Bistable State of Protons for Low-Voltage Memories.

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmental-friendly processing, low acoustic impedance and mechanical flexibility. Their ferroelectric mechanism is mainly ascribed to the order-disorder transition of molecules, such as spherical 1,4-diazabicyclo[2.2.2]octane (DABCO) and quinuclidine. Here, we present two molecular ferroelectrics, [HDABCO][TFSA] and its deuterated one [DDABCO][TFSA] (TFSA = bis(trifluoromethylsulfonyl)ammonium), whose ferroelectricity is triggered by the proton ordering. This is the first time that the protons show a thermally fluctuated bistablity with a double-well potential in DABCO-based ferroelectrics. A large deuterium isotope effect (T = ~53 K) not only proves that they are hydrogen-bonded ferroelectrics, but also extends the ferroelectric working temperature range to room temperature. The super-fast polarization switching of 100 kHz and ultra-low coercive voltage of 1 V (far less than 5 V required for commercially available ferroelectric devices), benefiting from the low energy for proton transfer, allow [DDABCO][TFSA] a great potential for memory devices with low-voltage, high-speed operation. This work should inspire further exploration of hydrogen-bonded molecular ferroelectrics for flexible and wearable devices with the low-power information storage.