<p>  </p> <p>Future artificial intelligence applications and data-intensive computations require the development of non-von Neumann architecture. Physical separation between a logic unit and a memory unit is one of the main bottlenecks of the traditional architecture, hindering unlocking the ultimate performance of electronic devices, such as power consumption and memory bandwidth limitation. However, to enable monolithic integration of high-performance logic and memory needs to resolve the fundamental thermal budget challenge of back-end-of-line (BEOL). In this regard, two-dimensional (2D) materials have drawn immense attention owing to their intrinsic performance, ultrathin bodies, and flexibility. The viability of low-temperature integration puts them in an advantageous position that rivals silicon technology.</p> <p><br></p> <p>Firstly, an entirely new phase change RRAM in MoTe2 can give rise to uniform switching by difference from a random filament formation of the conventional RRAM device. For a large memory array to function properly, it is crucial to have high nonlinearity of I-V characteristics for each device to suppress the sneak-path current. I experimentally demonstrate a proof-of-concept heterostructure consisting of 2D materials with the functionalities of the memory (MoTe2) and selector (WSe2). Next, a heterogeneously integrated 1-selector/1-resistor (1S1R) Ta2O5/MoTe2 RRAM cell was built for the first time employing 2D layered MoTe2 films, showing decent on/off-current ratios of ~730 and high nonlinearities of ∼5700. These values are considered state-of-the-art for built-in nonlinear RRAM devices to date. </p> <p><br></p> <p>Secondly, I demonstrate that a pure nitric oxide treatment at elevated temperatures provides a stable p-doping for monolayer WSe2. This approach allows achieving record high hole current densities of ~300 μA/μm and low contact resistances of ∼950 Ω·μm, while preserving the transistor on/off current ratio >2×106. This scalable pathway significantly improves the performance of p-type WSe2 transistors, opening new opportunities for p-type 2D materials to enable CMOS implementations for next-generation high-performance electronics. </p> <p><br></p> <p>Thirdly, I demonstrate all MoTe2 1-transistor/1-resistor (1T1R) memory cells, fabricated at low temperatures. The 1T1R cells can be switched with voltage ~ 1V, close to typical CMOS logic voltages. This demonstration underscores the potential of 2D materials and their monolithic integration toward the realization of future memory technologies. </p> <p><br></p> <p>Lastly, I adopt machine-learning (ML) algorithms to evaluate the design and process co-optimization from a vast number of 2D transistor device characteristics. This framework greatly optimizes the electrical performance of 2D transistors, serving as guidance for advancing future 2D electronics.</p>

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "October 2009." Includes bibliographical references (p. 147-162). Also available via the World Wide Web.

The <i>spin</i> of an electron has for long excited researchers both with respect to its fundamental physics and technological applications. Consequently, the traditional field driven switching of ferromagnets gave way for more scalable current driven switching based on the well-known spin transfer torque phenomenon. However, in the quest for better energy-efficiency, the manipulation of electron spin through pure voltage driven or voltage-assisted mechanisms are being intensely explored. In this research, we demonstrate that the very physics and the characteristics of such voltage driven devices enable interesting possibilities with respect to memory, neuromorphic and logic applications. We rely on the recent experimental demonstrations of two novel voltage effects on nano-magnets - the voltage controlled magnetic anisotropy (VCMA) and the pure voltage driven magneto-electric (ME) effect. Specifically, we propose in-situ, in-memory, vector logic operations by exploiting the voltage asymmetry and precessional switching dynamics of the VCMA effect to construct 'stateful' logic gates. Stateful logic are those in which the same device acts as a storage element and compute engine, simultaneously. In addition, we show that the pure voltage driven mono-domain switching and domain-wall motion of nano-magnets through the ME effect can be leveraged to construct neuro-mimetic devices exhibiting leaky-integrate-fire dynamics of biological neurons and as well as non-volatile synaptic elements. Further, we propose a voltage driven logic-device using the ME switching and demonstrate that the proposed logic-device can be used to construct a complete cascadable logic family including XNOR, IMP (implication), NAND and NOR gates. Additionally, we present an energy and area efficient content addressable memory using a logic compatible ME-XNOR device. The presented research shows that voltage driven switching can augment the very functionality and widen the application scope of spin based devices and circuits.

Advances in experimental techniques such as nanofabrication, characterization and synthesis have resulted in the development of many novel and interesting materials and devices. Surfaces and interfaces play an indispensible role for nanoelectronics development. ZnO and graphene have drawn tremendous research interests in recent years, due to their exceptional merits in electrical, optical and magnetic applications. This thesis attempts to ferret out the current experimental research progress, particularly, the frontiers of ZnO and graphene based surfaces and interfaces, and employs first principles to explore their electronic structures, to acquire mechanistic understanding of experimental findings, and to shed light on rational design of functional devices. / Finally, the magnetic properties of graphene by organic molecule modification are investigated by first principles method. For the first time, we demonstrate that methoxyphenyl group can introduce a delocalized p-type ferromagnetism into graphene sheet, with the Curie temperature (T c) above room temperature. Each aryl group can totally induce 1 muB into molecule/graphene system. Moreover, an around 1.1 eV direct band gap is introduced into both majority and minority spin bands of graphene by methoxyphenyl group modification. Zigzag graphene nanoribbon (GNR) shows strong site-specific magnetism by aryl group adsorption near the edge. At specific site of GNR, each molecule could totally induce 3&sim;4 mu B into molecule/GNR hybrid system. / First, we study the controllable modulation of the electronic structures of ZnO(10 1&macr; 10) surface functionalized by various types of carboxylic acids. The calculated structural results are consistent with the experimental ones attained by the Fourier transform infrared attenuated total reflectance (FT-IR-ATR). Mercapto-acetic acid molecules are found to contribute an abundance of band gap states into ZnO. Mercapto-acetic monolayer functionalized ZnO (10 1&macr; 10) is on the verge of metal-to-insulator transition, which is consistent with the experimental finding of an conductivity increase by 6 orders of magnitude. Mercapto-acetic acid functionalized ZnO (10 1&macr; 10) surface shows a strong configuration-dependence for both electronic structure and adsorption energy. Moreover, mercapto-acetic acid molecule functionalized ZnO also shows facet-dependent characteristic in which the monolayer functionalized ZnO (2 1&macr; 1&macr; 0) does not show metal-to-insulator transition. Acetic acid does not contribute to the band gap states of ZnO (10 1&macr; 10), whereas benzoic acid and 9-anthracenecarboxylic acid do contribute an abundance of band gap states to ZnO(10 1&macr; 10). / Second, we study the band gap opening of graphene bilayer by F4-TCNQ doping and externally applied electric filed effects. With F4-TCNQ concentration of 8.0x1013 molecules/cm2, the electrostatic charge transfer between each F4-TCNQ molecule and graphene is 0.45 e, and the built-in electric field Ebi between the graphene layers could achieve 0.070 V/A. The charge transfer and band gap opening of the F4-TCNQ doped bilayer graphene can be further modulated by externally applied electric field (Eext ). At 0.077 eV/A, the gap opening at the Dirac point ( K) DeltaEK = 306 meV and the band gap Eg 253 meV are around 71% and 49% larger than those of the pristine bilayer under the same Eext. By combining F4-TCNQ molecular doping and Eext, the p-type semiconductor bilayer graphene are attained, with the band gap and hole concentration varied in a wide range. / These four theoretical sub-topics stem from the experimental advances in ZnO and graphene based surfaces and interfaces. They form the mechanistic understanding of the respective surfaces and interfaces down to the molecular level. / Third, the self-assembly mechanism of PTCDA ultrathin films on graphene with the coverage in a range of 0.3&sim;3 monolayers (MLs) are interrogated by first principles method. For alpha modification mode, with critical thickness of 1 ML, the growth of PTCDA on graphene follows the Stranski-Krastanov (SK) growth mode. In contrast, for beta modification mode, the PTCDA can form two complete MLs on graphene substrate. From the thermodynamical viewpoint, alpha modification mode is more stable than beta modification mode. At 1 ML, the PTCDA follows a continuous and planar&dot; packing arrangement on graphene, which is almost unperturbed by typical defects in graphene substrate. This is in consistentcy with the experimental findings. For alpha modification mode with 2 and 3 ML coverage, the bulk-like phases appear. At the same time, the total charge transfer between PTCDA and graphene per 5&check;3x5 super cell at 2 MLs saturates with 0.42e, which is larger than those of 1 or 3 ML coverage. / Tian, Xiaoqing. / Adviser: Jianbin Xu. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Over the past decade there has been a great deal of interest in graphene, a 2-dimensional allotrope of carbon with exceptional mechanical and electrical properties. Its outstanding mobility, minimal size, and mechanical stability make it an appealing material for use in next generation electronic devices. Epitaxial graphene growth on silicon carbide is a reliable, scalable method for the production of high quality graphene films. Recent work has shown that the SiC can be patterned prior to graphitization, in order to selectively grow graphene nanostructures. Graphene nanoribbons grown using this technique do not suffer from the rough edges caused by lithographic patterning, and recent measurements have revealed extraordinary transport properties. In this thesis the magnetic properties of these nanoribbons are investigated through spin polarized current injection. The sensitivity of these nanoribbons to spin polarized current is interesting from a fundamental physics standpoint, and may find applications in future spintronic devices.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 144-147).

In the recent past, graphene has been discovered and studied as one of the most promising materials after silicon and carbon nanotube. Its atomically thin structure, pristine dangling bonds free surface and interface, ultra-fast charge transport capability, semi-metallic behavior, ultra-strong mechanical ruggedness, promising photonic properties and bio-compatibility makes it a material to explore from all different perspectives to identify potential application areas which can augment the quality of our life. Therefore, in this doctoral work the following critical studies have been carried out meticulously with key findings are listed below: (1) A simplistic and sustainable growth process of double or multi-layer graphene (up to 4” substrate coverage with uniformity) using low-cost atmospheric chemical vapor deposition (APCVD) technique. [presented in MRS Fall Meeting 2012 and in IEEE SIECPC 2012) (2) A buried metallic layer based contact engineering process to overcome the sustained challenge of contact engineering associated with low-dimensional atomically thin material. (presented in IEEE Nano 2013 and archieved in conference proceedings) (3) Demonstration of a fin type graphene transistor (inspired by multi-gate architecture) with a mobility of 11,000 cm2/V.s at room temperature with an applied drive-in voltage of ±1 volt to demonstrate for the first time a pragmatic approach for graphene transistor for mobile applications which can maintain its ultra-fast charge transport behavior with ultra-low power consumption. [Published in ACS Nano 2013] (4) Further a meticulous study has been done to understand the harsh environment compatibility of graphene for its potential use in underwater and space applications. [Published as Cover Article in physica solidi status – Rapid Research Letters, 2014] (5) Due to its highly conductive nature and low surface-to-volume ratio it has been used to replace conventional gold based anodic material in microbial fuel cells (used for water purification in self-sustained mode) to demonstrate its effectiveness as a sustainable low-cost mechanically robust transparent material. [Published in ACS Nano 2013, in Energy Technology 2014 as a Cover Article and in Nature Publishing Group Asia Materials 2014] (6) Extensive study to stabilize graphene surface and to use the phenomena for development of a sensor which can monitor the quality of water. [presented in MRS Fall Meeting 2013 and in MRS Fall Meeting 2014] (7) By using graphene as an expose transistor architecture with ultra-scale high-k dielectric, to develop a series of sensor for glucose monitoring. Sensitivity, selectivity, response rate and refresh time has been studied and optimized. [pending review in Nature Scientific Reports 2015] (8) From the lessons learnt during the development of glucose monitoring sensor cell, a sophisticated low-cost ultra-low power mobile graphene based non-invasive sensor has been assembled and clinically trialed in collaboration with King Faisal Hospitals in Jeddah and in Makkah. [pending review in Science 2015] As a future direction, this thesis also discusses potential of graphene growth on electrochemically deposited metallic seed layers and consequential usage in stretchable and transparent graphene antenna development for fully flexible only graphene based integrated electronic system integration.

<p dir="ltr">As silicon (Si) technology advances to 3 nm node and beyond, vertically stacking in 3D is considered as the primary choice to increase the density of transistors per unit area for better chip performance. Therefore, looking for new materials capable of replacing Si in back-end-of-line (BEOL) compatible monolithic 3D (M3D) integration has become one of the most important topics in the current field of electronic devices. Recent developed atomic layer deposition (ALD) deposited indium oxide (In₂O₃) field-effect transistors (FETs) have realized excellent electrical performance including field effect mobility over 100 cm²/V·s, on/off ratio up to 10¹⁷ and on-state current (I_ON) over 2.5 mA/μm in nanometer thin In₂O₃ FETs, providing promising prospect for next generation electronics. In this thesis, four main In₂O₃ related topics are discussed to examine the practicality of ALD In₂O₃ as channel material in BEOL compatible applications. First, the bias stability of planar In₂O₃ transistors and the effect of tin doping are studied. Second, gate-all-around (GAA) In₂O₃ FETs are implemented to improve I_ON up to record high 20 mA/μm, and its reliability is systematically measured and analyzed. Third, multilayer In₂O₃ FETs are constructed to investigate the possibility of vertical stacking. Last, vertical full oxide transistors with In₂O₃ gate are demonstrated to prove the feasibility of potential 3D integration.</p>

Fabrication process of capacitors and Schottky diodes with nanogap electrodes is explained in this Thesis. The Schottky diode is made with IGZO in the nanogap, whereas the capacitor is made with ZrO2 in the nanogap which acts as the dielectric. Moreover, the electric characterization of both the diode and capacitor was obtained for different frequencies and different diameters. The end result showed that as the frequency increases the diode performance increases, but the capacitance of the capacitors decreases. Also, the barrier height and concentration were obtained using the Mott-Schottky plot for different frequencies. The 10MHz had the highest carrier concentration (5.9E+18cm-3) and barrier height (1V).