De Novo Discovery of [Hdabco]BF4 Molecular Ferroelectric Thin Film for Nonvolatile Low-Voltage Memories.

Abstract

To date, the field of ferroelectric random access memories (FeRAMs) is mainly dominated by inorganic ferroelectric thin films like Pb(Zr,Ti)O3, which suffer from the issues of environmental harmfulness, high processing temperatures, and high fabrication costs. In these respects, molecular ferroelectric thin films are particularly advantageous and thus become promising alternatives to the conventional inorganic ones. For the prospect of FeRAMs applications, they should fulfill the requirements of effective polarization switching and low-voltage, high-speed operation. Despite recent advancements, molecular ferroelectric thin films with such high performance still remain a huge blank. Herein we present the first example of a large-area continuous biaxial molecular ferroelectric thin film that gets very close to the goal of application in FeRAMs: [Hdabco]BF4 (dabco = diazabicyclo[2.2.2]octane). In addition to excellent film performance, it is the coexistence of a low coercive voltage of ∼12 V and ultrafast polarization switching at a significantly high frequency of 20 kHz that affords [Hdabco]BF4 considerable potential for memory devices. Particularly, piezoresponse force microscopy (PFM) clearly demonstrates the four polarization directions and polarization switching at a low voltage down to ∼4.2 V (with an ∼150 nm thick film). This innovative work on high-performance molecular ferroelectric thin films, which can be compatible with wearable devices, will inject new vitality to the low-power information field.