Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-13
2001-02-27
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C257S290000, C257S292000
Reexamination Certificate
active
06194702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to active pixel sensors and in particular an active pixel sensor which approximately doubles the available signal for a given quanta of light.
2. Description of Related Art
A conventional Active Pixel Sensor (APS) cell consists of an np diode in the p-substrate, an NFET transfer device, a source-follower amplifying transistor, a pre-charge transistor, and a bit switch transistor. Electron-hole pairs are produced in the diode by impinging photons. The electrons are collected in the pre-charged n region of the diode, and eventually transferred to the source-follower gate for amplification. A p-type pinning layer is often included at the surface of the diode.
In APS cells, pn diodes collect electrons generated by incoming light. The electron charge is amplified and the signal-to-noise ratio is proportional to the charge level. Holes generated by the light are not collected and recombine in either of the p-type terminals.
FIG. 1
a
illustrates a schematic cross-section of the photodiode and the transfer gate.
FIG. 1
b
illustrates the schematic of the circuit embodied in each Active Pixel Sensor device
10
. The number of electrons collected determines the level of gate drive on the source-follower transistor
12
. The source potential is transferred down the column through the bit switch
14
, where it can be processed appropriately for video imaging. In the conventional cell
10
, holes equal in number to the electrons are created and are shunted to the substrate
16
creating a substrate current which exits the cell through the ground line.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an active pixel cell device for video imaging whereby the size of the pixel cell is reduced.
It is another object of the present invention to provide an active pixel sensor which produces an output signal and a complementary output signal.
It is another object of the present invention to provide an active pixel sensor device with improved common-mode mode noise rejection.
It is another object of the present invention to provide an active pixel sensor device with improved signal-to-noise ratio.
It is another object of the present invention to provide an active pixel sensor device with reduced fixed pattern noise.
It is another object of the present invention to provide an active pixel sensor device with a reduced size collection area.
A further object of the invention is to provide an active pixel sensor device which approximately doubles the output current relative to conventional active pixel sensor devices.
It is yet another object of the present invention to provide an active pixel cell device which virtually eliminates substrate current.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, an active pixel sensor cell comprising: a photosensitive device; a first device coupled to the photosensitive device; and a second device coupled to the photosensitive device; wherein the photosensitive device generates charges in response to electromagnetism impinging on the photosensitive device, the first device draws a first type of generated charge away from the photosensitive device, and the second device draws a second type of generated charge away from the photosensitive device.
In another aspect, the device of the present invention is directed to an active pixel sensor cell comprising: a photosensitive device; a first active pixel sensor circuit adapted to create a path for electron flow from the photosensitive device; and a second active pixel sensor circuit adapted to create a path for hole flow from the photosensitive device.
In another aspect, the present invention is directed to a method of using an active pixel sensor device comprising the steps of: (a) providing an active pixel sensor cell device comprising: a photosensitive device; a first active pixel sensor circuit adapted to create a path for electron flow from the photosensitive device; a second active pixel sensor circuit adapted to create a path for hole flow from the photosensitive device; (b) collecting light with the photosensitive device; (c) creating a first current of electron flow from the photosensitive device to the first active pixel sensor circuit; and (d) creating a second current of hole flow from the photosensitive device to the second active pixel sensor circuit.
In another aspect, the present invention is directed to a method of using an active pixel sensor device comprising the steps of: (a) providing an active pixel sensor cell device comprising: a photosensitive device; a first active pixel sensor circuit adapted to create a path for electron flow from the photosensitive device comprising: a first transfer device in series with the photosensitive device adapted to transfer electrons from the photosensitive device; a first pre-charge device adapted to collect electrons which flow through the first transfer device; a first source-follower device adapted to amplify the electrons collected by the first pre-charged device; and a first bit switch device adapted to control an output signal; and a second active pixel sensor circuit adapted to create a path for hole flow from the photosensitive device comprising: a second transfer device in series with the photosensitive device adapted to transfer holes from the photosensitive device; a second pre-charge device adapted to collect holes which flow through the second transfer device; a second source-follower device adapted to amplify the holes collected by the second pre-charged device; and a second bit switch device adapted to control a second output signal; (b) collecting light with the photosensitive device; (c) creating electron-hole pairs by impinging photons; (d) transferring electrons from the photosensitive device with the first transfer device; (e) collecting electrons in the first circuit pre-charge device; (f) amplifying electrons with the first circuit source-follower device; (g) switching electrons with the first bit switch device in order to control a first output current; (h) transferring holes from the photosensitive device with the first transfer device; (i) collecting holes in the second circuit pre-charge device; (j) amplifying holes with the second circuit source-follower device; (k) switching the holes with the second bit switch device in order to control a second output current; and (l) processing the first and second output current signals for video imaging.
In yet another aspect, the present invention is directed to a method of making an active pixel sensor device comprising the steps of: (a) providing an n type wafer substrate; (b) creating an insulating region having first and second sides; (c) creating a first isolation region in the n-epitaxy layer and on the first side of the insulating region; (d) creating a second isolation region in the n-epitaxy layer and positioned on the second side of the insulating region; (e) implanting a p-diode region in the n-epitaxy region positioned on the first side of the insulating region; (f) implanting a p-body region in the substrate on the second side of the insulating region; (g) implanting an n-type diode in a portion of the p-diode region; (h) depositing gate material on the n-epitaxy layer for defining first and second gate regions, the first gate region aligned over an edge of the p-diode region, the second gate region aligned over an edge of the n diode region; (i) implanting a p pinning layer in the n-epitaxy layer and between the first and second gate regions; (j) implanting a p+ source/drain in the epitaxy layer and between the first isolation region and the first gate region; and (k) implanting an n+ source/drain in the n-epitaxy layer and between the second
Hook Terence B.
Johnson Jeffrey B.
Wong Hon-Sum P.
DeLio & Peterson LLC
International Business Machines - Corporation
Le Que T.
Luu Thanh X.
Peterson Peter W.
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