RESUMO
Plasma-enhanced atomic layer deposition (PEALD) is utilized to improve the barrier properties of an organic chip-film patch (CFP) when it is used as an implant to prevent moisture and ions from migrating into the embedded electronic circuits. For this purpose, surface condition and material properties of eight modifications of Al2O3-TiO2 nanolaminates sequentially deposited on polyimide PI-2611 films are evaluated in detail. The effect of stress-induced warpage of the deposited Al2O3-TiO2 on the wafer level is calculated with the Stoney equation and reveals higher tensile stress values while increasing the thickness of Al2O3-TiO2 nanolaminates from 20 up to 80 nm. Contact angle measurement and atomic force microscopy are used to investigate the surface energy and wettability, as well as the surface morphology of polyimide-Al2O3-TiO2 interfaces. We show that plasma treatment of pristine polyimide leads to an enhanced adhesion force of the PEAL-deposited layer by a factor of 1.3. The water vapor transmission rate (WVTR) is determined by exposing the coated polyimide films to 85% humidity and 23 °C and yields down to 1.58 × 10-3 g(H2O)/(m2 d). The data obtained are compared with alternative coating processes using the polymers parylene-C and benzocyclobutene (BCB). The latter shows higher WVTR values of 1.2 × 10-1 and 1.7 × 10-1 g(H2O)/(m2 d) compared to the PEALD-PI-2611 systems, indicating lower barrier properties. Two Al2O3-TiO2 modifications with low WVTR values have been chosen for encapsulating the CFP substrates and exposing them in a long-time experiment to chemical and mechanical loads in a chamber filled with phosphate-buffered saline at 37 °C, pH 7.3, and a cyclically applied pressure of 160 mbar (â¼120 mm Hg). The electrical leakage behavior of the CFP systems is measured and reveals reliable electrical long-term stability far beyond 11 months, highlighting the great potential of PEALD-encapsulated CFPs.
RESUMO
Presbyopia describes the eye's physiological loss of the ability to see close objects clearly. The adaptation to different viewing distances, termed accommodation, is achieved by a change in the curvature of the eye lens induced by the ciliary muscle. A possible approach to correct presbyopia could be to detect the ciliary muscle's neuromuscular signals during accommodation and transfer these signals electronically to a biomimetic, micro-optical system to provide the necessary refractive power. As a preliminary step toward such a described system, a novel three-dimensional and biocompatible lift-off method was developed. In addition, the influence of the distance between the electrically conducting surfaces of the lens on the accommodated signal amplitudes was investigated. Compared to the conventional masking methods, this process has the advantage that three-dimensional surfaces can be masked with biocompatible gelling sugar by utilizing a direct writing process with a dispensing robot. Since gelling sugar can be used at room temperature and is water-soluble, the process presented is suitable for materials that should not be exposed to organic solvents or excessively high temperatures. Apart from investigating the shrinkage behavior of the gelling sugar during the physical vapor deposition (PVD) coating process, this paper also describes the approaches used to partially coat a commercial scleral contact lens with an electrically conductive material. It was shown that gelling sugar withstands the conditions during the PVD processes and a successful lift-off was performed. To investigate the influence of the spacing between the electrically conductive regions of the contact lens on the measured signals, three simplified electrode configurations with different distances were fabricated using a 3D printer. By testing these in an experimental setup, it could be demonstrated that the distance between the conductive surfaces has a significant influence on the amplitude. Regarding the described lift-off process using gelling sugar, it was found that the dispensing flow rate has a direct influence on the line uniformity. Future work should address the influence of the viscosity of the gelling sugar as well as the diameter of the cannula. It is assumed that they are the prevailing limitations for the lateral resolution.
