Teardown Compares Combo Sensors

A look inside three top combination sensors shows how vendors are taking very different routes to arrive at competitive products.

We did chip teardowns of three of the leading nine-axis inertial measurement units (IMUs) released in 2013: the BMX055 from Bosch Sensortec, STMicroelectronics' LSM9DS0, and the InvenSense MPU-9250. Each player's cost is very similar, despite their use of very different techniques.

Driven by the benefits of integrated devices and price decreases per function, the market for combo sensors is expected to grow from $446 million in 2013 to $1.97 billion in 2018, according to a report from Yole Development. At this growth rate, combo sensors will rise from 21% of the global inertial consumer market in 2013 to 66% by 2018.

The market acceptance of combo solutions has been extremely quick for six-axis IMUs and six-axis e-compass devices. The relatively new nine-axis solutions we examined will no doubt be followed by more innovative solutions. Combo sensors are becoming mainstream in consumer systems and also find use in cars, but smartphones remain the application that will drive the market for the next few years.

Prices are dropping sharply, with some IMUs sold to some large-volume customers for less than a dollar per unit in 2013. Prices for the nine-axis devices in this teardown are still relatively high, but cost pressures on them will rise as they reach volume production.

The three components use different packaging, with footprints that range from 4x4 mm (16 mm²) for the STMicroelectronics part to 3x3 mm (9 mm²) for the InvenSense device. STMicroelectronics and Bosch Sensortec use LGA packages, while InvenSense uses a QFN package.

The three packages vary widely in size.

Strong differences in internal structure emerged after we removed the epoxy resin. For example, STMicroelectronics and Bosch use five die, but InvenSense only uses two -- one die for a six-axis accelerometer/gyroscope and one for a three-axis magnetometer.

Thus, each player varied widely in the silicon area they used, from 19 mm² for STMicroelectronics to 14 mm² for Bosch and just 8 mm² for InvenSense. More silicon die requires more wire bonding for connecting them. The STMicroelectronics IMU uses 76 wire bondings, compared to 25 for the InvenSense device.

The devices under the epoxy resin show even greater diversity.

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