A deep trench (DT) MEMS resonator includes a periodic array of unit cells, each of which includes a single DT formed in a semiconductor substrate and filled with a material whose acoustic impedance is different than that of the substrate. The filled DT is used as both an electrical capacitor and a mechanical structure at the same time, making it an elegant design that reduces footprint and fabrication complexity. Adding a second DT to each unit cell in a DT MEMS resonator forms a dual-trench DT (DTDT) MEMS resonator. In a DTDT unit cell, the first DT is filled with a conductor to sense, conduct, and/or generate an acoustic wave. The second DT in the DTDT unit cell is filled with an insulator. The width, filling, etc. of the second DT in the DTDT unit cell can be selected to tune the acoustic passband of the DTDT unit cell.