Organic light emitting display

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application Nos. 10-2006-0006010 and 10-2006-0006537 filed in Republic of Korea on Jan. 19, 2006 and Jan. 20, 2006, respectively, the entire contents of which are hereby incorporated by reference.

1. Field

This document relates to an organic light emitting display (OLED).

2. Related Art

Among flat panel display devices, light emitting display has an advantage in that it has high response speed and low power consumption. The light emitting display can also be manufactured thin in size and light in weight because of not requiring backlight unit.

In particularly, organic light emitting display (OLED) has an organic light emitting layer between an anode and a cathode. Holes from the anode and electrons from the cathode are combined within the organic light emitting layer to create hole-electron pairs, i.e., excitons. The OLED emits light by energy generated while the excitons return to ground state.

Recently, dual emission type OLED is increasingly employed for mobile communication devices such as mobile phones.

In one related art, dual emission type OLED was fabricated such that two panels were separately fabricated and then attached. In this case, the fabrication cost of the device increased and the device became thick because the two separate panels were attached.

In another related art, dual emission type OLED comprised sub-pixels each having a top emission region and a bottom emission region. But, the device cannot obtain a sufficient emitting area because each single pixel is divided into the two parts, so its luminance is reduced.

An aspect of this document is to provide an organic light emitting display (OLED) which is fabricated at a low cost, thinner and has an improved luminance.

In an aspect, the OLED comprises a substrate, first and second driving units positioned on the substrate, a first light emitting diode (LED) connected with the first driving unit and comprising a first organic light emitting layer and a second emitting diode electrically connected with the second driving unit and comprising a second organic light emitting layer.

The implementation of this document will be described in detail Referring to the following drawings in which like numerals refer to like elements.

FIG. 1 is a sectional view showing an organic light emitting display (OLED) according to a first embodiment of this document.

FIG. 2 is a sectional view showing an OLED according to a second embodiment of this document.

FIG. 3 is a sectional view showing an OLED according to a third embodiment of this document.

FIG. 4 is a sectional view showing an OLED according to a fourth embodiment of this document.

Hereinafter, an implementation of this document will be described in detail referring to the attached drawings.

First Embodiment

Referring to FIG. 1 , an organic light emitting display (OLED) 100 according to a first embodiment of the present invention comprises a first unit and a second driving unit 110 A and 110 B positioned on a substrate 105 . The first and second driving units 110 A and 110 B comprise at least one driving transistor, respectively. Herein, although not shown, the driving transistor may comprise a semiconductor layer, a gate electrode positioned corresponding to the semiconductor layer, a gate insulation layer positioned between the semiconductor layer and the gate electrode, and source and drain electrodes electrically connected with the semiconductor layer. The first and second driving units 110 A and 110 B may further comprise a switching transistor and a capacitor, respectively.

An insulation layer 115 is positioned on the first and second driving units 110 A and 110 B. The insulation layer 115 can be an insulation layer for planarization and comprise a transparent dielectric material. The insulation layer 115 can be formed to expose the source and drain electrodes of the driving units 110 A and 110 B. In FIG. 1 , the insulation layer 115 is formed to be lower than the driving units 110 A and 110 B, but without being limited thereto, the insulation layer 115 can be formed to be higher than the driving units 110 A and 110 B so long as it can expose the source or drain electrode of the driving units 110 A and 110 B via a via hole.

A first emitting diode 120 electrically connected with the first driving unit 110 A is positioned on the first driving unit 110 A and the insulation layer 115 . And a second emitting diode 160 electrically connected with the second driving unit 110 B is positioned on the first emitting diode 120 .

Here, the first emitting diode 120 comprises a first anode 130 , a first organic light emitting layer 140 and a first cathode 150 , and the second emitting diode 160 comprises a second anode 170 , a second organic light emitting layer 180 and a second cathode 190 . Accordingly, the first cathode 150 and the second anode 170 electrically contact with each other.

The first anode 130 of the first emitting diode 120 is electrically connected with the first driving unit 110 A, and the second cathode 190 of the second emitting diode 160 is electrically connected with the second driving unit 110 B. In this case, because of height difference between the second emitting diode 160 and the second driving unit 110 B, a connection layer 195 can be positioned on the second driving unit 110 B. Thus, the second cathode 190 can be electrically connected with the second driving unit 110 B via the connection layer 195 .

Although not shown, a metal wiring for supplying power can be connected with the first cathode 150 and the second anode 170 .

The first and second anodes 130 and 170 may comprise a material with a high work function, for example, indium tin oxide (ITO), and the first and second cathodes 150 and 190 may comprise one or more of metals such as Al, Ca, Mg, and LIF/Al which have a low work function and high reflexibility. In particular, the second cathode 190 can be a transflective electrode comprising a transparent conductive layer and a metallic layer or a transflective electrode made of a thin metal.

Because the first cathode 150 comprising metal is positioned under the second anode 170 , light generated from the second emitting diode 160 can be reflected by the first cathode 150 and then emitted to an upper side of the second emitting diode 160 . Light generated from the first emitting diode 120 can be reflected by the first cathode 150 and then emitted to a lower side of the first emitting diode 120 .

As described above, in the first embodiment of the present invention, with the bottom-emission type first emitting diode 120 and the top-emission type second emitting diode 160 formed in the stacked structure, the dual emission type OLED can be implemented without reducing an aperture ratio.

In addition, because the first emitting diode 120 and the second emitting diode 160 are electrically connected with the first and second driving units 110 A and 110 B, respectively, they can be separately driven, so power consumption can be reduced and the screens can be effectively changed.

Second Embodiment

Referring to FIG. 2 , an OLED 200 according to a second embodiment of the present invention includes first and second driving units 210 A and 210 B positioned on a substrate 205 . The first and second driving units 210 A and 210 B comprise at least one driving transistor, respectively.

A first insulation layer 215 is positioned on the first and second driving units 210 A and 210 B. The first insulation layer 215 can be formed to expose source or drain electrode of the first and second driving units 210 A and 210 B.

A first emitting diode 220 electrically connected with the first driving unit 210 A is positioned on the first driving unit 210 A and the first insulation layer 215 . A second emitting diode 260 electrically connected with the second driving unit 210 B is positioned on the first emitting diode 220 , and a second insulation layer 255 is positioned between the first and second emitting diodes 220 and 260 .

Here, the first emitting diode 220 includes a first anode 230 , a first organic light emitting layer 240 and a first cathode 250 , and the second emitting diode 260 includes a second anode 270 , a second organic light emitting layer 280 and a second cathode 290 .

The first anode 230 of the first emitting diode 220 is electrically connected with the first driving unit 210 A, and the second cathode 290 is electrically connected with the second driving unit 210 B. In this case, because of a height difference between the second emitting diode 260 and the second driving unit 210 B, a connection layer 295 can be positioned on the second driving unit. Accordingly, the second cathode 290 can be electrically connected with the second driving unit 210 B via the connection layer 295 .

Although not shown, a metal wiring for supplying power can be connected with the first cathode 250 and the second anode 270 .

The first and second anodes 230 and 270 may comprise a material with a high work function, for example, ITO, and the first and second cathodes 250 and 290 may comprise one or more of metals such as Al, Ca, Mg, and LIF/Al which have a low work function and high reflexibility. In particular, the second cathode 290 can be a thin transflective electrode.

Because the first cathode 250 comprising metal is positioned under the second anode 270 , light generated from the second emitting diode 260 can be reflected by the first cathode 250 and then emitted to an upper side of the second emitting diode 260 . Light generated from the first emitting diode 220 can be reflected by the first cathode 250 and then emitted to a lower side of the first emitting diode 220 .

As described above, in the second embodiment of the present invention, with the bottom-emission type first emitting diode 220 and the top-emission type second emitting diode 260 formed in the stacked structure, an aperture ratio of the OLED is not reduced. In addition, because the first and second emitting diodes 220 and 260 are electrically connected with the first and second driving units 210 A and 210 B, respectively, the first and second emitting diodes 220 and 260 can be driven separately.

Also electrodes that comprise each different material cannot contact with each other, because the second insulation layer 255 is positioned between the first and second emitting diodes 220 and 260 , so a driving voltage can be reduced.

Third Embodiment

Referring to FIG. 3 , an OLED 300 according to a third embodiment of the present invention includes first and second driving units 310 A and 310 B positioned on a substrate 305 . The first and second driving units 310 A and 310 B comprise at least one driving transistor, respectively.

An insulation layer 315 is positioned on the first and second driving units 310 A and 310 B. The insulation layer 315 can be formed to expose source or drain electrode of the first and second driving units 310 A and 310 B.

A first emitting diode 320 electrically connected with the first driving unit 310 A is positioned on the first driving unit 310 A and the insulation layer 315 . A second emitting diode 360 electrically connected with the second driving unit 310 B is positioned on the first emitting diode 320 .

Here, a first electrode 330 is positioned under a first organic light emitting layer 340 , a second electrode 390 is positioned on a second organic light emitting layer 380 , and a third electrode 350 is positioned between the first and second organic light emitting layers 340 and 380 .

Namely, the first and second electrodes 330 and 390 are anodes of the first and second emitting diodes 320 and 360 , respectively, and the third electrode 350 is a common cathode of the first and second emitting diodes 320 and 360 .

The first electrode 330 is electrically connected with the first driving unit 310 A, and the second electrode 390 is electrically connected with the second driving unit 310 B. In this case, because of height difference between the second emitting diode 360 and the second driving unit 310 B, a connection layer 395 can be positioned on the second driving unit 310 B to resolve the step. Accordingly, the second electrode 390 can be electrically connected with the second driving unit 310 B via the connection layer 395 . Although not shown, a metal wiring for supplying power can be connected with the third electrode 350 .

The first and second electrodes 330 and 390 may comprise a material with a high work function, for example, ITO, and the third electrode 350 may comprise one or more of metals such as Al, Ca, Mg, and LIF/Al which have a low work function and high reflexibility.

Accordingly, light generated from the first and second organic light emitting layers 340 and 380 is reflected by the third electrode 350 , the common cathode, and emitted toward the first and second electrodes 330 and 390 , respectively.

As described above, the OLED 300 according to the third embodiment of the present invention has such an advantage in that it has a large emitting area and a separate driving can be possibly performed.

In addition, because the OLED 300 uses the third electrode 350 as the common cathode of the first and second emitting diodes 320 and 360 , a processing time and cost for its fabrication can be reduced and the OLED can be implemented to be thinner.

Fourth Embodiment

Referring to FIG. 4 , in the OLED 400 according to the fourth embodiment of the present invention, a first electrode 430 is used as an anode of a first emitting diode 420 and a third electrode 490 is used as a cathode of the second emitting diode 490 . A third electrode 450 is used as a cathode of the first emitting diode 420 and as an anode of a second emitting diode 460 .

Although the third electrode 450 is used as the common electrode of the first and second emitting diodes 420 and 460 , it plays a different role in each emitting diode. Thus, in this case, the third electrode 450 cannot have a proper work function in performing the two roles.

Thus, the third electrode 450 can be made of a metal having a low work function, and surface treatment is performed on one surface of the third electrode to have a high work function by using at least one of mechanical, chemical, plasma, laser surface processing methods in order to increase the work function. The treated surface of the third electrode is opposite to the second emitting layer in third electrode

In other words, the second electrode 450 can perform the role of the cathode of the first emitting diode 420 by comprising a metal having a low work function and also perform the role of the anode of the second emitting diode 460 by comprising one surface having a high work function.

In the above-described embodiments of the present invention, the first and second driving units are positioned on the same planar surface, but without being limited thereto.

Although the present invention has been described with reference to certain exemplary embodiments, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention defined in the appended claims, and their equivalents.