AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Monday Sessions
       Session OE+EM-MoA

Paper OE+EM-MoA8
Localized Growth and Electrical Characterization of Polypyrrole on Temperature Programmed Microhotplates

Monday, November 2, 1998, 4:20 pm, Room 327

Session: Organic Thin Film Devices II: Transitors and Transport
Presenter: C. Kendrick, National Institute of Standards and Technology
Authors: C. Kendrick, National Institute of Standards and Technology
R.E. Cavicchi, National Institute of Standards and Technology
S. Semancik, National Institute of Standards and Technology
Correspondent: Click to Email
Arrays of microhotplates fabricated at CMOS foundries have been post-processed to realize suspended, heatable structures that have previously allowed localized deposition of SnO@sub 2@ by thermally activated CVD.@footnote 1@ This work presents an electrochemical, self-lithographic technique for the growth of polypyrrole on the micromachined platforms and a study of the effect of rapid heating/cooling cycles on film conductivity during gas exposure. Electropolymerization was performed in a sealed flow cell containing Ag-pseudoreference and Pt-counter electrodes mounted directly on the chip package and filled with a solution of acetonitrile, 0.1M LiClO@sub 4@, and 50mM pyrrole. Optical microscopy indicates that polypyrrole growth begins on the Au-plated microhotplate contacts and expands laterally, forming a continuous film. The effects of NO@sub x@, NH@sub 3@, CO, H@sub 2@, and methanol vapors on film resistance have been measured for different film dopings and temperature schedules. The highest sensitivities are found for the strongly oxidizing and reducing gases NO@sub x@ and NH@sub 3@, respectively, where resistance changes have been shown to be caused by changes in carrier concentration brought about by a weak charge transfer interaction between adsorbates and the film. We show that resistance changes (@DELTA@R/Ro) due to 100ppm NO@sub x@ exposure can be increased from ~15% at 25°C to ~30% when periodically pulsing the sensor to 150°C. A similar increase in sensitivity is observed for periodic heating during exposure to NH@sub 3@. Information on analyte adsorption rates and dynamics can also be extracted from the transient resistance characteristics observed between temperature pulses. @FootnoteText@ @footnote 1@S. Semancik, R. E. Cavicchi, K. G. Kreider, J. S. Suehle, and P. Chaparala, Sensors and Actuators B 34, 209 (1996).