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Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Electrical and Computer Engineering

Year Degree Awarded

2018

Month Degree Awarded

February

First Advisor

Qiangfei Xia

Subject Categories

Electronic Devices and Semiconductor Manufacturing | Nanotechnology Fabrication

Abstract

This dissertation addresses the challenges for device scaling and novel application of nanoscale memristive devices and device arrays through demonstrating the first working sub-10 nm memristor array, the first ultra-dense atomic scale working memristor array and the first high performance nanoscale radiofrequency switch based on memristive devices.

Nanoimprint lithography is used to generate the sub-10 nm cross-point memristor array. The imprint mold with sub-10 nm features is generated by using wet chemical method to shrink the larger features on a master mold. The imprinting, pattern transfer and metallization process are closely monitored to enforce optimal conditions for sub-1 nm critical dimension (CD) control. With these efforts, cross-point arrays of 8 nm memristors are demonstrated. These 8 nm devices display highly reduced operation current and largely improved uniformity that are attributed to the dimensional restriction for tailoring the growth of conductive channel.

A novel nanofin electrode structure with ultra-high aspect ratio, is designed to overcome the challenges related to fabrication, interconnection and device/array functions for building the atomic scale memristive devices with ultrahigh density. Accordingly, a fabrication approach based on metal/insulator supper lattice layer deposition is developed and integrated with other necessary process to build the first 2 × 2 nm2 working memristor arrays with 4.48 Tbit/inch2. This approach has also been further pushed for even higher resolution by demonstrating memristor arrays with 1.6 × 1.6 nm2 cell size and 14 Tbit/inch2 density. HfO2 based atomic scale switches with 2 nm feature size displayed ultralow switching current and abnormal switching behaviors, which is linked to the electronic bipolar resistance switching mechanism. Furthermore, the array function with random accessibility is also demonstrated and critical issues such as capacitive coupling, thermal and electric cross-talk are discussed with simulation. Based on these findings with respect to atomic scale fabrication and device/array function, the scaling limit for memristor are tentatively projected.

High performance reconfigurable switch used in radiofrequency circuit demands low ON state resistance and low OFF state capacitance to provide high quality wideband transmission. For this reason, nanoscale radiofrequency switch based on existing technologies is unavailable because of their bulk switching mechanism and relative high ON resistivity. A memristor structure consisted of a nanoscale air gap between a Ag anode and a Au cathode is built to implement a nanoscale radiofrequency switch. Devices display low actuation voltages and large dynamic range with small ON resistance, which is induced by the growth/fracture of a nanoscale conductive filament as confirmed by scanning electron microscopy. Further study reveals that the switching properties could be modulated by controlling programming and environmental conditions. The devices have also demonstrated highly competitive insertion loss and isolation properties up to 110 GHz that projects a significant bandwidth up to 60.2 THz. Excellent linearity and power handling capability are also measured.

Available for download on Friday, February 01, 2019

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