FPGA-basierter Wafer-Level Test und Charakterisierungsmethoden für MEMS Beschleunigungssensoren

Abstract

In this thesis, new FPGA-based wafer-level test methods for MEMS accelerometers were developed and validated. The main focus of this thesis is the test for adhesion failure of the MEMS movable structures called stiction testing, which is characterised for different sensor and configuration parameters. From the results a new mechanism leading to enhanced stiction occurences by stimulating the electrode fingers of the devices has been found. The effect has been studied systematically and a method for detecting critical modes has been implemented. Additionally, two improvements of the state of the art tests were introduced. The implementation of the proposed high-dynamic pulse method enhances the sensitivity of the test for out-of-plane cores, while the usage of the opposite electrode for the release process expands the range of measurable stiction forces. The second objective was to reduce test time for functional tests that are used in production, while also improving the precision and the coverage of characterisation tests used in the development process of new MEMS designs. The implementation of the new test step „sensitivity curve“ and a cavity leakage test based on the measured data of the sensitivity curve enabled a significant reduction in overall test time. The new cavity leakage test also enables a damping measurement for highly damped devices, which could not be measured accurately so far.