Micro Fabrication Techniques for Magnetic Information Storage Devices: From Bubbles to Thin Film Recording Heads to Nano Magnetic Structures

This lecture examines magnetic device structures from the perspective of thin film processing. Techniques for forming magnetic device structure minimum features will be compared with semiconductor processing. Future storage density growth in both magnetic memories and magnetic recording will be projected using semiconductor roadmaps. The “nano” characteristics (thickness and length scale) of next generation magnetic thin film heads and magnetic memory devices will be compared with solid state semiconductor designs.
In the last 25 years, the bit cell size for storage products incorporating magnetic device structures decreased from 156 µm² bit cells (IBM 3390 Disk Drive) to 0.007 µm² (Hitachi Travelstar 5K100 Mobile Disk Drive). For the same period, the bit cell size in non-volatile memory products incorporating magnetic device structures decreased from 625 um² (TI 100 Kbit Bubble Memory) to 1.6 um² (Motorola 4 Mbit MRAM). These 103 to 105 increases in information storage densities resulted from increased understanding in the physics of magnetic phenomena, from advances in material science and engineering for magnetic thin films, from development of new magnetic modeling techniques, and from dramatic improvements in the capability to fabricate magnetic device structures with smaller minimum features.
The manufacture of cost effective magnetic device based information storage products requires high yield processing technologies for the magnetic transducer or memory element in these products. Such processing technologies are now producing devices with 120 nm features (80 GBit/in² storage densities) and these same processing technologies are extendable to 30 nm features (1TBit/in² storage densities). The lecture will conclude with discussions on nano-scale processing challenges.