Kenji Kuroki

Numerical and Experimental Analyses of Nanometer-Scale Flying Height Control of Magnetic Head With Heating Element

Hard drives featuring sliders with active flying-height (FH) control using thermal expansion of a heating element have been recently introduced in products. This approach allows to actively compensate for static FH variations and achieves sub-3-nm clearance during read/write operation. This paper describes a nonlinear numerical model of a perpendicular magnetic recording head for accurate simulation of pole-tip protrusions and their effect on FH change under various conditions, such as at an elevated drive temperature, with the heater activated or during write operation. The model integrates an electrical-thermomechanical finite-element model of slider and a full air-bearing solver, and includes lapped pole-tip recession and slider/disk deformation due to air-bearing pressure. We are able to predict key parameters that are not easily measurable (e.g., minimum/reader/writer FH, different protrusion profiles for ambient temperature, heater actuation, and during writing). We also present novel experimental methods for measuring protrusion and clearance delta profiles with angstrom-level resolution. The modeling results are compared to experimental data under various test conditions showing excellent agreement. From this method, we are able to quickly evaluate and optimize different heater, head, and ABS designs.

Contact/Clearance Sensor for HDI Subnanometer Regime

The fundamental performance of contact/clearance sensor, namely embedded contact sensor (ECS), is addressed in this paper. Both simulation and experiment results revealed that ECS is a promising sensor for low clearance and high reliability at subnanometer regime. The ECS dc signal intrinsically comes from multiple sources including TFC heater, air-bearing surface cooling, and friction heating at head/disk contact. Both ECS dc and ac signals detect head/disk contact. The dc signal comes from the sensor resistance change due to friction heating at contact, but the ac signal is dominated by spacing modulation caused by air-bearing vibration, and partially from the pulse-like friction heating. ECS ac signal responds significantly to disk microwaviness at narrow clearance region. Furthermore, ECS could detect asperities, pit, and lube mogul. The mechanism for asperity detection is friction heating. The mechanism for pit detection is worse cooling when sensor flying over the pit. That for mogul detection is better cooling at narrower spacing when the sensor is flying over the mogul.

Production and Performance of

An alternative has been sought for the very hard ceramic material (Al2O3 plus TiC) used as the substrate for magnetic recording heads. We have substituted silicon as the substrate and slider body material; the primary insulator enclosing the recording head was made of SiO2. We built and tested these sliders with full read and write capability in disk drives. Si provides improvement with respect to hardness, modulus, and thermal conductivity, and adds the potential of active electronics located immediately adjacent to the recording head. We describe a novel means of producing heads, using entirely dry etching, rather than diamond sawing. The sliders were etched from the finished wafers in the form of individual sliders, rather than rows of sliders, and were processed individually through to completion. Conventional air bearings were etched into the sliders, suspensions were attached, and drives were built and tested. The outcome shows a profound advantage in the mechanical head/disk interaction, particularly under shock conditions. Other results and slider characterization are described.