High-Q X Band Aluminum Nitride Combined Overtone Resonators

We experimentally demonstrate a new class of micro-electro-mechanical system (MEMS) resonators, aluminum nitride (AlN) Combined Overtone Resonators (CORs). AlN CORs utilizing a combination of the 2
^nd
(A2) and 3
^rd
(A3) order asymmetrical Lamb-wave overtone at 8.8 GHz are built using one-micron aluminum nitride plates fabricated with a simple 2-mask process. Mechanical quality factor Q
_m
and loaded quality factor Q
_l
as high as 1100 and 750 are achieved (corresponding to f*Q
_m
=9.7e12 and f*Q
_l
=6.6e12), being the highest reported for piezoelectric MEMS resonators operating in X band and higher bands. Those devices show near 50 Ω termination impedances (56 Ω), low motional resistance Rm values (20 Ω) and an electromechanical-coupling coefficient k
_t
²
of 0.3%. Frequency tuning capability by varying pitch size is also demonstrated. Lowcost X band narrow band filters and oscillators can be easily built using such a new resonator technology with relaxed photolithography requirements and simple fabrication processes.