B.S.T.J. Briefs: Air-Insulated Beam-Lead Crossovers for Integrated Circuits

Air-insulated crossovers for integrated circuit interconnections have been developed which feature low capacitance and dual dielectrics for high yield and reliability. This type of crossover is fabricated using beam lead technology and is applicable to integrated circuit chips as well as substrates. The cross section drawing in Fig. 1 shows a crossover with dual dielectric insulation consisting of a 5 micron air gap in series with a 2000 A layer of Zr0 2 . Fig. 2 is a plan view photograph of a typical pattern. The dual dielectric crossover will not fail under mechanical load even if the top conductor is deflected until it touches the bottom level, since the ZrO-> has a breakdown strength by itself of approximately 100 volts. (See Fig. 3.) Any pinholes in the solid dielectric will not lead to short circuits either, as they would if the top level metallizing were applied by deposition. When the external force is released, the top beam lead will elastically return to its original position, and the air gap will once again sustain over 200 volts. The fabrication procedure is as follows. A Ti-Pt lower level contact pattern is formed according to methods previously described.1 A layer of Zr-Cu is then deposited, and feed-through holes etched where contact to the lower level is desired. The top layer, a gold beam lead, is electroformed using the copper as a base, and the copper is etched away. Thermal oxidation of the Zr layer to Zr0 2 completes the structure: two levels of metallization separated by a Zr0 2 -air dielectric.