1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device and a method of fabricating the same, and more particularly, to an OLED display device including a metal layer containing nickel to reduce contact resistance.
2. Description of the Related Art
Flat panel display devices, such as organic light emitting diode display devices or liquid crystal display devices, have N×M unit pixels disposed in a matrix, and they may be classified into passive matrix types or active matrix types, depending on their driving methods. In the active matrix type, a pixel electrode, defining an emission region, and a unit pixel drive circuit, for applying a current or voltage to the pixel electrode, are formed in a unit pixel region. The unit pixel drive circuit includes at least one thin film transistor.
A thin film transistor generally includes a semiconductor layer, a gate electrode, and source and drain electrodes. Here, source and drain regions are at edge portions of the semiconductor layer, and a channel region is between the source and drain regions. Also, the thin film transistor is used as a switching device for controlling the operation of an unit pixel and a driving device for driving the pixel.
However, a conventional OLED display device, including a thin film transistor, has reduced charge mobility because of high contact resistance between the source and drain electrodes, which are formed of aluminum, and a first electrode that is a transparent conductive layer. Due to the reduction in charge mobility, signal delay may occur, thereby causing deterioration in display quality of the OLED display device. Also, since the source and drain electrodes formed of aluminum are easily oxidized in the atmosphere, an oxide layer may be formed between the source and drain electrodes and the first electrode, resulting in an increase in contact resistance therebetween. Also, a top-emission OLED display device uses a first electrode, including a reflective layer, which has high contact resistance between the reflective layer and the transparent conductive layer of the first electrode. Thus, charges are not easily transported to an organic layer, and luminous efficiency of the OLED display device is lowered.