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Fabrication and Investigation on the High Dielectric Constant Thin Film and Advanced Cu-Induced Resistance Switching Non-volatile MemoryYang, Po-Chun 22 December 2011 (has links)
This thesis contains four parts. In the first part, we investigate the post treatment of low-temperature-deposited high dielectric constant (high-k) thin films to enhance their properties. The high-pressure oxygen (O2 and O2+UV light) is employed to improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this study, 13nm HfO2 thin films are deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 ¢J are performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO2 film after O2 and O2+UV light treatments can be improved from 3.12¡Ñ10-6 A/cm2 to 6.27¡Ñ10-7 and 1.3¡Ñ10-8 A/cm2 at |Vg| = 3 V. The leakage current density is significantly suppressed and the current transport mechanism is transformed from trap-assisted tunneling to Schottky-Richardson emission due to the passivation of traps inside HfO2 film and interfacial layer. The proposed treatment is applicable for the future flexible electronics.
In the second part of this thesis, we study the memory characteristics of CoSi2 nanocrystals with SiO2 or Al2O3/HfO2 multiple layer tunnel oxide. Due to the property of high-k, it can provide thicker physics thickness than thermal oxide (SiO2) under identical equivalent oxide thickness (EOT) and enhances the reliability without reducing the programming speed. By engineering the different dielectric constant materials and the energy band structure, the performance of nonvolatile memory can be improved. The device that employs HfO2/Al2O3/HfO2 as tunnel oxide exhibits better memory window and carrier injection efficiency than the device employing thermal oxide. Furthermore, the device employs Al2O3/HfO2/Al2O3 as tunnel oxide present the better retention characteristics than the device employs HfO2/Al2O3/HfO2 as tunnel oxide. The corresponding mechanisms were also discussed.
For the advanced nonvolatile application, high-k material - hafnium oxide was applied on the resistance switching nonvolatile memory device as resistive switching layer with TiN/Ti/HfO2/TiN structure in the third part of this thesis. By using a thin Ti layer as the reactive buffer layer into the anode side, the proposed device exhibits superior bistable characteristics. Since the Ti can easily absorb oxygen atoms from buried HfO2, the TiN/Ti bi-layer can greatly improve the resistive switching characteristics. The mechanism of the proposed device is dominated by the redox reaction between the Hf and HfOX. In addition, the proposed device has multi-bit storage ability to enhance the storage density. From the temperature-dependent measurements, the low ambient temperatures would cause the formation and rupture of the conduction path with discordant quality and quantity during every switching cycle, which give rise to a wide distribution of the HRS and LRS resistance and instability of resistive switching properties.
In the fourth part of this thesis, we investigate the characteristics of an advanced Cu-induced resistance switching non-volatile memory with Pt/Cu/SiON/TiN/SiO2/Si structure. By inserting a Cu ultra thin film between the SiON layer and Pt top electrode, the device exhibits bipolar resistive switching characteristics after a forming process at 13.6 V. However, the forming and resistive switching process can not be observed in the device if the Cu thin film is omitted. Additionally, we employ a two-step forming process to reduce the forming voltage to 7.5 V. During the forming process, the bias-induced Cu could form a filament-like stretched electrode, but the ¡§set¡¨ and ¡§forming¡¨ voltage of the proposed device take place on different polarity. Therefore, we suppose a bipolar switching mechanism, and our device is dominated by the formation and rupture of the oxygen vacancies in a conduction path between the Cu filament and TiN button electrode. The device also demonstrates stable resistance states during 105 cycling bias pulse operations and acceptable retention characteristics after an endurance test at 85¢J. The I-V switching curves are analyzed to realize the carrier transport mechanisms in different bias regions and resistance states. Additionally, the effective thickness of the resistance switching layers (deff) for the samples with different SiON thickness is also extracted from the related mechanism and demonstrated that the deff is independent with the initial SiON thickness. The corresponding mechanisms and the deff verify the bipolar switching is dominated by the formation and rupture of the oxygen vacancies in conduction path between Cu filament and TiN bottom electrode.
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Novel Symmetric Dielectric Barrier Discharge Atmospheric Pressure Plasma Ion Source for Mass Spectrometry ApplicationsChiang, Cheng-Hung 11 September 2012 (has links)
Qualitative and quantitative analysis of trace substances determined by Mass spectrometry has unique advantages which can¡¦t be replaced. For example, the detection limit of common gas sensors are difficult to lower than 1 ppm, and the sensitivity, selectivity, period of use and stability are not ideal. The detection limit of mass spectrometer is general low to 0.01 ppm. Furthermore, all substances in the sample can be simultaneous analysis by mass spectrometer, but single gas sensor measurements cannot.
In this study, dielectric barrier discharge plasma is used in environmental mass spectrometry analysis. This study develops an innovative balanced T-shaped dielectric barrier discharge (DBD) plasma generator for generating atmospheric plasma to replace the linear type plasma generator. Through the change of the geometric configuration and the drive phase develop T-shaped dielectric barrier discharge plasma, the balanced design can fully cancel the high potential and noise.
The main objective of this study for the more traditional linear electrodes of the study's original novel T-shaped electrodes of different, including mass spectrometry, spectroscopy, and some basic electrical measurements, and by changing the electrode design, voltage, temperature, gas flow, gas flow rate, diameter and other parameters of the dielectric, and compare their differences and to explore the most suitable parameters.
The results showed that T-shaped design of the research and development of innovation through the elimination of the exit pressure put EFI flame can indeed significantly reduce sample oxidation and generate fragments of the situation, and thus improve the mass spectrum of readability and debris interference, thus improving the detection limit , especially for some with a benzene ring and long-chain carbon samples. The experimental results confirm that the development of the Institute of Atmospheric Pressure Plasma free system can be prolonged to produce high concentrations of plasma gas as a free source of the mass spectrometry system, and provides more than 107 cm-3 ion concentration. MS-free analysis of the system can be directly on the gas, liquid and solid samples, the test do not need complicated traditional mass spectrometry analysis of the required sample pre-treatment steps, you can get a clear identification of high mass spectrometry signal. In addition to introducing the basic principles and structure of the atmospheric pressure plasma discharge device, and take advantage of many samples test for the different plasma mass spectrometry free system performance verification.
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Electric field manipulation of polymer nanocomposites: processing and investigation of their physical characteristicsBanda, Sumanth 15 May 2009 (has links)
Research in nanoparticle-reinforced composites is predicated by the promise for
exceptional properties. However, to date the performance of nanocomposites has not
reached its potential due to processing challenges such as inadequate dispersion and
patterning of nanoparticles, and poor bonding and weak interfaces. The main objective
of this dissertation is to improve the physical properties of polymer nanocomposites at
low nanoparticle loading. The first step towards improving the physical properties is to
achieve a good homogenous dispersion of carbon nanofibers (CNFs) and single wall
carbon nanotubes (SWNTs) in the polymer matrix; the second step is to manipulate the
well-dispersed CNFs and SWNTs in polymers by using an AC electric field.
Different techniques are explored to achieve homogenous dispersion of CNFs and
SWNTs in three polymer matrices (epoxy, polyimide and acrylate) without detrimentally
affecting the nanoparticle morphology. The three main factors that influence CNF and
SWNT dispersion are: use of solvent, sonication time, and type of mixing. Once a dispersion procedure is optimized for each polymer system, the study moves to the next
step. Low concentrations of well dispersed CNFs and SWNTs are successfully
manipulated by means of an AC electric field in acrylate and epoxy polymer solutions.
To monitor the change in microstructure, alignment is observed under an optical
microscope, which identifies a two-step process: rotation of CNFs and SWNTs in the
direction of electric field and chaining of CNFs and SWNTs. In the final step, the
aligned microstructure is preserved by curing the polymer medium, either thermally
(epoxy) or chemically (acrylate). The conductivity and dielectric constant in the parallel
and perpendicular direction increased with increase in alignment frequency. The values
in the parallel direction are greater than the values in the perpendicular direction and
anisotropy in conductivity increased with increase in AC electric field frequency. There
is an 11 orders magnitude increase in electrical conductivity of 0.1 wt% CNF-epoxy
nanocomposite that is aligned at 100 V/mm and 1 kHz frequency for 90 minutes.
Electric field magnitude, frequency and time are tuned to improve and achieve desired
physical properties at very low nanoparticle loadings.
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Development of Approach to Estimate Volume Fraction of Multiphase Material Using DielectricsLee, Sang Ick 2010 May 1900 (has links)
Most engineering as well as pavement materials are composites composed of two or
more components to obtain a variety of solid properties to support internal and external
loading. The composite materials rely on physical or chemical properties and volume
fraction of each component. While the properties can be identified easily, the volume
fraction is hard to be estimated due to the volumetric variation during the performance in
the field. Various test procedures have been developed to measure the volume fractions;
however, they depend on subjective determination and judgment. As an alternative,
electromagnetic technique using dielectric constant was developed to estimate the
volume fraction. Empirical and mechanistic approaches were used to relate the
dielectric constant and volume fraction. While the empirical models are not very
accurate in all cases, the mechanistic models require assumptions of constituent
dielectric constants. For those reasons, the existing approaches might produce less
accurate estimate of volume fraction. In this study, a mechanistic-based approach using
the self consistent scheme was developed to be applied to multiphase materials. The
new approach was based on calibrated dielectric constant of components to improve
results without any assumptions. Also, the system identification was used iteratively to
solve for dielectric parameters and volume fraction at each step. As the validation
performed to verify the viability of the new approach using soil mixture and portland
cement concrete, it was found that the approach has produced a significant improvement
in the accuracy of the estimated volume fraction.
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Analytical Techniques and Operational Perspectives for a Spherical Inverted-F AntennaRolando, David Lee 2010 December 1900 (has links)
The spherical inverted-F antenna (SIFA) is a relatively new conformal antenna
design that consists of a microstrip patch resonator on a spherical ground. The SIFA
resembles a planar inverted-F antenna (PIFA) that has been conformally recessed onto a
sphere. The basic design, simulation, and fabrication of a SIFA were recently reported.
The aim of this thesis is to provide a three-fold improvement to the study of the SIFA:
the fabrication of a dielectric-coated SIFA, a new analytical model based on the cavity
method, and the analysis of a randomly oriented SIFA’s operation in a remote
networking scenario.
A key improvement to the basic SIFA design is the addition of a lossy dielectric
coating to the outside of the sphere for purposes of impedance stability, bandwidth
control, and physical ruggedization. The first contribution of this thesis is the fabrication
of such a dielectric-coated SIFA. Two antennas are fabricated: a coated SIFA operating
at 400 MHz, and an uncoated SIFA operating at 1 GHz for comparison. Both SIFAs are
constructed of foam and copper tape; the coating is comprised of silicone rubber and carbon fiber. The fabricated designs perform with reasonable agreement to
corresponding simulations, providing a basic proof of concept for the coated SIFA.
The SIFA was previously studied analytically using a transmission line model.
The second task of this thesis is to present a new model using the cavity method, as
employed in microstrip patches. The SIFA cavity model uses a curvilinear coordinate
system appropriate to the antenna’s unique geometry and is able to predict the antenna’s
performance more accurately than the transmission line model.
The final portion of this thesis examines the performance of the SIFA in a remote
network scenario. Specifically, a line-of-sight link between two SIFAs operating in the
presence of a lossy dielectric ground is simulated assuming that each SIFA is randomly
oriented above the ground. This analysis is performed for both uncoated and coated
SIFAs. A statistical analysis of the impedance match, efficiency, and power transfer
between these antennas for all possible orientations is presented that demonstrates a
design tradeoff between efficiency and predictability.
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Investigation Of Physical Properties Of Different Cake Formulations During Baking With Microwave And Infrared-microwave CombinationSakiyan Demirkol, Ozge 01 January 2007 (has links) (PDF)
The main objective was to determine the variation of physical properties of different cake formulations during baking in microwave and infrared-microwave combination ovens.
In the first part of the study, rheological and dielectric properties of cake batter with different formulations were determined. Different concentrations of fat and different types of emulsifier and fat replacer were used. The variation of formulation had a significant effect on the apparent viscosity of the cake batter. Cake batter was found to show shear thinning and time independent behaviour for all formulations. Dielectric properties of cake batter were dependent on formulation, frequency and temperature.
In the second part of the study, physical properties (dielectric properties, volume, texture, color and porosity) of cakes baked in microwave and infrared-microwave combination oven were determined. In addition, starch gelatinization during baking was investigated. For comparison, cakes were also baked in conventional oven.
Formulation and baking time were found to affect physical properties and gelatinization degree of cakes. Addition of fat to the formulation was found to increase the dielectric properties and gelatinization degree of microwave and infrared-microwave combination baked cakes. For both microwave and combination baking, cake samples with SimplesseTM had the highest volume but the firmest texture. Addition of maltodextrin resulted in a more uniform structure for infrared-microwave combination baking.
There was insufficient gelatinization in microwave baked cakes ranging from 70 to 78% depending on fat content. The gelatinization degree ranged from 88 to 93% in conventionally baked cakes. Combining infrared with microwaves increased gelatinization degree (80-90%).
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Preparation Of Pnzt Thin Films By Solution Deposition And Their CharacterizationKayasu, Volkan 01 February 2008 (has links) (PDF)
The aim of this study is to produce Nb doped PZT thin films and then investigate the
effects of Nb+5 ion on the structural, dielectric and ferroelectric properties. Niobium
(Nb) doped lead zirconate titanate thin films (PNZT) were produced by solution
deposition with nominal compositions, Pb(1-0.5x)(Zr0.53Ti0.47)1-xNbxO3 where x = 0.00 -
0.07. Single and multi-layered films were deposited onto (111)-Pt/Ti/SiO2/Si-(100)
substrates by spin coating. PZT compositions near the morphotropic phase boundary
(MPB) was chosen because excellent ferroelectric and dielectric properties were
achieved in this area.
The effects of sintering temperature, sintering time, variation of thickness in the
films and change of niobium content were investigated with regard to phase
development, microstructure, and ferroelectric and dielectric characteristics. The best
results were obtained in double layered films (390 nm) which were sintered at 600
° / C for 1 h. Grain size of the films decreases with increasing Nb content except for 1
at % Nb doped films. The average grain size of 1 at % Nb doped thin films was
calculated as 130 nm by using FESEM.
Optimum doping level was found in 1 at % Nb doped films. For 1 at % Nb doped
[Pb0.995(Zr0.53Ti0.47)0.99Nb0.01O3] films, remnant polarization (Pr) of 35.75 & / #956 / C/cm2 and
coercive field (Ec) of 75.65 kV/cm have been obtained. The maximum dielectric
constant was achieved in 1 at % Nb doped films which was 689. Tangent loss values
were found between 2-4 % and these values were independent of Nb concentrations.
Ferroelectric and dielectric properties were decreased at higher Nb doping levels
because of the changes in the grain size, distortion of the crystal structure and
pinning of the domains.
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Studies On The Development Of Magnetoelectric Ceramic CompositesBasaran, Yanki 01 June 2008 (has links) (PDF)
The aim of this thesis work was to develop magnetoelectric (ME) composites consisting of piezoelectric and magnetostrictive components. The piezoelectric constituent was selected as a PZT ceramic modified by strontium, bismuth and manganese. The magnetostrictive phase was nickel ferrite (NF) ceramic doped by cobalt, copper and manganese. The properties of component phases were optimized in order to enhance the ME effect in the composite.
In the first part of the thesis, effects of sintering temperature on the dielectric and piezoelectric properties of PZT and on the electrical and magnetic properties of NF ceramics were investigated in the temperature range covered from 1150 to 1250 ° / C. The best piezoelectric properties in PZT were attained at 1250 ° / C. At this sintering temperature, values of piezoelectric strain coefficient, dielectric constant, and electromechanical coupling coefficient were 434 pC/N, 1320 and 0.48, respectively. NF ceramics showed poor densification / 80 %TD was attained at 1250 ° / C. In order to obtain higher densities in ferrites, Bi2O3 was used as a sintering aid. Addition of Bi2O3 enhanced densification up to 97 %TD, and improved electrical and magnetic properties of ferrites. Highest DC-resistivity of 1.15*10^8 ohm-cm and highest magnetostriction of ~26 ppm were attained in NF ceramics doped with 1 wt% Bi2O3.
In the second part of the thesis, ME composites were manufactured either as bulk composites or as laminated composites. The efficiency of different composite types was evaluated in terms of voltage output in response to the applied magnetic field. Higher outputs were observed in laminated composites.
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Investigation Of Dc Generated Plasmas Using Terahertz Time Domain SpectroscopyKaraoglan, Gulten 01 June 2010 (has links) (PDF)
This thesis is on the topic of investigation of the characteristics of DC Glow Discharge plasmas. Emphasis is given on characterizing the plasma electron density. The methods of generating and detecting THz pulses are described. THz transmission spectroscopy and plasma emission spectroscopy is examined. Transmission spectrum is taken for Air, gaseous Nitrogen and Argon plasmas. Moreover, emission spectrum of Air, N2 and Ar plasma analysis were done respectively. It was found that the transmission of terahertz pulses through nitrogen plasma was considerably affected compared to that of the argon plasma. Initially Drude model theory of electron conduction is employed to analyze the plasma density.
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Critical Behaviour Of The Thermodynamic Quantities For The Thermotropic And Ferroelectric Liquid Crystals Close To The Phase TransitionsKilit, Emel 01 February 2011 (has links) (PDF)
The specific heat Cp has been showed at various temperatures in the literature, which shows a
sharp increase labeled as the lambda-transition at the critical temperature. This transition has been
observed previously among the phases of solid-nematic-isotropic liquid in p-azoxyanisole
(PAA) and anisaldazine (AAD), and among the phases of solid-smectic-cholesteric-isotropic
liquid in cholesteryl myristate (CM). In this thesis work, we analyze the experimental data for
the temperature dependence of Cp and the thermal expansion alpha_p and also pressure dependence
of alpha_p by a power-law formula. From the analysis of pressure dependence of alpha_p, we calculate
the temperature dependencies of specific heat Cp and of the isothermal compressibility kappa_T for
the phase transitions considered in PAA, AAD and CM. Our calculations for the temperature
dependence of the p and kappa_T can be compared with the experimental data when available in
the literature.
Polarization, tilt angle and the dielectric constant have been reported in the literature at various
temperatures close to the solid-smectic C*-smectic A-isotropic liquid transition in the
ferroelectric liquid crystals of A7 and C7. The mean field model with the free energy expanded in terms of the order parameters (polarization and tilt angle) has been reported in the
literature previously. In this thesis work, we apply the mean field model first time by fitting
the expressions derived for the temperature dependence of the polarization, tilt angle and
the dielectric constant to the experimental data for A7 and C7 from the literature. Since the
mean field model studied here describes adequately the observed behaviour of A7 and C7, the
expressions for the temperature dependence of the polarization, tilt angle and the dielectric
constant which we derive, can also be applied to some other ferroelectric liquid crystals to
explain their observed behaviour.
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