Effects of grain boundary states on the low-frequency noise in positive-temperature coefficient ceramic resistors

This work reports, for the first time, a low-frequency (LF) noise study in barium titanate ceramic resistors. Several PTC resistors with different additives, including Y, Mn, and Nb, were prepared. The temperature dependence of the resistivity and the grain morphology of these samples were found to be strongly governed by the type of additives. Low-frequency noise measurements at room temperature and above the Curie point were conducted. Experiments show that the LF noise behaviors are governed by grain boundary tunneling at room temperature and by trapping and detrapping of the grain boundary states at temperatures above the Curie point. These observations provide additional information on the current conduction and distribution of grain boundary states in these materials