Over the past few decades, metal phthalocyanines (MPcs) have been thoroughly investigated as active materials in organic field-effect transistors (OFETs) towards the commercialization of flexible integrated circuits and displays. One of several advantages to MPcs as building blocks for OFETs is the high degree of functionality, from which the choice of metal ion, substituents along with the phthalocyanine framework and axially bound ligands can synergistically tune the physical and self-assembly properties of the material. Recent interest has been directed to the introduction of main-group elements as the central ion of MPcs as an avenue to install both hole and electron transport properties and improve device performance. To prepare materials that are suitable to be employed as the semiconducting active layer in organic field-effect transistors, a family of novel silicon phthalocyanine derivatives was prepared. The synthesis and optoelectronic properties of those new axially disubstituted silicon phthalocyanines are detailed in this work. Axial ligand variation mainly includes alkylsiloxy derivatives. The emphasis of the current thesis, however, is on tailoring the Pc backbone, which includes replacing the four benzene units with pyrazine moieties, extending the degree of conjugation with naphthalene, and introducing substituents on their peripheral positions. Several metal-containing tetra-2,3-pyrazinoporphyrazines are also described, but their applications are limited due to the difficulty of purification. Specifically, Chapter 1 serves as a comprehensive review of main-group phthalocyanines and their use as active materials in organic field-effect transistors. In Chapter 2, silicon tetra-2,3-pyrazinoporphyrazine complexes are explored. The isosteric substitution of CH groups in Pc macrocycle for nitrogen atoms leads to an obvious hypsochromic shift in their main absorption band, and their relatively low energy levels make them promising air-stable n-type organic semiconducting materials for OFETs. The synthesis and characterization of silicon tetra(tert-butyl)-2,3-naphthalocyanine complexes are described in Chapter 3. The extension of π-conjugation leads to obvious bathochromic shifts in the main absorption band. In addition, the introduction of tert-butyl groups on the periphery of the molecule reduces the tendency of the naphthalocyanine molecules to aggregate, thereby increase their solubility. Chapter 4 covers the synthesis and characterization of zinc tetra-2,3-pyrazinoporphyrazine and cobalt tetra-2,3-pyrazinoporphyrazine, whereas more future works are expected. The fifth chapter provides a conclusion to this work, and possible future directions of the research conducted herein.

No description available.

With the development of modern electronics, the demand for high quality power supplies has become more urgent than ever. For power MOSFETs, maintaining the trend of reducing on-state resistance (conduction loss) without sacrificing switching performance is a severe challenge. In this work, our research is focused on implementing strained silicon and silicon germanium in power MOFETs to enhance carrier mobility, thus achieving the goal of reducing specific on-state resistance. We propose an N-channel super-lattice trench MOSFET, a P-channel sidewall channel trench MOSFET and P-Channel LDMOS with strained Si/SiGe channels. A set of fabrication processes highly compatible with conventional Si technology is developed to fabricate proposed devices. The mobility enhancement is observed to be 20%, 40% and 35% respectively for N-channel, Pchannel trench MOSFET and LDMOS respectively and the on-state resistance is reduced by 10%, 20% and 22% without sacrificing other device performance parameters.

Reduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is of great significance for determining its potential application. In this dissertation, I demonstrate fabrication of high-yield solution based graphene field effects transistor (FET) using AC dielectrophoresis (DEP) and investigate the detailed electronic transport properties of the fabricated devices. The majority of the devices show ambipolar FET properties at room temperature. However, the mobility values are found to be lower than pristine graphene due to a large amount of residual defects in RGO sheets. I calculate the density of these defects by analyzing the low temperature (295 to 77K) charge transport data using space charge limited conduction (SCLC) with exponential trap distribution. At very low temperature (down to 4.2 K), I observe Coulomb blockade (CB) and Efros-Shklovskii variable range hopping (ES VRH) conduction in RGO implying that RGO can be considered as a graphene quantum dots (GQD) array, where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. This was further confirmed by studying RGO sheets of varying carbon sp 2 fraction from 55 – 80 % and found that both the localization length and CB can be tuned. From the localization length and using confinement effect, we estimate tunable band gap of RGO sheets with varying carbon sp 2 fraction. I then studied one dimensional RGO nanoribbon iv (RGONR) and found ES VRH and CB models are also applicable to the RGONR. However, in contrast to linear behavior of decrease in threshold voltage (Vt) with increasing temperature (T) in the RGO, sub linear dependence of Vt on T was observed in RGONR due to reduced transport pathways. Finally, I demonstrate synthesis and transport studies of RGO/nanoparticles (CdS and CeO2) composite and show that the properties of RGO can be further tuned by attaching the nanoparticles.

<p> The Metal-Oxide Semiconductor Field-Effect Transistor is first analyzed from an active R-C transmission line view-point. The small signal circuit model and the noise model of the device are then derived and experimental results presented.</p> <p> A Chronologically arranged bibliography concerning MOS devices and associated noise studies is included at the end of this thesis.</p> / Thesis / Master of Engineering (MEngr)

Single-walled carbon nanotubes (SWNTs) are ideal for use in nanoelectronic devices because of their high current density, mobility and subthreshold swing. However, assembly methods must be developed to reproducibly align all-semiconducting SWNTs at specific locations with individually addressable gates for future integrated circuits. We show high yield assembly of local-gated semiconducting SWNTs assembled via AC-dielectrophoresis (DEP). Using individual local gates and scaling the gate oxide shows faster switching behavior and lower power consumption. The devices were assembled by DEP between prefabricated Pd source and drain electrodes with a thin Al/Al2O3 gate in the middle, and the electrical characteristics were measured before anneal and after anneal. Detailed electron transport investigations on the devices show that 99% display good FET behavior, with an average threshold voltage of 1V, subthreshold swing as low as 140 mV/dec, and on/off current ratio as high as 8x105. Assembly yield can also be increased to 85% by considering devices where 2-5 SWNT bridge the gap between source and drain electrode. To examine the characteristics of devices bridged by more than one SWNT, similar electron transport measurements were taken for 35 devices with electrodes bridged by 2-3 SWNT and 13 devices connected by 4-5 SWNT. This high yield directed assembly of local-gated SWNT-FETs via DEP may facilitate large scale fabrication of CMOS compatible nanoelectronic devices.

No description available.

No description available.

No description available.

<p> In this thesis, the current-voltage (I-V) behaviour of Liquid Organic Field-Effect Transistor (LOFET) was systematically studied with respect to the gate voltage, channel length and channel fluid. LOFETs in both internal and external gate modes were successfully fabricated in four-probe configuration. </p> <p> It was discovered that the effect of gate voltage on the source-to-drain current of LOFETs was significant. The drain current clearly increased when the gate voltage increased. This phenomenon was found in all LOFETs samples with different channel fluids and channel lengths. In addition, it was also proved that anions are the majority carriers in LOFETs. The concentration of anions inside the LOFET channel increased while applying a larger voltage to the gate, resulted in an increase of the drain current. This achievable gate modulation set up a solid foundation for further research on the manipulation of ionic and molecular species. </p> <p>It was also obtained that the drain current was changed with variable channel lengths. The current through the LOFET channel decreased while the channel length increased. At the same time, the difference between drain current in various channels evidently increased when the gate voltage increased from 0 to 5V. This was found to be due to the anion concentration change with varying gate voltages. </p> <p> The drain currents through LOFET channels filled with fluids of different polarities were also measured. It was observed that when the polarity of the molecule increased from that of 4,4'-Dihydroxybiphenyl to that of 2-Amino-4 Phenylphenol, the drain current increased significantly. At the same time, the difference between drain current in specific solutions was also more significant, when applying higher voltage to the gate. Combining these results with the gate modulation above, there is great potential of developing new sensing techniques and even logic operation in the future. </p> <p> This work represents a step towards a new group of cheap and effiecient electronic components of LOFETs. Guided by systemic observations from the effects of gate voltage, channel length and fluid structure, there is no doubt that LOFET will become a more attractive research topic because of its promising advantages, such as easy fabrication, low cost and its highly sensitive response. </p> / Thesis / Master of Applied Science (MASc)