ABSTRAT In this thesis, we focused on the fabrication and frequency-modulation of £f/4 mode dual-band solidly mounted resonators and filters. To accomplish the Bragg reflector, the RF/DC magnetron sputtering system with dual targets is adopted to deposit alternating layers of quarter-wavelength Mo and SiO2 thin films. We tune the fabrication parameters in accordance with the AFM measurement and achieve a low roughness of 2.9nm on a nine-layer reflector. The piezoelectric layer, aluminum nitride (AlN) thin films, is deposited on the Bragg reflector by means of reactive RF magnetron sputtering. We alter the distance between substrate and target is altered to deposit AlN with various c-axis tilting angle which results in longitudinal and shear acoustic waves at the same time. Furthermore, we use mass loading effect to modulate the resonance frequency and fabricate £k- ladder type filters. In various numbers of reflector layers, the optimum frequency response is obtained with return loss of -26dB, in a SMR on a 3.5 pair reflector. To investigate the relationship between longitudinal and shear resonance in different resonance frequency, we alter the c-axis tilting angle of AlN as well as various mass loading on the SMRs. Based on the experimental results, the ratio of longitudinal to shear resonance frequency remains a constant value despite various c-axis tilting angle of AlN and mass loading on the SMRs. In addition, the electromechanical coupling coefficient, Kt2, of shear resonance raises with the increase of c-axis tilting angle of AlN. Finally,we have successfully fabricated SMRs with frequency modulataion of 3,899.68 Hz-cm2/ng and £k-ladder type filters with 26 MHz bandwidth.

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.

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.

In this study, AlN films are deposited using reactive RF magnetron sputter on various bottom metals, such as Mo, Al and Pt. The orientation of piezoelectric AlN thin films on different bottom electrode materials are investigated. Moreover, the acoustic Bragg reflectors deposited by DC magnetron sputter are composed of alternating layers of high and low acoustic impedance materials. To improve the performance of the reflectors, rapid thermal anneal and deposition process control over roughness of the thin film are also investigated. The resonance characteristics are improved obviously by deposition process control over thin films. The roughness control is the key factor of good frequency responses of SMR. In addition, the more layer of the reflectors the better the frequency response we obtained. The frequency responses of SMR are slightly improved by rapid thermal annealing procsess. Although defects in the thin films would be eliminated, nevertheless the thin film roughness became worse after annealing. This phenomenon would limit the improvement of frequency responses.

Recently, there are great demands for RF band pass filters with smaller size/volume, lighter weight, and higher performance for advanced mobile/wireless communication system. However, fabricated RF filters using traditional lumped element, dielectric resonators, or surface acoustic wave¡]SAW¡^filters have difficulties in on-chip integration, power handling capability, and temperature compensation. Alternatively, thin-film bulk acoustic wave resonator¡]FBAR¡^filters are very suitable devices for MMIC¡¦s since they can be fabricated on Si or GaAs substrates at a lower magnitude than lumped elements or dielectric resonators, plus they have a much lower insertion loss and higher power handling capabilities than surface acoustic wave devices and full integration with other CMOS RF IC circuitry for realizing a goal of system on chip¡]SOC¡^. In their simplest form, practical FBARs consist of a sputtered piezoelectric thin film sandwiched between top and bottom electrodes onto which an electric field is then applied. An FBAR must have two acoustically reflecting surfaces in order to trap energy and produce resonating characteristics. For this purpose, the thin film bulk acoustic resonator has to be isolated acoustically from the substrate. In view of this, in order to obtain a high Q factor and reduce spurious responses, this paper proposed the air gap type resonator using the sacrificial layer etching. The thickness of the AlN thin film used for piezoelectric thin film of Air-gap FBAR is 1um. Pt/Ti with 3000Å/300Å thickness is used as the top and bottom electrode. The device has a resonance frequency of 1.2GHz, and S11-paparameter of -25dB is also obtained.

In this study, highly C-axis oriented AlN thin films stacked upon Al bottom electrode on Si and Glass substrate are deposited with Reactive RF magnetron sputtering Technique. Three different sputtering systems were utilized to evaluate the optimized growth parameters. Room temperature growth was applied to the all system. During thin film growing , the substrate bias condition, sputtering work pressure, sputtering power and the N2 concentration are those key parameters to be adjusted in order to gain smooth surface morphology and highly C-axis prefer orientation AlN thin films. The crystallography of the deposited films was analyzed by x-ray diffraction (XRD). Film surface morphology was characterized by scanning electron microscopy (SEM). Meanwhile, transmission electron microscopy (TEM) was adopted to observe the microstructure and determine the grain size of the film. The results of the XRD patterns showed that in a 17cm long sputtering working distance condition, the AlN (002) can be obtained and the peak intensity can be increased when the sputtering power was fixed meanwhile reduced the working pressure and applied the negative bias on the substrate. The surface morphology can be improved with long working sputtering distance. The micrography of the TEM reveals that there is a transition region between Al metal and AlN film. Fine column structures can be observed in the initial growth stage. The size of the grain increased as the film became thicker. Strong AlN (002) ring pattern was obtained from the region of the top of the film. It indicates that the AlN (002) will not appear till the thickness of the film reach the critical thickness.

The solidly mounted resonator (SMR) is constructed of a Bragg reflector and a piezoelectric layer AlN. In order to obtain an appropriate SMR for the high frequency communication applications and high sensitivity bio-sensor applications, the Bragg reflector, the AlN, and the loading effect have been investigated thoroughly. The thesis presents the influences of surface roughness of the Bragg reflector and materials¡¦ selection on the resonance characteristics of an SMR. Three combinations of thin films, AlN/Al, Mo/Ti, and Mo/SiO2, are adopted. Originally, an AlN/Al multi-layer is used as the Bragg reflector. The poor surface roughness of this Bragg reflector results in a poor SMR frequency response. To improve the surface roughness of Bragg reflectors, a Mo/Ti multi-layer with a similar coefficient of thermal expansion is adopted. By controlling deposition parameters, the surface roughness of the Bragg reflector is improved. Finally, a material combination of Mo/SiO2 with high acoustic impedance ratio of 4.7 is adopted. Better resonance characteristics of SMR are obtained. The experimental results show a distinct resonance phenomenon around 2.5 GHz and excellent noise restraint. Afterwards, a ¼£f mode SMR is experimentally realized. The selection of high and low acoustic impedance for the first layer beneath piezoelectric layer results in the ¼£f mode and ½ £f mode resonance configurations, respectively. The coupling coefficient Keff2 of 6.9% is obtained, which is in agreement with the theoretical analysis. Following, the theoretical analysis upon the dual mode frequency-shift was characterized, and a modified formula was carried out. The c-axis tilted angle of AlN was altered as well as the various mass loading on the SMR. Based on the experimental results, the dual resonance frequencies showed a nonlinear decreasing trend with a linear increase of the mass loading. Furthermore, the ratio of the longitudinal resonant frequency to the shear resonant frequency remained at a range around 1.76 despite the various c-axis tilted angles of AlN and gradual mass loading on the SMR. The electromechanical coupling coefficient, keff2, of the shear resonance rose with the increase of the c-axis tilted angle of AlN. However, the longitudinal resonance fades away with the AlN c-axis tilted angle, and the quality factor of the longitudinal resonance decreases. Finally, the dual mode resonances are improved by tilting the off-center substrates toward the sputtering source and successfully enhance the longitudinal resonance while preserve the shear resonance at the same time. Not only the shear resonance for the liquid-based sensing application, but also an outstanding longitudinal resonance could be obtained. The practicability of the dual-mode resonator is extended for the applications of high frequency wireless communication and high sensitivity bio-chemical sensors.

In this study, the ladder-type filters based on back-etched thin film bulk acoustic resonator (TFBAR) were fabricated with several patterns to investigate the influence on their frequency responses. The highly c-axis oriented ZnO films were deposited on silicon substrates by reactive RF magnetron sputtering. The optimal two-step deposition temperature for ZnO films is 100 ¢J, which is obtained by means of SEM AFM, and XRD analysis. According to the experimental results, it leads to good resonance responses as TFBAR filters are fabricated with the patterns of large resonance area, two stages and the ratio of shunt/series resonance area is equal to two. Herein, conventional thermal annealing (CTA) was adopted to improve the frequency responses of TFBAR filters. Because CTA treatment can release stress and improve surface roughness of ZnO and Pt films, it enhances the frequency responses of TFBAR filters. The optimal CTA treatment temperature for TFBAR filters is 400 ¢J. Finally, TFBAR filters show the good performances with insertion loss of -8.138 dB, band rejection of 10.9 dB and bandwidth of 37.125 MHz.

abstract: Different environmental factors, such as ultraviolet radiation (UV), relative humidity (RH) and the presence of reducing gases (acetone and ethanol), play an important role in the daily life of human beings. UV is very important in a number of areas, such as astronomy, resin curing of polymeric materials, combustion engineering, water purification, flame detection and biological effects with more recent proposals like early missile plume detection, secure space-to-space communications and pollution monitoring. RH is a very common parameter in the environment. It is essential not only for human comfort, but also for a broad spectrum of industries and technologies. There is a substantial interest in the development of RH sensors for applications in monitoring moisture level at home, in clean rooms, cryogenic processes, medical and food science, and so on. The concentration of acetone and other ketone bodies in the exhaled air can serve as an express noninvasive diagnosis of ketosis. Meanwhile, driving under the influence of alcohol is a serious traffic violation and this kind of deviant behavior causes many accidents and deaths on the highway. Therefore, the detection of ethanol in breath is usually used as a quick and reliable screening method for the sobriety checkpoint. Traditionally, semiconductor metal oxide sensors are the major candidates employed in the sensing applications mentioned above. However, they suffer from the low sensitivity, poor selectivity and huge power consumption. In this dissertation, Zinc Oxide (ZnO) based Film Bulk Acoustic Resonator (FBAR) was developed to monitor UV, RH, acetone and ethanol in the environment. FBAR generally consists of a sputtered piezoelectric thin film (ZnO/AlN) sandwiched between two electrodes. It has been well developed both as filters and as high sensitivity mass sensors in recent years. FBAR offers high sensitivity and excellent selectivity for various environment monitoring applications. As the sensing signal is in the frequency domain, FABR has the potential to be incorporated in a wireless sensor network for remote sensing. This study extended our current knowledge of FBAR and pointed out feasible directions for future exploration. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Union between top-down and bottom-up assembly is inevitable when scaling down physical, chemical, and biological sensors and probes. Current sensor/probe-based technologies are firmly founded on top-down manufacturing, with limitations in cost of production, manufacturing methods, and material constraints. As an alternative to such limitations, contemporary synthesis techniques for one-dimensional nanostructures have been combined with established methods of micro-fabrication for the development of novel tools and techniques for nanotechnology. More specifically, this dissertation is a systematic study of the synthesis and characterization of ZnO nanostructures for piezoelectric applications. Within this study the following goals have been achieved: 1) rational design and control of a diversity of novel ZnO nanostructures, 2) improved understanding of polar-surface-dominated (PSD) phenomena among Wurtzite crystal structures, 3) confirmation of Taskers Rule via the synthesis, characterization, and modeling of polar-surface-dominated nanostructures, 4) measurement of the surface-charge density for real polar surfaces of ZnO, 5) confirmation of the electrostatic polar-charge model used to describe polar-surface-dominated phenomena, 6) dispersion of ZnO nanobelts onto the selective layers of surface acoustic wave (SAW) devices for gas sensing applications, 7) manipulation of ZnO nanostructures using an atomic force microscope (AFM) for the development of piezoelectric devices, 8) fabrication of bulk acoustic resonator (BAR) and film bulk acoustic resonator (FBAR) devices based on the integrity of individual ZnO belts, 9) electrical characterization of a ZnO belt BAR device, 10) prediction and confirmation of the electrical response from a BAR device using a one-dimensional Krimholt-Leedom-Matthaei (KLM) model, and 11) development of a finite element model (FEM) to accurately predict the electrical response from ZnO belt BAR and FBAR devices in 3D.