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Research Papers

Fabrication of Three-Dimensional Functional Microstructures on Curved Substrates Using Three-Dimensional Microlens Projection

[+] Author and Article Information
Lei Li

Department of Integrated Systems Engineering,
The Ohio State University,
210 Baker Systems, 1971 Neil Avenue,
Columbus, OH 43210

Sebastian Scheiding

Fraunhofer Institute for Applied Optics
and Precision Engineering,
Albert-Einstein-Straße 7,
Jena 07745, Germany;
Institute of Applied Physics,
Friedrich Schiller University Jena,
Jena 07745, Germany
e-mail: Sebastian.scheding@iof.fraunhofer.de

Ramona Eberhardt

Fraunhofer Institute for Applied Optics and
Precision Engineering,
Albert-Einstein-Straße 7,
Jena 07745, Germany

Andreas Tünnermann

Fraunhofer Institute for Applied Optics and
Precision Engineering,
Albert-Einstein-Straße 7,
Jena 07745, Germany;
Institute of Applied Physics,
Friedrich Schiller University Jena,
Jena 07745, Germany

Donggang Yao

Georgia Institute of Technology,
School of Materials Science and Engineering,
801 Ferst Drive, N.W.,
Atlanta, GA 30332
e-mail: yao@gatech.edu

Allen Y. Yi

Department of Integrated Systems Engineering,
The Ohio State University,
210 Baker Systems, 1971 Neil Avenue,
Columbus, OH 43210
e-mail: yi.71@osu.edu

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro- AND Nano-Manufacturing. Manuscript received November 29, 2012; final manuscript received June 18, 2013; published online August 13, 2013. Assoc. Editor: Ashutosh Sharma.

J. Micro Nano-Manuf 1(3), 031006 (Aug 13, 2013) (9 pages) Paper No: JMNM-12-1080; doi: 10.1115/1.4025060 History: Received November 29, 2012; Revised June 18, 2013

In this research, an innovative 3D micromachining process for functional microstructures on curved surfaces is introduced. An injection molded 3D polymethylmethacrylate (PMMA) microlens array was used as projection optics. A layer of positive photoresist SPR 220 was spin coated on a curved substrate. Preselected patterns were projected onto the photoresist by using a home-built exposure system. Microstructures were created on the curved substrate after development. The 3D projection micromachining method was evaluated through several experiments, and predesigned masks were prepared to fabricate microstructure array of various dimensions and distributions, demonstrating its 3D micromachining capabilities. Finally, this method was utilized to control the surface roughness of the curved substrates by generating microsquare protuberance arrays, forming a 3D functionally graded material (FGM). Further experimental results using a goniometer showed that this method can create functional microstructures for wettability control on steep curved substrates. All these results indicated that the proposed micromachining process is capable of fabricating 3D microstructures on curved surfaces and provides a cost-effective solution to challenging manufacturing problems.

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References

Figures

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Fig. 4

Mask for exposure calibration (the black portion represents the printed pattern on the transparent sheet, while the white part represents the transparent region)

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Fig. 5

Mask for resolution evaluation

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Fig. 6

Microstructures control through mask design: (a) 3D evaluation mask of the OSU OPTICS logo. (b) Boundary elimination mask with rectangular patterns. (c) Fill factor evaluation mask with triangular array.

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Fig. 7

(a) SEM scan of a close up view of the finished microstructure (b) photoresist exposure time for different final spin speeds

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Fig. 8

(a) Close up view of the printed mask. (b) SEM of the finished microstructures. (c) Cross section of region C. (d) Cross section of region D.

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Fig. 10

Microsquare design for sample 2. A layer of SPR 220 was left at the base of the square array in order to completely cover the PMMA substrate, so the influence of PMMA to the wettability change is isolated.

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Fig. 11

(a) and (b) display the sessile water droplet on the smooth photoresist surface. (c) and (d) display the sessile water droplet on the machined photoresist surface.

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Fig. 9

(a) Microstructure array for the logo of OSU OPTICS. (b) Close up view of the individual microstructure. (c) SEM of the finished microsquare protuberance array. (d) SEM of the triangular array with high fill factors.

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Fig. 3

Schematic of the 3D microlens array imaging

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Fig. 2

(a) Cross section of the 3D projection microlens array and the curved substrate. (b) OPD map of individual lenslet.

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Fig. 1

Schematic of the 3D micromachining system

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