Marie Angelopoulos

Polymeric anodes for improved polymer light-emitting diode performance

We have studied polyaniline and polyethylenedioxythiophene transparent electrodes for use as hole-injecting anodes in polymer light emitting diodes. The anodes were doped with a variety of polymer and monomer-based acids and cast from either water or organic solvents to determine the effect of the dopant and solvent on the hole-injection properties. We find that the anodes with polymeric dopants have improved device quantum efficiency and brightness relative to those with small molecule dopants, independent of conductivity, solvent, or type of conducting polymer. For the most conducting polymer anodes [σ>2(Ωcm)−1], diodes could be made without an indium tin oxide underlayer. These diodes show substantially slower degradation.

Conducting polymers in microelectronics

Conjugated polymers in the nondoped and doped conducting state have an array of potential applications in the microelectronics industry. Conducting polymers are effective discharge layers as well as conducting resists in electron beam lithography, find applications in metallization (electrolytic and electroless) of plated through-holes for printed circuit board technology, provide excellent electrostatic discharge protection for packages and housings of electronic equipment, provide excellent corrosion protection for metals, and may have applications in electromagnetic interference shielding. This paper reviews some of these applications and briefly describes possible future applications of conducting polymers for use as interconnections or for electronic devices.

Use of Polyaniline and Its Derivatives in Corrosion Protection of Copper and Silver

This study examines the use of spin-applied conjugated polymers such as polyanilines for corrosion and dissolution protection of silver and copper. In particular, attention is given to the protection that these polymers provide under conditions of an applied potential and at elevated temperature. These particular conditions are those in which current inhibitors such as benzotriazole do not provide acceptable protection for the metal. A number of polyaniline derivatives are studied, including the unsubstituted parent polymer and the substituted poly-o-phenetidine both nondoped and doped, with several different protonic acids. The polymers are readily soluble in organic solvents and can be applied as thin coatings onto the metal surface. The corrosion protection of the resulting structure is determined by electrochemical and inductively coupled plasma techniques using water as an electrolyte and under varied conditions in which the material is processed and doped. The poly-o-phenetidine is found to adhere well to the metal surface and provides exceptional protection both under an applied potential and at elevated temperature.

Polymeric anodes for organic light-emitting diodes

Abstract Polymer light-emitting diodes based on PPV, for example MEH-PPV, are known to be susceptible to photo-oxidative degradation. The formation of the carbonyl species in the polymer results in quenching of the luminescence. In addition the oxidation process reduces the conjugation of the polymer, leading to lower charge carrier mobilities and consequently higher operating voltages. Previous in situ FTIR studies revealed that even in a dry inert atmosphere polymer oxidation occurs, and that ITO can act as the source of oxygen. In order to explore further the nature of the oxidation mechanism and to provide guidance for its elimination, we have studied the behavior of MEH-PPV LEDs prepared with conducting polymer anodes. When a layer of polyaniline is present between the ITO and the MEH-PPV the device characteristics improve dramatically: the injection voltage drops, the luminous efficiency increases and, most significantly, the rate of decay of the luminance decreases by up to two orders of magnitude. These data not only confirm that ITO is a source of oxygen, but also imply that the oxidation mechanism is due to direct interfacial reaction. We compare several different forms of polyaniline, with different dopants, as well as a derivative of a polythiophene.

Aqueous-based photoresist drying using supercritical carbon dioxide to prevent pattern collapse

A supercritical drying process was developed to eliminate the capillary forces naturally present during normal drying of photoresist materials. Supercritical carbon dioxide (scCO2), organic solvents and surfactants were used to prevent the collapse of high-aspect-ratio structures fabricated from aqueous-based photoresist. Nondistorted resist lines were patterned with this process with aspect ratios of at least 6.8. Water rinsed resist structures cannot be dried directly with scCO2 due to the low solubility of water in the supercritical phase. In our process we introduced the replacement of the aqueous rinse by n-hexane mediated by a compatible surfactant. The surfactant allowed to incorporate the aqueous phase into micellar microdomains in the organic phase while keeping the interfacial tension at values close to zero. Noncollapsed supercritically dried structures were rewet in n-hexane or water and dried using nitrogen at atmospheric pressure. Under these conditions, the patterns were collapsed as a resu...

Effect of selected processing parameters on solution properties and morphology of polyaniline and impact on conductivity

Abstract Interchain H-bonding between amine and imine sites in emeraldine base (EB) results in aggregate formation. The aggregation is present in the as synthesized EB; the level of aggregation is dependent on the polymerization conditions. Reduction of EB to the leucoemeraldine form eliminates the imine sites and thus, the interchain H-bonding and the aggregation are also eliminated. The degree of aggregation in the EB powder determines the solubility and solution characteristics of the polymer. Solvents such as m-cresol and additives such as LiCl which dope EB are most efficient at solvating the polymer and thus, deaggregating the chains, Deaggregation facilitates chain expansion. The degree of aggregation and chain expansion in EB solutions significantly impact the overall properties of both the non-doped and doped polymer such as the optical absorption, conductivity and degree of crystallinity. Crystalline EB films are attained from solutions consisting of low polymer concentration where the polymer is well solvated and highly deaggregated. Highly crystalline non-stretched EB films are attained by the introduction of a plasticizer which imparts local mobility allowing the chains to crystallize.

Conducting polyanilines: Discharge layers for electron‐beam lithography

This paper describes the use of electrically conducting polyanilines as discharge layers for electron‐beam (e‐beam) lithography. The emeraldine oxidation state polyaniline is a soluble material which can be doped by various cationic reagents, most commonly protonic acids, to afford conductivity on the order of 10° Ω−1 cm−1. The conducting polyanilines are incorporated as thin interlayers (2000 A) in a multilayer resist system consisting of a planarizing underlayer (2.8 μm) and the imaging resist (1.2 μm) on top. We find that various acid‐treated polyanilines eliminate charging during e‐beam patterning of the resist, i.e., zero pattern displacements are observed as compared to the case where a conducting interlayer is not incorporated into the resist system. In the latter case placement errors greater than 5 μm are observed as a result of charging. A minimum conductivity of 10−4 Ω−1 cm−1 is required for the polyaniline interlayers in order to observe zero pattern displacement. In addition, we have simplifi...

Effect of thin-film imaging on line edge roughness transfer to underlayers during etch processes

For the patterning of sub-100 nm features, a clear understanding of the origin and control of line edge roughness (LER) is extremely desirable, from a fundamental as well as a manufacturing perspective. With the migration to thin photoresists coupled with bottom antireflective coating (ARC)-hardmask underlayers, LER analysis of the developed resist structures is perhaps an inaccurate representation of the substrate roughness after the etch process, since those underlayers can play a significant role in increasing/decreasing linewidth variations during the image transfer process and hence can impact the device performance. In this article, atomic force microscopy is used to investigate the contribution of the imaging resist sidewall topography to the sidewall roughness of the final etched feature in thin photoresists, ARC, and hardmasks. Resist systems suitable for 248 and 193 nm lithography as well as fluorine-containing resists were processed using N2-H2 or fluorocarbon plasma etch. It is shown that the ...

Water soluble conducting polyanilines: Applications in lithography

A new class of water soluble conducting polyanilines has been developed. This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid. The resulting polyanilines readily dissolve in water. These materials can be applied as removable discharge layers for electron‐beam lithography and for mask inspection by scanning electron microscopy. They can be spin‐applied directly on top of resists without any interfacial problems. Image distortion as a result of charging during resist exposure is not observed with these materials. After exposure the polyaniline is readily and cleanly removed during the resist develop. By incorporating cross‐linkable functionality on the polyaniline backbone, water soluble polyanilines that are radiation curable are attained. Upon irradiation these materials cross‐link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge applications. In addition, the cross‐linkable polyanilines can be us...

Effect of organic vapors on the molecular conformation of non-doped polyaniline

Abstract A series of studies have been carried out on polyaniline (emeraldine base; EB) thin films deposited on glass substrates from aqueous solutions of polymerizing aniline (“ in-situ ” EB-I film). These films exhibit a Vis/UV spectrum in which the exciton peak has an absorption maximum at ~600 nm. Exposure of EB-I film to NMP vapor results in a red-shift of the exciton peak to ~650 nm (EB-II film). Doping of EB-II film by aq. HCl vapor gives a more delocalized electronic structure and higher electrical conductivity than those of the doped EB-I film. It is concluded that EB-I and EB-II exist in “tight coil” and “expanded coil” conformations respectively which do not change on doping in aqueous HCl.