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Flying Instability due to Organic Compounds in Hard Disk Drive

Flying Instability due to Organic Compounds in Hard Disk Drive Hindawi Publishing Corporation Advances in Tribology Volume 2012, Article ID 170189, 6 pages doi:10.1155/2012/170189 Research Article Flying Instability due to Organic Compounds in Hard Disk Drive Koji Sonoda Advanced Technology Development Department, Storage Products Design and Production Division, Toshiba Corporation, 2-5-1 Kasama, Sakae-ku, Yokohama 247-8585, Japan Correspondence should be addressed to Koji Sonoda, koji4.sonoda@toshiba.co.jp Received 27 July 2012; Accepted 2 December 2012 Academic Editor: Norio Tagawa Copyright © 2012 Koji Sonoda. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The influence of organic compounds (OCs) on the head-disk interface (HDI) was investigated in hard disk drives. The drives were tested at high temperature to investigate the influence of gaseous OC and to confirm if the gaseous OC forms droplets on head or disk. In the experiment, errors occurred by readback signal jump and we observed the droplets on the disk after full stroke seek operation of the drive. Our results indicate that the gaseous OC condensed on the slider and caused flying instability resulting in drive failure due to slider contact with a droplet of liquid OC. Furthermore, this study shows that kinetic viscosity of OC is an important factor to cause drive failure using alkane reagents. 1. Introduction The drives were placed with the top cover down to avoid dropping the hydrocarbon oil to disk. This hydrocarbon To achieve 1 Tb/in recording density, a head-disk clearance oil has a wide distribution of molecular weight from about below 2 nm is required. At this small clearance flying instabil- 100 to 500 grams per mole. For the drive test, several ity, which results in a few nanometers of clearance variation, 10000 rpm test drives were built. Tests were conducted at may cause read/write errors due to the high sensitivity of a controlled temperature of 55 C to volatilize components magnetic recording performance to clearance. In addition of the hydrocarbon oil. The test sequence is shown in to direct contact between head and disk, collision between a Figure 1. First, full stroke seeks between maximum outer lubricant droplet and head may cause vibrations and induce radius (OD) and minimum inner radius (ID) without a read/write “signal jump” such as reported by Li et al. write/read operation (no dynamic flying height control) were [1]. Fowler and Geiss [2] observed droplets of OC (alkane) conducted for 10 hours. The flying height is about 10 nm on the head that can cause the stiction at the HDI with a during the full stroke seek. Next, a sequential write operation visualization setup. With these references, we used model OC from OD to ID was conducted. Then, a sequential read instead of using lubricant for accelerated testing to facilitate operation similar to the sequential write was conducted. The droplet observation as it is difficult to observe the lubricant flying height is 3.0 nm with dynamic flying height control droplet on the disk covered with the lubricant film. We found in the sequential write and read operation. If a readback that OC, specifically hydrocarbons, can also make the flying error occurred, Viterbi metric margin (VMM) measurement head unstable by contact with a droplet of OC during the (read only) near the error position was performed to map write operation, resulting in an unrecoverable read error. In the error location. VMM is a function conceived as a means this study, drive level test was carried out to investigate the of measuring signal quality during Viterbi decoding. The influence of OC on reliability of head disk interface (HDI). margin means the difference between the actually received data path (continuous 0/1 data) and ideal path. VMM 2. Experimental Details correlates with sector error rate (SER). When the VMM is To investigate the influence of OC, we applied 30 mg of larger, SER is worse. The details of VMM measurement are hydrocarbon oil to the inside top cover of test drives. shown in [3]. 2 Advances in Tribology Full seek Sequential Sequential w/o W/R write read 10 hours (all data) (all data) No Yes VMM measurement Error Max seek velocity during full seek operation ∼2.7 m/s at middle radius Figure 1: Sequence of drive test accelerated by OC. The fly condition is passive (no dynamic flying height control) during the full stroke seek operation without write/read operation. 4.5 3.5 2.5 Sector Figure 2: VMM changes near the error position. 1.75 5 PE 1.5 0 1.25 −5 −10 Servogain 0.75 −15 0 50 100 150 Servosector Figure 3: Relative servogain and position error (PE) changes when head may contact droplets. We also tested drives where 100 µLofalkane(paraffin position, indicated by red circle. Readback errors occurred or saturated hydrocarbon) solutions were injected into the at 2 sectors in a sequential read operation. No errors were inside of the drive enclosure on the base casting near the detected in a sequential write operation. If the head cannot motor to understand what component of the OC causes the read the servodata and fails to set the positioning, the drive error. The test sequence is the same as the above test shown reports an error in a write operation. To determine if the in Figure 1. Table 1 shows the alkanes we used for test and errors were caused by a media magnetic defect or scratch amount of volume/weight loaded into the drives. The weight the media was rewritten and VMM was remeasured. The of icosane, pentacosane, and triacontane excludes hexane’s VMM at the error positions recovered to normal value with weight. In addition, test temperature was varied to investigate rewriting, so it was concluded that there was no media the influence of kinetic viscosity of alkanes. magnetic defect or scratch present. Figure 3 shows servogain and position error (PE) changes when abnormal servogain variation was detected in write 3. Results and Discussion operation. The large servogain means that the amplitude of the servo signal is small because automatic gain controller 3.1. Signal Change Measurement Induced by Flying Instability. (AGC) adjusts the gain to maintain the signal level. When Figure 2 shows an example of VMM changes near the error Relative servogain Log (VMM) PE (% track pitch) Advances in Tribology 3 1000 cylinders Figure 4: OSA image of media surface near the error location. 0.5 0.4 1.5 1.2 0.3 0.9 0.2 Cross-section 0.6 0.1 0.3 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Width (µm) (µm) Figure 5: The droplet observation on the media by AFM.  2.5 media Droplet Head travel Move to direction outer radius 30 20 20 30 Radius (mm) (a) Droplet 0.4 mm (b) Figure 6: Droplet distribution map (a) and OSA image (b) on the media. The droplets in the down-track direction are located progressively further toward the disk outer radius, consistent with the head travel direction from inner to outer diameter. (µm) Radius (mm) Height (µm) 4 Advances in Tribology 1 Table 1: Alkanes used for tests. Acceleration Density Volume Weight MP Max Formula (g/mL) 0.8 1600 acceleration (µL) (mg) ( C) at 20 C Hexane C H 0.70 70 −95.0 6 14 0.6 Hexadecane C H 0.77 77 18.0 16 34 Icosane C H 100 0.76 76 36.7 20 42 0.4 800 Pentacosane C H (Hexane 0.80 80 53.0 25 52 Solution) Triacontane C H 0.78 78 65.8 30 62 0.2 400 Density data from International Chemical Safety Cards (ICSCs) or Material Safety Data Sheet (MSDS). Velocity MP: melting point. 0 0.2 0.4 0.6 Time (ms) These observations suggest that the droplets are volatile Figure 7: Radial velocity and acceleration of the head in full stroke liquid. seek operation. Figure 6 shows the location of several droplets and the OSA image of representative droplets. The path of the droplets follows a spiral path toward the outer radius. A radial velocity of about 0.2 m/s is calculated from the path. the relative servogain changed from about 1.0 to 1.4 by This velocity value indicates that the droplets dropped from flying instability, the flying height rise can be calculated to head to media at the maximum acceleration in the full stroke be around 7.5 nm using the Wallace spacing loss equation seek operation, as shown in Figure 7. [4]. Although the 64 kHz sampling frequency in this study Figure 8 shows an optical microscopy image of the head is not large enough to identify specific ABS vibration modes, surface after the test. Some droplets were observed at the such as pitch and roll mode, the vibration frequency can be slider trailing edge and deposited ends. To identify whether estimated roughly to be 5 to 10 kHz which may correspond the droplets are hydrocarbon or not, we analyzed these to that of suspension torsion mode. droplets on the head surface by Raman spectroscopy. The On the other hand, PE was not seen to change signif- droplet on head surface was identified as hydrocarbon since icantly at the region where the servogain varied greatly. It the Raman spectrum of the droplet matched that of the indicates that the vibration does not move the cross-track reference hydrocarbon oil shown in Figure 9. direction, but vertical direction. The write operation was completed with no error being detected even though data 3.3. The Influence of Kinetic Viscosity of Organic Compound. could not be recorded correctly. Figure 10 shows the result of the alkane injection test. In general, melting point of higher molecular weight OC is 3.2. Droplet Observation. To further investigate the cause higher as shown in Table 1. Therefore, lower molecular of the errors, we performed a drive teardown analysis and weight and high temperature make the OC more volatile. inspected the media and head surfaces for evidence of OC However, this result shows that higher molecular weight which may have caused the error. Before the drive teardown, is prone to induce the error in spite of the amount of the media was DC-erased around the error position to evaporated OC. In addition, for pentacosane (C25) time to facilitate identification of the error location by an optical failure of the test at lower temperature (50 C) is shorter than surface analyzer (OSA). No droplet was observed at the error the one at higher temperature (75 C). It indicates that there may be another factor, distinct from the amount of gaseous location on the media surface indicated by red circle in Figure 4. We speculate that the droplets were removed by OC causing the error. contacts with head during write/read operations. To test this Figure 11 shows examples of VMM changes near the hypothesis, we measured the media surface from another error position or the position where VMM exceeds 3.8. drive after full stroke seek operation only. Based on full Larger and longer VMM change occurred in the test for ◦ ◦ surface mapping of the media by OSA, several droplets were C25 at 50 C compared to other two tests (for C25 at 75 C detected. Figure 5 shows one of the droplets measured by and for C16 at 66 C). That may be one of the reasons AFM. The shape of this droplet is dome-like. The height of why the droplets at the test for C25 at 50 C have higher this droplet is about 100 nm, tall enough to make contact viscosity or larger size for. On the other hand, VMM between the head and the droplet on the media. changes also appeared in the other two tests in Figure 11 Although we attempted to analyze the droplet by Auger even if no error occurred. This implies the existence of the electron spectroscopy and Raman spectroscopy, we did not droplets at the three tests in Figure 11. From these results, succeed because the droplet vanished during their electron we inferred that the higher kinetic viscosity associated with or laser irradiation inherent in the Auger and Raman lower temperature and higher molecular weight or volume of techniques. Furthermore, some droplets disappeared when alkane droplets are one of the significant factors which cause simply storing the media for a week at room temperature. drive failure. To clarify the relationship between the kinetic Velocity (m/s) Acceleration (m/s ) Advances in Tribology 5 (a) (b) (c) Figure 8: Optical microscope images (a) overall picture of ABS; (b) deposited ends of head; (c) enlarged picture of red square area in (a). No error Reference (hydrocarbon oil) Droplet on head surface Temperature in drive C6 C16 C20 C25 C30 Figure 10: Alkane injection test result. The tests over 300 h were truncated. 800 1600 1000 1200 1400 −1 Raman shift (cm ) is about 5 cSt in the test. However, we need further study Figure 9: Droplet analysis by Raman spectroscopy. to separate from the droplet size (or volume) influence on inducing drive failure. viscosity of alkanes and occurrence of drive failure, plots of 4. Conclusion the test results were made as shown in Figure 12.Wededuce from Figure 12 that there is a critical kinetic viscosity of OC We studied the drive failure caused by the contact between for inducing drive failure, and the critical kinetic viscosity the droplet of OC (hydrocarbon) and head. From our Intensity (a.u.) Time to failure (hours) 67 C 66 C 50 C 35 C 73 C 63 C 50 C 75 C 69 C 61 C 50 C 70 C 6 Advances in Tribology 4.5 3.5 2.5 1 3 5 7 9 11131517192123252729313335373941 Relative sector C16 66 C C25 75 C C25 50 C ◦ ◦ ◦ Figure 11: VMM change comparison near the error position (C25 50 C) or the position where VMM exceeds 3.8 (C16 66 C, C25 75 C) in the alkane injection tests. References [1] J. Li, J. Xu, and Y. Aoki, “Simulation on contact between the droplet and the slider at head-disk interface based on water- hammer pressure model,” Microsystem Technologies, vol. 16, no. 1-2, pp. 57–65, 2010. C25 [2] D. E. Fowler and R. H. Geiss, “Chemical contamination at C30 ◦ the head-disk interface in a disk drive,” IEEE Transactions on 70 C C20 Y 61 C Magnetics, vol. 36, no. 1, pp. 133–139, 2000. [3] K. Aruga, “Probabilistic analysis of off-track capability assum- 69 C ing geometric track misregistration model for higher track 75 C density disk drives,” IEEE Transactions on Magnetics, vol. 45, no. 63 C N C16 35 C N ◦ 11, pp. 5022–5025, 2009. 73 C 50 C [4] R. L. Wallace, “The reproduction of magnetically recorded 66 C signal,” Bell System Technical Journal, vol. 30, pp. 1145–1173, 0 20 40 60 80 100 Temperature ( C) Y: error occurred N: no error occurred Figure 12: Correlation between kinetic viscosity of alkanes and the occurrence of drive errors. investigations, we speculate the mechanism of the flying instability induced the OC as follows. (1) OC evaporated from inside top cover condenses into a droplet on the head due to the pressurization under ABS, or is adsorbed to disk surface. The OC adsorbed on the disk surface is picked up to the head surface then, the droplet is generated by accumulating the picked up OC. (2) Droplets on the head transfer to the media by inertia force as the head seeks over the media. (3) A large vibration occurs due to contact between the head and the droplet in the case of high kinetic viscosity components of OC or forming large droplet of OC. Kinetic viscosity (cSt) VMM (Log) International Journal of Rotating Machinery International Journal of Journal of The Scientific Journal of Distributed Engineering World Journal Sensors Sensor Networks Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Volume 2014 Journal of Control Science and Engineering Advances in Civil Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Submit your manuscripts at http://www.hindawi.com Journal of Journal of Electrical and Computer Robotics Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 VLSI Design Advances in OptoElectronics International Journal of Modelling & Aerospace International Journal of Simulation Navigation and in Engineering Engineering Observation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2010 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com http://www.hindawi.com Volume 2014 International Journal of Active and Passive International Journal of Antennas and Advances in Chemical Engineering Propagation Electronic Components Shock and Vibration Acoustics and Vibration Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Advances in Tribology Hindawi Publishing Corporation

Flying Instability due to Organic Compounds in Hard Disk Drive

Advances in Tribology , Volume 2012 – Dec 13, 2012

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Hindawi Publishing Corporation
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Copyright © 2012 Koji Sonoda. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Abstract

Hindawi Publishing Corporation Advances in Tribology Volume 2012, Article ID 170189, 6 pages doi:10.1155/2012/170189 Research Article Flying Instability due to Organic Compounds in Hard Disk Drive Koji Sonoda Advanced Technology Development Department, Storage Products Design and Production Division, Toshiba Corporation, 2-5-1 Kasama, Sakae-ku, Yokohama 247-8585, Japan Correspondence should be addressed to Koji Sonoda, koji4.sonoda@toshiba.co.jp Received 27 July 2012; Accepted 2 December 2012 Academic Editor: Norio Tagawa Copyright © 2012 Koji Sonoda. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The influence of organic compounds (OCs) on the head-disk interface (HDI) was investigated in hard disk drives. The drives were tested at high temperature to investigate the influence of gaseous OC and to confirm if the gaseous OC forms droplets on head or disk. In the experiment, errors occurred by readback signal jump and we observed the droplets on the disk after full stroke seek operation of the drive. Our results indicate that the gaseous OC condensed on the slider and caused flying instability resulting in drive failure due to slider contact with a droplet of liquid OC. Furthermore, this study shows that kinetic viscosity of OC is an important factor to cause drive failure using alkane reagents. 1. Introduction The drives were placed with the top cover down to avoid dropping the hydrocarbon oil to disk. This hydrocarbon To achieve 1 Tb/in recording density, a head-disk clearance oil has a wide distribution of molecular weight from about below 2 nm is required. At this small clearance flying instabil- 100 to 500 grams per mole. For the drive test, several ity, which results in a few nanometers of clearance variation, 10000 rpm test drives were built. Tests were conducted at may cause read/write errors due to the high sensitivity of a controlled temperature of 55 C to volatilize components magnetic recording performance to clearance. In addition of the hydrocarbon oil. The test sequence is shown in to direct contact between head and disk, collision between a Figure 1. First, full stroke seeks between maximum outer lubricant droplet and head may cause vibrations and induce radius (OD) and minimum inner radius (ID) without a read/write “signal jump” such as reported by Li et al. write/read operation (no dynamic flying height control) were [1]. Fowler and Geiss [2] observed droplets of OC (alkane) conducted for 10 hours. The flying height is about 10 nm on the head that can cause the stiction at the HDI with a during the full stroke seek. Next, a sequential write operation visualization setup. With these references, we used model OC from OD to ID was conducted. Then, a sequential read instead of using lubricant for accelerated testing to facilitate operation similar to the sequential write was conducted. The droplet observation as it is difficult to observe the lubricant flying height is 3.0 nm with dynamic flying height control droplet on the disk covered with the lubricant film. We found in the sequential write and read operation. If a readback that OC, specifically hydrocarbons, can also make the flying error occurred, Viterbi metric margin (VMM) measurement head unstable by contact with a droplet of OC during the (read only) near the error position was performed to map write operation, resulting in an unrecoverable read error. In the error location. VMM is a function conceived as a means this study, drive level test was carried out to investigate the of measuring signal quality during Viterbi decoding. The influence of OC on reliability of head disk interface (HDI). margin means the difference between the actually received data path (continuous 0/1 data) and ideal path. VMM 2. Experimental Details correlates with sector error rate (SER). When the VMM is To investigate the influence of OC, we applied 30 mg of larger, SER is worse. The details of VMM measurement are hydrocarbon oil to the inside top cover of test drives. shown in [3]. 2 Advances in Tribology Full seek Sequential Sequential w/o W/R write read 10 hours (all data) (all data) No Yes VMM measurement Error Max seek velocity during full seek operation ∼2.7 m/s at middle radius Figure 1: Sequence of drive test accelerated by OC. The fly condition is passive (no dynamic flying height control) during the full stroke seek operation without write/read operation. 4.5 3.5 2.5 Sector Figure 2: VMM changes near the error position. 1.75 5 PE 1.5 0 1.25 −5 −10 Servogain 0.75 −15 0 50 100 150 Servosector Figure 3: Relative servogain and position error (PE) changes when head may contact droplets. We also tested drives where 100 µLofalkane(paraffin position, indicated by red circle. Readback errors occurred or saturated hydrocarbon) solutions were injected into the at 2 sectors in a sequential read operation. No errors were inside of the drive enclosure on the base casting near the detected in a sequential write operation. If the head cannot motor to understand what component of the OC causes the read the servodata and fails to set the positioning, the drive error. The test sequence is the same as the above test shown reports an error in a write operation. To determine if the in Figure 1. Table 1 shows the alkanes we used for test and errors were caused by a media magnetic defect or scratch amount of volume/weight loaded into the drives. The weight the media was rewritten and VMM was remeasured. The of icosane, pentacosane, and triacontane excludes hexane’s VMM at the error positions recovered to normal value with weight. In addition, test temperature was varied to investigate rewriting, so it was concluded that there was no media the influence of kinetic viscosity of alkanes. magnetic defect or scratch present. Figure 3 shows servogain and position error (PE) changes when abnormal servogain variation was detected in write 3. Results and Discussion operation. The large servogain means that the amplitude of the servo signal is small because automatic gain controller 3.1. Signal Change Measurement Induced by Flying Instability. (AGC) adjusts the gain to maintain the signal level. When Figure 2 shows an example of VMM changes near the error Relative servogain Log (VMM) PE (% track pitch) Advances in Tribology 3 1000 cylinders Figure 4: OSA image of media surface near the error location. 0.5 0.4 1.5 1.2 0.3 0.9 0.2 Cross-section 0.6 0.1 0.3 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Width (µm) (µm) Figure 5: The droplet observation on the media by AFM.  2.5 media Droplet Head travel Move to direction outer radius 30 20 20 30 Radius (mm) (a) Droplet 0.4 mm (b) Figure 6: Droplet distribution map (a) and OSA image (b) on the media. The droplets in the down-track direction are located progressively further toward the disk outer radius, consistent with the head travel direction from inner to outer diameter. (µm) Radius (mm) Height (µm) 4 Advances in Tribology 1 Table 1: Alkanes used for tests. Acceleration Density Volume Weight MP Max Formula (g/mL) 0.8 1600 acceleration (µL) (mg) ( C) at 20 C Hexane C H 0.70 70 −95.0 6 14 0.6 Hexadecane C H 0.77 77 18.0 16 34 Icosane C H 100 0.76 76 36.7 20 42 0.4 800 Pentacosane C H (Hexane 0.80 80 53.0 25 52 Solution) Triacontane C H 0.78 78 65.8 30 62 0.2 400 Density data from International Chemical Safety Cards (ICSCs) or Material Safety Data Sheet (MSDS). Velocity MP: melting point. 0 0.2 0.4 0.6 Time (ms) These observations suggest that the droplets are volatile Figure 7: Radial velocity and acceleration of the head in full stroke liquid. seek operation. Figure 6 shows the location of several droplets and the OSA image of representative droplets. The path of the droplets follows a spiral path toward the outer radius. A radial velocity of about 0.2 m/s is calculated from the path. the relative servogain changed from about 1.0 to 1.4 by This velocity value indicates that the droplets dropped from flying instability, the flying height rise can be calculated to head to media at the maximum acceleration in the full stroke be around 7.5 nm using the Wallace spacing loss equation seek operation, as shown in Figure 7. [4]. Although the 64 kHz sampling frequency in this study Figure 8 shows an optical microscopy image of the head is not large enough to identify specific ABS vibration modes, surface after the test. Some droplets were observed at the such as pitch and roll mode, the vibration frequency can be slider trailing edge and deposited ends. To identify whether estimated roughly to be 5 to 10 kHz which may correspond the droplets are hydrocarbon or not, we analyzed these to that of suspension torsion mode. droplets on the head surface by Raman spectroscopy. The On the other hand, PE was not seen to change signif- droplet on head surface was identified as hydrocarbon since icantly at the region where the servogain varied greatly. It the Raman spectrum of the droplet matched that of the indicates that the vibration does not move the cross-track reference hydrocarbon oil shown in Figure 9. direction, but vertical direction. The write operation was completed with no error being detected even though data 3.3. The Influence of Kinetic Viscosity of Organic Compound. could not be recorded correctly. Figure 10 shows the result of the alkane injection test. In general, melting point of higher molecular weight OC is 3.2. Droplet Observation. To further investigate the cause higher as shown in Table 1. Therefore, lower molecular of the errors, we performed a drive teardown analysis and weight and high temperature make the OC more volatile. inspected the media and head surfaces for evidence of OC However, this result shows that higher molecular weight which may have caused the error. Before the drive teardown, is prone to induce the error in spite of the amount of the media was DC-erased around the error position to evaporated OC. In addition, for pentacosane (C25) time to facilitate identification of the error location by an optical failure of the test at lower temperature (50 C) is shorter than surface analyzer (OSA). No droplet was observed at the error the one at higher temperature (75 C). It indicates that there may be another factor, distinct from the amount of gaseous location on the media surface indicated by red circle in Figure 4. We speculate that the droplets were removed by OC causing the error. contacts with head during write/read operations. To test this Figure 11 shows examples of VMM changes near the hypothesis, we measured the media surface from another error position or the position where VMM exceeds 3.8. drive after full stroke seek operation only. Based on full Larger and longer VMM change occurred in the test for ◦ ◦ surface mapping of the media by OSA, several droplets were C25 at 50 C compared to other two tests (for C25 at 75 C detected. Figure 5 shows one of the droplets measured by and for C16 at 66 C). That may be one of the reasons AFM. The shape of this droplet is dome-like. The height of why the droplets at the test for C25 at 50 C have higher this droplet is about 100 nm, tall enough to make contact viscosity or larger size for. On the other hand, VMM between the head and the droplet on the media. changes also appeared in the other two tests in Figure 11 Although we attempted to analyze the droplet by Auger even if no error occurred. This implies the existence of the electron spectroscopy and Raman spectroscopy, we did not droplets at the three tests in Figure 11. From these results, succeed because the droplet vanished during their electron we inferred that the higher kinetic viscosity associated with or laser irradiation inherent in the Auger and Raman lower temperature and higher molecular weight or volume of techniques. Furthermore, some droplets disappeared when alkane droplets are one of the significant factors which cause simply storing the media for a week at room temperature. drive failure. To clarify the relationship between the kinetic Velocity (m/s) Acceleration (m/s ) Advances in Tribology 5 (a) (b) (c) Figure 8: Optical microscope images (a) overall picture of ABS; (b) deposited ends of head; (c) enlarged picture of red square area in (a). No error Reference (hydrocarbon oil) Droplet on head surface Temperature in drive C6 C16 C20 C25 C30 Figure 10: Alkane injection test result. The tests over 300 h were truncated. 800 1600 1000 1200 1400 −1 Raman shift (cm ) is about 5 cSt in the test. However, we need further study Figure 9: Droplet analysis by Raman spectroscopy. to separate from the droplet size (or volume) influence on inducing drive failure. viscosity of alkanes and occurrence of drive failure, plots of 4. Conclusion the test results were made as shown in Figure 12.Wededuce from Figure 12 that there is a critical kinetic viscosity of OC We studied the drive failure caused by the contact between for inducing drive failure, and the critical kinetic viscosity the droplet of OC (hydrocarbon) and head. From our Intensity (a.u.) Time to failure (hours) 67 C 66 C 50 C 35 C 73 C 63 C 50 C 75 C 69 C 61 C 50 C 70 C 6 Advances in Tribology 4.5 3.5 2.5 1 3 5 7 9 11131517192123252729313335373941 Relative sector C16 66 C C25 75 C C25 50 C ◦ ◦ ◦ Figure 11: VMM change comparison near the error position (C25 50 C) or the position where VMM exceeds 3.8 (C16 66 C, C25 75 C) in the alkane injection tests. References [1] J. Li, J. Xu, and Y. Aoki, “Simulation on contact between the droplet and the slider at head-disk interface based on water- hammer pressure model,” Microsystem Technologies, vol. 16, no. 1-2, pp. 57–65, 2010. C25 [2] D. E. Fowler and R. H. Geiss, “Chemical contamination at C30 ◦ the head-disk interface in a disk drive,” IEEE Transactions on 70 C C20 Y 61 C Magnetics, vol. 36, no. 1, pp. 133–139, 2000. [3] K. Aruga, “Probabilistic analysis of off-track capability assum- 69 C ing geometric track misregistration model for higher track 75 C density disk drives,” IEEE Transactions on Magnetics, vol. 45, no. 63 C N C16 35 C N ◦ 11, pp. 5022–5025, 2009. 73 C 50 C [4] R. L. Wallace, “The reproduction of magnetically recorded 66 C signal,” Bell System Technical Journal, vol. 30, pp. 1145–1173, 0 20 40 60 80 100 Temperature ( C) Y: error occurred N: no error occurred Figure 12: Correlation between kinetic viscosity of alkanes and the occurrence of drive errors. investigations, we speculate the mechanism of the flying instability induced the OC as follows. (1) OC evaporated from inside top cover condenses into a droplet on the head due to the pressurization under ABS, or is adsorbed to disk surface. The OC adsorbed on the disk surface is picked up to the head surface then, the droplet is generated by accumulating the picked up OC. (2) Droplets on the head transfer to the media by inertia force as the head seeks over the media. (3) A large vibration occurs due to contact between the head and the droplet in the case of high kinetic viscosity components of OC or forming large droplet of OC. Kinetic viscosity (cSt) VMM (Log) International Journal of Rotating Machinery International Journal of Journal of The Scientific Journal of Distributed Engineering World Journal Sensors Sensor Networks Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Volume 2014 Journal of Control Science and Engineering Advances in Civil Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 Submit your manuscripts at http://www.hindawi.com Journal of Journal of Electrical and Computer Robotics Engineering Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 VLSI Design Advances in OptoElectronics International Journal of Modelling & Aerospace International Journal of Simulation Navigation and in Engineering Engineering Observation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2010 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com http://www.hindawi.com Volume 2014 International Journal of Active and Passive International Journal of Antennas and Advances in Chemical Engineering Propagation Electronic Components Shock and Vibration Acoustics and Vibration Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014

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Published: Dec 13, 2012

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