Optimizing energy performance of magnetic tunnel junctions for STT-RAM application

  • Ilyas A.H. Farhat

Student thesis: Master's Thesis

Abstract

This research project studies the magnetic tunnel junction (MTJ) energy performance, focusing on minimization of energy losses through engineering the anisotropy energy of the free layer (ferromagnetic layer), leading towards nanoengineering of the split hysteresis loop. A step-like (vicinal) interface structure is proposed, fabricated and characterized for tuning the anisotropy energy of the junction to enhance the energy performance of the device. An analytical study has been conducted on the energy performance using MATLAB, focusing on the threshold current density required for switching and its dependence on various parameters. The study concentrates on the geometrical parameters to control the current required for switching through scaling down the junction. Two circuit models were developed for the junction using LTSpice® and C¯adence CAD tools. The LTSpice® model was developed using SPICE netlist that describes the behavior of the device. Due to lack of flexibility and limitations in SPICE modeling, C¯adence model was developed using VerilogA. The model takes into account the dynamic behavior of the device and supports experimental findings. A scaling road-map was proposed for scaling the device down and controlling the switching current, taking into account the limitations and constraints required for the functionality of the device as a memory element. The nanofabrication process of the junction with the step-like interface structure between the ferromagnetic layer and the tunnel barrier was conducted. MgO and Al2O3 tunnel barriers were considered in the study, where the ferromagnetic layers considered includes F e and F eCo. The thickness of the oxide barrier was ranged from ∼ 1nm to ∼ 4nm, while the ferromagnetic layers thickness ranged from ∼ 3nm to ∼ 8nm. The MTJs were patterned in elliptical shapes, where the cross-sectional area ranges from (40nm × 120nm) to (750nm × 1500nm). Characterization of the fabricated MTJs includes magnetic characterization (M −H hysteresis curves) and transport characterization (Tunnel Magnetoresistance (TMR) vs. magnetic field, TMR vs. bias voltage, TMR vs. temperature and resistance-area product).
Date of Award2015
Original languageAmerican English
SupervisorAbdel Isakovic (Supervisor)

Keywords

  • Optimizing Energy Performance
  • magnetic Tunnel Junctions
  • STT-RAM Application

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