Strain Transfer Analysis of Surface-Bonded MEMS Strain Sensors

The transmission of strain fields in adhesively bonded MEMS strain sensors is analyzed. In strain sensors that are attached to host structures using adhesive layers such as epoxy, complete strain transfer to the sensor is hindered due to the influence of the adhesive layer on the transfer. This paper presents an analytical model, validated by finite element method simulation, to provide insight and accurate formulation for strain transfer mechanism for bonded sensors. A shear-lag parameter has been introduced to account for the component geometry and properties. The model is capable of predicting the strain transmission ratio through a sensor gauge factor, and it clearly establishes the effects of the flexibility, length, and thickness of the adhesive layer and MEMS sensor substrate. Finally, modifications to sensor substrates, by the implementation of micromachined tapered edges and trench etching, are proposed in order to increase the strain transmission ratio. It has been found, for the selected case study, that the sensor sensitivity could be enhanced by up to 30%. This work on bonding analysis is applicable for performance prediction and calibration in sensor systems design.