Nano fabrication approaches for patterned magnetic recording media

Abstract

Bit patterned media (BPM) have received increased attention in recent years as the primary candidate for 1 Terabit/in² or higher recording density. A patterned media consists of an array of well-defined magnetic nanostructures, each of which can store one bit of data. In the simplest scheme, the structures could be magnetic pillars and dots with a single easy axis of magnetization. The direction of magnetization is interpreted as a binary 1 or 0. Some of the main technical issues in the BPM include the difficulty in fabricating small nano-island arrays in a periodic fashion over large areas, reliability/reproducibility of magnetic bit characteristics, wear and head flyability issue which is associated with the media surface roughness, and processing cost. This thesis deals with investigation of various fabrication approaches, nanostructural features, and magnetic properties for the bit patterned media.

In Chapter 1, the science and technology of patterned magnetic recording media are discussed. In Chapter 2, fabrication of an array of high-coercivity magnetic Co/Pd multilayered islands using pre-patterned Si nanopillars template is described. The Si nanopillars have been prepared by advanced electron beam lithography (EBL) and reactive ion etching (RIE). In Chapter 3, the flying instability of the read/write recording head-slider on the topographically rough surfaces of the nano-patterned media is discussed, and technical approaches to overcome such a problem is described, such as planarization of nanopatterned topography by refilling the trenches and flatten the surface of the BPM. I have investigated the head flyability on BPM by fabricating nano pillar geometry with different topography. For flyability testing that requires a relatively large area, I have also fabricated nano pillars on 2.5 inch glass disks with a distribution of pillar size and periodicity using the “silver ball-up process” and RIE.

The process, structure and properties of planarized vs. non-planarized nano fabricated and imprinted BPM, are described in Chapter 4. A Si substrate was spin-coated with a thin PMMA layer, and a periodic island array was made by nano-imprinting lithography (NIL) with the patterned nanofeatures. The subsequent pattern transfer to the Si substrate was performed by using RIE process. A Co/Pd multilayer film was sputtered on the pre-patterned substrate. A HSQ layer was first spin coated on the patterned media to fill the trenches and subsequently re-etched by RIE to remove the overfilled regions on the substrate for planarization. In Chapter 5, the effect of magnetic island geometry on switching field distribution is discussed.