Moore Foundation grantees at Berkeley Lab have broadened the horizons for ferroelectrics, a class of materials used in electronic components in cell phones, and as radio-frequency tags in passports and transit cards.
Ferroelectric materials exhibit a spontaneous electric polarization that can be reversed using an applied electric field. In typical ferroelectrics, there is an optimal temperature at which this polarization occurs. By creating a polarization gradient in a thin film of ferroelectric material, the Berkeley Lab team expanded the temperature range in which ferroelectric behavior is present.
The Berkeley Lab team’s discovery, reported recently in Nature Communications, could also lead to devices capable of supporting wireless communications in extreme environments, from inside nuclear reactors to Earth’s polar regions.
In this study, the researchers created and studied a thin film of barium strontium titanium oxide, a widely-used ferroelectric material. In this — and most — ferroelectric materials, gradients are difficult to generate because they require a lot of energy. However, because of the thinness of the film engineered by the Berkeley Lab team — 150 nanometers, not much wider than a human hair — a polarization gradient was built into the film using naturally occurring defects based on strain and chemical imbalances.
By identifying "knobs" to adjust these imbalances, the team showed how compressive strain can be used to enhance polarization in the film. In addition, recent advances in electron microscopy were used to obtain atomic-scale structural data of the film, and to directly measure the strain and polarization gradient. Both theory and prior experimental experience were used to guide synthesis efforts, based on accumulated knowledge on how various changes in the overall crystal structure of a film changes the competition between forces.
“The new polarization profile we have created gives rise to a nearly temperature-insensitive dielectric response, which is not common in ferroelectric materials,” said study principal investigator Lane Martin, a faculty scientist at Berkeley Lab and associate professor of materials and engineering at UC Berkeley. “By making a gradient in the polarization, the ferroelectric simultaneously operates like a range or continuum of materials, giving us high-performance results across a 500-degree Celsius window. In comparison, standard, off-the-shelf materials today would give the same responses across a much smaller 50-degree Celsius window.”
Martin, a grantee through the foundation’s Emergent Phenomena in Quantum Systems initiative, says this wider temperature range could shrink the number of components needed in electronic devices and potentially reduce the power draw of wireless phones.
“The smartphone I’m holding in my hand right now has dielectric resonators, phase shifters, oscillators — more than 200 elements altogether — based on similar materials to what we studied in this paper. About 45 of those elements are needed to filter the signals coming to and from your cell phone to make sure you have a clear signal. That’s a huge amount of real estate to dedicate to one function.”
The discovery by the Berkeley Lab team is helping accelerate the scientific community’s understanding of thin film ferroelectric materials, which may eventually lead to important, currently unanticipated, technological applications. Supporting the Berkeley Lab team of researchers is an example of a key strategy within the EPiQS initiative: flexible funding which supports timely projects with a high potential to make breakthroughs and aims to enhance experimental capabilities at leading research institutions and to enable rapid responses to new developments in the field.
Read the full article from Berkeley Lab here.
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