Submitted by Nilton Francelosi Azevedo Neto (nilton@fc.unesp.br) on 2018-11-22T13:54:33Z No. of bitstreams: 1 Azevedo Neto- Tese POSMAT-2018.pdf: 3312025 bytes, checksum: 69a53514543bbe65b47c2fd62ddb6168 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-11-22T16:48:03Z (GMT) No. of bitstreams: 1 azevedoneto_nf_dr_bauru.pdf: 3312025 bytes, checksum: 69a53514543bbe65b47c2fd62ddb6168 (MD5) / Made available in DSpace on 2018-11-22T16:48:03Z (GMT). No. of bitstreams: 1 azevedoneto_nf_dr_bauru.pdf: 3312025 bytes, checksum: 69a53514543bbe65b47c2fd62ddb6168 (MD5) Previous issue date: 2018-09-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A motivação para este trabalho foi buscar uma melhor compreensão sobre o processo de crescimento dos filmes de óxido de cobalto pela técnica de DC magnetron sputtering reativo. Os filmes de interesse foram depositados sobre substratos de sílica amorfa (a -SiO2 ), aluminato de lantânio (LaAlO3 ) e safira - c (Al2O3- c) usando diferentes valores de potência de deposição e fluxo de oxigênio . As condições de crescimento dos filmes foram analisadas utilizando simulação computacional do processo de sputtering reativo baseada no modelo de Depla, medidas da emissão óptica das espécies presentes no plasma e monitor amento da taxa de crescimento através de uma microbalança de quartzo. Os resultados de difração de raios X mostraram que em baixa potência é obtida a fase Co3O4 espinélio, enquanto que em alta potência os filmes apresentaram a fase CoO cúbica . A s simulações computacionais do processo de sputtering reativo indicaram que , quando as potências de deposição são baixas, o processo de crescimento dos filmes ocorre com o alvo no regime “envenenado” . Em contraste, altas potencias favorece m o regime metálico do alvo. Medidas de emissão do plasma de deposição mostraram que em baixa potência de deposição a intensidade da linha de emissão do oxigênio é alta , porém com o aumento da potência sua intensidade diminui e a d a linha do cobalto aumenta. O s filmes de Co 3 O 4 depositados sobre substratos cristalinos apresentaram resultados promissores . Medidas de difração de raios X de alta resolução , utilizando radiação síncrotron , indicaram que a deposição do Co 3 O 4 sobre Al2O3 - c resultou em crescimento epitaxial na qual a direção [ 111] do cristal de Co 3 O 4 é perpendicular à superfície do substrato de safira - c (0001). Enquanto que a deposição sobre LaAlO 3 resultou em crescimento com forte textura de orientação, com as direções [220] e [400] perpendiculares à superfície dos substratos . Os espectros Raman dessas amostras apresentaram picos de vibração bem definidos e característicos da fase Co 3 O 4 e a análise do Raman polarizado do s filmes de Co 3 O 4 sobre Al 2 O 3 - c concorda m com as regras de seleção para a orientação [111] . Para os filmes c om fase Co 3 O 4 , medidas de transmitância na região do UV - Vis - NIR mostraram alta absorção na região do visível e bandas de absorção no infravermelho próximo relacionadas a transições eletrônicas dos íons de Co 2+ e Co 3+ . Para esse crescimento observou - se também resposta intensa de fotocondutividade com exc itação em 405 nm e 532 nm em 10 K. Testes preliminares de fotocatálise indicaram que os filmes de Co 3 O 4 produzidos possuem uma pequena atividade fotocatalítica para degradação do corante Rodamina B. Neste trabalho uma correlação direta entre as condições de crescimento e as mudança s de fase do s filmes foi obtida, demonstrando a versatilidade da técnica de sputtering para crescimento de filmes de óxido de cobalto para estudos científicos e aplicações tecnológicas. / The motivation for this work was to obtain a better understanding of the growth process of cobalt oxides by the DC magnetron reactive sputtering technique. The films were dep osited on amorphous silica (a-SiO2), lanthanum aluminate (LaAlO3) and sapphire-c (c-Al2O3) substrates using different values of deposition power and oxygen flow. The conditions of growth of the films were analyzed using the optical analysis of the species present in the plasma and the monitoring of the growth rate through a quartz microbalance. The X-ray diffraction results showed that at lower powers the Co3O4 phase was obtained, while at high er power s the films presented the CoO cubic phase. The computational simulations of the reactive sputtering process indicated that, at low deposition power, the gro wth process of the films occurs with the target in the "poisoned" regime, while in high powers it favors the metallic regime of the target. Plasma emission measurements showed that at low deposition power the oxygen intensity is high while at high power it s intensity decreases and that of cobalt increases. The Co 3 O 4 films deposited on crystalline substrates showed promising results. High - resolution X-ray diffraction measurements using synchrotron radiation indicated that the deposition of Co3O4 on c-Al2O3 resulted in epitaxial growth , in which the direction [111] is perpendicular to the surface of the c - sapphire (0001) substrates. However, the deposition on LaAlO 3 resulted in growth with strong texture in the directions [220] and [400]. The Raman spectra of these samples showed well - defined vibration peaks characteristic of the Co3O4 phase . The polarized Raman analysis of Co 3 O 4 deposited on c-Al2O3 agrees with the selection rules for the [111] orientation, in agreement with the high resolution X-ray diffraction analysis . In the optical transmittance measurements , t he films with Co 3 O 4 phase displayed high absorption bands in the region of the visible and near - infrared . These bands are related to el ectronic transitions of the Co2+ and Co3+ ions. For these films , strong photoconductivity responses were observed for excitations at 405 nm and 532 nm at 10 K . Preliminary photocatalysis tests indicated that the Co3O4 films produced by sputtering have a small photocatalytic activity for Rhodamine B (RhB) dye degradation. Concluding , a direct correlation between the growth conditions and the phase changes of the films was obtained, demonstrating the versatility of the sputtering technique for the growth of cobalt oxide films for scientific studies and technological applications.

Reactive Sputtering is a widely used technique in processing of thin compound films. Such films can be sputtered from metal targets, which are comparatively cost efficient. Also the fact that sputtering from metal targets can ccur in the dc mode reduces the cost of the sputtering equipment. To keep the deposition process stable, its necessary to know the effects of target poisoning including its hyteresis behavior. The aim of this work was to nvestigate the evolution of reactive gas coverage on a titanium magnetron target surface, by real time, in-situ ion beam analysis during magnetron sputtering. A cylindrical 2 inch magnetron was used for reactive sputtering of TiN. It was operated in an Ar/N2 gas mixture at achamber pressure of about 3∙10-3 mbar. The argon/nitrogen flux ratio was variated between 0 and 20%. The nitrogen concentration on the target was determinated using the 14N(d, α)12C, nuclear reaction at a deuterium beam energy of 1.8 MeV. Depending on the adjusted nitrogen flow the target incorporation varies between 0 and about 1∙1016 N∙cm-2. Further the expected hysteresis behaviour ofnitrogen partial pressure, target voltage and nitrogen concentration at increasing/decreasing nitrogen gas flow is confirmed. The lateral distribution of nitrogen was measured across the diameter of target surface. In the zone of higher erosion (the \"race track\") the nitrogen concentration is 50% lower than in the middle or the edge of the target. A deposition zone in the center of the target could not be detected. By increasing the nitrogen flow into the chamber a saturation in nitrogen content in the target was found at an Ar/N2 flow ratio of about 10%. Assuming nitrogen implantation with a depth of 2.5 nm under the influence of typical target voltage during magnetron sputtering, this saturation is at a concentration value where stoichiomtric TiN is formed. Within the precision of the measurements, a mobile fraction of nitrogen could not determined. The concentration in the target remains unchanged after switching off the magnetron.

The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult. In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low. In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth. / Report code: LiU-TEK-LIC-2007:1.

<p>The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al₂O₃, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.</p><p>In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr₂O₃ nucleation layer. Moreover, it was found that an additional requirement for the formation of the <em>α</em> phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of <em>α</em> alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline <em>α</em>-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10^-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.</p><p>In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the <em>α</em> phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.</p> / Report code: LiU-TEK-LIC-2007:1.

The explosive development of the telecom industry and in particular wireless and mobile communications in recent years has lead to a rapid development of new component and fabrication technologies to continually satisfy the mutually exclusive requirements for better performance and miniaturization on the one hand and low cost on the other. A fundamental element in radio communications is time and frequency control, which in turn is achieved by high performance electro-acoustic components made on piezoelectric single crystalline substrates. The latter, however, reach their practical limits in terms of performance and cost as the frequency of operation reaches the microwave range. Thus, the thin film electro-acoustic technology, which uses thin piezoelectric films instead, has been recently developed to alleviate these deficiencies. This thesis explores and addresses a number of issues related to thin film synthesis on the one hand as well as component design and fabrication on other. Specifically, the growth of highly c-axis textured AlN thin films has been studied and optimized for achieving high device performance. Perhaps, one of the biggest achievements of the work is the development of a unique process for the deposition of AlN films with a mean c-axis tilt, which is of vital importance for the fabrication of resonators operating in contact with liquids, i.e. biochemical sensors. This opens the way for the development of a whole range of sensors and bio-analytical tools. Further, high frequency Lamb wave resonators have been designed, fabricated and evaluated. Performance enhancement of FBAR devices is also addressed, e.g. spurious mode suppression, temperature compensation, etc. It has been demonstrated, that even without temperature compensation, shear mode resonators operating in a liquid still exhibit an excellent performance in terms of Q (200) and coupling (~1.8%) at 1.2 GHz, resulting in a mass resolution better than 2 ng cm-2 in water, which excels that of today’s quartz sensors.

Cu2ZnSnS4 (CZTS) is a thin film solar cell material that only contains abundant elements and for which promising conversion efficiencies of 9.2 % have been shown. In this thesis composition measurements and reactive sputtering of precursors for CZTS films have been studied. These precursors can be annealed to create high quality CZTS films. Accurate control and measurement of composition are important for the synthesis process. The composition of a reference sample was determined using Rutherford backscattering spectroscopy. This sample was thereafter used to find the composition of unknown samples with x-ray fluorescence measurements. Pros and cons with this approach were discussed. The reactive sputtering process, and the resulting thin films, from a CuSn- and a Zn-target sputtered in H2S-atmosphere were investigated and described. A process curve of the system was presented and the influence of sputtering pressure and substrate temperature were examined. The pressures tested had little influence on the film properties but the substrate temperature affected both composition and morphology, giving less Zn, Sn and S and a more oriented film with increasingly facetted surface for higher temperatures. The precursors produced with this method are suggested to have a disordered phase with randomized cations, giving a CZTS-like response from Raman spectroscopy but a ZnS-pattern from x-ray diffraction measurements. The films have an excellent homogeneity and it is possible to achieve stoichiometric sulfur content. The complete steps from precursors, to annealed films, to finished solar cells were investigated for three controlled compositions and three substrate temperatures. The films sputtered at room temperature cracked when annealed and thus gave shunted solar cells. For the samples sputtered at higher temperatures the trend was an increased grain size for higher copper content and increased temperature. However, no connection between this and the electrical properties of the solar cells could be found.

L’objectif de ce travail est de déterminer expérimentalement les paramètres d’entrée des logiciels de simulation, puis de comparer les résultats expérimentaux et numériques pour différents métaux ainsi que pour leurs oxydes. La configuration GLAD a été volontairement choisie pour les structures inclinées particulières qu’elle permet.Le processus de formation de dépôt en phase vapeur (PVD) peut être divisé en trois étapes : l'éjection d'atomes de la cible, le transport vers le substrat et la croissance des couches minces. Chacune est simulée par un logiciel : SRIM pour l’éjection de matière de la cible suite à l’impact avec un ion, SIMTRA pour le transport des atomes de la cible jusqu’au substrat et Simul3D pour la croissance des dépôts. L’évolution des propriétés des couches inclinées (angle d’inclinaison des colonnes β, épaisseur de la couche, contraintes résiduelles, etc) en fonction de la position et de l’angle d’orientation du substrat est étudiée.Les résultats expérimentaux et numériques se complètent mutuellement et permettent une meilleure compréhension des nombreux aspects de l’étude. / The objective of the present work is to determine experimentally the input parameters of the modelling software and then to compare experimental and numerical results in the case of different metals and their oxides. The GLAD configuration was deliberately chosen for the particular angled structures it allows.The Physical Vapor Deposition (PVD) process can be divided in three steps: ejection of atoms from the target, transport to the substrate and growth of the thin films. Different softwares have been developed for each step: SRIM is a computer program that calculates the interactions of energetic ions; SIMTRA simulates the transport of the atoms from the target to the substrate and Simul3D simulates the growth of the film. The evolution of the thin angled films’ properties (column tilt angles β, thickness, residual stress, etc.) versus the orientation of the substrate is studied.The experimental and numerical results complement each other and allow a better understanding of the many aspects of the study.

Le but de ce travail de thèse est d’étudier les propriétés d’un plasma réactif ainsi que les caractéristiques structurales, optiques et électriques de couches minces d’oxynitrure de tantale (TaOxNy) élaborées par pulvérisation cathodique radiofréquence. L’élaboration de ce matériau ternaire par pulvérisation d’une cible de tantale au moyen d’un plasma contenant à la fois de l’argon, de l’oxygène et de l’azote est complexe en raison de phénomènes d’empoisonnement de la cible. L’analyse de la composition du plasma par spectroscopie d’émission optique et le suivi de l’évolution de certaines raies représentatives d’espèces excitées dans le milieu, nous ont permis de déterminer les conditions optimales au dépôt de films de types TaOxNy sur une large gamme de compositions. Grâce à une étude par diffraction des rayons X et spectroscopie de photoélectrons X, nous avons suivi les évolutions structurales de couches ayant subi ou non un recuit thermique. Nous avons montré de quoi étaient constituées les parties amorphes et cristallisées de ces films et déterminé la taille des domaines de cohérence. Enfin, les propriétés optiques (indice de réfraction, gap optique, paramètre d’Urbach) et diélectriques ont été corrélées à la structure des matériaux. / The aim of this thesis is to study the properties of a reactive plasma as well as the structural, optical and electrical properties of tantalum oxynitride thin films (TaOxNy) prepared by radiofrequency sputtering. The elaboration of this ternary material by sputtering a pure tantalum target using plasma containing both of argon, oxygen and nitrogen is complex due to the target-poisoning phenomenon. The analysis of the composition of the plasma by optical emission spectroscopy and monitoring the evolution of some representative line of excited species in this environment, allow us to determine the optimal conditions to deposit TaOxNy films over a wide range of composition. Thanks to a study by X-ray diffraction and X-ray photoelectron spectroscopy, we followed the structural evolution of the films subjected or not to a rapid thermal annealing. We showed by what were constituted the amorphous and crystalline parts of the films and determined the size of the crystalline domains. Finally, the optical properties (refractive index, optical gap, Urbach parameter) and dielectric behavior have been correlated with the structure of materials.

O óxido de zinco é um material semicondutor que apresenta alta transparência óptica no espectro visível, alta energia de ligação de éxcitons e piezoeletricidade. Por suas propriedades, ele é utilizado na área de sensores, eletrodos transparentes e dispositivos optoeletrônicos. No entanto, sua utilização ainda é limitada pela dificuldade de obtenção de condutividade tipo p, cujo principal dopante é o nitrogênio, devido à assimetria de dopagem ocasionada por defeitos intrínsecos do material, dopagem em valências diferentes das esperadas e formação de níveis de aceitadores profundos na banda proibida. A aplicação em dispositivos piezoelétricos também exige alta resistividade e ótimas propriedades cristalinas. Muitos processos de deposição estabelecidos hoje ainda utilizam altas temperaturas, o que impede sua deposição sobre superfícies ou substratos sensíveis a altas temperaturas. O objetivo deste trabalho é desenvolver técnicas de deposição de filmes de ZnO, principalmente em baixas temperaturas ( 100°C), pelo método de magnetron sputtering de rádio frequência, para avaliar a influência dos gases de processo nas características estruturais, estequiométricas, elétricas e ópticas dos filmes. Para isso, foram obtidos filmes utilizando pressão total de argônio, e pressões parciais de argônio e oxigênio e argônio e nitrogênio, utilizando alvo cerâmico de óxido de zinco ou alvo metálico de zinco. Para alvo de ZnO, filmes com condutividade tipo n foram obtidos em ambiente de argônio, em condições que geraram deficiências de oxigênio. Filmes altamente resistivos foram obtidos com a utilização de pressão parcial de oxigênio no gás de processo, em condições que resultaram em filmes estequiométricos, inclusive com condutividade tipo p. Condutividade tipo p mais alta foi observada, apenas por ponta quente, para uma amostra obtida em argônio logo após a utilização de nitrogênio na câmara de processo, que provavelmente sofreu influência da dopagem não intencional do cobre, que foi identificado como um contaminante do processo devido à estrutura da câmara. Para alvo de Zn, observou-se a formação de nitreto de zinco, que demonstrou alta capacidade de oxidação em ambiente atmosférico, e portanto, transforma-se naturalmente ao longo do tempo ou por processos de oxidação térmica em ZnO dopado com nitrogênio. Filmes de ZnO produzidos a partir de nitreto de zinco foram os únicos dos testados que apresentaram fotoluminescência característica do ZnO, mesmo para processos onde não houve aquecimento intencional. / Zinc oxide is a multifunctional semiconductor, which presents high optical transparency in the visible range, high exciton binding energy and piezoelectricity. Due to its properties, ZnO is used in several areas, such as sensors, transparent electrodes and optoelectronics. However, its usage is still limited by the lack of p-type conductivity, which is very difficult to achieve because of intrinsic material defects, unwanted valence states of doping elements and formation of deep acceptor levels. Piezoelectric devices also demand high electrical resistivity and excellent crystallographic properties. Many current deposition processes still apply high temperatures, preventing material deposition onto temperature sensitive substrates and surfaces. The main goal of this investigation is to develop low temperature ( 100°C) deposition techniques by radio frequency magnetron sputtering, to evaluate the influence of process gases in structural, stoichiometric, electrical and optical properties. Thin films were obtained using either pure argon, argon and oxygen or argon and nitrogen partial pressures, by sputtering ceramic ZnO or metallic Zn targets. For ZnO target, n-type conductivity was achieved in argon environment, by creating oxygen deficient films. High resistivity was observed by using oxygen partial pressure, resulting in stoichiometric material and changing carrier type from electrons to holes. Higher p-type conductivity was observed, only by Seebeck measurement, for a nonintentionally heavily doped sample, as there was copper originating from the deposition chamber. For Zn target, zinc nitride formation was observed, showing high capability of transforming itself into nitrogen-doped ZnO by air exposure or thermal annealing. ZnO films produced from zinc nitride were the only ones that exhibited photoluminescence, even when there was no intentional heating involved.

The requirements of the consumer market on high frequency devices have been more and more demanding over the last decades. Thus, a continuing enhancement of the devices’ performance is required in order to meet these demands. In a macro view, changing the design of the device can result in an improvement of its performance. In a micro view, the physical properties of the device materials have a strong influence on its final performance. In the case of high frequency devices based on piezoelectric materials, a natural way to improve their performance is through the improvement of the properties of the piezoelectric layer. The piezoelectric material studied in this work is AlN, which is an outstanding material among other piezoelectric materials due to its unique combination of material properties. This thesis presents results from experimental studies on the synthesis of AlN thin films in view of telecom, microelectronic and sensor applications. The main objective of the thesis is to custom design the functional properties of AlN to best suit these for the specific application in mind. This is achieved through careful control of the crystallographic structure and texture as well as film composition. The piezoelectric properties of AlN films were enhanced by doping with Sc. Films with different Sc concentrations were fabricated and analyzed, and the coupling coefficient (kt2) was enhanced a factor of two by adding 15% of Sc to the AlN films. The enhancement of kt2 is of interest since it can contribute to a more relaxed design of high frequency devices. Further, in order to obtain better deposition control of c-axis tilted AlN films, a new experimental setup were proposed. When this novel setup was used, films with well-defined thicknesses and tilt uniformity were achieved. Films with such characteristics are very favorable to use in sensors based on electroacoustic devices operating in viscous media. Studies were also performed in order to obtain c-axis oriented AlN films deposited directly on Si substrates at reduced temperatures. The deposition technique used was HiPIMS, and the results indicated significant improvements in the film texture when comparing to the conventional Pulsed DC deposition process.