Micro-Electro-Mechanical Systems (MEMS) varactors have the potential to replace conventional varactor diodes, due to their high loss and non-linearity, in many applications such as phase shifters, oscillators, and tunable filters. The objective of this thesis is to develop novel MEMS varactors to improve the capacitance tuning ratio, linearity, and quality factor. Several novel varactor configurations are developed, analyzed, fabricated and tested. They are built by using standard MEMS fabrication processes, as well as monolithic integration techniques in CMOS technology. The first capacitor consists of two movable plates, loaded with a nitride layer that exhibits an analog continuous capacitance tuning ratio. To decrease the the parasitic capacitance, a trench in the silicon substrate under the capacitor is adopted. The use of an insulation dielectric layer on the bottom plate of the MEMS capacitor increases the capacitors’ tuning ratio. Experimental and theoretical results are presented for two versions of the proposed capacitor with different capacitance values. The measured capacitance tuning ratio is 280% at 1 GHz. The proposed MEMS vararctor is built using the MetalMUMPs process. The second, third, and fourth capacitors have additional beams that are called carrier beams. The use of the carrier beams makes it possible to obtain an equivalent nonlinear spring constant, which increases the capacitors’ analog continuous tuning ratio. A lumped element model and a continuous model of the proposed variable capacitors are developed. The continuous model is simulated by commercial software. A detailed analysis for the steady state of the capacitors is presented. The measured capacitance tuning ratios of these three capacitors are 410%, 400% and 470%, respectively at 1 GHz. Also, the selfresonance frequency is measured and found to exceed 11 GHz. The proposed MEMS variable capacitors are built by the PolyMUMPs process. The fifth novel parallel-plate MEMS varactor has thin-film vertical comb actuators as its driver. Such an actuator can vertically displace both plates of the parallel-plate capacitor. By making use of the fringing field, this actuator exhibits linear displacement behavior, caused by the induced electrostatic force of the actuator’s electrodes. The proposed capacitor has a low parasitic capacitance and linear deflection due to the mechanically connected and electrically isolated actuators to the capacitor’s parallel-plates. The measured tuning capacitance ratio is 7:1 (600%) at 1 GHz. The fabricated MEMS varactor exhibits a self resonance frequency of 9 GHz and built by MetalMUMPs process. The sixth parallel-plate MEMS varactor exhibits a linear response and high tuning capacitance ratio. The capacitor employs the residual stress of the chosen bi-layer, and the non-linear spring constants from the suspended cantilevers to obtain a non-linear restoring force that compensates for the nonlinear electrostatic force induced between the top and bottom plates. Two existing techniques are used to widen the tuning range of the proposed capacitor. The first technique is to decrease the parasitic capacitance by etching the lossy substrate under the capacitor’s plates. The second technique is employed to increase the capacitance density, where the areas between the top and bottom plates overlap, by applying a thin film of dielectric material, deposited by the atomic layer deposition (ALD) technique. The measured linear continuous tuning ratio for the proposed capacitor, built in the PolyMUMPs process, is 5:1 (400%). The seventh and eighth MEMS variable capacitors have plates that curl up. These capacitors are built in 0.35 μm CMOS technology from the interconnect metallization layers. The plates of the presented capacitors are intentionally curled upward to control the tuning performance. A newly developed maskless post-processing technique that is appropriate for MEMS/CMOS circuits is proposed. it consists of dry and wet etching steps, developed to integrate the proposed MEMS varactors in CMOS technology. Mechanically, the capacitors are simulated by the finite element method in ANSYS, and the results are compared with the measured results. The seventh capacitor is a tri-state structure that exhibits a measured tuning range of 460% at 1 GHz with a flat capacitance response that is superior to that of conventional digital capacitors. The proposed capacitor is simulated in HFSS and the extracted capacitance is compared with the measured capacitance over a frequency range of 1 GHz to 5 GHz. The eighth capacitor is an analog continuous structure that demonstrates a measured continuous tuning range of 115% at 1 GHz with no pull-in. The measured quality factor for both CMOSbased capacitors is more than 300 at 1.5 GHz. The proposed curled-plate capacitors have a small area and can be realized to build a System-on-Chip (SoC). Finally, a tunable band pass filter that utilizes the MEMS variable capacitors in 0.18 μm CMOS technology from TSMC is designed, modeled and fabricated.

RF/microwave tunable filters are widely employed in radar systems, measurement instruments, and communication systems. By using tunable filters, the frequency bandwidth is utilized effectively and the system cost and complexity is reduced. In the literature, various tuning techniques have been developed to construct tunable filters. Mechanical tuning, magnetic tuning, and electrical tuning are the most common. In terms of quality factor, power handling capability, and linearity, mechanical tuning is superior to the other two tuning techniques. Unfortunately, due to their bulky size, heavy weight, and low tuning speed, mechanically tunable filters have limited applications. MicroElectroMechanical Systems (MEMS) technology has the potential to produce highly miniaturized tunable filters; however, most of the MEMS tunable filters reported so far have a relatively low quality factor. The objective of the research described in this thesis is to investigate the feasibility of using MEMS technology to develop tunable filters with a high quality factor. The integration of MEMS tuning elements with a wide range of filter configurations is explored, from micromachined filters to traditional dielectric resonator filters, from planar filters to cavity filters. Both hybrid integration and monolithic integration approaches are carried out. To achieve tunability, MEMS tuning elements are embedded within RF and microwave filters. Tuning is accomplished by disturbing the electromagnetic fields of resonators with nearby MEMS tuning elements, which in turn change the resonant frequency of the resonators. First, the proposed tuning concept is experimentally demonstrated by integrating a surface micromachined planar filter with MEMS thermal actuators as the tuning elements. Then, a novel micromachined ridge waveguide filter embedded with similar MEMS tuning elements is proposed and constructed by using the EFAB^{TM} micromachining technique. A power handling analysis is performed for the newly devised 3D micromachined filter, and potential failure mechanisms such as air breakdown are identified. For the first time, a tunable dielectric resonator bandpass filter, incorporating vertical long-throw MEMS thermal actuators as tuning elements, is developed to achieve a wide tuning range, high quality factor, and large power handling capability. Several prototype tunable filter units are fabricated and tested. The experimental results reveal that the tunable filters maintain a relatively high quality factor value over a wide tuning range. In addition to the hybrid integration approach, a monolithic integration approach is investigated. A novel surface micromachining process is developed to allow monolithic integration of MEMS tuning elements into micromachined filters. Due to a stress mismatch, MEMS actuators fabricated by this process obtain a vertical deflection of several hundred microns, resulting in a wide tuning range. Various latching mechanisms are created, based on the micromachining processes that are used to fabricate the MEMS tuning elements. These out-of-plane latching mechanisms with multi-stable states have the potential to be adopted not only for tunable filter applications but also for switches and phase shifters.

Micro-Electro-Mechanical Systems (MEMS) varactors have the potential to replace conventional varactor diodes, due to their high loss and non-linearity, in many applications such as phase shifters, oscillators, and tunable filters. The objective of this thesis is to develop novel MEMS varactors to improve the capacitance tuning ratio, linearity, and quality factor. Several novel varactor configurations are developed, analyzed, fabricated and tested. They are built by using standard MEMS fabrication processes, as well as monolithic integration techniques in CMOS technology. The first capacitor consists of two movable plates, loaded with a nitride layer that exhibits an analog continuous capacitance tuning ratio. To decrease the the parasitic capacitance, a trench in the silicon substrate under the capacitor is adopted. The use of an insulation dielectric layer on the bottom plate of the MEMS capacitor increases the capacitors’ tuning ratio. Experimental and theoretical results are presented for two versions of the proposed capacitor with different capacitance values. The measured capacitance tuning ratio is 280% at 1 GHz. The proposed MEMS vararctor is built using the MetalMUMPs process. The second, third, and fourth capacitors have additional beams that are called carrier beams. The use of the carrier beams makes it possible to obtain an equivalent nonlinear spring constant, which increases the capacitors’ analog continuous tuning ratio. A lumped element model and a continuous model of the proposed variable capacitors are developed. The continuous model is simulated by commercial software. A detailed analysis for the steady state of the capacitors is presented. The measured capacitance tuning ratios of these three capacitors are 410%, 400% and 470%, respectively at 1 GHz. Also, the selfresonance frequency is measured and found to exceed 11 GHz. The proposed MEMS variable capacitors are built by the PolyMUMPs process. The fifth novel parallel-plate MEMS varactor has thin-film vertical comb actuators as its driver. Such an actuator can vertically displace both plates of the parallel-plate capacitor. By making use of the fringing field, this actuator exhibits linear displacement behavior, caused by the induced electrostatic force of the actuator’s electrodes. The proposed capacitor has a low parasitic capacitance and linear deflection due to the mechanically connected and electrically isolated actuators to the capacitor’s parallel-plates. The measured tuning capacitance ratio is 7:1 (600%) at 1 GHz. The fabricated MEMS varactor exhibits a self resonance frequency of 9 GHz and built by MetalMUMPs process. The sixth parallel-plate MEMS varactor exhibits a linear response and high tuning capacitance ratio. The capacitor employs the residual stress of the chosen bi-layer, and the non-linear spring constants from the suspended cantilevers to obtain a non-linear restoring force that compensates for the nonlinear electrostatic force induced between the top and bottom plates. Two existing techniques are used to widen the tuning range of the proposed capacitor. The first technique is to decrease the parasitic capacitance by etching the lossy substrate under the capacitor’s plates. The second technique is employed to increase the capacitance density, where the areas between the top and bottom plates overlap, by applying a thin film of dielectric material, deposited by the atomic layer deposition (ALD) technique. The measured linear continuous tuning ratio for the proposed capacitor, built in the PolyMUMPs process, is 5:1 (400%). The seventh and eighth MEMS variable capacitors have plates that curl up. These capacitors are built in 0.35 μm CMOS technology from the interconnect metallization layers. The plates of the presented capacitors are intentionally curled upward to control the tuning performance. A newly developed maskless post-processing technique that is appropriate for MEMS/CMOS circuits is proposed. it consists of dry and wet etching steps, developed to integrate the proposed MEMS varactors in CMOS technology. Mechanically, the capacitors are simulated by the finite element method in ANSYS, and the results are compared with the measured results. The seventh capacitor is a tri-state structure that exhibits a measured tuning range of 460% at 1 GHz with a flat capacitance response that is superior to that of conventional digital capacitors. The proposed capacitor is simulated in HFSS and the extracted capacitance is compared with the measured capacitance over a frequency range of 1 GHz to 5 GHz. The eighth capacitor is an analog continuous structure that demonstrates a measured continuous tuning range of 115% at 1 GHz with no pull-in. The measured quality factor for both CMOSbased capacitors is more than 300 at 1.5 GHz. The proposed curled-plate capacitors have a small area and can be realized to build a System-on-Chip (SoC). Finally, a tunable band pass filter that utilizes the MEMS variable capacitors in 0.18 μm CMOS technology from TSMC is designed, modeled and fabricated.

This thesis presents the first fully tunable substrate integrated waveguide (SIW) filter implemented with PIN diodes and RF MEMS switches. The methodology for tuning SIW filters is explained in detail and is used to create three separate designs. Each SIW cavity is tuned by perturbing via posts connecting or disconnecting to/from the cavity's top metal layer. In order to separate the biasing network from the SIW filter, a three-layer PCB is fabricated using Rogers RT/duroid substrates. The first tunable design utilizes the Philips BAP55L PIN diode. This two-pole filter provides six frequency states ranging from 1.55 GHz to 2.0 GHz. Fractional bandwidth ranges from 2.3 percent – 3.0 percent with insertion loss and return loss better than 5.4 dB and 14 dB respectively for all frequency tuning states. The second tunable design utilizes the Radant RMSW-100 MEMS switch, providing six states ranging from 1.65 GHz to 2.1 GHz. Fractional bandwidth for this filter varies from 2.5 percent - 3.0 percent with insertion loss and return loss better than 12.4 dB and 16 dB respectively for all states. The third design utilizes the OMRON 2SMES-01 RF MEMS relay, providing fourteen states ranging from 1.19 GHz to 1.58 GHz. Fractional bandwidth ranges from 3.6 percent - 4.4 percent with insertion loss and return loss better than 4.1 dB and 15 dB respectively for all frequency states. Two of the three designs (Philips PIN diode and OMRON MEMS) produced good results validating the new SIW filter tuning methodology. Finally, to illustrate the advantage of microstrip planar structures integrated with SIW structures, low pass filters (LPFs) are implemented along the input and output microstrip-to-SIW transition regions of the tunable SIW filter. With minimal change to the overall filter size, this provides spurious suppression for the additional resonant modes inherently present in waveguide structures. The implemented design utilizes the same OMRON MEMS tunable SIW filter specifications. This two-pole tunable filter provides the same performance as the previous OMRON MEMS design with exception to an added 0.7 dB insertion loss and spurious suppression of -28 dB up to 4.0 GHz for all frequency tuning states.

This thesis presents a novel monolithic phased array implemented using the RF MEMS technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. The RF MEMS phase shifter employed in the system consists of three sections with a total of 28 unit cells, and it occupies an area of 22.4 mm &amp / #61620 / 2.1 mm. The performance of the phase shifters is improved using high-Q metal-air-metal capacitors in addition to MEMS switches as loading elements on a high-impedance coplanar waveguide transmission line. The phased array is fabricated monolithically using an in-house surface micromachining process, where a 1.2-&amp / #61549 / m thick gold structural layer is placed on a 500-&micro / m thick glass substrate with a capacitive gap of 2 &amp / #61549 / m. The fabrication process is simple, requires only 6 masks, and allows the implementation of various RF MEMS components on the same substrate, such as RF MEMS switches and phase shifters. The fabricated monolithic phased array occupies an area of only 6 cm &amp / #61620 / 5 cm. The measurement results show that the phase shifter can provide nearly 20&amp / #61616 / /50&amp / #61616 / /95&amp / #61616 / phase shifts and their eight combinations at the expense of 1.5 dB average insertion loss at 15 GHz. The phase shifters can be actuated with 16 V, while dissipating negligible power due to its capacitive operation. It is also shown by measurements that the main beam can be steered to 4&amp / #61616 / and 14&amp / #61616 / by suitable settings of the RF MEMS phase shifters.

In this thesis 10x10 reconfigurable reflectarray is designed at 26.5 GHz where the change in the progressive phase shift between elements is obtained with RF MEMS switches in the transmission lines of unit elements composed of aperture coupled microstrip patch antenna (ACMPA). The reflectarray is illuminated by a horn antenna, and the reflected beam is designed to switch between broadside and 40&deg / by considering the position of the horn antenna with respect to the reflectarray. In the design, the transmission line analysis is applied for matching the ACMPA to the free space. The full wave simulation techniques in HFSS are discussed to obtain the phase design curve which is used in determining two sets of transmission line lengths for each element, one for the broadside and the other for switching to the 40&deg / at 26.5 GHz. The switching between two sets of transmission line lengths is sustained by inserting RF MEMS switches into the transmission lines in each element. Two types of RF MEMS switches, series and shunt configurations, are designed for the switching purpose in the reflectarray. The phase errors due to nonideal phase design curve and type of the RF MEMS switch are reduced. The possible mutual coupling effects of the bias lines used to actuate the RF MEMS switches are also eliminated by the proper design. To show the validity of the design procedure, a prototype of 20x20 reflectarray composed of ACMPA elements is designed at 25GHz and produced using Printed Circuit Board (PCB) technology. The measurement results of the prototype reflectarray show that the main beam can be directed to the 40&deg / as desired. The process flow for the production of the reconfigurable reflectarray is suggested in terms of integration of the wafer bonding step with the in-house standard surface micromachined RF MEMS process.

This thesis presents the theory, design, fabrication, and measurement results of novel reconfigurable impedance tuner, phase shifter, and vector modulators using the RF MEMS technology. The presented circuits are based on triple stub topology, and it is shown both theoretically and experimentally in this thesis that it is possible to control the insertion phase and amplitude of the input signal simultaneously using this topology. The presented circuits are implemented using an in-house, surface micromachining fabrication process developed at METU, namely METU RF MEMS Fabrication Process, which is implemented using six masks on quartz substrates. The RF MEMS impedance tuner is designed to operate in 6-20 GHz frequency band, and it covers the Smith Chart with 1331 impedance points. The measurement results of 729 impedance points of the fabricated impedance tuner show that a wide Smith Chart coverage is obtained in the entire band. The RF MEMS phase shifter is designed to cover 0-360 degrees range 10 degree steps at 15 GHz center frequency. The measurement results of the fabricated phase shifter show that the average phase error is 1.7 degrees, the average insertion loss is -3.1 dB, and the average return loss is -19.3 dB for the measured 21 phase states. The phase shifter can also work up to 30 GHz and 40 GHz with average insertion losses of -5 dB and -8 dB, respectively. The designed RF MEMS vector modulator operates in 22.5-27.5 GHz band, and it has 3 amplitude and 8 phase states. The measurement results of the fabricated vector modulator show that the amplitude error is 0.5 dB, the phase error is 4 degrees, and the return loss is -15 dB on average among the 24 measured states at each of 22.5, 25, and 27.5 GHz frequencies.

This thesis presents fabrication of shunt, capacitive contact type RF MEMS switches which are designed according to given mm-wave performance specifications. The designed switches are modified for investigation in terms of reliability and lifetime. To observe the real-time performance of switches a time domain measurement setup is established and a CV (capacitance vs. voltage) curve measurement system is also included to measure CV curves, pull-in and hold-down voltages and the shifts of these due to actuations. By using the established setup reliability and lifetime measurements under different bias waveforms in different environments are performed. After investigation for the most suitable condition for improving lifetime long-term tests are performed and the outstanding result of more than 885 hours of operation under cycling bias waveform is obtained.

In this work, various components for low power RF telemetry applications have been investigated. These designed, fabricated and tested devices include radio frequency (RF) micro-electro-mechanical systems (MEMS) switches, single-pole-double-throw (SPDT) RF MEMS switches, nano fabricated capacitors and switching devices, and micromachined microstrip patch antennas.Coplanar waveguide (CPW) RF capacitive switches in shunt and series configuration were designed for high isolation, low insertion loss, and fast switching speed. Switches with > 35 dB isolation, < 0.3 dB insertion loss and switching speeds in the 10's of microseconds were fabricated and measured. These switches were packaged using photo-imagable resists and flip-chip bonding techniques. The MEMS shunt switch topology was also implemented into a single-pole-double-throw (SPDT) design by utilizing two such switches in a series and a shunt configuration, offset by a quarter wavelength section to provide a RF shor t at the input of the shunt switch in the off state. This type of design has the advantage of requiring a simple on-off (0 V and 35 V) bias supply to select the switch state.Also, the use of a focused ion beam (FIB) tool to mill sub-micron gaps in CPW transmission line structures was investigated. Nearly ideal capacitors in the micro- and mm- frequency range with capacitance of 8-12 fF were obtained using this milling technique. The FIB's capability to mill such small gaps at an oblique angle was also utilized to fabricate RF nano switches. These devices were switched with speeds of less than 300 ns with voltages of less than 20 V. Finally, solid state and packaged MEMS switches were integrated into a novel binary amplitude shift keyed (BASK) modulating RF telemetry system to provide the modulation of a redirected 10 GHz continuous wave (CW) signal. A pair of cross-polarized micromachined microstrip patch antennas was used in the system to receive the CW signal and re-transmit th e modulated signal. A transmission range of over 25 m was demonstrated with the solid state switch reflectenna.

The main purpose of this dissertation was to address key issues in the design and analysis of RF/microwave filters for wireless applications. Since RF/microwave filters are one of the bulkiest parts of communication systems, their miniaturization is one of the most important technological challenges for the development of compact transceivers. In this work, novel miniaturization techniques were investigated for single-band, dual-band, ultra-wideband and tunable bandpass filters. In single-band filters, the use of cross-shaped fractals in half-mode substrate-integrated-waveguide bandpass filters resulted in a 37 percent size reduction. A compact bandpass filter that occupies an area of 0.315 mm2 is implemented in 90-nm CMOS technology for 20 GHz applications. For dual-band filters, using half-mode substrate-integrated-waveguides resulted in a filter that is six times smaller than its full-mode counterpart. For ultra-wideband filters, using slow-wave capacitively-loaded coplanar-waveguides resulted in a filter with improved stopband performance and frequency notch, while being 25 percent smaller in size. A major part of this work also dealt with the concept of 'hybrid' RF MEMS tunable filters where packaged, off-the-shelf RF MEMS switches were used to implement high-performance tunable filters using substrate-integrated-waveguide technology. These 'hybrid' filters are very easily fabricated compared to current state-of-the-art RF MEMS tunable filters because they do not require a clean-room facility. Both the full-mode and half-mode substrate-integrated waveguide tunable filters reported in this work have the best Q-factors (93 - 132 and 75 - 140, respectively) compared to any 'hybrid' RF MEMS tunable filter reported in current literature. Also, the half-mode substrate-integrated waveguide tunable filter is 2.5 times smaller than its full-mode counterpart while having similar performance. This dissertation also presented detailed analytical and simulation-based studies of nonlinear noise phenomena induced by Brownian motion in all-pole RF MEMS tunable filters. Two independent mathematical methods are proposed to calculate phase noise in RF MEMS tunable filters: (1) pole-perturbation approach, and (2) admittance-approach. These methods are compared to each other and to harmonic balance noise simulations using the CAD-model of the RF MEMS switch. To account for the switch nonlinearity in the mathematical methods, a nonlinear nodal analysis technique for tunable filters is also presented. In summary, it is shown that output signal-to-noise ratio degradation due to Brownian motion is maximum for low fractional bandwidth, high order and high quality factor RF MEMS tunable filters. Finally, a self-sustained microwave platform to detect the dielectric constant of organic liquids is presented in this dissertation. The main idea is to use a voltage- controlled negative-resistance oscillator whose frequency of oscillation varies according to the organic liquid under test. To make the system self-sustained, the oscillator is embedded in a frequency synthesizer system, which is then digitally interfaced to a computer for calculation of dielectric constant. Such a system has potential uses in a variety of applications in medicine, agriculture and pharmaceuticals.