Organic light emitting display

1. An organic light emitting display, comprising:

a substrate;

a driving thin film transistor (TFT) on the substrate, the TFT including a semiconductor layer formed of a source electrode, a drain electrode, and an N-type oxide semiconductor;

at least one insulating layer formed on the driving TFT;

a pixel defining layer defining a pixel region on the insulating layer;

a cathode electrode coupled to a drain electrode of the driving TFT and patterned to correspond to the pixel region;

an electron injection layer arranged on the cathode electrode over the entire surfaces of the pixel defining layer and the cathode electrode, and formed of a material whose band gaps are 3.4 eV to 5.0 eV selected from the group consisting of an oxide, a nitride, a fluoride, and diamond;

an organic light emitting layer formed on the electron injection layer to correspond to the cathode region; and

an anode electrode formed on the organic light emitting layer.

2. The organic light emitting display as claimed in claim 1 , wherein the N-type oxide semiconductor is formed of an oxide selected from the group consisting of ZnO, ZnGa 2 O 4 , ZnIn 2 O 4 , In 2 O 3 , ZnInGaO 4 , and ZnSnO 4 .

3. The organic light emitting display as claimed in claim 1 , wherein the cathode electrode is formed of a material selected from the group consisting of ITO, Ag, and Al.

4. The organic light emitting display as claimed in claim 1 , wherein the electron injection layer is formed of a compound selected from the group consisting of MgO, Al 2 O 3 , SiO 2 , Si 3 N 4 , and LiF.

5. The organic light emitting display as claimed in claim 1 , wherein the electron injection layer has a thickness of 1 nm to 2 nm.

6. The organic light emitting display as claimed in claim 1 , further comprising an electron transport layer between the electron injection layer and the organic light emitting layer.

7. The organic light emitting display as claimed in claim 1 , wherein the substrate is transparent, and the cathode electrode is formed of ITO doped with Cs.

8. The organic light emitting display as claimed in claim 1 , further comprising a switching TFT coupled to the gate electrode of the driving TFT.

9. The organic light emitting display as claimed in claim 8 , wherein the switching TFT is an N-type TFT.

10. The organic light emitting display of claim 1 , wherein the at least one insulating layer further comprises a planarizing layer and a passivation layer.

11. The organic light emitting display of claim 1 , wherein the cathode electrode is coupled to the drain electrode through a via hole.

12. The organic light emitting display of claim 1 , wherein at least one of a hole injection layer and a hole transport layer are disposed between the organic light emitting layer and the anode electrode.

13. The organic light emitting display of claim 8 , wherein the switching TFT is a P-type TFT.

14. A pixel circuit of an organic light emitting display comprising:

an N-type driving thin film transistor (driving TFT) with a gate electrode, drain electrode and source electrode;

a switching thin film transistor (switching TFT) with a gate electrode, drain electrode and source electrode;

a data line coupled to the drain electrode of the switching TFT;

a scan line coupled to the gate electrode of the switching TFT;

a capacitor coupled to the gate electrode of the driving TFT and the source electrode of the driving TFT, and

an organic light emitting diode (OLED) with a cathode coupled to the drain electrode of the driving TFT and an anode coupled to a power voltage,

wherein:

the source electrode of the driving TFT is coupled to a reference voltage, and

the gate electrode of the driving TFT is coupled to the source electrode of the switching TFT.

15. The pixel circuit of claim 14 , wherein the switching TFT is an N-type TFT.

16. The pixel circuit of claim 14 , wherein the switching TFT is a P-type TFT.