Neste trabalho, apresento um estudo sobre a fabricação e caracterização físico-química de filmes finos de nitreto de alumínio (AlN) obtidos pela técnica de pulverização catódica reativa por rádio frequência (r.f sputtering) utilizando um alvo de alumínio puro. Visto que o AlN é um material que apresenta piezoeletricidade e compatibilidade com a tecnologia MOS, o objetivo principal desse trabalho é definir os parâmetros de processo de deposição que resultem em um material com propriedades adequadas para sua utilização como elemento atuador e/ou sensor em sistemas micro eletromecânicos (MEMS). O estudo da influência dos parâmetros de processo foi realizado em três etapas. Na primeira realizei um estudo preliminar sobre a influência da pressão de processo e potência de r.f. Na segunda etapa realizei um estudo sobre a influência da relação entre o gás reativo (N2) e o pulverizante (Ar) nas características físicoquímicas do material. Na 3º etapa estudei o efeito da temperatura de deposição nas características do filme que apresentou as propriedades mais propícias para aplicações em MEMS. Propriedades como índice de refração, composição química e stress residual não apresentaram grandes variações com a mudança da composição gasosa da atmosfera de deposição, no entanto, os resultados de difração de raios-X mostraram que os filmes obtidos com 30% de N2 possuem maior cristalização na direção que apresenta maior piezoeletricidade, sendo assim, mais favorável para ser utilizado como sensor/atuador na fabricação de MEMS. No estudo sobre o efeito da temperatura de deposição verificamos que o filme crescido a 250°C apresentou as melhores propriedades para as aplicações em MEMS desejadas. Para finalizar o trabalho a constante piezoelétrica de carga foi obtida utilizando capacitores de placas paralelas de molibdênio e o AlN como dielétrico, obtendo um coeficiente piezoelétrico de carga d33 de 0,5 pm/V. / I present a study on the production and physicochemical characterization of aluminum nitride thin films (AlN) obtained by r.f. reactive magnetron sputtering, using a target of pure aluminum. Since AlN is a material that presents piezoelectricity and compatibility with MOS technology, the main objective of this work is to define the process parameters that will result in a material with properties suitable for its use as an actuator / sensor in micro electromechanical systems (MEMS). The process parameters influence study was performed in three steps. First I conducted a preliminary study on pressure process and rf power influence. In the second step was studied the influence of the reactive (N2) and sputtering (Ar) gas ratio on the material physical and chemical properties. Last but not least, I studied the temperature deposition effects in the AlN thin film obtained in the gas ratio which presented the most favorable properties for MEMS applications. Properties such as refractive index, chemical composition and residual stress did not show considerable variations with changing in the atmosphere deposition, however X-ray diffraction results showed films obtained with 30% N2 have higher crystallization in (002) direction, which is the one with greater piezoelectricity response and thus, more favorable to be used as sensor / actuator in MEMS fabrication. The study on deposition temperature effects has shown maximum (002) crystallization direction is achieved in films grown at 250° C. Piezoelectric coefficient was defined using parallel plate capacitors method using AlN as dielectric resulted in a d33 piezoelectric coefficient of 0,5 pm/V.

The temperature coefficient of frequency (TCF), electromechanical coupling coefficient (K2) and surface acoustic wave (SAW) velocity are the major factors when choosing the substrates for surface acoustic wave devices. There exist a wide range for the designer to controll the above factors. This thesis adopted several methods to change the properties of SAW devices. First, the SAW velocity is increased using aluminum nitride (AlN) thin films deposited on z-cut LiNbO3 substrates. Besides, the ST-quartz is adopted as substrate for comparison to clarify the temperature characteristic of AlN itself. The well-known positive TCF material, silicon dioxide (SiO2), is also deposited on z-cut LiNbO3 substrates for the purpose of improving the TCF of SAW devices. Finally, the optimal piezoelectric bilayer structures will be conducted for the improvement of the properties of SAW devices on LiNbO3 substrate. AlN and SiO2 thin films are selected to be deposited on z-cut LiNbO3 and ST-cut quartz substrates using the reactive RF magnetron sputtering. The characteristics of AlN thin films are evaluated using the analyses of XRD, SEM and AFM. The optimized growth parameters of highly c-axis oriented AlN films deposited on LiNbO3 substrate are sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. On the other hand, the optimal parameters for highly c-axis oriented AlN films deposited on quartz substrate are sputtering pressure of 15 mTorr, nitrogen concentration of 30%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. In addition, the interdigital transducers (IDTs) are fabricated on LiNbO3, AlN/LiNbO3, SiO2/LiNbO3, quartz and AlN/quartz substrates, respectively. The characteristic parameters of SAW devices are measured by Hewlett-Packard (HP) 8720 network analyzer. For SiO2/LiNbO3 SAW devices, the SiO2 thin films reveal the compensation of TCF, but the surface wave velocity remain almost unchanged. For AlN/quartz SAW devices, the positive temperature coefficient of AlN is clarfied by taking ST-quartz substrates as comparison. For AlN/LiNbO3 SAW devices, the characteristic improvements of frequency increase and TCF compensation of LiNbO3 SAW devices are achieved at the same time.

The need for post-CMOS nanoelectronics has led to the investigation of innovative device structures and materials. Graphene, a zero bandgap semiconductor with ballistic transport properties, has great potential to extend diversification and miniaturization beyond the limits of CMOS. The goal of this work is to study the growth of graphene on SiC using the novel method of selective graphitization. The major contributions of this research are as follows - First, epitaxial graphene is successfully grown on selected regions of SiC not capped by AlN deposited by molecular beam epitaxy. This contribution enables the formation of electronic-grade graphene in desired patterns without having to etch the graphene or expose it to any detrimental contact with external chemicals. Etching of AlN opens up windows to the SiC in desirable patterns for subsequent graphitization without leaving etch-residues (determined by XPS). Second, the impact of process parameters on the growth of graphene is investigated. Temperature, time, and argon pressure are the primary growth-conditions altered. A temperature of 1400oC in 1 mbar argon for 20 min produced the most optimal graphene growth without significant damage to the AlN capping-layer. Third, first-ever electronic transport measurements are achieved on the selective epitaxial graphene. Hall mobility of about 1550 cm2/Vs has been obtained to date. Finally, the critical limitations of the selective epitaxial graphene growth are enumerated. The advent of enhanced processing techniques that will overcome these limitations will create a multitude of opportunities for applications for graphene grown in this manner. It is envisaged to be a viable approach to fabrication of radio-frequency field-effect transistors.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 126-147). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 168-180).

Studies have been done to determine rare-earth elements’ optical and luminescent properties using wide bandgap nitride semiconductors as suitable hosts. Research done here will contribute to the information needed to further study rare-earth elements and their unique properties. Thin films of rare-earth elements erbium, terbium, ytterbium, and both erbium and ytterbium doped into AlN are studied by laser excitation. A 532 nm Nd: YAG green laser and 783nm crystal infrared laser are used for excitation in conjunction with a spectrometer to measure photoluminescence. With the 532 nm laser, AlN: Er emits peaks at 554 nm, 561 nm, and 1552 nm, AlN: Tb emits peaks at 549 nm and 562 nm, AlN: Yb emits peaks at 966 nm, and co-doped AlN: ErYb contains peaks including both AlN: Er and AlN: Yb. Energy transfer occurred from Er to Yb resulting in an increased magnitude and peak shift. The 783 nm laser gave peaks at 1563nm for AlN: Er, 1508 nm and 1533 nm for AlN: Tb, and 1567nm for AlN: ErYb. No detectable peaks were given for AlN: Yb. A peak shift was detected in comparison of AlN: Er and AlN: ErYb. A magnetic field of 1000 G was applied to AlN: ErYb resulting in an increase in intensity of the major peak at 561nm with a splitting, creating a secondary peak at 564.5 nm. Biomedical applications can be used from the high penetration ability of lower wavelength lasers and the use of a magnetic field, which is not harmful to the human body. Enhanced green emission in erbium can be useful in future optical, photonic, and electrical devices. / Department of Physics and Astronomy

Thin film technology is of great significance for a variety of products, such as electronics, anti-reflective or hard coatings, sensors, solar cells, etc. This thesis concerns the synthesis of thin functional films, reactive magnetron sputter deposition process as such and the physical and functional characterization of the thin films synthesized. Characteristic for reactive sputtering processes is the hysteresis due to the target poisoning. One particular finding in this work is the elimination of the hysteresis by means of a mixed nitrogen/oxygen processing environment for dual sputtering of Alumina-Zirconia thin films. For a constant moderate flow of nitrogen, the hysteresis could be eliminated without significant incorporation of nitrogen in the films. It is concluded that optimum processing conditions for films of a desired composition can readily be estimated by modeling. The work on reactively sputtered SiO2–TiO2 thin films provides guidelines as to the choice of process parameters in view of the application in mind, by demonstrating that it is possible to tune the refractive index by using single composite Six/TiO2 targets with the right composition and operating in a suitable oxygen flow range. The influence of the target composition on the sputter yield is studied for reactively sputtered titanium oxide films. It is shown that by using sub-stoichiometric targets with the right composition and operating in the proper oxygen flow range, it is possible to increase the sputter rate and still obtain stoichiometric coatings. Wurtzite aluminum nitride (w-AlN) thin films are of great interest for electro-acoustic applications and their properties have in recent years been extensively studied. One way to tailor material properties is to vary the composition by adding other elements. Within this thesis (Al,B)N films of the wurtzite structure and a strong c-axis texture have been grown by reactive sputter deposition. Nanoindentation experiments show that the films have nanoindentation hardness in excess of 30 GPa, which is as hard as commercially available hard coatings such as TiN. Electrical properties of w-(Al,B)N thin films were investigated. W-(Al,B)N thin films are found to have a dielectric strength of ~3×106 V/cm, a relatively high k-value around 12 and conduction mechanisms similar to those of AlN. These results serve as basis for further research and applications of w-(Al,B)N thin films. An AlN thin film bulk acoustic resonator (FBAR) and a solidly mounted resonator (SMR) together with a microfluidic transport system have been fabricated. The fabrication process is IC compatible and uses reactive sputtering to deposit piezoelectric AlN thin films with a non-zero mean inclination of the c-axis, which allows in-liquid operation through the excitation of the shear mode. The results on IC-compatibility, Q-values, operation frequency and resolution illustrate the potential of this technology for highly sensitive low-cost micro-biosensor systems for applications in, e.g. point-of-care testing.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xiii, 109 p. : ill. Includes abstract. Includes bibliographical references (p. 102-109).

Thesis (PhD)--Macquarie University, School of Mathematics, Physics, Computing and Electronics, 1999. / "1998"--T.p. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 107-111). Also available on the Internet.