Amorphous and Polysilicon TFTs for OLED Grayscale Control

The patent applies different channel materials to different transistor types based on their specific functional requirements. Polysilicon channel regions are used in switching transistors (second, third, fourth, fifth, sixth transistors) where high mobility is critical for fast switching. Amorphous silicon channel region is used in the driving transistor (first transistor) where voltage control range and grayscale precision are paramount. This local differentiation resolves the contradiction by optimizing each transistor's material properties for its specific role in the pixel circuit.

The pixel circuit is segmented into multiple transistor functions: the first transistor (driving transistor) handles voltage control and grayscale generation using amorphous silicon for its wide voltage range, while the second through sixth transistors (switching transistors) handle current switching and signal routing using polysilicon for its high mobility. This segmentation allows each transistor type to be optimized independently, resolving the contradiction between voltage range and current capability.

The patent employs a multi-functionality strategy where the first transistor serves dual purposes: it acts as the driving transistor that controls the OLED brightness and also functions as a storage element that maintains the voltage level during the display period. The capacitor (first capacitor) works in conjunction with the first transistor to maintain charge. This multi-functionality reduces the need for additional separate components, partially offsetting the complexity introduced by using different channel materials.