Heat-assisted magnetic recording is a promising approach for enabling large increases in the storage density of hard disk drives. A laser is used to momentarily heat the recording area of the medium to reduce its coercivity below that of the applied magnetic field from the recording head. In such a system, the recording materials have a very high magnetic anisotropy, which is essential for the thermal stability of the magnetization of the extremely small grains in the medium. This technology involves new recording physics, new approaches to near field optics, a recording head that integrates optics and magnetics, new recording materials, lubricants that can withstand extremely high temperatures, and new approaches to the recording channel design. This paper surveys the challenges for this technology and the progress that has been made in addressing them.

Heat Assisted Magnetic Recording

A lithographic apparatus configured to project a patterned beam of radiation onto a target portion of a substrate is disclosed. The apparatus includes a first radiation dose detector and a second radiation dose detector, each detector comprising a secondary electron emission surface configured to receive a radiation flux and to emit secondary electrons due to the receipt of the radiation flux, the first radiation dose detector located upstream with respect to the second radiation dose detector viewed with respect to a direction of radiation transmission, and a meter, connected to each detector, to detect a current or voltage resulting from the secondary electron emission from the respective electron emission surface.

Lithographic apparatus, and device manufacturing method

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities >500 Gb/in2. Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/in2 and beyond. All of the unique components necessary for a working HAMR system have been demonstrated. Although HAMR permits writing on high Hc media with lower magnetic fields and can produce higher write gradients than conventional magnetic recording, head/media spacing and the development of high Hc media with small grains remains challenging

Heat-Assisted Magnetic Recording

Optical data storage has had a major impact on daily life since its introduction to the market in 1982. Compact discs (CDs), digital versatile discs (DVDs), and Blu-ray discs (BDs) are universal data-storage formats with the advantage that the reading and writing of the digital data does not require contact and is therefore wear-free. These formats allow convenient and fast data access, high transfer rates, and electricity-free data storage with low overall archiving costs. The driving force for development in this area is the constant need for increased data-storage capacity and transfer rate. The use of holographic principles for optical data storage is an elegant way to increase the storage capacity and the transfer rate, because by this technique the data can be stored in the volume of the storage material and, moreover, it can be optically processed in parallel. This Review describes the fundamental requirements for holographic data-storage materials and compares the general concepts for the materials used. An overview of the performance of current read-write devices shows how far holographic data storage has already been developed.

From the surface to volume: concepts for the next generation of optical-holographic data-storage materials.

We report a procedure and a material to make patterned surface topologies by light, both in a dynamic way where the structures disappear after exposure or such that the deformations remain permanently. The method is based on a photosensitized cross-linked liquid crystal network with chiral–nematic molecular order. The polymer network is made photoresponsive by a small concentration of copolymerized azobenzene monomers. Upon exposure with patterned UV light, the molecular order parameter in the network is decreased by the trans-to-cis isomerization of the azobenzene, resulting in a density decrease and corresponding local volume increase. Under normal conditions, the polymer network behaves fully elastic and the surface deformation is fast and reversible. To induce permanent deformation, the polymer network needs to be adjusted by chain transfer agents to control the kinetic chain length of the network main chains and allow out of the plane reorientation of the azobenzene moieties and a corresponding loss ...

Light-Induced Formation of Dynamic and Permanent Surface Topologies in Chiral–Nematic Polymer Networks

A readout method using a near field optical head has been proposed as a technique to read out over 30 Gbytes on a 12 cm disc. For the purpose of reading out the RF signal in the system, a gap servo is required to maintain a constant air gap between the solid immersion lens (SIL) and the disc. In this paper, we propose a practical near field readout system with a similar system to an ordinary optical disc, where a biaxial device is used as an optical head actuator and the gap error is detected optically. First, we explain the gap servo system by which it is possible to control the air gap from a far field initial position to a near field target position at a relatively high speed without a head colliding with a disc. Second, we report the result of applying this gap servo system to a 30 Gbyte and a 50 Gbyte ROM disc. Finally, its performance is confirmed by comparing simulated signal with an observed signal.

Gap Servo System for a Biaxial Device Using an Optical Gap Signal in a Near Field Readout System

We developed a high-density near-field optical recording disc system using a solid immersion lens. The near-field optical pick-up consists of a solid immersion lens with a numerical aperture of 1.84. The laser wavelength for recording is 405 nm. In order to realize the near-field optical recording disc, we used a phase-change recording media and a molded polycarbonate substrate. A clear eye pattern of 112 GB capacity with 160 nm track pitch and 50 nm bit length was observed. The equivalent areal density is 80.6 Gbit/in2. The bottom bit error rate of 3 tracks-write was 4.5×10-5. The readout power margin and the recording power margin were ±30.4% and ±11.2%, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.44.3537/pdf

High-Density Near-Field Optical Disc Recording

An optical pickup device and an optical recording and reproducing apparatus are suitable for use with a near-field optical recording and reproducing system. An optical pickup device comprises an objective lens composed of a solid immersion lens (SIL) the objective lens having a numerical aperture greater than 1, a beam splitter configured to reflect both of a p-polarized light component and an s-polarized light component of reflected lights from an optical recording medium when the optical pickup device irradiates the optical recording medium with a bundle of rays in a predetermined polarized state from a light source through the objective lens, a divider configured to divide incident light into a p-polarized light component and an s-polarized light component reflected by the beam splitter, and a photo-detector configured to separately detect the p-polarized light component and the s-polarized light component divided by the divider.

Optical pickup device, recording and reproducing apparatus and gap detection method

The present invention is applicable to a recording apparatus of a CD or DVD, a recording method thereof and a recording medium, and an object of the present invention is to clearly record a second information such as characters and figures between two recording levels in an optical disk. The second information is recorded in a predetermined area in a radius direction and a angular direction on the optical information recording medium, and further, the second information is recorded according to a change of a pit width based on a change of power of the laser beam, a change of a pit length based on an on/off control of the laser beam, or a change of depression or bulge of the pit based on a change in the vicinity of the on/off control of the laser beam. Whereby it is possible to record the second information such as a watermark pattern or a visible image, which is capable of being confirmed by seeing a disk.

Optical and visual information recording medium, optical and visual information recording apparatus and method

We describe a method of obtaining an optical air gap control signal for near-field optical disc systems. Because of the total reflection on the surface of a solid immersion lens (SIL), the polarization state of the reflected light differs from that of the incident light. However, when the SIL is close to a disc surface, the polarization state difference between the reflected and the incident light becomes small. We used this difference to obtain an air gap control signal. Both observed and calculated results show that this signal is negligibly affected by the pits on the disc. Thus, our air gap servo system is stable. We show the observed readout signals of a 40 GB ROM disc (with a 12 cm diameter) obtained by an optical head with a 1.4 NA objective lens and a 405nm wavelength GaN LD. Comparisons between observed and calculated results are made.

Tsutomu Ishimoto

Papers

Gap Servo System for a Biaxial Device Using an Optical Gap Signal in a Near Field Readout System

High-Density Near-Field Optical Disc Recording

Optical pickup device, recording and reproducing apparatus and gap detection method

Optical and visual information recording medium, optical and visual information recording apparatus and method

Readout Method for Read Only Memory Signal and Air Gap Control Signal in a Near Field Optical Disc System