Tunable polytetrafluoroethylene electret films with extraordinary charge stability synthesized by initiated chemical vapor deposition for organic electronics applications

Abstract

Bulk polytetrafluoroethylene (PTFE) possesses excellent chemical stability and dielectric properties. Indeed, thin films with these same characteristics would be ideal for electret applications. Previously, the electret properties of PTFE-like thin films produced by rf sputtering or plasma enhanced chemical vapor deposition were found to deteriorate due to structural changes and surface oxidation. In this article, the technique of initiated chemical vapor deposition (iCVD) is evaluated for electret applications for the first time. The iCVD method is known for its solvent-free deposition of conformal, pinhole-free polymer thin films in mild process conditions. It is shown that PTFE thin films prepared in this way, show excellent agreement to commercial bulk PTFE with regard to chemical properties and dielectric dissipation factors. After ion irradiation in a corona discharge the iCVD PTFE thin films exhibit stable electret properties, which can be tailored by the process parameters. Due to the mild deposition conditions, the iCVD technique is suitable for deposition on flexible organic substrates for the next-generation electret devices. It is also compatible with state-of-the-art microelectronic processing lines due to the characteristics of conformal growth and easy scaling up to larger size substrates.

Nanoscale control by chemically vapour-deposited polymers

“…Flexible electret films of with high charge stability were fabricated by iCVD polytetrafluoroethylene (PTFE). 89 The performance of triboelectric nanogenerators was systematically investigated for an iCVD fluoropolymer over the thickness range from 0.5 to 12 μm. 90 All-fabric triboelectric generators for wearable electronics were also demonstrated with conformal and breathable iCVD fluoropolymers.…”

Outstanding performance of parylene polymers as electrets for energy harvesting and high‐temperature applications

“…These exceptional performances of Parylene AF‐4 to keep electric charges against temperature are confirmed when compared with the recent work of Schröder et al . on initiated CVD (i‐CVD) deposition of PTFE (13‐μm thick) . These authors show that i‐CVD increases of about 35 °C the value of T 1/2 compared to commercial Teflon AF and finally they obtain T 1/2 = 175°C.…”

“…Indeed, some fluoropolymers are known for being very good electrets. Among them, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and MEMS‐compatible amorphous fluorinated polymers such as Teflon AF and CYTOP, are some of the most well‐known polymer electrets employed for energy harvesting applications. Using fluoro‐Parylene AF‐4 as electret is quite rare in the literature.…”

Electrowetting‐Assisted Generation of Ultrastable High Charge Densities in Composite Silicon Oxide–Fluoropolymer Electret Samples for Electric Nanogenerators

“…Widely used chemically similar Teflon FEP displays significantly higher values of the trap‐modulated mobility at lower temperatures (e.g., 1.6 · 10 −16 m 2 V −1 s −1 at 145 °C, [ 51 ] and 10 −15 m 2 V −1 s −1 at 185 °C [ 59 ] ). Spin‐coated films of Teflon AF and other amorphous polymers as well as recently reported ultrastable evaporated FP layers [ 56,57,60 ] display a sharp decay of their surface potential within minutes upon exceeding the glass transition temperature (160 °C for Teflon AF 1600). [ 49,60,61 ] Nevertheless, the systematic analysis of these materials suggested charge lifetimes of thousands of years at room temperature.…”

“…Spin‐coated films of Teflon AF and other amorphous polymers as well as recently reported ultrastable evaporated FP layers [ 56,57,60 ] display a sharp decay of their surface potential within minutes upon exceeding the glass transition temperature (160 °C for Teflon AF 1600). [ 49,60,61 ] Nevertheless, the systematic analysis of these materials suggested charge lifetimes of thousands of years at room temperature. Given the higher stability of our samples, the lifetime of the charge in h‐EWCI charged composite electrets can be expected to exceed any commercially relevant product lifetime by far.…”