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ElectroComponent Science and Technology
Volume 8 (1981), Issue 1-2, Pages 3-8

Thin Film Technology Used in Bell System Telecommunication Circuits

Bell Telephone Laboratories, 555 Union Boulevard, Allentown 18103, Pennsylvania, USA

Copyright © 1981 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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 μm for conductors and 50 μm 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.