Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-02-25
2003-09-09
Lao, Lun-Yi (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S044000, C345S046000, C257S059000, C257S040000, C313S505000
Reexamination Certificate
active
06618029
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active-matrix-type display apparatus which uses light-emission elements, such as EL (electroluminescence) elements that emit light when driving current flows through an organic semiconductor film or LED (light-emitting diode) elements, and thin-film transistors (hereinafter referred to as “TFTs”) that control the light-emission operation of this light-emission element. More particularly, the present invention relates to layout optimization technology for improving the display characteristics thereof.
2. Description of Related Art
Active-matrix-type display apparatuses which use current-control-type light-emission elements, such as EL elements or LED elements, have been proposed. Since any of the light-emission elements used in this type of display apparatus may emit light by itself, unlike a liquid-crystal display device, a back light is not required, and there are advantages in that viewing angle dependence is small.
FIG. 22
shows, as an example of such a display apparatus, a block diagram of an active-matrix-type display apparatus which uses charge-injection-type organic thin-film EL elements. In a display apparatus
1
A shown in this figure, formed on a transparent substrate are a plurality of scanning lines “gate”, a plurality of data lines “sig” extending in a direction intersecting the extension direction of these scanning lines “gate”, a plurality of common power-feed lines “com” which are parallel to these data lines “sig”, and pixels
7
corresponding to the intersections of the data lines “sig” and the scanning lines “gate”. With respect to the data lines “sig”, a data-side driving circuit
3
comprising a shift register, a level shifter, video in, and an analog switch is formed. With respect to the scanning lines, a scanning-side driving circuit
4
comprising a shift register and a level shifter is formed. Further, each of the pixels
7
is formed with a first TFT
20
in which a scanning signal is supplied to its gate electrode via the scanning lines, a holding capacitor “cap” for holding an image signal supplied from the data lines “sig” via this first TFT
20
, a second TFT
30
in which an image signal held by this holding capacitor “cap” is supplied to its gate electrode, and light-emission elements
40
to which driving current flows from the common power-feed lines “com” when these are electrically connected to the common power-feed lines “com” via the second TFT
30
.
Specifically, as shown in FIGS.
23
(A) and
23
(B), in all the pixels
7
, the first TFT
20
and the second TFT
30
are formed using two island-shaped semiconductor films, a relay electrode
35
is electrically connected to the source and drain regions of the second TFT
30
via a contact hole of a first interlayer insulation film
51
, and a pixel electrode
41
is electrically connected to the relay electrode
35
via a contact hole of a second interlayer insulation film
52
. On the side of the upper layers of this pixel electrode
41
, a positive-hole injection layer
42
, an organic semiconductor film
43
, and a counter electrode “op” are multilayered. Here, the counter electrode “op” is formed over a plurality of pixels
7
in such a manner as to extend across the data lines “sig” and the like. Further, the common power-feed lines “com” are electrically connected to the source and drain regions of the second TFT
30
via the contact hole.
In contrast, in the first TFT
20
, a potential holding electrode “st” which is electrically connected to the source and drain regions is electrically connected to an extended portion
310
of a gate electrode
31
. On the side of the lower layers thereof, a semiconductor film
400
opposes this extended portion
310
via a gate insulation film
50
, and since this semiconductor film
400
is made to conduct by impurities introduced thereinto, this semiconductor film
400
, together with the extended portion
310
and the gate insulation film
50
, constitute the holding capacitor “cap”. Here, the common power-feed line “com” is electrically connected to the semiconductor film
400
via the contact hole of the first interlayer insulation film
51
. Therefore, since the holding capacitor “cap” holds an image signal supplied from the data lines “sig” via the first TFT
20
, even if the first TFT
20
is turned off, the gate electrode
31
of the second TFT
30
is held at a potential corresponding to the image signal. Therefore, since the driving current continues to flow to the light-emission element
40
from the common power-feed lines “com”, the light-emission element
40
continues to emit light.
However, in comparison with the liquid-crystal display apparatus, in the display apparatus
1
A, there is a problem in that the display quality cannot be improved because the pixels
7
are narrower by an amount corresponding to the requirement of the second TFT
30
and the common power-feed lines “com”.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a display apparatus capable of improving display quality by expanding the light-emission area of pixels by improving the layout of pixels and common power-feed lines formed on a substrate.
In order to solve the above-described problems, the present invention provides a display apparatus comprising on a substrate: a plurality of scanning lines; a plurality of data lines extending in a direction intersecting the extension direction of the scanning lines; a plurality of common power-feed lines parallel to the data lines; and pixels formed in a matrix by the data lines and the scanning lines, each of the pixels comprising: a first thin-film transistor in which a scanning signal is supplied to its first gate electrode via the scanning lines; a holding capacitor for holding an image signal supplied from the data lines via the first thin-film transistor; a second thin-film transistor in which the image signal held by the holding capacitor is supplied to its second gate electrode; and a light-emission element having an organic semiconductor film, which emits light by driving current that flows between a pixel electrode and a counter electrode when the pixel electrode is electrically connected to the common power-feed line via the second thin-film transistor in a section between the layers of the pixel electrodes formed for each of the pixels and the counter electrodes opposing the pixel electrodes, wherein pixels in which the driving current is passed in a section between the pixels and the common power-feed lines are arranged on both sides of the common power-feed lines, and the data lines pass on a side opposite to the common power-feed lines with respect to the pixels.
Specifically, in the present invention, since a data line, a group of pixels connected thereto, one common power-feed line, a group of pixels connected thereto, and a data line for supplying a pixel signal to the group of pixels are assumed to be one unit and this is repeated in the extension direction of scanning lines, pixels for two rows are driven by one common power-feed line. Therefore, the formation area of common power-feed lines can be made more narrow than in a case in which a common power-feed line is formed for each group of pixels for one row, the light-emission area of the pixels can be expanded correspondingly. Therefore, it is possible to improve display performance, such as luminance, contrast ratio, and so on.
When the construction is formed in this manner, it is preferable that, for example, in a section between two pixels arranged in such a manner as to sandwich the common power-feed line, the first thin-film transistor, the second thin-film transistor, and the light-emission elements be disposed in linear symmetry about the common power-feed line.
In the present invention, also, it is preferable that the pitch of the centers of the formation areas of the organic semiconductor films be equal at every interval between adjacent pixels along the extension direction of the scanning lines. When the cons
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