Proton exchange-enhanced surface activated bonding for facile fabrication of monolithic lithium niobate microfluidic chips

Abstract

In the quest to enhance the functionality and efficiency of lab-on-a-chip systems, integrating diverse physical phenomena such as acoustics, optics, and electronics into a single platform has emerged as a pivotal strategy. Lithium niobate (LiNbO3, or LN) stands out for its exceptional piezoelectric and electro-optic properties, making it an ideal candidate for such integrated systems. However, the full exploitation of LN in microfluidic applications has been hindered by the complex challenges associated with its fabrication. Addressing this gap, our research introduces a facile fabrication method for creating monolithic LN microfluidic chips. By employing a proton exchange-assisted surface-activated bonding technique, we achieve high-strength, flawless bonding at lower temperatures, overcoming the traditional barriers of LN machining. This method eliminates the chemical stability of LN by removing lithium ions and significantly enriches the surface with functional groups, leading to a bonding strength exceeding 10 MPa after annealing at 150 °C. Additionally, we have optimized an argon plasma etching process to ensure the creation of smooth LN channels at room temperature. The development of a fully integrated LN chip through this approach demonstrates superior performance, especially in surface acoustic wave (SAW) applications, compared to conventional PDMS/LN hybrids. This breakthrough not only realizes the fabrication process of LN microfluidic devices but also opens new avenues for the advancement of integrated microsystems across various scientific and technological domains.