Think outside the chip: MEMS-based systems solutions - Embedded.com

Think outside the chip: MEMS-based systems solutions

MEMS is an acronym for MicroElectroMechanical Systems. However most MEMS implementations to date have not been systems at all, but rather devices. The level of integration either monolithically or heterogeneously has been minimal at best.

A key conference next month will shed lots more light on the MEMS-based systems solutions (MBSS) topic. First, on June 7, at the Sensors Expo in Rosemount (Chicago) Illinois, 15 speakers will address the topic of MBSS in a session entitled Think Outside the Chip: MEMS-Based Systems Solutions. Note that Sensors Expo will be co-located with the Embedded Systems Conference. The morning keynote will be provided by Professor Thomas Gessner of Fraunhofer Chemnitz (Germany), who has been a major advocate of this approach for many years. His presentation called Examples of Smart Systems Solutions: From Monitoring Systems to Micro Analysis Systems will provides detailed case studies on a number of interesting and emerging applications on Smart System Integration. The afternoon keynote, Dr. Peter Hartwell of HP Labs, will present the paper Applying New MEMS Architecture to Achieve Low-Cost, Ultra-Sensitive Wireless Sensors for Mission Critical Applications which details the autonomous MEMS sensing network described above. Another afternoon keynote, Dr. Gereon Meyer of VDI/VDE (Germany), will make a presentation entitled Thinking Outside the Chip: The European Platform of Smart Systems (EPoSS). There will also be a panel discussion at the conclusion of the session addressing. This is named Integration Tradeoffs for a Design for Manufacturing World.

Some of the most successful earlier monolithic “systems” have been demonstrated by Analog Devices in their inertial sensor product line and with Akustica in their microphone product line. It's interesting to note that ADI has gradually migrated from their monolithic integration strategy to that of an ASIC/device approach. Akustica stays steadfast in its pure monolithic approach.

MBSS use front-end MEMS, with a combination of one or many sensors, actuators and or structures, which function with other devices. This could include signal conditioning ASICS, DSP embedded software, energy creation and storage, and networking communications functions. All of these functions need to be interconnected and contained in a small, robust, low-cost package that has the ability to be tested in a high-throughput fashion. The concepts of classical system engineering that can bring the design team together from Day 1 are tied in with co-design principles that acknowledge the interaction of the MEMS, other electronics and packaging. And they all embrace the design for manufacturing (DFM) and test principles that are required.

Approaches to MBSS
MBSS fall into two categories. The first is enabling engine that drives the solution. This concept is driven by MEMS technology that is the intellectual property of the creator of the solution. An example is the recently introduced high-sensitivity accelerometer introduced by HP that will be used to create a wireless autonomous sensor network for seismic oil and gas exploration applications. In this design, HP has partnered with Shell Oil to create a mesh network of sensors that will monitor the response of the earth into which they've been embedded that will measure a spectral response of the ground as the ground is pounded by a machine. The development of sophisticated algorithms in this system will provide valuable information for ground-based oil and gas exploration.

Note that HP is not planning to sell the high-performance accelerometer to the merchant market, but rather use it as an enabling engine for many types of low-level, large-dynamic-range vibration measurements. They also have plans to extend the application of this data-acquisition strategy for the monitoring of civil engineering structures, including dams, tunnels, and bridges to determine the structural integrity of these systems to provide early warning to avert fatalities due to structural failure. HP plans to sell the solution to its customers, increasing the value add of the accelerometer engine to include massive cloud computing and data analysis, all using HP’s competencies.The second MBSS approach is called commoditized integration. Here, standard off-the-shelf MEMS devices are used in conjunction with ASICs and DSP with proprietary application software and packaging to create a solution. Examples of this approach are being demonstrated by Schrader Electronics in its tire pressure monitoring systems. These use standard off-the-shelf pressure and motion sensors.

Hillcrest Laboratories and Movea, in their human-machine interface device for gesture recognition products, employ MEMS accelerometers and gyros. The value added to these commoditized solutions is the knowledge of the application and the ability to successfully accomplish intelligent systems integration and provide software programming specific to the application. All of this is neatly packaged in a low-cost device.

Drivers for MBSS adoption
There are a number of drivers, both technical and business, that will make MBSS adoption a major business success for MEMS. The most significant of these are cost, availability, market expansion, and the need for product differentiation and optimization of gross margin on the part of the solution supplier. A downward price spiral that has occurred over the past 15 years when $5 (high-volume) devices were introduced. ADI's ADXL 50 one-axis accelerometer for automotive airbag applications displaced electromechanical systems costing three times as much.

Now, a three-axis accelerometer can be had for less than $0.75 (in large volumes) from a number of suppliers including Bosch, Kionix, and STMicroelectronics. MEMS gyros are following the same path but are still selling in the low single digits for large volumes. Invensense is leading the charge in this area.

Pressure sensors have also seen significant price declines. This maturing or commoditization has enabled large-volume applications including mobile phones and games to adopt these low-cost devices as integral to their strategy of providing many more functions and higher performance and efficiency. This helps create product differentiation between phone suppliers. In addition, the necessity of the MEMS device to work in conjunction with a signal processor in the form of a commercially available ASIC and/or DSP from many vendors including e2V, SiWare Systems, Austria Microsystems, Triad Semiconductor, and Microchip provides solution designers with a wide choice of partners. As one can see, the barriers to entering the MBSS market from a commoditized approach can be lower than that of the enabling engine approach.

However, the enabling engine approach has a number of companies actively pursuing application opportunities. This includes Polychromix, who has created a hand-held optical spectrometer, and C2V (which has recently been acquired by Thermo Fisher) who has created a MEMS microfluidic gas chromatograph. Research shows that portable analytical instruments hold great promise to propel MEMS-based spectrometers and chromatographs into the laboratory diagnostics and medical point of care application sectors.

One of the other major adoption drivers of MBSS is the quickly developing MEMS packaging and testing area. Ten years ago, MEMS packaging was an afterthought. Today, it's a product differentiator and an area of great development. Because MEMS packaging and cost typically represent over 50% of the bill of materials, MEMS suppliers, especially those of price-sensitive consumer devices, have introduced low-cost packaging and test strategies. Hence, the infrastructure to support the development of MBSS is alive and well and ready to support the development of a broad range of future MBSS implementations.

Although MBSS has been around for many years, the proliferation of this approach is being fueled by the availability of low-cost MEMS devices and signal conditioning ASICs and DSP, as well as packaging and high-throughput testing. The need for gesture recognition in games, toys, computer peripherals (mice), medical, sports, and fitness bodes well for this approach. In addition, as the need to better understand the quality of food and water as well as the chemical and biological composition of many substances to enhance society’s quality of life, MBSS for spectrometers and chromatographs for handheld instruments will fuel the enabling engine concept.

About the author
Roger H. Grace , an expert in the MEMS field, is the President of Roger Grace Associates. He can be reached at .

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