PH Sensitive WO3-Based Microelectrochemical Transistors.
Interim technical rept.,
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF CHEMISTRY
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Electrochemical properties of an array of closely spaced 1.2 um Au or Pt microelectrodes approx. um wide x approx. 50 micrometers um long x 0.1 micrometer high coated by a 0.15 micrometers thick layer of polycrystalline WO3 are reported. The WO3 is deposited on the electrode by rf sputtering of a WO3 target. The cyclic voltammetry of these microelectrodes indicates that WO3 connects individual microelectrodes, since the voltammogram of a pair of microelectrodes driven together is indistinguishable from that of an individual microelectrode. WO3 becomes a good conductor upon electrochemical reduction in aqueous solutions. The change in resistance of WO3 connecting two microelectrodes as a function of electrochemical potential spans four orders of magnitude, from approx. 1,000,000 to approx. 100 ohms. A pair of WO3-connected microelectrodes functions as a microelectrochemical transistor that is sensitive to pH. The cyclic voltammetry is pH-dependent and consistent with pH-dependent transistor characteristics, which indicate that the device is turned on at more positive electrochemical potentials in acidic media. In basic solutions, more negative potentials are needed to turn on WO3-based transistors. The maximum slope of the drain current, I sub D,vs. gate voltage, V sub G, plot at fixed drain voltage, V sub G, gives a transconductance of 12 mSmm of gate width.
- Physical Chemistry
- Electrical and Electronic Equipment