Sensitivity Enhancement in Vacuum Packaged Resonant MEMS Strain Sensors with On-Chip Strain Amplification Mechanism

A new strain sensor design based on vacuum packaged Double-Ended Tuning Fork silicon resonators with a strain amplification mechanism is presented. The sensors are fabricated with a Silicon On Insulator MEMS process including a thin-film vacuum encapsulation technology that permits to obtain high-Q resonators operating at a vacuum level around 160 mTorr. Within the encapsulation, a strain amplification structure consisting in a long beam connected to the DETF resonator is integrated in order to increase the sensitivity of the device to the applied strain. Thanks to such amplification, an unprecedented sensitivity of
$200 \text{Hz}/\mu\varepsilon$
in bending tests on steel is demonstrated, operating the sensors in closed loop with an external readout circuit.