Novel Architecture for Inertial Grade SOI MEMS Inertial Sensors

This work reports, for the first time, on a novel architecture for realizing high performance miniaturized micromachined inertial sensors based on silicon on insulator (SOI) technology. The new sensors are essential components for high precision inertial navigation systems (INS) serving a wide range of applications varying from automotive to space. Similar to the state-of-the-art designs and architectures, our novel architecture utilizes SOI technology, which is crucial for realizing such electro-mechanical sensors. This is mainly due to the fact that it allows for having stress free suspensions and relatively very large proof masses (for bulk rather than surface micromachined MEMS) coupled with the flexibility of choosing between the presence or absence of electrical isolation between the upper and lower parts of the SOI wafer depending on the sensor's layout. This accordingly enables having the electrical contacts isolated from the rest of the sensor's structure. Typically, vibratory micromachined gyroscopes (VMG) and accelerometers are designed in-plane, i.e. the suspension and the proof mass vibrate in the same plane parallel to the substrate surface. Such in-plane architecture reduces dramatically the sensor's fill factor (typically around 17%); hence the Brownian noise level and overall sensitivity are degraded due to the reduced proof mass. Thus, a dramatic enhancement in performance can be achieved by improving the fill factor as this has a direct impact on increasing the proof mass significantly. Accordingly, we introduced, for the first time, the vertically suspended micromachined inertial sensor displayed in Figs. 1 and 2. Such design allows increasing the fill factor by more than a factor of four (up to 80-90%). Moreover, this design offers a decoupled geometric design of the proof mass and the support stiffness dimensions. The performance of the proposed sensors was analyzed using finite element method (FEM) to determine the natural mode shapes and frequencies in addition to the mechanical stability and the drive-sense mode decoupling (1-2% similar to common designs) for the MEMS gyroscopes.