The c-axis textured aluminum nitride (AlN) thin films with columnar grains perpendicular to Molybdenum(Mo)/ Polyimide(PI)/Si(111) substrate could be obtained through reactive magnetron sputtering at room temperature. The full width at half maximum of the X-ray diffraction rocking curves and E2 (high) peak of Raman spectrum of the AlN thin films were 2.2° and 18.6?cm-1, respectively. The thin film bulk acoustic resonators (FBARs) with Mo/AlN/Mo/PI/Si (111) configuration were fabricated, and a PI/Mo heterostructure was used as acoustic isolation layer for the FBARs. The resonant frequency response of the FBARs was measured using a vector network analyzer, and an effective coupling coefficient of 5.4% was achieved.