Defect prevention in silica thin films synthesized using AP-PECVD for flexible electronic encapsulation

Abstract

Abstract. Industrially and commercially relevant roll-to-roll atmospheric pressure-plasma enhanced chemical vapour deposition was used to synthesize smooth, 80 nm silica-like bilayer thin films comprising a dense 'barrier layer' and comparatively porous 'buffer layer' onto a flexible polyethylene 2,6 naphthalate substrate. For both layers, tetraethyl orthosilicate was used as the precursor gas, together with a mixture of nitrogen, oxygen and argon. The bilayer films demonstrated exceptionally low effective water vapour transmission rates in the region of 6.1×10 -4 g m -2 day -1 (at 40°C, 90% relative humidity), thus capable of protecting flexible photovoltaics and thin film transistors from degradation caused by oxygen and water. The presence of the buffer layer within the bilayer architecture was mandatory in order to achieve the excellent encapsulation performance. Atomic force microscopy in addition to solvent permeation measurements, confirmed that the buffer layer prevented the formation of performance-limiting defects in the bilayer thin films, which likely occur as a result of excessive plasma-surface interactions during the deposition process. It emerged that the primary function of the buffer layer was therefore to act as a protective coating for the flexible polymer substrate material.

The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

“…The static films were deposited for 60 s on a silica buffer layer which served as a protective layer to prevent any plasma interaction with the bare PEN foil [4]. The silica buffer was deposited at a precursor flow of 8.2 · 10 −3 slm and a web speed of 800 and 400 mm·min −1 , to prepare a thin protective layer of 20 and 40 nm [11,39]. For the WVTR measurements two types of dynamic films were deposited single barrier films and bilayer barrier films.…”

“…To further investigate the role of the defect formation mechanism at higher gas flows the bilayer architecture is investigated [5,39]. A porous so-called buffer layer is first deposited on the PEN substrate followed by a barrier layer deposited at different carrier gas flow rate Q = 5 to 40 slm.…”

“…·day −1 can be achieved for an effective barrier thickness of only 40 nm as the buffer layer is essentially characterized by a non-existent moisture barrier with a WVTR = 1 g·m −2 ·day −1 [39].…”

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers

“…With regard to materials, TFE studies performed using various inorganic-based materials such as SiO x and SiN x and Al 2 O 3 demonstrated superior encapsulation performance in many studies. , Al 2 O 3 , which can be degraded by hydrolysis under high-temperature and high-humidity conditions, has a disadvantage in terms of long-term reliability of the device . Another issue is the difficulty of dry etching of Al 2 O 3 with NF 3 or CF 4 reactive gas for cleaning the chamber wall from the point of maintenance of the mass-production large-area deposition equipment.…”

Open-Air Plasma-Deposited Multilayer Thin-Film Moisture Barriers

“…Multilayer thin-film barrier structures offer significant advantages compared to single layers yet retain compatibility with flexible devices . Alternating layers of inorganic and organic layers lead to synergistic effects: the inorganic layer effectively blocks moisture or oxygen, and the organic layer passivates defects such as pinholes in the inorganic layer while also smoothing out roughness on underlying layers. − As a result, multilayer structures demonstrate more impressive barrier properties and have achieved a 15× reduction in the oxygen transmission rate for OLED devices. Recent work has applied the multilayer barrier concept to perovskite solar cells. − In one example, a combination of aluminum-doped zinc oxide and atomic layer-deposited (ALD) tin oxide led to 350 h stability in ambient lab air conditions .…”