The non-linear thermal behavior of SU-8

SU-8 is widely used as a material for sensors and actuators or as a bonding layer for microelectromechanical systems (MEMS). Therefore, its physical properties, such as the Young's modulus and the thermal expansion coefficient were broadly investigated. However, no reliable data can be found around 0°C. Therefore, the thermal expansion of the material in the temperature range of -30°C up to +30°C was examined. The thermal expansion was measured via the deflection of appropriate designed structures with the help of an optical microscope. A sealable chamber with a Peltier-element was built and utilized to control the temperature and the ambient atmosphere (N2). It was found, that SU-8 shrinks, when absorbed water vanishes due to an N2 purge. Additionally, the thermal expansion of the SU-8 exhibits a non linear behavior in the range from -20°C to +20°C.