Bit Error Rate Improvement of Hard Disk Drive

The objective of this research is to improve the performance of the read-write head process in Hard disk drive manufacturing with respect to Bit Error Rate (BER). With the preliminary survey, the process capability index (Cpk) of BER was 0.72 which is less than the one side acceptable value at 1.25. To improve Cpk of BER, five phases of Six sigma approach are applied starting from define, measure, analyze, improvement and control phases. At 95% confidence, thermal protrusion, writing current amplitude, writing current overshoot, number of defects on media and writing head width are the significant factors for Bit Error Rate due to their p-value less than 0.05. Since the number of defects and writing head width are uncontrollable factors, the experiment are designed and performed based of general factorial design with three levels of each controllable factor. At 5% significance level, there are the interaction effects between the thermal protrusion and the writing current amplitude as well as the interaction affects between the writing current amplitude and the writing current overshoot. With the general linear model (GLM), the suggested values for the thermal protrusion, writing current amplitude and writing current overshoot are 35 DAC, 10 mA and 9 mA, respectively. Under the suggested condition, Cpk of BER is increased from 0.72 to 2.38 and the percentage of defective due to head related failure is reduced from 21.85% to 9.86%.

Frictional Heating Effect on Thermal Protrusion in Head Disk Interface

For increasing areal density in hard disk drives (HDDs), the physical clearance between the read/write element and the surface of the disk has been continuously decreasing to 1 nm or below [1]. At such a low clearance, the contact between the head and the disk is inevitable to occur, so head wear is becoming a critical issue in the development of HDD. The contact between the head and the disk induces a frictional heating, which may generate an additional thermal protrusion in the contact area of the head, and causes more wear. On the other hand, the target clearance in a HDD is generally determined by pulling back a setting TFC power from the touchdown point, accurately identifying the touchdown point is very significant for the clearance control in hard disk drive. A thermal protrusion is caused by friction-heating in the status of touchdown. Therefore, it is very necessary to quantitatively understand on friction induced thermal protrusion and clearance loss.