Teresita Ordonez Graham

N-type organic thin-film transistor with high field-effect mobility based on a N,N′-dialkyl-3,4,9,10-perylene tetracarboxylic diimide derivative

N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) thin films have been implemented into organic thin-film field-effect transistors. Mobilities up to 0.6 cm2 V−1 s−1 and current on/off ratios >105 were obtained. Linear regime mobilities were typically half of those measured in the saturation regime. X-ray studies in reflection mode suggest a spacing of ∼20 A for thin evaporated films of PTCDI-C8H, which is consistent with the value of ∼21±2 A obtained from our simulations when an interdigitated packing structure is assumed.

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.

Field-effect transistors comprising molecular beam deposited α,ω-di-hexyl-hexathienylene and polymeric insulator

Abstract Insulated-gate field-effect transistors (IGFETs) comprising molecular beam deposited α,ω-di-hexyl-hexathienylene (DH6T) as the semiconductor layer and different polymeric gate insulators were fabricated and tested. Field-effect mobility values up to 0.13 cm 2 V −1 s −1 were obtained, which are the highest values obtained from thin-film transistors of DH6T.

Operational and environmental stability of pentacene thin-film transistors

We report the effects of repeated stressing and environmental exposure on the operational stability of pentacene thin-film transistors (TFTs). Pentacene TFT channels were deposited by thermal evaporation and by spin coating and thermally converting soluble precursors. For a given dielectric thickness and applied voltage, pentacene TFTs with shorter channel lengths and therefore higher current densities have the largest decrease in field-effect mobility, on-current, and subthreshold slope and the largest threshold voltage shift with device cycling. Devices measured in ambient nitrogen show little degradation and devices fabricated on thinner dielectrics, operated at lower voltages with similarly high current densities in air, show reduced degradation. These results are consistent with degradation by thermal oxidation and suggest that reducing the operational power (by device scaling) and limiting channel exposure to ambient air improves device stability.

Directed Assembly of Single-Walled Carbon Nanotubes via Drop-Casting onto a UV-Patterned Photosensitive Monolayer

We report the use of a novel UV-sensitive self-assembled monolayer to selectively deposit single-walled carbon nanotubes from solution using heterogeneous surface wettability. This process combines ubiquitous photopatterning techniques with simple solution processing to yield highly selective and densely packed carbon nanotube patterns. The essential concept behind this process is the change in surface chemistry caused by the UV-induced monolayer reaction. Selective deposition of carbon nanotubes was achieved by drop-casting, and the resulting films show local ordering, indicating that further development of this process will lead to simple technique for large-scale integration.

Device scaling in sub-100nm pentacene field-effect transistors

Reported here is the fabrication of 20–100nm channel length pentacene field-effect transistors (FETs) with well-behaved current-voltage characteristics. Using a solution deposition method, pentacene grains span entire devices, providing superior contacts. Varying the gate oxide thickness, the effects of scaling on transistor performance is studied. When the channel length to oxide thickness exceeds 5:1, electrostatically well-scaled nanometer FETs are prepared. The results show that the device characteristics are dominated by the contacts. Decreasing the oxide thickness lowers the device turn-on voltage beyond simple field scaling, as sharper bending of the gate potential lines around the contacts more effectively reduces the molecule/source interfacial resistance.

New high conductivity lead (Pb)-free conducting adhesives

Solder interconnection technology is currently in need of alternatives to address environmental issues associated with lead (Pb) abatement, and elimination of fluxes and flux cleaning solvents, and technical challenges related to extending to fine pitch assembly. Electrically conducting adhesive technology is one of the alternatives being actively considered in this context. The most common conductive adhesive used today is an epoxy resin filled with fine silver particles. Silver particles provide electrical conduction, while epoxy provides adhesive bonding of the components to a substrate. This material has several limitations such as low electrical conductivity, low joint strength, increase in contact resistance upon thermal cycling, and silver migration. In order to overcome these limitations, a new formulation is proposed based on alternative Pb-free conducting filler powders and tailored polymer resins. This new material provides a metallurgical bonding as well as polymer adhesive bonding leading to an increase in joint strength and in electrical conductivity. Several potential applications of these adhesive materials such as glass-to-board connection in LCD packaging, SMT package assembly to PCB, and direct chip attachment to a high density card are discussed.

Solvent, LICL, and Temperature Effects on the Morphological Structure and Electronic Properties of Polyaniline

Extensive gel permeation chromatography coupled with surface structure measurements clearly indicate that polyaniline (pani) base has a tendency to aggregate as a result of interchain hydrogen-bonding. The aggregation is present in the solid state powder; the extent of aggregation is found to be significantly dependent on the synthetic conditions. Pani base powders having a high degree of aggregation have significantly reduced solubility. The degree of aggregation of pani base in solution is found to be dependent on the solvent, concentration, and temperature. As the solvent becomes a better solvent for the base material, the less aggregated is the structure. Solvents which can strongly interact with the polymer disrupt the aggregation. In addition, salts such as LiCl which complex the polymer via a “pseudo-doping” process, also disrupt the internal pani hydrogen-bonding and deaggregate the polymer. As the polymer is deaggregated to different levels by a solvent or by LiCl, the individual chains can better be solvated and thus a conformational change also occurs. The chains adapt a more expanded coil type of conformation. The degree of expansion depends on the solvation power of the solvent. As the level of deaggregation and subsequent chain expansion increases, a significant red shift is observed in the λmaximum of the exciton absorbance and the surface structure of the polymer becomes smoother. It is found that the LiCl induced morphological changes results in increased conductivity upon doping pani base with a protonic acid.

Factors Affecting Metal/Polymer Interface Durability in Microelectronics Packaging: Chemistry and Water Uptake

Durability of metal/polymer interfaces is essential for the long-term reliability of high performance microelectronics packages. Such interfaces undergo stresses during production and in service. In this work, we report on the durability of interfaces formed between reactive metals and polyimides (PI) that have been subjected to stresses simulating both types of environment. The P1 surfaces were treated by Ar RF plasmas prior to metal deposition, and durability was determined by measuring the 90 degree peel strength as a function of environmental exposure. The durability of Cr and Ti/PMDA-ODA interfaces through processing stresses (i.e., large thermal excursions) depends on the PI surface modification and the metal reactivity. For both, we observed interfacial degradation due to oxidation of the metal–the cause is water absorbed by the polyimide. These studies, coupled with water transport measurements, suggest that the physical structure of the interface is the dominant factor. To determine the durability under service environmental stresses (e.g., temperature/humidity), we correlated peel strengths with interfacial chemistry and water uptake. In this case, Ar and O 2 plasmas were used. For Ta/BPDA-PDA, the durability depends on the type of plasma treatment. Ar-treated specimens maintain strength through 500 hours T/H stressing whereas those treated by O 2 plasma alone fail at 165 hours. The differences here can be explained by the interfacial chemistry–Ta/Ar-etched surfaces form a stable TaG-like structure whereas the Ta/O 2 -etched surfaces form a metastable, sub-oxide structure that transforms to Ta 2 O 5 during stressing. Ta/PMDA-ODA interfaces fail readily under these conditions due to the increased water uptake of the PI.

Ta/polyimide adhesion durability

The adhesion durability of Ta to plasma-modified polyimide surfaces has been investigated under thermal exposure. The failure mechanism was correlated with Auger analysis. Resistance to oxidation at the Ta/polyimide interface was found necessary to obtain a durable metal/polymer adhesion strength.