Carrier-transfer mechanisms and Al2O3sensors for low and high humidities

It is shown that the humidity-sensitive surface conduction of porous alumina can be explained in terms of two complementary carrier-transfer mechanisms. At low humidities, a phonon-induced electron tunnelling is postulated between donor water sites; this tunnelling is assisted by anionic groups on the sensor surface. At high humidities, protonic conduction dominates. These mechanisms provide useful design guidelines for fabricating sensors of desired response characteristics. They are compatible with a variable activation-energy model proposed in this paper.