Polarization inverted two layer ScAlN thin film resonator fabricated by applying external electric field

Abstract

ScAlN has high piezoelectricity and ferroelectricity. BAW filters with polarization inverted multilayer structure allow the further improvement of the power durability. In this study, by growing the Al-polar ScAIN film on the N-polar film, the polarization inverted two-layer ScAIN thin films resonator were fabricated. Unusual N-polar ScAIN film was obtained by a polarization inversion treatment to the as-grown usual Al-polar films. Polarity of the ScAlN films was determined by a press test. kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of as-grown Al-polar ScAIN and N-polar ScAlN films after the polarization treatment (-190 V (2.0 MV/cm) at 300 °C) were estimated to be 7.7% and 5.6%, respectively. Because of an incomplete polarization inversion, kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the film after polarization inversion treatment slightly decreased compared with the as-grown films. Second overtone mode excitation was observed at GHz range, and fundamental mode was suppressed.