Thin-film tantalum nitride resistors

Corrosion Failures of Thin-Film Tantalum Nitride Resistors. 460... 

Thin-film tantalum nitride resistors are used in hybrid integrated circuit and silicon thin film integrated circuit applications. The tantalum nitride is sputter deposited. After deposition and patterning, the resistors are stabilized by heating in air to form a protective surface layer of tantalum pentoxide. In the presence of environmental or manufacturing contamination, atmospheric moisture, and applied voltage, the surface pH may become basic. As shown in Fig. 9-19, strong bases convert the protective tantalum... 

Figure 9-19. Schematic illustration of corrosion of tantalum nitride thin-film resistors. Basic solutions of contaminants convert the protective tantalum pentoxide to a tantalate salt and then oxidize the underlying tantalum nitride to form more tantalate, thereby increasing the film resistance.

Thin-fikn circuits typically consist of three layers of material deposited on a substrate. The bottom layer serves two purposes It is the resistor material and it also provides the adhesion to the substrate. The adhesion mechanism of the film to the substrate is an oxide layer that forms at the interface between the two. The bottom layer must therefore be a material that oxidizes readily. The most common types of resistor material are nichrome (NiCr) and tantalum nitride (TaN). Gold and silver, for example, are noble metals and do not adhere well to ceramic surfaces. 

---