| AVS 56th International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM2-TuM |
| Session: | Complex and Multifunctional Oxides |
| Presenter: | P. Maksymovych, Oak Ridge National Laboratory |
| Authors: | P. Maksymovych, Oak Ridge National Laboratory S. Jesse, Oak Ridge National Laboratory P. Yu, University of California, Berkeley R. Ramesh, University of California, Berkeley A.P. Baddorf, Oak Ridge National Laboratory S.V. Kalinin, Oak Ridge National Laboratory |
| Correspondent: | Click to Email |
Electron tunneling underlies numerous devices relevant to information technology and has been proposed in future energy harvesting and quantum computing applications. Replacing a conventional insulator in the tunnel junction with an electronically correlated material can yield new types of electronic functionality. In one such concept, dubbed ferroelectric tunneling, the tunneling barrier height is controlled by the polarization of a ferroelectric oxide, enabling non-volatile conduction states that can be switched with electric field. Although ferroelectric tunneling has been thoroughly theorized, a convincing experimental demonstration of this phenomenon is still lacking. The key challenge is to find a material system that simultaneously satisfies the dimensional constraints for tunneling and ferroelectricity, as well as to assure that the conductance is not dominated by extrinsic effects of charge injection and filamentary conduction, which is ubiquitous in complex oxides.
In this talk we will demonstrate a highly reproducible polarization control of local electron transport through epitaxial Pb(Zr0.2Ti0.8)O3 films. Despite being 30-50 nm thick, conductive atomic force microscopy revealed that the films possessed spatially and temporally reproducible local conductivity in the regime of Fowler-Nordheim electron tunneling. This is likely due to a strong electric field in the sub-surface region (excess of 106 V/cm) created by the relatively sharp metal tip. Local I-V characteristics exhibited strong hysteretic behavior across the surface. By combining conducting atomic force microscopy with piezoresponse force microscopy, we have, for the first time, directly correlated local events of ferroelectric and resistive switching [1]. The large spontaneous polarization of PZT produced as strong as 500-fold enhancement of FN-tunneling conductance upon ferroelectric switching, sufficient to demonstrate a local non-volatile memory function. The physical mechanism of the observed effect was traced to the polarization-dependence of the height and possibly width of the metal-ferroelectric Schottky barrier.
By observing the role of inherent disorder in ferroelectrics and comparing films grown on different electrode materials, we have shown that the switching voltage and the magnitude of conductance hysteresis are subject to electrostatic control via ferroelectric switching. Variable-temperature measurements and local effects due to dielectric non-linearities will also be discussed.
[1] P. Maksymovych, S. Jesse, P. Yu, R. Ramesh, A. P. Baddorf, S. V. Kalinin, Science (2009) in press.