Automotive MEMS Research Articles

Experimental Evaluation of Vibration Influence on a Resonant MEMS Scanning System for Automotive Lidars

This paper demonstrates a vibration test for a resonant MEMS scanning system in operation to evaluate the vibration immunity for automotive lidar applications. The MEMS mirror has a reinforcement structure on the backside of the mirror, causing vibration coupling by a mismatch between the center of mass and the rotation axis. An analysis of energy variation is proposed, showing direction dependency of vibration coupling. Vibration influences are evaluated by transient vibration response and vibration frequency sweep using a single tone vibration for translational y- and z- axis. The measurement results demonstrate standard deviation (STD) amplitude and frequency errors are up to 1.64 % and 0.26 %, respectively, for 2 grms single tone vibrations on y axis. The simulation results also show a good agreement with both measurements, proving the proposed vibration coupling mechanism of the MEMS mirror. The phased locked loop (PLL) improves the STD amplitude and frequency errors to 0.91 % and 0.15 % for y axis vibration, corresponding to 44.4 % and 43.0 % reduction, respectively, showing the benefit of a controlled MEMS mirror for reliable automotive MEMS lidars.

Can automotive MEMS be reliably used in space applications? An assessment method under sequential bi-parameter testing

Commercial Off-The-Shelf (COTS) automotive inertial measurement units were subjected to severe accumulative stress conditions: thermal shocks (high temperature gradients), temperature cycling (low gradients) and mechanical vibration are combined in an A-then-B sequential testing procedure, with the aim to promote failure acceleration and improve lifetime prediction. The maximum stresses, applied individually, did not cause failure on the selected components. On the other hand, accumulative bi-parameter testing conditions resulted in die attach delamination. Three batches of devices tested with different preconditioning (A-then-B or B-then-A) display different reliability figures. Failure mode and effects analysis (FMEA) is established. A Finite Element Analysis (FEA) is done based on a destructive physical analysis of the devices to confirm the correlation between the stresses applied and the physics of the failure in order to understand the thermomechanical behavior of the devices, linking it to observed failures.

Parametric topology optimization of a MEMS gyroscope for automotive applications

Automotive MEMS gyroscopes are used for various purposes, such as rollover prevention and dynamic stability. Although, employment of gyroscopes for automotive applications is reported, what is not discussed is the gyro topology design and optimization for these applications. This article reports parametric topology size optimization of a MEMS gyroscope proper for automotive applications. The structure optimization of a translational dual-mass Coriolis vibratory gyroscope (CVG) with electrostatically sense/excitation mechanism is presented for automotive applications. Fabrication considerations conform to the X-FAB procedures, and application uncertainty is inherent in the vehicle lateral model. The proposed design approach takes into account the inaccessible levels of application uncertainty to optimization, which provides results that are more reliable, compared with the ideal models. More than thirteen thousand virtual cases are studied, in which the gyroscope performance specifications including scale factor, linearity, etc. are calculated. The double-lane-change (DLC) maneuver based on ISO 3888-1 is performed on the optimal candidates in order to apply the vehicle application constrains. The suggested optimal solution is the one with the least yaw rate error with respect to the target yaw rate instructed by the maneuver, which suits best for the automotive application. The results show that the yaw rate error of DLC maneuver improved from about 40% to about 1.4% using the optimization algorithm, which shows the effectiveness of the proposed method.

Automotive MEMS sensors based on additive technologies

The application of MEMS devices is one of the recent trends in sensor technology. However, traditional silicon MEMS have some intrinsic limitations, when applied to the monitoring of high temperature/high humidity processes. Thin ceramic films of alumina, zirconia or LTCC fixed on rigid frame made of the same ceramic material in combination with ink and aerosol jet printing of functional materials (heaters, temperature, pressure, gas sensitive elements) provides a cheap, flexible, and high-performance alternative for silicon MEMS devices used as gas sensors, gas flowmeters, lambda probes, bolometric matrices for automotive and general application.

(Invited) Deep Silicon Etching - Increasingly Relevant >20 Years on!

In the early 1990’s researchers at the Robert Bosch facility in Stuttgart invented a novel method of etching very deep features into silicon. This led to a patent being granted in 1994. Originally intended as a method of fabricating devices for the then emerging automotive MEMS sector, its use has since diversified to cover virtually all other MEMS markets. Most recently the use of the Bosch Process has expanded into through silicon via (TSV) etching in 3D packaging applications. This paper describes what is possible today using the Bosch process and will consider future applications and uses. The diversity of the approach is illustrated through various examples including cavities etched at high rates, features with aspect ratios of 90:1, profile tilt to ~±0.15°, TSVs for wafer stacking and the increasing demand for more precise control including end-point detection down to 0.05% open area.

(Invited) Deep Silicon Etching Increasingly Relevant >20 Years on!

In the early 1990’s researchers at the Robert Bosch facility in Stuttgart invented a novel method of etching very deep features into silicon. This led to a patent being granted in 1994. Subsequently (and still) referred to as the ‘Bosch’ process it was first licensed to SPTS who shipped the first commercial systems in 1995. Originally intended as a method of fabricating devices for the then emerging automotive MEMS sector, its use has since diversified to cover virtually all other MEMS markets. Most recently the use of the Bosch Process has expanded into through silicon via (TSV) etching in 3D packaging applications. In 2014 in Amsterdam the inventors (Franz Laermer and Andrea Urban) were awarded the IEEE Jun-Ichi Nishizawa Medal for revolutionising MEMS by enabling the proliferation of many of the everyday devices that surround us today (such as the inertial sensors in airbags and various chip-sets in smart phones, gaming consoles and laptop computers). This paper will describe what is possible today using the Bosch process and will consider future applications and uses. The diversity of the approach will be illustrated through various examples including cavities etched at high rates, features with aspect ratios of 90:1, profile tilt to <0.2°, TSVs for wafer stacking and the increasing demand for more precise control including end-point detection below 0.5% open area. The types of devices that require such performance will also be discussed – everything from inertial MEMS, integrated passives, microphones, power semiconductors, microphones, interposers and stacked memory die. The relevance of the Bosch process to newer application areas such as die singulation and BioMEMS will be discussed. The developments in reactor designs necessary in achieving these advancements will also be reviewed. The longevity of the Bosch approach is in part due to the lack of alternative methods able to achieve the same results in Si. A brief comparison with the competing technologies of wet chemical etching, single step plasma etching, cryogenic etching and LASER drilling will be presented. 300mm wafers are in routine use for Bosch etching of TSVs as part of advanced wafer level packaging integration schemes. However 300mm wafers are now also being considered for MEMS to maximise the die per wafer or to allow direct bonding and integration of MEMS functionality with the best available CMOS chip-sets. The latest results for deep silicon etching of 300mm will also be presented.

TRI-AXIAL MEASUREMENT OF GAIT WITH MINIATURE GYROSCOPE SENSORS

Automotive MEMS gyroscopes are used for various purposes, such as rollover prevention and dynamic stability. Although, employment of gyroscopes for automotive applications is reported, what is not discussed is the gyro topology design and optimization for these applications. This article reports parametric topology size optimization of a MEMS gyroscope proper for automotive applications. The structure optimization of a translational dual-mass Coriolis vibratory gyroscope (CVG) with electrostatically sense/excitation mechanism is presented for automotive applications. Fabrication considerations conform to the X-FAB procedures, and application uncertainty is inherent in the vehicle lateral model. The proposed design approach takes into account the inaccessible levels of application uncertainty to optimization, which provides results that are more reliable, compared with the ideal models. More than thirteen thousand virtual cases are studied, in which the gyroscope performance specifications including scale factor, linearity, etc. are calculated. The double-lane-change (DLC) maneuver based on ISO 3888-1 is performed on the optimal candidates in order to apply the vehicle application constrains. The suggested optimal solution is the one with the least yaw rate error with respect to the target yaw rate instructed by the maneuver, which suits best for the automotive application. The results show that the yaw rate error of DLC maneuver improved from about 40% to about 1.4% using the optimization algorithm, which shows the effectiveness of the proposed method.

Charge Transfer to MEMS Pressure Sensors By Glow Discharge Plasmas

Electrical charging resulting in temporary performance degradation of automotive MEMS pressure sensors has been observed. A method of charge transfer from the outside of a statically charged hose, along the inside the hose, through the module port, to a sensor inside the module is proposed. Specifically, the existence of a glow discharge plasma through the hose, is analyzed with respect to temporary performance degradation. The Paschen equation is used to theoretically predict the breakdown voltage in terms of pressure and distance in the rarified, charged environment to which the ports of the pressure sensors are exposed. Experimental results show no glow or performance degradation in the dark discharge regime, over repeated trials. In the glow discharge regime, visible purple glow with accompanying degradation is observed. At the transition point between the dark and glow regimes, at 20 torr and 5000 V for a discharge distance of 3.5 cm in this experiment, repeated trials resulted in a mixture of glow/degradation and nonglow/unaffected cases. Other proposed modes of charge transfer are qualitatively ruled out, while a quantitative correlation between glow and performance degradation is observed. Therefore, the glow discharge plasma is indicated as the most likely charge transfer mechanism