In this study, Sezawa-mode surface acoustic wave (SAW) devices were employed to construct the allergy biosensor. To fabricate Sezawa-mode SAW devices, the RF magnetron sputtering method for the growth of piezoelectric ZnO thin films onto Si3N4/Si is adopted and influences of the sputtering parameters are investigated. The properties of the ZnO thin films are investigated by X-ray diffraction and scanning electron microscopy which reveal a high c-axis-preferred orientation. A back-etched resonator is used in this study. The wet etching of (100)-oriented silicon wafers is used to form a back-side cavity which is used as the sensing area. Low-stress silicon nitride was deposited by low-pressure chemical vapor deposition (LPCVD) as the etching mask for the integrated SAW device. To investigate the sensing characteristics of SAW, gold (Au) layer was initially deposited onto the sensing area of SAW devices as the binding layer in biochemical sensor and the surface of the Au layer was treated with oxygen plasma to enhance the hydrophilic properties of the Au layer. The self assembly monolayers (SAMs) is used to decorate surface of Au layer and the sandwiched enzyme-linked immunosorbent assay is used for detecting the concentration variation of immunoglobulin E (IgE) in human serum. The frequency response is measured using an E5071C network analyzer. The resonance frequency of the Sezawa-mode SAW device is 1.49 GHz. The sensitivities of the Sezawa-mode biosensor is calculated to be 6.64 MHz cm2/ng for human IgE detection.

Both non-polar (10-10) (m-plane) and polar (0001) (c-plane) zinc oxide (ZnO) have a good lattice match with lithium aluminum (LiAlO2, LAO) (200) substrate, so it is difficult to control the epitaxial orientation. Therefore, this research is to explore how the growth parameters influence on the crystal orientation of ZnO film grown by plasma assisted molecular beam epitaxy. The experimental results show that m-plane ZnO can be grown with low zinc flux and low oxygen pressure. Increasing zinc flux and oxygen pressure will lead to increase in growth rate, and consequently, c-plane ZnO will nucleate on the substrate besides m-plane zinc oxide. The substrate temperature is one of the main factors that influence the choice of zinc oxide epitaxial orientation. High temperature will promote the m-plane zinc oxide nucleation, while low temperature will conduct to the c-plane zinc oxide nucleation. Under low zinc flux and low oxygen pressure, epitaxy of ZnO with different crystalline orientations can be achieved through changing the substrate temperature. The surface morphology and roughness of the substrate will affect the particle size and surface morphology of ZnO epilayers. When the substrate is smooth, the crystal size of the epitaxial film is large and the surface is flat with many rectangular stripes, taking on the platform-like morphology. If the substrate is rough with many scratches, the particle size becomes small and the surface is granular-like and rather rough. Furthermore, when the substrate is rough, it is difficult to control the different orientations of ZnO epitaxial films through changing the substrate temperature.

Wide band gap semiconductors ZnO/GaN attracted a great deal of interests for decade, due to their wide direct band, high electron binding energy, excellent chemical and thermal stability, good heat conductivity and capability, high electron mobility and transparent properties at room temperature. They have many potential applications such as laser, biosensor, piezoelectric power generator, nano-electromechanical systems and flat panel field emission displays. However, unexpected contact loading during processing or packaging may induce residual stresses and/or an increase in defect concentration in ZnO/GaN wafer or thin film, causing possible degenerated reliability and efficient operation of the piezoelectric and photonic device. To ensure and improve the performance of devices based on ZnO/GaN, a better understanding of the mechanical/optoelectronic response under different processing and loading conditions and even the measuring methods are necessary. In this thesis, our aim is to reveal a comprehensive investigation of the mechanical responses on polar/non-polar GaN/ZnO single crystal under low dimensional stress. We try to provide the fundamental theoretical and experimental studies for further application and researches, such as tension testing, residual stress, low temperature cathodoluminescence and Raman spectroscopy analysis. In this study, the theoretical Young¡¦s modulus and Poisson ratio of ZnO/GaN are extracted from elastic constants for comparison and further estimation. The nano-scaled mechanical properties, such as Young¡¦s modulus, hardness and yield stress, are identified by using the nanoindentation system. The experimental values were fitting by the Hertzian contact theory. The results are in good agreement with the theoretical predictions. No significant strain rate influence is observed over the strain rate from 1x10-2 s-1 to 1x10-4 s-1. The comparisons of mechanical properties between the polar and non-polar planes of ZnO are firstly examined. The results reveal that the non-polar planes are softer than the polar plane. Both a-plane and m-plane ZnO have lower hardness and yield stress than c-plane ZnO. The microstructure and deformation mechanism are analyzed by using X-TEM and SEM. No pop-out or slope changing was found in their load-displacement curves, suggesting no phase transformation, twining or crack domain deformation occurred under microcompression and nanoindentation testing. Taking all considerations for the higher resulting Schmid factor and lower Burgers¡¦ vector, the most possible slip system for c-plane hexagonal structures is the pyramidal plane. The a-plane has shorter burger¡¦s vector on the slip plane which leads the lower yield stress than c-plane. To erase the effect of FIB induced Ga ion implantation, the c-plane ZnO was annealed at 900oC for 1 hour. We found that the yield stress under microcompression decreases and the intensity of the cathodoluminescence spectrum increases after the annealing process. This result indicates that the thermal treatment is a good way to refine the crystal quality and decrease the defects density. The E2 peak of Raman spectrometer exhibits high residual compression stress constrain in the c-plane GaN thin film. Due to the high surface/volume ratio of pillar, nil residual stress remains in the GaN pillar after the FIB milling process. Even after the yield point, nil residual stress remains in the c-GaN pillar. Results indicate that the one dimensional geography is a good way to erase residual stress.

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Thin Film bulk acoustic wave devices have the advantages of low loss, low temperature coefficient of the resonant frequency, and high power handling. These excellent characteristics are suitable for the applications on high frequency communication systems. In this study, thin film bulk acoustic wave filters using the ladder-type filter and stacked crystal filter configurations were investigated. Platinum was chosen as the top and bottom electrodes. To improve the platinum adhesion on SiNx/SiO2/Si substrates, a seeding layer of titanium is used. Highly c-axis oriented piezoelectric zinc oxide thin films were deposited by two-step deposition method under room temperature. As resonant area decreases, the band rejection of ladder-type filter will increase. Because the resonant area decreased, the distance between signal and ground will increase the results in an increased insertion loss. On the other hand, stacked crystal filters have larger band rejection and less 3dB bandwidth, which are suitable for the application of narrow band filters.

The highly c-axis oriented ZnO films were deposited on silicon substrates by reactive RF magnetron sputtering in this study. The optimal two-step deposition parameters for ZnO films, which are oxygen concentrations of 70 % (1st step) and 50 % (2nd step), RF power of 100 W and sputtering pressure of 25 mTorr, are obtained by means of XRD, SEM and AFM analysis. Al films are deposited under optimal deposition parameters, which are DC power of 100 W and sputtering pressure of 4 mTorr, to form IDT electrodes with low sheet resistances. Therefore, Al/ZnO/Si layered SAW devices were fabricated under these optimized manufacturing parameters. An oscillator based on a Al/ZnO/Si layered SAW device was fabricated for the application of UV detection and then investigating the acoustoelectric effect between surface acoustic wave and ultraviolet light illumination. Due to the fact that the sensor sensitivity is directly proportional to the resonance frequency, in this study the SAW device with high resonance frequency of Sezawa mode is adopted to form SAW oscillator for high sensitivity. The resonance frequency of SAW oscillator is 751.41 MHz. The optimal detecting zone for UV light is the center of IDT electrode with maximum sensitivity of 8.12 ppm/(£gW/cm2).

In this study, T-ladder type thin film bulk acoustic wave filters had been fabricated based on thin film bulk acoustic wave resonators. The titanium (Ti) seeding layer and platinum (Pt) for bottom electrode were deposited on silicon substrates by a dual-gun DC sputtering system. Field-emission scanning electron microscopy, atomic force microscopy and the four-point probe method showed that the Pt bottom electrode deposited on the Ti seeding layer exhibited favorable characteristics, such as a surface roughness of 0.69 nm and a sheet resistance of 2.27 £[/¡¼. The ZnO piezoelectric film was deposited using the two-step deposition method by RF magnetron sputtering. Field-emission scanning electron microscopy, atom force microscopy and X-ray diffraction revealed that ZnO piezoelectric film exhibited excellent characteristics, such as a the high preferred c-axis orientation and a rigidly precise surface structure with surface roughness of 7.37 nm. The wet etching process is adopted to fabricate cavity of device. The concentration of 30 wt% KOH and etching temperature of 100 ¢J had been indicated appropriate for etching processes. Finally, the top electrodes of the devices are varied to approach the performances of device applications. The results showed the highest coupling coefficient (kt2) of FBAR device can be obtained using platinum top electrode. The high coupling coefficient of FBAR device is appropriate for wide passband filter. The annealing processes had been used in order to improve the characteristics of piezoelectric films. The stress of ZnO film has been improved from -1.656 Gpa to 0.611 Gpa through the annealing process. At the annealing temperature of 400¢J, the ZnO piezoelectric film exhibited excellent characteristics, such as a large grain size with smooth surface. The quality factor of FBAR device using ZnO film with 400¢J annealing was better than that without annealing. The optimal conditions of fabrication processes are adopted to fabricate top electrode, bottom electrode and piezoelectric film. The T-ladder type FBAR band pass filter was constructed by FBAR resonators. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The 3-dB bandwidth, insertion loss and band rejection of the T-ladder type thin film bulk acoustic wave filter are 79MHz, -3.5 dB and 8.4dB at 2,379MHz, respectively.

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Nanowire structure plays an important role in the development of nanotechnology. However, further study shows that the shape of nanowires may not be the ideal morphology for some applications such as solar cells and sensors. Thus, the purpose of this thesis is to find a low cost and high yield approach to the synthesis of other morphologies of nanostructures in order to further improve the performance of these nanodevices. To this end, a chemical approach has been extended to the synthesis ZnO nanocones and platelets. With UV illumination, the synthesis of ZnO nanocones was achieved on GaN films on sapphire and gold films on silicon substrates. Both TEM and XRD results show that as-grown ZnO nanocones are single crystals. The formation of ZnO nanocones could be explained by the absorption process of photons. The UV light induced thermal gradient modifies the heat distribution as well as the reagent transport. The chemical reaction system is kinetically limited and results in ZnO nanocones. If the UV light is blocked, the ZnO nanowires result. In addition, the density of ZnO nanocones is higher than ZnO nanowires grown without UV illumination. By this chemical approach, ZnO platelets could also be obtained on GaN films deposited by PLD, whose c-axis is parallel to the surface of the substrate. The diameters and the thickness of the platelets depend on the quality and thickness of GaN film. TEM results illustrate that the obtained ZnO platelets are single crystals grown along the <0 1 1 0> direction within the {0 0 0 1} planes. Relative growth rates of various facets were altered by the presence of [1 0 0] textured GaN film. The suppression of the growth along c axis can also be achieved by citrate anions as a structure-directing agent to adsorb selectively on ZnO basal planes. Electrical measurement shows that the resistance of ZnO platelets is about 20-40 GΩ¸ and it is higher than that of ZnO nanowires. Piezoelectric potential calculation results also indicate that the piezoelectric potential is higher than for ZnO nanowires with the same external applied stress. These procedures and results demonstrate an easy and low cost way to fabricate ZnO nanocones and platelets, which may aid the utilization of nanostructures in solar cells, sensors and other applications to further improve their performance.

<p>The mechanism for defect related green emission from zinc (ZnO:Zn) and sulfur doped ZnO (ZnO:S) are determined through optical characterization of the green and UV emission bands. ZnO:Zn is prepared by heating ZnO in a slightly reducing atmosphere for 1 hour and sulfur doped ZnO is similarly obtained with a small amount of sulfur added. Photoluminescence (PL), photoluminescence excitation spectra (PLE), and quantum efficiency measurements are analyzed to determine the mechanism of the green defect emission. Low temperature PL and PLE measurements are used to assign activation energies to the emission processes and connect them with donor bound excitons in ZnO. It was determined that both ZnO:Zn and ZnO:S have a similar green emission mechanism. This common mechanism involves the formation of donor bound excitons <italic>I_3a</italic> and <italic>I₉</italic>, which were determined to be the mediators between photoexcitation of excitons and the transfer of energy to the defect responsible for green emission. The most efficient excitation processes for both the green and band edge emissions at low temperatures is through direct excitation of the neutral donor bound exciton <italic>I₉</italic> or by ionizing the neutral donor bound exciton <italic>I_3a</italic>. The ionization of <italic>I_3a</italic> eliminates this exciton localization site and simultaneously creates a bound exciton at <italic>I₉</italic>. The <italic>I₉</italic> bound exciton can then either transfer energy to the defect responsible for the green emission or contribute to the free exciton population through a phonon assisted transition. At room temperature a resonant absorption peak associated with <italic>I₉</italic> is still present in the absorption band for ZnO:Zn suggesting partial localization at <italic>I_3a</italic> and <italic>I₉</italic> of free excitons with low kinetic energy (excitations below the band gap) continues to be the intermediate between excitons and the energy transfer to the green emitting defect. </p><p>In ZnO:S, the addition of sulfur creates ZnS domains within the lattice leading to a type II band alignment at the interface of ZnO and ZnS domains. This band alignment at the interface increases the density of free electrons in ZnO, which may then encounter an ionized <italic>I_3a</italic> site converting it to its neutral form. Increasing the density of free electrons, a result of the type II band alignment, increases the chances of returning an ionized <italic>I_3a</italic> to its neutral form and thus increases the green emission. These results can lead to informed optimization of ZnO:S as a potential white light emitting phosphor.</p> / Dissertation