A 36GHz Trilayer AlN/ScAlN/AlN Periodically Poled FBAR

As mm-wave communication bands become widely utilized, the demand for high performance, low cost, and compact sized frontend filters is increasing. Both quality factors and electromechanical coupling coefficients in conventional single layer bulk acoustic wave (BAW) resonators rapidly degrade at mm-wave frequencies due to challenges associated with very thin films. A periodically poled thin film bulk acoustic resonator (FBAR) addresses these challenges by aligning the piezoelectric coefficients in a thick multilayer structure. In this work, a new mm-wave trilayer AlN/ScAlN/AlN periodically poled FBAR employing molecular beam epitaxy (MBE) growth is presented. The trilayer FBAR has been polarization switched by applying triangular voltage pulses between the top and bottom electrodes. After poling, the piezoelectric coefficient in the ScAlN layer is reversed for optimum operation in the third resonance mode. The resonator achieves a measured electromechanical coupling coefficient of 6.7% and a mechanical quality factor of 252 at 36 GHz.