This paper presents the first demonstration of a high frequency (2.8 GHz), lateral field excited (simple two masks fabrication process), combined lateral-thickness extensional mode of vibration aluminum nitride (AlN) micro-electromechanical systems (MEMS) resonator with unprecedentedly high figure of merit (kt2⋅Q> 45). For the first time, a single interdigital electrode was employed to excite a high frequency mode of vibration in an AlN plate (1.5 μm thick) by making use of both the d33 and d31 AlN piezoelectric coefficients. The resulting MEMS resonator showed high quality factor, Q∼2000, (thanks to the high quality AlN film directly deposit on top of the Silicon substrate) and the highest electromechanical coupling coefficient ever reported for AlN MEMS resonators employing a single electrode, kt2∼2.5% (thanks to the coherent combination of d33 and d31 coefficients to transduce one single mechanical mode of vibration).