Abstract
Compared with ferroelectric oxides, organic ferroelectric materials are lightweight, flexible and easy to process. They are ideal for applications in the next-generation portable electronics. Here, we demonstrate the room-temperature growth of imidazolium perchlorate (C3N2H5ClO4) ferroelectric films on various substrates, including Pt-coated Si, quartz and, more importantly, on flexible and transparent polyethylene terephthalate (PET). The films have a preferred (0 −1 −1) or (1 0 −1) orientation. The former shows a piezoelectric response comparable with the response of the Pb(Zr0.2Ti0.8)O3 film. This is attributed to the smaller elastic constant of the film, which makes it less susceptible to substrate clamping. When grown on PET, the film is transparent and can be bent to radii of a few millimetres without affecting its ferroelectric properties. Our discovery may significantly promote the application of molecular ferroelectrics in flexible and transparent electronics. Flexible organic ferroelectric films exhibiting a high piezoelectric response have been fabricated by researchers in China and Singapore. Organic ferroelectric materials possess many advantages over ferroelectric oxides, including being lightweight, flexible and easy to process as well as usually being transparent. These properties make them ideal for use in flexible and portable electronic devices, but this requires growing thin films of them on substrates. Now, Guoliang Yuan and co-workers have achieved room-temperature growth of high-quality thin films of the ferroelectric imidazolium perchlorate (C3N2H5ClO4) on various substrates. Importantly, they succeeded in growing thin films on polyethylene terephthalate (PET) substrates and show that the system can be bent to radii of a few millimetres without affecting its ferroelectric properties. This demonstration raises the possibility of using molecular ferroelectrics in flexible and transparent electronics. The transparent C3N2H5ClO4 ferroelectric film on ITO coated PET substrate can be bent to 3.1 mm radius without affecting its ferroelectric properties. Furthermore, its local piezoelectric response is comparable to that of Pb(Zr0.2Ti0.8)O3 film.
Highlights
Ferroelectric materials possess spontaneous polarizations that usually originate from the collective displacement of ions in the crystals
Applying an electric field leads to polarization reversal that is coupled with a strain response known as the piezoelectric effect
We demonstrate millimeter-scale dendritic film growth from a single nucleus on the ITO/polyethylene terephthalate (PET) (Figure 1b), quartz and Pt-coated Si (Pt/Si) substrates (Supplementary Figure S1)
Summary
Ferroelectric materials possess spontaneous polarizations that usually originate from the collective displacement of ions in the crystals. Ferroelectricity was originally discovered in Rochelle salts[4] and later in several other molecular systems.[5] the rapid development of the field took place only after the discovery of ferroelectricity in perovskite oxides, for example, BaTiO3 and Pb(Zr,Ti)O3.6,7 these oxide ferroelectrics are more attractive for applications because of their larger polarization and piezoelectric coefficients, they usually contain heavy metals and, are not environmental friendly. They require a high processing temperature, making them incompatible with current microelectronic systems. During the past several years, molecular ferroelectrics have attained significant advancements, and their properties are comparable with those of BaTiO3.9–12 For example, the trigonal imidazolium perchlorate (C3N2H5ClO4) crystal has a polarization of ~ 8 μC cm − 2 at room temperature, a high Tc of 100 °C and a low coercive field.[12,13]
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