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.