Collaborative Research: Spintronics Without Spin Injection

The continued scaling of CMOS technology is being driven by various approaches including spin-based electronics (or 'spintronics') due to potential gains in low-power operation, and by the prospect of realizing new forms of non-volatile, on-chip data storage. However, spintronic devices typically exhibit poor magnetoresistive values, except at cryogenic temperatures, and there are often practical issues regarding their manufacturability. Consequently, the full potential impact of spintronics on technology and society has remained unrealized. The ability to induce a high degree of spin polarization in epitaxially-formed graphene layers, deposited on complex oxides, is a major goal of this research; one that will allow the development of high performance, non-volatile, spin-based devices, capable of operating above room temperature. Social and economic benefits of such advances is huge, allowing not only the continuation of smaller, cheaper, and faster computing, but also making possible the development of massively-parallel, yet low-power and fault-tolerant, computer architectures. Graduate students will be trained in the interdisciplinary aspects of understanding fundamental relationships between surface/interface chemistry, charge and spin transport, and device physics. This mentoring also extends to the recruitment of undergraduate and high school students through existing, proven programs at the University of Buffalo, the University of Nebraska-Lincoln and at the University of North Texas. In the interest of a new generation of post-CMOS nanoelectronics, technological challenges of spintronic devices include achieving high-fidelity spin-polarized carrier injection into a nonmagnetic semiconductor, and; realization of electrical schemes for the manipulation of magnetism while not compromising the possible energy gains offered by spintronics. This program provides a solution by realizing practical, graphene-based spintronic devices, based on industry-compatible graphene growth methods and operating at or above room temperature. These devices feature directly-grown, high-quality graphene on magnetic/multiferroic oxide substrates, and will exploit the spin polarization induced in the graphene channel through its interaction with the substrate, thereby obviating the need for efficient spin injection from ferromagnetic electrodes. The devices will furthermore be switched by means of the electric field applied across insulating oxides, thereby ensuring low-power operation. This project combines studies of the interfacial-chemistry of graphene/oxide hetero-junction formation, its effects on graphene spin polarization, and the development and testing of spin-field effect transistors. These devices are based on the direct growth of graphene/oxide heterojunctions, including Co3O4(111), Cr2O3(0001), and other ordered multiferroic oxides. The goal is to have a fundamental insight into how surface chemistry impacts spin transport, and also to yield manufacturable graphene-based spintronic devices, capable of exhibiting superior per-formance (MR>200%) in operation above room temperature.