8 inch Surface and Bulk Acoustic Wave devices based on POI substrate for 5G
Résumé
The availability of Piezoelectric-On-Insulator (POI) substrates, made of a thin single crystal LiTaO3 film atop a silicon substrate, has promoted the development of innovative Surface and Bulk Acoustic Wave devices (SAW and BAW). However, these substrates are so far only commercially available in 4 and 6 inch diameter. In this work, we successfully fabricate acoustic devices based on 8-inch POI substrates. SAW resonators display an electromechanical coupling coefficient of 8.83% at a resonance frequency of 1.6 GHz. Film Bulk Acoustic Resonator (FBAR) and Solidly Mounted Resonator (SMR), which integrate more complex layer stacks, such as a buried electrode and acoustic isolation structures, have been also fabricated. The FBAR exhibits a single resonance at 2.8 GHz, with an electromechanical coupling coefficient of 8.75% and a quality factor close to 190. The SMR based on a dielectric (AlN/SiO2) Bragg mirror exhibits a coupling coefficient of 6.1% and a quality factor of 405 at 4 GHz. A Temperature Coefficient of Frequency (TCF) of -14 and -22 ppm/°C at resonance and antiresonance are obtained respectively. Such TCF values are among the lowest ever reported for LiNbO3 and LiTaO3 BAW resonators. These results offer promising perspectives towards the development of SAW and BAW filters on 8-inch POI substrates.