JP2002310762A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow sensor in which a high-accuracy temperature compensation can be performed over a long period. SOLUTION: The flow sensor is provided with a heater 3 which generates heat when a current is made to flow, temperature sensor 4a, 4b which are arranged near the sensor, a resistance thermometer sensor 5 which measures an ambient temperature and a control circuit which controls the current flowing to the heater. A change in the temperature distribution of the heat from the heater changed according to the flow rate or the like of a fluid is detected by the temperature sensors. The control circuit is provided with a bridge circuit wherein a first branch which connects the sensor 5 and a first fixed resistance in series and a second branch which connects the heater and a second fixed resistance in series are connected in parallel. The bridge circuit is formed on the same semiconductor substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As a sensor having a bridge circuit,
For example, a flow sensor and a humidity sensor are known.
As this flow sensor, there is a thermal flow sensor using a heater.

FIG. 1 shows an example of such a flow sensor.
There is such as shown in FIG. As shown in FIG. 1, a concave void 1a is formed on the upper surface of a semiconductor substrate (for example, silicon) 1 and a flat insulating film 2 is formed on the entire upper surface of the semiconductor substrate 1. As a result, the gap 1a is covered with the insulating film 2, and the gap 1a located below the insulating film 2 exhibits a heat insulating effect, thereby making it difficult for the heat of the semiconductor substrate 1 to be transmitted to the insulating film 2.

A heater 3 and first and second temperature sensors 4a and 4b are formed on a portion of the upper surface of the insulating film 2 located above the gap 1a. At this time, the first and second sides of the heater 3 along the gas flow,
The second temperature sensors 4a and 4b are respectively arranged. Then, the insulating protective film 6 is formed so as to cover the upper surface of the insulating film 2.
Is formed, and the above-described heater 3, the first and second temperature sensors 4a and 4b are also covered with the protective film 6. Of course, the protective film 6 is not formed above the heater 3 and the electrode pad 7 formed at the end of the first and second temperature sensors 4a and 4b, and is exposed to the outside. It can be connected to the circuit.

In the flow sensor having such a configuration, the atmosphere around the heater 3 is also heated by the heat generated by applying a current to the heater 3 through the electrode pad 7. At this time, in a calm atmosphere where there is no gas flow, the temperature becomes a uniform temperature distribution centered on the heater 3 and the temperature gradually decreases as the distance from the heater 3 increases. Therefore, the first and second temperature sensors 4
If a and 4b are arranged at an equal distance from the heater 3 (symmetrical about the heater 3), the first and second
The temperatures at the positions of the temperature sensors 4a and 4b become equal.

In this state, if there is a flow of gas, the air heated by the heater 3 flows to the downstream side, so that the temperature on the downstream side rises and the temperature on the upstream side falls. Change. Since the degree of change in the temperature distribution changes in accordance with the flow rate and the flow velocity, the amount of change is determined by the first and second temperature sensors 4 arranged on both sides of the heater 3.
a, 4b.

The first and second temperature sensors 4a, 4
As b, a resistance type that detects a temperature by detecting a change in resistance value due to a temperature change, a thermomobile type that outputs a voltage corresponding to a temperature difference between two contacts, or the like can be used.

By the way, the ambient temperature at the place where the flow sensor is installed is not constant but naturally fluctuates. Even if the ambient temperature fluctuates, the output of the flow sensor needs to output a value corresponding to the flow rate. As a flow sensor having such a temperature compensation function, there is a technique disclosed in, for example, JP-A-2000-131094. Although temperature compensation can be performed by using such an invention, since a plurality of operational amplifiers and amplifier circuits are required, the configuration is complicated and the cost is increased.

Therefore, as a flow sensor capable of performing temperature compensation with a simple configuration, the present applicant has designed a control circuit for energizing the heater 3 as a bridge circuit as shown in FIGS. Developed a flow sensor and filed an application in Japanese Patent Application No. 2000-347282. Briefly describing such a flow sensor of the prior application, as shown in FIG. 3, in addition to a heater 3, a temperature measuring resistor 5 for measuring an ambient temperature of the flow sensor, and first and second fixed resistors 8a and 8b are provided. Provide.
Since the heater 3 is also a resistor, a bridge circuit is formed by the four resistors.

More specifically, a first fixed resistor 8a and a temperature measuring resistor 5 are connected in series between a power supply voltage Vcc and a ground, and a second fixed resistor 8b and a heater 3 are connected in series.
When the first and second fixed resistors 8a and 8b are on the power supply voltage Vcc side,
The resistance temperature detector 5 and the heater 3 are on the ground side. And
The midpoint between the first fixed resistor 8a and the resistance temperature detector 5 is
Of the second fixed resistor 8b and the heater 3
Is connected to the non-inverting input terminal of the operational amplifier 9 to form a bridge circuit.

Further, a transistor 11 is inserted between the output of the constant voltage circuit 10 for generating the power supply voltage Vcc and the first and second fixed resistors 8a and 8b, and the output of the operational amplifier 9 is provided at the base of the transistor 11. Given.

Therefore, for example, when the temperature of the heater 3 drops due to a change from a thermal equilibrium state in a windless state to a state with gas flow, the potential of the non-inverting input terminal of the operational amplifier 9 decreases,
The operation of driving the transistor 11 and supplying the current to be in the thermal equilibrium state again is repeated. When the ambient temperature changes, the resistance value of the resistance temperature detector 5 changes, the voltage division ratio with the first fixed resistor 8a changes, and the potential of the inverting input terminal of the operational amplifier 9 changes. A similar operation is performed to operate so as to be in a thermal equilibrium state. This allows
The thermal equilibrium state of the heater 3 can be maintained at a temperature higher than the ambient temperature by a certain temperature.

The circuit shown in FIG. 4 has a circuit between the output of the constant voltage circuit 10 and the ground in addition to the circuit shown in FIG.
The first and second voltage dividing resistors 12a and 12b connected in series are connected, and the first and second voltage dividing resistors 12a and 12b are connected.
The midpoint of 12b, the first fixed resistor 8a and the midpoint of the resistance bulb 5 are connected via a resistor 13. As a result, the output voltage Vcc of the constant voltage circuit 10 is divided by the first and second voltage dividing resistors 12a and 12b, and applied to the temperature measuring resistor 5 via the resistor 13.

With this configuration, the first and second voltage dividing resistors 1
By appropriately selecting the resistance values of the resistors 2a and 12b and the resistor 13, the current flowing into the bridge circuit through the resistor 13 can be freely set. Therefore, an error in the heat generation temperature of the heater 3 due to a change in the ambient temperature can be reduced, and higher accuracy can be achieved.

As an actual flow sensor for realizing the above-described circuit, as shown in FIGS.
A temperature measuring resistor 5 for measuring an ambient temperature is formed in a region of the upper surface of the insulating film 2 where there is no gap 1a. Then, the resistance temperature detector 5 is also covered with an insulating protective film 6.
Of course, the electrode pad 7 is exposed. On the other hand, the other resistors and the like constituting the bridge circuit use resistive elements outside the semiconductor substrate 1.

With this configuration, the heater 3 is
The semiconductor device 1 is thermally isolated from the semiconductor substrate 1 by the gap 1a provided thereunder. Conversely, the temperature measuring resistor 5 conducts heat with the semiconductor substrate 1 but is thermally disconnected from the heater 3. Therefore, the temperature sensor 5 can accurately detect the ambient temperature.

The flow sensors shown in FIGS. 3 to 6 are excellent because the temperature can be guaranteed with a simple configuration. However, although the heater 3 and the temperature measuring resistor 5 are formed on the semiconductor substrate 1, the other resistors 8a, 8b,
Since the resistors 12a, 12b, and 13 use the resistive element outside the semiconductor substrate 1, it has been found that the following problems occur.

That is, the resistance values of the heater 3 and the resistance temperature detector 5 may fluctuate with time. Since the change in these resistance values is different from the change with time in the resistance value of an external resistor such as a ceramic resistor, the balance of the bridge circuit may be lost, and accurate heater control may not be performed. As a result, the measurement accuracy also decreases.

Further, it is necessary to accurately measure the resistance values of the heater 3 and the resistance temperature detector 5, and to select and adjust the first and second fixed resistors 8a and 8b used in the bridge circuit. Therefore, although the temperature can be assured with a simple configuration as compared with Japanese Patent Application Laid-Open No. 2000-131094, there still remains a problem that it takes time and effort. SUMMARY OF THE INVENTION It is an object of the present invention to provide a flow sensor capable of performing high-precision temperature compensation for a long time and simplifying a circuit.

[0020]

According to the present invention, there is provided a flow sensor, comprising: a heating resistor which generates heat by flowing an electric current; a temperature detecting means disposed near the heating resistor;
A temperature measuring resistor for measuring an ambient temperature, and a control means for controlling a current flowing through the heating resistor, wherein a change in a temperature distribution of heat from the heating resistor, which changes according to a flow rate or a flow velocity of a fluid, A flow sensor for detecting by a temperature measuring means, wherein the control means connects a first branch connecting the temperature measuring resistor and a first fixed resistor in series, and connects the heating resistor and a second fixed resistor in series. A bridge circuit in which the second branches are connected in parallel, and the temperature measuring resistor, the first fixed resistor, the heating resistor, and the second fixed resistor are formed on the same semiconductor substrate. The heating resistor corresponds to the heater 3 in the embodiment. Further, the temperature detecting means includes first and second temperature detecting means.
It corresponds to the temperature sensors 4a and 4b.

According to the present invention, by energizing the heating resistor so that the bridge circuit is parallel, the temperature of the heating resistor can be maintained in a thermal equilibrium state at a certain temperature higher than the ambient temperature. .

Further, according to the present invention, the resistance used for the bridge circuit is integrated on the same semiconductor substrate as the heater, the resistance temperature detector, and the temperature sensor. This makes it possible to control the heater with a high degree of accuracy.
Even if the resistivity changes with the passage of time, by forming the same semiconductor substrate, the degree of the change can be considered substantially the same, so that the equilibrium state of the bridge circuit can be maintained. Therefore, stable characteristics can be obtained over a long period. Further, since each resistor can be formed with a high precision dimension by a semiconductor process, a desired bridge circuit can be formed without adjustment and cost can be reduced.

Preferably, the line width, the thickness and the material of the temperature measuring resistor and the first fixed resistor are such that the respective resistance values are etched while maintaining a constant ratio in an etching step. Is set. Similarly, the line width, thickness, and material of the heating resistor and the second fixed resistor may be set such that the respective resistance values are etched while maintaining a constant ratio during the etching process. In this case, when a constant voltage is applied between both terminals of the first and second branches, the potential at the midpoint position of the first branch becomes half of the whole. Similarly, the potential at the midpoint of the second branch is also half of the whole. Therefore, the potential difference between the two middle points becomes zero.

Here, maintaining a constant ratio during etching is defined only by the ratio of the resistance values of the paired resistors, regardless of the resistivity, the thickness, the length, or the line width. However, "constant" does not always mean exactly the same, but includes a predetermined allowable range. As an example, if the fluctuation range is 10% or less, if the temperature fluctuation of the heating resistor can be controlled at a level that does not cause a practical problem, the allowable range is 10%.
%. Of course, this numerical value is an example, and is determined by actual specifications and the like.

The temperature measuring resistor and the first fixed resistor are formed so as to have the same line width and thickness, and the heating resistor and the second fixed resistor have the same line width and thickness. May be formed. In this case, assuming that the first fixed resistor and the material forming the resistance temperature detector have the same resistivity, they can obtain the same resistance value. Therefore, the same resistance value can be obtained by forming the dimension and shape with high precision. And it is relatively easy to form such dimensions and shapes with high accuracy by a semiconductor process. The same can be said for the relationship between the second fixed resistor and the heating resistor.

Further, the same effect as described above can be obtained by forming the temperature measuring resistor and the first fixed resistor with the same material, and forming the heating resistor and the second fixed resistor with the same material. Achievable, said resistance temperature detector and said first
This can also be achieved by forming the fixed resistor with a material having the same resistivity, and forming the heating resistor and the second fixed resistor with a material having the same resistivity.

On the other hand, the bridge circuit is set so as to be balanced when the heating resistor generates heat, or the third fixed resistor is connected to the second fixed resistor so that the bridge circuit is parallel when the heating resistor generates heat. A resistor may be connected.

Furthermore, the area of the second fixed resistor can be formed so as to be larger than the area of the heating resistor. With this configuration, heat generated by the second fixed resistor can be suppressed.

[0029]

FIG. 7 and FIG. 8 show a first embodiment of the present invention. As shown in the figure, the configuration for exhibiting the basic function as a flow sensor is the same as that of the conventional one. That is, a flat insulating film 2 is formed on the entire upper surface of the semiconductor substrate 1 in which the void 1a is formed.
As a result, the insulating film 2 comes into contact with the upper surface of the semiconductor substrate 1 at the inner portion of the gap 1a, and is separated from the surface of the semiconductor substrate 1 at the portion of the gap 1a. Therefore, the gap 1a located below the insulating film 2 exhibits a heat insulating effect, and it becomes difficult for the heat of the semiconductor substrate 1 to be transmitted to the insulating film 2.

The heater 3 and the first and second temperature sensors 4a and 4b are formed on a portion of the upper surface of the insulating film 2 located above the gap 1a. At this time, the first and second temperature sensors 4a and 4b are arranged on both sides of the heater 3 along the flow of the gas, that is, on the upstream side and the downstream side. Then, an insulating protective film 6 is formed so as to cover the upper surface of the insulating film 2, and the above-described heater 3, the first and second temperature sensors 4a and 4b are also covered with the protective film 6.
The first and second temperature sensors 4a and 4b are formed to have the same dimensions and shape, and are formed so as to be line-symmetric about the heater 3. Further, a temperature measuring resistor 5 is formed in a region on the upper surface of the insulating film 2 which does not face the gap 1a. Such a configuration is the same as the invention according to the earlier application.

Here, in the present invention, the first and second fixed resistors 8 forming a bridge circuit with the heater 3 and the temperature measuring resistor 5 are provided in a region on the upper surface of the insulating film 2 which does not face the gap 1a.
a, 8b are also formed. Then, the first fixed resistor 8a
(Resistance value: R1) and the resistance bulb (resistance value: Rb) 5
Since they are made of the same material and have the same thickness, length and width (the same plane shape), they have the same resistance value (R1 =
Rb). Further, a second fixed resistor (resistance value: R2) 8
Since b and the heater (resistance value: Rh) 3 are also made of the same material and have the same thickness, length and width, they have the same resistance value (R2 = Rh). Therefore, R1Rh = R2Rb.

Further, the first fixed resistor 8a and the resistance temperature detector 5
Are formed in parallel in the vicinity. Therefore, since both lines can be formed by the same process, even if the line width is reduced by over-etching at the time of patterning, both resistors 8a,
5 can have the same resistance value (R1 = Rb).
The same applies to the case of the second fixed resistor 8b and the heater 3.

As a result, even if the device is manufactured relatively roughly, the resistance satisfying R1Rh = R2Rb can be easily formed, so that the heater 3 can be controlled with high precision. Note that the heater control circuit in the present embodiment is the same as that shown in FIG.
Alternatively, each circuit shown in FIG. 4 can be used.

The heater 3, the first and second temperature sensors 4
Similarly to a and 4b and the resistance temperature detector 5, the upper surfaces of the first and second fixed resistors 8a and 8b are also covered with the protective film 6, and
The protective film 6 is not formed above the electrode pad 7 formed at the end of each resistor, is exposed to the outside, and can be connected to an external circuit via the electrode pad 7. The heater 3, the first and second temperature sensors 4a and 4b, the resistance temperature detector 5, and the first and second fixed resistors 8a and 8b are, for example,
After forming a predetermined metal film on the entire upper surface of the insulating film 2 by sputtering or vapor deposition, it can be formed by patterning and etching unnecessary portions. In addition, not only the manufacturing process but also each resistor can be formed in the same process using, for example, PolySi formed by doping a predetermined amount of ions, and the manufacturing process and the material used are arbitrary.

Further, in this embodiment, the heater 3, the temperature measuring resistor 5, the first and second fixed resistors 8 constituting the bridge circuit are provided.
Since a and 8b are made of the same material and are arranged on the same substrate, it is possible to prevent the specific resistance from being greatly changed as compared with the others due to aging, thereby preventing the balance from being lost. The basic operation principle is the same as that of the invention of the prior application shown in FIGS.

The manufacturing process for forming the gap 1a, the insulating film 2, the heater 3, the first and second temperature sensors 4a and 4b, and the resistors 5, 8a and 8b is as follows.
Since a conventional general semiconductor process can be used, a detailed description thereof will be omitted. In addition, this flow sensor is used not only as a flow meter but also as a humidity sensor and a gas sensor as a matter of course. This is the same in the following embodiments.

Further, in this embodiment, an example is shown in which the same material, thickness, length, and line width are the same, but since the length hardly changes at the time of etching, the material, thickness, and line width are not changed. If the width is the same, the same effect can be obtained.
Furthermore, as long as the etching rates are substantially the same, different materials may have the same resistivity.

Further, in the present embodiment, R1 = Rb, R2 =
Although the resistance value is set to Rh, it is not always necessary to make the resistance values equal in the present invention, and the relationship of R1Rh = R2Rb may be established. Therefore, the materials and shapes may be different.

The fact that the resistivity, the thickness, the length, and the line width are the same does not need to be completely the same, and it is needless to say that the range includes a predetermined range which is allowed according to the application. That is, for example, in the case of detecting the presence or absence of the flow rate, if each of them is 10% or less, it is possible to perform the heater control at a level that is not problematic in practical use, and each of them is 5%.
In the following case, highly accurate heater control can be performed, and the heater control can be used for flow rate measurement and the like.

FIGS. 9 and 10 show a second embodiment of the present invention. In the present embodiment, the heater control circuit shown in FIG. 3 is based on the first embodiment as shown in FIG. Then, a third fixed resistor 14 (resistance value: r) for adjustment is provided between the transistor 11 and the second fixed resistor 8b.

With this configuration, for example, when the heater 3 is formed of a material having a positive temperature coefficient of resistance, the heater 3 generates heat by energization, and the resistance value Rh increases. At this time, in the circuit shown in FIG. 3 in which the third fixed resistor 14 is not provided, in the case of a steady state (no heat generation of the heater 3), R1R
When h = R2Rb, the output of the operational amplifier 9 becomes zero and the heater 3 does not generate heat.

By the way, when the heater 3 generates heat, the first
The middle point between the fixed resistor 8a and the resistance temperature detector 5;
It is necessary to make the potential difference between b and the middle point of the heater 3 zero.
Therefore, as described above, R satisfying R1Rh = R2Rb
1, R2, Rh, and Rb are formed on the same substrate, and a third fixed resistor 14 (resistance: r) having the same resistance as the increase in the resistance of the heater 3 is added to balance the bridge circuit. It was configured to adjust.

That is, the resistance value of the heater 3 is R
When h changes to Rh ', R1Rh' = (R2 +
r) Third fixed resistor 1 having a resistance value r that satisfies Rb
4 is provided. In the present embodiment, the third fixed resistor 14 is provided outside the semiconductor substrate 1, and a bridge circuit satisfying the above conditions can be easily formed only by adjusting the fixed resistor.

In the illustrated example, the third fixed resistor 14
Shows an example in which a single resistor is used, but a circuit in which a plurality of resistors are connected may be used. Note that the other configuration and operation and effect are the same as those of the above-described first embodiment, and a detailed description thereof will be omitted.

In the embodiment described above, the third
Although the example in which the fixed resistor 14 is separately provided is shown, the present invention is not limited to this, and as shown in FIGS.
The fixed resistor 14 may also be formed at a predetermined position (region where the void 1a is not formed) of the semiconductor substrate 1 (insulating film 2).

In particular, in the example shown in FIG. 12, although a plurality of third fixed resistors 14 are formed, all of them may be used, but a desired pattern is connected by wire bonding or the like to form the second fixed resistor 8b. By connecting to, the resistance value r of the third fixed resistor 14 can be adjusted. Thus, for example, the resistance value r can be adjusted to correspond to a change in the resistance value due to the rising temperature of the heater 3. Therefore, when the rising temperature of the heater 3 is increased, the sensor as a high flow rate sensor is increased. When the temperature is lowered, it can be used as a low flow rate sensor.

When the temperature coefficient of resistance is negative, a resistance R2 'having a value of R2-r, which is obtained by subtracting a decrease r of the resistance value due to heat generation from R2, is provided. Further, the same effect can be obtained by setting the resistance value of the second fixed resistor 8b without providing the third fixed resistor 14 and considering the resistance value of the heater 3 at the time of heating from the beginning.

FIG. 13 shows a third embodiment of the present invention. In the present embodiment, the pattern shape of the second fixed resistor 8b is different based on the first embodiment described above. That is, the area of the second fixed resistor 8b is increased to prevent heat generation in the second fixed resistor 8b. Thereby, the heater 3 can be controlled with high accuracy.

Further, the length and width of the second fixed resistor 8b are
Since the pattern has a similar shape which is twice as large as the pattern shape of the heater 3, the resistance value R2 of the second fixed resistor 8b and the heater 3
Have the same resistance value Rh. Therefore, R1Rh = R2
The relationship of Rb can be maintained. In this example, the length and width are doubled, but the present invention is not limited to this, and may be n times, and is not limited to a similar shape.
The area of the second fixed resistor 8b may be increased in a different shape.

FIG. 14 shows a fourth embodiment of the present invention. In the present embodiment, the pattern shape of the second fixed resistor 8b is improved. That is, four resistance patterns 8b 'having the same shape as that of the heater 3 are formed, and the four resistance patterns 8b' are appropriately connected to form the second fixed resistance 8b.
b. That is, the four resistance patterns 8b 'are arranged close to and parallel to each other,
Two adjacent resistance patterns 8b 'are connected in parallel, and two sets of resistance patterns 8b' connected in parallel are connected in series. Therefore, the resistance value R of the second fixed resistor 8b
2 and the heater 3 have the same resistance value Rh.

As a result, the heater control can be performed with higher accuracy than in the third embodiment. That is, for example,
When the design value of the heater line width is 10 μm, the line width of the second fixed resistor 8b of the third embodiment is 20 μm. Here, assuming that the line width is reduced by 2 μm due to over-etching during patterning of the heater 3 and the second fixed resistor 8 b, the heater line width becomes 8 μm (80% of the design value), The second fixed resistor 8b is 18 μm
(90% with respect to the design value), resulting in a difference in resistance value. On the other hand, when the line width of the resistance pattern 8b 'constituting the second fixed resistor 8b and the line width of the heater 3 are set to be the same as in the present embodiment, the line width becomes narrower due to over-etching. But R2 = Rh, R
Since 1Rh = R2Rb, the heater can be controlled with higher accuracy.

In order to form a bridge circuit, it is necessary to electrically connect the respective resistors. As a connection form, for example, a wiring pattern 15 is formed on a predetermined layer on the semiconductor substrate 1 as shown in FIG. And its wiring pattern 1
5, the predetermined electrode pads 7 can be connected to each other. This wiring pattern 15 is preferably formed of a material having a low resistance value such as gold. And the wiring pattern 15
May be formed on the same layer as each resistor, that is, on the insulating film 2 or on the protective film 6. Such a configuration is preferable since a circuit can be easily configured since wiring work is eliminated.

As another connection form, as shown in FIG. 16, by connecting predetermined electrode pads 7 of the respective resistors (including the heater 3) by wire bonding 16, R1Rh = R2Rb. A bridge circuit can also be formed. By employing the method using the wire bonding 16 in this manner, it is possible to flexibly cope with a circuit change, addition of a resistor, and the like.

Further, as shown in FIG. 17, it is also possible to use a mixed type in which both the wiring pattern 15 and the wire bonding 16 are appropriately used. According to this configuration, it is possible to flexibly cope with a circuit change, an addition of a resistor, and the like, and it is possible to reduce wiring work.

Although the connection modes shown in FIGS. 15 to 17 are examples applied to the first embodiment, they can be applied to other embodiments and modifications in the same manner. Needless to say.

[0056]

As described above, according to the present invention, a bridge circuit is formed on the same semiconductor substrate as a control means for supplying current to a heating resistor (heater), so that high-precision temperature compensation can be performed for a long time. Thus, the circuit can be simplified.

[Brief description of the drawings]

FIG. 1 is a plan view showing a conventional example.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a circuit diagram showing an example of a flow sensor including a heater control circuit according to the prior application.

FIG. 4 is a circuit diagram showing another example of a flow sensor including a heater control circuit according to the prior application.

FIG. 5 is a plan view showing an example of a flow sensor according to the prior application.

FIG. 6 is a sectional view taken along line BB of FIG. 5;

FIG. 7 is a plan view showing the first embodiment of the present invention.

FIG. 8 is a sectional view taken along line CC of FIG. 7;

FIG. 9 is a plan view showing a second embodiment of the present invention.

FIG. 10 is a circuit diagram showing a second embodiment of the present invention.

FIG. 11 is a plan view showing a modification.

FIG. 12 is a plan view showing a modification.

FIG. 13 is a plan view showing a third embodiment of the present invention.

FIG. 14 is a plan view showing a fourth embodiment of the present invention.

FIG. 15 is a diagram illustrating an example of a connection mode.

FIG. 16 is a diagram illustrating an example of a connection mode.

FIG. 17 is a diagram illustrating an example of a connection mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Insulating film 3 Heater 4a 1st temperature sensor 4b 2nd temperature sensor 5 RTD 6 Protective film 7 Electrode pad 8a 1st fixed resistance 8b 2nd fixed resistance 9 Operational amplifier 10 Constant voltage circuit 11 Transistor 12a 1st Voltage dividing resistor 12b Second voltage dividing resistor 13 Resistance 14 Third fixed resistor 15 Wiring pattern 16 Wire bonding

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoshi Nozoe 801 Shidokoji Shimogyo-ku, Shimogyo-ku, Higashi-iri, Higashi-iri, Minami-Fudo-cho, OMRON Corporation 2F035 EA08 EA09

Claims (8)

[Claims] 1. A heating resistor that generates heat by flowing an electric current, a temperature detecting unit disposed near the heating resistor, a temperature measuring resistor that measures an ambient temperature, and a current that flows through the heating resistor. A flow sensor for detecting, by the temperature measuring means, a change in a temperature distribution of heat from the heating resistor, which changes in accordance with a flow rate or a flow rate of a fluid, wherein the control means comprises: A first branch in which a temperature resistor and a first fixed resistor are connected in series, and a bridge circuit in which a second branch in which the heating resistor and a second fixed resistor are connected in series are connected in parallel; A flow sensor, wherein a resistor, the first fixed resistor, the heating resistor, and the second fixed resistor are formed on the same semiconductor substrate. 2. The temperature measuring resistor and the first fixed resistor,
The line width, the thickness and the material are set so that the respective resistance values are etched while maintaining a constant ratio during the etching step. The heating resistor and the second fixed resistor are used during the etching step. 2. The flow sensor according to claim 1, wherein a line width, a thickness, and a material are set so that each resistance value is etched while maintaining a constant ratio. 3. The temperature measuring resistor and the first fixed resistor,
The heating resistor and the second fixed resistor are formed to have the same line width and thickness, and the heating resistor and the second fixed resistor are formed to have the same line width and thickness.
3. The flow sensor according to claim 1. 4. The heating resistor and the second fixed resistor are formed of the same material, and the temperature measuring resistor and the first fixed resistor are formed of the same material. The flow sensor according to claim 1. 5. The temperature measuring resistor and the first fixed resistor are formed of a material having the same resistivity, and the heating resistor and the second fixed resistor are formed of a material having the same resistivity. The flow sensor according to any one of claims 1 to 4, wherein: 6. The flow sensor according to claim 1, wherein the bridge circuit is set to be balanced when the heating resistor generates heat. 7. The device according to claim 1, wherein a third fixed resistor is connected to the second fixed resistor so that the bridge circuit is balanced when the heating resistor generates heat. The flow sensor as described. 8. The device according to claim 1, wherein the area of the second fixed resistor is formed to be larger than the area of the heat generating resistor. Flow sensor.