Electrochemically Deposited Aluminum for MEMS Thermal Actuator

In this study, a micro electro mechanical system (MEMS) thermal actuator using an electrochemically deposited thick Al is reported for the first time. Due to the fine columnar shape of the grain, the electrical resistivity of the Al film was as high as 100-150 n/m, which is an order of magnitude higher than the bulk value. Such a high resistivity benefits to facilitate the Joule heating during the operation of the thermal actuator. Meanwhile, the coefficient of thermal expansion (CTE) of the electrochemically deposited Al film was experimentally evaluated to be 20-27 ppm/K, which is consistent with the previous reports. With such a large CTE, the material has a potential to enhance the working displacement and force of a thermal actuator. The suspended structure was fabricated using a tetraethyl orthosilicate (TEOS) chemical vapor deposition (CVD) SiO2 as a sacrificial layer. The tip displacement of the fabricated v-shape thermal actuator was around 10 μm at 3 V actuation voltage. The demonstration can open up a new class of MEMS thermal actuator using electroplated Al films as the structural material.