Effects of actuation methods and temperature on adhesion force between polycrystalline silicon surfaces in MEMS

Abstract

The adhesion force between polycrystalline silicon surfaces in MEMS structures is studied using three different test structures. Electrostatic and thermal actuations are used to bring the two surfaces into contact and mechanical force stored in the structures is used to separate them. In particular, the devices consist of (i) double-clamped beam that is actuated electrostatically and measured optically, (ii) suspended plate that is actuated electrostatically and measured capacitively, and (iii) thermally actuated and optically measured beams. The devices are fabricated using PolyMUMPs® process. The results show that the adhesion force in tested structures has little or no dependence on the apparent contact surface and is highly affected by the test environment and the actuation methods. The test results at high temperatures (100-130 °C) show that in absence of capillary and electrostatic forces, the adhesion force drastically decreases and mainly depends on the number of contacting asperities.