Scientists from the Oak Ridge National Laboratory's Department of Energy recently delved into the intriguing properties of hafnium oxide, also known as hafnia, due to its potential applications in cutting-edge semiconductor technology.
Hafnia and similar materials exhibit a phenomenon called ferroelectricity, making them capable of retaining data even when power is disconnected. This property holds promise for nonvolatile memory technologies, which could revolutionize computer systems by reducing heat generation during data transfers to short-term memory.
The scientists set out to explore whether the surrounding atmosphere influences hafnia's ability to change its internal electric charge arrangement when subjected to an external electric field. Their goal was to shed light on the peculiar behaviors observed in hafnia research. These findings were recently published in Nature Materials under the title “Ferroelectricity in Hafnia Controlled via Surface Electrochemical State.”
Kyle Kelley, a researcher at the Center for Nanophase Materials Sciences (CNMS) at ORNL, conducted the experiments and conceived the project in collaboration with Sergei Kalinin from the University of Tennessee, Knoxville.
Typically, materials used for memory applications have a surface layer that hampers their ability to store information. As materials shrink to nanometer-scale thickness, this surface layer becomes a significant hindrance. By altering the surrounding atmosphere, the scientists could manipulate the behavior of this surface layer, transitioning hafnia from an antiferroelectric to a ferroelectric state.
Kelley emphasized that these findings offer a path for predictive modeling and device engineering of hafnia, crucial for the semiconductor industry. Predictive modeling allows scientists to estimate the properties and behavior of unknown systems based on previous research. While this study focused on hafnia alloyed with zirconia, future research could apply these findings to predict hafnia's behavior when combined with other elements.
The research relied on atomic force microscopy in both glovebox and ambient conditions, as well as ultrahigh-vacuum atomic force microscopy, all available at CNMS. The Materials Characterization Facility at Carnegie Mellon University provided electron microscopy characterization, while collaborators from the University of Virginia led materials development and optimization.
ORNL's Yongtao Liu performed ambient piezoresponse force microscopy measurements.
The theoretical foundation of this research project stemmed from a longstanding collaboration between Kalinin and Anna Morozovska at the Institute of Physics, National Academy of Sciences of Ukraine. Kalinin commended his colleagues in Kiev for their dedication to advancing science even in challenging conditions.
The team hopes their discoveries will inspire further research into the role of controlled surface and interface electrochemistries in computing device performance, offering new insights into how interfaces affect device properties positively. Traditionally, surfaces were kept clean in semiconductor technology, while surface science explored atomic-level phenomena. This research illustrates the connection between surface properties and electrochemistry, demonstrating how surface manipulation can influence bulk material properties.
Source: Oak Ridge National Laboratory