With the development of display technologies, organic light-emitting diode (OLED) display technology gradually becomes mature and OLED display devices are increasingly used in different display fields.
A basic driving unit in an OLED display device is shown in FIG. 1. The driving unit comprises two thin-film transistors (TFT) and a storage capacitor Cst to form a 2T1C structure. A scanning signal Vgate is input to a gate of a first thin-film transistor, and a data signal Vdata is input to a source of the first thin-film transistor. A drain of the first thin-film transistor is connected to a gate of a second thin-film transistor. A source of the second thin-film transistor is connected to a digital power supply Vdd, and a drain thereof is connected to a digital ground Vss. The storage capacitor Cst is arranged between the gate of the second thin-film transistor and the source thereof. A light-emitting diode is connected in series between the drain of the second thin-film transistor and the digital ground Vss.
The first thin-film transistor functions as a switch. When the gate of the first thin-film transistor is turned on, a data signal is transmitted from the source of the first thin-film transistor to the drain thereof. That is, the data signal is transmitted to the gate of the second thin-film transistor. The second thin-film transistor plays a role of regulating grayscale of the light-emitting diode. Magnitude of a current flowing through the light-emitting diode is controlled by a voltage difference Vgs between the gate of the second thin-film transistor and the source thereof, and the voltage difference Vgs is maintained by the storage capacitor Cst.
For the first thin-film transistor and the second thin-film transistor which have different functions, electrical properties required are different. For the first thin-film transistor, it is required that a sub-threshold of an IdVg curve thereof is small, so that the first thin-film transistor can be turned on or turned off quickly. For the second thin-film transistor, it is required that a sub-threshold of an IdVg curve thereof is large, which is beneficial for grayscale debugging of an OLED. However, in existing OLED display devices, the manufacturing procedure and the structure of the first thin-film transistor are the same as those of the second thin-film transistor. Therefore, the requirements for different electrical properties of the first thin-film transistor and the second thin-film transistor cannot be met.
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