Humidity influence on the adhesion of SU-8 polymer from MEMS applications

¹ Technical University from Cluj-Napoca, Micro and Nano System Laboratory, 400641, B-dul Muncii 103-105, Romania
² Laboratory of Modeling, Simulation and CAD, National Institute for R&D in Microtechnologies - IMT Bucharest, 126A Erou Iancu Nicolae Street, 077190, Bucharest, Romania

^* Corresponding author: Corina.Barleanu@omt.utcluj.ro

Abstract

In this paper, the adhesion behaviors of SU-8 polymer thin film from MEMS application were investigated as a function of relative humidity. The adhesion test between the AFM tip and SU-8 polymer have been extensively studied using the atomic force microscope (AFM), for a relative humidity (RH) varying between 20 and 90%. The samples for tests are SU-8 polymers hard baked at different temperatures. The hard bake temperature changes the tribo-mechanical properties of polymers. The paper reports the measurements and the modeling of adhesion forces versus humidity in controlled ranges between 20 to 90%RH. To investigate the effect of relative humidity on adhesion for SU-8 polymer hard baked we used an analytical method which encompasses the effect of capillarity as well as the solid-to-solid interaction. While the capillary force expression is considered to be the sum of the superficial tension and the Laplace force for the solid-solid interaction is expressed by the Derjagin, Muller and Toropov (DMT) model of solids adhesion. The analytical results obtained are in accordance with those obtained experimentally.