TY - GEN

T1 - Optical and mechanical properties of a polyimide membrane for tunable lenses

AU - Kelb, Christian

AU - Hoheisel, Dominik

AU - Reithmeier, Eduard

AU - Rissing, Lutz

PY - 2012/10/19

Y1 - 2012/10/19

N2 - With its chemical resistance and easy structurability, polyimide (PI) makes for a fine candidate for membranes of tuneable optical systems. Disadvantages of the material are its high absorption coefficient and its mechanical stability, which prevents high deections of the membrane. To improve the optical capabilities of the material, different variations of processing of the membrane are used. For fabrication of the PI membrane, a photosensitive PI precursor is used. The precursor is spin coated on a 4"' Si wafer. After a prebake, the wafer is exposed to UV light. To manipulate the optical properties, different types of postbake are investigated. Afterwards, the backside of the wafer is structured by Deep Reactive Ion Etching (DRIE). Thus, a temporary photoresist etching mask is manufactured by photolithography on the wafer backside. Circular structures with a diameter of 2 mm are then etched through the wafer to fabricate the membranes. The absorption coefficient of the different manufactured membranes is measured. For future use of the membrane as part of a variable optical system, a FEM-Model is built to predict the behaviour of the membrane under mechanical loads, especially considering strains and stresses induced by the different postbake types. The results of the FEM-Model are compared with experimental data obtained via digital image processing methods. Comparative data using different membrane materials are also presented to compare the performance of the PI membrane.

AB - With its chemical resistance and easy structurability, polyimide (PI) makes for a fine candidate for membranes of tuneable optical systems. Disadvantages of the material are its high absorption coefficient and its mechanical stability, which prevents high deections of the membrane. To improve the optical capabilities of the material, different variations of processing of the membrane are used. For fabrication of the PI membrane, a photosensitive PI precursor is used. The precursor is spin coated on a 4"' Si wafer. After a prebake, the wafer is exposed to UV light. To manipulate the optical properties, different types of postbake are investigated. Afterwards, the backside of the wafer is structured by Deep Reactive Ion Etching (DRIE). Thus, a temporary photoresist etching mask is manufactured by photolithography on the wafer backside. Circular structures with a diameter of 2 mm are then etched through the wafer to fabricate the membranes. The absorption coefficient of the different manufactured membranes is measured. For future use of the membrane as part of a variable optical system, a FEM-Model is built to predict the behaviour of the membrane under mechanical loads, especially considering strains and stresses induced by the different postbake types. The results of the FEM-Model are compared with experimental data obtained via digital image processing methods. Comparative data using different membrane materials are also presented to compare the performance of the PI membrane.

KW - Membrane lens

KW - Polyimide

KW - Tunable lens

UR - http://www.scopus.com/inward/record.url?scp=84872925394&partnerID=8YFLogxK

U2 - 10.1117/12.929773

DO - 10.1117/12.929773

M3 - Conference contribution

AN - SCOPUS:84872925394

SN - 9780819492067

T3 - Proceedings of SPIE - The International Society for Optical Engineering

BT - Polymer Optics and Molded Glass Optics

T2 - Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials II

Y2 - 15 August 2012 through 16 August 2012

ER -