Ultrathin, dual-sided silicon neural microprobes realized using BCB bonding and aluminum sacrificial etching

This paper presents an innovative fabrication process for dual-sided silicon-based microprobe arrays using (i) temporary wafer bonding applying B-staged bisbenzo-cyclobutene (BCB), (ii) wafer grinding, (iii) deep reactive ion etching (DRIE), and (iv) the electrochemical removal of a sacrificial aluminum layer. The dual-sided microprobes comprise aligned electrodes on the front and rear of 120-μm-wide and only 50-μm-thick probe shafts. The temporary BCB bonding to a glass substrate is compatible with process temperatures up to 300°C and with DRIE. Furthermore, dual-side mask alignment is enabled by the high optical transparency of both the glass substrate and the BCB bonding layer. Even at this exploratory stage, probes realized using this process sequence have exhibited a yield of functional electrodes of better than 96% after probe assembly. Initial in vivo electrophysiology recordings in a rat brain have demonstrated an satisfactory probe performance.