To sustain an areal growth rate of 60% - 100% per year, the track density and linear density is constantly increasing. Our next generation of mobile drives have more than 73,000 tracks per inch.
At such small track dimensions, the slider has difficulty to remain on track. Off-track vibrations, or track mis-registrations (TMR), are mainly caused by the actuator vibrations, suspension modes, disk flutter, and airflow. These “low frequency” excitations can be usually compensated for with a closed loop controller. However, head disk interactions caused by contamination, scratches, disk micro-waviness or lubricant stick slip phenomena cannot be controlled actively. They usually cause a disturbance of the slider air bearing, which leads to flying height variations and contact. Short contacts or stick slip type phenomena can even cause the slider body to resonate at its eigenfrequencies.