Community Research and Development Information Service - CORDIS

Prototypes of atomic force microscopy probes for electrical measurements in liquid media

Prototypes of Atomic Force Microscope probes for electrical measurements in liquid media have been designed and fabricated.

The structure of the probes is a cantilever in the plane surface of a silicon chip with a tip in the upward direction at its end. They include a conducting layer for electrical measurements. The cantilevers are fabricated on silicon nitride with the tip made of polycrystalline silicon. The conducting layer is gold for biocompatibility reasons.

In the fabrication process the following aspects have been implemented:
- The backside photolithography is made at the beginning, before the fabrication of the tip, to avoid damaging the tips.

- A metallisation scheme conssting of 2 nm Cr to improve the adhesion of gold plus 20nm Au has been used, to avoid etching problems with the initial one (Ti/Ni/Au);

-The thicknesses of the silicon nitride layers has been corrected to improve the residual stress behaviour of the cantilever. The new values are 250nm for the structural layer and 200 to 300nm for the passivation layer;

- An innovative photolithography method to eliminate the passivation dielectric layer only at the apex of the tip, thus avoiding parasitic parallel current paths near the cantilever tip when measuring in an aqueous medium. The method is based on depositing a thick photoresists that covers the chip but not the tip apex.

The structure of the chips containing the cantilevers is defined by wet silicon micromachining, to avoid the silicon wafer sawing process that would damage the fragile cantilevers and tips. Chips have been designed with both rectangular and V-shaped cantilevers, with spring constants ranging from 0.01N/m to 1N/m, suitable for contact mode scanning of biological samples. Cantilever lengths range from 150 to 300m and widths from 30 to 60um.

Related information

Result In Brief

Reported by

08193 Bellaterra
Follow us on: RSS Facebook Twitter YouTube Managed by the EU Publications Office Top