JPS6244843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a continuous disk that uses a charged wall to transfer magnetic bubbles.
This invention relates to the composition of magnetic garnet films used in magnetic bubble devices. Contiguous bubble elements using charged walls differ from elements using conventional discrete patterns made of permalloy, etc., and are based on AIP Conf.Proc. No. 10. No. 339
As shown in Page (1973), this is a new type of bubble device that uses a continuous bead-like pattern to drive bubbles through a charged wall to perform memory operations. As shown in the above-mentioned literature, the pattern formation method for this element is usually performed by ion implantation. The role of ion implantation is to form a pattern by directing the magnetization of the surface layer of the garnet film in the in-plane direction of the garnet film using the magnetostrictive effect. Furthermore, in order to orient magnetization in-plane by ion implantation, the absolute value of strain-induced magnetic anisotropy energy K _a by ion implantation must be
uniaxial magnetic anisotropy energy K _u (grown film). As the bubble diameter becomes smaller, the value of K _u increases, so it is becoming increasingly difficult to directly implant ions into the bubble layer and direct the magnetization in-plane. It is known that even if the amount of ions implanted is increased unnecessarily in an attempt to increase the strain caused by ion implantation, the ion implanted layer will be fractured and it will no longer be a ferromagnetic material, so there is an upper limit to the strain that can be applied. . In order to solve this problem, IEEE Trans.on Mag., MAG, Volume 13,
As shown on page 174 (1977), it was proposed to adopt a double film in which the garnet film for the bubble support layer and the garnet film for the drive layer, which directs magnetization in the plane of the film by ion implantation, have different compositions. ing. However, manufacturing a magnetic garnet film with a double film structure is not practical because the process is complicated and it is difficult to control the film thickness. Naturally, it is desirable that a bubble element using microbubbles is also composed of a single layer film. In order to achieve a continuous disk magnetic bubble element with a single-layer film structure, the bubble material must simultaneously satisfy the requirements for properties as a bubble layer and as a drive layer. must be maintained. As the bubble diameter becomes smaller, the uniaxial anisotropy energy (K
As mentioned above, it is necessary to increase the value of _u ). Furthermore, K _u must be large enough to direct the magnetization of the surface layer in-plane by ion implantation. This point will be further explained quantitatively using FIG. FIG. 1a is a cross-sectional view showing the configuration of a continuous disk magnetic bubble element, in which a mask pattern 12 formed in contact with a garnet film 11 on a Gd ₃ Ga ₅ O ₁₂ substrate 10 is shown.
The garnet film under the _mask pattern is protected from ion implantation, while the surface layer 13 of the garnet film outside the mask pattern is ion implanted, and the uniaxial difference in this area is The directional energy becomes K _i . At this time, the strain caused by ion implantation has a significant gradient at the boundary.
A boundary region 14 with a certain width should exist in this part. Therefore, the effective uniaxial anisotropy K′ _u (=K _u −2πM ² _s ) taking into account the demagnetizing field is calculated from the value of the film without ion implantation to the value K′ _i of the outer surface of the mask pattern, as shown in 15. (=K _i −2πM ² _s
)
through the boundary region 14. The inventors have determined that K _u −2π in the non-ion implanted region
When the absolute values of M ² _s and |K _i −2πM ² _s | of the ion implantation region are balanced, and Q = 1 just holds at the boundary, a stable contiguous disk transfer margin can be obtained. We experimentally discovered that this is an essential requirement. In addition, the present inventors found that in order to obtain a stable transfer margin over a wide temperature range, it is essential that the material satisfy K _u −2πM ² _s = |K _i −2πM ² _s | over a wide temperature range. We have discovered that this is the case, and have come up with the present invention. In other words, more than necessary |
When K _i | is increased, Q extends to the inside of the pattern boundary.
<1, the magnetization begins to fall in-plane even under the pattern, and a magnetic pole appears at the edge of the pattern, which inhibits continuous disk bubble transfer. On the other hand, it has been found that when |K _i | is small, the charged wall is weak and transfer is impossible unless the in-plane rotating magnetic field is made larger than necessary. It can be understood from the above conditions that in order to be able to operate in a wide temperature range, it is necessary that K _u -2πM ² _s = |K _i -2πM ² _s | holds true in a wide temperature range. Furthermore, as the damage level due to ion implantation increases, the strain applied to the garnet film increases, but the amount of change in uniaxial anisotropy energy K is not proportional to the strain forever, but saturates and eventually decreases. It is known that FIG. 2 shows the measurement results by the present inventors, and shows that K〓 reaches saturation when the ion implantation damage level exceeds 1.1 eV/ ^Å3 . Further, the results of determining the Curie temperature of the garnet film as the signal disappearance temperature due to the ion-implanted layer based on the temperature change of ferromagnetic resonance are shown in FIG. 22. It can be seen that the Curie temperature is significantly lower than in the non-ion implanted part depending on the damage level. It is not a good idea to increase the damage level more than necessary. The present invention shows that the charged wall is weak at temperatures within 50 degrees Celsius (for example, temperatures of 100 degrees Celsius or higher when the Curie temperature is 150 degrees Celsius) compared to the Curie temperature _Tc of the ion-implanted layer, making continuous disk bubble transfer impossible. They are finding out. Based on these facts, the present invention allows K u −2πM ² _s = K _u −2πM 2 s =
|K _i −2πM ² _s | can be achieved, and the ion implantation damage level that can achieve this condition is 1.1 eV/Å ³
The Curie temperature of the ion-implanted layer is
The object of the present invention is to provide a material that can simultaneously satisfy four conditions: the temperature can be maintained at 130° C. or higher, and the bubble diameter is suitable for the intended bit period. More specifically, the requirements for material properties are as follows: In order to achieve K _u −2πM ² _s = |K _i −2πM ² _s | at a damage level of 1.1 eV/Å ³ or less, K at 25°C is required. _u value is 60000erg/ ^cm2
It must have a value of 45,000 erg/cm ² or less, and it must have a Q of 2.5 or more and less than 3 to ensure bubble stability. Katsu-30
Constantly K _u − over a wide temperature range from °C to +80 °C
It is necessary that 2πM ² _s = |K _i −2πM ² _s |. The present invention satisfies these conditions by creating a continuous disk that is stable over a wide temperature range.
The object of the present invention is to provide a practical garnet film composition having a bubble transfer margin. Furthermore, this composition contains Bi and has a large Faraday rotation coefficient as described in Japanese Patent Application No. 1988-88910, so that magnetic bubbles can be easily observed visually, and from this point of view as well, it is excellent in practical use. The present inventors have developed various garnet film compositions,
That is, as a result of measuring the 4 μm period continuous disk element transfer margin and its temperature change by using garnet film compositions with various magnetic properties and varying the ion implantation conditions,
It is expressed by the composition formula YxSmyLu _3-(x+y+z+u) Bi _z Ca _u Fe _5-u Ge _u O ₁₂ , and the values of x, y, z, and u are respectively
0.50≧x≧0.30, 0.30≧y≧0.10, 0.35≧z≧0.20
It has been discovered that garnet having a composition within the range of 0.80≧u≧0.60 is the optimal material composition, and the present invention has been completed. With a composition similar to that of the present invention (YSmLuCa) ₃
(FeGe) ₅ O ₁₂ is used in 4 μm periodic contiguous disks and magnetic bubble elements, as shown in the Institute of Electronics and Communication Engineers Electronic Components and Materials Study Group materials.
Described in CPM80-73. Unlike this, the material of the present invention has Bi in its molecular formula.
Although it contains 0.20 to 0.35, by including Bi, the amount of Sm can be reduced enough to achieve the same K _u , and in the end, (YSmLuCa) ₃ (FeGe) ₅ O ₁₂
For the (YSmLuBiCa) ₃ (FeGe) ₅ O ₁₂ of the present invention, the |K ₁ |/K _u ratio could be reduced by 20% for the same K _u , making bubble transfer possible in a lower rotating magnetic field. . It is known from the Journal of Applied Physics that the smallest rotating magnetic field that can be transferred by a continuous disk is proportional to |K ₁ |.
As described in the paper on Volume 50, No. 6, Page 4246. When the amount of Bi is less than 0.20 per molecular formula, |K ₁
There was virtually no effect of reducing |. The present invention will be explained in detail with reference to Examples below. Example 1 Using the melt composition shown in Table 1 _, Y _0.49
Sm ₀ . ₁₀ Lu ₁ . ₃₇ Bi ₀ . ₃₀ Ca ₀ . ₇₄ Fe ₄ . ₂₆ Ge ₀ . ₇₄ O ₁₂ garnet film on a (111)Gd ₃ Ga ₅ O ₁₂ substrate at 820°C
It was grown to a thickness of 1.28 μm. The magnetic properties of this garnet film were as shown in Table 2. K _u =
Q = 2.5 was secured at 47000erg/cm ² . 100keV−3.5 ^× 10 ¹⁵ He + /cm ² +40keV− corresponding to a damage level of 0.9eV/Å ³ using ferromagnetic resonance.
Double ion implantation of 1.5×10 ¹⁵ He ⁺ /cm ² was performed, and H _k −4πM _s of the non-ion implanted part and the ion implanted part
The results of measuring H _ki -4πM _s are shown in FIG.
There is a relationship of Ku−2πM _s ² =M _s /2(Hk−4πM _s ), Ki−2πM _s ² =M _s /2(Hki−4πM _s ), and H _k −4πM _s = |H _ki −4πM If _s | holds true, then K _u −2πM ² _s = |K _i −2πM ² _s | holds true. From FIG. 3, it can be seen that K _u -2πM ² _s = |K _i -2πM ² _s | holds over the range from -30°C to +100°C. The temperature change of the bias magnetic field margin with the in-plane rotating magnetic field Hr = 50 Oe of the 4 μm period CD transfer margin is as shown in Figure 4, and stable operation was guaranteed from -30°C to +80°C. In addition, K _i -2πM ² _s of the ion-implanted layer in Fig. 3 is 0 at 155°C.
This indicates that the Curie temperature of the ion-implanted layer is 155°C, which exceeds the minimum Curie temperature of 150°C that guarantees the temperature characteristics. From the above, it was confirmed that this material has a sufficient contiguous disk margin over a wide temperature range. Furthermore, the Faraday rotation coefficient was -3200°/cm, and bubbles could be sufficiently observed using a polarizing microscope. Example 2 Using the melt composition shown in Table 1 _, Y _0.30
Sm _0.28 Lu _{1.38 Bi 0.30} Ca _0.74 Fe _{4.26 Ge 0.74 O 12 garnet} film was deposited on a ( _{111 )} Gd ₃ Ga ₅ O ₁₂ substrate at 1.31 at ₈₃₅ ℃.
It was grown to a thickness of μm. The magnetic properties of this garnet film are shown in Table 2, and K _u =58000erg/
We were able to secure Q = 2.6 in cm ² . After forming a 4 μm periodic contiguous disk pattern with Cr/Au, 100 keV−3.5×10 ¹⁵ He ⁺ /cm ² + was applied, which corresponds to ion implantation with a damage level of 0.9 eV/Å ³ .
Ion implantation was performed at 40 keV−1.5×10 ¹⁵ He ⁺ /cm ² . From −30℃ to +80℃ K _u −2πM ² _s = |K _i −
2πM ² _s | was established. In-plane rotating magnetic field 50Oe
The contiguous disk transfer margin was always 13% over the temperature range of -30°C to +80°C. The Curie temperature of the ion-implanted layer was 158°C. _{Example 3 Y 0.50 from} the melt shown in Table 1
Sm _0.30 Lu _{1.20 Bi 0.20} Ca _0.80 Fe _{4.20 Ge 0.80 O 12} garnet film on ₍ 111)Gd _{3 Ga 5 O 12} substrate at 0.90
It was grown to a thickness of μm. The magnetic properties of this garnet film are shown in Table 2, and K _u =45000erg/
Q = 3.0 was secured at cm ² . Photoresist 4 μm periodic continuous disk pattern
After forming with AZ-1350J, 100keV-4.25×10 ¹⁵ He ⁺ /cm ² corresponds to a damage level of 1.1eV/Å ³ .
+40keV-2.0×10 ¹⁵ He ⁺ /cm ² ion implantation was performed. The contiguous disk transfer margin with an in-plane rotating magnetic field of 50 Oe was always able to maintain a margin rate of 11% from -30°C to +80°C. The Curie temperature of the ion-implanted layer was 150°C. Example 4 Y _0.41 from the melt _shown in Table 1
A _{Sm0.15Lu1.49Bi0.35Ca0.60Fe4.40Ge0.60O12 garnet film} was _{grown to a thickness of} 1.16 _μm on _{a ( 111 ) Gd3Ga5O12 substrate .} The magnetic properties of the film were as shown in Table 2. 3μm period contiguous with Au mask
Ion implantation to form a disk transfer path and correspond to a damage level of 1.1 eV/Å ³ (conditions are as in Example 3)
), and then measured the temperature change of the contiguous disk and transfer margin.
A stable 10% was always maintained over a temperature range of 30°C to +80°C. The Curie temperature of the ion-implanted layer was 140°C. Comparative Example 1 A sample with a completely different composition from Examples 1 to 4.
Example ₁ Gd _{0 . 16} Sm _{0 . 18} Tm _{1 . 73} Bi ₀ . ₃ Ca ₆₃ Fe _{4 . 37 Ge} 0 . A continuous disk device was formed in the same manner as in Steps 4 to 4. The temperature changes of H _ki −4πM _s and H _k −4πM _s in the ion-implanted part and the non-ion-implanted part are shown in FIG.
The average value of H _k -4πM _s in the non-ion-implanted area was exactly zero in the range of 30°C to 60°C, as shown by the broken line in the figure, but became positive below 20°C, and conversely became negative above 70°C. was. For this reason, the formation of a charged wall is weak at low temperatures below 20°C, and a continuous disk transfer margin cannot be obtained unless a large in-plane magnetic field is applied. Furthermore, at high temperatures of 70°C or higher, magnetic poles appeared under the pattern and bubble transfer was not smooth, making it not a desirable material. _Yx
In SmyLu _3-(x+y+z+u) Bi _z Ca _u Fe _5-u Ge _u O ₁₂ ,
When x > 0.50, K _u is less than 45000erg/cm ² and u
Depending on the value of , the bubble diameter may become too large or
Q was less than 2.5, which was not appropriate. Conversely, when x < 0.30, K _u is approximately 60000 erg/cm ² or more, and even if ion implantation is performed at a damage level of 1.1 eV/Å ³ , |K _i −2πM ² _s | is small and the charged wall rotates weakly. Contiguous disk transfer margin could not be achieved without increasing the magnetic field. When y>0.30, the lattice constant of the film was 12390 Å even at the lower limit of Bi content z=0.20, and the mismatch with the substrate was large and inappropriate. When z>0.20, the lattice constant became even larger. When y<0.10, K _u <45000erg/cm ² . When z>0.35, the coercive force H _c of the garnet film exceeded 1 Oe and became an obstacle to the movement of bubbles along the transfer pattern. When z<0.20, the Faraday rotation coefficient was small and difficult to see visually, which was inconvenient. Also｜K ₁ ｜
was virtually the same as the system without Bi, and no effect of Bi addition was observed. 4π when u<0.60
M _s exceeded 800G and it was not possible to secure Q = 2.5. When u > 0.80, the bubble diameter becomes too large when 4πM _s is less than 550G, and if all the bubbles are packed in each bit position of the continuous disk transfer path, the margin width becomes small due to the interaction between the bubbles. It was inappropriate. As described above, according to the present invention, by using a single layer epitaxial garnet film on a (111)Gd ₃ Ga ₅ O ₁₂ substrate, a contiguous disk/magnetic bubble element having a sufficient operating margin over a wide temperature range can be achieved. can be made.

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【table】

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【table】 [Brief explanation of the drawing]

Figure 1a is a cross-sectional view showing the configuration of an ion-implanted continuous disk magnetic bubble element.
10 is a substrate, 11 is a magnetic garnet film, 12 is a mask pattern, and 13 is an ion implantation layer. b is a graph showing the change in lattice strain near the mask pattern boundary, and c is a graph showing the change in effective uniaxial anisotropy energy near the mask pattern boundary. Second
The figure shows the uniaxial anisotropy energy K〓 induced by ion implantation and the Curie temperature T _c of the ion implanted layer as a function of the ion implantation damage level. FIG. 3 is a diagram showing temperature changes in the anisotropic magnetic field of the garnet film used in Example 1 of the present invention. Figure 4 shows a 4 μm periodic contiguous film formed using the garnet film of Example 1 of the present invention.
FIG. 3 is a diagram showing temperature changes in disk transfer margin. FIG. 5 is a diagram showing temperature changes in the anisotropic magnetic field of the garnet film used in Comparative Example 1.

Claims (1)

[Claims] 1. Rare earths (including yttrium) used in contiguous disks and magnetic bubble elements.
The compositional formula of the bismuth-calcium-iron-germanium garnet film is YxSmyLu _3-(x+y+z+u) Bi _z Ca _u Fe _5-u Ge _u O ₁₂ , where x, y, z , u are in the range of 0.30≦x≦0.50, 0.10≦y≦0.30, 0.20≦z≦0.35, and 0.60≦u≦0.80, respectively.