This work developed a process to provide physical, electrical, and environmental protection to the electrical lead system of an optical switch device. A literature review was conducted to find materials and processes suitable to the stress-sensitive, high voltage characteristics of many optical switch devices. An automatic dispensing dam and fill process, and three candidate materials (two epoxy and one silicone) were selected for investigation. Experimental and analytical techniques were used to evaluate the materials. Methods applied included interferometric die warpage measurements, electrochemical migration resistance tests (ECMT), thermal cycling, and finite element analysis. The silicone dam and fill system was selected based upon the results of die warpage and electrochemical migration resistance tests. A modified, selective dam and fill process was developed and preliminary reliability testing was performed. The paper provides detailed instructions for successful encapsulation of the optical switch's lead system.

This Thesis relates to the continually advancing field of microelectromechanical systems (MEMS). With MEMS technology, there are many different areas of concentration available for research. This Thesis addresses analysis and preliminary characterization of a cantilever-type MEMS chemical sensor for detection of chemicals and organic components operating at room temperature (20˚C and sea level pressure of 1 atm). Such sensors can be useful in a wide variety of applications. There currently exist several different types of MEMS chemical sensors. Each is based on a different detection method, e.g., capacitive, thermal, resistive, etc., and is used for specific tasks. Out of all currently available detection methods, the most common is the gravimetric method. The gravimetric sensor works by absorbing the chemical in a special material, usually a polymer, which alters the overall mass of the sensing element that can then be measured, or detected, to identify the chemical absorbed. One of the more exciting developments in the field of gravimetric chemical MEMS has been with the advancement of cantilever-type sensors. These cantilevers are small and usually on the order of only about 300 m in length. In order to utilize the gravimetric method, a cantilever is coated with a polymer that allows an analyte to bond to it and change its mass, which in turn changes the resonant frequency of the cantilever. The change in frequency can then be measured and analyzed and from it, the amount of absorbed mass can be calculated. Current research in the cantilever-type resonating sensors for the detection of hydrogen is developing measurement capabilities of 1 ppm (part-per-million). In this Thesis number of sample cantilevers were qualitatively assessed and their dimensional geometry measured. Based on these measurements, frequency data were obtained. In addition, the overall uncertainty in the resonant frequency results was calculated and the contributing factors to this uncertainty were investigated. Experimental methods that include laser vibrometry, optoelectronic laser interferometric microscopy (OELIM), and atomic force microscopy (AFM), were utilized to measure the frequency responses of the samples. The analytically predicted natural frequencies were compared to the experimental data to determine correlation subject to the uncertainty analysis. Parametric analyses involving chemical absorption processes were also conducted. Such analyses considered different parameters, e.g., damping and stiffness as well as changes in their values, to determine contributions they make to the quality of the frequency data and the effect they have on sensitivity of the MEMS cantilever-type chemical sensors. Once these parametric analyses were completed, it was possible to estimate the sensitivity of the cantilever, or the ability for the cantilever to detect frequency shifts due to absorption of the target chemical. Results of the parametric analyses of the fundamental resonant frequency were then correlated with the sensitivity results based on the chemical absorption. This Thesis correlates many results and ideas and probes problems revolving around the analysis and characterization of a MEMS cantilever-type chemical sensor.

The Bistable Aerial Platform (BAP) has been developed in order to further enlarge the repertoire of devices available at the microscale. This novel device functions as a switch in that its platform can lock in two positions, up or down. Herein, it will be examined and explained, but a true understanding of its workings requires a better understanding of its compliant constituent parts. The Helico-Kinematic Platform (HKP), which serves as an actuator for the BAP, is currently under investigation by another researcher and will be merely touched upon here. The focus, therefore, will rest on the analysis of the Quadrantal Bistable Mechanism (QBM), the principle component of the BAP. A preliminary pseudo-rigid-body model, an aid for the understanding of compliant mechanisms, will also be examined for the QBM. The models developed for these two devices, the HKP and QBM, can later be combined to form a full model of the Bistable Aerial Platform.

Varactors form an important part of many communication circuits. They are utilized in oscillators, tunable matching networks, tunable filters and phase-shifters. This thesis deals with the design, analysis, characterization and applications of a novel MEMS varactor. Lower actuation voltage and higher dynamic range are the two important issues widely addressed in the study of MEMS varactors. The pull-in instability, due to which only 33% of the gap between plates could be covered smoothly, greatly reduces useful dynamic range of MEMS varactors. We propose a torsional MEMS varactor that exploits “displacement amplification” whereby pull-in is overcome and wide dynamic range is achieved. The torsion beam in the device undergoes torsion as well as bending. Behavior of the device has been analyzed through torque and force balance. Based on the torque balance and the force balance expressions, theoretical limits of torsion angle and bending for stable operation have been derived. Torsional MEMS varactors and its variants are fabricated through a commercial fabrication process (polyMUMPS) and extensive characterization has been carried out. Capacitance-voltage characteristics show a maximum dynamic range of 1:16 with parasitic capacitance subtracted out from the capacitance values. A bidirectional torsional varactor, in which the top AC plate moves not only towards bottom plate but also away from bottom plate, is also tested. The bottom AC plate is isolated from low resistivity substrate with a thin nitride layer. This gives rise to large parasitic capacitances at higher frequencies. So to avoid this, a varactor with both AC plates suspended in air is designed and fabricated. A dynamic range of 1:8 including parasitic capacitances has been achieved. Self-actuation is studied on fabricated structures and a torsional varactor that overcomes self-actuation has been proposed. Hysteresis behavior of the torsional varactor is analyzed for different AC signals across the varactor plates. Effects of residual stress on C-V characteristics are studied and advantages and disadvantages of residual stress on device performance are discussed. The torsional varactors have been cycled between Cmax and Cmin for 36 hours continuously without any failure. High-frequency characteristics of torsional varactors are analyzed through measurements on one-port and two port configurations. Measurements are done on polyMUMPS devices to study the capacitance variation with voltage, quality factor (Q) and capacitance variation with frequency. Effects of substrate are de-embedded from the device and characteristics of device are studied. An analog phase shifter based on torsional varactor proposed and analyzed through HFSS simulations. Very high tuning range can be achieved with a LC-VCO based on torsional varactors. A LC VCO with the torsional varactor as a capacitor in LC tank is designed. The torsional varactor and IC are fabricated separately and are integrated through wire bonding. Bond-wires are used as inductors.

This thesis treats the development of packaging and integration methods for the cost-efficient encapsulation and packaging of microelectromechanical (MEMS) devices. The packaging of MEMS devices is often more costly than the device itself, partly because the packaging can be crucial for the performance of the device. For devices which contain liquids or needs to be enclosed in a vacuum, the packaging can account for up to 80% of the total cost of the device. The first part of this thesis presents the integration scheme for an optical dye thin film NO2-gas sensor, designed using cost-efficient implementations of wafer-scale methods. This work includes design and fabrication of photonic subcomponents in addition to the main effort of integration and packaging of the dye-film. A specific proof of concept target was for NO2 monitoring in a car tunnel. The second part of this thesis deals with the wafer-scale packaging methods developed for the sensing device. The developed packaging method, based on low-temperature plastic deformation of gold sealing structures, is further demonstrated as a generic method for other hermetic liquid and vacuum packaging applications. In the developed packaging methods, the mechanically squeezed gold sealing material is both electroplated microstruc- tures and wire bonded stud bumps. The electroplated rings act like a more hermetic version of rubber sealing rings while compressed in conjunction with a cavity forming wafer bonding process. The stud bump sealing processes is on the other hand applied on completed cavities with narrow access ports, to seal either a vacuum or liquid inside the cavities at room temperature. Additionally, the resulting hermeticity of primarily the vacuum sealing methods is thoroughly investigated. Two of the sealing methods presented require permanent mechanical fixation in order to complete the packaging process. Two solutions to this problem are presented in this thesis. First, a more traditional wafer bonding method using tin-soldering is demonstrated. Second, a novel full-wafer epoxy underfill-process using a microfluidic distribution network is demonstrated using a room temperature process. / <p>QC 20130325</p>

Several fabrication techniques for surface micromachined 3-D structures have been developed for RF components. The fabrication techniques all have in common the use of epoxy patterning and subsequent metallization. Techniques and structures such as embedded conductors, epoxy-core conductors, a reverse-side exposure technique, a multi-exposure scheme, and inclined patterning are presented. The epoxy-core conductor technique makes it easy to fabricate high-aspect-ratio (10-20:1), tall (~1mm) RF subelements as well as potentially very complex structures by taking advantage of advanced epoxy processes. To demonstrate feasibility and usefulness of the developed fabrication techniques for RF applications, two test vehicles are employed. One is a solenoid type RF inductor, and the other is a millimeter wave radiating structure such as a W-band quarter-wavelength monopole antenna. The embedded inductor approach provides mechanical robustness and package compatibility as well as good electrical performance. An inductor with a peak Q-factor of 21 and an inductance of 2.6nH at 4.5GHz has been fabricated on a silicon substrate. In addition, successful integration with a CMOS power amplifier has been demonstrated. A high-aspect-ratio inductor fabricated using epoxy core conductors shows a maximum Q-factor of 84 and an inductance of 1.17nH at 2.6GHz on a glass substrate with a height of 900um and a single turn. Successful W-band monopole antenna fabrication is demonstrated. A monopole with a height of 800um shows its radiating resonance at 85GHz with a return loss of 16dB. In addition to the epoxy-based devices, an advanced tunable ferroelectric device architecture is introduced. This architecture enables a low-loss conductor device; a reduced intermodulation distortion (IMD) device; and a compact tunable LC module. A single-finger capacitor having a low-loss conductor with an electrode gap of 1.2um and an electrode thickness of 2.2um has been fabricated using a reverse-side exposure technique, showing a tunability of 33% at 10V. It shows an improved Q-factor of 21.5. Reduced IMD capacitors consist of wide RF gaps and narrowly spaced high resistivity electrodes with a gap of 2um and a width of 2um within the wide gap. A 14um gap and a 20um gap capacitor show improved IMD performance compared to a 4um gap capacitor by 6dB and 15dB, respectively, while the tunability is approximately 21% at 30V for all three devices due to the narrowly spaced multi-pair high resistivity DC electrodes within the gap. Finally, a compact tunable LC module is implemented by forming the narrow gap capacitor in an inductor shape. The resonance frequency of this device is variable as a function of DC bias and a frequency tunability of 1.1%/V is achieved. The RF components developed in this thesis illustrate the usefulness of the application of micromachining technology to this application area, especially as frequencies of operation of RF systems continue to increase (and therefore wavelengths continue to shrink).

The goal of this research was to develop acoustic sensors and actuators for microfluidic applications. To this end, capacitive micromachined ultrasonic transducers (cMUTs) were developed which generate guided acoustic waves in fluid half-spaces and microchannels. An interdigital transducer structure and a phased excitation scheme were used to selectively excite guided acoustic modes which propagate in a single lateral direction. Analytical models were developed to predict the geometric dispersion of the acoustic modes and to determine the sensitivity of the modes to changes in material and geometric parameters. Coupled field finite element models were also developed to predict the effect of membrane spacing and phasing on mode generation and directionality. After designing the transducers, a surface micromachining process was developed which has a low processing temperature of 250C and has the potential for monolithically integrating cMUTs with CMOS electronics. The fabrication process makes extensive use of PECVD silicon nitride depositions for membrane formation and sealing. The fabricated interdigital cMUTs were placed in microfluidic channels and demonstrated to sense changes in fluid sound speed and flow rate using Scholte waves and other guided acoustic modes. The minimum detectable change in sound speed was 0.25m/s, and the minimum detectable change in flow rate was 1mL/min. The unique nature of the Scholte wave allowed for the measurement of fluid properties of a semi-infinite fluid using two transducers on a single substrate. Changes in water temperature, and thus sound speed, were measured and the minimum detectable change in temperature was found to be 0.1C. For fluid pumping, interdigital cMUTs were integrated into microchannels and excited with phase-shifted, continuous wave signals. Highly directional guided waves were generated which in turn generated acoustic streaming forces in the fluid. The acoustic streaming forces caused the fluid to be pumped in a single, electronically-controlled direction. For a power consumption of 43mW, a flow rate of 410nL/min was generated against a pressure of 3.4Pa; the thermodynamic efficiency was approximately 5x10-8%. Although the efficiency and pressure head are low, these transducers can be useful for precisely manipulating small amounts of fluid around microfluidic networks.

This dissertation presents the research on several different projects. The first project is a via-less CPW RF probe pad to microstrip transition; The second, the third, and the fourth one are reconfigurable microwave circuits using RF MEMS switches: an X-band reconfigurable bandstop filter for wireless RF frontends, an X-band reconfigurable impedance tuner for a class-E high efficiency power amplifier using RF MEMS switches, and a reconfigurable self-similar antenna using RF MEMS switches. The first project was developed in order to facilitate the on-wafer measurement for the second and the third project, since both of them are microstrip transmission line based microwave circuits. A thorough study of the via-less CPW RF probe pad to microstrip transition on silicon substrates was performed and general design rules are derived to provide design guidelines. This research work is then expanded to W-band via-less transition up to 110 GHz. The second project is to develop a low power reconfigurable monolithic bandstop filter operating at 8, 10, 13, and 15 GHz with cantilever beam capacitive MEMS switches. The filter contains microstrip lines and radial stubs that provide different reactances at different frequencies. By electrically actuating different MEMS switches, the different reactances from different radial stubs connecting to these switches will be selected, thus, the filter will resonate at different frequencies. The third project is to develop a monolithic reconfigurable impedance tuner at 10 GHz with the cantilever DC contact MEMS switch. The impedance tuner is a two port network based on a 3bit-3bit digital design, and uses 6 radial shunt stubs that can be selected via integrated DC contact MEMS switches. By selecting different states of the switches, there will be a total of 2^6 = 64 states, which means 64 different impedances will be generated at the output port of the tuner. This will provide a sufficient tuning range for the output port of the power amplifier to maximize the power efficiency. The last project is to integrate the DC contact RF MEMS switches with self-similar planar antennas, to provide a reconfigurable antenna system that radiates with similar patterns over a wide range of frequencies.

A comprehensive study of the High-pass/Low-pass topology has been performed, increasing the understanding of error sources arising from bit layout issues and fabrication tolerances. This included a detailed analysis of error sources in monolithic microwave phase shifters due to device size limitations, inductor parasitics, loading effects, and non-ideal switches. Each component utilized in the implementation of a monolithic high-low pass phase shifter was analyzed, with its influence on phase behavior shown in detail. An emphasis was placed on the net impact on absolute phase variation, which is critical to the system performance of a phased array radar system. The design of the individual phase shifter filter sections, and the influence of bit ordering on overall performance was also addressed. A variety of X-band four- and five-bit phase shifters were fabricated in a 200 GHz SiGe HBT BiCMOS technology platform, and further served to validate the analysis and design methodology. The SiGe phase shifter can be successfully incorporated into a single-chip T/R module forming a system-on-a-chip (SoC). Reduction in the physical size of transmission lines was shown to be a possibility with spinel magnetic nanoparticle films. The signal transmission properties of phase lines treated with nanoparticle thin films were examined, showing the potential for significant size reduction in both delay line and High-pass/Low-pass phase topologies. Wide-band, low-loss, and near-hermetic packaging techniques for RF MEMS devices were presented. A thermal compression bonding technique compatible with standard IC fabrication techniques was shown, that uses a low temperature thermal compression bonding method that avoids plastic deformations of the MEMS membrane. Ultimately, a system-on-a-package (SoP) approach was demonstrated that utilized packaged RF MEMS switches to maintain the performance of the SiGe phase shifter with much lower loss. The extremely competitive performance of the MEMS-based High-pass/Low-pass phase shifter, despite the lack of the extensive toolkits and commercial fabrication facilities employed with the active-based SiGe phase shifters, confirms both the effectiveness of the detailed phase error analysis presented in this work and the robust nature of the High-pass/Low-pass topology.

This thesis reports the development of advanced readout and control electronics for MEMS gyroscopes developed at METU. These gyroscope electronics are separated into three main groups: high sensitive interface circuits, drive mode amplitude controlled self oscillation loops, and sense mode phase sensitive amplitude demodulators. The proposed circuits are first implemented with discrete components, and then integrated on CMOS chips. A self oscillation loop enabling constant amplitude drive mode vibrations independent of sensor parameters and ambient conditions is developed. A fully functional angular rate system, which is constructed by employing this advanced control electronics together with the transresistance amplifier type interfaces and sense mode electronics, is implemented on a dedicated PCB having 5.4x2.4 cm2 area. This system demonstrates an impressive performance far better than the best performance achieved by any angular rate system developed at METU. Bias instability and angle random walk values are measured as 14.3 &ordm / /hr and 0.126 &ordm / /&amp / #8730 / hr, respectively. The scale factor of the system is found as 22.2 mV/(&ordm / /sec) with a nonlinearity of 0.01%, and a zero rate output of 0.1 &ordm / /sec, in &plusmn / 50 &ordm / /sec measurement range. CMOS unity gain buffer (UGB) and transimpedance amplifier (TIA) type resistive and capacitive interfaces are characterized through AC, transient, and noise tests. It is observed that on chip biasing mechanisms properly DC-bias the high impedance nodes to 0 V potential. UGB type capacitive interfaces demonstrate superior performance than TIA counterparts due to stability problems associated with TIA interfaces. CMOS differential drive mode control and sense mode demodulation electronics give promising results for the future performance tests.