Full platinum nanoprobes for electrically conducting scanning probe methods

Recently electrically conducting SPM probes were used as read/write sensor of magneto-resistive nanopillars and ferroelectric domains in the development of >1 Tb/inch2 data storage. Since metal coated (platinum (Pt) or Pt/iridium) silicon (Si) probes are not suitable at high current densities, probes with an entire metallic tip and high electrical conductivity (i.e. low contact resistance) form a solution. We present the fabrication and characterization of hybrid SPM probes with full metallic cantilever and tip. The body of the probes consists of the photopolymer SU-8. Recently, we presented the fabrication and analysis of a SPM probe with full tungsten cantilever and tip, based on a back-side KOH release principle. Here, we present a probe with Pt as the cantilever-tip material, based on a top-side dry release. The Pt tip has a radius of curvature below 20 nm. A tip sharpness controlling method is presented. The process is based on a surface molding technique where a pyramidal mould made in KOH solution is used to form the tip. Oxidation sharpening of the mould yields very sharp tips. Sputter deposition guarantees with its good step coverage an excellent mould filling with Pt. Stress control in the metal layer is important for straight cantilevers and is done by adjustment of deposition parameters. After a dry structuring of the cantilever, a double layer of SU-8 is used to form the body of the probe, consisting of a 10-um-thick and a 200-um-thick layer, respectively. Proper surface treatment prior to SU-8 spinning ensures a good adhesion between the SU-8 and the metal. The use of SU-8 forms a substantial advantage over bonding or Si-etching techniques. The open honey-comb body structure of the body keeps the body rigid and enables a top-side dry etch release. AFM imaging has been shown and IV analysis of the probes on a gold sample was performed. The measured contact resistance between tip and substrate values around 10 Ohm. This is one order of magnitude lower than for metal coated probes. The Pt probe shows reproducible curves at currents higher than 10 mA, as needed for switching of magneto-resistive nanopillars. Due to the low contact resistance, Joule heating of the tip remains limited, preventing melting of the tip. Besides use in future data storage, the probes are promising in contact and non contact mode (e.g. Kelvin Probe Microscopy).