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Proceedings Paper

Simple volume expanding fabrication method for focal length controlled micro-lens array
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Paper Abstract

This study describes easy fabrication method for micro-lens array which has desired focal length in such a way that without the use of reflow technique. The process includes conventional lithographic process only which can be compatible with general semiconductor process. As constituent material, Negative photo-resist SU-8 with its developer PGMEA is used. Two main phenomena during lithography process are adjusted to expand the volume of the PR. During UV exposure, hardening proceeds from the top of the PR. Just after first exposure, using this property, very thin membrane on the top of the surface of the PR can be formed by short time exposure. In the development process, unexposed area of the PR is removed by chemical reaction with developer which causes the volume expansion if the unexposed area is covered with thin cured film. This method is to form the lens as the molecules in the volume are not easily escaped from the covered region. The thickness of the thin film depends on the exposure dose of 2mJ cm-2 μm-1 which determines the degree of expansion. The symmetrical volume expansion creates the membrane of lens shape and the focal length is directly related with second exposure dose. An extended research of affecting the change of the focal length of lens using volume expansion method by changing any other elements is discussed. This process can achieve a focal length selective for the applications of micro-optics.

Paper Details

Date Published: 13 March 2015
PDF: 7 pages
Proc. SPIE 9374, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VIII, 93741B (13 March 2015); doi: 10.1117/12.2078293
Show Author Affiliations
Junoh Kim, KAIST (Korea, Republic of)
Muyung Lee, KAIST (Korea, Republic of)
Cheol Joong Kim, KAIST (Korea, Republic of)
Jin Su Lee, KAIST (Korea, Republic of)
Yong Hyub Won, KAIST (Korea, Republic of)

Published in SPIE Proceedings Vol. 9374:
Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VIII
Georg von Freymann; Winston V. Schoenfeld; Raymond C. Rumpf; Henry Helvajian, Editor(s)

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