Specifications and yields of composite magnetic films for a high-density memory

General design equations have been derived which relate magnetic film parameters to memory operating currents and bit geometry. The application of these equations is demonstrated in determining the magnetic specifications of a memory having 12 500 bit/in². These characteristics were most easily realized in a composite magnetic film vacuum deposited sequentially from melts of 50-percent Co, 47-percent Ni, and 3-percent Fe and 83-percent Ni and 17-percent Fe. This is an excellent way of achieving characteristics which lie between those of any two layers taken separately as long as the total thickness is less than the exchange length, i.e., <2000Å. Before etching and final processing, yields to magnetic specifications of 80 percent were achieved using these composite films.