Jan 15 2015
North Carolina State University researchers have made significant advancements with regards to multiferroic materials including the ability of integrating them onto a silicon chip, paving the way for the manufacture of new electronic memory devices. Prototypes of the devices have already been created, and are being subjected to testing procedures.
Multiferroic materials, in general, have both ferromagnetic and ferroelectric characteristics. “These multiferroic materials offer the possibility of switching a material’s magnetism with an electric field, or switching its electric polarity with a magnetic field – making them very attractive for use in next-generation, low-power, nonvolatile memory storage devices,” said Dr. Jay Narayan, senior author of the study and John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State.
Using bilayer thin films for creating multiferroic material was a known concept. Researchers previously use ferroelectric barium titanate (BTO) and ferromagnetic lanthanum strontium magnese oxide (LSMO) as bilayer materials. However, these thin films are unsuitable for large-scale applications owing to their inability to integrate onto a silicon chip. This is due to the fact that the constiutents of the thin films tend to dissolve in silicon.
By contrast, the research team has developed two different ways of improving the multiferroic material properties. One is by developing a method that enhances the ferromagnetic properties of BTO to make it multiferroic without using LSMO, while the other is producing buffer layers for integrating the multiferroic BTO/LSMO bilayer film or the multiferroic BTO on to the silicon chip. The team used a high-power nanosecond pulse laser for inducing oxygen vacancy-related defects in the BTO material, making it multiferroic. These defects are responsible for the development of ferromagnetic properties in the BTO.
The buffer layers produced use magnesium oxide (MgO) and titanium nitride (TiN). The TiN is produced as a single crystal over the silicon substrate, while the MgO is laid on the TiN as a single crystal. Following this, the BTO, or BTO/LSMO bilayer film is deposited on the MgO. The buffer layers thus formed ensures efficient function of the multiferroic material without affecting the silicon transistors and dissolving into the silicon.
“We’ve already fabricated prototype memory devices using these integrated, multiferroic materials, and are testing them now.” Then we will begin looking for industry partners to make the transition to manufacturing, ” Narayan said.
The work is described in the Journal of Applied Physics as two different papers, and it was supported by the U.S. Army Research Office under grant number W911NF-04-D-0003. Lead author on both papers was Dr. Srinivasa Singamaneni, a postdoctoral researcher at NC State, and co-authors include Dr. John Prater, of the U.S. Army Research Office and NC State, Dr. Wu Fan, a former NC State Ph.D. student who is now a postdoctoral researcher at Princeton, Dr. Frank Hunte, an assistant professor of materials science and engineering at NC State and Sandhyarani Punugupati, a Ph.D. student at NC State.