Microstrip tantalum resistors deposited through electron beam techniques

A specific need arose for the terminating resistors of an X-band circulator to be integral with the ferrite metallization. The ferrite was gadolinium doped yttrium iron garnet. The need was related to both improved performance, since the impedance desired was purely resistive, and to lower fabrication costs with the elimination of discrete chip resistors and their associated test, mounting, and bonding procedures. Tantalum was selected as the thin film resistor material because of its stability and because trimming to a desired resistance is straightforward. This stability is greatest in the range from 50 to 100 ohms per square. The uniqueness of this application lies in the use of electron beam techniques with reactive deposition and doping of tantalum to produce thin film resistors on a ferrite.