Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-09-16
2002-06-18
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S292000, C257S350000, C257S435000
Reexamination Certificate
active
06407418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device which can operate at high speed and a method of manufacturing the semiconductor device, as well as an image sensor apparatus and an image reader both having the semiconductor device.
2. Description of the Related Art
As image sensors which read an image and output an image signal in accordance with the image, there are known a MOS type sensor, a CCD sensor and the like. The image sensor is also classified into a compact type image sensor and a close-contact type image sensor.
Whichever the type, the image sensor has higher resolution and lower sensitivity as the light receiving area of each of the light receiving elements which are the constituent elements for the image sensor is smaller. That is, the higher the resolution of an image sensor is, the slower the reading speed becomes. There are two reasons for slower reading speed. The first is the increase of storage time resulting from the lowered sensitivity. The second is the increase of scanning time for scanning all of the light receiving elements.
It is desirable that the resolution of the sensor in a main scanning direction and that in a sub-scanning direction are equal to each other two-dimensionally. If so, the sensitivity of the sensor is inversely proportional to the square of the resolution. Namely, if the resolution is doubled, the sensitivity is lowered to one-fourth.
In designing an image reader, the optical resolution of the reader is, in many cases, determined at the time the image sensor is selected. Therefore, apparatus designers have trouble in selecting an image sensor to be mounted on the image reader in view of optical resolution and reading speed.
An image reader is conventionally provided with switching means for switching over reading concentration and can read an image with a resolution lower than an optical resolution. The switching of reading concentration is, however, carried out by image process such as thinning-out process for changing the sampling concentration of an image signal per unit length or averaging process for averaging image signals after the images are read with the optical resolution characteristics of the image reader. For that reason, the switching of the reading concentration does not substantially change the area of light receiving elements and it still requires lot of reading time.
To remove the above disadvantage, recently disclosed are image sensors switching over reading concentration to a low level, increasing reading speed or improving an S/N ratio by outputting the sum of the signals of a plurality of adjacent light receiving elements (Japanese Patent Application Laid-Open No. 6-276365 and No. 9-205518 and “ISSCC 98, DIGEST OF TECHNICAL PAPERS, p174” and the like).
FIG. 1
is a circuit diagram showing the structure of a conventional image reader disclosed by the Japanese Patent Application Laid-Open No. 6-276365.
FIGS. 2A and 2B
are timing charts showing the operation of the image reader shown in FIG.
1
. It is noted that
FIG. 2A
indicates the operation of the reader while images are read with high resolution and that
FIG. 2B
indicates the operation thereof while images are read with low resolution.
The image reader disclosed by this Japanese Patent Application Laid-Open No. 6-276365 is provided with light receiving elements PD
2
-ml and the like, switching elements T
2
-ml and the like, control lines G
2
-m and the like connected to the switching elements T
2
-ml and the like, respectively and a driver circuit driving the control lines G
2
-m and the like, as shown in FIG.
1
.
In this image reader, if an image is read with high resolution, one control line is driven simultaneously as shown in FIG.
2
A. If an image is read with low resolution, two or more control lines are driven at one time as shown in FIG.
2
B. If the control lines are driven as shown in
FIG. 2B
, signals of two or more light receiving elements adjacent to a common data line are simultaneously outputted and a low resolution image can be obtained without conducting image processing such as averaging process.
In addition, since charges of the two or more light receiving elements are transferred by a single driving operation, the number of driving operations is decreased and reading time is shortened accordingly.
Although reading time is shorter than that for previous image sensors, the light receiving area is not doubled in case of reducing the resolution by half. Therefore, the sensitivity of the reader is nothing more than half as high as that of a low resolution sensor. Further, since a plurality of light receiving elements are switched on once, the mixture of feedthrough noise caused by the switching operation disadvantageously increases.
Meanwhile, in an image sensor according to the Japanese Unexamined Patent Application Publication No. 9-205518, a plurality of light receiving elements are arranged in columns and outputs from the respective rows of the elements are composed and sequentially outputted in a low resolution mode to thereby increase the sensitivity of the sensor in the low resolution mode.
Even with the image sensor disclosed by this publication, the sensitivity is only doubled when the resolution is halved and the sensitivity is nothing more than a half as high as that of the low resolution sensor as in the case of the above publication.
According to “ISSCC98, DIGEST OF TECHNICAL PAPERS, p174”, a two-dimensional CMOS area sensor is provided with column integrators and column memories on all column output lines and with a global integrator on the final output line of the sensor, whereby the sum of the signals of light receiving elements adjacent to one another two-dimensionally can be outputted.
With this imager, the sum of the outputs from the light receiving elements is obtained two-dimensionally, the sensitivity increases fourfold when the resolution is halved and the same sensitivity as that of a low resolution sensor can be obtained.
Nevertheless, due to its complicated circuit arrangement, the imager has disadvantage of lower yield, the great increase of the chip area and the like. Further, in consideration of the present transistor performance, more fine manufacturing process is required than that for a crystalline silicon LSI and it is quite difficult to adapt this imager to a thin film transistor driving type image sensor.
Moreover, there is disclosed a character reader in which two image sensors, i.e., a high resolution CCD sensor and a low resolution CCD sensor, are installed and the output signals of the two sensors are switched to thereby read characters at high speed with low resolution (Japanese Patent Application Laid-Open No. 6-231301).
The character reader disclosed by this publication is intended to solve the challenges shared among the readers. However, since the two sensors are mounted on the reader, two optical systems or two optical paths are needed. As a result, the reader has disadvantage in that the apparatus becomes larger in size, the number of assembly steps increases and the like. Besides, the reader disclosed by this publication differs from the preceding readers in technical concept.
Further, there is disclosed an image reader consisting of an image sensor in which a plurality of lines, on which a plurality of light receiving elements are arranged in one direction, are arranged in a plurality of sub-scan directions (Japanese Patent Application Laid-Open No. 4-56461). In this image reader, signal charges stored in light receiving elements on the respective lines are line-shifted in sub-scanning direction for every sub-scanning cycle.
There is also disclosed an image reader intended to realize high resolution and high transfer efficiency (Japanese Patent Application Laid-Open No. 4-261258). According to this publication, there are provided a plurality of light receiving elements for conducting photoelectric transfer, color filters having difference spectral characteristics formed on the light receiving elements, respectively, illumination
Fujieda Ichiro
Haga Hiroshi
Okumura Fujio
NEC Corporation
Ngo Ngan V.
Scully Scott Murphy & Presser
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