Ion-implanted Bubble Devices Research Articles

Influence of conductor steps in passivation stress in magnetic bubble memory devices

Stress from the overlay passivation (sputtered SiO2) significantly degrades bubble propagation margins in ion-implanted bubble devices. The present work investigated the stress field from the passivation by computer simulations (boundary element method). In order to reduce the passivation stress, a buffer layer between the passivation and the conductors was investigated. The effects of two factors in the buffer layer have been discussed: (i) Young’s modulus of the buffer layer and (ii) a planarizing characteristic of the buffer layer. The simulation shows that changing Young’s modulus is not effective in reducing the passivation stress. On the other hand, a degree of planarization has a great relation with the passivation stress, i.e., the passivation stress decreases with increasing the planarization by the buffer layer. Therefore, we introduced the thermal-reflow-type polyimide which exhibits excellent planarization. The devices with this structure were fabricated and showed no influence from SiO2 passivation.

Computer simulation of gates for ion-implanted devices

A computer simulator has been constructed which can be used to model the operation of current-activated gates used in ion-implanted magnetic bubble devices. Input parameters for the simulator include the geometry of the implanted patterns, magnetic characteristics of the bubble film, implanted layer thickness, conductor geometry, amplitude and phase of currents in conductors, and the frequency and amplitude of the drive field. The forces that act on the bubble are computed, and the resultant bubble wall motion is computed. The operation of various gates for ion-implanted devices has been analyzed. Simulation of propagation on ion-implanted patterns has been performed, and the predicted failure modes are the same as those observed in experimental devices. The simulated bias margins of both propagation and gate operation correspond well with experimentally obtained margins. >

Roles of a hard bubble suppression layer in ion-implanted bubble devices

A so-called hard bubble suppression (HBS) layer, formed throughout the surface of a bubble garnet film in an ion-implanted bubble device, has been investigated for its role in determining device operational characteristics. The HBS layer has a tendency to weaken charged wall strength and to diffuse bias field distributions by the charged wall at a propagation pattern cusp. Existence of the HBS layer degrades bubble generator current margins in a high current ampiltude region and bubble circulation bias margins in a low bias field region. A bubble detector/annihilator requires the HBS layer in a stretch and retract area for stable annihilation operation. In order to solve the contradictory roles in the device, a partial HBS ion-implantation process has been developed with He+ ions through a detector NiFe film and an SiO 2 layer masked with an Au lead conductor layer.

Charged Wall Behavior Observed by Bubble Run-Out Method

A new potential well measurement method, utilizing bubble run-out phenomena, is discussed, with emphasis on its application in observing charged wall behavior, as well as in measuring the potential well depth itself. The method is applied to bubbles in ion implanted propagation patterns on 1 μm bubble garnet films with different magnetostriction constants. Bubble run-out directions are found to be reflected by the strength of stress relaxation-induced magnetic anisotropies along ion-implantation pattern edges. The charged wall length and its stray field distribution were also estimated using this method. It is concluded that this method is one of the most useful tools available for operation error mode analysis in ion-implanted bubble device development.

Hydrogen out-diffusion suppression effect of overlayers in H+2 -implanted magnetic bubble garnet

Hydrogen out-diffusion suppression effect of overlayer deposited on H+2 -implanted magnetic bubble garnet has been investigated using gas mass spectroscopy and secondary ion mass spectroscopy. It has been found that oxide films such as SiO2, SiO, TiO2, and Al2O3 or nitride film such as Si3N4 effectively suppress out-diffusion of hydrogen during annealing, keeping a large anisotropy field change induced by hydrogen implantation after the annealing. Hydrogen depth profiles have also been found to have a sharp peak at the boundary between overlayer and garnet which can suppress out-diffusion of hydrogen. Metal films such as Au, Mo, and Ni–Fe alloy have been found not to act as suppressors of hydrogen out-diffusion. Annealing hydrogen-implanted garnet with an oxide overlayer on the surface is useful for ion-implanted bubble device fabrication because of thermal stability of large anisotropy change induced by implantation.

Bidirectional m/m Transfer Gates for 4 Mb Ion-Implanted Bubble Devices

Roles of a compensation conductor on m/m gates for 4 Mb ion-implanted contiguous disk bubble devices were described. The C-loop to S-loop distance was adjusted for gate operation improvement. The compensation conductor cancelled unnecessary magnetic fields near the gate and reduced propagation errors of bubbles near the gate conductor. Bias margins for consecutive transfer operations have been improved even for long data pages.

A Bubble Generation Mechanism for Ion-Implanted Bubble Devices

A new mechanism of bubble generation in ion-implanted bubble devices has been proposed based on minimum generation current characteristies. This model shows that bubble nucleation requires a 180° magnetic wall shift in the transition layer between the ion-implanted and bubble layers which can be used to logically explain bubble generation in ion-implanted devices.

Block Replicate Gates for Ion-Implanted Bubble Devices

A two-layer conductor is used for replicating bubbles in ion-implanted bubble devices. The first layer is a parallel conductor used to cut the bubbles which have been stretched by the hairpin conductor in the second layer. There was sufficient operation margin even with a low drive field and a bias field margin of 22.5 Oe was obtained at a drive field of 60 Oe. Error brought on by the stretch pulse will be improved by lengthening the corner pattern. In addition, replicate-in/transfer-out operation was verified.

New method for potential well measurements using bubble runout in ion-implanted bubble devices

A new potential well measurement method has been developed by the use of bubble runout phenomena around bubble propagation patterns. The new method reveals not only bubble potential well distributions but also magnetization distributions around the propagation patterns by observing a domain extension direction after bubble runout. The method has been applied to an ion-implanted bubble device for 1-μm bubbles and has verified the role of stress relief anisotropy for magnetic charge distributions along nonimplanted pattern edges.

Operation temperature ranges for ion-implanted bubble devices with 1 µm bubbles

Operation temperature ranges for He+ and H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + ion-implanted bubble devices with 1 μm bubbles have been studied under a 100 kHz circular in-plane drive field condition. Samples are 4 Mb on-chip-cache bubble memory chips, which were fabricated on (YSmLuBiCa) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeGe) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> LPE garnet films. For He+ implantation, the high temperature limit for the operation is restricted to 50°C at 1.2 eV/Å <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> damage level. On the other hand, for H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + implantation, an operation temperature range, from 0°C to 95°C, has been obtained with more than 30 Oe bias field margin at 0.8 eV/Å <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> damage level. The maximum operation temperature linearly decreases with increasing lattice strain for both implantations. This results from Curie temperature decrease in the implanted layer with increasing lattice strain. However, 35°C difference in operation temperature range is found between He+ and H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + implantation at the same lattice strain. There seems to be a local difference in magnetic characteristics between He+ and H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + implanted layers.

Hydrogen depth profiles in ion implanted magnetic bubble garnets

The hydrogen depth profiles of ion implanted magnetic bubble garnet films have been measured by elastic recoil analysis using 44 MeV chlorine ions. The garnets were triply implanted with Ne, N, and H and were then annealed with or without a surface coating of SiO2. At 250 °C, H was found to diffuse throughout the damaged surface layer but not into the underlying undamaged material. At 350 °C, H diffused out of the uncoated garnet, but was sealed into the implant damaged layer by the thin oxide coating. The deposition of the oxide layer at low temperature after implantation but before processing resulted in a constant H concentration profile extending throughout the implant damaged region of the bubble garnet. This retention of hydrogen correlates with previously reported improvements in propagation behavior of oxide coated ion implanted bubble devices.

Elastic Recoil Analysis of Hydrogen in Ion-Implanted Magnetic Bubble Garnets Using 44 MeV Chlorine Ions

ABSTRACTElastic recoil analysis using 44 MeV chlorine ions is a precise and timesaving method of measuring hydrogen profiles of ion implanted magnetic bubble garnets. Neon, nitrogen and hydrogen ion-implanted modified yttrium iron garnets, which are used for magnetic bubble devices based on ion implanted propagation patterns, (12P2), were studied with respect to their hydrogen concentration-depth distributions. A description and calibration of the elestic recoil analysis setup are presented along with the necessary simple algorithms to obtain the final hydrogen concentration-depth profiles from the measured energy spectra generated by recoiled protons. The garnet samples were annealed with or without a surface coating of SiO2. At 250°C, the hydrogen was found to diffuse throughout the aamaged surface layer but not into the underlying undamaged material. At 350°C, the hydrogen diffused out of the uncoated garnet, but was sealed into the implant damaged garnet layer by the thin oxide coating. Such hydrogen retention correlates with previously reported beneficial effects of an oxide layer deposited at a low temperature after implantation but before processing on ion implanted bubble devices.

4Mb on-chip-cache bubble memory chips with 4 µm period ion-implanted propagation patterns

4Mb ion-implanted bubble devices (IIBD) with on-chip-cache organization (OCCO) have been designed for 1μm bubbles, and characterized for all functional elements in the devices. The 4Mb memory chip with 9.5×11.8 mm chip size consists of the same two 2Mb units, each of which is divided into 1Mb even and odd sites with 300 strorage loops (s-loops) and cache loops (c-loops), whose bit lengths are 4160 bits and 130 bits, repectively. Basic bit cell size is 4 × 4 μm. The 4Mb chip has an OCCO structure with the following distinguishing functional elements: (1) Bidirectional N-shape transfer gates. (2) A major line replicator with 2 crossed hairpin conductors. (3) DRO detector with folded thin NiFe elements. (4) A hairpin nucleation generator in a 240° super track. (5) Even bit minor loops. Operating margins for the 4Mb IIBD fabricated on (YSmLuBiCa) 3 (FeGe) 5 O 12 are well balanced in all functional elements, and obtained as 25 Oe, sufficient for practical use. It has been found that in-plane holding field applied to stop/start (s/s) direction is necessary for s/s stabilization, and that anisotropy along pattern edges due to stress relief acts a significant role for bit instability and for c-s gate operation. LPE film thickness has been optimized as 1.1 μm for 100-120 keV He+ implantation.

New ion-implantation method for 4-µm period bubble device

It is well-known that bubble propagation margins for ion-implanted bubble devices depend strongly on ion-implantation conditions. A new ion-implantation method is reported that can significantly improve bubble propagation margins for minor loops with 4 × 4 μm bit cell size. The implantation was done through a Mo thin film layer so that the lattice strain and the anisotropy field change would be more uniform through the depth of the implanted layer. With this method, minor loops can be formed by hydrogen single implantation. Consequently simplification of the implantation process is achieved.

イオン注入バブルデバイスにおけるマイナーループ間転送ゲートの動作解析

Transfer modes from cache to storage loops in ion-implanted bubble devices with on-chip cache organization have been studied. The advance mode (MODE-A) in data transfer from cache to storage loops (c-s transfer), which is required by the data recurrence condition, was simulated using the gate pseudo-operation technique where current was not applied to the gate conductor. The difference in bubble behaviors in c-s transfer operation among three samples with different δλ values (≡λ100-λ111) can be explained qualitatively based on the lattice strain relaxation model. According to the model, a strong negative chargedwall due to the difference between magnetostriction constants, λ100 and λ111, rises at the pattern edge normal to the [121] direction, which is almost equal to the rotating drive field direction corresponding to the gate pulse end phase for MODE-A operation. A potential barrier formed by the negative charged-wall is found which prevents a bubble from moving in the right direction along the corner pattern edge. Therefore, in order for c-s transfer to operate stably in MODE-A, the difference between λ100 and λ111 must be sufficientlly diminished.

Design consideratons and performance of a detector for contiguous-disk bubble devices

A destructive readout (DRO) detector structure for ion-implanted bubble devices employing a current activated expander is described. The design has been evaluated using 1-μm diameter bubbles, in devices with a storage cell area of 18 μm2. Bias field margins of ∼10 percent are achieved and are compatible with other components on the chip. The detector has been operated at drive field frequencies between 100 and 400 kHz, and over a temperature range of 30°C to 80°C. Results show that the device can be operated over a reasonable temperature range without recourse to temperature tracking of the control currents. Signal sensitivities of 3 mV/mA are reported, and experimental data show that signal levels of 4 mV/mA (or 12 mV assuming nominal operating conditions) are quite feasible by reducing the spacing between the sensor element and the garnet film. Signal amplitude is independent of chip temperature during normal operation.

A bidirectional loop-to-loop transfer gate for ion-implanted bubble devices with on chip cache organization

A new bidirectional loop-to-loop transfer gate has been designed with an N-shape conductor stripe. It is characterized for use with ion-implanted bubble devices with on chip cache organization (OCCO). The gate is operated in 4 modes for He+ ion implanted devices with 1 μm diameter bubbles. Only one of the 4 transfer modes is found to be usable for bidirectional transfer operation, according to bubble data recurrence considerations between cache and storage loops, and according to operation margin stability. Composite operation margins are obtained as 25 Oe for greater than 55 Oe in-plane drive field, even for consecutive data transfer. The bidirectional transfer gate makes possible ion-implanted bubble devices for high access performance, even in high bit density large capacity memories.

Design and characteristics of 4 µm period ion-implanted bubble devices with major line block replicate gate

A block replicate gate composed of an ion-implanted minor loop and a permalloy major line has been developed for 4 μm period bubble devices. This gate employs a hybrid permalloy and ion-implanted bubble device with no junction between the patterns. Test chips incorporating this replicate gate, the folded minor loop, and the cusp-to-cusp bidirectional transfer gate have been fabricated and characterized for a 100 kHz triangular drive field. A bias field margin of 30 Oe was obtained at 70 Oe ± 10 % peak drive field.

Review of ion-implanted bubble devices: P. I. Bonyhard Microelectronics J. 12 (5), 5 (1981)

Review of ion-implanted bubble devices: P. I. Bonyhard Microelectronics J. 12 (5), 5 (1981)

Modeling of transfer gates in ion-implanted bubble devices

In-plane domain structures of rudimentary transfer gates for 2μm bubble devices are calculated by numerical minimization of energy. Results are compared with failure mechanisms observed through high speed optical sampling techniques. Insights into the formation of charged walls are obtained in addition to general design rules for such gates. A uniaxial anisotropy term along the pattern edge was found necessary for the general formation of charged walls, as was previously suggested. The need for this term is especially apparent when the applied field is directed along an easy magnetization direction, a condition that occurs in the model transfer gates. The experimental study shows that small local radii of curvature for both the major and minor loop elements result in lower minimum drive fields. Also, positioning the major loop cusp far from the minor loop element reduces the loss of low bias margin that results from strip-out.