Abstract
We propose a method for fabricating high-hardness plasma-polymer-fluorocarbon (PPFC) thin films with controllable optical and surface properties via manipulation of the target composition design and sputtering power density. The carbon/polytetrafluoroethylene (PTFE) composite polymeric material targets with the low electrical resistance were prepared by press-molding using a mechanically mixed powder of PTFE, carbon nanotubes, and graphite. The composite targets showed electrical sheet resistances of 0.1–100 Ω/sq. PPFC thin films were deposited by mid-range frequency (MF) sputtering at power densities within 0.62~4.92 W/cm2. The maximum surface hardness of the PPFC thin film was 4.75 GPa, which was 21.6 times higher than that of fluorocarbon thin film sputtered from PTFE under the same conditions. With the increase of the carbon concentration in the target, the carbon cross-linking density of the PPFC thin film increased but the fluorine concentration decreased. The concentration of fluorine in the PPFC thin films grew with increasing sputtering power density. The MF sputtered carbon-rich PPFC thin films are controllable with physical properties of optical transmittance, surface hardness and surface water repellency which could be applied as protective layers for transparent flexible devices.
Highlights
Plasma-polymer-fluorocarbons (PPFC) are fluorinated polymers such as polytetrafluoroethylene (PTFE) or fluorinated organic gases like CF4 or C2F6 that are formed through glow discharge[1]
diamond like carbon (DLC) is high in brittleness and difficult to apply as a flexible protective layer with a small radius of curvature, as well as having low optical transmittance; these properties limit its applicability in transparent flexible devices
We presented a novel method for PPFC thin film fabrication using carbon nanotube (CNT)/PTFE composite targets, which could use a mid-range frequency (MF) power source, whereas conventional polymer targets can only be sputtered with 13.56 MHz radio frequency power sources, with reflected noise
Summary
Plasma-polymer-fluorocarbons (PPFC) are fluorinated polymers such as polytetrafluoroethylene (PTFE) or fluorinated organic gases like CF4 or C2F6 that are formed through glow discharge[1]. In foldable and rollable flexible displays, transparent layers capable of protecting display surfaces are indispensable[15,16]; plasma polymer thin films are suitable candidates for such layers. DLC is high in brittleness and difficult to apply as a flexible protective layer with a small radius of curvature, as well as having low optical transmittance; these properties limit its applicability in transparent flexible devices. PPFC thin films prepared by sputtering using a fluorine-containing polymer such as PTFE are among the candidates for flexible protective layers to overcome the disadvantages of DLC. The composite targets were used for MF sputtering at power densities of 2.46–4.92 W/cm[2] to fabricate carbon-rich PPFC thin films. The structural, surface, and optical properties of the thin films were compared and analyzed according to the carbon concentration of the target and the sputtering power density
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