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Bhagwati Prasad1 Yen-Lin Huang1 Zuhuang Chen1 Humaira Taz2 Anoop Damodaran1 S Manipatruni3 Chia-Ching Lin3 D Nikonov3 I Young3 Ramamoorthy Ramesh1 4

1, University of California Berkeley, Berkeley, California, United States
2, University of Tennessee, Knoxville, Tennessee, United States
3, Intel Corp., Hillsboro, Oregon, United States
4, University of California, Berkeley, Berkeley, California, United States

Over the last couple of decades, there have been continuous efforts to scale down both logic and memory components of microelectronic devices to nano regimes in the pursuit of enhancing speed and storage density, respectively [1]. However, with reducing the dimension of these devices, the significant energy losses in the form of heat has been one of the key issues for the microelectronic industry [2]. In order to continue further improvement in device-level or even bring next breakthrough in computing devices, a novel physical mechanism beyond-CMOS concept is needed to be explored.
The electric-field manipulation of magnetism in mutltiferrroic based devices promises to reach in the energy landscape of atto-Joule (aJ) range for per bit operation in logic and memory devices [3]. Among other multiferroic materials, BiFeO3 (BFO) exhibits robust magnetoelectric coupling at room temperature [4]. The canted antiferromagnetically aligned spins in BFO, give arise to the weak ferro-magnetism due to the Dzyaloshinskii–Moriya(DM) interaction, causes strong exchange interaction with ultrathin ferromagnet, e.g. CoFe, which can be exploited to electrically control the spin valve device [5]. Here we have demonstrated scaling behavior of applied voltage to electrically control the spin-valve devices at room temperature by engineering the strain state and doping level in BFO thin films. We show that with reducing the thickness of BFO layer down to 20 nm along with 10-15 % of La doping, the switching voltage can be reduced to sub volt regime (~150 mV). Besides this, we have shown large angle dependent exchange bias in these system that can be reversible controlled by electric field. The magnetic coupling of BFO with CoFe in these devices is strongly stabilized by its ferroelectric (FE) ordering. Orientation of the device structure with respect of the BFO FE domains play a crucial role in determining the degree of exchange bias and its manipulation with electric field. In addition to these findings, enhancement of magnetoelectric coupling with miniaturization of these devices down to ferroelectric domain size (~ 200 nm) provides a pathway to integrate BFO as a key material in the fabrication process for ultra-low energy, non-volatile beyond-CMOS computing.

[1] Ferain I. et al., "Multigate transistors as the future of classical metal-oxide-semiconductor field-effect transistors" Nature 479 310-316 (2011).
[2] Meindl J. D et al., "Limits on silicon nanoelectronics for terascale integration." Science 293 2044-2049 (2001).
[3] Manipatruni S., et al., "Spin-orbit logic with magnetoelectric nodes: A scalable charge mediated nonvolatile spintronic logic" arXiv preprint arXiv:1512.05428 (2015).
[4] Wang J. et al., Epitaxial BiFeO3 multiferroic thin film heterostructures. Science 299, 1719–1722 (2003)
[5 Heron J. T. et al., "Deterministic switching of ferromagnetism at room temperature using an electric field", Nature 516, 370–373 (2014).

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