Pump-probe thermoreflectance measurements of critical interfaces for thermal management of HAMR heads
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Pump-probe thermoreflectance measurements of critical interfaces for thermal management of HAMR heads Gregory T. Hohensee1, Mousumi M. Biswas1, Ella Pek2, Chris Lee1, Min Zheng1, Yingmin Wang1, and Chris Dames3 1
Western Digital Corporation, 1250 Reliance Way, Fremont CA 94539, U.S.A. Materials Science and Engineering, Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A. 3 Mechanical Engineering, University of California Berkeley, Berkeley CA 94720, U.S.A. 2
ABSTRACT For heat-assisted magnetic recording (HAMR) heads, a major reliability limiter is the peak near-field transducer (NFT) temperature. Since the NFT is nanoscale, heat sinking is controlled by materials and interfaces within a few 100 nm of the NFT. Heat sinks can be metallic to take advantage of the 10x-100x higher thermal boundary conductance (TBC) of metal/metal interfaces, versus nonmetal interfaces. Oxide formation at these interfaces can greatly decrease the TBC and contribute to NFT failure. Likewise, the thermal resistance of material between the NFT and media recording layer greatly influences the NFT operating temperature. Here we use pump-probe thermoreflectance techniques (FDTR, TDTR) to study metal-metal interfaces and detect partial oxidation of a buried metallic thin film, as well as evaluate the interface thermal conductance of amorphous-amorphous interfaces in a film stack representative of a HAMR head-media interface. INTRODUCTION The current hard disk drive technology of perpendicular magnetic recording (PMR) has been approaching a capacity limit dictated by the superparamagnetic limit.[1] Heat-assisted magnetic recording (HAMR) is one of the most promising paths to continued areal density scaling, and thus higher storage capacity in hard drives.[2,3] HAMR works by integrating an optical waveguide and plasmonic near-field transducer (NFT) adjacent to the magnetic write pole, facing the recording media just a few nanometers away. The plasmonic field from the NFT extends to the media recording layer to generate a sub-100 nm hotspot on the media, which enables writing as the media reaches its Curie temperature. A central challenge in HAMR is nanoscale thermal management of the NFT.[4] The NFT dissipates some laser energy as heat, and can be back-heated from the media hot spot. With heat comes reliability challenges: Au is a non-reactive and efficient plasmonic material, but can be mechanically unstable at high temperature. While the media hotspot travels over the spinning media, the recording head is constantly under heat load while writing to the disk. Reducing NFT temperature is one of the most direct ways to ensure longer lifetimes for HAMR heads and bring HAMR closer to a commercial product. In general, the NFT has two principal heat flow pathways that determine its temperature. First is the NFT-to-media path; it determines both back-heating and global heat sinking, since the media temperature can be low compared to the NFT away from the hotspot. Second is heat sinking back into the HAMR
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