Stefan Sassen

Silicon angular rate sensor for automotive applications with piezoelectric drive and piezoresistive read-out

In this work a silicon angular rate sensor for automotive applications with a new architecture is presented. It is based on the vibrating tuning fork principle with excitation direction of the tines perpendicular to the wafer surface. This arrangement allows the design of tines with significant inertial masses which lead to substantial signal. The oscillation of the tines is excited by a piezoelectric drive using an AlN thin film layer. The angular rate to be measured causes a torsional oscillation of the stem. The torsional amplitude is proportional to the angular rate and is measured by a piezoresistive read-out structure. We use silicon bulk micromachining based on a new twofold SOI-technique.

Tuning fork silicon angular rate sensor with enhanced performance for automotive applications

This paper reports on a silicon angular rate sensor designed for automotive applications like overroll protection and electronic skidding protection. The sensor is based on a tuning fork principle with the tines being piezoelectrically excitated perpendicular to the wafer surface. Due to the Coriolis effect, an angular rate parallel to the axis of the stem generates a periodic torque, which results in a torsional oscillation of the stem. This torsional oscillation is detected with an implanted piezoresistor located in the middle of the stem. A slot in the center of the stem enhances the shear stress at the read-out piezoresistor position resulting in a higher sensitivity. The latest sensor design with a split electrode allows an electronic compensation of mechanical imbalance in order to reduce the sensor offset and offset drift. Additionally, this electrode configuration can generate a periodic torque to perform a permanent test of the sensor functioning and the sensitivity during operation.

Anodic bonding of evaporated glass structured with lift-off technology for hermetical sealing

Abstract This paper reports on an enhanced anodic bonding technology of thin e-beam evaporated glass layers ( d ≤5 μm) for micromachined silicon sensors and actuators. This MOS-compatible technology has been developed for bonding between a silicon wafer with electrical structures and a bulk micromachined silicon wafer. A bonding frame structure can be realized with hermetically sealed metal feedtroughs especially suited for capacitive sensors with a small sensing gap and fast RC-time constants. A lift-off technology for structuring the glass using metal as a sacrificial layer has been developed, because the substrates were heated to about 300°C in order to enhance the quality of the glass layer. A simple model for the current flow during the bonding process is given. The numerically calculated current–voltage behaviour is compared with measured data. An electrostatically excitated silicon resonator is realized to demonstrate the applicability of this technology.

Robust and Selftestable Silicon Tuning Fork Gyroscope with Enhanced Resolution

Advanced automobile electronic systems like overroll protection , electronic skidding protection and x-by-wire systems require at least one robust and reliable angular rate sensor. Therefore a silicon micromachined gyroscope based on a tuning fork structure was developed with all resonant frequencies being above 10kHz and the primary and secondary gyroscope oscillation frequency being close to 40kHz. Additionally no other resonant frequencies arc within a bandwidth of 10kHz around the gyroscope modes in order to be insensitive to random vibrations occurring in automotive applications and to withstand high shock impacts .