CMOS micromachined probes by die-level fabrication for extracellular neural recording

In this paper, we present the design, fabrication and characterization of CMOS micromachined probes for extracellular neural recording. A convenient fabrication process is proposed for making integrated recording probes at the die level, providing a low-cost solution for academic research as compared to the more expensive wafer-level approach adopted in prior work. The devices are fabricated in a standard 0.35 µm CMOS process, followed by post-CMOS micromachining steps to form the probes. The on-chip circuit, used for recording action potential signals of neural activities, provides a stable dc bias when operating in electrolyte. The subthreshold transistor at the circuit input provides a tunable resistance value between 10 MΩ up to GΩ. The circuit consumes a total power of 790 µW and has an output noise of 19.3 µV Hz −1/2 at 100 Hz. The recorded action potential from the stimulated ventral nerve cord of a crayfish is about 0.6 mV with a pulse width of about 1.2 ms.