Dedicated Servo Recording System and Performance Evaluation

Abstract

The perpendicular magnetic recording (PMR) in hard disk drives is approaching its physical limitation. The emerging technologies, such as heat assisted magnetic recording and microwave assisted magnetic recording have been proposed to record on magnetic media with thermally stable smaller size grains at higher areal density (AD). However, in the media fabrication, achieving wellisolated small size of grains is more challenging than obtaining high K u material as recording media. Reducing the number of grains per bit is a major path for keeping AD growth of PMR in recent years. To minimize the SNR penalty at a smaller grain number per bit, pushing more on track density is the right approach. With the 2-D magnetic recording (TDMR) readers for inter-track interference cancellation, the off-track read capability is improved significantly for allowing a narrower track read. In the drive working environment, when the external vibration or other mechanical disturbance happens during the writing process, it creates more track squeeze at adjacent tracks and leaves a very narrow track at some locations of the track. When the track width is narrower than the squeeze to death width in the 747 curve, it causes hard failure in the channel. To solve the track squeeze problem, this paper proposes to add an additional magnetic recording layer in between the data recording layer and the soft underlayer of conventional PMR media. This additional recording layer is used to record servo information only. The continuous positioning error signal is able to improve the servo performance and to provide the real-time monitoring of the positioning error. When it is under bad servo conditions, the writing process can be stopped to avoid nontolerable track squeeze. The continuous servo signals are designed to be of moderate intensity at very low frequency, and its impact on data signal has been minimized. The linear density gap between the dedicated servo media and the conventional PMR media is able to be controlled within 3%. As the dedicated servo system keeps only around 100 wedges of track ID and sector ID at the data layer, the surface area saving at the data layer can break even in capacity. The dedicated servo technology together with TDMR readers is the key technology to achieve ultrahigh track density during both writing and reading processes.Index Terms-Continuous position error signal (PES), dedicated servo, dedicated servo media, perpendicular magnetic recording (PMR), servo control.

Enhancement of Thermal Conductance at Metal-Dielectric Interfaces Using Subnanometer Metal Adhesion Layers

“…In this technology, a near-field transducer (NFT) heats the magnetic media in a localized region (∼ 50 nm) through the delivery of electromagnetic radiation focused by a gold (Au)-dielectric plasmonic interface. [5][6][7] Heat generated due to parasitic losses in the Au itself is dissipated to the dielectric and results in peak NFT temperatures hundreds of degrees above the ambient temperature. 5 High thermal conductivity dielectrics such as aluminum nitride (AlN) or sapphire (Al 2 O 3 ) would be preferred, therein making their interface with Au the clear bottleneck to heat dissipation.…”

Enhanced architecture and implementation of spectrum shaping codes

“…(2) In information storage fields, spectrum shaping codes have spectrum nulls at specific frequencies ( Pelusi et al, 2015 ). In addition, it is expected to enhance the performance of dedicated servo recording systems by using the shaping codes ( Ng et al, 2015 ; Yuan et al, 2015 ), which is a promising technology for ultra-mobile hard disk drives. Shaping codes with spectrum nulls at non-zero frequencies effectively reduces interference between data signals and narrow band signals.…”