Active pixel sensor with fully-depleted buried photoreceptor

Details Active pixel sensor with fully-depleted buried photoreceptor Active pixel sensor with fully-depleted buried photoreceptor

2000-03-01

2002-05-14

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S214100, C257S292000

Reexamination Certificate

active

06388243

ABSTRACT:

BACKGROUND
Active pixel sensors are well known in the art. The basic active pixel sensor is described in U.S. Pat. No. 5,471,515.
Active pixel sensors can use different kinds of active elements as their charge receiving elements.
FIGS. 1A-1C
show three different examples of three of the common image sensing active elements.
A basic photodiode active pixel is shown in FIG.
1
A. This includes a photodiode
100
on the substrate below an active oxide
102
. The photodiode is connected directly to an output transistor
104
. A gate
106
connects the photodiode
100
to a diffusion region
108
that is held at voltage VDD.
The photodiode can be reset by activating gate
106
, connecting the photodiode to VDD. Subsequent accumulation of charge changes the voltage on the photodiode.
The basic photogate active pixel sensor is shown in FIG.
1
B. The active photogate
120
connects to the output transistor
122
through a transfer gate
124
. This facilitates correlated double sampling in which the level of the photogate is first tested, then charge is transferred, and the value obtained again. Only the difference between the two charge amounts are used as an indication of the output. Hence, the output better indicates the amount of photogenerated electrons.
FIG. 1C
shows the so-called pinned photodiode used as an active element in an active pixel sensor. The pinned photodiode is shown in U.S. Pat. No. 5,625,210. A transfer gate with channel implant
140
is used to transfer the charge out of the photodiode
142
. The channel implant is used to adjust the bias of the pinned photodiode to facilitate charge output.
SUMMARY
The present system teaches using a fully-depleted buried photoreceptor with a coupled floating diffusion. The photoreceptor can be a “buried” diode, with an overlying portion of substrate.


REFERENCES:
patent: 4242695 (1980-12-01), Ouchi et al.
patent: 5471515 (1995-11-01), Fossum et al.
patent: 5563429 (1996-10-01), Isagai
patent: 5567632 (1996-10-01), Nakashiba et al.
patent: 5625210 (1997-04-01), Lee et al.
patent: 5903021 (1999-05-01), Lee et al.
patent: 5942774 (1999-08-01), Isogai et al.
patent: 6040593 (2000-03-01), Park
patent: 6180969 (2001-01-01), Yang et al.
patent: 6184055 (2001-02-01), Yang et al.

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