Smarter, cheaper, and yes, smaller microelectromechanical systems (MEMS) sensors and actuators have taken the consumer electronics sector by storm. They’ve infiltrated conventional consumer products across the board, from smart mobile phones, pads, video games, and remote controllers to cameras, audio speakers, and microphones.
MEMS mania within the consumer world is just starting to percolate, though. Spearheaded by accelerometers, magnetometers, gyroscopes, and pressure and temperature sensors, forecasts show MEMS devices finding their way into unimagined applications, paving the way to a vast network called the Internet of Things (IoT). The IoT is a new lexicon coined to describe a universe of trillions of interconnected sensors and actuators that will enable the monitoring and control of just about anything.
Smart phones and tablets will become crucial elements in this all-encompassing interconnected world, enabling an IoT with a vast array of new application possibilities. Add MEMS pressure, humidity, temperature, and flow sensors, as well as concurrent advances in wireless sensor networks and energy-harvesting technologies, to the mix, and the potential number of IoT applications extrapolates to untold numbers.
Wireless-sensor-network supplier Libelium predicts that smart phones and wireless sensor networks will generate more than 50 sensor applications to help drive the IoT. These will span agricultural, medical, infrastructure monitoring, transportation, geophysical, ecological, Smart Grid metering, industrial, and transportation fields, each with its own sub-specialties. Britain-based Juniper Research predicts that by 2016, there will be 4 billion MEMS sensors specifically aimed at augmenting reality location-based services.
Sensors of all types will usher in a new era of personal awareness and control. Armed with location data, they will allow examiners to draw a Google map of a route taken by an individual, calculating the exact time and date right down to the second. As such, products like iPhones and iPads become powerful security/surveillance and forensic tools, potentially giving “big brother” a bird’s-eye view of our every move.
Navigating Navigation Advances
Looming on the horizon is the ability for smart phones to navigate inside buildings, malls, and complex structures. This will couple with present-day capabilities of navigating through city streets and highways inside and outside one’s vehicle.
Building navigation is the culmination of efforts by researchers at the Fraunhofer Institute of Technology, working with Bosch Corp. and others. They’re developing the MST-Sense smart-phone navigation system, which can be embedded directly into a smart phone or plugged into one. It tracks the movements and position of its users in precise detail. The tiny module operates autonomously and doesn’t rely on the phone’s processor, saving battery power.
“While mobile phones have significantly contributed to the commercialization success of MEMS, many other large-volume (and more profitable) opportunities exist or are quickly emerging,” says Roger Grace, president of Roger Grace Associates, a marketing consulting firm specializing in MEMS.
“MEMS devices are uniquely suited for many other applications, especially systems-based solutions. Some of these include wireless communications networks, portable analytical instruments, medical point-of-care diagnostics, toys, appliances, and lest we forget, automotive,” Grace says.
“Smart buildings are particularly promising applications. All the elements exist—many types of sensors including air-flow, temperature, humidity, light, presence, air-quality, etc.,” he adds. “These sensors lend themselves well to low-power, energy-conscious applications. What is needed is the systems-engineering application algorithm development and, of course, fulfilling the customer’s needs.”
Another in that camp is Yang Zhao, founder, president, and CEO of MEMSIC Inc. “MEMS devices are becoming smarter thanks to Internet access, which will spread their functionalities via smart phones to applications previously not possible.”
Zhao cites MEMSIC’s recent three-axis anisotropic magnetoresistance (AMR) magnetometer, the MMC3316xMT, as an example of what lies ahead (Fig. 1). The device features leading-edge performance with 14-bit operation over a wide ±16-gauss range with ±2% full-scale accuracy, 0.5% of full-scale offset, and 0.5% of full-scale repeatability on each axis.
The device’s insensitivity to external magnetic interferences and low-profile LGA package (2.0 by 2.0 by 1.0 mm) suit it for a wide range of applications. The MMC3316xMT comes with MEMSIC’s sensor integration algorithm, which removes the effects of hard and soft iron interferences, as well as motion-sensor integration software.
Another recent beneficiary of the MEMS thermal gas-flow principle is a MEMSIC high-accuracy, residential gas-meter, flow-sensing module that measures 54 by 13.5 by 10 mm. Thanks to on-chip signal-processing circuitry, the monolithic CMOS device becomes a complete sensing system. According to the company, the easy-to-integrate module (with small startup flow) can measure mass gas flow up to 100 standard liters/minute (SLM) with ±1.5% accuracy. It also maintains a turn-down ratio of more than 100:1.
Despite some naysayers warning us that the Internet is overloaded and could crash at any moment, it has a vast capacity for machine-to-machine (M2M) communications. IBM, for example, predicts that there will be 1 trillion Internet nodes by 2015. It’s confident that the availability of the Internet Security Protocol (IPsec) will allow the IoT to accommodate the vast universe of cloud-ready devices. Not surprisingly, IBM and other large firms like HP are well ahead of the curve in terms of being prepared for the IoT.
IBM’s mote sensors, developed to optimize heat and humidity levels produced by huge servers at large data centers, are now finding their way into applications such as the preservation of art elements in museums. The company also uses wireless communications for smart-metering applications as well as cloud-based analytics to optimize vehicle traffic management.
In a similar vein, HP created the Smart Planet-like Central Nervous System for the Earth (CeNSE) model. It makes greater use of cloud-based IoT sensory data for business-oriented applications like geophysical exploration.
Janusz Bryzek, vice president of sensor development at Fairchild Semiconductor, says we’re on the verge of a trillion-MEMS sensor market, a great deal of it targeting the consumer-electronics sector, but also some for medical and military/aerospace applications. “The next generation of the Nintendo Wii game controllers will each contain about 100 MEMS devices to connect games with the real world,” he says.
A MEMS pioneer and entrepreneur, Bryzek founded a number of MEMS startups, the most recent of which is Jyve Inc., which Fairchild Semiconductor acquired about a year ago. Jyve is known to be developing inertial MEMS sensors, probably gyroscopes, for the low-cost consumer electronics market of smart phones and tablets, by using a disruptive technology. Presently, three-axis MEMS gyroscopes implement a comb-drive architecture, but it’s approaching its limits for bringing down costs.
Benedetto Vigna, executive vice president and general manager of STMicroelectronics’ Analog, MEMS and Sensors Group, believes that with MEMS gyroscopes selling at about $1.50 in large quantities, they will spur on greater use of smart phones and tablets. However, depending on the volumes and customer specifications, that price can escalate to $3 to $5. Some experts believe that the price must drop to $1 or less for wider consumer electronics appeal.
STMicroelectronics now offers sensors with 9° of freedom in a smaller form-factor package. The company’s LSM333D combines a three-axis accelerometer, three-axis magnetometer, and three-axis gyroscope in a 3.5- by 6- by 1-mm package (Fig. 2). Designed for high-performance inertial sensing applications, it will abet advanced measurement and location-sensitive apps, location-based services, and indoor navigation. The company says that volume production of this device, expected soon, will offer an even smaller 4- by 4- by-1-mm package with a footprint of 16 mm3.
The LSM333D features a selectable full-scale magnetic range of ±2 to ±12 gauss, a linear full-scale selectable acceleration range of ±2 to ±16 gs, and a selectable full-scale rotational acceleration range of ±250°/s to ±2000°/s. It also includes SPI and I2C serial interfaces, smart power management, an embedded temperature sensor, and an embedded FIFO for free-fall/magnetic-field detection.
In a trend-setting move for the consumer-electronics market, Bosch Sensortec integrated a programmable MEMS tri-axial 12-bit accelerometer and a programmable MEMS tri-axial 16-bit gyroscope in one package. The company claims the 6°-of-freedom BMI055 features the smallest inertial management unit (IMU) footprint, being housed in a 3.0- by 4.5- by 0.95-mm land-grid array (LGA) package (Fig. 3). It’s designed for smart phones and tablets, as well as gaming products.
The IMU’s accelerometer features typical noise density of 150 µg/√Hz, while the gyroscope measures 0.014°/s/√Hz. The accelerometer has an acceleration range of ±2 g to ±16 g and two interrupt engines, and it’s compatible with Bosch Sensortec’s 9°-of-freedom BSX2.0 FusionLib software platform. The gyroscope’s range extends from ±125°/s to ±2000°/s. It includes FIFO buffers and operates from common voltage supplies. Zero-g offset is typically 70 mg. I2C and SPI digital interfaces are also available. Operating at full-speed data rates, both the accelerometer and gyroscope dissipate a mere 200 µA and 5 mA, respectively.
According to Leopold Beer, Bosch Sensortech’s global marketing manager, “Our expertise in an all in-house MEMS technology capability, software algorithm development, and sensor fusion allow us to easily tailor an IMU platform for a specific application. This allows designers to benefit from a one-stop solution for 6°-of-freedom applications, in which the accelerometer, gyroscope, and software are all handled under one roof.”
Interest in magnetic MEMS technology continues to grow, as evidenced by a 3-million krona grant Silex Microsystems Inc. received from the Swedish Governmental Agency for Innovative Systems (VINNOVA). Funding will support the development of cutting-edge ferroelectric materials for next-generation smart phones. Silex is the world’s largest pure-play MEMS foundry.
“Magnetic MEMS is a key material for future MEMS products because it enables multi-axis sensor integration,” says Throbjorn Eberfors, Silex’s chief technologist. “Smart-phone applications already include e-compass integration, and multi-axis sensors are combining magnetic sensing with gyroscope functions to enable multiple degrees of freedom sensors to get to the market.”
Silex has developed a Met-Via through-silicon via (TSV) process that allows the use of high-value and high-Q inductors.
At France’s CEA-Leti, researchers are crafting a nine-axis MEMS sensor (a three-axis accelerometer, three-axis magnetometer, and three-axis gyroscope) on a 5-mm2piece of silicon that won’t compromise performance. Lower performance comes as a result of the need for a smaller mass, creating less capacitance.
The key to CEA-Leti’s approach is the combining of MEMS and nanoelectromechanical systems (NEMS) technologies. Combining the two technologies provides the benefit of high inertial sensitivity (an attribute of MEMS) and high force sensitivity (an attribute of NEMS nano-gauges used in this project).
A thin MEMS layer provides inertial mass that’s suspended by one of its extremities via a hinge anchored to the substrate. Attached to this is a suspended silicon nanowire that acts as piezoelectric transducer. This strain gauge features a 250- by 250-nm cross-section. The motion of the mass creates mechanical strain, resulting in a measurable resistance change in the nanowire’s resistance.
RF MEMS
RF MEMS devices have not seen wide-scale adoption in smart phones or tablets in large volumes. But that’s changing.
Starting last September, WiSpry began incorporating RF MEMS technology in Samsung smart phones in larger volumes. WiSpry is focused on producing dynamically programmable RF devices using integrated RF CMOS and RF MEMS (Fig. 4). Its solution, implemented as an application-specific standard product, provides multi-band capability across the Smith Chart with the potential of up to 3-dB improvements.
Such circuitry will be integrated with a partner that makes smart mobile phones. The tunable matching-impedance circuit dynamically rematches the power amplifier’s output to the antenna, under software control, while the phone is in use.
“Our roadmap leads us to having our own handset module,” says Jeff Hilbert, WiSpry’s founder and president. “Tunable RF MEMS are the last missing piece in software-defined radio. It improves connectivity, cost, performance, size, weight, and component count.”
Hilbert says that a 3-dB improvement in smart-phone transmission and reception can translate into huge savings for both users and OEMs. He notes that according to estimations, even a 1-dB improvement can drive a requirement for 14% more cell-phone sites to provide the same level of coverage, creating hundreds of millions of dollars of capital expenditures. Consumers benefit through higher data rates, fewer dropped calls, longer battery life, and potentially thinner and lighter handsets.
The emphasis on smart-phone thinness is very challenging for incorporating an RF MEMS front end, though. “Having screens take up the entire front end of the phone is nice for users, but it is a nightmare for designers,” says Hilbert. “Bearing in mind that touchscreens have metal plates behind them brings up the challenge of ‘Where do you put the antenna?’”
System-Level Emphasis
Design of MEMS consumer electronics occurs at the “system” level, tackling software, testing, and packaging issues to ensure that such products are more suitable and cost-effective for their markets. Some experts dub this system-level description as “sensor fusion.” MEMSIC’s Zhao prefers that term when describing sensors and actuators that need to meet future and demanding network integration, reliability, security, and standardization requirements that will make them more useful for the IoT.
Many MEMS experts agree that software will be the key to consumer electronics advances and ultimately the product differentiator. They feel that acceleration of MEMS R&D efforts will be aided by developing better software design tools and adopting uniform design processes.
Speaking at the SensorCon 2012 meeting in March in Santa Clara, Calif., Sensor Platforms CTO Kevin Shaw called Apple’s voice-recognition Siri software an example of this trend. He believes it represents a high-level integrated sensor system that automatically activates the iPhone.
The next movement in smart phones and tablets is exemplified with the Freespace MotionEngine for Mobile from Hillcrest Labs. This embedded software solution manages and enhances the combined performance of motion sensors commonly found in smart phones and tablets, namely accelerometers, magnetometers, and gyroscopes (Fig. 5). It enables today’s motion-based applications and provides the foundation for next-generation user experiences.
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