Characterization of a “Solid-State” Microelectrochemical Diode Employing a Poly (vinyl alcohol)/Phosphoric Acid Solid-State Electrolyte: Rectification at Junctions between WO₃ and Polyaniline

The functionalization of an array of eight, closely spaced (~1.2 μm) Pt or Au microelectrodes each ~50 μm long, 2 μm wide, and 0.1 μm thick with redox-active WO₃ and polyaniline and the electrochemical characterization of the WO₃/polyaniline junction are reported. Chips consisting of microfabricated WO₃ covering three of the available eight microelectrodes have been analyzed by Auger electron spectroscopy. The remaining five microelectrodes are available for further derivatization with polyaniline or can function as counterelectrodes. By placing a counterelectrode and a Ag quasi-reference electrode directly on the microchip and by coating the assembly with a thin film of poly (vinyl alcohol) /H₃PO₄ solid polymeric electrolyte, the electrochemical system becomes self-contained. The solid polymer electrolyte is a good room-temperature H⁺ conductor only when exposed to a H₂O-containing atmosphere. Complex impedance studies show as much as a 10³ change in H⁺ conductivity from H₂O-saturated to H₂O-free gaseous atmosphere above the polymer electrolyte. The changes in conductivity of WO₃ upon reduction or polyaniline upon oxidation allow demonstration of solid-state microelectrochemical transistors with these materials. The combination of WO₃ and polyaniline on the chip allows demonstration of a microelectrochemical diode.