NL7905544A - METHOD FOR FORMING A MONOCRYSTALLINE LAYER OF AN OXYDIC MATERIAL WITH SPINAL OR GARNET STRUCTURE ON A SUBSTRATE. - Google Patents

Description

^ 'PM 9541? * H.Y. PHILIPS 'GLOW LAMP PACKAGE IN Eindhoven.

A method of forming a monocrystalline layer of an oxidic material with a spinel or garnet structure on a substrate. -

The invention relates to a method for forming a monocrystalline layer of an oxidic material, in particular of a ferromagnetic oxidic material, with a spinel or garnet structure on a deposition surface of a single crystal-line substrate crystal, wherein the substrate crystal is melted immersed containing a lead flux and components for the oxidic material, which is kept melt at a constant temperature and in a supercooled state and wherein the substrate crystal is immersed in the melt until a layer of the desired thickness is epitaxially on the outlet has grown.

For various applications, it is known to grow monocrystalline layers with a magnetic garnet or spinel composition by epitaxy from a "fluxed melt" on special deposition surfaces of non-magnetic substrates.

For example, applications in magnetic bubble domain memories require thin layers of rare earth iron garnet with uniaxial anisotropy in which single-walled bubble domains can be generated and advanced (see U.S. Patent 20.

3,995,939, for application in thin film magnetic heads, thin layers of spinel ferrite, in particular nickel zinc ferrite and manganese zinc ferrite, are required for the magnetic circuit (see Netherlands Patent Application 7510951, which has been laid open to view) »and for luminescent screens, thin films monocrystalline 25 layers of activated aluminum grenade or gallium grenade employed.

Suitable metal oxides for a flux which dissolves components of an epitaxially growable grenade or spinel layer and allow monocrystalline layers to grow at a temperature substantially below its melting point are lead oxide, bismuth oxide and boron oxide.

790 55 44 I. - j ί. 2 ί

These oxides have been found in practice to lead lead oxide, especially in combination with boron oxide, to be the most suitable in terms of viscosity, suitable temperature range for layer growth and impurity contamination in the grown crystals coming.

As will be explained hereinafter, it offers certain advantages to grenade and spinel layers on natural facets of substrate crystals (in the case of grenades these planes are parallel to 'dei' crystallographic (110) or (211) planes; in the case of spinels these planes grow parallel to the crystallographic (111) plane). However, it appears that the use of a lead oxide-based flux in that case results in (mostly cone-shaped) mounds in the surface of the layer.

These mounds complicate the further processing of the layers 15 into a bubble domain memory, or. to a magnetic head of the thin film type and can also hinder domain movement in bubble domain memories by holding domain walls ("domain wall pinning").

The object of the invention is now to provide a method of the type mentioned in the preamble which provides hilly, smooth layers with garnet and spinel structure, respectively.

To this end, the method according to the invention is characterized in that

that a substrate crystal is provided to which a deposition surface is 25 °

formed, the normal of which makes an angle of minimum 0.5 and maximum • 10 ° with the normal of a natural facet of that substrate crystal.

\

By growing on a deposition surface that makes a (small) angle with a natural facet, single crystalline garnet and spiral layers appear to be able to grow a melt containing lead flux which do not have conical hillocks.

A further advantage of the use of such a natural facet-related deposit surface is that it offers the possibility of easily adjusting the growth rate to a desired low value.

The use of a deposition plane oriented parallel to an arbitrary crystallographic plane (for example a (111) plane 'in the case of grenades) does not offer this possibility.

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It is important that the growth rate is kept low, because this prevents the formation of a (transitional) layer during the first phase of the growth process, the composition of which varies widely. In the case of a misorientation of the deposition surface with respect to the natural facet of more than 10 °, the growth rate has become practically equal to that which occurs when growing on a deposition surface oriented parallel to an arbitrary crystallographic plane. A preferred form of the method according to the invention is characterized in that such a combination of supercooling of the melt and orientation of the depositing surface is chosen that the growth rate of the layer is at most half the growth rate of the same layer. growing on a deposition plane parallel to a (111) crystallographic plane. For example, in the case of monocrystalline layers with a garnet structure, the growth rate can be kept sufficiently low by using the supercooling at the most at an angle of approximately 1 ° with a natural faceting deposit surface, equal to 40 ° 0.

This aspect of the invention is of great interest to submicron cron bubble domain memories that require extra thin shell layers (less than 1 µm). In these thin layers, a transition layer (which may have a thickness of 0.1 µm or more) accounts for a significant portion of the total layer thickness. In such a thin layer, due to the variation in chemical composition of the transition layer 25, the magnetic properties will also vary in the direction perpendicular to the surface. This is undesirable, and the prevention of the occurrence of a transition layer is therefore very important.

When the growth rate cannot be set to a desired low value, as is the case when the deposition plane is a plane oriented parallel to any crystallographic plane, it is necessary to dip the substrate horizontally and to melt a vertical rotate shaft to grow thin layers which are as uniform as possible in thickness and of equal composition throughout. Since the method according to the invention makes it possible to grow at a desired low growth rate, a much simpler growth technique is used, in which the substrate is immersed in vertical position 790 5 5 44 £ 4 and in principle not rotated. need to be.

The invention also provides a method as described above for growing a layer of spinel ferrite on a substrate crystal with a cubic crystal structure, characterized in that the natural facet of the substrate crystal is parallel to a crystallographic (111) plane is flat, and the normal of the barrier surface makes an angle of at least 0.5 ° and at most 10 ° with the normal of the natural facet.

W Good results (sufficiently smooth layer) are obtained with spinel ferrites in particular when the misorientation of the depositing surface (with respect to a natural facet) is between 1.5 ° and 3.5 °.

Single crystals of magnesium oxide (MgO), zinc gallate (ZnGagO. \ Spinel (MgAlgO ^) and sapphire (AlgO ^) are in principle suitable as substrate crystals for epitaxial growth of spinel ferrite layers, but all have their own disadvantages.

A preferred form of the process according to the invention is characterized in that the substrate crystal is zinc ortho-titanate (ZngTiO4). The bit material has a lattice constant which is very well adapted to that of the spinelfer reeds to be grown thereon, in particular MhZn ferrite, and is available in sufficiently large dimensions and with little lattice errors, especially if it is Bridgman technique has grown.

25

The invention also relates to a magnetic structure which is particularly suitable for use in bubble domain memories, which structure comprises a monocrystalline, non-magnetic substrate with a depositing surface, and a monocrystalline layer of an oxidic deposited on the depositing surface. , ferrous

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magnetic material with a spinel or grenade structure, as well as means for generating or detecting a magnetic field change in the layer, comprising and characterized in that the depositing surface has a normal which makes an angle between 0.3 ° and 10 ° with the normal on a natural facet of the substrate crystal, will be explained by way of example below with reference to the following experiments and the drawing. This shows 790 55 44 5

Pig. 1a is a schematic drawing of a section through a hill on an epitaxially grown grenade film (from the height of the hill and the size of the base, the base angle oek can be determined); shows 5

Pig. 1b the value of £ for the highest hills on the film of fig. 1a as a function of the supercooling ^ T (the dotted line shows the theoretical relationship) and shows 10

Pig. 2 the growth rate as a function of subcooling ^ I for growth of the film of FIG. 1 a on deposition planes with a misorientation of 1.1 ° from (110) planes and for growth on deposition planes parallel to the (111 ) surfaces.

Yoorbeeld_1.

For the growth of layers of type (Y Gd) ^ (Mn Ga Pe) ^ 0 ^ 2q, a melt was composed with a saturation temperature of about 930 ° C from the following components:

PbO 1351.2 grams B2 ° 3 - 28.05

Pe O

2 ^ 3 107.83 25 ^ a2 ^ 3 10.34 ft Y2 O5 .4.24

GdgO2 4.80 ,,

Mn02 9.00 ,,

A first series of gadolinium-gallium-garnet substrates 30 was fabricated with faces whose normal was successively angled at 0 °, 1 °, 2 °, 4 ^, 6 °, 8 °, and 10 ° with the normal of the crystallographic (110 ) flat.

These substrates were melt-immersed at a temperature of 8r8 ° C (global 52 ° subcooling) for 3.5 minutes and 35 'yielding layer thicknesses of 3.2 µm for an angle of 10, to 6.3 µm for a angle of 10 °. Smooth layers were found to be formed on the substrates with a misalignment of 2 ° and higher. The growth rate was 0 ° misori -1.

Orientation 0.94 µm min and the growth rate increased with increasing misorientation to 1.80 µm min for misorientation of the deposition plane. The final value of the growth rate is equal to that 5 when using a (111) oriented substrate.

A second series of gadolinium-gallium garnet substrates, the deposition face of which was successively angled at 0 °, 1 °, and 4 ° from the normal on the crystallographic (110) plane, was subcooled at a temperature of 913 ° C (about 17 ° ) immersed in the melt for 10 minutes to yield layer thicknesses of 0.4 µm for 0 ° misorientation, 1.9 µm for 1 ° and 3.9 µm for 4 ° misorientation of the deposition face to the (110) face.

In this case, smooth layers were found to be formed on the substrates with a misorientation of 1 ° and higher. The growth rates were ..

. 0.06yum min "" * for 0 ° misorientation, 0.32yum min "^ for 1 ° misorientation and 0.65yum for 4 ° misorientation of the depositing surface.

For a deposit with (111) orientation, the growth rate at -1, the same immersion temperature, was 0.92 µm min.

Example 2.

20. - ·

For the growth of layers of (YLa) 3 (EeGa) ^ 0 ^ 2 layers, a melt was composed with a saturation temperature of about 975 ° O from the following components:

PbO 1680.0 grams '25 B205' 36.92 ,, Y2 ° 3 13.598 ,,

La20j 10,12 ,, .95,13 »»

GagOj 18.56 ,,

A first and a second gadolinium-gallium-garnet substrate 30 were provided with a (III) oriented depositing surface, and a third gadolinium-gallium-garnet substrate with a depositing surface with a misorientation of 2 ° to the (110) plane.

These substrates were melt-immersed at a temperature of about 955 ° C (globally 20 ° subcooling) until layers about 1 µm thick had grown on them.

The first substrate was immersed in a horizontal position, and rotated about 7 revolutions per minute on a 7905544 * 7 vertical axis, the second and third immersed in a vertical position and not rotated.

The homogeneity of the formed layers was examined using spin wave resonance measurements. This method is valid. 5 wrote in an article by B. Hoekstra, R.P. van Stapele and J.M. Robertson in Journal of Applied Physics, 48, page 'J82 (1977). Using spin wave resonance, the variation of the magnetic anisotropy, c.q. the magnetization in a layer can be determined. The so-called perpendicular resonance spectrum was compared in a sub-layer adjacent directly to the depositing surface (the so-called transition layer) with a sub-layer further away from the depositing surface. The difference in the field strengths at which a peak in the resonance spectrum is found (öHj.) Is a measure of homogeneity.

15 In the layer grown on the first substrate, a H Hj_ of 600 Oe was measured, in the layer grown on the second substrate a & HA of 1294 Oe, and in the layer grown on the third substrate a & HJ. from 89 Oe.

The homogeneity of the layers grown on the substrates with a small mis-orientation of the deposition surface with respect to a natural facet was thus clearly the best.

Example 3 · _. To grow layers of the type, a melt was composed with a saturation temperature of about 25 q 950 C from the following components:

PbO 1500 grams b2o3 31 »19 ,, ί · β203 136.30 ,, 30 Y2 ° 3 9.64”

A first series of gadolinium-gallium-garnet substrates were manufactured whose deposition planes were parallel to the crystallographic (110) planes with an accuracy of - 0.2 °.

These substrates (indicated by "I" in Fig. 1a) were each immersed at a different temperature in the supercooled melt and kept in the melt until a monocrystalline layer * (1 to 5 µm thick) was obtained. the film surface (3 hills present), the base angle £ (fig. 1a) was measured with 79 0 5 5 44 * 8 8 with the help of an interference microscope of the neighing type. The course of the mound angle E found as a function of the hypothermia ^! (ie the difference between the saturation temperature and the immersion temperature) is given in Fig. 1b.

A second series of gadolinium-gallium-garnet substrates was prepared with depositing faces whose normal angle was 1.1 ° to the normal on the crystallographic (110) plane. These substrates were each again immersed in the supercooled melt at a different temperature and kept in the melt until a layer (2 to 6 µm thick) was obtained. The growth rate ,. being the layer thickness divided by the immersion time, depends on the subcooling as shown in fig. 2 (curve. a).

Clear hills were observed on the surfaces of the layers grown on the 1.1 ° misoriented substrates if the subcooling was greater than or equal to 75 ° C.

On the surfaces of films grown with subcooling of 42 ° C and 57 ° C, some degree of hill formation was still noticeable, but the irregularities were not conical. Truly undulating layers are only obtained if (at a misorientation of 1.1 ° with respect to the crystallographic (110) direction) the hypothermia is less than about 40 ° C.

A third series of gadolinium-gallium-garnet substrates were prepared with deposition surfaces parallel to the crystallographic (111) surfaces and immersed in the supercooled melt again at different immersion temperatures. The growth rates determined in this way are also shown in Figure 2 (curve. B). If the hypothermia is less than 40 ° C, it will be seen from Figure 2 that the growth rate on the deposition surface with a misorientation of 1.1 ° from the (110) plane is less than half the growth rate on the deposition surface. is parallel to the crystallographic (111) plane.

Comparison of the results shown in Fig. 1b and Fig. 2 shows that no hills are found on the film surface if the misorientation of the substrate deposition plane relative to the (110) plane is greater than the base angle of the hills. Since the magnitude of this base angle depends on the degree of subcooling of the melt, any misorientation of the substrate deposition plane will include a critical value of subcooling, above which hills, including no hills, are found. Judging from the results shown in Fig. 1 b, a misorientation of 0.5 ° will include a critical value of subcooling ΔΤ of 25 ° 0 while for 2 ° misorientation there will be a critical value of £ ® greater than 90 °. The results of the first-grown series of Example 3 are in good agreement with the above claims: with a subcooling of 17 ° 0, a critical value of the misorientation (above which no hills are found) is less than 1 °, and at under-10 cooling of 52 ° C, the misorientation must be greater than 1 °. In the latter case, smooth layers were only obtained when growing on substrates with a misorientation of 2 ° or more.

Assuming subcooling of more than 10 ° C is desired to grow monocrystalline films in a reproducible manner, it is apparent from Figure 1b that the misorientation of the deposition plane relative to the crystallographic (110) plane in in any case Ö should be 3 ° and that 2 ° is sufficient to grow to a hypothermia of approximately 90 ° hilly layers.

Example 4 · 20

To grow zinc ferrite (ZnPe ^ O ^) layers, a melt with a saturation temperature of about 840 ° C was composed of the following components:

PbO 405 grams 25 B2 ° 3 12 ”

ZnO 4.524 ,, ïe205 31.94 ,,

A series of zinc titanate (ZngTiO ^) substrate crystals was manufactured using the Bridgman process and provided with 3fl depositing faces whose normals successively angled 0 °, 1 °, 2 °, 3 °, 4 °, 6 °, and 10 ° with the normal of the (111) plane.

These substrate crystals were equally immersed in the melt at temperatures between 750 and 83Ο0 C, so that layers with 3g a thickness of 3-6 yum grew on them (as the misorientation of the deposition surface with respect to the natural facet also increases, the growth rate also increases. to). The smoothest layers were found to be formed on the substrates with a misorientation of the deposition face 790 5 5 44 10 with respect to the (111) face of 2 ° and 3 °.

Corresponding results were obtained with zinc titanate sustrate crystals with different misorientations of the deposition face with respect to the (111) face immersed in melts having the following compositions: 4a By growing Mg]? 20 ^:

PhO 405 grams 10 b2o5 13.5 ,, ie2 ° 3 30.1 ,,

MgO 0.76 ,, (saturation temperature 825 ° C; growth temperatures between 800 and • 820 ° C).

15 4 "b Yoor growing MPe20 ^:

PhO405 grams B205 13.5 ,,

Pe205 30.1 "20 MO 1.4 f" (saturation temperature 850 ° C; growth temperatures between 740 and 840 ° C).

4c Yoor growing, from Lin KPe0 (.O.

^ PbO 55Ο grams b2o5 57

Pe20 ^ 38.4 ,,

LigCO220.1 (saturation temperature 858 ° C; growth temperatures between 800 and 845 ° C).

30 4d Yoor growing (MhZnJPegO ^:

Pb 2 1 * 2 ^ 7 106 grams ^ e2 ^ 3 1.1.2 ,,

MnCO, 66.7 ,, • JE '

ZnO 0.4, (saturation temperature 858 ° C; growth temperatures between 925 and 1015 ° C).

790 5 5 44

Claims (8)

1. A method of forming a monocrystalline layer of an oxidic material having a spinel or garnet structure on a deposition surface of a monocrystalline substrate crystal, wherein the substrate crystal is immersed in a melt containing a lead flux and components for the oxidic material, which melts kept at a constant temperature and in a super-cooled state, and wherein the substrate crystal is immersed in the melt until a layer of the desired thickness has grown epitaxially on the deposition surface, characterized in that a substrate crystal is provided to which a deposit surface is formed, the normal of which forms an angle of at least 0.3 ° and at most 10 ° with the normal of a natural facet of that substrate crystal. 2. Process according to claim 1, characterized in that the melt contains a PbO-BgO2 flux. A method according to claim 1 or 2, wherein the oxidic material is a rare earth garnet, and the substrate crystal is a rare earth gallium garnet, characterized in that the natural facet of the substrate crystal is attached to a crystal. tallographic (110) or (211) plane is parallel plane. A method according to claim 3? characterized in that the melt has super cooling of a minimum of 10 ° and a maximum of $ 00 Q and that the normal of the depositing surface makes an angle of at least Θ, 3 ° and of a maximum of 2 ° with the normal of the natural facet. The method according to claim 4, characterized in that the normal of the depositing surface makes an angle of at least 0.5 ° and at most 1.5 ° with the normal of the natural facet and in that the melt has a super cooling of minimum 25 ° and maximum 70 °. 6. A method according to claim 3, characterized in that a combination of supercooling of the melt and orientation of the depositing surface is chosen such that the growth rate of the layer is at most half of the growth rate of the same layer which is a deposition parallel to a (111) crystallographic plane is grown. The method according to claim 3, characterized in that the layer is grown to a thickness of at most 1 µm. 8. A method according to claim 1 or 2, wherein the magnetic 790 5 5 44 * 3 iron oxide is a spinel ferrite, and the substrate crystal has a cubic crystal structure, characterized in that the natural facet of the substrate crystal has a crystallographic ( 111) plane is parallel plane. Method according to claim 8, characterized in that the normal of the depositing surface makes an angle of at least 1.5 ° and at most 3 »5 ° with the normal of the natural facet. 10. A method according to claim 8 or 9, characterized in that the substrate crystal is zinc ortho-titanate. 11. A method according to claim 1, characterized in that the substrate crystal is immersed in the melt with the depositing surface in vertical position. 12. Magnetic device, comprising a monocrystalline, non-magnetic substrate with a deposition surface, and a monocrystalline layer of an oxidic, ferromagnetic material with a spinel or garnet structure deposited on the deposition surface, and means for generating a magnetic field change or detectable, characterized in that the deposition surface has a normal which makes an angle between 0.3 ° and 10 ° with the normal on a natural facet of the substrate crystal. 25 30 35 790 5 5 44