Effective fixation of polar orientation in P(VDF-TrFE) thin films via carbon-coated method

• Breakthrough in Stabilizing Edge-on Molecular Alignment via Carbon Interface Engineering: This study pioneers a vacuum-evaporated carbon layer strategy to permanently fix edge-on molecular chain orientation in P(VDF-TrFE) ultrathin films, retaining aligned lamellae at 200 °C (surpassing conventional 150 °C thermal limits). This resolves dipole-electric field mismatches in high-temperature processing, enabling scalable low-voltage flexible microelectronics without epitaxial crystallization or mechanical shearing. • Mechanistic Elucidation of Edge-on Orientation Fixation: First experimental evidence of carbon-induced chemical bonding (via C C bonds) and physical interactions that anchor molecular chains parallel to substrates, as rigorously validated by in situ FTIR analyses. The established correlation between carbon layer thickness/thermal history and orientation stability provides a quantitative framework for tailoring ferroelectric performance. This mechanistic understanding advances fundamental knowledge of interface-directed polymer crystallization, enabling precise control over dipole alignment for enhanced piezoelectric coefficients. • Extended Processing Window for Device Integration: Demonstrated expansion of the thermal processing range (> 150 °C) for oriented P(VDF-TrFE) ultrathin films without compromising phase transition behavior – a critical advancement unachievable through prior methods. This temperature resilience allows compatibility with industrial semiconductor fabrication processes, addressing a key barrier to integrating ferroelectric polymers into next-generation flexible MEMS, non-volatile memories, and energy-efficient microsystems requiring sub-100 nm film architectures. Ultrathin ferroelectric P(VDF-TrFE) films are vital for next-generation non-volatile memory devices, yet their performance degrades as treatment temperatures above 150 °C due to the formation flat-on lamellae, which causes dipole-electric field misalignment. Here, we have successfully fixed the edge-on orientation at high temperatures via vacuum-evaporating thin carbon layers on the surface of P(VDF-TrFE) films. This edge-on orientation is correlated with the formation of new carbon-carbon bonds and physical diffusion bonding between the thin P(VDF-TrFE) film and the carbon layer, which fixes molecular chains parallel to the carbon layer and serves as nuclei, effectively inducing polymer melt-regrowth into edge-on lamellae. Furthermore, by controlling the erasing temperature and carbon layer thickness, the fixing effect of the carbon layer can be modulated. Notably, the carbon coating remains effective even for relatively thick P(VDF-TrFE) films and does not alter the Curie transition behavior. Furthermore, we present ferroelectric polarization data that demonstrate the carbon-coated films retain high remanent polarization, significantly improving low-field polarization compared to uncoated films after melt-recrystallization at 200 °C. This provides an efficient approach to extending the processing temperature range of P(VDF-TrFE) ultrathin films, thereby advancing their integration into high-temperature flexible electronics. Vacuum-evaporated carbon layer stabilizes the edge-on molecular chain orientation in P(VDF-TrFE), ensuring dipole alignment remains matched to the electric field direction even after high-temperature processing.