A compact eigth-terminal piezotransducer for stress measurements in silicon

Mechanical stress compromise the performance and structural integrity of Integrated Circuits (ICs). Stress-sensing devices are becoming important tools to detect and correct stress related problems, improving the performance and yield of ICs. This works introduces a new Eight Terminals Silicon Piezotransducer (8TSP) fabricated using a commercial CMOS process, designed to measure the stress state on the (100) silicon surface. Each sensor integrates a resistor rosette in a single octagonal plate, and the complete stress state can be estimated by the relation between the resistance change in different directions, since the change of resistivity in silicon can be related to mechanical stress by the piezoresistive effect. In order to characterize the device, a four-point-bending apparatus using a circular substrate was designed to have control of both magnitude and direction of the applied uniaxial stress. The device was attached to a disk and stress was applied in the main crystallographic directions to observe the piezoresistance characteristics and calibrate the sensor. We applied stress in some other directions and the stress behavior fit the predicted by the theory. Those results confirm that the 8TPS can be used to find the stress state over the surface of a silicon chip.