JPH077008B2 - Flow velocity sensor - Google Patents

Description

The present invention relates to a flow velocity sensor for detecting a flow rate of a fluid, and more particularly to a flow velocity sensor having a micro diaphragm structure using a silicon substrate or the like as a base.

[Conventional technology]

Conventionally, as a flow velocity sensor of this type, for example, Japanese Patent Laid-Open No. 60-
There is one disclosed in Japanese Patent No. 142268, the outline of which is No. 8
This will be described with reference to FIGS. In FIG. 8, 1 is a semiconductor base made of silicon, 2 and 3 are openings for etching, 4 are through holes, 5 is a thin film supporting portion, 6 is its root,
Reference numeral 7 is a thin film heater element, 8 and 9 are thin film temperature sensitive resistance elements, and 10 is a thin film ambient temperature measuring resistance element formed on the semiconductor base 1. That is, a through hole 4 that communicates the openings 2 and 3 on both sides is formed on the semiconductor base 1 by anisotropic etching, and the upper portion of the through hole 4 is spatially isolated from the semiconductor base 1. As a result, the thin film support portion 5 which is thermally insulated from the semiconductor base 1 is formed. On the surface of the thin film supporting portion 5, a downstream law detecting portion 11 as a sensor body is formed by arranging a heater element 7 and temperature sensitive resistance elements 8 and 9 sandwiching the heater element 7 by a normal thin film forming technique. Has been done. Further, an ambient temperature measuring resistance element 10 is formed at a corner of the semiconductor base 1. Reference numeral 17 is a slit-like opening formed in the central portion of each of the openings 2 and 3 on the semiconductor base 1.
Semiconductor (silicon) base 1 surrounded by 2, 3 and 17
By anisotropically etching the lower side with a solution such as KOH through these openings, a through hole 4 having an inverted trapezoidal cross section, that is, a void portion 4 is formed, and at the same time, in the void portion 4. Therefore, the thin film support portion 5 in which the heater element and the temperature-sensitive resistance elements 8 and 9 are thermally insulated and supported is formed from the semiconductor base 1.

Here, when the fluid 21 flows in the direction of the arrow shown in FIG. 8 under the control of the heater element 7 at a certain higher temperature than the ambient temperature, the temperature-sensitive resistance element 8 on the upstream side.
Is cooled and the temperature is lowered, whereas the temperature-sensitive resistance element 9 on the downstream side uses the flow of fluid as a medium.
The heat conduction from the is promoted and the temperature rises, resulting in a temperature difference. For this reason, by incorporating the temperature-sensitive resistance elements 8 and 9 into a Wheat East Sumbredge circuit (not shown) and converting the temperature difference into a voltage, a voltage output according to the flow velocity of the fluid can be obtained. The flow velocity of the fluid can be detected.

By the way, since the thin film support portion 5 of this sensor element is very thin and weak, it is not possible to use a general dicing saw when cutting the chip in the manufacturing process. Therefore, the element cutting is performed by braking, but it is necessary to etch the cutting street 18 shown in FIG. 9 in order to facilitate the braking. Further, in order to keep the shape of the chip uniform, it is necessary to etch the streets 18 in the anisotropic etching which is the final step of manufacturing the chip.

Due to the above restrictions, the sensor element is designed as shown in FIG. 9 by using a silicon wafer having the (001) plane as the surface, the cutting streets 18 arranged parallel to the [110] direction, and the opening 2, Align the end of 3 with the [110] direction and set the thin film support 5
End is not parallel to [110] direction (eg [100] direction)
It was necessary to design like. As a result, the flow velocity sensor had to be used with its corners facing the flow direction of the fluid 21, as shown in FIG.

[Problems to be Solved by the Invention]

As described above, since the conventional flow velocity sensor uses its corners in the flow direction of the fluid, when measuring a fluid with a particularly high flow velocity, as shown in FIG. The turbulence 22 reaches the flow velocity detection unit 11. Therefore, the sensor output becomes unstable due to the vortex generated at the corner, and the measurement reproducibility is deteriorated.

Further, the position of the root 6 of the thin film supporting portion 5 is 6a, 6b in FIG.
And 6c, the sensitivity of the sensor varied. That is, the etching stop position of the void 4 is varied due to the temperature, concentration, etc. of the etching liquid. As a result, when the root of the thin film support 5 is as shown by 6b in FIG. The thermal insulation of each element 7,8,9 on the support part 5 to the semiconductor base 1 is improved,
On the other hand, in the case of 6c in FIG. 9, the thermal insulation is lowered and the sensitivity is lowered, while the sensitivity is increased.

The present invention has been made in view of the above points, and an object thereof is to provide a flow velocity sensor that stabilizes the sensor output and improves the reproducibility of the characteristics between sensor elements.

[Means for Solving the Problems]

In order to achieve the object described above, the flow velocity sensor of the present invention is provided with a flow velocity detecting portion, which is composed of a thin film heater element and independent thin film temperature sensitive resistance elements on both sides of the heater element, on the base. The lower part of the section is removed by anisotropic etching with a solution through an etching opening provided on the surface of the base, and has a diaphragm structure in which the flow velocity detecting section is supported separately from the base. The opening for etching is a square having a slit-shaped opening extending in the [100] direction as a unit element on the base surface of the flow velocity detection unit, and a plurality of these slit-shaped openings being diagonal lines. The etching areas are arranged so that they overlap.

[Action]

In the present invention, when measuring a fluid, the straight end portion of the sensor can be oriented with respect to the flow direction without directing the corner portion of the sensor causing the vortex generation in the flow direction. The turbulence including the vortex generated at does not reach the detection part of the sensor, the sensor output becomes unstable, and the reproducibility of measurement is improved.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments showing the drawings.

FIG. 1 is a schematic perspective view showing an embodiment of the flow velocity sensor according to the present invention, and FIG. 2 is a detailed plan view of the flow velocity detecting portion of FIG. As shown in FIGS. 1 and 2, the flow velocity sensor of this embodiment has a thin film heater element 7 and independent thin film temperature sensitive resistance elements 8 and 9 on both sides of the heater element 7, as shown in FIGS. Is provided on the surface of the semiconductor base 1. Etching openings 12 are provided on the surface of the semiconductor base 1 for removing the semiconductor base below the flow speed detector 11 by anisotropic etching using a solution. Are formed. As shown in FIG. 3, the opening 12 has a plurality of slit-shaped openings 12a extending in the [100] direction with respect to the semiconductor base 1 having the (001) surface as a unit element. Each slit-shaped opening 1 by combining the openings 12a
A square region 14 having a diagonal line 2a, that is, an etching region 14 removed by anisotropic etching of one slit-shaped opening 12a is arranged so as to partially overlap. And, each root 11a of the flow velocity detecting section 11 is [110] of the semiconductor base 1.
The end 12b of the opening 12 is provided so as to be oriented.

Then, when anisotropic etching is performed on the sensor element having such a configuration by a method similar to the conventional method, the lower side of the flow velocity detection unit 11 is
A large number of slit-shaped openings 12a provided on the surface of the semiconductor base 1.
Since it is removed by anisotropic etching through the opening 12 made of, it is possible to form a flow velocity sensor having the diaphragm portion 13 in which the flow velocity detecting portion 11 is supported separately from the semiconductor base 1. At this time, the cutting street portion 18 (see FIG. 9) is formed by the same process as the conventional one, and the flow velocity detecting portion 11 of the element is used.
Is parallel to the straight end. In addition,
In the drawings, the same reference numerals indicate the same or corresponding parts.

As described above, according to the flow velocity sensor of the above-described embodiment, the flow velocity detection unit 11 including the pair of temperature sensitive resistance elements 8 and 9 and the heater element 7 placed between them is used as shown in FIG.
Since they are arranged so as to face each other in the flow direction of 21, the flow velocity can be detected by directing the straight end 11a of the flow velocity detecting unit 11 in the flow direction 21. As shown in FIG. 2, the flow velocity detecting section 11 is constructed so as to have a line symmetrical structure with the center line 7a of the heater element 7 as an axis. That is, the etching opening 12 is 12 at the center line 7a of the heater element 7.
When the etching opening 12, the heater element 7, and the temperature-sensitive resistance elements 8 and 9 are arranged in line symmetrical positions about the center line 7a as an axis, the heater has a shape as shown in FIG. The heat from the element 7 is equally transmitted to the temperature sensitive resistance elements 8 and 9 on both sides. Therefore, in the flow velocity sensor of this embodiment, since the difference between the upstream and downstream temperature-sensitive resistance elements 8 and 9 is used as the output, thermal imbalance other than the flow velocity is canceled by the above configuration. It becomes possible to accurately output only the signal.

Furthermore, turbulence due to eddies generated from the corners of the flow velocity sensor
As shown in FIG. 4, in the flow velocity sensor of the present embodiment, the turbulence 22 does not reach the flow velocity detecting section 11, so that the influence of can be eliminated. That is, FIG. 4 (b)
FIG. 4B is a sectional view taken along the line II ′ of FIG. The flow of the fluid 21 can be regarded as a substantially two-dimensional flow on the flow velocity detection unit 11, and a stable flow can be formed on the flow velocity detection unit 11 as shown in FIG. As a result, the sensor output was stable and the measurement reproducibility could be improved. Incidentally, since the turbulence from the corner portion spreads at an angle of 15 to 20 ° in the case of turbulent flow, it is necessary to arrange the flow velocity detection section 11 at a place where the turbulence does not reach.

Also, as shown in FIG. 4 (b), the front edge portion 15 of the sensor element dug by anisotropic etching is inclined at an angle θ of 54.7 °, and the fluid creates a vortex. It is becoming less likely to occur.

Further, in FIG. 2, the reason why a large number of thin slit-shaped openings 12a are combined as the etching openings 12 is as follows.
This is to ensure that the lower portion of the flow velocity detecting portion 11 can be etched without omission as shown in FIG. 3 and that the etching can be performed quickly and uniformly. This will be further described with reference to FIGS. 6 and 7.

Both FIG. 6 and FIG. 7 have an opening that allows the lower part of the region 14 to be etched. However, in order to etch the entire region 14, it is necessary to etch downward only as shown in the sectional view of FIG. 7B, and FIG. You can see that it takes twice as long. For example, when the area 14 is a square having a side of 0.5 mm, the depth is about 0.18 mm in the case of FIG. 6 and 0.35 mm in the case of FIG. At this time, if a silicon wafer having a thickness of 0.63 mm is used and the same amount is etched from the back surface, the remaining amount is 0.27 mm in the case of FIG. 6 and it penetrates in the case of FIG. Not available.

Also, a thin slit-shaped opening is used as the etching opening 12.
It was confirmed by an experiment that the anisotropic etching progresses uniformly over the region 14 by arranging a large number of 12a in the entire area of the flow velocity detecting unit 11. At this time, since the root 11a of the flow velocity detecting unit 11 parallel to the [110] direction coincides with the (111) plane left by anisotropic etching, the etching does not proceed further. Thus, the root 11a of the flow velocity detector 11 is determined without being influenced by the process parameter, that is, the etching stops at the (111) plane (to be exact, extremely slow) due to the characteristic of anisotropic etching. This is determined regardless of the process conditions, and it is possible to suppress variations in characteristics among the sensor elements. In FIG. 6, reference numeral 16 denotes an inverted trapezoidal space between the semiconductor base 1 formed by anisotropic etching and the diaphragm portion 13 supporting the flow velocity detecting portion 11, and in FIG. 12 ₀ slit-like opening for forming the etched region 14, 16a is a gap portion similar to the gap portion 16.

〔The invention's effect〕

As described above, according to the present invention, a part of the pedestal is removed by anisotropic etching, and a flow velocity detection part including a thin film heater element and a pair of thin film temperature sensitive resistance elements is placed on the diaphragm left on the removed part. In the flow velocity sensor equipped with
An opening for etching is formed by combining a number of slit-like openings with a thin slit-like opening extending in the [100] direction as a unit element on the base surface of the flow velocity detecting unit, and each slit-like opening. Since the etching areas created by the sensors are arranged so as to overlap with each other, the straight end portion of the sensor can be directed to the flow direction of the fluid. As a result, the turbulence including the vortex generated at the corner does not reach the flow velocity detection unit as in the conventional case, and the sensor output becomes stable and the measurement reproducibility is improved.

Further, according to another invention of the present invention, the end of each slit-like opening in the etching opening is aligned with the line in the [110] direction of the base, so that the root of the flow velocity detection part Therefore, there is an effect that the sensor element can be formed with good reproducibility.

Further, according to another invention of the present invention, in the above-mentioned sensor, the flow velocity detecting portion has a line-symmetrical structure with the central axis of the heater element as an axis, so that an adverse effect on output due to thermal imbalance other than the flow velocity is improved. There is.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a flow velocity sensor according to an embodiment of the present invention, FIG. 2 is a detailed plan view of the flow velocity detecting portion of FIG. 1, and FIG. 3 is a diagram for explaining an etching method in the above embodiment. 4 (a) and 4 (b) are conceptual views for explaining the function and effect of the above-described embodiment and a sectional view taken along the line II 'of FIG. 4 (a), and FIG. 6 (a) and 6 (b) are partial plan views for explaining the above-mentioned embodiment and a sectional view taken along the line II-II 'of FIG. 6 (a).
6 (a) and (b) are partial plan views of an etching process for the purpose of comparison with FIG. 6 and III-I in FIG. 6 (a).
II 'sectional view, FIG. 8 is a schematic perspective view of a flow velocity sensor according to a conventional example, and FIG. 9 is an explanatory view of an etching process in the manufacturing process of FIG. DESCRIPTION OF SYMBOLS 1 ... Semiconductor base, 7 ... Thin film heater element, 8, 9 ... Thin film temperature sensing resistance element, 10 ... Thin film surrounding temperature measuring resistance element, 11 ... Flow velocity detecting part, 12 ... Etching opening, 12a ...
Slot-like openings, 13 ... Diaphragm portion, 14 ... Etching area, 16 ... Void portion.

Claims (3)

[Claims] 1. A flow velocity detecting section comprising a thin film heater element and independent thin film temperature sensitive resistance elements on both sides of the heater element is provided on a base, and the lower side of the flow velocity detecting section is on the surface of the base. The etching structure has a diaphragm structure which is removed by anisotropic etching using a solution through an etching opening provided, and supports the flow velocity detecting section separately from the base, and the etching opening section detects the flow velocity. A thin slit-shaped opening extending in the [100] direction is used as a unit element on the surface of the base of the section, and a large number of these are combined so that the square etching areas with diagonal diagonal lines overlap each other. Flow rate sensor characterized by. 2. The flow velocity sensor according to claim 1, wherein the etching openings are formed by aligning the ends of each slit-shaped opening with a line in the [110] direction of the base. 3. The flow velocity sensor according to claim 2, wherein the structure of the flow velocity detecting portion is configured to be line-symmetrical with the center line of the heater element as an axis.