Ferroelectric Tunnel Junctions

Ferroelectric tunnel junction (FTJ) is a tunnel junction in which two metal electrodes are separated by a thin ferroelectric layer. The spontaneous polarization of the ferroelectric layer can be switched by an applied electric field. The electrical resistance of a FTJ strongly depends on the orientation of the electric polarization. This phenomenon is known as tunneling electroresistance (TER). There are at least three mechanisms which are responsible for the TER effect resulting from the switching of ferroelectric polarization: (i) change in the electrostatic potential profile across the ferroelectric barrier: (ii) change in the transmission coefficient across interfaces; (iii) change in the attenuation constant of the barrier.

Using a ferroelectric barrier in a magnetic tunnel junction makes a multiferroic tunnel junction (MFTJ), whose transport properties depends on both the ferroelectric polarization of the barrier and the magnetization orientation of the electrodes. In MFTJs the spin polarization of tunneling electrons is affected by the ferroelectric polarization and thus the TER effect coexists with tunneling magnetoresistance (TMR) making MFTJ a four-state resistance device. Our first-principles and model calculations demonstrate the significance of these phenomena and pave the way for the experimental realization of FTJs and MFTJs.

References
  1. M. Li, L. L. Tao, and E. Y. Tsymbal, “Domain-wall tunneling electroresistance effect,” Physical Review Letters 123, 266602 (2019).
  2. Q. Yang, L. L. Tao, E. Y. Tsymbal, and V. Alexandrov, “Ferroelectric tunnel junctions enhanced by a polar oxide barrier layer,” Nano Letters 19, 7385−7393 (2019).
  3. A. Alexandrov, M. Y. Zhuravlev, and E. Y. Tsymbal, “Tunneling anisotropic magnetoresistance in ferroelectric tunnel junctions,” Physical Review Applied 12, 024056 (2019).
  4. Konstantin Klyukin, L. L. Tao, Evgeny Y. Tsymbal, and Vitaly Alexandrov, "Defect-Assisted Tunneling Electroresistance in Ferroelectric Tunnel Junctions," Physical Review Letters  121, 056601 (2018); Featured on the cover page of Physical Review Letters.
  5. M. Li, L. L. Tao, J. P. Velev, and E. Y. Tsymbal, “Resonant tunneling across a ferroelectric domain wall,” Physical Review B 97, 155121 (2018).
  6. H. Wang, Z. R. Liu, H. Y. Yoong, T. R. Paudel, J. X. Xiao, R. Guo, W. N. Lin, P. Yang, J. Wang, G. M. Chow, T. Venkatesan, E. Y. Tsymbal, H. Tian & J. S. Chen, "Direct observation of room-temperature out-of-plane ferroelectricity and tunneling electroresistance at the two-dimensional limit," Nature Communications 9, 3319 (2018).
  7. Weichuan Huang, Yue-Wen Fang, Yuewei Yin, Bobo Tian, Wenbo Zhao, Chuangming Hou, Chao Ma, Qi Li, Evgeny Y. Tsymbal, Chun-Gang Duan, and Xiaoguang Li, “Solid-state synapse based on magnetoelectrically coupled memristor,” ACS Applied Materials & Interfaces 10, 5649–5656 (2018).
  8. E. Y. Tsymbal and J. P. Velev, News & Views “Ferroelectric tunnel junctions: Crossing the wall,” Nature Nanotechnology 12, 614 – 615 (2017).
  9. J. P. Velev, J. D. Burton, M. Y. Zhuravlev, and E. Y. Tsymbal, Invited Review Article: “Predictive modelling of ferroelectric tunnel junctions,” npj Computational Materials 2, 16009 (2016).
  10. X. Liu, J. D. Burton, and E. Y. Tsymbal, “Enhanced tunneling electroresistance in ferroelectric tunnel junctions due to reversible metallization of barrier,” Physical Review Letters 116, 197602  (2016).
  11. E. Y. Tsymbal and H. Kohlstedt, "Tunneling across a ferroelectric," Science 313, 181 (2006).
  12. Y. W. Yin, J. D. Burton, Y-M. Kim, A. Y. Borisevich, S. J. Pennycook, S. M. Yang, T. W. Noh, A. Gruverman, X. G. Li, E. Y. Tsymbal, and Q. Li, "Enhanced tunnelling electroresistance effect due to a ferroelectrically induced phase transition at a magnetic complex oxide interface" Nature Materials 12, 397–402 (2013).
  13. E. Y. Tsymbal, A. Gruverman, V. Garcia, M. Bibes, and A. Barthélémy, Invited Review Article:"Ferroelectric and Multiferroic Tunnel Junctions," MRS Bulletin 37, 138-143 (2012).
  14. D. J. Kim, H. Lu, S. Ryu, C.-W. Bark, C.-B. Eom, E. Y. Tsymbal, and A. Gruverman, "Ferroelectric Tunnel Memristor," Nano Letters 12, 5697–5702 (2012).
  15. J. D. Burton and E. Y. Tsymbal, "Giant tunneling electroresistance effect driven by an electrically controlled spin valve at a complex oxide interface," Phys. Rev. Lett. 106, 157203 (2011). 
  16. J. M. López-Encarnación, J. D. Burton, E. Y. Tsymbal, and J. P. Velev, “Organic Multiferroic Tunnel Junctions with Ferroelectric Poly(vinylidene fluoride) Barriers”, Nano Letters 11, 599 – 603 (2011).
  17. A. Gruverman, D. Wu, H. Lu, Y. Wang, H. W. Jang, C.M. Folkman, M. Ye. Zhuravlev, D. Felker, M. Rzchowski, C.-B. Eom and E. Y. Tsymbal, "Tunneling electroresistance effect in ferroelectric tunnel junctions at the nanoscale," Nano Lett. 9, 3539 (2009).
  18. M. Ye. Zhuravlev, Y. Wang, S. Maekawa, and E. Y. Tsymbal, "Tunneling Electroresistance in Ferroelectric Tunnel Junctions with a Composite Barrier," Appl. Phys. Lett. 95, 052902 (2009).
  19. J. P. Velev, C.-G. Duan, J. D. Burton, A. Smogunov, M.K. Niranjan, E. Tosatti, S. S. Jaswal, and E. Y. Tsymbal, "Magnetic tunnel junctions with ferroelectric barriers: Prediction of four resistance states from first-principles," Nano Lett. 9, 427 (2009).
  20. J. P. Velev, C.-G. Duan, K. D. Belashchenko, S. S. Jaswal, and E. Y. Tsymbal, "Effect of ferroelectricity on electron transport in Pt/BaTiO3/Pt ferroelectric tunnel junctions," Phys. Rev. Lett. 98, 137201 (2007).
  21. M. Y. Zhuravlev, R. F. Sabirianov, S. S. Jaswal, and E. Y. Tsymbal, "Giant electroresistance in ferroelectric tunnel junctions," Phys. Rev. Lett. 94, 246802 (2005); ibid. 102, 169901 (2009).

FTJ
Schematic band diagram of a ferroelectric tunnel junction.

MRSEC PFM-CAFM
Tunneling electroresistance effect: Polarization pattern of a thin ferroelectric film in the form of the MRSEC logotip (top) and the same pattern imaged by detecting local tunneling current across the film (bottom).

Magnetic, ferroelectric, and multiferroic  tunnel junctions, and their resistance response to magnetic and electric fields.

Polarization controlled transition from the direct to resonant tunneling regime.