Unveiling the double-well energy landscape in a ferroelectric layer.

Abstract

The properties of ferroelectric materials, which were discovered almost a century ago¹, have led to a huge range of applications, such as digital information storage², pyroelectric energy conversion³ and neuromorphic computing^4,5. Recently, it was shown that ferroelectrics can have negative capacitance^6-11, which could improve the energy efficiency of conventional electronics beyond fundamental limits^12-14. In Landau-Ginzburg-Devonshire theory^15-17, this negative capacitance is directly related to the double-well shape of the ferroelectric polarization-energy landscape, which was thought for more than 70 years to be inaccessible to experiments¹⁸. Here we report electrical measurements of the intrinsic double-well energy landscape in a thin layer of ferroelectric Hf_0.5Zr_0.5O₂. To achieve this, we integrated the ferroelectric into a heterostructure capacitor with a second dielectric layer to prevent immediate screening of polarization charges during switching. These results show that negative capacitance has its origin in the energy barrier in a double-well landscape. Furthermore, we demonstrate that ferroelectric negative capacitance can be fast and hysteresis-free, which is important for prospective applications¹⁹. In addition, the Hf_0.5Zr_0.5O₂ used in this work is currently the most industry-relevant ferroelectric material, because both HfO₂ and ZrO₂ thin films are already used in everyday electronics²⁰. This could lead to fast adoption of negative capacitance effects in future products with markedly improved energy efficiency.