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 bistability
with a double-well potential in DABCO-based ferroelectrics. A large
deuterium isotope effect (ΔT = ∼53 K)
not only proves that they are hydrogen-bonded ferroelectrics but also
extends the ferroelectric working temperature range to room temperature.
The superfast polarization switching of 100 kHz and ultralow 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.