Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1998-12-18
2001-05-08
Lee, Eddie C. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S254000, C257S417000, C438S053000
Reexamination Certificate
active
06229190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to pressure sensors, and specifically, to fluid media compatible integrated pressure sensors.
2. Background Information
FIG. 1
a
illustrates a schematic view of a conventional, commercially available semiconductor pressure sensor
1
, which is a Motorola™ MPX4100 pressure sensor. This device integrates a silicon sensor, bipolar operational amplifier circuitry, and thin film resistor networks to provide an output signal and temperature compensation on a single die. As shown, the pressure sensor
1
includes a sensing element
2
, a thin film temperature compensation and first gain stage
3
, and a second gain stage and ground reference shift circuitry
4
. A vacuum is sealed behind the sensor diaphragm, providing a pressure reference.
FIG. 1
b
illustrates a cross-sectional view of the conventional pressure sensor
1
of
FIG. 1
a.
Referring to
FIG. 1B
, the pressure sensor
1
includes a die
5
having a diaphragm
6
and is attached to a backing wafer
7
to form a sealed vacuum reference cavity
8
. The backing wafer
7
is attached to an epoxy plastic case
9
by way of a die bond, as shown by numeral
10
. The die
5
is interconnected to a leadframe
11
by way of one or more wire bonds
12
. A metal or plastic cap
13
having an opening
14
is mounted to the case
9
, for directing external pressure to the sensor. The case
9
has a second opening
15
on the opposite side of the opening
14
with an associated hole through the backing wafer
7
for gage or differential pressure sensing. A fluoro or silicone gel
16
is coated over the die
5
to provide a minimal amount of protection for the die surface and wire bonds
12
from harsh environments, while allowing the pressure signal to be transmitted to the diaphragm
6
.
However, the pressure sensor
1
has a primary drawback in that its operating characteristics are based on use of dry air as the pressure media. Media other than dry air may have adverse effects on sensor performance and long-term stability.
FIG. 2
is a typical prior art sensor
20
for fluid media compatible applications. The sensor package
20
includes a sensor die
21
which is placed in a metal housing
22
with hermetic glass feed-through pins
23
. The sensor die
21
has an integral glass or silicon constraint bottom
24
which provides a sealing cavity
25
therebetween for vacuum reference and stress isolation from the housing. The die attach material is typically a soft material such as RTV. A metal diaphragm
26
is welded to the metal housing
22
and an inside cavity
27
formed therein is filled with oil to allow transfer of pressure to the sensor die
21
. This configuration isolates the sensor die
21
from the fluid media. The use of the metal diaphragm is the primary packaging technique available today for more demanding applications, with variations in pressure and ability to apply most fluids to the sensor package. However, this type of package only generally addresses specific applications and is very expensive.
Therefore, there is a need in the industry for a pressure sensor that is compatible with fluid media as well as gaseous media and overcomes the drawbacks mentioned above.
SUMMARY OF THE INVENTION
The present invention comprises a semiconductor pressure sensor compatible with fluid and gaseous media. The semiconductor pressure sensor includes a semiconductor die and a silicon cap that is bonded to the semiconductor die, and a pressure port hermetically attached to the semiconductor die. The semiconductor die includes a diaphragm that incorporates piezoresistive sensors thereon, and a stress isolation mechanism for isolating the diaphragm from packaging and mounting stresses. The silicon cap includes a cavity for allowing the diaphragm to deflect. The sensor capsule and pressure port may be incorporated into a plastic housing. In one embodiment, an integral vacuum reference is formed within the cavity. The semiconductor die and portions of the package exposed to the fluid media are optionally coated with one or more chemical resistant coatings.
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Bryzek Janusz
Burns David W.
Cahill Sean S.
Nasiri Steven S.
Blakely , Sokoloff, Taylor & Zafman LLP
Lee Eddie C.
Maxim Integrated Products Inc.
Wilson Allan R.
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