Exploiting Voltage Driven Switching of Ferromagnets for Novel Spin based devices and circuits
thesisposted on 10.06.2019 by Akhilesh Ramlaut Jaiswal
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The spin of an electron has for long excited researchers both with respect to its fundamental physics and technological applications. Consequently, the traditional field driven switching of ferromagnets gave way for more scalable current driven switching based on the well-known spin transfer torque phenomenon. However, in the quest for better energy-efficiency, the manipulation of electron spin through pure voltage driven or voltage-assisted mechanisms are being intensely explored. In this research, we demonstrate that the very physics and the characteristics of such voltage driven devices enable interesting possibilities with respect to memory, neuromorphic and logic applications. We rely on the recent experimental demonstrations of two novel voltage effects on nano-magnets - the voltage controlled magnetic anisotropy (VCMA) and the pure voltage driven magneto-electric (ME) effect. Specifically, we propose in-situ, in-memory, vector logic operations by exploiting the voltage asymmetry and precessional switching dynamics of the VCMA effect to construct 'stateful' logic gates. Stateful logic are those in which the same device acts as a storage element and compute engine, simultaneously. In addition, we show that the pure voltage driven mono-domain switching and domain-wall motion of nano-magnets through the ME effect can be leveraged to construct neuro-mimetic devices exhibiting leaky-integrate-fire dynamics of biological neurons and as well as non-volatile synaptic elements. Further, we propose a voltage driven logic-device using the ME switching and demonstrate that the proposed logic-device can be used to construct a complete cascadable logic family including XNOR, IMP (implication), NAND and NOR gates. Additionally, we present an energy and area efficient content addressable memory using a logic compatible ME-XNOR device. The presented research shows that voltage driven switching can augment the very functionality and widen the application scope of spin based devices and circuits.