Low-Temperature Atomic Layer Deposited Oxide on Titanium Nitride Electrodes Enables Culture and Physiological Recording of Electrogenic Cells

Abstract

The performance of electrode arrays insulated by low-temperature atomic layer deposited (ALD) titanium dioxide (TiO 2) or hafnium dioxide (HfO 2) for culture of electrogenic cells and for recording of extracellular action potentials is investigated. If successful, such insulation may be considered to increase the stability of future neural implants. Here, insulation of titanium nitride electrodes of microelectrode arrays (MEAs) was performed using ALD of nanometer-sized TiO 2 or hafnium oxide at low temperatures (100-200 • C). The electrode properties, impedance, and leakage current were measured and compared. Although electrode insulation using ALD oxides increased the electrode impedance, it did not prevent stable, physiological recordings of electrical activity from electrogenic cells (cardiomyocytes and neurons). The insulation quality, estimated from leakage current measurements, was less than 100 nA/cm 2 in a range of 3 V. Cardiomyocytes were successfully cultured and recorded after 5 days on the insulated MEAs with signal shapes similar to the recordings obtained using uncoated electrodes. Light-induced electrical activity of retinal ganglion cells was recorded using a complementary metal-oxide semiconductor-based MEA insulated with HfO 2 without driving the recording electrode into saturation. The presented results demonstrate that low-temperature ALD-deposited TiO 2 and hafnium oxide are biocompatible and biostable and enable physiological recordings. Our results indicate that nanometer-sized ALD insulation can be used to protect electrodes for long-term biological applications.

Expression of Channelrhodopsin‐2 in Rod Bipolar Cells Restores ON and OFF Responses at High Spatial Resolution in Blind Mouse Retina

“…Here, CMOS‐MEAs [ 74 ] (CMOS‐MEA 5000, Multi Channel Systems MCS GmbH, 65x65 electrodes on 1 mm$$^{2}$$) were used without the top dielectric layer or with hafniumoxide [ 75 ] to image retinal activity. In addition, a so‐called sensor reset was implemented to prevent electrodes from drifting out of their working range.…”

Corrosion and Protection of Silicon Nitride Insulators in Microelectrode Array Applications

“…To ensure a consistent insulation performance throughout the cell culture period, a more chemically stable coating can be applied, as shown here. ALD TiO 2 layers have been applied for biological studies by Herrera-Morales [38] and more recently by Dollt et al [45]. In the latter, the approach was to form an insulating coating over the electrodes, which we did not see as beneficial due to the increased electrode impedance levels.…”

Extracellular electrical stimulation by ferroelectric displacement current in the switching regime

“…( 14) yields a CIC of 35.7 µC/cm 2 , which is dominated by the contribution 2P r . Therefore, another interesting CMOS compatible material class is Al 1−x Sc x N, which exhibit ferroelectric properties with P r up to 110 µC/cm 238 resulting in a CIC above 200 µC/cm 2 , which is in the range of previously reported stimulation-thresholds for small conductive microelectrodes (30 µm in diameter) 20 and which is approximately two orders of magnitude above the CIC of stateof-the-art capacitive microelectrodes [15][16][17][18][19] . Note, that the CIC of ferroelectric microelectrodes might be further increased by the fabrication of 3D structures 23 .…”

“…Here, the discovery of ferroelectricity in HfO 2 -based thin films represents a real breakthrough due to the full CMOS compatibility of this material class and outstanding ferroelectric properties at the nanoscale [23][24][25] . Moreover, conventional dielectric HfO 2 layers have been previously utilized in capacitive biochips 16,17,19 , which demonstrates their biocompatibility. Note, that materials with ferroelectric properties also exhibit dielectric properties but not vice versa.…”