2, Intel Corporation, Portland, Oregon, United States
Over the past 50 years, Moore’s law has successfully predicted and motivated the scaling of the length scale of transistors on Si wafer. This continuous scaling and development of semiconductor technology have enabled an incredible growth of the computational power of personal electronics from generation to generation. However, several physical limitations, especially power dissipation, have halted this exuberant era for semiconductor manufacturing industry. Thus, the development of low-power consumption and non-volatile memory in nanoscale is becoming a critical key to trigger another technological evolution. Here, we demonstrate a low-voltage (1V) and non-volatile manipulation of ferromagnetism at room temperature via the heterostructure of Pt/Co0.9Fe0.1/Cu/Co0.9Fe0.1/BiFeO3. BiFeO3 (BFO) is a multiferroic material exhibiting two order parameters, ferroelectricity, and antiferromagnetism, above room temperature. It also shows a weak ferromagnetism (Mc) induced by the canted spin configuration described by the Dzyaloshinskii–Moriya (DM) interaction. Moreover, these ferroic orderings are strongly coupled. Thus one can switch the ferroelectric polarization (P) and the weak ferromagnetism (Mc) simultaneously by an electrical field. We utilized this electrically controllable Mc in BFO to manipulate the magnetic property of the CoFe layer and created a non-volatile low- and high-resistive state. Yet, to realize the sub-one-volt switching of ferroic ordering in BFO, we need to scale the thickness of BFO down to few nanometers range. In this work we will provide a comprehensive understanding of the evolution of ferroelectricity and antiferromagnetism in BFO as the scaling of thickness via several techniques including photoemission electron microscopy (PEEM), X-ray magnetic linear dichroism (XMLD), X-ray magnetic circular dichroism (XMCD), HR-transmission electron microscopy (HRTEM), and Piezo-force microscopy (PFM).
Finally, with this background knowledge, we are able to design a proper material combination to achieve one-volt switching of two resistive states at room temperature. Our results provide a solid building block for ultra-low power consumption spintronics beyond Moore’s law.