K. Betsui

Electron emission properties of Spindt-type platinum field emission cathodes

Electron emission properties of Spindt-type platinum field emission cathodes were investigated. The current–voltage characteristics together with the current fluctuation during long term operation were evaluated in ultrahigh vacuum. The changes of the emission properties in hydrogen, oxygen or carbon monoxide gas ambient were also investigated. Significant improvement of the emission properties was found when the cathode was operated in carbon monoxide ambient under a certain condition. It was found that the effect of the improvement lasted at least 200 h, and resistance against the oxygen exposure was also improved. The changes of the electron emission properties during long term operation in ultrahigh vacuum and in gas ambient were analyzed with the Seppen–Katamuki chart, of which ordinate and abscissa are slope and intercept of Fowler–Nordheim plot. The electron emission properties were distributed along a straight line in the Seppen–Katamuki chart, and those of the cathode improved by carbon monoxide ...

Magnetic and crystalline properties of ion-implanted garnet films with plasma exposure

The implantation induced anisotropy field change, ΔHk, and lattice strain, Δd/d, in ion implanted films have been found to be enhanced considerably by exposing films to plasma of H 2 , He, Ne and Ar gases in the substrate temperature greater than 100°C. The enhanced ΔHk is twice as large as the as-implanted value in typical experiments, and it is comparable to the ΔHk of the hydrogen ion implanted layer. The enhanced ΔHk of the exposed film decreases greatly with increasing annealing temperature, but this can be prevented coating the surface with an SiO 2 layer. The changes of ΔHk profiles in plasma exposure are obtained by FMR technique. ΔHk is enhanced not only at the surface but also deep in the implanted layer. The origin of this effect is probably ascribed to the diffusion of the residual hydrogen into the implanted layer.

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.

Cusp-to-cusp transfer gate using folded minor loop organization for ion-implanted bubble devices

Ion-implanted bubble devices using the folded minor loop organization have been developed to relax spatial restrictions on function pattern design and improve the reliability of gate conductors. A cusp-to-cusp transfer gate using this organization has been designed in which bubbles are transferred between the cusps of the propagation patterns of the major line and minor loops. A 180° inside turn has also been designed in order to realize the folded minor loop organization. Test chips incorporating 4 μm period devices with the folded minor loop organization have been fabricated and characterized for a 100 kHz triangular drive field.

Design of a block replicate gate for ion-implanted bubble devices

A block replicate gate has been designed for 4 μm period ion-implanted bubble devices. The gate consists of a conductor lying across a V-shaped unimplanted pattern between the minor loop end and the major line. Replication is accomplished by stretching the bubble with a stretch pulse through the conductor, cutting the domain by means of the charged wall formed at the edge of the V-shaped pattern together with a pulse of short duration, then restoring the bubble to the original condition by means of another stretch pulse. A bias field margin of 20 Oe was obtained with an error rate of 10-5for a 100 kHz, 80 Oe peak triangular drive field.

Design of 2 µm-period minor loops in hybrid bubble memory devices

The folded minor loops for hybrid bubble memory devices with 2 μm period propagation tracks have been developed by designing junctions between permalloy and implanted tracks, as well as designing inside and outside turns. The junction from the permalloy to the implanted tracks has been successfully designed utilizing the deep potential well of the permalloy pattern for bubbles to cross the boundary. The junctions were operated successfully for the first time using 0.6 μm bubbles optimized for 2 μm period tracks. We also designed the outside and inside turns considering the demagnetizing field and the crystalline axis of the implanted layer respectively. As a result, good bias margins of turns were obtained. The bias field levels of all elements agreed quite satisfactorily. Overall bias field margins of 40 Oe has been obtained with the quasi-static drive field of 70 Oe.

Fabrication and Operating Characteristics of Ion-Implanted Bubble Memory Chips for a 16M-Bit Device

A test chip using ion-implanted functions for a 16-Mbit bubble memory device has been designed, fabricated and characterized. A new delineation process for ion-implanted tracks using SiO2 ion-implantation masks is effective for reducing defects in minor loops. As a result, a bias margin of 22 Oe was obtained for minor loop bubble propagation. Test chip operation over a wide temperature range, from ¿25°C to 80°C, has been realized.

Effect of Plasma Exposure on Magnetic Properties of Ion-implanted Bubble Garnet Film with Suppression of Growth-induced Anisotropy

When ion-implanted garnet crystal films are exposed to plasma, the change in induced anisotropy field ¿Hk is enhanced. The role of growth-induced anisotropy in this effect was investigated by using annealing at 1000°C to suppress growth-induced anisotropy while studying the effect of Ar plasma exposure on Ne+-implanted films of bubble garnet. The increase in ¿Hk was concluded to be unrelated to any suppression of growth-induced anisotropy, and is thought to originate in an effective increase in the magnetostriction constants.

Effects of Ion-Implantation in Magnetic Garnet

Ion implantation in magnetic garnet films induces anisotropy field change ¿Hk. The primary origin of the ¿Hk is the stress-induced anisotropy, but it has been reported that ion implantation also induces nonmagnetostrictive anisotropy change due to growth-induced anisotropy suppression. Hydrogen ion implantation induces a large ¿Hk due to the chemical effects of the hydrogen in the implanted layer. The ¿Hk in ion-implanted garnet is significantly increased by exposing implanted films to plasma of hydrogen or rare gases. These large anisotropy changes in hydrogen implantation and plasma exposure are attributed to the change in valence state of Fe ions. This reports reviews these recent developments on ion-implanted garnets.

Effects of Plasma Exposure on Magnetization of Ion-implanted Bubble Garnet

Exposure to plasma results in an increase in the change in induced anisotropy field ¿H<inf>k</inf> of ion-implanted garnet film. In this work, the change in saturation magnetization was also studied. Ne⁺ ions were implanted into (YSmLuCa)<inf>3</inf> (GeFe)<inf>5</inf> O<inf>12</inf> film and then exposed to plasma. Whereas a linear decrease in saturation magnetization 4¿M<inf>s</inf> with implantation dose was seen, plasma exposure caused an increase which was also proportional to the dose. The temperature dependence of 4¿M<inf>s</inf> indicated that plasma exposure raised the T<inf>c</inf>, which had fallen from 246°C to 180°C with implantation, back to 198°C. Occlusion of hydrogen in the plasma may be partially responsible for this behavior.