Wafer-Scale Fabrication of 42° Rotated Y-Cut LiTaO₃-on-Insulator (LTOI) Substrate for a SAW Resonator

Abstract

A high-performance filter is the key component in 5G communication. A surface acoustic wave (SAW) resonator fabricated on a piezoelectric thin film instead of piezoelectric bulk substrate can achieve a higher quality factor (Q) and a lower temperature coefficient of frequency (TCF). Here we performed the fabrication of 4 in. 42° rotated Y-cut LiTaO3-on-insulator (LTOI) hybrid substrate applied for the surface acoustic wave (SAW) radio-frequency (RF) resonators. This heterogeneous substrate combining a submicrometer single crystalline LT thin film on a Si wafer was achieved by using the ion-cut process with direct wafer bonding. The kinetics of surface blistering and the defects evolution in 75 keV H+ implanted LT samples were investigated by annealing at various temperatures ranging from 170 to 230 °C. The activation energy for forming the blistering crack is around 1.34 eV. After direct wafer bonding, a wafer-scale LT thin film with single crystalline quality was successfully transferred onto the Si substrate. The crystalline quality was further improved via a postannealing at 400 °C, which is demonstrated by the reduction of the full width at half-maximum of the XRD rocking curve from 167 to 48 arcsec. The roughness of the blistering surface of the LT thin film was significantly reduced from 12 to 0.2 nm by an optimized chemical mechanical polishing (CMP) process, in which the damage layer of 30 nm was removed as well. Finally, a 350 MHz one-port SAW resonator based on the fabricated LTOI substrate was demonstrated.