A Study On The Key Technologies Of The Light Delivery System For Heat-assisted Magnetic Recording

With the development of new technologies such as cloud,Internet of things,artificial intelligence,and 5G communication,massive data processing and data storage are constantly challenging the existing storage architecture.In the enterprise level storage system,magnetic storage will continue to play a leading role because of its advantage of performance price ratio.However,the trilemma issue of thermal stability,writability,and the grain size has constrained the increasing the areal density of conventional magnetic recording by further reducing the grain size.To maintain the thermal stability of the small grain size,the magnetic anisotropy needs to be increased,but at the cost of increasing switching magnetic filed beyond the limit of the write head.Addressing this trilemma issue,heat-assisted magnetic recording(HAMR)with the ultra-small light spot for temporarily heating the magnetic grain has been considered as the potential technique to improve the areal data density over 1 Tb/in2 in hard disk drives.The coercivity of the magnetic grain decreases with the temperature rising at the write cycle,and the data can be written to the recording bit when the small grain is heated over the Curie temperature by the small light spot.At present,one of the key difficulties hindering the development of HAMR technology is the low energy efficiency of HAMR.Firstly,we demonstrated the mechanism between the field modes of the waveguide and the NFT.The field mode with higher coupling efficiency can be the output field of the laser,which is important for the coupling efficiency from the laser to waveguide.We demonstrated two novel resonator-antenna systems as the light delivery system for HAMR.We numerically analyzed the interaction mechanism between the resonator waveguide and the antenna.The localized enhanced resonated field of the resonator can improve the electric field enhancement of the antenna.Based on the interaction mechanism,we proposed the ring resonator to achieve higher electric field enhancement of light spots as the resonated field can be several times higher than input light under the resonance condition.The input laser energy can be recycled by limiting the energy in the ring waveguide without using higher power laser sources.Numerical results show that the nanofocusing performance in the ring resonator system would be much better than normal light systems..Secondly,we numerically optimized the lollipop near-field transducer in the two waveguide resonator system.Numerical results show that the nanofocusing performance in the resonator system would be much better than normal light systems.The maximum electric field enhancement of light spots can be 124 in the ring-lollipop system.The proposed resonator-antenna system can effectively increase the nanofocusing performance of the light delivery system for HAMR.Furthermore,we designed a novel near-field transducer to further improve the performance of the ultra-small spot for the semi-circle resonator system.Finally,the magnetic medium structure has been optimized for higher performance.For better impedance matching between the NFT and media.The effects of thickness of mangnetic media and heatsink were numerically investigated in the two waveguide resonator systems.The field enhancement in thin-film media can easily reach the normal value for the light spot size of about 20–40 nm in the resonator system.For the bit patterned media,the thermal profile in the magnetic media can be reduced smaller than the profile of the light spot,which means that the areal density of HAMR can be further improved by the packed patterned media.Numerical results show that the size of light spots can be about 20–40 nm with a good field enhancement.Combined with bit patterned media,the performance can be improved several times than the thin-film structure.The thermal profile of the light spot shows that the areal density of HAMR can further improve beyond the limit size of light spots,and the recording bit can be reduced to 10×12 nm2 corresponding to the areal density of about 5 T b/in2.