Patent Application
20080218073
This invention relates generally to electroluminescent (EL) displays, and more particularly, to displays composed of individually produced EL elements or nixels each having electrical contacts on the same side of the EL element or nixels.
Electroluminescence (EL), a well-known phenomenon commonly exploited in flat panel displays, is the conversion of electrical energy to light via the application of an electrical field to a phosphor. Commonly used EL devices include Light Emitting Diodes (LEDs), laser diodes, and EL displays (ELDs). Typically, an ELD is in the form of a thin film electroluminescent (TEEL) device, which is a solid-state device generally comprising a phosphor layer positioned between two dielectric layers, and further including an electrode layer on the surface of each dielectric layer to form a five-layer structure, where the electrode layers define the outer layers and the phosphor layer defines the inner middle layer.
Co-pending U.S. application Ser. No. 11/526,661, filed Sep. 26, 2006, and entitled “Electroluminescent Apparatus and Display Incorporating Same,” which is incorporated herein in its entirety by reference, discloses electroluminescent (EL) nixels (pixel devices) that are individually produced such that EL displays may be produced by assembling as many of the individual nixels as required. The electroluminescent (EL) nixels generally include a laminate of a rear electrode, a first dielectric layer, an EL phosphor layer, a second dielectric layer, and a front electrode. At least one of these two electrodes needs to be transparent for light to escape the display device.
In each of the above-described structures, electrical connections to these EL nixels must be made between the front electrodes and the rear electrodes. However, in some applications, electrical connections to the front (emissive) electrodes are difficult to make because such electrical connections interfere with EL emission from the front electrodes. Further, the front electrode electrical connections require yet another processing step that may introduce additional errors during production.
The systems and methods of the present invention produce an individually sized and shaped modular EL element or chip. According to an embodiment of the invention, these EL elements may be “nixels” as illustratively described herein, which are individually sized and modular shaped EL elements that are adapted to form part of an integrated ELD having multiple electrical contacts on the same side of the EL element structure. Alternatively, the EL elements may be sphere-supported thin film phosphor electroluminescent (SSTFEL) devices, as described in WO 2005/024951 A1, published Mar. 17, 2005, and entitled “Sphere-Supported Thin Film Phosphor Electroluminescent Devices.” While the systems, methods, and apparatuses below for single-sided electrical contacts may be disclosed in the context of nixels, they are for illustrative purposes only. Indeed, it will be appreciated that these systems, methods, and apparatuses for single-sided electrical contacts may also apply to SSTFEL devices or other EL elements as well.
More particularly the present invention provides an EL element or nixel structure that makes use of two rear or substantially same-sided electrodes that are electrically separated by a small gap or other non-conductive (e.g., insulating) material, but that generally cover the rear area of the EL element or nixel laminate. These two electrodes may generally be equal in area and each cover approximately half the EL element or nixel area, according to an embodiment of the invention.
An individual EL element or nixel of the present invention may be manufactured independently of other EL elements or nixels prior to being integrated into an ELD unit, and can be tested and sorted according to predetermined performance characteristics. An EL element or nixel may be adapted to be joined with other EL elements or nixels to form a pixel, a subpixel or a plurality of pixels or subpixels for an ELD. The EL element or nixel of the present invention can be formed in a variety of shapes and sizes to suit a variety of ELD applications. Because each EL element or nixel may be manufactured separately, each EL element or nixel can be processed according to its own manufacturing requirements. For example, an EL element or nixel that includes a first type phosphor may be processed at a different temperature than an EL element or nixel that includes a second type phosphor. In addition, each EL element or nixel can be individually tested and sorted according to its mechanical, optical, electrical, or other characteristics. Placement of an EL element or nixel relative to other ELD elements or nixels can thus be controlled to meet desired user specifications and to optimize ELD performance.
Embodiments of the present invention can be used to produce EL elements or nixels in a variety of shapes and sizes. As mentioned previously, the mechanical attributes of the EL elements or nixels can be influential factors affecting the types of ELDs in which they are incorporated as well as the methods by which they are combined to form an ELD. The EL elements or nixels can be variably sized and shaped by using die cutting, punching, or other techniques to form a desired EL element or nixel shape.
According to an embodiment of the invention, there is an electroluminescent (EL) display element. The EL display element may include a dielectric layer having an upper surface and a lower surface, and a top conductive layer having an upper surface and a lower surface, where the top conductive layer and the dielectric layer are positioned opposite one another so that the lower surface of the top conductive layer faces the upper surface of the dielectric layer. The display element also includes a phosphor layer, where the phosphor layer is arranged between the dielectric layer and the top conductive layer, and a bottom conductive layer having an upper surface and a lower surface, where the bottom conductive layer and the dielectric layer are positioned opposite one another so that the upper surface of the bottom conductive layer faces the lower surface of the dielectric layer, and where the bottom conductive layer forms a first bottom electrode and a second bottom electrode.
According to another embodiment of the invention, there is an electroluminescent (EL) display element. The EL display element includes a dielectric layer having an upper surface and a lower surface, and a top conductive layer having an upper surface and a lower surface, where the top conductive layer and the dielectric layer are positioned opposite one another so that the lower surface of the top conductive layer faces the upper surface of the dielectric layer and where the top conductive layer forms a first top electrode and a second top electrode. The EL display element also includes a phosphor layer, where the phosphor layer is arranged between the dielectric layer and the top conductive layer, and a bottom conductive layer having an upper surface and a lower surface, where the bottom conductive layer and the dielectric layer are positioned opposite one another so that the upper surface of the bottom conductive layer faces the lower surface of the dielectric layer, and where the bottom conductive layer is patterned to form a first bottom electrode, a second bottom electrode, and a third bottom electrode.
According to yet another embodiment of the invention, there is a method for fabricating an electroluminescent (EL) display element. The method includes providing a dielectric layer having an upper surface and a lower surface, depositing a phosphor layer over the upper surface of the dielectric layer, and arranging a top conductive layer such that the top conductive layer and the dielectric layer sandwich the phosphor layer. The method further includes arranging a bottom conductive layer such that the bottom conductive layer and the phosphor layer sandwich the dielectric layer, where the bottom conductive layer forms a first bottom electrode and a second bottom electrode.
Accordingly, embodiments of the invention can be used to produce variously shaped and sized EL elements or nixels that can be combined to form an ELD with each electroluminescent element or nixel having both electrical contacts (e.g., electrodes) on one side of the electroluminescent element. The EL elements or nixels can be selectively arranged to make an ELD in which ELD performance can be optimized for a particular application.
The invention will be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings, which form part of this application, and in which:
In general, the systems, methods, and apparatuses presented herein are directed to an individually formed, modular electroluminescent (EL) element or chip. According to an embodiment of the invention, these EL elements may be “nixels” as illustratively described herein, which are individually sized and modular shaped EL elements that are adapted to form part of an integrated ELD having multiple electrical contacts on the same side of the EL element structure. Alternatively, the EL elements may be sphere-supported thin film phosphor electroluminescent (SSTFEL) devices, as described in WO 2005/024951 A1, published Mar. 17, 2005, and entitled “Sphere-Supported Thin Film Phosphor Electroluminescent Devices,” which is hereby incorporated by reference as if fully set forth herein. While the systems, methods, and apparatuses below for single-sided electrical contacts may be disclosed in the context of nixels, they are for illustrative purposes only. Indeed, it will be appreciated that these systems, methods, and apparatuses for single-sided electrical contacts may also apply to SSTFEL devices or other EL elements as well.
As used herein, the term “module” may refer to a self-contained component of a system, which has a well-defined interface to the other components. Typically something is modular if it includes or uses modules which can be interchanged as units without disassembly of the module. Design, manufacture, repair, etc. of the modules may be complex, but this is not relevant; once the module exists, it can easily be connected to or disconnected from the system.
As required, specific embodiments of the invention are disclosed herein. It should be understood, however, that these are merely exemplary embodiments of the invention that can be variably practiced. Drawings are included to assist the teaching of the invention to one skilled in the art; however, they are not drawn to scale and may include features that are either exaggerated or minimized to better illustrate particular elements of the invention. Related elements may be omitted to better emphasize the novel aspects of the invention. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ embodiments of the invention.
According to an exemplary embodiment of the invention,
Still referring to
According to an embodiment of the invention, the dielectric layer 15 may be a ceramic dielectric layer. The ceramic dielectric layer 15 may be composed of barium titanate, BaTiO3 (BT) or barium strontium titanate, Ba0.5Sr0.5TiO3 (BST). It will be appreciated that other materials may be used for the dielectric layer 15, including glass, metal oxides, or other dielectric material. The EL phosphor layer 14 may include metal oxide phosphors and sulfide phosphors. Such metal oxide phosphors and methods of production are described in U.S. Pat. Nos. 5,725,801; 5,897,812; 5,788,882 and U.S. patent application Ser. No. 10/552,452, which patents and application are herein incorporated by reference. Metal oxide phosphors include: Zn2Si0.5Ge0.5O4:Mn, Zn2SiO4:Mn, Ga2O3:Eu and CaAl2O4:Eu. Sulfide phosphors include: SrS:Cu, ZnS:Mn, BaAl2S4:Eu, and BaAl4S7:Eu. Where sulfide phosphors are utilized for the EL phosphor layer 14, the sulfide phosphors may be sealed on the front and the sides of the EL chip 10. The sealing layer may vary in thickness according to an embodiment of the invention. Indeed, the sealing layer may be a thin glass coating, according to an embodiment of the invention.
It will be appreciated that alternatives to the EL chip 10 are available without departing from embodiments of the invention. For example, according to another embodiment of the invention,
During operation of the EL chip 10, as illustrated in
According to a first embodiment of the invention, the EL chip 10 may be operated in a push-pull configuration. With a push-pull configuration, equal and opposite voltages may be applied to the bottom electrode layers 16 and 18, to provide a virtual ground (e.g., a substantially zero potential) at the conductive layer 12. According to a second embodiment of the invention, the EL chip 10 may be operated as if at least two discrete EL devices were connected in series so that the voltage across conductive layer 12 may be shared between two EL devices. In this second embodiment, the row voltages applied to the bottom electrode layer 16 may be driven at twice the typical row voltage (e.g., 160V up to 320V) used for discrete EL devices with top and bottom electrodes, but at half the current. By applying twice the typical row voltages to the bottom electrode layer 16, the EL chip 10 capacitance may be about four (4) times smaller than for discrete EL devices with top and bottom electrodes since with both electrodes on a single side, the EL chip 10 includes essentially two half-size discrete EL devices in series. The lowered capacitance may enable an increase in the refresh rate by a factor of four (4), as refresh rates may be fundamentally limited by high EL panel capacitance. Furthermore, this increased refresh rate may decrease the required column or modulation voltages applied to the bottom electrode layer 18 by a factor of two (2). In particular, by increasing the refresh rate by a factor of 4, the modulation voltages normally decrease by a factor of 4. However, because the series connection of essentially two half-size discrete EL devices doubles the drive voltage applied to bottom electrode layer 16, there may be a net decrease in modulation voltage applied to bottom electrode layer 18 by a factor of 2.
As indicated above, the row voltages applied to bottom electrode layer 16 are doubled since the row voltages are normally set according to the threshold voltage of the EL element or nixel. If the row voltages need to be reduced, the thickness of the phosphor layer 14 may be reduced. However, there the higher row voltages may not problematic for several reasons. For example, there are only 1080 rows versus 5760 columns in a single scan full HD display, and only 540 rows versus 11,520 columns in a dual scan HD display. Further, a reduction in column voltages applied to bottom electrode layer 18 may compensate for higher row voltages applied to bottom electrode layer 16. Row driver voltage requirements may be reduced by floating the row drivers, which is commonly used in plasma displays. Furthermore, increasing refresh rate makes grayscale easier to implement and further provides more control over pixel refresh rates.
Therefore, the modular EL chips with the electrical contacts (e.g., electrodes) formed on one side thereof may be assembled into an electroluminescent matrix-addressed display comprising a plurality of electroluminescent pixels arranged in a 2-dimensional array, each pixel being electrically connected across a unique combination of one of conductive row electrodes and one of conductive column electrodes, with the row connected to the first rear electrode of the electroluminescent pixel and the column connected to the second rear electrode of the electroluminescent pixel. Thus, embodiments of the invention provide a discrete electroluminescent display module, an EL element or nixel, having both electrical contacts on the same side thereof, that can be individually manufactured, tested, sorted and selectively positioned to make an ELD in accordance with the invention.
The methods of the invention can produce a flexible display with scalable dimensions that avoids the limitations imposed by prior art processes that employ glass to provide structure. Exemplary embodiments are included herein as examples of an invention that can be variably implemented and practiced, and as such, are not considered to be limitations, since modifications and alternative embodiments will be apparent to those skilled in the art. Thus, the invention encompasses all the embodiments and their equivalents that fall within the scope of the appended claims.
