This paper reports the design concept and the implementation of a new class of aluminium nitride (AlN) thin film resonators, whose resonant frequencies are above 2.5GHz, achieving k 2 eff as high as 8%, high than that of bulk acoustic wave (BAW) resonators. The functional layer of the resonator is formed by a 1µm-thick AlN film sandwiched between top and bottom molybdenum (Mo) layers with the thicknesses of 0.26µm and 0.2µm, respectively. The bottom electrode is of a plate structure, in order to ensure subsequent high-quality AlN growth by avoiding fine-pattern electrodes underneath AlN; while the top electrode is design to be one array of electrically connected comb fingers, allowing the design freedom to adjust the resonator frequency by lithographically patterning of the top electrode layer. Great potential is demonstrated by this new class of resonators in achieving ultra wideband filter for 5G application.