distribution of the board | substrate of a sensor element. It is a top view which shows the sensor element in a 2nd Example. It is a circuit diagram which shows the drive / detection circuit of the sensor element in a 2nd Example. It is detail drawing of the thin film part periphery in a 2nd Example. It is a top view which shows the sensor element in a 3rd Example. It is a detailed view around the thin film portion in the third embodiment. It is a top view which shows the sensor element in a 4th Example. It is a circuit diagram which shows the drive / detection circuit of the sensor element in a 4th Example. It is detail drawing of the thin film part periphery in a 4th Example. It is a top view which shows the sensor element in a 5th Example. It is detail drawing of the thin film part periphery in a 5th Example. It is a top view which shows the sensor element in a 6th Example.

  Examples according to the present invention will be described below.

  A first embodiment according to the present invention will be described below.

  The configuration of the sensor element 1 of the thermal type flow meter according to this embodiment will be described with reference to FIGS. The substrate 2 of the sensor element 1 is disposed so as to be exposed to an air flow 6 of air that is a fluid to be measured, and the substrate 2 is made of a material having good thermal conductivity such as silicon or ceramic. Then, an electrical insulating film 3 a is formed on the substrate 2, and the substrate 2 is etched from the back surface to form a cavity and form a thin film portion 4.

  A heating resistor 5 as a heating means is formed on the surface near the center of the electrical insulating film 3a on the thin film portion 4. Further, on the thin film portion 4, upstream temperature sensors 8 a and 8 b are formed on the upstream side of the heating resistor 5, and downstream temperature sensors 9 a and 9 b are formed on the downstream side of the heating resistor 5. The upstream temperature sensors 8a and 8b are upstream of the air flow 6 with respect to the center of the heating resistor 5, and the downstream temperature sensors 9a and 9b are downstream of the air flow 6 with respect to the center of the heating resistor 5. good. The outermost surface of the sensor element 1 is covered with an electrical insulating film 3b, and the electrical insulating film 3b serves as a protective film in addition to performing electrical insulation. On the electrical insulating film 3 a outside the thin film portion 4, a temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  The heating resistor 5, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the temperature sensitive resistor 10 are made of a material having a relatively large resistance temperature coefficient whose resistance value changes depending on the temperature. For example, a semiconductor material such as polycrystalline silicon or single crystal silicon doped with impurities, a metal material such as platinum, molybdenum, tungsten, or a nickel alloy, a thermocouple, a thermistor, or the like can be used.

Further, the electrical insulating films 3a and 3b are formed into a thin film of about 2 microns thickness by using a laminated film in which these are combined in addition to silicon dioxide (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ), and the thermal insulation effect is sufficient. The structure obtained is as follows.

  Further, at the end of the sensor element 1, the heating resistor 5, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the electrode pad 13a for connecting the temperature sensitive resistor 10 to the drive / detection circuit, 13b, 13c, 13d, 13e, 13f, and 13g are provided. These electrode pads are made of aluminum or the like.

  The heating resistor 5 and the electrode pads 13b and 13c are connected by wirings 18a and 18b. The upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are connected on the substrate 2 of the sensor element 1 so as to form a bridge circuit. Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit configured by the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b for supplying a reference voltage and detecting a differential voltage. Furthermore, the wirings 18c, 18d, 18e, and 18f are connected to the electrode pads 13d, 13e, 13f, and 13g.

  The thermal type flow meter which is an embodiment of the present invention operates as follows. A temperature distribution 14 shown together with the cross-sectional configuration of the sensor element 1 shown in FIG. 2 is a distribution of the surface temperature of the sensor element 1. The solid line of the temperature distribution 14 indicates the temperature distribution of the thin film portion 4 when there is no wind. The heating resistor 5 is heated so as to be higher than the temperature of the air flow 6 by ΔTh. The broken line of the temperature distribution 14 is the temperature distribution of the thin film portion 4 when the air flow 6 flows. When the air flow 6 flows, the upstream side of the heating resistor 5 is cooled by the air flow 6 to lower the temperature, and the downstream side passes through the heating resistor 5 and heated air flows to increase the temperature. Therefore, the flow rate is measured by measuring the temperature difference ΔTs between the upstream side and the downstream side of the heating resistor 5 by the upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b.

  Next, the drive / detection circuit of the sensor element 1 will be described. FIG. 3 shows a drive / detection circuit for the sensor element 1. A bridge circuit is configured in which a series circuit composed of the heating resistor 5 and the resistor 11 and a series circuit composed of the temperature sensitive resistor 10 and the resistor 12 are connected in parallel. An intermediate voltage of each series circuit of the bridge circuit is taken out and connected to the amplifier 15. The output of the amplifier 15 is connected to the base of the transistor 16. The collector of the transistor 16 is connected to the power source VB, and the emitter is connected to the heating resistor 5 and the temperature sensitive resistor 10. Further, the resistor 11 and the resistor 12 are connected to a reference potential or connected to a ground potential. By appropriately setting the resistance balance of the heating resistor 5, the resistor 11, the temperature sensitive resistor 10, and the resistor 12, the temperature Th of the heating resistor 5 is a constant temperature ΔTh (= Th-Ta) is controlled to be higher.

  In the present embodiment, the heater temperature control circuit is configured to control the heating temperature of the heating resistor 5 by the amplifier 15 and the transistor 16, but the difference voltage of the bridge circuit is detected, and a current corresponding to the detected difference voltage is generated. Any structure may be used as long as it is supplied to the heating resistor 5. For example, the difference voltage of the bridge circuit is converted to a digital signal by an AD converter, the converted digital signal is corrected, and then converted to a voltage or current by DA conversion to control the heating current of the heating resistor 5 But you can.

  A bridge circuit in which a series circuit composed of the upstream temperature sensor 8a and the downstream temperature sensor 9b and a series circuit composed of the downstream temperature sensor 9a and the upstream temperature sensor 8b are connected in parallel is configured, A reference voltage Vref is applied. When the air flow 6 causes a temperature difference between the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b, the resistance balance of the bridge circuit changes and a differential voltage is generated. This differential voltage is detected by the amplifier 17, and an output corresponding to the air flow rate is obtained.

  The configuration of the wiring around the thin film portion 4 in this embodiment will be described in detail with reference to FIG. A wiring 19a connected to one end of the upstream temperature sensor 8a and a wiring 19d connected to the other end of the upstream temperature sensor 8a are provided. Further, a wiring 19b connected to one end of the upstream temperature sensor 8b and a wiring 19c connected to the other end of the upstream temperature sensor 8b are provided. Moreover, the wiring 20a connected to the end of the downstream temperature sensor 9a and the wiring 20d connected to the other end of the upstream temperature sensor 9a are provided. Moreover, the wiring 20b connected to the end of the downstream temperature sensor 9b and the wiring 20c connected to the other end of the downstream temperature sensor 9b are provided. The wiring 19a and the wiring 19d constitute a first wiring, the wiring 19b and the wiring 19c constitute a second wiring, the wiring 20a and the wiring 20d constitute a third wiring, and the wiring 20b and the wiring 20c constitute a fourth wiring. Configure the wiring. The first to fourth wires are connected to the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b in the thin film portion 4.

  These first to fourth wirings pass through the side 4a along the flow of the air flow 6 among the four sides (side 4a, side 4b, side 4c, side 4d) of the end portion of the thin film portion 4, and the thin film portion 4 In a region sandwiched by two lines Y1 and Y2 that are drawn out and pass through two sides (side 4c, side 4d) that intersect the fluid flow among the four sides of the end of the thin film portion 4, the first to first The fourth wiring is connected to form a bridge circuit.

  A method for connecting the bridge circuit using the first to fourth wirings will be described with reference to FIG. The downstream temperature sensor 9a and the upstream temperature sensor 8b are connected in series by connecting the wiring 20a forming the third wiring and the wiring 19b forming the second wiring. The upstream temperature sensor 8a and the downstream temperature sensor 9b are connected in series by connecting the wiring 19a forming the first wiring and the wiring 20b forming the fourth wiring. The downstream temperature sensor 9a and the upstream temperature sensor 8a are connected via a wiring 20d forming a third wiring and a wiring 19d forming a first wiring. The upstream temperature sensor 8b and the downstream temperature sensor 9b are connected via a wiring 19c forming a second wiring and a wiring 20c forming a fourth wiring. Thus, the first to fourth wirings are connected to form a bridge circuit.

  However, in order to connect these first to fourth wirings as a bridge circuit for temperature detection, it is necessary to cross any of the first to fourth wirings. In this embodiment, as shown in FIG. 4, in order to connect the wiring 19b and the wiring 20a, the wiring 21c formed in another layer is used. As the wiring 21c, it is desirable to use a metal material having a relatively low resistivity using aluminum wiring or the like.

  The upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b and the wirings 19a, 19b, 19c, 19d and the wirings 20a, 20b, 20c, 20d connecting them are the four sides of the end portion of the thin film portion 4. Are arranged in a region sandwiched by two lines Y1 and Y2 passing through two sides (side 4c, side 4d) intersecting the flow direction of the air flow 6. In other words, a closed loop formed including the upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b and the wirings 19a, 19b, 19c, 19d, and the wirings 20a, 20b, 20c, 20d connecting them, Of the four sides at the end of the thin film portion 4, the configuration is located in a region sandwiched by two lines Y <b> 1 and Y <b> 2 passing through two sides (side 4 c and side 4 d) intersecting the flow direction of the air flow 6.

  Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit configured as described above, and the power supply to the bridge circuit and the differential voltage of the bridge circuit are taken out. The reference voltage Vref is supplied from the wiring 18c, the wiring 18f is connected to the ground potential, and the differential voltage is taken out by the wiring 18d and the wiring 18f. More specifically, the wiring 18c is connected to any part of the wiring 19d and the wiring 20d, the wiring 18f is connected to any part of the wiring 19c and the wiring 20c, and the wiring 18d is any of the wiring 20a and the wiring 19b. The wiring 18e is connected to one of the wiring 19a and the wiring 20b.

  However, in order to connect these wirings 18c, 18d, 18e, and 18f to the bridge circuit, it is necessary to intersect with other wirings. In the present embodiment, as shown in FIG. 4, a wiring 21a formed in another layer is used to connect the wiring 18c to the bridge circuit. Further, the wiring 21b formed in another layer is used to connect the wiring 18f to the bridge circuit. As the wiring 21a and the wiring 21b, it is desirable to use an aluminum wiring or the like and a metal material having a relatively low resistivity.

  The effects obtained by the configuration of this embodiment will be described below.

  FIG. 6 shows a schematic view of the analysis result of the stress distribution of the substrate 2 of the sensor element 1 received when the sensor element 1 in this embodiment is bonded and fixed to another support member. The stress distribution in FIG. 6 is fixed by covering the periphery of the sensor element 1 with resin, and is pulled from the two directions of the upper end 22a of the sensor element 1 and the lower end 22b of the sensor element 1 due to the difference in thermal expansion between the sensor element 1 and the resin. It is assumed that The stress when the sensor element 1 is pulled in this way is concentrated in the corners 23a, 23b, 23c, and 23d at the end of the thin film portion 4. Further, since the peripheral portion of the sensor element 1 is also bonded with resin, the stress becomes relatively large.

  In the above stress distribution, comparing the region sandwiched between the lines Y1 and Y2 with other regions, it can be seen that the region sandwiched between the lines Y1 and Y2 has a lower stress. Therefore, a closed loop formed by including the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b and the wirings 19a, 19b, 19c, and 19d and the wirings 20a, 20b, 20c, and 20d that connect the upstream temperature sensors 8a and 8b. By forming so as to be located in a region sandwiched between Y1 and line Y2, the stress applied to these wirings can be reduced. As the influence of stress on the wiring, piezoresistive change and wiring deterioration due to stress occur.

  By adopting the configuration of this embodiment, it is possible to reduce the stress applied to the wirings 19a, 19b, 19c, and 19d and the wirings 20a, 20b, 20c, and 20d that form the closed loop of the bridge circuit. Thereby, the detection accuracy of the temperature difference between the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b can be increased, and a highly accurate thermal flow meter can be obtained. In particular, the detection of a low flow rate is more effective because the detection voltage is very small.

  In this embodiment, the same material as that used for the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b can be used as the material for forming the first to fourth wirings. Moreover, you may form with the material different from the material used for the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b. For example, the wiring 21c can be made of a plurality of materials. In this case, the region of the wiring 19b extends from the portion connected to the upstream temperature sensor 8b to the portion where the wiring 18d is connected to the closed loop of the bridge circuit, and includes the wiring 21c.

  In this embodiment, as shown in FIG. 4, the first wiring (wiring 19a, wiring 19d), the second wiring (wiring 19b, wiring 19c), the third wiring (wiring 20a, wiring 20d), and the fourth wiring. Although all the wirings (wiring 20b, wiring 20c) are drawn out of the thin film portion 4, as another method, for example, the wiring 19d forming the first wiring and the wiring 20d forming the third wiring are connected to the thin film portion 4 It can also be connected inside. That is, one of at least two wires of each of the first to fourth wires is drawn out of the thin film portion 4, and the other wire is connected to another wire inside the thin film portion 4. A connected configuration may be used.

  However, in the case of using a wiring formed in another layer, such as the wiring 21a, the wiring 21a is preferably located outside the thin film portion 4. This is because there is a high possibility that contact resistance increases or breaks at a connection portion connecting wirings formed in a plurality of layers, for example, a void is generated at the interface of the connection portion due to stress. In particular, the effect becomes significant when exposed to high temperatures. For this reason, it is desirable to avoid the thin film portion 4 that becomes high in the connection portions of the wirings formed in a plurality of layers.

  Further, in this embodiment, in addition to the above, it is desirable to configure as follows. In the configuration diagram of FIG. 4, the fifth connected to the heating resistor 5 on one side of the region divided by the center line X passing along the flow of the air flow 6 and passing through the center of the heating resistor 5. Wiring (wiring 18a, wiring 18b) are drawn out of the thin film portion 4, and the first to fourth wirings (wirings 19a to 19d, wirings 20a to 20d) are out of the thin film portion 4 on the other region side. Configure to be pulled out. With this configuration, since the first to fourth wirings and the fifth wiring are drawn from different sides, it is easy to form a wide line width and reduce the wiring resistor. By reducing the resistance values of the first to fourth wirings, the wiring resistance is reduced, and the influence of resistance change due to stress can be further reduced, and the decrease in temperature detection sensitivity due to the voltage drop of the wiring resistance can be reduced. . In addition, since the resistance value of the fifth wiring is reduced, power loss and heat generation by the fifth wiring can be reduced, which is effective in reducing power consumption. Further, a voltage is supplied to the fifth wiring to drive the heating resistor 5, so that the influence of electrical noise generated by this voltage does not affect the first to fourth wirings. In addition, the electrical connection can be reduced by increasing the distance between the fifth wiring and the first to fourth wirings.

  The fifth wiring is connected to the heating resistor 5 and is used for passing a current through the heating resistor 5. In addition, the fifth wiring detects the resistance change of the heating resistor 5 and controls the temperature of the heating resistor 5. It can also be used.

  The fifth wiring is connected to both ends of the heating resistor 5 on the high potential side and the low potential side. At least the wiring connected to the high potential side (wiring 18b) and the wiring connected to the low potential side (wiring) 18a) Consists of two wires. As a material for forming the fifth wiring, the same material as that used for the heating resistor 5, the upstream temperature sensors 8a and 8b, and the downstream temperature sensors 9a and 9b can be used, and it is different from the material. It may be formed of a material, or may be composed of a plurality of materials.

  Furthermore, wiring (wiring 18c, wiring 18d, wiring 18e, wiring 18f) for taking out the intermediate voltage of the bridge circuit is provided on the sensor element 1 substrate 2, and these wirings are arranged downstream of the air flow 6 with respect to the thin film portion 4. When extending so as to pass through, it is desirable to configure as follows. Two voltage supply wirings (wiring 18c, wiring 18f) for supplying voltage to the bridge circuit are provided, and the detection wiring (wiring 18d, wiring 18e) has a portion sandwiched between the two voltage supply wirings (wiring 18c, wiring 18f). That is, it extends in a region formed by two voltage supply wirings (wiring 18c, wiring 18f). The two voltage supply wirings can be connected to a ground potential or a fixed potential. With such a configuration, the detection wiring (wiring 18d and wiring 18e) is connected to the ground potential or the fixed potential wiring (wiring 18c and wiring 18f). It is possible to reduce electrical noise generated from the enclosed heating resistor 5 and the wiring 18b connected to the heating resistor 5, and mixing of electromagnetic waves from the external environment, which is advantageous for high accuracy.

  A second embodiment according to the present invention will be described below. In the present embodiment, the configuration different from that of the first embodiment will be described, and the same configurations as those of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The configuration of the sensor element 24 of the thermal type flow meter according to this embodiment will be described with reference to FIG. FIG. 7 is a plan view showing the sensor element 24. A heating resistor 5 as a heating means is formed near the center on the thin film portion 4. Further, upstream temperature sensors 8 a and 8 b are formed on the thin film portion 4 on the upstream side of the heating resistor 5, and downstream temperature sensors 9 a and 9 b are formed on the downstream side of the heating resistor 5. The upstream temperature sensors 8 a and 8 b are arranged upstream of the air flow 6 with respect to the center of the heating resistor 5, and the downstream temperature sensors 9 a and 9 b are arranged downstream of the air flow 6 with respect to the center of the heating resistor 5. . On the electrical insulating film 3 a outside the thin film portion 4, a temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  Further, at the end of the sensor element 24, electrode pads 13a, 13b are connected to connect the heating resistor 5, the upstream temperature sensors 8a, 8b, the downstream temperature sensors 9a, 9b, and the temperature sensitive resistor 10 to the drive / detection circuit. , 13c, 13d, 13e, 13f, and 13g.

  The heating resistor 5 and the electrode pads 13b and 13c are connected by wirings 18a and 18b. The upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are connected so as to form a bridge circuit. Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit constituted by the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b in order to supply a reference voltage and detect a differential voltage. Furthermore, the wirings 18c, 18d, 18e, and 18f are connected to the electrode pads 13d, 13e, 13f, and 13g.

  Next, the drive / detection circuit of the sensor element 24 will be described with reference to FIG.

  A bridge circuit is configured in which a series circuit composed of the resistor 11 and the heating resistor 5 and a series circuit composed of the resistor 12 and the temperature sensitive resistor 10 are connected in parallel. An intermediate voltage of each series circuit of the bridge circuit is taken out and connected to the amplifier 15. The output of the amplifier 15 is connected to the base of the transistor 16. The collector of the transistor 16 is connected to the power supply VB, and the emitter is connected to the resistor 11 and the resistor 12. The heating resistor 5 and the temperature sensitive resistor 10 are connected to the ground potential. By appropriately setting the resistance balance of the heating resistor 5, the resistor 11, the temperature sensitive resistor 10, and the resistor 12, the temperature Th of the heating resistor 5 is a constant temperature ΔTh (= Th-Ta) is controlled to be higher.

  A bridge circuit in which a series circuit composed of the upstream temperature sensor 8a and the downstream temperature sensor 9b and a series circuit composed of the downstream temperature sensor 9a and the upstream temperature sensor 8b are connected in parallel is configured, A reference voltage Vref is applied. When the air flow 6 causes a temperature difference between the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b, the resistance balance of the bridge circuit changes and a differential voltage is generated. An output corresponding to the air flow rate is obtained from the differential voltage by the amplifier 17.

  The configuration of the wiring around the thin film portion 4 in this embodiment will be described in detail with reference to FIG. A wiring 19a connected to one end of the upstream temperature sensor 8a and a wiring 19d connected to the other end of the upstream temperature sensor 8a are provided. Further, a wiring 19b connected to one end of the upstream temperature sensor 8b and a wiring 19c connected to the other end of the upstream temperature sensor 8b are provided. Moreover, the wiring 20a connected to the end of the downstream temperature sensor 9a and the wiring 20d connected to the other end of the upstream temperature sensor 9a are provided. Moreover, the wiring 20b connected to the end of the downstream temperature sensor 9b and the wiring 20c connected to the other end of the downstream temperature sensor 9b are provided. The wiring 19a and the wiring 19d constitute a first wiring, the wiring 19b and the wiring 19c constitute a second wiring, the wiring 20a and the wiring 20d constitute a third wiring, and the wiring 20b and the wiring 20c constitute a fourth wiring. Configure the wiring. And these 1st-4th wiring passes along the side 4b along the flow of the airflow 6 among four sides (side 4a, side 4b, side 4c, side 4d) of the edge part of the thin film part 4, and the thin film part 4 In the region sandwiched by two lines Y1 and Y2 that pass through two sides (side 4c, side 4d) that intersect with the fluid flow among the four sides at the end of the thin film portion 4 and drawn out of the first side The fourth wiring is connected to form a bridge circuit.

  A different configuration from the first embodiment is that the first to fourth wirings are drawn out from the side 4 b opposite to the side 4 a at the end of the thin film portion 4. Also in the present embodiment, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the wirings 19a, 19b, 19c, and 19d that connect them, and the wirings 20a, 20b, 20c, and 20d are formed in the thin film portion 4. Of the four sides of the end portion, it is arranged in a region sandwiched by two lines Y1 and Y2 passing through two sides (side 4c, side 4d) intersecting the fluid flow. In other words, a closed loop formed including the upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b and the wirings 19a, 19b, 19c, 19d, and the wirings 20a, 20b, 20c, 20d connecting them, It is the structure located in the area | region pinched | interposed by two lines Y1 and Y2 which pass through 2 sides (side 4c, side 4d) which cross | intersect a fluid flow among four sides of the thin film part 4 edge part.

  Further, in this embodiment, in addition to the above, it is desirable to configure as follows. In the configuration diagram of FIG. 9, the fifth connected to the heating resistor 5 on one side of the region divided by the center line X passing along the flow of the air flow 6 and passing through the center of the heating resistor 5. The wiring (wiring 18 a and wiring 18 b) is drawn out of the thin film portion 4, and the first to fourth wirings are drawn out of the thin film portion 4 on the other side. With this configuration, since the first to fourth wirings and the fifth wiring are drawn from different sides, it is easy to form a wide line width and reduce the wiring resistor. By reducing the resistance values of the first to fourth wirings, it is possible to reduce the wiring resistance and further reduce the influence of resistance change due to stress, and to reduce the decrease in temperature detection sensitivity due to the voltage drop of the wiring resistance. it can.

  Further, as shown in FIG. 7, after the fifth wiring (wiring 18a, wiring 18b) is drawn to the outside of the thin film portion 4, it extends so as to pass the upstream side of the air flow 6 with respect to the thin film portion 4. It is said. In this case, it is desirable to configure as follows. Of the fifth wiring (wiring 18a, wiring 18b) comprising at least two wirings, the wiring (wiring 18b) closer to the thin film portion 4 has a low potential and the wiring far from the thin film portion 4 (wiring 18a) has a higher potential. It is configured to be a potential. Specifically, as shown in the circuit diagram of FIG. 8, the wiring 18b is connected to the ground potential, the wiring 18a is connected to the resistor 11, and the current flows in the direction from the wiring 18a to the wiring 18b. . As a result, the low-potential-side wiring 18b can be set to the ground potential, whereby the wiring 18b connected to the ground potential can be provided between the high-potential-side wiring 18a and the thin film portion 4. . As a result, electrical noise generated from the high-potential side wiring 18a can be reduced from being transmitted to the upstream temperature sensors 8a, 8b, etc. formed in the thin film portion 4, which is advantageous for high accuracy.

  In the present embodiment, the fifth wiring (wiring 18 a, wiring 18 b) extends upstream of the air flow 6 with respect to the thin film portion 4, but on the downstream side of the air flow 6 with respect to the thin film portion 4. The structure which extends may be sufficient.

  A third embodiment according to the present invention will be described below. In the present embodiment, the configuration different from that of the first embodiment will be described, and the same configurations as those of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The configuration of the sensor element 25 of the thermal type flow meter according to this embodiment will be described with reference to FIG. FIG. 10 is a plan view showing the sensor element 25. A heating resistor 5 as a heating means is formed near the center on the thin film portion 4. Further, on the thin film portion 4, upstream temperature sensors 8 a and 8 b are formed on the upstream side of the heating resistor 5, and downstream temperature sensors 9 a and 9 b are formed on the downstream side of the heating resistor 5. The upstream temperature sensors 8 a and 8 b are arranged upstream of the air flow 6 with respect to the center of the heating resistor 5, and the downstream temperature sensors 9 a and 9 b are arranged downstream of the air flow 6 with respect to the center of the heating resistor 5. . On the electrical insulating film 3 a outside the thin film portion 4, a temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  Further, at the end of the sensor element 25, an electrode pad 13a for connecting the heating resistor 5, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the temperature sensitive resistor 10 to the drive / detection circuit. , 13b, 13c, 13d, 13e, 13f, and 13g.

  The heating resistor 5 and the electrode pads 13b and 13c are connected by wirings 18b and 18a. The upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are connected so as to form a bridge circuit. Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit constituted by the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b in order to supply a reference voltage and detect a differential voltage. Furthermore, the wirings 18c, 18d, 18e, and 18f are connected to the electrode pads 13d, 13e, 13f, and 13g.

  As shown in FIG. 11, the sensor element 25 is located on one side of the heating resistor 5 in the region divided by the center line X along the flow of the air flow 6 and passing through the center of the heating resistor 5. The wiring 18a at one end is drawn out of the thin film portion 4, and the first wiring (wiring 19a, wiring 19d), the second wiring (wiring 19b, wiring 19c), and the third wiring (wiring 20a) are provided on the other region side. The wiring 20d), the fourth wiring (wiring 20b, wiring 20c) and the wiring at the other end of the heating resistor 5 (wiring 18b) are drawn out of the thin film portion 4. In the case of such a configuration, in addition to the above, it is desirable to configure as follows. Of the wirings (wirings 18a and 18b) connected to both ends of the heating resistor 5, the wiring (wiring 18b) on the side from which the wirings connected to the first to fourth temperature detection bodies are drawn out has a low potential. The wiring (wiring 18a) is configured to have a high potential. Specifically, as shown in the circuit diagram of FIG. 8, the wiring 18b is connected to the ground potential, the wiring 18a is connected to the resistor 11, and the current flows in the direction from the wiring 18a to the wiring 18b. . With this configuration, the low potential side wiring 18b connected to the heating resistor 5 can be connected to the ground potential. By doing so, the distance between the high potential side wiring 18a connected to the heating resistor 5 and the first to fourth wirings connected to the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b. The electrical noise generated from the high-potential-side wiring 18a connected to the heating resistor 5 can be reduced from being mixed into the first to fourth wirings, which is advantageous for high accuracy. .

  A fourth embodiment according to the present invention will be described below. In the present embodiment, the configuration different from that of the first embodiment will be described, and the same configurations as those of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The configuration of the sensor element 26 of the thermal type flow meter according to this embodiment will be described with reference to FIG. On the thin film portion 4, upstream temperature sensors 8 a and 8 b disposed upstream from the center of the thin film portion 4 and downstream temperature sensors 9 a and 9 b disposed downstream from the center of the thin film portion 4 are formed. On the electrical insulating film 3 a outside the thin film portion 4, a temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  Furthermore, at the end of the sensor element 26, electrode pads for connecting the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the resistors constituting the temperature sensitive resistor 10 to the drive / detection circuit. 13a, 13b, 13d, 13e, 13f, and 13g are provided.

  The upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are connected to form a bridge circuit. Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit constituted by the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b in order to apply a voltage and take out a differential voltage. Furthermore, the wirings 18c, 18d, 18e, and 18f are connected to the electrode pads 13d, 13e, 13f, and 13g.

  Next, the drive / detection circuit of the sensor element 26 will be described.

  FIG. 13 shows a drive / detection circuit for the sensor element 26. A bridge circuit is configured in which a series circuit composed of the downstream temperature sensor 9a and the upstream temperature sensor 8b and a series circuit composed of the upstream temperature sensor 8a and the downstream temperature sensor 9b are connected in parallel. A bridge circuit is configured in which a series connection including the bridge circuit and the resistor 11 and a series circuit including the resistor 12 and the temperature-sensitive resistor 10 are connected in parallel. An intermediate voltage between the bridge circuit composed of the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b and the resistor 11, and an intermediate voltage between the resistor 12 and the temperature sensitive resistor 10 are extracted, and an amplifier is obtained. 15 is connected. The output of amplifier 15 is connected to the 16 bases of the transistors. The collector of the transistor 16 is connected to the power source VB, and the emitter is connected between the resistor 11 and the resistor 12. In addition, the potential between the upstream temperature sensor 8b and the downstream temperature sensor 9b and the other potential of the temperature sensitive resistor 10 are connected so as to be the ground potential. By appropriately setting the combined resistance of the bridge circuit composed of the flow-side temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b and the resistance balance of the resistor 11, the temperature-sensitive resistor 10 and the resistor 12, the flow-side temperature sensor A current flows through 8a and 8b and the downstream temperature sensors 9a and 9b, and is heated to a predetermined temperature Th. The temperature Th is controlled so as to be higher than the temperature Ta of the air flow 6 by a constant temperature ΔTh (= Th−Ta).

  As a heating means of the thin film portion 4 in the present embodiment, the upstream temperature sensors 8a, 8b and the downstream temperature sensor 9a, by passing a current through the upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b, 9b is configured to generate heat.

  Also in the present embodiment, as shown in FIG. 14, the upstream temperature sensors 8a and 8b, the downstream temperature sensors 9a and 9b, and the wirings 19a, 19b, 19c and 19d connecting them, the wirings 20a, 20b, 20c and 20d. Are arranged in a region sandwiched by two lines Y1 and Y2 passing through two sides (side 4c, side 4d) intersecting the fluid flow among the four sides at the end of the thin film portion 4. In other words, a closed loop formed including the upstream temperature sensors 8a, 8b and the downstream temperature sensors 9a, 9b and the wirings 19a, 19b, 19c, 19d, and the wirings 20a, 20b, 20c, 20d connecting them, It is the structure located in the area | region pinched | interposed by two lines Y1 and Y2 which pass through 2 sides (side 4c, side 4d) which cross | intersect a fluid flow among four sides of the thin film part 4 edge part.

  In this embodiment, since the first to fourth wirings are connected to a region sandwiched between Y1 and Y2 having a lower stress than other regions, and a bridge circuit is formed, the bridge circuit It is possible to reduce the stress applied to the wirings 19a, 19b, 19c, 19d and the wirings 20a, 20b, 20c, 20d forming the closed loop. Thereby, the detection accuracy of the temperature difference between the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b can be increased, and a highly accurate thermal flow meter can be obtained. In particular, the detection of a low flow rate is more effective because the detection voltage is very small.

  A fifth embodiment according to the present invention will be described below. In the present embodiment, the configuration different from that of the fourth embodiment will be described, and the same configurations as those of the fourth embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The configuration of the sensor element 27 of the thermal type flow meter according to this embodiment will be described with reference to FIG. FIG. 15 is a plan view showing the sensor element 27. On the thin film portion 4, upstream temperature sensors 8 a and 8 b disposed upstream from the center of the thin film portion 4 and downstream temperature sensors 9 a and 9 b disposed downstream from the center of the thin film portion 4 are formed. On the electrical insulating film 3 a outside the thin film portion 4, a temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  Further, at the end of the sensor element 27, there are electrodes for connecting the upstream side temperature sensors 8a and 8b, the downstream side temperature sensors 9a and 9b, and each resistor constituting the temperature sensitive resistor 10 to the drive / detection circuit. The formed electrode pads 13a, 13b, 13d, 13e, 13f, and 13g are provided. These electrode pads are made of aluminum or the like.

  The upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are connected to form a bridge circuit. Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit constituted by the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b in order to apply a voltage and take out a differential voltage. Furthermore, the wirings 18c, 18d, 18e, and 18f are connected to the electrode pads 13d, 13e, 13f, and 13g.

  The configuration of the wiring around the thin film portion 4 in this embodiment will be described in detail with reference to FIG. The wires connected to the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b are two sides (side 4a, side) along the flow of the air flow 6 among the four sides at the end of the thin film portion 4. 4b) is pulled out of the thin film portion 4 and sandwiched by two lines Y1 and Y2 passing through the sides (side 4c, side 4d) intersecting the fluid flow among the four sides of the end portion of the thin film portion 4 In the region, wiring is connected and a bridge circuit is formed.

  Specifically, the configuration is as follows. A wiring 19a connected to one end of the upstream temperature sensor 8a and a wiring 19d connected to the other end of the upstream temperature sensor 8a are provided. Further, a wiring 19b connected to one end of the upstream temperature sensor 8b and a wiring 19c connected to the other end of the upstream temperature sensor 8b are provided. Moreover, the wiring 20a connected to the end of the downstream temperature sensor 9a and the wiring 20d connected to the other end of the upstream temperature sensor 9a are provided. Moreover, the wiring 20b connected to the end of the downstream temperature sensor 9b and the wiring 20c connected to the other end of the downstream temperature sensor 9b are provided. The wiring 19a and the wiring 19d constitute a first wiring, the wiring 19b and the wiring 19c constitute a second wiring, the wiring 20a and the wiring 20d constitute a third wiring, and the wiring 20b and the wiring 20c constitute a fourth wiring. Configure the wiring. And these 1st-4th wiring passes the edge | side 4a and edge | side 4b along the flow of the airflow 6 among the four edges (side | edge 4a, edge | side 4b, edge | side 4c, edge | side 4d) of the edge part of the thin film part 4. It is pulled out of the thin film portion 4. In this embodiment, the wiring 19 a forming the first wiring, the wiring 19 b forming the second wiring, the wiring 20 a forming the third wiring, and the wiring 20 b forming the fourth wiring are formed from the side 4 b at the end of the thin film portion 4. Pulled out. Also, the side where the wiring 19d forming the first wiring, the wiring 19c forming the second wiring, the wiring 20c forming the third wiring, and the 20d forming the fourth wiring are opposed to the side 4b at the end of the thin film portion 4. Pulled out from 4a. Furthermore, in the region sandwiched by two lines Y1 and Y2 passing through two sides (side 4c, side 4d) intersecting the fluid flow among the four sides at the end of the thin film portion 4, the first to fourth wirings Are connected to form a bridge circuit.

  In this embodiment, since the first to fourth wirings are connected to a region sandwiched between Y1 and Y2 having a lower stress than other regions, and a bridge circuit is formed, the bridge circuit The stress received by the wirings 19a, 19b, 19c, 19d and the wirings 20a, 20b, 20c, 20d can be reduced. Thereby, the detection accuracy of the temperature difference between the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b can be increased, and a highly accurate thermal flow meter can be obtained. In particular, the detection of a low flow rate is more effective because the detection voltage is very small.

  A sixth embodiment according to the present invention will be described below. In the present embodiment, the configuration different from that of the first embodiment will be described, and the same configurations as those of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  The configuration of the sensor element 28 of the thermal type flow meter according to this embodiment will be described with reference to FIG. A heating resistor 5 as a heating means is formed near the center on the thin film portion 4. Further, upstream temperature sensors 8 a and 8 b are formed on the thin film portion 4 on the upstream side of the heating resistor 5, and downstream temperature sensors 9 a and 9 b are formed on the downstream side of the heating resistor 5. The upstream temperature sensors 8 a and 8 b are arranged upstream of the air flow 6 with respect to the center of the heating resistor 5, and the downstream temperature sensors 9 a and 9 b are arranged downstream of the air flow 6 with respect to the center of the heating resistor 5. . On the sensor element 28 outside the thin film portion 4, the temperature sensitive resistor 10 whose resistance value changes according to the temperature of the air flow 6 is disposed.

  Similar to the first embodiment, the upstream temperature sensor 8a and the downstream temperature sensor 9b are connected in series by connecting the wiring 19a forming the first wiring and the wiring 20b forming the fourth wiring. The downstream temperature sensor 9a and the upstream temperature sensor 8a are connected via a wiring 20d forming a third wiring and a wiring 19d forming a first wiring. The upstream temperature sensor 8b and the downstream temperature sensor 9b are connected via a wiring 19c forming a second wiring and a wiring 20c forming a fourth wiring. Thus, the first to fourth wirings are connected and connected as a bridge circuit. The method of configuring the bridge circuit in this embodiment is the same as that in the first embodiment.

  Wirings 18c, 18d, 18e, and 18f are connected to the bridge circuit configured as described above, and the power supply to the bridge circuit and the differential voltage of the bridge circuit are taken out. A reference voltage is supplied from the wiring 18c, the wiring 18f is connected to the ground potential, and a differential voltage is taken out by the wiring 18d and the wiring 18f. More specifically, the wiring 18c is connected to any part of the wiring 19d and the wiring 20d, the wiring 18f is connected to any part of the wiring 19c and the wiring 20c, and the wiring 18d is any of the wiring 20a and the wiring 19b. The wiring 18e is connected to one of the wiring 19a and the wiring 20b.

  Further, the wiring 18c, the wiring 18d, the wiring 18e, and the wiring 18f are connected to a temperature detection circuit 29 formed on the same substrate as the sensor element 28. The wiring 18a, the wiring 18b, and the temperature sensitive resistor 10 are connected to a heater temperature control circuit 30 formed on the same substrate as the sensor element 28.

  For example, the temperature detection circuit 29 is the amplifier 17 using the operational amplifier shown in the circuit configuration of FIG. The heater temperature control circuit 30 is the amplifier 15 and the transistor 16 using the operational amplifier shown in the circuit configuration of FIG. The temperature detection circuit 29 and the heater temperature control circuit 30 are semiconductor integrated circuits formed on the same substrate as the sensor element 28 using a semiconductor process.

  In this embodiment, the amplifier 17 is used as the temperature detection circuit 29, but an AD converter or the like can also be used as another configuration for detecting the differential voltage of the bridge circuit. In addition to the AD converter, a digital signal processing circuit or the like can be provided. In the present embodiment, the heater temperature control circuit 30 is configured to control the heating temperature of the heating resistor 5 by the amplifier 15 and the transistor 16. However, the difference voltage of the bridge circuit is detected, and the heater temperature control circuit 30 corresponds to the detected difference voltage. Any structure that supplies current to the heating resistor 5 may be used. For example, the difference voltage of the bridge circuit is converted into a digital signal by an AD converter, corrected using a digital signal processing circuit, and then converted into a voltage or current by DA conversion to control the heating current of the heating resistor 5. It may be configured.

  With the above structure, the lengths of the wiring 18c, the wiring 18d, the wiring 18e, and the wiring 18f can be shortened, and the stress applied to the wiring 18c, the wiring 18d, the wiring 18e, and the wiring 18f can be reduced. Further, it is not necessary to provide the electrode pads 13e and 13f and bonding wires of the first embodiment between the bridge circuit composed of the upstream temperature sensors 8a and 8b and the downstream temperature sensors 9a and 9b and the temperature detection circuit 29. It becomes possible to reduce the size. Further, there is no need to consider deterioration or disconnection of the bonding wire, contact portion with the pad portion, or disconnection, and a highly accurate and highly reliable thermal flow meter can be obtained. Note that the same effect can be obtained by combining the embodiments with other embodiments.

1, 24, 25, 26, 27, 28 Sensor element 2 Substrate 3a, 3b Electrical insulating film 4 Thin film portion 5 Heating resistor 6 Air flow 8a, 8b Upstream temperature sensors 9a, 9b Downstream temperature sensor 10 Temperature sensitive resistor 11, 12 Resistors 13a to 13g, 13h to 13j Electrode pad 14 Temperature distribution 15, 17 Amplifier 16 Transistors 18a to 18f, 19a to 19d, 20a to 20d, 21a to 21c, 21d Wiring 22a Upper end 22b of the sensor element Lower end 23a-23d Corner | angular part 29 Temperature detection circuit 30 Heater temperature control circuit

Claims (13)

A substrate disposed so as to be exposed to the flow of the fluid to be measured, a thin film portion formed by removing a part of the substrate into a rectangular shape, a heating means provided in the thin film portion, and a thin film portion The thin film portion including at least the first to fourth temperature detectors provided and the first to fourth wirings connected to the first to fourth temperature detectors, respectively, and the flow of the fluid to be measured In the thermal flow meter for detecting the flow rate of the fluid under measurement by detecting the change in the temperature distribution on the first to fourth temperature detectors,
The first to fourth temperature detectors are connected to the first to fourth wirings in the thin film portion,
The first to fourth wirings are led out of the thin film part through the side along the flow of the fluid to be measured among the four sides of the end part of the thin film part, and the end part of the thin film part A thermal circuit characterized in that a bridge circuit is formed by connecting the first to fourth wirings in a region sandwiched by two lines passing through a side intersecting the fluid flow among the four sides of Flowmeter. The thermal flow meter according to claim 1, wherein
The heating means is a heating resistor that generates heat when current is passed therethrough,
A fifth wiring connected to the heating resistor in the thin film portion on one side of the region divided by a center line passing along the flow of the fluid to be measured and passing through the center of the heating resistor. A thermal type flow meter which is drawn out of the thin film portion, and the first to fourth wirings are drawn out of the thin film portion on the other region side. The thermal flow meter according to claim 2, wherein
The thermal flow meter, wherein the fifth wiring is extended so as to pass upstream or downstream of the flow with respect to the thin film portion after being drawn out of the thin film portion. The thermal flow meter according to claim 3,
A thermal flowmeter characterized in that, among the fifth wires drawn out of the thin film portion, a wire closer to the thin film portion has a low potential, and a wire far from the thin film portion has a high potential. The thermal flow meter according to claim 2, wherein
A detection wiring for extracting an intermediate voltage of the bridge circuit is electrically connected to any of the first to fourth wirings;
The thermal flow meter, wherein the detection wiring is extended with respect to the thin film portion so as to pass upstream or downstream of the flow. The thermal flow meter according to claim 5, wherein
Two voltage supply wirings for supplying a voltage to the bridge circuit are electrically connected to any of the first to fourth wirings;
The thermal flow meter, wherein the detection wiring is extended in a region formed by the two voltage supply wirings. The thermal flow meter according to claim 1, wherein
The heating means is a heating resistor that generates heat when current is passed therethrough,
Of the region divided by a center line along the flow of the fluid to be measured and passing through the center of the heating resistor,
On one region side, the wiring at one end connected to the heating resistor is drawn out of the thin film portion,
The thermal flow meter characterized in that, on the other region side, the first to fourth wirings and the wiring at the other end connected to the heating resistor are drawn out of the thin film portion. The thermal flow meter according to claim 7, wherein
Of the wires connected to both ends of the heating resistor, a thermal flow rate characterized in that the other region side has a low potential on the side leading to the outside of the thin film portion and the other wire has a high potential. Total. The thermal flow meter according to claim 1, wherein
The thermal flow meter, wherein the heat generating means is the first to fourth temperature detectors. The thermal flow meter according to claim 9, wherein
The first to fourth wirings connected to the first to fourth temperature detectors in the thin film portion are both sides of two sides along the fluid flow among the four sides of the end portion of the thin film portion. The first to fourth wirings in a region sandwiched between two lines that are drawn out from the thin film portion and pass through the sides intersecting the fluid flow among the four sides of the end portion of the thin film portion A thermal flow meter characterized in that a bridge circuit is formed by connecting wires. The thermal flow meter according to claim 1, wherein
Forming a temperature detection circuit comprising a semiconductor integrated circuit on the substrate;
The thermal flow meter, wherein the temperature detection circuit is connected to the bridge circuit formed by connecting the first to fourth wirings. The thermal flow meter according to claim 2, wherein
A thermal flow meter, wherein a heater temperature control circuit comprising a semiconductor integrated circuit is formed on the substrate, and the fifth wiring is connected to the heater temperature control circuit. In the thermal type flow meter according to claim 9 or 10,
A thermal flow meter, wherein a heater temperature control circuit made of a semiconductor integrated circuit is formed on the substrate and connected to any one of the first to fourth wirings.