JPH0232224A - Silicone vibration type strain sensor - Google Patents

Abstract

PURPOSE:To enable high-accuracy, high-stability detection by providing a damping base in the recessed part of a sensor chip, holding the gap between a diaphragm and the damping base narrow, and charging silicone oil in the gap. CONSTITUTION:The damping base 19 is stored in the recessed part 11 of the sensor chip 10 and fixed to a base chip 16 while a flow hole 20 is held in the center, and a gap DELTA is maintained between its upper part and the bottom part of the diaphragm 13. Then the silicone oil 21 is charged in the recessed part 11. Consequently, the gap DELTA is reduced almost to, for example, 150mum in the silicone oil 21 and then the Q factor of resonance is about 0.5, so that large damping effect is obtained. Therefore, the whole vibration due to the self- oscillation of the vibration type strain gauge 14 is suppressed, and consequently various characteristics are improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a silicon vibrating strain sensor using a vibrating strain gauge, and particularly relates to a silicon vibrating strain sensor that uses a vibrating strain gauge, and in particular a silicon vibrating strain sensor with improved resonance characteristics of a diaphragm to which the vibrating strain gauge is attached. Regarding vibration type strain sensors.

<Prior Art> FIG. 5 shows a vertical cross-sectional view of a vibrating strain sensor using a conventional vibrating strain gauge. This type of vibration strain sensor is disclosed, for example, in Japanese Patent Application No. 70361/1983.

10 is a recess 11 formed by etching a silicon single crystal substrate.
This is a sensor chip in which a diaphragm 13 is formed to be thinner than a surrounding thick portion 12, and a vibrating strain gauge 14 is formed at a predetermined position on the diaphragm 13.

This vibrating strain gauge 14 has a vibrating beam fixed to the sensor chip 10 at both ends and having a thin air gap around it, and this vibrating beam is connected to an external circuit to cause automatic oscillation. The measured pressure P is determined by utilizing the fact that the resonance frequency changes due to distortion caused by the applied measured pressure P.

The thick interior 12 of this sensor chip 10 has a through hole 15 in the center.
It is bonded to a base chip 16 made of single crystal silicon.

The thick portion 12 of the sensor chip 10 and the base chip 16 are joined via a thermal oxide film. For this bonding, a thermal oxide film is formed in advance before bonding the respective surfaces of the thick part 12 and the base chip 16, and these are heated and oxidized immediately after, for example, for about an hour, so that the surfaces become hydrophobic. For example, 100
By heat treatment in an oxidizing atmosphere at 0°C,
The gaps between the thermal oxide films are filled and they are completely bonded. The thickness of this thermal oxide film is thin, for example 0.7 on one side.
The total length of μn1 is about 1.4 μm.

The base chip 16 is joined to a cylindrical joint 18 made of, for example, Kovar, which has a pressure introduction hole 17 in the center so that the through hole 15 and the pressure introduction hole 17 communicate with each other.

<Problems to be Solved by the Invention> However, in such conventional vibrating strain sensors, the vibrating strain gauge is coupled to an external circuit to cause self-oscillation, and the measured pressure is detected from changes in the resonance frequency. Since this resonance causes the entire sensor chip to resonate through the diaphragm, there is a problem that the sensor's input/output characteristics and other characteristics deteriorate.

In this case, simply enclosing a highly viscous fluid such as silicone oil into the recess will not provide the desired damping effect and will not improve these mechanical characteristics.

Means for Solving the Problems> In order to solve the above problems, the present invention etches a silicon substrate to form a recess, thereby forming a diaphragm thinner than the surrounding thick part. A sensor chip on which a vibrating strain gauge is formed, a base chip that is joined to the thick inside and has a through hole in the center, and a base chip that is housed in a recess and has a communication hole in the center with a predetermined narrow gap between it and the diaphragm. It includes a damping base fixed to the base chip, silicone oil sealed in the recess, and a joint in which the pressure introduction hole opened in the center communicates with the through hole and is joined to the base chip. This is what I did.

Function: The damping base is fixed to the base chip by maintaining a predetermined narrow gap between the diaphragm and the diaphragm in the recess of the sensor chip, and by filling this recess with silicone oil, automatic oscillation of the vibrating strain gauge is achieved. The overall vibration caused by this is suppressed, which improves the mechanical characteristics.

<Example> Next, the configuration of the present invention will be described using the drawings. FIG. 1 is a longitudinal sectional view showing the configuration of one embodiment of the present invention.

Note that parts having the same functions as those in the conventional configuration are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

Reference numeral 19 denotes a damping base made of silicon single crystal that can be housed in the recess 13. A communication hole 20 is formed in the center, and the bottom of the damping base is thermally oxidized into the base chip 16 so as to communicate with the through hole 15. It is joined. A predetermined gap Δ is maintained between the upper part and the bottom of the diaphragm 13.

21 is silicone oil, and by sealing this silicone oil inside the recess 11, the vibrating strain gauge 1
4 is damped and removed by the narrow gap Δ. The degree of this effect will be discussed later.

Next, a manufacturing method for manufacturing such a vibrating strain sensor will be explained with reference to FIG.

FIG. 2(a) shows an etching process for forming a through hole 15 in a silicon substrate 22 that will eventually become a base chip 16.

The through hole 15 is formed by, for example, anisotropic etching, and a thin thermal oxidation layer [23] of, for example, about 0.7 μm is formed on the upper and lower surfaces.

FIG. 2A shows an etching process for forming communication holes 20 in a silicon substrate 24 that will eventually become the damping base 19.

A thermal oxide film 25 is also formed on the upper and lower surfaces in the same manner as in FIG. 2(a).

FIG. 2(B) shows a thermal oxidation bonding process in which these silicon substrates 22 and 24 are brought together and thermally oxidized bonded.

This step is similar to the thermal oxidation bonding of the sensor chip 10 and base chip 16 shown in FIG. 5.

FIG. 2(c) shows a step of forming a mesa structure on a silicon substrate 24. As shown in FIG.

A photomask is fixed at a predetermined position on the upper surface of the silicon substrate 24, and alkali etching is performed using hydrazine (N2H4) or the like to form a mesa 41! A damping base 19 bonded to the base chip 16 is formed as m.

FIG. 2(d) shows a sensor chip with a processed diaphragm.

This sensor chip 10 is processed in a separate process to form a diaphragm 13 and a vibrating strain gauge 14 thereon. The surrounding area is covered with thermal oxidation 11!26.

The process shown in FIG. 2(e) shows the process of thermal oxidation bonding.

In this process, the intermediate process chip formed in FIG. 2(C) and the sensor chip shown in FIG.
and the gap Δ is set to a predetermined value.

Thereafter, the base chip 16 is joined to the joint 18 and silicone oil 21 is sealed therein, thereby producing a vibrating strain sensor.

The damping effect of the vibrating strain sensor manufactured in this way will be explained using FIGS. 3 and 4.

FIG. 3 is a model for simulating this damping effect, and FIG. 4 is a characteristic diagram showing the results of this simulation.

27 is a substrate made of Kovar or the like, and a silicon base 28 is fixed on this substrate. A protruding portion 29 having a flat upper surface is formed in the center of the silicon base 28 . A silicon chip 30 is fixed in contact with this protrusion 29 . A coin-shaped piezoelectric element 31 is fixed on top of this chip 30. And this chip 30
There is a gap between the base 28 and the protrusion 29! are separated by only

FIG. 4 shows the characteristics measured when the model shown in FIG. 3 was caused to resonate under various media conditions.

The horizontal axis indicates the gap 2 between the chip 30 and the base 28, and the vertical axis indicates the Q factor of resonance generated in the model by vibrating the piezoelectric element 31.

Curve 8 shows the characteristics when this model resonates in the atmosphere, curve 8 shows the characteristics when it resonates in Freon gas, and curve C shows the characteristics when it resonates in silicone oil. .

Gap between any curves! It shows a tendency for the Q factor to decrease as the value decreases. In silicone oil, if the gap is reduced to, for example, about 150 μm, the Q factor is about 0.5, indicating a significant damping effect.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the damping base is provided in the recess of the sensor chip, the gap between the diaphragm and the damping base is kept narrow, and silicone oil is applied between the damping base and the damping base. Since it is encapsulated, it is possible to prevent the entire structure from resonating due to the resonant frequency of the vibrating strain gauge, and a highly accurate and highly stable silicon vibrating strain sensor can be realized.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing the configuration of one embodiment of the present invention, and FIG.
The figure is a process diagram showing the process of manufacturing the silicon vibrating strain sensor shown in FIG. 1, and FIG. 3 is a vertical cross-sectional view showing a model for estimating the effect of the silicon vibrating strain sensor shown in FIG.
FIG. 4 is a characteristic diagram showing the characteristics when the model shown in FIG. 3 is caused to resonate in various medium conditions, and FIG. 5 is a longitudinal sectional view showing the configuration of a conventional silicon vibration strain sensor. 10...sensor chip, 11...recess, 12...
Thick part - 113...Diaphragm, 14...Vibrating strain gauge, 16...Base chip, 19...Damping base, 21...Silicon oil, 25...Thermal oxide film, Δ... Gap, 27... Substrate, 28... Base, 29... Protrusion, 30... Chip, 1... Piezoelectric element. Figure 7A and base gear muff. )Lrn

Claims (1)

[Claims] A sensor chip has a vibrating strain gauge formed on a diaphragm made by etching a silicon substrate to form a recess, thereby making the diaphragm thinner than the surrounding thick part, and a through hole in the center that is joined to the thick part. a damping base housed in the recess and having a circulation hole in the center and fixed to the base chip while maintaining a predetermined narrow gap with the diaphragm; and a viscous fluid sealed in the recess. and a joint in which a pressure introduction hole opened in the center communicates with the through hole and is joined to the base chip.