Wissenschaftliche Publikationen "Sensorik + Aktorik"

It is mandatory for manufacturers of reusable medical devices to specify the maximum of allowed sterilization cycles. This work focuses on the fabrication of an autonomous sterilization cycle counter in MEMS technology. Surface microm-achining is applied utilizing vapor HF (vHF) etching and subsequent polymer anti-stiction coating as an efficient tech-nique to remove sacrificial buried oxide layers and to release micro structure without stiction. The vHF etching process has been optimized and reaches etch rates of 900 nm/min for the buried oxide with a uniformity of more than 95 % across a 100 mm wafer. Based on this process a compatible design with perforated structures is implemented. Finally, devices of the sterilization cycle counter are successfully tested by a simulated sterilization cycle temperature test.

 

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Piezoresistive accelerometers are a popular and widely used method of acceleration sensing due to their simplicity in fabrication, packaging and inherent ruggedness. These devices usually have simpler electronics for example compared to capacitive sensors. There are products available without ASICs as well. [1] This work takes an existing high-g piezoresistive accelerometer as a reference sensor and works on optimizing this design. The work delves into different design and optimization techniques to deliver novel high-performance piezoresistive acceleration sensor prototypes. These techniques exploit the device physics and mechanics to point towards the new designs. The sensor is designed and optimized to have higher bandwidth. The adaptation of SOI wafers instead of currently used epitaxial wafers, results in smaller chip size, enabling more chips/wafer and reducing the sensor cost. Extra emphasis has been laid to maintain high sensitivity, for specified doping of the piezoresistors, while still not compromising much on the resonance frequency. Finite element analysis with ANSYS Workbench offers insights into the device performance and helps in the determination of some key sensor parameters for the new designs. It also helps to establish trends and this provides an idea for the successive models. After several iterations and incorporating different optimization techniques, new models are achieved.

 

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In this paper we present a hybrid microsystem for acquisition and counting of sterilisation cycles. The device includes a micromechanical counter mechanism and a thermal actuator based on a shape memory alloy (SMA). The device is designed to count 100 sterilization cycles. The basic functionality is investigated on a hotplate using a thermal temperature profile with a peak temperature of 135 deg C. In this manner, counting of thermal cycles is demonstrated.

 

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This work provides an analytical non-linear model for the capacitive transduction in MEMS transducers with perforated counter-electrodes, especially applicable to capacitive MEMS microphones. Starting from an electrostatic description of a perforated unit cell of the transducer, analytical formulations of the variable capacitance and electrostatic forces are derived, accounting for the deflection profile of a clamped circular plate. A lumped implementation into conventional circuit simulations tools is enabled via behavioral modeling based on hardware description languages, such as Verilog-A. Therefore, the analytical model is approximated via Taylor series expansions, allowing for a stable and non-linear behavioral implementation. The resulting model finally enables both a small- and large-signal analysis of capacitive MEMS microphones, precisely accounting for non-linearities in the capacitive transduction. This allows to simulate the harmonic distortion of the microphone's output signal and to account for electrostatic spring-softening in simulations of its bias voltage dependent sensitivity.

 

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MEMS are minute electro-mechanical systems that are able to sense small changes in the environment and are responsible for a large chunk of the sensor market. MEMS inertial sensors such as gyroscopes and accelerometers have helped in realizing new products across a multitude of fields. One of the next aspects of MEMS Inertial sensors is the Internet of Things [IOT] and Industry 4.0. Hence, the following work depicts a sensor element design for vibration detection in Out Of Plane [OOP] axis (z-axis) proposed for closed loop control considering a system bandwidth of 20 kHz. The current work highlights the concept of an "anti-phase" design type sensor element developed considering either top or bottom electrodes allowing for the possibility of closed loop control. The translational motion of the sensor element along with the larger mass elements provides higher performance and lower noise. The analysis indicates a sensor element with size 1mm*1mm showcasing a specific open loop sensor sensitivity per area of 1.12 nF/g/m 2 with resonance frequency of 10.5 kHz and can be considered as a viable alternative to see-saw design type.

 

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Im Rahmen dieser Arbeit wurde der Einfluss der Montage eines CMOS-integrierten Sensorsystems auf das Sensorverhalten untersucht. Hierzu wurden Sensorchips einerseits mittels eines epoxidbasierten Klebstoffs und andererseits durch reaktives Fügen auf Zugproben aus Edelstahl befestigt, und es wurde der Einfluss des Fügeprozesses auf die Spannungsverteilung im Sensorchip untersucht. An einer Zugprüfeinrichtung wurden für beide Fügevarianten die Sensorkennlinien aufgenommen. Beide Varianten zeigen ein lineares Sensorverhalten, wobei der reaktiv gefügte Sensorchip eine ca. 2,5- fach höhere Empfindlichkeit aufweist. Zur Ermittlung der Dehnungs-Kopplung wurde für beide Fügevarianten die tatsächliche Chipdehnung mithilfe von Dehnmessstreifen ermittelt und in Relation zur Dehnung der Zugprobe gebracht. Der auf diese Weise ermittelte Kopplungsfaktor beträgt beim geklebten Chip etwa 0,18, beim reaktiv gebondeten Chip liegt er mit 0,43 deutlich darüber.

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