Display device formed of a multi-color light emitting material and method of making same

A display device comprising a multi-color light emitting layer and method of depositing the multi-color light emitting layer over a glass substrate are provided. The display device comprises multiple light emitting materials deposited over a glass substrate in coplanar relationship to each other. The method provides depositing one light emitting polymer material over one portion of the glass substrate and depositing other light emitting polymer materials over other portions of the glass substrate, such that the multiple light emitting polymer materials are deposited in a coplanar relationship to each other. The light emitting polymer materials are deposited using flexographic mats, the relief portion of which have patterns corresponding to the respective portions of the glass substrate being covered by the light emitting polymer materials being deposited.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning to the drawings, the preferred embodiments of the present invention will now be described. Referring initially to FIG. 1 , the display device according to the present invention is indicated generally by reference numeral 10 . At the base of the display device 10 is a glass substrate 12 , which is preferably formed of passivated soda-lime glass preferably to a thickness of 0.4 to 1.1 mm. As those of ordinary skill in the art will appreciate, other transparent materials, including borosilicate and other glasses or amorphous or polysilicon structures, could be used as the base layer. In addition, non-transparent materials, including a processed silicon substrate, could also be used as the base layer provided that the cathode layer was a transparent material. A conductive layer 14 , preferably formed of indium tin oxide (ITO), is deposited over the glass substrate 12 . The conductive layer 14 may be formed by vacuum depositing the ITO onto the surface of the glass substrate 12 . As those of ordinary skill in the art will appreciate, other deposition techniques well known in the art may be employed. Once the ITO material is deposited over the entire surface of the glass substrate 12 , the conductive layer 14 is then etched, using, for example, a photo-etch process, to form an array of parallel strips, which form anodes 16 , as shown in FIG. 2 . The conductive layer 14 is preferably 2000-3000 Angstroms in thickness in order to minimize the resistance of the anode conductors. As those of ordinary skill in the art will appreciate, other transparent conductive materials could be used to form the anode layer 14 . Next, a hole transport layer 18 is deposited over the conductive anode layer 14 , as shown in FIG. 1 . The hole transport layer 18 is preferably formed of PEDT—PSS, and is deposited to a thickness of approximately 200 to 400 angstroms. The hole transport layer 18 is preferably deposited over the entire structure by spin coating a solution of PEDT—PSS onto the surface of conductive layer 14 . However, as pointed out above, vacuum deposition or other deposition techniques known in the art may also be used. Next, a multi-color light emitting layer 20 is deposited over the hole transport layer 18 . The multi-color light emitting layer 20 is preferably formed as follows. First, an organic light emitting material 22 (shown in FIG. 3 ), which when activated emits a particular color, is deposited over a portion of the hole transport layer 18 . Preferably, the organic light emitting material 22 is a polymer selected from the group consisting of doped-poly-phenylene vinylene (doped-PPV), poly-arylenes or poly-fluorenes. Although, as those of ordinary skill in the art will appreciate, other polymer or non-polymer organic materials may be used. The organic light emitting material 22 is preferably deposited over a portion of the hole transport layer 18 using a flexographic mat 24 , which contains relief areas 26 corresponding to the region over the hole transport layer 18 where it is desired to deposit the organic light emitting material 22 , as shown in FIG. 4 . In particular, the organic light-emitting material 22 is applied to the flexographic mat 24 , which in turn, is pressed over the surface of the hole transport layer 18 . After the organic light emitting material 22 is deposited over the desired portion of the hole transport layer 18 , the material is heated. More specifically, the entire structure is placed in a convection oven and heated to 100 to 150 degrees Centigrade for a period of 30-90 minutes so as to dry bake the organic light-emitting material 22 onto the surface of the hole transport layer 18 . Next, another organic light emitting material 28 (shown in FIG. 3 ) is deposited over another portion of the hole transport layer 18 different from the portion covered by the first organic light-emitting material 22 . The organic light emitting material 28 emits a different color than the organic light-emitting material 22 . Preferably, the organic light emitting material 28 is also a polymer selected from the group consisting of doped-PPV, poly-arylenes or poly-fluorenes. Again, however, as those of ordinary skill in the art will appreciate, other polymer or non-polymer organic materials may be used. The organic light emitting material 28 is preferably deposited over a portion of the hole transport layer 18 using a different flexographic mat 30 , which contains a different relief area 32 corresponding to the region over the hole transport layer 18 where it is desired to deposit the organic light emitting material 28 , as shown in FIG. 4 . The organic light emitting material 28 is applied to the flexographic mat 30 , which in turn, is pressed over the surface of the hole transport layer 18 . After the organic light emitting material 28 is deposited over the desired portion of the hole transport layer 18 , the material is heated. More specifically, the entire structure is placed in a convection oven and heated to 100 to 150 degrees Centigrade for a period of 30-90 minutes so as to dry bake the organic light emitting material 28 onto the surface of the hole transport layer 18 . Although only two light emitting materials are shown in FIG. 3 , as those of ordinary skill in the art will appreciate, other light-emitting materials may be used to cover different portions of the display device. 10 . Regardless of how many different light emitting materials are ultimately deposited, all such materials are deposited so as to be in coplanar relationship with one another, as shown in FIG. 3 . The result is a single multi-color light emitting layer 20 , which is preferably 200 to 400 angstroms in thickness. Next, an electron transport layer 34 is deposited over the multi-color light emitting layer 20 , as shown in FIG. 1 . The electron transport layer 34 is preferably formed of a cyano-PPV and is deposited to a thickness of approximately 200 to 400 angstroms. The electron transport layer 34 is preferably deposited over the entire structure by spin coating a solution of poly(cyano tere-phthalylidene) onto the surface of the multi-color light emitting layer 20 . However, as pointed out above vacuum deposition, or other deposition techniques known in the art may also be used. Next, a conductive metal layer 36 is deposited over the electron transport layer 34 , as shown in FIG. 1 . The conductive metal layer 36 is preferably formed of a very thin film of lithium fluoride (0.5-1.0 nm) overcoated with a thick film (approx. 200 nm) of aluminum, although other similar materials can be used. The metal conductive layer 36 is preferably deposited to a thickness of approximately 2000 angstroms. The conductive metal layer 36 is preferably deposited over the entire structure by vacuum deposition onto the surface of the electron transport layer 34 , however, as pointed out above spin coating a solution of lithium fluoride or aluminum, or other deposition techniques known in the art may be used. Once conductive metal layer 36 is deposited over the entire surface of the electron transport layer 34 , the conductive metal layer 36 is then etched, using, for example, a plasma or a photo-etch process, to form an array of parallel strips, which form cathodes 38 , as shown in FIG. 5 . Alternatively, the cathode may be vacuum deposited via a patterned shadow mask. Another alternative would be to deposit onto the anode structure an array of separator ribs that would define the gaps between cathodes. The array of cathodes 38 is disposed in a different plane than the array of anodes 16 . The array of cathodes 38 are also disposed in perpendicular relationship to the array of anodes 16 , so as to form a matrix or grid. The matrix or grid formed by said array of anodes and array of cathodes in turn forms a matrix of pixels, having for example an approximate size of 300 microns by 300 microns. A particular pixel is activated by activating the anode row and cathode column that defines the pixel. What is displayed on the display screen is a dot or microsquare of the color given off by the particular light emitting material disposed between the portion of the anode and cathode defining the pixel. Anode rows and cathode columns are activated (selected) using addressing techniques well known in the art. Finally, a layer of protective material 40 , preferably formed of a metal can containing an oxygen getter, is deposited over the conductive metal layer 36 to a thickness of approximately 0.2 mm. The layer of protective material 40 is preferably attached to the coated glass substrate by using an adhesive. However, other protective layers may also be used such as a polymer multi-layer or an inorganic hard-coat or a glass sheet. As those of ordinary skill in the art will appreciate, the present invention is susceptible to various modifications and alternative forms. For example, in one alternate embodiment, an inverted structure is used where the cathode is the first layer deposited on the substrate and the anode is the final layer. Furthermore, additional process steps may be used in constructing a completed display device in accordance with the present invention. It should be understood also that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.