MEMS has only recently been added to the lexicon at the analyst company, Gartner, confessed its research director, Stephan Ohr. The admission was made as he introduced a panel discussion on how MEMS is fuelling growth, at the GlobalPress Summit in Santa Cruz. The company has tracked non-optical sensors, in which accelerometers dominate for several years but has identified triggers in several markets that will contribute to a CAGR of double digitals this year. It predicts that non-optical sensors will experience 16.2% growth this year and the automotive market, the largest and longest established market will increase from $2billion in 2008 to $2.8billion in 2014. The largest growth, however, will be in the consumer market, with a project 20% CAGR for motion sensors, which are used in handsets, detecting which way the screen is held and moving text to landscape or portrait formats; and location-based devices. The gaming market is expected to see a 15% CAGR as Nintendo's Wii continue to use gyroscopes and rotational sensors for balance and movement.
Wave after wave
Analog Devices' Mark Martin spoke of the three waves of MEMS. Initially, there were stability control systems, he explained, where they were used in automotive airbags. Around 2005, three or more MEMS were being integrated into a single package and used by Nintendo in the Wii and by Apple in the iPhone and suddenly, he says, consumers and engineers became exposed to what motion sensing can do. The third wave is the mass adoption of MEMS into the broader market of industrial and medical markets. He sees factory automation, where reliable and robust MEMS will be expected to operate in extreme conditions for at least 10 years as one area for future use. He also sees the medical sector as a benefactor of this third wave, with portable and precision medical equipment.
The company has been manufacturing MEMS for 20 years, and by combining its digital signal processing expertise with its MEMS technology, Martin believes the company has an advantage. It recently added two MEMS microphones to its range. The ADMP404 and ADMP405, join the previously announced ADMP401 analogue output and ADMP421 digital output MEMS microphones which are in production. The two additional analogue output microphones (Figure 1) show the evolution of MEMS and progress from ECMs (electret condenser microphones) with a performance that offers higher SNR and superior matching, when compared with ECM models, and which exhibit a higher mechanical shock resistance, consume less current and have a wider operating temperature range.
Sounding out MEMS
The two new microphones use the company's iMEMS technology and enable hands-free communication and voice recognition as they have wind noise suppression. The ADMP404 is a low cost, low power, analogue output, bottom-ported, omnidirectional MEMS microphone, and also includes an impedance converter and an output amplifier. Sensitivity is -38dBV, suitable for both near-field and far-field applications. The SNR is 62dB A-weighted and the microphone has a flat, wideband frequency response from 100Hz to 15kHz.
The ADMP405 differs only in that it has a specially designed low-frequency 200Hz roll-off. This is claimed to be an industry first and allows engineers to filter wind or fan noise energy at the transducer for a clearer audio signal that can be conditioned with any downstream signal processing. It is this feature that allows engineers to integrate full voice recognition, beyond what is possible with the more simple command and control voice recognition version, for example, hands-free, translator and dictation applications.
Software development
Kionix's Eric Eisenhut agreed that signal processing has brought about a change in MEMS. He described MEMS as delivering the "context awareness of external conditions" and explained how by sensing them can improve them. Today's MEMS have more functionality brought about through two routes: system integration innovation and through blocks of signal processing. He explained how understanding software is the key to making sensors integrated and accessible to an integrator. MEMS companies have to understand what kernels provide, for example, to expand applications into medical and the fitness market, where portability and reliability combine.
In response, the company has introduced Gesture Designer, a software engine which captures and manages signatures for today's consumer devices that are operated by gesture commands, where pages are turned using a sweeping gesture across the screen, for example. The embedded engine enhances software development with the ability to interpret sensor outputs and to customise the data for specific applications according to the end use.
Another panelist, Coventor's president and CEO, Mike Jamiolkowski, so put great store in software, but warned that MEMS has to be democratised. In other words it needs to be available for all engineers and supported with an ecosystem. He urged attendees to realise that MEMS is not one product or one model any more. The fact that it is estimated to cost $45million to develop a new MEMS product over a period of four to five years means that it is not available to the masses, he argued. Instead an ecosystem of collaboration and support can result in EDA companies, such as Cadence and Matlab whose tools interface with the system's control system, can work with CMOS foundries and fables design companies to produce new MEMS on existing processes, reducing development time to between six to 12 months. This is the kind of turnaround time that the consumer market demands. He noted that smartphones, which make up a relatively small percentage of the world's 1.4billion handsets can exploit for inertia devices, navigational devices and microphones. In addition, prices will be driven down with either multiple chips or processing layers onto MEMS or integrating different MEMS into the same package.
Another panelist, Applied Materials' Jack Blaha, responsible for 200mm products and enhancements, agreed that partners and co-operation are needed. He observed "There is no Moore's law here". He observed that equipment manufacturers are already leveraging semiconductor technology to serve MEMS needs.
The panel agreed that MEMs is a diverse market and the industry must provide solutions for a range of problems, with different technology challenges. It must also share process and hardware expertise as well as software skills to develop MEMS-based products.
Compact for consumers
Another panel member, Dr Frank Melzer, CEO Bosch Sensortec, a wholly owned subsidiary of Robert Bosch, expounded the virtues of advancing technology. The company has been reducing the package sizes of sensors. In 2007, it created LGA housings of 3mm from the conventional 4mm. The BMA220 digital sensor has gone one step further and is in what is claimed to be the world's smallest digital acceleration sensor. It measures 2x2x0.98mm including LGA housing, and marks a 55% reduction in surface area over current 3x3mm LGA housings, claims the company.
The tri-axial g-sensor is for low-power consumer applications such as mobile phones, handheld devices, computer peripherals, man-machine interfaces, virtual reality and game controllers. It measures accelerations in three, perpendicular axes, sensing tilt, motion, shock and vibration.
The intelligent, interrupt engine provides a hardware or software designer with control over various motion detection scenarios that can be identified and then signaled to the system via an interrupt pin.
The sensor can be used in 3D spatial orientation in mobile phones, in PDAs and in game controllers. It can also be used to target reactions to movements, such as the ability to mute a mobile phone's ring tone.
The Bosch sensor is an example of the integration that other panel members mentioned, in an effort to bring MEMS technology into new areas, or the third wave. For example, the evaluation electronics mean that there is no need for signal evaluation by the host application's microcontroller. This saves energy and is claimed to significantly extend battery life, making it particularly suitable for the battery-sensitive consumer mobile device market.
Another power saving feature is the sensors's power management module which optimises the sensor's power consumption for specific requirements. The sensor does not have to continuously operate at full power.
An ASIC runs algorithms for motion recognition, so that the sensor can autonomously and automatically distinguish between a random movement, a change in the device's spatial position, the difference between a single and double taps and between slow and fast changes in movement. All of the motion recognition parameters are customer-programmable.
MEMS compass
Finally, an example of the collaboration that the panel members believe is inevitable to grow MEMS was introduced earlier this year. ST Microelectronics integrated a three-axis digital accelerometer with a three-axis digital magnetic sensor, in a single module.
According to iSuppli, the market for MEMS digital compasses for use in mobile phones will grow from 8million units in 2008 to 540million units in 2013, a CAGR of 129%. Three-axis magnetometers provide so-called heading functions, which can be combined with a smartphone's GPS positioning information to locate on user on a digital map. According to the analysts, AKM Semiconductor dominates the three-axis magnetometer market with its Hall-effect sensor technology, however, magneto-resistive sensor technology, which offers higher sensitivity is challenging this. Magneto-resistive sensors can support location based services, where the user can point at a building and get and accurae heading. The layar augmented reality browser application displays real-time digital information over a phone's camera screen to show information such as nearby pubs, restaurants, shops or properties for sale.
The LSM303DLH (Figure 2) uses Honeywell's AMR (anisotropic magneto-resistive) technology to measure the strength and direction of the earth's magnetic field and determine the heading relative to magnetic north. The technology provides the same sensitivity on the z axis as on the x and y ones, eliminating the need for flux concentrators that are used in Hall-effect sensors which can shift the sensor offset after it has been magnetised. The three-axis sensing is claimed to reduce measurement errors in ultra-low magnetic field strength environments such as metal buildings, automotives or in higher latitudes.
The digital compass module also has embedded features, such as wake-up, power-down function and 6D recognition, which signals if the device is up or down along all three axes. The device has a linear acceleration full-scale of ±2, ±4 and ±8g and a magnetic field full-scale from ±1.3 to ±8g(2), both selectable by the user.
Forward direction orientation gives application developers licence to improve the use of a limited display size for maps by putting the current user position at the bottom of the map with the rest of the display in the forward, or up ahead, direction.
The magnetic sensor design has a high level of accuracy, with a built-in offset cancellation circuit to minimise the need for calibration, and patented set and reset straps that de-gauss, or de-magnetise, the sensor for each measurement.
Figure 1: MEMS is eclipsing ECM in microphone technology.
Figure 2: Magnetic sensors deliver the navigation features on smartphones.
