Mechanical resonator for hermeticity evaluation of RF MEMS wafer-level packages

Masters Thesis from the year 2002 in the subject Electrotechnology, grade: 1.0 (A), University of Applied Sciences Berlin (FB1), language: English, abstract: Common test standards for evaluating the hermeticity of microsystem packages are unsuitable for small MEMS-devices. It is the task of this Master thesis to create a universal test device to measure and to compare the hermeticities of different wafer-level packaging concepts, especially for RF MEMS devices. Resonator structures were found to be most suitable to measure low pressures and low pressure changes over time, due to the high sensitivity of their Q-value to the pressure in the cavity. The resonators are electrostatically actuated by using a novel coupling concept of the excitation voltage. The detection of the resonator movement is done by laser-interferometry. Sensors fulfilling the specific demands were designed, simulated and fabricated in the cleanroom. The fabrication process is based on SOI (Silicon On Insulator) wafers. Finally, the sensors were evaluated and characterized. A suitable resonator with a length of 500 m reaches a Q-factor of 8070, at an ambient pressure of 0,02 mbar, and a resonance frequency of 36329 Hz. The sensitivity of the Q-value to pressure change is 4000 %/mbar at 0,02 mbar. This work was carried out within the Summit RF MEMS project, a collaborative project involving Ericsson, the Royal Institute of Technology-S3, Acreo and Saab Ericsson Space.