Semiconductor device manufacturing: process – With measuring or testing – Optical characteristic sensed
Reexamination Certificate
2000-02-29
2002-03-05
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
With measuring or testing
Optical characteristic sensed
C438S016000, C438S030000, C438S048000, C257S231000, C257S232000, C257S233000, C257S072000, C257S290000, C257S291000, C257S292000, C257S293000
Reexamination Certificate
active
06352869
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of solid state photo-sensors and imagers, and more specifically to semiconductor based imagers referred to as Active Pixel Sensors (APS).
BACKGROUND OF THE INVENTION
Active Pixel Sensors (APS) are solid state imagers wherein each pixel contains a photo-sensing means with associated active circuitry elements. These active circuitry elements typically are means to perform a pixel reset function, or some means to transfer charge, means to perform a voltage conversion, or circuitry elements used in amplification. APS devices have been operated in a manner where each line or row of the imager is selected and then read out using a column select signal (analogous to a word and bit line in memory devices respectively). Prior art devices have been disclosed in which all of these components have been located entirely within a single pixel boundary.
Inclusion of these active circuit element components in each pixel reduces the fill factor for the pixel because it takes up area that could otherwise be used for the photodetector. This reduces the sensitivity and saturation signal of the sensor which in turn adversely affects the photographic speed and dynamic range of the sensor, performance parameters that are critical to obtaining good image quality. Additionally, inclusion of these active circuit elements within the pixel places a limitation on the minimum size of the pixel, which adversely affects the size and cost of the image sensor.
In order to build high resolution, small pixel APS devices, it is necessary to use sub &mgr;m CMOS processes in order to minimize the area of the pixel allocated to the row select transistor and other parts of the amplifier in the pixel. In essence, it takes a more technologically advanced and more costly process to realize the same resolution and sensitivity APS device when compared to a standard charge coupled device (CCD) sensor. However, APS devices have the advantages of single 5V supply operation, lower power consumption, x-y addressability, image windowing and the ability to effectively integrate signal processing electronics on-chip, when compared to CCD sensors.
A typical prior art APS pixel is shown in FIG.
1
. The pixel comprises a photodetector
14
, that can be constructed from either a photodiode or photogate technology, a transfer gate
15
, a floating diffusion
16
, reset transistor
18
with a reset gate
19
, a row select transistor
8
with a row select gate
9
, and signal transistor
7
which is a source follower amplifier. Inclusion of all these components within a single pixel results in a reduction in the fill factor, sensitivity and minimum size of the pixel.
Referring to
FIG. 2A
in conjunction with
FIG. 2B
, one approach to providing an image sensor with the sensitivity of a CCD and the advantages of an APS device, is to improve the fill factor and sensitivity of an APS device by reducing the amount of area allotted to components within a single pixel while maintaining the desired features and functionality of the pixel architecture.
Referring to
FIG. 2A
in conjunction with
FIG. 2B
, U.S. patent application Ser. No. 08/808,444, entitled “Active Pixel Sensor With Inter-Pixel Function Sharing” by Guidash discloses a manner in which fill factors for APS devices can be increased. This prior art device of Guidash teaches the sharing of various components typically employed within an Active Pixel Sensor. Sharing of the floating diffusion, source follow amplifier, row select transistor, and reset transistor between two row adjacent photodetectors and transfer gates are disclosed here to assist in increasing the fill factor of the pixel architecture. The basic concept utilized by Guidash for increasing fill factor is the fact that a row at a time is read out during operation of the sensor. Accordingly, Guidash was able to provide a single floating diffusion
26
and a single amplifier
27
for pixels located in two adjacent rows, instead of requiring one for every pixel as in the APS device shown in FIG.
1
. Since only one row is read out at a time, a single floating diffusion
26
, reset transistor
28
, row select transistor
29
and signal transistor
27
(typically a source follower transistor) can be used for two adjacent pixels in separate rows.
While allowing for the sharing of components and increasing the fill factors within active pixel sensors, the device shown in
FIG. 2
does not allow for the combining of function between both rows and columns, and accordingly the increase in fill factor that would result from such an architecture.
It should be readily apparent from the foregoing discussion that there remains a need within the art for an APS architecture that will allow for the combining of electrical functions between row as well as column pixels and the resulting increase in fill factor.
SUMMARY OF THE INVENTION
This invention addresses the aforementioned problems within prior art Active Pixel Sensor (APS) devices. It comprises a pixel and column circuitry architecture innovation that provides a higher fill factor pixel or a smaller pixel. By sharing components between adjacent columns and adjacent rows, components can be shared by four (4) separate photodetectors and transfer gates instead of two (2). This invention provides a means to further improve fill factor and further diminish the minimum pixel size by sharing the aforementioned components additionally between two column adjacent photodetectors and transfer gates, so that these components are now shared by four separate photodetectors and transfer gates, while maintaining the ability to selectively address specific pixels of the APS device.
Briefly summarized, according to one aspect of the present invention is an image sensor having a plurality of pixels arranged in a series of rows and columns comprising: a semiconductor material of a first conductivity type having at least two adjacent row pixels and at least two adjacent column pixels formed within the substrate, and at least one electrical function integrated within the adjacent pixels that is shared between the adjacent pixels.
These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention has the following advantages:
High fill factor, sensitivity and saturation signal for the same pixel size.
Smaller pixel and device size for the same fill factor, providing a lower cost device.
REFERENCES:
patent: 4636865 (1987-01-01), Imai
patent: 5144447 (1992-09-01), Akimoto et al.
patent: 5237190 (1993-08-01), Wu et al.
patent: 5243180 (1993-09-01), Nam
patent: 5280186 (1994-01-01), Lee
patent: 5338948 (1994-08-01), Sims
patent: 5418387 (1995-05-01), Nakamura et al.
patent: 5517043 (1996-05-01), Ma et al.
patent: 5600159 (1997-02-01), Monoi et al.
patent: 5867215 (1999-02-01), Kaplan
patent: 6107655 (2000-08-01), Guidash
patent: 6160281 (2000-12-01), Guidash
patent: 0 757 476 (1997-02-01), None
patent: 0 862 219 (1998-09-01), None
patent: 63-261744 (1988-10-01), None
Eiji Oba et al., “Imaging Circuits and Systems”/Papers 11.1-11.5,IEEE International Solid-State Circuits Conference,pp. 180-189 and 452-454.
Hon-Sum Wong, “Technology and Device Scaling Considerations for CMOS Imagers”,IEEE Transactions on Electron Devices,vol. 43, No. 12, Dec. 1996, pp. 2131-2142.
Eric R. Fossum, “Active Pixel Sensors: Are CCD's Dinosaurs?”, Jet Propulsion Laboratory, California Institute of Technology,SPIEvol. 1900, pp. 2-14.
Robert M. Guidash, U.S. Patent Application Serial No. 08/808,444, Active Pixel Sensor with Inter-Pixel Sharing, filed Feb. 28, 1997.
R. H. Nixon et al., 128/128 CMOS Photodiode-type Active Pixel Sensor With On-Chip Timing, Control and Signal Chain Electronics Center For Space Microelectronics Technology, Jet Propulsion Laboratory—California Institute of Technolog
Eastman Kodak Company
Lee Granvill D.
Smith Matthew
Watkins Peyton C.
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