In this study, a two-step deposition method using RF reactive magnetron sputtering is proposed to obtain high quality Piezoelectric ZnO thin films for film bulk acoustic resonators (FBARs). The titanium (Ti) seeding layer and platinum (Pt) bottom electrode were deposited by a dual gun DC sputtering system. The properties of thin film are investigated using the scanning electron microscope (SEM), Atomic force microscope (AFM) and the four-point probe method. The results show that the Pt bottom electrode deposited on the Ti seeding layer has lots of favorable characteristics, such as the crystallite size smaller than 10 nm, a surface roughness of 0.69 nm and a sheet resistance of 0.26 Ω/¡¼. The bottom electrode with the low resistance and the low surface roughness contribute markedly to the performances of the FBAR device. The Ttwo-step deposition method was adopted for ZnO thin film deposition, The 1st step deposition is focused on lowering the surface roughness of ZnO seeding layer films. The c-axis preferred orientation of ZnO film This is accompanied by the 2nd step deposition where the sputtering parameters O2 concentration arewere controlled to enhance the c-axis preferred growth of ZnO films. The AFM image shows that the surface roughness of the ZnO film is drastically reduced. It is also observed by monitoring the XRD spectra that the films deposited by two-step method reveal the high c-axis preferred orientation. Finally, the frequency response of ZnO-FBAR device using the two-step sputtering method shows the excellent performance at center frequency of 1.804GHz with the return loss of nearly 60dB and the electro-mechanical coupling coefficient of 3.2%.

El objetivo de la presente tesis es la síntesis de materiales ternarios basados en óxido de zinc (ZnO), mediante la técnica de electrodeposición. Por primera vez, se han sintetizado electroquímicamente los compuestos Zn1-xCdxO, Zn1-xCoxO y Zn1-xMnxO en forma de capas finas mediante este procedimiento. Los materiales sintetizados presentan interesantes aplicaciones optoelectrónicas, fotovoltaicas y magnéticas. La electrodeposición se ha realizado en una celda electroquímica de tres electrodos. El electrolito empleado ha sido dimetilsulfóxido (DMSO) con una disolución de KClO4 0.1 M. Las condiciones óptimas definidas a partir del estudio voltamétrico son: 90ºC de temperatura y un potencial de -0.9V. Los precursores de la disolución fueron ZnCl2, CdCl2, CoCl2 y MnCl2 disueltos en presencia de óxigeno en saturación. Los materiales depositados se han estudiado mediante diversas técnicas de caracterización: " La difracción de rayos X y la espectroscopia de dispersión Raman para evaluar el tipo de estructura cristalina y la calidad de las muestras depositadas. " La espectroscopia de energía dispersiva EDS para identificar la composición química de las películas. " La microscopía electrónica de barrido para estudiar la morfología. " La microscopia de fuerza atómica para el estudio de las características de la superficie. También se han realizado diferentes medidas de caracterización óptica y magnética: " La transmitancia para estudiar las propiedades ópticas de las capas depositadas. " La susceptibilidad magnética para estudiar la respuesta magnética de los materiales. Los resultados muestran la síntesis de muestras de capas finas de los compuestos Zn1-xCdxO, Zn1-xCoxO y Zn1-xMnxO. En función de la concentración del segundo metal (Cd, Co, Mn) se observan modificaciones en la estructura cristalina. Para los tres compuestos, cuando la concentraciones de iones Cd+2, Co+2 y Mn+2 son pequeñas, se obtienen capas finas de compuesto donde se produce la sustitución de iones / Tortosa Jorques, MD. (2011). PREPARACIÓN Y CARACTERIZACIÓN DE CAPAS FINAS DE SEMICONDUCTORES TERNARIOS DE ZnO MEDIANTE ELECTRODEPOSICIÓN [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11037

Zinc oxide (ZnO) has gained many interests in the research of wide band-gap semiconductor materials nowadays. ZnO has attracted much attention because of its high excition bound energy (60meV), and it¡¦s promising to gain application in the field of optoelectronic such as ultraviolet light emitting devices (UV-LED) and laser diode (LD) etc. This study aims to investigate the growth condition of ZnO and to control the growth direction. ZnO was grown on LiAlO2 (LAO) (100) substrates by chemical vapor deposition (CVD) with zinc source Zn(C5H7O2)2. The different reacting temperature from 500¢J to 650¢J and the flow rate of oxygen were studied. In the result of scanning electron microscope (SEM), the surface morphology of ZnO showed two different structures, hexagonal structure and non-hexagonal film structure. And the side view of hexagonal structure showed double layers. The key factor for the transformation of double layers from film to column structure is the equilibrium of growth temperature and substrate stress. The crystals structures and epitaxial relationship were studied by X-ray Diffraction Pattern (XRD), Electron Backscattering Diffraction (EBSD). There are two kinds of ZnO epitaxial growth on LiAlO2 (100) substrate, one is c-plane of ZnO(0001)// LiAlO2 (100) and another one is m-plane of ZnO(10 0)// LiAlO2 (100), the latter one has a smaller lattice mismatch. The results of the strong UV and green emission peaking were shown in photoluminescence (PL) spectrum. Under the control of substrate temperature, c-plane polarized ZnO films were grown at 500 ¢J, and m-plane nonpolar ZnO films were grown at 650¢J. Rectangular structure could be formed between 550¢J and 650¢J. With the increase of substrate temperature, the size of rectangular became larger. At last, uniformed film would be formed at 650¢J. In addition to benefit the formation of m-plane structure, high temperature helps the sideward growth to form uniform film. In the experiment of oxygen flow, we found that c-plane hexagonal structure appeared on the m-plane film while the oxygen flow lowered to 50 sccm. And there were large numbers of oxygen vacancies measured by PL. The oxygen flow of 100 sccm is more suitable to obtain higher quality m-plane film than 400 and 50 sccm. At last, the growth time experiments were done under the growth temperament of 600¢J.Island structures of c-plane and m-plane ZnO combined with the growth time increased, and the island become larger. The XRD measurement showed that crystallinity of ZnO become better with the growth time increased.

In this study, ZnO film bulk acoustic resonators (FBARs) are proposed to fabricate the mass sensor of high sensitivity. The acoustic cavity is achieved by potassium hydroxide (KOH) etching. The FBAR structures are made of highly C-axis-oriented piezoelectric ZnO thin films using the technique of two-step deposition method. The titanium (Ti) seeding layer, platinum (Pt) bottom electrode, and aluminum (Al) top electrode were deposited by DC sputtering system using a dual gun. Finally, The remnants of silicon and silicon nitride (SiNx) are removed by reactive ion etching (RIE) etching. Furthermore, the two resonant frequencies of longitudinal mode and shear mode had been obtained. From the experimental results of loading effect with titanium and molybdenum, the mass sensitivity of the longitudinal mode and the shear mode are about 3200 Hz cm /ng and 1100 Hz cm /ng respectively, which are larger than those of quartz resonator or other reports. The measurement system was composed of a thermoelectric cooling module to investigate the temperature coefficient of frequency (TCF) of the mass sensor, which is about -70.67 ppm/. Bisides, the positive TCF material, silicon dioxode (SiO2) is deposited on ZnO thin films for the purpose of improving the TCF of FBAR devices. For SiO2/ZnO FBAR devices, the SiO2 reveal the compensation of TCF.

In this study, the FBAR devices fabrication was used by back-etched type. The titanium (Ti) seeding layer and platinum (Pt) bottom electrode were deposited by DC sputtering system using a dual gun. To improve the platinum (Pt) adhesion, a seeding layer titanium (Ti) is used. The piezoelectric zinc oxide (ZnO) thin films were deposited by RF reactive magnetron sputtering. By increase the substrate temperature and annealing treatment in order to improve the ZnO thin films quality. The FBAR device was fabricated with different top electrode of Al, Mo and Pt that was compared different frequency response characteristic. When ZnO thin films are deposited on Pt/Ti/SiNx/Si substrate by RF reactive magnetron sputtering, due to the lattice mismatch between the Zno thin film and Pt electrode and rapid deposition rate, the ZnO films have high Zn interstitials and O vacancy, which introduce the stress in ZnO films. By thermal annealing treatment the stress could be relaxed and the defects in ZnO films could be suppressed. We used the ZnO films at the different annealing temperature to fabricated the FBAR device, and also discussed the resonant characteristics of the FBAR device with the stress in the ZnO films. Top electrode of Al is suitable for using as electrode materials for FBAR device. The Al top electrode revealed the best frequency response characteristic among the various top electrodes in this research. Postdeposition annealing at 400¢Jmakes ZnO films more suitable for high Q FBAR device, it makes ZnO films with stronger c-axis (002) orientation, denser structure, smoother surface and relieved stress. The resonant frequency, the effective electromechanical coupling coefficient ( k eff ) and the quality factor (Q) were about 2.21GHz, 2.88% and 2659, respectively.

Optical properties of hybrid structures based on zinc oxide nanocrystals (NCs) and Gallium Nitride quantum well (QW) has been studied. The ZnO NCs thin films on the top of GaN QW structures were fabricated using spin coating. The surface morphology was characterized by scanning electron microscopy (SEM). We have performed temperature dependence time-resolved photoluminescence (TRPL) measurements of the bare AlGaN/GaN QW structures and hybrids, containing ZnO NCs. It was found that at some temperatures the QW PL decay has shorter decay time in the presence of ZnO NCs thin film compared to the bare QW. The effect was stronger for the samples with thinner cap layers. The results are discussed in terms of three models such as exciton nonradiative energy transfer (NRET), tunneling effect, and piezoelectric field influence on the QW exciton energy.

Gas sensors are devices that can convert the concentration of an analyte gas into an electronic signal. Zinc oxide (ZnO) is an important n-type metal oxide semiconductor which has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensors. The size reduction of ZnO sensors to nanometer scale provides a good opportunity to dramatically increase their sensing properties in comparison with their macroscale counterparts.<p> In this work, two kinds of ZnO nanostructures (nanowires and nanorods) were studied. ZnO nanowires were synthesized by electrodeposition while porous anodic aluminum oxide served as a growth template. Three types of ZnO nanowires with different diameters were obtained. Meanwhile, ZnO nanorods were prepared by a hydrothermal route from ZnO nanoparticle seeds. However, the aspect ratio (length/width) of nanorods was significantly smaller than that of nanowires. Both nanowires and nanorods were characterized by optical microscopy, scanning electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy and energy dispersive spectroscopy.<p> The sensing performance of the synthetic ZnO nanostructures were investigated by three gases: saturated water vapour in air, saturated ethanol vapour in air, and carbon monoxide in air. Both ZnO nanostructures showed good sensitivity and selectivity to ethanol vapour. At high temperature, the ZnO nanosensors were up to seven times more responsive to ethanol vapour than water vapour and over 200 times more responsive to ethanol vapour than CO. Due to the size dependence, ZnO nanowires with the smallest diameter is considered the best sensor candidate among ZnO nanowires.<p> On the basis of previous work, Au/ZnO/Au multimetallic nanobarcodes were also synthesized by electrodeposition, and their sensing characteristics are to be investigated in the future.

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In this study, we prepare the zinc oxide nanotip with aqueous solution deposited on ZnO nucleation layer. The directions of nanotip are formed with different ZnO nucleation layer time. The thermal annealing with N2 ambiance at 300 ¢J for 1 hr increase the UV emission and decrease the defects. We use ZnO nanotip as an anti-reflection layer because of surface roughness and optical interference. ZnO nanotip with rough surface decreases reflection and enhance the transmission, so we use ZnO nanotip as an anti-reflection layer, after growin ZnO nanotip on solar cell the efficiency of solar cell was enhancement.

In this study, epitaxial ZnO films were grown by chemical vapor deposition (CVD) on LSAT(100) substrate. A high-quality [100] (La0.3,Sr0.7)(Al0.65,Ta0.35)O3 (LSAT) single crystal with the diameter of 60mm was grown by Czochralski pulling technique in our lab. Epi-ready LSAT substrates with rms roughness of 0.30nm ~ 0.35nm were used for all of the experiments. Nonpolar ZnO with [11-20] orientation (a-plane) was directly grown on a (100) LSAT substrate without any buffer layer by chemical vapor deposition (CVD) method. (100) LSAT single crystal substrate is loaded in a 2¡¨ quartz tube inserted to a two-temperature zone furnace. Zinc acetylacetonate hydrate (Zn(C5H7O2)2¡DxH2O, Lancaster) source was vaporized at the lower temperature of 130~140oC. The vapor was carried by a mixture of N2/O2 gas flow into the high temperature zone where the (100) LSAT substrate was located. At first, the pressure of the quartz chamber was pumped to 8¡Ñ10-3 Torr, and then kept at 150 ~ 250 Torr. The flows rates of both O2 and N2 are 500sccm. During the growth, the temperature was varied from 700 to 780oC. The growth conditions were controlled by adjusting the growth temperatures and chamber¡¦s pressures. The overall reaction was: Zn(C5H7O2)2 +12O2¡÷ZnO+ 10CO2 +7H2O Scanning electron microscope [(SEM), JEOL JSM-6330TF)] is used to examine the different surface morphologies of ZnO epitaxial film. The orientation and structure were investigated by X-ray diffraction pattern (XRD) using a Siemens D5000 X-ray diffractometer with a Cu anode at 40 kV and 30 mA. The wavelength of X-ray radiated from the Cu K£\1 is 0.1540 nm. The X-ray scan step is 0.01¢X. A JEOL 3010 scanning transmission electron microscope (STEM) operated at 200kV was employed to characterize the microstructures and orientation of the nonpolar ZnO film. Cross-sectioned TEM samples were prepared using the focus ion beam lift-out method. A Pt layer of about 8nm in thickness was pre-deposited on the sample to prevent charging. Room temperature photoluminescence (RT-PL) measurements were performed using a 325nm He-Cd laser. The emitted light was detected by a Jobin-Yvon TRIAX 550 monochromator with 0.025nm resolution.