Electronic Design

MEMS The Word... In Consumer Electronics

A maturing technology with a multitude of low-cost functions pushes MEMS into a growing number of electronic products.

Demand for devices that can sense motion, orientation, and location is surging, and it runs the gamut from the hottest video games to critical medical technology. With accelerometers and gyroscopes based on microelectromechanical systems (MEMS) rapidly maturing, that demand is being met.

Many of the latest consumer products include one or more MEMS IC functions that measure and control factors like movement, position, force, and even temperature. As a result, MEMS ICs not only play a key role in accelerometers and gyroscopes, but also pressure sensors, microphones, timing devices, filters, switches, microdisplays, infrared temperature sensors, and micromotors.

“MEMS are now becoming quite popular in numerous consumer applications. As a result of the rapidly decreasing costs of MEMS components over the past few years, products that could have used MEMS functionality in the past are now rapidly adopting MEMS,” says Roger Grace, marketing consultant and president of Roger Grace Associates.

“This increases the user’s ease of operation and provides enhanced functionality, which results in creating the necessary differentiation for their products in a very competitive and quick-changing market,” says Grace.

“If you go back about five years, there were no market drivers for MEMS ICs in consumer electronics products. Today, consumer electronics MEMS IC makers are competing against each other for feature differentiation, and this is fueling the need for MEMS ICs, such as the Wii and iPhone, which in turn are driving the volumes and reducing unit prices for MEMS,” says Steven Nasiri, CEO and founder of Invensense.

“To meet these new market needs, all new-generation MEMS products with disruptive solutions are required,” Nasiri explains. “Also, there is a growing need for MEMS foundry services to support a host of new venture-backed fabless MEMS companies.”

Large-volume unit prices for MEMS ICs used in consumer electronics products hover in the $1.00 to $1.50 level. Key drivers include motion sensors, such as accelerometers and gyroscopes, and microphones. For instance, three-axis accelerometers used in the Nintendo Wii video game system and the Apple iPhone are reportedly priced at the $1 level, if not lower. The accelerometers come from STMicroelectronics and Analog Devices.

MEMS-based products with location and motion awareness give users greater interaction with their surroundings, extending their reach beyond that provided by PCs and Web-enabled handsets. Personal navigation devices (PNDs), free-space pointers, indoor navigation, and vibration cancellation for hard-disk drives are just some of the products that take advantage of this technology.

For example, Analog Devices’ dualaxis ADXL 320 iMEMS accelerometers and SA601 SigmaDSP system-on-a-chip (SoC) audio processor form the core of the Hot Hand motion controller for guitar motion effects from Source Audio LLC. ADXL 330 iMEMS three-axis accelerometers also are in the Motion Enabled Prototype Phone from Keynetic for single-hand menu navigation, two-handed gaming, automatic screen rotation, and more. In Garmin’s Forerunner 50 sport watch, you’ll find the ADXL dual-axis iMEMS accelerometers for running, cycling, and motion fitness activities.

The popular Guitar Hero video game uses Freescale Semiconductor’s three-axis motion-sensing MMA7360L accelerometers (Fig. 1). The MMA7361L/68L/41L/31L are designed for a wide range of consumer applications.

Sensor Platforms is another company targeting the MEMS market. “We’re not just addressing sensor interface issues, but also sensor applications. We will combine our expertise in sensor control algorithms, advanced heuristics, and precision analog/mixed-signal CMOS designs with ‘commodity’ sensors on the market,” says Bill Eichen, CEO of Sensor Platforms.

Sales of MEMS accelerometers and gyroscopes have been rapidly increasing over the last couple of years, particularly accelerometers. This rate is expected to gather more steam over the next few years, forming the largest share of the inertial sensing market, according to several projections.

MEMS accelerometer ICs now offer lower cost, higher sensitivity, better temperature offsetting, faster response times, lower power consumption, and smaller packages. The LIS331 family of low-power three-axis MEMS “nano” linear accelerometers from STMicroelectronics targets low-g applications and can withstand up to 10,000 g of shock, all in a 3- by 3- by 0.9-mm plastic package (Fig. 2).

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These ICs also now feature more intelligence. For example, users can program the threshold levels of many MEMS accelerometers to detect taps, shocks, clicks, and pulses to enable devices like pedometers. For instance, STMicroelectronics offers this kind of functionality in its FC30 smart 3D orientation and clickdetection standalone sensor.

According to Freescale Semiconductor, its three-axis accelerometers are 77% smaller than previous-generation units. The company additionally says that its MMA7455L family, housed in 3- by 5- by 1-mm plastic land-gridarray packages (LGAs), represents the thinnest devices available. The devices’ digital output eliminates the need for an analog-to-digital converter (ADC).

“We’ve been in the MEMS gaming business for quite some time and as a result have learned a lot on how to address this market,” says Michelle Kelsey, Freescale’s marketing manager for inertial sensors. She points to three important steps that MEMS sensor manufacturers must master to succeed: understanding the sensing concept for gaming, adding sensing capabilities to the user’s body, and allowing this capability to extend beyond the user and the game via wireless technology.

Using mass air thermal-convection sensing, Memsic developed a three-axis accelerometer that withstands 50,000 g of shock for use in cell phones. Measuring Z-axis acceleration with thermal convection is difficult, but Memsic uses a pseudo-differential approach where a signal proportional to the ambient temperature is subtracted from the sensor’s common-mode signal. However, this method is inherently less sensitive than a true differential approach, and it can be more susceptible to drift errors.

“This device, which is a single-chip upgrade of our two-chip (in one package) product, withstands five times the levels of shock that other accelerometers on the market feature,” says Steve Profit, Memsic’s director of product marketing. Memsic’s dual-axis magnetic MEMS sensor, the MMC202xMV, targets cell-phone navigation uses. A triple-axis version is expected soon.

Kionix has also entered into the three-axis consumer electronics fray with accelerometers and inclinometers for mobile phones, PNDs, PDAs, game controllers, and cameras. Featuring a form factor of 3 by 3 by 0.9 mm, its KXSD9 provides a high degree of flexibility and consumes 220 µA (50 µA in its low-power mode) at 1.8 V. The KXRB5 measures 3 by 5 by 0.9 mm and offers 75-µg/√Hz noise sensitivity.

Beyond accelerometers lie MEMS gyroscopes. According to Invensense, its IDG-1100 dual-axis gyros are the smallest around, housed in tiny 4- by 5- by 1.2-mm packages. Each chip integrates both the MEMS resonating structures and compensating CMOS electronics at the silicon-wafer level.

“Our dual-axis motion-sensing gyroscopes can be found in many common consumer products, such as digital still and video cameras with image-stabilization features, PNDs, pointing devices, video games, TV and multimedia remote controls, and others,” says CEO Steven Nasiri.

STMicroelectronics’ LLISY300AQL is a 7- by 7- by 1.5-mm, surface-mount, single-axis, yaw gyroscope for angular-rate sensing up to 300°/s (full scale). Available in a 28-lead LGA, it operates from 2.7 to 3.6 V and produces an analog output. It also reduces the power in applications like game controllers, intuitive pointers, personal or vehicle navigation, and image stabilization.

Bosch-Sensortec is developing a multimedia reference design that will allow OEMs to craft more accurate and more sensitive navigation, using the company’s next-generation MEMS ICs. It’s working with Swiss navigational device maker Numerix SA to combine a Bosch barometric pressure sensor with Numerix’s GPS chip set.

Mobile phones will be major drivers for low-cost MEMS ICs. Phillipe Kahn, chairman of Fullpower Technologies Inc. and inventor of the camera phone, predicts there will be 10 billion MEMS chips in mobile phones by 2010. “Motion detection with MEMS accelerometers will soon enable all kinds of functions, such as shaking your cell phone to pick up a call. No buttons, no fingers. Just simple, natural gestures,” he says.

Freescale Semiconductor’s MMA 73xxL family of three-axis MEMS accelerometers is a good example of how these devices are being tailored to meet mobile-phone requirements. The 73xxL accelerometers dissipate 2.2 to 3.6 V at 400 µA and 3 µA in standby. Packaging is a 3- by 5- by 1-mm LGA. They offer temperature-compensation offset and self-testing for freefall detection diagnosis. And, four user-selectable range versions (1.5 g, 1.5/6 g, 3/11 g, and 4/12 g) are available.

Although only a small percentage of cell phones offers builtin GPS capability, the outlook looks very rosy for newer phones containing GPS chips for PND functionality. Telnap Inc. has a GPS chip set with PND service at a modest monthly cost of about $4. Unlike a standalone PND, it provides a hosted solution with a continuously updated database. Similarly, the latest 3G iPhone model includes GPS capability,

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With funding from Motorola, Siimpel Corp. is developing a digital camera for mobile phones. Siimpel has demonstrated a sugar-cube-sized camera with zoom and auto-focus features that can fit into a normal-sized mobile phone with no external parts, thanks to the use of a MEMS actuator (Fig. 3).

Even the mobile phone’s display is benefiting from MEMS technology. The first reflective interferometric-modulation (iMOD) mirasol microdisplay comes from Qualcomm MEMS Technologies (Fig. 4). This color LCD requires no backlighting and can be viewed in direct sunlight.

Texas Instruments uses its MEMS digital light processing (DLP) Pico chip set for mobile display solutions. These chips enable mobile-phone, digital-camera, portable-media-player, and video-game users to go beyond the limitations of their small display screens to a much larger projected display.

Two years ago, MEMS microphone chip sales totaled between 10 million and 15 million. Yet several analysts say that figure will balloon to several hundred million units within the next few years. MEMS microphones can be found in laptops and notebooks, mobile phones, PDAs, headsets, and hearing aids.

Today, nearly two dozen companies are poised to join this projected boom. For instance, Omron plans to make shipments this year. It also purchased an older IBM fab facility with 8-in. wafer production capability from Epson.

Knowles Acoustics was the first company to introduce MEMS microphones with an analog-output unit back in 2005. MEMS Sonion followed with its SiMic TC200A for mobile phones and with its digital-output version, the DigiSimic, which measured a mere 2.6 by 1.6 by 0.9 mm.

Next, Akustica offered tiny analog-output and digital-output devices built on a standard CMOS process. The company also will soon introduce an analog-output MEMS microphone with an ultra-small form factor intended for mobile phones, wired headsets, and Bluetooth headsets. The company has entered into a cross-licensing agreement with Knowles to strengthen both of their market positions as well.

Nearly all electronic circuits require a timing element in the form of an oscillator. Silicon MEMS technology is now replacing conventional quartz crystal oscillators in many consumer electronics products. In fact, analysts say that MEMS oscillators for mobile phones will create a market totaling approximately $500 million within three to four years.

“MEMS silicon oscillators are widely available off the shelf. Designers are not just curious and becoming more familiar with them, they’re also demanding them in their applications,” says Venkat Bahl, Discera’s vice president of marketing. “They’re relatively lower-cost, fairly accurate, smaller-size, and easier to integrate upwards on a chip than conventional oscillator technologies.”

Discera and SiTime both produce silicon MEMS oscillators that operate from 1 to 125 MHz. Also, Discera has signed a worldwide distribution agreement with Digi-Key. Vectron International competes in this area as well with oscillators made using bulk acoustic-wave (BAW) and surface acoustic-wave (SAW) technologies.

Silicon Clocks targets higher frequencies for use in mobile phones via its patented silicon-germanium MEMS technology. The company is producing devices that operate from 100 to 675 MHz. And last year, WiSpry introduced the first integrated RF MEMS oscillator for mobile phones, employing a digital capacitor array on a CMOS die.

MEMS manufacturers are striving toward greater production efficiencies. This means maximizing the number of known-good die, minimizing testing and packaging costs, and increasing IC reliability levels.

“It is important to make use of existing manufacturing methodologies to bring down costs to consumer electronics levels,” says Benedetto Vigna, group vice president and general manager of STMicroelectronics’ MEMS healthcare, RF transceivers, and sensors product division.

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“This will enable us to produce costeffective MEMS gyroscopes and other needed functions,” he adds. Vigna additionally foresees “some form of MEMS sensor fusion in embedded systems, with the sensor being combined with a microprocessor and signal-conditioning circuitry on the chip.”

Most MEMS IC manufacturers are working very hard to get to the $1/chip threshold and below by using 6-in. and larger diameter silicon wafers in manufacturing. Earlier this year, Freescale Semiconductor established an 8-in. fabrication facility in Austin, Texas, for high-volume production of MEMS ICs.

Other captive MEMS IC manufacturers that design and produce their own devices, such as Analog Devices, Hewlett-Packard, STMicroelectronics, and Texas Instruments, have the capability to manufacture MEMS ICs on 8-in. wafers and may well already be doing so.

To control testing and packaging costs, which take up to 70% to 80% of a MEMS IC’s total outlay, many companies are moving away from die-level packaging to wafer-level packaging. They’re also trying to develop techniques that take full advantage of standard CMOS processes for maximum cost-effectiveness.

“A large factor in rapidly reduced MEMS IC prices is the use of design for manufacturability (DFM) and test strategies by device producers. Products that are finding their way into portable electronics have adopted very sophisticated packaging/ interconnect and testing concepts into the design of the chip and its components,” says Roger Grace.

“This approach of ‘integrated design,’ i.e., concurrent development of device, interconnect, package, and the way it is tested—as has been adopted by volume suppliers like Analog Devices and Freescale Semiconductor—will migrate down to the smaller-volume applications as well as small to medium-size suppliers of MEMS products as time goes by,” he adds.

SVTC Technologies was formed to provide complete access to a full-scale, process development foundry for MEMS designers. The company offers a full complement of advanced CMOS equipment, development support tools and expertise, and commercialization services.

About four years ago, the nonprofit Infotonics Technology Center was founded as a world-class facility for helping MEMS designers by taking a product idea from concept through production, all within a consolidated process flow. The center was originally funded by Xerox, Kodak, and Cornell University. Other funding comes from the state government of New York and the U.S. government.

Economies of scale can be obtained using present 6-in. wafers, as long as foundries producing those wafers can satisfy a large market demand for MEMS ICs. It isn’t productive for, say, a line with 8-in. wafers to be under-utilized by being used less than 24 hours a day, unless some other non-MEMS IC function is also produced on those same 8-in. wafers.

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