1. Field of the Invention
The present invention relates to liquid crystal displays and methods of their fabrication. Some embodiments aim at improving adhesion between a low resistance metal wiring feature and an insulating substrate while providing high transmittance of light traveling through one or more layers of the liquid crystal display.
2. Description of the Related Art
Currently, liquid crystal displays are among the most extensively used types of flat panel displays. A liquid crystal display includes one or two substrates with field generating electrodes, and a liquid crystal layer between the electrodes. Voltages are applied to the electrodes to rearrange the molecules of the liquid crystal layer, thereby controlling the amount of light transmitted through the liquid crystal.
There is a growing demand for increasing the size and resolution of the liquid crystal display.
In many liquid crystal displays, the field generating electrodes are provided in two substrates. One of the substrates (the thin film transistor substrate) includes a plurality of pixel electrodes arranged in a matrix. The other substrate (the common electrode substrate) includes a single common electrode spread over much of the substrate's surface. Voltages are applied to the pixel electrodes to form an image. The thin film transistor substrate includes thin film transistors (TFT), which are three-terminal elements, and which are connected to the pixel electrodes to control connections between the pixel electrodes and a source of power. The liquid crystal display also includes a plurality of wiring features such as gate lines and data lines. The gate lines transmit signals for controlling the thin film transistors. The data lines transmit the voltages to be applied to the pixel electrodes when the transistors are on. Currently, wiring features of low specific resistance are needed for large liquid crystal displays. However, if the gate lines are formed using a material having very low specific resistance such as copper (Cu), copper may diffuse into the silicon active areas of the thin film transistors, and as a result the gate line resistance may increase or the adhesion between the gate line and the insulating substrate may be compromised.
To counter this problem, it has been proposed to include other layers into wiring features in addition to a metal layer of very low resistivity. However, such structures are vulnerable to metal migration due to the galvanic effect between the copper and the other layers. Also, the manufacturing productivity is reduced.
Accordingly, there is still a need for high-productivity manufacturing processes to fabrication liquid crystal displays with wiring features made using low resistivity materials such as copper and with good adhesion between the wiring features and the insulating substrate.