Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2000-10-06
2003-04-01
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S241000, C257S249000, C348S320000, C348S322000
Reexamination Certificate
active
06541805
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a solid-state image pickup device serving as an area image sensor and a method of driving the same, and in particular, to a solid-state image pickup device of interline transfer type including a plurality of photoelectric converter columns and a plurality of vertical transfer charge-coupled devices (CCD) and a method of driving the same.
b) Description of the Related Art
After mass production techniques for CCD have been established, video cameras, electronic still cameras, and the like using a CCD-type solid-state image pickup device serving as an area image sensor are rapidly coming into wide use. The CCD-type solid-state image pickup devices are classified by structure into several kinds, for example, a solid-state image pickup device of interline transfer type (to be abbreviated as “IT-CCD” herebelow).
An IT-CCD includes a semiconductor substrate and a large number of photoelectric converter elements or simply photoelectric converters arranged on a surface of the substrate in columns and rows with a fixed pitch. Each of the photoelectric converter columns and rows includes a plurality of photoelectric converters. Each photoelectric converter ordinarily is a photodiode.
A photoelectric converter being composed of a pn photodiode is produced as follows. A p-type well is formed on a desired surface of, for example, a semiconductor substrate and then an n-type region having a desired contour is formed in the p-type well. When necessary, a p
+
-type region is formed on the n-type region. Signal charge is stored or accumulated in the n-type region. That is, the n-type region functions as a signal charge storing or accumulating region.
In this specification, a term “photoelectric converter (element)” indicates only the signal charge storing region in some cases. Also, “adjacent to a photoelectric converter” means “adjacent to a signal charge storing region constituting a photoelectric converter”, and “contiguous to a photoelectric converter” means “contiguous to a signal charge storing region constituting a photoelectric converter”.
Adjacent to each photoelectric converter column, one charge transfer channel is formed. An IT-CCD therefore includes a plurality of charge transfer channels. Each charge transfer channel is used to transfer signal charge accumulated in each photoelectric converter of the photoelectric converter column adjacent to the charge transfer channel.
On the surface of the semiconductor substrate, a plurality of transfer electrodes is formed with an electrically insulating film therebetween. The electrodes intersect the charge transfer channels in a plan view. Each intersection between the transfer electrodes and the charge transfer channels in the plan view serves as one charge transfer stage. That is, one charge transfer channel and a plurality of charge electrodes constitute one vertical charge CCD.
In this specification, a region constituting the charge transfer stage in each transfer electrode of the vertical transfer CCD is called “transfer path forming section”.
Each vertical transfer CCD of an IT-CCD of interlace drive type usually includes two charge transfer stages for one photoelectric converter. Each vertical transfer CCD of an IT-CCD of overall pixel readout type usually includes three or four charge transfer stages for one photoelectric converter. One IT-CCD includes vertical transfer CCDs as many as there are photoelectric converter columns formed in the IT-CCD.
Each photoelectric converter accumulates therein signal charge by achieving photoelectric conversion. The signal charge accumulated in the photoelectric converter is read out to an associated charge transfer channel at a predetermined point of time.
To control the operation to read signal charge from the photoelectric converter to the charge transfer channel, a readout gate region is formed for each photoelectric converter being contiguous thereto on the surface of the semiconductor substrate. The readout gate region is ordinarily constituted of a region of a conductivity type opposite to those of a photoelectric converter and a charge transfer channel. Each readout gate region is contiguous also to a predetermined section of a charge transfer channel corresponding to the photoelectric converter.
On each readout gate region, a readout gate electrode zone is formed. Each readout gate electrode zone is ordinarily constituted of part of a transfer path forming section of a predetermined transfer electrode constituting a vertical transfer CCD.
Signal charge read out to each charge transfer channel is transferred to an output transfer path by each vertical transfer CCD including the charge transfer channel. The output transfer path is ordinarily composed of a CCD (to be called “horizontal CCD” in some cases herebelow).
The output transfer path being composed of a horizontal transfer CCD includes of N charge transfer stages for one vertical transfer CCD. One charge transfer stage ordinarily includes one potential barrier region and one potential well region, and N is two. When each charge transfer stage has a uniform potential, N is three or more.
The output transfer path sequentially transfers the received signal charge in a longitudinal direction (to be referred to as “row direction” herebelow) of the photoelectric converter row to an output unit. Like the vertical transfer CCD, the output transfer path is formed also in the semiconductor substrate.
The vertical and horizontal transfer CCDs each have a function of photoelectric conversion like the photodiode. To prevent unnecessary photoelectric conversion in the vertical and horizontal transfer CCDs, a light shielding film is formed in an area ranging from a light sensing section with the photoelectric converters to the horizontal transfer CCD. The light shielding film has an opening of a predetermined contour on each photoelectric converter (photodiode). One opening is disposed for one photoelectric converter. The opening is ordinarily within a signal charge accumulating region of the photoelectric converter in a plan view.
One photoelectric converter, one readout gate region formed contiguous to the photoelectric converter, one readout gate electrode zone covering the readout gate region in a plan view, and two to four charge transfer stages (of the vertical transfer CCD) corresponding to the photoelectric converter constitute one pixel. In a surface of each photoelectric converter, an exposed section thereof in the opening in a plan view serves as a light receiving section of the pixel.
Therefore, in the IT-CCD, a contour in a plan view of each opening formed in the light shielding film and an area of the opening in a plan view substantially determine a contour and an area of the light receiving section of each pixel, respectively.
With development of use of the IT-CCD, improvement in performance such as resolution and sensitivity of the IT-CCD has been desired.
The resolution of the IT-CCD strongly depends on density of pixels in the IT-CCD. The resolution can be more easily increased when the pixel density becomes higher. The sensitivity of the IT-CCD strongly depends on an area of the light receiving section of each pixel. The resolution can be more easily increased when the area of each pixel becomes larger.
Japanese Patent Publication Ser. No. 2825702 describes an IT-CCD (referred to as “solid-state image pickup device” in the publication and as “IT-CCD” in this specification). As known, by the IT-CCD, the pixel density can be increased while suppressing the reduction in the area of the light receiving section of each pixel.
The IT-CCD includes a plurality of photoelectric converters formed with a fixed pitch in columns and rows. Each of the photoelectric converter columns and rows includes a plurality of photoelectric converters. Each photoelectric converter in even photoelectric converter columns is shifted in a direction of the column relative to associated ones of said photoelectric converters of the odd photoelectric converter columns by
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fuji Photo Film Co. , Ltd.
Tran Minh Loan
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