Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2002-08-15
2003-12-09
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S078000, C438S088000
Reexamination Certificate
active
06660537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to charge carriers in a semiconductor material and, more particularly, to a method of inducing charge carriers to move through the semiconductor material.
2. Description of the Related Art
Semiconductor devices often utilize an electric field to induce the movement of charge carriers through a semiconductor material from one location to another location. For example, an n+/p− photodiode is a semiconductor device that utilizes an electric field to collect photo-generated electrons.
FIG. 1
shows a cross-sectional diagram that illustrates a prior art n+/p− photodiode
100
. As shown in
FIG. 1
, photodiode
100
includes a p− substrate
110
and an n+ region
112
that is formed in substrate
110
. When n+ region
112
is formed in substrate
110
, a depletion region
114
is formed that separates substrate
110
from n+ region
112
.
In operation, photodiode
100
is first reset by placing a positive potential on n+ region
112
with respect to p− substrate
110
. The potential difference across the n+/p− junction reverse biases the junction, increasing the size of depletion region
114
and the magnitude of the electric field across the junction.
Once reset, light energy, in the form of photons, is collected by photodiode
100
which forms a number of electron-hole pairs. The electrons from the electron-hole pairs that are formed in depletion region
114
move under the influence of the electric field towards n+ region
112
, where each additional electron collected by n+ region
112
reduces the positive potential that was placed on n+ region
112
during reset. On the other hand, the holes formed in depletion region
114
move under the influence of the electric field towards p− substrate
110
.
In addition, the electrons, which are from the electron-hole pairs that are formed in p− substrate
110
within a diffusion length of depletion region
114
, diffuse to depletion region
114
and are swept to n+ region
112
under the influence of the electric field. Further, the electrons that are formed in n+ region
112
remain in n+ region
112
.
After photodiode
100
has collected light energy for a period of time, known as the integration period, sense circuitry associated with the photodiode detects the change in potential on n+ region
112
. As noted above, the electrons collected by n+ region
112
reduce the magnitude of the positive potential that was originally placed on n+ region
112
. Once the change in positive potential has been sensed, photodiode
100
is reset and the process is repeated.
One measure of photodiode
100
is the efficiency with which photodiode
100
can collect the photo-generated electrons. Not all of the electrons from the electron-hole pairs are collected by n+ region
112
. Instead, a number of electrons recombine with holes. When an electron recombines with a hole, the photo information associated with the electron is lost.
One limitation of photodiode
100
is that when photodiode
100
is reset, the space charge distribution is unequal.
FIG. 2
shows a perspective view that illustrates the n+ region
200
of a prior art n+/p− photodiode following reset. As shown in
FIG. 2
, n+ region
200
is a square-shaped area that has a contact region
210
.
During reset, a positive voltage is applied to contact region
210
for a predetermined period of time. When the positive voltage is removed, a number of zones of decreasing positive charge, such as zones Z
1
-Z
5
, result. When the electrons are then collected during the integration period, an unequal space charge distribution results.
The change in potential that occurs during the integration period can be detected by electrically connecting the potential on n+ region
112
to the gate of a source-follower transistor. An electrical connection to n+ region
112
is typically made by forming a contact on the surface of n+ region
112
. However, as shown in
FIG. 2
, the potential sensed by the contact depends on the zone Z
1
-Z
5
the contact is located in.
SUMMARY OF THE INVENTION
The present invention provides a method of inducing charge carriers to move through a semiconductor material to a collection region in the semiconductor material. The method utilizes a conductive trace that is formed over and insulated from the semiconductor material.
In accordance with the present invention, the method includes the step of making a sawtooth current flow through the conductive trace. The sawtooth current induces charge carriers to move through the semiconductor material to the collection region. The sawtooth current has a plurality of periods.
Each sawtooth period has a first edge and a second edge. The second edge has a steeper slope than the first edge, and induces charge carriers to move through the semiconductor material. The first edge, on the other hand, causes substantially no charge carriers to move through the semiconductor material.
REFERENCES:
patent: 6208497 (2001-03-01), Seale et al.
patent: 6297155 (2001-10-01), Simpson et al.
patent: 6355971 (2002-03-01), Schligtenhorst et al.
Hopper Peter J.
Hwang Kyuwoon
Lindorfer Philipp
National Semiconductor Corporation
Niebling John F.
Pickering Mark C.
Simkovic Viktor
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