Effect of electrodes on GHZ ZnO thin film bulk-acoustic-wave resonator

Thin film bulk acoustic resonators (FBARs) were prepared with ZnO films usi ng Al and Cr/Au electrodes. ZnO films were deposited by RF sputtering. Al a nd Cr/Au electrodes were prepared by DC sputtering and thermal evaporation respectively. S parameters were measured with a network analyzer. From TEM images, it is apparent that there are some defects on ZnO with Al electrode while no defects are detected on ZnO with Cr/Au. Also, an intermediate lay er is observed between ZnO and Al but nothing between ZnO and Au. As a resu lt of those differences, the resonant frequency, the width between series a nd parallel frequency and the value of S-11 between peak and valley, are di fferent between the FEAR samples with Al or Cr/Au even thou,bh bath FEAR sa mples have the same thickness of ZnO.