Driving Substrate TFT Layout for Mobility and Leakage Control

The patent divides the thin-film transistor structure into two distinct types: first TFTs with dual active layers for high mobility applications, and second TFTs with single active layer for good off-state characteristics. This segmentation allows different circuit units to use appropriate transistor types based on their specific requirements, resolving the contradiction between mobility and off-state characteristics.

The patent applies different active layer configurations to different locations in the circuit. High mobility is achieved locally in first TFTs using dual active layers where speed is critical, while good off-state characteristics are achieved locally in second TFTs using single active layers where leakage control is critical. This local quality approach allows both requirements to be satisfied in different parts of the same circuit.

The patent segments the transistor population into two groups based on their mobility requirements. Only first TFTs that require high mobility use the complex dual active layer structure, while second TFTs use the simpler single active layer structure. This segmentation reduces overall device complexity compared to making all TFTs dual-layer.

The patent applies the dual active layer structure only partially - specifically to first TFTs where high mobility is required - rather than excessively applying it to all TFTs. This partial action achieves the necessary mobility improvement in critical paths while avoiding the complexity penalty in non-critical areas.