6–20 GHz 30% ScAlN Lateral Field-Excited Cross-Sectional Lamé Mode Resonators for Future Mobile RF Front Ends
Gabriel Giribaldi, Luca Colombo, Matteo Rinaldi
Abstract
This paper reports on 30% Scandium-doped Aluminum Nitride (ScAlN) Lateral Field-Excited (LFE) Cross-sectional Lame’ Mode Resonators (CLMRs) with unprecedented performance in the 6-20 GHz range. By combining high-crystallinity 30% ScAlN piezoelectric thin-films, a lithographic tunability of the resonance frequency, and a simple 3-mask post-CMOS compatible fabrication process, we propose a technology platform that can enable the mass-production of low-loss, wide-band, and compact microacoustic filtering devices spanning a wide spectrum portion on the same chip for the next-generation RF front-ends of handsets. The present work demonstrates a successful scaling of the microacoustic technology well beyond the sub-6 GHz 5G band, as well as the outstanding capabilities of high-crystallinity 30% ScAlN piezoelectric layers in delivering high-quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) and high-electromechanical coupling ( <italic 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"><i>t</i></sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) resonators, notably exceeding the state-of-the-art in terms of relevant figures of merit. Furthermore, we experimentally investigate the impact of geometrical parameters such as tethering configuration and width-over-length ratio on the devices’ 3dB quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3<i>dB</i></sub> ), power linearity, and Temperature Coefficient of Frequency (TCF). By adopting a statistical approach for data analysis, we determine the optimal geometry to maximize the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> . Moreover, we experimentally demonstrate that a fully tethered device’s configuration ensures superior power linearity, lower TCF, and higher device yield, and select that as best design trade-off between all the variables under consideration. Finally, we discuss a further scaling of LFE CLMRs, both in terms of higher doping levels in the piezoelectric layer, in order to enhance the performance of microacoustic filters, and in terms of higher operation frequencies, in order to reach and cover the mm-waves spectrum.