Teflon Amorphous Fluoropolymer Research Articles

Teflon AF–Coated Nanotextured Aluminum Surfaces for Jumping Droplet Thermal Rectification

AbstractJumping droplet thermal diodes (JDTDs) are promising candidates to achieve thermal rectification for next‐generation thermal control. However, most prior demonstrations of JDTDs have relied on monolayer‐coated copper‐based superhydrophobic (SHPB) surfaces, while lower‐cost aluminum JDTDs with more durable thin polymeric coatings have not been explored. In this work, a JDTD is constructed that employs SHPB aluminum surfaces coated with protective thin films of Teflon AF (amorphous fluoropolymer) 1601. Measurements for different heating orientations, gap heights (H), and fill ratios (ϕ) show that a maximum thermal rectification ratio of 7 can be achieved for H = 2.4 mm and ϕ = 10%. A thermal circuit is demonstrated that uses the JDTD to rectify time‐periodic temperature profiles, achieving thermal circuit effectiveness values up to 30% of the ideal‐diode limit. Coupon‐level durability tests and device‐level cycling show that dip coated Teflon AF enables stable operation of Al JDTDs over >20 cycles, improving on the performance of a monolayer‐coated surface that fails after 5 cycles. The findings of this work signify that Teflon AF coated Al SHPB surfaces can be used for thermal rectification and motivate future research into Al JDTDs for advanced thermal management applications.

Organic thin-film transistors with inkjet-printed electrodes on hydrophobic Teflon-AF gate dielectric with reversible surface properties

Printed organic thin-film transistors (OTFTs) are promising for flexible, low-cost electronics; however, a major challenge is that successive processing steps of multiple solution-processed layers can interfere with each other. In particular, hydrophobic fluoropolymers are a promising group of materials to fabricate gate dielectrics with low charge trap density and properties such as good thermal stability, chemical inertness, low dielectric constant, and water repellency. However, the main difficulty in incorporating hydrophobic fluoropolymers in printed electronic devices is their low surface energy. Plasma treatment is a common method for surface modification that renders these hydrophobic layers wettable to print subsequent layers. This plasma processing can also affect the interface with the organic semiconductor (OSC) and transistor performance, which is studied here for the first time. The morphological and surface chemical properties of Teflon amorphous fluoropolymer (Teflon-AF) films change after plasma treatment and gradually reverse after post-annealing of subsequent layers as demonstrated here. Here, we fabricate solution-processed OTFTs with Teflon-AF as the gate dielectric. We report OTFTs with inkjet-printed source and drain electrodes with a minimum channel length of 20 μm on Teflon-AF for the first time. We show that the annealing of the inkjet-printed electrodes changes the morphology and the surface chemistry of the Teflon-AF gate dielectric underneath, thus reversing the effect of the plasma. We show that this electrode post-annealing step can improve the transistor performance by improving the interface between the Teflon-AF gate dielectric and the OSC in terms of smoothness and hydrophobicity. The transistor parameters such as mobility, on/off current ratio, and threshold voltage all follow a trend explained here by the properties of the Teflon-AF films. Increasing the post-annealing temperature to just below complete surface reversibility decreases surface roughness and trap-sites created after plasma treatment leading to optimized device performance. We characterize the Teflon-AF surface with contact angle measurement, roughness measurement, Fourier transform infrared spectroscopy (FTIR), and x-ray photoelectron spectroscopy (XPS). This understanding of the reversibility of the Teflon-AF surface helps achieve optimal performance of devices and systems incorporating fluoropolymers. • The challenge of processing OTFT layers on hydrophobic dielectrics is addressed. • 20 μm channel OTFTs with inkjet-printed electrodes on hydrophobic dielectric are achieved. • Teflon-AF surface changes after plasma and reverses after post-annealing. • Electrode annealing changes the morphology and surface chemistry of the dielectric. • Electrode annealing can improve the gate dielectric/organic semiconductor interface.

Performance Enhancement of Organic Light–Emitting Diodes Using Electron–Injection Materials of Metal Carbonates

Abstract Performance of organic light-emitting diodes was investigated depending on the electron-injection materials of metal carbonates (Li2CO3 and Cs2CO3 ); and number of layers. In order to improve the device efficiency, two types of devices were manufactured by using the hole-injection material (Teflon-amorphous fluoropolymer -AF) and electron-injection materials; one is a two-layer reference device ( ITO/Teflon-AF/Alq3/Al ) and the other is a three-layer device (ITO/Teflon-AF/Alq3/metal carbonate/Al). From the results of the efficiency for the devices with hole-injection layer and electron-injection layer, it was found that the electron-injection layer affects the electrical properties of the device more than the hole-injection layer. The external-quantum efficiency for the three-layer device with Li2CO3 and Cs2CO3 layer is improved by approximately six and eight times, respectively, compared with that of the two-layer reference device. It is thought that a use of electron-injection layer increases recombination rate of charge carriers by the active injection of electrons and the blocking of holes.

InP/GaAsSb DHBTs Fabricated in a Low-Temperature Teflon Planarization Process

We demonstrate InP/GaAsSb/InP double heterojunction bipolar transistors (HBTs) fabricated in a low-temperature planarization process based on a spin-on Teflon amorphous fluoropolymer interlevel dielectric with ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 1.9 and a low dissipation factor. Devices with 0.3-μm-wide emitters show excellent junction characteristics, cutoff frequencies f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> = 362 GHz and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> = 450 GHz, a peak current gain β = 28, and a common-emitter breakdown voltage BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CEO</sub> = 5.1 V. Teflon is seen to be an advantageous alternative to common benzocyclobutene and polyimide planarization dielectrics. A side-by-side comparison of devices fabricated in Teflon and airbridge processes shows nearly identical performances. The present approach is equally applicable to GaAs- and GaInAs-based HEMT and HBT technologies.

Flow control of thermotropic lipid monolayers

There is an increasing interest in using liquid crystalline media as mobile phases in two-dimensional nanofluidic systems. Their small-scale, reduced dimensionality, and plentiful opportunities for functionalisation render such phases advantageous. However, flow control has been difficult to achieve, as the wetting processes which drive area expansion are not dynamically controllable. Here, we report on temperature-controlled monolayer spreading of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) on the hydrophobic substrates SU-8, and Teflon AF (amorphous fluoropolymer). The gel/liquid phase transition of DEPE at Tc ∼ 38 °C is exploited to toggle spreading of a molecular lipid film on SU-8. We observed that on Teflon AF, DEPE monolayer spreading occurs even below Tc, and exhibits strongly accelerated spreading above the phase transition temperature. Our results demonstrate that switching DEPE monolayer spreading on and off, or, alternatively, switching between fast and slow area expansion, is a feasible approach towards establishing control over lipid film flow in two-dimensional fluidic systems. We also present a chip-based device integrating a patterned surface for 2D-microfluidics and on-chip heating.

Coaxially Electrospun PVDF−Teflon AF and Teflon AF−PVDF Core−Sheath Nanofiber Mats with Superhydrophobic Properties

This work reports the coaxial electrospinning of poly(vinylidene fluoride) (PVDF)-Teflon amorphous fluoropolymer (AF) and Teflon AF-PVDF core-sheath nanofiber mats yielding superhydrophobic properties. The coaxial electrospinning configuration allows for the electrospinning of Teflon AF, a nonelectrospinnable polymer, with the help of an electrospinnable PVDF polymer. PVDF-Teflon AF and Teflon AF-PVDF core-sheath fibers have been found to a have mean fiber diameter ranging from 400 nm to less than 100 nm. TEM micrographs exhibit a typical core-sheath fiber structure for these fibers, where the sheath fiber coats the core fiber almost thoroughly. Water contact angle measurements by sessile drop method on these core-sheath nanofiber mats exhibited superhydrophobic characteristics with contact angles close to or higher than 150 degrees. Surprisingly, PVDF-Teflon AF and Teflon AF-PVDF nanofiber mat surface properties were dominated by the fiber dimensions and less influenced by the type of sheath polymer. This suggests that highly fluorinated polymer Teflon AF does not advance the hydrophobicity beyond what surface physics and slightly fluorinated polymer PVDF can achieve. It is concluded that PVDF-Teflon AF and Teflon AF-PVDF core-sheath electrospun nanofiber mats may be used in lithium (Li)-air batteries.

Solder bump creation by using droplet microgripper for electronic packaging

A simple and effective method to create solder bumps by using a droplet microgripper for electronic packaging is described. A reusable droplet microgripper was realised simply by patterning a Teflon amorphous fluoropolymer on a glass substrate to make a 5×5 hydrophilic opening site array of 300 µm-diameter circles and 600 µm pitches. The microgripper was used to self-arrange solder balls of 300 µm diameter on its wetted sites. After transferring the solder balls to a flux-coated soldering substrate by an alignment process, solder bumps were successfully created on the corresponding solder ball lands through a reflow process.

An on-line instrument for mobile measurements of the spatial variability of hexavalent and trivalent chromium in urban air

The Steam-Jet Aerosol Collector-long Pathlength Absorbance Spectroscopy (SJAC-LPAS), an on-line continuous instrument for mobile measurements of spatial distribution of water-soluble hexavalent and trivalent chromium in ambient aerosols, has been developed and is presented here. The system collects particles with the SJAC and analyzes the collected sample on-line using the diphenycarbazide (DPC) colorimetric method. By using a Teflon AF (Amorphous Fluoropolymer) liquid core wave guide, the limit of detection has been significantly improved, allowing on-line measurements at ambient concentrations. The limit of detection for Cr(VI) is 0.2 ng m −3. Water-soluble Cr(III) can also be measured by oxidizing it to Cr(VI) in a parallel line using hydrogen peroxide before the detection with the DPC method. The concentration of Cr(III) is then determined as the difference between the two lines (Cr(VI) and Cr(VI) plus Cr(III)). The instrument was specifically designed to be used on a mobile platform to study spatial distribution of the pollutant within a city on a scale of 100 m. Special attention was given to the time resolution and the stability of the instrument performance under driving conditions. The time resolution of the instrument is 15 s. At a typical driving speed of 30 km h −1 the instrument can detect variations in chromium concentration (“hot spots”) on the scale of about 150 m. The instrument has proven to operate reliably and capture temporal and spatial variability of Cr(VI) concentration during four mobile measurement campaigns in Wilmington, DE.

Fabrication of amorphous silicon thin-film transistor by micro imprint lithography

We studied ultraviolet micro imprint lithography (UV-MIL) for the manufacture of amorphous silicon (a-Si) thin-film transistors (TFTs) using a master mold. A teflon amorphous fluoropolymer produced by rotary vacuum evaporation was used to detach the imprint resist from a master mold. To remove the residual resist layer, the sample was dipped in acetone and then dry etched by reactive ion etching. The a-Si TFT having 10μm channel length produced by UV-MIL exhibited a field-effect mobility of 1.2cm2/Vs, threshold voltage of 1.9V and on/off current ratio of 108.

Determination of Chlorinated Hydrocarbon Species in Aqueous Solution Using Teflon Coated ATR Waveguide/FTIR Spectroscopy

The potential of an optical sensor based on mid-infrared spectroscopy, utilising a zinc selenide (ZnSe) attenuated total reflectance (ATR) element coated with an amorphous Teflon polymer, to determine chlorinated hydrocarbon species (CHC) in an aqueous environment is examined. The polymer coating concentrates the analytes within the penetration depth of the Fourier transform infrared (FTIR) evanescent wave and excludes water from the region. Teflon AF (Amorphous Fluoropolymer) is a family of amorphous copolymers based on polytetrafluoroethylene (PTFE), and is commercially available in two polymeric grades. Teflon AF is highly amorphous in nature with a large 'void volume', exhibits excellent chemical resistance and low water absorption. Such properties identify it as an excellent candidate for enrichment coating on an ATR/FTIR sensor. The potential of both polymeric grades of Teflon AF as enrichment membranes for ATR/FTIR analysis of CHC species was examined and contrasted. A rapid, repeatable, reversible response was observed with both grades to a range of CHC species. Linear responses in the mg/L region, with detection limits in the low mg/L region were achieved with the system used.

A novel structural amorphous fluoropolymer film with an ultra-low dielectric constant

Amorphous fluoropolymer (AF) thin film (0.9–1 μm), which has no-pinhole and uniform surface and numerous pores in the matrix, has been prepared from a solution of Teflon AF 1600 by a spin-coating method. Thermal annealing at 400°C for 30 min does not cause obvious deterioration of the film surface morphology. The mechanism for the formation of the film with a novel structure is discussed. By capacitance–voltage ( C– V) and current–voltage ( I– V) measurements, the electricity properties of the AF film are defined. The substitution of SiO 2 ( k=4.0) with the AF film ( k=1.57) will decrease the resistance–capacitance (RC) delay by about 61%.

Effects of thermal treatment on porous amorphous fluoropolymer film with a low dielectric constant

Amorphous fluoropolymer (AF) thin films have been prepared from Teflon AF 1600 solution by spin-coating. Scanning electron micrograph (SEM) observations reveal that the film has planar and compact surface without any pinhole, and there are many pores in the matrix. By capacitance–voltage ( C– V) and current–voltage ( I– V) measurements, the dielectric constant of the AF film is equal to 1.57 at 1 MHz, and breakdown strength is 2.07 MV cm −1. The Fourier transform infrared spectroscopy (FTIR) spectra and X-ray diffraction (XRD) patterns of the films show that the films have excellent thermal stability below 400°C, and thermal treatment does not change amorphous nature of the films. X-ray photoelectron spectroscopy (XPS) spectra reveal decomposition of CF 3 groups due to annealing at 400°C, leading to a remarkable increase in CF 2 groups. Possible decomposition mechanisms of AF film are also discussed.

Effect of vacuum ultraviolet radiation on the gap fill properties of Teflon amorphous fluoropolymer film deposited by direct liquid injection

In this work, the roles of vacuum ultraviolet (VUV) photons in improving the gap fill properties of a low dielectric constant (K) material (Teflon amorphous fluoropolymer, K=1.93) deposited by direct liquid injection assisted rapid photothermal chemical vapor deposition technique are discussed. A qualitative explanation is presented wherein it is proposed that high-energy photons provide photoexcitation of the species involved in the deposition of Teflon AF/sup TM/, thereby lowering the activation energy and migrational enthalpy required for surface diffusion leading to a higher molecular mobility on the patterned surface.

A Comparative Study of Spin‐On and Chemical Vapor Deposited Teflon Amorphous Fluoropolymer Thin Films

Dielectric materials with dielectric constant (K) less than the conventionally used (K = 3.9) are gaining importance particularly for low voltage operated integrated circuits due to their ability to reduce signal propagation delays, power dissipation, and cross talk when used as interconnect dielectrics. In this paper, we report for the first time a low temperature chemical vapor deposition technique for the deposition of the copolymeric Teflon amorphous fluoropolymer 1600 which is a new low K material with a value of K of about 1.93. The principle of direct liquid injection in an ultraviolet (UV) light‐assisted rapid isothermal processing system was followed. The film properties for films processed using our technique and the conventional spin‐on method were compared. A significant improvement in dielectric performance and material usage efficiency was observed for the films processed using chemical vapor deposition.

A computerized direct liquid injection, rapid isothermal processing assisted chemical vapor deposition system for a Teflon amorphous fluoropolymer

Chemical vapor deposition (CVD) has for long been the mainstay for the deposition of critical device layers in integrated circuit technology. For the development of fast, high density, low voltage operated integrated circuits, materials with dielectric constant (K) less than that of the conventionally used SiO2 (K=3.8) are required, due to their ability to reduce signal propagation delays, power dissipation, and cross talk when used as inter level dielectrics. The copolymeric Teflon amorphous fluoropolymer (AF) is a new low K material with K=1.9. A direct liquid injection system for the CVD of Teflon AF for interlevel dielectric applications in an ultraviolet (UV) light enhanced rapid isothermal processor is reported for the first time, to the best of our knowledge. Computer interfaced electronics were designed to permit atomizing and desolvating the liquid precursor at any desired instant and interval of time. A closed loop control system monitored and regulated the substrate temperature. The films were processed with and without the UV light source. An improvement in film properties was observed when the UV source was used during processing. Our technique offers considerable advantages over other reported methods for the processing of Teflon AF.

Chemical Vapor Deposited Teflon Amorphous Fluoropolymer as an Interlevel Dielectric Material for Low Power Integrated Circuits

AbstractThe development of materials with dielectric constant (K) less than SiO2(K=3.9) is essential to meet the stringent speed, power dissipation and crosstalk requirements that are driving the low power integrated circuit (IC) paradigm. Both the low K dielectric and the processing methodology used for it should satisfy several important criteria before the technique can be accepted in future mainstream low power IC manufacturing. We had reported earlier a chemical vapor deposition (CVD) technique for the deposition of DuPont's Teflon amorphous fluoropolymer 1600 (bulk K=1.93) using the principle of direct liquid injection. The processing was carried out with and without an ultra violet (UV) light source in a computerized rapid isothermal processing (RIP) system.Recently, we have extensively characterized the films and examined the suitability of our technique in light of some of the requirements of the future IC industry. Our results indicate that the processed films exceed several of the established dielectric performance standards outlined in recent roadmaps for sub 0.25 μm ICs. The film properties were improved when the UV source was used during processing. CVD processed films in general demonstrated significant improvements in terms of manufacturability, throughput, cost, and dielectric properties over the same films processed by alternate techniques.

Deposition of amorphous fluoropolymer thin films by thermolysis of Teflon amorphous fluoropolymer

Thin films (0.3–5 μm) of an amorphous fluoropolymer (AF) derived from the copolymeric material Teflon AF 1600 were deposited on Si (100) wafers by vacuum pyrolysis. Infrared spectroscopy indicated that the composition of the deposited films was similar to the source material. The deposited films were amorphous by x-ray diffraction. The surface morphology contained micropores which did not extend through films deposited at a low rate. The refractive index was ∼1.2 at 633 nm. Comparisons are made to films derived from ordinary Teflon (also by pyrolysis). The mechanism for the repolymerization of the Teflon AF copolymer at the substrate surface is discussed.