Transparent Indium Tin Oxide Microelectrode Arrays for Measuring Beating Cardiomyocytes

This thesis study was made, to develop the microfabrication process for transparent microelectrode arrays (MEAs) using indium tin oxide (ITO). This was done in order to measure bioelectrical data from cardiomyocytes (CMs), without owing any obscurities due to electrodes, as it happens in the conventional MEAs. The study was carried out in three tier (parts) fashion, wherein the 1st tier was dedicated in development of transparent ITO films. The 2nd tier involved with, the transparent ITO films that were developed in the 1st tier, to be patterned into microstructures present in the MEAs. The 3rd and the final tier dealt with two important tasks. The first including, optimizations needed in the previous two tiers, in order to come up with a viable microfabrication process to develop transparent ITO MEAs. The second task of the 3rd tier covered all the necessary testing required to ensure for the best possible quality of measurements of the bioelectric signals. The study showed that the ITO layers developed had very good transparencies of more than 90% transmissions possible, with sheet resistances in the range of 13-46 Ω/sq. The results from cell experiments showed that the MEAs not only measured electrical signals of cardiomyocytes aggregates but also owed no obscurities via microscopes, in the process. The electrode impedance measurements showed that the electrodes were comparable with commercially available ITO MEAs with mean values of 1200 kΩ. The measurements of noise levels were measured in reference to a commercial titanium nitride (TiN) MEA and the noise levels were comparable. Data from other literature studies was compared to ITO electrodes from this study to theirs, it was discovered that noise levels from this study were much better than their ITO electrodes and even certain gold (Au) electrodes. The process for ITO layer deposition was done using electron beam physical vapour deposition (EB-PVD), and later the annealing was made at temperatures from 300-500 °C. The MEA microfabrication of the ITO layers was done, by dry etching the ITO layers using reactive ion etching (RIE) device through argon. The insulation layer of silicon nitride was deposited using plasma enhanced chemical vapour deposition (PECVD) process by the personnel at the Optoelectronic Research Centre (ORC) of Tampere University of Technology. The insulation layer was also patterned using dry etching, by the same device. The beating cardiomyocyte and noise measurements were done at BioMediTech