MEMS devices and microfluidic chips can be manufactured through eutectic bonding, anodic bonding, adhesive bonding or fusion / direct bonding.
The profound know-how of Micronit GmbH allows the fabrication of systems with up to 21 glass layers as well as closed chambers which can be used for reference pressure measurements in a chip. For MEMS applications, free suspended membranes of oxide or nitride are required, which are built using bonding and back etching.
There are different wafer bonding techniques, such as
- Fusion bonding of silicon
- Fusion / direct bonding of glass
- Eutectic bonding
- Anodic bonding
- Thermo-compression bonding
- Adhesive bonding
Fusion or direct bonding is a technique that joins two or more wafers of the same material together. Fusion bonding is conducted at high temperatures, which makes the bond as strong as the mechanical strength of the base material. However, direct bonding at lower temperatures is also feasible.
Anodic bonding is a bonding technique that allows two or more wafers of different materials (silicon with glass) to be bound together. The bonding is done at low temperatures.
The process of anodic bonding is usually done at 400°C, which is a lower temperature than used for direct bonding. For the European project BIOINTENSE, Micronit developed a special low temperature bonding process at less than 180°C. The low temperature maintains the biological/chemical characteristics of the infused sensors and reduces the tension in glass and silicon layers.
Using eutectic bonding means forging a material bound connection through application of pressure and temperature treatment between two silicon or glass wafers. An established eutectic alloy is gold-silicon.
During adhesive bonding of PCB resp. SU-8 bonding, polymers are applied to structured wafers and then structured with their own layout. The bonding is done with a second wafer, which might be structured as well. Both wafers must not necessarily be of the same material.