Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-01-21
2001-08-28
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S318000, C430S319000, C313S504000, C313S510000
Reexamination Certificate
active
06280909
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electroluminescent display screen having a transparent substrate, a surface of which is provided with a first, transparent electrode layer, with a layer of insulating material in which windows within which the first electrode layer is exposed are formed in accordance with a pattern to be displayed, with a layer of an organic electroluminescent material which is provided on the layer of insulating material and, within the windows in the layer of insulating material, on the first electrode layer, and with a second electrode layer which is provided on the layer of electroluminescent material. The invention also relates to a method of manufacturing such an electroluminescent display screen.
During operation of such a display screen, an electric current flows from the first electrode layer through the windows in the layer of insulating material to the second electrode layer. The layer of electroluminescent material then luminesces in accordance with the pattern formed in the layer of insulating material, which pattern is then visible through the transparent substrate. Patterns formed in the layer of insulating material can thus be displayed. A display screen of this type may be used, for example, in mobile telephones or watches, or in car or plane instrument panels. The pattern may be, for example, a word, a number or an icon.
A display screen of the type described in the opening paragraph is known from WO 98/03043, in which the first, transparent electrode layer is a layer of ITO (indium tin oxide) and the layer of insulating material is a layer of a positive photoresist. The photoresist is exposed in accordance with the pattern to be displayed and is subsequently developed, with the desired pattern being formed in the layer of insulating material. The layer of electroluminescent material, which consists of a customary double layer of an organic electroluminescent material, is deposited on the photoresist and, in the windows in the photoresist, on the first electrode layer. The second electrode layer consists of a layer of magnesium coated with a layer of silver. The insulating layer is also provided with a window which leaves open a bond pad of the first electrode layer for external contacting of the first electrode layer. This bond pad is located at the edge of the substrate, next to the pattern to be displayed. This bond pad is shielded by a mask during the deposition of the layer of electroluminescent material and the second layer of electrode material.
It has been found in practice that a pattern to be displayed may exhibit local differences in brightness during display. These differences particularly become manifest when the pattern to be displayed is, for example, a relatively large word or icon.
OBJECTS AND SUMMARY OF THE INVENTION
It is, inter alia, an object of the invention to provide an electroluminescent display screen in which no local differences in brightness occur in the pattern during display of this pattern, even if this pattern is a relatively large word or icon.
According to the invention, the display screen as described in the opening paragraph is therefore characterized in that the first electrode layer is provided with a top layer of metal on which the layer of insulating material is present, while the windows are formed both in the layer of insulating material and in the metal top layer.
During operation of the display screen, electric currents flow from the bond pad through the first electrode layer and then through the windows in the layer of insulating material to the second electrode layer. In the case of relatively large patterns, the different windows of the pattern to be displayed are located at distances from the connection electrode, which distances have relatively large differences. Since the first electrode layer of ITO in the known display screen has a relatively large resistivity, these different distances represent electrical resistances which differ from each other. These differences may be so large that the electric currents flowing through the different windows also have relatively large differences. This leads to said local differences in brightness. By providing a metal top layer on the first electrode layer, the differences between said electrical resistances are eliminated. The occurrence of local differences in brightness is thereby inhibited.
In a preferred embodiment of a display screen according to the invention, a pattern of mutually isolated segments is formed in the first electrode layer and the metal top layer, and the windows in the insulating layer and the top layer are provided at the area of the segments. A pattern to be displayed can thus be formed at the area of each segment. The display screen is extremely suitable for use in an instrument panel for cars or airplanes. The display screen may comprise a number of segments with icons indicating, for example, which light has been switched on. It may also comprise segments with words giving, for example, a warning such as “fasten your seatbelts”. A number of groups of seven segments arranged in the conventional manner may also be added for displaying characters alternating with figures, with which, for example, speed, number of revolutions and temperature can be indicated. Due to the metal top layer provided on the first electrode layer, a display screen can be made on which a large number of these icons, words and changing characters and with figures are displayed with equal brightness.
The occurrence of differences in brightness within a pattern to be displayed is even further inhibited when an edge of the segments is covered by the metal top layer and the layer of insulating material.
The segments may be externally contacted in a simple manner when also a pattern of bond pads and conductor tracks is formed in the first electrode layer and the metal top layer, each conductor track connecting one of the bond pads to one of the segments. Since the external contact is established with the metal top layer, voltage loss between an external voltage source and the pattern to be displayed is avoided as much as possible.
The invention also relates to a method of manufacturing a display screen of the type described in the opening paragraph, in which a first, transparent electrode layer is provided on a surface of a plane substrate, whereafter a layer of insulating material is provided in which windows within which the first electrode layer is exposed are formed in accordance with a pattern to be displayed, whereafter a layer of an organic electroluminescent material is deposited on the layer of insulating material and, within the windows in the layer of insulating material, on the first electrode layer, and subsequently a second electrode layer is deposited on the layer of electroluminescent material.
To suppress local differences in brightness when displaying the pattern to be displayed, the first electrode layer is provided with a metal top layer on which the layer of insulating material is present, with the windows being formed both in the layer of insulating material and in the top layer. According to the invention, this is realized in a simple manner in that, prior to depositing the layer of insulating material, the first, transparent electrode layer is first coated with a metal top layer, whereafter the layer of insulating material is provided on the metal top layer, and subsequently the windows are formed in the layer of insulating material and also in the metal top layer.
A pattern of mutually isolated segments is preferably formed in the first electrode layer and in the metal top layer, with the windows being formed in the layer of insulating material at the area of the segments. The display screen is then eminently suitable for use in car and airplane instrument panels. According to the invention, this is easily realized in that, after the first electrode layer is coated with the metal top layer, a pattern of mutually isolated segments is formed in the electrode layer and the metal top layer, between which segments th
Gill Richard E.
Liedenbaum Coen T. H. F.
Wuijts Maria C.
McPherson John A.
U.S. Philips Corporation
Waxler Aaron
LandOfFree
Electroluminescent display screen for displaying fixed and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electroluminescent display screen for displaying fixed and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electroluminescent display screen for displaying fixed and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2494959