JP3044582B2 - Gas rate sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas rate sensor for detecting an angular velocity based on a deflection of a gas flow inside the sensor when the angular velocity acts on a sensor body.

[0002]

2. Description of the Related Art In a gas rate sensor of this type,
In order to be able to accurately detect the angular velocity, it is necessary to eject gas straight from the nozzle hole into the gas passage as a laminar flow toward the heat wire pair provided in the gas passage so that the angular velocity can be accurately detected. In the gas rate sensor (see Japanese Patent Publication No. 64-4623), helium (H) having a high kinematic viscosity is used so that a stable laminar flow can be obtained in a relatively large gas passage.
e) gas is used.

In general, a heat transfer coefficient is high in He gas or the like having a high kinematic viscosity, but in the past, since a bare wire such as tungsten is used as a heat wire as it is, a gas having a large heat transfer coefficient is used. The required rate sensitivity, that is, the degree of change of each resistance value of the heat wire pair according to the deflection of the gas flow is obtained.

Recently, a semiconductor substrate is etched by micromachining using an IC manufacturing technique to form a nozzle hole and a gas passage, and a heat wire is formed on a surface of a bridge portion formed in the gas passage. A semiconductor gas rate sensor has been developed in which a pair of heat wires is formed in a gas passage by depositing platinum or the like, which is a material for the above, and etching the same, for example (see JP-A-3-29858).

However, in such a semiconductor gas rate sensor, a portion of the heat wire, which is patterned in a planar manner, is usually covered and protected by a protective film such as SiN. If a gas having a large heat transfer coefficient is used, the surface temperature of the heated heat wire is too low, so that it is difficult to obtain a required rate sensitivity, and gas convection generated in the heat wire portion (see FIG. 4) The surface temperature of the heat wire is also greatly reduced by the flow of gas indicated by the dotted line), resulting in a corresponding detection error and a decrease in the angular velocity detection accuracy.

[0006]

The problem to be solved is that when a gas having a large heat transfer coefficient such as Ne is used in a semiconductor gas rate sensor, it becomes difficult to obtain a required rate sensitivity, and an angular velocity cannot be obtained. That is, the detection accuracy is reduced.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a semiconductor gas rate sensor uses a gas having a small heat transfer coefficient to obtain a required rate sensitivity and is affected by gas convection generated in a heat wire portion. To obtain a stable laminar flow while receiving low kinematic viscosity,
The objective of accurately detecting angular velocity has been achieved.

[0008]

According to the present invention, since the heat transfer coefficient of the gas in the gas flow jetted toward the heat wire pair is small,
The surface temperature of the heat wire does not become too low, and the degree of decrease in the surface temperature of the heat wire due to convection of the gas generated in the heat wire portion does not matter, and even if a gas having a low kinematic viscosity is used, In a semiconductor gas rate sensor, the size of the gas passage is very small, and the gas flow velocity is small, so that a stable laminar flow can be obtained.

[0009]

1 to 3 show one structural example of a sensor body in a semiconductor gas rate sensor.

Here, a lower semiconductor substrate 1 and an upper semiconductor substrate 2 in which a half hole 31 forming a nozzle hole 3 and a half groove 41 forming a gas passage 4 connected thereto are formed in a semiconductor substrate by etching, The nozzle holes 3 and the gas passages 4 are formed by overlapping the half holes 31 and the half grooves 41 so as to abut each other and bonding them together.

The lower semiconductor substrate 1 is etched to form a bridge portion 6 extending over the gas passage 4, and a pair of heat wires 51 and 52 are formed on the upper surface of the bridge portion 6 by patterning. Has an electrode portion 7 formed therein.

Each of the patterned heat wires 5
1, 52 are made of Si because of their strength retention, protection during the manufacturing process, prevention of deterioration at high temperatures and prevention of gas adsorption.
It is covered with a protective film such as N.

The sensor body thus constructed is installed in a gas-sealed housing and a micropump (not shown) provided on the sensor body side is driven, whereby the nozzle of the sensor body is driven. The gas is ejected from the hole 3 into the gas passage 4 as a laminar flow, and the direction and the degree of deflection of the gas flow when the angular velocity acts on the sensor main body are detected by the output difference between the pair of heat wires 51 and 52. You.

According to the present invention, such a semiconductor gas rate sensor is characterized in that a gas having a small heat transfer coefficient, such as nitrogen (N ₂ ) or argon (Ar), is used as a used gas.

Generally, the efficiency of heat release from a heated heat wire into a gas is determined by the heat transfer coefficient of the gas and the surface temperature of the heat wire.

Therefore, when the heat wire is covered with the protective film and the surface temperature of the heat wire is high, if a gas having a high heat transfer coefficient such as the conventional He is used, the surface temperature becomes too low and the heat wire becomes necessary. In addition, it becomes difficult to obtain a high sensitivity, and the convection of the gas generated in the heat wire portion significantly lowers the surface temperature, resulting in a detection error, which deteriorates the angular velocity detection accuracy.

FIG. 4 shows the flow of gas in the gas passage 4, and convection as shown by a dotted line in the figure occurs at the heat wire 5.

However, as in the case of the present invention, N ₂ , A
When a gas having a small heat transfer coefficient such as r is used, the surface temperature does not decrease too much, a sufficiently required rate sensitivity is obtained, and the surface temperature decreases due to convection generated in the heat wire portion. Is no longer a problem and the detection error is eliminated.

Incidentally, the heat transfer coefficient of He gas is about 0.142 [W / m · K], the heat transfer coefficient of N ₂ gas is about 0.024 [W / m · K], A
The heat transfer coefficient of the r gas is about 0.016 [W / m · K].

FIG. 5 shows the change in the resistance value of the heat wire when the N ₂ gas and the He gas are blown onto the heat wire heated to 200 ° C. while changing the flow rate of each.

In the case of N ₂ gas, approximately 10 to 100 cc
Although a large rate sensitivity can be obtained in a wide flow rate range of up to / cc / min, He gas shows only a small sensitivity in a low flow rate range of about 5 cc / min or less. That is, in a semiconductor gas rate sensor, N ₂ gas having a smaller heat transfer coefficient is more advantageous in terms of rate sensitivity.

FIG. 6 shows that N ₂ gas is supplied at a flow rate of 30 cc / m ₂ .
FIG. 7 shows the characteristics of the change amount of the resistance value of the heat wire with respect to the change of the flow velocity when flowing through the gas passage in the semiconductor gas rate sensor. Are shown respectively.

[0023] In the case of He gas flow velocity distribution only not obtained a small change in the resistance value of the heat wires even by supplying a large flow rate is not accurately obtained, with respect to the change in flow rate in the case of N ₂ gas Shows a large resistance value change of the heat wire,
The change in the resistance of the heat wire relative to the resistance R (Ｒ
Rmax- △ Rmin) becomes almost 20%,
An accurate flow velocity distribution that is consistent with the theory is obtained.

Since a gas rate sensor measures the amount of change in the gas flow velocity distribution in the horizontal direction, it is necessary to obtain an accurate gas flow velocity distribution in order to accurately detect the angular velocity acting on the sensor body. Is important, and this also shows the advantage of N ₂ gas having a small heat transfer coefficient.

Further, the lighter the gas, the greater the heat transfer coefficient.
Since the gas such as N ₂ having a small heat transfer coefficient has a large molecular weight and is heavy, convection generated in a heat wire portion is reduced,
The extent to which the surface temperature of the heat wire is reduced by convection is of little concern.

In addition, a gas having a small heat transfer coefficient such as N ₂ or Ar has a low kinematic viscosity, and a conventional gas rate sensor has a large gas passage and a large gas flow velocity, so that a stable laminar flow is obtained. However, in a semiconductor gas rate sensor, a sufficiently stable laminar flow can be obtained even when the kinematic viscosity of the gas used is low because the gas passage is very small and the flow velocity of the gas is small.

As shown in FIG. 4, when the flow velocity of the gas in the gas passage 4 is v, the kinematic viscosity coefficient of the gas is ν, and the dimension of the gas passage 4 is 1, the Reynolds number Re = v · l / ν is A stable laminar flow is obtained at a value of 1000 or less.

As the kinematic viscosity coefficient ν of N ₂ gas, ν = 1.
It is about 4 × 10 ⁻⁵ m ² / s, and the kinematic viscosity coefficient ν of He gas is about ν = 1.1 × 10 ⁻⁴ m ² / s.

For example, in the conventional gas rate sensor, when l = 1 mm and v = 100 m / sec, the Reynolds number Re becomes Re = 10 ^-1 / ν. In this case, if He gas is used, the Reynolds number Re Becomes 1000 or less and becomes a laminar flow. If the gas is N ₂ gas, the Reynolds number R
When e becomes 1000 or more, turbulence occurs.

For example, in a semiconductor gas rate sensor, when l = 100 μm and v = 10 m / sec,
The Reynolds number Re becomes Re = 10 ⁻³ / ν , and in this case, the laminar flow occurs when the Reynolds number Re becomes 1000 or less in any of the He gas and the N ₂ gas.

The use of a gas having a small heat transfer coefficient is widely applied not only to a semiconductor gas rate sensor but also to general sensors for detecting a change in gas flow rate or flow rate.

[0032]

As described above, in the semiconductor gas rate sensor according to the present invention, nitrogen or argon having a small heat transfer coefficient is used.
By using the gas according to (1), the required rate sensitivity can be obtained without excessively lowering the surface temperature of the heat wire. However, there is an advantage that a stable laminar flow can be obtained even though the angular velocity is low, and the angular velocity can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a perspective view of a sensor main body in a semiconductor gas rate sensor.

FIG. 2 is a plan view of a lower semiconductor substrate of a sensor main body in the semiconductor gas rate sensor.

FIG. 3 is a sectional view taken along line AA of FIG.

FIG. 4 is a diagram showing a gas flow in a gas passage.

FIG. 5 is a characteristic diagram of a heat wire resistance value with respect to a change in gas flow rate.

FIG. 6 is a characteristic diagram showing a change amount of a heat wire resistance with respect to a change in a flow rate of N ₂ gas.

FIG. 7 is a characteristic diagram illustrating a change amount of a heat wire resistance with respect to a change in a flow rate of He gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower semiconductor substrate 2 Upper semiconductor substrate 3 Nozzle hole 4 Gas passage 5 Heat wire 51 Heat wire 52 Heat wire

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-65165 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01P 9/00 G01C 19/00

Claims (1)

(57) [Claims] 1. A pair of heat-sensitive resistance elements provided in a gas passage based on deflection of the gas flow generated when an angular velocity acts on the gas flow ejected from the nozzle hole into the gas passage. In a gas rate sensor for detecting an angular velocity from an output difference generated in a heat wire, a gas passage is formed by micromachining by etching a semiconductor substrate, and a gas of nitrogen or argon is used. Gas rate sensor.