A simple approach to fabricate multi-layer glass microfluidic chips based on laser processing and thermocompression bonding

Glass is an ideal material for microfluidic chips because of its pressure resistance, chemical stability, optical transparency, and thermal stability. Two-layer or three-layer microfluidic glass chips, composed of one or two cover layers and one structural layer, have been widely applied to two-dimensional microfluidic systems. Due to the fabrication difficulties in aligning and bonding multiple glass layers, multi-layer glass chips (more than three layers) are underutilized, although they are essential to deliver more complicated microfluidic functionalities and achieve more accurate microfluidic manipulations. This work proposes a fabrication process based on rapid laser cutting of single glass layers and one-time thermocompression bonding of multi-layer chips and demonstrated it with a five-layer microfluidic chip for three-dimensional (3D) hydrodynamic focusing. The pressure and temperature are the key parameters for multi-layer bonding, which are experimentally determined to be 0.4 MPa and 605 ℃. Five-layer glass microfluidic chips could be fabricated within 6 h with a bonding strength of 0.6 MPa. This simple, easy-to-operate fabrication method for the rapid production of multi-layer glass microfluidic chips will be conducive to the wide application of multi-layer microfluidic glass chips.