Journal of Telecommunications and Information Technology, 2007, nr 2

kwartalni

Defect Induced Aging and Breakdown in High-k Dielectrics

abstract: High-k dielectrics have been employed in the metal-oxide semiconductor field effect transistors (MOSFETs) since 45 nm technology node. In this MOSFET industry, Moore’s law projects the feature size of MOSFET scales half within every 18 months. Such scaling down theory has not only led to the physical limit of manufacturing but also raised the reliability issues in MOSFETs. After the incorporation of HfO2 based high-k dielectrics, the stacked oxides based gate insulator is facing rather challenging reliability issues due to the vulnerable HfO2 layer, ultra-thin interfacial SiO2 layer, and even messy interface between SiO2 and HfO2. Bias temperature instabilities (BTI), hot channel electrons injections (HCI), stress-induced leakage current (SILC), and time dependent dielectric breakdown (TDDB) are the four most prominent reliability challenges impacting the lifetime of the chips under use. In order to fully understand the origins that could potentially challenge the reliability of the MOSFETs the defects induced aging and breakdown of the high-k dielectrics have been profoundly investigated here. BTI aging has been investigated to be related to charging effects from the bulk oxide traps and generations of Si-H bonds related interface traps. CVS and RVS induced dielectric breakdown studies have been performed and investigated. The breakdown process is regarded to be related to oxygen vacancies generations triggered by hot hole injections from anode. Post breakdown conduction study in the RRAM devices have shown irreversible characteristics of the dielectrics, although the resistance could be switched into high resistance state.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Nanoscale characterisation of dielectrics for advanced materials and electronic devices

PhD ThesisStrained silicon (Si) and silicon-germanium (SiGe) devices have long been recognised for their enhanced mobility and higher on-state current compared with bulk-Si transistors. However, the performance and reliability of dielectrics on strained Si/strained SiGe is usually not same as for bulk-Si. Epitaxial growth of strained Si/SiGe can induce surface roughness. The typical scale of surface roughness is generally higher than bulk-Si and can exceed the device size. Surface roughness has previously been shown to impact the electrical properties of the gate dielectric. Conventional macroscopic characterisation techniques are not capable of studying localised electrical behaviour, and thus prevent an understanding of the influence of large scale surface roughness. However scanning probe microscopy (SPM) techniques are capable of simultaneously imaging material and electrical properties. This thesis focuses on understanding the relationship between substrate induced surface roughness and the electrical performance of the overlying dielectric in high mobility strained Si/SiGe devices. SPM techniques including conductive atomic force microscopy (C-AFM) and scanning capacitance microscopy (SCM) have been applied to tensile strained Si and compressively strained SiGe materials and devices, suitable for enhancing electron and hole mobility, respectively. Gate leakage current, interface trap density, breakdown behaviour and dielectric thickness uniformity have been studied at the nanoscale. Data obtained by SPM has been compared with macroscopic electrical data from the same devices and found to be in good agreement. For strained Si devices exhibiting the typical crosshatch morphology, the electrical performance and reliability of the dielectric is strongly influenced by the roughness. Troughs and slopes of the crosshatch morphology lead to degraded gate leakage and trapped charge at the interface compared with peaks on the crosshatch undulations. Tensile strained Si material which does not exhibit the crosshatch undulation exhibits improved uniformity in dielectric properties. Quantitative agreement has been found for leakage at a device-level and nanoscale, when accounting for the tip area. The techniques developed can be used to study individual defects or regions on dielectrics whether grown or deposited (including high-κ) and on different substrates including strained Si on insulator (SSOI), strained Ge on insulator (SGOI), strained Ge, silicon carbide (SiC) and graphene. Strained SiGe samples with Ge content varying from 0 to 65% have also been studied. The increase in leakage and trapped charge density with increasing Ge extracted from SPM data is in good agreement with theory and macroscopic data. The techniques appear to be very sensitive, with SCM analysis detecting other dielectric related defects on a 20% Ge sample and the effects of the 65% Ge later exceeding the critical thickness (increased defects and variability in characteristics). Further applications and work to advance the use of electrical SPM techniques are also discussed. These include anti-reflective coatings, synthetic chrysotile nanotubes and sensitivity studies.Overseas Research Students Awards Scheme (ORSAS), School International Research Scholarship (SIRS), Newcastle University International Postgraduate Scholarship (NUIPS) and the Strained Si/SiGe platform grant

Program and abstract volume

The primary aim of the conference is to assess the state of the art and reliability of micro-Raman spectroscopy as well as luminescence-based spectroscopy and microscopy and related techniques in Earth and planetary sciences.Spanish National Research Council, Lunar and Planetary Institutescientific organizing committee Javier Garcia-Guinea (Chair)PARTIAL CONTENTS: Cystine-Apatite Renal Calculi: EPMA, Raman and ESEM-CL Study / A. Iordanidis, J. Garcia-Guinea, and V. Correcher -- Molecular Characterization of a Temperate Beachrock Formation in the Nerbioi-Ibaizabal Estuary (Arrigunaga Beach, Bay of Biscay) / A. Iturregi, N. Arrieta, I. Martinez-Arkarazo, X. Murelaga, J. I. Baceta, A. Sarmiento, and J. M. Madariaga -- Thermoluminescence and Shock Metamorphism of Ordinary Chondrites / A. I. Ivliev, V. A. Alexeev, and N. S. Kuyunko -- Spectra Cathodoluminescence and Crystal Lattice: Cerite Versus Whitlockite / A. Jorge, J. Garcia-Guinea, L. Tormo, M. Furio, A. Fernandez-Cortes, S. Cuezva, and S. Sanchez-Moral -- New Raman Spectroscopic Data of Almahata Sitta Meteorite / M. Kaliwoda, R. Hochleitner, V. H. Hoffmann, T. Mikouchi, A. M. Gigler, and W. W. Schmahl -- Thermoluminescence as One of the Methods for Determination of the Crystal Lattice Structure of Quartz / L. L. Kashkarov, G. V. Kalinina, and S. N. Shilobreeva -- Optical Absorption, Cathodo- and Radioluminescence in Diaspore / M. I. Kati, M. Turemis, I. C. Keskin, B. Tastekin, M. Hatipoglu, R. Kibar, A. Cetin, and N. Can -- In Situ Study of a Collection of 20 Meteorites Using Raman Spectroscopy / Th. Katsaros and Th. Ganetsos -- Clarification of Shock-Induced Effect on Cathodoluminescence of Alkali Feldspar / M. Kayama, H. Nishido, T. Sekine, T. Nakazato, A. Gucsik, and K. Ninagawa -- Characterization of Radiation Effects in Albite by Cathodoluminescence / M. Kayama, H. Nishido, S. Toyoda, K. Komuro, and K. Ninagawa -- Thermoluminescence of the Blue and White Chalcedony from Turkey / I. C. Keskin, M. I. Kati, M. Turemis, B. Tastekin, R. Kibar,A. Cetin, and N. Can -- Structure and Luminescence Characteristics of Aquamarine from Turkey / R. Kibar, M. I. Kati, A. Cetin, M. Turemis, I. C. Keskin, B. Tastekin, M. Hatipoglu, and N. Can -- Compositional Analyses of F, Cl and OH by Raman Spectroscopy in Apatite from Mafic-Ultramafic Pipes of the Ivrea Verbano Zone (NW Italy) / P. Kollegger, F. Zaccarini, R. J. Bakker, G. Garuti, and O. A. R. Thalhammer

Synthesis and Properties of Ferroelectric Perovskite Oxide Thin Films

The growth of oxide thin films has long been of great interested for materials scientists for the application in advanced technologies such as nanoelectronics, photovoltaics and sensors. Atomic layer deposition (ALD) is known for being a non-expensive, low-vacuum and low-temperature deposition method able to conformally coat even high-aspect-ratio materials and structures. ALD has been mainly applied to prepare binary oxides such as ZnO and TiO2, and the synthesis of functional complex oxides such as BiFeO3 and CoFe2O4 has little been studied. In the first part of this work, the application of ALD to the preparation of complex oxide thin films based on the Bi-Fe-O system is explored. The important aspects of the ALD approach such as (a) the growth of amorphous Bi-Fe-O by ALD, (b) the epitaxial crystallization of the multiferroic perovskite BiFeO3 films on different substrates, (c) appearance of impurity phases in the films are addressed. Ultimately, the dissertation aims at dispelling the widely held notion that atomic layer deposition is not appropriate for attaining high-quality chemically complex oxide films in the epitaxial form, demonstrating the applicability as an inexpensive, facile, and highly scalable route. The second part of this work is devoted to the preparation and characterization of new ferroelectric thin films as photovoltaic materials. Large optical band gaps of ferroelectric oxides make the optical absorption impractical for solar cell applications. Recently a new strategy for band gap lowering by doping the perovskite KNbO3 with Ba on the A-site and Ni on the B-site resulting in the generation of Ni2+-O vacancy pairs has been shown to significantly increase the optical absorption without loss of ferroelectricity. Using pulsed laser deposition, the synthesis approach to thin films of these new oxides was developed despite significant challenges for the stoichiometry control. The chemical doping approach to the reduction of the band gap was extended to produce new visible-light-absorbing ferroelectric thin films in another perovskite oxide. These materials showed a switchable photovoltaic effect under the visible light illumination along with the retention of the ferroelectric order. This dissertation demonstrates the feasibility of thin film deposition of aforementioned doped ferroelectric oxide perovskites and their ferroelectric photovoltaic properties, which can be extended to other ferroelectric oxides, and provide important information on the synthesis of such materials as thin films.Ph.D., Materials Science and Engineering -- Drexel University, 201

The mineralogical deportment of radionuclides in South Australian Ca-Au-(U) ores

Iron-oxide copper gold (IOCG)-uranium deposits represent South Australia’s primary resource base for copper production. The presence of daughter radionuclides (RN) from the 238U decay series within the ores necessitates a detailed understanding of their mineralogical deportment as a pre-requisite for attempts to remove or reduce RN concentrations. Research presented in this thesis contributes towards this knowledge by identifying and characterising potential RN-carriers, migration of radiogenic lead via geological processes, and provides evidence for RN sorption during processing. Novel approaches to RN reduction are proposed based on mineralogical-geochemical results. Evidence for migration of Pb within the deposit and during processing is relevant for any assessment of RN deportment, especially since the Pb-chalcogenides galena, clausthalite (PbSe) and altaite (PbTe) are often hosted within Cu-(Fe)-sulphides. Lead isotope values measured in-situ by laser ablation inductively coupled plasma mass spectrometry suggest an overwhelmingly radiogenic origin for Pb and thus extensive decoupling of radiogenic Pb from parent U- and Th-minerals. Calculated 207Pb/206Pb ratios suggest Pb mobilisation during an event that postdates the initial Mesoproterozoic Fe-Cu-Au-U mineralisation event, an interpretation consistent with other studies in the Olympic Cu-Au province which indicate cycles of replacement-remobilization-recrystallization. A nanoscale study of the most common of the three Pb-chalcogenide minerals, clausthalite, by high-angle annular dark field scanning transmission electron microscopy, proved highly instructive for identifying mechanisms of remobilization and overprinting. Characteristic symplectite textures involving clausthalite and host Cu-(Fe)-sulphides are indicative of formation via reaction between Se that pre-existed in solid solution within Cu-(Fe)-sulphides and migrating Pb. Observed superstructuring of clausthalite nanoparticles within chalcopyrite provides a direct link between solid solution and symplectite formation. Sr-Ca-REE-bearing aluminium-phosphate-sulphates (APS) of the alunite supergroup are a minor component of the Olympic Dam orebody. They appear paragenetically late, often replacing earlier REE-minerals. Characterisation of these compositionally zoned phases allowed them to be defined as minerals that span the compositional fields of woodhouseite and svanbergite, and also a REE- and phosphate-dominant group displaying solid solution towards florencite. A nanoscale secondary ion mass spectrometry study of RN distributions in APS minerals in acid-leached copper concentrate revealed that APS minerals readily sorb products of 238U decay, notably 226Ra and 210Pb, whereas U remains in solution. Many APS phases, particularly those that are Pb-bearing, are stable over a wide range of pH and Eh conditions and at temperatures up to 450 °C. As such, synthetic APS phases represent viable candidates not only for the removal of radionuclides from metallurgical streams, but also for their safe storage and isolation from surrounding environments. Ca-Sr-dominant phases display preferential enrichment by Pb (notably 210Pb) during flotation. 210Pb uptake then increases during subsequent acid leaching. Mixed Ca- and Sr-bearing APS phases were synthesised by modifying existing recipes to test the role of compositional variability of APS phases on the sorption rate of Pb from dilute Pb(NO3)2 solution. Lead incorporation by the synthetic APS phases was confirmed, whereby Pb replaces Ca, but not Sr, within the APS crystal structure. Extended X-ray absorption fine structure analysis of the resulting solids reveals the nature of Pb sorption by the synthesized material. The data showed that the dynamic incorporation of Pb by APS phases occurred overwhelmingly at pH 3.5, thus verifying that uptake of Pb by synthetic APS phases may represent a robust mechanism to achieve both reduction and immobilisation of 210Pb within metallurgical processing streams.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering & Advanced Materials, 202

Piezotronic Bicrystals and Hexagonal Nano-Platelets: A TEM Study on Structure and Chemistry of Functionalized Zinc Oxide

TEM and SEM investigations of piezotronic ZnO bicrystals were conducted with the aim to study the relationship between interface structure and electrical properties. In this context, the term “piezotronic” refers to the manipulation and tuning of electrostatic potential barriers at doped varistor-type grain boundaries via piezoelectric charges generated upon mechanical load. To this end, varistor-type inversion-boundary bicrystals were synthesized in tail-to-tail (000-1)|(000-1) or head to head (0001)|(0001) orientation with respect to the c axis, providing an optimized piezotronic response for load applied in directions. Different synthesis methods are compared and specific tilt configurations as well as undoped reference bicrystals were examined. Furthermore, ZnO nanocrystals, i.e., hexagonal platelets and rod shaped twins, were investigated, as both the bicrystals and the nanocrystals hold a large potential for functionalization and the development of novel devices. Finally, the dopant-related varistor-effect itself, which underlies the piezotronic applications, is – despite decades of research – still not completely elucidated and the examined bicrystals are well suited model systems for respective studies on specific dopant/grain-boundary situations. Since the varistor-effect is attributed to potential barriers at doped grain-boundaries, respective interfaces were investigated by atomic-resolution HAADF STEM; the main method in this thesis, capable of delivering structural as well as chemical information. These measurements were complemented with conventional TEM, ABF STEM, electron diffraction and EDS methods in order to fully characterize the bicrystals as well as control and verify their successful synthesis. The TEM results were interpreted with respect to the findings from corresponding electrical measurements. In doing so, the focus laid upon the successful doping with bismuth, which is essential to obtain varistor behavior and hence, for the subsequent piezotronic manipulation. As a main result, it was found that doping with Bi, being insoluble in ZnO, is by no means trivial and demands appropriate synthesis procedures and/or bicrystal configurations, which provide suitable segregation sites. Otherwise, Bi retracts from the interfaces and forms electrically inactive secondary phases. The presence of such segregation sites was found to be related to the respective structural coherence of the grain boundary. While highly coherent interfaces did not feature any significant Bi doping, semi- or incoherent interfaces exhibited a clear Bi decoration, which was also reflected by the electrical measurements revealing the absence or occurrence of varistor behavior, respectively. The required incoherency could be introduced either via a special synthesis procedure (epitaxial solid-state transformation) leading to a strongly curved defect-rich interface or by applying specific tilt configurations to diffusion-bonded bicrystals with a flat interface. The latter comprises two different cases: Semi-coherent configurations, where a coincidence-site lattice (CSL) is formed and CSL points act as semi-periodic segregation sites, and highly incoherent situations, where the interface structure is strongly and irregularly disordered. In addition to the structural characterization, thermodynamic aspects were considered, indicating that all three types of Bi-segregation (curved, flat semicoherent, flat incoherent) can be explained qualitatively by applying Gibbs adsorption isotherm, which describes the lowering of surface or interface energies depending on the decoration by impurity atoms. Due to the special case of an insoluble dopant, which is available in a quasi-infinite reservoir with respect to the limited amount of segregation sites, the segregation of Bi depends only on a) the energy difference between the undecorated and decorated interface, and b) the actual quantity of segregation sites. Both a) and b) are higher for incoherent interfaces and approach zero for the case of maximum coherency. The TEM results as well as the thermodynamic considerations were found to be not only in perfect agreement with previous ZnO bicrystal studies but also with comparable situations in other, completely different material systems. In consequence, they are considered to be applicable to all cases of interfacial segregation of insoluble dopants. The main goal behind the synthesis of the hexagonal ZnO platelets is their self-assembled tessellation upon Langmuir-Blodgett deposition. However, a synthesis route needed to be established first. TEM investigations were performed in order to characterize the obtained mineralization products and provide feedback for the optimization of the synthesis. In doing so, the same methods as for the bicrystals could be employed, in particular, ABF STEM and NBED for determining the absolute direction of the c-axis. This was an important issue for both the hexagonal platelets, where inversion twinning needed to be ruled out, as well as for the rod shaped twins, whose twinning character could be identified this way. In addition, the TEM investigations revealed a surface coverage of the hexagonal facets by residuals from the precipitation process. In consequence, an additional calcination step was added to the synthesis procedure, which was shown to successfully remove this coverage and simultaneously increase the quality of the surfaces from rough to almost atomically flat. Regarding the rod-shaped twins, actually a side-product of the synthesis experiments, the TEM findings revealed a situation similar to the piezotronic inversion-boundary bicrystals. In all cases, the crystallites were found to be accurate tail-to-tail inversion twins with anti-parallel c-axes and a disordered interface, probably capable of incorporating dopants such as Bi. In consequence, they are seen as holding potential for further development in their own right, especially against the background that the original “piezotronics” were established based on ZnO nanocrystals (nanowires)