Revolutionising smart devices with BFO on silicon
Potential applications for BFO integrated onto silicon include new magnetic memory devices, smart sensors and spintronics technologies
Researchers from North Carolina State University say they have, for the first time, integrated a material called bismuth ferrite (BFO) as a single crystal onto a silicon chip, opening the door to a new generation of multifunctional, smart devices.
The high-resolution TEM micrograph at the top of this article shows BFO grown on a silicon substrate and aligned with an LSMO (lanthanum strontium manganese oxide) electrode.
BFO has both ferromagnetic and ferroelectric properties, meaning that it can be magnetised by running an electric current through the material. Potential applications for BFO include new magnetic memory devices, smart sensors and spintronics technologies.
Integrating the BFO into the silicon substrate as a single crystal makes the BFO more efficient by limiting the amount of electric charge that 'leaks' out of the BFO into the substrate.
The researchers performed heteroepitaxial growth of ferroelectric (FE) - antiferromagnetic BFO on ferromagnetic LSMO, integrated on Si(100) using pulsed laser deposition via the domain matching epitaxy paradigm.
The BFO/LSMO films were epitaxially grown on Si(100) by introducing epitaxial layers of SrTiO3/MgO/TiN. The authors investigated the magnetic behaviour of this five layer heterostructure, in which a d5 system (Fe3+) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn3+/Mn4+ in LSMO.
The temperature- and magnetic field-dependent magnetisation measurements revealed an unexpected enhancement in magnetic moment and improved magnetic hysteresis squareness originating from the BFO/LSMO interface.
"This work means we can now look at developing smart devices that can sense, manipulate and respond to data more quickly because it all happens on one chip - the data doesn't need to be relayed elsewhere," say Jay Narayan and John C. Fan, Distinguished Chair Professor of Materials Science and Engineering at NC State and senior author of a paper describing the work.
The researchers also found that they can switch the polarity of the BFO's magnetic field with as little as four volts, which is comparable to the voltage needed in existing integrated circuits. This is a key to developing functional technologies because higher voltages and fields are impractical and use more energy, which could damage and disrupt electronic functions.
Similarly, the researchers found that a low-strength, external magnetic field - measured at 300 Oersted, a unit of magnetic field strength - can also switch the BFO's polarity. This is significant because external magnetic fields don't generate heat in the BFO, which could be important for some applications.
This work is detailed in the paper, "Interface Magnetism in Epitaxial BiFeO3-La0.7Sr0.3MnO3 Heterostructures Integrated on Si(100)," by S. S. Rao et al published online in Nano Letters. DOI: 10.1021/nl4023435