Advances in Room-Temperature Surface-Activated Bonding for Heterogeneous Optoelectronic Integration

  Prof. Ryo Takigawa

  Professor, Kyushu University, Japan   

Abstract: 

Heterogeneous integration and advanced packaging technologies are essential for nextgeneration photonic, electronic, and MEMS systems. Die- and wafer-level bonding are key enablers for such integration, and low-temperature solid-state bonding is particularly advantageous for enhanced functionality, device miniaturization, and reduced power consumption. Surfaceactivated bonding (SAB), together with plasma-activated bonding, has significantly expanded the range of materials that can be integrated. Die- and wafer-level bonding of III–V semiconductors such as InP, electro-optic materials, and piezoelectric materials have been extensively explored to realize heterogeneous integration on dissimilar material platforms. Moreover, these lowtemperature bonding techniques enable the stacking of multiple functional layers within a low thermal budget, thereby facilitating three-dimensional heterogeneous integration. This presentation introduces SAB-based room-temperature direct bonding and intermediatelayer bonding technologies for heterogeneous integration and packaging of III–V photonic devices and LiNbO₃ RF photonic devices. First, a room-temperature bonding method using metal bump or film for integrating III–V laser diodes and LiNbO₃ modulator chips onto Si platforms is presented as a promising approach for passive alignment and surface mounting of photonic chips. Next, room-temperature wafer-bonding technologies for III–V semiconductors and LiNbO₃ are described for heterogeneous photonics wafer, and the characteristics of the resulting bonding interfaces are discussed. Finally, room-temperature transfer bonding of LiNbO₃ thin-film chips and the realization of air/LiNbO₃ thin-film/air structures are presented as enabling technologies for the heterogeneous integration and advanced packaging. These developments demonstrate the potential of room-temperature SAB as a versatile platform for high-density heterogeneous optoelectronic integration. 

Speaker Biography:

Ryo Takigawa received the Ph.D. degree from the University of Tokyo, Japan, in 2012. He was a researcher with the National Institute of Advanced Industrial Science and Technology (AIST), Japan, from 2012 to 2013, and joined Kyushu University, Japan, as an Assistant Professor in 2013. From 2008 to 2009, he was a guest researcher at Fraunhofer IZM, Germany. He was a Visiting Associate Professor at imec, Belgium, from 2023 to 2024. Since 2026, he has been a Professor with Kyushu University. His current research interests include heterogeneous integration and advanced packaging technologies based on low-temperature bonding for future photonic and electronic systems.