Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-12-13
2004-09-07
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
Reexamination Certificate
active
06787987
ABSTRACT:
The invention relates to an electroluminescent color display panel comprising a plurality of pixels arranged in rows and columns to form a grid pattern, each pixel comprising at least two color sections, a first color section of which emits light of a first color, and a second color section, emits light of a second color being different from the first color.
The invention also relates to a method of manufacturing an electroluminescent color display panel, and to an electronic device comprising the electroluminescent color display.
Electroluminescent display panels, comprising a plurality of organic electroluminescent devices are known. An electroluminescent device is a device, which, while making use of the phenomenon of electroluminescence, emits light when the device is suitably connected to a power supply. The term electroluminescence includes several phenomena which have the common feature that light is emitted by an electric discharge in gases, liquids and solid materials. Generally, an electroluminescent device comprises one or more layers made of an electroluminescent material disposed between a cathode and an anode. Electroluminescent display panels are also known, wherein numerous light-emitting devices are formed on a single substrate, arranged in groups in a regular grid pattern, each group forming a picture element, also referred to as pixel. Several light-emitting devices forming a column of the grid may share a common first electrode, i.e. a common anode, also referred to as anode line. Several light-emitting devices forming a row of the grid may share a common second electrode, i.e. a common cathode, also referred to as cathode line. The individual light-emitting devices in a given group emit light when their associated cathode line and anode line are activated at the same time. Activation may be by rows and columns or, as in an active matrix, with individual anode pads.
European patent application EP 0 767 599 discloses a 3 color organic electroluminescent display device comprising a matrix of the electroluminescent elements (herein also referred to as pixels). Each pixel in the matrix has one or more emitting devices for red, green and blue in order to display a color image, each emitting device being associated with an intersection of a column and a row of matrix electrodes. As shown in FIG. 1 of EP 0 767 599, the emitting devices for red are arranged on a column, or vertical line. In the same manner, the emitting devices for green and blue are arranged on vertical lines. A pixel comprises emitting devices of three vertical lines. This pixel layout is further referred to as ‘V-line’. Alternatively, it is possible to form a pixel pattern with a delta arrangement of red, green and blue in the display panel and also draw a bent or meandered cathode pattern on the display panel.
A disadvantage of the prior-art electroluminescent color display is that it provides a low image quality, in particular when moving images are displayed on low-resolution displays.
It is an object of the present invention to provide an electroluminescent color display panel having a perceptibly improved image quality.
To this end, a first aspect of the invention provides an electroluminescent color display panel as defined in claim
1
. A second aspect of the invention provides a method of manufacturing an electroluminescent display panel as defined in claim
9
. A third aspect of the invention provides an electronic device as defined in claim
13
. Advantageous embodiments are defined in the dependent claims.
In accordance with the first aspect of the invention, the positional arrangement of the first and second color sections within a first pixel is different from the positional arrangement of the first and second color sections within a second pixel, wherein the first pixel is adjacent to the second pixel.
The different positional arrangement of the first and second color sections within two adjacent pixels disrupts pure grid-correlated patterns in the image, which patterns may arise from the arrangement of the pixels in a grid. This disruption of the grid-correlated patterns improves the perceived image quality. The adjacent pixels of a first pixel may comprise horizontally, vertically or diagonally neighboring pixels of the first pixel.
In color displays, the chosen arrangement of the color sections within a pixel determines the quality of the perceived image to a large extent. In the prior-art electroluminescent color display panels, the arrangement of the color sections within a pixel is the same for each pixel. Moreover, characteristic of this type of color display panel is that the pixels are usually arranged in a grid pattern comprising vertical columns and horizontal rows. The purely horizontally and/or vertically oriented pixel structures, with the same arrangement of the color sections within the pixels, clearly show a lower image quality, especially on low-resolution displays, because the human eye has a tendency to focus on correlated patterns originating from the pixel layout, which do not belong to the actual image. In the electroluminescent color display panel according to the invention, the pixels are still arranged in a grid pattern comprising vertical columns and horizontal rows. However, purely horizontally and/or vertically correlated patterns are disrupted because two adjacent pixels comprise a different arrangement of the color sections within the pixel.
An embodiment of the invention as defined in claim
2
is characterized in that two adjacent pixels in a column comprise a different arrangement of the color sections within the pixel. The disruption of the vertically correlated patterns improves the perceived image quality, as will be illustrated in the Figures.
Naturally, an equivalent embodiment may comprise two adjacent pixels in a row, which comprise a different arrangement of the color sections within the pixel. The disruption of the horizontally correlated patterns improves the perceived image quality.
An embodiment of the invention as defined in claim
3
is particularly useful when a printing technique, such as inkjet printing, is used in the manufacture of the color sections. When the first color sections are adjacently arranged on a plurality of parallel, laterally spaced lines, such a line of color sections can be printed by moving the printing head or heads, along the line or lines (the latter, in the case where more than one line is printed simultaneously). It is preferred that also the other color sections, which, in operation, emit light of the same color, are adjacently arranged on a plurality of parallel, laterally spaced lines. Preferably, the laterally spaced lines of the various color sections are substantially parallel. Although the pattern of emissive material of this embodiment is still a line-wise correlated color pattern, this correlated pattern is subjectively less annoying than a pure vertical or horizontal one.
The first color sections are adjacently arranged, and there is a small distance between two printing positions. Thus, the traveling distance of the printing head between two printing positions is small. This yields an efficiency advantage in the production process, because the time in which the printing head travels between two printing positions and does not contribute to the printing process, is small.
The advantage mentioned in the previous paragraph is even more exploited by an embodiment as defined in claim
4
. In accordance with an embodiment as defined in claim
4
, the first color sections, which are arranged on one slanting line, form a continuous strip of electroluminescent material. When using a printing technique, such as inkjet printing, this embodiment allows printing of a continuous line of deposited electroluminescent material of a specific color. Of course it is possible to interrupt the deposition at the appropriate positions, but this introduces problems in the manufacturing process related to positioning of the printing head above the substrate at the desired locations. Furthermore, after activation of the
Duineveld Paulus Cornelis
Liedenbaum Coen Theodorus Hubertus Fransiscus
Snijder Pieter Jacob
Krishnan Sumati
Patel Vip
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