Washington: Researchers led by an Indian-origin scientist have successfully integrated multiferroic materials on a silicon chip, an advance that paves the way for new electronic memory devices.
"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, John C Fan Distinguished Chair Professor of Materials Science and Engineering at North Carolina State University.
Multiferroic materials have both ferroelectric and ferromagnetic properties.
Ferroelectricity is a property of certain materials by which they possess a spontaneous electric polarisation that can be reversed by the application of an external electric field.
Ferromagnetism is a physical phenomenon in which certain electrically uncharged materials strongly attract others.
Researchers had previously known that a multiferroic material can be created by layering barium titanate (BTO), which is ferroelectric, and lanthanum strontium magnese oxide (LSMO), which is ferromagnetic.
But these "bilayer" thin films were not feasible for large-scale use because they could not be integrated on a silicon chip - the constituent elements of the thin films would diffuse into the silicon.
Narayan and his team advanced the work in two ways.
They developed a technique to give BTO ferromagnetic properties, making it multiferroic without the need for LSMO.
They also developed buffer layers that can be used to integrate either the multiferroic BTO or the multiferroic BTO/LSMO bilayer film onto a silicon chip.
To make BTO multiferroic, the researchers used a high-power nanosecond pulse laser to create oxygen vacancy-related defects into the material. These defects create ferromagnetic properties in the BTO.
The buffer layers are titanium nitride (TiN) and magnesium oxide (MgO). The TiN is grown as a single crystal on the silicon substrate. The MgO is then grown as a single crystal on the TiN.
The BTO, or BTO/LSMO bilayer film, is then deposited on the MgO. The resulting buffer layers allow the multiferroic material to function efficiently without diffusing into the silicon and destroying silicon transistors.
"We've already fabricated prototype memory devices using these integrated, multiferroic materials, and are testing them now," said Narayan.
"Then we will begin looking for industry partners to make the transition to manufacturing," he said.
