Flying Height Adjustment Research Articles

Dynamic Flying Height Adjustment in Hard Disk Drives Through Feedforward Control

A dynamic model of the resistance heater element in a thermal flying height control (TFC) slider of a hard disk drive is identified and used for dynamic flying height control. Experimental data obtained on a spin stand and a generalized realization algorithm are used for identification of a discrete-time dynamic model of the thermal actuator. The flying height change is measured in two different ways: using servo burst information written onto the disk surface and using information written in the data sectors only. The resistance change of the thermal actuator based on the input power level is measured. Based on the identified discrete-time model of the heater and using convex optimization techniques, a computational scheme is proposed to obtain optimized feedforward input profiles to the heater element that minimize repeatable flying height variations and enable low flying heights.

Effects of environmental temperature and humidity on thermal flying height adjustment

Thermal actuated sliders are being widely used in today’s hard disk drive industry for its advantages of easier control of flying height (FH) and less risk of contacts with the disk. This article uses a coupled-field analysis method, which includes an air bearing model, a heat transfer model and a thermal-structural finite element model to investigate the FH changes of thermal actuated sliders at various environmental conditions. The mechanism of water vapour’s contribution to air bearing pressure loss is explained and a new humidity model is proposed to calculate this pressure loss. The temperature effects are also considered in the simulation models. It is observed that the environmental temperature and humidity have significant effects on slider’s FH changes, but their effects on the thermal protrusion height are limited. A humidity sensitivity study is also made and the results are discussed. It is found that the slider with thermal protrusion on its trailing pad will be more sensitive to the humidity. Besides air bearing stiffness, some other factors such as peak pressure, protrusion shape and air bearing surface (ABS) design will also contribute to the slider’s humidity sensitivity.

Integrated Electromagnetic Second Stage Microactuator for a Hard Disk Recording Head

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A slider with an integrated microactuator (SLIM) allows actuating a read-write element of a hard disk drive (HDD) in both the vertical direction allowing a flying height adjustment as well as in the lateral direction allowing a second stage actuation. The microactuator system consists of a pair of electromagnetic variable reluctance (VR) micro actuators. The microactuator system is fabricated using thin-film technology. Each actuator has a permalloy C-core carrying a two-layer spiral Cu coil with a total of 16 turns. The insulation materials are SU-8 (in the lateral direction) and Si<formula formulatype="inline"> <tex Notation="TeX">$_{3}$</tex></formula>N<formula formulatype="inline"> <tex Notation="TeX">$_{4}$</tex></formula> (in the vertical direction). The total size of one magnetic VR microactuator is 460 <formula formulatype="inline"><tex Notation="TeX">$\, \mu$</tex></formula>m<formula formulatype="inline"><tex Notation="TeX">$\, \times \,$</tex></formula>300 <formula formulatype="inline"><tex Notation="TeX">$\, \mu$</tex></formula>m<formula formulatype="inline"><tex Notation="TeX">$\, \times \,$</tex></formula>61 <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex></formula>m. This paper discusses design considerations, presents the FEM simulation conducted, describes the fabrication technology, and provides experimental results. </para>

Flying height adjustment technologies for high-density magnetic recording

The flying height adjustment technology becomes important to achieve the stable ultra low flying height for recording density 1 Tb/in² in hard disk drive. The possible approaches towards flying height adjustment, advantages and disadvantages of different adjusting methods are discussed. Finally, the flying stability of thermal actuated slider is studied taking into account the short-range interaction forces. It is noticed that the flying height of thermal actuated slider is less sensitive to the short-range interactions than the normal slider and can sustain larger shocks. The thermal actuated flying height adjusting technology is more suitable for ultra-low flying height applications.

Optimized Design of Heaters for Flying Height Adjustment to Preserve Performance and Reliability

We developed a thermal flying-height control (TFC) slider to control the flying height of magnetic recording heads. The slider basically consists of a small heater fabricated near the read/write element. This study discusses the effect of heater size and heater location on the change in the flying height at the read/write element. We also discuss the resulting temperature rise due to the additional heat applied by the heater. Specifically, we have found that small heaters generally resulted in lower heater power per unit change in the flying height and lower head temperature rise per unit change in the flying height. In terms of heater location, we have found that a heater closer to the air-bearing surface (ABS) also tends to result in a larger change in the flying height because of the larger protrusion shape. However, the head temperature rose significantly. Therefore, shorter ABS/heater distance was a trade off lower power against higher rise in head temperature. We concluded that smaller heaters and the shorter ABS/heater distance are better as long as head reliability is ensured

Fabrication and experimental study of Al2O3-TiC sliders with piezoelectric nanoactuators for flying height control

A gap flying height (FH) of less than 5 nm between the read/write element and the surface of the disk is required for ultrahigh density recording. A stable and constant FH must also be sustained in the presence of altitude and temperature changes and manufacturing tolerance. A FH adjustment or controlled slider that is capable of adjusting its gap FH has been proposed previously. In this paper we demonstrate an inexpensive and low-temperature approach for integrating piezoelectric materials in the fabrication of current small form-factor Al2O3-TiC sliders. A bulk PZT sheet is bonded onto the back of row-bars and the sliders are separated by a standard dicing process. It requires no deep reactive-ion etching (DRIE) or high temperature processes and is suitable for mass production. A conventional design and a new special air bearing surface (ABS) design have been fabricated and tested by an optical profiler and a FH tester. A nonflying actuation stroke of 0.6–0.8 nm/V has been observed. The FH measurements showed that the ABS plays a key role in increasing the actuation efficiency, which also agrees well with the numerical analysis.

Flying height adjustment by slider’s air bearing surface profile control

A new active slider structure is proposed for the flying height adjustment. A bulk PZT ceramic is bonded onto the backside of slider directly. The PZT actuator adjusts the flying height by control of air bearing surface profile. The total thickness of the active slider is same as a standard pico slider. This structure is easy to fabricate and compatible with standard product, it also keeps the air bearing surface intact. The thicknesses of the PZT and the glue are optimized with numerical simulations. This active slider has been demonstrated and the observed flying height adjustment is 2.3nm.

Friction Control of Active-Head Slider During Flying Height Adjustment

To reduce the risk of head crash when a slider contacts a smooth disk during flying height adjustment, a novel tapping method for reducing the friction and lowering the risk of head crash was developed. An active-head slider was designed and fabricated to demonstrate the usefulness of the tapping approach. It is also found that micro-vibration is significantly effective in avoiding a high friction force and protecting a head from the crash due to head-disk contact during the flying height adjustment.

Flying-Height Adjustment Technologies of Magnetic Head Sliders

Two of many parameters that need to be controlled in designing magnetic recording sliders with the desired flying height are manufacturing tolerances and environmental variations. To reduce the effect of these two parameters, we have developed an adjustable flying-height slider. This slider carries a piezoelectric microactuator to control the flying height. After simulating the piezoelectric deflection and its effect on the flying characteristics, we designed an air-bearing and fabricated a slider using silicon micro-electromechanical systems processing. Optical measurements showed that the flying height of the slider changed as electric voltage was applied to the microactuator. The observed stroke of 6 nm/15 V is less than the simulated stroke because of contact between the slider and the disk, but it is still large enough to reduce the effect of the two mentioned parameters.

Flying-height adjustment of a magnetic head slider with a piezoelectric micro-actuator

The current design of magnetic disk head sliders needs two extra margins in flying height design: one for manufacturing tolerance and one for environmental variations. To reduce these margins, we have developed an adjustable flying height slider. This slider carries a piezoelectric microactuator and its flying height can be controlled. After simulating the piezoelectric deflection and flying characteristics, we designed an air-bearing surface for the slider and fabricated it by silicon microelectromechanical systems processing. Several of the fabrication problems previously reported were solved, and the slider's change in the flying height as an electric voltage was applied to the microactuator was optically observed. The observed stroke of this flying height adjustment, 6 nm/15 V, was less than the simulated stroke because of contact between the head and the disk, but it is still large enough to reduce the two current flying-height margins.

219 マイクロ圧電アクチュエータによる磁気ヘッドスライダ摩擦制御および浮上量調整

219 マイクロ圧電アクチュエータによる磁気ヘッドスライダ摩擦制御および浮上量調整