Robert Earl Rottmayer

Heat Assisted Magnetic Recording

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

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

Integrated Heat Assisted Magnetic Recording Head: Design and Recording Demonstration

Scaling the areal density, while maintaining a proper balance between media signal-to-noise ratio, thermal stability, and writability, will soon require an alternative recording technology. Heat assisted magnetic recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g., by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) magnetic field delivery; 2) optical delivery; and 3) magnetic and optical field delivery integration. Thousands of these HAMR heads were built into sliders and head-gimbal assemblies, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~ lambda/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. A magnetic force microscopy image of HAMR media shows that non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, but transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is ~350 nm, but the written track is ~200 nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned.

Challenges in 1 Teradot∕in.2 dot patterning using electron beam lithography for bit-patterned media

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots∕in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist Z...

A new design for an ultra-high density magnetic recording head using a GMR sensor in the CPP mode

In this paper, we present a new head design consisting of a GMR multilayer read element within the write head gap. The GMR read element operates in the CPP mode and is biased by an exchange coupled soft film acting like a permanent magnet. This design has many advantages over the conventional MR and spin-valve bead designs. The most significant advantage is that the read back voltage amplitude is virtually independent of track width. The cross-track profile is well defined. The read and write gaps are coincident and the device is relatively simple and is potentially suited to high yield manufacture. From the micromagnetic analysis, it is estimated that with this head design, recording density as high as 25 Gbits/in/sup 2/ can be achieved.

A perpendicular write head design for high-density recording

In this paper, we discuss a single-pole perpendicular head design and process that is suitable for densities of the order of 100 Gb/in/sup 2/. The single-pole write head was integrated with a narrow-track bottom spin valve reader. The design uses a single-turn coil to generate magnetomotive force in the head. Because of the very short yoke length that is achieved by using a single-coil turn, this writer design has a very low head inductance. Low magnetic impedance of the head makes it suitable for high data rate writing. Using the finite element model (FEM), the head geometry was optimized to write on media with coercivity (H/sub c/) of 5000 Oe. Because of the very efficient head structure, a write current below 100 mA was sufficient. As trackwidths are reduced, the field contours at the media show significant curvature, resulting in written-in transition curvature. Because of the very small yoke structure, no degradation of low-frequency amplitude up to /spl plusmn/90 Oe of external field is observed.

Current-perpendicular-to-plane multilayer sensors for magnetic recording

We investigated current-perpendicular-to-plane giant magnetoresistance multilayer (CPP-ML) sensors with an active region of (1.0-nm CoFe/1.8-nm Cu) /spl times/ 15 nm. These sensors would allow a shield-to-shield spacing of less than 50 nm. Square CPP-ML devices ranging in size from 120 to 365 nm on a side have been fabricated and tested. In this paper, we focus on the magnetotransport properties of the 140 nm devices, which were measured at room temperature. The average device characteristics were found to be R/sub max/=1.0 /spl Omega/, R/sub min/=0.81 /spl Omega/, DR=191.1 /spl Omega/, and DR/R/sub min/=23.7. These values were measured by using a four-point probe geometry; the data were not corrected for lead or contact resistance and no current crowding was observed. After correction for buffer and seed layer resistances, the magnetoresistance had an intrinsic DR/R/sub min/ value of 55.6%. Our measured results are in good agreement with values obtained with a simple two-current series resistance model. We demonstrate that our CPP-ML structures are viable candidates to replace current-in-plane spin valves as the next generation magnetic recording readback sensor.

Exchange coupling of sputter deposited NiCo–O/NiFe thin films

NiCo–O serving as the exchange layer in a spin valvestructure has the advantage of being corrosionresistant and unable to shunt sensing current in the read element. In this work, NiCo–O/NiFe thin films are studied. The films are deposited on Si wafers using rf sputtering. The antiferromagnetic NiCo–O films were reactively sputtered from alloy targets; one has a 55 at. % of Co and the other 60 at. % of Co. The chamber atmosphere is an Ar/O2 mixture containing ∼10% O2. For films with optimal structures, the exchange strength is around 40–45 Oe. The coercivity of the pinned layer is between 18–26 Oe. The exchange strength and coercivity as a function of NiCo–O thickness (with NiFe thickness fixed at 200 A) and NiFe thickness (with NiCo–O fixed at 250 A) are examined. The exchange field is found to increase with the antiferromagnet thickness initially and then flatten out or drop slightly when the antiferromagnet thickness is beyond 200–250 A. Blocking temperature of the bilayer films is also measured, and is found to increase with NiCo–O thickness. NiCo–O with lower Co content shows slightly higher blocking temperature.

Magnetic force microscopy study of submicron track width recording in thin‐film media

The magnetic force microscopy (MFM) technique is used to investigate the writing properties of a set of thin‐film heads with track widths ranging from 2 to 0.5 μm. MFM images show that track edge percolation occurs at lower densities than on‐track intertransition percolation. Track edge percolation results in track edge fluctuations and effective track width reduction. As the head track width is reduced to the near‐micron or submicron ranges, the track edges become dominant portions of the track and consequently cause severe degradation of the recording tracks. Track edge percolation is caused by a poor edge field gradient and is possibly enhanced by pole tip corner saturation. In order to achieve high‐density narrow track recording, high moment writing heads become necessary.

The road to HAMR

Heat assisted magnetic recording (HAMR) was initially proposed in the 1990s to achieve storage densities not limited by superparamagnetism. The key to HAMR has been to find an efficient near field transducer that can operate with a nearby magnetic recording pole. An integrated HAMR head has now been demonstrated which can record at a track width of 50 nm and an areal density of ∼240 Gb/in2 on high coercivity FePt media.