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 LiTaO 3 -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.

Development and Application of SAW Filter

“…The process flow for transferring LT thin films) First, the LT sample was implanted at 75 kev H + , and through direct wafer bonding, the single-crystal-level LT thin film was Transferred to a Si substrate, post-annealing at 400 °C further improved the crystalline quality, and then a 30 nm damaged layer was removed by an optimized chemical mechanical polishing (CMP) process, resulting in a significant increase in the blistered surface roughness of the LT film from 12 nm. It was reduced to 0.2 nm, and finally a 350 MHZ single-port surface acoustic wave resonator was designed using the prepared LTOI (LiTaO 3 -on-insulator) substrate [ 79 ].…”

Recent progress of integrated circuits and optoelectronic chips

“…It has been reported that InP heterojunction bipolar transistors (HBTs) can be integrated on Si materials platforms within silicon fabrication facilities [59], as presented in Figure 8(c). Based on the ion-cutting technology [60][61][62][63], the researchers realized different kinds of wafer scale heterogeneous integration materials, e.g., GaAs/Si, InP/Si, LiTaO 3 /Si, LiNbO 3 /Si, SiC/Si, and Ga 2 O 3 /SiC, as shown in Figure 8(d).…”

Strain Balanced Self‐Supporting Single‐Crystalline LiNbO3 Thin Films for Flexible Electronics

“…Ion slicing process is a feasible and versatile approach for the transfer of single‐crystalline films, which was first proposed by Bruel in 1995, [ 18 ] and has been applied to the mass production of Si‐on‐Insulator (SOI) wafers for years. It has also been successfully extended to the transfer of functional single‐crystalline films onto heterogeneous substrates in waferscale, such as InP‐on‐Si, [ 19 ] SiC‐on‐Si, [ 20 ] Ga 2 O 3 ‐on‐SiC, [ 21 ] and LiTaO 3 ‐on‐Si. [ 22 ] In recent years, lithium niobate, an artificial crystal with exceptional electro‐optical, pyroelectric, ferroelectric, and piezoelectric properties, has regained widespread attention.…”