Among communication filters, SAW Filters have been largely used in RF and IF filters of mobile phone because of their small size, high reliability, and the capability to be mass produced. But with increasing of working frequency and miniaturization of SAW package, SAW filters are more sensitive to interference introduced by the package and SAW Pattern. Discrepancy in performance between design and measurement can be large if the packaging effects are not considered. In this thesis, we use the full wave analysis approach that combining full wave simulator HFSS (High Frequency Structure Simulator) with circuit software to simulate the package effects and the electromagnetic effects of SAW pattern. Our approach has been applied to several cases and measurements are also carried out to verify our results. Good agreements are obtained. We also use this method to discuss the electromagnetic effects inside package, such as the change of the bond wire length. With an accurate prediction, we can save factory design time and production cost.

In this thesis we investigate various aspects of SAW devices and strain sensitive spin species in ZnO and LiNbO₃ for coupling surface acoustic waves to spin ensembles. Firstly, we performed a series of ESR experiments exploring the potential of Fe³⁺ impurities in ZnO for spin-lattice coupling. This spin system has already been identified as a high potential quantum technology component due to its long coherence time. We show that the system also has good properties for spin-lattice coupling experiments, with a strain-coupling parameter G₃₃ = 280 ± 5GHz/strain, which is about 16 times larger than the largest reported for NV centres in diamond. We found that the LEFE effect as well as the spin Hamiltonian parameter D have a linear temperature dependence. As the relative change in each coincide, this strongly supports the notion that the modification of D by an electric field is a multiplicative effect rather than an additive one, D = D₀(1 + κΕ). The LEFE coefficient we measured is several times larger for Fe³⁺:ZnO than for Mn²⁺:ZnO. Secondly, we have fabricated and characterised SAW devices on bulk ZnO crystals and Fe doped lithium niobate. We found that the nominally pure ZnO was conductive at room temperature due to n-type intrinsic doping, and electrical losses inhibited any transmission through a SAW delay line above T = 200K. The one-port resonator measured down to milli-Kelvin temperatures showed excellent quality factors of up to Q ≃ 1.5 x 10⁵ in its superconducting state. Finally, we performed a surface acoustic wave spin resonance (SAWSR) experiment using a one-port SAW resonator fabricated on Fe²⁺:LN. We observed a clear signal at T ≃ 25 K, at a field near the expected one for a Δm_s = 2 transition between the |−1⟩ and |+1⟩ states. We concluded it to be a transition induced by acoustic coupling since the signal intensity did not tend to zero when the magnetic field was parallel to the crystal anisotropy axis. Furthermore, this tells us that the coupling is due to a modulation of the E zero-field splitting parameter rather than D. We investigated the dependence on microwave power and found the saturation limit. We performed a measurement of Fe³⁺:LN as well to reassure ourselves that the resonance is not magnetically excited by the field around the IDT.

No description available.

A surface acoustic wave (SAW) is a combination of a mechanical wave and a potential wave propagating on the surface of a piezoelectric substrate at the speed of sound. Such waves are widely applied in not only the communication industry, but also in quantum physics research, such as nanoelectronics, spintronics, quantum optics, and even quantum information processing. Here, I focus on low-dimensional electron transport and SAWs in GaAs and ZnO semiconductor heterostructures. The ability to pattern quantum nanostructures using gates has stimulated intense interest in research into mesoscopic physics. We have performed a series of simulations of gate structures, and having with the optimised boundary conditions and we find them to match experimental results, such as the pinch-off voltage of one-dimensional channels and SAW charge transport in induced n-i-n and n-i-p junctions. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software. With the calculated potential, we have modelled the process how a dynamic quantum dot is driven by a SAW and have analysed error mechanisms in SAW-driven quantisation (I=Nef, where N is the number of electrons in each SAW minimum, and f is the SAW resonant frequency). From energy spectroscopy measurements, we probe the electron energy inside a SAW-driven dynamic quantum dot and find that the small addition energy, which is around 3meV, is the main limitation for the SAW quantisation. To increase the confinement of SAW-driven quantum dots, we deposit a thin ZnO film, with a better piezoelectric coupling than GaAs, on a GaAs/AlGaAs heterostructure using high-target-utilisation sputtering (an Al2O3 buffer layer is deposited to protect the 2DEG during sputtering). With the ZnO, the SAW amplitude is greatly improved to 100 meV and the RF power required for pumping electrons using a SAW is greatly reduced. Finally, we have studied low-dimensional electron transport in a MgZnO/ZnO heterostructure. We have developed a technique for patterning gates using a parylene insulator, and used these to create one-dimensional quantum wires and observe electron ballistic transport with conductance quantised in units of 2e2/h The increasing electron effective mass as the 1D electron density decreases indicate that the electron-electron interaction in this MgZnO/ZnO heterostructure is strong. Because of these strong interactions, the 0.7 anomaly is observed just below each quantised plateau, and are much stronger than in GaAs quantum wires. Furthermore, we have also calculated the SAW-modulated spontaneous and piezoelectric polarisation in the ZnO heterostructure, and have observed a sign of this SAW-modulation in 2DEG density, which is different from the classical SAW-pumping mechanism. Our results show that a ZnO heterostructure should provide a good alternative to conventional III-V semiconductors for spintronics and quantum computing as they have less nuclear spins. This paves the way for the development of qubits benefiting from the low scattering of an undoped heterostructure together with potentially long spin lifetimes.

Mercury (Hg) has always been a serious risk to the environment and human health. It is a very common contamination in petroleum industry, which may lower product quality, threaten operation safety and worker’s health even at a very low concentration. Consequently the detection of mercury is very necessary. Gold is widely used as sensing material of mercury because it has a specific affinity with mercury and the adsorption of mercury changes characteristics of gold such as resistivity and effective mass density. In this thesis, common methods for sensing mercury vapor concentration were summarized and a surface acoustic wave (SAW) sensor utilizing the adsorption of mercury on gold electrodes was proposed for 1 μg/m3 level low concentration mercury vapor detection. The working principle of SAW sensor was studied and finite element method models were built to optimize the sensor design. The influence of several physical structure parameters such as electrode width and pitch on the sensor sensitivity and response time were studied using the simulation model. According to the simulation results a prototype of SAW sensor was designed and fabricated. The sensor was then analyzed with network analyzer and tested with mercury vapor. Preliminary results were presented and analyzed in this work. Finally potential future work was proposed and discussed.

In this thesis, the author proposes and develops novel multilayered Surface Acoustic Wave (SAW) devices with unique attributes for gas sensing applications. The design, simulation, fabrication and gas sensing performance of three multilayered SAW structures has been undertaken. The investigated structures are based on two substrates having high electromechanical coupling coefficient: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3), with a piezoelectric zinc oxide (ZnO) intermediate layer. Sensitivity towards target gas analytes is provided by thin film indium oxide (InOx) or tungsten trioxide (WO3). The high performance of the gas sensors is achieved by adjusting the intermediate ZnO layer thickness. Sensitivity calculations, undertaken with perturbation theory illustrate how the intermediate ZnO layer can be employed to modify the velocity-permittivity product of the supported SAW modes, resulting in highly sensitive conductometric SAW gas sensors. The work contained within this thesis addresses a broad spectrum of issues relating to multilayered SAW gas sensors. Topics include finite-element modelling, perturbation theory, micro-fabrication, metal oxide deposition, material characterisation and experiential evaluation of the layered SAW sensors towards nitrogen dioxide (NO2), hydrogen (H2) and ethanol gas phase analytes. The development of two-dimensional (2D) and three dimensional (3D) finite-element models provides a deep insight and understanding of acoustic wave propagation in layered anisotropic media, whilst also illustrating that the entire surface of the device can and should be used as the active sensing area. Additionally, the unique and distinctive surface morphology of the layered structures are examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline structure and orientation of the ZnO and WO3 layers are also examined by X-ray Diffraction Spectroscopy (XRD). The novel multilayered SAW structures a re shown to be highly sensitive, capable of sensing NO2 and ethanol concentration levels in the parts-per-billion and parts-per-million range, respectively, and H2 concentrations below 1.00% in air. The addition of platinum or gold catalyst activator layers on the WO3 sensitive layer is shown to improve sensitivity and dynamic performance, with response magnitudes up to 50 times larger than bare WO3. The gas sensing performance of the investigated structures provide strong evidence that high sensitivity can be achieved utilising multilayered SAW structures for conductometric gas sensing applications.

In the present thesis, diamond-like carbon thin films were deposited on Si(100) and LiNbO3 substrates by a planar capacitor plasma-enhence-chemical-vapor-deposition system. The reaction gases were C2H2,CH4,O2 and mixed with Ar (95¢M) and H2(5¢M).The influence of the growth of the thin film from different substrates and three different source gases flow ratios have been studied. The bi-layers structure of SAW(Surface Acoustic Wave) device was then fabricated. The interdigital transducers (IDTs) were fabricated on the bi-layers structure. The conditions of the DLC thin film of the bi-layers structure was varied in order to discuss its effects on SAW devices. In addition to Raman analyses, SEM and AFM have been employed to characterize the DLC thin film quality. From the experimental results of Raman spectrum analysis reveals that the DLC film has wide and flat spectrum region at wavelength of 1585~1600cm-1 of G-band and 1390cm-1 of D-band .It indicates that the DLC film contains much graphite sp2 bonds and a small part of amorphous DLC sp3 bonds. The optimal deposition conditions of the DLC film have been found for the reaction gas of C2H2 and Ar, from which the insertion loss of the SAW filter shows the quality better than from the others. SEM and AFM analyses shows that the roughness of the DLC film is below 10 nm and the faces of the DLC films are flat to be made into devices.

Wireless Surface Acoustic Wave (SAW) devices were fabricated and tested using planar Lithium Niobate (LiNbO₃) as substrate. The working frequencies were in the 180 MHz and 360 MHz range. Using a network analyser, the devices were interrogated with a wireless range of more than 2 metres. Trials with Electron Beam Lithography (EBL) to fabricate SAW devices working in the 2450 MHz with a calculated feature size of 350 nm are discussed. Charging problems became evident as LiNbO₃ is a strong piezoelectric and pyroelectric material. Various attempts were undertaken to neutralise the charging problems. Further investigation revealed that sputtered Zinc Oxide (ZnO) is a suitable material for attaching SAW devices on irregularly shaped material. DC sputtering was used and several parameters have been optimised to achieve the desired piezoelectric effect. ZnO was sputtered using a magnetron sputtering system with a 75 mm Zn target and a DC sputter power of 250 Watts. Several trials were performed and an optimised material has been prepared under the following conditions: 9 sccm of Oxygen and 6 sccm of Argon were introduced during the process which resulted in a process pressure of 1.2x10⁻² mbar. The coatings have been characterised using Rutherford Backscattering, X-ray diffraction, SEM imaging, and Atomic force microscopy. SAW devices were fabricated and tested on 600 nm thick sputtered ZnO on a Si substrate with a working frequency of 430 MHz. The phase velocity has been calculated as 4300m/s. Non-planar samples have been coated with 500 nm of sputtered ZnO and SAW structures have been fabricated on using EBL. The design frequency is 2450 MHz, with a calculated feature size of 1 µm. The surface roughness however prevented a successful lift-off. AFM imaging confirmed a surface roughness in the order of 20 nm. Ways to improve manufacturability on these samples have been identified.

Wireless surface acoustic wave (SAW) sensors offer unique advantages over other sensor technologies because of their inherent ability to operate in harsh environments and completely passive operation, providing a reliable, maintenance-free life cycle. For certain SAW sensor applications the challenge is building a wirelessly interrogatable device with the same lifetime as the SAW substrate. The design of these application intensive sensors is complicated by the degradation of device bond wires, die adhesive, and antenna substrate. In an effort to maximize the benefits of the platform, this dissertation demonstrates wafer-level integrated SAW sensors that directly connect the thin film SAW to a thick film on-wafer antenna. Fully integrated device embodiments are presented that operate over a wide range of temperatures using different fabrication techniques, substrates, and coding principles.

Compared to the much more common photonic crystals that are used to manipulate light, phononic crystals (PnCs) with inclusions in a lattice can be used to manipulate sound. While trying to propagate in a periodically structured media, acoustic waves may experience geometries in which propagation forward is totally forbidden. Furthermore, defects in the periodicity can be used to confine acoustic waves to follow complicated routes on a wavelength scale. Using advanced fabrication methods, we aim to implement these structures to control surface acoustic wave (SAW) propagation on the piezoelectric surface and eventually interact SAWs with quantum structures. To investigate the interaction of SAWs with periodic elastic structures, SAW interdigital transducers (IDTs) and PnC fabrication procedures were developed. GaAs is chosen as a piezoelectric substrate for SAWs propagation. Lift-off photolithography processes were used to fabricate IDTs with finger widths as low as 1.5 micron. PnCs are periodic structures of shallow air holes created in GaAs substrate by means of a wet-etching process. The PnCs are square lattices with lattice constants of 8 and 4 micron. To predict the behavior of a SAW when interacting with the PnC structures, an FDTD simulator was used to calculate the band structures and SAW wave displacement on the crystal surface. The bandgap (BG) predicted for the 8 micron crystal ranges from 180 MHz to 220 MHz. Simulations show a shift in the BG position for 4 micron crystals ranging from 391 to 439 MHz. Two main waveguide geometries were considered in this work: a simple line waveguide and a funneling entrance line waveguide. Simulations indicated an increase in acoustic power density for the funneling waveguides. Fabricated device evaluated with electrical measurements. In addition, a scanning Sagnac interferometer is used to map the energy density of the SAWs. The Sagnac interferometer is designed to measure the outward displacement of a surface due to the SAW. Interferometric measurements confirmed waveguiding in the modified funnel entrance waveguide embedded in the 4 micron PnC. However, they also revealed strong dissipation of the SAW in the waveguide due to the non-vertical sidewalls resulting from the wet-etch process. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-11-29 15:53:46.369