Ferroelectric Lithography

The ability to selective manipulate a surface, either at the micron scale or nano scale, is the at the heart of every lithography technique. Lithography techniques very greatly from top-down lithography techniques, such as standard optical lithography at the micron-scale to dip-pen lithography at the nano-scale, which allow for complex patterning to bottom-up lithography techniques, such as a self assembled monolayer, which allow for long range order but not always complex patterning. There is also the possibility of a hybrid technique that combines top-down and bottom-up techniques to allow for the advantages of both methods.

Our group has developed a lithography technique that has the ability to create features down to 20nm and the ability to deposit various materials to influence the eventual device characteristics. The properties of ferroelectrics and the ability to manipulate these properties is the main driving force of this lithography technique. Ferroelectric films contain electric dipoles that are intrinsic to the atomic structure of the compound. For example in a cubic perovskite, the displacement of the body center cation in the unit cell produces a dipole in the structure. Dipole-dipole interaction between cells cause polarization alignment resulting in ferroelectric domains. Polarization discontinuities in the vicinity of surfaces and interfaces result in polarization bound charge that significantly affects materials properties.

Below are a few examples of our ability to manipulate the ferrelectric surface of a PZT thin film. The patterns can be as simple as boxes or stars to parallel line to very complex patterns, such as the portrait of the Vice Provost of Penn. These patterns were created by scanning over the surface with an AFM tip and alternating the voltage between +10V and -10V to selective reorient the domains in the pattern that is desired. Our group has also shown that ferroelectric domains can be reoriented by selectively exposing the surface to the electron beam of a SEM. In this method the domain orientation is controlled by the imaging current of the beam.