JPH04332822A - Thermal flow rate sensor - Google Patents

Abstract

PURPOSE:To improve response by forming a heat generating resistor and a heater temperature detecting resistor vertically via a thin insulation layer. CONSTITUTION:A first insulation layer 3 is formed on a first single crystal silicon layer 1 and a heater temperature detecting resistor 2 formed thereon. A second insulation layer 6 is formed on a second single crystal silicon layer 4 formed on the layer 3 and on a heater temperature detecting resistor 5 formed thereon. The insulation layer 3 can be thin up to a submicron order, so that the resistors 2, 5 placed on and under it can be close to each other. Therefore time required for heat conduction between the resistors 2, 5 is shortened and response is improved. In addition the resistors 2, 5 are electrically insulated by the insulation layer 3 so that they will not electrically contact with each other.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal flow rate sensor for measuring the intake air amount of an engine, and more particularly to an improvement in a temperature-sensitive resistance element for detecting the flow rate.

0002

2. Description of the Related Art Generally, in electronically controlled fuel injection systems for automobile engines, it is important to accurately measure the amount of air intake into the engine in order to control the air-fuel ratio. Conventionally, vane type air flow sensors have been mainstream, but thermal type flow sensors are becoming more popular because they are small, can provide a mass flow rate, and have good responsiveness. This thermal flow sensor generates heat by supplying current to a temperature-sensitive resistor placed in the intake air.
This method utilizes the phenomenon of heat transfer from the heating element to the intake air, and a constant temperature measurement method with excellent responsiveness is generally used as a detection circuit. 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 a certain temperature higher than the intake air temperature, and the amount of heat transferred from the heating element to the air is measured.

FIG. 16 shows a cross-sectional plan view of a flow rate detection element of a conventional thermal flow rate sensor. Illustrated flow rate detection element 1
0 is shown in, for example, Japanese Unexamined Patent Publication No. 2-44211, and in the figure, 1 is an insulating substrate, 2 is a heating element temperature detection resistor for detecting the temperature of the heating resistor, and 5 is the insulating substrate 1.
A heat-generating resistor having temperature dependence is formed by processing a metal thin film such as platinum deposited thereon into a meandering shape, 11 is a holding member, and 12 is a lead. The flow rate detection element configured as described above is small and has excellent mass productivity because many elements can be manufactured from a single substrate.

As shown in FIG. 17, the flow rate detection element 10 having the above-described structure is provided with a heating resistor 5 on the insulating substrate.
A fluid temperature detection resistor 14 having a similar structure is disposed in a flow path pipe 16 together with a fluid temperature detection element 15 formed thereon. Flow rate detection element 10, fluid temperature detection element 15
It is also mechanically fixed by a holding member 11 provided on the tube wall, and is electrically connected to an external control circuit.

Further, the heating element temperature detection resistor 2 and the fluid temperature detection resistor 14 are shown in FIG. 18 together with other fixed resistors.
Configure a bridge circuit as shown in . The heat generating resistor 5 is independent from this bridge circuit. In the figure 2
1, 22, and 23 are fixed resistors, 24 is a differential amplifier, 25 is a power transistor, 26 is an input terminal, and 27 is an output terminal. A connection point P between the fixed resistors 22 and 23 and a connection point Q between the fixed resistance 21 and the heating element temperature detection resistor 2 are connected to the input terminal of the differential amplifier 23. The output of the differential amplifier 24 is connected to the bridge via a power transistor 25. Further, a heat generating resistor 5 is connected to the emitter terminal of the power transistor 25, and the other end of the heat generating resistor 5 is grounded.

Next, the operation will be explained. In the bridge circuit, the resistance values of the fixed resistors 21, 22, and 23 are determined so that an equilibrium state is reached 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 constant temperature ΔT. ing. In other words, the bridge circuit operates so that the temperature difference between the heating element temperature detection resistor 2 and the fluid temperature detection resistor 14 is always ΔT. For example, when the temperature difference between both 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 high level and acts on the transistor 25. As a result, the power supplied to the heat generating resistor 5 increases, the temperature of the heat generating resistor 5 rises, and the temperature of the heat generating element temperature detecting resistor 2 also rises. When the temperature difference between the fluid temperature detection resistor 14 and the heating element temperature detection resistor 2 becomes equal to ΔT, the differential amplifier 24
output becomes low level, and the increase in power supplied to the heat generating resistor 5 is stopped.

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

[0008]

[Problems to be Solved by the Invention] In the thermal flow sensor configured as described above, the temperature of the heat generating resistor 5 is detected by the heat generating element temperature detecting resistor 2, so that the heat of the heat generating resistor 5 is detected by the heat generating element temperature detecting resistor 2. It takes time for the heat to be transmitted to the temperature detection resistor 2 by conduction. The time required for this heat conduction affects the responsiveness of the sensor, and in order to improve the responsiveness, this heat conduction time must be shortened as much as possible. The time required for heat conduction can be shortened by shortening the distance between both resistors, but in conventional thermal flow sensors, the heat generating resistor 5 and the temperature detecting resistor 2 are placed on the same plane of the board as described above. Because it is formed,
There is a limit to how the two resistors can be brought close to each other, which depends on processing techniques such as etching and laser trimming. Also, if they are brought too close together, there is a risk of electrical contact and a short circuit.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a thermal flow sensor that can improve responsiveness.

0010

[Means for Solving the Problems] A thermal flow rate sensor according to the present invention includes a first single-crystal silicon layer, a heating resistor formed on the first single-crystal silicon layer, and a first single-crystal silicon layer. A first insulating layer formed on the silicon layer and the heat generating resistor, a second silicon single crystal layer formed on the first insulating layer, and a heat generating layer formed on the second single crystal silicon layer. The present invention is characterized in that it includes a fluid flow rate detection element including a body temperature detection resistor and a second insulating layer formed on the second single crystal silicon layer and the heating element temperature detection resistor.

[0011]

[Operation] The thermal flow rate sensor of the present invention includes a flow rate detection element that includes a first single crystal silicon layer, a heating resistor formed on the first single crystal silicon layer, and a first single crystal silicon layer. A first insulating layer formed on the silicon layer and the heat generating resistor, a second silicon single crystal layer formed on the first insulating layer, and a heat generating layer formed on the second single crystal silicon layer. A body temperature detection resistor, a second insulating layer formed on the second silicon layer and the heating element temperature detection resistor, and a contact hole provided at both ends of the heating element temperature detection resistor and the heating element temperature detection resistor. Since it is constructed from electrically connected aluminum wiring, the distance between the heat generating resistor and the heat generating element temperature detecting resistor can be shortened, and the time required for heat conduction between the two resistors can be shortened.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a flow rate detection element in a thermal flow sensor showing a first embodiment of the present invention, and FIG.
-II line sectional view, FIG. 3 is also III-III in FIG.
FIG. In the figure, 1 is a first single-crystal silicon layer made of a single-crystal silicon substrate, 2 is a heating element temperature detection resistor formed by diffusion in this first single-crystal silicon layer 1, and 3 is a first single-crystal silicon layer. SiO2 or Si3N4 formed on layer 1 and heating element temperature detection resistor 2
4 is a second single-crystal silicon layer formed on the first insulating layer 3; 5 is a heating resistor formed in the second single-crystal silicon layer 4 by diffusion; 6 is a first insulating layer such as is a second insulating layer formed on the second single crystal silicon layer 4 and the heat generating resistor 5. The technique for forming the second single crystal silicon layer 4 on the first insulating film 3 is SOI (Silicon on
It can be obtained by depositing polycrystalline silicon on an insulating layer using a CVD method, melting it with a laser or the like, and recrystallizing it.

Contact holes are etched in the first and second insulating layers 3 and 6 at both ends of the heating element temperature detecting resistor 2 and the heating resistor 5, and the contact holes formed on the insulating layer are formed through these contact holes. The aluminum wires 7, 8 and both resistors 2, 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 single crystal silicon layer 4 covering the first insulating layer 3 and the second insulating layer 6 are Etching the first insulating layer 3
A contact hole is formed in the exposed part.

The flow rate detection element designated by the reference numeral 10 formed as described above is fixed to the holding member 11 in a cantilever structure as shown in FIGS. 4 and 5.
The terminal 12 formed on the holding member 11 and the electrode lead-out portion 9 of 0 are electrically connected by a bonding wire 13.

FIG. 6 shows a cross-sectional view of the flow rate detection element 10 disposed in a fluid passage. In the figure, 15 is a fluid temperature detection element in which a fluid temperature detection resistor 14 is formed;
16 is a conduit, 17 is a flow rate detection conduit, 18 is a rectifying net, and 19 is a drive circuit. The fluid temperature detection element 15, like the flow rate detection element, is fixed to the holding member and electrically connected to the terminal on the holding member by a wire. The six terminals are connected to the drive circuit 19 and constitute the bridge circuit shown in FIG. Furthermore, in order to avoid the influence of heat from the heat generating resistor 5, the fluid temperature detecting resistor 15 is installed upstream of the flow rate detecting resistor 10.

Flow rate detection element 1 formed as described above
0, since the first insulating layer 3 can be made thin to the order of submicrons, the heating element temperature detection resistor 2 and the heat generating resistor 5 located above and below it can be made very close to each other. The time required for heat conduction between both resistors 2 and 5 is shortened. As a result, responsiveness is improved. Also,
Since there is an electrically insulating layer between the two resistors, there is no fear of electrical contact.

FIG. 7 shows a plan view of a flow rate detection element according to a second embodiment, FIG. 8 shows a sectional view taken along the line VIII--VIII in FIG. 7, and FIG. 9 shows a sectional view taken along the line IX--IX in FIG. Each is shown. In the above embodiment, a part of the first insulating layer 3 was exposed and a contact hole was formed in that part, but in this embodiment,
A third insulating layer 19 is formed on the back surface of the first single crystal silicon layer 1, and a contact hole is formed from the back surface of the first single crystal silicon layer 1. Therefore, there is no need to expose a part of the first insulating layer 3. In this case, aluminum wiring 7,
8 will be formed on both sides of the flow rate detection element 10, so as shown in FIGS. 10 and 11, the aluminum wiring 7
is directly electrically connected to the terminal 12 of the holding member 11 by a conductive material such as solder. The aluminum wiring 8 is connected to the terminal 12 by a bonding wire 13 as in the previous embodiment. The other configurations are the same as those of the previous embodiment. Also in this embodiment, the heat generating resistor 2 and the heat generating resistor 5 can be placed very close to each other, and the time required for heat conduction between the two resistors is shortened. As a result, responsiveness is improved.

FIG. 12 shows a plan view of the flow rate detection element 10 according to the third embodiment, and FIG.
The cross-sectional view taken along line II is shown in FIG.
A line cross-sectional view is shown. The structure is the same as the first embodiment, but in this embodiment the second
As a method of forming the single crystal silicon layer 4, SOI technology is not used, but the single crystal silicon layer 4 is formed by bonding two single crystal silicon substrates together. The manufacturing method is shown in FIG.
) to (e). Two single-crystal silicon substrates are prepared, and a heating element temperature detection resistor 2 is formed on one and a heat generating resistor 5 is formed on the other by diffusion (a). Next, insulating layers 3 and 6 of SiO2, Si3N4, etc. are formed on the diffusion-treated surface of each substrate (b), and each single-crystal silicon substrate is etched from the back surface to a thickness approximately equal to the diffusion depth. Then, an insulating layer 19 is formed on the back surface of one substrate (c) and bonded 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 interconnections 7 and 8 (e). The method of connection to the holding member 11 and other aspects are the same as those of the second embodiment. In this embodiment as well, the heating element temperature detection resistor 2 and the heat generating resistor 5 can be formed very close to each other, reducing the time required for heat conduction between the two resistors and improving responsiveness. Ru.

[0019]

As described above, according to the present invention, the heat generating resistor and the heat generating element temperature detecting resistor are formed one above the other with a very thin insulating layer interposed therebetween. The distance between the two resistors is shortened, and the time required for heat conduction between both resistors is shortened. As a result, the responsiveness of the sensor is improved.

[Brief explanation of drawings]

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

FIG. 2 is a cross-sectional view of the flow rate detection element taken along line II-II in FIG. 1;

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

FIG. 4 is a plan view of the holding member attachment portion in the first embodiment of the invention.

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

FIG. 6 is a cross-sectional view of the in-duct fitting portion of the thermal flow sensor according to the present invention.

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

8 is a cross-sectional view of the flow rate detection element taken along line VIII-VIII in FIG. 7. FIG.

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

FIG. 10 is a plan view of a holding member attachment part in a second embodiment of the invention.

11] FIG. 10 is a cross-sectional view of the flow rate detection element taken along the line XX in FIG. 9. [FIG.

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

13 is a cross-sectional view of the flow rate detection element taken along line XIII-XIII in FIG. 12. FIG.

14 is a cross-sectional view of the flow rate detection element taken along the line XIII-XIII in FIG. 12. FIG.

FIG. 15 is a manufacturing process diagram of a flow rate detection element in a third embodiment of the present invention.

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

FIG. 17 is a diagram showing the installation of a conventional flow rate detection element in a fluid passage.

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

[Explanation of symbols]

1 First single crystal silicon layer 2 Resistor for detecting heating element temperature 3 First insulating layer 4 Second single crystal silicon layer 5 Heat generating resistor 6 Second insulating layer 7, 8 Aluminum wiring 10 Flow rate detection element

Claims (4)

[Claims] 1. A first monocrystalline silicon layer;
a heat generating resistor formed on the single crystal silicon layer, a first insulating layer formed on the first single crystal silicon layer and the heat generating resistor, and a first insulating layer formed on the first insulating layer. a second silicon single crystal layer, a heating element temperature detection resistor formed on the second single crystal silicon layer, and a second heating element temperature detection resistor formed on the second single crystal silicon layer and the heating element temperature detection resistor. A thermal flow rate sensor characterized by comprising a fluid flow rate detection element comprising an insulating layer. 2. A claim characterized in that aluminum wiring is provided on the fluid flow rate detecting element and electrically connected to both ends of the heat generating resistor and the heat generating element temperature detecting resistor via contact holes. The thermal flow sensor according to item 1. 3. The thermal method according to claim 1, wherein the second single crystal silicon layer is formed by recrystallizing a polycrystalline silicon layer formed on the first insulating layer. flow rate sensor. 4. The thermal flow sensor according to claim 1, wherein the second single crystal silicon layer is formed by bonding another single crystal silicon substrate onto the first insulating layer. .