Development of wafer-level batch fabrication for combined atomic force–scanning electrochemical microscopy (AFM–SECM) probes

This study presents a wafer-level batch fabrication process for the integration of ring microelectrodes into atomic force microscopy (AFM) probes recessed from the apex of the insulating tip. Such integrated probes record electrochemical data at a defined and deliberately selected distance from the sample surface, while simultaneously imaging the sample topography. Three hundred and twenty four combined AFM–SECM probes are fabricated from a 4″ SOI (silicon on insulator) wafer using standard IC batch microfabrication processes without adopting any sequential writing-type procedures such as focused ion beam (FIB) milling/deposition or electron beam lithography (EBL). Low cost and high reproducibility of the batch fabrication process renders these combined probes highly suitable for imaging of multiple sample surface properties. Degradation effects of such bifunctional probes resulting from mechanical wear or electrode fouling, which may be experienced by AFM–SECM probes having the electroactive area exposed at the tip apex are avoided by using silicon carbide as AFM tip material, and by recessing the electroactive area from the tip apex. In addition, this design enables a constant electrode-to-sample distance during electrochemical imaging. The functionality of the developed bifunctional batch-fabricated AFM–SECM probes was demonstrated by imaging a platinum disk microelectrode, and comparing the obtained topological image quality with images obtained by conventional silicon nitride AFM probes.