A bulk-micromachined three-axis accelerometer using silicon direct bonding technology and polysilicon layer

A three-axis piezoresistive accelerometer has been fabricated by bulk-micromachining and SDB (silicon direct bonding) technologies using a polysilicon layer. The results of FEM (finite-element method) simulation for each acceleration direction have been utilized to detect the three-dimensional acceleration and eliminate cross-axis sensitivities. The relative changes of resistance as a function of temperature in LPCVD polysilicon layers with boron implantation dose are described. TCO (temperature coefficient of offset) shifts for the X-, Y- and Z-axis Wheatstone bridge outputs are only about 0 to 0.07, 0.028 to -0.016 and 0.007 to -0.004 %F.S. in the 25-160 degrees C range, respectively. The resonance frequencies of the fabricated accelerometers are 6.560, 8.930 and 18.350 kHz at the first, second and third mode, respectively. The sensitivities of the fabricated sensor for X-, Y- and Z-axis acceleration are about 0.276, 0.226 and 0.793 mV (Vg)(-1) at room temperature. The cross-axis sensitivity for X-, Y- and Z-axis acceleration is about 0.01 mV (V g)(-1), which represents the elimination of cross-axis sensitivities, as designed. (C) 1998 Published by Elsevier Science S.A. All rights reserved.