Sean Michael Scott

On/Off micro-electromechanical switching of AlN piezoelectric resonators

We report the first switchable piezoelectric resonator as a building block for a new class of adaptive and reconfigurable filters. The resonator integrates AlN contour-mode resonator and RF MEMS capacitive switch technologies to change the coupling between the RF signal electrodes and the AlN piezoelectric film. Modeling reveals that a 1.5 μm gap minimizes coupling, while a 10 nm gap couples nearly as efficiently as an electrode in intimate contact, suggesting that high contrast can be achieved using this approach. Measurements of a 400 μm × 150 μm two-port resonator demonstrate a switching ratio of 13 dB, a Q of 170, and a center frequency of 240 MHz. Research is continuing with goals of improving the device Q and switching ratio, extending the device operation to other frequencies, and extending the approach to adaptive and reconfigurable filters.

A frequency selective surface with integrated limiter for receiver protection

The design and simulation of a frequency selective surface (FSS) with integrated limiter for receiver-protection are presented. The FSS operates as normal until a certain power threshold is reached, at which point the temperature increase triggers a dramatic resistance change across the element, and the insertion loss changes from 0.2 dB to 20 dB. The limiting action is completely passive and automatically reversible. By placing the limiter outside of the system, no portion of the front-end risks damage from high-power signals, a level of protection not offered in conventional limiters. Finally, the design is compatible with standard lithography processes, requires no diodes, ferrites, or additional components, and can potentially be integrated on flexible substrates.

MEMS switching of contour-mode aluminum nitride resonators for switchable and reconfigurable radio frequency filters

Switching of transducer coupling in aluminum nitride contour-mode resonators provides an enabling technology for future tunable and reconfigurable filters for multi-function RF systems. By using microelectromechanical capacitive switches to realize the transducer electrode fingers, coupling between the metal electrode finger and the piezoelectric material is modulated to change the response of the device. On/off switched width extensional resonators with an area of 24 dB switching ratio at a resonator center frequency of 635 MHz. Other device examples include a 63 MHz resonator with switchable impedance and a 470 MHz resonator with 127 kHz of fine center frequency tuning accomplished by mass loading of the resonator with the MEMS switches.