Abstract:
A light emitting display may include cathode columns with a folded arrangement so that each column includes two selectively activatable sections. Each column section may be selectively activated or deactivated depending on whether defects are associated with a given section.

Description:
BACKGROUND 
     This invention relates generally to displays for processor-based systems and appliances. 
     Emissive displays include light emitting devices that emit light in response to a potential. In one embodiment, each pixel may be formed of an organic light emitting device. The organic light emitting device may emit light associated with a particular color in a color gamut. Alternatively, a filter may be used to produce a desired light color. 
     Polymer displays or organic light emitting displays use layers of light emitting polymers. Unlike liquid crystal devices, the polymer displays actually emit light. Light emission may be advantageous for many applications. 
     Generally, polymer displays use at least one semiconductor conjugated polymer sandwiched between a pair of contact layers. The contact layers produce an electric field which injects charge carriers into the polymer layer. When the charge carriers combine in the polymer layer, the charge carriers decay and emit radiation in the visible range. 
     One semiconductive conjugated polymer that may be used in polymer displays is poly(p-phenylenevinylene) (PPV) which emits green light. Another polymer that emits red-orange light is poly(methylethylhexyloxy-p-phenylenevinylene) (MEHPPV). Other polymers of this class are also capable of emitting blue light. In addition nitrile substituted conjugated polymers may be used in forming polymer displays. 
     Active matrix polymer displays may be formed from a substrate such as glass or metal foil covered with an array of active elements. In one conventional structure, the active elements may be thin film transistors (TFTs). In contrast, in passive matrix displays, thin film transistors may be unnecessary. Generally, an entire column is activated at a time and row signals are then sequentially applied to that column. 
     In a number of cases, individual pixels forming an array of light emitting devices may be defective. The pixels may be defective because of improper formation, contamination, or other defects. Commonly, if the defect rate is too high, the entire display may be discarded. 
     Thus, there is a need for ways to make displays in a more economical fashion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a bottom plan view of one embodiment of the present invention; and 
     FIG. 2 is an enlarged, schematic cross-sectional view taken generally along the lines  2 — 2  in FIG. 1 in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the backside of a display  11  may be made up of a plurality of cathode columns  10 ,  12 ,  14  and  16  that run in a first direction and a plurality of anode rows  22  which extend generally transversely thereto. Each set  23  of three rows  22  may form a pixel that emits three different colors to form an appropriate color gamut. In the illustrated embodiment, each color is produced by a light emitting device arranged at the intersection of a column  10 ,  12 ,  14  or  16  and a row  22 . In other embodiments, other layouts may be possible. 
     Each pixel is formed in the region where a cathode column  10 ,  12 ,  14  or  16  overlays an anode row  22 . When appropriate potentials are applied between the cathode  10 ,  12 ,  14  or  16  and an anode row  22 , light is emitted into the page in FIG.  1 . 
     In one embodiment of the present invention, the cathode columns  10 ,  12 ,  14  and  16  may be formed of aluminum. The rows  22  may be formed of indium tin oxide (ITO) so that they are both conductive and substantially light transmissive. 
     Referring to FIG. 2, a pixel  32  of a passive matrix light emitting device includes a cathode column  10  and an anode row  22  that sandwich a light emitting layer  24 . In one embodiment of the present invention, the layer  24  may be an organic light emitting device (OLED). When appropriate potentials are applied between the cathode column  10  and anode row  22 , light is emitted by the light emitting layer  24  and that light passes through the substantially transparent anode  22 . That light is then filtered, in some embodiments, by a color filter  26  to produce a desired color of light. In some cases, the light emitting layer  24  may not produce the exact color which is appropriate for a particular color gamut. The emitted color may be altered by using a color filter  26  in some embodiments. Light then passes through the glass substrate  30 . 
     Referring back to FIG. 1, each column  10 ,  12 ,  14  and  16  includes a pair of selectively coupled sections  10   a  and  10   b ,  12   a  and  12   b ,  14   a  and  14   b  and  16   a  and  16   b . In effect, each column  10 - 16  has a folded architecture to form a pair of sections such as the sections  10   a  and  10   b . Each pair of sections may be joined by a selector  20  at one end of a column  10 - 16  and by a multiplexer  18  on the other end. The multiplexer  18  provides a potential to one or both of the sections of a pair and the selector  20  selectively joins the pair of sections or it leaves them unjoined. 
     Referring to the sections  12   b  and  14   a , a conductive particle A is causing the two sections  12   b  and  14   a  to short to one another. In such case, the column  12   b  may not be driven while the column  12   a  is driven under control of the multiplexer  18   b . At the same time, the selector  20   b  is deselected so that a potential is only applied to the column  12   a . Likewise, with respect to the column  14 , the multiplexer  18   c  only drives the section  14   b  and the selector  20   c  does not join the sections  14   a  and  14   b.    
     Conversely with respect to the column  10 , there are no defects and therefore either or both sections  10   a  and  10   b  may be driven by the multiplexer  18   a . The selector  20  joins the columns  10   a  and  10   b  to produce a folded, unitary column  10 . 
     Finally, referring to the column  16 , a column open B is present in the section  16   b . In such case, the multiplexer  18   d  may drive only the section  16   a  and the selector  20   d  deselects the section  16   b . Alternatively, both columns  16   a  and  16   b  may be driven but the column  16   b  may be isolated or deselected by the selector  20   d . In this way, the section  16   b  of a folded column  16  may be deselected while the remainder of the folded column (the section  16   a ) may still be used. In some cases, additional or redundant columns or column sections may be provided to enable a display to still be useful even when a substantial number of defects are detected. 
     Defects may be detected in post-manufacturing examinations as one example. Once the defects are detected, rather than discarding the display  11 , the multiplexers  18  and the selectors  20  may be programmed to deactivate the affected sections. The multiplexers  18  and the selectors  20  may be controlled through appropriate electrical signals provided from a controller associated with the display  11 . Alternatively, the selectors  20  and multiplexers  18  may be mask programmed, for example using laser light to cut or make connections. As still another alternative, the selectors  20  and multiplexers  18  may be programmed by selectively blowing fuses. In mask programming or fuse programming embodiments, a plurality of conductive paths may be selectably programmed to either connect the sections of a given column or to prevent them from being connected and to either provide a potential to a given section or to prevent the provision of such a potential to a particular section. 
     Because the folded sections that form the columns  10 - 16  are placed relatively close together, the fact that one section does not work may not be noticeable to a user since each section is responsible for a relatively minute portion of the light produced by the overall display  11 . Thus, in some embodiments, a folded architecture may enable sections which may or may not be redundant, to be selectively activated depending on the nature of defects associated with any particular section. 
     While the present invention has been described with respect to an embodiment using organic light emitting devices, other displays may be implemented using the techniques described herein including those that utilize liquid crystal displays (LDCs) and inorganic light emitting devices. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.