New Devices Made from Combining Silicon Microfabrication and Conducting Polymers

Abstract

Conducting polymers have been developed primarily for macroscopic use in batteries, electromagnetic shielding, coatings, displays, and solar cells (commercial applications have been discussed by Schoch and Saunders, 1992, and Studt, 1991). Chief among their attributes is their high conductivity in the doped state, which approaches that of copper (for an introduction, see Kaner and MacDiarmid, 1988; Reynolds, 1988; or Kanatzidis, 1990). This is due to the pattern of alternating single and double bonds, or conjugation, that gives them their other commonly used name, “conjugated polymers”. (See Figure 1.) Dopants added to the material donate (or remove) electrons from the chain, delocalizing the electron cloud in the immediate vicinity and distorting the bond lengths. This results in the formation of bond alternation domain walls (called solitons or polarons and bipolarons, depending on whether the material has a degenerate ground state) which have energy levels within the polymer’s band gap. At high doping levels, they can link together to form energy bands through which the electrons can travel. Charge is thought to hop between polymer chains Because conductivity is higher along a chain than between chains, stretching a sheet of conducting polymer, which orients the chains, results in conductivity anisotropies as high as 100–1000 (e.g. Schimmel et al., 1991).