Gas flow type angular velocity sensor

BACKGROUND OF THE INVENTION

The present invention relates to a gas flow type angular velocity sensor for detecting an angular velocity from a change of resistance in each of a pair of heat wires consisting of temperature-sensitive resistance elements when a flow of gas is forced into a gas path in a sensor body through a nozzle hole and directed toward the pair of heat wires being deflected by the action of an angular velocity of the sensor body, wherein a first semiconductor substrate having a groove formed thereon for forming the gas path and a second semiconductor substrate having the pair of heat wires formed thereon are adhesively coupled with each other to form the sensor body.

A sensor of this type is known from EP-A-0405452.

In detail, EP-A-0405452 discloses a gas flow type angular velocity sensor, wherein a body portion including a gas path and a pair of heat wires arranged in the gas path is manufactured by semiconductor micromachining on the basis of IC technology.

In this type of an angular velocity sensor, the body portion is constructed in such a way that a lower semiconductor substrate having an etched half groove and an upper semiconductor substrate having a half groove etched thereon are bonded to each other so as to precisely couple the half grooves to form a gas path in the assembled body portion.

The lower semiconductor substrate has a bridge portion etched therein whereon a pair of heat wires are formed by patterning.

Each of the lower and upper semiconductor substrates also has an etched half-hole forming a nozzle hole when both substrates are coupled with each other. The lower semiconductor substrate has electrode portions formed by patterning on both sides of paired heat wires.

The problem faced in manufacture of the above-mentioned conventional device is that many micromachining operations are required for forming a half-groove on each of the lower and the upper semiconductor substrates and much labour is further required for precisely coupling with each other the half-grooves on both substrates to form a gas path therein.

Another problem is that the manufacturing process involves the possibility of damaging the paired heat wires when the bridge portion is formed by etching a part of the lower semiconductor substrate underneath the paired heat wires previously formed by depositing material such as platinum on the lower semiconductor substrate.

SUMMARY OF THE INVENTION

The object of the present invention resides in providing a gas flow type angular velocity sensor wherein a body is composed of two semiconductor substrates, one having a groove formed thereon constituting a gas path and the other having only a pair of heat wires formed thereon by patterning (without forming a groove), so as to produce a high-strengh structure and to reduce steps of forming a groove in the sensor body thereby saving labour for positioning the gas path when assembling both substrates, thus improving workability of said body.

For the accomplishment of this object, the gas flow type velocity sensor is characterized in that only one of the two semiconductor substrates has a groove formed thereon, only the other having the pair of heat wires formed thereon.

Advantageous designs of the sensor under the present invention are described in the subclaims.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1

is a front sectional view showing a sensor body of a gas flow type angular velocity sensor embodying the present invention.

Fig. 2

is a plan view showing a lower semiconductor substrate of the sensor body.

Fig. 3

is a rear side perspective view of an upper semiconductor substrate.

Fig. 4

is a view showing a process for forming paired heat wires and electrodes on the lower semiconductor substrate.

Fig. 5

is a front sectional view showing a sensor body of another embodiment of the present invention.

Fig. 6

is a view showing a process for forming a pair of heat wires in the form of a bridge over a lower semiconductor substrate.

In the drawings, 1 is a lower semiconductor substrate, 2 is an upper semiconductor substrate, 4 is a gas path, 40 is a groove forming a gas path, 51 is a heat wire, 52 is a heat wire and 7 is a electrode portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, the preferred embodiments of the present invention will be described in detail as follows:

   As shown in Figs. 1 - 3, a gas flow type angular velocity sensor according to the present invention is so constructed that a lower semiconductor substrate 1 having a pair of heat wires 51, 52 formed thereon by patterning and an upper semiconductor substrate 2 having a groove 40 etched thereon for forming a gas path 4 are placed on and bonded with each other to form a sensor body having a gas path 4 including therein the paired heat wires 51 and 52.

An electrode portion 7 is formed by patterning on each side of a paired heat wires 54 and 53 on the lower semiconductor substrate 1.

As shown in Fig. 4, the paired heat wires 51, 52 and the electrodes 7 can be formed on the lower semiconductor substrate 1, for instance, by forming a SiN-layer 8 on the lower semiconductor substrate 1 made of silicone (Si), by depositing a material 9 such as platinum on the SiN-layer to form the paired heat wires 51, 52, by forming the electrodes 7 at both sides of the heat wires and then by forming thereon a protecting film 10 made of SiN.

A small groove 30 communicating with a groove 40 is formed integrally on the upper semiconductor substrate 2. When the upper and lower substrates are placed on and bonded with each other, a nozzle hole for forcing gas into the gas path is formed between the small groove 30 and the lower semiconductor substrate 2.

In the gas flow type angular velocity sensor having thus constructed sensor body, gas is forced by a miniature pump (not shown) into the gas path 4 through the nozzle hole of the sensor body and laminarly flows therealong. When a deflection of the gas flow in the gas path 4 of the sensor body is caused by the action of an angular velocity applied to the gas flow, it can be detected electrically by a change of differential resistance in the paired heat wires 51 and 52.

In practice, a bridge circuit composed of a standard resistance and the heat wires 51, 52 has an output which is amplified by an amplifier as a signal of the detected angular velocity.

Since the sensor body according to the present invention, wherein a gas path can be formed by a groove 40 made by etching method only on the upper semiconductor substrate 2 when the upper and the lower semiconductor substrates 1 and 2 are simply coupled and bonded with each other, as compared with the aforementioned conventional sensor body wherein gas path is formed by two half-grooves made by etching method on the upper and the lower semiconductor substrates, it is possible to reduce groove forming steps and save labour for positioning the gas path in the sensor body at the time of assembling the substrates, thereby making it easier to manufacture and assemble the sensor body.

According to the present invention, since a pair of heat wires 51, 52 are formed only by patterning on the semiconductor substrate without etching a portion under the paired heat wires, the sensor body may have a structure of increased strength and therefore heat wires may not be damaged by stress.

Fig. 5 shows another embodiment of the present invention, wherein a pair of heat wires 51, 52 are formed in form of a bridge built over the top surface of a lower semiconductor substrate 1 and arranged in the substantially middle of cross-section of a gas path 4 so as to increase the sensitivity of detecting a degree of gas flow deflection.

On the contrary, if a pair of heat wires 51, 52 are formed on an lower semiconductor substrate 1 constituting a wall surface of a gas path as shown in Fig. 4, gas flow along a wall surface of the gas path 4 may be reduced, resulting in lowering of the sensitivity of the gas flow deflection sensor.

In Fig. 6, a bridge of the paired heat wires may be build over the top surface of the low semiconductor substrate 1 in such a way that a sacrificing layer 11 made of PSG or SiO₂ is formed by photoetching on a lower semiconductor substrate made of silicone (Si), a film 12 of SiN is formed on the sacrificing layer, and heat wire material such as platinum is deposited on the SiN-film and formed in a given pattern of paired heat wires by etching, an electrode 7 is formed at each side of the paired heat wires, a SiN-film 12 is formed and then the sacrificing layer 11 is removed with an etchant of hydrofluoric acid.

The gas flow type angular velocity sensor according to the present invention, which body including a pair of heat wires in a gas path formed therein is manufactured by adhesively assembling two semiconductor substrates, one having the groove constituting the gas path and the other having only the paired heat wires formed thereon by pattern etching (without forming the groove), has such an advantage that the body may have effectively simplified structure of improved strength, and be readily manufactured and easily assembled because of saving a number of manufacturing steps for forming a groove and omitting laborious positioning works when assembling components.