Study of rewritable thin-film memories using ferroelectric polymers

1. 采用旋涂技术制备了铁电VDF/TrFE（偏氟乙烯/三氟乙烯）共聚物超薄膜。我们的目标是形成亚微米薄膜，其极化可以由低于约10v的电压控制。通过多次试验，确定了最佳的溶剂、溶液密度和旋转速率条件。得到了厚度为220 nm的具有铁电D-E迟滞特性的薄膜。这种薄膜可用作集成电路中的存储器。然而，为了制造真正的存储器，需要更高质量的薄膜，包括更高有序的晶体，因为在上述亚微米薄膜中观察到的极化反转开关过程与在厚度大于1μm.2的薄膜中观察到的过程相比并不那么清晰。记忆有三个基本动作：写、读和初始化。在读取方面，我们研究了样品薄膜的光透过率变化是否可以用于存储器的开关过程，以便将其用作光学电路的存储器。我们以VDF/TrFE共聚物和向列相液晶5CB组成的PDLC（聚合物分散液晶）为样品。对PDLC施加外加电场，实现了P（VDF/TrFE）的极化取向。铁电极化产生的内部电场影响了液晶5CB的分子取向，改变了PDLC的透光率。这一结果表明，光透过率的变化可以用于PDLC存储器的读取机制。这些结果表明，利用聚合物的铁电特性可以获得有机薄膜存储器。

1. Ultra thin films of ferroelectric VDF/TrFE(vinylidene fluoride/ trifluoroethylene) copolymers were produced by use of spin-coating technique. We took aim at forming of submicron films whose polarization can be controlled by voltages less than about 10 V. The best condition for solvent, solution density and rate of rotation of spin coater was chosen by many tests. As the result, a thin film of 220 nm in thickness which exhibits a ferroelectric D-E hysteresis was obtained. This film can be used as a memory in an integral circuit. However, films of higher quality including higher ordered crystals are required to make a real memory, because the polarization reversal switching process observed in the submicron films described above is not so clear in comparison with those observed in films with the thickness more than 1μm.2. Memories have three elementary actions of writing, reading and initializing. About reading, we studied whether the change in the optical transmittance of the sample films can be used for the switching process of memories or not, in order to use them as the memory for optical circuit. We took up PDLC (polymer dispersed liquid crystal) composed of VDF/TrFE copolymer and nematic liquid crystal 5CB as a sample. The polarization of P(VDF/TrFE) was oriented by applying an external electric field to PDLC. The internal electric field originating from the ferroelectric polarization affected molecular orientation of the liquid crystal 5CB and changed the optical transmittance of PDLC. This result suggests that the changes in the optical transmittance can be used for the reading mechanism of the PDLC memory.From these results we conclude that the organic thin-film memory can be obtained using the ferroelectric properties of polymers.