JP2529895B2 - Flow sensor - Google Patents

Description

Description: [Industrial application] The present invention relates to a flow sensor for detecting an extremely minute flow velocity of gas.

[Prior Art] FIG. 2 is a perspective view showing a configuration of, for example, a microbridge flow sensor as a flow sensor. In the figure, as a base, for example, in the central portion of the semiconductor substrate 1, a through hole 4 for communicating the left and right openings 2 and 3 is formed by anisotropic etching.
Is formed, and a bridge portion 5 that is spatially separated from the semiconductor substrate 1 in a bridge shape and is thermally insulated from the semiconductor substrate 1 is formed above the through hole 4. A thin film heater element 6 and temperature measuring resistance elements 7 and 8 sandwiching the thin film heater element 6 are arranged on the surface of the bridging portion 5. Further, thin film ambient temperature measuring resistance elements 9 are formed at the corners of the semiconductor substrate 1.
Incidentally, 10 is a surface protective film made of a material having a low thermal conductivity.

FIGS. 3A and 3B are explanatory views showing the operation of the microbridge flow sensor shown in FIG. here,
The figure (a) shows the temperature distribution of each element, and the figure (b) has shown sectional drawing of the BB 'line of FIG.

In such a configuration, if the heater element 6 is controlled at a certain temperature th ₁ (for example, 63 ° C .: ambient temperature reference) higher than the ambient temperature, the temperatures t ₁ , t ₂ of the temperature measuring resistance elements 7, 8 (for example, As shown in FIG. 3, 35 ° C .: ambient temperature standard) is substantially symmetrical about the temperature th ₁ of the heater element 6. At this time, for example, when gas flows in the direction of arrow 11 shown in FIG. 2, the temperature measuring resistance element 7 is cooled upstream and the temperature is lowered by ΔT ₁ . On the other hand, in the temperature-measuring resistance element 8 on the downstream side, heat conduction from the heater element 6 is promoted by using the flow of gas as a medium, and the temperature rises by ΔT _2, resulting in a temperature difference. Therefore, the resistance temperature element 7,8
By incorporating in the Wheatstone bridge circuit,
The temperature difference can be converted into a voltage, and a voltage output according to the flow velocity can be obtained.

Thus, the conventional microbridge flow sensor
It has a thin film bridge structure with an extremely small heat capacity formed by thin film technology and anisotropic etching technology, and has excellent characteristics such as extremely fast response speed, high sensitivity, low power consumption, and good mass productivity. have.

[Problems to be Solved by the Invention] However, in the conventional microbridge flow sensor, the temperature measuring resistance element 7, the heater element 6, and the temperature measuring resistance element 8 are sequentially arranged from the upstream side through which the gas flows toward the downstream side. Therefore, although a predetermined function can be obtained, when a part of the heater element 6 deteriorates due to long-term use, there is a problem in that it cannot be detected. Further, in the microbridge flow sensor configured as described above, since a relatively high voltage, for example, about 2.2V is applied to the heater element 6 to measure the flow velocity, there is a high risk of explosion. It was impossible to measure the flow velocity with mixed gas.

[Means for Solving the Problems] In order to solve such problems, the present invention is configured such that a heater element includes a first heater element and a second heater element that are electrically independent of each other. A first slit is provided along the length direction of the first heating element between the resistance temperature detector and the first heating element, and the second heating element and the second heating element
The second slit is provided along the lengthwise direction of the second heating element between the resistance temperature detector and the second resistance element.

[Operation] In the flow sensor according to the present invention, the heater element is composed of the first heater element and the second heater element, so that the heater balance can be checked and the driving voltage of the heater can be reduced to about 1/2. It can be set as follows, and the influence of each heater element on each temperature measuring resistance element becomes almost equal.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an embodiment of a flow sensor according to the present invention. FIG. 1 (a) is a plan view of a main part seen from above, and FIG. 1 (b) is a sectional view taken along the line BB '. Therefore, the same or corresponding parts as those in the above-mentioned drawings are designated by the same reference numerals. In the figure, on the through-hole 4 formed in the semiconductor substrate 1, the membrane portion 5 ′ has slit-shaped openings 12 _{1 to} 12 ₄ communicating with the through-hole 4 in the central portion, and from the upstream side to the downstream side. the first membrane portion 5 ₁ towards, the second membrane unit 5, _second and third and the membrane portion 5 ₃ is formed, the first membrane portion 5 ₁ of the surface of the upstream side measuring of the first A temperature measuring resistance element 7 as a temperature resistance body is formed. Also in the second membrane portion 5 ₂ of the surface it is a second heater element 6 ₂ formed as a first heater element ₆₁ and the second heating element as a first heating element. The first heater element 6 ₁ and the second heater element 6 ₂ are formed to have substantially the same resistance value. Third downstream further
The membrane portion 5 ₃ of the surface temperature measuring resistance element 8 is formed as a second RTD. In addition, 5 ₄ , 5 ₅
Is a plurality of slit-shaped openings 12 ₅ and 12 communicating with the through hole 4.
₆ is a fourth membrane portion as a gas inlet and a fifth membrane portion as a gas outlet, each of which has ₆ formed.

In the flow sensor thus configured, the first
The same voltage of about 1.1V is applied between the terminals of the heater element 6 _{1 and} the terminals of the second heater element 6 ₂ respectively, and the temperature of each sensor element 7, 8 has a constant temperature difference from the ambient temperature. The flow velocity of the gas is measured by controlling so that

Here, when one resistance value of the heater element 6 in the conventional microbridge flow sensor is R ₁ and the other resistance value is R ₂ , the heat amount H ₁ on the resistance value R ₁ side and the heat amount on the resistance value R ₂ side H ₂ is as follows respectively.

On the other hand, assuming that the resistance value R ₁ and heat quantity H ₁ ′ of the first heater element 6 ₁ in this embodiment are the resistance value R ₂ and heat quantity H ₂ ′ of the second heater element 6 ₂ , Then, when the heater element deteriorates with time and the resistance value shifts to become R ₂ = αR ₁ , the equation (1) becomes as follows.

Further, the equation (2) is as follows.

The equation (3) is as follows.

Further, the equation (4) is as follows.

Becomes

Therefore, the difference in the amount of heat of the conventional microbridge flow sensor is as follows.

Further, the difference in the amount of heat of the micro diaphragm flow sensor in this embodiment is as follows.

Therefore, comparing the differences, Thus the deviation of the resistance value R _2, the deviation of the resistance value R ₂ by the heater element will be obtained largely as the difference between the heat of the heater element.

In addition, in the above-described embodiment, the case where the micro-diaphragm flow sensor is applied to the micro-diaphragm structure of the flow sensor as the flow sensor has been described. It goes without saying that the effect of can be obtained.

[Effects of the Invention] As described above, according to the present invention, the heating element includes the first heating element and the second heating element, and the first resistance temperature detector and the first heating element. A first slit is provided between the second heating element and the second resistance temperature detector along the length direction of the first heating element between the second heating element and the second heating element. Since the second slit is provided along the line, deterioration of the heating element and the resistance temperature detector can be confirmed by checking the balance between the two heating elements. In addition, since the driving voltage of the heating element can be set to 1/2, it is possible to detect the flow velocity in a gas mixture that has a risk of explosion. Furthermore, it is possible to obtain an extremely excellent effect such that it can be checked at the time of manufacture that the influence of each heating element on each resistance bulb is equal.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an embodiment of a flow sensor according to the present invention, FIG. 2 is a perspective view for explaining the configuration of a conventional microbridge flow sensor, and FIG. 3 is for explaining the operation of FIG. It is a figure. 1 ... semiconductor substrate, 2,3 ... opening, 4 ... through hole, 5 ',
5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ , 5 ₅ ...... Membrane part, 6 ₁ , 6 ₂ ...... Heater element, 7,8 ...... Temperature resistance element, 9 ...... Ambient temperature resistance element, 10 ... … Protective film, 12 _{1 to} 12 ₆ … Opening.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Gunji 1-12-2 Kawana, Fujisawa-shi, Kanagawa Yamatake Honeywell Co., Ltd. Fujisawa factory (72) Inventor Setsuo Kuboji 1-2-2 Kawana, Fujisawa-shi, Kanagawa No. Yamatake Honeywell Co., Ltd. Fujisawa Plant (72) Inventor Shigeru Aoshima 1-12-2 Kawana, Fujisawa City, Kanagawa Yamatake Honeywell Co., Ltd. Fujisawa Plant (56) Reference JP-A-2-64417 (JP, A) )

Claims (1)

(57) [Claims] 1. A thin film membrane structure which is held in the air and through which a gas flows is provided on an upper surface of a base, and a first resistance temperature detector, a heating element, and a second temperature measuring device are arranged from upstream to downstream of the thin film membrane structure.
The temperature-measuring resistive elements are sequentially arranged in the gas flow direction so that the resistive element patterns intersect with each other, and the heating elements are composed of a first heating element and a second heating element that are electrically independent of each other. Then, a first slit is provided between the first resistance temperature detector and the first heating element along the length direction of the first heating element, and the second heating element and the second heating element are provided. A flow sensor, wherein a second slit is provided between the resistance temperature detector and the second resistance element along the length direction of the second heating element.