A Compact Eight-terminal Piezotransducer for Stress Measurements in Silicon
Keywords:Piezoresistance Sensors, Strain-Stress Chip
Deformations in the crystalline structure have an important impact in electric characteristics of the semiconductors, like carrier mobility and concentration. Since mechanical stress and strain are related, an induced stress in silicon chips compromise the performance and structural integrity of Integrated Circuits (ICs). Reason why stress sensing devices are becoming important tools to detect and correct stress related problems, improving the performance and yield of ICs. This work shows the design and characterization of an Eight Terminals Silicon Piezotransduzer (8TSP), a stress sensor device based on the piezoresistive effect and designed to estimate the stress state over the (100) silicon surface. The multi-terminal device integrates a resistor rosette in a single octagonal plate, allowing to change the bias direction and to take measure in different orientations, the relationship between those observations can be used to estimate both direction and magnitude of the stress in a certain area. In order to characterize the device, a four-point-bending apparatus using a circular substrate has to be 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.