Microsystems Technology

MEMS Inertial Sensors

Micro Electro Mechanical Systems (MEMS) combine small device size with low cost in production and high reliability. This results in an increased application in the automotive industry, where MEMS inertial sensors are used for active and passive safety systems as well as for vehicle body control, e.g. electronic stability program (ESP) and navigation systems, even in cheaper models. Also consumer applications like mobile phones, laptops or game consoles urge for compact and low-cost inertial sensors. To enhance functionality and reduce size and cost of the sensor modules the development roadmap leads from one axis sensors to multi axis sensors on one chip and further on to a complete inertial measurement unit (IMU) on one chip. 3-axis accelerometers are already in production with high volume, but the combination of accelerometers with angular rate sensors in one chip is more difficult due to different operating conditions. This puts strong effort on sensor design and fabrication technology. To overcome this challenge ISIT developed together with its industrial partner SensorDynamics the technology platform PSM-X2, which allows the combined fabrication of accelerometers and angular rate sensors on one chip and therefore opens the way to a highly integrated fabrication of IMUs. This new concept is realized now with the combi sensor SD755, which contains, in a first step, one accelerometer and one angular rate sensor. The SD755 is now available on the market and fulfils all requirements for automotive qualification based on AEC-Q100.

Following table summarizes important performance data of the SD755 combi sensor, which key benefits are mechanical robustness, a wide temperature range and high longtime stability.

Parameter Angular rate sensor Acceleration sensor
Measurement range 1
Measurement range 2
± 100 °/s
± 300 °/s
± 2 g
± 5 g
Resolution of Measurement range 1 0,0039 °/s/LSB 207,1 µg/LSB
Resolution of Measurement range 2 0,0156 °/s/LSB 414,2 µg/LSB
Signal to noise (Measurement range 1) < 0,1 °/s @25Hz < 2mg @40Hz
Sensitivity error ± 2 % ± 2,5 %
Linearity error ± 0,2% FS ± 0,2% FS
Offset error @25° incl. aging 0,5 °/s 0,03 g
Cross sensitivity against rotation
Cross sensitivity against acceleration
2%
0,1 °/s/g
-
2%
Recovery time after 50 g shock 5 ms
Shock stability in use 1500 g
Temperature range -40°C to +125°C
Interface SPI