Low-cost plastic memories from a ‘forgotten’ commodity polymer
March 18, 2013
Scientists from the Zernike Institute for Advanced Materials of the University of Groningen and the German Max Planck Institute for Polymer Research have discovered a way to make a plastic memory from a commodity polymer. They have published their discovery in the journal Nature Materials.
Mainz/Groningen. The polymer they used is PVDF – polyvinylidene fluoride. This low-cost material is often used for membrane filters and packaging foils. It is well-known that PVDF is thermally and chemically extremely stable, but for application in a memory cell ferroelectric properties are essential. In other words, the material must exhibit an electric polarization, comparable to the north and south poles of a magnet. The polarization of ferroelectric materials can be switched by application of an electric field. The bistable polarization state can be used to store information.
Making a functional electric switch from neat PVDF is notoriously difficult. “There are two reasons for this”, says professor of physics Dago de Leeuw, one of the authors of the Nature Materials article. “First, it was very challenging to make a smooth, thin film from PVDF.” Comprising films were rough, resembling microscopic sand paper. “In addition, conventional processing yields non-ferroelectric thin films because the PVDF crystallises in a non-polar phase.”
University of Groningen PhD student Mengyuan Li was able to resolve these problems. She used an alternative way to make thin films from PVDF. “Controlling the processing conditions turned out to be the crucial step” says Li. “Usually you make this type of film at room temperature. PVDF, however, turns into a lovely smooth thin film at high temperatures”, explains De Leeuw. As a bonus, the films became ferroelectric after applying a short electrical pulse.