Abstract
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 accessible1–14. 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 heterostructure4,7,14 or improving the subthreshold swing of a transistor8–12. 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 SrTiO3/PbTiO3 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.
| Original language | English |
|---|---|
| Pages (from-to) | 468-471 |
| Number of pages | 4 |
| Journal | Nature |
| Volume | 565 |
| Issue number | 7740 |
| DOIs | |
| State | Published - Jan 24 2019 |
| Externally published | Yes |
Funding
Acknowledgements This work was supported in part by the AFOSR YIP programme, LEAST (one of the SRC/DARPA supported centres within the STARNET initiative), ASCENT (one of the SRC/DARPA supported centres within the JUMP initiative), and the Berkeley Center for Negative Capacitance Transistors and the Multicampus Research Programs and Initiatives (MRPI) of the University of California. Electron microscopy experiments and equipment were supported by the Cornell Center for Materials Research, through the National Science Foundation MRSEC programme, award DMR 1719875. The work at Penn State was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award FG02-07ER46417. Z.J.H. acknowledges support from NSF-MRSEC grant number DMR-1420620 and NSF-MWN grant number DMR-1210588. R.R. and S.D. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, under grant GBMF5307. R.R. also acknowledges funding from the Army Research Office. J.I. acknowledges support from the Luxembourg National Research Fund under grant C15/ MS/10458889 NEWALLS. P.G.-F. and J.J. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grant number FIS2015-64886-C5-2-P, and P.G.-F. acknowledges support from Ramón y Cajal grant no. RyC-2013-12515.