Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Electrical Engineering

First Advisor's Name

Sakhrat Khizroev

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Jean Andrian

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Georgakopoulos Stavros

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Pezhman Mardanpour

Fourth Advisor's Committee Title

Committee Member

Keywords

Spintronics, Nanoparticle, spin transfer torque

Date of Defense

3-28-2019

Abstract

Spintronics is a rapidly growing research field due to scalability, integrablility within existing VLSI architecture, significantly reduced switching energy and latency while maintaining stable bit orientation (Spin-up, Spin-down). For the first time sub-5nm Spin Transfer Torque –Magnetic Tunneling Junctions (STT-MTJ) were investigated utilizing various Integrated Circuit (IC) fabrication techniques to evaluate novel concepts in logic switches.

Tunneling Magnetoresistance (TMR) was measured in STT-MTJ stacks of Ta/CoFeB/MgO/CoFeB/Ta with differing diameter ferrimagnetic CoFe2O4 nanoparticles (10nm, 4nm and 2nm) embedded in the MgO layer. MR was detected in the 2nm and 4nm particle devices and demonstrated evidence of single electron transport.

Tri-layer STT-MTJ devices were fabricated using a thin film stack of Ta/Ru/Ta/CoFeB(M1)/MgO/CoFeB(M2)/MgO/CoFeB(M3)/Ta. The overall diameter of the stack was reduced to sub-20nm using Focused Ion Beam (FIB) to mill away extra material. The coercivities of the ferrimagnetic CoFeB layers were modified during thin film deposition by altering sputter conditions. Field Applied- Magnetic Force Microscopy (FA-MFM) was used to detect four different magnetic intensities corresponding to three discreet resistances in the singly addressed device, making this architecture a candidate for neuromorphic computational applications.

Lastly a lithographic-less architecture was developed to mass fabricate and electo-mechanically probe multi-layered, single point, sub-5nm particle based STT-MTJ devices using off-the-shelf anodized nanoporous alumina. Once fabricated, the devices were probed to measure their IV characteristics and magnetoresistance (MR). The unprecedented MR changes on the order of 50,000% at room temperature suggest quantum mechanical behavior.

Identifier

FIDC007684

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