Ferroelectrics comprise an important group of
materials, which are characterized by a permanent electric polarization. This
polarization can be switched which provides a possibility of using
ferroelectrics in data storage and memory devices. Typically, polarization is
switched by the application of the external electric field. Nebraska MRSEC researchers
have shown that polarization can be switched by purely mechanical means: simply
by pushing the tip of a scanning probe microscope against the ferroelectric
surface [Science 6, 59 (2012)]. The tip-induced pressure causes a stress gradient in ferroelectric film, which affects the electrical polarization as an electric field. This is the first
experimental observation of the mechanically induced reversal of ferroelectric
polarization.
This discovery opens a
new direction in low-energy nanoelectronics through a drastic reduction of
energy consumed during programming steps in data storage. Furthermore, it opens
the door for multiferroic memories with mechanical writing and electrical
reading of data. Just as important is the fact that demonstration of the
voltage-free control of polarization removes the problems associated with the
application of large electric fields to ferroelectric films: there is no charge
injection, no dielectric breakdown and no leakage current. Finally, due to
highly-localized tip pressure the domain size can be as small as several
nanometers thus allowing extremely high-density (~Tb/in2) data
storage.
Domain writing process in a ferroelectric
film by tip-induced mechanical pressure (left) and a resulting domain pattern
visualized by piezoresponse force microscopy (right). Domain size is
approximately 20x30 nm2.
