JP3269877B2 - 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 minute gas rate sensor for detecting an angular velocity from a deviation of a gas flow impinging on a pair of detectors. It relates to a gas rate sensor that can be obtained.

[0002]

2. Description of the Related Art Conventionally, as described in, for example, JP-A-3-29858, a gas rate sensor (gas type angular velocity detector) is provided with a gas passage or the like in each of an upper semiconductor substrate and a lower semiconductor substrate. Grooves were formed by etching or the like, and these were combined and bonded. Prior to the etching, a film such as silicon nitride (SiN) or Pt for forming a heat wire bridge and a pair of detecting portions provided thereon is formed on the lower semiconductor substrate by a sputtering method or the like. Was. Conventionally, the Pt line for the detection unit is generally formed in a straight line.

[0003]

Generally, it is effective to increase the gas flow rate to improve the sensitivity of the gas rate sensor. However, if the gas flow rate is increased beyond a certain limit, the offset voltage value starts to fluctuate greatly, so that the function of the sensor cannot be performed. Therefore, it has been extremely difficult to improve the sensitivity by increasing the gas flow rate.

FIG. 10 is a circuit diagram illustrating the offset current. In the figure, when a bridge is formed in which the resistances of the detection units S1 and S2 are equal and the resistances of the comparison resistors R1 and R2 are also equal, the input rotation speed is zero and the inside of the sensor chip is precisely formed. If so, the flow velocity of the gas impinging on the pair of detectors S1, S2 should be equal, so that the voltage V1 at the terminal T1 of the bridge and the voltage V2 at the terminal T2 should be equal. Here, V1-V2 is called an offset voltage. This offset voltage is applied to chip 1
The gas flow is deflected because the inside is not precisely formed, the detection units S1 and S2 vibrate, or the detection unit S1
If there is a difference between the sensitivities of S2 and S2, they will vary rather than become zero. It should be noted that the offset voltage does not need to be always 0 because the offset voltage can be corrected as long as the value is stable without fluctuation.

As for the Pt line of the detecting portion, the sensitivity of the conventional linear line is insufficient and the quality (resistance value) during mass production varies. A technique for forming a platinum thin film temperature sensor in a comb shape is disclosed in Japanese Patent Laid-Open No. 63-26370.
As described in Japanese Patent Application Publication No. 2 (1993), when this temperature sensor was applied to the semiconductor gas rate sensor according to the present invention, sufficient sensitivity could not be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem of the prior art. It is an object of the present invention to provide a method in which the offset voltage value does not fluctuate even if the gas flow rate is increased, and the resistance is reduced. It is an object of the present invention to provide a highly sensitive gas rate sensor having a small value variation.

[0007]

A gas rate sensor of the present invention to solve the above-mentioned object, according to an aspect of the offset voltage is stabilized by Rukoto to have a deflection in the heat wire bridge
The gas flow velocity range has been expanded . Further, the detection unit includes:
It is preferably formed in a serpentine shape having a plurality of bent portions, and more preferably, the bent portions are formed in a curved shape.

[0008]

According to the present invention, the heat wire bridge is prevented from being slightly moved up and down (fluttering) due to the gas flow by making the heat wire bridge flexible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing an example of a gas rate sensor chip according to the present invention. As shown in the figure, a gas rate sensor chip 1 is formed by combining a lower semiconductor substrate 2 and an upper semiconductor substrate 3.

The lower semiconductor substrate 2 is formed into a box-shaped half body by forming a half groove by etching, and a bent heat wire bridge 5 according to the present invention straddles the upper side walls 4a and 4b in the long side direction. . A pair of detectors 6a and 6b for detecting a change in the gas flow direction are provided on the central side surface of the heat wire bridge 5. The lower half of the gas injection hole 7 is formed at a position facing the detection units 6a and 6b.

On the other hand, the upper semiconductor substrate 3 is also formed as a box-shaped half by forming a half groove by etching, and has a gas inlet 8 and a gas outlet 9 at the bottom near both ends in the long side direction.
Are drilled respectively. An upper half of the gas injection hole 7 (not shown) is formed near the center of the gas inlet 8. The upper semiconductor substrate 3 is combined with the lower semiconductor substrate 2 to constitute the gas rate sensor chip 1 according to the present invention.

FIG. 2 is a side sectional view showing an example of the heat wire bridge 5 of the gas rate sensor chip 1 according to the present invention. In the figure, the heat wire bridge 5 has a deflection d, and the maximum value dmax of the deflection at the central portion is such that the ratio dmax / l ₁ to the length l ₁ of the heat wire bridge 5 is 0.2% or more. Preferably it is in the range of 2%. If dmax / l ₁ is less than 0.2%, the effect of the present invention may not be exhibited, and if it exceeds 2%, the sensitivity may be reduced.

FIG. 3 is a process chart showing an example of a method for forming a deflection according to the present invention. In FIG. 1A, a semiconductor film 11 for forming a heat wire bridge 5 is formed on a silicon wafer 10 by, for example, a sputtering method. The semiconductor film 11 is, for example, SiN / Pt
/ SiN in this order.

In order to produce the deflection according to the present invention, the difference in the coefficient of thermal expansion between the silicon wafer 10 and the semiconductor film 11 is used. That is, for example, the sputtering method
When performed at 00 ° C., the semiconductor film 11 mainly composed of SiN has a smaller coefficient of thermal expansion than the silicon wafer 10 composed of Si. Therefore, when the semiconductor film 11 is cooled to room temperature, as shown in FIG. Warping. Subsequently, when Si under the semiconductor film 11 is removed by etching or the like to form a bridge, a part of the warpage is eliminated as shown in FIG. 3C, and the semiconductor film 11 can be bent. Further, the magnitude of the deflection d can be controlled by changing the conditions for forming the semiconductor film 11 during sputtering.

The above embodiment will be described in more detail. Example 1 Under the following conditions, SiN (1.2
Micron thickness) / Pt (0.2 micron thickness) / SiN (1.
A semiconductor film 11 composed of three layers (thickness of 2 microns) was formed by sputtering. Sputter deposition condition pressure: 0.45 Pa, temperature: 300 ° C, high frequency power: 1
kw, Ar / N ₂ flow ratio: 1/2, target: Si

Then, a pattern made of a photoresist is formed on the silicon wafer 10, and the lower semiconductor substrate 2 is formed by etching using the pattern as a mask, and is bonded to the upper semiconductor substrate 3 separately formed. Two gas rate sensor chips 1 (referred to as a-1 and a-2)
Manufactured. The maximum deflection dmax of these gas rate sensor chips 1 is about 30 microns {(dmax / l ₁ ) = 1%}.
Met.

COMPARATIVE EXAMPLE 1 Three gas rate sensor chips 1 (b-b) were prepared in the same manner as in Example 1 except that the pressure at the time of sputtering film formation was set to 0.6 Pa.
1, b-2, b-3). The maximum deflection dmax of these gas rate sensor chips 1 was almost 0.

The evaluations of the gas rate sensor chips 1 of Example 1 and Comparative Example 1 are shown in FIG. 4 and FIG. That is, FIG. 4 is a graph showing the correlation between the N ₂ gas flow rate (cc / min) flowing in the gas rate sensor and the offset voltage (mV). As is clear from FIG.
The curves -1 to b-3 show that the offset voltage drops sharply when the N ₂ gas flow rate is 40 cc / min or more, whereas
The -1 and a-2 of the curve up to N ₂ gas flow rate of 60 cc / min was stable.

FIG. 5 is a graph showing the correlation between the N ₂ gas and the sensitivity (detection output voltage) of the input rotation speed. As is clear from the figure, the correlation between the deflection of the heat wire bridge and the sensitivity is extremely small.

On the other hand, in the detecting section according to the present invention, it is preferable that the Pt line is formed in a zigzag shape. The reason is that a large resistance value is required for the detection unit to obtain sufficient sensitivity, but there is also a dimensional restriction. FIG. 6 is a plan view illustrating an example of the detection unit according to the present invention. As shown in the figure, the detection unit 6 is formed integrally with the heat wire bridge 5,
A zigzag Pt wire 13 is built in a base material 12 made of a semiconductor.

The above embodiment will be described in more detail. Example 2 A 1.2 micron thick SiN film was formed on a silicon wafer by sputtering, and a 0.4 micron thick Pt film was deposited thereon. Next, this Pt film was etched to form a serpentine Pt line 13 having a line width of 5 μm, a length (l _{2 in} FIG. 6) of 1 mm, and a resistance of 135Ω at room temperature. When forming the Pt line 13, the folded portion of the Pt line 13 was made into three types, that is, L type, V type and R type (curved) as shown in FIG.

Then, a 1.2 μm thick SiN film is further formed on the Pt line 13 by sputtering, and then the silicon wafer itself is formed into the shape of the lower semiconductor substrate 2 shown in FIG. The wafer was cut vertically and horizontally to obtain a lower semiconductor substrate 2, which was combined with an upper semiconductor substrate 3 formed separately to obtain a gas rate sensor chip 1. In addition, regarding the lower semiconductor substrate 2, as shown in FIG.
And the lower semiconductor substrate 2 at each of 36 points was selected from each area.

The resistance value of the gas rate sensor chip 1 prepared as described above is adjusted by flowing a current of 0.1 mA at room temperature.
Each type (V-type and R-type) and each area (A to F areas) were examined, and the deviation value of the resistance value (Ω) was obtained. The results are shown in FIG. 9. When viewed from the entire silicon wafer region, those having the curved R-type Pt line 13 have a small deviation value (variation in resistance value), and those having the V-type have a small variation. There were many.

The reason why the variation in the curved R type is small is considered as follows. That is, in the semiconductor process, as the shape of the bent portion of the pattern becomes an acute angle, precise fine processing becomes more difficult and an error is more likely to occur.
Therefore, the smallest variation in the shape is the curved R type, and the variation in the resistance value is also small because the variation in the shape is small.

[0025]

According to the present invention as described above,
Since the heat wire bridge has a bend, the detection unit does not move up and down even if the gas flow rate in the sensor chip is increased. Therefore, since there is no change in the offset voltage value, a highly sensitive gas rate sensor can be obtained.

If the detection section is formed in a serpentine shape having a plurality of bent portions, a large resistance value can be obtained, and the sensitivity of the gas rate sensor can be increased. Further, if the bent portion is formed in a curved shape, the variation in the resistance value can be reduced, so that the reliability of the gas rate sensor can be increased.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an example of a gas rate sensor chip according to the present invention.

FIG. 2 is a side sectional view showing an example of a heat wire bridge of the gas rate sensor chip according to the present invention.

FIG. 3 is a process chart showing an example of a method for forming a flexure according to the present invention.

FIG. 4 is a graph showing a correlation between an N ₂ gas flow rate and an offset voltage according to an example and a comparative example.

FIG. 5 is a graph showing a correlation between N ₂ gas and sensitivity of an input rotation speed according to an example and a comparative example.

FIG. 6 is a plan view showing an example of a detection unit according to the present invention.

FIG. 7 is a schematic view showing a folded portion of a Pt line according to the present invention.

FIG. 8 is a plan view showing a division surface of the silicon wafer according to the present invention.

FIG. 9 is a graph showing the relationship between the type of the Pt line folded portion and the resistance deviation value of the gas rate sensor chip according to the present invention.

FIG. 10 is a circuit diagram illustrating an offset current according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas rate sensor chip, 2 ... Lower semiconductor substrate, 3
... Upper semiconductor substrate, 4a, 4b, upper surface of side wall, 5: heat wire bridge, 6, 6a, 6b, detector, 7: gas injection hole, 8: gas inlet, 9: gas outlet, 10: silicon wafer , 11: semiconductor film, 12: base material, 13: Pt
Line, dmax: maximum value of deflection, l ₁ : length of heat wire bridge 5, l ₂ : length of Pt line.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshiaki Kuriyama 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. Field surveyed (Int. Cl. ⁷ , DB name) G01P 9/00 G01C 19/00

Claims (3)

(57) [Claims] 1. A gas rate sensor for providing a heat wire bridge having a pair of detectors in a gas flow path and detecting an angular velocity from a bias of a gas flow hitting the detectors.
To be provided with a deflection in the heat wire bridge
The gas rate sensor has an extended gas flow rate range in which the offset voltage is stable . 2. The device according to claim 1, wherein the detection unit is formed in a serpentine shape having a plurality of bent portions.
A gas rate sensor as described. 3. The gas rate sensor according to claim 2, wherein the bent portion is formed in a curved shape.