JP3454265B2 - Thermal flow sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity sensor used in a place where a flow velocity measurement of a fluid such as air is required, such as an engine control of an automobile and an air conditioner. It is about expansion.

[0002]

2. Description of the Related Art FIG. 34 shows, for example, JP-A-60-14226.
Conventional thermal type flow velocity sensor disclosed in Japanese Patent Publication No. 8 (conventional example 1)
FIG. 35 is a cross-sectional view of an essential part of FIG. In the figure, 1 is a silicon substrate, 2 is an air space formed on the silicon substrate 1 by etching, 3 and 4 are thin film members, that is, thin-walled portions bridged on the air space 2, 5 is a heating resistor, 6, Reference numeral 7 is an upstream side and downstream side thin film temperature sensitive resistor, respectively, and 8 is a comparative resistance for monitoring the temperature of the surrounding air. The upstream and downstream thin-film temperature sensitive resistors 6 and 7 are arranged symmetrically with the heating resistor 5 in between. The heating resistor 5 and the thin film temperature sensitive resistors 6 and 7 are surrounded by thin insulating layers 9 and 10 made of, for example, silicon nitride to form thin portions 3 and 4.

The basic operation of this conventional thermal type flow velocity sensor will be described. In FIG. 35, the heating resistor 5 is heated to a temperature higher by 200 ° C. than the temperature of the silicon substrate 1. The temperature of the silicon substrate 1 is almost the same as the temperature of the surrounding air and is measured by the comparative resistor 8. When there is no air flow, the thin film temperature sensitive resistors 6 and 7 are heated to an average of about 140 ° C. by the heat of the heat generating resistor 5. That is, since the thin film temperature sensitive resistors 6 and 7 are arranged symmetrically with respect to the heat generating resistor 5, the temperatures of these two sensors become the same when the flow velocity of air is 0, and the thin film temperature sensitive resistors are There is no difference in the resistance values of the bodies 6 and 7. Therefore,
Even if a minute measurement current is passed through the two temperature sensitive resistors 6 and 7, no voltage difference occurs.

When there is a flow of air, the temperature-sensitive resistor 6 located on the upstream side is cooled because heat is carried away by the flow of air toward the heater 5, while the temperature-sensitive resistor 7 located on the downstream side is cooled. Will be heated by the air flow from the heater 5. FIG. 36 shows the flow velocity dependence of the temperature of the temperature sensitive resistors 6 and 7. As the flow velocity increases, the temperature of the temperature-sensitive resistor 6 on the upstream side decreases and the temperature of the temperature-sensitive resistor 7 on the downstream side increases. The difference in resistance value between the temperature sensitive resistors 6 and 7 caused by this causes a difference in voltage value,
The flow velocity is measured from this potential difference. FIG. 37 is a graph in which the vertical axis represents the temperature difference between the two temperature sensitive resistors. It can be seen that the flow velocity (horizontal axis) and the temperature difference (vertical axis) have a one-to-one correspondence and can be used as a flow velocity sensor.

38 and 39 show examples of circuits for implementing these functions. The circuit shown in FIG. 38 is for controlling the temperature of the heater 5, and the circuit shown in FIG. 39 obtains a voltage signal proportional to the difference in resistance value between the temperature sensitive resistors 6 and 7. It is for.

The temperature control circuit shown in FIG. 38 is composed of a Whiston bridge circuit 46 for keeping the temperature of the heater 5 higher than the ambient temperature detected by the comparison resistor 8 by a constant temperature. The Hoiston bridge circuit 46 constitutes one side by the heater 5 and the resistor 45, and the other side by the comparison resistor 8 and the resistors 47 and 48. Amplifier 49,5
The integrating circuit consisting of 0 operates so that the bridge circuit 46 is balanced by changing the potential of the output, and keeps the electric power consumed by the heater 5 constant.

The circuit shown in FIG. 39 has a temperature sensitive resistor 6 located upstream of the heater 5 and a temperature sensitive resistor 7 located downstream thereof.
To detect the difference between and. This circuit
A constant current power supply unit 52 including an amplifier 72, an amplifier 66,
The differential amplifier 54 is composed of 68 and 70. The constant current power supply unit 52 has a high impedance resistor 56,
58, and a Hoiston bridge circuit having a variable resistor 60 for zero adjustment and temperature sensitive resistors 6 and 7 on the other side. The gain of the differential amplifier 54 is adjusted by the variable resistor 62.
The output terminal 64 outputs an output voltage proportional to the difference in resistance value between the temperature sensitive resistors 6 and 7.

[0008]

In order to make the thermal flow velocity sensor of this type have a wide measurable flow velocity range and high sensitivity, the temperature of the temperature sensitive resistors 6 and 7 is large over a wide flow velocity range. It is desirable to change. However, in the conventional thermal type flow velocity sensor, when the flow velocity is 0, the temperature-sensitive resistor 7 on the downstream side has already been heated up to about 60 to 70% of the temperature of the heater 5, so that the heat is transmitted from the heater 5 via air. The amount of heat generated is small, and the saturation temperature is reached at a relatively low flow rate. Referring to FIG. 36, the downstream temperature-sensitive resistor 7 is actually
It can be seen that the temperature change is small, and that it is already saturated at 10 m / s or more.

FIG. 40 shows a heater 5 and a temperature sensitive resistor 6,
7 is a schematic diagram showing heat transfer in FIG. In the figure, Q1 is the heat transfer amount from the heater 5 to the air, Q2 is the heat transfer amount transferred from the heater 5 to the upstream temperature-sensitive resistor 6 through the thin film member, and Q3 is the downstream side from the heater 5 through the thin film member. The heat conduction amount transmitted to the temperature-sensitive resistor 7, Q4 is the heat transfer amount from the upstream temperature-sensitive resistor 6 to the air, and Q5 is the heat transfer amount from the air to the downstream temperature-sensitive resistor 7.

Looking at the downstream temperature-sensitive resistor 7, Q3
And two heat inflows of Q5 are occurring. Of these, Q3 does not depend on the flow velocity, and only Q5 has flow velocity dependency. Q5 is proportional to the temperature difference between the air passing over the temperature sensitive resistor 7 and the temperature sensitive resistor 7 itself. It can be considered that most of the heat inflow when the flow velocity is 0 is due to Q3, but as shown in FIG. 36, the temperature sensitive resistor 7 is already heated to 140 ° C. at this time. For this reason, the temperature difference between the temperature sensitive resistor 7 and the air becomes small, and Q5 proportional to this temperature difference cannot be increased. Therefore, the temperature rise of the temperature sensitive resistor 7 is small even in the presence of the flow. Moreover, if the temperature rises to some extent, the temperature difference from the air will be further reduced, and will approach the saturation state. As a result, as shown in FIG. 37, the change in the temperature difference between the upstream and downstream temperature-sensitive resistors 6 and 7 becomes smaller as the flow velocity increases, and the sensitivity decreases.

As for the upstream temperature-sensitive resistor 6, a part of the heat quantity Q2 transferred from the heater 5 becomes Q4 and is transferred to the air. Although Q2 does not depend on the flow velocity of air, Q4 increases as the flow velocity increases, so the temperature of the temperature sensitive resistor 6 drops as the flow velocity increases. In this case, the larger the value of Q2, the wider the variation range of Q4, which is advantageous for improving the sensitivity and expanding the measurable flow velocity range. As shown in FIG. 36, the temperature of the upstream temperature-sensitive resistor 6 changes with a large inclination. However, when it is used for engine control of an automobile, for example, the flow velocity range (0 to 2000 cm / sec) shown in FIG. 36 is insufficient, and a measurement range of at least 0 to 10000 cm / sec is necessary. Assuming that the temperature change gradient of the upstream temperature-sensitive resistor 6 in FIG. 36 is (−40 ° C.) / (2000 cm / sec), this temperature change gradient gradually decreases until the flow velocity reaches 10000 cm / sec. It is clear that we will do it. As a result, as the flow velocity increases, the change in temperature difference between the temperature sensitive resistors 6 and 7 on the upstream side and the downstream side becomes small, and the sensitivity decreases.

Further, F. Research by Mayer et al. (F. Maye
r et al: Transducers'95 Eurosensors IX 132-C2 pp.
528-531), it is reported that the temperature of the temperature-sensitive resistor 7 on the downstream side decreases as the flow velocity increases. This phenomenon has also been confirmed by an experiment conducted by the inventor of the present application (FIG. 41). In addition, research by Li Qui et al. (Li Qui et
al: Transducers'95 Eurosensors IX 130-C2 pp.520-5
23), it has been reported that the temperature difference 6, 7 between the temperature sensitive resistors in the upstream and the downstream decreases at a certain flow rate or higher. These reports show that binarization of the output (there are two flow velocity points corresponding to one output) can occur when the flow velocity increases. This limits the expansion of the measurable flow velocity range.

As described above, the conventional thermal type flow velocity sensor using the temperature difference has a problem in that the flow velocity increases, the sensitivity decreases, and the measurable flow velocity range cannot be widened.

Further, as another conventional example (conventional example 2),
In Japanese Patent Laid-Open No. 4-230808, there is a space between the heater 5 and the upstream temperature-sensing section 6, and between the heater 5 and the downstream temperature-sensing section 7.
There is described an example in which slits are respectively provided between and to improve the sensitivity. By providing the slits on both sides of the heater 5 in this way, the amount of heat transferred from the heater 5 to the upstream and downstream temperature-sensitive parts 6, 7 via the thin portion is reduced, and the temperature of each temperature-sensitive part 6, 7 rises. Is lower than that without slits. When the flow velocity is 0, heat is transferred to the temperature sensing parts 6 and 7 only by natural convection and heat conduction of air. When the wind blows in this state, heat is transferred to the downstream temperature-sensitive portion 7 by forced convection, so that the temperature rises sharply and the sensitivity of the sensor is improved. However, since the temperature of the upstream temperature-sensitive portion 6 is originally low, the amount of heat taken away by the forced convection is small and the temperature change is small, which causes a decrease in the sensitivity of the sensor. As described above, the sensitivity is improved in the downstream temperature-sensitive portion 7, but the sensitivity is decreased in the upstream temperature-sensitive portion 6, so that the total sensitivity is not improved so much. Thus, if the slits are provided on both sides of the heater 5, the effect of improving the sensitivity cannot be expected so much.

The present invention has been made to solve the above problems, and an object thereof is to obtain a thermal type flow velocity sensor which can improve the sensitivity and can expand the measurable flow velocity range.

[0016]

A thermal type flow velocity sensor according to a first aspect of the present invention is a semiconductor device comprising a heat generating portion and upstream and downstream temperature detecting portions respectively arranged upstream and downstream of the heat generating portion. Along with the thin-walled portion of the substrate, a fluid temperature detecting portion is provided on the upstream side of the upstream temperature detecting portion, and when the heat generating portion is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting portion, The flow velocity signal obtained from the heating current supplied to the heat generating portion and the flow velocity signal obtained from the temperature difference between the upstream and downstream temperature detecting portions are added to detect the flow velocity.

The thermal type flow velocity sensor according to the second aspect of the present invention adds the two flow velocity signals described in the first aspect of the invention.
Each flow velocity signal is weighted according to the flow velocity.

In the thermal type flow velocity sensor according to the third aspect of the present invention, the heat generating portion, the upstream side temperature detecting portion disposed upstream of the heat generating portion, and the heat generating portion are provided in the vicinity of the heat generating portion so that the temperature becomes equivalent to that of the heat generating portion. The thin-walled portion of the semiconductor substrate is provided with the disposed heat generation temperature detection unit, and the fluid temperature detection unit is provided upstream of the upstream temperature detection unit, and the heat generation unit detects the fluid temperature detected by the fluid temperature detection unit. On the other hand, when driven by a constant temperature difference, the flow velocity signal obtained from the heating current supplied to the heat generating unit and the flow velocity signal obtained from the temperature difference between the upstream temperature detecting unit and the heat generating temperature detecting unit are added. The flow velocity is detected.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Reference Example 1. Hereinafter, reference examples of the present invention will be described with reference to the drawings. FIG. 1 is a top view showing a main part of a thermal type flow sensor according to a first embodiment of the present invention, and FIG. 2 is A- of FIG.
It is an A'line sectional view. However, the cross-sectional view of FIG. 2 shows the top view of FIG. 1 in a somewhat enlarged manner, and this is the same in the following similar cross-sectional views along the line AA ′. In the figure,
Reference numeral 1 is a silicon substrate, 2 is an air space formed by etching the silicon substrate 1 from the back, and 3 is a diaphragm-type thin portion provided on the air space 2. Reference numeral 5 is a heat generating portion, that is, a heat generating resistor, 6 and 7 are upstream and downstream temperature detecting portions, that is, upstream and downstream temperature-sensitive resistors, which are respectively arranged on the upstream side and the downstream side of the heat generating resistor 5, and 8 is upstream. A fluid temperature detecting portion arranged upstream of the side temperature-sensitive resistor 6 to measure the temperature of the fluid, that is, a temperature-sensitive resistor for detecting fluid temperature, 9 and 10 are insulating layers, 11 is a heating resistor 5 and a downstream temperature-sensitive resistor. Slits 12 provided between the resistor 7 and the heating resistor 5, the upstream and downstream temperature-sensitive resistors 6 and 7, and both ends of the fluid temperature detecting temperature-sensitive resistor 8 are bonded to the bonding pads 13, respectively. Wiring to connect. The thin portion 3 is composed of insulating layers 9 and 10, a heating resistor 5 sandwiched between the insulating layers 9 and 10, and temperature sensitive resistors 6 and 7.

The heating resistor 5, the upstream and downstream temperature sensitive resistors 6 and 7, and the fluid temperature detecting temperature sensitive resistor 8 are formed into a thin film by a film forming technique such as sputtering or vapor deposition, and then etched. It is formed by patterning so as to have a desired resistance value. It is desirable to use highly reliable platinum or the like as the resistance material.

The heating resistor 5 is driven by a constant temperature difference so that it is always higher than the temperature of the air measured by the fluid temperature detecting temperature sensitive resistor 8 by a constant temperature. FIG. 3 shows a simplified circuit diagram of the drive circuit. Heating resistor 5,
Temperature-sensitive resistor 8 for detecting fluid temperature, and fixed resistors 14 and 1
5 forms a bridge circuit. When the temperature of the heating resistor 5 changes due to the fluctuation of the flow velocity of the air, or the temperature of the air changes and the temperature of the temperature-sensitive resistor 8 for detecting the fluid temperature changes, and the balance of the bridge circuit is lost, The differential amplifier 16 and the transistor 17 work to control the heating current flowing through the heating resistor 5 and restore the original balanced state. As a result, the temperature difference between the heating resistor 5 and the fluid temperature detecting temperature sensitive resistor 8 is always kept constant. 18 is a power supply.

In such a flow velocity sensor of the type in which the temperature difference between the pair of temperature sensitive resistors 6 and 7 located on the upstream and downstream sides of the heater 5 is detected to measure the flow velocity, the measurable flow velocity range is widened and the sensitivity is increased. In order to improve the temperature difference, it is desirable that the temperature difference between the temperature sensitive resistors 6 and 7 greatly changes over a wide flow velocity range. To do this, each temperature sensitive resistor 6,7
It is necessary for the temperature of the to vary significantly over a wide flow rate range.

In this reference example, since the slit 11 is provided between the heating resistor 5 and the downstream temperature-sensitive resistor 7, the downstream temperature-sensitive resistor 7 is formed from the heating resistor 5 via the thin portion 3. The amount of heat transferred to the heat conduction can be greatly reduced. That is, Q3 in FIG. 40 becomes small. Therefore, the temperature of the downstream temperature-sensitive resistor 7 when the flow velocity is 0 is much lower than when the slit 11 is not provided. Since the heat transfer amount (Q1) transmitted from the heating resistor 5 to the air is not affected by the slit 11, it may be considered that the temperature of the air downstream of the heating resistor 5 does not change. As a result, the temperature difference between the downstream temperature-sensitive resistor 7 and the air flowing above it when the flow velocity is 0 is much larger than when the slit 11 is not provided. Since the amount of heat transferred from the air to the temperature sensitive resistor 7 is proportional to this temperature difference, when a flow of air occurs, a large amount of heat is transferred to the temperature sensitive resistor 7, and the temperature change becomes very large.

FIG. 4 shows an example of the temperature distribution of the thin portion 3.
The dotted line 19 is the temperature distribution when the flow velocity is 0, the solid line 20 is the temperature distribution when the air flow is present, and the shape of the solid line 20 changes depending on the flow velocity of the air. When the air flow exists, the temperature of the upstream temperature-sensitive resistor 6 drops by ΔTu, and the temperature of the downstream temperature-sensitive resistor 7 rises by ΔTd. As described above, due to the effect of the slit 11, ΔTd takes a much larger value than in the conventional case. Therefore, the upstream temperature-sensitive resistor 6
Of the temperature difference between the temperature sensitive resistor 7 and the downstream temperature-sensitive resistor 7 (ΔTu + Δ
Td) also increases, and the sensitivity of the flow velocity sensor improves. Further, since the downstream temperature-sensitive resistor 7 has a low original temperature,
Allows more heat inflow until reaching saturation temperature,
The measurable flow velocity range can be expanded.

Further, the heating resistor 5 and the upstream temperature-sensitive resistor 6
Since there is no slit between the heating resistor 5 and
The heat quantity Q2 is transferred by heat conduction from the to the upstream temperature-sensitive resistor 6 through the thin portion 3 and the temperature of the upstream temperature-sensitive resistor 6 when the flow velocity is 0 is the downstream side as shown by the dotted line 19 in FIG. It is higher than that of the temperature sensitive resistor 7. Therefore, the temperature drop ΔTu in the presence of the air flow is large, and the sensitivity is not lowered unlike the conventional example 2.

FIG. 5 shows a simple circuit diagram for detecting the above temperature difference. This is a bridge circuit using the temperature sensitive resistors 6 and 7 on one side and the fixed resistors 21 and 22 on the other side. 23 is a power supply. The output voltage 24 can be set to 0 when the flow velocity is 0 by selecting appropriate values for the fixed resistors 21 and 22. Output voltage 24 (Vout) for this circuit
Is expressed by the following equation (1).

[0027]

[Equation 1]

Here, Vc is the voltage of the power supply 23, Ru and Rd are the resistance values of the temperature sensitive resistors 6 and 7, Ru0 and Rd0 are the resistance values of the temperature sensitive resistors 6 and 7 when the flow velocity is 0, respectively. ΔRu
Is the resistance value decrease amount when the temperature of the temperature sensitive resistor 6 is decreased by ΔTu, and ΔRd is the resistance value increase amount when the temperature of the temperature sensitive resistor 7 is increased by ΔTd.

Further, as shown in the circuit diagram of FIG. 6, if the adjusting resistor 25 is inserted in series with the temperature sensitive resistor 7 so that Ru0 = Rd0, the output voltage 24 (Vout) becomes ).

[0030]

[Equation 2]

In both cases, the amount of change in temperature difference (ΔTu
The larger ++ Td), the larger the change in output voltage,
It can be seen that the flow velocity sensitivity is improved.

Reference Example 2. 7 is a top view showing a main part of a thermal type flow velocity sensor according to a second embodiment of the present invention, and FIG. 8 is A- of FIG.
It is an A'line sectional view. In the figure, 1 is a silicon substrate,
Reference numeral 2 is an air space formed by etching the silicon substrate 1 from the front side. Reference numeral 3 denotes a micro-bridge type thin portion provided on the air space 2, which is composed of insulating layers 9 and 10 and a heating resistor 5 and temperature sensitive resistors 6 and 7 sandwiched between the insulating layers 9 and 10. There is.

Also in this reference example, since the slit 11 is present, the same operation as in the reference example 1 increases the amount of change in the temperature difference between the upstream temperature-sensitive resistor 6 and the downstream temperature-sensitive resistor 7. Therefore, it is possible to improve the sensitivity and expand the measurable flow velocity range.

Reference Example 3. FIG. 9 is a top view showing a main part of the thermal type flow sensor according to the third reference example of the present invention. In the figure, the thin-walled portion 3 of the silicon substrate 1 is provided with a heat-generating resistor 5, a temperature-sensitive resistor 6a, 6b on the upstream side of the heat-generating resistor 5, and a temperature-sensitive resistor 7a, 7b on the downstream side. .
The two upstream temperature-sensitive resistors 6a and 6b and the two downstream temperature-sensitive resistors 7a and 7b are both formed to have the same temperature.

FIG. 10 is a circuit diagram for detecting a temperature difference. In the figure, the numbers of the resistors correspond to the numbers of the heating resistor 5 and the temperature sensitive resistors 6a, 6b, 7a, 7b, 8 respectively. A constant temperature difference drive circuit is configured by a bridge circuit configured by the differential amplifiers 37c and 37d, the heating resistor 5, and the temperature sensitive resistor 8 for detecting fluid temperature. The upstream temperature-sensitive resistors 6a and 6b and the downstream temperature-sensitive resistors 7b and 7a form a full bridge circuit. The bridge circuit is connected to the constant voltage source 42, and the bridge output is connected to the input of the differential amplifier 37a. FIG. 11 shows the relationship between the flow velocity and the output voltage. When the bridge circuit is adjusted to be balanced when the flow velocity is zero, the output voltage 39 (V ₃₉ ) of the differential amplifier 37a
Is expressed by the following equation (3). V ₃₉ = K (ΔR ₆ −ΔR ₇ ) V _D / (2R + ΔR ₆ + ΔR ₇ ) (3) where K is the amplification factor of the differential amplifier 37 a and ΔR is the resistance value at zero flow velocity. A variation, R is the resistance value of the temperature sensitive resistors 6 and 7 at zero flow velocity, and V _D is the voltage of the constant voltage power supply 42.

Although not shown, the temperature difference detecting circuit of the conventional thermal type flow velocity sensor is a half bridge circuit in which one side of the bridge is a fixed resistor, and the output voltage 39C when the fixed resistance value is R is V _39C = K (ΔR ₆ −ΔR ₇ ) V _D / 2 (2R + ΔR ₆ + ΔR ₇ ) (4), and the present invention is twice as sensitive.

In this reference example, the diaphragm type structure in which the silicon substrate 1 is etched from the back side to form the air space is described. However, the micro bridge type structure in which the silicon substrate 1 is etched from the front side to form the air space. It goes without saying that the same effect can be obtained in the above.

Reference Example 4. FIG. 12 is a top view showing a main part of the thermal type flow velocity sensor according to the fourth reference example of the present invention. In the thin portion 3 of the silicon substrate 1, a heat generation temperature detecting portion, that is, a heat generation temperature detecting temperature sensitive resistor 35 is formed in the vicinity of the heat generation resistor 5 so as to have the same temperature as that of the heat generation resistor 5. Temperature-sensitive resistors 6 and 7 are formed on the upstream side and the downstream side of the heating resistor 5 at substantially equal distances. Due to the fluid flow from the flow direction (FLOW), the upstream temperature-sensitive resistor 6 and the downstream temperature-sensitive resistor 7
Indicates that the resistance value fluctuates due to the cooling effect, but the temperature of the heating resistor 5 configured in the constant temperature difference drive circuit as shown in FIG. 13 hardly changes depending on the flow velocity.

In FIG. 13, the numbers of the resistors correspond to the numbers of the heating resistor 5 and the temperature sensitive resistors 6, 7, 8, 35. A constant temperature difference drive circuit is constituted by a bridge circuit constituted by the differential amplifiers 37c, 37d, the heating resistor 5, and the temperature sensitive resistor 8 for detecting the fluid temperature. 38
Reference numerals a, 38b and 38c denote constant current sources, which supply constant currents to the three temperature sensitive resistors 6, 7, and 35. Each of the temperature sensitive resistors 6, 7, and 35 is formed of platinum or nickel whose resistance value linearly changes with respect to a temperature change. The differential amplifier 37a outputs the voltage difference between the heat-generating temperature detecting temperature sensitive resistor 35 and the upstream temperature-sensitive resistor 6, and the differential amplifier 37b outputs the heat-generating temperature detecting temperature-sensitive resistor 35 and the downstream temperature-sensitive resistor. The voltage difference in the resistor 7 is output. The comparator 36 uses the output voltage 3 of the differential amplifier 37a.
9 and the output voltage 40 of the differential amplifier 37b are input, and the output 41 is inverted depending on the magnitude relationship between the two.

FIG. 14 shows the relationship between the flow velocity and the temperature of the temperature sensitive resistor forming portion. In the figure, 35t indicates the temperature of the temperature-sensitive resistor 35 for detecting heat generation temperature, 7t indicates the temperature of the downstream temperature-sensitive resistor 7, and 6t indicates the temperature of the upstream temperature-sensitive resistor 6. Generally, in the laminar flow heat transfer, due to the formation of the boundary layer, the heat transfer coefficient becomes smaller toward the downstream side, so that the temperature of the temperature sensitive resistor on the downstream side becomes higher than that of the temperature sensitive resistor on the upstream side. Further, the heat generation flow in the heat generating resistor 5 is conducted through the thin portion 3 and also propagates to the downstream side through the air flow, so that the temperature of the temperature sensitive resistor on the downstream side rises. Therefore, as shown in FIG. 14, the temperature of the temperature sensitive resistor 6t, 7t changes depending on the flow velocity.

FIG. 15 shows the relationship between the output signal corresponding to the flow velocity and the temperature of the temperature sensitive resistor. In the figure, the forward direction is the flow velocity in the flow direction (FLOW) in FIG. 12, and the opposite side across the output shaft represents the flow velocity in the reverse flow direction. Reference numerals 39 and 40 correspond to the signals 39 and 40 in the electronic circuit of FIG. Therefore, the signal 39 is proportional to the temperature difference between the heat-generating temperature detecting temperature-sensitive resistor 35 and the upstream temperature-sensitive resistor 6, and the signal 40 is between the heat-generating temperature detecting temperature-sensitive resistor 35 and the downstream temperature-sensitive resistor 7. The relationship is proportional to the temperature difference. Reference numeral 44 indicates a conventional flow velocity signal proportional to the difference between the temperature of the upstream temperature-sensitive resistor 6 and the temperature of the downstream temperature-sensitive resistor 7. The signals of 39 and 40 are not targets across the axis where the flow velocity is zero, but show high flow velocity sensitivity. The flow direction is determined by comparing the magnitudes of the flow velocity signal 39 and the flow velocity signal 40, and the flow velocity is detected using the larger output such as the signal 39 in the forward direction and the signal 40 in the reverse direction. By doing so, the flow velocity can be detected more accurately than in the conventional case. Although not shown, the flow velocity may be detected using the difference signal between the signals 39 and 40.

In this reference example, the diaphragm type structure in which the silicon substrate 1 is etched from the back side to form the air space is described. However, like the reference examples up to now, the silicon substrate 1 is etched from the front side and the air is removed. It goes without saying that the same effect can be obtained even in the microbridge structure having the space.

Embodiment 1. 16 is a top view showing a main part of the thermal type flow sensor according to the first embodiment of the present invention, and FIG.
FIG. 17 is a sectional view taken along the line AA ′ of FIG. 16. In this figure, the air space 2 is formed by etching the silicon substrate 1 from the back side, and the thin diaphragm portion 3 is provided on the air space 2.

In the present embodiment, the following 2
It has two flow velocity detecting means. First, as shown in FIG. 18, a heating resistor 5 and a fluid temperature detecting temperature-sensitive resistor 8 and fixed resistors 14 and 15 form a bridge circuit, and a heating current supplied to the heating resistor 5 is supplied to the bridge circuit. Output voltage 26
Is detected and the flow velocity is measured from this voltage. This method is called a heating current detection type. The other is to detect the temperature difference between the temperature sensitive resistors 6 and 7 as an output voltage 24 by a bridge circuit constituted by the temperature sensitive resistors 6 and 7 and the fixed resistors 21 and 22, as shown in FIG. A method of measuring the flow velocity from this voltage. This method is called a temperature difference detection type. This temperature difference detection type is exactly the same as that shown in FIG.

FIG. 20 shows the relationship between the flow velocity and the output of the heating current detecting type flow velocity sensor measured by the inventor of the present application. In addition, in FIG. 21, the flow velocity sensitivity ([%
/%]: Indicates the rate of change in output when the flow velocity changes by 1%). As shown in FIG. 21, the heating current type flow velocity sensor has low sensitivity in the low flow velocity region, the sensitivity increases as the flow velocity increases, and is substantially stable at a certain flow velocity or higher. For comparison,
22 and 23 show the relationship between the flow rate and the output, and the relationship between the flow rate and the sensitivity when the samples having exactly the same shape are used as the temperature difference detection type flow rate sensor. As described in the description of the conventional example, the temperature difference detection type has very excellent sensitivity in the low flow velocity region, but the sensitivity decreases as the flow velocity increases. This tendency can be seen from FIG. In this experiment, measurement was performed only up to 50 m / sec, but there is no doubt that the sensitivity will further decrease in the flow velocity range higher than this.

That is, the heating current type has low sensitivity in the low flow velocity region, and the temperature difference detection type has low sensitivity in the high flow velocity region. Therefore, by adding the outputs of both using the addition circuit as shown in FIG. 24, the disadvantages of each other can be compensated. In FIG. 24, 27, 28, and 29 are resistors for weighting, and by appropriately selecting these values, the ratio at the time of addition and the value of the addition output voltage 32 can be adjusted. Specifically, the added output voltage 32 (Vou
t) is expressed by the following equation (5).

[0047]

[Equation 3]

Since the output voltage 32 appears inverted in this adding circuit, another inverting circuit is required after this, but it is omitted in FIG. When Vo1 and Vo2 have almost the same voltage values, for example, if 10 kΩ, 20 kΩ, and 20 kΩ are selected as R ₂₇ , R ₂₈ , and R ₂₉ ,
Each of 1/2 of Vo1 and Vo2 is added, and the value of the output voltage Vout is almost the same as Vo1 and Vo2. By adding the heating current detection type output and the temperature difference detection type output as described above, it is possible to obtain a flow velocity sensor having excellent sensitivity over the entire flow velocity region.

Embodiment 2. 25 is a top view showing a main part of a thermal type flow velocity sensor according to a second embodiment of the present invention, and FIG.
FIG. 26 is a sectional view taken along the line AA ′ of FIG. 25. In this figure, the air space 2 is formed by etching the silicon substrate 1 from the front side, and the microbridge thin portion 3 is provided on the air space 2.

Also in this example, a heating current detection type output signal using the heating resistor 5 and the fluid temperature detecting temperature sensitive resistor 8 and a temperature difference detection type output signal using the temperature sensitive resistors 6 and 7 are used. By adding the signal, the same effect as in the first embodiment can be obtained. That is, a heating current detection type output signal having low sensitivity in the low flow velocity region and high sensitivity in the high flow velocity region and a temperature difference detection type output signal having high sensitivity in the low flow velocity region and low sensitivity in the high flow velocity region are added. By using the signal as the final output signal, it is possible to obtain a flow velocity sensor having excellent sensitivity in the entire flow velocity region.

Embodiment 3. FIG. 27 is a top view showing a main part of a thermal type flow velocity sensor according to a third embodiment of the present invention, and FIG.
FIG. 28 is a sectional view taken along the line AA ′ of FIG. 27. In this figure, the air space 2 is formed by etching the silicon substrate 1 from the back side, and the thin diaphragm portion 3 is provided on the air space 2. Further, as in the case of Reference Example 3, the two upstream temperature-sensitive resistors 6a and 6b and the two downstream temperature-sensitive resistors 7a and 7b are formed in an S shape as shown in FIG. 9, for example. Both may be formed to have the same temperature.

Also in this embodiment, the first embodiment
Similarly to the above, the heating current detection type output signal 26 using the heating resistor 5 and the fluid temperature detecting temperature sensitive resistor 8 and the temperature difference detection type output signal 24 using the temperature sensitive resistors 6a and 7a are used.
And is added to obtain a flow velocity sensor having excellent sensitivity. At this time, as shown in FIG. 29, the upstream and downstream temperature-sensitive resistors 6b and 7b are added to the weighting resistors of the adding circuit.
To use. Since the slits 11 are provided in the thin portion 3, the temperature-sensitive resistor 6b has a higher temperature than the temperature-sensitive resistor 7b when the flow velocity is 0. If the temperature-sensitive resistors 6b and 7b are made of the same material having the positive temperature coefficient of resistance and have the same shape, the resistance value of the temperature-sensitive resistor 6b becomes larger than the resistance value of the temperature-sensitive resistor 7b. As the flow velocity increases, the temperature sensitive resistor 6
The temperature of b is decreased and the temperature of the temperature sensitive resistor 7b is increased. Therefore, the resistance value of the temperature sensitive resistor 6b decreases, and the temperature sensitive resistor 7b
The resistance value of b increases. The situation is shown in FIG. The curve 33 is the flow velocity dependence of the resistance value of the temperature sensitive resistor 6b, and the curve 34
Is the flow velocity dependence of the resistance value of the temperature sensitive resistor 7b.

The addition output 3 in the addition circuit shown in FIG.
2 is represented by the following equation (6).

[0054]

[Equation 4]

Here, R _6b is the resistance value of the temperature sensitive resistor 6b,
R _7b represents the resistance value of the temperature sensitive resistor 7b. In this equation, if R _6b and R _7b change as shown in FIG. 30, the temperature difference detection type output signal Vo2 becomes dominant at a low flow velocity, and the heating current detection type output signal at a high flow velocity. Vo1 becomes dominant. For example, the temperature sensitive resistor 6
b and 7b, the resistance value when the temperature is 0 ° C. is 500Ω, the temperature coefficient of resistance is 3000 ppm, and the temperatures when the flow velocity is 0 are 160 ° C. and 80 ° C., respectively, the temperature-sensitive resistor 6b when the flow velocity is 0, The resistance values of 7b are 740Ω and 620Ω, respectively. For example, when R ₂₇ is 1 kΩ, the addition coefficients of the heating current detection type output signal Vo1 and the temperature difference detection type output signal Vo2 are 1.35 and 1.61, respectively, and when the flow velocity is 0, the temperature difference detection type The output signal Vo2 will be weighted about 20% more. On the contrary, if the flow velocity increases and the temperatures of the temperature sensitive resistors 6b and 7b reverse to 80 ° C. and 160 ° C., respectively, this time the heating current detection type output signal Vo1 is weighted by about 20%. Is charged.

As described above, according to this embodiment, the characteristic of the temperature difference detection type, which is excellent in the sensitivity in the low flow velocity region, appears more prominently in the low flow velocity region, and the sensitivity in the high flow velocity region is higher in the high flow velocity region. The characteristic of the excellent heating current detection type will be more prominent. Further, even in the high flow velocity region which could not be detected accurately only by the temperature difference detection type, by highly weighting the heating current detection type, it is possible to detect with high precision, and the measurable flow velocity range is expanded. As a result, it is possible to obtain a flow velocity sensor having excellent sensitivity in a wide range of flow velocity.

In this embodiment, the heating resistor 5
Although the temperature-sensitive resistors 6a and 7a located farther away from each other are used for flow velocity detection and the temperature-sensitive resistors 6b and 7b located closer to each other are used for weighting resistors, the same applies even if they are used in reverse. The effect of is obtained. Further, in this embodiment, the diaphragm type structure in which the silicon substrate 1 is etched from the back side to form the air space is described. However, the silicon substrate 1 is etched from the front side as in the previous embodiments and reference examples. Needless to say, the same effect can be obtained even in the microbridge structure having the air space.

Fourth Embodiment 31 is a top view showing a main part of a thermal type flow sensor according to a fourth embodiment of the present invention, and FIG.
FIG. 32 is a sectional view taken along the line AA ′ of FIG. 31. In this figure, the air space 2 is formed by etching the silicon substrate 1 from the back side, and the thin diaphragm portion 3 is provided on the air space 2.

In the present embodiment, the following 2
It has two flow velocity detecting means. First, there is a method in which a bridge circuit is constituted by the heating resistor 5, the fluid temperature detecting temperature sensitive resistor 8 and a fixed resistor, and the heating current flowing through the heating resistor 5 is detected to measure the flow velocity. This method is shown in FIG.
This is exactly the same as the heating current detection type shown in. Another one
One is the temperature-sensitive resistor 6 by the bridge circuit composed of the temperature-sensitive resistor 6, the heater temperature sensor 35 and the fixed resistor.
This is a method of measuring the flow velocity by detecting the temperature difference between the temperature sensing resistor 35 for detecting heat generation temperature and the temperature sensing resistor 35. This method is exactly the same as the temperature difference detection type with the heating element temperature 5 shown in Reference Example 4.

As described above, the heating current type has low sensitivity in the low flow velocity region, and the temperature difference detection type has low sensitivity in the high flow velocity region. Therefore, if the heating current type output voltage 26 (Vo1) and the temperature difference detection type output voltage 31 (Vo3) from the constant temperature point are added using the addition circuit as shown in FIG. You can make up for the disadvantages. In FIG. 33, 27, 28, and 29 are resistors for weighting, and by appropriately selecting these values, the ratio at the time of addition and the value of the addition output voltage 32 can be adjusted. Specifically, the added output voltage 32 (Vout) is expressed by the following equation (7).

[0061]

[Equation 5]

As described above, by adding the output of the heating current detection type and the output of the temperature difference detection type of the heating element temperature, it is possible to obtain a flow velocity sensor having excellent sensitivity over the entire flow velocity region.

In this embodiment, the diaphragm type structure in which the silicon substrate 1 is etched from the back side to form the air space has been described. However, the silicon substrate 1 is exposed in the same manner as in the above embodiments and reference examples. It goes without saying that the same effect can be obtained even in the microbridge type structure in which the air space is formed by etching.

[0064]

As described above, according to the first aspect of the invention, the heat generating portion and the upstream and downstream temperature detecting portions respectively arranged on the upstream side and the downstream side of the heat generating portion are provided with a thin semiconductor substrate. And a fluid temperature detecting section upstream of the upstream temperature detecting section, and the heat generating section is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting section. Since the flow velocity signal obtained from the heating current supplied to the flow velocity signal and the flow velocity signal obtained from the temperature difference between the upstream side and the downstream side temperature detecting portion are added to detect the flow velocity, the portions having low sensitivity to each other are detected. Complementing each other, it is possible to obtain a flow velocity sensor with improved sensitivity over a wide range of flow velocity.

Further, according to the second invention, in order to add the two flow velocity signals described in the first invention, the respective flow velocity signals are weighted according to the flow velocity. Compensate for the less sensitive parts more effectively,
A flow velocity sensor with improved sensitivity can be obtained over a wide range of flow velocity.

Further, according to the third invention, the heat generating portion, the upstream temperature detecting portion disposed upstream of the heat generating portion, and the heat generating portion are disposed in the vicinity of the heat generating portion so as to have the same temperature. A heat generation temperature detection unit is provided in the thin portion of the semiconductor substrate, and a fluid temperature detection unit is provided on the upstream side of the upstream temperature detection unit, and the heat generation unit is provided for the fluid temperature detected by the fluid temperature detection unit. Flow rate signal obtained from the heating current supplied to the heat generating section and the flow rate signal obtained from the temperature difference between the upstream temperature detecting section and the heat generating temperature detecting section when the constant temperature difference drive is performed. Therefore, it is possible to obtain a flow velocity sensor having an improved sensitivity over a wide range of flow velocity by complementing each other in insensitive portions.

[Brief description of drawings]

FIG. 1 is a top view showing a main part of a thermal type flow sensor according to a first reference example of the present invention.

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

FIG. 3 is a circuit diagram schematically showing a constant temperature difference drive circuit according to a first reference example of the present invention.

FIG. 4 is a temperature distribution diagram according to Reference Example 1 of the present invention.

FIG. 5 is a circuit diagram schematically showing a temperature difference detection circuit according to a first reference example of the present invention.

FIG. 6 is a circuit diagram schematically showing another temperature difference detection circuit according to the first embodiment of the present invention.

FIG. 7 is a top view showing a main part of a thermal type flow sensor according to a second reference example of the present invention.

8 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 9 is a top view showing a main part of a thermal type flow sensor according to a third reference example of the present invention.

FIG. 10 is a circuit diagram showing a temperature difference detection circuit according to a third reference example of the present invention.

FIG. 11 is a characteristic diagram showing a relationship between a flow velocity and an output voltage according to Reference Example 3 of the present invention.

FIG. 12 is a top view showing a main part of a thermal type flow sensor according to a fourth embodiment of the present invention.

FIG. 13 is a circuit diagram showing a temperature difference detection circuit according to Reference Example 4 of the present invention.

FIG. 14 is a characteristic diagram showing flow velocity dependence of resistor temperature according to Reference Example 4 of the present invention.

FIG. 15 is a characteristic diagram showing the relationship between the flow rate and the output signal according to the temperature of the temperature sensitive resistor according to the fourth embodiment of the present invention.

FIG. 16 is a top view showing a main part of the thermal type flow sensor according to the first embodiment of the present invention.

17 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 18 is a circuit diagram schematically showing a heating current detection circuit according to the first embodiment of the present invention.

FIG. 19 is a circuit diagram schematically showing a temperature difference detection circuit according to the first embodiment of the present invention.

FIG. 20 is a characteristic diagram showing the flow velocity dependence of the output signal of the heating current detection circuit according to the first embodiment of the present invention.

FIG. 21 is a characteristic diagram showing flow velocity dependence of sensitivity of the heating current detection type according to the first embodiment of the present invention.

FIG. 22 is a characteristic diagram showing the flow velocity dependence of the output signal of the temperature difference detection circuit according to the first embodiment of the present invention.

FIG. 23 is a characteristic diagram showing flow velocity dependence of sensitivity of the temperature difference detection type according to the first embodiment of the present invention.

FIG. 24 is a circuit diagram showing a simplified addition circuit according to the first embodiment of the present invention.

FIG. 25 is a top view showing a main part of a thermal type flow sensor according to a second embodiment of the present invention.

FIG. 26 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 27 is a top view showing a main part of a thermal type flow velocity sensor according to a third embodiment of the present invention.

28 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 29 is a circuit diagram showing a simplified addition circuit according to the third embodiment of the present invention.

FIG. 30 is a characteristic diagram showing the flow velocity dependence of the weighting resistance of the adder circuit according to the third embodiment of the present invention.

FIG. 31 is a top view showing a main part of a thermal type flow sensor according to a fourth embodiment of the present invention.

32 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 33 is a circuit diagram showing a simplified addition circuit according to the fourth embodiment of the present invention.

FIG. 34 is a cross-sectional view showing a main part of a conventional thermal type flow velocity sensor.

FIG. 35 is a top view of FIG. 34.

FIG. 36 is a characteristic diagram showing the flow velocity dependence of the temperature of the temperature sensitive resistor according to the conventional example.

FIG. 37 is a characteristic diagram showing the flow velocity dependence of the temperature difference of the temperature sensitive resistor according to the conventional example.

FIG. 38 is a diagram showing a heater temperature control circuit according to a conventional example.

FIG. 39 is a diagram showing a temperature difference detection circuit according to a conventional example.

FIG. 40 is a schematic diagram for explaining how heat is transferred in a thin portion according to a conventional example.

FIG. 41 is a characteristic diagram showing the flow velocity dependence of the temperature of the temperature sensitive resistor according to the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate, 2 Air space, 3 Thin part, 5 Heating resistor, 6,6a, 6b Upstream temperature-sensitive resistor, 77a, 7b Downstream temperature-sensitive resistor, 8 Fluid temperature detection temperature-sensitive resistor, 11 Slit, 35 Thermosensitive resistor for detecting heat generation temperature.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-60-142268 (JP, A) JP-A-8-68677 (JP, A) JP-A-8-54270 (JP, A) JP-A-4-54 27825 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01F 1/68-1/699

Claims (3)

(57) [Claims] 1. A thin-walled portion of a semiconductor substrate is provided with a heat generating portion and upstream and downstream temperature detecting portions arranged on the upstream side and the downstream side of the heat generating portion, respectively, and upstream from the upstream temperature detecting portion. A fluid temperature detection unit on the side, when the heat generation unit is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit, a flow velocity signal obtained from a heating current supplied to the heat generation unit, A thermal type flow velocity sensor configured to detect a flow velocity by adding a flow velocity signal obtained from a temperature difference between the upstream side and the downstream side temperature detecting portions. 2. The thermal flow velocity sensor according to claim 1, wherein in adding the two flow velocity signals according to claim 1, each flow velocity signal is weighted according to the flow velocity. 3. A semiconductor device comprising: a heat generating section, an upstream temperature detecting section arranged upstream of the heat generating section, and a heat generating temperature detecting section arranged in the vicinity of the heat generating section so as to have the same temperature as the heat generating section. Along with the thin-walled portion of the substrate, a fluid temperature detecting portion is provided on the upstream side of the upstream temperature detecting portion, and when the heat generating portion is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting portion, A thermal formula for detecting a flow velocity by adding a flow velocity signal obtained from a heating current supplied to the heat generation unit and a flow velocity signal obtained from a temperature difference between the upstream temperature detection unit and the heat generation temperature detection unit. Flow sensor.