Abstract
The ferroelectric switching characteristics of a vinylidene fluoride and trifluoroethylene copolymer were significantly changed via the chemical modification of a gold electrode with an alkanethiol self-assembled monolayer (SAM). The alkanethiol SAM-Au electrode successfully suppressed the leakage current (dark current) from the electrode to the bulk ferroelectric. Smaller leakage currents led to the formation of an effective electric field in the bulk ferroelectric. At switching cycles ranging from 10 to 100 kHz, significant changes in the ferroelectric properties were observed. At 100 kHz, a remanent polarization (Pr) of 68 mC·m−2 was measured, whereas a very small Pr value of 2.4 mC·m−2 was measured for the sample without a SAM. The switching speed of the SAM-Au electrode is as twice as fast as that of the unmodified electrode. A large potential barrier was formed via the insertion of a SAM between the Au electrode and the ferroelectric, effectively changing the ferroelectric switching characteristics.
Highlights
Ferroelectric polymers such as poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene (P(VDF/TrFE)) have been extensively investigated because of the spontaneous polarization due to the β-phase crystallite and their ferroelectric switching
The P(VDF-TrFE) MEK solution was spin-coated at 1000 rpm for 30 s onto a 5 mm φ gold electrode evaporated onto a silicon substrate; the resulting sample was subsequently thermally annealed at 140 °C for 2 h under a vacuum
The PEDOT-PEG lauryl nitromethane solution was spin-coated onto the P(VDF-TrFE) thin film at 1000 rpm for 30 s, and a tiny gold electrode was evaporated onto the sample using a 117 μm ×117 μm mesh mask (PEDOT-PEG sample)
Summary
Ferroelectric polymers such as poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene (P(VDF/TrFE)) have been extensively investigated because of the spontaneous polarization due to the β-phase crystallite and their ferroelectric switching. Organic ferroelectric switching of P(VDF-TrFE) has attracted attention in the field of nonvolatile memory devices [1,2,3,4]. We previously measured ferroelectric switching at frequencies between 10 and 100 kHz and reported the ferroelectric properties of P(VDF-TrFE) copolymer thin films [5]. To obtain sufficient remanent polarization at a higher cycling frequency of 100 kHz, we applied a high electric field of MV·m−1 to the P(VDF-TrFE) copolymer [5]. This field is too high to apply in electronic devices.
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