The instability of angstrom-scale head-disk interface induced by electrostatic force

Summary form only given. When the storage density is coming into several Tb/in², the head-disk spacing will drop into angstrom-scale regime [1]. At such small clearance, the electrostatic and intermolecular forces have become increasingly significant. It was reported that the electrostatic force produced by electronic potential difference between head and disk can be larger than the van der Waals force even if the slider and disk are both grounded[2],[3]. However, the electrostatic induced head disk interface instability and the relevant reliability were not well addressed in past. Therefore, this work investigates the instability of angstrom-scale head-disk interface induced by electrostatic force. First, the hysteresis effect of the touchdown-takeoff was investigated with/without eliminating the electronic potential difference. The electrical powers of thermal flying-height control (TFC) [4] head was supplied and then released to capture the hysteresis effect. It is found that a significant improvement of the hysteresis effect has been achieved when the electrostatic potential was eliminated. Second, a wear test over 60 hours when the head-disk clearance was set at an angstrom scale was performed. It is also found that the wear robustness has been greatly improved by eliminating the electrostatic potential. This study will help the design of the head-disk system for better reliability, especially for wear and flying stability. In this study, a touchdown-takeoff test was carefully developed to capture the electrostatic potential induced slider hysteresis effect. During the test, the TFC power was supplied suddenly and then release gradually and slider vibration was measured by laser Doppler velocimetry (LDV). This manipulation helps to capture the slider´s late take-off when the TFC power gradually release. During the experiment, the electrostatic force (EF) can be eliminated by applying an external voltage to the disk, where the voltage was carefully - alibrated before the experiment. As illustrated in Fig. 1, the vibration of the slider has much fast release rate when the EF was removed. To evaluate the influence of the electrostatic force on head-disk tribological reliability, a anti-wear test was conducted when the EF was removed or not. The backoff of the slider was set at 1 mW, corresponding the anglestrom level clearance between slider and disk. The wearing duration was set at 60 hours to 90 hours. After the wearing test, the writer shield and reader shield of the magnetic head were inspected by atomic force microscope (AFM). As illustrated in Fig.2, no matter the reader shield or writer shield, the wear amount is extremely small when the EF was removed. This means that the EF has great impact on the tribological reliability of head-disk interface.