1. Field of the Invention
The present invention relates to a display unit which is suitably applied to an organic electro luminescence display or liquid crystal display for example, and also relates to a method of manufacturing the same.
2. Description of the Related Art
In recent years, development of next-generation displays is active due to an increasing demand for space-saving, high luminance, low power consumption and so on. In such situation, the organic electro luminescence display (organic EL display) using an organic light emitting element attracts attention as those satisfying such demands. In the organic electro luminescence display, wide viewing angle is available due to its light-emitting feature. What is more, since no backlight is necessary, it is possible to realize power saving and high responsiveness and further to reduce thickness in dimension. In addition, the organic electro luminescence display attracts more attention due to its flexibility when using a plastic plate as a substrate to utilize the flexible nature inherent to organic luminescent materials.
As for a drive system of the organic electro luminescence display, the active matrix system, in which a thin film transistor (TFT) is used as its drive element, recognizes advantages in response time and resolution compared with the passive matrix system of related art, thereby considered to be much suitable for the organic electro luminescence display having features as mentioned above.
As for the thin film transistor used in the active matrix organic electro luminescence display, at least a switching transistor for controlling the tone of a pixel and a drive transistor for controlling light emission of the organic light emitting element are necessary. A capacitor is connected to a gate electrode of the drive transistor to hold an electric charge in accordance with a display signal.
Due to its enlarged display size and advanced fineness, such active matrix organic light emitting element suffers from disadvantages of longer and finer gate wiring, source signal line and current supply line. However, the resistance of wiring increases in proportion to the length and in inverse proportion to the cross-section area. Such increase in resistance results in a distortion of signal waveform and transmission delay of signals, thereby leading to unevenness and degradation of image quality.
In order to lower the wiring resistance, usage of a low resistance material such as aluminum (Al) may be useful. However, such low resistance material as aluminum (Al) does not have enough thermal resistance. Since it is inevitable in the manufacturing process of a thin film transistor, which includes a gate insulating film for example, to raise the temperature of a substrate to 300° C. or more, independent usage of aluminum (Al) may cause a hillock due to the thermal stress, thereby deterioration of insulation quality is observed in interlayer insulating films.
For example, disclosure by Japanese Patent Publication No. 2003-45966 shows that a scanning line 3a and a main portion 61a of a data line 6a are made of a low resistance metal such as aluminum or an aluminum alloy. Here, at the wiring intersection, a relay portion 62a of the data line 6a, which is made of a refractory metal, is disposed under the scanning line 3a and a capacitance line 3b. Such divided wiring enables to suppress the generation of hillock at the intersection even when the relay portion is exposed to high temperature in the manufacturing process of a thin film transistor.