1/f noise and its unusual high-frequency deactivation at high biasing currents in carbon black polymers with residual 1/f^ (= 2.2) noise and a preliminary estimation of the average trap energy

We have performed noise measurements on 5 different carbon black polymer composite resistive gas sensors, both in an inert chemical atmosphere (dry nitrogen) and in an active chemical atmosphere (with toluene or ethanol vapour). All the sensors exhibited the presence of significant 1/f noise for biasing currents in the ?A range; moreover, we show that the level of 1/f noise is strongly dependent upon the chemical environment and, in particular, the concentration of the vapour. These results, obtained for the first time with this chemically sensitive nanocomposite material, should help in the creation of circuit models and also in the design of low noise chemical sensors using carbon-black composite materials. Additionally, in the thinnest sensor, at sufficiently high biasing currents we found the deactivation of 1/f noise above a certain frequency, with an unexpected residual 1/f? excess noise (? around 2.2) which, to our knowledge, has not been observed before. Interestingly, this unusual excess noise was almost insensitive to the presence of either toluene or ethanol vapour; this observation may offer insight on the origins of both 1/f and the measured 1/f? excess noise in composite polymer resistors. Finally, we have estimated the available noise energy per trap for a given adsorption process which may be used to characterize the noise fluctuations in a chemical environment. We believe that our work will also enable the construction of better SPICE models to help in the design of advanced CMOS transduction circuitry.