SOI 3-axis accelerometer with a stress reduction structure

We developed a novel stress reduction structure (SRS) for a capacitive SOI 3-axis accelerometer for the advanced motion control of automobiles and robots. To improve the stability of the sensor output against temperature change, an FEM thermal stress analysis was carried out on a model with a sensor chip, a circuit board, and a package. The FEM results showed that the thermal stress caused by the different coefficients of thermal expansion bent the sensor chip and produced a change in the z-electrode gap. The zero output drift especially in the Z-axis direction by sensor chip bending should be minimized. The SRS was composed of grooves in both the lower and upper Si layers around the detection part of the sensor. Two types of low-stiffness suspensions for stress reduction and for wiring were formed in either the upper or the lower Si layer to connect both sides of the grooves. The experimental results showed that the ratio of zero output drift decreased by a factor of 8.9 by using the proposed SRS.