Lab talk
Mar 17, 2009
Giant piezoelectric resistance in FTJs
Researchers at the Hong Kong Polytechnic University have found that applying a mechanical stress to a ferroelectric tunnel junction (FTJ) may modify the structure's tunnel barrier enough to create changes in its electric resistance by orders of magnitude – a phenomenon dubbed giant piezoelectric resistance (GPR).
Using a thermodynamic model and taking into account polarization charge screening in the electrodes and the near-surface inhomogeneous polarization distribution, the group has modeled the tunneling conductance of FTJs and presented the data as a function of the applied mechanical stress (see figure).
The team's results show that the conductance of FTJs can be modulated not only via the polarization orientations, but also by the applied stress, giving rise to a GER-like effect, which can be defined as a GPR effect. Similar to reversing the polarization, reversing a modest applied stress may also change the height of the tunnel barrier enough to produce orders of magnitude change in the electro-resistance.
Indeed, the sensitivity of the GPR system to the applied mechanical stress shows that the GPR system may have sufficient strength to be potentially useful in applications of high-sensitivity electronic and mechanical sensors, memories or other nano-devices.
The researchers presented their work in Nanotechnology.
About the author
This work was performed in the Department of Electronics and Information Engineering of the Hong Kong Polytechnic University, in Prof. Chung Ho Woo's Solid-State Electronics group. Research is performed on multi-physical properties of materials and structures in nano-dimensions, with particular attention paid to the phase-transition regime. Much of this work is done in collaboration with other international groups, including UKAEA Culham (Sergei Dudarev), Russian Academy of Science (Moscow, Alexei Semenov), Max-Planck Institute of Metal Research (Stuttgart, Werner Frank), Atomic Energy of Canada (Malcolm Griffiths), RPI (Hanchen Huang), U of Illinois (Lumin Wang), and Chinese institutes like CAS Solid State Physics Institute (Enge Wang), SYSU (Biao Wang), and Institute of Nano-Science NUAA (Wanlin Guo).
The results of these studies have put the group in a unique position of international strength and leadership in Hong Kong. To name a few examples, the discovery in 2002 of the 3D-Schwoebel-Ehrlinch barrier, a fundamental quantity that controls crystal growth, attracted a full-page review in Nature in the same year. Success in the development of nano-structured copper thin film in 2003 was included in the Frost & Sullivan's Technical Insight Alert, as a notable item in advanced coating and surface technology. Just published by the group in Physical Review B as an editor-recommended paper, is the world's first large-scale spin-lattice dynamic simulation of ferromagnetic materials applicable to the phase-transition regime. Their work on GPR is another interesting idea along this line of excellent work.
Dr Yue Zheng got his PhD from Harbin Institute of Technology in 2007. He has been with Prof. Woo's group since 2003 as a research student and is now a University Postdoctoral Fellow. He has recently been appointed associate professor at SYSU of China.
