Thin ferroelectric poly(vinylidene fluoride-chlorotrifluoro ethylene) films for thermal history independent non-volatile polymer memory

摘要

In this study, we investigated the molecular and microstructures of thin poly(vinylidene fluoride-chlorotrifluoro ethylene) (PVDF-CTFE) copolymer films with three different CTFE compositions of 10, 15, 20 wt% with respect to PVDF in relation with their ferroelectric properties. All PVDF-CTFE annealed at 130 ℃ showed consecutive TT7T trans conformation with p type crystals while films molten and re-crystallized from a temperature above their melting points exhibited a type crystals with characteristic TGTG conformation. Micro-structures of the films treated with the two different thermal histories also supported the formation of β and α type crystals with hundreds of nanometer scale sphere caps and micron level spherulites, respectively. Interestingly, PVDF-CTFE films with both α and p type crystals gave rise to relatively high remnant polarization of approximately 4 μC/cm~2 in metal/ferroelectric/metal capacitors regardless of the composition of CTFE. The ferroelectric polarization of a PVDF-CTFE film independent of thermal processing history allowed a wide processing window and easy fabrication protocol, resulting in a nonvolatile ferroelectric field effect transistor memory which exhibited saturated hysteresis loops with the current ON/OFF ratio of approximately 10~3 at ±60 V sweep and reliable data retention.