Microlever with combined integrated sensor/actuator functions for scanning force microscopy

A novel silicon microfabricated sensor head for the scanning force microscope (SFM) is presented. The force sensor consists of a cantilever and an adjacent counter-electrode forming the two plates of a capacitor. Force-induced cantilever deflections are monitored by capacitive detection. Typical lever dimensions of 800 um x 40 um and a gap of 3 um yield an active sensing capacitance C=O.l pF. The expected sensitivity in terms of vertical cantilever motion is dC/dz=10 fF/m. In addition to the sensing capability, the microlever can also be z-actuated by applying controlled voltages. This allows both the tip-to-sample distance and the cantilever/system compliance to be adjusted. Expressions are derived for the amplitude of cantilever deflections under electrostatic actuation in the static and dynamic modes as pertinent to applications of SFM in the contact and non-contact modes. The microlever is fabricated using silicon bulk- and surface-micromachining techniques including fusion bonding and sacrificial layer etching. First measurements of the static and dynamic deflections of cantilevers are analysed and show promising results. The reported device basically represents a module of an SFM microsystem with integrated cantilever deflection sensor and adjustment capability