Switchable nanoelectronic devices beyond silicon
Creators: name: NIRANTAR, Shruti
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400908
subject: Microelectronics
classificationCode: 401605
subject: Functional materials
classificationCode: 401804
subject: Nanoelectronics
classificationCode: 401807
subject: Nanomaterials

description: Silicon-based electronics have been the mainstay of the electronics industry for several decades, but silicon is now approaching its physical limits where it would fail to keep up with future demands. Areas such as internet-of-things, crypto-currencies, and space explorations have brought in distinctive challenges in the world of electronics for size, speed, weight, and storage capacity. These challenges demand alternatives to silicon to serve next-generation electronics. <br><br>
This thesis explores new material combinations and designs at nanoscale for next-generation fundamental electronic devices. It presents three devices - the two-terminal cross-point device based on amorphous vanadium oxide (a-VOx), the two-terminal hybrid cross-point device based on a-VOx and amorphous strontium titanium oxide (a-STO), and the three-terminal semiconductor-free, field-emission, nanoscale air channel transistor.<br><br>
First device, the two-terminal cross-point device based on a-VOx shows condition-dependent apolar volatile threshold switching (TS) post-electroforming and electroforming-free non-volatile bipolar resistive switching (BRS). This work proves that the apolar volatile TS in the a-VOx film is due to insulator-to-metal (IMT) transition in local crystal islands of vanadium dioxide based on nanostructural changes observed in situ during biasing in transmission electron microscopy. This apolar volatile threshold switching has significant application as a selector in crossbar arrays to reduce sneak-path or leakage current. <br><br>
Second device, the two-terminal cross-point hybrid device with a stack of a-STO and a-VOx thin films shows the combined characteristics of one resistor switch and one selector(1R1S) series combination. Here a-STO acts like a resistor switch and a-VOx as a selector. This hybrid device achieves nearly six times reduction in the sneak-path current. This combination would increase the accuracy, storage capacity, and power efficiency of a-STO based crossbars by incorporating a-VOx as a selector.<br><br>
Resistive switching crossbars have the potential to serve as the programmable logic and neuromorphic circuits for next-generation memory devices, given there is an acceptable understanding of the operating mechanisms. Considering this need, this thesis further introduces a novel protocol to visually observe nanostructural changes in real-time operations using in situ transmission electron microscopy (TEM) during biasing for cross-point device architectures. This protocol is a reliable, time-efficient, and economic to reveal the switching mechanism in any type of resistive switching material, and thereby predict its practical applicability.<br><br>
Third device, the all-metal air channel transistor. Electron emission has always had vital importance in the field of electronics. Initially, an extensive critical review of theories, materials, applications, current research directions, and future prospects of electron emission devices is carried out with insights into combining the best of field emission vacuum tubes with current advanced nanofabrication technology for a superior transistor technology. This thesis further introduces a proof-of-concept device for a semiconductor-free, field emission, nanoscale transistor technology operating in air, unlike a conventional vacuum encapsulation of field emission devices. This work enables a technology where metal-based switchable nanoelectronics can be created on any dielectric surface with low energy requirements, with a specific focus on developing radiation immune and light-weight electronics in the future.<br><br>
This thesis presents novel devices, material combinations, fabrication methods, and material characterization techniques with a unique and innovative use of standard instruments and micro-nano fabrication and characterization processes, to serve the future of switchable nanoelectronics devices beyond silicon.