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 2nd (A2) and 3rd (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 Omega termination impedances (56 Omega), low motional resistance R-m values (20 Omega) and an electromechanical-coupling coefficient kt(2) of 0.3%. Frequency tuning capability by varying pitch size is also demonstrated. Low-cost 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.