Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal
Reexamination Certificate
2001-01-23
2002-06-04
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
C257S417000, C257S416000, C257S429000
Reexamination Certificate
active
06399994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device for surface-shape recognition, more particularly relates to an electrostatic capacity type semiconductor device for surface-shape recognition for sensing fine topology of human fingerprints etc.
2. Description of the Related Art
Due to the growth of the information society, interest has risen in security in modern society. For example, in an information society, personal authentication has become an important key in constructing electronic cashing and other systems. Further, much research activity is going on regarding authentication as a defensive measure against theft and illicit use of credit cards.
Accordingly, much technology has been disclosed regarding surface shape recognition as represented by fingerprint sensors.
Here, the methods of detection in fingerprint and other shape recognition includes the optical detection method and the electrostatic capacity detection method.
The electrostatic capacity detection method is a method for detecting the value of the electrostatic capacity (hereinafter also simply referred to as a capacity value) between an electrode of a shape recognition sensor and for example a finger. The electrostatic capacity type is advantageous for mounting in a portable terminal etc. since it enables easy reduction of the size of the device, so there is active work being conducted on development of electrostatic capacity type sensors.
Here, an explanation will be made of a semiconductor device for surface-shape recognition according to the related art. Specifically, an explanation will be made of one for sensing the fine topology of human fingerprints etc.
FIG. 1
is a sectional view of an electrostatic capacity type semiconductor device for surface-shape recognition.
A gate electrode
30
forming a word line is formed above a channel formation region of a semiconductor substrate
10
via a not illustrated gate insulating film. Further, source and drain diffusion layers
11
are formed in the semiconductor substrate
10
at the two side portions of the gate electrode
30
. Thus, a transistor Tr is formed. One of the source and drain diffusion layers
11
of the transistor Tr is connected to a not illustrated bit lines.
An inter-layer insulating film
20
made of for example silicon oxide is formed covering the transistor Tr. Sensor pad electrodes
31
each formed by a laminate of a barrier metal layer made of for example Ti and an aluminum layer etc. are formed at an upper layer thereof while arranged in a matrix. A sensor pad electrode
31
is formed connected to the other source or drain diffusion layer
11
of the transistor Tr formed in a lower layer thereof by a not illustrated contact etc.
A first protective film
21
of an insulator made of for example a silicon nitride is formed over the entire surface while covering the sensor pad electrodes
31
and clearances between the sensor pad electrodes
31
. A neutralization electrode
32
a
fixed to a certain potential and made of for example Ti is formed at an upper layer of the first protective film
21
. A second protective film
22
of an insulator made of for example silicon nitride is formed over the entire surface while covering the first protective film
21
and the neutralization electrode
32
a
. Here, the surface of the second protective film
22
at the upper portion of the neutralization electrode
32
a
forms a convex shape M.
As described above, a semiconductor device for surface-shape recognition using a region wherein the sensor pad electrodes
31
are arranged in a matrix as a shape recognition surface is formed.
Next, an explanation will be made of the operation of a semiconductor device for surface-shape recognition.
As shown in
FIG. 2A
, when for example a human finger
7
touches the shape recognition surface of the semiconductor device for surface-shape recognition, capacitors are formed from the sensor pad electrodes
31
, the first protective film
21
and the second protective film
22
, and the finger
7
. The first protective film
21
and the second protective film
22
act as part of the capacitor insulating film. In the above description, the distances d between the sensor pad electrodes
31
and the finger
7
(for example d
1
, d
2
, . . . ) fluctuate in accordance with the topology
70
of the fingerprint. Accordingly, there arises a difference in the capacitances of the capacitors formed by the sensor pad electrodes
31
arranged above the shape recognition surface in the matrix. Therefore, it has become possible to recognize the shape of a fingerprint etc. by reading and detecting charges stored in the sensor pad electrodes
31
by a semiconductor element such as a transistor formed on the substrate
10
.
Here, each sensor pad electrode
31
forms a unit cell of the shape recognition surface of the semiconductor device for surface-shape recognition.
The capacitors configured by the sensor pad electrodes
31
have distances d equal to ∞ in all unit cells of the shape recognition surface of the semiconductor device for surface-shape recognition in a state where the finger
7
or the like does not touch the
10
shape recognition surface. Accordingly, the electrostatic capacity value C
s
becomes equal 0 in all unit cells.
On the other hand, in a state where the finger
7
or the like touches the shape recognition surface, as shown in
FIG. 2B
, in an n-th unit cell, capacitors of the electrostatic capacity value C
Sn
are formed from the sensor pad electrode
31
, the first protective film
21
and the second protective film
22
, and the finger
7
. The electrostatic capacity value C
Sn
is represented by:
C
Sn
=&egr;·&egr;
0
·S
/d
n
Here, S is the area contributing to the capacitor of each electrode, d
n
is a distance between the electrode of the n-th unit cell and the finger (for example d
1
, d
2
, . . . ), and n is the number of each unit cell (n=1, 2, 3, . . . ).
As the configuration for reading the electrostatic capacity value C
Sn
in the unit cells, there is employed a configuration wherein the capacitors formed from the sensor pad electrode
31
of each unit cell, the first protective film
21
and the second protective film
22
, and the finger
7
are connected to one source or drain diffusion layer
11
of the transistor using for example a word line WL (WL
1
, WL
2
, . . . ) as the gate electrode, the other source or drain diffusion layer
11
is connected to a bit line BL (BL
1
, BL
2
, . . . ), and further a capacitor of a electrostatic capacity value C
B
is connected to the bit line BL.
In the above configuration, by the touch of the finger in a state where V
CC
is applied to the bit line BL (V
CC
precharge), a potential change of the bit line BL represented by:
&Dgr;
V
n
=[C
Sn
/(
C
B
+C
Sn
)]·
V
CC
occurs. By detecting this potential change &Dgr;Vn in each cell, the electrostatic capacity value C
Sn
for every unit cell is calculated and image processing is performed to recognize the shape of the object.
Here, for example the human body etc. is generally sometimes charged. Therefore, in the conventional semiconductor device for surface-shape recognition, as shown in
FIG. 2A
, in order to prevent damage of the semiconductor device for surface-shape recognition due to discharge of static electricity to the shape recognition surface when the charged human puts his finger close to the shape recognition surface of the semiconductor device for surface-shape recognition, the neutralization electrode
32
a
fixed at for example the ground potential is provided near the surface of the shape recognition surface.
However, since the neutralization electrode
32
a
is formed at a predetermined position above the first protective film
21
made of for example silicon nitride, while the second protective film
22
made of for example silicon nitride is formed while covering the entire surfaces of the neutralization electrode
32
a
and the first protective film
21
, and the shape recognition surface forms
Meier Stephen D.
Sonnenschein Nath & Rosenthal
Sony Corporation
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