| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF-WeM |
| Session: | Thin Films for Encapsulation, Packaging, and Biomedical Devices |
| Presenter: | A.M. Coclite, Massachusetts Institute of Technology |
| Authors: | A.M. Coclite, Massachusetts Institute of Technology F. De Luca, Massachusetts Institute of Technology K.K. Gleason, Massachusetts Institute of Technology |
| Correspondent: | Click to Email |
Encapsulant barrier coatings, which prevent the permeation of water through flexible plastic substrates, are an enabling technology for the commercialization of OPV devices. Such protective coatings are made of multilayer stacks where multiple dense, inorganic layers are alternated with soft, organic ones. The inorganic layer contains inevitably some pinholes and defects. The roles of the organic layer are creating a tortuous and longer path among the defects of two successive inorganic layers, filling the pores of the inorganic underlayer limiting the propagation of defects from one inorganic layer to the other and smoothening the substrate surface roughness.
We obtained good barrier properties (WVTR= 10-2 g/cm2/day at 25°C, RH=85%) with a bilayer obtained by coupling initiated-PECVD (iPECVD) and plasma enhanced CVD (PECVD) at very low thickness of inorganic layer (25 nm).
SiOx layers were deposited through PECVD in MW plasma at high power and high oxygen dilution. The silanol and organic groups were not detectable by IR spectroscopy, resulting in dense film with high flexibility and high critical tensile strain. High critical tensile strain implies that the coating can be bent and stretched to a relatively big extent before cracking. Inorganic films obtained by other technologies (i.e. Al2O3 ALD coatings) showed smaller critical strain values.
Organic coatings were deposited through a new process named iPECVD with enhanced monomer structure retention compared to a conventional plasma deposition and faster deposition rate if compared to conventional iCVD processes from organosilicon monomer. The deposition conditions were tuned to obtained good planarizing properties. The deposition of planarizing organic layers was demonstrated by depositing the coating on the top of some microspheres (1 µm in diameter) which served as model defects on the surface. Increasing the thickness of the coating, the degree of planarization (DP), both local (DLP) and global (DGP), increases. The DLP increases much faster than the DGP: when the coating is 1µm-thick the DLP is already 99%, for the global planarization instead a 1.8µm-thick-coating is needed to reach DGP= 99%.
The great advantage of a similar approach is that we deposit the multilayer in a large-area reactor, maintaining the same organosilicon precursor and the same reactor configuration for both deposition of silica-like and organosilicon layers. A detailed investigation of the barrier and mechanical properties changing the number of layers in the stack and the measurements conditions will be presented in order to demonstrate the robustness of the following approach to create flexible ultra-high barrier layer.