(a) Field of the Invention
The present invention relates to a thin film transistor array panel; for example an array panel using polysilicon as a semiconductor.
(b) Description of Related Art
A thin film transistor array panel is used as a circuit substrate to individually drive each pixel in a flat panel display, such as a liquid crystal display or an organic light emitting display.
A typical liquid crystal display (LCD) includes two panels provided with field-generating electrodes. A first panel includes an array of pixel electrodes to apply voltages across associated pixel regions, while a second panel includes a common electrode. A liquid crystal (LC) layer is interposed between the two panels. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer. The orientation of LC molecules in the LC layer depends on the local electric field, and applying appropriate voltages to the pixel regions adjusts the polarization of incident light in the regions to display the desired image.
An organic light emitting display (OLED) is a self emissive display device, which displays images by exciting an emissive organic material to emit light. The OLED includes an anode (hole injection electrode), a cathode (electron injection electrode), and an organic light emission layer interposed therebetween. When the holes and the electrons are injected into the light emission layer, they are recombined and emit light upon pair annihilation.
A storage capacitor is provided for enhancing the voltage storing capacity in pixels of the above-described flat display types. The storage capacitor maintains a pixel voltage of pixels during a non-selected time to display an image.
The storage capacitor may have one of two different structures: a layered structure of a semiconductor layer/an insulating layer/a storage electrode, or a gate electrode/an insulating layer/a data line in the thin film transistor array panel including a semiconductor layer made of polysilicon.
Decreasing the thickness of the insulating layer may increase the storage capacitance in the former structure, but may complicate the manufacturing process, since an additional doping process is necessary to form a semiconductor layer having sufficient conductivity. Because the insulating layer is relatively thick in the latter structure, an overlapping area between the gate electrode and the data line must be increased to increase the storage capacitance, thereby decreasing an aperture ratio of the pixels.