NanoEMS - Page 3.
Full integration - the single-chip IMU motion sensor
With all four-motion sensors capable of being manufactured in the standard CMOS flow, NanoEMS uniquely enables them to be placed on the same CMOS chip.
Indeed together with the sensors, the electronics can be consolidated, optimized, and deployed on the same chip: namely signal conditioning, digital conversion and ‘intelligent’ digital signal processing.
This prospect of a single-chip motion sensor delivers a host of benefits:
- size: 10-axis motion sensor in the same tiny form factor as today’s discrete sensors
- cost: all standard processes - overall manufacturing costs can be reduced by at least two thirds
- performance/features: co-design of electronics and MEMS enables performance optimization, reduced power and smart new detection features
From single-chip to smart to super-smart
The CMOS integration and simple packaging capabilities enabled by NanoEMS technology truly transform the roadmap for motion sensing devices, shifting the focus from today’s discrete single and dual-function sensors implemented as multi-chip modules, to:
- single-chip, multi-function, motion sensors
- single-chip, 9 or 10-axis NanoIMUs
- smart, single-chip nanoIMUs with on-chip sensor fusion intelligence
- and onwards to ‘super-smart’ reconfigurable sensors.
Fusion intelligence in its simplest form takes the individual data streams provided by the 2, 3 or 4 types of motion sensors, and processes them into simple, standard motion vectors that can be directly used by the application without preprocessing.
As well as combining the datastreams, internal corrections can be made to compensate the inherent weaknesses of each sensor: for instance, compass readings can compensate the gyroscope’s inherent drift; gyro and accelerometer can be used to validate the compass reading against magnetic interference, and the accelerometer provides tilt-correction for the compass: accurate headings otherwise require the compass to be held flat whereas phones are usually tilted towards the user.
With NanoEMS, the processing electronics required to implement the fusion intelligence (the ‘fusion ASIC’) can be co-designed and co-integrated with the sensor cells to create the smallest, most flexible smart sensor solution with lowest manufacturing cost. Clever codesign techniques allow the electronics to mitigate the effects of both temperature and time related changes in the MEMS structures, defined by the mechanical properties of the interconnect metal used to build them. This leads to the very beneficial side effect of autocalibration, significantly reducing and even eliminating the need to factory-calibrate each axis of each sensor: a significant fab-time cost adder for traditional approaches.
Even further flexibility and performance optimization is offered by the concept of super-smart reconfigurable sensors, made possible by the NanoEMS integration and generic sensor cell capabilities.
Beyond the realization of single-chip sensors, single-chip IMUs and single-chip intelligent IMUs, NanoEMS technology today enables the visionary concept of reconfigurable sensors
, the benefits being:
- optimum performance (accuracy and bandwidth) at the lowest power consumption
- improved reliability
- lowest cost
The reconfigurable sensor concept leverages the unique properties of NanoEMS technology:
- smaller NanoEMS sensor devices: at 100-300µm, sensor cells are typically 5-10 times smaller on a side than traditional MEMS equivalents;
- Monolithic integration of MEMS sensors with electronics;
- Dynamically scaleable performance: the MEMS structures used, and the co-design of MEMS with electronics allows dynamic adjustment of performance parameters to minimize power
MEMS for free: the next generation of NanoEMS sensors will use fewer metal layers to implement the mechanical structures, so MEMS may be deployed above the electronics, so occupying no incremental real-estate.
Small MEMS devices, coupled with deploying the MEMS above the electronics allow placing many MEMS cells on the chip, introducing the idea of redundancy.
Firstly, redundancy improves yield (and hence, cost) and long-term reliability: any defective MEMS cells may be dynamically switched out, with another, on-chip MEMS deployed in its place automatically.
Secondly, redundancy may be used to realize reconfigurability. Imagine a fusion ASIC with sufficient intelligence to control an array of NanoEMS sensor cells deployed above it. Depending on the type of motion currently experienced or expected by the application, the ‘fusion ASIC’ may choose to deploy one or any number of these sensors, dynamically switching in or switching out the sensor cells as required, thus providing the application with the optimum desired motion-tracking performance at minimum power at each instant in time. In this sense, there is no need to drive a sensor at ‘rated power’ at all times to cover the few situations where maximum sensitivity or range are required. The performance and hence the power is dynamically tuned. In this scenario the following strategies are possible:
Any combination of accelerometer, compass, gyro or pressure sensor may be activated dynamically as needed, the others powered down to save current drain 1, 2 or 3 axes of each of the motion sensors may be deployed dynamically as required by the application deploying 2 or more similar axes of one type of sensor allows signal averaging, which effectively reduces noise and improves accuracy performance (bandwidth, resolution or accuracy) may be dynamically adjusted to need by selecting different MEMS types and changing the active current in the MEMS additional compass MEMS may be deployed to track ferrous materials and other magnetic sources (like loudspeakers) in the environment, which would otherwise corrupt the heading reading. Similarly a compass device can be activated from time to time to compensate the long-term drift of a gyroscope.
So ‘super-smart’ reconfigurability is achieved by deploying a ‘fusion ASIC’ and an array of tiny NanoEMS motion sensor cells on the same chip. According to the instantaneous sensing requirements of the application, the ASIC selects which sensor cells are to be used and configures their performance using the strategies described above: type of motion detection, range, resolution, tracking accuracy, noise, and current drain. The size, cost, scalability, flexibility, reliability and miserly current-drain promised by reconfigurability will result in a wealth of applications from exciting, new, motion-enabled, consumer applications including motion-enabled accessories, toys, games and sports/health equipment to low-energy sensor nodes in advanced remote sensor networks.
NanoEMS concept has already demonstrated the lowest-cost single-chip 3D electronic compass device, but offers considerably more by virtue of its unique abilities to shrink the size of the mechanical elements of motion sensors, realize all motion sensors in standard CMOS using generic motion cells and integrate combinations of motion sensors with control and intelligence all on the same chip.
NanoEMS unlocks the barriers preventing integration of different sensor MEMS with the electronics, enabling an exciting motion sensor roadmap from lowest-cost single-chip discrete sensors, to multi-sensor nanoIMUs offering up to 10 axes of motion sensing in the same tiny form factor as today’s discrete sensors, to smart nanoIMUs with integrated sensor fusion intelligence, and ultimately to super-smart reconfigurable sensor modules.
About the Author
Josep Montanyà i Silvestre is the CTO of Baolab. Josep received an M.S. degree in telecommunication engineering from UPC (Barcelona) in 1996. He has 13 years of experience in the electronics and software industries and 6 years in the MEMS field. His work on his Ph.D thesis for a novel design for an RF MEMS was the inspiration for the founding of Baolab in 2003. He continues to pioneer the development of MEMS with his work as CTO at Baolab driving the NanoEMS technology.