TABLE I.
Selection of the fabrication process according to the requirements of the application (optical, geometrical, electrical, and thermal).
| Possible processing routes and criteria for their selection (preferred process options are shown in bold) | |||||
|---|---|---|---|---|---|
| Step | Selection to be made | Route A | Route B | ||
| 1 | Materials involved in the microfabrication process | • Glass/glass (take this route if the application requires optical transparency of the device) | • Glass/silicon (a more common and well established route) | ||
| 2 | Patterning method | Microchannels | • Wet etching in HF/HCl• Dry etching (recommended only if vertical walls or high aspect ratio structures are required) | • Dry etching of the silicon• For complex microfluidic devices requiring multiple channel layers, the silicon wafer can be patterned on both sides and via holes etched through the wafer to connect them; alternatively, the glass can be patterned (by wet etching) as well as the silicon. | |
| Through-holes for fluidic ports | • Wet etching • Sand-blasting • Drilling | • Dry etching • Laser-drilling • Sand-blasting | |||
| 3 | Bonding method | No electrical connection | The device operates above ∼200 °C | • Fusion bonding • Anodic bonding with metallic or a:Si layer | • Anodic bonding |
| The device operates at or below ∼200 °C | • Adhesive bonding • Anodic bonding with metallic or a:Si layer • Fusion bonding | • Anodic bonding • Adhesive bonding | |||
| With electrical connection | The device operates above ∼200 °C | • Anodic bonding (the thickness of the metallic layer can be critical) • Bonding using an intermediate layer | • Anodic bonding (the thickness of the metallic layer can be critical) | ||
| The device operates at or below ∼200 °C | • Adhesive bonding • Anodic bonding (the thickness of the metallic layer can be critical) | • Adhesive bonding • Anodic bonding (the thickness of the metallic layer can be critical) | |||
| 4 | Fluid connections | • Permanent: push-fit tubing into polymer ports (optionally fix with glue or PDMS) • Permanently attached ferrule with removable capillary tubing (e.g., Nanoport) • Temporary: push-fit capillary tubing into PDMS device (permanent if PDMS is plasma-treated) • Mechanically clamped chip-holder | |||