JPS6143794B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic bubble memory devices, and more particularly to improvements in magnetic bubble memory chips.

Generally, a magnetic thin film has an easy axis of magnetization of the magnetic domain in the in-plane direction, but certain magnetic materials, such as single crystals such as orthoferrite and magnetic garnet, have a strong uniaxial anisotropy that has an easy axis of magnetization only in the C-axis direction. It has directionality. When such a material is made into a thin film with a surface perpendicular to the C-axis, when no external magnetic field is applied, the upward magnetization direction and the downward magnetization direction form stripes with approximately equal areas, as shown in Figure 1a. They are in a state of alternating patterns. When a downward bias magnetic field H _B is applied to this thin film, the number of upward magnetic domains decreases, the downward magnetic domains expand, and after passing through the state shown in Figure 1b, the upward magnetic domains finally form as shown in Figure 1c. becomes a small cylinder with a diameter of several μm. This cylindrical magnetic domain is called a magnetic bubble domain. Moreover, if the bias magnetic field is further strengthened from the state shown in FIG. 1c, the magnetic bubble domain suddenly collapses and disappears from a certain radius. To create a new magnetic bubble domain from this state, it is necessary to locally apply a pulsed magnetic field of several thousand Oe in the opposite direction to the bias magnetic field. This magnetic field is called a nucleation magnetic field (H _N ).

The magnetic bubble memory device utilizes the fact that this magnetic bubble domain can be moved freely within a magnetic thin film by a magnetic field, and is made by forming a Permalloy thin film on a substrate using a Taber as shown in Figure 2a or a Taber as shown in Figure 2b. A propagation path is formed by forming a matrix of patterns such as half disks, and information is stored as "1" where there is a magnetic bubble and "0" where there is no magnetic bubble. Therefore, magnetic bubbles must be generated according to the information to be stored. FIG. 3 shows a nucleation type bubble generator, which is one type of bubble generator, and is a combination of a conductor pattern 1 for generating a local magnetic field and a pickaxe-shaped permalloy pattern. This bubble generator generates bubbles 3 by passing a pulsed current through the conductor pattern 1 to generate a magnetic field in the opposite direction to the bias magnetic field. However, when generating bubbles with this nucleation type generator, as the temperature rises, the nucleation magnetic field (H _N ) decreases, making it easier to generate bubbles, and sometimes two bubbles are generated, or even if the conductor Bubbles 4 may also occur along the pattern. If such bubbles enter the propagation path, information will be disturbed and the reliability of the bubble memory operation will be greatly affected. The present invention has been devised to improve this drawback.

For this reason, in the present invention, a chip is formed by forming a substrate from a magnetic material with uniaxial anisotropy, and on which patterns such as a magnetic bubble generator, a divider, a propagation path, a detector, etc. are formed from a thin film metal. In the magnetic bubble memory device, a barrier is formed in the chip at least around a portion that does not allow the leakage or intrusion of unnecessary bubbles by applying a strain force to the crystal of the substrate to block unnecessary bubbles. It is characterized by the presence of

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings.

Generally, magnetic thin films such as orthoferrite used in magnetic bubble memories are sensitive to strain, and it is known that bubbles are trapped at the edges of the pattern due to strain in the conductor pattern. The present invention utilizes the distortion of this crystal to create a barrier to prevent unnecessary bubbles from passing through. To impart strain to a magnetic thin film, a method is used in which a raw film is formed using a material with a coefficient of thermal expansion significantly different from that of the magnetic thin film, or a method is used in which a pattern is formed by heating the substrate to a high temperature. The magnitude of distortion can also be changed by changing the film thickness or pattern width.

As an example, a plan view of a chip in which an aluminum pattern having a large coefficient of thermal expansion is arranged around a nucleation type magnetic bubble generator is shown in FIG. 4, and a cross section taken along the - line is shown in FIG. In the figure, 5 is a substrate, 6 is a conductor pattern for a magnetic bubble generator, 7 is a permalloy pattern for a magnetic bubble generator, 8 is a permalloy pattern for a propagation path, and 9 is an aluminum plate formed as a barrier, which is the main point of the present invention. This pattern is formed directly on the substrate 5 so as to surround the conductor pattern of the bubble generator. Note 1
0, 11, 12, and 13 are insulating layers using SiO ₂ or SiO.

In a chip formed in this manner, when the conductor pattern 6 of the bubble generator is energized, extra bubbles 15 may be generated in addition to the regular bubbles 14. This surplus bubble 15 starts to move and move during the operation of the memory, but the aluminum pattern 9
has a large coefficient of thermal expansion and is formed directly on the substrate, giving a large strain to the substrate 5. Therefore, the surplus bulb 15 cannot come out of the aluminum pattern 9. Therefore, unnecessary bubbles are prevented from flowing into the propagation path.

In this way, unnecessary bubbles generated from crowded patterns such as corners of valve generators, dividers, or their conductors, and bubbles protruding from the propagation path due to entanglement at low bias are also suppressed. can do.

Figure 6 shows Mo/Au/Mo (thickness 150/2500/150
This figure shows the bubble restraining force due to the pattern of Al-Cu (2800 Å thick) and Al-Cu (2800 Å thick). The vertical axis of the figure represents the restraining force, and the left side of the horizontal axis plots Mo/Au/Mo with circles, and the right side plots Al-Cu with x marks. The restraint force is expressed as: restraint force = (minimum magnetic field gradient for passing bubbles under the pattern) - (minimum magnetic field gradient for free bubble movement), and the substrate temperature during pattern deposition is 250/80/80°C for Mo/Au/Mo. So, Al−Cu
It is 150°. As shown in the figure, Al− has a large coefficient of thermal expansion.
It can be seen that Cu has a greater binding force.

As explained above, the present invention improves the reliability of the magnetic bubble memory by forming a pattern on the substrate that distorts the substrate, thereby blocking the passage of unnecessary bubbles and preventing malfunction of the memory. be.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the principle of magnetic bubble generation, FIG. 2 is a plan view of a magnetic bubble propagation pattern, FIG. 3 is a plan view of a magnetic bubble generator, and FIG. 4 is a magnetic bubble memory device according to an embodiment of the present invention. FIG. 5 is a partially enlarged plan view of the chip, and FIG. 5 is a cross-sectional view taken along the line V-V.
FIG. 6 is a graph showing the bubble restraining force of the pattern. 5... Substrate, 6... Conductor pattern of magnetic bubble generator, 7... Permalloy pattern of magnetic bubble generator, 8... Pattern for propagation path, 9... Aluminum pattern, 15... Unnecessary bubble.

Claims (1)

[Claims] 1. A magnetic bubble memory comprising a substrate made of a magnetic material with strong uniaxial anisotropy and a chip on which patterns such as a magnetic bubble generator, divider, propagation path, detector, etc. are formed using thin film metal. The device is characterized in that the chip is provided with a barrier that applies strain to the crystals of the substrate and dams up unnecessary bubbles, at least around a portion that does not allow the leakage or intrusion of unnecessary bubbles. Magnetic bubble memory device.