Resistive switching and nanoscale chemical mapping of phase separation in PVDF/PMMA/F8T2 ternary thin films

Abstract

In recent years organic ferroelectric/semiconducting blend film has attracted much attention due to its integration of both resistive switching and electrical rectifying properties. In all reported blend structures, P(VDF-TrFE), the copolymer of vinylidene fluoride and trifluoroethylene, is used as the ferroelectric phase, which is blended with organic semiconductors to form phase-separated structure. As another representative ferroelectric polymer, poly(vinylidene fluoride) (PVDF) has its own advantages of even larger polarization and low cost. However, PVDF has much complicated crystalline phases in which its non-polar α phase is the most thermally stable. Effective phase transformation from the α to the ferroelectric phases is still an open question especially for PVDF thin films. Till now seldom work has been reported on PVDF-based ferroelectric/semiconducting resistive films. Here we reported the fabrication and structural and electrical characterizations of PVDF-based ferroelectric/semiconducting ternary resistive films. Poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) was used as semiconducting phase which was phase separated with PVDF phase in PVDF/F8T2 blends. Poly(methyl metacrylate) (PMMA) was introduced into PVDF to promote its ferroelectric γ and β phases. This PVDF/PMMA/F8T2 ternary film showed good resistive switching performance with ON/OFF ratio up to 103, which was comparable to and even larger than those values obtained from blends with P(VDF-TrFE) as the ferroelectric phase. However, the introduction of PMMA also complicateed the basic understanding on phase separation and thus resistive switching mechanism in this ternary film. To clarify this, nanoscale chemical mapping was conducted to distinguish the local distributions of all three phases, the results of which showed obvious nanoscale phase separation in this ternary blend film.