May 24, 2012, MEMS Business Forum, Santa Clara, CA—Frank Melzer from Bosch Sensortec talked about the growing movement of MEMS into consumer products. the abilities to increase levels of integration in silicon are resulting in smaller, lower cost, higher performance devices.
MEMS started over 25 years ago with single-axis motion sensors. Now, markets in mobile communications, security, gaming, and other areas are driving sensor developments. The latest products are a finely tuned collection of hardware and software to detect multiple degrees of freedom.
It is still possible to shrink devices and reduce area. The 6x6mm 3-axis accelerometer is now a 2x2mm 3-axis accelerometer and a 3-axis gyroscope. The designs for the sensor has to change to reduce its size, since the test mass is part of the IC.
The challenges for design are in the market requests for high performance. Accelerometers try for 8-14 bit resolution, gyroscopes need low noise and power consumption, magnetometers need high dynamic range and resolution. Barometric sensors need to resolve one floor change. The pressure sensor will always be in a separate package since the sensor needs to be open to air to be useful.
The latest 9-degrees of freedom devices have challenges in technology, quality, logistics, and software sensor fusion. Data synchronization across the sensors and performance matching are difficult and there are no standards for the separate and collective functions. geomagnetic sensors make the software integration more difficult, since the domain expertise is different from that need for an inertial sensor.
Optimization is difficult unless you can get a single vendor for both the hardware and software. Users need a total solution. The system requirements for an integrated set of sensors; accelerometer, gyroscope, and magnetometer, have to address high dynamic range and low temperature coefficient of operation and drift. The size of the test mass for a gyroscope is the current limiter in overall size.
The technologies and capabilities are capable of significant size reductions, but the practical minima are still a long was away. Sensor detector circuits are capable of detecting an amplitude of femtometers or the spacing of 5 atoms. Capacitance changes in the range of 10-19 to 10-21 are possible but this value represents a fraction of an electron at 5V.
The most likely implementations for sensor fusion is the apps processor, but the processing could be in other areas. Data processing at the sensor allows for different architectures and reduces the volume of data transfers. The functions require software and the integrated package has to have fusion tools to handle the whole subsystem. The industry needs to develop standards for the various types of sensors and software.