Fabrication of flexible microlens arrays through vapor-induced dewetting on selectively plasma-treated surfaces

Microlens arrays have been increasingly employed as key components in building micro-optical systems. Conventional fabrication methods, such as grayscale lithography, ink-jet printing, and photoresist thermal reflow, are often constricted by certain drawbacks, including mask resolution, high fabrication cost, and complexity of processes. In this paper, we present a low-temperature dewetting method that enables fabrication of microlens arrays on polymeric surfaces in a rapid and cost-effective way. As the demonstration of such a technique, vapor-induced dewetting of SU-8 thin films has been carried out on heterogeneous polydimethylsiloxane (PDMS) substrates that were selectively pre-treated with low-energy sulfur hexafluoride (SF6) or oxygen (O2) plasma. The dewetted SU-8 droplets are self-organized to directly form well-aligned microlens arrays on the O2-plasma-treated regions, with various lens curvatures ranging from ∼27° to ∼47° as the processing temperature rises from 20 °C to 80 °C. The exposure to the solvent vapor allows for the realization of dewetting at low temperatures. The optical performance of such microlens arrays has been characterized by testing their imaging capabilities.

[1]  Yanchun Han,et al.  Dewetting of polymethyl methacrylate on the patterned elastomer substrate by solvent vapor treatment , 2007 .

[2]  Ashutosh Sharma,et al.  Dewetting of Stable Thin Polymer Films Induced by a Poor Solvent: Role of Polar Interactions , 2012 .

[3]  F. Cacho-Nerin,et al.  Shaping mesoporous films using dewetting on X-ray pre-patterned hydrophilic/hydrophobic layers and pinning effects at the pattern edge. , 2011, Langmuir : the ACS journal of surfaces and colloids.

[4]  Yanchun Han,et al.  Ordered pattern formation from dewetting of polymer thin film with surface disturbance by capillary force lithography , 2004 .

[5]  Gabi Gruetzner,et al.  Directly fabricated multi-scale microlens arrays on a hydrophobic flat surface by a simple ink-jet printing technique , 2012 .

[6]  A. M. Higgins,et al.  Anisotropic spinodal dewetting as a route to self-assembly of patterned surfaces , 2000, Nature.

[7]  A. Karim,et al.  Pattern-Directed Dewetting of Ultrathin Polymer Films , 2002 .

[8]  A. A. Darhuber,et al.  Dewetting of thin liquid films on chemically patterned substrates: front propagation along narrow lyophobic stripes and stripe arrays , 2013 .

[9]  Ho-Cheol Kim,et al.  Nanopatterning of thin polymer films by controlled dewetting on a topographic pre-pattern. , 2008, Soft matter.

[10]  James J. Feng,et al.  Simulations of the breakup of liquid filaments on a partially wetting solid substrate , 2012 .

[11]  A. A. Darhuber,et al.  Dry-spot nucleation in thin liquid films on chemically patterned surfaces , 2011 .

[12]  S. Bankoff,et al.  Long-scale evolution of thin liquid films , 1997 .

[13]  Stephan Herminghaus,et al.  Gaining control of pattern formation of dewetting liquid films , 2001 .

[14]  F. Okano,et al.  Microlens arrays for integral imaging system. , 2006, Applied optics.

[15]  Brian P. Crum,et al.  Super Hydrophobic Parylene-C Produced by Consecutive ${\rm O}_{2}$ and ${\rm SF}_{6}$ Plasma Treatment , 2014, Journal of Microelectromechanical Systems.

[16]  Ashutosh Sharma,et al.  Instability and Pattern Formation in Thin Liquid Films on Chemically Heterogeneous Substrates , 2000 .

[17]  Wenhua Zhang,et al.  Pattern-directed to isotropic dewetting transition in polymer films on micropatterned surfaces with differential surface energy contrast. , 2007, Soft matter.

[18]  Ashutosh Sharma,et al.  Control of morphology in pattern directed dewetting of thin polymer films , 2008 .

[19]  Sharma,et al.  Instability and morphology of thin liquid films on chemically heterogeneous substrates , 2000, Physical review letters.

[20]  B. Javidi,et al.  Integral imaging with improved depth of field by use of amplitude-modulated microlens arrays. , 2004, Applied optics.

[21]  Teodor Veres,et al.  Microlens array fabrication by enhanced thermal reflow process: Towards efficient collection of fluorescence light from microarrays , 2009 .

[22]  Mark Bowen,et al.  ADI schemes for higher-order nonlinear diffusion equations , 2003 .

[23]  Ashutosh Sharma,et al.  Enhanced Self‐Organized Dewetting of Ultrathin Polymer Films Under Water‐Organic Solutions: Fabrication of Sub‐micrometer Spherical Lens Arrays , 2010, Advanced materials.

[24]  Liping Zhao,et al.  Efficient implementation of a spatial light modulator as a diffractive optical microlens array in a digital Shack-Hartmann wavefront sensor. , 2006, Applied optics.

[25]  Ashutosh Sharma,et al.  Creation of ordered patterns by dewetting of thin films on homogeneous and heterogeneous substrates. , 2002, Journal of colloid and interface science.

[26]  L. Leibler,et al.  On the sorption of gases and liquids in glassy polymers , 1993 .

[27]  Carl V. Thompson,et al.  Solid-State Dewetting of Thin Films , 2012 .

[28]  Ching-Kong Chao,et al.  Applying ANN/GA algorithm to optimize the high fill-factor microlens array fabrication using UV proximity printing process , 2005 .

[29]  Yanchun Han,et al.  Pattern formation by dewetting of polymer thin film , 2011 .

[30]  Andreas Bräuer,et al.  Microlens array based LCD projection display with software-only focal distance control , 2013, Photonics West - Optoelectronic Materials and Devices.

[31]  E. Charbon,et al.  Inkjet printing of SU-8 for polymer-based MEMS a case study for microlenses , 2008, 2008 IEEE 21st International Conference on Micro Electro Mechanical Systems.

[32]  Patrick Degenaar,et al.  Multi-site optical excitation using ChR2 and micro-LED array , 2010, Journal of neural engineering.

[33]  Wen Li,et al.  Plasma-treated switchable wettability of parylene-C surface , 2012, 2012 7th IEEE International Conference on Nano/Micro Engineered and Molecular Systems (NEMS).

[34]  L. Schwartz,et al.  Simulation of Droplet Motion on Low-Energy and Heterogeneous Surfaces , 1998 .

[35]  Yanchun Han,et al.  Patterning thin polymer films by surface-directed dewetting and pattern transfer , 2003 .

[36]  Kuan-Liang Lai,et al.  Accelerated Publication: Patterning of polystyrene thin films by solvent-assisted imprint lithography and controlled dewetting , 2012 .

[37]  Masayoshi Esashi,et al.  Fabrication of three-dimensional microstructure using maskless gray-scale lithography , 2006 .

[38]  L. Schwartz,et al.  Dewetting Patterns in a Drying Liquid Film. , 2001, Journal of colloid and interface science.

[39]  Edoardo Charbon,et al.  Hybrid polymer microlens arrays with high numerical apertures fabricated using simple ink-jet printing technique , 2011 .

[40]  Theo Rasing,et al.  Macroscopic Hierarchical Surface Patterning of Porphyrin Trimers via Self-Assembly and Dewetting , 2006, Science.

[41]  Hong-Bo Sun,et al.  High numerical aperture microlens arrays of close packing , 2010 .

[42]  D. Bonn,et al.  Wetting and Spreading , 2009 .

[43]  Reiter,et al.  Dewetting of thin polymer films. , 1992, Physical review letters.