Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Reexamination Certificate
1999-10-08
2001-10-30
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
C257S254000, C257S414000, C257S415000, C438S048000, C073S862046, C382S124000, C382S125000
Reexamination Certificate
active
06310371
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor chip, and more particularly, to a fingerprint sensor chip.
2. Description of the Prior Art
In semiconductor processing, a fingerprint sensor chip is a type of functional chip used as a biometric sensor, sequentially packaged with a fingerprint discriminator. The fingerprint sensor chip comprises approximately ninety thousand metal plates arranged as a 300×300 pixel matrix, these plates positioned between an inter-metal dielectric (IMD) layer and a protective layer. Each of the metal plates is used as a sensor plate of the fingerprint chip. When a user touches the protective layer, each of the sensor plates senses the static voltage from the surface contact of the user's finger. The voltages recorded by each sensor plate will vary with the undulating surface of the user's finger, and together they form a pattern of the fingerprint. This pattern can be passed on to image recognition circuits to provide recognition and discrimination of the fingerprint.
Please refer to FIG.
1
and FIG.
2
.
FIG. 1
is a schematic diagram of the layout of sensor areas
23
on a fingerprint sensor chip
13
according to the prior art.
FIG. 2
is a cross-sectional schematic diagram along line
2
—
2
of the fingerprint sensor chip
13
shown in FIG.
1
. The prior art fingerprint sensor chip
13
is formed on a dielectric layer
12
of a semiconductor wafer
10
on which a plurality of rectangular sensor areas
23
arranged in a matrix format are defined. The fingerprint sensor chip
13
comprises conductors
14
positioned on the dielectric layer
12
surrounding each of the sensor areas
23
, an IMD layer
15
covering the dielectric layer
12
and the conductors
14
, a plurality of metal plates
22
positioned on the IMD layer
15
above each sensor area
23
, and a protective layer
24
covering the metal plates
22
and the IMD layer
15
. The IMD layer
15
is a complex structure that comprises a spin on glass (SOG) layer
18
and a silicon oxide layer
20
. The SOG layer
18
fills the space between each conductor
14
and smoothes the outer-most sides of each conductor
14
. The silicon oxide layer
20
covers the dielectric layer
12
, the conductors
14
and the SOG layer
18
.
Each of the conductors
14
is used as an electrical connection to pattern recognition circuits or any other internal circuitry of the fingerprint sensor chip
13
. Each of the metal plates
22
is used as a sensor plate of the fingerprint sensor chip
13
. The protective layer
24
is used to protect the internal circuitry of the fingerprint sensor chip
13
. When a user touches the protective layer
24
, each of the metal plates
22
senses static voltages from the surface contact of the user's finger. Then, the voltage variations across all the metal plates
22
are combined to produce a pattern of the fingerprint.
However, the SOG layer
18
positioned on the outer-most walls of the two adjacent conductors
14
and the surface of the dielectric layer
12
form a groove, which makes the surface of the silicon oxide layer
20
uneven. Consequently, the surfaces of the metal plates
22
formed on the groove are lowered in their centers and raised at their edges. When the user touches the fingerprint sensor chip
13
, the distances from the center of the metal plate
22
to the user's finger and those from the edges of the metal plate
22
to the user's finger are not the same. This difference will effect the sensitivity and accuracy of the metal plates
22
.
Also, the surface of the protective layer
24
has protrusions and depressions, in relation to the raised edges of each metal plate
22
. When the fingerprint sensor chip
13
undergoes a cleaning process with a high-pressure water column, such as is done after mounting on a printed circuit board (PCB), cracks can easily form in the sunken surface of the protective layer
24
. These cracks will allow water to permeate into the electric conductors
14
and lead to short-circuiting. Furthermore, during the packaging of the fingerprint sensor chip
13
, cracks in the protective layer
24
can cause it to more easily pull away from the surface of the chip, rendering the device inoperable.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a fingerprint sensor chip to solve the above-mentioned shortcomings.
In a preferred embodiment, the present invention provides a fingerprint sensor chip formed on a semiconductor wafer, the semiconductor wafer comprising a first dielectric layer, the fingerprint sensor chip comprising:
a plurality of rectangular sensor areas arranged in a matrix format on the semiconductor wafer, each of the sensor areas being surrounded by electric conductors;
a second dielectric layer covered on the sensor areas and the conductors, the surface of the second dielectric layer positioned above each of the sensor areas being formed as a protruding rectangular platform with a shallow trench surrounding the platform, the shallow trench being positioned above the conductors around the sensor area;
a rectangular metal plate positioned on the top end of each of the rectangular platforms which is used as a sensor plate of the fingerprint sensor chip; and
a protective layer positioned on the surface of the semiconductor wafer for covering and protecting each of the metal plates and the second dielectric layer.
It is an advantage of the present invention that the fingerprint sensor chip provides an even finger contact surface and even rectangular sensor plates, which enhances the sensitivity and accuracy of the fingerprint sensor chip. Also, this design helps to avoid damage to the chip in subsequent packaging and cleaning processes.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.
REFERENCES:
patent: 5373181 (1994-12-01), Scheiter et al.
patent: 5400662 (1995-03-01), Tamori
patent: 5869791 (1999-02-01), Young
patent: 6060756 (2000-05-01), Machida et al.
patent: 6088471 (2000-07-01), Setlak et al.
patent: 363221483 (1988-09-01), None
patent: 2000356506 (2000-12-01), None
Hsu Winston
Mintel William
United Microelectronics Corp.
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