PH-Sensitive Ni(OH)2-Based Microelectrochemical Transistors.

Properties of arrays of closely spaced 1.2 micron Au or Pt microelectrodes approx. 2 micron wide x 50 micron long x 0.1 micron high coated with cathodically grown films of NiOH2 are reported. Electrical connection of microelectrodes by NiOH2 was verified by cyclic voltammetry. The ratio of anodic charge to cathodic charge in cyclic voltammograms for the NiOH2 NiOOH interconversion exceeds one. However, it is shown that excess charge in the anodic cyclic voltammetric wave for oxidation of NiOH2 does not affect the conductivity of NiOH2 films. The steady state resistance of NiOH2 connecting two microelectrodes has been measured as a function of potential from 0 V to 0.7 V vs. SCE, and was typically found to vary from approx. 10 to the minus 7th power to approx. 0.0001 ohms. The measured resistance corresponds to a resistivity of approximately 30 ohm-cm in the oxidized state. The decrease in resistance is caused by electrochemical oxidation of insulating Ni OH2 to conducting NiO OH. At fixed drain voltage, VD, the gate current, IG, and the drain current, ID, can be measured simultaneously as the gate voltage, VG, is varied at a given frequency.