Contributed by: St.J. Dixon-Warren
STMicroelectronics is a leading player in the consumer electronics MEMS market. They offer a broad range of products targeted at mobile computing devices, and Chipworks regularly finds ST devices in our teardown analyses. ST manufactures a range of MEMS sensors, including accelerometers, gyroscopes, digital compasses, inertial modules, pressure sensors, and microphones. A trend in the industry has been the integration of multiple sensor functionality into a single package, for example combining three-axis accelerometer and three-axis gyroscope functionality. This lowers the final cost for system integration of six-axis sensing for the mobile device manufacturers.
The LSM330DLC represented an early example of integrated functionality. It integrated a three-axis accelerometer and three-axis gyroscope into a single 4 mm x 5 mm x 1 mm LGA package. Chipworks found this device in a variety of Samsung devices, including the Galaxy S III, Galaxy S3 LTE, and Galaxy Note. We also found it in the Orbotix Sphero.
X-ray analysis shows that the LSM330DLC simply contains separate co-packaged accelerometer and gyroscope dies. The accelerometer is connected to an ASIC with V656A 2010 die markings, while the gyroscope ASIC has V701 2010 die markings. The two devices are mounted side-by-side in the package, with each ASIC die stacked over the corresponding MEMS cap and die. This will still bring some advantages to the mobile device system integrators, but it hardly counts as an integrated MEMS device.
The accelerometer MEMS die found in the LMS330DLC is laid out with three separate sensor, one for each linear direction X, Y, and Z. Interdigitate polysilicon capacitor plates are used to sense the motion of the X and Y proof mass, while the Z proof mass lies over a polysilicon plate on a torsion hinge, which allows vertical motion out of the plane. A frit glass seal was used to seal a hermetic cap over the MEMS structures. The MEMS structures were fabricated using ST’s well established THELMA process.
The gyroscope die has a similar layout to the L3G4200D that was found by Chipworks in the iPhone 4, and which was discussed in detail in a previous blog posting.
As an aside, Bosch also offers an integrated six-axis sensor, the BMI055, but in a slightly smaller 3 mm x 4.5 mm package. Chipworks’ analysis shows it also contains separate MEMS gyroscope and accelerometer sensors.
The LSM330 is another example of an ST device that integrates accelerometer and gyroscope functionality. The device’s specifications are similar to the LSM330DLC. It is provided in a very small 3 mm x 3.5 mm x 1 mm LGA package, but this time it contains only one MEMS die and two ASIC dies. One of the ASIC dies has V756A 2011 die markings, while the other has the same V701A 2010 die markings seen in the LSM330DLC. The V701A controlled the gyroscope sensor die in the LSM330DLC and presumable serves the same function here, so we can assume that the V756A controls the accelerometer sensor die.
One of the LSM330 ASIC dies is mounted on top of the MEMS cap, while the other is mounted beneath the MEMS die. The larger bottom ASIC is the V701A that controls the gyroscope signal, while the smaller top ASIC is the V756A that controls the accelerometer signal.
The LSM330 MEMS die features two major innovations. First, a gold seal, rather than a frit glass seal, was used to seal on the hermetic MEMS cap. The gold seal uses much less space on the die, which would increase the number of die per wafer and lower the cost. A second major innovation is the integration of the gyroscope and accelerometer sensors onto a single die. The gyroscope and accelerometer sensors were sealed hermetically in separate cavities in the cap die. The LSM330 can thus be truly labeled as an integrated six-axis MEMS device. The MEMS structures were manufactured in the same THELMA process used for all of ST’s MEMS inertial sensors.
The integration of increased functionality into a single component has been a relentless trend in the semiconductor industry. A few years ago, only single-axis accelerometers were available, and then three-axis accelerometers appeared and were offered by a number of manufacturers. Three-axis gyroscopes appeared next, and now we have six-axis combination inertial sensors that combine accelerometer and gyroscope functionality. It is worth noting that ST was not the first to market with a combination MEMS inertial sensor. The SensorDynamics SD755, which was analyzed by Chipworks in 2009, was the first combination sensor, albeit only with single-axis gyroscope and accelerometer functionality. SensorDynamics was recently acquired by Maxim.
Related Chipworks Reports
- SensorDynamics SD755 Fail-Safe Single Axis Accelerometer and Single Axis Gyroscope MEMS Process Review
- STMicroelectronics L3G4200D 3-Axis Gyroscope Sensor Module 1: MEMS Overview Analysis