1,721,074 research outputs found
Robust tuners for high-Q RF tunable resonators and preselect filters
No full textReconfigurable radio frequency (RF)/microwave components are needed to realize high performance multi-band/multi-mode radios. Such tunable components can potentially reduce the system complexity. However, careful attention must be given to their design in order to satisfy strict system level requirements. The objective of this dissertation is to develop tunable technologies for high-Qu preselect filters. The first part of the dissertation focuses on deploying electrostatic fringing-field actuated (EFFA) MEMS in tunable evanescent-mode cavity-based resonators. EFFA MEMS tuners provide analog frequency coverage that is not limited by the conventional pull-in instability. Furthermore, total lack of dielectric layers and no overlap between the pull-down electrode and movable beams significantly enhances the device robustness. The modeling, design, and experimental validation of EFFA MEMS is presented and discussed. A tunable resonator based on EFFA MEMS with a Qu of 280–515 from 12.5–15.5 GHz, tuning speed of 145–190 microseconds, and vibration-induced sideband amplitude of -40 dBc at 15g is demonstrated. The second half of the dissertation addresses the electromechanical performance of MEMS-based tunable resonators. A tunable resonator is developed based on parallel-plate field MEMS tuners demonstrating a Qu of 600-1100 from 10.5–13 GHz and a tuning speed of 84–112 microseconds. Finally, an all-silicon tunable resonator based on identical tuners demonstrates a Qu of 500–735 (75-85 % of simulation) from 15.2–17.8 GHz and tuning speeds of less than 20 microseconds
Liquid Metal Droplet and Micro Corrugated Diaphragm RF-MEMS for reconfigurable RF filters
No full textWidely Tunable RF Filters that are small, cost-effective and offer ultra low power consumption are extremely desirable. Indeed, such filters would allow drastic simplification of RF front-ends in countless applications from cell phones to satellites in space by replacing switched-array of static acoustic filters and YIG filters respectively. Switched array of acoustic filters are de facto means of channel selection in mobile applications such as cell phones. SAW and BAW filters satisfy most criteria needed by mobile applications such as low cost, size and power consumption. However, the trade-off is a significant loss of 3-4 dB in modern cell phone RF front-end. This leads to need for power-hungry amplifiers and short battery life. It is a necessary trade-off since there are no better alternatives. These devices are in mm scale and consume mW. YIG filters dominate applications where size or power is not a constraint but demand excellent RF performance like low loss and high tuning ratio. These devices are measured in inches and require several watts to operate. Clearly, a tunable RF filter technology that would combine the cost, size and power consumption benefits of acoustic filters with excellent RF performance of YIG filters would be extremely desirable and imminently useful. The objective of this dissertation is to develop such a technology based upon RF-MEMS Evanescent-mode cavity filter. Two highly novel RF-MEMS devices have been developed over the course of this PhD to address the unique MEMS needs of this technology. The first part of the dissertation is dedicated to introducing the fundamental concepts of tunable cavity resonators and filters. This includes the physics behind it, key performance metrics and what they depend on and requirements of the MEMS tuners. Initial gap control and MEMS attachment method are identified as potential hurdles towards achieving very high RF performance. Simple and elegant solutions to both these issues are discussed in detail and have proved pivotal to this work. The second part of the dissertation focuses on the Liquid Metal Droplet RF-MEMS. A novel tunable RF MEMS resonator that is based upon electrostatic control over the morphology of a liquid metal droplet (LMD) is conceived. We demonstrate an LMD evanescent-mode cavity resonator that simultaneously achieves wide analog tuning from 12 to 18 GHz with a measured quality factor of 1400-1840. A droplet of 250-μm diameter is utilized and the applied bias is limited to 100 V. This device operates on a principle called Electro-Wetting On Dielectric (EWOD). The liquid metal employed is a non-toxic eutectic alloy of Gallium, Indium and Tin known as Galinstan. This device also exploits interfacial surface energy and viscous body forces that dominate at nanoliter scale. We then apply our Liquid Metal Droplet (LMD) RF-MEMS architecture to demonstrate a continuously tunable electrostatic Ku-Band Filter. A 2-pole bandpass filter with measured insertion loss of less than 0.4dB and 3dB FBW of 3.4% is achieved using a Galinstan droplet of 250μm diameter and bias limited to 100V. We demonstrate that the LMD is insensitive to gravity by performing inversion and tilt experiments. In addition, we study its thermal tolerance by subjecting the LMD up to 150° C. The third part of the dissertation is dedicated to the Micro-Corrugated Diaphragm (MCD) RF-MEMS. We present an evanescent-mode cavity bandpass filter with state-of-the-art RF performance metrics like 4:1 tuning ratio from 5 to 20 GHz with less than 2dB insertion loss and 2-6% 3dB bandwidth. Micro-Corrugated Diaphragm (MCD) is a novel electrostatic MEMS design specifically engineered to provide large-scale analog deflections necessary for such continuous and wide tunable filtering with very high quality factor. We demonstrate a 1.25mm radius and 2μm thick Gold MCD which provides 30μm total deflection with nearly 60% analog range. We also present a detailed and systematic MCD design methodology for relevant applications. To further demonstrate MCD versatility, we implement a bandstop MCD filter that cascades nine separate resonators to achieve a 6-24 GHz continuous tuning. The disseration concludes with a Galinstan Magnetohydrodynamic (MHD) micropump and summary of my doctoral work. Although presented at the very end of this dissertation, the MHD micropump was indeed the very starting point for all my doctoral research efforts. The invaluable lessons learned here paved the way for development of both LMD and MCD RF-MEMS
Reconfigurable Cavity Filters with Contactless Tuners
No full textThe recent development of tunable microwave filters has shown their great potential for being an integral component in future wireless systems across a wide range of applications. In the last decade, filters based on tunable evanescent-mode (EVA) cavity resonators have demonstrated high performance with high quality factor (Q), wide tuning range and high power handling. However, the implementation of these filters suffers from practical limitations and reliability issues which restricted the practical utilization of these filters in different real-system applications. This dissertation will present and evaluate several practical and novel solutions to overcome these practical challenges without compromising the filter performance.The first part of the dissertation focuses on the design of microwave and mmwave quasi-absorptive bandstop filters with passive absolute bandwidth compensation utilizing micromachined cavity filters. The second part of the dissertation presents a novel method to tune substrate-integrated-waveguide (SIW) cavity filters using contactless tuners. In this work, a new tuning mechanism is proposed to overcome the mechanical reliability issues and the sensitive assembly of conventional tunable cavity filters. Furthermore, a new utilization of dual-mode SIW resonators is introduced in order to improve response selectivity and realize constant absolute bandwidth filters without compromising filter size and performance
Characterization and modeling of creep in RF-MEMs tunable components and circuits
No full textCreep in thin film metals is a potentially significant failure mechanism in RF-MEMS. Materials that creep exhibit a time-dependent response to a constant force and are widely employed in RF-MEMS, including thin film metals such as Au, Al, and Ni. Creep in RF-MEMS devices in this work is characterized through a highly-accurate capacitance-sensing setup, under a special bi-state bias condition. In particular, the devices are kept continuously biased (on-state) for up to 1,400 hours, but the bias voltage is momentarily removed for one minute every hour to record the off-state capacitance. The capacitance measurement uncertainty is less than 200 aF and the long-term stability is better than 4 fF. Furthermore, creep behavior under the same bi-state bias condition is investigated with a confocal microscope-based setup. A physics-based creep model for nanocrystalline nickel devices reveals that the observed creep deformation is dominated by Coble creep. Furthermore, a compact computer-aided-design (CAD) model that may be utilized to simulate the creep behavior of RF-MEMS varactors in RF circuits and sub-systems is developed based on the aforementioned measurements. This model is capable of calculating the long-term response of RF-MEMS devices to an arbitrary input waveform. It is experimentally-validated with measurements of Ni varactors that extend up to 760 hours. Its effectiveness is demonstrated with a tunable RF-MEMS resonator and an RF-MEMS phase shifter. The proposed creep model along with the measurements up to 1,400 hours can improve the understanding of long-term operation of RF-MEMS devices and may lead to more reliable designs. They may also play a key role in lifetime evaluation and prediction
Modeling and characterization of non-ideal effects in high-performance RF MEMS tuners
Get PDFThe emerging standards for the next-generation wireless communication system demand for multi-band RF front-ends. Reconfigurable RF devices based on MEMS technology have emerged with the potential to significantly reduce the system complexity and cost. Robust operation of RF MEMS tuners under the non-ideal effects due to fabrication uncertainties and environmental variations is critical in achieving reliable RF MEMS reconfigurable devices. Therefore, it is essential to model and characterize these non-ideal effects, and further to alleviate these non-ideal effects by design optimization. In this dissertation, the effects of non-perfect anchor support, residual stress, and temperature sensibility of MEMS tuners have been studied. The anchor supports of MEMS beams, which are widely used as tunable components, are often far from the ideally assumed built-in or step-up conditions. An equation-based nonlinear model for inclined supports in non-flat fixed-fixed beams has been developed and validated by experimental results. Residual stress developed during the fabrication presents the major challenges in developing reliable MEMS tuners. An efficient extraction method for in-plane residual stress has been proposed using a single beam test structure. This method has been demonstrated by wafer-scale measurements of electrostatically actuated beams. The statistic and spatial distribution of extracted residual stresses on a quarter wafer is presented, and the accuracy of this method is evaluated by uncertainty analysis. With the awareness the residual stress effects, the design optimization has been conducted for designing stress-tolerant micro-corrugated diaphragm tuners used in tunable cavity resonators/filters. Furthermore, the temperature sensitivity issue results from the mismatch of material properties between the structure material and substrate has been discussed and a thermally-stable RF MEMS tuner based on a nonuniform micro corrugated diaphragm has been proposed and experimentally validated over a wide temperature variation
Modeling and Validation of S-Drive: A Nestable Piezoelectric Actuator
Get PDFThis dissertation introduces a novel, nestable piezoelectric actuator, called the s-drive. In the s-drive actuator, the piezoelectric material is sandwiched between two conductors, and the electrodes are configured such that an application of a voltage causes an extension on two beams and compression on the other two beams to produce a large lateral deflection in the form of an \u27s\u27 shape. The s-drive gets its name from the characteristic \u27s\u27 shape that appears upon actuation. The designs of one-dimensional (1D) and two-dimensional (2D) arrays of axial-mode and shear-mode s-drives, for magnifying displacement and shear, are also presented in this work. Experimental results from the fabricated s-drive and its 1D nested arrays are presented for validation of the finite element analysis simulations and the developed analytical model of the s-drive and its nested arrays. Additionally, the design of a new type of channel flow piezo pen, designed as a variation of s-drive, that is able to produce large deflections, with multiple degrees of freedom, and might handle multiple inks with the capability of writing on any surface in either wet or dry, clean or dirty environments is presented. The s-drive, unlike electrostatic actuators, can work in relatively unclean environments, require lower power than electrothermal actuators, require lower driving voltages than electroactive polymers, and are geometrically configured to magnify small piezoelectric strains into larger deflections. These microactuators are expected to have applications in scanning probe microscopy, microassembly, nanolithography, and micro- and macro-scale robotics
Dynamic monitoring of ohmic contact RF MEMS switches
No full textRF system complexity is steadily increasing due to demands for multiband and multifunction operation within a single device while maintaining or reducing size, cost, and power consumption. To combat this, efforts are ongoing to develop reconfigurable RF subsystems. RF MEMS switches comprise a crucial building block for such systems. However, cost and reliability concerns have hindered their widespread adoption. In this work, an ohmic contact RF MEMS switch is developed utilizing single-crystal-silicon (SCS) as the structural material while maintaining state-of-the-art performance. Unlike thin-film metals commonly employed in RF MEMS switches, SCS is essentially defect-free and has well-known and repeatable material properties. This makes the switch design insensitive to process variations and amenable to high- yield manufacturing. Measured devices exhibit on state insertion loss of less than 0.3 dB and off state isolation of higher than 30 dB up to 40 GHz and switching time under 4 microseconds. This switch is then used as a repeatable platform for developing an ultra-low-power (60-250 microwatt) IC based in-situ real-time monitoring technique for RF MEMS switch dynamics. The ability to record extremely small displacement bounces (\u3c20 nm) alongside the entire settling event with 99% accuracy in determining contact timing relative to LDV measurements is demonstrated experimentally. Changes in dynamic behavior of RF MEMS switches over lifetime operation are then utilized as a readily and simply observable method of failure prediction for a commercially available device. Rapid increases in the number of bounces are observed which indicate approximately 50-75% of total operation has elapsed
VHF lumped-element reconfigurable filters design and applications in field-programmable filter array
Get PDFThe increasing demand for limited space in crowded frequency spectrum is creating new challenges to RF frontend communication systems. High gain tunable antennas, tunable filter with high selectivity and isolation, large signal-to-noise ratio tunable low noise amplifiers are demanded. This thesis demonstrates novel tunable filter synthesis that may help in developing solutions for future RF frontend filter applications. The proposed coupling scheme enable the tuning of center frequency, order, response shape, bandwidth, and transmission zero spectral location. Also, this coupling scheme can be used to implement a field-programmable filter arrays (FPFAs) design
Air Line Coax Spatial Combiner with Odd Ports
No full textAn X-band radial power combiner based on an airline coax with 0.15 dB measured insertion loss, 8 dB minimum port-to-port isolation, 33% bandwidth, and the ability to handle kilowatt power levels is presented in this work. The design can readily be scaled to arbitrary frequencies or any number of ports. The methods used to select the parameters and optimize the design are presented. The models are validated by a 9-port X-band proof-of-concept combiner
Compact multi-physics models for large-displacement multilayer cantilevers in RF MEMS circuits, antennas and sensors
No full textWe demonstrate compact analytical multi-physics models that accurately predict the deformed shape of a variety of multilayer cantilevers and the associated electrical characteristics when employed in several practical sensor and RF applications. We pay particular attention to structures relying on large mechanical displacements in order to achieve the desired performance. Practical applications of these cantilevers are shown in several important cases including; (a) a harsh-environment temperature sensor; (b) high-Q three-dimensional inductors; (c) an electrothermal actuator for highly tunable inductor; and (d) mm-wave on-chip antenna with high radiation efficiency. In all cases, obtaining large deflections is key in achieving the required performance. For example, the capacitance variation of the developed temperature-sensitive capacitor (first application) depends on the distance between its upper and lower electrodes. For the 85 micron tip deflection of bimorph capacitor, about 2.5:1 ca-pacitance variation from room temperature to 213 degrees C is experimentally obtained. Electro-thermo-mechanical model is proposed to predict capacitance in terms of temperature. Besides the temperature sensors, a pre-stressed metal 3-D inductor is analyzed (second application). Contrary to conventional inductor models, the developed models include both mechanical and electrical components. Starting from basic process parameters such as residual stress of the cantilevers beams the model provides the self-assembled inductor characteristics. A tunable MEMS inductor with electrothermal actuators is the third application investigated. This inductor is based on an integrated transformer architecture with one inductor is shorted. Tunability is accomplished by varying the magnetic coupling coefficient which is dominated by the distance between the two inductors. Design rules for optimized performance are provided. The fabricated tunable inductor shows about 2:1 inductance variation. Finally, mm-wave on-chip antennas with high radiation efficiency are presented. The residual stresses in thin films result in out-of-plane structures over a ground plane that isolates the radiating elements from the high-loss substrate. Consequently, these antennas achieve high radiation efficiency of more than 60 percent
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