Manufacturing Equipment Technologies for Hard Disk’s Challenge of Physical Limits 222 Manufacturing Equipment Technologies for Hard Disk’s Challenge of Physical Limits Kyoichi Mori OVERVIEW: To meet the world’s growing demands for volume information, Brian Rattray not just with computers but digitalization and video etc. the HDD must Yuichi Matsui, Dr. Eng. continually increase its capacity and meet expectations for reduced power consumption and green IT. Up until now the HDD has undergone many innovative technological developments to achieve higher recording densities. To continue this increase, innovative new technology is again required and is currently being developed at a brisk pace. The key components for areal density improvements, the disk and head, require high levels of performance and reliability from production and inspection equipment for efficient manufacturing and stable quality assurance. To meet this demand, high frequency electronics, servo positioning and optical inspection technology is being developed and equipment provided. Hitachi High-Technologies Corporation is doing its part to meet market needs for increased production and the adoption of next-generation technology by developing the technology and providing disk and head manufacturing/inspection equipment (see Fig. 1). INTRODUCTION higher efficiency storage, namely higher density HDDS (hard disk drives) have long relied on the HDDs will play a major role. computer market for growth but in recent years To increase density, the performance and quality of there has been a shift towards cloud computing and the HDD’s key components, disks (media) and heads consumer electronics etc. along with a rapid expansion have most effect. Therefore further technological of data storage applications (see Fig. 2). advances in manufacturing and inspection equipment In line with the increasing volumes of information, are sought to support these. the HDD requires increases of both capacities and Increased areal density has caused bit size to densities. Furthermore, in recent years, data centers get ever smaller, resulting in recent areal densities controlling massive amounts of information are of something like 650 Gbit/in² or the equivalent said to consume hundreds of megawatts of power. of 1,000 bits of data in a 1-micron square. To cope From an environmental perspective, low power with this Hitachi High-Technologies Corporation consumption IT (information technology) must be has promoted development of high precision head promoted and is being actively pursued in Japan positioning technology along with high frequency through the “Green IT Initiative.” In this regard, electronics for the smaller signals. Disk manufacturing & inspection Head inspection equipment Disk tester Cleaning machine Quasi tester Head tester Disk Fig. 1—HDD Manufacturing and Inspection Equipment Products. The increasing densities of HDDs Optical inspection Imprint Write pole profiler Head places high demands on the reliability and quality of the manufacturing and HDD inspection equipment used in their configuration production. These Hitachi High- Technologies Corporation products HDD: hard disk drive were designed to meet these demands. Hitachi Review Vol. 60 (2011), No. 5 223 Transfer speed Gbit/s the read method changed from the electromagnetic 10 Home electronics (video recorder, etc.) induction of thin film heads to a magnetoresistive type and a decade or so later traditional longitudinal HDD in 3 to 5 years Mobile (digital movies, etc.) recording was surpassed by perpendicular recording. 1 Server Cell phone, PC camera/audio, Manufacturing and Inspection Equipment Mbit/s mobile PC 100 Technology Flash Inspection equipment plays an important role in (NAND) trying to maintain highly efficient manufacturing and HDD 10 assure stable quality. Flash per chip HDD: per platter Furthermore, recent areal density increases have 1 Volume been accompanied by miniaturization of the magnetic 1 Mbyte 1 Gbyte 1 Tbyte domains and decreases in the head-disk spacing, PC: personal computer warranting ever sophisticated inspection equipment Fig. 2—Storage Technology Adoption. year after year. Whereas past growth in the market for HDDs has been based Currently, track pitch is being squeezed down to primarily on their use in computers, new applications such as around 70 nm, requiring high precision head positioning the cloud and consumer electronics are growing rapidly. servo technology for inspection equipment. To read the test signals correctly requires track mis-registration of the head to less than 3% of track TechnoloGY For increASinG HDD pitch. Fig. 4 shows the signal on a disk, read as denSitY the head is repeatedly scanned sideways across it, HDD Technology Transitions plotting the signal strength relative to the distance HDD have a long history dating back to the world’s from the track center. From this we determine that first HDD announced by International Business positioning repeatability is of the order of 1 nm, and Machines Corporation (IBM) in 1956. Since then thus highly stable. recording density has grown massively, increasing by 8 digits. Technical Trends for High Density To maintain the fast and continuous pace of areal Increasing areal density beyond 1 Tbit/in² is said density improvements over the years has taken many to be extremely difficult with existing technology. In technological innovations (see Fig. 3). In the 1990s order for the recorded bit to be smaller the grain size of the recording layer must be smaller requiring an Areal recording density 1 Tbit/in2 100 Track profile repeatability measured 10 times Gbit/in2 10 3,500 60% yearly 1 3,000 AFC disk 100 Perpendicular 2,500 recording 10 nm First HDD 30% yearly Mbit/in2 10 GMR/TMR/CPP 2,000 “RAMAC” head 1 Thin film disk 1,500 AMR head 100 Coated disk Amplitude (uV) 1,000 Thin film head kbit/in2 10 500 1 0 1950 1960 1970 1980 1990 2000 2010 −0.25 −0.2 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 0.2 0.25 Year Cross-track position (µm) AMR: anti-magnetoresistive AFC: anti-ferromagnetically coupled GMR: giant magnetoresistive TMR: tunneling magnetoresistive CPP: current perpendicular to plane Fig. 4—Head Positioning and Repeatability. Fig. 3—HDD Areal Density and Technology Transitions. Head inspection requires a relative positioning accuracy To satisfy market demand, HDDs have achieved a continuous between disk and head of 3% or less of track pitch. The graph increase in their areal densities over a span of more than shows the disk write signal read back from the head and 50 years thanks to numerous technological innovations. indicates positioning repeatability of about 1 nm. Manufacturing Equipment Technologies for Hard Disk’s Challenge of Physical Limits 224 Bit patterned media Energy assist Shingled recording switch polarization. Thus, small bits can be recorded Track width in high Ku recording layers. Assist energy solutions in the form of laser light utilizing near-field optics Laser Write head Head or microwaves from high frequency magnetic field Track width oscillators are being considered. However, focusing Head Direction of the energy into a minute spot is something that Heat of rotation must be built in to a new head. spot M−2 (3) Bit patterned media M−1 M An innovation of the disk sees a move away from M+1 the traditional continuous granular recording layer Fig. 5—Technologies for Increasing HDD Density. to one of isolated magnetic domains with each one While achieving areal densities in excess of 1 Tbit/in2 is representing a single recorded bit of data. The mutual difficult using conventional technologies, Hitachi has come up interference between adjacent bits is minimized so, with a number of innovative technologies which it is developing even for low Ku recording layers, SNR and thermal to address this challenge. instability effects are improved. However, the bit location/synchronization not to mention the high improvement in SNR (signal-to-noise ratio) to read. volume production of the new disk manufacturing Data though would then be vulnerable to decay from processes still pose problems. the super paramagnetic effect’s thermal instability, These innovative technologies are being considered which in turn would require a high Ku (anisotropy but to achieve areal density of 4 Tbit/in² will likely energy) recording layer but the small magnetic field require a combination of both energy assist recording head could no longer write to it and this vicious circle and bit patterned media. is the so-called “tri-lemma in magnetic recording.” Bit patterned media has servo information pre- Several innovations are proposed to break through embedded on the disk and requires positioning this barrier (see Fig. 5). technology to account for eccentricity and otherwise (1) Shingled recording implement track following. To cope with these Technically there are no great hurdles so this is technology trends, the following equipment technology said to be close to implementation. Large Ku recording is being developed: layers with large magnetic field heads overwriting (a) Non- write-read certify inspection technology part of the previous data leave a narrow remnant to (b) Head inspection technology for early process stage form the track. The drawback is that conventional (c) Patterned media volume manufacturing technology random access writing will not be possible and must be accounted for with new formatting methods and OpticAL mediA teStinG EQuipment additional memory. The last step of the disk manufacturing process (2) Energy assisted recording is performing a glide test, checking the surface for This is primarily an innovation for the head, when asperities to assure the fly ability of the head, and a writing a bit of data, additional energy is applied certify inspection to examine magnetic characteristics to the area enabling the use of low field strength to and defects that influence read and write. Scattering detector Mirror Laser Reflection detector Disk Fig. 6—Optics Configuration. The machine uses laser light to inspect the disk. This can inspect Spindle motor the entire disk more quickly than the previous method of inspection using heads.