MEMS integration and intelligence are the trend of breaking out point for timing oscillators

　　Zhao Yanhui, senior application engineer of the micromechanical product line of Analog Devices (ADI), believes that MEMS technology will have the following development trends in the future:

　　First, miniaturization will reduce power consumption. Micron or even nanometer-level micro devices will appear, while reducing power consumption;

　　Second, miniaturization improves accuracy while miniaturizing, making the MEMS accelerometer have the noise characteristics of a quartz accelerometer, ensuring the small size of the MEMS gyroscope while obtaining the zero-bias stability of the fiber optic gyroscope;

　　Third, the trend of integration and intelligence, that is, the integrated manufacturing technology of MEMS and IC and the integrated manufacturing technology of multi-parameter MEMS sensors have been developed, and signal detection has a certain degree of intelligence based on integration.

　　These trends require semiconductor manufacturers to provide highly integrated MEMS sensor modules with higher precision, better stability and greater intelligence.

　　The demand for MEMS sensors in 2013 is still very strong, which includes the demand from traditional automobile and consumer markets, as well as the demand from emerging industries, medical, communication, well logging and military industries. Indoor navigation applications will be a driving factor for the volume growth of new MEMS barometers in 2013; and as people's requirements for the quality of recording, video calls, etc. become higher and higher, high signal-to-noise ratio MEMS microphones will be used in more and more mobile phones or tablets. As high-temperature MEMS devices are verified by more and more customers, more and more MEMS products will be seen in extreme working areas such as well logging. The Internet of Things and home medical care will be another killer application after the automotive and consumer application fields, and their potential market and growth trend will be like today's smartphones. However, due to the lack of unified standards and customer awareness in the market, it is expected to take about 2 years to grow in volume.

　　Consumer electronics require highly integrated MEMS with multiple functions

　　Strong market demand for multifunctional personal electronic devices such as smartphones, tablets, portable medical devices, GPS instruments, etc. has accelerated the development of MEMS sensor technology. Sun Chong, sensor product application manager of Freescale Semiconductor, said that in the consumer field, driven by the smartphone and tablet markets, MEMS motion sensors will continue to maintain rapid development. "Now the application of independent inertial sensors is very common. With the development and maturity of 3D IC and TSV technology, we will see more and more multi-axis combined inertial sensors IMU (acceleration + magnetism, acceleration + gyroscope, acceleration + gyroscope + magnetism) appear to meet the requirements of smaller size and lower cost. At the same time, with the popularization and development of terminal products such as smart TVs and TV boxes that integrate network, audio and video, and games, there will be more and more handheld remote controls with integrated IMUs."

　　Due to their cost advantages and irreplaceability, MEMS inertial sensors, especially accelerometers, are still the most important MEMS devices in consumer electronics. MEMS inertial sensors are mainly used to achieve motion capture and human-computer interaction. For example, in smartphones and tablets, the automatic switching of screen display between landscape and portrait modes requires the use of gravity accelerometers to accurately detect angle changes, while also meeting stringent volume and power consumption requirements.

　　In the consumer electronics market, in addition to the existing MEMS inertial sensors, pressure sensors, infrared sensors and microphone arrays, some environmental sensors and biosensors are also gradually being used in this market. "The fusion (i.e. integration) of MEMS sensors will continue to drive innovation. Integrating sensors into a single package will help simplify sensor integration in consumer products," said Harmeet Bhugra, general manager of IDT's MEMS division.

　　Eric F. Pabo, MEMS business development manager at EVG, believes that the biggest challenge facing design engineers when adding MEMS devices to designs is how to convert the output of MEMS devices into information that is beneficial to the device function or the device owner to the greatest extent. This A/D (analog to digital) conversion and software are actually very difficult. It is very difficult to make different MEMS devices work together to calibrate and correct each other, but at the same time it has outstanding advantages - sometimes called sensor fusion. Several MEMS manufacturers have solved this problem by packaging a 3-axis accelerometer, a 3-axis gyroscope, a 3-axis magnetometer and an ASIC together. The ASIC performs all signal processing and outputs the processed information through a standard interface such as USB. STMicroelectronics (ST), Bosch Sensortec and Invensense all provide this type of product.

　　Wang Weiying, senior manager of MEMS product marketing department of EPCOS Greater China under TDK Group, pointed out that the current MEMS in the industry requires many production processes. In order to effectively reduce costs and improve supply flexibility without sacrificing specifications and performance, this is an important threshold that needs to be broken through in the addition of MEMS devices to consumer electronic products. In the future, applications will tend to combine individual functions into a single intelligent (multiple detection function) product.

　　EPCOS's main products currently include sensors that combine the functions of detecting atmospheric pressure, temperature, and altitude. In addition to the advantages in size and height, the device itself can provide cost-effective products while ensuring specification performance. For example, in the application of positioning system products, EPCOS's pressure sensor can improve accuracy to within 25cm. This helps to improve the sensitivity judgment of consumer products such as handheld products and game consoles while moving. The changes in temperature and pressure can also show differences in seconds. EPCOS's T5400 is the smallest digital pressure sensor on the market, developed specifically to meet the needs of mobile devices and their peripherals (Figure 1). T5400 enriches the design of applications in the fitness and outdoor fields such as heart rate monitoring, sports shoes or bicycle computers, and can also be combined with an altimeter to track altitude changes. It also helps to improve indoor navigation when there is no available GPS signal.

　　Freescale's FXOS8700CQ, which has been in mass production, is a 6-axis IMU device that integrates a 12-bit three-axis accelerometer and a three-axis magnetometer, and the PCB footprint is only 3mm×3mm. The FXOS8700 has a directional resolution of 0.1 degrees and can provide a heading accuracy of less than 5 degrees, providing an ideal solution for high-performance motion detection and eCompass. The FXOS8700 has low power consumption characteristics and rich embedded functions, especially the automatic interrupt output when the magnetic field vector amplitude exceeds the limit, the magnetic field component exceeds the limit, the built-in embedded hard magnetic self-calibration function, and supports low-power hard magnetic offset compensation. It can be widely used in smart phones, tablets, personal navigation devices and other devices, providing applications such as motion detection, electronic compass, games, augmented reality and location services.

　　The ADXL362 is the industry’s lowest power MEMS accelerometer from Analog Devices (Figure 2). This 3-axis digital MEMS accelerometer consumes only 300nA in motion detection wake-up mode, which is 60% lower than the closest competing sensor in the same mode. In full-speed measurement mode, the current consumption is 2μA at a data rate of 100Hz, which is 80% lower than competing MEMS accelerometers operating at the same frequency. In addition to its inherent low-power operation, the ADXL362 MEMS accelerometer has other important features that can improve system-level power efficiency. The ADXL362 also has an enhanced sample activity detection function that can accurately distinguish between different types of motion. This feature avoids false detections, preventing the sensor from unnecessarily turning on the system and shortening battery life. The ADXL362 can be used as part of an intelligent, continuously operating, motion-activated switch. When equipped with a wake-up status output pin, the motion sensor can bypass the processor to instantly trigger the switch to start system functions, further reducing system power consumption. The extremely low power consumption makes the ADXL362 suitable for a variety of applications where battery life is extremely important, from healthcare to infrastructure monitoring.

　　MEMS brings innovation to automobiles, industry and other fields

　　MEMS pressure sensor is mainly used to detect the pressure of fluid or solid, and can transmit signals remotely. It is the most commonly used sensor in industrial applications, and is often used as a front-end component of automatic control. Therefore, it is widely used in various industrial control environments, including petrochemical, papermaking, water treatment, electricity, shipbuilding, machine tools and public equipment industries. The packaging process of MEMS pressure sensor can usually make the piezoresistive sensitive core small in size, high in sensitivity, and good in stability, and combine the varistor with the strain material in the form of a Wheatstone bridge, so as to ensure that the piezoresistive pressure sensor has strong overload capacity and strong resistance to shock pressure. This is very suitable for measuring pressure changes in a high range, especially above 1Mpa, with good linearity and high accuracy, and is suitable for measuring various media compatible with strain materials.

　　Eric F. Pabo of EVG pointed out that in addition to the consumer electronics field, the application of MEMS sensors in the automotive market will continue to grow, because more automotive markets use systems such as TMPS (tire pressure monitoring system) and ESC (electronic stability control system). Some past dedicated MEMS devices such as microbolometers will appear in high-end automotive applications and then gradually move to the mid- and low-end markets as device costs decrease. MEMS will continue to be used in more industrial fields and appear in the field of durable consumer goods. However, the scale of these two latest application markets will not be larger than consumer MEMS devices.

The innovation and breakthroughs brought by MEMS sensors in environmental and industrial applications come from widespread use based on reduced costs. For environmental applications, imagine if sensors were already present in billions of smartphones around the world, they could be used to collect and report environmental information. As the cost per node of sensors using MEMS devices continues to decrease, the industrial application of MEMS devices will inevitably increase. A MEMS microphone plus an MPU (microprocessing unit) and a radio communication line can be used to monitor the noise level of large motors or rotating motors and perform spectral analysis of the noise. When the sensed sound and spectral characteristics are wrong or other problems are detected, a signal will be sent to a central monitoring station for maintenance.

　　Pressure sensors are expected to become the highest-selling MEMS device due to their relatively high price and expanding range of applications in automotive, industrial and medical fields. Due to differences in compensation level, die calibration and packaging type, the average price of MEMS pressure sensors currently varies greatly, ranging from a few dollars to tens of dollars for high-value industrial and medical applications, to hundreds of dollars for specialized applications such as aircraft hydraulic systems or flight data measurement, including industrial application combinations under harsh media, temperature and pressure conditions. A new application of MEMS pressure sensors in automobiles is powertrain pressure sensing. In the industrial field, the main applications of MEMS pressure sensors include heating, ventilation and air conditioning (HVAC), level measurement, and various industrial process and control applications.

　　The latest development of MEMS focuses on timing oscillators

　　Additionally, pollution and pollen detection is becoming a hot topic for environmental sensors, especially given the high levels of smog/allergens in large cities. In industrial applications, robotics will continue to drive demand for increasingly sophisticated sensors.

　　Sun Chong of Freescale also said that MEMS devices are increasingly being used in the environment and industry, such as MEMS chemical gas and pressure sensors, which will promote the miniaturization and portability of detection and sensing equipment, making it more convenient for environmental monitoring and industrial detection. At the same time, it is expected that wireless IoT nodes using MEMS sensors will also be increasingly used in the environment and industry. For industrial applications, Freescale's MMA8491 is a low-power 12-bit three-axis acceleration sensor that consumes less than 400nA when sampling second by second, and the shutdown current is less than 10nA. The MMA8491 is very suitable for use in wireless IoT nodes, providing features such as device tracking, vibration, and tilt detection. The MMA8491 provides a package shape suitable for industrial fields with high reliability requirements.

　　Analog Devices' ADXL377 is the industry's first commercially available high-range triaxial accelerometer. The ADXL377 measures acceleration from high-impact events caused by shock and vibration over a full-scale range of ±200g without signal saturation. This measurement range, combined with the analog output that continuously captures impact data, makes the ADXL377 an ideal sensor for contact sports, where impact forces can be detected to understand indicators of traumatic brain injury (TBI).

　　Harmeet Bhugra, general manager of IDT's MEMS division, believes that the latest developments in MEMS technology are concentrated in the field of oscillators (timing references). "So far, MEMS has only been adopted in consumer products such as mobile phone sensors, and the next stage of rapid development will revolve around timing oscillators. MEMS oscillators are greatly driven by data center enterprise applications such as high-performance routers, switches, and storage clusters, and their performance has been sufficiently improved." IDT has launched timing oscillators for cloud computing and enterprise applications. Its 4H performance MEMS oscillator has a typical phase jitter performance of 100 femtoseconds (fs) and an integrated frequency margin setting capability (Figure 3). The ultra-low phase jitter and adjustable output frequency of IDT's high-performance oscillator significantly reduce the bit error rate (BER) of 10 Gigabit Ethernet (10GbE) switches, routers, and other related network equipment.

　　MEMS clock devices enter the mobile phone market

　　In addition to inertial sensors, traditional quartz crystals are also being replaced by silicon MEMS devices. With standard semiconductor processes and high-volume plastic packaging technology, silicon clock devices have revolutionized the delivery cycle and supply of clock crystal devices, and their size is also smaller. "One application area that has seen significant growth is the use of MEMS clock chips to replace traditional quartz clocks, which can bring users higher performance, flexibility, reliability, smaller component size and lower power consumption." Piyush Sevalia, executive vice president of marketing at SiTime, said. He believes that in the next two years, the popularity of MEMS clocks in various applications will drive the growth of the MEMS industry. New applications for MEMS clocks include smartphones, tablets, digital cameras, sports and fitness equipment (such as watches), medical and health equipment (blood pressure monitors, blood sugar testers, etc.), electronic accessories (such as MP3, headphones) and computer peripherals (wireless mice, touchpads, etc.).

　　SiTime's MEMS clock devices, including oscillators, resonators and clock generators, have been widely adopted in various consumer and mobile electronic products. In addition, SiTime components have programmable functions, providing users with great flexibility and new features, such as frequency accuracy up to 6 decimal places. SiTime's silicon MEMS timing devices are integrated with low-power MEMS and programmable analog circuits, using a complete silicon process. Following the launch of high-end silicon MEMS for system equipment, industrial control and consumer electronics, SiTime's latest SiT15xx series 32kHz MEMS oscillators (Figure 4) overcome the limitations of quartz-based devices in many ways, reducing the footprint by 85%, reducing power consumption by 50%, and improving reliability by 15 times, all of which contribute to the realization of smaller, lower power and more durable mobile electronic products. In addition, various medical fitness devices and various smart wearable products that are currently very popular, such as smart watches, smart glasses, etc., are also very suitable for the use of silicon MEMS clock oscillators.