Publications

A six-bit time delay circuit operating from DC to 18 GHz is reported. Capacitively loaded transmission lines are used to reduce the physical length of the delay elements and shrink the die size. Additionally, selection of the reference line lengths to avoid resonances allows the replacement of series-shunt switching elements with only series elements. With through-wafer transitions and a packaging seal ring, the 7 mm x 10 mm circuit demonstrates <2.8 dB of loss and 60 ps of delay with good delay flatness and accuracy through 18 GHz. © 2008 IEEE.

This paper reports the development of narrow-bandwidth, post-CMOS compatible aluminum nitride (AlN) MEMS filters operating in the very (VHF) and ultra (UHF) high frequency bands. Percent bandwidths less than 0.1% are achieved utilizing a mechanically coupled filter architecture, where a quarter wavelength beam attached in low velocity coupling locations is used to connect two AlN ring resonators. The filter bandwidth has been successfully varied from 0.09% to 0.2% by moving the attachment of the coupling beam on the ring to locations with different velocity at resonance. Insertion losses of 11 dB are obtained for filters centered at 99.5 MHz with low termination impedances of 200 &Omega. Utilizing a passive temperature compensation technique, the temperature coefficient of frequency (TCF) for these filters has been reduced from -21 ppm/C to 2.5 ppm/C. The reduced TCF is critical for narrow bandwidth filters, requiring only 13% of the filter bandwidth to account for military range (-55 to 125 C) temperature variations compared to 100% for uncompensated filters. Filters operating at 557 MHz are realized using overtone operation of the ring resonators and coupling beam where higher insertion losses of 32 dB into 50 ω are seen due to the finite resonator quality factor and narrow bandwidth design. Overtone operation allows for the implementation of fully differential and balun type filters where the stop-band rejection is as high as 38 dB despite the increased Insertion loss. © 2008 IEEE.

This paper reports the development of narrow-bandwidth, post-CMOS compatible aluminum nitride (AlN) MEMS filters operating in the very (VHF) and ultra (UHF) high frequency bands. Percent bandwidths less than 0.1% are achieved utilizing a mechanically coupled filter architecture, where a quarter wavelength beam attached in low velocity coupling locations is used to connect two AlN ring resonators. The filter bandwidth has been successfully varied from 0.09% to 0.2% by moving the attachment of the coupling beam on the ring to locations with different velocity at resonance. Insertion losses of 11 dB are obtained for filters centered at 99.5 MHz with low termination impedances of 200 &Omega. Utilizing a passive temperature compensation technique, the temperature coefficient of frequency (TCF) for these filters has been reduced from -21 ppm/C to 2.5 ppm/C. The reduced TCF is critical for narrow bandwidth filters, requiring only 13% of the filter bandwidth to account for military range (-55 to 125 C) temperature variations compared to 100% for uncompensated filters. Filters operating at 557 MHz are realized using overtone operation of the ring resonators and coupling beam where higher insertion losses of 32 dB into 50 ω are seen due to the finite resonator quality factor and narrow bandwidth design. Overtone operation allows for the implementation of fully differential and balun type filters where the stop-band rejection is as high as 38 dB despite the increased Insertion loss. © 2008 IEEE.

We designed, fabricated and measured the performance of nanoelectromechanical (NEMS) switches. Initial data are reported with one of the switch designs having a measured switching time of 400 ns and an operating voltage of 5 V. The switches operated laterally with unmeasurable leakage current in the 'off' state. Surface micromachining techniques were used to fabricate the switches. All processing was CMOS compatible. A single metal layer, defined by a single mask step, was used as the mechanical switch layer. The details of the modeling, fabrication and testing of the NEMS switches are reported.

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Low Temperature Cofired Ceramic (LTCC) has proven to be an enabling medium for microsystem technologies, because of its desirable electrical, physical, and chemical properties coupled with its capability for rapid prototyping and scalable manufacturing of components. LTCC is viewed as an extension of hybrid microcircuits, and in that function it enables development, testing, and deployment of silicon microsystems. However, its versatility has allowed it to succeed as a microsystem medium in its own right, with applications in non-microelectronic meso-scale devices and in a range of sensor devices. Applications include silicon microfluidic ''chip-and-wire'' systems and fluid grid array (FGA)/microfluidic multichip modules using embedded channels in LTCC, and cofired electro-mechanical systems with moving parts. Both the microfluidic and mechanical system applications are enabled by sacrificial volume materials (SVM), which serve to create and maintain cavities and separation gaps during the lamination and cofiring process. SVMs consisting of thermally fugitive or partially inert materials are easily incorporated. Recognizing the premium on devices that are cofired rather than assembled, we report on functional-as-released and functional-as-fired moving parts. Additional applications for cofired transparent windows, some as small as an optical fiber, are also described. The applications described help pave the way for widespread application of LTCC to biomedical, control, analysis, characterization, and radio frequency (RF) functions for macro-meso-microsystems.

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Radio Frequency Microelectromechanical Systems (RF MEMS) are advantageous for reconfigurable antennas providing the potential for steering, frequency agility, and tunable directivity. Until RF MEMS switches can consistently reach cycles into the billions (if not trillions), limited reliability outweighs the promised benefits, preventing the deployment of RF MEMS into systems. Understanding failure mechanisms is essential to improving reliability. This paper describes preliminary reliability results and tests conducted in a vacuum chamber to investigate and understand the impact of contamination related failure mechanisms. © 2006 IEEE.

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A Ka-Band RF MEMS enabled frequency reconfigurable triangular microstrip patch antenna has been designed for monolithic integration with RF MEMS phase shifters to demonstrate a low-cost monolithic passive electronically scanned array (PESA). This paper introduces our first prototype reconfigurable triangular patch antenna currently in fabrication. The aperture coupled patch antenna is fabricated on a dual-layer quartz/alumina substrate using surface micromachining techniques. Full-wave MoM simulation results will be compared to laboratory measurements in the oral presentation. © 2005 IEEE.

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A Ka-band RF MEMS enabled frequency reconfigurable triangular microstrip patch antenna has been designed for monolithic integration with RF MEMS phase shifters to demonstrate a low-cost monolithic passive electronically scanned array (PESA). This paper introduces our first prototype reconfigurable triangular patch antenna currently in fabrication. The aperture coupled patch antenna is fabricated on a dual-layer quartz/alumina substrate using surface micromachining techniques.