Stress Relaxation Mechanism With a Ring-Shaped Beam for a Piezoresistive Three-Axis Accelerometer

A novel stress-relaxation structure with a ring-shaped beam for ensuring stability in a piezoresistive three-axis accelerometer assembled using wafer-level encapsulation and resin-mold packaging is proposed and evaluated in this paper. The reduction of the unstable increase in sensitivity due to buckling against three stress sources, i.e., the thermal stress in device fabrication, wafer bonding, and resin molding, was evaluated by both computer simulation and experiments on test samples. The measured increase in sensitivity due to stress during wafer bonding and resin molding was kept at 1.26 times using the ring-shaped beam, compared with 7.64 times when using a conventional straight beam. In addition, the standard deviation in the sensitivity of resin-molded samples was kept at 0.04 mV/G using the ring-shaped beam, compared with 2.19 mV/G using the straight beam. The sensitivity variation against the temperature change was also kept small and linear; thus, the effect of the ring-shaped beam was confirmed.

[1]  K. Okada.  Tri-Axial Piezoresistive Accelerometer , 1992 .

[2]  Wolfgang Kuehnel,et al.  A surface micromachined silicon accelerometer with on-chip detection circuitry , 1994 .

[3]  A. Tseng,et al.  Low stress packaging of a micromachined accelerometer , 2001 .

[4]  Masayoshi Esashi,et al.  Integrated silicon capacitive accelerometer with PLL servo technique , 1993 .

[5]  MEMS Wafer-Level Packaging with Conductive Vias and Wafer Bonding , 2007, TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference.

[6]  K. Yamada,et al.  A novel silicon accelerometer with a surrounding mass structure , 1990 .

[7]  Xin Zhang,et al.  Accurate Assessment of Packaging Stress Effects on MEMS Sensors by Measurement and Sensor–Package Interaction Simulations , 2007, Journal of Microelectromechanical Systems.

[8]  Gang Zhang,et al.  A post-CMOS micromachined lateral accelerometer , 2002 .

[9]  K. Najafi,et al.  Vacuum packaging technology using localized aluminum/silicon-to-glass bonding , 2002, Technical Digest. MEMS 2001. 14th IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.01CH37090).

[10]  A. Leung,et al.  Micromachined accelerometer based on convection heat transfer , 1998, Proceedings MEMS 98. IEEE. Eleventh Annual International Workshop on Micro Electro Mechanical Systems. An Investigation of Micro Structures, Sensors, Actuators, Machines and Systems (Cat. No.98CH36176.

[11]  W. Fang,et al.  A novel stress isolation guard-ring design for the improvement of a three-axis piezoresistive accelerometer , 2011 .

[12]  Jaume Esteve,et al.  Twin-mass accelerometer optimization to reduce the package stresses , 2000 .

[13]  C. Hierold,et al.  A pure CMOS surface micromachined integrated accelerometer , 1996, Proceedings of Ninth International Workshop on Micro Electromechanical Systems.

[14]  Benedetto Vigna.  MEMS Epiphany , 2009, 2009 IEEE 22nd International Conference on Micro Electro Mechanical Systems.

[15]  H. V. Allen,et al.  Accelerometer systems with self-testable features , 1989 .

[16]  F. Ayazi,et al.  A 2.5-V 14-bit /spl Sigma//spl Delta/ CMOS SOI capacitive accelerometer , 2004, IEEE Journal of Solid-State Circuits.

[17]  Charles S. Smith.  Piezoresistance Effect in Germanium and Silicon , 1954 .

[18]  K. Najafi,et al.  An all-silicon single-wafer micro-g accelerometer with a combined surface and bulk micromachining process , 2000, Journal of Microelectromechanical Systems.

[20]  Farrokh Ayazi,et al.  A 2.5V 14-bit ΣΔ CMOS-SOI capacitive accelerometer , 2004 .

[21]  M. Schmidt.  Wafer-to-wafer bonding for microstructure formation , 1998, Proc. IEEE.

[22]  Y. Kanda,et al.  A graphical representation of the piezoresistance coefficients in silicon , 1982, IEEE Transactions on Electron Devices.

[23]  Pasqualina M. Sarro,et al.  Design considerations for the thermal accelerometer , 1992 .

[24]  L.M. Roylance,et al.  A batch-fabricated silicon accelerometer , 1979, IEEE Transactions on Electron Devices.

[25]  Hidekuni Takao,et al.  Analysis and design considerations of three-dimensional vector accelerometer using SOI structure for wide temperature range , 1996 .

[26]  B. Boser,et al.  Surface micromachined accelerometers , 1995, Proceedings of the IEEE 1995 Custom Integrated Circuits Conference.

[27]  N. Hablutzel,et al.  Low-cost packaging of inertial MEMS devices , 2003 .