| 학회 | 한국고분자학회 |
| 학술대회 | 2005년 가을 (10/13 ~ 10/14, 제주 ICC) |
| 권호 | 30권 2호 |
| 발표분야 | 기능성 고분자 |
| 제목 | Investigation of Switchability of Ferroelectric P(VDF/TrFE)(72/28) Thin Film as Nonvolatile Ferroelectric Polymer Random Access Memory |
| 초록 | The copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with VDF content 50 to 85 mole %, have recently attracted a great deal of attention in their applications to nonvolatile ferroelectric polymeric random access memory (NvFePoRAM) devices[1-2]. Memory function with non-destructive readout capability is performed by electrically switching between the ‘0’ and ‘1’ states in a ferroelectric capacitor device structure with much larger remnant polarization, which is mainly dependent on the degree of crystallinity, which in turn is dependent on film thickness[3]. Our objective is to fabricate P(VDF/TrFE)(72/28) copolymers based NvFePoRAM for flash memory applications in which the polymeric film thickness should be ＜100nm in order to operate them below 10V to achieve 1MV/cm for the switching of electrical dipoles[4]. The main disadvantage in ultrathin films is that with reduced film thickness ＜100nm, the crystallization process is strongly hindered, resulting in a low degree of crystallinity. This in turn, leads to reduction in ferroelectric polarization and increase in dipole switching time[3]. Hence, in the first step towards understanding ferroelectric switching characteristics of VDF/TrFE(72/28) ultrathin films(＜100 nm), an attempt has been made to study the effect of applied electric field at varying temperature, bias voltage and frequencies using capacitance and polarization measurements. Different thickness films (100 and 250 nm) of P(VDF/TrFE)(72/28) copolymer were prepared by spin casting its methylethylketone(MEK) solution with a spinner over patterned ITO glass (used as bottom electrode) and aluminum electrodes of 2x3 mm2 size vacuum deposited on the top surface of the P(VDF/TrFE) films served as the top electrode. Bistable C-E hysteresis curves were observed for P(VDF/TrFE)(72/28) thick film (250 nm) with increasing cycles of the bias electric field and the paraelectric-to-ferroelectric phase change is irreversible even when the electric field is removed(Figure 1(a)). C-E measurements were also used to study the effect of temperature during heating-cooling upon bias electric field and the observed field-induced phase transition results are also reported in this study. Polarization vs. bias electric field measured at different frequencies exhibited bistable P-E hysteresis curves shown in Figure 1(b) and the results are also reported here. Figure 1. (a) Bistability showing –Ec and +Ec in P(VDF/TrFE)(72/28) 250 nm thick film, and (b) bistable P-E hysteresis curves at different frequencies upon bias electric field observed for P(VDF/TrFE)(72/28) 250 nm thick film at 30oC. References (1) A.J. Lovinger, Science, 220, 1115 (1983). (2) K. Omote, H. Ohigashi and K. Koga, J. Appl. Phys., 81, 2760 (1997). (3) Q.M. Zhang, H. Xu, F. Fang, Z.Y. Cheng and F. Xia, J. Appl. Phys., 89, 2613 (2001). (4) F. Xia, H. Xu, F. Fang, B. Razavi, Z.Y. Cheng, Y. Lu, B. Xu and Q. M. Zhang, Appl. Phys. Lett., 78, 1122 (2001). This study was supported by "The National Research Program for the 0.1 Terabit Non-Volatile Memory Development Sponsored by Korea Ministry of Science & Technology" |
| 저자 | A. Anand Prabu1, 이종순1, 장유민1, 김갑진1, 이한섭2 |
| 소속 | 1경희대, 2인하대 |
| 키워드 | P(VDF/TrFE)(72/28); Ferroelectric; Switchability; Bistability; RAM; field-induced phase transition |
