Irreversible Bonding of Polydimethylsiloxane‐Lithium Niobate using Oxygen Plasma Modification for Surface Acoustic Wave based Microfluidic Application: Theory and Experiment
Chunhua He, Jinhui Yao, Canfeng Yang, Jianxin Wang, Bo Sun, Guanglan Liao, Tielin Shi, Zhiyong Liu
Abstract
Abstract Acoustic microfluidic chips, fabricated by combining lithium niobate (LiNbO 3 ) with polydimethylsiloxane (PDMS), practically find applications in biomedicine. However, high‐strength direct bonding of LiNbO 3 substrate with PDMS microchannel remains a challenge due to the large mismatching of thermal expansion coefficient at the interface and the lack of bonding theory. This paper elaborately reveals the bonding mechanisms of PDMS and LiNbO 3 , demonstrating an irreversible bonding method for PDMS‐LiNbO 3 heterostructures using oxygen plasma modification. An in‐situ monitoring strategy by using resonant devices is proposed for oxygen plasma, including quartz crystal microbalance (QCM) covered with PDMS and surface acoustic wave (SAW) fabricated by LiNbO 3 . When oxygen plasma exposure occurs, surfaces are cleaned, oxygen ions are implanted, and hydroxyl groups (‐OH) are formed. Upon interfaces bonding, the interface will form niobium‐oxygen‐silicon covalent bonds to realize an irreversible connection. A champion bonding strength is obtained of 1.1 MPa, and the PDMS‐LiNbO 3 acoustic microfluidic chip excels in leakage tests, withstanding pressures exceeding 60 psi, outperforming many previously reported devices. This work addresses the gap in PDMS‐LiNbO 3 bonding theory and advances its practical application in the acoustic microfluidic field.