SPIN-ORBIT TORQUE FIELD-EFFECT TRANSISTOR (SOTFET): A MEMORY DEVICE PROPOSAL, MODELLING, AND EXPERIMENTS

Abstract

With the significant progress in spintronics within the recent few decades, spin-based devices have received broad research interest from both academia and industry, such as spin-based memory devices based on giant magnetoresistance (GMR), spin-transfer torques (STTs), and more recently, spin-orbit torques (SOTs). Spin-based memory devices present advantages over other memory devices due to their non-volatility, fast read/write speed, high endurance, etc., but suffer from the limited read-out signal due to the nature of GMR. On the other hand, the ferroelectric-based device shows significantly better read-out signal over spin-based devices while suffering from endurance and fatigue problems. Motivated by the spin-based and ferroelectric-based devices and aiming to combine their virtues, we propose the device concept of spin-orbit torque field-effect transistor (SOTFET), which is made possible by the recently developed magnetoelectric multiferroic materials. The magnetoelectric multiferroic materials simultaneously possess magnetization and polarization as two order parameters coupled by the magnetoelectric effect, which presents a potential path to couple ferromagnetic states with ferroelectric states. In this work, the roadmap of the SOTFET from a device concept towards its realization is presented. This dissertation will start with the motivations of the proposed SOTFET device concept and the background knowledge of the physics and materials that make SOTFET possible. Following the introduction, the device structure and working principle of the SOTFET are demonstrated. The main section of the dissertation will focus on the modeling of the SOTFET, coming up with an analytical SOTFET model, which serves as a wonderful tool for us to understand the SOTFET operation better, explore the parameter space of the SOTFET, and guide the follow-up experiments. The experimental efforts of demonstrating SOTFET are presented later in this dissertation, and we will see how the SOTFET model guides us to design better experiments. The applications of the SOTFET model for in-memory computing are then briefly covered. In the last section, the future of SOTFET and the challenges to fabricate an actual SOTFET device are thoroughly discussed.