Jason E. Ritchie

Fabrication of conducting polymer interconnects.

A nonmechanical approach to the construction of complex three-dimensional interconnect arrays has been developed with the use of conducting polymer dendrites. Electrically independent connections between pairs of wires in an array were successfully grown through alternating-current electrochemical polymerization of poly(3-methylthiophene), without mechanical or optical masking steps. The electrically active links were insulated by subsequent electropolymerization of 4-vinylpyridine or 2-methylthiophene or by the dip-coating of the connections in a polystyrene solution.

Star-Shaped MePEGn Polymers as H+ Conducting Electrolytes

Proton conducting electrolytes composed of a mixture of MePEG(7)SO(3)H acid and a four-armed, PEG-based, star molecule were prepared. Four MePEG(n) (n = 3, 7, 12) arms were attached to a pentaerythritol or tetrakis(dimethylsilyl) orthosilicate core to form the star molecules. We have examined the structure of these star electrolytes to observe how the structure of an electrolyte affects the observed ionic conductivity. In terms of structural parameters, these star electrolytes showed large volume fractions of PEG, high fluidities, and large fractional free volumes, all of which predict larger ionic conductivities. Through a comparison of the conductivity and structural parameters in a variety of different star electrolytes, we have shown that each of these three structural parameters are important and can strongly affect the observed ionic conductivity. Walden plots indicated a large extent of ion-pairing in our star electrolytes and that MePEG(7)SO(3)H acid was a weak acid in our star electrolytes.

Understanding the Mechanism of Ionic Conductivity in an Anhydrous Proton-Conducting Electrolyte Through Measurements of Single-Ion Diffusion Coefficients

The single-ion diffusion coefficients of H + and MePEG n SO - 3 ions have been electrochemically measured in a series of anhydrous proton-conducting electrolytes composed of mixtures of MePEG n SO 3 H acid (where n = 3, 7, 12, or 16) dissolved in our MePEG 7 polymer. The electrochemically measured H + single-ion diffusion coefficients in this electrolyte are dependent on temperature such that, at low temperatures (25°C), the H + cation is the primary charge carrier in the four acid/polymer solutions tested. However at high temperatures, the diffusion coefficients of the MePEG 7 SO - 3 and MePEG 12 SO - 3 anions are larger than the corresponding H + diffusion values, yielding a smaller fraction of charge carried by H + (t H+ values of 0.29 and 0.41, for the MePEG 7 SO 3 H and MePEG 12 SO 3 H mixtures at 85°C). While the diffusion coefficient of the large MePEG 16 SO - 3 anion does not overtake D H+ at 85°C, its transference number nonetheless increases with increasing temperature. We conclude that our electrolyte is dominated by Grotthus conductivity at low to moderate temperatures, while the contribution of the vehicle mechanism of H + conductivity increases at high temperatures.

Effects of Bulky Copolymers on Ion Transport in an Anhydrous Proton-Conducting Electrolyte

Anhydrous proton-conducting electrolytes composed of a mixture of MePEG 7 SO 3 H [where PEG is poly(ethylene glycol)] acid and a sol-gel-based MePEG 3 copolymer were prepared. These copolymers were prepared by mixing the MePEG 3 (CH 2 ) 3 Si(OCH 2 CH 3 ) 3 monomer and different bulky comonomers: phenyltriethoxysilane, diphenyldimethoxysilane, and isobutyltrimethoxysilane. The MePEG 3 copolymers showed smaller volume fractions of PEG and nearly the same fractional free volume as the parent MePEG 3 polymer. End-group analysis showed that the incorporation of bulky group decreased the degree of condensation in the sol-gel polymer. This loss of condensation lead to an increase in the fluidity of the MePEG 3 copolymers, which in turn resulted in larger ionic conductivities in the copolymers compared with the parent MePEG 3 polymer.

Volume fraction of ether is a significant factor in controlling conductivity in proton conducting polyether based polymer sol-gel electrolytes.

We have synthesized several copolymers of methyl polyethylene glycol siloxane (MePEG7SiO3)m and methyl polypropylene glycol siloxane (MePPGnSiO3)m as hydrogen ion (H(+)) conducting polymer electrolytes. These copolymers were prepared by a sol-gel polymerization of mixtures of the MePEG and MePPG monomers. We synthesized these H(+) conducting polymer electrolytes in order to study the relationship between observed ionic conductivity and structural properties such as viscosity, fractional free volume, and volume fraction of ether. We found that viscosity increased as the fraction of the smaller comonomer increased. For the MePPG2/MePPG3 copolymer, an increase in fractional free volume increased the fluidity. The heterogeneous copolymers (PEG/PPG copolymers) obeyed the Doolittle equation, while the homogeneous (PEG/PEG and PPG/PPG) copolymers did not. The increase of FFV did not, however, correspond to an increase in conductivity, as would have been predicted by the Forsythe equation. The conductivity data did correspond to a modified Forsythe equation substituting Volume Fraction of Ether (V(f,ether)) for FFV. We conclude that the proton conductivity of MePEG copolymers is more dependent on the volume fraction of ether than on the fractional free volume.

Molecular engineering of organic conductor / high-Tc superconductor assemblies

Abstract Organic monolayers on high-T c superconductors have allowed for the precise structural control of composite organic conductor / high-Tc superconductor assemblies. These hybrid systems display a number of novel electronic and structural properties. This paper discusses the utility of the monolayer self-assembly procedure for the preparation of both conductive polymer and crystalline charge transfer salt layers which are supported directly on top of cuprate superconductor thin film samples.

Properties of Conducting Polymer Interconnects

The possibility of using conducting polymer dendrites as electrical connections has been explored. AC electropolymerization of dendritic conducting polymers can be used to connect two different platinum wires. The polymerization conditions were varied in order to improve morphology, strength, conductivity, and to shorten the time needed to make connections. The variables involved in this study include electrolyte and monomer concentrations and the type of conducting polymer used (3-methylthiophene and aniline). Another area of study has been the exploitation of the inherent doping and undoping properties associated with conducting polymers to store information in the connections in the form of a resistance value. To this end, the connections were doped to known conductivity values and the persistence of conductivity was monitored over time.