Contributed by St.J. Dixon-Warren and R. Krishnamurthy, Chipworks
Invensense is a leader in the MEMS gyroscope market segment. According to Yole, they experienced nearly 500% growth 2009 over 2008. They now hold the #1 position in the MEMS gyroscope for consumer electronics market.
Chipworks recent had a look inside their new three-axis digital gyroscope, the ITG-3200. The device is built using the Nasiri, single-chip, MEMS process, where the MEMS layer is sandwiched between a fusion-bonded cap wafer and the ASIC. The ASIC and MEMS are bonded using eutectic metal bond. The SEM image in Figure 1 provides a tilt-view of the corner of the MEMS chip, where the MEMS layer can be seen between the cap and ASIC die.
Figure 1 Tilt View SEM of ITG-3200 Chip
Cross-sectional analysis of the ITG-3200, Figure 2, reveals the internal structure of the part. The integrated MEMS-ASIC chip is mounted over a lead frame in the molded plastic package. The MEMS layer is formed beneath a cavity in the cap.
Figure 2 ITG-3200 Package Cross Section
The ASIC and MEMS die were carefully separated in our lab. Figure 3 is a photograph of the ASIC die, deprocessed to polysilicon to reveal the ASIC architecture. Cavities are present in the ASIC beneath the location of the removed X and Y MEMS sensors to allow out-of-plane motion.
Figure 3 ITG-3200 ASIC Polysilicon Die Photograph
The ITG-3200 represents a major milestone in the development of gyroscopes for consumer electronics; however, Invensense can expect competition in this market space. STMicroelectronics already has a three-axis gyroscope on the market, the LPYR540AH, which was recently analyzed by Chipworks and found to be a four-chip solution. The ITG-3200 gyroscope is 60% smaller than the LPYR540AH. Curiously, Chipworks analysis suggests that the LPYR540AH uses out-of-plane deflection of the vibrating proof mass to detect rotation in the XY plane, while the ITG-3200 uses in-plane deflection. Chipworks anticipates arrival of the STMicroelectronics L3G4200D, which will likely contain an integrated 3-axis MEMS gyroscope sensor plus a separate ASIC in a 4 mm x 4 mm x 1 mm package size, and so will be a direct competitor for the ITG-3200.
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