Domain stabilization effect of interlayer on ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer ultrathin film

Abstract

A charge injection material, poly(3,4-ethylene dioxythioohene)-poly(styrene sulfonic) acid, is introduced as a buffer layer between metal electrodes and a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer ultrathin film. The buffer layer not only prevents the reactions between P(VDF-TrFE) layer and the top electrode during metallization process, which leads to the loss of polarization, but also supplies the amount of charges needed for compensation of the ferroelectric dipoles to stabilize the domain during switching process so that the fatigue property was improved tremendously. The sandwiched structure shows prominent ferroelectric properties in a 50 nm P(VDF/TrFE) film. A coercive electric field of 52 MV/m and a remnant polarization of 88 mC/m2 are recorded. With two additional organic interlayers, 33 nm thick in total, the coercive field decreases. After more than 1×107 cycles of switching, the polarization remains as high as 68 mC/m2. Moreover, the cell still has good ferroelectric properties at 60 °C. Even as the thickness of P(VDF/TrFE) film is down to 25 nm, a remnant polarization of 54 mC/m2 is obtained.

Ferroelectric Properties and Polarization Switching Kinetic of Poly (vinylidene fluoride-trifluoroethylene) Copolymer

“…Improved device performance with higher P r and faster switching speeds were achieved. A P r of more than 70% of its initial value can be achieved after 1×10 7 cycles of switching for 50 nm thick P(VDF-TrFE) film devices, as shown in Figure 20 [Xu et al, 2007[Xu et al, , 2009. Xu et al also found that the conducting polymer buffer layers improve the degree of crystallinity of the thin films [Xu et al, 2009].…”

“…Therefore, it allows the copolymer to crystallize into the ferroelectric phase at temperatures below the melting point. The copolymer crystal structure, phase transition behavior and ferroelectric properties are affected by the ratio of VDF/TrFE content and the synthesizing conditions [Yamada & Kitayama, 1981]. The experimental data from UT Dallas shown in this chapter are for P(VDF-TrFE) copolymer with 70/30 (VDF/TrFE), synthesized using a suspension polymerization process.…”

“…For organic electronic systems, the physical and chemical processes on the interface need to be considered when metal is deposited on the organic materials. Reactive metals such as Ti, Ni and Al can react with the organic materials and form an interfacial layer, which can degrade the electrical properties [Xu et al, 2009]. For P(VDF-TrFE) copolymer, Ti and Ni can react with the fluorine atom in the -CF 2 -components and create TiF x and NiF x at the interface, respectively [Xu et al, 2009;Chen & Mukhopadhyay, M., 1995].…”

“…Reactive metals such as Ti, Ni and Al can react with the organic materials and form an interfacial layer, which can degrade the electrical properties [Xu et al, 2009]. For P(VDF-TrFE) copolymer, Ti and Ni can react with the fluorine atom in the -CF 2 -components and create TiF x and NiF x at the interface, respectively [Xu et al, 2009;Chen & Mukhopadhyay, M., 1995]. For chemically inert metals, such as Au, less chemical reaction occurs between the metal atom and P(VDF-TrFE).…”

“…The first one is the melt and press method [Yamada & Kitayama, 1981]. The copolymer crystallizes into or phases when it is slowly cooled to room temperature from the melt.…”