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

Master's 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 µm 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.