Takashi Katsumata

High Accuracy Yaw Rate Sensor for Preventive Safety System

With a recent growing awareness of vehicle safety, the need for preventive safety systems is also increasing. This has promoted the practical use of new preventive safety systems, notably Adaptive Cruise Control (ACC) and Lane Keeping Assist (LKA) and the compulsory installation of existing preventive safety systems such as Electronic Stability Control (ESC) in all vehicles. In ESC and other preventive safety systems, tracking of actual vehicle behavior is important, and the yaw rate sensor is a key sensor necessary to keep track of the behavior. The need for high-accuracy yaw rate sensors has been increasing day by day in the context of the practical use of new preventive safety systems and the need for upgrading existing preventive safety systems. We have already implemented the capacitive accelerometer for air bags that features an element configuration using a general-purpose single-crystal SOI wafer, and a stacked structure comprising a sensor chip and a circuit chip. This time we have successfully developed a high-accuracy yaw rate sensor by applying the technology of the capacitive accelerometer. (1) Optimization of the sensor element configuration (using a frame structure to reduce leakage vibrations). (2) Flip-chip bonding of the sensor chip and the circuit chip using a cross layout to achieve both the reduction of heat deformation/parasitic capacity and the avoidance of interference between resonance frequencies. Utilizing the above two techniques has enabled us to achieve the high accuracy of the yaw rate sensor. As a result, we have developed a yaw rate sensor with a zero-point accuracy of ±3°/s (actual value: ±0.5°/s) in the ±100°/s range.