Dynamic Head-Disk Interface Instabilities With Friction for Light Contact (Surfing) Recording

Abstract

Recent advances in hard-disk drive technology involve the use of a thermal fly-height control (TFC) pole tip protrusion to bring the read/write recording elements of the slider closer to the disk surface and thus achieve Terabit per square inch recording densities. A dynamic, contact mechanics-based friction model of the head-disk interface (HDI) that includes roughness and accounts for the TFC geometry and its influence on the HDI dynamics is presented. The model is based on physical parameters and does not include any empirical coefficients. Experimental flyability/touchdown measurements were performed and used to examine in detail the HDI contact criterion in the presence of surface roughness and dynamic microwaviness. Using the model, a procedure is outlined that identifies the optimal clearance and light contact conditions, i.e., the amount of thermal actuation that minimizes, both, the clearance, as well as the flying height modulation. Through calculation of the time varying interfacial forces, mean pressure and shear stress at the HDI can be predicted and used to characterize the contact regime. Based on our results, a light contact regime with reduced bouncing vibrations and low stresses (thus, low wear) that would enable surfing recording is identified.Index Terms-Dynamic model, friction, hard-disk drive (HDD), head-disk interface (HDI), thermal fly-height control (TFC).

Characterization of light contact in head disk interface with dynamic flying height control

“…3. The light contact or lubricant surfing has been widely discussed (Vakis et al 2009;Ng et al 2009;Canchi and Bogy 2010;Li et al 2010). In order to extract information from the weak signal in the region III in Fig.…”

“…Juang and Bogy (2007) investigated the relationship between air bearing surface design and thermal actuation of a slider. More recently work can be found in (Xu et al 2009;Hua et al 2009;Vakis et al 2009;Shiramatsu et al 2009;Li et al 2009;Tani et al 2009;Ng et al 2009;Canchi and Bogy 2010;Knigge et al (2006); Li et al 2010;Canchi and Bogy 2010). Although the above studies have clarified many aspects of current-induced thermal pole tip protrusion, there are still many areas lacking of understanding.…”

Optimization of thermal fly-height control slider geometry for Tbit/in2 recording

“…Wear on the disk, through either design or instability-induced head crashes, is undesirable because it could affect the integrity of the magnetic layer and result in loss of data. Thermal fly-height control (TFC) technology was designed to avoid dynamic instabilities induced by sub-5-nm clearances by using a thermal element to create a protrusion or bulge around the read/write elements of the slider and bring them closer to the rotating disk surface while the slider body remains flying nominally at *10 nm (Lee and Strom 2008;Vakis et al 2009). …”

“…A dynamic contact model with friction, specific to the TFC geometry was developed by Vakis et al (2009), which allows for the calculation of the dynamically changing clearance between the read/ write elements and the disk and the interfacial contact, friction and adhesive forces. TFC geometry was used in conjunction with the contact model formulation to identify the limits over which the interface is under the influence of perceptible forces and, hence, calculate the nominal area of contact which affects both near-and at-contact operation.…”

“…TFC geometry was used in conjunction with the contact model formulation to identify the limits over which the interface is under the influence of perceptible forces and, hence, calculate the nominal area of contact which affects both near-and at-contact operation. Experimentally measured dynamic microwaviness, topographical roughness and material properties were used as inputs to the dynamic contact/ friction model without any empirical coefficients (Vakis et al 2009). …”