Knowledge Bank

Glass is a desired material for microfluidic and nanofluidic chips due to chemical inertness, temperature stability, and optical clarity. Given the desire to maintain chemical uniformity for flow conduits, it is well known that thermal fusion bonding is the preferred method to bond two distinct glass substrates. Furthermore, thermal fusion bonding is known to achieve higher bond strength compared to other bonding techniques (e.g., anodic bonding). The purpose of this research is to develop a reliable recipe for successful fusion bonding of all-glass nanochannels. In this research, a device with inverted Y-shaped nanochannels is used as a model system. The nanochannels are 500 nm in depth and are fabricated via standard lithography and wet etching. The width of the channel is 100 µm at the entry of the channel and reduces to 50 µm at each bifurcated leg. The channel is etched in a sodium borosilicate glass slide which is subsequently capped with soda-lime-silica glass slide in which holes were drilled to act as reservoirs for working fluid inlet to subsequently seal the channel from the ambient environment. In this research, we have investigated thermal bonding parameters including the variation of temperature, the use of weights to apply a constant pressure on the glass slides, and the use of surface activation processes. Our results indicate that sealed glass-glass channels can be bonded at a temperature of 600℃ over 10 hours along with simultaneous application of weight over the bonding area (a load of 1.14 kg corresponds to a pressure of 9.3 kPa applied over the entire area of the channel containing cover glass). The devices will be used for subsequent electrical manipulation of ions and molecules.