Volatility Transition from Short-Term to Long-Term Photonic Transistor Memory by Using Smectic Liquid Crystalline Molecules as a Floating Gate

Rod-like molecules with liquid crystalline phase transitions show highly ordered stacking and orientation, which is promising as the floating gate electret in high-performance photonic field-effect transistor (FET) memory. In this work, a series of rod-like molecules, alkyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C_n-DNTT), are investigated with a smectic liquid crystalline phase transition. The photonic FET memory featuring these rod-like molecules is correlated with their morphology and crystallographic properties. A volatility transition from short−term to long−term memory behavior is found by utilizing the smectic liquid crystalline phase transitions (SmX, X = H, K, E) to orient the stacking in the floating gate. Accordingly, the annealed 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) polycrystalline film with the optimized alkyl chain length achieved preferential end-on orientation associated with the herringbone-type stacking to store charges during photowriting, along with effective charge tunneling for the trapped charges during electrical erasing. Therefore, the resultant photonic FET memory provided a superior ON/OFF current ratio of up to 10⁵ with retention of 10⁴ after 10⁴ s. The results demonstrate that rod-like molecules with smectic liquid crystalline phase and highly ordered orientation have great potentials for developing high-performance photonic FET memory.