Inertialsensorik

Fraunhofer ENAS Chemnitz, the Center for Microtechnologies (ZfM) of TU Chemnitz and EDC Electronic Design Chemnitz have worked together in close cooperation since 2009. In joint project teams we develop micromechanical inertial sensors with integrated electronics for various applications. Inertial sensors detect acceleration, inclination or angular rate in open space without the need of an external reference frame. The developed inertial sensors are based on the principle of inertia and transform the mechanical movement most often into a capacitance change. The MEMS gyroscopes play a special role as they need a forced oscillation. They are based on a vibrating mass to generate a force under the presence of an angular velocity. This so called Coriolis force leads to a deflection with respect to the angular velocity and creates a detectable signal.

Within the last years, we have been developing a high-precision MEMS gyroscope from scratch across several stages of development. The MEMS layout has been developed by Fraunhofer ENAS. The system design for the electro-mechanics has been done by ENAS within a closed joint work with EDC. The development of the MEMS technology and the fabrication of prototypes have been done at the ZfM. The SME memsfab has access to this technology and can provide a small series of the MEMS if required. The integrated circuits have been developed by EDC and were fabricated in a reliable 180 nm low noise technology of the foundry X-FAB.

System demonstrators

The gyroscope systems consist of a micromechanical element that is sensitive to an angular velocity about the z-axis. We use a multi-mass approach with two Coriolis masses fabricated in our high aspect ratio silicon technology. The mechanical elements are double-decoupled. The integrated circuit drives the MEMS into resonance at a stable amplitude. The capacitance change from the mechanics is picked up with the fully differential read out electronics and processed with the digital signal processor inside the integrated circuit.

We have developed different system demonstrators with respect to ASIC and MEMS revisions and with different packaging approaches. This includes the usage of standard IC packages as well as chip on board (CoB) approaches and system demonstrators in standard Kovar packages. The target parameters as well as achieved results are summarized in Tab 1. All measurements but the scale factor temperature coefficient have been carried out at room temperature.

MEMS Gyroscope System

• Digital angular velocity sensor with SPI interface
• ensitive on angular rates about the z-axis (yaw)
• ± 450 °/s input range
• 5 °/h resolution = 14 mdps (milli degree per seconds)
• In run bias stability < 1 °/h
• Angle random walk (noise) < 0,03 °/√h (0,00043 °/s/√Hz)
• Operating temperature range from -40 °C to 85 °C
• Package dimensions 17 x 17 mm²