An electrical domain with an area smaller than 1 nm² could offer a clue to fitting more memory onto a chip. Researchers working with Washington University in St. Louis observed domains that small in zirconia, a material chemically similar to an insulator already used in silicon transistors.In a separate study, they identified a way to switch the electrical structure of thin films made from that insulator, known as hafnia.The studies involved Washington University materials scientist Rohan Mishra and collaborators at the University of Nebraska–Lincoln, Georgia Tech and South Korea’s UNIST, among others. The teams combined atomic-scale simulations with electron microscopy and experiments to see how changes in the two materials could help meet growing demand for denser data storage as AI use expands.Turning a chip insulator into a memory candidateHafnia forms a thin insulating layer in silicon transistors. Its appeal for memory lies in a property called ferroelectricity. An electric field can flip the direction of a ferroelectric material’s polarization, and the material holds that orientation after the field is removed. Those two orientations could encode digital information.Most ferroelectric materials lose that behavior when thinned below about 10 nanometers. Earlier work by researchers in Germany showed that hafnia behaves differently. It can become ferroelectric in extremely thin films, even though the bulk material typically lacks that property.To understand what drives the change, Mishra’s team worked with researchers at the University of Nebraska–Lincoln to grow single-crystal films of lanthanum-doped hafnia.Guodong Ren, then a doctoral student in Mishra’s group, used electron microscopy to resolve individual columns of atoms. The crystal structure his team identified matched its computational predictions.Switching hafnia with an electric fieldThe findings suggest engineers could grow hafnia in a stable antiferroelectric structure and then use an electric field to switch it during operation. In an antiferroelectric structure, neighboring polarizations point in opposite directions. The applied field can drive the film into a different electrical state.“Instead of fighting nature, we can grow high-quality antiferroelectric films and we can then switch them during operation,” Mishra said.The same materials could also have a role in energy storage. Mishra said antiferroelectrics can store large amounts of energy, making them candidates for high-energy-density capacitors.Oxygen helps stabilize tiny zirconia domainsIn the zirconia study, researchers found regions smaller than one square nanometer in which electrical polarization pointed in a consistent direction. Extra oxygen atoms helped balance the charge where neighboring regions met.The team’s calculations predicted that these boundaries, known as domain walls, could conduct electricity and move when a voltage was applied. If engineers can control that movement, the walls could eventually serve as components in memory devices.The two studies point to different ways of controlling electrical behavior at the scale of individual atoms. Hafnia offers a route through a switchable crystal structure, while zirconia raises the possibility of using the boundaries themselves. Hafnia’s existing role in silicon transistors gives engineers a familiar material to work with as they explore how to turn those findings into memory. The studies were published in Advanced Materials and Science journals.