A Mechanically Coupled Piezoelectric MEMS Filter Based on Support Transducer Topology

This paper presents the development and experimental results of a two-port, low insertion loss (1.9dB) MEMS filter based on a Support Transducer (ST) topology using thin-film piezoelectric (AlN) on substrate (TPoS) technique at 10MHz. The filter utilizes mechanically coupled (quarter-wavelength, λ/4) radial contour mode disks to form a desirable passband after termination. The ST is designed using length extension (LE) mode to maximize overall transduction efficiency and a high-velocity coupling scheme to drive the central disks. The properly matched filter achieved 0.8%-bandwidth (80kHz) with <0.5dB in-band ripple under a small matching impedance of (39+j375)Ω for channel-select applications. The fabricated filter has a measured minimum insertion loss of 13dB without termination while a flat pass-band response with a maximum insertion loss of 1.9dB with termination. The proposed design achieves a better insertion loss using a lower matching impedance compared to the previous single resonator ST design, thus enabling high-performance MEMS channel-select filters. The presented results demonstrate the potential of the proposed design for applications in wireless communication systems, especially for IoT devices.