Triple layer SiO2/AlN/SiO2 composite thin film bulk acoustic wave resonators (TFBARs) were studied for applications in atomic clocks. The TFBAR's were tuned to 3.4 GHz, corresponding to half the hyperfine splitting of the ground state of rubidium Rb-87 atoms. The quality factor (Q) was equal to 2300 and the temperature coefficient of the resonance frequency f(r) amounted to 1.5 ppm/K. A figure of merit Qf(r) of similar to 0.8 x 10(13) Hz and a thickness mode coupling factor of 1% were reached. Such figures are ideal for frequency sources in an oscillator circuit that tracks the optical signal in atomic clocks. (C) 2011 American Institute of Physics. [doi:10.1063/1.3603944]