Ph.D Thesis

Ph.D StudentMahameed Rashed
SubjectThermal Effects in Microsystems (MEMS) and
Applications in Novel Microdevices
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata


Due to the small scale of MicroElectroMechanical Systems (MEMS), the thermoelastic coupling effect can be used for actuation. Thermoelastic micro-actuators are very simple to fabricate and they typically require low operating voltages. However, thermoelastic coupling may have an adverse effect in microsystems because it dissipates mechanical energy. In this work thermoelastic actuation and thermoelastic damping in micro-systems are investigated.

In a previous research a temperature-gradient thermoelastic actuator was developed. A preliminary analysis of this actuation method was performed. The analysis showed that the actuation scheme can be used to build microresonators with high frequencies compared to the prevalent thermoelastic actuation methods. In the present work, an advanced analysis of the actuation method was performed to consider large deflection amplitudes. Test structures were fabricated and their experimental results were found to be in agreement with the model predictions. To further demonstrate the feasibility of temperature-gradient thermoelastic actuator, a tilting micromirror device was designed and fabricated which achieved a periodic angular deflection of ±8.5° at 9.5 kHz, while driven by a 1.5 Volt source.

In order to increase the quality factor Q of MEMS resonators it is essential to identify the dominant energy dissipation mechanisms and eliminate them by using improved design and fabrication methods. In this work, it was theoretically shown that thermoelastic incompatibility between Silicon structures and their native-oxide layers induces thermoelastic damping. This damping dominates in structures that are packaged in vacuum and vibrate in pure axial motion. Analytic solutions of the thermoelastic response of axially loaded laminated bars were used to determine the material parameters which affect thermoelastic damping. The analysis suggests that thin shield-layers can significantly reduce thermoelastic damping which is associated with native-oxide layers in Silicon resonators.