For many decades discrete NTCR-components (NTCR: Negative Temperature Coefficient Resistors) are manufactured with classical ceramic technology for temperature sensing in various applications. The ongoing movement to miniaturization and the increasing trend to integration in microelectronics with the vision of new applications drive the development of thin film processing of NTCR-materials.
In this contribution, the results concerning NTCR thin films based on Ni-Mn-Co-oxide with spinel structure, which were deposited on oxidized silicon wafers by Chemical Solution Deposition (CSD) from acetate and acetic acid based precursors, are presented. The effect of processing conditions on microstructure, electrical properties and long-term resistance drift were investigated. Thin films crystallized at temperatures of 750°C and above contained NiO/MnO/CoO solid solutions with rock-salt structure as secondary phases, which in turn change the composition of the spinel phase. The fraction of this secondary phase, but also film orientation, depends on the number and sequence of crystallization processes. Differences in rated resistivity and its temperature dependence could be attributed to the fraction of secondary phase and actual spinel composition. For the observed differences in the long-term resistance drift in addition to the phase composition the differences in microstructure were identified to correlate with the observed effects. A model is suggested that correlates oxygen transport along grain boundaries with existing aging mechanisms.