Bias Field Margin Research Articles

Partial grooving in vertical Bloch line memory

Partially grooved regions in magnetic garnets, used to stabilize minor-loop stripe domains in vertical Bloch line memories have been investigated using arrays of grooves in garnets with a zero-field stripe-width of 2.36 mu m and thickness of 2.26 mu m. Rectangular grooved regions were used to confine the minor loop stripes, using a groove depth of 10% and groove widths of 1.5 mu m and 2.00 mu m. Major line regions were defined by two successive 10% grooving steps. Bias field margins were measured experimentally and computed using a two-dimensional, magnetic-domain computer simulation. The computed margins were shown to be in quantitative agreement with experimentally measured bias field margins. Interpretation of the simulations and the experimental data in these samples indicates that magnetostatic effects dominate magnetostrictive effects in defining bias field stability.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bloch line propagation with Co-Pt bit patterns in stripe domains confined by grooves

Bloch Line (BL) pair propagation using a field-access scheme has been investigated in the straight pair of stripe domains stabilized around completely etched grooves. Potential wells to define the bit position for the BL pairs were produced by the stray field from Co-Pt thin-film patterns with high coercivity. By applying a series of asymmetric triangular bias pulsed fields, a BL pair was propagated at 500 kHz with a 14% bias field margin. At 1 MHz, however, the bias field margin was only 7%. This reduction was due to the long relaxation time of the domain walls. The drive field margins depended on the orientation of the propagation direction relative to the magnetized direction of the Co-Pt bit patterns. This dependence became small when the in-plane bias field was decreased. >

Overwrite characteristics of magneto-optical disks by exchange-coupled RE-TM quadrilayered films

The direct overwrite characteristics by light power modulation on a magnetooptical disk with exchange coupled rare-earth-transition-metal (RE-TM) quadrilayers film are described. In this system, it is important to investigate the relationship between the laser power and the bias field margins. These margins are defined by the Curie temperature and the temperature dependence of the reversal field of each layer. Good recording characteristics were obtained, such as a carrier-to-noise ratio >49 dB on a bit length of 0.76 mu m. A fairly wide power margin of +or-20% was obtained, and a wide tolerance on the bias magnet construction was allowed. For achieving a read cycle of more than 10/sup 8/, it was necessary to keep the read power smaller than 1.5 mW at 2400 rpm. >

Major line operation in vertical Bloch line memory

The operation of a major line in a vertical Bloch line memory using a partial garnet grooving architecture was studied experimentally and numerically. The major line was fabricated on a 5-μm bubble garnet using three conductor layers and a 10% garnet grooving. The major line contains a bubble generator, a bubble propagation track, a bubble expander for bubble detection, and a bubble annihilator. The minimum current for bubble generation was 350 mA, at 50 ns pulse width. The bubble propagation track was a typical dual conductor design with a 5-μm-wide conductor and a 20-μm circuit period. The minimum drive current was 5 and 10 mA at an operating frequency of 250 and 500 kHz, respectively. The bias field margin was from 84 to 100 Oe. The bubble expander was a modification of the propagation track. The meandering conductor and the groove width were gradually increased to stretch the bubble into a stripe. The bias field margin was from 82 to 84 Oe. The numerical model includes the effect of the garnet grooving, and the simulation results agree with the experimental data.

Bloch line propagation with film thickness modulation bit patterns (abstract)

Bloch line (BL) propagation with a field-access scheme is necessary for the memory with low power consumption and high storage density. Previously we reported the field-access propagation using Co-Pt bit patterns.1 In these propagation patterns, (a) the drive field margins depend on the BL propagating direction to the magnetized direction of Co-Pt patterns and (b) the operating bias field margins are different at each corner of the stripe domain. The purpose of this paper is to solve these two problems. A new propagation method has been investigated using film thickness modulation patterns.2 The materials used here were magnetic bubble garnet films with composition of (YSmLuCa)3(FeGe)5O12. Fundamental characteristics of the samples are as follows: saturation induction 4πMs 200 G, anisotropy field Hk 1700 Oe, stripe width w and thickness h 5 μm. The thickness modulation patterns with an amplitude of about 1000 A were fabricated with the ion milling method. The stripe domains were stabilized around the 100% etched grooves, and aligned with 18 μm period. BL pair was propagated in the all part of the stripe domain walls at 500 kHz frequency, applying the triangular bias pulsed field with 50 ns rise time and 1000 ns fall time. As the result of the experiments, it has been found that the drive field margins are independent of BL propagation direction and the difference in the operating bias field margins at the each corner of the stripe domain becomes smaller. The BL propagation around the stripe domain was achieved with 5% bias field margin at the drive field of 8.5 Oe.

Characteristics of Bloch line memory read operation in 2 mu m bubble material

The read operation performance in Block line memory has been studied using a typical 2- mu m bubble material. A reasonable operation margin for chopping detection of a vertical Block line was obtained with a hair-pin-type chopping conductor with a 4- mu m pattern width and 1.5- mu m pattern gap. The chopping current margin and the bias-field margin are 146 mA+or-4.1%, and 107 Oe+or-6.1%, respectively. Domain-wall configurations during the chopping process have been studied numerically and compared with experimental results. Simulation results suggest that operation performance degradation can be ascribed to horizontal Bloch line nucleation during the chopping process. >

Characteristics of Bloch line memory with major/minor-loop structure

The characteristics of the functions of a vertical Bloch line memory (VBL) with major/minor-loop structure and field access scheme, except for the detector, were investigated. The memory is composed of a major line with two-level conductor patterns, minor loops utilizing stabilized ring-shaped domains, and read/write gates with three-level conductor patterns. Bubbles generated at the bubble generator are propagated on the major line with greater than 4-mA drive current at 500-kHz frequency. Stretching of the ring-shaped domain head is well controlled by the presence or absence of a bubble in the major line. The round propagation for a VBL pair is achieved quasi-statically by a pulsed bias field with 6.5-Oe potential barrier for a 4.0- mu m-period track. Bias-field margins of 8.5 Oe for the minor loop and 13 Oe for the major line were obtained, verifying the feasibility of this device. >

Planar Process for 16 Mb Bubble Memory Devices Using Thermal Reflow‐Type Polyimide

A new planar process using thermal reflow‐type polyimide has been developed for 16 Mb bubble memory devices. Planarizing characteristics of several types of polyimides were evaluated quantitatively to select an appropriate one for high density bubble devices. Step height and film thickness have a relation of . The larger coefficient corresponds to the better planarization in step height. Taper angle θ and film thickness have a relation of . The larger coefficient corresponds to the better planarization in taper angle. From these evaluations the thermal reflow‐type polyimide shows better planarization in step height and taper angle by about 50% than the conventional polyimides do. This is presumably due to the thermal reflow that occurred at the baking treatment after the spin‐coating of prepolymer solution. Characteristics of the devices using the thermal reflow‐type polyimides were evaluated and the results showed three times as large bias field margins as that obtained by conventional devices.

Quasistatic Bubble Propagation in 1.5 μm Period Ion-Implanted Tracks for 64 Mbit Magnetic Bubble Memory Devices

Ion-implanted tracks with a 1.5 μm period for use in 64 Mbit magnetic bubble memory devices have been fabricated and operated. The bubble material used was (BiSmLu) 3 (FeAl) 5 O 12 garnet film, supporting 0.45 μm bubbles. The resist mask patterns for implantation were formed using a 1/10 reduction projection aligner, using rectangular patterns on a reticle. The bubble propagation tracks were fabricated by double deuterium implantation and annealed at 400°C for 30 minutes, with an SiO 2 layer deposited on the garnet surface to stabilize the implanted layer. An operating bias field margin in excess of 7% was stably obtained in quasistatic bubble propagation. This shows that the ion-implanted devices have great potential for use in 64 Mbit magnetic bubble memory devices.

Characteristics for Bloch line memory with field access scheme

The characteristics of functions such as read/write gate operation and vertical Bloch line (VBL) propagation have been investigated for a VBL memory with a field access scheme. The memory is compared of a minor loop utilizing a stabilized ring-shaped domain and a read/write gate with three-level conductor patterns. Potential wells that define the VBL bit position are formed by an in-plane field from a zigzag conductor for evaluation of VBL propagation. The read/write gate and VBL pair propagation operations are confirmed. A bias field margin of 7 Oe (10%) is obtained, verifying the feasibility of this device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Operation of major line bubble propagation path for Bloch line memory

A novel type of current-access bubble propagation path for the major line of a vertical Bloch line memory has been designed and processed on an as-grown 5- mu m bubble garnet film that is standard except for its thickness of 2.1 mu m. The bubble propagation path consists of a meandering conductor and high-coercive-force hard magnetic patterns in CoPt which provide an offset force for the bubble motion. A reasonable bias field margin (14% of midbias field value) for the bubble propagation was measured in a test chip. The bias field compatibility between bubbles on the major line bubble propagation path and confined stripe domains for the minor loop have been confirmed experimentally. >

Propagation of Vertical Bloch Line Pairs around Stripe Head by Single Phase Current

This note reports on a new method to propagate vertical Bloch line (VBL) pairs, which are the information units in the recently proposed VBL memory, around stripe heads by single phase current. The method reported has simpler conductor patterns than the method to propagate by two circuit currents. The bias field margin for the propagation has been obtained by computer simulation and the reliability of the method has been confirmed.

Asymmetric Chevron type junctions for hybrid bubble memory devices with 16-Mbit/cm/sup 2/ storage density

Junctions between Permalloy and ion-implanted tracks for high-density hybrid bubble memory devices (>or=16 Mb/cm/sup 2/) using 0.5- mu m-diameter bubbles have been investigated at a 100-kHz drive field. The conventional junctions developed for 4-Mb/cm/sup 2/ devices have been found not to work at all. A novel type of asymmetric chevron (AC) junction has been proposed and operated. With the large volume of AC Permalloy patterns and the shallow ion-implanted channel, AC junctions show an operating bias-field margin of more than 6%. The feasibility of junctions for hybrid devices with 16-Mb/cm/sup 2/ storage density has been confirmed. >

Controlling Bloch lines and domain chopping for multiple stripes aligned in parallel

Controlling vertical Bloch line (VBL) position and stripe domain chopping in multiple stripe domains, aligned in parallel by a period of 12 μm, are studied experimentally using a 5-μm bubble garnet film. Patterned high coercive-force CoPt films aligned in parallel are used for stabilizing the stripe domain. During the stripe stretching process, the VBL motion at the stripe head was controlled by the dc conductor current to get two different wall states: one with a VBL at the stripe head and the other without VBL. Stripe chopping experiments for VBL detection have been performed using hairpin and meandering conductors. We found that the meandering conductor presents excellent characteristics; the bias field margin and the chopping pulse amplitude margin are 58 Oe±6% and 133 mA±11%, respectively, for one stripe. VBL generation by the meandering conductor has also been studied using the same sample.

Bloch line propagation by field-access scheme with Co-Pt bit patterns

Bloch line (BL) pair propagations has been investigated by a field-access scheme, applying triangular pulses to a rocking conductor. The stripe domain was stabilized by a current. Current bit confinement initially revealed a bit potential of 0.4 to 1.8 Oe for 2.5- mu m-period tracks. Then noncurrent bit confinement patterns were produced in Co-Pt films with high coercivity (1.5 kOe) and high residual flux density (5 kG). A film thickness of 350 AA produced a bit potential of 1.5 Oe when the spacing between the Co-Pt film and the garnet surface was 1 mu m. Bit-by-bit propagation of a BL pair was achieved with a 5 to 6% bias field margin in a drive field greater than 3.3 Oe.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

６４Ｍｂｉｔ磁気バブル素子用１．５μｍ周期イオン折込み転送路におけるバブルの基本転送

Ion-implanted tracks with 1.5μm period for 64M bit magnetic bubble memory devices have been fabricated and operated. The bubble material used here is (BiSmLu)3(FeAl)5O12 garnt film supporting 0.45μm bubbles. The resist mask patterns for implantation were formed by a 1/10 reduction projection aligner using rectangular patterns on a reticle. The bubble propagation tracks were fabricated by double deuterium implantation and annealed at 400°C for 30 min with a SiO2 layer deposited on the garnet surface to stabilize the implanted layer. More than 7% operating bias field margin was stably obtained in quasistatic bubble propagation. This shows that the ion-implanted devices have great potential for 64M bit magnetic bubble memory devices.

Bloch line propagation on a ring-shaped domain by pulsed bias fields

Vertical-Bloch-line (VBL) propagation by pulsed bias fields has been investigated experimentally. A ring-shaped domain wall, stabilized in a 10%-deep ring-shaped groove on a garnet film supporting 5- mu m diameter bubbles, was used as a track. Potential wells to define the VBL bit position were formed by an in-plane field from a zigzag conductor. VBL pairs were propagated on a corner wall as well as on a straight wall by pulsed bias fields, which are generated by a loop conductor surrounding the ring-shaped domain. More than 28% bias field margin of more than 28% have been obtained for the round propagation. >

Characteristics of bubble memory devices using multilayer permalloy films

We have investigated the bias field and detector's signal characteristics of a bubble memory device using multilayer Permalloy interleaved with Si spacers. Coercivity of two-layer Permalloy stripe pattern becomes minimum in the range from 3 to 5 nm of the Si spacer thickness, and is reduced to approximately half that with a single-layer Permalloy. In the three-layer Permalloy device, the bias field margin increases 2.7 Oe on the average, and the amplitude of signal increases by 30%, the maximum of noise amplitude is only about one-tenth, and the drive field causing maximum noise level is reduced to half, compared with a single-layer Permalloy device. The calculated decrease in potential well of three-layer Permalloy pattern is in good agreement with increase in bias field margin.

Dual gate with replicate and pseudo-swap functions using double conductor layers for ion-implanted devices

A new functional gate which has the dual function of the block replicate and pseudo-swap(annihilate and replicate-in) gate for the high density ion-implanted devices has been proposed and characterized. The dual gate is composed of ion-implanted tracks and two hair-pin conductors in two layers; one conductor to stretch bubbles and the other to annihilate and cut them. Both functions of the dual gate were realized with 0.9-μm-bubbles in the temperature range of -25°C to +90°C. The minimum rotating field H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> of 35 Oe and the bias field margin of 11.8 % (47 Oe) with H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> of 60 Oe at 55°C were obtained. The dual gate enables the 16 to 64Mb bubble memory devices with compatibility to the BMC (Bubble Memory Controller) of conventional 4Mb Permalloy devices.

A new junction design for ion-implanted and permalloy hybrid bubble memory devices

A new junction for the swap-gate side using the corner-Permalloy pattern in hybrid bubble memory devices has been designed and characterized. The design is based on the corner-type junction for the replicate-gate side and the conventional swap gate. The junction where bubbles propagate from the corner-Permalloy pattern or the transfer-in Permalloy pattern to ion-implanted tracks is composed of the ion-implanted cusp and three Permalloy-pattern tips. The junction bias field margin is greater than 10% for the rotating field range of 50 to 60 Oe and the temperature range of 20 to 65°C. The characteristics improvement is realized by the enlarged Permalloy patterns with large curvature.