Abstract
Keywords VSC, Acceleration Sensor, SOI, Stack structure, Safety system
Abstract - In order to reduce the traffic accident casualties, highly sophisticated safety system has been developed one after another and been mounted in vehicle, along with rising needs for car safety. Safety system is broadly classified as preventive safety and crash safety. Vehicle Stability
Control (VSC) and Antilock Brake System (ABS) represent preventive safety, and airbag represents crash safety. Acceleration sensor detecting acceleration applied to vehicle is indispensable to these systems, and is the key sensor for vehicle safety system. Especially VSC is an important system, which can control sideslip, unstable phenomenon nearly causing critical accident. VSC will be increasingly adopted for vehicles in the future. VSC detects the condition likely to cause sideslip, based on the data from steering angle sensor, yaw rate sensor and lateral acceleration sensor. Also it drives brake actuator and throttle actuator, and automatically controls brake oil pressure of each wheel and engine output.
We have already achieved airbag accelerometer, whose features are its element shape of versatile monocrystal SOI wafer and stack structure of stacked sensor chip and circuit chip. By applying this technology, we succeeded in developing high sensitivity and high accuracy both of which were the challenges for accelerometer.
High sensitivity is achieved by optimizing element shape (which means softening beam and increasing capacity between electrodes). High accuracy and high reliability are achieved by lowering Youngs Modulus of adhesive film of stack structure in order not to be sensitive to thermal stress or package stress. Furthermore, high accuracy is achieved by embedding temperature compensation circuit.
+/- 1.5G to +/-250G accelerometers were completed with same technology through this development.