Optical and Mechanical Properties of a Polyimide Membrane for Tunable Lenses

Christian Kelb; Dominik Hoheisel; Eduard Reithmeier; Lutz Rissing

doi:10.1117/12.929773

19 October 2012 Optical and mechanical properties of a polyimide membrane for tunable lenses

Christian Kelb, Dominik Hoheisel, Eduard Reithmeier, Lutz Rissing

Proceedings Volume 8489, Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials II; 84890F (2012) https://doi.org/10.1117/12.929773
Event: SPIE Optical Engineering + Applications, 2012, San Diego, California, United States

Abstract

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 deflections 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.

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Christian Kelb, Dominik Hoheisel, Eduard Reithmeier, and Lutz Rissing "Optical and mechanical properties of a polyimide membrane for tunable lenses", Proc. SPIE 8489, Polymer Optics and Molded Glass Optics: Design, Fabrication, and Materials II, 84890F (19 October 2012); https://doi.org/10.1117/12.929773

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KEYWORDS

Semiconducting wafers

Etching

Confocal microscopy

Manufacturing

Silicon

Deep reactive ion etching

Photomasks

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