JPS5981516A - Micro flow sensor - Google Patents

Abstract

PURPOSE:To improve homogeneity, reliability, and productivity by providing >=2 P-N junctions in a resistive base board, feeding a current to the base board and heating them, and bringing this base board into contact with gas to be measured and measuring the flow rate of the gas from the difference between voltages developed at the two P-N junctions. CONSTITUTION:When the current I is fed to the base board 14, the board is heated up to T deg.K and two P-N junctions 20 and 21 are also heated. Further, a forward current If is flowed to those P-N junctions 20 and 21 from terminals 18c-18f to develop voltages proportional to absolute temperature T deg.K between the terminals 18c and 18d, and 18e and 18f. When the gas to be measured is flowed through a capilary 13, heat is absorbed by the gas greatly at an upstream point A of the base board to heat the gas, and a relatively small amount of heat corresponding to the difference between the temperature of the heated gas and the temperature of the board 14 at a downstream point B is absorbed at the point B. The difference in temperature between the points A and B of the board varies depending upon the flow rate, so the voltage Vd of both P-N junctions which reflects the temperature is measured to measure the gas flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microflow sensor used to measure a flowing liquid of gas (hereinafter referred to as a gas to be measured).

When a resistor such as a nichrome wire or a platinum wire is heated by passing an electric current through it and is brought into contact with the gas to be measured, the resistor is cooled and its resistance value is reduced. In this case, if the temperature of the gas to be measured before it comes into contact with the resistor is constant, and the various conditions other than the trench flow rate are constant, the change in the resistance value of the resistor corresponds to the flow rate of the gas to be measured. Therefore, the flow rate of the gas to be measured can be indirectly measured by detecting the change in resistance value.

Current microflow sensors are based on this principle. In order to manufacture the microflow sensor used for actual measurements with good performance, as shown in Figure 1, a resistance wire such as a platinum wire is attached to the circumferential surface of a thin tube 1 through which the gas to be measured flows.
The resistance wire 2 is formed by winding the resistance wire 2 or by depositing the resistance wire 2 by electroplating or vapor deposition. Note that the reason why three lead wires 3 are provided on the resistance wire 2 is to enable connection to a bridge circuit in order to more accurately measure the resistance change of the resistor.

By the way, although the current micro flow sensor has been devised in terms of manufacturing as described above, it has the following drawbacks. In other words, since resistance wire is a very fine wire of 10 to 50 μm, it is very difficult to wind it evenly, and as a result, the heat generation conditions differ due to the difference in the degree of adhesion, resulting in lack of homogeneity and large variations between elements. Product reliability is lacking.

It's a trench, it's difficult to automate because it's such a thin wire.
Even today, it is labor-intensive and must be carried out by skilled personnel (lack of productivity). Due to these drawbacks, even though it has a wide range of applications (gas flow rate mixing devices, semiconductor manufacturing field, flow control of internal combustion engines, etc.), it is currently not fully utilized.

The present invention provides an extremely useful microflow sensor that can solve all of the problems of homogeneity, reliability, and productivity at once in the current situation.

The microflow sensor according to the present invention has two or more PN junctions on or in a resistive substrate, generates heat by passing an electric current through the substrate, and also brings the substrate into contact with a gas to be measured. , the gist is that the flow rate of the gas to be measured is measured from the difference between the current flowing or the voltage generated between the two PN junctions.

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is an overall perspective view of the micro flow sensor, and FIG. 3 is a sectional view of FIG. 2. In the figure, 1o is a liquid casing, inside which there is an electrical connection such as glass or ceramics.
A thermally insulating material 11 is provided. A single narrow groove 12 is formed in the center of the upper surface of this substance 11, and irregularly shaped capillaries ↓ 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3 types of capillaries are formed at each end of the thin groove 12 to allow the gas to be measured to flow in and out.
13 has been inserted.

Further, the upper part of the narrow groove 12 is closed by a substrate 14, which can be called the heart of the microflow sensor of the present invention, so that the gas to be measured introduced through the irregular diameter capillary 13 comes into contact with the substrate 14. The top of this substrate 14 is filled with foamed heat insulating material 15 or the like to be heat-insulated, and the casing 1
0 is assembled by closing the upper part with a lid 16. 17 in the figure are connection pins connected to each terminal 18 of the board 14 by a wire 19.

The substrate 14 is made of a material having resistivity, for example, a resistivity of 1.
5 to 25 n- (constructed of N-type or P-type semiconductor of Hn, with current terminals 18a at both ends for passing current.

18b, and two PN junctions 20 and 21 are formed inside by hole holes as shown in FIG. Lead terminals 18c to 18f are provided in the P and N regions of each PN junction 20 and 21, respectively.

22 in the figure is 5in2 or S i 02+ S i3N4
23 is a metal conductor made of aluminum or gold, etc., and current terminals 18a, 181) are attached to this board 14.
When passing through MtJji', I, the substrate 14 generates 20 joules of heat due to its own resistance I<a, and is heated to a white temperature. (1, 21 are also heated. Therefore, each PN junction 20, 21, 4:, jA child 18C~
If a directional current ■f is passed sequentially from 1.8f, terminal 18
A voltage VJ proportional to the absolute temperature 1'' K is generated between 188.c and 18d and 188.18f as shown in the following equation.

■Ma=c(xβx T However, J is the ratio of the Boltzmann constant to the electric charge q of the electron (
l/q), β is the natural logarithm zn (if+Jr) of the sum of the forward current If and the reverse current Ir.

By the way, if we assume that the gas to be measured flows through the capillaries 13 and 13, at point A of the substrate located on the upstream side, the gas to be measured receives a large amount of heat and heats the gas, and at point B on the downstream side, the gas is heated. A relatively small amount of heat corresponding to the difference between the temperature of the gas and the temperature of the substrate 14 at point B is absorbed. In this case, if we look at the relative change in the amount of heat transferred at point B based on the amount of heat transferred at point A, we can see that when the flow rate of the gas to be measured is low, the amount of heat transferred at point B is also small, and when the gas flow rate is large, the amount of heat transferred at point B is small. The amount of heat absorbed at a point also increases depending on the gas flow rate. This is because if the gas flow rate is low, the gas will be heated to a temperature closer to the substrate temperature when passing through point A, so the amount of heat lost at point 13 will be small, whereas if the gas flow rate is high, the gas will pass through point A. This is thought to be due to the fact that even when the gas is heated, the temperature of the gas as a whole does not rise much due to the large flow rate, and as a result, a large amount of heat is wasted even at point B.

As a result, the temperature difference between points A and B of the substrate changes depending on the flow rate, so the gas flow rate can be measured by measuring the voltage vJ across both PN junctions that reflects this temperature. . However, the gas flow rate can be similarly measured by measuring current instead of this voltage.

A circuit for measuring gas flow rate, that is, each terminal 18 of the substrate 14
As shown in FIG. 7, the external circuit that processes the output voltage ■d of C~1.8
It is composed of an amplifier A2 that amplifies the output voltage Vdz between 8f and a differential amplifier A3 that takes the difference between the outputs of both amplifiers AI+A2. In the figure, )il is a power supply voltage for passing a current through the substrate 14, E2 is a power supply voltage for passing a forward current If through the PN junctions 20 and 21, and Tr, Tr2 are constant current circuits.

In the above embodiment, only two PN junctions are formed in the substrate 14, but it goes without saying that three or more PN junctions may be formed. Further, in the embodiment described above, the PN junctions 20 and 21 are formed in the substrate 14, but they may be mounted on the substrate 14 as shown in FIG.

Alternatively, as shown in FIG. 6, the substrate 14 is a P-type semiconductor 14a.
and N-type semiconductor 14b are connected in series,
The junction between two pairs of P-type semiconductors and N-type semiconductors is PN.
It can also be used as the junctions 20 and 21.

In this case, the forward current I flowing through the PN junctions 20 and 21 is
There is an advantage that the current f and the current for heating the substrate 14 can be used together, and that the external circuits to be connected to the respective terminals 18a to 18a of the substrate 14 can also be simplified as shown in FIG.

Since the microflow sensor according to the present invention is constructed as described above, it has the following effects.

That is, the two or more PN junctions 20, 21 can be formed in a semiconductor process, such as by holes in the substrate 14 or by mounting on the substrate, so that they can be formed uniformly and reliably by current semiconductor technology. It is possible to manufacture elements with high performance, and productivity is also significantly improved compared to conventional methods.

Therefore, it can be used in a wide range of fields such as semiconductor devices, 1M gas mixing devices, and flow rate control for internal combustion engines.

[Brief explanation of the drawing]

Figure 1 shows a conventional micro slow sensor, Figure 2 shows a conventional micro slow sensor.
The figure is an overall perspective view of a micro flow sensor as an embodiment of the present invention, FIG. 3 is a sectional view of FIG. 2, FIG. 4 is a sectional view showing a substrate and a PN junction formed thereon, FIG.
FIG. 6 is a cross-sectional view showing another embodiment of the substrate and the PN junction formed thereon, and FIGS.
014...board, 20, 21...PN junction.

Claims (1)

[Claims] When two or more PN junctions are provided on or in a resistive substrate, an electric current is passed through the substrate to generate heat, and the substrate is brought into contact with a gas to be measured, so that the current flowing through the two PN junctions or Microflow sensor 0 characterized in that the flow rate of a gas to be measured is measured from the difference in voltage generated.