Heterosystem-integrated carbon nanotube sensors for on-ASIC condition monitoring

This work demonstrates modular integrability of CNT-based nanodevices on top of the BEOL interconnect stack of a conventional ASIC enabling additional condition monitoring features in the framework of advanced prognostic health monitoring concepts. We highlight in particular a Nanoelectromechanical system (NEMS) technology featuring suspended CNTs with controllable prestrain to ensure detectability of smallest strain variation along with changes in the packing environment. The NEMS is generated by a CMOS-compatible surface micromachining process flow making use of a relaxation of prestrained layer stacks after local removal of a sacrificial-layer. Corresponding critical dimensions and design are derived from FE-simulations. The impressed strain into the nanomaterial is confirmed by Raman spectroscopy. According to this analysis, the CNT specific G-band exhibits a clear blue shift of 6.2 cm-1 upon membrane release indicating on axially acting tensile strain between up to 0.8%. For the piezoresistive sensors this corresponds to a significant reduction of the strain detection limit to 30 MPa and gauge factor of up to 644, which is around 5 times higher than for conventional Si-based strain gauges.