Computer graphics processing and selective visual display system – Display driving control circuitry – Physically integral with display elements
Reexamination Certificate
1999-06-03
2001-01-09
Hjerpe, Richard A. (Department: 2774)
Computer graphics processing and selective visual display system
Display driving control circuitry
Physically integral with display elements
C345S206000, C257S059000, C257S072000, C349S042000, C349S043000
Reexamination Certificate
active
06172671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of an active matrix type liquid crystal display and more particularly to a structure of an active matrix type liquid crystal display into which a peripheral driving circuit is integrated.
2. Description of Related Art
There has been known an active matrix type liquid crystal display having a structure in which a thin film transistor is provided individually in each of several hundreds×several hundreds pixel electrodes provided in a matrix. The thin film transistor provided in each pixel has a function of controlling electric charge input/output to/from each pixel electrode.
There has been also known one having a structure called a peripheral driving circuit integrated type in which a pixel matrix portion is integrated with a peripheral driving circuit on a same glass substrate. This peripheral driving circuit integrated structure is useful in that the production cost can be lowered and the whole structure can be miniaturized.
Either P- or N-channel type thin film transistor is provided as a switching element in the pixel matrix circuit in general. Further, a circuit composed of P-channel and N-channel type thin film transistors is provided in the peripheral driving circuit.
SUMMARY OF THE INVENTION
In the peripheral driving circuit integrated liquid crystal display as described above, the thin film transistors provided in the pixel matrix circuit and the peripheral driving circuit are fabricated on the same substrate in the same time.
However, required transistor characteristics is different in the pixel matrix circuit and in the peripheral driving circuit in general.
For instance, although the thin film transistor provided in the pixel matrix circuit is not required to operate at such high speed, it is required to have a low OFF current characteristic strictly because it is required to have a charge retaining function in the pixel electrode.
Meanwhile, the thin film transistor provided in the peripheral driving circuit is required to have characteristics of operating at high speed and of flowing a large current preferentially. A thin film transistor composing a buffer circuit in particular is required to have the characteristics of operating at high speed and of flowing a large current.
Further, the thin film transistor provided in the peripheral driving circuit is required that its characteristics deteriorate less because it is required to operate at high speed. That is, because the higher the speed of the operation, the more the influence of the deterioration is actualized, one which is influenced least by that is required.
Further, the mobility of the N-channel type thin film transistor is higher than that of the P-channel type thin film transistor by two to three times in general. It poses a problem in terms of the operational balance when a CMOS structure is adopted. It poses a problem in the peripheral driving circuit in particular in which the CMOS structure is adopted.
Then, it has been necessary to correct the difference of the mobility of the N-channel type thin film transistor and the P-channel type thin film transistor.
Accordingly, it is an object of the present invention disclosed in the present specification to provide a peripheral driving circuit integrated active matrix type liquid crystal display which satisfies the above-mentioned various requirements.
One of the inventions disclosed in the present specification is characterized in that in active matrix type display having a structure in which a pixel matrix portion and a peripheral driving circuit portion (which is composed of an N-channel driver and a P-channel driver in the examples of the present invention) are provided on the same substrate,
an N-channel type thin film transistor having a source region and a drain region which are high concentrate impurity regions and impurity regions whose concentration is lower than that of the source and drain regions, the impurity region provided between a channel region and the source region and between the channel region and drain region, respectively, so that their dimension is the same on the source and drain sides each other is provided in the pixel matrix portion; and
an N-channel type thin film transistor having a source region and a drain region which are high concentrate impurity regions and impurity regions whose concentration is lower than that of the source/drain region between a channel region and the source region and between the channel region and drain region so that the dimension of that on the drain side is larger than that on the source side; and a P-channel type thin film transistor having no low concentrate impurity region are provided in the peripheral driving circuit portion.
One of the other inventions disclosed in the present specification is characterized in that a fabrication method of an active matrix type display having a structure in which a pixel matrix portion and a peripheral driving circuit portion are provided on the same substrate comprises steps of:
doping impurity which gives N type conductivity to regions which are to be source and drain regions of an N-channel type thin film transistors provided in the pixel matrix portion and in the peripheral driving circuit portion through a non-self-alignment process; and
doping impurity which gives P type conductivity to regions which are to be source and drain regions of a P-channel type thin film transistor provided in the peripheral driving circuit portion through a self-alignment process.
Another invention is characterized in that a fabrication method of an active matrix type display having a structure in which a pixel matrix portion and peripheral driving circuit portion are provided on the same substrate comprises steps of:
doping impurity which gives N type conductivity to regions which are to be source and drain regions of an N-channel type thin film transistors provided in the pixel matrix portion and in the peripheral driving circuit portion through a non-self-alignment process;
doping impurity which gives N type conductivity to regions adjacent to the regions which are to be source and drain regions of the N-channel type thin film transistors in concentration lower than that of the regions which are to be the source and drain regions through a self-alignment process; and
doping impurity which gives P type conductivity to regions which are to be source and drain regions of a P-channel type thin film transistor provided in the peripheral driving circuit portion through a self-alignment process.
Another invention in which the above-mentioned structure is modified further is characterized, in that the region to which the impurity which gives N type conductivity is doped in the self-alignment process is composed of first regions formed adjacent to the source region and second regions formed adjacent to the drain region, the dimension of the first region is larger than a positioning accuracy in the non-self-alignment process during which the impurity which gives N type conductivity is doped, and the dimension of the second region is larger than that of the first region in the peripheral driving circuit portion. Thereby, high reliability may be given to the N-channel type driver portion without reducing its driving capability.
It is noted that the dimension described above is defined as what is in the direction along a moving path of carriers.
In the structure in the present invention, the N-channel type driver portion and the P-channel type driver portion are shown as elements which compose the peripheral driving circuit. Beside the circuit for directly driving the pixel matrix portion (which is generally called as a driver circuit), a shift register circuit and various data processing circuits and memory circuits may be included in the concept of the peripheral driving circuit.
The peripheral driving circuit described in the present specification refers mainly to the driver circuit. Accordingly, the inventions disclosed in the present specification need not be provided with all
Shibuya Tsukasa
Takenouchi Akira
Yoshinouchi Atsushi
Zhang Hongyong
Fish & Richardson P.C.
Hjerpe Richard A.
Nguyen Kimnhung
Semiconductor Energy Laboratory, Inc.
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