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

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 degrees C showed consecutive TTTT trans conformation with beta type crystals while films molten and re-crystallized from a temperature above their melting points exhibited alpha type crystals with characteristic TGTG conformation. Microstructures of the films treated with the two different thermal histories also supported the formation of beta and alpha type crystals with hundreds of nanometer scale sphere caps and micron level spherulites, respectively. Interestingly, PVDF-CTFE films with both alpha and beta type crystals gave rise to relatively high remnant polarization of approximately 4 mu C/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. (C) 2011 Elsevier B. V. All rights reserved.