Radio Frequency Microelectromechanical Systems in Defence and Aerospace

For all onboard systems applications, it is important to have very low-loss characteristics and low power consumption coupled with size reduction. The controls and instrumentation in defence and aerospace continually calls for newer technologies and developments. One such technology showing remarkable potential over the years is radio frequency microelectromechanical systems (RF MEMS) which have already made their presence felt prominently by offering replacement in radar and communication systems with high quality factors and precise tunability. The RF MEMS components have emerged as potential candidates for defence and aerospace applications. The core theme of this paper is to drive home the fact that the limitations faced by the current RF devices can be overcome by the flexibility and better device performance characteristics of RF MEMS components, which ultimately propagate the device level benefits to the final system to attain the unprecedented levels of performance.Defence Science Journal, 2009, 59(6), pp.568-567, DOI:http://dx.doi.org/10.14429/dsj.59.156

Utilisation of microsystems technology in radio frequency and microwave applications

The market trends of the rapidly growing communication systems require new product architectures and services that are only realisable by utilising technologies beyond that of planar integrated circuits. Microsystems technology (MST) is one such technology which can revolutionise radio frequency (RF) and microwave applications. This article discusses the enabling potential of the MST to meet the stringent requirements of modern communication systems. RF MST fabrication technologies and actuation mechanisms empower conventional processes by alleviating the substrate effects on passive devices and provide product designers with high quality versatile microscale components which can facilitate system integration and lead to novel architectures with enhanced robustness and reduced power consumption. An insight on the variety of components that can be fabricated using the MST is given, emphasizing their excellent electrical performance and versatility. Research issues that need to be addressed are also discussed. Finally, this article discusses the main approaches for integrating MST devices in RF and microwave applications together with the difficulties that need to be overcome in order to make such devices readily available for volume-production.peer-reviewe

Monolithic Integration Piezoelectric Resonators on CMOS for Radio-Frequency and Sensing Applications

Software cognitive radios and Internet of Things (IoT) are recent interest areas that need low loss and low power consumption hardware. More specifically, the area of software cognitive radios requires that hardware be frequency agile and highly selective. Meanwhile, IoT relies on multiple low power sensor networks. By combining Complementary Metal Oxide Semiconductors (CMOS) technology with piezoelectric Micro-Electro-Mechanical Systems (MEMS), we can fabricate Systems-on-Chip (SoC) that can be used as filters or references (oscillators) and highly selective sensors. In this work we developed a die-level compatible process for the monolithic integration of Bulk Acoustic Resonators (BAWs) on CMOS for low power, reduced area and high-quality passives for radio frequency applications. Using CMOS as a fabrication substrate some stringent requirements were added to maintain the dies and the technology’s integrity. A few of these limitations were the need for a low thermal budget fabrication process, die handling and electro-static discharge (ESD) protection. The devices were first fabricated on glass for modeling extraction that was later used for the design of the integrated circuits (IC). Three integrated circuits were designed as substrates for the integration using IBM’s 180nm and TSMC’s 65nm technology. A monolithic BAW oscillator with a resonance frequency of 1.8GHz was demonstrated with an FOM ~186dBc/Hz, comparable to other academia work. Using the developed process, a membrane BAW structure (FBAR) was integrated as well. Using a susceptor coating and zinc oxide’s (ZnO) high temperature coefficient of frequency (TCF) the device was studied as an alternative uncooled infrared sensor. Finally, a reprogrammable IC and an RF PCB were designed for volatile organic compound (VOC) testing using self-assembled monolayers (SAMs) as the absorber layer

Ultra-Low Power Wake Up Receiver For Medical Implant Communications Service Transceiver

This thesis explores the specific requirements and challenges for the design of a dedicated wake-up receiver for medical implant communication services equipped with a novel “uncertain-IF†architecture combined with a high – Q filtering MEMS resonator and a free running CMOS ring oscillator as the RF LO. The receiver prototype, implements an IBM 0.18μm mixed-signal 7ML RF CMOS technology and achieves a sensitivity of -62 dBm at 404MHz while consuming \u3c100 μW from a 1 V supply

Doctor of Philosophy

dissertationThis thesis presents the design, fabrication and characterization of a microelectromechanical system (MEMS) based complete wireless microsystem for brain interfacing, with very high quality factor and low power consumption. Components of the neuron sensing system include TiW fixed-fixed bridge resonator, MEMS oscillator based action-potential-to-RF module, and high-efficiency RF coil link for power and data transmissions. First, TiW fixed-fixed bridge resonator on glass substrate was fabricated and characterized, with resonance frequency of 100 - 500 kHz, and a quality factor up to 2,000 inside 10 mT vacuum. The effect of surface conditions on resonator's quality factor was studied with 10s of nm Al2O3 layer deposition with ALD (atomic layer deposition). It was found that MEMS resonator's quality factor decreased with increasing surface roughness. Second, action-potential-to-RF module was realized with MEMS oscillator based on TiW bridge resonator. Oscillation signal with frequency of 442 kHz and phase noise of -84.75 dBc/Hz at 1 kHz offset was obtained. DC biasing of the MEMS oscillator was modulated with neural signal so that the output RF waveform carries the neural signal information. Third, high-efficiency RF coil link for power and data communications was designed and realized. Based on the coupled mode theory (CMT), intermediate resonance coil was introduced and increased voltage transfer efficiency by up to 5 times. Finally, a complete neural interfacing system was demonstrated with board-level integration. The system consists of both internal and external systems, with wireless powering, wireless data transfer, artificial neuron signal generation, neural signal modulation and demodulation, and computer interface displaying restored neuron signal

Design, Optimization and Fabrication of Amorphous Silicon Tunable RF MEMS Inductors and Transformers

High performance inductors are playing an increasing role in modern communication systems. Despite the superior performance offered by discrete components, parasitic capacitances from bond pads, board traces and packaging leads reduce the high frequency performance and contribute to the urgency of an integrated solution. Embedded inductors have the potential for significant increase in reliability and performance of the IC. Due to the driving force of CMOS integration and low costs of silicon-based IC fabrication, these inductors lie on a low resistivity silicon substrate, which is a major source of energy loss and limits the frequency response. Therefore, the quality factor of inductors fabricated on silicon continues to be low. The research presented in this thesis investigates amorphous Si and porous Si to improve the resistivity of Si substrates and explores amorphous Si as a structural material for low temperature MEMS fabrication. Planar inductors are built-on undoped amorphous Si in a novel application and a 56% increase in quality factor was measured. Planar inductors are also built-on a porous Si and amorphous Si bilayer and showed 47% improvement. Amorphous Si is also proposed as a low temperature alternative to polysilicon for MEMS devices. Tunable RF MEMS inductors and transformers are fabricated based on an amorphous Si and aluminum bimorph coil that is suspended and warps in a controllable manner. The 3-D displacement is accurately predicted by thermomechanical simulations. The tuning of the devices is achieved by applying a DC voltage and due to joule heating the air gap can be adjusted. A tunable inductor with a 32% tuning range from 5.6 to 8.2 nH and a peak Q of 15 was measured. A transformer with a suspended coil demonstrated a 24% tuning range of the mutual coupling between two stacked windings. The main limitation posed by post-CMOS integration is a strict thermal budget which cannot exceed a critical temperature where impurities can diffuse and materials properties can change. The research carried out in this work accommodates this temperature restriction by limiting the RF fabrication processes to 150°C to facilitate system integration on silicon

Realization of a low noise amplifier using 0.35 um SiGe-BicMOS Technology for IEEE 802.11a applications /

The trend demand for towards interactive multimedia services has forced the development of new wireless systems that has greater bandwidths. The evolution of current wireless communication systems has been very rapid. The main goal has been small-size and low-cost transceivers that can be designed for different applications. Data communication systems in compliant with IEEE 802.11a wireless local area network (WLAN) standard has found widespread use, meeting the market demands, for the last few years. Next generation WLAN operates in the 5-6 GHz frequency range. A front-end receiver capable of operating within this frequency range is essential to meet the current and future of products. One of the critical components, allowing the common use of the technology can be attributed to the high performance Low Noise Amplifiers (LNA) in the receiver chain of the 802.11a transceivers. In IEEE 802.11a, there are three frequency bands; 5.15GHz - 5.25GHz, 5.25GHz - 5.35GHz and 5.725GHz - 5.825GHz. In this thesis, we designed and fabricated a single-stage cascode amplifier with emitter inductive degeneration using 0.35 ´m-SiGe BiCMOS process for IEEE 802.11a receivers. The electromagnetic (EM) simulations of the passive components are performed by using Agilent MOMENTUM® tool and all the parasitic components are extracted and compensated, a crucial step for optimizing the performance parameters of the LNA. The simulation results are very similar to measurement results, confirming the effectiveness of design methodology provided in this work

Fully Integrated High-Performance MEMS Lumped Element Filters for Reconfigurable Radios.

In this research, we present RF MEMS filters which address the most challenging performance requirements of modern RF front-end systems, namely multi-band processing capability, low energy consumption, and small size. These filters not only provide a wide tuning range for multiple-band selection, but also offer low loss, high power handling capability, fast tuning speed, and temperature stability. Two different technologies are considered for tunable lumped element filter targeting UHF range. The first technology is a tunable RF MEMS platform based on surface micromachining, enabling fabrication of continuously tuned capacitors, capacitive and ohmic switches, as well as high-Q inductors, all on a single chip. The filter is in a third-order coupled resonator configuration. Continuous electrostatic tuning is achieved using three tunable capacitor banks each consisting of one continuously tunable capacitor and three switched capacitors with pull-in voltage of less than 40V. The center frequency of the filter is tuned from 1GHz to 600MHz while maintaining a 3dB-bandwidth of 13 to 14% and insertion loss of 2%. The filter occupies a small size (1.5 cm x 1.0 cm). This filter shows the best published performance yet in terms of insertion loss, out-of-band rejection, temperature stability, and tuning range. The second technology is based on a new tuning mechanism utilizing phase-change (PC) materials. PC technology has been investigated and adopted in memory industry due to its fast transition time in nano second range, small size, and high resistance change ratio. Although PC materials offer several benefits, they have not been considered for RF applications because of their limited power handling capability and relatively higher on-resistance in their current form. In this work, germanium tellurium (GeTe) is considered as it offers a low on-resistivity and pronounced resistance change ratio of up to 106. To characterize RF properties of GeTe, different types of RF switches have been fabricated and compared. Such PC switches can be monolithically integrated with other micromachined components to implement reconfigurable front-end modules, potentially offering high tuning speed, low loss, high linearity, and small size.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98038/1/yhshim_1.pd