| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Monday Sessions |
| Session TF-MoA |
| Session: | Emerging ALD Applications |
| Presenter: | T. Ryynänen, Tampere University of Technology, Finland |
| Authors: | T. Ryynänen, Tampere University of Technology, Finland J. Lekkala, Tampere University of Technology, Finland L. Ylä-Outinen, University of Tampere, Finland S. Narkilahti, University of Tampere, Finland J. Hämäläinen, University of Helsinki, Finland M. Leskelä, University of Helsinki, Finland |
| Correspondent: | Click to Email |
We promote atomic layer deposition (ALD) and especially ALD deposited iridium oxide (IrOx) thin film [1] as a novel alternative to improve electrical characteristics of microelectrode arrays (MEAs) used in stem cell and other tissue engineering applications. The additional microelectrode coating on microelectrode base material is traditionally used to decrease impedance and noise levels, and to increase charge transfer capacity of microelectrodes in MEAs. However, most of the common microelectrode coatings suffer from certain drawbacks. For example 1) electrochemical activation used to decrease the impedance of sputtered IrOx by one decade is not applicable for long term cell measurements due to rather fast deactivation, 2) widely used electrodeposited platinum (Pt black) suffers often from poor adhesion on underlying microelectrode base material, and 3) lately actively studied carbon nanotube (CNT) coatings still have unsolved issues related to difficult fabrication processes and concerns about biocompatibility and long term adhesion. Thus there is obvious demand for another stable solution in addition to sputtered titanium nitride (TiN) thin film favored by one of the leading commercial MEA manufacturers.
In our initial studies the about 120 nm thick ALD IrOx layer decreased the impedance of 30 µm diameter titanium microelectrodes down to 450 kΩ at 1 kHz, which is several times less than without the coating and consistent with the impedance reported for unactivated sputtered IrOx coated microelectrodes [2]. Stem cell growth experiments performed with human embryonic stem cell derived neuronal cells (hESC-N) [3, 4] showed that in field potential measurements ALD IrOx thin film decreases the noise level significantly compared to non-coated microelectrodes. Also, no biocompatibility or adhesion problems were detected. Even if already as such the ALD IrOx thin film clearly improves the MEA performance, we expect that by optimizing the thin film thickness and ALD process parameters from the default 3000 cycles of Ir(acac)3 and ozone, the impedance level of the ALD IrOx coated microelectrodes can be decreased even further. Thus impedance levels of 100 kΩ and below could be reached, which would make ALD IrOx thin film a strong competitor for the other commonly used microelectrode coatings. In addition to offering an economical, easily controllable, and highly reproducible fabrication process for a thin film improving the electrical characteristics of MEAs, ALD technology may in the future offer also other interesting coating solutions for cell culturing platforms, for example controlling cell growth via functionalized coatings.
[1] J. Hämäläinen et al., Chem. Mater. 20 (2008) 2903.
[2] S. Gawad et al., Front. Neuroeng. 2 (2009) 1.
[3] R. Lappalainen et al., Regen. Med. 5 (2010) 749.
[4] T. Heikkilä et al., Exp. Neurol. 218 (2009) 109.