Resistance of polyaniline films as a function of electrochemical potential and the fabrication of polyaniline-based microelectronic devices

Anodic growth of polyaniline films on a Au microelectrode array has been carried out to add to the characterization of polyaniline and to fabricate polyaniline-based microelectronic devices, diodes and transistors, that function when the polyaniline-functionalized microelectrode array is immersed in an electrolyte solution. The microelectrode array is a set of eight Au electrodes, 0.1 μm thick, 4.4 μm wide, and 50 μm long, each individually addressable and separated from each other by 1.7 μm. Polyaniline can be deposited in controlled amounts by electrochemical oxidation of aniline. When the polyaniline is deposited in sufficient amounts, two or more of the eight Au microelectrodes can be connected in the electrical sense. Current can pass between two connected microelectrodes when there is an applied potential between them. The magnitude of the current at a given applied potential depends on the electrochemical potential of the polyaniline. In 0.5 M NaHSO₄/H₂O the current (at a fixed applied potential) is maximum at an electrochemical potential of ∼+0.4 V vs. SCE and declines by a factor of > 10⁶ upon reduction to +0.1 or oxidation to +0.7 V vs. SCE. Owing to the large change in resistance upon change in electrochemical potential, the functionalized microelectrodes can function as diodes or transistors. The small spacing between the microelectrodes is crucial to device function, owing to the limited conductivity of the polyaniline. The switching time of a transistor-like device is faster than 0.1 s.