Planar process for 8-µm period bubble devices using polyimide resin

A new and simple planar process using polyimide resin, polyimide iso-indroquinazolinedione (PIQ^®), has been developed for 8-μm period bubble devices. PIQ is strongly heat resistant. This material is used as an interlaminar dielectric between conductor and Permalloy patterns. The PIQ layer effectively covers the steep steps of Au/Mo conductor patterns, thereby eliminating the problem of Permalloy step coverage at conductor edges. A 256-kbit memory device with an 8-μm period fabricated by the planar process exhibits an overall bias margin of more than 10 percent over the temperature range 15°C to 80°C for 300-kHz operation at a drive field of 55 Oe. PIQ does not introduce constraints on other process parameters or chip designs. Reproducibility and reliability of bubble devices fabricated by the PIQ process have been good.