L’échographie haute résolution est une technique d’imagerie médicale permettant une observation du corps de très bonne définition, à faible profondeur (quelques micromètres). Pour réaliser cela, des ondes ultrasonores sont utilisées (quelques dizaines de mégahertz), produites par l’élément actif de la sonde: un film piézoélectrique. Pour atteindre de telles fréquences, cet élément doit être d’une épaisseur déterminée: de l’ordre de la dizaine de micromètres. Aujourd’hui, le PZT, zirconotitanate de plomb, est le matériau piézoélectrique démontrant les meilleures propriétés pour de telles applications. Mais des évolutions législatives sont en cours pour restreindre son utilisation, du fait des risques que représente le plomb pour la santé et l’environnement. Le défi actuel dans le domaine des matériaux piézoélectriques est de trouver un matériau de substitution. C’est l’objectif de cette étude. Un matériau piézoélectrique sans-plomb choisi dans la littérature, le BHT, ou titanate de baryum dopé à l’hafnium, est étudié, dans le but de remplacer le PZT dans les appareils échographiques. Le procédé sol-gel composite est ensuite utilisé pour sa mise en œuvre sous forme de films épais piézoélectriques. / Ultrasonography is a medical imaging technique that allows exploring, with high resolution, a body in a few micrometers depth. For this purpose, ultrasonic waves , produced with a piezoelectric film, are used. This film must have a thickness of at least few micrometers to yield megahertz waves. Nowadays , PZT , lead zirconate titanate, is the key material for such applications. But since recently, a change has come in lead exploitation. It is recommended by the authorities to use another material when it is possible, which became a big challenge in piezoelectric material researches . Therefore, the aim of this study is to investigate a lead-free piezoelectric material in the purpose to use it in ultrasound echography. The selected material is BHT, barium hafnate titanate, and it is shaped as a thick film using sol-gel composite proceed.

Made available in DSpace on 2014-10-09T12:33:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

abstract: In this research, our goal was to fabricate Josephson junctions that can be stably processed at 300°C or higher. With the purpose of integrating Josephson junction fabrication with the current semiconductor circuit fabrication process, back-end process temperatures (>350 °C) will be a key for producing large scale junction circuits reliably, which requires the junctions to be more thermally stable than current Nb/Al-AlOx/Nb junctions. Based on thermodynamics, Hf was chosen to produce thermally stable Nb/Hf-HfOx/Nb superconductor tunnel Josephson junctions that can be grown or processed at elevated temperatures. Also elevated synthesis temperatures improve the structural and electrical properties of Nb electrode layers that could potentially improve junction device performance. The refractory nature of Hf, HfO2 and Nb allow for the formation of flat, abrupt and thermally-stable interfaces. But the current Al-based barrier will have problems when using with high-temperature grown and high-quality Nb. So our work is aimed at using Nb grown at elevated temperatures to fabricate thermally stable Josephson tunnel junctions. As a junction barrier metal, Hf was studied and compared with the traditional Al-barrier material. We have proved that Hf-HfOx is a good barrier candidate for high-temperature synthesized Josephson junction. Hf deposited at 500 °C on Nb forms flat and chemically abrupt interfaces. Nb/Hf-HfOx/Nb Josephson junctions were synthesized, fabricated and characterized with different oxidizing conditions. The results of materials characterization and junction electrical measurements are reported and analyzed. We have improved the annealing stability of Nb junctions and also used high-quality Nb grown at 500 °C as the bottom electrode successfully. Adding a buffer layer or multiple oxidation steps improves the annealing stability of Josephson junctions. We also have attempted to use the Atomic Layer Deposition (ALD) method for the growth of Hf oxide as the junction barrier and got tunneling results. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2013

Made available in DSpace on 2014-10-09T12:33:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / O presente trabalho realiza a investigação dos parâmetros hiperfinos, incluindo a sua natureza dinâmica, em compostos ligantes em solução a temperatura ambiente (295 K) e resfriada (77K) através da espectroscopia de Correlação Angular γγ Perturbada (CAP). Para a realização das medidas experimentais, utilizou-se núcleos de prova radioativos de 111In111Cd, 181Hf181Ta e 111mCd111Cd, que decaem através de cascata gama. As amostras foram preparadas diluindo-se soluções com os núcleos radioativos em água, quando se investigou a interação do núcleo de prova com o ligante água; adicionando-se soluções com os núcleos radioativos em solução tampão, quando se investigou a interação do núcleo de prova com os íons ligantes provenientes do próprio tampão (CO32- e HCO31-) e com o OH1-; e adicionando-se soluções com os núcleos radioativos em soluções do ligante ácido etilenodiaminotetracético (EDTA), este em pH entre 4,0 e 5,0, (que corresponde ao pH da própria solução saturada do EDTA) e em solução tampão de pH entre 9 e 10. Assim foi possível investigar os efeitos gerados por cada um desses métodos de preparação de amostras nas medidas CAP. Finalmente foi feita uma análise comparativa para os vários métodos de inserção dos núcleos de prova na amostra, considerando-se aspectos químicos e nucleares. A inexistência de medidas para esse tipo de amostra, justifica a importância dos resultados obtidos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Tantalum carbide (TaC) and hafnium carbide (HfC) possess extremely high melting points, around 3900 oC, which are the highest among the known materials. TaC and HfC exhibit superior oxidation resistance under oxygen deficient and rich environments, respectively. A versatile material can be expected by forming solid solutions of TaC and HfC. However, the synthesis of fully dense solid solution carbide is a challenge due to their intrinsic covalent bonding which makes sintering challenging. The aim of the present work is to synthesize full dense TaC-HfC solid solutions by spark plasma sintering with five compositions: pure HfC, HfC-20 vol.% TaC (T20H80), HfC- 50 vol.% TaC (T50H50), HfC- 80 vol.% TaC (T80H20), and pure TaC. To evaluate the oxidation behavior of the solid solutions carbides in an environment that simulates the various applications, an oxygen rich, plasma assisted flow experiment was developed. While exposed to the plasma flow, samples were exposed to a temperature of approximately 2800 oC with a gas flow speed greater than 300 m/s. Density measurements confirm near full density was achieved for all compositions, with the highest density measured in the HfC-contained samples, all consolidated without sintering aids. Confirmation of solid solution was completed using x-ray diffraction, which had an excellent match with the theoretical values computed using Vegard’s Law, which confirmed the formation of the solid solutions. The solid solution samples showed much improved oxidation resistance compared to the pure carbide samples, and the T50H50 samples exhibited the best oxidation resistance of all samples. The thickness of the oxide scales in T50H50 was reduced more than 90% compared to the pure TaC samples, and more than 85% compared to the pure HfC samples after 5 min oxidation tests. A new Ta2Hf6O17 phase was found to be responsible for the improved oxidation performance. Additionally, the structure of HfO2 scaffold filled with molten Ta2O5 was also beneficial to the oxidation resistance by limiting the availability of oxygen.

In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS-determined mean U-Pb radiogenic isotopic ratios of 0.084743 +/- 0.000027 for Pb-206/U-238 and 0.67676 +/- 0.00023 for Pb-207/U-235 (weighted means, 2s uncertainties). Its Pb-206/U-238 age of 524.36 +/- 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The delta O-18 value (determined by laser fluorination) is 8.26 +/- 0.06 parts per thousand VSMOW (2s), and the mean Hf-176/Hf-177 ratio (determined by solution ICP-MS) is 0.282396 +/- 0.000004 (2s). The SIMS-determined delta Li-7 value is -0.6 +/- 0.9 parts per thousand (2s), with a mean mass fraction of 1.0 +/- 0.1 mu g g(-1) Li (2s). Zircon M127 contains similar to 923 mu g g(-1) U. The moderate degree of radiation damage corresponds well with the time-integrated self-irradiation dose of 1.82 x 10(18) alpha events per gram. This observation, and the (U-Th)/He age of 426 +/- 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U-Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.

Hafnium based high-κ dielectrics are considered potential candidates to replace SiO2 or SiON as the gate dielectric in complementary metal oxide semiconductor (CMOS) devices. Hydrogen is one of the most significant elements in semiconductor technology because of its pervasiveness in various deposition and optimization processes of electronic structures. Therefore, it is important to understand the properties and behavior of hydrogen in semiconductors with the final aim of controlling and using hydrogen to improve electronic performance of electronic structures. Trap transformations under annealing treatments in hydrogen ambient normally involve passivation of traps at thermal SiO2/Si interfaces by hydrogen. High-κ dielectric films are believed to exhibit significantly higher charge trapping affinity than SiO2. In this thesis, study of hydrogen trapping in alternate gate dielectric candidates such as HfO2 during annealing in hydrogen ambient is presented. Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) were used to characterize these thin dielectric materials. It was demonstrated that hydrogen trapping in bulk HfO2 is significantly reduced for pre-oxidized HfO2 prior to forming gas anneals. This strong dependence on oxygen pre-processing is believed to be due to oxygen vacancies/deficiencies and hydrogen-carbon impurity complexes that originate from organic precursors used in chemical vapor depositions (CVD) of these dielectrics.

The material class of hafnium oxide-based ferroelectrics adds an unexpected and huge momentum to the long-known phenomenon of pyroelectricity. In this thesis, a comprehensive study of pyroelectric and electrocaloric properties of this novel ferroelectric material class is conducted. hafnium oxide is a lead-free, non-toxic transition metal oxide, and abundant in the manufacturing of semiconductor devices. The compatibility to existing fabrication processes spawns the possibility of on-chip infrared sensing, energy harvesting, and refrigeration solutions, for which this dissertation aims to lay a foundation. A screening of the material system with respect to several dopants reveals an enhanced pyroelectric response at the morphotropic phase boundary between the polar orthorhombic and the non-polar tetragonal phase. Further, a strong pyroelectric effect is observed when applying an electric field to antiferroelectric-like films, which is attributed to a field-induced transition between the tetragonal and orthorhombic phases. Primary and secondary pyroelectric effects are separated using high-frequency temperature cycles, where the effect of frequency-dependent substrate clamping is exploited. The piezoelectric response is determined by comparing primary and secondary pyroelectric coefficients, which reproduces the expected wake-up behavior in hafnium oxide films. Further, the potential of hafnium oxide for thermal-electric energy conversion is explored. The electrocaloric temperature change of only 20 nm thick films is observed directly by using a specialized test structure. By comparing the magnitude of the effect to the pyroelectric response, it is concluded that defect charges have an important impact on the electrocaloric effect in hafnium oxide-based ferroelectrics. Energy harvesting with a conformal hafnium oxide film on a porous, nano-patterned substrate is performed, which enhances the power output. Further, the integration of a pyroelectric energy harvesting device in a microchip for waste heat recovery and more energy-efficient electronic devices is demonstrated. High dielectric breakdown fields of up to 4 MV/cm in combination with a sizable pyroelectric response and a comparably low dielectric permittivity illustrate the prospect of hafnium oxide-based devices for future energy conversion applications.

Atomic layer deposition (ALD) is a technique by which surface-based reactions between a precursor molecule (often metal-containing) and a co-reactant (e.g. H2O, O2 or H2) yield highly uniform and conformal (ultra-)thin films. The precursor and co-reactant are each delivered in the gas phase, separated from one another by inert gas purge steps. The self-limiting nature of these surface-based reactions allows the thickness of the film to be controlled solely by the number of ‘precursor – purge – co-reactant – purge’ cycles. This nano-scale control of film thickness allows for a large number of applications such as in flat panel displays, fuel and solar cells, and microelectronic devices. The first goal of this project was the pursuit of new low-temperature methods for main group elemental ALD using silyl-substituted precursor molecules. The second goal of the project was the development of alternative methods for thin film deposition of group 4 (M = Hf, Zr) oxides that would encourage effective (ie. void-free) filling of narrow (<20 nm) trenches in high-aspect-ratio (HAR) substrates. This thesis includes the development of new precursor molecules and reaction pathways, evaluation of precursor molecular structures, thermal stability, volatility and solution reactivity, identification of appropriate experimental conditions for ALD, and characterization of the resulting thin films. ALD of elemental antimony was achieved on hydrogen-terminated silicon (H-Si) and SiO2/Si substrates using Sb(SiMe3)3 (2-1) and SbCl3 in the temperature range 23- 65 °C. The mirror-like films were confirmed to be composed of crystalline antimony by XPS (for the film deposited at 35 °C) and XRD, with low impurity levels and strong preferential orientation of crystal growth relative to the substrate surface. To the best ofour knowledge, this is the first example of room temperature thermal ALD (with demonstrated self-limiting growth) of a pure element. Film growth at 35 °C exhibited a substrate-enhanced mechanism, characterized by faster film growth for the first ~125 ALD cycles, where substantial deposition is occurring on the original substrate surface (GPC (growth-per-cycle) = 1.3 Å on SiO2/Si, and 1.0 Å on H-Si), and slower film growth (GPC = 0.40 Å on SiO2/Si, and 0.27 Å on H-Si) after ~125 cycles, once much of the initial substrate surface has been covered. Films deposited using 500-2000 ALD cycles were shown to be continuous by SEM. The use of less than 250 cycles afforded discontinuous films. However, in this initial growth phase, when deposition is occurring primarily on the original substrate surface, in-situ surface pre-treatment by Sb(SiMe3)3 or SbCl3 (50 x 0.4 or 0.8 s pulses), followed by the use of longer precursor pulses (0.4 or 0.8 s) during the first 50 ALD cycles resulted in improved nucleation. For example, on H-Si, a continuous 6.7 nm thick film was produced after initial pre-treatment with 50 x 0.8 s pulses of SbCl3, followed by 50 ALD cycles using 0.8 s pulses. The use of longer ALD pulses in the first 50 ALD cycles following surface pre-treatment is likely required in order to achieve complete reactivity with an increased density of reactive surface sites. Boranes featuring bulky silyl or sterically unencumbered trimethylgermyl groups, in combination with a stabilizing dimethylamido group, were pursued as potential precursors for ALD of elemental boron. This ALD process would employ a boron trihalide (BX3; X = F, Cl, Br, I) co-reactant, exploiting the thermodynamically favourable formation of tetrel-halide bonds as a driving force. This work required multistep syntheses of alkali metal silyl reagents, {(Me3Si)3Si}Li(THF)2 (3-1) and tBu3SiNa(THF)n (3-2), and previously un-isolated [Me3GeLi(THF)2]2 (3-3), and their reactions with B(NMe2)Cl2 (3-4). The boranes {(Me3Si)3Si}2B(NMe2) (3-8) and (tBu3Si)(Me3Ge)B(NMe2) (3-12) were successfully synthesized, spectroscopically and crystallographically characterized, and assessed for their suitability as precursor molecules for boron ALD. Unfortunately, deposition attempts on SiO2/Si using 3-8 and BCl3 led to minor film growth (GPC = 0.01 Å). However, the enhanced volatility and solution-state reactivity of 3-12 in comparison to 3-8 makes it a promising precursor candidate for future ALD reactor studies. Attempts to synthesize bis(trimethylgermyl)(dimethylamido)borane from the 2:1 reaction of 3-3 with 3-4 resulted in the formation of a lithium trigermylamidoborate, {(Me3Ge)3B(NMe2)}Li(THF)2 (3-13). ALD can give rise to uniquely uniform and conformal ultra-thin films, but voids often remain after attempted filling of narrow high-aspect-ratio trenches. To achieve void-free trench-filling, ALD (or CVD; chemical vapour deposition) methods which deposit a flowable material are desirable, and this initially-deposited material can be converted to the target material (e.g. a metal oxide) by post-deposition annealing, or potentially at the deposition temperature on a longer timescale than flowable behaviour. In this work, a new HfO2 ALD process was developed using [Hf(NMeEt)4] in combination with β- hydroxyisovaleric acid (IVA; CMe2(OH)CH2CO2H) that introduces the potential for flowability. Self-limiting growth was observed at 100, 250, and 300 °C, with a GPC of 1.5- 2.2 Å on planar SiO2 substrates. Films deposited at 100 °C consisted of amorphous HfO2 with significant carbon content (~22 at%) and <1 at% nitrogen. After annealing at 400 °C in vacuo for 1 hour, the films were composed of amorphous HfO2 with low (<1 at%) carbon content. The co-reactant in this work, β-hydroxyisovaleric acid, was chosen with the following criteria in mind: Firstly, the carboxylic acid group may be sufficiently acidic to cleave linkages between chemisorbed hafnium species and the surface, generating flowable non-surface-tethered hafnium carboxylate species (with low volatility, so that they are not lost from the surface). Secondly, the hydroxyl groups of the ligands can potentially serve as reactive sites for the hafnium precursor delivered in the next pulse. Thirdly, fairly low-energy pathways should exist for deprotonated IVA ligands to decompose to generate oxide or hydroxide ligands with release of volatile by-products, such as CO2 and isobutene, or acetone and ketene. Experiments to gain insight into the nature of reactivity between [Hf(NMeEt)4] and IVA and a structurally similar carboxylic acid are described. These include (a) solution-state reactions between [Hf(NMeEt)4] and IVA or pivalic acid (tBuCO2H), with formation of [H2NMeEt]2[Hf(κ2-O2CCH2CMe2OH)2(κ2- OC(O)CH2CMe2O)2] (4-1) and [Hf5(μ3-O)4(κ2-O2CtBu)4(μ-O2CtBu)8] (4-2), (b) attempted ALD using pivalic acid (which lacks a hydroxyl group) in place of IVA, and (c) roomtemperature solution reactions between [Hf(NMeEt)4] and 4 equiv. of IVA to form 4-1, followed by removal of volatiles, heating at 200 °C, and volatile/soluble product analysis by NMR spectroscopy and GC-MS headspace analysis. Compounds 4-1 and 4-2 were isolated and crystallographically characterized. Heteroleptic zirconium(IV) complexes were designed, synthesized, spectroscopically and crystallographically characterized, and assessed as potential precursor molecules to enable flowable ZrO2 ALD. The envisaged process would operate via the deposition of oligomeric, one-dimensional chains that, if grown untethered on a functionalized substrate, could potentially flow to the bottoms of trenches. Reaction of one equivalent of H2(acen), H2(cis-Cyacen) or H2(trans-Cyacen) with [Zr(CH2SiMe3)4] at room temperature afforded [Zr(acen)(CH2SiMe3)2] (5-1), [Zr(cis-Cyacen)(CH2SiMe3)2] (5-2) or [Zr(trans-Cyacen)(CH2SiMe3)2] (5-3), respectively (acen = C2H4(NCMeCHC(O)Me)2; Cyacen = 1,2-C6H10(NCMeCHC(O)Me)2). These alkyl compounds are trigonal prismatic in the solid state, and whereas 5-1 and 5-3 decomposed without sublimation above 120 °C (5-10 mTorr), 5-2 sublimed in >95% yield at 85 °C (5-10 mTorr). However, heating solid 5-2 at 88 °C under static argon for 24 hours resulted in extensive decomposition to afford H2(cis-Cyacen) and SiMe4 as the soluble products. Compound 5-2 reacted cleanly with two equivalents of tBuOH to afford [Zr(cis-Cyacen)(OtBu)2] (5-4), but excess tBuOH caused both SiMe4 and H2(cis-Cyacen) elimination. The 1:1 reaction of H2(acen) with [Zr(NMeEt)4] did not proceed cleanly, and 8-coordinate [Zr(acen)2] (5-5) was identified as a by-product; this complex was isolated from the 2:1 reaction. A zirconium amido complex, [Zr(acen)(NMeEt)2] (5-6) was accessed via the reaction of 1 with two equiv. or excess HNMeEt, but decomposed readily in solution at room temperature. More sterically hindered [Zr(acen){N(SiMe3)2}2] (5-7) was synthesized via the reaction of [Zr(acen)Cl2] with two equivalents of Li{N(SiMe3)2}, but was also thermally unstable as a solid and in solution at room temperature. Compounds 5-1 to 5-3, 5-5 and 5-7 were crystallographically characterized. / Dissertation / Doctor of Science (PhD) / The focus of this work is the development of new processes to deposit ultra-thin films of main group elements and transition metal oxides. The deposition method utilized in this work is atomic layer deposition (ALD), which involves the use of a precursor molecule (which contains the target element) and a co-reactant. These chemical species must be appropriately reactive towards one another, and display adequate volatility and thermal stability. The feasibility of a precursor/co-reactant combination can be assessed using solution-state reactivity studies. For main group element ALD, silyl-containing compounds (E(SiR3)3, E = Sb, B) have been investigated as precursors in combination with EX3 (X = F, Cl, Br, I) coreactants, due to the potential for thermodynamically favourable Si-X bond formation to drive the required surface-based reactions. For metal oxide ALD (MO2; M = Hf, Zr), new ALD methods have been proposed to enable gap-free filling of narrow trenches on the surface of a silicon wafer. This work involved the design, synthesis, and evaluation of new ALD precursor molecules and reactions, ALD reactor studies for thin film deposition, and characterization of the resulting films.

<p>As a scalable and CMOS compatible novel ferroelectric material, the ferroelectric HZO thin film has been the promising material for various applications and continues to attract the attention of researchers. Achieving strong ferroelectricity and fast switching speed in ultrathin FE HZO film are crucial challenges for its applications towards scaled devices.</p> <p>The ferroelectric and anti-ferroelectric properties of HZO are investigated systematically down to 3 nm. The ferroelectric polarization, switching speed and the impact of ALD tungsten nitride electrodes are studied. Record high Pr on FE HZO and record high PS on AFE HZO are achieved with WN electrodes, especially in ultrathin sub-10 nm regime. The polarization switching speed of FE and AFE HZO, associated with C-V frequency dispersion, are also qualitatively studied. On the other side of the scaling limit, ferroelectric/dielectric stack superlattice structure is found to enhance the ferroelectricity in thick films which would have severely degraded.</p> <p>Ultrafast direct measurement on the transient ferroelectric polarization switching is used to study the switching speed in FE HZO with a crossbar MFM structure. Sub-nanosecond characteristic switching time of 925 ps was achieved, supported by the nucleation limited switching model. The impact of electric field, film thickness and device area on the polarization switching speed is systematically studied. The ferroelectric switching speed is significantly improved compared to previous reports and more importantly is approaching GHz regime, suggesting FE HZO to be competitive in high-speed non-volatile memory technology. Record fast polarization switch speed of 360 ps is obtained in sub-μm crossbar array FE HZO MFM devices. It also unveils that domain wall propagation speed in HZO is the limiting factor for switch speed and more aggressively scaled devices will offer much faster switch speed.</p> <p>The first experimental determination of nucleation time and domain wall (DW) velocity by studying switching dynamics of ferroelectric (FE) hafnium zirconium oxide (HZO) was performed. Experimental data and simulation results were used to quantitatively study the switching dynamics. The switching speed is degraded in high aspect ratio devices due to the longer DW propagation time or with dielectric interfacial layer due to the required additional tunneling and trapping time by the leakage current assist switch mechanism.</p>