Packaging, low power & custom MEMS process place Invensense at the top in 6-axis motion sensing
7/12/2012 3:45 AM EDT
InvenSense Inc. (Sunnyvale, CA), which specializes in the development of motion sensing devices utilizing the MEMS technology, announced the availability of the smallest 6-axis of motion tracking component based on its proprietary MEMS technology.
Using its patented Nasiri-Fabrication process which combines MEMS on CMOS, the new 6-axis motion sensing solution MPU-6500 (Motion Processing Unit) combines a 3D accelerometer and a 3D gyroscope in the same silicon substrate along with the patented Digital Motion Processor (DMP) hardware accelerator with MotionFusion and run-time calibration firmware. InvenSense claims that its MotionFusion sensor fusion algorithms enable manufacturers to eliminate the costly and complex selection, qualification, and system-level integration of discrete devices in motion-enabled products and guarantees optimal performance for consumers.
While its predecessors MPU-6000 and MPU-6050 were the first inertial MEMS that combined 3D accelerometers and 3D gyroscopes in the same silicon substrate, the second generation MPU-6500 ups the ante by offering it in a small 3x3x0.9mm QFN package, the smallest for a 6-axis MPU or IMU (inertial measurement unit) in the industry today. The MPU-6500 also includes a secondary I2C port that can connect an external magnetometer device from different vendors to complete 9-degrees-of-freedom sensing.
MPU-6500 is the world’s first motion sensor to operate at 1.8 volts and consumes only 6.1mW of power in full operating mode and only 18uA of current in low-power mode. In a phone conversation with the author on Monday, Daniel Goehl, VP of Worldwide Sales at InvenSense, explained that “we wanted to raise the bar in reducing package size, cost, power consumption while improving performance and make additional sensing integrations seamless. To that end, we have largely succeeded in delivering a motion tracking device with nearly 60 percent lower power, a 45 percent smaller package, industry-leading consumer gyroscope performance, and major improvements in accelerometer noise, bias, and sensitivity.”
According to InvenSense press release, MPU-6500 incorporates breakthrough gyroscope performance of only ±5dps zero-rate-output and 0.01dps/√Hz of noise; and delivers dramatically improved accelerometer specifications including a typical offset of only ±60mg, 250µg/√Hz of noise. The MPU-6500 software drivers are fully compliant with Google’s latest Android 4.1 Jelly Bean release, and support new low-power DMP capabilities that offload the host processor to reduce power consumption and simplify application development.
The 6-axis motion sensors market is dominated by Bosch Sensortec and STMicroelectronics competing with many others including InvenSense. How ever, IMU’s from Bosch Sensortec (BMI055) and ST (LSM330DLC) are 33 percent and 45 percent larger in package size, respectively. The BMI055 is supplied in a LGA 3.0 x 4.5 x 0.95 mm package where as the LSM330DLC is provided in a 4 x 5 x 1.1mm LGA 28-pin package. Both products appear to be limited by available packaging technology options –the LSM330DLC for example is a System-in-Package (SiP) utilizing substrates which are ideal for heterogeneous integrations of other sensors (compass for example) but use larger real estate and result in higher package thicknesses. The resulting moisture sensitivity levels (MSL) are also typically inferior to those of lead frame-based packages.
The InvenSense MPU-6500 on the other hand is offered in a QFN lead frame package utilizing co-located gyro and accelerometers bonded to CMOS IC wafer. In the patented Nasiri-Fabrication process, the MEMS wafer also doubles as cap and is eutectically bonded to the CMOS IC wafer using various interconnect technologies. This process has the advantage of eliminating the redundancy of wafer cap (that both Bosch and ST devices use as an intermediary between CMOS IC wafer and the MEMS wafer), thereby reducing cost and package thickness. The process of bonding CMOS MEMS with any CMOS IC wafer by vertically stacking is accomplished by using a number of interconnects technologies developed and qualified for production by InvenSense. The 2.5D versions of lateral integrations are also possible using Si-interposers to realize SiPs that may be otherwise challenging (finer routing for example) in substrate-based packages used by ST and Bosch Sensortec.
InvenSense is targeting the application of MPU-6500 device for smart phones, tablets, wearable sensors, and other consumer markets. InvenSense believes the new MPU-6500 addresses the market requirements for high-performance applications such as pedestrian navigation, context-aware advertising, and other location-based services, along with supporting the specifications for emerging wearable sensor applications such as remote health monitoring, sports and fitness tracking, and other consumer applications.
According to latest research reports by Yole, MEMS market is set to cross $21 billion by 2017; of which, about 25 percent will be the share of motion sensing components (accelerometers, gyroscopes, magnetometers and pressure sensors combinations). InvenSense believes this can be even larger share than what is forecast as many new markets for MPU’s are in early stages of adoption.
InvenSense is fabricating the wafers for MPU-6500 at two of the major foundries, TSMC and Global Foundries, on 8-inch wafers. It is using older process technologies (0.18 um) that results in lower costs to the customer. To encourage and support developer partners, InvenSense recently began a shuttle program called the “NF-Shuttle” (link).
As a fabless MEMS developer, InvenSense’ foray into the growing market of MEMS motion sensors is not without risks. This market space is largely dominated by the IDM MEMS vendors like STMicroelectronics and Bosch Sensortec. STMicroeletronics for example is becoming a dominant player in MEMS market by offering a wide range of MEMS devices. How ever, a major portion of its MEMS business, as much as 90 percent of its IDM business, is done with 2 devices only (accelerometers, gyroscopes). Bosch Sensortec, on the other hand, uses its captive fab infrastructure dedicated to address automotive market demands.
To mitigate its risks against large IDM MEMS players, InvenSense has both foundries on allocation. In addition, it has built wafer banks on reserve and has similar risk mitigation steps in place for packaging and final test. It appears to be confident to address volume demands of the growing market for motion sensors.
MPU-6500 is sampling now to selected customers with mass production slated for Q4 2012.
MP Divakar is a technologist in the Silicon Valley, specializing in semiconductor backend, packaging, thermal management and test. In addition to juggling two startups, he manages to contribute at IEEE Communication and Power Electronics societies. He is a regular commentator at the EE Times portal.