Yoshifumi Mizoshita

Vibration minimized access control for disk drives

A new access control method called SMART (Structural Vibration Minimized Acceleration Trajectory) has been developed for hard disk drives. The access formula is derived from a minimum-jerk cost function. The closed loop of access mode is based on velocity control and the target velocity to keep minimum-jerk is easily calculated as a function of position by a DSP controller. With SMART control the high harmonics of the actuator acceleration are suppressed in comparison with conventional control. Residual vibration after the access operation and spacing fluctuation of the head slider are both greatly decreased.

Spin-valve read heads with NiFe/Co/sub 90/Fe/sub 10/ layers for 5 Gbit/in/sup 2/ density recording

Successful use of a NiFe/Co/sub 90/Fe/sub 10/ bilayer as a soft magnetic free layer in spin-valve films with a GMR enhanced structure comprised of NiFe/Co/sub 90/Fe/sub 10//Cu/Co/sub 90/Fe/sub 10//FeMn is outlined. The GMR ratio of the spin-valve film with Co/sub 90/Fe/sub 10/ is over 7% and the coercivity of the free NiFe/Co/sub 90/Fe/sub 10/ bilayers is less than 5 Oe. A merged inductive/spin-valve head was fabricated with a read track-width of 1.3 /spl mu/m and a read gap-length of 0.26 /spl mu/m using spin-valve film with a Ta(50 /spl Aring/)/NiFe(45 /spl Aring/)/Co/sub 90/Fe/sub 10/(30 /spl Aring/)/Cu(32 /spl Aring/)/Fe/sub 10/(22 /spl Aring/)/FeMn(100 /spl Aring/)/Ta(100 /spl Aring/) structure and 260 /spl Aring/ thick domain control Co/sub 78/Cr/sub 10/Pt/sub 12/ magnet layers. Its read/write performance was tested on a low noise CoCr/sub 17/Pt/sub 5/Ta/sub 4/ thin film disk with an Mr/spl middot/t of 0.41 memu/cm/sup 2/ and a coercivity of 2500 Oe. There is no Barkhausen noise in the readback waveform. The result of the microtrack sensitivity profiles reveals an effective read track-width of 0.8 /spl mu/m. A normalized output for a track-width of 880 /spl mu/Vpp//spl mu/m and D/sub 50/ of 166 kFCI was obtained. Using a PRML channel, a bit error rate of less than 10/sup -8/ was obtained without error correction at a data rate of 3.3 MB/s and at a linear density of 217 kBPI on a thin film disk with an Mr/spl middot/t of 0.72 memu/cm/sup 2/. Thus, 5 Gbit/in/sup 2/ density recording with a linear density of 217 kBPI and a track density of 23 kTPI is possible.

Microactuator control for disk drive

The nonlinear response of a conventional actuator which depends on the ball-bearing friction is the main factor for determining the high track density of hard disk drives. We cannot get enough servo loop gain in the low-frequency region with a conventional single actuator because of its hysteresis characteristics. We have developed a new planar piezoelectric microactuator which is lightweight and applicable for a hard disk drive. Also we introduced a two-stage servo controller and realized a high servo bandwidth over 1 kHz and enough tracking-error reduction in the low-frequency region.

Stiction free slider for the smooth surface disk

We describe the superior tribological performance for a slider with three cylindrical pads on the air bearing surfaces on a smooth surface disk. Using photolithography, we can form the cylindrical pads with a controlled surface area and uniform height on the air bearing surfaces of a magnetic head. In addition to the reduction of the apparent contact area of the head/disk interface, by applying an excessive amount of lubricant to the vertical surface of the pads, we can lower the static friction with an ultra smooth surface (Ra=0.3 nm). Moreover, we observed no wearing of the pads after 100,000 CSS cycles.

Development of integrated suspension system for a nanoslider with an MR head transducer

The requirements for a suspension assembly with a 2-mm nanoslider and a magnetoresistive (MR) head transducer to improve the head-disk interface are discussed. An integrated suspension system with a miniature monolithic flexible body with the signal pattern directly on the body is introduced. Experiments showed that the suspension system has good characteristics to carry a nanoslider and an MR head transducer. >

A new integrated suspension for pico-sliders (pico-CAPS)

Ultralow loadforce pico-sliders must be used to further improve the reliability of magnetic disk drives. We now propose a new integrated suspension for pico-sliders with MR heads, called pico-CAPS. The pico-CAPS features a monolithic body and has a direct signal pattern. It is light and has ultralow stiffness and a high resonant frequency. Our tests show that the pico-CAPS makes the flying pico-slider stable. Its shock resistance is high, and its electrical characteristics allow the high data transfer rate of over 40 MB/s.

NiFe/CoFeB Spin-valve Heads For Over 5 Gbit/in/sub 2/ Density Recording

This paper outlines the successful use of NiFe/(Co/sub 90/Fe/sub 10/)/sub 100-x/Bx (x=5, 10%) for soft magnetic, thermally stabilized spin-valves. The GMR effect in the NiFe/CoFeB spinvalve increases after annealing. The annealing effect of CoFeB on CoFeB/Cu interfaces is investigated by high resolution TEM-EDX analysis. Merged inductive NiFe/CoFeB spin-valve heads with a read gap length of 0.18 /spl mu/m and a write gap length of 0.28 /spl mu/m having NiO(400 /spl Aring/)/NiFe(10 /spl Aring/)/CoFeB/sub 5/(10 /spl Aring/)/Cu(32 /spl Aring/)/CoFeB/sub 5/(20 /spl Aring/)/Ta(100 /spl Aring/) spin-valve film and high Bs laminated FeZrN/NiFe top poles were fabricated. Their read/write performance were tested on a low noise CoCr/sub 19/Pt/sub 5/Ta/sub 2/Nb/sub 2/ thin-film disk with an Mrt of 0.6 memu/cm/sup 2/ and a coercivity of 2600 Oe. A normalized output per track-width of 1000 /spl mu/Vpp//spl mu/m and a 50% rolloff linear density (D/sub 50/) of 182 kFCI is obtained. This performance well exceeds the performance of 5 Gbit/in/sup 2/ spin-valve heads. The measured S/N was 26.8 dB for a spin-valve head with with a narrow read track-width of 0.68 /spl mu/m, and the feasibility of 8 G bit/in/sup 2/ recording density is studied using a 1/7 code Narrow Band PRML channel.

Viterbi detector including PRML and EPRML

The authors develop an integrated-Viterbi detector which can handle partial-response maximum-likelihood (PRML) and extended PRML (EPRML). Class 4 partial response (PR4) and extended PR4 (EPR4) equalization can be accepted according to the recording density. The EPRML performance is superior to that of PRML for a normalized recording density above 1.8, but inferior at lower densities. Experimental results agree with theoretical values and prove that the performance of this Viterbi detector is superior, by 8 dB, to that of conventional peak detectors when the normalized recording density is 2.7. >

Dynamic characteristics of a magnetic head slider

The estimation of the dynamic characteristics of magnetic head sliders is essential for the design of the recent disk file systems with reduced head-to-disk spacing. This paper presents a method for measuring the head slider flying height fluctuation caused by disturbances on the disk and head arm vibration. A numerical analysis of the head assembly including suspension spring and gas-bearing slider is presented. The experimental and analytical results are compared and it is clarified that the many resonant peaks of head sliders spacing fluctuation in the low frequency region are caused by the resonance of the suspension spring.

A negative pressure microhead slider for ultralow spacing with uniform flying height

A negative-pressure head slider for ultralow flying has been developed which features a newly shaped air bearing surface that gains sufficient suction force because the distance between the two side rails gradually widens from the leading to the trailing edge of the slider. The slider has a fast takeoff, and the flying height is insensitive to disk velocity. It also avoids the dust accumulation problem seen in the conventional negative-pressure slider. The sliders absence of taper suppresses generation to floating force, resulting in a microslider with relatively wide siderails. The flare angle of the siderails also contributes to making the flying height insensitive to the yaw angle, resulting in a uniform flying height over the entire disk surface. The recess needed to generate suction is a shallow 2 mu m, so the flexible rail shape is easily manufactured using photolithography. >