Copper Damascene Process-Based High-Performance Thin Film Lithium Tantalate Modulators

Abstract

Interfacing electrical and optical systems is a ubiquitous requirement for modern networks. Competitive footprint, efficiency, and bandwidth figures have propelled interest in deploying integrated electro-optic modulators based on Pockels materials for such tasks. Due to its wide usage in legacy bulk electro-optic modulators, and triggered by the availability of 'on insulator' wafers, lithium niobate based devices have seen major advances. Recently, even more favorable properties have been demonstrated in lithium tantalate based devices, featuring similar Pockels effect, but exhibiting lower bias drift and lower birefringence, while equally benefiting from existing volume usage in wireless RF filters. Despite major progress in integrated modulators, these newly emerged ferro-electrical modulators cannot be integrated tightly with electronics yet using standardized processes, such as flip-chip bonding. Here, we overcome this bottleneck by incorporating the copper Damascene process in the fabrication of integrated lithium tantalate modulators. We demonstrate modulators featuring microwave losses that are ~10% lower than in designs relying on conventional gold electrodes. Our results allow us to reach data transmission figures on par with those of electro-optic modulators fabricated with other low-resistivity, yet less common, metals. Specifically, our fabricated modulators are able to achieve data transmission rates of 416 and 540 Gbit/s while preserving bit error ratios below the 25% SD-FEC threshold in a PAM4 and PAM8 transmission schemes, respectively. Together with the commercial availability of lithium tantalate as a Pockels material, our results open a path towards scalable and direct chip-on-wafer embedding of EO modulators with micro-electronic integrated circuits.