Design of Low-Power DFFs With Unipolar Thin-Film Transistor

Thin-film transistors (TFTs) have become the foundation of modern flexible and large-area electronics, enabling applications such as displays, wearable sensors, and IoT systems. However, realizing energy-efficient sequential circuits with unipolar TFTs remains challenging due to limited voltage swing and substantial direct-path current. This work presents the design and analysis of three low-power D flip-flops (DFFs), a Dynamic TFT Flip-Flop (DTFF), and two generations of Static TFT Flip-Flop (STFF-I and STFF-II), implemented using unipolar amorphous silicon (a-Si:H) TFTs. The first-generation STFF-I DFF, fabricated and measured on glass and flexible substrates, achieves a 79.8% reduction in total power relative to a conventional design. The STFF-II DFF incorporates optimized feedback control to achieve full-swing static operation with reduced switching delay. The DTFF design uses dynamic bootstrap-assisted feedback to suppress direct-path current while maintaining a compact area. All circuits were benchmarked in simulation against prior TFT-based DFFs and evaluated in subsystem-level implementations, including a 3-bit counter, frequency divider, and TFT-based scan-chain structures. The proposed DTFF achieves up to 77% lower power and 69% lower Power-Delay-Product (PDP) than state-of-the-art designs. These results establish the DTFF, STFF-I, and STFF-II designs as compact, energy-efficient sequential building blocks for next-generation flexible and large-area electronics.