Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-25
2003-04-22
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000
Reexamination Certificate
active
06552768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driver circuit of a display device. More specifically, the present invention relates to a driver circuit of a liquid crystal display (hereinafter, referred to as “LCD”) using thin film transistors (hereinafter, referred to as “TFTs”) for making up a scan driver circuit and an image signal driver circuit.
2. Description of the Related Art
Recently, a new TFT has been under development for use as a driver element or a pixel driver element of an active matrix type LCD, and such a TFT utilizes an active layer made of polysilicon film that is obtained by irradiating a laser beam to an amorphous silicon film.
Especially, since each of the TFTs of the driver circuit needs high electron mobility, the polysilicon having higher electron mobility than the amorphous silicon is useful as the active layer.
A TFT constituting the conventional driver circuit will be explained as follows.
FIG. 1
is a block diagram showing a conventional LCD, and
FIG. 2
is a plan view showing a relationship between the position of the TFT of each driver circuit and irradiation of a laser beam. In
FIG. 2
, each channel of the driver circuits
102
and
105
is illustrated in a hatched box.
The driver circuit of the LCD includes a LCD panel
100
, a scan signal driver circuit
102
and an image signal driver circuit
105
, which are disposed on the LCD panel
100
. The scan signal driver circuit
102
supplies a scan signal to the display pixel portion
108
including a plurality of display pixels
101
. The image signal driver circuit
105
supplies a display signal to the display pixel portion
108
. The driver circuits
102
and
105
are respectively disposed in horizontal and vertical directions of the display pixel portion
108
in the LCD, and circuits
102
and
105
are disposed in directions perpendicular to each other with respect to the display pixel portion
108
of the LCD.
The scan signal driver circuit
102
includes a shift register
103
and buffer TFTs
104
for supplying the signal from the shift register
103
to the display pixels
108
. Each of the shift register
103
and the buffer TFTs
104
is made of the TFT.
The image signal driver circuit
105
includes a shift register
106
and sampling TFTs
107
, each of which is constituted by the TFT.
The active layer of the above-mentioned TFT is made of polysilicon. This polysilicon is made by irradiating a laser beam
109
to an amorphous silicon film formed on a substrate. The laser beam
109
, e.g., a belt-shaped excimer laser having a dimension of 500 &mgr;m×150 mm, is scanned in the direction for example from the left end to the right end of the LCD panel (in the direction of the arrow
12
in
FIG. 2
) by the feeding pitch of 35 &mgr;m.
However, directions of the channel width W of the TFTs
102
and
107
making up the driver circuits are different from each other.
In other words, as shown in
FIG. 2
, the direction of the channel width W in the scan signal driver circuit
102
is the same as the scanning direction of the laser beam shown in the arrow
12
. On the other hand, the direction of the channel width W in the image signal driver circuit
105
is perpendicular to the scanning direction of the laser beam shown in the arrow
12
.
If the channel width W of each TFT is 300 &mgr;m, the channel length L is 7 &mgr;m, and the feeding pitch of the laser is 35 &mgr;m, which means that the laser is scanned eight or nine times for the scan signal driver circuit
102
, while only once for the image signal driver circuit
105
in direction of the channel length L of the circuit
105
since the laser is scanned in the direction of the channel length L.
Therefore, if the energy of the laser irradiated to each spot varies, the crystal size of the polysilicon formed by the irradiation may vary. In this case, characteristics of the TFT, e.g., the electron mobility, may vary.
As a result, the image signal supplied from the sampling TFT of the image signal driver circuit
105
to the display pixel portion may be not uniform among the signal lines, and unevenness may show up on the display. This is the problem to be solved.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problem by providing a driver circuit of the display device, which can adjust the channel width direction of the TFT of the scan signal and image signal driver circuits so that each channel of the TFTS of the driver circuits is irradiated by the laser plural times for a uniform display.
In the present invention, the channel width direction of a buffer thin film transistor of a scan signal driver circuit for supplying a scan signal to a display pixel is identical with the channel width direction of a sampling thin film transistor of an image signal driver circuit for supplying an image signal to the display pixel.
In addition, the channel width directions of the buffer thin film transistor of the scan signal driver circuit for supplying the scan signal to the display pixel and the sampling thin film transistor of the image signal driver circuit for supplying the image signal to the display pixel are identical with a scanning direction of a laser beam irradiated to an active layer of the thin film transistors.
In another aspect, the present invention provides a driver circuit of a display device having display pixels arranged in a matrix on a substrate. A scan signal driver circuit for supplying a scan signal to the display pixels extends along one of adjacent sides on the peripheral area of the substrate. An image signal driver circuit for supplying an image signal to the display pixels extends along the other side of the adjacent sides on the peripheral area of the substrate. The channel width direction of the buffer thin film transistor of the scan signal driver circuit is identical with the channel width direction of the sampling thin film transistor of the image signal driver circuit.
In another aspect of the present invention, the channel width directions of the buffer thin film transistor of the scan signal driver circuit and the sampling thin film transistor of the image signal driver circuit are identical with the scanning direction of the laser beam irradiated to the active layer of the thin film transistor in the above-mentioned driver circuit.
In addition, a plurality of the sampling thin film transistors whose channel width direction is identical with the extending direction of the image signal driver circuit is arranged in parallel in the direction away from the display pixels to make up one unit. A plurality of the units are arranged in the extending direction of the image signal driver circuit.
Furthermore, a plurality of the sampling thin film transistors whose channel width direction is identical with the extending direction of the scan signal driver circuit are arranged in parallel in the direction away from the display pixels to make up one unit. A plurality of the units are arranged in the extending direction of the scan signal driver circuit.
Furthermore, the channel width directions of the thin film transistors making up a scan signal side shift register and an image signal side shift register are identical with the scanning direction of a laser beam irradiated to an active layer of the thin film transistors.
In another aspect, the present invention provides a driver circuit of the display device that is a liquid crystal display device performing display by driving a liquid crystal disposed between a pair of substrates. On one of the substrates, pixel electrodes constituting the display pixels, display thin film transistors performing in accordance with the scan signal to supply the image signal to the pixel electrodes, a scan signal driver circuit for supplying the scan signal to the pixel electrodes, and an image signal driver circuit for supplying the image signal to the pixel electrodes are formed. An active layer including the channels of the display thin film transistors, the buffer thin film transistors of the sc
Hogan & Hartson LLP
Parker Kenneth
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