Program Highlights

Mechanical Writing of Polarization

Haidong Lu and Alexei Gruverman
Nebraska MRSEC

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.

These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0820521.

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.