JPH0625685B2 - Flow sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flow sensor for detecting an extremely minute flow velocity of gas.

[Conventional technology]

FIG. 4 is a perspective view showing a conventional micro-bridge flow sensor. In the figure, a through hole 4 that connects the left and right openings 2 and 3 is formed in the center of the semiconductor base 1 by anisotropic etching. Above the through hole 4, the through hole 4 from the semiconductor base 1 is bridged. Bridge portions 5 that are spatially separated from each other and are thermally insulated from the semiconductor base 1 are formed. A thin film heater element 7 and thin film temperature measuring resistance elements 8 and 9 sandwiching the thin film heater element 7 are arranged on the surface of the bridging portion 5. Further, a thin film ambient temperature measuring resistance element 10 is formed at a corner of the semiconductor base 1.

5 (a) and 5 (b) are explanatory views showing the operation of the micro-bridge flow sensor shown in FIG. Where the figure
(a) shows the temperature distribution of each element, and (b) shows the section taken along the line IVB-IVB 'in FIG. Incidentally, 6 is a protective film made of a material having a low thermal conductivity.

Now, if the heater element 7 is controlled at a certain temperature t _h4 , t _h5 higher than the ambient temperature (for example, 63 ° C .: ambient temperature reference), the temperature t ₆ , t of the temperature measuring resistance elements 8, 9 is t ₆ .
₇ (for example, 35 ° C .: ambient temperature reference) is substantially symmetrical with respect to the temperatures t _h4 and t _h5 of the heater element 7 as shown in FIG. 5 (a). At this time, for example, the arrow 11 shown in FIG.
When the gas from the direction of moves, the temperature measuring resistance element 8 on the upstream side is cooled and the temperature is lowered by ΔT ₆ . On the other hand, in the temperature-measuring resistance element 9 on the downstream side, heat conduction from the heater element 7 is promoted by using the flow of gas as a medium, and the temperature rises by ΔT _7, resulting in a temperature difference. Therefore, by incorporating the heater elements 8 and 9 into the Wheatstone bridge circuit, the temperature difference can be converted into a voltage, a voltage output corresponding to the flow velocity can be obtained, and the gas flow velocity can be detected as shown in FIG. it can.

As described above, the conventional micro-bridge flow sensor has a thin film bridging structure having an extremely small heat capacity formed by the thin film technology and the anisotropic etching technology, and has an extremely fast response speed, high sensitivity and low power consumption It also has excellent features such as good mass productivity.

[Problems to be Solved by the Invention]

However, the conventional micro-bridge flow sensor has a slit-shaped central opening 12 as shown in FIG. 7 to form two bridging portions 5a and 5b.
2 has a structure in which the heater element 7 is sandwiched between the two and the temperature measuring resistance elements 8 and 9 are formed on the outer side thereof, and the temperature distribution due to the heating of the heater element 7 generated by the flow of the gas moving from the arrow 11 Is detected by the change in the resistance value of the temperature measuring resistance elements 8 and 9, but since the temperature measuring resistance elements 8 and 9 are arranged only in the portion where the temperature change is high, the change in the resistance value is caused by the flow velocity. Therefore, when the flow velocity decreases, for example, the average flow velocity is 10 cm / s.
There was a problem that it became difficult to measure the flow velocity in the low flow velocity region of about ec.

[Means for Solving the Problems]

In order to solve such a problem, the present invention provides at least two sets of bridging portions on the surface of a base, and the first lateral temperature is directed from the upstream side to the downstream side where gas flows on the surface of each bridging portion. The resistor, the heating element, and the second resistance temperature element are arranged in sequence, and each first side resistance temperature element, each heating element, and each second resistance temperature element are connected in series. is doing.

[Action]

In the present invention, the resistance change with respect to the flow rate of the gas is increased by connecting the resistance temperature detectors in series, so that the temperature change proportional to the flow rate is integrated and output.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of a flow sensor according to the present invention, and the same parts as those in the above-mentioned drawings are designated by the same reference numerals. In the figure, on the upper surface of the central portion of the semiconductor base 1, inflow openings 2 ₁ , 2 ₂ and outflow openings 3 are formed along the direction of the arrow 11 through which gas flows by anisotropic etching.
_1, 3 ₂ communicating with two pairs of through holes 4 _1, 4 ₂ are formed, spatially separated from the semiconductor base 1 in Buritsuji form the top of the through holes 4 _1, 4 _2, As a result, the bridging portions 5 ₁ , 5 which are thermally insulated from the semiconductor base ₁ , respectively.
₂ is formed. _On the surface of each of these bridging portions 5 ₁ and 5 ₂ , although not shown, heater elements 7 ₁ and 7 ₂ each of which is sandwiched by a protective film and each of which is a thin film pattern, and upstream of each of which is a thin film pattern are formed on both ends thereof. A twin bridge structure having the temperature measuring resistance elements 8 ₁ and 8 ₂ and the downstream side temperature measuring resistance elements 9 ₁ and 9 ₂ arranged to have a first flow sensor unit 13 ₁ and a second flow sensor unit 13 ₂ respectively is provided. It is configured to have. The upstream temperature measuring resistance elements 8 ₁ and 8 ₂ formed on the bridging portions 5 ₁ and 5 ₂ are connected in series via the pattern connecting portion 8a, and are connected between the external circuit connecting electrode terminals 8b and 8c. The heater elements 7 ₁ and 7 ₂ are connected in series with the ambient temperature measuring resistance element 10 via the pattern connecting portions 7 a and 7 b, and the external circuit connecting electrode terminals 7 c and 7 are connected.
Similarly, the downstream temperature measuring resistance elements 9 ₁ and 9 ₂ are also connected in series via the pattern connecting portion 9a, and are connected between the external circuit connecting electrode terminals 9b and 9c.

According to such a configuration, the upstream temperature resistance elements 8 ₁ and 8 ₂ are connected in series to configure one set of upstream temperature resistance elements having a large resistance change, and the downstream temperature resistance elements 9 ₁ , 9 ₂ will be a set of downstream-side temperature measuring resistance element having a large series connected with the resistance value change is configured, the resistance value variation characteristic as shown in FIG. 2
II is about twice the resistance change characteristic I of the single bridge structure (see the fourth example). Therefore, the first flow sensor section
Assuming that each temperature difference between the flow rate F of 13 ₁ and the second flow sensor section 13 ₂ is ΔT ₁ and ΔT ₂ , the temperature change proportional to the flow rate F is integrated, and its sensitivity S ₂ is (ΔT ₁ + ΔT ₂ )
/ F and the single bridge structure (S ₁ = ΔT ₁ /
About twice the sensitivity of F) is obtained.

FIG. 3 is a plan view showing another embodiment of the flow sensor according to the present invention, and the same parts as those in the above-mentioned drawings are designated by the same reference numerals. In the figure, the difference from FIG. 1 is that the upper surface of the semiconductor base 1 has a third flow sensor section 13 having a configuration substantially similar to that of the first flow sensor section 13 ₁ and the second flow sensor section 13 _{2. 3} is provided and has a triple pledget structure. That is, in the figure, 2 ₃ is an inflow opening, 3 ₃ is an outflow opening, 4 ₃ is a through hole, 5 ₃ is a bridge portion, 7
₃ is a heater element, 8 ₃ is an upstream side temperature measuring resistance element, 9 ₃ is a downstream side temperature measuring resistance element, and the upstream side temperature measuring resistance elements 8 ₁ , 8 ₂ , 8 ₃ have pattern connecting portions 8a, 8d, respectively. Is connected in series between the electrode terminals 8b and 8c, and the heater elements 7 ₁ , 7 ₂ and 7 ₃ together with the ambient temperature measuring resistance element 10 are connected to the pattern connecting portion 7a,
It is connected in series between the electrode terminals 7c and 7d via 7b and 7e, and is further connected to the downstream temperature measuring resistance elements 9 ₁ , 9 ₂ and 9
Similarly, _{3 is} also connected in series between the electrode terminals 9b and 9c via the pattern connecting portions 9a and 9d.

Even in such a configuration, the resistance change is large due to the series connection of the upstream side temperature measuring resistance elements 8 ₁ , 8 ₂ and 8 _{3 and} the series connection of the downstream side temperature measuring resistance elements E ₁ , 9 ₂ and 9 _3. The upstream temperature-measuring resistance element and the downstream temperature-measuring resistance element are configured, and as shown in FIG. 2, the resistance value change characteristic III is about three times the resistance value change characteristic I of the single bridge structure. Become. Therefore, the first flow sensor unit 13 ₁ , the second flow sensor unit 13 ₂ ,
If the respective temperature differences with respect to the flow rate F of the third flow sensor unit 13 ₃ are ΔT ₁ , ΔT ₂ and ΔT ₃ , the temperature change proportional to the flow rate F is integrated and its sensitivity S ₃ is (ΔT ₁ + ΔT ₂
+ ΔT ₃ ) / F, which is about three times as sensitive as the single bridge structure.

Further, according to the above-mentioned configuration, a plurality of thin film bridging structures, the first resistance temperature detector, the heating element, and the second heating element are provided on the semiconductor base 1.
Due to the provision of the temperature-measuring-resistor, the conventional structure has the same resistance length as that of the present embodiment, but the shape of the semiconductor base becomes too large, which causes a problem in strength. Is eliminated, and the resistor area can be increased.

Although the micro-bridge structure has been described in the above-described embodiments, the present invention is not limited to this, and it is needless to say that the same effect can be obtained even when applied to a diaphragm structure.

〔The invention's effect〕

As described above, according to the present invention, by connecting the resistance temperature detectors in series, the resistance value change with respect to the flow rate of the gas increases, so the temperature change amount proportional to the flow rate is integrated and output, Therefore, the temperature change in the low flow rate region can be detected, and the sensitivity improving effect can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a flow sensor according to the present invention, FIG. 2 is a view showing the relationship between the cumulative number of flow sensor units and changes in resistance value, and FIG. 3 is a flow sensor according to the present invention. FIG. 4 is a plan view showing another embodiment, FIG. 4 is a perspective view showing a conventional flow sensor, FIGS. 5 (a) and 5 (b) are explanatory views showing the operation of the flow sensor shown in FIG. 4, and FIG. FIG. 7 is a characteristic diagram showing the relationship of the flow velocity with respect to the voltage output, and FIG. 1 ... Semiconductor base 2 ₁ , 2 ₂ , 2 ₃ , 3 ₁ , 3 ₂ , 3
₃ ... Aperture 4 ₁ , 4 ₂ , 4 ₃ ... Through hole 5 ₁ ,
5 ₂ , 5 ₃ ...... Bridge portion, 7 ₁ , 7 ₂ , 7, ₃ ... Heater element, 8 ₁ , 8 ₂ , 8 ₃ ...... Upstream temperature measuring resistance element, 9 ₁ , 9 ₂ , 9, ₃ ... ... Downstream temperature measuring resistance element, 10 ... Ambient temperature measuring resistance element, 13 ₁ ... 1st flow sensor section, 13 ₂ ... 2nd flow sensor section, 13 ₃
...... Third flow sensor unit.

Claims (1)

[Claims] 1. At least two sets of thin film bridging structures in which gas flows are provided on the upper surface of a base, and a first resistance temperature detector, a heating element, and a second thermometer are arranged from upstream to downstream of each bridging structure. 1. The flow sensor, wherein the resistance temperature detectors are sequentially arranged and the first resistance temperature detectors, the heating elements, and the second resistance temperature detectors are connected in series to each other.