Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2002-09-11
2004-07-27
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S214100, C257S292000, C348S302000
Reexamination Certificate
active
06768093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state imaging device and a driving method thereof. More particularly, the present invention relates to a solid state imaging device using a MOS (Metal-Oxide-Semiconductor) image sensor of a threshold voltage modulation system, the solid state imaging device being used for a video camera, an electronic camera, an image input camera, a scanner, a facsimile or the like, and relates to a driving method thereof.
2. Description of the Prior Art
Since a semiconductor image sensor such as a CCD (Charge Coupled Device) image sensor and a MOS image sensor is excellent in mass productivity, the semiconductor image sensor has been applied to almost all types of image input devices accompanied with the progress in a pattern micro fabrication technology.
Particularly, in recent years, the applicability of the MOS image sensor has been recognized again because of the advantages thereof, i.e., smaller power consumption compared with that of the CCD image sensor, and the capability of making a sensor element and a peripheral circuit element by the same CMOS (Complimentary Metal-Oxide-Semiconductor) technology.
In consideration of such a social trend, the present inventor has improved the MOS image sensor, and filed a patent application regarding a sensor element having a carrier pocket (high-density buried layer) under a channel region (Japanese Paten Application No. Hei 10-186453) to obtain a patent thereof (Registered Number 2935492).
In the invention according to the patent (Registered Number 2935492), a photo diode
111
and an insulated gate field effect transistor for optical signal detection (hereinafter, occasionally referred to as a MOS transistor for optical signal detection, or simply as a MOS transistor) are formed as placed adjacently to each other. The MOS transistor is provided with a ring-shaped carrier pocket in a well region under a channel region. The carrier pocket has a higher acceptor density than that of a peripheral portion thereof and serves as a potential well storing holes as carriers. In a state where the well region including the carrier pocket is depleted, holes are generated in the well region of the photo diode by light irradiation, followed by transferring the optically generated holes and storing in the potential well of the carrier pocket. As a result, negative charges of acceptor ions in the carrier pocket are neutralized and a threshold voltage is changed.
Further, the above-described MOS image sensor has a circuit constitution shown in
FIG. 8
of the patent (Registered Number 2935492). A series of operations of the MOS image sensor are passed through an initializing period, a storing period and a reading-out period by a control signal supplied from the CMOS circuit. During the initializing period, optically generated holes remaining in a hole pocket
25
are discharged to the substrate
11
through applying a positive voltage to each electrode. During the storing period, optically generated holes are generated by light irradiation and then stored in the carrier pocket
25
. Then, during the reading-out period, an optical signal proportional to the storage amount of the optically generated holes is detected.
However, the control signal supplied from the CMOS circuit is directed to the trend of lowering a voltage thereof, and this trend is contrary to a request of more perfectly performing the initialization by applying a high voltage during the initializing period.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a solid state imaging device, which is capable of being maintaining a low-voltage operation of a CMOS circuit and performing more perfectly an initializing operation, and a driving method thereof.
Incidentally, with such a constitution, in the case where an acceptor density or a pattern shape in the carrier pocket
25
is not even, as shown in
FIG. 10A
, the potential does not become even over the entire region of the carrier pocket
25
, and variation in height of the potential, that is, variation in depth of the potential well partially occurs occasionally.
In such a case, as shown in
FIG. 10C
, with regard to injection of holes having a potential at a low level, the holes are partialized at a place where the potential well is deeper, and a potential in the channel region is varied corresponding to this deviation. For this reason, there are problems that modulation of the threshold voltage does not become even in the channel region, element current distribution does not reflect storing distribution of the hole to lose linearity to a volume of stored holes, thus a so-called black batter occurs.
The second object of the present invention is to provide a driving method of a solid state imaging device, which is capable of modulating evenly a threshold voltage over the entire channel region of an insulated gate field effect transistor for light detection.
The present invention is related to the solid state imaging device. As a basic constitution thereof, as shown in
FIG. 3
, it is characterized in that the solid state imaging device of the present invention comprises a unit pixel
101
including a photo diode
111
and a MOS transistor
112
for optical signal detection placed adjacently to the photo diode
111
, in which a gate electrode of the MOS transistor
112
is connected to a vertical scanning signal (VSCAN) driving scanning circuit
102
, and a source region is connected to a voltage boost scanning circuit
108
. Further, it is characterized in that the drain region is connected to the drain voltage (VDD) driving scanning circuit
103
in addition to the foregoing constitution.
Moreover, in unit pixel
101
, as shown in FIG.
1
and
FIG. 2A
, the photo diode
111
and the MOS transistor
112
are formed in well regions
15
a
and
15
b
connected to each other, and the unit pixel
101
comprises a high-density buried layer (carrier pocket)
25
for storing optically generated charges in the well region
15
b
in a peripheral portion of the source region
16
of the MOS transistor
112
.
In a driving method of the present invention, a voltage boost scanning circuit
108
is connected to the source region
16
of the MOS transistor
112
for optical signal detection, and in an initializing period, a boosted voltage is applied to the source region
16
from the voltage boost scanning circuit
108
in the state that the vertical scanning signal (VSCAN) driving scanning circuit
102
is isolated from the gate electrode
19
, or in addition to the isolation of the circuit
102
, the drain voltage (VDD) driving scanning circuit
103
is isolated from the drain region
17
a
. Thus, a boosted voltage higher than a power supply voltage of the VSCAN driving scanning circuit
102
is applied further to a gate electrode
19
through a capacitor between the source region
16
and the gate electrode
19
from the voltage boost scanning circuit
108
, in addition to a gate voltage having applied thereto during the storing period. In other words, since a high voltage is applied to the source region
16
and the gate electrode
19
, a sweeping operation of the stored charges from the carrier pocket
25
can be performed more perfectly.
As described above, as the solid state imaging device of the present invention comprises the boosted voltage scanning circuit
108
, the first object of more perfectly performing the sweeping operation while maintaining to lower the outer supply voltage is attained.
Moreover, the present invention is related to a driving method of the solid state imaging device. As shown in
FIG. 8
, a voltage is applied to the gate electrode
19
of the insulated gate field effect transistor
112
for optical signal detection so that most of the optically generated charges stored in the carrier pocket
25
are discharged from the carrier pocket
25
during the initializing period and a specified amount thereof is made to remain in the carrier pocket
25
.
In other words, the present invention, particularly as show
Innotech Corporation
Lorusso, Loud & Kelly
Pyo Kevin
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