JPS6260756B2 - - Google Patents

Description

[Detailed description of the invention] TECHNICAL FIELD The present invention relates to a bubble magnetic domain element.

Conventionally, in a bubble magnetic domain (hereinafter referred to as a bubble) element, a method is well known in which a transfer pattern made of a soft magnetic material is provided on a bubble holding layer and bubbles are transferred by an in-plane rotating magnetic field. Here, the conventional transfer pattern consists of periodic elements with gaps between them, and the processing limit of this gap has been one of the major limitations in increasing the density of conventional bubble elements. Furthermore, it is well known that even if a gap-free pattern is created using conventional methods, normal transfer cannot be obtained.

However, recently, devices with no gaps in the transfer pattern, so-called continuous disks (hereinafter referred to as continuous disks), are being developed.
A device (referred to as a CD) has become possible using the ion implantation method disclosed in US Pat. No. 3,828,329, and its development is progressing.

In this ion implantation method, a mask is provided in the pattern area, and ion implantation is performed to form an in-plane magnetized layer on the film surface outside the pattern while leaving the magnetization under the pattern on the film surface perpendicular to the film surface. . The in-plane magnetization layer is created by applying an in-plane magnetic field.
It generates a well) and attracts and drives bubbles to it.

Regarding the ion implantation method, IEEE Transactions on Magnetics (IEEE Trans.Magn.), Volume MAG-15,
As stated on page 1657 (1979):
The bubble transfer margin may be rapidly reduced by heat treatment (annealing) at 350°C to 400°C.
Furthermore, it has been reported that annealing at 300° C. also changes the margin, making it equivalent to the result of double implantation by changing the implantation energy. Improving the non-uniformity of the in-plane magnetization layer due to ion implantation and the deterioration of characteristics due to annealing are currently important issues for ion-implanted CD devices.

An object of the present invention is to provide a CD transfer bubble device that uses a CD pattern to increase the density of the bubble device and uses a uniform in-plane magnetization layer that is less likely to deteriorate its characteristics due to heat treatment or the like.

According to the present invention, saturation magnetization is achieved on the single crystal surface of the substrate.
It has a bubble retention layer of Ms and is formed on top of it.
In a bubble element in which bubbles are transferred by in-plane magnetic field rotation through a CD pattern, the CD
The pattern remains in the bubble retaining layer by etching the bubble retaining layer, and the etching depth is approximately equal to the remaining film thickness h of the bubble retaining layer.
0.1 times or more and about 0.5 times or less, and on top of the bubble retaining layer, there is an in-plane magnetization layer with a thickness t and a saturation magnetization M satisfying about 0.1 or more and less than about 0.5 expressed in tM/hMs. As a result, a bubble element with high bubble density, a uniform in-plane magnetization layer, and little deterioration due to heat treatment etc. can be obtained.

The in-plane magnetization layer may be a yttrium iron garnet single crystal film, or a part of the yttrium ions replaced with calcium ions, or part or all of the yttrium ions replaced with rare earth ions, or a part of the yttrium ions replaced with rare earth ions. It is appropriate to use a material in which some portions are replaced with nonmagnetic ions such as gallium ions, aluminum ions, germanium ions, or silicon ions.

The bubble device of the present invention is an "electronic material" proposed by Gargis and Lee, in addition to the ion-implanted CD.
The CD element described on page 96 of the August 1979 issue, and the IEEE Trans.Magn. magazine.
CD element by Cohen et al. described in MAG-15, page 1654 (1979) (all use permalloy, henceforth referred to as permalloy CD element)
It is structurally different from That is, permalloy CD is
A permalloy film is formed on the entire surface of the bubble retention layer through a smaller spacing on the CD pattern. To drive the bubble, an in-plane rotating magnetic field Hr is applied to the permalloy cross section interrupted by the spacing difference.
A magnetic pole induced by is used.

The bubble element of the present invention is the same as a permalloy CD in that an in-plane magnetization layer with steps is formed on the entire surface of the bubble retention layer, but as shown in Figure 1, the thickness of the bubble retention layer in the CD pattern area is It differs from a permalloy CD in that it is larger than other parts.

In addition, since the in-plane magnetization layer is formed on the bubble retaining layer without any spacing, and a single crystal film is used as the in-plane magnetization layer, the in-plane magnetization layer is formed at the step part as shown in Figure 1. Continuously formed points are also permalloy.
Different from CD.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a schematic diagram of a membrane cross section passing through a pattern portion of a bubble element of the present invention. Here, 11 is a single crystal substrate, 12 is a bubble retention layer with saturation magnetization Ms and thickness h, 13 is an in-plane magnetization layer with saturation magnetization M and thickness t,
14 represents a bubble.

By forming the membrane of FIG. 1 in accordance with the present invention, transfer as shown in FIG. 2 can be obtained. 21 is
CD pattern, 22 represents the slope of the in-plane magnetization layer at the pattern boundary. 1 to 6 are in-plane rotating magnetic fields
Indicates the direction of Hr. Black circles indicate bubbles in each Hr direction. As shown in Figure 2, one bit can be transferred per hour rotation.

In the bubble element of the present invention, the large thickness of the bubble retaining layer in the CD pattern portion not only provides bubbles with edge affinity to the pattern edges, but also allows the bubbles to cross the pattern during transfer. This is essential in order to avoid errors on the opposite track.

Furthermore, the continuity of the in-plane magnetization layer at the stepped portion is necessary to prevent the generation of steep magnetic poles due to Hr and to ensure stable bubble transfer.

In addition, in the present invention, if tM/hMs is selected to be approximately 0.5 or more and approximately 1.2 or less, rather than approximately 0.1 or more and less than approximately 0.5, a bubble element that can perform bubble transfer of 2 bits per Hr rotation, as shown in an example later, can be obtained. It will be done.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 For the substrate 11, a normal Gd ₃ Ga ₅ O ₁₂ (111) single crystal was used. 4πMs is 398 as bubble retention layer 12
(YSmLuCa) ₃ (FeGe) ₅ O ₁₂ garnet having a Gaussian diameter, a characteristic length l of 0.20 microns, and a thickness of 2.23 microns was grown by liquid phase epitaxial growth. On top of this, an etching control layer and a resist layer are formed, and the film thickness h of the bubble retaining layer other than the pattern area is determined by ion milling.
The bubble retention layer is Δ so that the
Etched by h0.53 micron. That is, Δh/
h=approximately 0.30. Incidentally, the pattern boundary was etched by oblique incidence ion etching so that it had an inclined part with a width of about 0.5 microns. The relationship between the etching control layer, the etching depth, and the width of the sloped portion, as well as the details of the control method, were in accordance with the "Taper Etching Method" of Japanese Patent Application No. 89558/1983.

Next, as an in-plane magnetization layer, a single crystal of yttrium iron garnet (YIG) having 4πM of 1750 Gauss and crystal magnetic anisotropy was grown by vapor phase epitaxial growth to a thickness t=approximately 0.07 microns. That is, tM/hMs is approximately
It was 0.17. In the YIG film, 4πM is larger than the bias magnetic field, and the magnetic anisotropy perpendicular to the film is small, realizing a sufficient in-plane magnetization layer. The temperature characteristics of the bubble extinguishing magnetic field were also good, about -0.21%/°C. [The YIG layer is also formed in the step part of the bubble layer in an inclined shape at an approximately constant angle due to its crystallinity.
It was confirmed by scanning electron microscopy (SEM) that the angle between the slope and the film surface was approximately 20 to 40 degrees Celsius, with good reproducibility.

Next, FIG. 3 shows the margin when bubbles are transferred quasi-statically using the CD pattern loop in this embodiment. The pattern has the shape shown in Figure 2, with three 21-bit loops arranged vertically and horizontally at a period of 8.5 microns. Solid line 31 in Figure 3
is a loop parallel to the easy axis of magnetization (the so-called good loop of the ion-implanted CD), and the broken line 32 is a loop perpendicular to the easy axis of magnetization (the super-bad loop of the ion-implanted CD).
loop) shows the bubble transfer margin.

As shown in Figure 3, a margin rate of approximately 10% or more is obtained when Hr = 20 to 80 Oe.

Furthermore, in the CD pattern of FIG. 2, the transfer margin does not depend greatly on the transfer crystal orientation, as shown at 31 and 32 in FIG. However, in a rectangular pattern such as a series of squares, the dependence of the transfer margin on the crystal orientation is observed, and as in the case of ion-implanted CDs, the margin for the loop perpendicular to the easy axis of magnetization is different from that for the loop parallel to the hard axis (good loop). ) was worse than

Error-prone tracks include ion implantation
In the CD element, the track was on the hard axis of magnetization, whereas in the bubble element of the present invention, the track was on the easy axis of magnetization. This is because in the case of ion-implanted CD, when Hr is in the direction of easy magnetization, magnetic charge walls are difficult to form, whereas in the bubble element of the present invention, when Hr is in the direction of difficult magnetization, the YIG step difference is due to the 3-fold symmetry of the YIG crystal. It is thought that errors are likely to occur in bubble drive because the generation of magnetic poles that attract bubbles to the area becomes weaker. The occurrence of errors due to the three-fold symmetry of YIG can be partially avoided by improving pattern design, similar to how to deal with three-fold symmetry errors in ion implantation CD.

Note that the YIG layer is a uniform single-crystal layer, and unlike ion-implanted layers, its characteristics hardly change due to annealing or the like.

Example 2 Same film configuration as Example 1, YIG thickness t is about 0.05
In the micron sample, similar 1-bit transfer was obtained, although the margin was narrower than in Example 1. However, with the same membrane configuration as in Example 1, t is about 0.03.
For samples with microns, or tM/hMs of approximately 0.08,
Even if Hr was increased to about 80 oersted, the bubble driving force was weak and the result was that there was almost no transfer margin.

From this result, the parameters of the membrane from which the transfer can be obtained
tM/hMs is about 0.1 or more.

Example 3 Same film configuration as Example 1, YIG thickness t is about 0.20
As in Example 1, a bubble transfer of 1 bit per revolution of the in-plane magnetic field was obtained for a sample with a micron, ie, tM/hMs of about 0.50. However, on the high bias magnetic field side of Hr = 40 to 60 etherstead, a bubble transfer phase of 2 bits occurs per revolution of the in-plane magnetic field, so a phenomenon was observed in which the margin was reduced.

Note that with the same film configuration as in Example 1, the film thickness of YIG is approximately
For samples in the range of 0.25 microns to about 0.8 microns, bubble transfer of 2 bits occurs per revolution of the in-plane magnetic field, and a film that meets the objectives such as halving the access time can be obtained.

Example 4 Same film configuration as Example 1, 4πMs = 510 Gauss, h = 2.0 microns, etching depth Δh =
A film of 0.48 microns or Δh/h=0.24 was formed. In this case, vertical etching was used instead of the taper etching of Example 1. on this membrane
YIG single crystal with thickness t = 0.10 microns or tM/hMs
= about 0.17, by vapor phase epitaxial method. In this case as well, the YIG film showed inclined growth similar to that in Example 1 at the pattern boundaries.

In this membrane. FIG. 4 shows the bubble transfer margin of the same CD pattern as in Example 1. solid line 31
indicates the loop parallel to the easy axis of magnetization, and the broken line indicates the margin of the loop perpendicular to the axis of easy magnetization. The margin ratio in Figure 4 is lower than that in Figure 3, but in the film of this example, etching grooves due to the vertical ion etching process were observed at the pattern boundaries of the bubble layer, which is thought to be due to a slight deterioration in the bubble transfer margin. It will be done.

Note that with the same film configuration as Example 1, 4πMs=530
Gauss, h=1.99 microns Etching depth Δh=
YIG on a film of 0.20 micron, i.e. Δh/h=0.10.
The thickness of the single crystal is t = 0.10 microns, that is, tM/hMs = approx.
Bubble transfer was obtained in a film grown epitaxially in a vapor phase with a ratio of 0.17, but the margin was smaller than that shown in FIG.

In addition, with the same film configuration as Example 1, 4πMs = 514
Gauss, h=2.00 microns Etching depth Δh=
YIG single crystal in a film of 0.93 microns, or Δh/h = 0.46, with a thickness of t = 0.10 microns, or tM/hMs = approximately 0.17.
Bubble transfer was also obtained in films grown epitaxially in the vapor phase. In this case as well, etching grooves due to the vertical ion etching process were seen at the boundaries of the bubble layer pattern, and the margins were not large. That is, if Δh/h is further increased, it is thought that the margin will decrease due to problems in the etching process.

From these results, a suitable value for the membrane parameter Δh/h is about 0.1 or more and about 0.5 or less.

As explained above, according to the present invention, the density of the bubble element can be increased by bubble transfer in a CD pattern without gaps, and CD transfer using a uniform in-plane magnetization layer with less characteristic deterioration due to heat treatment etc. A bubble element can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a film of a bubble magnetic domain element of the present invention, FIG. 2 is a partial plan view of an example of a CD pattern of the present invention, and a schematic diagram of bubble transfer positions in each in-plane magnetic field direction. The figure shows the CD transfer margin of a bubble in the first embodiment of the present invention, and FIG. 4 is a diagram showing the CD transfer margin of a bubble in the fourth embodiment. Here, 11 is a single crystal substrate,
12 is a bubble retention layer, 13 is an in-plane magnetization layer, 14 is a bubble, 21 is a CD pattern, 22 is an inclined pattern boundary of the in-plane magnetization layer, and the diagonal circles in FIG. 2 are in-plane magnetic field directions 1, 2, and 3. , 4, 5, and 6, respectively. 31 is CD parallel to the axis of easy magnetization
In addition, 32 is the bubble transfer margin of Example 1 in the CD loop perpendicular to the easy axis of magnetization, 41 is the bubble transfer margin in the CD loop parallel to the easy axis of magnetization, and 42 is the bubble transfer margin in the CD loop perpendicular to the easy axis of magnetization. The bubble transfer margin of Example 4 is shown.

Claims (1)

[Claims] 1 Contiguous disk bubble magnetic domain that has a bubble retaining layer with saturation magnetization Ms on the single crystal surface of the substrate, and transfers bubbles by in-plane magnetic field rotation via a gapless periodic transfer pattern formed on the layer. In the element, the pattern shape of the periodic transfer pattern remains in the bubble retaining layer by etching the bubble retaining layer, and the etching depth is approximately 0.1 times or more and approximately 0.5 times or less the remaining film thickness h of the bubble retaining layer. and an in-plane magnetization layer having a thickness t and a saturation magnetization M is formed on the bubble retaining layer so that the in-plane magnetization layer satisfies about 0.1 or more and less than about 0.5 expressed in tM/hMs. bubble magnetic domain element.