Graduation Year

2013

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Sanjukta Bhanja

Keywords

Boolean logic, Emerging devices, energy minimization, multilayer, nanofabrication

Abstract

The continuous scaling down of the metal-oxide-semiconductor field-effect transistor (MOSFET)

has improved the performance of electronic appliances. Unfortunately, it has come to a

stage where further scaling of the MOSFET is no longer possible due to the physical and the

fabrication limitations. This has motivated researchers towards designing and fabricating novel

devices that can replace MOSFET technology. Carbon Nanotube Field-Effect Transistors, Single

Electron Tunneling Junctions, Nano-Magnetic Devices, and Spin Field-Effect Transistors are some

prospective candidates that could replace MOSFET devices. In this dissertation, we have studied

the computational performance of Nano−Magnetic Devices due to their attractive features such

as room temperature operation, high density, robustness towards thermal noise, radiation hardened

nature and low static power dissipation.

In this work, we have established that data can be propagated in a causal fashion from a driver

cell to the driven cells. We have fabricated a ferromagnetic wire architecture and used a magnetic

force microscopy (MFM) tip to provide localized magnetic inputs. This experiment validated two

important phenomena; (1) a clocking field is essential to propagate data and (2) upon removal of the

clocking field data can be propagated according to the input data.

Next, we have fabricated and captured MFM images of a nano-magnetic logic architecture

that has computed the majority of seven binary variables. The architecture was designed by interconnecting

three three-input majority logic gates with ferromagnetic and antiferromagnetic wire

architectures. This seven input majority logic architecture can potentially implement eight different

logic functions that could be configured in real-time. All eight functions could be configured by

three control parameters in real-time (by writing logic one or zero to them).

Even though we observed error-free operations in nano-magnetic logic architectures, it became

clear that we needed better control (write/read/clock) over individual single layer nano-magnetic

devices for successful long-term operation. To address the write/clock/read problems, we designed

and fabricated amultilayer nano-magnetic device. We fabricated and performed a set of experiments

with patterned multilayer stacks of Co/Cu/Ni80Fe20 with a bottom layer having a perpendicular

magnetization to realize neighbor interactions between adjacent top layers of devices. Based on the

MFM images, we conclude that dipolar coupling between the top layers of the neighboring devices

can be exploited to construct three-input majority logic gates, antiferromagnetic and ferromagnetic

wire architectures.

Finally, we have experimentally demonstrated a magnetic system that could be used to solve

quadratic optimization problems that arise in computer vision applications. We have harnessed

the energy minimization nature of a magnetic system to directly solve a quadratic optimization

process. We have fabricated a magnetic system corresponding to a real world image and have

identified salient features with true positive rate more than 85%. These experimental results feature

the potentiality of this unconventional computing method to develop a magnetic processor which

solves such complex problems in few clock cycles.

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