Active-head slider with piezoelectric actuator using shear-mode deformation

The active-head slider technology for hard disk drive is one of the most promising means to decrease flying height. This paper describes a piezoelectric flying height control slider which has a faster dynamic response compared with conventional active-head sliders. This slider can be also adapted to the conventional slider-fabrication process. PZT layer located near the magnetic head has shear mode deformation by applying electric voltage between the upper and lower electrodes when the flying height of magnetic head needs to be decreased or increased. We fabricated a prototype with single crystal Si substrate for feasibility study. Our evaluation of the prototype revealed that the piezoelectric constant of the shear mode deformation was 0.88 nm/V, and the dynamic response was 50 kHz. The shape of the air bearing surface was optimized by simulations using a robust design method. We found that the stroke was 8 nm for an applied voltage of 11 V if the flying height was 11 nm with no deformation in PZT.     

Novel piezoelectric actuator control slider using transverse-mode deformation

This work proposes a novel structure design of active slider with a piezoelectric actuator at the top of the slider body and a soft layer between the substrate and head elements, to efficiently control the flying height of slider. A parametric simulation was performed to obtain an optimize dimension of PZT actuator and the most efficient soft material. Then three types of slider structures were designed and investigated with considering air bearing effects to achieve large actuation efficiency.     

Adaptive flying height modulation control of hybrid active slider with thermal and piezoelectric actuators

Hybrid active slider is an effective means to increase the storage density of hard disk, but its effectiveness is compromised by the flying height modulation (FHM), the bounding vibrations associated with the slider. There is a need to reduce the FHM through real time control. The hybrid active slider exhibits a very complex dynamic behavior which causes a big challenge for the traditional controller relying on an exact dynamic model. Without the requirement of an exact knowledge of the dynamics of the slider, this paper proposes an adaptive control scheme to control the flying height modulation. It is designed from the model with uncertain parameters and can guarantee the convergence of FHM. The details of the controller design and the proof of its performance are presented, and simulation results are provided to verify the effectiveness of the controller.     

Active-head sliders using piezoelectric thin films for flying height control

This paper describes design and fabrication of a MEMS-based active-head slider using a PZT thin film for flying height control in hard disk drives. A piezoelectric cantilever integrated in the air bearing slider is used to adjust the flying height individually. An air bearing surface (ABS) geometry that minimizes the aerodynamic lift force generated beneath the head has been designed based on the molecular gas film lubrication (MGL) theory. The sliders with PZT actuators were fabricated monolithically by silicon micromachining process. Performance of the actuator was tested by using an optical surface profiler. Furthermore, the fabricated slider was mounted on a suspension and the flying height of the slider above a spinning disk has been measured by multiple wavelength interferometry. Change in the head-disk spacing has been successfully confirmed by applying voltage to the actuator.     

Slit design for the thermal flying height control slider

In this work, we propose a novel thermal flying height control (TFC) slider, by designing a slit near the thermal heater in the slider. Design of the slit can reduce the mechanical constraints on the head elements and concentrate the heat around head elements. In turn, head elements can achieve more thermal protrusion and flying height reduction compared to the traditional TFC slider. The simulation results show that the application of the slit achieves a flying height reduction of 1.4 nm at writer and 1.7 nm at reader. Parametric study indicates that a trade off among the slit thickness (a), the distance of the slit to ABS (d) and thermal heater (t) should be optimized to achieve both large flying height reduction and small difference of flying height between reader and writer.     

Simulation of thermal flying height control slider with built-in contact sensor

This work investigates the piezoelectric contact sensor in the thermal flying height control (TFC) slider. A finite element model is built for the thermal flying height control slider with a piezoelectric contact sensor, which is used to detect the contact between the slider and disk. A constant force is applied at the maximum thermal protrusion point of air bearing surface. The simulation results show that the ZnO sensor with shear-mode is more sensitive to contact force than that with transverse-mode. The sensitivity of contact sensor can be increased by reducing the cross-sectional area of sensor, increasing the thickness of sensor, and choosing a short distance of sensor to air bearing surface. In addition, the thermal-stress effects from TFC heater on contact sensor are significantly large and the amplitude of thermal-stress inducing output voltage is orders larger than that induced by contact force. However, by optimizing the distance of sensor to ABS, it is possible to eliminate the thermal-stress effects. Finally, the response time of thermal-stress induced electrical voltage of contact sensor is about 0.3?ms.     

An efficient thermal actuator design for the thermal flying height control slider

In this work, we propose a novel thermal actuator by designing a thermal insulator, a thermal conductor, and their combination to the traditional thermal heater. The thermal-structure simulation coupled with air bearing simulation is used to simulate the actuation by the thermal actuator, as well as the effects on flying performance of slider being actuated. The simulation results show that an additional 0.8–1.1 nm flying height reduction can be obtained by applying the proposed thermal actuator when the flying height of TFC slider is about several nanometers.     

Contact between a thermal flying height control slider and a disk asperity

Contact between a thermal flying height control slider and an asperity on a disk is investigated using finite element analysis. The finite element model developed accounts for transient elastic–plastic deformation and heat generation due to frictional heating. Plastic deformation and temperature rise of the read/write element are determined as a function of flying height of the slider, location of the read/write element as well as material properties of typical disk asperities. The model shows good agreement with experimental data. Significant plastic deformation and temperature rise were observed in the shield and alumina regions of the slider. Hard and stiff disk asperities, such as alumina asperities, result in more damage to the slider than soft and compliant nickel-phosphorus ones.     

Time dependent simulation of active flying height control of TFC sliders

A time-dependent numerical simulation procedure is implemented to simulate the flying height response of a typical thermal flying height control (TFC) slider as a function of the power input to the heater element. The Reynolds equation is used in conjunction with a TFC slider finite element model to determine the change in the thermal protrusion and flying height of the slider. The power input signal to the heater element is optimized using convex optimization to minimize flying height variations of the slider. The optimization procedure is applied to a typical experimentally measured flying height profile. The numerical simulation results are in excellent qualitative agreement with experimental measurements.     

Numerical simulation of thermal flying height control sliders in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the most promising techniques to extend the recording density in hard disk drives beyond 1?Tb/in². Although the diameter of the spot on the disk that is heated by the laser beam is very small, on the order of nanometers, high local temperatures on the disk and the heat dissipated in the slider during the light delivery process can cause thermal deformations of both the disk and the slider, thereby affecting the flying characteristics at the head-disk interface. In this paper, a finite element model is developed which incorporates a HAMR optical system into a thermal flying height control (TFC) slider with dual heater/insulator elements to study the effect of heat dissipation in the wave guide on the thermal deformation and flying characteristics of a HAMR-TFC slider. In addition, the power input of the laser and design parameters of the heaters are investigated.     

Examination of flying height of magnetic head slider in simulations and measurements at nanometer-order spacing

This paper describes a comparison with the experimental flying heights and the simulated flying heights, which were calculated by using the linearized Boltzmann equation and the conventional modified Reynolds equations. The experiments were measured under the ambient pressure from atmospheric pressure to 6.7 × 10^?3 MPa. The calculated results of the linearized Boltzmann equation were almost the same as the experimental results from the high spacing range to the low spacing range of 10 nm. At the slider spacing of 10 nm, it was confirmed that the difference between the experimentally measured results and the calculated results of the linearized Boltzmann equation was less than 5%, and the differences in the conventional slip flow approximation equations were over 30%.     

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.     

A circular arc slider with a high flying height supported by parallel flat springs for optical disc devices

We have investigated a circular arc slider with a high flying height that is suitable for optical disc devices to reduce the thickness of the device and to achieve a higher recording density over a wider recording area. Our proposed slider was supported by parallel flat springs to reduce the tilting motions of the slider in the pitching and rolling directions. Two types of slider were examined: (1) a positive pressure slider with a single shallow pocket on the slider surface, and (2) a negative pressure slider with two shallow pockets. The static and dynamic characteristics of our proposed slider were investigated both theoretically and experimentally. It was found that our proposed sliders followed a disc surface with the amplitude of axial runout of 100 μm with a focusing error of 30 μm_p-v in the focusing direction and a tilt angle of <6 min_p-v in the pitching and rolling directions.     

Servo signal processing for flying height control in hard disk drives

A novel method of measuring the relative head-medium spacing based on a measurement in the servo sectors is developed and simulated using a read back signal model. The spacing measurement is tested experimentally on a spin stand where the flying height is varied using the resistance heater element in a thermal flying height control slider. In addition, voltage step response measurements were obtained. The data were used to perform system identification and estimate the dynamics of the thermal actuator. The model can potentially be used for thermal flying height control.     

Active flying-height control slider using MEMS thermal actuator

Today’s head/disk interface design has a wide flying height distribution due to manufacturing tolerances, environmental variations, and write-induced thermal protrusion. To reduce the magnetic spacing loss caused by these effects, we developed an active head slider with a nano-thermal actuator. The magnetic spacing of these sliders can be controlled in situ during drive operations. After simulating the heat transfer in the slider to obtain the thermal deformation of the air-bearing surface, we fabricated a thermal actuator using thin-film processing. An evaluation done using a read/write tester showed a linear reduction in the magnetic height as electric power was applied to the actuator. The actuator’s stroke was 2.5 nm per 50 mW with a time constant of 1 ms. There was no significant impact on the reliability of the read element.     

Simulation of a pad slider flying on a wavy surface

This paper describes following-up characteristic of a pad slider to a wavy surface. The pad slider comprises a leading pad and a trailing pad. We use a sine wave to replace an actual wavy surface. The response of the pad slider due to the sine wave is analyzed by computer simulation. The response of the pad slider is evaluated from variation in slider flying height (FH). A variation gain that is a ratio of FH fluctuation and wave amplitude is defined to explain the following-up characteristic of slider. To analyze the following-up characteristic, different wavelengths are used as parameter to calculate the variation gain. Because pads on the air-bearing surface of the slider are able to occur at two pressure peaks on the leading edge and trailing edge that enable a pitching motion of the slider, the slider can follow the disk waviness with a wavelength that is shorter than the slider length. The variation gain is 0.33 for the wavelength that is equal to the slider length. However, the slider cannot follow the disk waviness with a wavelength that is shorter than the pad length. The variation gain is greater than 1 for the wavelength 0.2 mm. To study the relationship between the variation gain and the dynamics of slider, a transient response simulation is carried out in order to investigate a natural frequency of slider. We set a projection on a plane surface. When the slider is flying over the projection, we can obtain a flying height response curve and a pitch response curve. The natural frequency of flying height and pitch angle can be known by FFT. The transient response of slider in pitch mode is compared with the variation gain. The simulation results make clear the fact that the following-up characteristic has correlation with the dynamics of the pitch model and the phase difference between a locus of head and a wave of disk surface.     

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

This paper presents an investigation of the light contact in a head disk interface with dynamic flying height control. The touchdown test is conducted for a dynamic flying height control slider and the response is recorded using AE sensor. The bouncing instability and light contacts are observed during thermal actuated touching down process of the slider. The physics-based simulation is conducted to correlate with the experiments, so as to characterize bouncing instability and the factors affecting bouncing instability. The enhanced spectrogram and HHT approaches are used to extract and characterize the non-stationary characteristics of the weak signal of slider response under light contact. It is found that the light contacts are constituted by a series of intermittent transient impact responses with frequency identical to slider??s pitch mode.     

Identification of contact bouncing vibrations using TFC active slider and adaptive fuzzy control for advanced active slider design

The recent advance of magnetic storage technology includes the active thermal fly-height control (TFC) technique that is able to reduce the clearance between read/write heads and disk surface to be of few nanometers. However, it has been estimated that TFC technique alone cannot provide the even smaller clearances necessary to achieve Tbit/in² recording densities due to the presence of bouncing vibrations and instability. In this work we investigate hybrid active slider technique with both thermal and piezoelectric actuators to achieve extremely high-density recording. The nonlinear system dynamics of thermal actuated slider is established by test-based identification. We propose an adaptive fuzzy control hybrid active slider design in which piezoelectric actuation is added to the existing thermal actuated slider design, so as to fully eliminate the high frequency bouncing vibrations. It can yield more than Tbit/in² recording density with sub-nanometer level clearance, while using the state-of-the-art and matured manufacturing techniques for active piezoelectric slider and TFC slider.     

High speed sub-micron bit detection using tapered aperture mounted optical slider flying above a patterned metal medium

Rapid advances in the development of the digital network society have necessitated both large capacity and higher data transfer rate for every type of digital storage equipment. Proximity optical recording based on the near-field interaction principle promises to provide breakthroughs in overcoming rigid optical diffraction limits and wave length shortening limits. We have previously presented a compact optical head assembly consisting of a combination of a pyramidal hole processed silicon slider and light-wave guide combined suspension. Attaining higher recording density requires both a much smaller sized aperture and a highly efficient laser power delivery mechanism. To satisfy these requirements, we have introduced a planar lens and tapered aperture processed optical slider, delivering laser power through a single mode optical fiber, and we have demonstrated sub-micron size (150–200 nm-long) bit signals at more than a 10 MHz frequency band.The authors would like to thank Mr. Tamotsu Kusumi and Tadashi Sasagawa, Nikon Corp. for their processing of fine 350 nm line and space patterns on thin chromium films using short wavelength light lithography. The authors would like to thank Dr. Hisataka Takenaka and Dr. Hisashi Ito, NTT Advance Tecnology Corp., for forming a high quality carbon protective overcoat on the patterned media. The authors also would like to thank Dr. Takanori Doi, Toda Corp., for his helpful suggestions and careful treatment in forming the lubricant layer on the patterned metal media. The authors would also like to thank Mr. Masanori Sahara and Mr. Takashi Suzuki for their useful advice in applying the APD in our readout system.     

Parametric characterization of piezoelectric valveless micropump

Experimental investigations are performed to determine the influence of electrical excitation and geometrical parameters on the performance of piezoelectric valveless micropumps fabricated on printed circuit board substrates. Strain gauges and shunt resistor are used in conjunction with a data acquisition system to form an effective transducer, capable of providing magnitude and phase response information pertaining to fluid–structure interaction. Effect of conical diffuser geometry on the displacement response and pressure flow characteristics are studied. With suitable variations in the design of the diffuser element and input excitation parameters, the ability of the valveless micropump can be extended to include forward, reversed and bidirectional flow features. The characteristic signatures of single and two peaks in flowrate or pressure data are captured in the displacement phase response. System identification approach is proposed to model and predict the performance of valveless micropumps.