JP3756734B2 - Capacitive pressure sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitive pressure sensor, and more particularly to a capacitive pressure sensor whose diaphragm and base are made of sapphire.
[0002]
[Prior art]
Conventionally, since the corrosion resistance and the like are excellent, a capacitive pressure sensor using sapphire for a diaphragm or a base is often used. This sensor is formed by forming a movable electrode on a sapphire wafer forming a diaphragm, forming a fixed electrode in a recess of another sapphire wafer, and bonding the two wafers together. Further, by opening a through hole in the sapphire wafer on the fixed electrode side, the lead wire connected to each electrode is drawn out.
[0003]
4A is a plan view showing a conventional capacitive pressure sensor, and FIG. 4B is a sectional view taken along the line BB ′. As shown in these drawings, the pressure sensor 110 includes a base 101 provided with a fixed electrode 101a in a recess, a diaphragm 102 provided with a movable electrode 102a, a reference electrode 102b, and pads 102c, 102d, 102e, and 102f. The lead pins are soldered to the pads. FIG. 4B shows only the lead pins 103a and 103b connected by the solders 103c and 103d. These lead pins 103a and 103b are electrically connected to the reference electrode 102b and the fixed electrode 101a, respectively, and are used for capacitance detection between the electrodes. Here, the lead pin immediately below the pad 102e not connected to any electrode is a hollow pin, and is used to introduce a reference pressure into the capacity chamber.
[0004]
In the pressure sensor 110 configured in this way, the diaphragm 102 bends according to the pressure difference between the outside of the sensor and the inside of the capacity chamber 101c, and the capacity changes due to the change in the distance between the movable electrode 102a and the fixed electrode 101a. The pressure is measured.
[0005]
Here, the manufacturing process of the pressure sensor 110 will be described.
The base 101 and the diaphragm 102 are manufactured by processing a sapphire wafer. That is, through machining, laser processing or ultrasonic processing of a sapphire wafer, through holes for inserting lead pins 103a, 103b, etc. are opened, recesses are formed by dry etching, and then fixed electrodes are formed by vapor deposition. 101a is formed. A plurality of these through holes and fixed electrodes 101a in the recesses are formed on the same sapphire wafer.
[0006]
On the other hand, the movable electrode 102a, the reference electrode 102b, and the pads 102c to 102f are formed on another sapphire wafer by vapor deposition or the like. Similarly to the above, a plurality of these movable electrodes 102a and pads 102c to 102f are formed on the same sapphire wafer. Thereafter, the two wafers processed as described above are aligned so that the fixed electrode 101a and the movable electrode 102a face each other, and are directly bonded in a predetermined heating atmosphere. The sapphire wafer is then diced to form a chip. Finally, after the chip on the base 101 side is the top surface, the lead pin is dropped into the through hole, and a granular or ring-shaped solid solder (Sn—Ag solder) is placed in the gap between the through hole and the lead pin. The sensor chip is completed by heating and melting and connecting the lead pin and the pad by the molten solder flowing into the through hole.
[0007]
Through the above steps, conventionally, a sapphire capacitive pressure sensor having excellent corrosion resistance could be easily mass-produced.
[0008]
[Problems to be solved by the invention]
However, when soldering after dropping the lead pin from the back side, it is known that the diaphragm is distorted when the molten solder solidifies. Such distortion is, for example, as shown in FIG. 4B. The distortion occurs in the vicinity of the pad forming chamber 101b and then expands to the central portion of the capacity chamber 101c to cause distortion in the entire diaphragm 102. As a result, the offset of the pressure sensor varies and the measurable pressure range is narrowed. The detailed cause of this phenomenon has not been clarified at present, but it is definitely reproduced by the above manufacturing process.
[0009]
The present invention is for solving such a problem, and it is possible to prevent the distortion of the diaphragm generated when soldering the lead pin from expanding to the center of the diaphragm and to improve the measurement accuracy as compared with the conventional type. An object is to provide a sensor.
[0010]
[Means for Solving the Problems]
In order to achieve such an object, a capacitive pressure sensor according to the present invention includes a base, a fixed electrode disposed on the base, and is formed on the base to surround the fixed electrode. A side wall portion, a diaphragm which is joined to the side wall portion so as to face the base, and forms a capacity chamber together with the base and the side wall portion; and a movable electrode which is disposed on the diaphragm and faces the fixed electrode; The first and second pad forming chambers formed in the side wall and extending between the base and the diaphragm, and the first and second pad forming chambers and the capacity chamber communicate with each other. First and second slits, a first pad disposed on the base in the first pad forming chamber, connected to the fixed electrode through the first slit, and the second slit The diaphragm in the pad forming chamber A second pad disposed on the base and connected to the movable electrode through the second slit; and first and second pads formed on the base and communicating with the first and second pad forming chambers, respectively. Through holes, and first and second lead portions inserted into the first and second pad forming chambers through the first and second through holes and connected to the first and second pads, respectively. The first and second slits have a smaller width than the diameters of the first and second pad forming chambers.
[0011]
Moreover, this invention includes the following structures as another aspect. That is, the diaphragm and the base are made of sapphire, silicon, glass, or diamond. Further, a reference electrode provided on the diaphragm side is further provided.
[0012]
Therefore, according to the present invention, the width of the connecting portion between the pad forming chamber and the capacity chamber is narrower than the conventional one, and the distortion of the diaphragm generated in the pad forming chamber during soldering extends to the capacity chamber. This eliminates this, and a diaphragm that is flatter than before can be obtained. Therefore, variations in offset of the pressure sensor can be prevented, and there is an advantage that the measurable pressure range is not narrowed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1A is a plan view showing one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA ′. As shown in these drawings, the pressure sensor 10 includes a base 1 provided with a fixed electrode 1a in a recess, a diaphragm 2 provided with a movable electrode 2a, a reference electrode 2b, and pads 2c, 2d, 2e, and 2f. The lead pins are soldered to the pads (in FIG. 1B, only the lead pins 3a and 3b connected by the solders 3c and 3d are shown).
[0014]
In the pressure sensor 10 configured in this manner, the diaphragm 2 bends according to the pressure difference between the outside of the sensor and the inside of the capacity chamber 1c, and the capacity changes due to the change in the distance between the movable electrode 2a and the fixed electrode 1a. The pressure is measured.
[0015]
Here, the manufacturing process of the pressure sensor 10 will be described.
The base 1 and the diaphragm 2 are manufactured by processing a sapphire wafer. That is, by machining, laser processing, or ultrasonic processing of a sapphire wafer, through holes for inserting lead pins 3a, 3b, etc. are opened, and concave portions are formed by dry etching using Ar atoms. The fixed electrode 1a is formed by vapor deposition or the like. A plurality of these structures are formed on the same sapphire wafer.
[0016]
On the other hand, the movable electrode 2a, the reference electrode 2b, and the pads 2c to 2f are formed on another sapphire wafer by vapor deposition or the like. As described above, a plurality of these structures are formed on the same sapphire wafer. Thereafter, the two wafers processed as described above are aligned so that the fixed electrode 1a and the movable electrode 2a face each other, and directly bonded in a predetermined heating atmosphere (for example, 400 to 1300 ° C.). . The sapphire wafer is then diced to form a chip. Finally, after the chip on the base 1 side is made the top surface, the lead pin is dropped into the through hole, and a granular or ring-shaped solid solder (Sn—Ag solder) is placed in the gap between the through hole and the lead pin and heated ( The sensor chip is completed by connecting the lead pins and the pads with the molten solder that has been melted by, for example, 300 ° C. and flowed into the through holes.
[0017]
The fixed electrode 1a, the movable electrode 2a, and the reference electrode 2b are formed of, for example, a Pt / adhesion enhancement film. Ti, V, Cr, Nb, Zr, Hf, Ta, or the like is used as the adhesion enhancing film. The pads 2c to 2f are formed of, for example, Au / barrier film / adhesion enhancing film. Pt or the like is used as the barrier film, and Nb or the like is used as the adhesion enhancing film.
[0018]
Here, the features of this embodiment will be described.
In the present embodiment, by narrowing the width of the communication portion (slit) between the pad forming chamber 1b and the capacity chamber 1c, the distortion of the diaphragm 2 generated in the pad forming chamber 1b is prevented from expanding to the capacity chamber 1c. can do.
[0019]
FIG. 2 is an enlarged plan view of the pad forming chamber according to FIG. As shown in the figure, in the present embodiment, the width X in the communication portion (slit) between the pad forming chamber 1b and the capacity chamber 1c is made smaller than the diameter of the pad forming chamber 1b (that is, X < Y). Therefore, the joint area between the diaphragm 2 and the base 1 at the communication portion is larger than that of the conventional one, and the distortion of the diaphragm 2 generated during soldering can be prevented from expanding to the capacity chamber 1c. When the shape of the pad forming chamber 1b is a polygon or the like, the diameter of the inscribed circle may be Y and the width X of the communication portion (slit) may be compared. Further, the above relationship of X and Y is established between each pad forming chamber and the capacity chamber. As specific values of X and Y, (0.3, 1.0) or the like is used. The unit of each numerical value is mm (millimeter).
[0020]
Here, experimental results according to the present embodiment will be described.
FIG. 3 is a graph comparing the flatness of the diaphragm in the present embodiment and the conventional example. The vertical axis represents the amount of deflection in the direction perpendicular to the wafer surface, and the horizontal axis represents the position on the alternate long and short dash line from the pad edge to the diaphragm edge.
As shown in FIG. 6A, the deflection at the pad edge is approximately 0 μm in the conventional example, whereas the deflection at the diaphragm edge is approximately 1.2 μm. On the other hand, as shown in FIG. 5B, in this embodiment, the deflection at the pad edge is approximately 0 μm, and the deflection at the diaphragm edge is also a very small value of less than 0.1 μm. Therefore, it can be seen that by using the present embodiment, it is possible to prevent the deflection generated in the pad forming chamber from expanding to the capacity chamber.
[0021]
Although the case where sapphire is used as the material for the diaphragm and the base has been described above, the present invention is not limited to this. For example, a single crystal material such as silicon, glass, or diamond may be used. Further, the reference electrode is not an essential component and may be added as necessary. Therefore, the present invention includes a configuration using only the movable electrode and the fixed electrode.
[0022]
【The invention's effect】
As described above, in the present invention, since the width of the communication portion (slit) between the pad forming chamber and the capacity chamber is narrower than the diameter of the pad forming chamber, the bonding area between the diaphragm and the base is larger than that of the conventional structure. It increases and both are firmly fixed. Therefore, the distortion of the diaphragm generated in the pad forming chamber during soldering does not spread into the capacity chamber, and a diaphragm that is flatter than before can be obtained. Further, it is possible to prevent variations in offset of the pressure sensor, and there is an advantage that the measurable pressure range is not narrowed. In addition, since the diaphragm is flat, temperature hysteresis that is an error in pressure measurement can be reduced.
[Brief description of the drawings]
FIG. 1A is a plan view showing one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA ′.
FIG. 2 is a plan view showing a pad forming chamber according to FIG. 1;
FIG. 3 is a graph comparing the flatness of diaphragms in the present embodiment and a conventional example.
4A is a plan view showing a conventional example, and FIG. 4B is a sectional view taken along line BB ′.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base, 1a ... Fixed electrode, 1b ... Pad formation chamber, 1c ... Capacitance chamber, 2 ... Diaphragm, 2a ... Movable electrode, 2b ... Reference electrode, 2c, 2d, 2e, 2f ... Pad, 3a, 3b ... Lead pin 3c, 3d ... solder, 10 ... pressure sensor, X ... width of communication portion, Y ... diameter of pad forming chamber.

Claims (3)

The base,
A fixed electrode disposed on the base;
A side wall formed on the base and surrounding the fixed electrode;
A diaphragm which is bonded to the side wall portion so as to face the base and forms a capacity chamber together with the base and the side wall portion;
A movable electrode disposed on the diaphragm and facing the fixed electrode;
First and second pad forming chambers formed in the side wall and extending between the base and the diaphragm;
First and second slits communicating the first and second pad forming chambers and the capacity chamber, respectively;
A first pad disposed on the base in the first pad forming chamber and connected to the fixed electrode through the first slit;
A second pad disposed on the diaphragm in the second pad forming chamber and connected to the movable electrode through the second slit;
First and second through holes formed in the base and communicating with the first and second pad forming chambers, respectively.
A capacitive type including first and second lead portions inserted into the first and second pad forming chambers through the first and second through holes and connected to the first and second pads, respectively. In the pressure sensor,
A capacitive pressure sensor, wherein a width of the first and second slits is smaller than a diameter of the first and second pad forming chambers. In claim 1,
The diaphragm and the base are made of sapphire, silicon, glass or diamond, and are capacitive pressure sensors. In claim 1,
A capacitive pressure sensor further comprising a reference electrode provided on the diaphragm side.

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