Patterned Piezoresistive Silicon Strain Gauge Devices for Use in Low Power Applications

Component monitoring systems are currently being developed to measure strain in rotating helicopter parts. The rotating nature of these parts requires the use of wireless nodes to record and transmit strain data to the rest of the component monitoring system. Power consumption is a key challenge in these systems, as they must operate for an extended period on internal or harvested energy. The focus of this work was to develop patterned piezoresistive silicon strain gauge sensors for use in low power systems. The piezoresistive properties of silicon are reviewed along with current piezoresistive strain gauge devices. First and second generation strain gauge devices are designed, fabricated and tested. An issue common to all bonded strain gauges is the strain transfer between the part and the gauge. This is especially important for bonded silicon gauges due to the transverse sensitivity of silicon and differences in mechanical properties of silicon and a metal part. Two models are developed to find the stress distribution on the surface of the silicon die when bonded to a strained part. Results from these models show the effect of Poisson ratio mismatch, die thickness, adhesive thickness and sensor location on strain sensitivity. The measured response from the second generation strain gauge is compared to the simulations. This shows that the fabricated strain gauge is working as expected.