2.5-inch Hard Disk Drive with High Recording Density and High Shock Resistance By KUSUMOTO Tatsuharu, TODA Akio Toshiba has developed the MQ01ABD100 dual-platter 2.5-inch hard disk drive (HDD) with a capacity of 1 TB in a chassis of 9.5 mm in height. In order to achieve a high mean surface recording density of 1,153 Mbit/mm 2 (744 Gbit/in 2 ), we have developed the following technologies: a low-density parity check (LDPC) coded modulation technology applying a new read channel architecture, a new write head structure, a smaller track pitch achieved by using a smaller grain size for the medium, and a newly designed mechanism and servo technology to improve the head positioning accuracy. In addition, this model features a newly developed arm, suspension, and base that enhance shock and vibration resistance. 1 Introduction Originally, 2.5-type HDDs were used primarily in notebook PCs for data storage. In recent years, market demand for large-capacity high-performance 2.5-type HDDs has been growing. Reasons for this trend include the rapid proliferation of large-capacity external storage devices which can be connected via USB (Universal Serial Bus) connections. Such external storage devices can inexpensively store massive amounts of data, such as video recorded from high-definition TVs and video or image data from digital cameras. In addition, other recent trends including the emergence of notebook PCs with better audio and visual performance contribute to the growing demand for even larger capacity, higher performance 2.5-type HDDs. To meet these demands for larger capacity and higher performance, Toshiba has developed the MQ01ABD100, a dualplatter 2.5-type HDD with a capacity of 1 TB in a chassis of 9.5 mm in height. 2 Overview of the MQ01ABD100 Table 1 lists the main specifications and Figure 1 shows the internal layout of the newly developed 2.5-type HDD, MQ01ABD100. Table 1. Specifications of newly developed HDD Item Specification Storage capacity 1 TB Number of heads 4 Number of platters 2 Linear recording density (average) 81.5 kbit/mm Track density (average) 14.2 k tracks/mm Modulation LDPC RPM 5,400 rpm Average seek time 12 ms Shock Vibration Operating (2 ms) 3,920 m/s 2 Non-operating (1 ms) 8,820 m/s 2 Operating (5 500 Hz) 9.8 m/s 2 Non-operating (15 500 Hz) 49 m/s 2 Figure 1. Internal layout of newly developed HDD We achieved higher positioning accuracy and improved shock resistance by designing anew the arm, suspension, and base. TOSHIBA Storage Products for ICT Society 10
This model, which contains two platters in a chassis of 9.5 mm in height, has achieved a high areal density approximately 1.37 times higher than our previous models, 1,153 Mbit/mm 2. To achieve this high areal density, we implemented the following changes to realize larger-capacity HDDs: use of a Low-Density Parity Check (LDPC) circuit applying a new read channel architecture; a finer write head structure; a smaller track pitch (center-to-center distance between neighboring tracks) by using a smaller magnetic granular size for the medium; and higher servo positioning accuracy using a newly designed mechanism. To increase performance, we added additional features to this model. A newly developed arm and base, among other changes, provide greater structural rigidity to enhance shock and vibration resistance. 3 Larger Capacity This model records data at a linear recording density of 81.5 kbit/mm. In the radial direction, the model features data cylinders (Note 1) with an average track recording density of 14.2 k tracks/mm. Improvements in recording density are predicated on improvements in linear and track recording densities. The LDPC circuit is employed to enhance linear recording density in order to improve error correcting capability. We used a new write head structure and a smaller magnetic granular size for the medium to improve track recording density. To record data at the track pitch of 0.07 μm, the head positioning accuracy must be 0.007 μm or less. To achieve such accuracy, we improved resonance characteristics of suspension and arm and newly designed the servo filter. In order to realize higher areal density, we employed the following technologies: (1) Use of an LDPC circuit We employed an LDPC circuit, which offers excellent data error correction capability. Parity bits (Note 2) are embedded into the blocks and the LDPC circuit performs data correction when reading data by changing the data until the parity bit matches the bit set. (2) New write head structure and smaller granular size for the medium A narrower track pitch requires a narrower write head as well. For this model, we reviewed the structure of the write head and improved its ability to write data. We reduced the granular size of magnetic material sputtered on the disk to realize a smaller width of track pitch. 4 Higher Performance To realize larger capacity and higher track density, higher positioning accuracy of the head is required. To achieve such higher positioning accuracy, a wider servo bandwidth is essential, which in turn requires the higher main resonant frequency of the mechanism (Figure 2). Motor Platter Head (Note 1) (Note 2) A cylinder is a group of tracks in the same area that spread across two or more surfaces of the recording disks. Parity bits are bits added to data to detect data errors. Actuator Figure 2. Newly developed mechanism We reviewed the structure to increase the mechanism s main resonant frequency to achieve higher track density. TOSHIBA Storage Products for ICT Society 11
High-rigidity arm Conventional model MQ01ABD100 HDD Increased 20% Gain (db) High-rigidity suspension 0 0 Figure 3. Newly developed arm and suspension We optimized the design of the entire arm and suspension structure. Figure 4. Main resonant frequency The new arm and suspension increase the main resonant frequency by 20%. plate Flexure Damper Load beam Voice coil Pivot Figure 6. Structure of new arm The thicker arms allow for higher vending rigidity, which in turn increases shock resistance. Head slider Figure 5. Structure of new suspension The lighter suspension increases shock resistance. 4.1 Improvement of Vibration and Shock Resistance We reviewed the entire arm structure to optimally design a more rigid arm and suspension, successfully improving the main resonant frequency by 20% (Figure 3). The design changes detailed below applied to mechanical parts except the actuator (Note 3). Through these modifications, we improved vibration and shock resistance by enhancing rigidity and making the resonance frequency higher (Figure 4): (1) Improved shock resistance by reducing the suspension s equivalent mass If a shock is applied while the heads are in motion over the disk, the heads may tap against the disk (Note 4), scratching the surface of the disk, which causes read errors. However, this tapping can be further reduced by using a smaller equivalent mass of suspension. In this model, we improved shock resistance by employing a suspension 12% lighter than that of our conventional models (Figure 5). (2) Improved shock resistance through a more rigid arm As with the equivalent mass of suspension, we improved the bending rigidity of the arm by approximately 20% by using a thicker arm (Figure 6). Improving the rigidity of the arm in this model reduced the vibrational amplitude of the heads occurring when a shock is applied, and as a result the shock resistance improved by approximately 25% to 30%. (Note 3) (Note 4) A mechanical device that converts an input electric signal into a physical action Leaving of dents on the disk due to a shock applied to cause the collision of the heads against the disk TOSHIBA Storage Products for ICT Society 12
Ribs Motor Figure 7. New base design We improved the shock resistance of the head by changing the thickness of the base; the base s arm mount and surrounding area are approx. 20% to 50% thicker than those of conventional models. Figure 8. New cover design We improved shock resistance through optimally designing the material and cover shape. (3) Improved shock resistance through a more rigid base As we did for the arm, we improved the bending rigidity of the base and thereby reduced the vibrational amplitude of the heads occurring when a shock is applied. Consequently, when a shock is applied, the vibrational amplitude of the motor is reduced by 8% to 13% and that of the actuator by 26% to 32% (Figure 7). (4) Improved shock resistance through a more rigid cover Response amplitude With a new top cover shape and material, we Low High increased the rigidity of the cover itself as well as Figure 9. New housing design The resonance bandwidth of the base has we doubled the width of the gap between the cover been approximately 6% wider and the rigidity 10% greater than that of conventional models. and the disk, and thereby the shock resistance was improved. (Figure 8). As a result of the improvements in the rigidity of the base and cover, the vibrational amplitude of the entire chassis has been reduced in this model by 10% (Figure 9). 4.2 Improvement of Head Positioning Accuracy As shown in Figure 10, the head positioning accuracy of the conventional mechanism was approximately 9 nm. As shown in Figure 11, this model has achieved targeted head positioning accuracy of 7 nm thanks to the wider servo bandwidth realized alongside the above-mentioned improved resonance characteristics of mechanical parts. TOSHIBA Storage Products for ICT Society 13
12 12 11 11 Head positioning accuracy (nm) 10 9 8 7 6 5 Target value : 9 nm 4 Head 0 3 Head 1 2 Head 2 1 Head 3 0 0 5,000 10,000 15,000 Head positioning accuracy (nm) 10 9 8 7 6 5 Target value : 7 nm 4 Head 0 3 Head 1 2 Head 2 1 Head 3 0 0 5,000 10,000 15,000 Figure 10. Head positioning accuracy of existing HDD The structures of current models prevent them from achieving the newly developed HDD s target positioning accuracy. Figure 11. Head positioning accuracy of newly developed HDD The newly developed HDD s target positioning accuracy is realized with the wider servo bandwidth enabled by the new mechanism design. 5 Conclusion The achievement of 2.5-type HDDs with 1 TB storage capacity has assured us of our ability to supply large-capacity, inexpensive storage systems capable of storing TV content and digital camera pictures in addition to conventional computer data storage usage. Toshiba will continue to develop HDDs with higher recording densities to realize large-capacity and high-performance storage. References (1) Kotaro Yamamoto et al, MK6021GAS 2.5-type Hard Disk Drive, Toshiba Rev., vol. 57, no.7, pp.8-10, 2002. KUSUMOTO Tatsuharu Ome Operations-Storage Products TODA Akio Ome Operations-Storage Products TOSHIBA Storage Products for ICT Society 14