1. Field of the Invention
This invention relates to a pressure sensor and particularly to an inexpensive and simple pressure sensor having good static pressure characteristics.
2. Description of the Related Art
A conventional pressure sensor has a silicon base 9 and a boss 10 (see, for example, JP-UM-A-5-50335). The conventional pressure sensor will now be described in detail with reference to FIG. 1. FIG. 1 is a sectional view of the conventional pressure sensor.
In FIG. 1, a metal 5, which is a metal base, has a hole 6 to which a pressure is applied. Also a glass 4, which is a base, has the hole 6 to which a pressure is applied. The glass 4 and the metal 5 are mounted to each other by Au eutectic bond or the like. The glass 4 performs electrical and mechanical insulation.
Also, the silicon base 9 has the hole 6 to which a pressure is applied. The silicon base 9 and the glass 4 are mounted to each other. The boss 10 is provided between the silicon base 9 and the glass 4.
A silicon sensor 1, which is a sensor, has a diaphragm 2 connected to the hole 6. The silicon sensor 1 has a strain gauge 3 for converting a strain (displacement) occurring in the diaphragm 2 to an electric signal. One side of the silicon sensor 1 is mounted to the silicon base 9.
The other side of the silicon sensor 1 contacts a room B. The hole 6 and the diaphragm 2 form a room A.
A static pressure is applied to the silicon sensor 1, the silicon base 9, the glass 4 and the other parts in the conventional example of FIG. 1.
In the conventional example of FIG. 1 constructed as described above, the pressure applied to the hole 6 is converted to an electric signal. The strain gauge 3 in the conventional example of FIG. 1 generates an electric signal based on the differential pressure between the room A and the room B and the static pressure.
When the static pressure is applied, the silicon sensor 1, the silicon base 9 and the glass 4 are deformed, respectively. Since the silicon sensor 1 and the silicon base 9 have a large Young's modulus, these are deformed slightly. Since the glass 4 has a small Young's modulus, it is deformed largely.
The silicon base 9 and the boss 10 in the conventional example of FIG. 1 restrain transfer of the influence of deformation of the glass 4 to the strain gauge 3 of the silicon sensor 1. The boss 10 reduces the bond area between the silicon base 9 and the glass 4.
Moreover, some conventional pressure sensors (semiconductor pressure converting apparatus) separately have a structure for detecting a differential pressure and a structure for detecting a static pressure, and also have a structure for reducing interference with a differential pressure signal while increasing output of a static pressure signal (see, for example, Japanese Patent No. 2,656,566).
However, the conventional example of FIG. 1 has a problem that an error occurs in the application of the static pressure (static pressure characteristics).
Specifically, since the Young's modulus of silicon is different from the Young's modulus of glass, when the static pressure is applied, the deformation of the silicon sensor 1 and the silicon base 9 differs from the deformation of the glass 4, and a strain based on the deformation of the glass is generated in the strain gauge 3.
Moreover, since the glass 4 has characteristics such as delayed elasticity and viscoelasticity, it causes a strain in the diaphragm 2 and thus causes a strain in the strain gauge 3. This causes an error in the conventional example of FIG. 1.
Also, the silicon base 9 and the boss 10 in the conventional example of FIG. 1 have problems of increase in the number of components, increase in the number of processing steps, and high cost.
Moreover, the formation of the boss 10 has a problem of deteriorating the yield of bond. The formation of the boss 10 also has a problem of lowering broken pressure reduce the bond area.
Meanwhile, the conventional example of Japanese Patent No. 2,656,566 has a problem that it does not restrain occurrence of an error in the static pressure characteristics and cannot acquire good static pressure characteristics.