JPH08122118A - Thermal type microflow-sensor - Google Patents

Abstract

PURPOSE: To provide a very small thermal type microflow-sensor with superior sensitivity and responsibility which can form a pin point type heating point in a heater line so that heat insulation from a substrate is easily achieved and heat loss is suppressed to the minimum. CONSTITUTION: A heater line 11 made of high temperature superconductive ceramics oxide formed on a substrate 10 is provided, and, relating to a heater line 11, a means such as a constriction part 13 for partially raising a resistance value so that a pin paint type heating point 12 is formed in the middle part is formed, and a pair of heater line pads 14 and 14 for connecting external power source are formed on both ends, and further, on the substrate part positioned at the lower part of the periphery of the such means as the constriction part 13, a cavity part 16 for heat insulation is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor,
In particular, the present invention relates to a thermal type micro flow sensor which can be installed in an extremely narrow place and can measure a flow rate in a limited part.

[0002]

2. Description of the Related Art The principle of measurement of a thermal type flow sensor will be described below based on the constant current method. That is, a heating wire (heater wire) heated to a predetermined temperature by passing a constant current is installed in a flow path such as a pipe through which a fluid passes. The heater wire is cooled by the fluid, and the resistance value of the heater wire changes (becomes smaller). The flow rate is measured by detecting this change with a voltmeter, for example.

When this type of sensor is installed in, for example, a gas meter or a gas leak detector, it must be extremely small. Therefore, in recent years, a thermal type micro flow sensor has been developed in which a fine heater wire is formed on a substrate such as silicon by using a semiconductor fine processing technique.

This thermal type micro flow sensor can be relatively easily manufactured by a mass production method, and is extremely small in size, consumes little power, and can be easily connected to other electric circuits such as a processing circuit. And so on.

[0005]

However, since the heater wire used in the conventional thermal type micro flow sensor is made of a metal material such as Pt having a large thermal conductivity and a small resistivity, the entire heater wire or its body is formed by applying electricity. Most of the heat is generated. As a result, heat loss is large, power is wasted, and sensor sensitivity and response speed are adversely affected. Further, there is a limit to miniaturization because it is difficult to perform thermal insulation between the heater wire and the substrate.

The present invention has been made in order to solve the above problems in the prior art, and an object of the present invention is to easily achieve thermal insulation between a substrate and minimize heat loss. As described above, it is possible to form a pinpoint heat generation point in the heater wire, and to provide a microminiature thermal microflow sensor having excellent sensor sensitivity and responsiveness.

[0007]

In order to achieve the above object, according to a main aspect of the present invention, a heater wire made of oxide high temperature superconducting ceramics is formed on a substrate by using a semiconductor fine processing technique. A means for partially increasing the resistance value so that a pinpoint heat generation point can be formed on the heater wire is provided at approximately the middle portion thereof, and a pair of external power supply connection heater wire pads is provided. There is provided a thermal type micro flow sensor characterized in that a cavity is formed in a substrate portion which is formed at both ends and is located under the periphery of the means.

The means for partially increasing the resistance value described in the above aspect is the formation of a constricted portion which partially thins the heater wire.

Further, the oxide high temperature superconducting ceramics described in the above embodiment is yttrium-based {ReBa ₂ Cu ₃ O
_7- δ (where Re is yttrium and rare earth elements)},
Bismuth-based {Bi ₂ Sr ₂ C _n-1 C _n O _{2n + 4} (n =
1, 2, 3)}, and thallium-based {Tl ₂ Ba ₂ Ca
_n-1 Cu _n O _{2n + 4} (n = 1,2,3)}, which is one ceramic selected from the group consisting of yttrium-based ceramics.
dBa ₂ Cu ₃ O _7- δ ceramics and YBa ₂ Cu ₃ O
There are _7- δ ceramics.

[0010]

[Function] Oxidation formed by interposing an electric insulating film on a substrate by using a semiconductor fine processing technique so that a means for partially increasing a resistance value such as a constricted portion is formed in a substantially middle portion. When a predetermined electric power is supplied to the heater wire made of the high temperature superconducting ceramics, a pinpoint heat generation point appears at the thinnest portion of the constricted portion. Since heat generation in other parts of the heater wire is suppressed, thermal insulation with the substrate is easily achieved and heat loss can be minimized.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in more detail with reference to the accompanying drawings.

1 (a) and 2 (a) are schematic perspective views showing two first and second embodiments of the present invention, respectively. FIG. 1 (b) and FIG. b) is a cross-sectional view thereof.

As is apparent from these figures, the substrate 10
GdBa ₂ Cu, for example, with an electric insulation film 10a interposed therebetween.
The heater wire 11 made of oxide high temperature superconducting ceramics such as ₃ O _7- δ ceramics is formed by using the semiconductor fine processing technique.

A pair of heater wire pads 1 for connecting to an external power source (not shown) at both ends of the heater wire 11.
4 and 14 are formed respectively, and one constricted portion 13 is formed in the substantially middle portion so that the resistance value of the portion increases. Further, the substrate portion located below the constricted portion 13 is subjected to anisotropic etching (FIG. 1) or isotropic etching (FIG. 2) through the etching hole 15 to improve the insulating property. A hollow portion 16 for forming is formed.

Although not shown, a thin film portion or a blind portion may be formed in place of the constricted portion 13, and this portion may have a composition having a large resistance value or may be replaced with a material having a large resistance value. Good.

When a predetermined electric power is supplied from the external power source to the heater wire 11 configured as described above, the thinnest portion (point) 12 of the constricted portion 13 having the maximum resistance value in the heater wire 11 is formed. The Joule heat causes pinpoint heat generation.

This heat generation mechanism is considered as follows. 1. First, when a predetermined voltage is applied to the heater wire 11,
The entire heater wire generates heat due to Joule heat. Then, 2. Due to the non-uniform microstructure of the heater wire 11, the temperature of the heating point 12 having the maximum resistance value of the heater wire 11 is 400 ° C.
If it becomes above, the resistance of the exothermic point 12 will rapidly increase with the generation of oxygen deficiency. And 3. As the resistance rapidly increases, the voltage applied to the heat generating point 12 also rapidly increases, and the temperature of the heat generating point 12 further rises. (Temperatures of other portions decrease as the applied voltage decreases.) FIG. 3 is a graph showing the temperature dependence of the resistivity with respect to the heating point 12 of the heater wire 11. According to this graph, 40
At the temperature of 0 ° C. or higher, the exothermic point 12 shows a rapid increase in resistivity accompanying the generation of oxygen vacancies. As described above, it is also a characteristic of the oxide high temperature superconducting ceramic wire rod such as GdBa ₂ Cu ₃ O _7- δ that the increase in resistivity with respect to temperature is extremely large as compared with the metal such as Pt. The increase in resistivity reaches its peak at about 900 ° C. Further, it is expected from FIG. 3 that the resistivity of the heat generating point 12 is considerably higher than that of other portions.

As is apparent from FIG. 3, 600 to 900
Temperature coefficient of exothermic point 12 at ℃ is 2 × 10 ^{-2 on} average
It can be seen that it is / ° C. This value is the conventional Pt or A
It is about 10 times larger than the value of a heater wire made of metal such as u. From this, the heating temperature of the heater wire 11 is set to 600 to 900.
By using as a flow sensor in a state of being set in the range of ° C, the sensor sensitivity can be increased about 10 times as compared with the conventional flow sensor.

Further, since the heat generation point 12 is a pinpoint heat generation point, not only the heat loss of the heater wire 11 itself is minimized, but also the heat insulation between the heater wire 11 and the substrate 10 is achieved. It will be easier. This makes it possible to obtain a thermal microflow sensor that consumes very little power and has excellent sensor sensitivity and responsiveness.

Further, since the oxide high temperature superconducting ceramics has a large resistivity and a small thermal conductivity, the conventional Pt and A
The measurement range can be remarkably widened as compared with a sensor in which u is a heater wire.

The above-mentioned characteristics are obtained by yttrium-based {R
eBa ₂ Cu ₃ O _7- δ (where Re is yttrium and rare earth elements)}, bismuth-based {Bi ₂ Sr ₂ Can _n-1 C
_{u n O 2n + 4 (n} = 1,2,3)}, thallium system {Tl ₂
It is presumed that it is a characteristic common to all high-temperature superconducting ceramics such as Ba ₂ C an _-1 Cu _n O _{2n + 4} (n = 1, 2, 3)}, and GdBa ₂ Cu ₃ O _7- δ and YBa ₂ C
It has been confirmed by experiments that u ₃ O _7- δ and bismuth-based ceramics have this characteristic.

In addition, it is considered that a local heat generation point occurs in metal and ceramics having a positive resistance characteristic thermistor (PTCR) effect.

The above description is merely illustrative of the preferred embodiments of the present invention and the scope of the present invention is not limited thereto.

[0024]

According to the present invention, a microminiature heater wire made of oxide high-temperature superconducting ceramics having a portion having a large resistance value such as a constricted portion is formed on a substrate by using the semiconductor fine processing technique. The heater wire can generate heat in a pinpoint manner at the thinnest portion such as a constricted portion. Therefore,
Thermal insulation between the heater wire and the substrate can be easily achieved and heat loss can be minimized. As a result, the thermal microflow sensor of the present invention consumes significantly less power and can be installed in an extremely narrow space.

Further, since the heater wire made of oxide high temperature superconducting ceramics has a relatively large resistivity and a small thermal conductivity, the flow rate can be measured in a wide measuring range.

Further, since this heater wire has an extremely large temperature coefficient of resistivity, it is possible to output a minute temperature change as a large resistance change. This and good thermal insulation can significantly improve sensor sensitivity and responsiveness.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, (a) is a schematic perspective view, and (b) is a sectional view.

FIG. 2 shows a second embodiment of the present invention, (a) is a schematic perspective view and (b) is a sectional view.

FIG. 3 is a graph showing the relationship between the temperature and the resistivity of the heating point of the heater wire used in each example of the present invention.

[Explanation of symbols]

 10 Substrate 10a Electric Insulating Film 10b Etching Mask 11 Heater Wire 12 Heat Generation Point 13 Constriction Part 14 Heater Line Pad 15 Etching Hole 16 Cavity Part

Claims (4)

[Claims] 1. A heater wire made of oxide high temperature superconducting ceramics, which is formed on a substrate by using a semiconductor fine processing technique, and has a resistance value so that a pinpoint heating point can be formed in the heater wire. Means for partially enlarging the area, and a pair of heater wire pads for connecting an external power source are formed at both ends of the area. Further, the board portion located under the means is thermally insulated. A thermal microflow sensor having a cavity for use therein. 2. The thermal microflow sensor according to claim 1, wherein the means for partially increasing the resistance value is the formation of a constricted portion. 3. The oxide high temperature superconducting ceramics,
Yttrium-based {ReBa ₂ Cu ₃ O _7- δ (where Re
Is yttrium and rare earth elements)}, bismuth-based {Bi
₂ Sr ₂ C _n-1 C _n O _{2n + 4} (n = 1,2,3)},
And thallium-based {Tl ₂ Ba ₂ Can _n-1 Cu _n O _{2n + 4}
The thermal microflow sensor according to claim 1, wherein the thermal microflow sensor is one ceramic selected from the group consisting of (n = 1, 2, 3)}. 4. The oxide high temperature superconducting ceramics,
The thermal microflow sensor according to claim 1, which is a GdBa ₂ Cu ₃ O _7- δ ceramics.