Nanoscale temperature of plasmonic HAMR heads by polymer imprint thermal mapping
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Nanoscale temperature of plasmonic HAMR heads by polymer imprint thermal mapping Gregory T. Hohensee1, Tan Nguyen1, Ella Pek2, Wan Kuang1,3, Ozgun Suzer1, and Marc Finot1 1
Western Digital Corporation, 1250 Reliance Way, Fremont CA 94539, U.S.A. Department of Materials Science and Engineering, Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A. 3 Department of Electrical and Computer Engineering, Boise State University, Boise, ID 83725, U.S.A. 2
ABSTRACT Polymer imprint thermal mapping (PITM) is a high-resolution thermal mapping technique that is especially valuable for nanoscale plasmonic devices. PITM leverages a ~50 nm polymer film coating that crosslinks irreversibly with temperature, which records the peak temperature rise of the surface in the local, linear reduction of polymer film thickness. Using AFM to measure topography before and after heating, but not during operation, PITM sidesteps plasmonic artifacts seen in other near-field thermometries, where the probe tip disturbs and is heated directly by the near- and far-field radiation around the plasmonic device. This is notably troublesome for characterizing heat-assisted magnetic recording (HAMR) heads for nextgeneration hard disk drives. HAMR heads use near-field transducers (NFTs) to focus light on a magnetic media, heating a nanoscale region to its Curie temperature to enable magnetic writing. The PITM proof-of-concept was introduced at The Magnetic Recording Conference (TMRC) in 2015: here, we present a mature technique capable of benchmarking finite-element thermal simulations of nanoscale devices. INTRODUCTION Heat-assisted magnetic recording (HAMR) is a next-generation hard disk drive technology that promises to extend gains in storage capacity that have been slowing down with the current perpendicular magnetic recording (PMR) technology.[1] HAMR operates by integrating an optical waveguide and plasmonic near-field transducer (NFT) structure adjacent to the magnetic write pole on the media-facing surface of the recording head. A laser is fed into the waveguide and couples to the NFT surface, where the high plasmonic field is absorbed in the media recording layer to generate a sub-100 nm hot spot on the media. The media hot spot can reach Curie temperatures near 700 K to enable writing of increasingly small bit sizes on high magnetic moment recording media.[2,3,4] A central challenge for HAMR heads is nanoscale thermal management of the NFT.[4] The NFT dissipates some optical energy as heat, and will also be back-heated from the media hot spot. Although Au is considered the most efficient, least reactive plasmonic metal, it may not be mechanically robust at high temperatures. Reducing NFT temperature is a direct route to ensuring longer lifetimes for HAMR heads and bring HAMR closer to a commercial product. There are few known nanoscale temperature metrology techniques capable of producing calibrated and spatially resolved data for a HAMR head near the NFT, because the NFT is a plasmonic structure. Th
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