THIN FILM TECHNOLOGY USED IN BELL SYSTEM TELECOMMUNICATION CIRCUITS.

This paper describes the thin film technology used for telecommunication circuits in the Bell System. Vacuum deposition and photolithography form the basis for the film processing steps. Nitrogen doped tantalum films are used to form the very stable thin film resistors and capacitors. Laser trimming is used to obtain precision RC active filters. Line widths down to 75 mu m for conductors and 50 mu m for resistors are readily achieved in production. The properties of the various components used in thin film integrated circuits are described and examples of completed circuits used in transmission, station, and switching systems are shown. Some key advantages of this technology are low cost due to batch processing techniques, high packing density and high precision of passive components.