Electronic Design

System-Level Challenges Await MEMS Technology

Microelectromechanical-systems (MEMS) technology is poised to have a greater impact on individuals of all ages, industries of all kinds, and our overall society. It is moving from a device-level technology to a system-level plateau that requires novel approaches both inside and outside the device.

Successes in these two areas will enable new platforms for intelligent sensing and context awareness, providing significant benefits in the consumer electronics, biomedical, industrial, environmental, communications, security, and transportation markets, as well as in infrastructure monitoring and financial applications.

MEMS device manufacturers must deal with a departure from the traditional business model of MEMS IC makers making devices for OEMs that package them into end products. They must focus on what the customer precisely needs, in what environment and how the end product is used, and how to make it more user-friendly to operate. And for those markets where low cost is the norm like consumer electronics, greater integration levels (i.e., merging CMOS and MEMS processes cost-effectively) is the name of the game.

These sentiments were borne out by presentations at two recent major MEMS conferences this year—the MEMS Technology Summit and the MEMS Executive Congress.

The MEMS Technology Summit brought together, as presenters, the “who’s who” of the MEMS community. It also served the dual purpose of reviewing the progress of MEMS over the last 25 years and providing a look into the future. Further, it commemorated the founding of MEMS industry pioneer Nova Sensor Inc. 25 years ago. Members of the founding team organized the event. The MEMS Industry Group (MIG) sponsored the MEMS Executive Congress.

“Thinking outside the chip involves the essence of system engineering. The chip is truly the enabler of the system. However, it requires the support of much other functionality, like thermal management and interconnect strategies, to create a solution optimally suited to the customer’s application,” says Roger Grace, president of Roger Grace Associates.

“The other main functionalities of this MEMS-based solution include the MEMS-to-system interface (frequently an ASIC with a microcontroller core with embedded software/algorithms), a power supply, and a networking chip, all robustly and cost-effectively packaged. The underlying principles (Fig. 1) to the creation of this approach are systems engineering, reliability analysis, design for manufacturing and test, and co-design,” Grace adds (see “related 3D IC packaging article”).

MEMS IC manufacturers are taking notice. For example, Freescale Semiconductor has unveiled a new era of sensing with the Xtrinsic portfolio. This brand of sensors is designed with the judicious combination of intelligent integration, logic, and customizable software to deliver smarter, more differentiated applications.

MEMS and non-MEMS semiconductor IC manufacturers are leveraging their capabilities and products into what they see as huge new market opportunities. Vida Ildereme, vice president and director of Intel’s Labs, says that Intel is looking at smart-sensing opportunities in embedded applications by developing embedded silicon-on-a-chip (SoC) ICs. The company intends to build on its leadership in microprocessors to pioneer new capabilities and strategic directions for embedded applications.

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“MEMS and other sensing technologies are becoming increasingly important to consumer electronics, smart-grid and medical market products,” Ildereme says. “Intelligent sensing and context-aware services are presenting huge opportunities in embedded markets with billions of wirelessly connected devices.”

Even the academic community, where nearly all MEMS technologies originated, is looking at lucrative market opportunities. According to Kensall Wise, a professor at the University of Michigan and formerly the director of the university’s Engineering Research Center for Wireless Integrated Micro Systems (WIMS), such wireless devices are driving the development of automotive and autonomous biomedical systems that are designed for “measuring the unmeasurable” areas.

A Vast Consumer Market
The consumer electronics market has been consuming multi-axis MEMS accelerometers and gyroscopes in record numbers over the last couple of years, for use in smart mobile phones, digital and still video cameras, notebook and laptop computers, electronic tablets, TV remote controls, video games and consoles, toys, personal navigation devices, and GPS units. Accelerometers and gyroscopes have been adding more functionalities to the chip while keeping sizes and costs down—two necessary requirements for the consumer electronics market (see “MEMS Inertial Sensors Push Performance Limits,” April 17, 2010, p. 28).

Newcomers like VTI Technologies, Sony, and Panasonic are joining established MEMS gyroscope manufacturers like Invensense, STMicroelemectonics, and Epson Toyocom. Bosch Sensortec and Kionix are also expected to enter this market.

Invensense has achieved a breakthrough in integrated MEMS gyroscopes with its MPU-6000, which features a digital motion processor as a hardware accelerator engine, as well as a three-axis gyroscope and accelerometer on a 4- by 4- by 0.9-mm die, resulting in a nine-axis sensor fusion.

Kionix, recently acquired by Rohm Co. Ltd. and the number three company by volume in MEMS inertial sensors for consumer applications, is leveraging its expertise in user-friendly accelerometers for the consumer market with the introduction of two new digital 5- by 5- by 0.9-mm gyroscopes, the dual-axis KGY-12 and the tri-axis KGY13 package in lead-grid arrays (Fig. 2). They’re aimed at specific applications with built-in algorithms for user-programmable, directional tap, directional shake, and free-fall activity monitoring tasks.

“Our biggest engineering head count is in applications engineering, which for us is developing the application for the end customer,” explains Greg Calvin, Kionix’s CEO. “Our customers want us to give them the end solution they are looking for—a register that tells them if the device moves, if it is in the portrait or landscape mode. They don’t want to bother with or aren’t capable of processing the raw data.”

Most MEMS gyroscopes work by using unbalanced open-loop vibrating masses like forks and combs. Silicon Sensing Systems Ltd., on the other hand, uses a 3-mm ring that resonates at 22 kHz in a closed-loop mode. The ring can be seen as an infinite number of tuning forks in a balanced, vibrating circular structure. The company says this approach leads to lower-cost, lower-power-dissipation, and lower-weight MEMS gyroscopes. Meanwhile, Qualtre is using bulk acoustic-wave (BAW) technology disks for its gyroscope, which it claims is less expensive to manufacture and has lower power dissipation than other gyroscopes.

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MEMS inertial management units (IMUs) comprising highly integrated MEMS accelerometers and gyroscopes have emerged as an offshoot of MEMS gyroscopes. These devices have been used for decades for navigation, flight control, and stabilization functions. Now higher integration levels are bringing down prices, enabling IMUs to be used in emerging healthcare and industrial applications.

New Horizons
Hewlett-Packard strategist Rich Duncombe recently unveiled his company’s plans to provide sensing solutions to those industries and entities that need them and sell these solutions as a service. This strategy would be a radical departure from the traditional business model of MEMS IC makers making devices for OEMs that package them into end products.

Although HP is a major manufacturer of inkjet print heads that use MEMS technology, the company plans to leverage its recent development of a low-power, low-noise, and high-resolution MEMS accelerometer sensor platform, building on it with customers who need this type of data.

“We’ve already announced a collaborative agreement with Shell Oil Co. to develop a wireless sensing system that acquires extremely high-resolution seismic data on land, in areas very difficult for Shell to do while exploring for oil wells,” Duncombe says.

“We’ll be providing this ‘system’ level solution to anyone that needs it, and we see plenty of market opportunities to do this,” he adds, noting that traffic system, infrastructure, and energy monitoring are tremendous opportunities. “Even the financial sector can use this type of service for biometrics and verification.”

Environmental and industrial applications may yet prove to be two of the largest potential markets for MEMS devices to fit into. Combined with autonomous wireless networks, MEMS sensors will usher in a new era of vibration and health monitoring of infrastructures and other structures like roadways, bridges, tunnels, dams, buildings, and airplanes.

Analog Devices recently introduced the first MEMS three-axis vibration analysis system to help industrial designers improve system performance and maintenance costs. The ADIS16227 iSensor vibration monitor uses a MEMS accelerometer and has an embedded programmable processor, all in a compact 15-mm3 package that enables directional sensing and spectral analysis to identify and classify individual sources of vibration.

The Optical Scene
MEMS technology is also finding use in displays and optical projection. The Mirasol display from Qualcomm MEMS Technologies uses an interferometric modulation technique where a simple vacuum-deposited thin-film structure is laid on a glass substrate. It will be used in an e-book device that will be available early this year, providing an XGA format at 15 frames/s (Fig. 3).

“This technology requires no backlighting and thus has low power consumption compared to other e-books and e-readers on the market,” explains Clarence Chui, senior vice president of engineering at Qualcomm. “It is competitive with products like the Kindle e-book but will feature much faster operation.”

One of the shining examples of successful MEMS optical implementation is the digital light projection (DLP) technology from Texas Instruments. DLP, which uses scanning MEMS mirrors, is the main projection component behind 2D and 3D digital cinema, projection TVs, conference-room projectors, and pico projectors.

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Microvision’s PicoP display’s engine can be found in a number of telecommunications, automotive, consumer electronics, and avionics applications. Its key component, a bi-directional MEMS scanning mirror, is connected to small flexures that allow it to oscillate vertically and horizontally to capture or reproduce an image pixel by pixel. The engine uses red, blue, and frequency doubled green laser diodes that together with the mirror create a full-color, brilliant, and uniform display over the entire field of view.

Samsung also is in the embedded MEMS pico projection business. Its SPH-W9600 as well as its GT-i8520 Galaxy beam projectors are used in mobile phones.

Serving The Environment
One development out of the University of Michigan’s Center for Wireless Integrated MicroSystems (WIMS) is a wristwatch-size gas chromatograph for environmental monitoring. The university would like to commercialize the device, which fits into the size of an iPod Shuffle (Fig. 4).

Aimed at environmental monitoring applications, it can detect some 30 to 50 organic-vapor pollutants per analysis at levels under 1 part per billion per analyte with analysis times ranging from a few seconds to 1 minute. The chromatograph is also useful for healthcare and defense applications.

Block Engineering is working on a miniature microspectrometer chemical gas sensor for low-cost military, commercial, and industrial applications. The ChemPen is not much larger than a fountain pen, and it’s projected to cost under $1000.

The device uses a sophisticated MEMS Fourier transform infrared (FTIR) technology. It will be fabricated on the MEMS Summit-V process developed at Sandia National Laboratories. Its software can be programmed to detect chemical-warfare agents as well as toxic industrial chemicals.

Hamamatsu has developed a miniaturized MEMS spectrometer head that weighs just 9 g for a wide range of visible-light applications between the wavelengths of 340 to 750 nm, at a spatial resolution of 12 nm. The C10988A measures 27.6 by 13 by 16.8 mm and is designed to be used in place of a standard mini-spectrometer where size and power dissipation are a problem. It combines Hamamatsu’s MEMS and image sensor technologies.

Also, the C10988A uses an aberration-corrected concave grating with a very short focal length and a blazed grating profile for high diffraction efficiency. Directly opposite the grating is a dedicated CMOS image sensor with an on-chip 750- by 750-µm MEMS slit. The distance between the sensor and slit is 1 mm, and the distance between the sensor and grating is 8.5 mm.

Improved Healthcare
“MEMS technology is moving from commercialization to personalization beyond present consumer electronics applications,” says Benedetto Vegna, vice president and general manager of STMicroelectronics’ sensors and high-performance analog vision business.

Such personalization will bring about dramatic developments in body area networks that monitor a person’s vital parameters, sensors that monitor patients’ whereabouts, and devices that allow people to communicate with their healthcare providers.

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We’re already witnessing the wide-scale availability of portable home healthcare devices for vital sign monitoring, as well as improved human implants for improved diagnostics and treatments, drug delivery systems, and fluid and cell handling, and MEMS devices are leading the way. MEMS sensors are being used for patient fall detection, motion and mobility tracking, implantable drug delivery and neural-stimulus systems, respiratory monitoring, and glucose and blood pressure monitoring.

MEMS pioneer Janusz Bryzek sees smart mobile phones as key instruments in enabling potential MEMS-based medical tools. He believes that applications such as pulmonary monitoring and analysis will play key roles in ultrasound imaging.

The University of Michigan has been a leader in the development of implantable MEMS devices for biomedical applications. These devices include probes for auditory and neural detection and stimulation applications, as well as MEMS pressure sensors for cardiac intra-atrial and vision intra-ocular applications. Many of the developments have culminated in products that are already on the market and are being used by clinics and other medical facilities worldwide.

On the horizon lie implantable pancreases, ocular devices, aural components, and cardiovascular devices. One FDA-approved implantable wireless RF-addressed pressure sensor (Fig. 5) from CaridoMEMS, an offshoot of the Georgia Institute of Technology, can be used to treat aneurisms, a leading cause of heart failures.

Known as the Champion, this tiny passive LC resonator transducer does not require a battery and is powered by external inductive coupling. Pressure changes deflect the transducer’s diaphragm and change the LC circuit’s resonant frequency.

The pressure sensor and its wireless antenna are inserted near the heart with a catheter, a procedure that takes only a few minutes. The device monitors blood pressure and sends results to a wireless scanner. When abnormal blood pressure readings taken over several days remain outside a desired range, doctors can be notified by phone for further action.

Mark Allen, a professor at Georgia Tech and CardioMEMS cofounder, reported promising results with the Champion. “Patients monitored with the device had 38% fewer hospitalizations than the current gold standard of care,” he says.

MEMS technology is also becoming very helpful in ophthalmic implants, as can be seen from a 25-year retinal prosthesis program at the Doheny Eye Institute at the University of Southern California, for the treatment of diseases such as retinitis pigmentosa and age-related macular degeneration. Professor Mark S. Humayun has reported encouraging results from a clinical trial funded by Second Sight Medical Products.

The Second Sight second-generation Argus II stimulates the retina electrically to induce visual perception. The implant, which works with a retinal pump, consists of an array of 60 electrodes that are attached to the retina (Fig. 6). The electrodes conduct information acquired from an external camera to the retina to provide a rudimentary form of sight to implanted subjects.

“MEMS technology has allowed us to build a novel mini ophthalmic pump that is miniature in size, is biocompatible, can be refilled while it is implanted, and can be programmed for drug delivery,” says Humayun.

These applications are just the beginning. MEMS technology will usher in a new era of enlightenment for everyone. As evidenced by the “enabling” theme of the last MIG MEMS Executive Congress, MEMS devices have plummeted in price and are becoming commodity items. They will spread everywhere to myriad market sectors, benefiting applications limited only by the designer’s imagination.

Learn more about system-level integration by attending the upcoming Smart Systems Integration 2011 Conference and Exhibition, March 22-23, Dresden, Germany, sponsored by the European Technology Platform on Smart Systems integration (EPoSS). Go to www.messago.de/en/SSI/main.htm.

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