JPH11248574A - Pressure sensor - Google Patents

Abstract

(57) [Problem] To provide a capacitance type pressure sensor having high sensitivity in a low pressure range and a wide measurable pressure range. The A thick portion surrounded by the thin portion in the pressure sensor composed of a fixed plate having a diaphragm and a fixed electrode to the movable electrode, a first thick portion 11 of the diaphragm 1a
A second thick portion 14 is provided in the middle of the thin portion surrounding the first thick portion, and a gap between the second thick portion 14 and the fixing plates 2 and 3 is formed by the first thick portion.
The gap between the first thick portion 11 and the fixed electrode 21 or 31 is smaller than the gap between the first thick portion 11 and the fixed electrode 21 or 31 when the pressure is applied. Or, it is made to contact 3. The sensitivity is high in a low pressure region until the second thick portion comes into contact with the fixing plate, and the sensitivity is low in the pressure region after the two thick portions come into contact, and the measurement pressure range is widened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type pressure sensor for measuring a pressure by using a displacement of a diaphragm caused by an applied pressure as a change in a capacitance value.

[0002]

2. Description of the Related Art There are many methods for measuring a pressure value. Among them, a method of replacing the pressure with the displacement of the diaphragm and measuring the displacement as a change in the capacitance value between the diaphragm and the fixed electrode facing the diaphragm,
This is a widely used method.

FIG. 6 shows an example of the structure of such a capacitance type pressure sensor according to the prior art. This example is a so-called differential pressure sensor in which fixed electrodes are symmetrically arranged on both sides of a diaphragm. The diaphragm 1 is made of a conductive elastic plate, for example, a single crystal silicon plate having a resistivity of about 0.1 Ωcm, and has a circular thick portion 11 as a movable electrode which is displaced by pressure, and It comprises an annular thin portion 12 concentric with the thick portion 11 that deforms and displaces the thick portion 11, and an outer peripheral portion 13. On both sides of the diaphragm 1, an insulating plate having a thermal expansion coefficient close to the diaphragm 1, for example, Pyrex glass plate or ceramic plate, two fixing plates 2 and 3 made of
Are joined to the outer peripheral portion 13 of the diaphragm 1 . Each of the fixing plates 2 and 3 has a pressure guiding hole for introducing pressure.
22 and 32 are formed, and the thick portion 11 of the diaphragm 1 is formed.
Fixed electrodes 21 and 31 are formed at positions opposed to. The thick portion 11 and the thin portion 12 of the diaphragm 1 are formed by etching from both surfaces by a depth corresponding to the thickness. Therefore, when no pressure is applied to the diaphragm 1 , the distance (gap) between the thick portion 11 and the fixed electrode 21 or 31 is substantially the same.

In this state, when a pressure is applied from the pressure guiding hole 32, the thin portion 12 of the diaphragm 1 bends and the thick portion 11
Is displaced upward, the distance between the thick portion 11 and the fixed electrodes 21 and 31 decreases and increases, respectively, the capacitance value increases and decreases, and the pressure can be measured by measuring them. Hereinafter, an example of a method of calculating the pressure by calculating the measured capacitance value will be described.

[0005] The capacitance value between the thick portion 11 and the fixed electrode 21 is C1, the capacitance value between the thick portion 11 and the fixed electrode 31 is C2,
The dielectric constant of the space between the thick part 11 and the fixed electrodes 21 and 31 is ε, the area of the thick part 11 is A, and the pressure is not applied between the thick part 11 and the fixed electrode 21 or 31. Assuming that the distance is the same and G is the displacement of the thick portion 11 due to the pressure P is Δ, C1 = εA / (G−Δ) and C2 = εA / (G + Δ).

When the F value is obtained by using the C1 and C2 by the following equation, F≡ (C1−C2) / (C1 + C2) = Δ / G. That is, since G is a constant value determined by each pressure sensor, the relationship that the F value is proportional to Δ is obtained.

When the bending of the thin portion 12 is small,
Since the displacement Δ is proportional to the pressure P, the pressure P can be obtained by obtaining the F value. The maximum stress a generated in the diaphragm 1 under the pressure P is generated at the outer peripheral portion of the thin portion 12 and is proportional to the pressure P. In a state where the pressure P increases and the thick portion 11 of the diaphragm 1 contacts the fixed electrode 21 of the fixed plate 2 and the upward displacement is prevented, the ratio of the increase of the maximum stress σ to the increase of the pressure is small. Become. This tendency can be considered similarly to the maximum stress of the beam. In other words, it can be considered that the thick portion 11 is in a cantilever state until it comes into contact with the fixed electrode 21 of the fixed plate 2, and after contact, it is in a state of a fixed beam at both ends. The relationship between the maximum stress σ and the pressure P is shown by a dotted line in FIG. The thick part 11 is the fixed electrode 21 of the fixed plate 2.
The pressure in contact with a the P1, the maximum stress at that time is sigma _1.

The relationship between the relative value of the output signal indicated as the F value and the pressure P is shown by a dotted line in FIG. The pressure increases linearly until the pressure reaches P1, and the output becomes a constant value when the pressure is equal to or higher than P1. In this example, the case where the fixed plates 2 and 3 are joined to both sides of the diaphragm 1 has been described.
Even in a pressure sensor in which a fixed plate is joined to only one side, the tendency of the capacitance value change is the same. However, in this case, since the F value cannot be obtained, the pressure is calculated from the capacitance value. As described above, the capacitance value is inversely proportional to (G−Δ) or (G + Δ).

In such a pressure sensor, when the thin portion 12 of the diaphragm 1 is made thinner in order to increase the sensitivity and improve the measurement accuracy, the measurement accuracy is improved, but the upper limit P1 of the measurable pressure value is reduced. Become. Conversely, P1
If the thickness of the thin portion 12 is increased in order to increase the measurement accuracy, the measurement accuracy decreases. In other words, the conventional pressure sensor has a problem that the range of the pressure that can be measured is narrowed in order to secure the required sensitivity.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a high sensitivity in a low pressure range,
Another object of the present invention is to provide a pressure sensor having a wide measurable pressure range.

[0011]

According to the present invention, there is provided a holding portion forming an outer peripheral portion, a thin portion surrounded by the holding portion, and a thick portion surrounded by the thin portion and thinner than the holding portion. A diaphragm for displacing the thick portion and the thin portion by the applied pressure, and a fixed electrode at a position facing the thick portion, and a pressure guiding hole for introducing a pressure applied to the diaphragm, and holding the same. A pressure plate for measuring the pressure applied to the diaphragm by a capacitance value of a capacitor formed by the thick portion and the fixed electrode, wherein the holding portion of the diaphragm and the thick portion And a second thick portion which is formed between the thin portions and is in contact with the fixed plate at a pressure lower than the pressure at which the thick portion contacts the fixed electrode when pressure is applied. Yes Invention of claim 1).

Until the second thick portion contacts the fixing plate,
Since the thick portion is displaced by the bending of the entire thin portion, the displacement of the thick portion with respect to a unit pressure change is large, and high sensitivity is obtained. After the second thick portion contacts the fixing plate,
Since only the deflection of the thin portion inside the thick portion displaces the thick portion, the displacement of the thick portion with respect to a unit pressure change is reduced, the measurable pressure range is extended to a high pressure region, and the maximum stress of the thin portion is Is also on a moderate uptrend.

According to the first aspect of the present invention, the second electrode is formed on the fixed plate at a position facing the second thick portion of the diaphragm (the second aspect of the invention). The second thick portion and the second electrode make contact before the thick portion and the first electrode make contact. In other words, the capacitor formed by the second thick portion and the second electrode has higher sensitivity than the capacitor formed by the thick portion and the first electrode. Therefore, by providing the second electrode, the sensitivity until the second thick portion contacts the fixing plate can be further increased.

Further, in the first aspect of the present invention, the fixing plates are provided on both sides of the diaphragm, and the capacitance values of the capacitors on both sides in the state where no pressure is applied are made substantially equal (the third aspect of the present invention). invention). By using a differential pressure sensor, the above-described calculation of the F value can be used.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the pressure sensor according to the present invention will be described below with reference to embodiments. Note that the same reference numerals are used for parts having the same functions as the conventional technology. [First Embodiment] FIG. 1 is a sectional view showing the structure of a first embodiment of the pressure sensor according to the present invention. This embodiment is a differential pressure sensor similar to the example of the conventional pressure sensor shown in FIG. 6, and has the same overall configuration as the conventional example, but the diaphragm 1a is different from the conventional example. .

The diaphragm 1a is made of a conductive elastic plate,
For example, a single crystal silicon plate with a resistivity of about 0.1Ωcm,
A first thick-walled portion 11 serving as a movable electrode that is displaced by pressure; and an annular ring concentric with the first thick-walled portion 11 and deformed by pressure to form the first thick-walled portion 11. A first thick portion 12a for displacing the first thick portion 11, a second thick portion 14 surrounding the outside thereof, being annular and concentric with the first thick portion 11, and being thicker than the first thick portion 11. Surrounding the outside, the first thick portion 11
And concentric with the first ring and deformed by pressure.
And a second thin portion 12b for displacing the thick portion 11 and the second thick portion 14, and an outer peripheral portion 13.

[0017] On both sides of this diaphragm 1a, similarly to the conventional example, the insulating plate having a thermal expansion coefficient close to the diaphragm 1a, for example, Pyrex glass plate or ceramic plate, two fixing plates 2 and 3 made of, the diaphragm 1a
Is joined to the outer peripheral portion 13. Pressure-imparting holes 22 and 32 for introducing pressure are formed in the fixed plates 2 and 3, respectively, and fixed electrodes 21 and 31 are formed at positions opposed to the first thick portion 11 of the diaphragm 1a . Thus, a variable capacitance capacitor is formed.

The first thick portion 11, the second thick portion 14, the first thin portion 12a and the second thin portion 12b of the diaphragm 1a are
It is formed by etching substantially symmetrically from both sides according to the thickness of each. The thickness of the second thick portion 14 is
Thinner, thicker than the first thick portion 11, and a thickness at which when the pressure is applied, the first thick portion 11 contacts the fixed plate 2 or 3 at a pressure lower than the pressure at which the first thick portion 11 contacts the fixed electrode 21 or 31. Is set to

Next, the characteristics of this embodiment will be described with reference to FIGS. FIG. 3 shows a pressure-output signal characteristic, and a bold line in the figure shows an output signal with respect to pressure in this embodiment (a dotted line is a characteristic of the above-described conventional example). In the conventional example, the second thick portion 14 contacts the fixing plate 2 or 3 at a pressure P2 lower than the pressure P1 which is the pressure at which the thick portion 11 contacts the fixed electrode 21 or 31. Up to the pressure P2 (low pressure side), it increases with a slightly gentler gradient than the dotted line in the conventional example, and above the pressure P2 (high pressure side), the second thick portion 14 is held by the fixed plate 2 or 3, First thick portion forming a capacitor
The displacement of 11 depends only on the deflection of the first thin portion 12a, and increases with a gentler gradient. When the first thick portion 11 contacts the fixed electrode 21 or 31 at the pressure P3, the first thick portion 11a The displacement of the meat portion 11 stops, and the output does not increase.

Thus, the pressure sensor of this embodiment is
It has high sensitivity on the low pressure side, lowers sensitivity on the high pressure side, and expands the pressure range that can be measured. Note that a change in sensitivity at the pressure P2 can be corrected by a signal processing circuit. FIG. 4 shows the pressure-maximum stress characteristics. A thin line indicates the maximum stress of the first thin portion 12a of this embodiment, and a thick line indicates the second thin portion.
The maximum stress of 12b is shown (the dotted line is the characteristic of the conventional example described above).
On the low pressure side, the maximum stress of the second thin portion 12b increases with a gentler gradient than the dotted line in the conventional example, and the maximum stress of the first thin portion 12a increases much more gently. On the high pressure side, the second thick portion 14 is held by the fixed plate 2 or 3,
The increase in the maximum stress of the thin portion 12b of the
The maximum stress of the first thin portion 12a increases sharply. However, the maximum stress as a whole is smaller than in the conventional example, and the reliability is improved.

As described above, by providing the second thick portion 14, the measurement pressure range can be expanded without significantly lowering the sensitivity on the low pressure side, and the maximum stress can be reduced to below that of the conventional example. Since it can be suppressed, reliability is improved. In this embodiment, the second thick portion 14
By changing the position and thickness (strictly speaking, the gap with the fixed plate 2 or 3), the magnitude of the pressure P1 and the sensitivity on the low pressure side and the high pressure side can be adjusted.

Also, as in this embodiment, the first thin portion
When the thickness of the second thin portion 12b is made the same as the thickness of the second thin portion 12b, it can be manufactured by the same processing steps as in the conventional example. [Second Embodiment] In this embodiment, the thickness of the second thin portion 12b is made smaller than the thickness of the first thin portion 12a. By reducing the thickness of the second thin portion 12b, the sensitivity in the region where the pressure is low is made higher than in the conventional example.

The thin line in FIG. 3 shows the pressure-output signal characteristic of this embodiment. FIG. 5 shows the pressure-maximum stress characteristics of this embodiment. The thin line and the thick line indicate the first thin portion 12a and the second thin portion, respectively.
, And the dotted line corresponds to the conventional example. Second
Since the thickness of the thin portion 12b of the second thin portion is reduced,
The second thick portion 14 contacts the fixing plate 2 or 3 at a pressure P4 lower than the pressure P2. Therefore,
In this region, the output signal increases more steeply than in the conventional example. That is, the sensitivity is high. When the pressure exceeds P4, the second thick portion 14 is held by the fixing plate 2 or 3, so that the increase in the maximum stress of the second thin portion 12b becomes gentle, and the maximum stress of the first thin portion 12a increases. Increase rapidly. However, the maximum stress as a whole is smaller than in the conventional example, and the pressure measurement range is wider than in the conventional example.

As described above, by providing the second thick portion 14 and reducing the thickness of the second thin portion 12b, the sensitivity on the low pressure side is made higher than in the conventional example, and the measurement pressure range is increased. It can be enlarged and the maximum stress can be suppressed to less than the conventional example. In this embodiment, the position and thickness of the second thick portion 14 (strictly speaking, the gap with the fixing plate 2 or 3), the thickness and width of the first thin portion 12a, and the second thin portion By selecting the appropriate thickness and width of 12b, it is possible to adjust the value of P4, the sensitivity on the low pressure side, the maximum stress, the sensitivity on the high pressure side, and the pressure measurement range. Can also be improved.

[Third Embodiment] FIG. 2 is a sectional view showing the structure of a third embodiment. This embodiment is different from the first or second embodiment in that the second fixed electrodes 23 and 33 are provided on the surfaces of the fixed plates 2 and 3 facing the second thick portion 14, respectively. Things. Since the second thick portion 14 contacts the second fixed electrode 23 or 33 in a low pressure range, the second thick portion 14 and the second fixed electrodes 23 and 33 form two capacitors. The F value is the first thick portion 11
And the fixed electrodes 21 and 31 form two capacitors F
The measurement is large compared to the value and can be performed with high sensitivity.

Therefore, the provision of the second fixed electrodes 23 and 33 enables more sensitive measurement on the low pressure side. Although the three embodiments described above are differential pressure sensors having two capacitors, it goes without saying that the fixed electrode is equally effective in a single pressure sensor.

The first thick portion 11 is circular, and the first thick portion 11 is circular.
Although the example in which the shapes of the second thin portions 12a and 12b and the second thick portion 14 are concentric rings has been described, it goes without saying that other shapes are similarly effective.

[0028]

According to the present invention, there is provided a holding portion forming an outer peripheral portion, a thin portion surrounded by the holding portion, and a thick portion surrounded by the thin portion and thinner than the holding portion. A diaphragm that displaces the thick part and the thin part by the applied pressure, and a fixed electrode at a position facing the thick part,
It has a pressure guiding hole for introducing pressure to be applied to the diaphragm,
And a fixed plate joined to the holding portion, wherein the pressure sensor measures a pressure applied to the diaphragm by a capacitance value of a capacitor formed by the thick portion and the fixed electrode. A second thick portion which is formed at a position intermediate with the thick portion and is sandwiched between the thin portions and which contacts the fixed plate at a pressure lower than the pressure at which the thick portion contacts the fixed electrode when pressure is applied. Since the thick portion is displaced by the bending of the entire thin portion until the second thick portion contacts the fixing plate, the displacement of the thick portion with respect to a unit pressure change is large, and high sensitivity is obtained. After the second thick portion comes into contact with the fixing plate, only the bending of the thin portion inside the second thick portion displaces the thick portion. Is small and the measurable pressure range is high Spread until a force area, the increase of the maximum stress of the thin portion also becomes gentle. Therefore, it is possible to provide a highly reliable pressure sensor having high sensitivity in a low pressure region, a wide measurable pressure range, and high reliability.

In the first aspect of the present invention, since the second electrode is formed on the fixed plate at a position facing the second thick portion of the diaphragm, the second electrode and the second thick portion are formed. The sensitivity with which the second thick portion contacts the fixing plate is further enhanced by the capacitor with the portion. Therefore, it is possible to provide a pressure sensor having higher sensitivity in a low pressure region (the invention of claim 2).

Further, according to the first aspect of the present invention, since the fixing plates are provided on both sides of the diaphragm, and the capacitance values of the capacitors on both sides in a state where no pressure is applied are substantially equal. The calculation of the F value can be used. Therefore, it is possible to output an output signal proportional to the displacement of the thick portion by a simple calculation, and to provide a pressure sensor having high sensitivity in a low pressure region, a wide measurable pressure range, and high reliability. (Invention of claim 3).

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a first embodiment of a pressure sensor according to the present invention.

FIG. 2 is a sectional view showing the structure of a third embodiment.

FIG. 3 is a pressure-output signal diagram showing a characteristic difference between the conventional example and the embodiment (first and second).

FIG. 4 is a pressure-maximum stress diagram showing the difference between the conventional example and the first embodiment.

FIG. 5 is a pressure-maximum stress diagram showing a difference between the conventional example and the second embodiment.

FIG. 6 is a sectional view showing the structure of an example of a conventional pressure sensor.

[Description of Signs] 1 , 1a diaphragm 11 thick portion, first thick portion 12 thin portion 12a first thin portion 12b second thin portion 13 outer peripheral portion 2, 3, 2a, 3a fixing plate 21, 31 Fixed electrode 22, 32 Pressure guiding hole 23, 33 Second fixed electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kimihiro Nakamura 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A holding portion forming an outer peripheral portion, a thin portion surrounded by the holding portion, and a thick portion surrounded by the thin portion and thinner than the holding portion, made of a conductive material, and being thick by an applied pressure. A diaphragm for displacing the portion and the thin portion, and a fixed plate having a fixed electrode at a position facing the thick portion, having a pressure guiding hole for introducing pressure applied to the diaphragm, and being joined to the holding portion. A pressure sensor for measuring a pressure applied to the diaphragm by a capacitance value of a capacitor formed by the thick portion and the fixed electrode, wherein the thin portion is located at an intermediate position between the holding portion of the diaphragm and the thick portion. And a second thick portion that contacts the fixed plate at a pressure lower than the pressure at which the thick portion contacts the fixed electrode when pressure is applied. 2. The pressure sensor according to claim 1, wherein a second electrode is formed on the fixed plate at a position facing the second thick portion of the diaphragm. 3. The pressure sensor according to claim 1, further comprising: fixing plates provided on both sides of the diaphragm, wherein the capacitors on both sides in a state where no pressure is applied are substantially equal. .