Compensation for flying-height loss due to thermal protrusion of magnetic head - Comparison of optical measurement using an active slider with built-in thermal actuator and numerical simulation results

To achieve an ultra-low flying height in magnetic head sliders for next generation hard disk drives, we are developing an individual and in-situ technique to adjust flying height using a built-in thermal actuator to compensate for flying-height deviations and variations. We have evaluated changes in the flying-height of a prototype slider by observing the amplitude of read back signals. However, the observed flying-height change is much smaller than the predicted value by simulation. To resolve this issue, we optically evaluated the slider's flying height at multiple positions, which revealed a "compensation effect' due to increasing air pressure. That is, the pressure on the air-bearing surface increases as the head protrudes downwards by thermal expansion, which lifts the slider upwards. The evaluation also showed a reduction in the pitch angle due to increasing air pressure. These results agree well with flying-height simulation results that take into consideration thermal expansion on the air-bearing surface.