Read-Rite puts ALD in production

The read head in a hard disk drive is a sandwich of ferroelectric materials, surrounded by a shield against stray magnetic fields. The gap dielectric insulates the head from the shield.

As data density increases, the entire head assembly shrinks, reducing the gap. According to Eddie Lee, an executive VP at Genus, current magnetic media store 40 Gbits/in² (corresponding to a 20 Gbyte hard drive) and require gap dielectrics in the 200 Å range. Even as thickness drops, however, the dielectric must still deliver high breakdown strength, low thermal stress, and good heat dissipation. The film must have good adhesion strength to withstand mechanical polishing of the head, and must conform to complex topography.

Most manufacturers use physical vapor deposition (PVD) to deposit the gap dielectric. Read-Rite recently switched to atomic layer deposition (ALD), putting two of Genus' Lynx2 systems into volume production.

Lee explained that ALD offers better conformality and superior yield for films less than 200 Å thick. ALD works by a self-limiting reaction. One precursor gas (TMA, for aluminum oxide gap dielectrics) reacts with the bare surface to create a single monolayer. Then a second precursor gas (water, in this case), reacts with the first to complete a layer of the desired film. The alternating gas flows repeat to build a film with the desired thickness.

As a surface reaction, ALD is inherently conformal. It is also relatively slow. It is best suited for applications, like gap dielectrics, requiring a few very precise layers.