Operating Bias Field Research Articles

Role of extrinsic factors on magnetoelastic resonance biosensors sensitivity

Magnetoelastic (ME) resonance devices are attractive for application as biosensors in health-related areas as they allow contactless detection of pathogenic agents with high sensitivity. After functionalization, they offer valuable diagnostic options that promote efficient capture of mass on the sensor surface through biological interactions. ME sensors are also sensitive to external factors such as temperature, magnetic fields, and variations in mass that can arise from processes unrelated to biological interactions, including corrosion and salt crystallization. This article evaluates extrinsic factors that affect the response of ME resonance sensors for diagnostic applications. In particular, the influence of heat treatments, operation temperature, applied DC magnetic field bias, and corrosive environment were studied. The control of all these factors is crucial for the design, fabrication, and functionalization of ME resonance biosensors and for the development of measuring instrumentation and effective measurement protocols. This work established maximum operating temperature and bias field variations to keep the sensor sensitivity. Heat treatment of the sensors before and after coating improved the signal-to-noise ratio and corrosion resistance. Further improvement in corrosion resistance was provided by cathodic protection, which has been proven beneficial for applications of ME resonance sensors in aqueous fluids.

Electrooptic Properties of InGaAsP Asymmetric Double Quantum Wells: Enhanced Slope Efficiency in Waveguide Electroabsorption Modulators

We present detailed theoretical estimates of the optical properties of InGaAsP quantum well (QW) electroabsorption modulators (EAMs) operating at ~1550 nm wavelength. Absorption coefficients of QWs are obtained from the linear optical susceptibility. Exciton states are calculated in momentum space, which includes valence-band mixing, mixing of excitons originating in different subband pairs, and exciton spin-related optical selection rules. Various line-broadening mechanisms relevant to InGaAsP-QWs are also included. Extending the study further to asymmetric double QWs (ADQWs) suggests that the small-signal modulation efficiency can be enhanced significantly at substantially lower operating bias voltage. Simple optimization of ADQW band structure results in a maximum slope efficiency ~3.8 times larger than that of SQW EAMs at a reduced operating bias field of 34 kV/cm compared with ~70 kV/cm for comparable SQWs.

A new junction design on a Permalloy corner pattern for ion-implanted and Permalloy hybrid bubble memory devices

A junction has been developed for hybrid bubble memory devices using ion-implanted tracks for high density data storage and Permalloy tracks for write and read functions. An 18- mu m diameter Permalloy corner pattern is used. Both the tapered ion-implanted edges and the operating bias field adjustment boundary at the junctions are located under the Permalloy corner pattern edges. Improved junction properties and analysis by visual inspection are reported. The bubble potentials and the phase of the rotating field, when a bubble reaches the junction boundary, were compared for the conventional and the corner-type junctions. Replicate gate performance for the corner-type junction was investigated. The replicate phase margin was greatly improved for the enlarged Permalloy corner pattern. The temperature dependences of the junction performance were measured between 0 and 80 degrees C. In this temperature range, the margins of the junctions were improved, making them suitable for hybrid bubble memory devices. >

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.

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.

Fabrication process for ion-implanted and Permalloy hybrid magnetic bubble memory devices

A fabrication process for ion-implanted and Permalloy hybrid bubble memory devices has been developed. The mask patterns of polyimide (PIQ) for ion-implanted tracks are fabricated using a tri-level resist process where the top imaging resists are delineated by deep UV contact printing. The minimum feature of the PIQ pattern is 0.75 mu m and can be controlled precisely. The sidewalls of PIQ patterns are smooth and vertical. At the junctions between ion-implanted and Permalloy tracks, tapered resist patterns are used as masks for implantation. Novolak-based resist is used and is reflowed thermally to obtain a tapered profile. Fabrication conditions, such as type of resist and baking temperature, were investigated to achieve good reproducibility. Tapered resist patterns are also used as masks for iron milling which reduces the thickness of garnet film in the area of the Permalloy tracks. This is necessary to adjust the operating bias field of Permalloy tracks to that of the ion-implanted tracks. A prototype of a 4-Mb memory device was fabricated, confirming the feasibility of the present process. >

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.

Design and characterization of ion-implanted tracks for 16 Mbit/cm<sup>2</sup>storage density bubble memory devices

The ion-implanted propagation tracks with contiguous disk patterns (CD tracks) have been confirmed to be better for high density propagation tracks (≥ 16 Mbit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) than those with snake patterns (snake tracks), because of less interactions between bubbles on the other side in the same track. The CD tracks with 1.8 µm × 2.0 µm cell size for 0.5 µm bubbles have been evaluated. The large operating bias field margin of 12.4 percent is obtained at the quasi-static operation with rotating field H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> of 60 Oe. The minimum rotating field is 40 Oe. Interdigital folded minor loops are proposed and operated. The proposed minor loops are composed of straight propagation tracks connected alternately to relax the in-side turns. The overall operating margin of 8.4 percent (46 Oe) is obtained at H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> = 60 Oe. The feasibility of 16 Mbit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> storage density bubble memory devices is confirmed.

Operating Bias Field Adjustment of Bubble Propagation Tracks on Ion-Implanted Permalloy Hybrid Type Magnetic Bubble Memory Devices

Reductions in cell size of ion-implanted Permalloy hybrid magnetic bubble memory devices give rise to large differences in operating bias field regions of ion-implanted and Permalloy propagation tracks. Attempting to utilize the dependence of the operating bias field on the thickness of the bubble garnet film, the authors ion-milled films to reduce their thicknesses, thereby lowering the bubble collapse field (H o ). The ion milling was found not to change the film coercivity. In this way, by shifting the permalloy track section field margin downward by 10 Oe, the bias field regions were matched, for a larger overall (common) bias field margin.

Start/Stop Operation in Ion-Implanted Magnetic Bubble Propagation Tracks

To study start/stop operations in ion-implanted magnetic bubble propagation tracks, H 2 was implanted at 35 keV and 1 × 1016/cm 2 and at 80 keV and 4.4 × 1016/cm 2 , and set four stop directions both parallel and normal to the linear propagation track. The characteristics were then measured at 100 kHz. From the DC in-plane magnetic field H dc dependence of the start/stop operating bias field margin, nonnegative H dc values resulted in a start/stop bias field margin equal to the continuous operation margin. In most experiments, start/stop bias field margins of 8 percent or more were obtained.

Reduction of cell size in hybrid bubble memory devices (abstract)

Hybrid bubble memory devices using ion-implanted and Permalloy bubble propagation tracks have been proposed and developed. In this paper, the reduction of the cell size from 4 to 3 μm will be discussed. In the hybrid devices, the minor loops are composed of ion-implanted tracks and the functions are composed of Permalloy tracks. To reduce the cell size, therefore, both of the tracks should be improved. For the 3-μm-period ion-implanted tracks, the bubble diameter is reduced from 1 to 0.8 μm. According to the reduction of a bubble diameter, magnetostrictive anisotropy Δλ=λ100−λ111 is increased from 5 to 8×10−6 because the Sm content is increased to increase the anisotropy field Hk. The large Δλ affects the characteristics of inside and outside turns in the ion-implanted tracks. To get a good margin for the turns, the anisotropy field change induced by ion implantation ΔHk should be larger than in 4-μm-period tracks. There is a new problem in 3-μm-period hybrid devices. In the hybrid devices, there is no deep ion implantation in the Permalloy track region, while there is a deep ion implantation in the ion-implanted track region. The effective bubble height is, therefore, different in the ion-implanted and Permalloy track region, and the bias field region where bubbles exist stable is different. In the typical 3-μm-period devices, the bias field region of the ion-implanted tracks is 20–30 Oe lower than that of the Permalloy tracks. The operating bias field adjustment (OBA) is needed. We have checked some OBA methods and found that the thinning of the garnet film in the Permalloy track region is a good method. Thinning the garnet film partially, the operating bias field can be adjusted easily and there is no harmful effect.

イオン打込み・パーマロイ複合型磁気バブルメモリ素子の動作バイアス磁界調製

In ion-implanted and Permalloy hybrid bubble memory devices, the operating bias field region of ion-implanted tracks is lower than that of Permalloy tracks when the cell size is less than 4μm × 4μm. This reduces the overall bias field margin. The operating bias field region of Permalloy tracks has been shifted using the garnet film thickness dependence of a bubble collapse field. Thickness of a garnet film under Permalloy tracks is reduced using the ion-milling technique. The ion-milled region has a low coercive field and shows a good bias field margin. It has been confirmed in hybrid bubble memory devices with a 3.5μm × 3.5μm cell size that the operating bias field adjustment made by thinning a garnet film can improve the overall bias field margin.

Operation of magnetic bubble logic devices

Dual-conductor current access magnetic bubble logic devices have been fabricated using 2 μm lithography on garnet with 2 μm diameter bubbles. The devices include an AND/OR gate, a comparator gate and a switch gate. The operating margins of these gates were measured at 100 K Hz and at 1 MHz with a sampling optical microscope. A 30 Oe operating bias field margin was obtained for all the logic gates. The experimental results are in good agreement with the computer simulation results. The simulated failure modes of operation are discussed.