The future of MEMS is multifaceted, complex, and subject to change, in response to the prevailing winds of investment by government and commercial entities
Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of micro fabrication.
The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters.
Likewise, the types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. The one main criterion of MEMS is that there are at least some elements having some sort of mechanical functionality whether or not these elements can move.
The term used to define MEMS varies in different parts of the world. In the United States they are predominantly called MEMS, while in some other parts of the world they are called “Microsystems Technology” or “micromachined devices”. While the functional elements of MEMS are miniaturized structures, sensors, actuators, and microelectronics, the most notable (and perhaps most interesting) elements are the microsensors and microactuators. Microsensors and microactuators are appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. In the case of microsensors, the device typically converts a measured mechanical signal into an electrical signal.
What will be the next big thing in MEMS and Sensors?
The future of MEMS is multifaceted, complex, and subject to change, in response to the prevailing winds of investment by government and commercial entities
We do not have a crystal ball, but we do know from history that most of today’s MEMS technologies originated in academic laboratories. We expect more to emerge overtime. This brief coverage highlights important new topics and future prospects. Criteria for note worthiness were commercial relevance, offers a solution to a known or anticipated problem or technology game-changers.
Nearly all the technologies listed here will need many more years of intensive development and probably more than $100M in investment to bring them all the way to the market. Nevertheless, they each hold potential to create new waves of commercial activity in the MEMS industry.
The emerging MEMS and sensor technologies to watch for are:
- Navigation- grade gyroscopes
- Zero quiescent power devices
- GaN resonators
- Graphene FET gas sensors
- Biodegradable Sensors
- Flexible Energy Harvesters
- Paper based devices
Navigation grade gyroscopes.
Several research groups are developing new MEMS gyro architecture which depart from conventional design. NTHU in Taiwan is pursuing mode making in ring-coupled structures, while Georgia tech is focusing on bulk acoustic wave structures to achieve improved bias stability and lower noise. Politecnico di Milano is leveraging the CEA-Leti M& NEMS piezoresistive nano-wire architecture for its ability to reject external vibration and shock. The target application for these next generation gyros will be navigating small vehicles without GPS assistance from minutes to hours.
When GPS is temporarily unavailable, such as indoors, narrow urban streets, or in a tunnel, inertial sensors would provide essential vehicle tracking data until the next GPS fix.
Amazon hopes to land packages on lawns and rooftops via drone, but this feat cannot be accomplished in all condition without navigation grade MEMS inertial sensors.
Zero quiescent power devices
Everyone is excited about the possibilities for the Internet of Things (IoT) but that excitement will fade rapidly if a sensor network will demand continual replacement of the drained batteries. Development of ultra low power electronics will be critical to IoT’s future success. To that end, at least two groups are working on innovative communication electronics which draw no power until some threshold event is detected by a sensor. Both cleverly employ tuned mechanical resonators to create electronic amplification under specifically sought conditions. UC Berkely’s device uses no power while waiting to receive VLF transmissions, and the Chinese Academy of Sciences devices consumes no power until it is triggered by a threshold vibration amplitude. The latter device uses kinetic energy harvested during the vibration event to drive an RF transmitter.
GaN Resonators
After Silicon MEMS, came quartz, silicon carbide, and diamond MEMS. Now Gallium nitride MEMS are coming too. The material’s wide band gap, high piezoelectric coefficients and ability to handle high temperature enable the wafer level integration of high performance RF MEMS resonators with high power and high frequency electronics. Two groups at MIT and University of Michigan, recently presented different approached for achieving optimized GaN resonators. These devices could be used as high GHz resonators for channel select filtering in RF receiver front ends.
Graphene FET gas sensors:
While it is relatively easy to create a gas sensor, far harder is creating a sensor selective to different species. A group at UC Berkely has developed a sensor based on a single Graphene field effect transistor (FET) which does not need elevated temperatures to operate and can discriminate between NH3, NO2 , H2O, CH3OH. This group has validated a novel transduction mechanism in which the shift in FET conductance versus gate voltage indicates the presence of different gases.
Biodegradable Sensors:
Detecting pressure changes in the body is useful for diagnosis and monitoring of many medical conditions. A pressure sensor made of biologically- compatible materials which could harmlessly degrade over time after implantation or swallowing would be enormously useful.
Researchers at Georgia tech and University of Pennsylvania have been developing a pressure sensor having a membrane made from bio degradable polymers with electrodes and inductor coils made of zinc.
The sensor transmits data in a manner similar to RFID, when energized by an external reader. The same group is also working on bio degradable batteries, which use the body’s own fluids as the battery’s electrolyte, and having magnesium and iron electrodes which dissolve harmlessly overtime.
Flexible Energy Harvesters:
The challenge with MEMS scale energy harvesters is that the small mass of the device inherently limits the kinetic energy which can be harvested. However, small energy harvesters arrayed into large format, flexible substrates could potentially generate useful quantities of power. Sogang University is pursuing polymer thread based harvesters which could then be woven into large area textile such as clothing, curtains, flags or sails. Researchers at CEA are focusing on plastic based harvesters which could be screen printed on to large sheets, such as for building or vehicle wrappers.
Paper Devices:
Paper is emerging as a potential substrate for ultra low cost sensors (<$0.01 per sensor). It is a low cost material and can be fabricated on high throughout, large format roll to roll equipment, in uncontrolled environments. Academic groups are developing surprising capabilities on this humble material, focusing primarily on medical diagnostic functions in low resource settings. The Whitesides group at Harvard has been leading the way on paper based electronics. A research group at SUNY Binghamton recently demonstrated a folded paper based battery, using bacteria as the electron source that could generate 0.5V. You read that right, bacteria found in a droplet of dirty water can attach themselves to electrodes and generate electrons as they metabolize.
Looking Forward: A trend away from Silicon?
In recent history, market demands for lower cost (and lower performance) devices eventually pushed some technologies on to cheaper substrates. LED’s migrated from sapphire to silicon, and microfluidics migrated from silicon, to glass, and is now on plastic on paper.
While not all sensors will be able to move to paper due to physical limitations with time, we may start to simpler sensors, where ultra low cost is the key to the market opportunity, migrating to paper. Manufacturing infrastructure for high volume production of paper based electronic devices still needs to be built. However, building this infrastructure could happen quickly under the right market conditions, given that paper handling machinery is already well known.
MEMS based products produced in 2005 had a value of $8 billion, 40% of which was sensors. The balance was for products that included micromachined features, such as ink jet print heads, catheters, and RF IC chips with embedded inductors.
Growth projections follow a hockey stick curve, with the value of products rising to $40 billion in 2015 and $200 billion in 2025! Growth to date has come from a combination of technology displacement, as exemplified by automotive pressure sensors and airbag accelerometers, and new products, such as miniaturized guidance systems for military applications and wireless tire pressure sensors. Much of the growth in MEMS business is expected to come from products that are in early stages of development or yet to be invented.
Some of these devices include disposable chips for performing assays on blood and tissue samples, which are now performed in hospital laboratories, integrated optical switching and processing chips, and various RF communication and remote sensing products. The key to enabling the projected 25 fold growth in MEMS products is development of appropriate technologies for integrating multiple devices with electronics on a single chip
Future scope:
The direction of development of MEMS systems is motivated by both the economic benefit derived from these systems and the new technological capabilities that they enable. For example the operating efficiency of combustion engines, energy conversion equipment, and many manufacturing processes will be improved by more capable MEMS systems. More advanced MEMS systems offer significant potential for technological advances in medical diagnostics, autonomous robotic systems, communications, and computer systems.
