Development of Nonvolatile Memory using Well-Ordered Ferroelectric Linear Molecules
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Development of Nonvolatile Memory using Well-Ordered Ferroelectric Linear Molecules Kenji Ishida1, Kazunari Katsumoto1, Shuichiro Kuwajima2, Toshihisa Horiuchi1, Hirofumi Yamada1, Kazumi Matsushige1 1
Department of Electronic Science and Engineering, Graduate School of Engineering,
Kyoto University, Kyotodaigaku Katsura, Nishikyo-ku, Kyoto 616-8510, Japan 2
Nanotech Support Project, Kyoto University, Kyotodaigaku Katsura, Nishikyo-ku, Kyoto
616-8510, Japan. ABSTRACT Ferroelectric vinylidene fluoride (VDF) molecular films were fabricated by simple vacuum evaporation method, and the ferroelectric properties and its fatigue were investigated. Formation of ferroelectric phase in VDF oligomer with low molecular weight is favored at low substrate temperature around -150˚C. The well-ordered VDF oligomer thin films exhibit a lager value of remanent polarization(130mC/m2) than that of Poly(VDF). Fatigues of polarization reversal can be performed over 10^5 cycles. The VDF oligomer films can be one of candidates for disposable nonvolatile memory with unique features such as flexible, wide areas and low cost processing. INTRODUCTION Novel materials, in both inorganic and organic fields, have been searched for realizing nonvolatile memory device. In particular, electronic devices based on organic materials has been now widely investigated to open new way to developing industrial device with unique characteristics such as flexibility, lightweight and low-cost processing. Poly(vinylidene fluoride)(PVDF) and its copolymer with trifluoroethylene [P(VDF-TrFE)] are well known to be ferroelectic polymer with large electric dipole moment, which is generated between fluorine and hydrogen atoms in the individual vinylidene fluoride (CH2CF2;VDF) units1, 2)
. These polymers have several crystal phases with different lattice constant, molecular packing
and conformation3-6). PVDF in the crystal phase of Form I has large spontaneous polarizations, because the electric dipoles are arranged to specific directions in unit cell. For realizing ferroelectric applications in PVDF it is necessary to control their crystal structures. However, it is hard to fabricate well-ordered polymer films with a smoothly surface, nanometer-thickness
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because polymers naturally have mixed structures of both crystalline and amorphous domain. The existence of the amorphous domain may be responsible for the decrease the ferroelectric performance. Therefore, new organic materials with high crystallinity are desired to develop the nonvolatile molecular memory. Newly synthesized ferroelectric VDF oligomers with low molecular weight have the possibility to fabricate high crystalline thin films and controlling their crystal phase. We attempt to fabricate the well-ordered ferroelectric oligomer with large dipoles, and characterize their structural and ferroelectric properties. 2. EXPEREMENTAL DETAILS
C
The VDF oligomer [CF3-(CH2CF2)n-I,
δ+ I
(n=10-29)] was newly synthesized by the telomerization method at Daikin Kogyo Co., Ltd.
H F
δ−
Fig.1. Sch
