Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-05-14
2001-10-30
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06308575
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of micro pressure sensor, and more particularly, to a manufacturing method for the miniaturization of silicon bulk-machined micro pressure sensors, and the structure of the micro pressure sensor manufactured by such a manufacturing method.
2. Description of Related Art
FIG. 5
shows the structure of a conventional micro-sensor fabricated by silicon bulk-micromachining. Such a micro-sensor is produced by bonding a bulk silicon wafer
51
to a glass substrate
52
. A cavity
53
is defined in a first face
511
of the bulk silicon wafer
51
before bonding such that a predetermined portion of the bulk silicon wafer
51
is provided as a diaphragm
54
Multiple resistors
55
and circuit connection (not shown) are formed on a second face
512
, which is opposite to the first face
511
, of the bulk silicon wafer
51
. Normally, there are four resistors
55
located on the edge of the diaphragm
54
so that the pressure asserted on the diaphragm
54
can be measured via the resistors
55
. This conventional micro-sensor suffers a disadvantage in that the dimension thereof is difficult to miniaturized. Because of the lattice structure of the bulk silicon wafer
51
, it is hardly to define a cavity
53
by known etching technique with side faces
531
perpendicular to the diaphragm
54
. Instead, the side faces
531
of the cavity
53
are always inclined with respect to the diaphragm
54
, which are known as the (111)-face slopes in the art. Such face slopes will result in wasting of chip area and therefore, prohibit the miniaturization of the silicon bulk-machined sensors.
FIG. 6
shows the structure of another conventional micro-sensor fabricated by silicon bulk-micromachining. This micro-sensor is produced by bonding a first bulk silicon wafer
61
to a second bulk silicon wafer
62
. The first bulk silicon wafer
61
is flat and provided as a diaphragm. The second bulk silicon wafer
62
has a cavity
63
defined in an upper face thereof. Multiple resistors
65
and circuit connection (not shown) are formed on the first bulk silicon wafer
61
for sensing the pressure asserted thereon. Because the resistors
65
has to be located on the edge of the cavity
63
, an alignment process must be undertaken when forming the resistors
65
. Further, since a high temperature annealing process has to be executed after bonding the first bulk silicon wafer
61
to the second bulk silicon wafer
62
to securely combine them together, the resistors
65
can be formed only after the bonding process to avoid being damaged by the high temperature. As a result, because the cavity
63
is inside the combination of the first and second bulk silicon wafers
61
,
62
and both of the bulk silicon wafers
61
,
62
are non-transparent, it is difficult to form the resistors
65
at desired positions with an alignment process. Therefore, there is a desired to improve the structure and the manufacturing method of the above micro pressure sensors to mitigate and/or obviate the aforementioned problems.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide a manufacturing method which is able to miniaturize the size of a silicon bulk-machined micro pressure sensor, and the structure of the micro pressure sensor manufactured by such a manufacturing method.
In accordance with one aspect of the present invention, the manufacturing method in accordance with the present invention includes a step to provide a bulk silicon wafer having an upper face formed thereon a desired circuit arrangement including a plurality of contact pads. The bulk silicon wafer defines a cutoff in an upper side portion thereof. A glass substrate is then provided to have an upper face defined therein a cavity having a relative small depth so that the side faces of the cavity are not significantly inclined with respect to the upper face of the glass substrate even though under cut in the side faces may be encountered due to an side etching effect. The glass substrate has a plurality of contact pads formed on the upper face thereof. The bulk silicon wafer is bonded to the glass substrate in such a manner that the upper face of the bulk silicon wafer is attached to the upper face of the glass substrate and the plurality of contact pads on the bulk silicon wafer securely attach to the plurality of contact pads on the glass substrate. An etching process is undertaken to reduce the bulk silicon wafer down to a thin membrane. Finally the bulk silicon wafer is etched to expose the contact pads on said glass substrate.
In accordance with another aspect of the present invention, the bulk-machined micro pressure sensor in accordance with the present invention includes a glass substrate having an upper face defined therein a cavity having a relative small depth, and a silicon membrane attached on the upper face of the glass substrate to cover the cavity. The miniaturization of such a micro pressure sensor is applicable because the cavity is so shallow such that the side faces of the cavity are not significantly inclined with respect to the upper face of the glass substrate even though undercut in the side faces may be encountered due to an side etching effect thereby eliminating the chip area wasting problem.
REFERENCES:
patent: 5614678 (1997-03-01), Kurtz et al.
patent: 5702619 (1997-12-01), Kurtz et al.
patent: 6150917 (2000-11-01), Meyer et al.
Chang Yih-Min
Yang Lung-Jieh
Bacon & Thomas
Chang Yih-Min
Oen William
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