Integrated microelectrode pore cavity device in silicon (111)

We present a novel approach for the fabrication of single pore microcavities in silicon (111) based on Silicon-on-Insulator substrates and a combination of optical and electron-beam lithography, reactive ion etching and anisotropic wet etching techniques. Using a dedicated sequence of physical vapor deposition, electroplating and surface chemical oxidation, a silver/silver chloride (Ag/AgCl) reference bottom electrode was integrated into the cavity. We have fabricated cavities of volume ∼180 fl terminated at their top with silicon-nitride membranes featuring a single access pore of diameter 150-500 nm, each. Scanning electron microscopy revealed the cavity structure to comprise a hexagonal geometry top silicon nitride membrane and a triangular bottom plane. Atomic force microscopy analysis was performed on the AgCl surface, showing a root-mean-square surface roughness of 43.5 nm, hence resulting in a favorable high surface area of the electrode. We fully characterized our cavities filled with potassium chloride electrolyte solutions in electrical measurements to verify functionality of the integrated reference electrodes. Measured ion currents were stable over 1 d and scaled properly with pore diameter and salt concentration. We suggest our device to serve as platform for the controlled investigation of (bio-) electrochemical processes in smallest confined volumes.