A Ferroelectric CMOS Microelectrode Array with ZrO₂ Recording and Stimulation Sites for In-Vitro Neural Interfacing

Abstract

A CMOS-based microelectrode array (CMOS-MEA) is presented, where a 10-nm-thick antiferroelectric ZrO2 layer is deposited in the post-CMOS process as functional electrode coating for 4225 recording sites and 1024 stimulation sites. Voltage noise measurements of the ZrO2 recording sites of the CMOS-MEA show reduced noise levels as compared to the same CMOS-MEA with uncoated TiN electrodes. Moreover, neural recordings of spontaneous activity of retinal ganglion cells reveal full functionality and biocompatibility of the insulating ZrO2 interface material. The stimulation current of the ZrO2 ferroelectric microelectrodes is investigated by applying triangular voltage signals to the stimulation sites of the CMOS-MEA. Up to voltage amplitudes of 3.2 V, the stimulation current consists of displacement current only, electrochemical (Faradaic) DC currents are suppressed. For voltage amplitudes above 2.2 V, we observe a voltage-dependent increase in the stimulation current which we attribute to the ferroelectric properties of the ZrO2 insulated microelectrodes. However, the enhancement of the charge injection capacity (CIC) of the insulated microelectrodes is below the full potential of antiferroelectric ZrO2 and requires further optimization. Nevertheless, our results demonstrate the potential of ferroelectric CMOS-MEAs for safe and efficient neural recording and stimulation.