| AVS 63rd International Symposium & Exhibition | |
| Advanced Surface Engineering | Wednesday Sessions |
| Session SE+2D+EM-WeA |
| Session: | Multifunctional Thin Films and Coatings |
| Presenter: | Kevin Fitzell, University of California at Los Angeles |
| Authors: | K. Fitzell, University of California at Los Angeles X. Li, University of California at Los Angeles K. Wong, University of California at Los Angeles G. Yu, University of California at Los Angeles S. Robbennolt, University of California at Los Angeles S.H. Tolbert, University of California at Los Angeles P.K. Amiri, University of California at Los Angeles K.L. Wang, University of California at Los Angeles J.P. Chang, University of California at Los Angeles |
| Correspondent: | Click to Email |
In contrast to manipulating magnetization with applied current, using an applied electric field can significantly reduce the required energy and result in less heat generation, leading to increased energy density. This can be accomplished using the voltage-controlled magnetic anisotropy (VCMA) effect, which forms the basis of next-generation magnetoelectric MRAM devices. Specifically, applying an electric field across a CoFeB/MgO interface can decrease the perpendicular magnetic anisotropy field as a result of the altered electron density at the interface, thus destabilizing the magnetization state and allowing for its efficient and deterministic reorientation with a small applied magnetic field. This operation principle stands in contrast to that of STT-RAM, which uses upwards of 100 fJ to write a single bit (300,000 times more energy than the actual energy barrier to switching).
Previous research on CoFeB/oxide interfaces has shown that increasing the dielectric constant of the oxide layer also increases the sensitivity of the interfacial magnetic anisotropy energy to an applied electric field. Lead zirconate titanate (PZT), having excellent ferroelectric properties including a large dielectric constant, is therefore a prime candidate for integration into such oxide layers in an attempt to maximize the VCMA effect. Using atomic layer deposition (ALD), PZT was thus incorporated into magnetic tunnel junctions having MgO/PZT/MgO multilayer composite tunneling barriers. Our group has shown that MRAM devices fabricated using these MgO/PZT/MgO tunneling barriers resulted in a 40% increase in the VCMA coefficient (and thus substantial energy savings) over magnetic tunnel junctions simply employing MgO tunneling barriers, despite the PZT layer being amorphous. Our most recent work has focused on the crystallization of these ultrathin PZT layers, which would cause an even larger dielectric response (even greater energy savings) and open an avenue toward four-state memory devices relying on the ferroelectric polarization of the PZT.