An 8-inch commercial aluminum nitride MEMS platform for the co-existence of Lamb wave and film bulk acoustic wave resonators
Tzu-Hsuan Hsu, Shao-Siang Tung, Yan-Ming Huang, Guan-Lin Wu, Chin‐Yu Chang, Yens Ho, Yung‐Hsiang Chen, Yelehanka Ramachandramurthy Pradeep, Rakesh Chand, Ming‐Huang Li
Abstract
Abstract This work investigates a co-design approach for fundamental symmetric Lamb wave (S 0 ) resonators (LWR) and film bulk acoustic wave resonators (FBAR) in a commercial 8-inch aluminum nitride (AlN) microelectromechanical system (MEMS) platform to enable multi-band operation. The platform utilizes surface micromachining to define local release cavities, providing an undercut-free solution for acoustic resonators to achieve a high quality factor ( Q ). However, being based on a standardized platform initially tailored for FBAR devices, many design considerations and trade-offs need to be investigated for the co-existence between LWR and FBAR design. Hence, to capture the optimal design window for S 0 LWRs while analyzing its performance impact on existing FBARs, the electrode configuration and its thickness are thoroughly investigated by the finite element method. In this work, a 2.2 GHz FBAR, a 700 MHz S 0 LWR, and a 2.19 GHz S 0 Lamé LWR are demonstrated for performance evaluation across different types of devices in this platform. The measurement results revealed a baseline performance for the FBAR device with an electromechanical coupling factor ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mtext>t</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> ) of 6.73% and Q of 3017 at 2.2 GHz, resulting in a high figure-of-merit (FoM = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mtext>t</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>⋅</mml:mo> <mml:mi>Q</mml:mi> </mml:math> ) over 200. In comparison, the 700 MHz S 0 LWR exhibits a high Q of 2532 as well and a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mtext>t</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> of 1.1% (FoM = 27.8), while the 2.19 GHz S 0 Lamé LWR also exhibits a high Q of 1752 and a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mtext>t</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> of 2.44% (FoM = 42.7), respectively. These performance indexes are all comparable with the current state-of-the-art, revealing the excellent potential of this AlN MEMS platform being implemented for future LWR development design or even mass production.