Carbon Film and Lubricant Layer Damage under Free Space Laser and NFT Heating Shaomin Xiong, Haoyu Wu and David Bogy 26th CML sponsor meeting 2014 CML
Outline New HAMR test bed configuration Experimental study on carbon film Free space at different power levels and repetitions NFT heating Experimental study on lubricant Samples with different substrates Free space at different power levels and repetitions NFT heating Conclusion CML 2014
New HAMR stage at CML Laser focus servo system MTI Fotonic sensor for disk run-out measurement PZT bender/actuator to drive the focusing lens Labview FPGA real-time to implement the control algorithm Laser modulation and spindle encoder/index synchronization (Spartan 6 FPGA card) Linear stage to move the slider and lens Image system to monitor the alignment of the laser to the NFT structure Labview user interface to control the experimental process CML 2014
Laser focus servo-system Demo Controller off on Beam spot: ~ 4 μ m along downtrack and 2 μ m along radial direction CML 2014
Experimental conditions Samples Samples for carbon film study 2.5 inch glass substrate Disks were exposed by free space directly under various power levels and repetitions Disks were dip lubed and a slider with NFT flying above the disk to expose the disk at different power levels and repetitions Disk were delubed and scanned by OSA Samples for lubricant study 3.5 inch disk with aluminum substrate 2.5 inch disk with glass substrate All samples were exposed by free space and NFT under various power levels and repetitions. Two expose modes Single track repetitive exposure using free space laser Shingled exposure using NFT CML 2014
Laser exposure on carbon film Normalized surface reflection When the input power is less than 125 mW, surface reflection increases as the exposure time increases When the power is higher than 125 mW, surface reflection becomes lower and drops as exposed longer. CML 2014
Carbon film under free space laser heating Carbon film was exposed by free space laser with ~4 μ m focus spot under different power levels The repetitions for those tracks are 10, 50, 100, 500, 1000 and 2000. 125 mW 84 mW 154 mW 10 Radial 3 50 100 1 OSA-Psp 6 500 4 1000 5 2 2000 5 4 6 3 1 2 AFM Topo Laser power or repetition increases Surface reflectivity Surface topography Material removed CML 2014
Carbon film under NFT heating Carbon film was shingled exposed by NFT with 50 nm focus spot The effective exposed repetitions for those 4 areas are 12, 6, 2, 1 respectively CML 2014
Lubricant under free space laser heating 2.5 inch glass substrate disk, exposed by free space laser with ~4 μ m focus spot at 110 mW under different repetitions Radial 1 5 50 500 1000 The exposed repetitions for those tracks are 1, 5, 50, 500, 1000 respectively. CML 2014
Lubricant under NFT heating 2.5 inch glass substrate disk, was shingled exposed by NFT with 50 nm focus spot Radial OSA-Qphase The effective exposed repetitions for those 4 areas are 12, 2 and 1 respectively CML 2014
Lubricant exposure 3.5 inch Al substrate disk, exposed by free space laser with ~4 μ m focus spot at 195 mW under different repetitions The laser focus spot is close to 4 μ m. The exposed repetitions for those tracks are 1, 5,10, 50,100, 1000 and 2000 respectively. CML 2014
Lubricant exposure 3.5 inch Al substrate disk, was shingled exposed by NFT with 50 nm focus spot mark The laser focus spot is close to 50 nm, disk speed is close to 4.1 m/s The effective exposed repetitions for those 5 areas are 12, 6, 12, 2 and 1 respectively CML 2014
Conclusion A HAMR test bed has been developed to study the head disk interface for HAMR systems Carbon films Carbon film reflectivity starts to change before surface topography changes Carbon film surface reflectivity change depends on the power input and repetition. The carbon film change induced by NFT heating is similar to that induced by free space heating. Heating duration and temperature are key factors for carbon changes. Lubricant lubricant loss happens for both free space heating and NFT heating. The loss depends on the power input and repetition. The amount of lubricant loss is different for different substrate when the input power is the same. But the lubricant loss shows similar trend for both substrates. The change of lubricant after NFT heating is much more than that after free space heating.Thermal stress plays an important role for lubricant depletion. Heating duration, temperature and thermal gradient are all important for lubricant optimization CML 2014
Intro Name: Haoyu Wu Education: University of Illinois at University of Tsinghua University Urbana-Champaign California, Berkeley
Experience Involved in the HAMR experiments Laser alignment Disk run-out measurement Mechanical stage design OSA and AFM operation Nanoindentation Data analysis for experiments
A Two-stage Heating Scheme for Heat Assisted Magnetic Recording Shaomin Xiong, Jeongmin Kim, Yuan Wang, Xiang Zhang and David Bogy CML 2014
Two-stage heating scheme Reduce the thermal load on the NFT/metal film thus improve the reliability of the NFT Two independent heating stages: • optical waveguide • near field transducer Media The laser input to the NFT in the second stage is less than that in a single stage heating system Shaomin Xiong, Jeongmin Kim, Yuan Wang, Xiang Zhang, David Bogy, "A two-stage heating scheme for heat assisted magnetic recording", Journal of Applied Physics, 115, 17B702 CML 2014
Optical modeling for the head finite-difference time-domain method by CST microwave studio Ta 2 O 5 core SiO 2 cladding Waveguide model gold film NFT model CML 2014
Comparison on the media To heat the media to the Curie point (400 ° C), the amount of power output from the head is. Single NFT heating system: 0.21 mW from the NFT Two-stages heating system: 2.7 mW from the waveguide and 0.15 mW from NFT Power from the NFT drops from 0.21 mW to 0.15 mW CML 2014
Comparison in the head Heat convection gold 100 nm, NFT two ‐ stages only Heat flux adiabatic Maximum 224.6 ° 167.2 ° C C temperature SiO 2 50 μ m protrusion 0.84 nm 0.60 nm stress 308 Mpa 219 Mpa Ambient: 27 ° C CML 2014
Conclusion An optical model was built to design the dual-stage heating system. A thermal-mechanical FEM model was used to evaluate the thermal behavior of media and head for this new scheme. An optimized design was demonstrated. The laser power to the NFT is reduced 30% for the two-stage scheme, compared with the single stage heating scheme. The maximum temperature and maximum thermal gradient are similar in both heating schemes. CML 2014
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