Generation of Spin Currents for Spintronic Logic Applications

Abstract

Current complementary metal oxide semiconductor (CMOS) technologies currently suffer drawbacks such as increased power consumption and device variability with scaling as well as volatility. In order to further advance computation technologies in the future, new and alternative devices are being explored to overcome these limitations. One promising approach is spintronic devices in which information is stored and computed based on the spin of electrons rather than the absence or presence of charge such as in CMOS. Spintronics offers many possible benefits including fast operational speed, low power consumption, and nonvolatility. This dissertation explores methods of generating spin polarized currents for the operation of logic devices and the fabrication of these devices for logic applications. The first device explored is a non-local lateral spin valve which can be used to generate a pure spin current and is the basic building block for the concept of all-spin logic. A unique top-down fabrication approach for lateral spin valves is created and demonstrated. Sub 100nm Co nanopillar devices are fabricated on a Cu channel using a top down approach that allows the entire material stack to be deposited initially under vacuum as opposed to devices fabricated using shadow beam lithography or lift-off techniques for ferromagnetic strips. A non-local signal is measured in these devices which indicates the top-down approach can successfully be used for integration of these devices. This demonstration is essential for these devices to be successfully implemented and scaled in computer applications at the industrial level. . In the second part of the dissertation, my research on spin Hall effect devices and the application of these devices for a spin Hall majority gate logic device are presented. The spin Hall effect is explored in bulk perpendicular TbFeCo/Ta devices which lays the groundwork for the following experiments. Then, a composite spin Hall structure is developed in order to switch perpendicular magnetization using the spin Hall effect without the need for an externally applied field. To demonstrate the ability to tune the material properties of a spin Hall channel, studies are also presented on a variety of multilayer spin Hall devices. Last, a three-input MTJ device is proposed for a spin orbit torque combined with spin transfer torque majority gate. Three MTJ devices are fabricated on Ta and three distinct switching states are shown corresponding to switching of the individual input elements. Additionally, simulation work is presented to verify the concept of the majority gate.