Yu Wei-jian. / Thesis submitted in: November 2000. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 70-71). / Text in English; abstracts in English and Chinese. / Yu Wei-jian. / TITLE PAGE --- p.i / THESIS COMMITTEE --- p.ii / ABSTRACT (English) --- p.iii / ABSTRACT (Chinese) --- p.iv / ACKNOWLEDGEMENTS --- p.v / TABLE OF CONTENTS --- p.vi / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.ix / Chapter CHAPTER 1 --- INTRUDUCTION --- p.1 / Chapter Section 1.1 --- Background of the BN System --- p.1 / Chapter 1.1.1 --- Desirable Properties of c-BN --- p.1 / Chapter 1.1.2 --- Phases in the BN System --- p.2 / Chapter 1.1.3 --- Phase Diagram of BN --- p.4 / Chapter 1.1.4 --- Synthesis Techniques for c-BN Films --- p.5 / Chapter 1.1.5 --- Characterization of BN Films --- p.6 / Chapter Section 1.2 --- Background of Theory --- p.7 / Chapter Section 1.3 --- Objectives --- p.9 / Chapter 1.3.1 --- Determination of Stable State of BN --- p.9 / Chapter 1.3.2 --- Phonon-dispersion Relations of BN --- p.9 / Chapter 1.3.3 --- "Phase (p, T) Diagram" --- p.10 / Chapter 1.3.4 --- Transformation Paths in Direct Compressions --- p.10 / Chapter Section 1.4 --- Roadmap --- p.11 / Chapter CHAPTER 2 --- METHODS --- p.12 / Chapter Section 2.1 --- Density Functional Theory (DFT) for E0 Calculation --- p.12 / Chapter Section 2.2 --- Direct Force-constant Method --- p.16 / Chapter Section 2.2 --- Quasi-harmonic Approximation --- p.26 / Chapter CHAPTER 3 --- RESULTS --- p.27 / Chapter Section 3.1 --- Stable State of BN --- p.27 / Chapter Section 3.2 --- Phonon-dispersion Relations --- p.29 / Chapter Section 3.3 --- "Phase (p, T) Diagram of BN" --- p.36 / Chapter Section 3.4 --- Transformation Paths via Direct Compression --- p.44 / Chapter 3.4.1 --- Direct Compression of h-BN and r-BN --- p.46 / Chapter 3.4.2 --- Direct Compression of t-BN --- p.50 / Chapter Section 3.5 --- Energy Barriers in the Transformation of h-BN to c-BN --- p.52 / Chapter CHAPTER 4 --- DISCUSSION --- p.58 / Chapter Section 4.1 --- Transition States in the Transformation of h-BN to c-BN --- p.58 / Chapter Section 4.2 --- Phonon-dispersion Relations --- p.60 / Chapter Section 4.3 --- Phase Diagrams --- p.62 / Chapter Section 4.4 --- Future Studies --- p.63 / Chapter 4.4.1 --- Cubic BN Films Formation --- p.63 / Chapter 4.4.1.1 --- Nanoarches Nucleation --- p.64 / Chapter 4.4.1.2 --- Growth: Interfaces Between h-BN {0001} and c-BN Planes --- p.64 / Chapter 4.4.2 --- Transformation Paths of w-BN to c-BN and h-BN to r-BN --- p.65 / Chapter CHAPTER 5 --- CONCLUSION --- p.66 / APPENDIX: Mechanistic Models in c-BN Films Formation --- p.67 / REFERENCES --- p.70

TiN is used commercially as a wear resistant coating on cutting tools and as a diffusion barrier in microelectronics. TiN has gained increased interest as a material for MEMS, however there has been very little work carried out in the area of patterning and releasing TiN for use as a structural MEMS material. This thesis presents an investigation into the patterning and release of filtered arc deposited TiN thin films using surface micromachining techniques. Two novel strategies are presented for patterning TiN thin films and are achieved using excimer laser micromachining and photolithographic wet-etching. TiN was deposited onto single crystal Si and Cr and Cu sacrificial layers on Si. The use of Cr as a sacrificial layer was found to facilitate the best quality patterning of the TiN and hence the majority of the work involved using Cr sacrificial layers. TiN was deposited using partial filtration and full filtration and differences in the ability to selectively laser pattern the TiN from the Cr sacrificial layer are presented. Various analytical techniques were employed to investigate the origin of the difference in laser patterning the TiN thin films. The establishment of TiN and Cr as a novel material combination for surface micromachined MEMS was extended by etching the Cr sacrificial layer to facilitate the release of TiN stress-measurement structures. The major finding of this thesis is that filtered arc deposited TiN thin film on Cr can be used as a material combination to surface micromachine freestanding TiN structures as high quality patterning and etch selectivity can be achieved using both excimer laser micromachining and photolithographic wet-etching.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Graduation date: 1995

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.

Polycrystalline AlN thin films were reactively deposited onto Al layers on negatively biased glass and Si substrates at temperatures < 80 oC by coherent magnetron sputtering. The target-to-substrate distance is 17 cm. The microstructures and morphology of the films grown at different bias voltages on the substrates were investigated. Typical thickness of the deposited film is 600 nm. The films were amorphous when no bias was applied to the substrates. Diffraction peak of AlN (002) direction was observed at bias voltages of -180 and -210 V. At a bias voltage of -210 V, the (002) granular crystal with the maximum diameter of 80 nm was obtained. In addition to the AlN (002) direction, AlN (100) direction was observed when the bias voltage was increased to -240 and -270 V. The peak of (002) plane vanished at a bias voltage of -320 V. Moreover, the deposited AlN films have specular reflectance owning to the large target-to-substrate distance. The maximum roughness of the films was 47.2¡Ó5.0 nm at a bias voltage of -210 V. The hardness and microstructure of aluminum nitride (AlN) thin films prepared by long-distance magnetron sputtering at room temperature has been investigated. The hardness and microstructure of the films were found to vary greatly with different substrate biases. At a bias voltage of ¡V210 V, the (002) polycrystalline AlN with the maximum hardness of 17.5 GPa was observed. The water droplet contact angle under this bias condition is larger than 90¢X indicating that hydrophobicity can be obtained at the film surface. In addition, hardness of (002) AlN films prepared by sputtering of AlN target at room temperature and by reactive sputtering of Al target at 400¢XC were discussed and compared with that of AlN films prepared by long-distance reactive sputtering.

Silicon and silicon nitride thin films were growth on Si and glass substrates at room temperature by ratio-frequency (r-f) magnetron sputtering. The electrical characteristics of the silicon nitride films were characterized using I-V and C-V measurement under different growth condition, including r-f power, nitrogen partial pressure, and hydrogen partial pressure. Minimum current leakages for MIS structure as low as 2¡Ñ10 A/cm were obtained at 1 MV/cm electrical field with hysteresis voltage about 2V. The root-mean square surface roughness of the silicon nitride film is less then 1nm. In addition, silicon nitride capacitors with indium-tin-oxide as electrodes were fabricated. Silicon thin films prepared by R.F. magnetron sputtering at room temperature are amorphous. The measurements on the variation of the photo-conductivity were used to characterize the characteristics of the Si film.

Aluminum nitride (AlN) thin films were deposited on Z-cut LiNbO3 substrates using the reactive RF magnetron sputtering in this thesis. By means of the analyses of XRD, SEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power of 165W and substrate temperature of 400¢J. The piezoelectric bi-layers structure of SAW devices was then fabricated. The interdigital transducers (IDTs) were fabricated on bi-layers structure. The AlN thin film thickness of piezoelectric bi-layers structure was varied in order to discuss its effects on SAW devices. From the experimental results, it reveals that the center frequency of SAW filters increases with the increased AlN thin films thickness. It means that the SAW velocity increases as the AlN thin films thickness increases. The effects of bi-layers structure on SAW devices can be discussed in detail by measuring the parameters of SAW devices like insertion loss (IL), electromechanical coupling coefficient (K2) and the temperature coefficient of delay (TCD).

Incorporation of nitrogen into ¢»-¢½ materials such as GaAsN and InGaAsN, have recently drawn much attention, due to the unique properties as well as potential device applications of such materials. The purpose of this thesis is to probe microscopic compositions and electronic structures in a series of N-based semiconductor compounds. For the material and electronic structure characterizations, X-ray photoelectron spectroscopy (XPS) with synchrotron radiation beam was adopted to analyze the sample quality under different growth and post-growth thermal annealing. Through detection of samples of InGaAsN in comparison with a series of samples of GaAsN, InAsN, InN, GaN, InGaAs and GaAs, the experimental result and analysis. Now X-ray photoelectron spectroscopy investigation on ¢»-¢½alloys containing a few percentage of nitrogen demonstrated the success of nitrogen incorporation. X-ray photoelectron spectroscopy investigation on InGaAsN films and curve fitting analysis, it can provide evidence of the existence of two principle N configurations, indicating the formation of N-In, N-Ga bonds. Through an estimation of the sample surface composition was made on the basis of the peak area: N-In/N-Ga larger than 3, it can provid direct evidence of the presence of preferential bonding of N to In. The incorporation of atomic nitrogen was added during the annealing. Right through X-ray photoelectron spectroscopy in annealed InGaAsN film can N-In and N-Ga bonds be observed to be increase, but N-In/N-Ga larger than 2, The bonds of atomic nitrogen is still N-Ga bonds.