No-yeol Park

Torque and unbalanced magnetic force in a rotational unsymmetric brushless DC motors

The pole-teeth-winding configuration in brushless dc motors determines torque and unbalanced magnetic force which are the resultants of the tangential and the normal magnetic force in a small air gap, respectively. This paper calculated torque and unbalanced magnetic force using FEM, Maxwell stress tensor to investigate the influence of pole-teeth-winding patterns on the performance from two common designs, i.e. the rotational symmetric 12-pole 9-tooth (12P9S) motor and the rotational unsymmetric 8-pole 9-tooth (8P9S) motor, and proposed the rotational unsymmetric 10-pole 9-tooth (10P9S) motor which achieves the high average torque of 12P9S motor and the low cogging torque of 8P9S at the same time. The analyses show that 8P9S and 10P9S motor tend to have less cogging torque because their bigger values of the least common multiple of pole and teeth reduce the cogging torque. The torque efficiency depends on pole-teeth-winding configuration. ABC-winding of 12P9S motor and three consecutive teeth winding of 10P9S motor utilize all six energized coil effectively to produce the high average torque. The normal magnetic force in a rotational unsymmetric design is not balanced and results in unbalanced magnetic force.

Effect of top Ru deposition pressure on magnetic and microstructural properties of CoCrPt-SiO2 media in two-step Ru layer

Two-step-deposited Ru layers of 20 nm have been employed as an underlayer for CoCrPt–SiO2 perpendicular magnetic recording media. The bottom Ru layer of 10 nm is deposited at 3 mTorr for good texture of hcp (0002) and the top Ru layer of 10 nm is deposited at various conditions. Sputtering power and Ar pressure are variables for the top Ru layer deposition. As the sputtering pressure of the top Ru layer increases, coercivity (Hc) of the CoCrPt–SiO2 layer increases and then saturates or slightly decreases with a further increase of sputter pressure. The Hc increase is mainly due to exchange decoupling among grains of CoCrPt. The c-axis alignment of the Ru layer by the two-step deposition method is much improved compared to that of a single-step-deposited Ru layer when the sputtering pressure is higher than 3 mTorr. The grain size of Ru layer is smaller and the grains are well separated by void boundaries when the top Ru sputtering pressure is high. There is a one-to-one relationship between small Ru grains...

Optimum design rule of hysteresis loop for ultrahigh density recording in single-layered perpendicular media

Micromagnetic studies have been performed to find optimum shape of hysteresis loop in a single-layered perpendicular medium for ultrahigh density recording. A good index that was inversely proportional to signal-to-noise ratio (SNR) was developed. By using this index, we found the optimum loop shape should have terms of the ratio of nucleation field to coercivity within -0.4 to -0.6, the loop slope within 2 to 4, and the ratio of grain thickness to grain diameter larger than 2.5.

Resistive Probe Storage: Read/Write Mechanism

We define probe storage in a broad sense, which includes most of the mechanically addressing storage devices such as hard disk drives and optical disk drives. Its history is briefly discussed from the era of inscription, which leads to the application of scanning probe microscopy (SPM), to probe storage devices. Most of the current activities regarding the SPM based probe storage device are reviewed with special emphasis on resistive probe storage and related methods that use ferroelectric materials as information media. We present the principle of the read/write mechanism using the resistive probe accompanied by a servo/tracking concept. Such resistive probes can be implemented into probe storage devices with ferroelectric media development, which shows promise for the terabit era.

Head design scheme for perpendicular recording with single layered media

For ultra high areal recording density, we suggest the perpendicular recording scheme with ring head and single layered media for easy implementation. To improve the perpendicular head field and its gradient, conventional ring head is modified by cutting the top pole edge. Head field was calculated with nonlinear finite element method. The write process was simulated with micromagnetics using the calculated head field of two heads (original and modified) at each magnetic grain of recording disk, instead of using Karlqvist head field. Both simulated and measured MFM images show that the transition of modified head is clearer than original one. Also, TAA and SNR of modified head are higher than results of original head. With simple modification, currently used ring head can be easily applied to high density perpendicular recording HDD system.

Strategies for improvement of tribological characteristics at the head/disk interface

Tribological optimization of the head/disk interface is crucial to attain reliable performance of hard disk drives. As the flying height of the slider above the disk continues to decrease with increase in recording density, the concern for surface damage is greater than ever before. In this work a novel method to reduce debris contamination by way of trapping the particles in micro-grooves on the slider surface to protect the head is proposed. Tests performed with dummy sliders with several types of strategically designed micro-grooves show that the grooves are effective in removing the wear debris at the slider/disk interface. Furthermore, concept for stiction-free slider design has been investigated. Micro-bumps were fabricated on a slider surface in order to reduce stiction. Preliminary tests show that compared with conventional sliders, these sliders result in significantly lower stiction during contact-start-stop tests performed on the data zone of a magnetic disk. The concepts proposed in this work may be utilized in the design of future sliders for low flying heads on super-smooth disks.

Recording physics of perpendicular recording with single layered medium and ring head

In this article, the recording physics of a ring head with a single layered perpendicular medium (Ring/SL) is studied and the results are compared with a single pole head with a double layered perpendicular medium (SPT/DL) by using various simulations and experiments. The Ring/SL has much lower effective medium coercivity than the SPT/DL due to the substantial longitudinal field component of ring head and the incoherent rotation mode of medium magnetizations. Furthermore, switching time of the Ring/SL is estimated as only 10%∼30% of the SPT/DL. In the Ring/SL, the head field gradient of 40 Oe/nm is enough for maximizing SNR. The Ring/SL shows very low noise characteristics especially at high linear density. The signal output of the Ring/SL is smaller than the SPT/DL, but it is large enough to be detected. Therefore, it can be concluded that the combination of single layered perpendicular medium and ring head is highly promising for ultrahigh density recording.

Diffraction limit of the focusing waveguide grating coupler for optical probe information storage

A focusing waveguide grating coupler (FWGC) has been applied to an optical information storage element. To achieve minimum diffraction, focusing and high-coupling efficiency with high power, several fabrication and design difficulties have to be overcome. In this work, we report some new strategies to improve the fabrication and design, and greatly improve the pattern quality in defining curved gratings in the nanometre range using single-step electron-beam lithography with a conventional exposure mode. We also present the optimum fabrication conditions for the FWGC and the minimum diffraction limit (1.1 µm) obtained for the structure, which is optically the smallest diffraction spot size obtainable from diffraction gratings focusing beams into a spot in air.

High density magnetic random access memory using a pair of asymmetrical cell

Magnetic random access memory (MRAM) is one of the most promising candidates to provide energy efficient and non-volatile memory. We present a new MRAM design using a pair of asymmetrical cells. The pair cells have parallelogram shaped to induce broken shape magnetic anisotropy along the short axis of the cell. One important advantage of the pair cells is that they can share the same Word and Bit lines intersection in the MRAM architecture. This means that the number of electrical current lines can be reduced and leading to higher recording density. The new concept is successfully demonstrated using finite element micromagnetic simulation.

New design of perpendicular magnetic recording media: hybrid media

To achieve both the high anisotropy energy and high SNR performance at ultra high areal recording density, we have studied paired recording layered PMR media named as hybrid media. Hybrid media consist of 1/sup st/ recording layer and 2/sup nd/ recording layer. 1/sup st/ recording layer and 2/sup nd/ recording layer have low noise properties and high anisotropy energy, respectively. 1/sup st/ and 2/sup nd/ recording layer are continuously and coherently stacked on the top of the underlayer.