George Tyndall

Hard Disk Drive Reliability Modeling and Failure Prediction

A reliability model for the hard disk drive (HDD) is developed, focusing on head-disk separation as the primary independent variable. Among the many factors contributing to reliability, the role of water vapor is described for the first time. An experimental method based on magnetic spacing loss theory is used to characterize the head-media separation as a function of temperature, altitude, humidity, and HDD operating mode. A statistical model based on these empirical data is developed to predict HDD reliability for various operating conditions. The predictive capability of the model is verified experimentally through application to HDD product reliability test data.

Effects of Humid Air on Air-Bearing Flying Height

The pressure distribution in a squeeze film air bearing depends on the water vapor pressure and the saturation vapor pressure of water at ambient temperature. When the water vapor pressure is compressed beyond the saturation vapor pressure, a portion of the water vapor condenses, thus reducing the total gas pressure in the air bearing. This condensation mechanism thus reduces the flying height of the slider. Using a magnetic recording system for experiments, we quantified the effect of condensation on flying height by measuring the dependence of magnetic spacing on relative humidity. We developed a numerical model based on the proposed mechanism that matches the experimental data and provides a detailed view of the air-bearing response to humidity.

Simulating the Air Bearing Pressure and Flying Height in a Humid Environment

For a hard disk drive operating in a humid environment, the water vapor in the sliders air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the sliders flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using two air bearing designs, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives.

Air Bearing Surface Designs in Consideration of Thermomechanical Actuation Efficiency

Thermomechanical actuation (TMA) at the transducer region of the air bearing surface (ABS) protrudes from the transducer toward the recording media. This actuation induces a change in the air bearing pressure and a concomitant lift of the slider. The actual actuation in flying height divided by the TMA protrusion, defined as the TMA efficiency, is intimately coupled to the ABS design. After introducing an expression describing the changes in the air bearing forces due to the TMA protrusion, three approaches are proposed that facilitate the optimization of the ABS design for improving the TMA efficiency. These approaches include (a) reducing the air bearing pressure, (b) reducing the size of the TMA affected area, and (c) decoupling the peak air bearing pressure area from the TMA affected area. To illustrate these approaches, several ABS designs are evaluated by comparing their TMA efficiencies.

Calculating Air Bearing Pressure and Flying Height in a Humid Environment

This paper proposes a model describing the adjustment of air bearing pressure in a humid environment. It is shown that the FH of a slider is strongly dependent on the partial pressure of water present in a hard disk drive. The FH loss induced by the humidity effect are calculated by introducing the adjusted pressure into the air bearing model. The model output is found to agree with the changes in fly height measured by experiment. Finally, the model is applied to analyze the FH sensitivity to temperature changes in a humid condition

Slider-disk clearance characterisation and optimisation for high-reliability magnetic hard disk drives

This paper deals with the tribological reliability and durability issues in modern magnetic recording hard disk drives where the slider flies over the disk at distances typically less than 10 nm and at linear velocities of dozens meters per second. Specifically, we address the slider-disk clearance, which is known to have a major impact on HDD reliability. We discuss clearance-measuring techniques, the theoretical relationship between the clearance and reliability, and the relative contributions of different factors such as disk surface roughness, slider dynamic pitch, and disk lubricant properties to the overall drive performance.

Air Bearing Surface Designs for Less Humidity Sensitivity

A slider in a hard disk drive lose its flying height (FH) in a humid environment, which is mainly caused by the vapor condensation and consequently the pressure drop in the air bearing. Since the FH loss is closely related to the air bearing surface (ABS) design, therefore it is possible to optimize an ABS so to reduce sliders FH sensitivity to the humidity change in the environment. In this paper, we study the humidity sensitivity in regards to the ABS designs and introduce the approaches of optimizing ABS for less humidity sensitivity. The results indicate that to increase air bearing stiffness through ABS optimization is effective in reducing the humidity sensitivity. In particularly, an optimized ABS can reduce humidity sensitivity 30% more than those not optimized.

Identification of the Multiple Flying Heights in a Loading Process

The slider of a Load/unload (LUL) drive can be loaded to a high flying stable state under certain conditions, which positions the read/write transducers much higher from the disk surface than the normal flying height (FH) and resulting in the issues in read or write. To avoid the issues caused by the high flying loading, it is necessary to find ways to recognize the existence of the high FH and eliminate it in the design stages. In this paper, we introduce a method that can identify the existences of the multiple FHs in loading process conveniently. The basic idea is to plot surfaces of air bearing forces in a domain of flying attitude, and then check if multiple FHs exist to generate the same air bearing forces that match the suspension forces. The analysis results indicate that the method is easy and efficient in identifying multiple FHs in loading process.Copyright

Flying Clearance Distribution With Thermo-Mechanical Actuation of Hard Disk Drive

Flying clearance distribution with thermo-mechanical actuation is characterized. Especially, what factors contributing to variation of flying clearance are identified based on thermo-mechanical actuation profiles taken from burn-in process of hard disk drives and Gage R&R test of touch down repeatability. In addition, the effect of static temperature compensation scheme on flying clearance distribution is investigated and disadvantages of static adaptation to temperature change are identified. In order to avoid catastrophic early HDI failures due to poor static temperature compensation, we need to dynamically adjust flying clearance whenever environmental change is detected. Otherwise we need to utilize individual temperature sensitivity values of each flying head to adjust thermo-mechanical actuation amount accordingly with temperature change.Copyright

Air Bearing Surface Design for Improving Efficiency of Thermomechanical Actuation

Thermomechanical actuation (TMA) at the transducer region of the air bearing surface (ABS) protrudes the transducers toward the recording media, yet also results in greater air bearing slider lift. The ratio of these two effects is defined as the TMA efficiency. An expression based on dimensional analysis is introduced to describe the changes of air bearing forces due to TMA protrusion. A framework is proposed that facilitates optimization of ABS design for improved TMA efficiency. On the basis of the theory presented, several ABSs are designed to have different TMA efficiency. Numerical solutions of these air bearings respect to the protrusion shows agreement with the proposed theory.Copyright