Tantalum nitride resistors

Results of accelerated testing of circuits prepared with this polymer as the dielectric layer are satisfactory. Circuits comprising two metallization and one polymer layer withstand a minimum of 500 cycles from -40 to +130 C with no loss of adhesion, cracking of the polymer, or open circuits. No mechanical or electrical failures occur during 1000 hours at 150°C in air, and the insulation resistance remains above 200 megohm during 500 hours at 85 C/85% RH/60 V (THB). Tantalum nitride resistors under the polymer change < 0.5% under these THB conditions. 

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 2.50 Effect of substrate alkali content on overload testing of tantalum nitride resistors. ... 

Device materials again may be conductive, semiconductive, dielectric, or resistive. Conductors are typically gold or aluminum, and resistors, sHicon monoxide or sHicon nitride. Tantalum nitride and nickel chromium are common resistor materials. 

The functional phase in thick-film resistors is a mixture of electrically conducting (or semiconducting) ceramic powders such as ruthenium dioxide (RUO2), bismuth ruthenate (Bi2Ru207), lead ruthenate (Pb2Ru206), and Ag-Pd-PdO mixtures for use in air-fired pastes and tantalum nitride (TaN) for nitrogen-fired pastes. The resistance of thick-film resistors is specified in terms of sheet resistance, which has units of ohms/square (Q/D). 

By adding small amounts of other gases, such as oxygen and nitrogen, to the argon, it is possible to form oxides and nitrides of certain target materials on the substrate. It is this technique, called reactive sputtering, which is used to form tantalum nitride, a common resistor material. 

The most common types of resistor material are nichrome (NiCr) and tantalum nitride (TaN). Although NiCr has excellent stability and TCR characteristics, it is susceptible to corrosion by moisture if not passivated by sputtered quartz or by evaporated silicon monoxide (SiO). TaN, on the other hand, may be passivated by simply baking in air for a few minutes. This feature has resulted in the increased use of TaN at the expense of NiCr, especially in military programs. The stabihty of passivated TaN is comparable to that of passivated NiCr, but the TCR is not as good unless annealed for several hours in a vacuum to minimize the effect of the grain boundaries. Both NiCr and TaN have a relatively low maximum sheet resistivity on alumina, about 400 S2/ for NiCr and 200 / for TaN. This requires lengthy and complex patterns to... 

TABLE 4.1 Characteristics of Typical Tantalum Nitride and Nichrome Resistors... 

Resistor material -> characteristic T Tantalum nitride Nichrome... 

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. 

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