Contacts

Category: Device Fabrication

Device Fabrication in microfluidics represents the precision micromachining and cleanroom microfabrication processes—specifically soft lithography, SU-8 photolithography, reactive ion etching, and polymer casting—utilized to translate computer-aided design (CAD) channel geometries into functional microchannel architectures on glass, silicon, and elastomer substrates.

Foundational Pillars
Principles & Methods
Topic Directory
Frequently Asked Questions

Foundational Pillars (Start Here)

SOFT LITHOGRAPHY

How to Clean a Microfluidic Chip: Maintenance and Protocol

Chemical cleaning workflows, pirana etch protocols, sonic bath degreasing, and surface regeneration for glass-PDMS bonded devices.

ACTUATOR INTEGRATION

A Microfluidic Droplet Generator Based on Piezoelectric Actuator

Integration of piezoelectric lead zirconate titanate (PZT) ceramic elements onto microfluidic chips for on-demand droplet dispensing.

BIO-DEVICE INTERFACING

A Droplet Microfluidic Platform for Automating Genetic Eng

Engineering multi-layer elastomeric microvalves, pneumatic control manifolds, and fluoropolymer tubing connectors for automated bioprocessing.

Standard Soft Lithography and Bonding Protocols

The gold standard microfluidic fabrication workflow centers on soft lithography. First, an SU-8 negative photoresist is spin-coated onto a polished silicon wafer to a calibrated thickness (typically 10 to 100 μm). UV exposure through a high-resolution photolithographic mask cross-links the channel geometry, followed by development to yield an embossed master mold. Liquid PDMS prepolymer and cross-linking curing agent are mixed at a 10:1 stoichiometric ratio, degassed in a vacuum desiccator, and cast over the master mold at 65–80°C.

Fabrication PhaseKey Operational ParametersChemical / Physical AgentsCommon Failure Modes & Mitigations
SU-8 Master PhotolithographySpin speed 1000–3000 RPM, UV dose 150–250 mJ/cm²SU-8 resist, PGMEA developerUnder-baking causes resist delamination; optimize soft/post-exposure bake ramp rates
Mold SilanizationVapor deposition, 30–60 min under vacuumTrichloro(1H,1H,2H,2H-perfluorooctyl)silaneIncomplete silanization leads to PDMS tearing during demolding
Oxygen Plasma BondingRF power 30–50 W, O2 pressure 0.2–0.5 mbar, 30–60 sOxygen plasma glow dischargeOver-exposure vitrifies PDMS surface; bond within 60 seconds of plasma activation
Interconnect CoringHollow punch tool 0.75–1.5 mm diameterHardened stainless steel biopsy punchTorn punch margins cause fluid leakage at high pumping pressures; use ethanol lubricant

Permanent sealing between the cured PDMS replica and a clean glass slide relies on oxygen plasma surface activation. Plasma bombardment removes surface methyl groups (-CH3) and exposes reactive silanol groups (-Si-OH). Conformal contact immediately forms covalent siloxane bonds (Si-O-Si) across the interface, yielding irreversible bond strengths exceeding 300–500 kPa capable of withstanding high hydrodynamic backpressures.

Topic Directory & Methodologies

Device Prototyping & Actuation

Bio-Device Fabrication & Automation

Frequently Asked Questions

What is the standard mixing ratio for PDMS elastomer fabrication?

The standard formulation for Sylgard 184 silicone elastomer is 10 parts base polymer to 1 part curing agent by weight. Increasing the crosslinker ratio (e.g., 5:1) increases chip stiffness and Young’s modulus, whereas decreasing it (e.g., 15:1) yields a softer, more compliant elastomeric membrane.

Why must silicon master molds undergo silanization before casting?

Freshly cured SU-8 photoresist on silicon bonds strongly to PDMS during thermal curing. Vapor-phase silanization with a fluorinated silane forms a low-surface-energy monolayer that acts as a release agent, preventing adhesion and allowing clean, non-destructive demolding of the elastomer.

How can PDMS hydrophobicity be modified for aqueous flow stability?

While oxygen plasma temporarily creates a hydrophilic surface with silanol groups, hydrophobic recovery occurs within hours as low-molecular-weight silicone chains migrate from bulk to surface. Permanent hydrophilic modification requires grafting hydrophilic polymers (PEG), layer-by-layer polyelectrolyte deposition, or sol-gel silica coatings.

What are the alternatives to soft lithography for commercial microfluidic manufacturing?

High-volume commercial manufacturing replaces PDMS soft lithography with precision injection molding or hot embossing of cyclic olefin polymers (COP/COC) and PMMA, as well as roll-to-roll laser micromachining, reducing unit costs from tens of dollars to pennies per consumable cartridge.


AI Editorial Policy