1. Field of the Invention
The present invention relates to an OLED (Organic Light Emitting Display) device. More particularly, the present invention relates to an OLED device achieving high aperture ratio and being advantageously applied to high resolution devices, in which an oxide semiconductor thin-film transistor having an active layer made of an oxide semiconductor and an LTPS (Low Temperature Poly-Silicon) thin-film transistor having an active layer made of an low temperature poly-silicon are supplied with the same gate voltage from the same gate line. Further, the present invention relates to an OLED device in which an oxide semiconductor thin-film transistor and an LTPS thin-film transistor are used as a switching thin-film transistor and a driving thin-film transistor for driving a single organic light-emitting element.
2. Description of the Related Art
As the era of information technology has begun, the field of display that visualizes the electrical information signals has been rapidly developing rapidly. In accordance with this, various flat display devices which are thinner, lighter and more efficient in power consumption have been developed fast to replace existing CRTs (Cathode Ray Tubes)
Examples of such flat display devices include an LCD (Liquid Crystal Display) device, an OLED (Organic Light Emitting Display) device, an EPD (Electrophoretic Display) device, a PDP (Plasma Display Panel) device, a FED (Field Emission Display) device, an EWD (Electro-Wetting Display) device, etc.
Among these, an OLED device emerges as the next generation display device having a self-emitting characteristic since it exhibits a good performance on LCD devices in terms of viewing angle, contrast, response time, power consumption, etc.
Commonly, flat display devices require a flat display panel as an essential element to produce images. Such a flat display panel includes a pair of substrates laminated on one another, with a layer of a luminescent material or a polarizing material between the substrates. The substrates of such a flat display panel are divided into emission regions in which arrays of pixels emit light, and element regions in which circuit elements to drive the pixels are disposed. In particular, in the element regions, a plurality of thin-film transistors (TFT) is disposed to drive the pixels and to operate the circuit elements.
An OLED device includes organic electroluminescent diodes with each consisting of an anode electrode, a film of organic compound, and a cathode electrode. Such an OLED device may be driven in a passive matrix manner in which an organic electroluminescent diode is connected between a gate line and a data line in a matrix to form a pixel, or in an active matrix manner in which the operation of a pixel is controlled by its thin-film transistor working as a switch.
In a pixel driving unit of an OLED device driven in an active matrix manner, a switching thin-film transistor of a pixel is operated by the voltage output from a circuit element via a gate line. When a data value of pixel goes through a data line to be stored in a storage capacitor, a pixel-driving current corresponding to the data value flows from a driving thin-film transistor to an organic electroluminescent diode causing the pixel to emit light as a result.
As customer's expectation for OLED devices is ever increasing, research is going on into OLED devices with high aperture ratio and high resolution. However, there are limits to reduce the sizes of thin-film transistors, capacitors and various types of supply lines required for driving OLED devices. Accordingly, efforts to implement OLED devices with high aperture ratio and high resolution are on going.
Previously in OLED devices, LTPS thin-film transistors solely or oxide semiconductor thin-film transistors solely have been used as switching thin-film transistors and driving thin-film transistors. When only one type of thin-film transistors is used, large area has been required for providing enough space for storage capacitors. To that end, space for storage capacitors needs to be large enough, so that the size of a pixel itself can be increased or the area occupied by a pixel driving unit in the pixel can become larger. This makes it difficult to manufacture a high-resolution or high-transparent panel.