1. Technical Field
This invention relates generally to thin film resistors, and more particularly to thin film resistors with improved reliability and higher current density capabilities
2. Discussion of The Related Art
Thin film resistors are utilized in integrated circuits in many important commercial applications They are frequently used where the integrated circuits are exposed to high temperatures such as in machine rooms, in interiors of automobiles, and in many other areas. In addition, thin film resistors are useful in "space" and "flight" applications which require a high degree of reliability. An important benchmark for such applications is that the resistors maintain constant resistance values over widely varying temperatures.
Currently, thin film resistors are manufactured with a resistor material evaporated directly onto the top surface of a wafer substrate. Electrically conducting contacts are then formed on designated areas of the resistor material and the remaining surface area is covered with a passivation layer of material such as silicon nitride. Unfortunately a thin film resistor produced according to this prior technology is susceptible to sharp increases in resistance value within the first few hundred hours of operation because the resistor material diffuses into the wafer substrate. Such increases in resistance, can render integrated circuits requiring specific resistance values inoperative or cause them to operate at a wrong frequency. These problems with thin film resistors are exacerbated by increasing temperature and current density.
Thus, it would desirable to provide a thin film resistor which would maintain a relatively constant resistance value when subjected to large current densities and high temperatures for extended periods of time. Further, it would be desirable to provide a technique for producing a thin film resistor with in which the resistor material does not diffuse into the substrate of the integrated circuit on which it is employed.