Fabrication and characterization of microsieve electrode array (μSEA) enabling cell positioning on 3D electrodes

Here the fabrication and characterization of a novel microelectrode array for electrophysiology applications is described, termed a micro sieve electrode array (μSEA). This silicon based μSEA device allows for hydrodynamic parallel positioning of single cells on 3D electrodes realized on the walls of inverted pyramidal shaped pores. To realize the μSEA, a previously realized silicon sieving structure is provided with a patterned boron doped poly-silicon, connecting the contact electrodes with the 3D sensing electrodes in the pores. A LPCVD silicon-rich silicon nitride layer was used as insulation. The selective opening of this insulation layer at the ends of the wiring lines allows to generate well-defined contact and sensing electrodes according to the layout used in commercial microelectrode array readers. The main challenge lays in the simultaneously selective etching of material at both the planar surface (contact electrode) as well as in the sieving structure containing the (3D) pores (sensing electrodes). For the generation of 3D electrodes in the pores a self-aligning technique was developed using the pore geometry to our advantage. This technique, based on sacrificial layer etching, allows for the fine tuning of the sensing electrode surface area and thus supports the positioning and coupling of single cells on the electrode surface in relation to the cell size. Furthermore, a self-aligning silicide is formed on the sensing electrodes to favour the electrical properties. Experiments were performed to demonstrate the working principle of the μSEA using different types of neuronal cells. Capture efficiency in the pores was >70% with a 70% survival rate of the cell maintained for up to 14 DIV. The TiSi₂-boron-doped-poly-silicon sensing electrodes of the μSEA were characterized, which indicated noise levels of <15 μV and impedance values of 360 k. These findings potentially allow for future electrophysiological measurements using the μSEA.