Thin Film Head Research Articles

Study on the overall performance of ZrO2 nanoparticle reinforced Co and CoP composite coating prepared by electrodeposition

Co coating and CoP alloy coating reinforced by ZrO2 nanoparticles are prepared on the surface of the brass substrate by DC electrodeposition to improve the magnetic property and corrosion resistance. The Co/ZrO2 and CoP/ZrO2 composite coating electrodeposited on the surface of brass can be used in the field of thin-film magnetic heads, thin-film sensors and electronic circuits. By comparing the performance of different cobalt-based alloy coatings, the influence of ZrO2 nanoparticles on the electrodeposition and performance of Co coating and CoP alloy coating is studied. It is found that cobalt electrodeposition is a typical irreversible process with diffusion control. The CoP alloy coating comprises about 81% Co and 19% P. However, the electrodeposited CoP/ZrO2 composite coating possesses about 86% Co, 3% P, and 11% Zr. The incorporation of a 15 g/L ZrO2 nanoparticle with the size of 50 nm is beneficial to improve the cobalt content and decrease the amount of phosphorus in the CoP/ZrO2 composite coating. The hardness of CoP alloy coating is about 350 HV. However, the surface hardness of Co/ZrO2 and CoP/ZrO2 composite coating is about 400 HV and 470 HV, respectively. All the cobalt-based coatings show cellular surface morphology. The ZrO2 nanoparticles incorporated in the cobalt coating can enter into the cobalt lattice or disperse at the grain boundary to refine the grain size and limit the displacement of magnetic domain to improve the corrosion resistance and coercivity extremely. It is found out that the electrodeposited CoP/ZrO2 composite coating has the best corrosion resistance with only 9.7 μA/cm2 corrosion current density and the largest coercivity of 665.1 Oe. The optimal corrosion resistance and good magnetic performance of prepared CoP/ZrO2 is a promising material in the field of microelectromechanical systems as micro pumps, magnetic read heads, micro motors, and so on.

An improved patent similarity measurement based on entities and semantic relations

Abstract Patent similarity measurement, as one of the fundamental building blocks for patent analysis, is able to derive technical intelligence efficiently, but also can detect the risk of infringement and evaluate whether the invention meets the criteria of novelty and innovation. However, traditional approaches make implicitly several assumptions, such as bag of words in each component, semantic direction irrelevance and so on. In order to relax these assumptions, this study proposes an improved methodology on the basis of entities and semantic relations (functional and non-functional relations), which takes semantic direction of each sequence structure and the word order information of each component into consideration. Meanwhile, an algorithm for calculating the global importance of each sequence structure is put forward. Finally, to verify the effectiveness and performance of the improved semantic analysis, a case study is conducted on the thin film head subfield in the field of hard disk drive. Extensive experimental results show that our approach is significantly more accurate.

From the Lab to Scaling-up: Case Studies of Electrodeposition Processes in the Photovoltaic Industry

Photovoltaic (PV), with more than 300 GW of cumulative capacity installed by the end of 2016, represents about 1.5% of the world electricity production. It is now obvious that the growth of PV will not only continue but even accelerate, as a key player for the energy transition, reaching up about 5 TW by 2050, as projected by the International Energy Association. The main reason for this development is due to a reduction by 10 of PV electricity cost in ten years. This trend makes PV electricity competitive with classical fossil or nuclear electricity in many regions of the world. The decrease in cost has resulted from improvement in materials and methods, an increase in solar energy conversion efficiency and in volume production. Research and Development plays a major role in this process proposing innovation and scientific breakthroughs in existing PV technologies and introduction of new technologies. Scaling effects have played a key role in decreasing the production costs but further progress along with innovative technologies will be needed to lower costs. The comparison between thin film technologies and wafer based technologies is typical of this paradigm. Thin film technologies are basically coating technologies which are inherently better adapted for large area processing (thousands of km2) compared to slicing individual crystalline wafers and assembling them as a mosaic. However, any defect on a part of a large area process induces a huge impact on the whole panel where the slices of Silicon are sorted to produce module. Moreover, the cost reduction of the wafer technology with scaling and the industrial maturity of silicon technology is so rapid that this technology is cost leading. As a consequence, the PV industrial sector is dominated at more than 90% by Silicon solar cells. The remaining 10% is composed of vacuum based thin films. Electrodeposition, despite intrinsic advantages, with real success in industry with, among numerous other examples, damascene copper in semiconductor or permalloys in thin film head, is almost absent of this PV industrial landscape. However, introduction of plating will be easier and more probable for new cell technologies, where new investment has to be done and for which stringer requirements emerge. In this context, we will discuss and make some prospective about two case studies involving electrodeposition in PV: plating contacts on Silicon and Cu-In-Ga based plating for thin films solar cells. On Silicon PV market, Copper represents an alternative to Silver screen printing. Copper has a much lower price than Silver with an equivalent bulk resistivity. Interdigited Back Contact (IBC) and Heterojonction (HJT) solar cells with Cu plating already exists for years. Nonetheless, Cu being a lifetime killer in c-Si, a Ni diffusion barrier is usually used. This approach has been demonstrated for front side metallization, based on Light Induced Plating. The case of emerging bifacial solar cells will be specifically discussed with the use of Ni/Cu or Ni/Ag plating. The remaining challenges will be discussed, including specificity of plating on both sides simultaneously, surface roughness issue and his impact on adhesion, ghost plating linked to surface passivation defects. For producing thin film solar cells, an alternative to vacuum based deposition methods (co evaporation, sputtering), which are presently used, is to use electrodeposition or printing. We will make a comprehensive description of the scale-up of the electrodeposited CIGS precursor layers from the laboratory scale of a rotating disk electrode to a full-size 60 cm x 120 cm compatible with 1 m2/min production of solar panels. More specifically, we will discuss the different fabrication approaches for electrodeposited precursor CIGS materials, development and recycling of solution chemistries for Copper, Indium and Gallium. Resulting fabrication of solar cells will be described. We will also present applications and devices which specifically take advantage from electrodeposition approach that is localized deposition on patterned substrate. The specific mechanism of electrodeposition in microelectrode array configuration and the challenge of upscaling will be discussed. References L. Tous et al, Energy Procedia 124, 922–929 (2017). Q. Huang, et al, Journal of The Electrochemical Society, vol. 158, issue 2, 2011, D57-D61 P.-P. Grand et al, WO 2012/052657 C. Broussillou et al, IEEE, New Orleans (2015) A. Duchatelet et al, Applied Physics Letters, 109 (2016), 253901

(Invited) New Developments in Magnetic Inductors for On-Chip Power Conversion, Including Fabrication

Integrated dc-dc power converters have been the subject of intense research interest over the past 10 – 12 years because they offer so many potential benefits, not just in promising savings of up 20% of board space, but also enabling control of individual chip voltages and delivering power at high voltage and low current, thus reducing power train I2R loss. Among the various power converter options, the inductive Buck converter is the most attractive because it can deliver a wide output voltage range with an expected high efficiency (≥ 90%). However, for on-chip applications, the inductive Buck converter is the least developed power converter, there being at present no such inductor ready for use in a standard CMOS back-end-of-line (BEOL) fabrication facility. Major strides towards the realization of on-chip power conversion have been made by IBM in case of its POWER8TM processor (1), and by Intel in case of its 4th generation (Haswell) processor (2), which uses near-chip- integrated power converters; although neither company’s new power converter used an integrated magnetic inductor. After highlighting the important role that magnetic inductors are expected to play in on-chip power conversion, this talk will describe new developments in magnetic materials for inductors, especially those employed at IBM, and the fabrication challenges faced in integrating these materials in inductors. Yoke material and thickness (typically 1 - 5 microns) can be tailored to reach desired inductance values (i.e., 1 – 30 nH) in thin-film ferromagnetic inductors, while endeavoring to maintain a high enough operating frequency (i.e., 20 – 200 MHz). Electrodeposition was an enabling technology for the thin-film magnetic recording head, and was thus used for yoke fabrication of our earlier inductors (3, 4). IBM and Columbia University recently demonstrated an efficiency of 82% in a World's first 3D-integrated inductor/voltage regulator that employed thru-silicon via technology and electrodeposited Ni45Fe55 yokes (5). Nevertheless, significant advancements in eddy current suppression through electrodeposition of either sufficiently resistive or insulating-layer-laminated magnetic layers have proved elusive. Thus, considerable efforts have gone into developing new, higher resistivity, sputtered magnetic alloys (> 100 µΩcm), usually with insulating lamination layers. A notable example produced by sputtering is amorphous Co91.5Zr4Ta4.5 (CZT), which has, for example, been used as the yoke material in inductors fabricated on top of 90 nm CMOS structures by Gardner et al. (6). We chose to explore sputtered, laminated, amorphous Co20Fe60B20 magnetic films due to their extremely soft magnetic soft properties (Hc ≤ 0.1 Oe) and low, magnetic-permeability-related, loss tangent (≤ 0.1) for a wide range of frequencies, and thermal stability up to 350oC. This required development of a new fabrication scheme to integrate the blanket-deposited, sputtered magnetic layers with 200 mm CMOS substrates. We employed ion beam etching (IBE) patterning methods since no other method, e.g., wet etching, could anisotropically etch all of the inductor yoke stack materials. Peak quality factors (Q) ≥ 12 (at 120MHz) were demonstrated on magnetic inductors containing laminated Co20Fe60B20 magnetic films as shown in Fig. 1, double the Q values of previous inductors that had electrodeposited Ni45Fe55. All inductor devices functioned across a 200 mm wafer, the consistent device performance observed indicative of a reliable, high-yield fabrication process. Fig. 1. Left: Comparison of Q values for inductors with sputtered Co20Fe60B20 materials and electrodeposited Ni45Fe55 (for the latter, see ref. 3). Right: Summary of Qpeak values for single-turn inductors on a 200 mm wafer. [1] Z. Toprak-Deniz et al., ISSCC Digest, 112 (2014). [2] E. A. Burton, et al., Proc. Applied Power Electronics and Expositions (IEEE-APEC), p. 432-439 (2014) [3] N. Wang et al., J. Appl. Phys., 111, 07E732 (2012). [4] N. Sturcken et al., ISSCC, 48, 244 (2013). [5] K. Tien et al., in VLSI Technology (VLSI technology), 2015 Symposium on, Kyoto, 2015, pp.C192-C193. [6] D. S. Gardner et al., J. Appl. Phys., 103, 07E927 (2008). Figure 1

Effect of Carbon Overcoat on Heat-Assisted Magnetic Recording Performance

Heat-assisted magnetic recording (HAMR) is a promising approach for enabling large increases in the magnetic data storage density. Amorphous carbon is the principal overcoat material of thin-film disks and magnetic heads in the HAMR systems. In this paper, we investigated the recording performance of media with a chemical vapor deposition (CVD) carbon overcoat (COC) and a sputtered COC. We observed that the carbon type has a significant impact on the HAMR recording performance and the heat absorption. Tunneling current atomic force microscopy analysis results show higher surface roughness and peak current in the disk with the sputtered carbon. Track profile and magnetic signal measurement results indicate 90% of the optimized laser current is not enough to fully write the disk with the CVD carbon, while the tracks on the sputtered carbon disk can be written using the same laser current. The difference in the two types of COC can be attributed to the difference in the carbon bonding structure, the optical and electrical properties, the roughness, and the heat absorption behavior.

The First Thin Film Electronic Package

The magnetic thin-film head, announced by IBM in 1979, marked the transformation of electrochemical technology from a shop art to a precision manufacturing process with far wider applications than the thin film head. An important application of electroplating was in the fabrication of the multichip module that provided the packaging for chips in advanced computers. These modules included copper strip lines for data transmission between chips. To minimize pulse distortion, these lines had to have precisely controlled propagation characteristics, and plating through a lithographic mask was the most effective way to insure the tight control on the geometry of the lines necessary to meet this requirement. This paper highlights the evolution of packaging for computers and tells how the scientists and engineers from the IBM T.J. Watson Research Center who had created the thin film head, worked with the development and manufacturing groups at IBM’s East Fishkill plant to bring electrochemistry into the manufacture of advanced packaging modules.

The First Thin Film Electronic Package: From Invention to Manufacturing

As late as the end of the 1970’s, electroplating was regarded as a mystical shop art that had no place in microelectronic fabrication. In 1979 IBM introduced a magnetic thin film head made possible by a newly invented process that was based on electroplating – an achievement that cast electroplating in a new light. Today, electroplating has spread into applications ranging from nanoscale patterning of copper BEOL wiring below 10 nanometers on silicon chips to the deposition of materials for synthesis into photovoltaic layers on 60 cm by 120 cm solar panels, and has also made possible the use of metal structures in MEMS devices. The successful production of the thin film head with its precisely patterned high aspect ratio copper coils and its permalloy elements with tightly controlled magnetic properties, which plating experts of the 1970’s deemed impossible to do by plating, made device fabricators receptive to the electrochemical technology they once shunned.An important new application of electroplating technology was in the fabrication of the multichip module. In advanced computers, these modules were multilayer ceramic structures that provided the power connections to the circuit chips and had a top layer of copper strip lines for data transmission between chips. The strip lines consisted of copper conductors with a rectangular cross-section that might be 6 µm high and 10 to 20 µm wide embedded in polyimide between two ground planes. These structures, which were essentially low-loss transmission lines, had to have precisely controlled propagation characteristics to minimize pulse distortion. Plating through a lithographic mask was an effective way of insuring the tight control on the geometry of the lines necessary to meet this requirement. One aspect of this talk will be to highlight the technical aspects of integrating electrochemical technology into the fabrication process for the transmission lines. The other will address how the scientists and engineers from the IBM T.J. Watson Research Center who had created the thin film head, worked with the development and manufacturing engineers at IBM’s East Fishkill plant to bring electrochemistry into their production line.

Keynote: Thin Film Magnetic Heads: Break-through of Electroplating into Electronics, Quantum Jump in Magnetic Storage

When IBM announced the random access magnetic disk storage system RAMAC 305 in 1957, it was hailed as a major break-through in data storage. By the early 1960s engineers realized that within a decade or so the system would not be able to achieve the higher areal density needed to meet the ever increasing demand for greater storage capacity. The limitation was that the hand-wound magnetic head could not be made any smaller to further increase the areal density on the discs. Many proposals were made and patents filed for small heads, but the technology to produce the required miniature 3-D structures did not exist.The first break-through came when we demonstrated that it is possible to electroplate the 3 µm thick, precise patterns of copper and permalloy required for a magnetic head through a photoresist mask on a thin, conductive seed layer. This was followed by exploratory investigations to achieve the required magnetic material properties of the metallic alloys and the invention of appropriate plating tools to build the head structures. Working side by side with the design engineers, functional requirements of the head could be balanced against fabrication process capabilities to produce a testable device.Our presentation will describe the structure of the inductive read/write heads, MR read-only heads and integrated MR read/inductive write heads. We will show that viable heads would not have been possible without several studies and inventions relating to plating solution chemistry, processing, materials and very uniform, high intensity, reproducible agitation in plating tools. Furthermore, all the process steps had to be carefully chosen to make sure no process step damaged any of the previously fabricated structure or interfered with subsequent steps. We were learning process integration before that concept even had a formal name. Once the prototype heads were built at the Yorktown Research lab and accepted for IBM’s next generation storage system, the next step was to design and build a pilot line in San Jose, IBM’s manufacturing site for magnetic storage. Electrochemical processes with the precision required for the thin film head had never before been run on a production line. Establishing the line required frequent visits to San Jose and often daily phone contact with their engineers. Furthermore, several of the engineers who were hired to run the San Jose line spent their first year with IBM in Yorktown doing research related to head fabrication, thus facilitating the transfer of this knowledge to San Jose.The five prong approach that prevailed from the first prototype to the final product was to concurrently develop the fabrication tools and to engage in studies related to the materials, the process, process control and process integration. Our preference was to use concrete data wherever possible, but to make the best engineering judgment if such data was not available. Studies were carried just far enough to obtain the information required to control the process and build the head. When time permitted, or if new problems surfaced, we could further pursue these studies. Where problems could be clearly defined and did not need head building capability, we tried to get professors and students interested in working on them.We have demonstrated that even in the absence of a full set of concrete data it is possible to build a relatively complex device by using the available information in combination with the best engineering judgment and then coming back to refine the technology into a full-fledged manufacturing process with all the necessary controls for optimum mass production.When the RAMAC 305 was first introduced, the disk size was 24 inches in diameter and the density of magnetic recording was 2 kilobits/in2. Today the disk size may be as small as two inches in diameter and the density is approaching a trillion bits per square inch – an increase of nearly 6 orders of magnitude in 50 years. In the same time, the cost of storage has dropped by 6 orders of magnitude. The successful use of electrochemistry in building the thin film head has underscored the importance of this field in both science and engineering. Electrochemical technology today is treated as a desirable fabrication approach in silicon chip fabrication, packaging, chip package attachment and MEMS. The thin film head has been a key factor in enabling the computers that now play a vital role in every aspect of our lives.

Magnetic Inductors and Their Increasing Importance in the Development of on-Chip Power Conversion

Major strides in on-chip power conversion have been made by IBM in case of their POWER8TM processor (1), and by Intel in case of their 4th generation (Haswell) processor (2), although neither company’s new on-chip voltage regulator (VR) uses an integrated inductor. After outlining why on-chip power conversion is so desirable, this talk will highlight the important role of magnetic inductors in power conversion, and will review recent developments in, and prospects for, magnetic materials for inductors, especially those formed by plating methods.Granular DC-DC power delivery, consisting of fast dynamic voltage scaling for each load through use of a dedicated VR, can significantly improve energy efficiency. Traditionally, the large size of the inductor component has impeded efforts to fabricate the VR in one module. The preferred approach to shrinking the inductor is to increase the switching frequency. The downside to higher frequency operation is reduced efficiency and increased heat dissipation. Thus, shrinking the inductor involves a compromise of space vs. performance, and placing the VRM with an integrated inductor on the processor using thin-film fabrication processes is a natural, if challenging, progression.In thin-film ferromagnetic inductors, yoke material and thicknesses (typically 1 - 3 microns) can be tailored to reach desired inductance values (e.g., 10 – 40 nH), while endeavoring to maintain high enough operating frequency (e.g., 50 – 100 MHz). Considerable efforts have gone into developing new magnetic alloys with higher resistivity (> 100 µΩcm) to reduce yoke eddy currents. A notable example produced by sputtering is amorphous Co91.5Zr4Ta4.5 (CZT) [3, 4], which seems to have become the standard against which other materials are compared. This has been used as the yoke material in inductors fabricated on top of 90 nm CMOS structures by Gardner et al. [5], for example.Electroplating has been a standard technique for the deposition of thick metal films due to its high deposition rate, conformal coverage and low cost. It was an enabling technology for the thin-film magnetic recording head, and was thus used for yoke fabrication for our inductors (6, 7). For the latter, Ni45Fe55 was chosen over Ni80Fe20 for its higher magnetic moment (1.6T), high anisotropy field, and higher electrical resistivity (40 µΩcm). Plated Co-based materials are attractive alternatives to Ni-Fe as yoke materials, e.g. due to their higher moment, especially if their resistivity can be made to approach or exceed 100 µΩcm. We are exploring the use of electrolessly-plated, Co-W-P films for inductor applications (8). The electroless Co-W-P films show excellent magnetic properties, with good magnetic anisotropy, and coercivity of less than 0.1 Oe (Fig. 1). The resistivity of the films is about 90-100 µΩcm, which is close to that of most amorphous Co-based alloys. [1] Z. Toprak-Deniz et al., ISSCC Digest, 112 (2014).[2] E. A. Burton, et al., Proc. Applied Power Electronics and Expositions (IEEE-APEC), p. 432-439 (2014)[3] K. Hayashi et al., J. Appl. Phys., 61, 2983 (1987).[4] D. S. Gardner et al., IEEE Trans. Magn. 43, 2615 (2007).[5] D. S. Gardner et al., J. Appl. Phys., 103, 07E927 (2008).[6] N. Wang et al., J. Appl. Phys., 111, 07E732 (2012).[7] N. Sturcken et al., ISSCC, 48, 244 (2013).[8] N. Wang et al., MMM-Intermag, paper HG-11, 2013 Fig. 1. Hysteresis loop (left) and SEM Xsection (right) of an electrolessly-plated Co-W-P films.This work was supported in part by Lawrence Livermore National Laboratory subcontract No. B601996 under prime contract DE-AC52-07NA27344 from the U.S. Government. Inductor fabrication was carried out in the Microelectronics Research Laboratory (MRL) at IBM’s T. J. Watson Research Center.

Hard disk drive thin film head manufactured using nanoimprint lithography

The lithographic requirements for the thin film head (TFH) industry are comparable to the semiconductor industry for certain parameters such as resolution and pattern repeatability. In other aspects such as throughput and defectivity, the requirements tend to be more relaxed. These requirements match well with the strengths and weaknesses reported concerning nanoimprint lithography (NIL) and suggest an alternative approach to optical lithography. We demonstrate the proof of concept of using NIL patterning, in particular Jet and Flash™ Imprint Lithography (J-FIL™) (Imprio, Jet and Flash Imprint Lithography, and J-FIL trademarks are the property of Molecular Imprints, Inc.), to build functional TFH devices with performance comparable to standard wafer processing. An Imprio™ 300 tool from Molecular Imprints, Inc. (MII) was modified to process the AlTiC ceramic wafers commonly used in the TFH industry. Templates were produced using commercially viable photomask manufacturing processes and the AlTiC wafer process flow was successfully modified to support NIL processing. Future work is identified to further improve lithographic performance including residual layer thickness uniformity, wafer topography, NIL→NIL overlay, and development of a large imprint field that exceeds what is available in optical lithography.

(Invited) Thin Film Magnetic Heads - Early Inventions and Their Ongoing Impact on Magnetic Storage and on Electrochemistry

Although many researchers in the 1960s hoped to use LSI techniques to batch fabricate magnetic read/write heads for data storage, building these devices entailed a much different set of requirements than LSI was addressing in circuit chip fabrication. Electroplating through a mask proved to be the way to pattern the magnetic elements and copper conductors of a thin film head, but this technology had to be integrated with a host of additional inventions to manufacture the device. This paper outlines the key inventions that had to be made as the head evolved from a laboratory demonstration to a manufactured product. The basic processes that were used to build the first thin film heads are still used to fabricate the heads in today's magnetic storage systems. The technology has also found its way into such diverse microelectronic applications as MEMS, NEMS, electronic packaging, semiconductor chip fabrication and, more recently, solar devices. The success of electroplating as one of the key processes in manufacturing the head has put a new focus on electrochemistry in both academia and industry.

Modification of polycrystalline nanodiamonds by using periodic magnetic field enhanced hydrogen plasma and the application on nanogrinding of thin film magnetic head

Polycrystalline nanodiamonds (NDs) derived from shock wave synthesis exhibits serious agglomeration in non-polar medium such as clean oil. Here we report an efficient new approach to modify the NDs by exposing the nanoparticles to periodic magnetic field (PMF) enhanced hydrogen plasma in the gas phase. The modification treatment transforms oxygenated groups on the NDs surface into CH terminations. The evolution of polycrystalline NDs has been carefully characterized by FTIR, Raman and XRD analysis and the enhancement mechanism of PMF was discussed. After this treatment, well-dispersed and stable suspensions of diamond nanoparticles in clean oil with average diameter of 74.7nm can be obtained. Subsequent nanogrinding of thin-film magnetic heads (TFH) validates their dispersion behavior. A smooth substrate (Ra∼0.387nm) surface and a planar recording surface (PTR∼0.048nm) were achieved.

A method to calculate the parameters of magnetization transition in hard discs with longitudinal recording

The conditions for determination of the parameters of the saw-toothed transition under the action of an external magnetic field (process of recording) and under no external field (process of demagnetization) were presented with the use of the effective fields. Examples of calculating the parameters of the saw-toothed transitions for various values of the coercitive force of the magnetic medium at recording under the action of the magnetic field of the thin-film head and during the progress of demagnetization were given.

Magnetic field of thin film heads for longitudinal recording on hard disks

Analytical expressions for the scalar magnetic potential vs. variation of magnetization in the pole of a thin-film magnetic head, pole dimensions, and the horizontal and vertical pole positions relative to the plane of the hard-disk working layer were established. Expressions for the magnetic stray fields vs. the horizontal and vertical poles were obtained by studying the pole domain structure vs. the external magnetic field and determining the domain of magnetization variation in the pole marginal zones vs. the external field. Expressions for the write fields of the thin-film heads were established as a superposition of the pole stray fields. Examples of calculations of the write fields were given for various kinds of the thin-film magnetic heads.

Review of perpendicular magnetic recording research at Fujitsu

Perpendicular magnetic recording (PMR) research and development (R&D) was carried out at Fujitsu for 32 years from 1978 to 2009, separated into three stages. We developed PMR for use in hard disk drives (HDDs). We sputtered Co–Cr alloy thin film onto a disk substrate and evaluated it using thin-film heads. Some interesting results were obtained at each stage. On the way we fabricated 1.8″ HDDs in 1992 and finally shipped the mass-produced PMR HDDs in 2006. Unfortunately, the HDD business at Fujitsu closed down. I would like to review the exceptional PMR research undertaken at Fujitsu.

Magnetization process of heat assisted magnetic recording by micro-magnetic simulation

Magnetization reversal in a uniform magnetic field and one bit recording process by a thin film head in the heat assisted magnetic recording system of TbFeCo medium are studied by using the micro-magnetic simulation and the heat equation. The Landau-Lifsitz-Gilbert equation is solved for magnetic parameters at temperatures as the time goes by. It is found that magnetization proceeds as a progressive wave, although this behaviour may not limit the recording speed. The recording bit is expanded by the thermal fluctuation. The expansion can be suppressed as the medium thickness increases, because the thermal fluctuation is small in the thick medium. So the control of the medium thickness is important very much to achieve a high-density heat-assisted recording.

Paradigm Shifts in Electronics Enabled by Electrochemical Micro/Nano Processing

Advances in electronic materials, processing technologies, and integration schemes have resulted in phenomenal miniaturization of electronic components. Since the development of through-mask plating for thin film heads in the1960s and 1970s, an enormous amount of industrial and academic R effort has positioned electrochemical processing among the most sophisticated processing technologies employed in the microelectronics industry today. Electrochemical processing has thus become an integral part of advanced wafer processing and an enabling technology for nanofabrication. In this review we begin with a brief discussion of the phenomenal advances in IC based electronics and Moores law as indicators of the paradigm shifts in microelectronics. We then highlight the important role played by electrochemical processing in the electronics industry. A detailed discussion of the dual Damascene plating technology and electroplated C4 technology form the key elements of the review. Finally, the challenges and opportunities offered by these technologies in extending Moores law are discussed. Keywords: Lead-free flip-chip interconnect technology, Chip-package interconnect, Electrochemical mechanical planarization, Electropolishing, Electroless capping, Chip metallization, Moore's law, Integrated circuit, Electrochemical processing

Thin-Film Processing Realities for ${\hbox{Tbit/in}}^{2}$ Recording

Magnetic recording has maintained a cost/bit advantage over solid-state storage by using a single transducer to self-assemble bits with sub-lithographic dimensions on an unpatterned substrate. This paper explores the ability of magnetic recording to maintain this advantage at 1 Tbit/in2 by examining the process challenges associated with the fabrication of head structures at this areal density. Specifically, this paper describes the minimum feature, F, and alignment requirements for the thin-film head structures supporting 1 Tbit/in2 densities and compares these requirements with the projected roadmaps of the semiconductor industry. These comparisons indicate that minimum feature head processing requirements will match semiconductor capabilities in the time frame for 1 Tbit/in2 recording product. Further, alignment requirements for the head structure will exceed projected semiconductor capabilities in this same time frame. The process implications of the technologies of discrete tracks and patterned bits are analyzed, which move the minimum feature requirements from the head structure to the disk media. These approaches require patterning sub-lithographic bit cell dimensions which by definition exceed semiconductor lithographic capabilities.

Narrow-track ring head for high-frequency magnetic recording

The dynamic magnetic moment method is employed to determine the field strength distribution of a thin-film ring head for high-frequency magnetic recording. The field is found to be broadly distributed in the track direction. The sharpness of the distribution is improved by adopting an appropriate processing gap and a side-erasing pole. These techniques are thus useful for narrow-track recording. The micromagnetic simulation leads to the fact that the width of the recorded track is affected by the frequency of recording, the core resistivity, and the subsequent transition pattern. These effects should therefore be considered in the design of track density.

Electron-beam patterning and process optimization for magnetic sensor fabrication

Electron-beam lithography has been widely applied to define critical features in magnetic recording thin-film heads. To be a viable resist candidate for read sensor fabrication, e-beam resists need to be optimized in three major aspects—resolution, etching resistance, and strippability. Here the authors investigated four typical resists for their applicability in the production of sub-50nm read sensors and extendibility into sub-30nm regime, including a negative-tone chemically amplified resist (CAR), a negative-tone non-CAR, a positive-tone CAR, and a positive-tone non-CAR. Pattern design for positive-/negative-tone resists, resist resolution capability, sloped resist pole profile, underlayer preparation for Si-containing imaging layer, hybrid lithography for low-sensitivity non-CARs, and process issues in ion-beam etching of sensor stacks are discussed in detail. Finally, 20nm giant magnetoresistive sensor fabrication was demonstrated.