Piezoelectric Properties of La-Doped PbTiO3 Films for RF Resonators

Bulk acoustic wave (BAW) resonators with 5-wt%-La2O3-doped PbTiO3 (PT) piezoelectric films were fabricated. The La-doped PT films had a dense, homogeneous morphology, as well as high crystallinity caused by the use of bottom electrodes with pure Pt-like surface layers. These PT films had remanent polarization of 110 mC/m2 at 200°C. Resonant frequencies of the fabricated devices were 1.4 GHz and 2.0 GHz. The electromechanical coupling coefficient (kt2) was estimated to be 11% at 1.4 GHz and 9.4% at 2.0 GHz, respectively. The PT films had superior kt2 in the GHz band. The capability of the RF devices with broad bandwidth was investigated.