【作者】 陈玮；

【导师】 陈进才；

【作者基本信息】 华中科技大学 ， 计算机系统结构， 2021， 博士

【摘要】 随着云、物联网、人工智能和5G通信等新兴技术的发展,海量的数据存储与处理对存储体系结构提出了严重的技术挑战。在企业级的存储体系中,磁存储因其性能价格比的优势,仍将继续发挥其主导的作用。为满足未来数据存储的要求,磁存储急需突破现有的关键技术瓶颈,继续提高存储面密度以进一步降低存储的成本。热辅助磁记录技术(heat-assisted magnetic recording,HAMR)是未来突破磁记录超顺磁技术瓶颈最具潜力的磁记录技术。HAMR技术引入光组件系统克服光衍射极限,实现激光能量在纳米尺度的聚焦,从而完成超小磁记录位的加热,辅助磁头的写入磁场完成数据的写入。为达更高密度的磁存储,HAMR加热的光斑尺寸要更小,目前的困境是加热光斑尺寸与光能效率存在冲突,小光斑尺寸造成光能效率过低,导致复杂的HAMR光写头设计和高成本的激光器选择。本文揭示谐振光场在HAMR光组件系统的作用机制,进而采用两个不同谐振系统来提高光能效率过低的问题,并降低HAMR光写头复杂性。另外,HAMR谐振光系统上,结合磁介质结构优化设计,突破光斑尺寸的限制,实现更高磁记录面密度。本文主要研究内容与创新性贡献如下:(1)针对光组件系统的波导结构进行建模仿真,揭示谐振波导的谐振光场耦合机制,设计了两个结构简单的谐振波导系统,实现光组件系统的光学性能的1~4倍提升。首先,基于波导本征光场模式与近场换能器表面等离子激元的激发原理,分离出有效的波导本征光场模式,完成激光器入射光场建模。采用波导本征光场模式作为激光发射光场,可以有效减小激光入射光场与波导耦合的能量损耗。然后,提出谐振光场用于激发近场换能器的表面等离子激元,从而提高近场换能器所产生超小光斑的场增强,进而提高近场换能器的光能量效率,谐振光场提高光能量耦合效率本质上是循环利用入射激光光场完成能量效率的提高。再则,根据谐振光场耦合机制,设计出简单无需复杂控制的半圆谐振波导系统,实现入射光场的二次利用,实现超小光斑性能的一倍提高。最后,进一步设计微环谐振波导,在满足临界耦合条件是,可以实现入射光场的多次循环利用,形成用于激发表面等离子激元的高场增强的波导谐振光场,再次实现超小光斑的场增强性能的提高,达到光场场增强的1~4倍提高。(2)针对近场换能器进行建模仿真,对近场换能器优化并重新设计,完成近场换能器光学性能的20%~50%提升。首先,研究分析近场换能器表面等离子激元的机制原理,从理论上对近场换能器进行优化设计建模。然后,基于谐振波导系统仿真建模,对近场换能器结构参数进行优化设计,对参数进行细调,实现超小光斑场增强的提高。最后,为进一步提高近场换能器所产生的超小光斑性能,设计了一个改进的新型长扁形近场换能器,光场场增强提升了20%。(3)针对介质层进行仿真建模,突破光斑尺寸的限制,实现面密度的两倍提升。首先,研究分析HAMR光组件系统与介质层阻抗理论模型。接着,研究谐振波导系统对传统连续薄膜介质层光学和热学的性能,深入探索光组件系统所产生的超小光斑对面密度提升的要求和限制。最后,针对图案化介质层进行建模仿真,在磁柱岛周围填充低折射不吸光材料,降低阻抗失配。结果表明,控制介质层结构参数,一方面可以四倍提高介质层的光热性能;另一方面在不增加激光功率和光组件系统复杂性下,面密度可以突破超小光斑尺寸的限制,实现面密度可以达到5 Tb/in2。更多还原

【Abstract】 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.更多还原