Polymer-based cantilevers with integrated electrodes
An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-um-thick photo-structured layer for the cantilever, and a 200-um-thick layer for the chip body. The releasing method is based on dry etching of a 2-um-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-um-long and 100-um-wide SU-8 cantilever were fabricated and tested.We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2x2 um2 Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of =1 N/m and a resonance frequency of=17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200 ohm, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 uT/Hz^1/2 at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications.