JP2842485B2 - 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 thermal type flow sensor for measuring an intake air amount of an engine, and more particularly to an improvement of a temperature sensing resistance element for detecting the flow rate.

[0002]

2. Description of the Related Art Generally, in an electronically controlled fuel injection system for an automobile engine, it is important to accurately measure the amount of air taken into the engine for controlling the air-fuel ratio. Conventionally, a vane-type air flow sensor has been mainly used as the air flow sensor. However, a thermal flow sensor having a small size, a high mass flow rate, and a high responsiveness is becoming widespread. This thermal type flow sensor supplies current to a temperature sensitive resistor disposed in the intake air to generate heat,
A constant temperature measuring method having excellent responsiveness is generally used as a detection circuit, utilizing a heat transfer phenomenon from the heating element to the intake air. The constant temperature measurement method is a method in which a bridge circuit and a differential amplifier are configured so that the temperature of the heating element is always higher than the intake air temperature by a constant temperature, and the amount of heat transfer from the heating element to the air is measured.

FIG. 16 is a cross-sectional plan view of a flow detecting element of a conventional thermal flow sensor. Illustrated flow sensing element 1
In the drawing, reference numeral 0 denotes an insulating substrate, 2 denotes a heating element temperature detecting resistor for detecting the temperature of a heating resistor, and 5 denotes an insulating substrate.
A heating resistor having a temperature dependency formed by processing a metal thin film of platinum or the like deposited thereon into a meandering shape, 11 is a holding member, and 12 is a lead. The flow rate detecting element configured as described above is small, and can be manufactured from a single substrate.

[0004] The flow rate detecting element 10 having the above-described structure.
As shown in FIG. 17, a fluid temperature detecting element 15 having a fluid temperature detecting resistor 14 having a structure similar to that of the heat generating resistor 5 formed on the insulating substrate is disposed in a flow path tube 16. . Flow rate detecting element 10, Fluid temperature detecting element 1
5, is mechanically fixed by a holding member 11 provided on the tube wall, and is electrically connected to an external control circuit.

The heating element temperature detecting resistor 2 and the fluid temperature detecting resistor 14 are connected together with other fixed resistors in FIG.
A bridge circuit as shown in FIG. The heating resistor 5 is independent of this bridge circuit. 2 in the figure
Reference numerals 1, 22, and 23 denote fixed resistors, 24 denotes a differential amplifier, 25 denotes a power transistor, 26 denotes an input terminal, and 27 denotes an output terminal. A connection point P between the fixed resistors 22 and 23 and a connection point Q between the fixed resistor 21 and the heating element temperature detecting resistor 2 are connected to the input terminals of the differential amplifier 23. The output of the differential amplifier 24 is connected to the bridge via a power transistor 25. A heating resistor 5 is connected to the emitter terminal of the power transistor 25, and the other end of the heating resistor 5 is grounded.

Next, the operation will be described. In the bridge circuit, the resistance values of the fixed resistors 21, 22, and 23 are determined so that the bridge circuit is in an equilibrium state when the temperature of the heating element temperature detection resistor 2 is higher than the temperature of the fluid temperature detection resistor 14 by a certain temperature ΔT. ing. In other words, the bridge circuit operates so that the temperature difference between the heating element temperature detecting resistor 2 and the fluid temperature detecting resistor 14 always becomes ΔT. For example, when the temperature difference between the two resistors becomes smaller than ΔT, the potential at the connection point Q becomes lower than the potential at the connection point P, and the output voltage of the differential amplifier 24 becomes a high level and acts on the transistor 25. As a result, the power supplied to the heating resistor 5 increases, and the heating resistor 5
, The temperature of the heating element temperature detecting resistor 2 also increases. When the temperature difference between the fluid temperature detecting resistor 14 and the heating element temperature detecting resistor 2 becomes equal to ΔT, the differential amplifier 2
4 becomes low level, and the supply of power to the heating resistor 5 stops increasing.

By controlling the power supply to the heating resistor 5, the temperature difference between the heating element temperature detecting resistor 2 and the fluid temperature detecting resistor 14 is kept constant. In this thermal equilibrium state, the heating current I is a function only of the mass flow rate Qm of the fluid. Therefore, the mass flow can be detected by measuring the heating current I at the output terminal 27 as a voltage drop in the heating resistor 5.

[0008]

In the thermal type flow sensor constructed as described above, since the temperature of the heating resistor 5 is detected by the heating element temperature detecting resistor 2, the heat of the heating resistor 5 is reduced. It takes time before it is transmitted to the temperature detecting resistor 2 by heat conduction. The time required for the heat conduction affects the response of the sensor, and the heat conduction time must be reduced as much as possible to improve the response. To reduce the time required for heat conduction, the distance between the two resistors may be reduced. However, in the conventional thermal flow sensor, the heating resistor 5 and the temperature detecting resistor 2 are provided on the same plane of the substrate as described above. Because it is formed
There is a limit depending on processing techniques such as etching and laser trimming for making the two resistors close to each other. Also, if they are too close, they may make electrical contact and cause a short circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a thermal type flow sensor capable of improving responsiveness.

[0010]

Means for Solving the Problems] thermal flow sensor according to the present invention, the inside of the first surface of the first single crystal silicon layer
The heating resistor formed in the
Extracted on the back side of the first surface of the single-crystal silicon layer
Wiring and a shape formed inside the first surface of the second single-crystal silicon layer;
The formed heating element temperature detection resistor and the heating element temperature detection
Of the first surface of the second single crystal silicon layer from the
A wiring taken out on the surface side and the first single-crystal silicon layer
And a first surface of the second single crystal silicon layer
And a first insulating layer provided between
A resistor and the heating element temperature detecting resistor are connected to the first insulating layer;
Provided with a fluid flow rate detecting element closely attached through
It is.

[0011]

The thermal flow sensor according to the present invention has a heating resistor.
The resistance and the heating element temperature detection resistor are closely connected via the first insulating layer.
Heating resistance and heating element temperature detection resistance
When the distance between the two resistors can be shortened and required for heat conduction between the two resistors.
The time is reduced. Also take out the wiring from the heating resistor
Out of the single-crystal silicon layer on the back side of the first surface, and
Wiring from the heating element temperature detecting resistor is connected to the second single crystal silicon
Since it was taken out on the back side of the first side of the recon layer, the heating resistor
More effective placement of close contact between resistance and heating element temperature detection resistor
Can be implemented

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a flow detecting element in a thermal flow sensor according to a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional view taken along the line III-III of FIG. In the figure, reference numeral 1 denotes a first substrate made of a single crystal silicon substrate.
Is a heating element temperature detecting resistor formed by diffusion in the first single crystal silicon layer 2, and 3 is a first single crystal silicon layer 1 and a heating element temperature detecting resistor 2.
A first insulating layer such as SiO ₂ or Si ₃ N ₄ formed on the first insulating layer; 4, a second single-crystal silicon layer formed on the first insulating layer 3; A heating resistor 6 formed by diffusion in the layer 4 is a second insulating layer formed on the second single-crystal silicon layer 4 and the heating resistor 5. A technique for forming the second single crystal silicon layer 4 on the first insulating film 3 is called an SOI (Silicon on insulator) technique,
It can be obtained by depositing polycrystalline silicon on the insulating layer by the method D, melting it by a laser or the like, and recrystallizing it.

Contact holes are etched in both ends of the heating element temperature detecting resistor 2 and the heating resistor 5 in the first and second insulating layers 3 and 6, and formed on the insulating layer through the contact holes. The aluminum wirings 7 and 8 and the resistors 2 and 5 are electrically connected. In this case, since it is necessary to form the aluminum wiring 7 on the first insulating layer 3, both sides of the second monocrystalline silicon layer 4 and the second insulating layer 6 covering the first insulating layer 3 Etching to make the first insulating layer 3
Are exposed, and a contact hole is formed in the exposed portion.

The flow rate detecting element indicated by reference numeral 10 formed as described above is fixed to the holding member 11 in a cantilever structure as shown in FIGS.
The terminal 9 formed on the holding member 11 is electrically connected to the terminal 9 formed on the holding member 11 by a bonding wire 13.

FIG. 6 is a sectional view showing a state in which the flow rate detecting element 10 is disposed in a fluid passage. In the figure, reference numeral 15 denotes a fluid temperature detecting element on which a fluid temperature detecting resistor 14 is formed,
16 is a conduit, 17 is a flow detection conduit, 18 is a rectifying net, and 19 is a drive circuit. The fluid temperature detecting element 15 is fixed to the holding member similarly to the flow rate detecting element, and is electrically connected to a terminal on the holding member by a wire. Six terminals are connected to the drive circuit 19, FIG. 1
The bridge circuit shown in FIG. In addition, in order to avoid the influence of heat of the heating resistor 5, the fluid temperature detecting resistor 1 is used.
5 is installed on the upstream side of the flow detection resistor 10.

The flow rate detecting element 1 formed as described above
0, the first insulating layer 3 can be thinned to the order of submicron, so that the heating element temperature detecting resistors 2 and the heating resistors 5 located above and below the first insulating layer 3 can be very close to each other. The time required for heat conduction between the two resistors 2 and 5 is reduced. As a result, responsiveness is improved. Also,
Since there is an electrical insulating layer between the two resistors, there is no fear of electrical contact.

FIG. 7 is a plan view of a flow rate detecting element according to the second embodiment, and FIG. 8 is a sectional view taken along line VIII-VIII of FIG.
FIG. 9 is a sectional view taken along line IX-IX of FIG. In the above embodiment, a part of the first insulating layer 3 was exposed and a contact hole was formed in that part. In the present embodiment, a third insulating layer 19 was formed on the back surface of the first single crystal silicon layer 1. Then, a contact hole is formed from the back surface of the first single-crystal silicon layer 1. Therefore, it is not necessary to expose a part of the first insulating layer 3. In this case, since the aluminum wirings 7 and 8 are formed on both surfaces of the flow rate detecting element 10, FIG.
As shown in FIG. 1 and FIG. 11, the aluminum wiring 7 is electrically connected to the terminal 12 of the holding member 11 directly by a conductive material such as solder. The aluminum wiring 8 is connected to the terminal 12 by the bonding wire 13 as in the above embodiment. Other configurations are the same as those in the above embodiment. Also in this embodiment, the heating resistor 2 and the heating resistor 5 can be brought very close to each other, and the time required for heat conduction between the two resistors can be reduced. As a result, responsiveness is improved.

FIG. 12 is a plan view of the flow rate detecting element 10 according to the third embodiment, FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12, and FIG. 14 is a sectional view taken along line XIIII-XIIII of FIG. Show. Although the structure is the same as that of the first embodiment, this embodiment uses SOI as a method of forming the second single-crystal silicon layer 4.
It is formed by laminating two single-crystal silicon substrates without using any technology. The manufacturing method is shown in FIGS. Two single-crystal silicon substrates are prepared, and a heating element temperature detecting resistor 2 is formed on one side and a heating resistor 5 is formed on the other side by diffusion (a). Next, insulating layers 3 and 6 such as SiO ₂ and Si ₃ N ₄
(B), and etching each single crystal silicon substrate from the back surface to a thickness of about the diffusion depth. Then, an insulating layer 19 is formed on the back surface of one substrate (c), and is joined to the back surface of the other substrate by anodic bonding to form a first single-crystal silicon layer 1 and a second single-crystal silicon layer 4. (D).
Finally, contact holes are etched in the second and third insulating layers 6 and 19 to form aluminum wirings 7 and 8 (e).
The connection method with the holding member 11 and others are the same as those in the second embodiment . Also in this embodiment, the heating element temperature detecting resistor 2 and the heating resistor 5 can be formed very close to each other, so that the time required for heat conduction between the two resistors is reduced, and as a result, the responsiveness is improved. You.

[0019]

As described above, according to the present invention, the heating resistor and the heating element temperature detecting resistor are connected via the first insulating layer.
Since they are closely attached, the heating resistor and the heating element temperature detection resistor
The distance between the resistors can be shortened, and it is necessary for heat conduction between the resistors.
To obtain a thermal flow sensor that can reduce the time
Can be. Also, take out the wiring from the heating resistor to the first
Take out on the back side of the first plane of the single crystal silicon layer and generate heat
The wiring taken out from the body temperature detecting resistor is connected to the second single crystal silicon.
Since it was taken out on the back side of the first side of the concrete layer,
More effective close contact arrangement between the heater and the heating element temperature detection resistor
To obtain a thermal flow sensor with good thermal responsiveness.
Can be

[Brief description of the drawings]

FIG. 1 is a plan view of a flow detecting element in a thermal flow sensor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the flow detecting element taken along line II-II in FIG.

FIG. 3 is a sectional view of the flow rate detecting element taken along line III-III in FIG. 1;

FIG. 4 is a plan view of a holding member attaching portion according to the first embodiment of the present invention.

FIG. 5 is a side view of the holding member attaching portion of FIG. 4;

FIG. 6 is a sectional view of a mounting portion in a conduit of the thermal type flow sensor according to the present invention.

FIG. 7 is a plan view of a flow rate detecting element in a thermal type flow rate sensor according to a second embodiment of the present invention.

8 is a cross-sectional view of the flow rate detecting element taken along line VIII-VIII in FIG.

FIG. 9 is a cross-sectional view of the flow detecting element taken along line IX-IX in FIG. 7;

FIG. 10 is a plan view of a holding member attaching portion according to a second embodiment of the present invention.

11 is a cross-sectional view of the holding member attachment section line X-X in FIG. 10.

FIG. 12 is a plan view of a flow rate detecting element in a thermal type flow rate sensor according to a third embodiment of the present invention.

FIG. 13 is a sectional view of the flow rate detecting element taken along line XIII-XIII in FIG.

14 is a cross-sectional view of the flow rate detecting element taken along line XIIII-XIIII in FIG.

FIG. 15 is a manufacturing process diagram of the flow rate detecting element according to the third embodiment of the present invention.

FIG. 16 is a configuration diagram showing a conventional flow rate detecting element.

FIG. 17 is a view showing a conventional flow detecting element installed in a fluid passage.

FIG. 18 is a circuit diagram of a bridge circuit used for a constant temperature measurement method in a thermal type flow sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first single-crystal silicon layer 2 heating element temperature detecting resistor 3 first insulating layer 4 second single-crystal silicon layer 5 heating resistor 6 second insulating layer 7, 8 aluminum wiring 10 flow rate detecting element

Continuation of the front page (72) Inventor Mikio Bessho 8-1-1, Tsukaguchi-Honmachi, Amagasaki-shi, Hyogo Mitsubishi Electric Corporation Industrial System Research Laboratory (56) References JP-A-57-93212 (JP, A) JP-A-61-88532 (JP, A) JP-A-62-284216 (JP, A) JP-A-62-88364 (JP, A) JP-A-2-278766 (JP, A) JP-A-62-123318 (JP JP-A-59-65231 (JP, A) JP-A-61-232661 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/68 F02D 35/00

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the first single-crystal silicon layer has a first surface.
The heating resistor formed on the side and the heating resistor
Extracted on the back side of the first surface of the first single crystal silicon layer
Wiring and the inside of the first surface of the second single crystal silicon layer.
The formed heating element temperature detection resistor and the heating element temperature detection
From the output resistance, the first surface of the second single crystal silicon layer
A wiring taken out on the back side and the first single-crystal silicon
A first side of the layer and a first side of the second monocrystalline silicon layer.
And a first insulating layer provided between the first and second surfaces.
And the heating element temperature detecting resistor are connected to the first insulation.
A thermal type flow sensor, comprising: a fluid flow rate detecting element which is disposed in close contact with a layer .