Design and Analysis of Lithium–Niobate-Based High Electromechanical Coupling RF-MEMS Resonators for Wideband Filtering

Abstract

This paper reports on a new type of microresonators enabled by micromachining of ion sliced <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -cut LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films. In operation, the device is excited into lateral vibrations, thus allowing the center frequency to be determined by the lithographically defined dimensions of the excitation electrodes. The demonstrated device has a high electromechanical coupling ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 11.5%-the highest attained for laterally vibrating microelectromechanical systems resonators. Device orientation was also varied to investigate its impact on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and experimental data have shown good agreement with theoretical predictions. Several key performance parameters, including the quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ), the static capacitance, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , the temperature coefficient of frequency (TCF), and the power handling, are also characterized and the related experimental data are presented. The devices demonstrate <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> 's up to 1800. The measured TCFs range from -55 to -69 ppm/K and can be considered sufficiently low for wideband RF filtering. The high electromechanical coupling and the high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of this new class of devices show promise for the implementation of multifrequency wideband multiplexers and filter banks for reconfigurable RF front-ends.