JPS636949B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bubble magnetic domain element. Conventionally, it is well known that a bubble magnetic domain element has a method in which soft magnetic materials are periodically arranged as a bubble transfer pattern on a bubble retaining layer and bubbles are transferred by an in-plane rotating magnetic field. That is, the transfer pattern has a periodic element consisting of a plurality or a single piece of soft magnetic material and a gap for one bit, and bubble transfer is performed for one bit per rotation of the in-plane magnetic field. In addition, for the purpose of increasing the density of bubble magnetic domain elements, US Patent No. 3828829
Contiguous disks with no gaps between transfer patterns are created according to the method of
Disk) elements have also been recently developed. In this element as well, the transfer pattern has a constant periodic element for one bit, and one bubble is transferred per rotation of the in-plane magnetic field.

In these bubble magnetic domain elements, the pattern period cannot be reduced arbitrarily if the bubble diameter is constant because of interaction between bubbles. Normally, the appropriate pattern period is about four times the bubble diameter.
Therefore, in a conventional bubble magnetic domain element, the access time required to transfer a bubble to the bubble access portion of the transfer path a certain distance away is approximately It could not be made shorter as long as it advanced by only one bit. In addition, in order to force the bubble speed to be faster and to shorten the access time, the pattern period can be made larger than four times the bubble diameter, but the drawback of reducing the bubble density of the device is that it is similar to the conventional bubble magnetic domain device. Ta.

The object of the present invention is to form a pattern on a bubble retaining layer in a bubble magnetic domain element which has a continuous pattern consisting of constant periodic elements for one bit and performs bubble transfer using an in-plane rotating magnetic field. An object of the present invention is to provide a bubble magnetic domain element characterized in that, by growing a bubble, two bits of bubble transfer can be performed per rotation of an in-plane magnetic field without reducing the bubble density.

According to the present invention, saturation magnetization is achieved on the single crystal surface of the substrate.
In a bubble magnetic domain element having a bubble retention layer of Ms, and in which bubbles are transferred by in-plane magnetic field rotation via a periodic transfer pattern formed thereon, the periodic transfer pattern is formed by etching the bubble retention layer. The pattern shape is formed so as to remain in the bubble retaining layer, and the etching depth is 0.1 times or more the remaining film thickness h of the bubble retaining layer.
0.5 times or less, and an in-plane magnetization layer with a thickness t and saturation magnetization M is formed on the bubble retaining layer so that tM/hMs satisfies 0.5 or more and 12 or less. A bubble magnetic domain element characterized by 2-bit bubble transfer is obtained.

Hereinafter, the present invention will be explained in detail with reference to the drawings. The structure of the film cross section perpendicular to the bubble transfer direction of the bubble magnetic domain element of the present invention is shown in FIG. 1C. Further, an explanation of the formation process is shown in FIGS. 1a and 1b. In FIG. 1a, a bubble retaining layer 12 is grown on a single crystal surface 11 of a substrate, and a mask pattern 14 is formed with a resist through an etching control layer 13 to be used as a sample. This sample is rotated within the plane as shown in FIG. It is processed so as to leave a pattern shape having an etching depth 16 and a constant taper angle 17 at the boundary. The etching depth 16 is the remaining thickness of the bubble retaining layer 1
Select a taper angle of 0.1 to 0.5 times 8 and a taper angle of 10° to 90°.

Here, a method of controlling the etching depth 16 and taper angle 17 by ion etching conditions such as the material and thickness of the etching control layer 13 and the resist 14 and the ion beam incident angle 15 is described in Japanese Patent Application No. 53-89558 55-16459), ``Taper etching method.''

After removing the resist 14 and the etching control layer 13 from the sample shown in FIG.

In the present invention, the in-plane magnetization layer 20 is made of yttrium, iron, or garnet single crystal, or a part or all of the yttrium ions are replaced with at least one type of ion selected from calcium ions, strontium ions, and rare earth ions. It may be an yttrium iron garnet single crystal or a non-quality soft magnetic material in which some of the iron ions are replaced with non-magnetic ions such as gallium ions, aluminum ions, germanium ions, silicon ions, etc. In addition, the bubble retaining layer 12
If a layer having a negative magnetostriction constant λ ₁₁₁ is selected, it may be an in-plane magnetization layer formed on the surface of the bubble retaining layer 12 by ion implantation into the sample shown in FIG. 1b.

In Fig. 1c, the saturation magnetization of the in-plane magnetization layer 20 and the bubble retention layer 12 are M and Ms18', respectively.If the thickness of the bubble retention layer is h, then the thickness t of the in-plane magnetization layer is tM/hMs. It should be selected so that it satisfies 0.5 to 1.2. In FIG. 1c, the pattern is a continuous pattern consisting of constant periodic elements for one bit. When a bias magnetic field Hz is applied perpendicular to the sample and an in-plane rotating magnetic field Hr is applied to a sample having the structure shown in Figure 1c and the properties described above, the bias magnetic field Hz is between the bubble runout magnetic field and the bubble collapse magnetic field. In the region on the high bias side, bubble transfer of 2 bits is obtained per rotation of the in-plane magnetic field. The pattern shape is based on US Patent No.
A rosary shaped like a string of circles (contiguous disc) numbered 4070658 will suffice. Alternatively, a contiguous disc made of a series of diamond shapes or diagonal rectangles may be used, but a continuous disc made of circles or diamond shapes with rounded ends will provide a good margin. FIG. 2 shows a cross section of the film including the direction of the in-plane magnetic field when a bias magnetic field is applied perpendicularly upward to the film and bubbles are transferred as the in-plane magnetic field rotates.

When the direction of the in-plane magnetic field is outward from the center of the pattern, the bubble 23 moves toward the inside of the pattern boundary, as shown in FIG. 2b, when the direction of the in-plane magnetic field is toward the center of the pattern, as shown in FIG. 2a. The bubble moves outside the pattern boundary. That is, it is considered that magnetic charges as shown in FIGS. 2a and 2b become an in-plane magnetic field and are induced in the inner part 21 and outer part 221 of the pattern boundary of the in-plane magnetized layer. In fact, when a bubble moves along a circular pattern, the in-plane magnetic field
The direction of Hr and the bubble position are shown in Figure 3a to f.

The plus and minus signs in FIG. 3 schematically represent magnetic charges thought to be induced by the in-plane magnetic field in the in-plane magnetization layer.

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

Example 1 As the substrate single crystal 11 in FIG.
Using Gd ₃ Ga ₅ O ₁₂ , a 2.2 micron bubble retaining layer made of (YSmLuCa) ₃ (FeGe) ₅ O ₁₂ garnet and having a characteristic length l of 0.2 microns was grown on its (111) plane by liquid phase epitaxial growth. Furthermore, a _SiO2 layer of about 8000 Å was sputter-deposited on this sample as an etching control layer, and a resist mask with a thickness of 1.9 microns was formed on it. The sample was rotated and irradiated with an ion beam for about 15 minutes from a direction tilted 20 degrees from the normal line of the sample, etching the bubble retention layer by 5300 Å. The etching rate of SiO ₂ is approximately 360 Å per minute.
On the other hand, since the etching rates of the resist and bubble retention layer were approximately 260 Å and 240 Å per minute, respectively, the taper angle of the pattern boundary wall of the bubble retention layer was approximately
A film having an angle of 45° approximately as shown in FIG. 1b was obtained. After removing the resist from this sample and completely removing the SiO ₂ layer with hydrofluoric acid, a yttrium iron garnet (YIG) single crystal film was deposited to a thickness of approximately 4000 Å as an in-plane magnetization layer using a vapor phase epitaxial method. grown. Since the YIG single crystal film grows almost uniformly as shown in FIG. 1c and has almost no anisotropy perpendicular to the film, it can serve as an in-plane magnetization layer that meets the purpose of the present invention. In the case of this embodiment, the bubble retaining layer has a 4πMs of about 400 Gauss, a film thickness h of 1.7 microns, and a YIG 4πM of about 1750 Gauss, so tM/hMs is about 1.0 with respect to the YIG thickness t. Also, the etching depth is approximately 0.3 times h.

FIG. 4 shows the bubble simple transfer margin in a circular continuous disk pattern with a period of 8.5 microns in the film of this example. In the area surrounded by the solid line in Figure 4, the bubble is 2 times per rotation of the in-plane magnetic field.
Transferred bit by bit. When the in-plane magnetic field Hr is zero, the bubble collapse magnetic field near the pattern is
229 Oe, the run-out magnetic field is
About 200 oersteds, both increase by 10 oersteds and decrease by about 2-3 oersteds. That is, the margin area for 2-bit transfer occurs in a slightly higher vial side area of the bubble existing area. The transfer margin in Figure 4 is for a loop perpendicular to the <112> axis of the crystal, but in the case of a loop balanced on the <112> axis, the transfer margin is almost the same, except for variations in the margin on the low bias side. The same result as in Figure 4 is obtained.

Even with a 6-micron periodic pattern in which squares of 8 microns on a side are connected with their vertices superimposed, a bubble transfer margin of 2 bits per rotation of the in-plane magnetic field was obtained, although the margin was even higher with a circular continuous pattern. widest, also
It was stable over a wide temperature range.

Example 2 Same configuration as Example 1, only YIG thickness t is 2000
As in Example 1, bubble transfer of 2 bits per rotation of the in-plane magnetic field was obtained in a sample with a tM/hMs of about 0.5. The margin was slightly narrower than in Example 1. In addition, the light increases tM/
A phenomenon in which the margin became narrower was observed when hMs reached approximately 1.5.

Example 3 Almost the same as Example 1, except that the ion etching was performed at normal incidence, so the angle 17 in FIG.
As expected, bubble transfer of 2 bits per rotation of the in-plane magnetic field was obtained. The ratio of the bias margin to the margin center value, that is, the margin rate, is as shown in Example 1.
It was about the same or slightly smaller.

Example 4 Same configuration as Example 3, but only the etching depth was 0.1 times the film layer h of the remaining bubble retaining layer.
Bubble transfer of 2 bits per revolution of the in-plane magnetic field was obtained for all samples with a magnification of 0.45.

The margin rates were all slightly smaller than in Example 3. Note that when the etching depth is less than 0.1 times the film thickness h, bubbles are less likely to be bound to the pattern boundaries;
At double or higher, bubbles enter the pattern,
Normal bubble transfer could not be obtained.

Example 5 As an alternative to YIG in Example 3, 4πM is approximately
In a sample in which a (YCa) ₃ (FeGe) ₅ O ₁₂ garnet film of 610 Gauss was grown by liquid phase epitaxial growth and the thickness t was 1.0 μm, that is, tM/hMs was 0.6, the Hc of the bubble-retaining film was high. Compared to Example 3,
Although the margin was quite small, 2-bit transfer was observed.

Example 6 Instead of growing YIG in Example 1, helium ions (He ⁺ ) were added to the surface of the bubble retention layer.
An in-plane magnetization layer was formed by implanting at an implantation dose of 3×10 ¹⁵ /cm ² at an accelerating voltage of 120 keV. In this case, the effective thickness t of the in-plane magnetization layer is estimated to be about 0.6 microns based on FMR data and the like. Therefore,
The thickness h of the bubble retaining layer is about 1.1 microns, that is, the tM/hMs of this sample is a little over 0.5, and the etching depth is about 0.5 times h. In this example as well, bubble transfer of 2 bits per rotation of the in-plane magnetic field was obtained.

In the above embodiments, a single crystal film is used as the in-plane magnetization layer, but it can be easily inferred that the effects of the present invention can be obtained even if an amorphous ferromagnetic film is used.

As explained above, according to the present invention, bubble transfer of 2 bits per rotation of an in-plane magnetic field can be achieved by using a continuous disk pattern that has a short pattern period and can be processed with conventional processing accuracy. This makes it possible to reduce access time by half while maintaining sufficient bubble density, which is of great industrial significance.

[Brief explanation of the drawing]

FIGS. 1a and 1b are diagrams for explaining the process of forming the film of FIG. 1c, and FIG. 1c shows a cross section of the film of the bubble magnetic domain element of the present invention. Figures 2a and b are cross-sectional views showing the bubble positions in the membrane cross section including the bias magnetic field and in-plane magnetic field directions, and Figures 3 a-f show the contiguous disk during one rotation of the direction of the in-plane magnetic field. FIG. 4 is a plan view showing the bubble position when the bubble transfers the pattern by 2 bits. FIG. 4 is a diagram showing the 2-bit simple transfer margin of the continuous disk transfer loop in the first embodiment of the present invention. Here, 11 is a substrate, 12 is a bubble retaining layer, 1
3 is the etching control layer, 14 is the resist mask, 15 is the ion implantation angle, 16 is the etching depth, 17 is the taper angle of the bubble retention layer at the pattern boundary, 18 is the thickness of the bubble retention layer outside the pattern, and 19 is the surface. The film thickness of the in-plane magnetization layer, 20 is the in-plane magnetization layer, 16' and 18' are the dimensions of the bubble retention layer after forming the in-plane magnetization layer, 21 is the thickness of the in-plane magnetization layer inside the pattern boundary, and 22 is the dimension of the pattern boundary. On the outside, 23 indicates a bubble, respectively.

Claims (1)

[Claims] 1. A bubble magnetic domain element having a bubble retaining layer with saturation magnetization Ms on a substrate single crystal plane, and in which bubbles are transferred by in-plane magnetic field rotation via a periodic transfer pattern formed thereon. In the etching process, the periodic transfer pattern is formed so that a pattern with tapered sidewalls remains in the bubble holding layer, and the depth of the etching is equal to the remaining film thickness h of the bubble holding layer. 0.1 times or more and 0.5 times or less, and a thickness t on the bubble retaining layer,
an in-plane magnetization layer with a saturation magnetization M is provided so as to be continuous on a tapered side wall portion of the bubble retention layer;
A bubble magnetic domain element characterized in that, by being formed so that tM/hMs satisfies 0.5 or more and 1.2 or less, bubble transfer of 2 bits is performed per one in-plane ground rotation. 2. The bubble magnetic domain element according to claim 1, wherein the in-plane magnetization layer is made of yttrium iron garnet single crystal. 3. Part or all of the yttrium ions in the in-plane magnetization layer are replaced with at least one type of ion selected from calcium ions, strontium ions, and rare earth ions, and one of the iron ions
gallium ion, aluminum ion,
2. The bubble magnetic domain element according to claim 1, comprising a single crystal of yttrium iron garnet substituted with non-magnetic ions such as germanium ions and silicon ions. 4. After the bubble retaining layer is etched so as to leave a negative magnetostriction constant λ ₁₁₁ and a continuous pattern consisting of constant periodic elements, ions are implanted into the surface to form an in-plane pattern of effective thickness t. The bubble magnetic domain element according to claim 1, wherein a magnetization layer is formed.