**1. Introduction**

Poly(vinylidene fluoride) (PVDF) exists five crystalline structures, α, ε, β, δ, and γ phases. Both α and ε phases are nonpolarized. The polar β, δ, and γ phases are very interesting in

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

various applications [1, 2]. In particular, the β-phase PVDF (expressed in TTTT conformation) is mostly desired for ferroelectric memories in the data storage fields. The dipole moments in the molecule stem from the strongly electronegative fluorine atoms predominantly, inducing the ferroelectricity of β-phase PVDF [3, 4].

used as polar solvents to dissolve PVDF [10, 12, 23]. The micrographs were obtained using the JEOL JSM-IT100 of thin films SEM were under different relative humidity by spin coating

Preparation and Device Applications of Ferroelectric β-PVDF Films

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The percentage of β-phase PVDF (β%) in films fabricated by spin coating method is mainly studied by Fourier transform infrared (FTIR) (BRUKER) spectroscopy and X-ray diffraction (XRD) (RIGAKU) techniques. It is found that the processing conditions such as solution concentration, spin rotation speed (rpm) and annealing temperature obviously affect the percentage of β-phase PVDF [26]. The value of β% was calculated and the different percentages for the corresponding films at different annealing temperatures were plotted

Meanwhile, Cardoso et al. successfully prepare thin PVDF films with high β-phase content by thermally annealing at 70°C [27]. A 160 nm thick PVDF film mainly consists of the ferroelectric β phase was prepared by rapid thermal annealing and humidity controlled spin coating method [10]. Ramasundaram et al. reported the fabrication of PVDF films dominantly with β

**Figure 1.** Scanning electron microscopy (SEM) micrographs of PVDF films prepared by spin coating with the relative humidity at (a) 20%, (b) 40%, (c) 60%, and (d) 80% [25]. This research was conducted at Center of High Technology

were evaluated, as shown in **Figure 1** [25].

phase using a heat-controlled setup of spin coating [9].

in **Figure 2**.

Materials New Mexico in 2017.

A number of methods have been proposed to prepare the PVDF films with the thickness up to several microns such as electric poling, hygroscopic salts, mechanical stretching, epitaxy with KBr, and solvent evaporation [5–7]. In contrast, the spin coating and Langmuir–Blodgett deposition techniques are two main methods to obtain the ferroelectric β-phase PVDF films with the thickness down to 300 nm or more less [8, 9]. Furthermore, spin coating can be used to fabricate the large area uniform films from the industrial point of view [10]. Langmuir– Blodgett (LB) deposition technique can prepare the ultra-thin PVDF films with the thickness of several nanometers [11]. In this chapter, we firstly report the main results about the fabrications of β-phase PVDF films by spin coating method and Langmuir–Blodgett deposition techniques. Then, the typical applications of β-phase PVDF films in several organic devices are introduced.
