Fabrication of bubble memory chips

Investigations have been made on the fabrication of accurate and uniform T-bar circuits. Chrome masks are preferable to emulsion masks, and furthermore, a minimum exposure and intimate contact have been demonstrated to be necessary for accurate and uniform pattern imaging on the AZ1350 resist. A newly developed chemical etchant, a nitric acid-base solution without ferric chloride, can almost eliminate undercutting of permalloy elements. Application of spin-on-glass prior to Permalloy evaporation can result in excellent step coverage at the places where T-bar circuits overlap conductors. Large memory chips having a capacity of 16 × 10
³
bits and a storage density of 10
⁵
bits/cm
²
have successfully been fabricated.