Encapsulated submillimeter piezoresistive accelerometers

While micromachined accelerometers are widely available and used in various applications, some biomedical applications require extremely small dimensions (<mm) or mass (<mg) that cannot be fulfilled with commercially available accelerometers. In this work, we present a fully packaged piezoresistive accelerometer that has the smallest dimension (0.034mm/sup 3/) ever published. We achieve miniaturization by using a film encapsulation technique with a thick epitaxial polysilicon layer. This packaging technique enables the dimensions of the die to be only tens of microns larger than the micromechanical structure. We have fabricated accelerometers as small as 0.034mm/sup 3/ (387/spl mu/m/spl times/387 /spl mu/m/spl times/230/spl mu/m) with noise floor of 0.25mg//spl radic/Hz. These ultra-miniature motion sensors have potential opening up new frontiers in biomedical science and engineering.

[1]  J. David Zook,et al.  Polysilicon sealed vacuum cavities for microelectromechanical systems , 1999 .

[2]  R. Howe,et al.  Microelectromechanical filters for signal processing , 1992, [1992] Proceedings IEEE Micro Electro Mechanical Systems.

[3]  G. Stemme,et al.  Low temperature full wafer adhesive bonding , 2001 .

[4]  J. Timonen,et al.  Elastic wave propagation in bone in vivo: methodology. , 1995, Journal of biomechanics.

[5]  Liwei Lin,et al.  Hermetic wafer bonding based on rapid thermal processing , 2001 .

[6]  H. Broman,et al.  Axial stiffness of human lumbar motion segments, force dependence. , 1998, Journal of biomechanics.

[7]  Khalil Najafi,et al.  An Ultra-Thin Hermetic Package Utilizing Electroplated Gold , 2001 .

[8]  R. Howe,et al.  Vacuum encapsulation of resonant devices using permeable polysilicon , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[9]  R. Abrams,et al.  Effect of Abdominal Vibroacoustic Stimulation on Sound and Acceleration Levels at the Head of the Fetal Sheep , 1997, Obstetrics and gynecology.

[10]  Carlos H. Mastrangelo,et al.  Electrical and optical characteristics of vacuum-sealed polysilicon microlamps , 1992 .

[11]  J. R. Mallon,et al.  Silicon fusion bonding for pressure sensors , 1988, IEEE Technical Digest on Solid-State Sensor and Actuator Workshop.

[12]  D. Wasserman,et al.  Response of the uterus to abdominal vibrations in sheep , 2000 .

[13]  T. Kenny,et al.  New thin film epitaxial polysilicon encapsulation for piezoresistive accelerometers , 2001, Technical Digest. MEMS 2001. 14th IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.01CH37090).

[14]  R. Howe,et al.  Batch transfer of microstructures using flip-chip solder bonding , 1999 .

[15]  K. Najafi,et al.  A low-temperature thin-film electroplated metal vacuum package , 2004, Journal of Microelectromechanical Systems.

[16]  Douglas Ray Sparks,et al.  Wafer-to-wafer bonding of nonplanarized MEMS surfaces using solder , 2001 .

[17]  Wafer-scale film encapsulation of micromachined accelerometers , 2003, TRANSDUCERS '03. 12th International Conference on Solid-State Sensors, Actuators and Microsystems. Digest of Technical Papers (Cat. No.03TH8664).

[18]  Silicon profile transformation and sidewall roughness reduction using hydrogen annealing , 2005, 18th IEEE International Conference on Micro Electro Mechanical Systems, 2005. MEMS 2005..

[19]  Qiang Zou,et al.  Implantable biaxial piezoresistive accelerometer for sensorimotor control , 2004, The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[20]  J. Fahrenberg,et al.  Assessment of posture and motion by multichannel piezoresistive accelerometer recordings. , 1997, Psychophysiology.

[21]  T. Kenny,et al.  Investigation of MEMS Resonator Characteristics for Long-Term and Wide Temperature Variation Operation , 2004 .

[22]  Daniel Lapadatu,et al.  Extremely miniaturized capacitive movement sensors using new suspension systems , 1994 .

[23]  J. Hasenkam,et al.  A new method for quantitative evaluation of perceived sounds from mechanical heart valve prostheses , 2000, Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine.

[24]  Denton A. Cooley,et al.  INITIATION OF CLINICAL USE OF THE JARVIK 2000 HEART , 2000 .

[25]  Liwei Lin.  MEMS post-packaging by localized heating and bonding , 2000 .

[26]  Toshiyuki Tsuchiya,et al.  Polysilicon vibrating gyroscope vacuum-encapsulated in an on-chip micro chamber , 2001 .

[27]  J. Mai,et al.  Low pressure and low temperature hermetic wafer bonding using microwave heating , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[28]  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).

[29]  T. Kenny,et al.  Investigation of energy loss mechanisms in micromechanical resonators , 2003, TRANSDUCERS '03. 12th International Conference on Solid-State Sensors, Actuators and Microsystems. Digest of Technical Papers (Cat. No.03TH8664).

[30]  J. Marek,et al.  A precision yaw rate sensor in silicon micromachining , 1997, Proceedings of International Solid State Sensors and Actuators Conference (Transducers '97).

[31]  D. Beebe,et al.  The fabrication of nonplanar spin-on glass microstructures , 1999 .

[32]  A. L. Evans,et al.  Recording accelerations in body movements , 2006, Medical and Biological Engineering and Computing.

[33]  Y. Tai,et al.  Sealing of micromachined cavities using chemical vapor deposition methods: characterization and optimization , 1999 .

[34]  T. Kenny,et al.  A high-performance planar piezoresistive accelerometer , 2000, Journal of Microelectromechanical Systems.

[35]  Thomas W. Kenny,et al.  Single wafer encapsulation of MEMS devices , 2003 .

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

[37]  Farshid Raissi,et al.  The application of fine-grained, tensile polysilicon to mechanicaly resonant transducers , 1990 .

[38]  Robert Puers,et al.  The characterization of a miniature silicon micromachined capacitive accelerometer , 1997 .

[39]  R. Wolffenbuttel,et al.  Vacuum sealing of microcavities using metal evaporation , 1997 .

[40]  M. Holi,et al.  In vivo assessment of osteoporosis in women by impulse response technique , 2003, TENCON 2003. Conference on Convergent Technologies for Asia-Pacific Region.

[41]  K. Najafi,et al.  Localized silicon fusion and eutectic bonding for MEMS fabrication and packaging , 1998, Journal of Microelectromechanical Systems.

[42]  Yoshida Takashi,et al.  Three-dimensional micromachining of silicon pressure sensor integrating resonant strain gauge on diaphragm , 1990 .

[43]  Robert Aigner,et al.  “Cavity-Micromachining” Technology: Zero-Package Solution for Inertial Sensors , 2001 .

[44]  G. Van der Perre,et al.  Potential of incorporated accelerometers for the in vivo assessment of hip stem loosening , 1994, Other Conferences.

[45]  T. Keller,et al.  Neuromechanical characterization of in vivo lumbar spinal manipulation. Part I. Vertebral motion. , 2003, Journal of manipulative and physiological therapeutics.