Fig 1.
Standard lithography and modified steps.
(A) Resin deposition. (B1) Full curing of base layer. (B2) Resin deposition for microstructure patterning. (B3) Replacement for step B1 and B2. (C) Exposure with photomask for pattern transfer.
Fig 2.
Curing processes of PUMA resin.
(A) Full curing by covering the resin with transparency sheet. (B) Control of curing by applying low vacuum or nitrogen shower. (C) Partial curing by exposing top surface of the resin to air.
Fig 3.
(A) Irradiation dose at distances from the source. (B) UV transmission of PUMA of different thicknesses for different exposure duration and lamp-to-sample distance of 13.0cm. (C) Attenuation of PUMA resin per millimeter of film thickness for different exposure durations and lamp-to-sample distance of 13.0 cm. (D) UV dose required for complete cure of PUMA resin of different thicknesses. (E) Thickness of PUMA resin remaining uncured for PUMA film of 1.0mm thickness exposed for different curing durations at lamp-to-sample distance of 3.5cm. (F) and (G) Conversion ratio and dimensionless concentration of oxygen versus depth for exposure duration of 5 to 360 seconds for covered sample. Dashed line corresponds to 60 seconds.
Fig 4.
SEM images of a typical microstructure for application in microfluidic devices fabricated using proposed technique.
Depth of microstructures in (A) and (B) is ~200.0 μm and camera angle is 70°.
Fig 5.
SEM images of an array of micropillars.
(A) Array of pillars with square cross-section. (B) and (C) Array of pillars with circular cross-section. Average dimension of each single pillar is 100 μ × 200 μ, (D × H) and aspect ratio ~2.0.
Fig 6.
SEM images of a negative polarity microstructure fabricated by two-step exposure lithography process using PUMA resin.
(B) Overall view of structure. (A) and (C) Close-up images of microstructures. Height of structure is ~50.0 μm and camera angle is 70°.