by Law Siu Wah = 超薄薄膜的應變和記憶效應 / 羅紹華. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Law Siu Wah = Chao bo bo mo de ying bian he ji yi xiao ying / Luo Shaohua. / Acknowledgement --- p.i / Abstract --- p.ii / 論文摘要 --- p.iv / Table of contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Magnetoresistance (MR) --- p.1 / Chapter 1.1.1 --- Colossal magnetoresistance (CMR) in rare-earth manganites --- p.2 / Chapter 1.1.2 --- Double exchange mechanism --- p.3 / Chapter 1.1.3 --- Jahn-Teller effect --- p.6 / Chapter 1.1.4 --- Tolerance factor --- p.8 / Chapter 1.1.5 --- The effect of doping --- p.10 / Chapter 1.2 --- Our motivation --- p.12 / Chapter 1.3 --- Scope of this thesis work --- p.12 / References --- p.14 / Chapter Chapter 2 --- Experimental methods / Chapter 2.1 --- Thin film deposition --- p.16 / Chapter 2.1.1 --- Facing Target Sputtering (FTS) --- p.16 / Chapter 2.1.2 --- Vacuum system --- p.19 / Chapter 2.2 --- Annealing systems --- p.20 / Chapter 2.2.1 --- Oxygen annealing system --- p.20 / Chapter 2.2.2 --- Vaccum annealing system --- p.21 / Chapter 2.3 --- Characterization --- p.22 / Chapter 2.3.1 --- Profilometer --- p.22 / Chapter 2.3.2 --- X-ray diiffraction (XRD) --- p.22 / Chapter 2.3.3 --- Resistance measurement --- p.24 / References --- p.25 / Chapter Chapter 3 --- Expitaxial growth of La0.67Ca0.33MnO3 single layer thin film / Chapter 3.1 --- Fabrication and characteristics of La0.67Ca0.33MnO3 target --- p.26 / Chapter 3.2 --- Substrate materials --- p.31 / Chapter 3.3 --- Epiaxial growth of LCMO thin film --- p.33 / Chapter 3.3.1 --- Deposition conditions --- p.33 / Chapter 3.3.2 --- Deposition procedure --- p.35 / Chapter 3.3.3 --- Oxygen annealing effect --- p.36 / References --- p.41 / Chapter Chapter 4 --- Strain effect in expitaxial growth of La0. 67Ca0 .33MnO3 thin films / Chapter 4.1 --- Introduction --- p.42 / Chapter 4.2 --- Preparation of LCMO ultra-thin film on different substrates --- p.45 / Chapter 4.2.1 --- Sample preparation --- p.45 / Chapter 4.2.2 --- Oxygen annealing treatment --- p.45 / Chapter 4.3 --- Resistance measurement --- p.50 / Chapter 4.3.1 --- Thickness effect --- p.50 / Chapter 4.3.2 --- Strain effect --- p.63 / Chapter 4.4 --- Discussions --- p.68 / References --- p.69 / Chapter Chapter 5 --- Memory effect and thermal effect of ultra-thin La0.67Ca0.33MnO3 films / Chapter 5.1 --- Introduction --- p.71 / Chapter 5.2 --- Sample description and measurement method --- p.72 / Chapter 5.3 --- Memory effect and thermal effect --- p.73 / Chapter 5.4 --- Discussion --- p.77 / References --- p.80 / Chapter Chapter 6 --- Conclusion / Chapter 6.1 --- Conclusion --- p.81 / Chapter 6.2 --- Future work --- p.82

The photovoltaic solar cell industry is growing rapidly, but high cost per watt is still an obstacle. Thin film solar cells, especially thin film solar cells using CIGS absorbers that have the highest proven efficiency, have the potential to reduce the cost through cheap manufacturing. Academic research concerning CIGS solar cells has so far been focused on cells with absorber layers deposited by co-evaporation, which can be used to make very high efficiency cells but is a deposition process ill suited for large scale production. In this thesis a process for depositing CIGS absorber layers by gas flow sputtering, a deposition technique enabling high rate depositions of low energy particles that is potentially easier to apply to a large scale production, has been outlined. Equipment for CIGS-deposition by gas flow sputtering has been prepared, characteristics of the process have been investigated and ultimately a series of first prototype CIGS absorber layers has been deposited as part of complete solar cells. A lot of focus in this thesis is on the practical work and problem solving around the equipment, e.g. pulsed DC power supplies and electrical connections, heating and heating control in a reactive vacuum environment, and on the basic functionality of the gas flow sputter, how process and film properties like deposition rate, thickness uniformity etc. vary with sputter conditions like pressure, gas flow etc. Following the process design the first prototype series produced crystalline CIGS absorbers of desired elemental composition and thickness but having rather small grain sizes, while the complete cells exhibited solar cell IV-characteristics but very poor efficiencies.

RF magnetron sputtering has been employed to deposit n-type epitaxial zinc oxide thin films on p-type silicon substrates to form p-n diode structures. Commonly found on silicon, native SiOx layers, typically of a few nanometer thick, would hinder the epitaxial growth of ZnO. In this thesis work, a crystalline metal oxide layer was introduced as a buffer layer by redox reaction between a metal layer and the native SiO2. Aluminum was first sputtered for 20 seconds (4 nm), 40 seconds (8 nm), 60 seconds (12 nm) to produce three sets of samples. Each set was then annealed in situ at 450¢J for 20 minutes, 40 minutes, 60 minutes, respectively, to generate 9 different fabrication conditions meant to ignite a redox reaction between aluminum and the silicon oxide. All samples were treated for comparison by rapid thermal annealing to 900¢J, intended to improve the crystalline quality of the buffer layer and thus the epitaxial zinc oxide. Means to characterize the samples included (1) cross-sectional TEM (Transmission Electron Microscopy) observations of the interfaces and defects in various regions of the formed material or device structures; (2) x-ray crystallography via £s-2£c and rocking scans in regards to the perfection of the crystal structures and the relative film-substrate orientations; (3) photoluminescence spectroscopy, which showed oxygen deficiency in the ZnO epitaxial thin films as judged by the peaks of near-edge luminescence and mid-gap impurity states. The resulted material structure is a pin diode with a transparent n-ZnO layer sandwiching in the middle an aluminum oxide insulating layer with the p-Si substrate. The electrically insulating aluminum oxide layer serves to increase the minority carrier accumulation effect, extending carriers¡¦ effective life times and hence enhancing the light emission efficiency. Measuring the current-voltage characteristics of the pin device structures provides insights into the interface charges, while high-frequency capacitance-voltage curves helps give a glimpse of the interfaces between ZnO and Al2O3 or AlOx, as well as those between Al2O3 or AlOx and silicon, all concerning the electronic accumulations at each interface. Keywords: sputtering, ZnO, Al2O3 , pin diode.

In this thesis, n-type ZnO thin films are grown on buffered p-type Si substrates by RF sputtering. The buffer is a pure nanometer-thick Al layer deposited onto a Si substrate that has a native SiOx over-layer. The Al- layer is meant to react with the native oxide and reduce it back to the pure Si formation when the Al-layer is itself oxidized into AlOx. The pin diodes with ZnO grown on AlOx are expected to outperform those with ZnO on SiOx on the aspects of electrical quality and crystallographic orientations. The transmission electron microscopy was employed to study the epitaxial relationship between the ZnO layers and the Si substrates, the crystal structure, and defects at the ZnO-Al or Al-SiOx interfaces. X-ray diffraction studies through £s-2£c, rocking curve, GIXRD and pole-figure scans were also conducted to see the differences between as-deposited and post-annealing treated samples concerning with the ZnO crystallographic orientations and general qualities. Through comparisons of the leakage current and the tunneling behaviors , the electrical measurements can be used to analyze the pin devices.

Lead zirconate titanate (PZT) thin films have been extensively investigated for many applications, such as MEMS devices (actuators, sensors, transducers, SAW devices) and memory devices (DRAM, NVFRAM). In this study, the sputtering deposition methods were used to fabricate the PZT thin films. Multilayer Si/SiO2/Ti/Pt was used as substrate, in which the thickness of SiO2, Ti and Pt layer was 250, 50 and 150nm. In order to improve the electric and piezoelectric properties of PZT thin films, the few nanometer thick layer of Ti on the platinum have been used for fabricating oriented PZT thin films. Then, the PZT thin films required the heat treatment for crystallization of perovskite structures. RTA and FA were taken for the heat treatment. The crystallographic and surface characteristics of PZT thin films were determined by XRD and Optical Microscope. Finally, PZT thin films deposited on two kinds of substrates were successfully transformed from amorphous phase to perovskite phase by two kinds of the annealing processes. The Ti seed layer yielded (111)-textured PZT even for thin seed layer. But, it also had less tolerances to anneal. Si/SiO2/Ti/Pt/PZT structures were the better way to fabricate the PZT thin films, which had the preferred orientations of (100¡^,(110¡^,and (200).

In this thesis, Bi4Ti3O12 thin films are deposited on ITO/glass and Pt/Ti/SiO2/Si substrates using RF magnetron sputtering at room temperature and two kinds of targets with different compositions of Bi4Ti3O12 and Bi4Ti3O12+4wt% Bi2O3, respectively, and then heated by a rapid thermal annealing (RTA) process in an oxygen atmosphere. Three topics are focused in this research, they are: (1) to study the effects of different fabricated conditions and substrates on the physical and electrical characteristics of Bi4Ti3O12; (2) to investigate the influence of bismuth evaporation during thermal process on the characteristics of thin films, and seeking for the methods of bismuth compensation; and (3) applying the Bi4Ti3O12 film as the insulting layer of AC thin film electroluminescence device with the phosphor layer of ZnS:TbOF, and investigating the interaction between the two films. The experimental results indicate that intensities of X-ray diffraction (XRD) peaks of the films are evident when annealing at 650¢J for 15 min or at 700¢J for 10 min using RTA process, and the optimal properties of polycrystalline Bi4Ti3O12 thin films can be obtained at 700¢J for 15 min. No dielectric breakdown phenomenon of the films is detected in the filed of 500 kV/cm, and the leakage current density was lower than 10-6 A/cm2. The dielectric constant can attain to 307, and the loss factor is 0.02 at 1 kHz. The residual polarization and coercive field are 3.7 £gC/cm2 and 80 kV/cm with a sinusoidal wave of 500 Hz, respectively. The optical transmittance of the film is close to 100% at the wavelength of 550 nm. Scanning electronic microscopy (SEM) observation reveals that the microstructures, grain sizes and thicknesses of the thin films strongly dependent on the substrates, that is, the Pt/Ti/SiO2/Si substrate provides a more suitable interface layer than ITO/glass substrate for the growth of Bi4Ti3O12 thin films. The energy dispersive spectrometer (EDS) results indicate that the Bi/Ti atomic ratio of the films is less than that of target, which suggests that evaporation loss of bismuth occurs during the heating process. Whereas, this phenomenon occurs near the surface of thin film, it is not apparent in the inner of film. Excess 4wt% Bi2O3 additive in the target or additional Bi2O3 powder in the annealing process can compensate the loss of bismuth in the films, and improve the characteristics of thin films. Finally, the interdiffusion and chemical reactions take place among the element Bi, S and O at the interface during the deposition of ZnS:TbOF on Bi4Ti3O12 films, which degrades the optical transmittance of thin films. A 100 nm SiO2 buffer layer sandwiched between the ZnS:TbOF and Bi4Ti3O12 films can prevent the interdiffusion of the two layers, and enhance the optical transmittance and dielectric breakdown of Bi4Ti3O12 films.

In this thesis, we use reactive RF magnetron sputtering to deposit zinc oxide (ZnO) buffer layer and main layer on SiO2/Si substrate at room temperature. After various annealing treatments, the ZnO nanowires can be obtained. The effects of buffer layer on the crystallization of ZnO main layer and the zinc-to-oxygen ratio in the main layer on the growth of the ZnO nanowires are analyzed by PL, SEM, XRD and EDS. Finally, the growth mechanism of the ZnO nanowires is investigated by various annealing temperatures. According to the experimental results, surplus zinc in the main layer is necessary for the ZnO nanowires growth. When the annealing temperature is higher than the melting point of zinc, it will melt and be extruded onto thin film surface as a result of the thermal stress. As soon as the melting zinc on the film surface reacts with the oxygen in the air, ZnO nanowires can be obtained. The optimum ZnO nanowires which possess better morphology and high density are revealed by conventional thermal annealing at 600¢J for 90 minutes.

Abstract Recently Cu has been used as a replacement of Al in microelectronics industry to its lower electrical resistivity and higher electromigration resistance than aluminum. It is essential to have high performance diffusion barrier to suppress the diffusion between Cu and Si . In this experiment ZrN was investigated as a possible diffusion barrier. All coatings were deposited by RF magnetron reactive sputtering system. The growth of ZrN has been evaluted at different vacuum condition¡BRF power¡Bgrowth time¡BN2 flow rate Ar flow rate and Zr or ZrN target. The thin films were then annealed at temperatures from 450 ¢J to 700 ¢J for 30 min to study its durability. In this work XRD was used to study the thin film structure, SEM and TEM study the microstructures and AFM to study the surface roughness . The film¡¦s resistivity was measured as a function of N2 flow rate and annealing temperature by four point probe . For pure Zr film Cu3Si phase has formed after annealing at 550 ¢J for 30 min . As to ZrN film, only CuZr2 is present after annealing at 650 ¢J for 30 min indicating the diffusion barrier is still effective. After annealing at 700 ¢J for 30 min, Cu3Si was detected indicating the failure of the diffusion barrier. Results up to now suggest that ZrN layer can be a successful candidate as a diffusion barrier between Cu and Si.

Abstract AlN thin films grown on Si¡BGlass¡BSiO2 and Si3N4 substrate by RF magnetron sputtering technique with AlN target has been studied.Room temperature growth was applied to this study.During thin film growing, sputtering work pressure, sputtering power, sputtering working distance and sputtering time are those key parameters to be adjusted in order to highly C-axis prefer orientation AlN thin films. The microstructures of the AlN films were examined by x-ray diffraction. TEM was adopted to observe grain growth of the AlN films. The results was compared with the results of reactive RF magnetron sputtering. The results of the X-ray patterns showed that the strong C-axis prefer orientation of the AlN films were obtained with AlN target. in a 17¢Q long sputtering working distance condition, chemical composition of substrate can help to growth of AlN films. The column structures of AlN films can be observed by TEM.

ZnO thin film is a suitable material for the phosphor layer of green emission of the electroluminescence (EL) device. Therefore, the luminescence mechanism of green emission of ZnO thin film is a key issue to be investigated. In this thesis, ZnO thin films are deposited on SiO2/Si substrates using sol-gel method and sputtering technology, and then post-annealed by a rapid thermal annealing (RTA) process under various annealing temperatures (200¢J~900¢J) and atmospheres (vacuum, ambient atmosphere and oxygen). The physical and photoluminescence (PL) characteristics were first discussed. Secondly, the relationship between the chemical composition and the PL properties were also investigated to figure out the dominant luminescent center of ZnO thin film. Finally, ZnO thin film was applied as the phosphor layer of AC thin film EL device and the characteristics were discussed. According to the experimental results of ZnO thin film prepared using sol-gel method and RTA process, the XRD patterns show a preferred (002) orientation after annealing. The grain size became larger with the increasing annealing temperature. From PL measurement, two ultraviolet (UV) luminescence bands were obtained, and the intensity became stronger when the annealing temperature was increased. The strongest UV light emission appeared at annealing temperature of 900¢J in oxygen. The X-ray photoelectron spectrum (XPS) demonstrated that a more stoichiometric ZnO thin film was obtained upon annealing in oxygen and more excitons were generated from the radiative recombination carriers consistently, and resulted in the strong UV emission. However, no green emission was obtained from ZnO thin film prepared by sol-gel method. The XRD patterns also exit an excellent preferred (002) orientation of ZnO thin film deposited using sputtering and RTA process. The grain size of ZnO thin film annealed at 200¢J~500¢J increased with the increasing annealing temperature, and then exhibited a melting state with the temperature of 600¢J~700¢J. A large and complete grain was observed at the temperature of 900¢J. The PL spectrum illustrated that a stronger UV emission intensity appeared at annealing temperature of 500¢J. On the other hand, the green light emission could be obtained as ZnO films were annealed above 500¢J and reached a maximum intensity at 900¢J. Based on the XPS analysis, the O1s peak of ZnO film revealed that the concentration of oxygen vacancy increased with the annealing temperature from 600¢J to 900¢J under an ambient atmosphere. The PL results demonstrated that the intensity of green light emission at 523nm also increased with temperature. Under various annealing atmospheres, the analyses of PL indicated that only one emission peak (523nm) was obtained, indicating that only one class of defect was responsible for the green luminescence. The green light emission was strongest and the concentration of oxygen vacancies was highest when the ZnO film was annealed in ambient atmosphere at 900¢J. According to the experimental results manifested above, room temperature was used to deposit films to increase the ratio of Zn atoms inside the thin film when using sputtering technique to deposit ZnO thin film. With the modulation of the annealing parameters, stronger green light emission could be obtained. The luminescence mechanism of the emission of green light from a ZnO thin film is associated primarily with oxygen vacancies. In addition, only UV light emission of ZnO thin film prepared using sol-gel method was obtained because of the better stoichiometry.