The preparation and ferroelectric properties of defect-free ultrathin films of vinylidene fluoride oligomer

The ultrathin, defect-free ferroelectric films of vinylidene fluoride oligomer were fabricated by vapor deposition. A narrow substrate temperature window was found to get high quality ferroelectric films. Ferroelectric phase was obtained when the substrate temperature was -90 degrees C. The ferroelectric phase is stable at room temperature, even after annealing at 120 degrees C for 30 min. A full memory stack based on the ferroelectric VDF oligomer may work as nonvolatile random access memory with superhigh density due to the smaller crystal grain comparing with that of poly(vinylidene fluoride-trifluoethylene) [P(VDF-TrFE)] copolymers. The cell shows prominent ferroelectric properties even as the thickness of VDF oligomer film is down to 60 nm with a coercive field of 95 MV/m and a remnant polarization of 125 mC/m(2). After 1x10(5) cycles of switching, no ferroelectric degradation was observed, the ratio of polarization before and after fatigue is close to 1, which is in contrast to P(VDF-TrFE) thin film where the ferroelectric degradation starts after 1x10(4) times of switching. The pulse polarization test shows that switching takes place as fast as a few microseconds to reach 90% of the saturated polarization. At 60 degrees C and 8 V operating voltage, the cell still shows excellent fatigue property.