Paper TF-MoA11
ALD Barriers for Protection of Electronic Devices in Biological Environment

Monday, October 30, 2017, 5:00 pm, Room 20

Encapsulation plays a significant role in the protection and lifetime enhancement of electronic devices. Devices like OPVs, OLEDs, biological implants, and thin film solar cells are susceptible to rapid degradation on exposure to the surrounding media containing moisture and ionic species. Encapsulation barriers hermetically seal the devices and thus, prevent the ingress of moisture or any other fluid that can affect the function and stability of the devices. It involves use of inorganic barrier layers deposited using vacuum deposition processes. Out of several vacuum deposition techniques used for this purpose, atomic layer deposition (ALD) has shown an outstanding performance by producing films which have water vapor transmission rate less than 10^-4 g/m²/day. However, the performance and reliability of ALD barrier films is subject to their stability and resistance to corrosion in the surrounding environment.

Recently, miniaturized medical devices have gained popularity because of their new treatment and monitoring capabilities, ease of application and enhanced portability. These devices include artificial pacemakers, cochlear implants, artificial heart valves, etc. These devices are exposed to different bodily fluids that have varying pH and salt concentrations. Any electronic device cannot be expected to last for long enough time to be used as an implant with any protective covering. Thus, it becomes imperative to look for a robust solution.

In this work, we explore the use of different metal oxides deposited using ALD at 100°C in biological environment. The materials include Al₂O­₃, HfO₂, TiO₂ and ZrO₂. Chemical stability of the ALD films is determined by using electrochemical impedance spectroscopy (EIS) whereas, biocompatibility of the ALD films is determined using MTT cell proliferation assay measurements. For chemical stability test using EIS, a 3 electrode setup was used to understand the mechanism of material degradation. The ALD deposited materials were exposed to phosphate buffer saline (PBS) solution, simulated sweat and saliva, and Dulbecco's Modified Eagle Medium (DMEM) for 21 days. Besides ALD Al₂O₃, other metal oxides have demonstrated enhanced corrosion resistance and stability in different solutions. ALD HfO₂ has better stability as compared to ALD Al₂O₃ but tends to develop crack with long exposure time. However, ALD TiO₂ and ZrO₂ were found to be most stable in all the biological solutions used for testing. All the ALD materials used during the test have been found to be biocompatible using MTT cell proliferation test. Finally, we demonstrate the application of these ALD materials for protection of active implantable devices.