Chisako Maeda

Preparation and Piezoelectric Property of Lead Titanate Thin Films for GHz-Band Resonators

Film bulk acoustic wave resonators (FBAWRs) at the GHz band were successfully fabricated using piezoelectric lead titanate, PbTiO 3 (PT) films on GaAs substrates by a process similar to that used in microwave integrated circuit (MIC) fabrication. PT films deposited on Pt/Ti bottom electrodes by RF magnetron sputtering oriented preferentially along the (111) crystal direction. Resonances of the bulk acoustic mode were observed around 1.9 GHz. The effective electromechanical coupling coefficient (k t 2 ) and electrical Q were estimated to be ∼9.4% and ∼65, respectively. The relationship between residual stress in the PT films and Q was investigated. It was found that stress in the PT film exerted a large influence on Q.

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.

Piezoelectric properties and micro structures of lead titanate thin films for GHz-band bulk acoustic wave filters

Abstract The bulk acoustic wave filters at GHz bands were fabricated using lead titanate, PbTiO3 (PT) piezoelectric films which were deposited by RF magnetron sputtering and were oriented along crystal direction. To improve the quality of PT films, the bottom electrodes which had the Ti-diffusion suppressible layers were designed and prepared. X-ray diffraction intensity of the PT(111) became 5 times larger and degree of crystal orientation became 2 times stronger in comparison with those of the former PT films. The filters using the improved PT films had the insertion loss of -14dB. The PT film had effective electromechanical coupling coefficient (k) of 31% and electrical Q of 50. This k value was superior to those of well-known ZnO and AlN piezoelectric films.