Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
2000-09-26
2002-05-14
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S223000
Reexamination Certificate
active
06388278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state image pickup device to be used as an area image sensor and its driving method, and more particularly to a solid state image pickup device suitable for use as an area image sensor of an electronic still camera, and its driving method.
2. Description of the Related Art
After mass production techniques for charge-coupled devices (CCD) have been established, video cameras, electronic still cameras and the like utilizing CCD type solid state image pickup devices as area image sensors are prevailing rapidly. CCD type solid image pickup devices are classified into several types, depending upon their structures. One type is an interline transfer type solid state image pickup device (this solid state image pickup device is hereinafter described as “IT-CCD” in abbreviation).
IT-CCD has a number of photoelectric conversion elements disposed along a plurality of columns and rows at a constant pitch. Each photoelectric conversion element column is constituted of a plurality of photoelectric conversion elements, and each photoelectric conversion element row is also constituted of a plurality of photoelectric conversion elements.
A number of photoelectric conversion elements each made of a p-n photodiode are formed, for example, by forming a p-type well in a desired principal surface of a semiconductor substrate and forming n-type regions (n-type impurity doped regions) having a desired shape in the p-type well as many as the number of photoelectric conversion elements to be formed. If necessary, a p
+
-type region (p
+
-type impurity doped region) is formed on each n-type region. Signal charges are accumulated in the n-type region. The n-type region functions as a signal charge accumulation region.
In this specification, the term “photoelectric conversion element” is used in some cases to mean only the signal charge accumulation region. In this specification, it is assumed that “adjacent to the photoelectric conversion element” means “adjacent to the signal charge accumulation region constituting the photoelectric conversion element” and that “contiguous to the photoelectric conversion element” means “contiguous to the signal charge accumulation region constituting the photoelectric conversion element”.
A charge transfer channel is formed adjacent to each photoelectric conversion element column. IT-CCD has a plurality of charge transfer channels. Each charge transfer channel is used for transferring signal charges accumulated in all photoelectric conversion elements of the photoelectric conversion element column adjacent to the charge transfer channel.
A plurality of transfer electrodes traversing in plan view each charge transfer channel are formed on an electric insulating film over the surface of the semiconductor substrate. A cross area in plan view between each transfer electrode and the charge transfer channel functions as one charge transfer stage. A vertical transfer CCD is therefore formed by the channel transfer channel and transfer electrodes.
In this specification, a charge transfer stage forming region of each transfer electrode constituting the vertical transfer CCD is called a “transfer path forming area”.
Generally, each vertical transfer CCD of an interlace drive type IT-CCD has two charge transfer stages per one photoelectric conversion element. Generally, each vertical transfer CCD of an all-pixel read type IT-CCD has three or four charge transfer stages per one photoelectric conversion element. One IT-CCD has vertical transfer CCDs same in number as the number of photoelectric conversion element columns formed in IT-CCD.
Each photoelectric conversion element photoelectrically converts incidence light into signal charges and stores the charges. The signal charges stored in each photoelectric conversion element are read to the corresponding charge transfer channel at a predetermined timing.
For a read control of signal charges from the photoelectric conversion element to the charge transfer channel, a readout gate region is formed adjacent to each photoelectric conversion element on the surface of the semiconductor substrate. This readout gate region has generally a conductivity type opposite to that of the photoelectric conversion element and charge transfer channel, in order to form a potential barrier relative to the signal charges. Each readout gate region is also adjacent to a predetermined region of the charge transfer channel.
A readout gate electrode structure is formed on the readout gate region. The readout gate electrode structure is constituted of a partial region of the transfer path forming area of a predetermined transfer electrode constituting the vertical transfer CCD. As a high voltage is applied to the readout gate structure to remove the potential barrier in the readout gate region, signal charges accumulated in the photoelectric conversion element can be read to the charge transfer channel.
Signal charges read to each charge transfer channel are transferred to an output transfer path by each vertical transfer CCD constituted of the charge transfer channel. The output transfer path is generally made of CCD (this CCD is called in some cases a “horizontal transfer CCD”).
The output transfer path made of the horizontal transfer CCD has N charger transfer stages per one vertical transfer CCD. Each charge transfer stage has usually one potential barrier and one potential well. In this case, N=2. If the charge transfer stage has a uniform potential, then N=3 or larger.
The output transfer path sequentially transfers the received signal charges along a lengthwise direction of the photoelectric conversion element row (this direction is hereinafter simply called a “row direction”), to an output unit. Similar to the vertical transfer CCD, the output transfer path is formed on the semiconductor substrate.
The vertical transfer CCD and horizontal transfer CCD have the photoelectric conversion function similar to photodiodes. In order to avoid unnecessary photoelectric conversion by the vertical transfer CCD and horizontal transfer CCD, a light shielding film is formed on an area from a photosensitive area with photoelectric conversion elements to the horizontal transfer CCD area. The light shielding film has an opening with a predetermined shape formed on each photoelectric conversion element (photodiode). An opening is formed for each photoelectric conversion element. Generally, the inner edge of the opening is inner in plan view than the outer edge, in plan view, of the signal charge accumulation region of the photoelectric conversion element.
A pixel is constituted of: one photoelectric conversion element; one readout gate region formed contiguous to the photoelectric conversion element; one readout gate electrode structure covering in plan view the readout gate region; and two to four charge transfer stages (two to four charge transfer stages on the vertical transfer CCD) associating to the photoelectric conversion element. The area of the photoelectric conversion element exposed in plan view in the opening functions as a light receiving area.
The shape and area of the light receiving area of the pixel of IT-CCD are therefore substantially determined by the shape and area, in plan view, of the opening formed in the light shielding film.
The performance such as a resolution and sensitivity of IT-CCD widely prevailing nowadays is desired to be improved further.
The resolution of IT-CCD depends largely on the pixel density. The higher the pixel density, the resolution is easier to be improved. The sensitivity of IT-CCD depends largely on the area of the light receiving area of each pixel. The larger the light receiving area of each pixel, the sensitivity is easier to be raised.
IT-CCD described in Japanese Patent Publication No. 2825702 (although this Publication has the title “Solid State Image Pickup Device”, in this specification it is described as “IT-CCD”) has an improved pixel density while the reduction in the light receiving area of
Masukane Kazuyuki
Suzuki Nobuo
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fuji Photo Film Co. , Ltd.
Meier Stephen D.
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