JP2852593B2 - Capacitive pressure 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 capacitance type pressure sensor for measuring a change in pressure of a medium to be measured, and more particularly to a chip structure of the capacitance type pressure sensor.

[0002]

2. Description of the Related Art In general, in a capacitance type sensor, it is necessary to use an insulating material for at least one of the substrates in order to minimize a parasitic capacitance generated between a pair of electrodes forming a sensing capacitance portion. I have.

Conventionally, as a capacitance type pressure sensor of this type, a cover glass 2 made of Pyrex having a fixed electrode 1 as shown in a cross section in FIG. And a silicon wafer 4 provided with a movable electrode 3 are disposed so that both electrode surfaces are opposed to each other with a gap G therebetween, and the peripheral portion thereof is joined by a joining portion 5 formed by anodic bonding. A pressure sensor has been proposed (JP-A-1-253627).

[0004]

However, in the above-mentioned conventional capacitive pressure sensor, the cover glass 2 and the silicon wafer 4 are made of different materials, and Pyrex and silicon have similar thermal expansion coefficients. However, they are not the same, and the temperature characteristics of the coefficient of thermal expansion are not the same, so that there is a problem that residual stress is generated at the time of joining, and this residual stress affects the displacement amount of the diaphragm. In addition, there is a problem that the value of the residual stress changes with time during use, thereby deteriorating accuracy.

Further, in the above-mentioned conventional capacitance type pressure sensor, since the cover glass 2 and the silicon wafer 4 are made of different materials, if the temperature changes during use, they are bonded due to a difference in thermal expansion coefficient. There is a problem that a thermal stress is generated in the portion 5 and the thermal stress affects a displacement amount of the diaphragm, resulting in a large temperature characteristic.

Further, since the silicon wafer 4 constituting the above-mentioned conventional capacitance type pressure sensor is easily corroded by a weak alkali or the like, when directly measuring the pressure of the liquid, the type of the liquid is considerably limited. There was a problem.

Therefore, the capacitance type pressure sensor of the conventional structure is affected by the residual stress of the substrate material constituting the package and the joint between the substrates, and adversely affects highly accurate and highly reliable pressure measurement. There was a problem.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and its object is to mass-produce with high accuracy without being influenced by the substrate material and the residual stress at the junction between the substrates. An object of the present invention is to provide a capacitance-type pressure sensor which has excellent reliability and enables highly reliable pressure measurement.

[0009]

In order to achieve the above object, the present invention provides a first sapphire substrate and a second sapphire substrate, each having a cavity at least one of which is provided with a depression, facing and closely contacting each other. It is formed by performing.

[0010]

According to the present invention, a first sapphire substrate;
The second sapphire substrate is directly adhered to and joined to the second sapphire substrate by the physicochemical bonding force of the sapphire without using a sealing material.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of a capacitive pressure sensor according to the present invention. FIG. 1 (a) is a plan view and FIG. 1 (b) is a sectional view thereof. In the figure, a sapphire substrate 11 is formed with a shallow concave portion 12 having a substantially square shape and a concave cross section in the center of the front surface side, and a conductive film at the bottom in the concave portion 12. A movable electrode 13 is formed as a first electrode to form a movable diaphragm structure.

Further, the second sapphire substrate 14
A fixed electrode 15 is formed as a second electrode made of the same material as that of the first sapphire substrate 11 and formed of a conductive film having a substantially square shape as a whole in a central portion on the surface side. And the sapphire substrate 1 on which the movable electrode 13 is formed
1 and the sapphire substrate 14 on which the fixed electrode 15 is formed are disposed with the two electrode forming surfaces facing each other via the concave portion 12, and the peripheral portions thereof are adhered to each other by direct bonding of sapphire without using a bonding material. To form a pressure sensor chip structure.

In this case, the surface of the substrate serving as a joint between the sapphire substrate 11 and the sapphire substrate 14 has a surface roughness Ra.
Is formed to have a flat mirror surface of about 10 ° or less, and a sapphire substrate 11 and a sapphire substrate 14 are opposed to each other at room temperature and bonded to each other.
By heating to about 0 ° C., the sapphires are brought into close contact with each other by physicochemical bonding force, and are firmly joined.

In such a configuration, the sapphire substrate 11 on which the movable electrode 13 is formed is displaced according to the pressure. Therefore, the pressure is measured by measuring the capacitance between the movable electrode 13 of the sapphire substrate 11 and the fixed electrode 15 of the sapphire substrate 14 which change in response to the change in pressure.

According to such a configuration, the sapphire substrate 11 and the sapphire substrate 14 are made of the same kind of material, and are closely bonded by a physicochemical bonding force without using a bonding material. After the joining of the substrate 11 and the sapphire substrate 14 is performed at a temperature higher than the operating temperature, even if the substrate 11 is cooled to the operating temperature, almost no residual stress is generated.

Further, even if there is a change in the operating temperature, the sapphire substrate 11 and the sapphire substrate 14 are made of the same kind of material, so that the temperature characteristics of the pressure sensor caused by the bonding are not adversely affected. Therefore, a highly accurate and highly reliable pressure sensor can be manufactured.

Since sapphire has better corrosion resistance than silicon and Pyrex, it is possible to directly measure the pressure of a liquid that cannot be used with silicon or Pyrex, for example, a weak alkaline liquid.

Further, since the sapphire substrate is used as the substrate of the capacitance type pressure sensor, in addition to the above-described effects, the alignment at the time of bonding the substrate can be easily performed from above the substrate by using the naked eye or an optical microscope. And productivity can be greatly improved.

Further, as for the sapphire substrate 11 and the sapphire substrate 14, it is relatively easy to obtain a wafer having almost no surface roughness that can be bonded without using a bonding material, and it is possible to easily constitute a high-precision pressure sensor. It is possible.

FIGS. 2A and 2B show a configuration of another embodiment of the capacitance type pressure sensor according to the present invention. FIG. 2A is a plan view and FIG. The same parts as those in the drawings are denoted by the same reference numerals. In the figure, a movable electrode 13 formed on a sapphire substrate 11 includes a sensing capacitor 13a and a reference capacitor 13b around the sensing capacitor 13a.

In such a configuration, the same effect as described above can be obtained, and due to the difference between the sensing capacitance portion 13a and the reference capacitance portion 13b in the peripheral portion, disturbances other than pressure, noise, and the like are canceled out, and high accuracy is achieved. Pressure measurement becomes possible.

Next, a method of manufacturing the capacitance type pressure sensor described with reference to FIG. 1 will be described. FIG. 3 is a cross-sectional view of a process for explaining one embodiment of a method of manufacturing a capacitance type pressure sensor. In the figure, first, as shown in FIG. 3A, a sapphire substrate 11 is prepared in which at least the surface of a peripheral portion to be opposed and joined is mirror-polished.

Next, as shown in FIG. 3B, a concave portion 12 is formed in a central portion of the sapphire substrate 11 by a dry etching method.

Next, as shown in FIG. 3C, a conductive thin film is formed in the concave portion 12 of the sapphire substrate 11 by CVD, sputtering or vacuum evaporation to form the movable electrode 13.

Next, as shown in FIG. 3D, a sapphire substrate 14 is prepared in which at least the surface of a peripheral portion which is arranged to be opposed and joined is mirror-polished.

Next, as shown in FIG. 3E, a fixed electrode 15 is formed by depositing a conductive thin film on the central portion of the sapphire substrate 14 by a CVD method, a sputtering method or a vacuum evaporation method.

Next, as shown in FIG.
The sapphire substrate 13 on which the fixed electrodes 15 are formed and the sapphire substrate 13 on which the electrode is formed are bonded together in a clean atmosphere without using a bonding material, with the electrode forming surfaces facing each other at around room temperature. Heat treatment is performed in an atmosphere to strengthen the bonding.

Next, as shown in FIG. 3 (g), the unbonded surface side of the sapphire substrate 13 is polished, and the sapphire substrate 13 is finished by grinding to a predetermined thickness corresponding to the pressure range.

In the above-described embodiment, the case where the shapes of the sapphire substrate 11 and the sapphire substrate 14 are square has been described. However, the present invention is not limited to this. Alternatively, it may be formed in various shapes such as an ellipse.

In the above-described embodiment, the recess 1
2 and the case where the shapes of the movable electrode 13 and the fixed electrode 15 are square are described. However, the present invention is not limited to this, and may be formed into various shapes such as a rectangle, a polygon, a circle, or an ellipse. Needless to say, it is good.

Further, in the above-described embodiment, the concave portion 1 provided between the sapphire substrate 11 and the sapphire substrate 14 is provided.
For example, vacuum, air, or other enclosures may be stored and used in 2.

FIG. 4 is a diagram showing a configuration of a capacitance type pressure sensor according to still another embodiment of the present invention. In the figure, reference numeral 21 denotes a first sapphire substrate. On the lower surface side of the first sapphire substrate 21, a shallow concave portion 22 having a concave cross section is formed.
A fixed electrode 23 made of a conductive film is formed on the inner bottom surface.

An electrode take-out hole 21a for the fixed electrode 23 is formed in the bottom surface of the groove 22 of the first sapphire substrate 21 so as to penetrate the outside. A lead of the fixed electrode 23 is provided in the inner surface of the electrode take-out hole 21a. The portion 23a is integrally formed and is drawn out to the upper surface of the first sapphire substrate 21 to form a fixed electrode extraction terminal 23b. Further, the first sapphire substrate 21 is provided with an atmospheric pressure introducing hole 21b in which the concave portion 22 communicates with the atmospheric pressure as shown in a perspective view as viewed obliquely from below in FIG. 4B.

On the lower surface of the first sapphire substrate 21 where the recess 22 is formed, a second sapphire substrate 24 is disposed so as to cover the recess 22, and the second sapphire substrate 14 is fixed. A movable electrode 25 and a terminal 25a for taking out the movable electrode 25 are formed on the upper surface side facing the electrode 23. In this case, the second sapphire substrate 24 is formed to be thinner than the first sapphire substrate 21 to form a movable diaphragm structure.

On the lower surface side of the second sapphire substrate 24, as shown in a perspective view as viewed obliquely from above in FIG.
6, a third sapphire substrate 27 provided with a measurement pressure introducing hole 27a communicating with the outside air of the concave portion 26 and a pressure applying concave portion 27b is provided. A pedestal 2 having an opening 28a communicating with the measurement pressure introducing hole 27a is provided on the lower surface of the third sapphire substrate 27.
8 are arranged.

Then, the first sapphire substrate 21 and the second
The respective peripheral joints between the sapphire substrate 24 and the third sapphire substrate 27 are closely adhered and fixed by direct joining of the sapphire, thereby forming a package structure of the capacitive pressure sensor chip.

In such a configuration, the movable diaphragm structure including the second sapphire substrate 24 on which the movable electrode 25 is formed is displaced according to the pressure introduced from the measurement introduction hole 27a. Therefore, the movable electrode 25 of the second sapphire substrate 24, which changes in response to the change in pressure,
The pressure is measured by measuring the capacitance of the gap G formed between the sapphire substrate 21 and the fixed electrode 23.

According to such a configuration, the measurement introduction hole 27
The measurement medium introduced from a is the second sapphire substrate 2
Since it has a contact structure only with the fourth and third sapphire substrates 27, it does not come into contact with easily corroded electrode materials such as the fixed electrode 23 and the movable electrode 25, so that the pressure of the measurement medium such as various gases, liquids, and water vapors is increased. Measurement becomes possible.

In addition, according to such a configuration, since the movable diaphragm structure and the main body such as a stainless steel tube to which the sensor chip is attached are separated from each other, the sensor chip received by the movable diaphragm structure is separated from the movable diaphragm structure. Since the influence of the residual stress generated at the joint portion with the main body is reduced, the influence of the error due to the residual stress is extremely reduced.

[0040]

As described above, according to the present invention,
By forming the pressure sensor chip structure with the same material of the first sapphire substrate and the second sapphire substrate,
Errors due to residual stress generated at the joint during manufacturing and thermal stress generated during use are less likely to occur. In addition, since the first sapphire substrate and the second sapphire substrate are joined to each other without using an adhesive, a submicron gap can be controlled.
When applied to a capacitive pressure sensor, a measurement capacitor gap with extremely good controllability can be obtained between the first sapphire substrate and the second sapphire substrate. Therefore, extremely excellent effects such as high-precision and highly reliable pressure measurement can be obtained. Further, since the package structure of the capacitive pressure sensor chip is made of the same material for the first sapphire substrate and the second sapphire substrate, these sapphire substrates have extremely high corrosion resistance. Since it is possible to directly contact the measurement medium such as gas, liquid, and water vapor, the pressure of all the measurement mediums can be reduced without using the sealing liquid that conventionally covered the surface of the sensor chip with silicon oil. A measurable pressure sensor is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a capacitance type pressure sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of another embodiment of the capacitance type pressure sensor according to the present invention.

FIG. 3 is a cross-sectional view of a step illustrating an example of a method for manufacturing the capacitance-type pressure sensor shown in FIG.

FIG. 4 is a diagram showing a configuration of a capacitance type pressure sensor according to still another embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a configuration of a conventional capacitance type pressure sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 sapphire substrate 12 concave portion 13 movable electrode 13 a sensing capacitance portion 13 b reference capacitance portion 14 sapphire substrate 15 fixed electrode 21 first sapphire substrate 21 a electrode extraction hole 21 b atmospheric pressure introduction hole 22 concave portion 23 fixed electrode 23 a lead portion 23 b fixed electrode extraction terminal 24 second sapphire substrate 25 movable electrode 25a movable electrode take-out hole 26 measurement pressure application recess 27 third sapphire substrate 27a measurement pressure introduction hole 27b pressure application recess 28 pedestal 28a opening 31 first sapphire substrate 32 recess 33 second Sapphire substrate 33a Atmospheric pressure introduction hole 33b Electrode extraction terminal 34 Strain gauge 35 Pedestal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-163514 (JP, A) JP-A-62-259475 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 9/12

Claims (1)

(57) [Claims] 1. A capacitance type pressure sensor having two parallel plate electrodes arranged in a cavity so as to face each other, wherein the cavity has a first sapphire substrate provided with a recess in at least one of the first and second sapphire substrates. An electrostatic capacitance type pressure sensor formed by opposing and closely contacting a sapphire substrate.