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Online Laboratory Magazine
10/21/2021

01/24/2019

Controversial theory of materials science finally proven

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Scientists at the Nanoelectronic Materials Laboratory (NaMLab gGmbH) in collaboration with Researchers at Dresden University of Technology and the National Institute of Materials Physics, Romania have demonstrated that thin layers of ferroelectric hafnium zirconium oxide can exhibit a phenomenon called "negative capacitance".

This means that such materials can amplify a voltage, which could be used to reduce the power dissipation of future electronics beyond conventional limits. While this peculiar behavior was already predicted over 70 years ago, until now, most scientists thought that it was impossible to show this experimentally. Since the materials used in this study can already be found in every advanced computer chip today, future products utilizing this new discovery, e.g. more efficient smartphones or computers, might not be far away.

While ferroelectric materials have been thoroughly investigated for almost a century, some fundamental questions have remained unresolved. One of them is related to the "Landau theory" of ferroelectrics from the 1940s, which is still used to describe the behavior of ferroelectric materials today. However, the theory also predicts a negative capacitance, which has been controversially discussed, especially in recent years. The theory suggests that an increase of electric charge can lead to a decrease of the voltage, which is exactly opposite to a regular capacitance. A scientist at NaMLab gGmbH has now first demonstrated a measurement of such a negative capacitance in exceptional agreement with Landau theory.

This discovery was enabled by using specially fabricated capacitors, consisting of a stack of ultrathin layers, to which extremely short voltage pulses were applied. The results have been published on January 14, 2019 in the prestigious journal Nature. "The fascinating thing is that the materials in which we discovered this promising effect are already used in every smartphone," said Michael Hoffmann, Ph.D. student at NaMLab and lead author of the study. "However, the next important step will be to use these findings to develop new devices, which in theory could be much more energy-efficient than anything that is possible today."

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Source: TU Dresden