Spatially resolved steady-state negative capacitance

• Published in: Nature (London) 2019-01, Vol.565 (7740), p.468-471
• Main Authors: Yadav, Ajay K., Nguyen, Kayla X., Hong, Zijian, García-Fernández, Pablo, Aguado-Puente, Pablo, Nelson, Christopher T., Das, Sujit, Prasad, Bhagwati, Kwon, Daewoong, Cheema, Suraj, Khan, Asif I., Hu, Chenming, Íñiguez, Jorge, Junquera, Javier, Chen, Long-Qing, Muller, David A., Ramesh, Ramamoorthy, Salahuddin, Sayeef
• Format: Article
• Language: English
• Subjects: 639/301/1005; 639/301/119/996; 639/766/119/996; Analysis; Capacitance; Domain walls; Electric fields; Electron microscopy; Energy; Equilibrium; Ferroelectric crystals; Ferroelectric devices; Ferroelectric materials; Ferroelectricity; Ferroelectrics; Flux density; Heterostructures; Humanities and Social Sciences; Lead titanates; Letter; Mapping; Materials; Measurement; Microscopy; multidisciplinary; Phase transitions; Physics; Polarizability; Polarization; Properties; Science; Science (multidisciplinary); Steady state; Strontium titanates; Superlattices; Thin films; Vortices
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-018-0855-y

Negative capacitance is a newly discovered state of ferroelectric materials that holds promise for electronics applications by exploiting a region of thermodynamic space that is normally not accessible 1 – 14 . Although existing reports of negative capacitance substantiate the importance of this phenomenon, they have focused on its macroscale manifestation. These manifestations demonstrate possible uses of steady-state negative capacitance—for example, enhancing the capacitance of a ferroelectric–dielectric heterostructure 4 , 7 , 14 or improving the subthreshold swing of a transistor 8 – 12 . Yet they constitute only indirect measurements of the local state of negative capacitance in which the ferroelectric resides. Spatial mapping of this phenomenon would help its understanding at a microscopic scale and also help to achieve optimal design of devices with potential technological applications. Here we demonstrate a direct measurement of steady-state negative capacitance in a ferroelectric–dielectric heterostructure. We use electron microscopy complemented by phase-field and first-principles-based (second-principles) simulations in SrTiO 3 /PbTiO 3 superlattices to directly determine, with atomic resolution, the local regions in the ferroelectric material where a state of negative capacitance is stabilized. Simultaneous vector mapping of atomic displacements (related to a complex pattern in the polarization field), in conjunction with reconstruction of the local electric field, identify the negative capacitance regions as those with higher energy density and larger polarizability: the domain walls where the polarization is suppressed. Imaging steady-state negative capacitance in SrTiO 3 /PbTiO 3 superlattices with atomic resolution provides solid microscale support for this phenomenon.