Atmospheric pressure roll‐to‐roll plasma enhanced CVD of high quality silica‐like bilayer encapsulation films

Abstract

A glow like atmospheric pressure dielectric barrier discharge in a roll‐to‐roll setup was used to synthesize 90 nm silica‐like bilayer encapsulation films composed of a 30 nm dense “barrier layer” and a comparatively less dense 60 nm “buffer layer” onto a polyethylene 2,6 naphthalate substrate by means of plasma enhanced chemical vapor deposition. Tetraethyl orthosilicate was used as the precursor gas, together with a mixture of nitrogen, oxygen, and argon. The microstructure, chemical composition, morphology, and permeation properties of the films were studied as a function of the specific energy delivered per precursor molecule, and oxygen concentration in the gas mixture, during the deposition of the barrier layer. The presence of the buffer layer within the bilayer architecture critically enhanced the encapsulation performance of the bilayer films, and this in conjunction with increasing the specific energy delivered per precursor molecule during the barrier layer deposition to a value of 20 keV, enabled an effective water vapor transmission rate as low as 6.9 × 10−4 g m−2 d−1 (at 40 °C, 90% relative humidity (RH)) to be achieved. Furthermore, the bilayer film structure has given rise to a remarkable 50% reduction in deposition energy consumption per barrier area with respect to single layer silica‐like films of equivalent encapsulation performance and thickness.

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

“…Because the power density remains unvaried, the specific energy delivered per precursor molecule (related to Yasuda parameter) is constant. For the current experimental conditions the DDR is around 75 to 80 nm·mm·s −1 (for Q = 10-30 slm) and the estimated energy spent per TEOS molecule is 6.5 keV/molecule, the specifics of the calculation can be found in [5,28]. The gradual decrease in the calculated DDR value from the static profiles with increasing gas flow is mainly attributed to a slight increase in the gas loss due to stronger convection, see Fig.…”

“…The increase in density of small (~1 μm) pinhole defects [28] must be the main reason for the gradual deterioration of the WVTR values for Q > 25 slm.…”

“…These functional foils can therefore be used for the protection of electronic components such as flexible solar cells, optical components like quantum dots or in food and medical packaging applications [18][19][20][21][22][23][24][25][26][27]. Effective water vapor transmission rate (WVTR) measurements showed that rates as low as 6.9 · 10 −4 g·m −2 ·day −1 (at 40°C, 90% RH) can be achieved using a bilayer film architecture [28]. In a recent study [11] the gradient film properties of films deposited on static substrate in an AP-PECVD reactor were investigated using spatially resolved ATR-FITR analysis.…”

Atmospheric-pressure diffuse dielectric barrier discharges in Ar/O2gas mixture using 200 kHz/13.56 MHz dual frequency excitation

“…According to the fast imaging analysis, during the single current pulse, this transient discharge evolved from a 'Townsend-like' mode to a 'glow-like' mode for each half cycle of the electric field [11,12]. It was also demonstrated that application of such a diffuse discharge as a plasma source for the roll-to-roll AP-PECVD process in conjunction with organosilicon precursors results in high quality inorganic silica-like thin films, which can be deposited on thermally sensitive polymeric substrates [14][15][16]. In this process, the increased discharge power density allows the synthesis of silica-like films with improved microstructure, lower impurities level and excellent gas diffusion barrier properties [16,17].…”

“…It was also demonstrated that application of such a diffuse discharge as a plasma source for the roll-to-roll AP-PECVD process in conjunction with organosilicon precursors results in high quality inorganic silica-like thin films, which can be deposited on thermally sensitive polymeric substrates [14][15][16]. In this process, the increased discharge power density allows the synthesis of silica-like films with improved microstructure, lower impurities level and excellent gas diffusion barrier properties [16,17]. Moreover, a higher power density is also required to increase the deposition rate and therefore the throughput of the PECVD process.…”