Electronic Design

Welcome To The Age Of Intelligent MEMS Sensors

The hype is finally turning into reality—microelectromechanical-systems (MEMS) sensors have turned into one of the hottest emerging component areas for medical, consumer, industrial, and automotive applications (Fig. 1). MEMS motion sensors such as accelerometers, inertial management units, and gyroscopes have enabled the straightforward integration of the physical world into the digital world for an improved man-machine interface. MEMS microphones, timing devices, temperature sensors, and micro-opto-electro-mechanical systems (MOEMS) also will play crucial roles in this scenario.

Bob Scannell, business development manager for Analog Devices’ iSensor product line, sees lower prices in intelligent MEMS inertial management units (IMUs) leading to improved vision-based alignment systems in the medical field. Applications like surgical navigation for joint replacement, imaging, prosthetics, and robotic platforms will also benefit. Moreover, he foresees higher-performance MEMS devices for many vehicle navigation applications, such as Analog Devices’ ADIS16405 high-precision tri-axis gyroscope, accelerometer, and magnetometer, which allows for in-field recalibration.

Nearly all MEMS experts are forecasting more highly integrated and intelligent MEMS systems that will open up a host of new applications. Such integrated devices will contain multiple motion sensors like gyros and accelerometers and multiple sensor types, all integrated with signal-conditioning circuitry that will serve medical, industrial, automotive, instrumentation, communications, military/aerospace, and even more consumer electronic products.

Roger Grace of Roger Grace Associates expects “MEMS-based solutions” to be a major “killer application” in the near future. The challenge will be system-level design, analysis, testing, embedding software, power management, and packaging for optimized solutions. Designers need to “think outside the chip,” he explains, focusing more on the system level rather than just the MEMS sensor chip itself.

While Sun Microsystems is known for computer servers and software, the company’s ambitious Sun Small Programmable Object Technology (Sun Spot) program is working with MEMS technology to produce some very intriguing future applications.

According to Roger Meike, senior director of the Sun Spot laboratory, “the next cool thing” could combine MEMS accelerometers, light, and temperature sensors in new classes of applications that will allow us to interact with the real world in ways limited only by one’s imagination (Fig. 2). “Should the next generation of inventors use the Java-based Sun Spot to build these devices, so much for the better,” he adds.

Motion/Pressure Sensors
MEMS motion sensors such as accelerometers, IMUs, and gyroscopes, as well as pressure sensors, will be the key drivers of new products with context and location awareness, gesture recognition, and ambient intelligence, leading to enhanced user interfaces. These products will find homes in consumer electronics, medical devices, industrial environments, computational products, toys, gaming devices, and automobiles.

Freescale Semiconductor’s MMA745xL three-axis digital-output accelerometers for mobile devices enable a wide variety of motion-sensing functions, such as tilt scrolling in all directions, gaming control, gesture recognition, and tap to mute. They also support theft protection, free-fall detection, and backup GPS, as well as other motion-based applications. 

Clustering several sensors like accelerometers, gyros, and pressure sensors into a single module is a trend that will definitely happen, says Benedetto Vigna, general manager of the STMicroelectronics MEMS Products Division. However, he cautions that “MEMS suppliers must be ready to listen to customer requests to develop a technology that will enable multiple-sensor fusion.”

To support this approach, STMicroelectronics has developed the Thick Epitaxial Layer for Microgyrsocopes and Accelerometers (THELMA) and VENice process for SENsor (VENSENS) platfoms for sensor integration. THELMA targets the manufacture of high-performance and low-cost motion sensors like accelerometers, gyros, and microphones, while VENSENS aims for the manufacture of extremely small pressure sensors. Both use a proprietary combination of manufacturing steps of bulk and surface micromachining (see the table).

As part of its strategy to bring economies of scale from its MEMS market in consumer applications to the automotive field, STMicroelectronics introduced the 3.3-V AIS326DQ three-axis accelerometer. Qualified to the AEC-Q100 automotive standard, it features a full-scale range of ±2 g or ±6 g in all three axes, operates from –40°C to 105°C, and can survive 10,000 gs of shock. 

 The company also offers an ultra-compact MEMS gyro that’s just 5 by 5 by 1.5 mm in a 16-pin land-grid-array (LGA) package with digital and analog outputs. According to ST, it’s the first in the industry with a low operating voltage range of 2.7 to 3. V.

The emphasis on low-voltage operation is part of a larger effort by MEMS manufacturers to reduce power dissipation, allowing the devices to be used in a greater number of battery-operated products. Kionix set an industry low with its KXTE9 digital-output three-axis accelerometer, which uses just 30 µA of current versus 200 to 300 for most other MEMS accelerometers. It also employs smart hardwired on-chip algorithms for orientation and activity monitoring to unburden a mobile device’s microcontroller.

The smallest MEMS gyros are made by Invensense, which provides motion-sensing solutions for portable consumer electronics. Its dual-axis gyros are housed in tiny 4- by 5- by 1.2-mm packages. Each chip integrates both the CMOS resonating structures and compensating CMOS electronics at the silicon-wafer level.

Loud and Clear
One of the most dynamic MEMS sectors is MEMS microphones. These tiny structures enable improved acoustic designs in portable consumer electronic devices, allowing users to hear conversations loud and clear. Market research firm iSuppli Corp. predicts MEMS microphone shipments will increase by 32% per year over the next four years.

MEMS-based microphones are opening the door to significant innovations made possible by their much smaller size, greater OEM design flexibility, higher-temperature manufacturing capability, improved noise cancellation, greater immunity to radio-frequency interference (RFI) and electromagnetic interference (EMI), and higher integration capabilities compared with conventional electret condenser microphones (ECMs).

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