Multilayered article including crystallization inhibiting layer and method for fabricating same

#The instant invention relates in general to phase change materials, and in particular to multilayered structures characterized by an increased crystallization temperature for one of the component layers thereof. Also included within the scope of the instant invention are methods for increasing the crystallization temperature of a material.

#Materials may be readily characterized in terms of the physical properties which they manifest. Among these properties are reflectivity of various wavelengths of light, electrical conductivity, thermal conductivity, density, specific heat and so forth. Materials may also be characterized in terms of the arrangement of the component atoms thereof. In crystalline materials, atoms are deterministically arranged in highly ordered, repetitive patterns. Amorphous materials in contradistinction, do not exhibit such a high degree of long range order. The term "amorphous" as used herein, is defined to include alloys or materials exhibiting long range disorder, although said alloys or materials may exhibit short or intermediate range order or even contain crystalline inclusions.

#The distinction between the amorphous and the crystalline state is an important one for a wide variety of materials insofar as many of the physical properties manifested by those materials will depend upon whether they are in the crystalline or the amorphous state. For example, in many materials electrical conductivity will vary by orders of magnitude for the crystalline and amorphous forms thereof. Likewise, optical properties such as reflectivity, optical absorption and index of refraction may also exhibit significant changes depending upon the degree of crystallinity or lack thereof.

#FIG. 1A is a cross sectional view of a multilayered article structured in accord with the principles of the instant invention and comprised of a layer of crystallizable material and a layer of crystallization inhibiting material;

#FIG. 1B is a cross sectional view of another multilayered article structured in accord with the principles of the instant invention, said article comprised of a plurality of layers of crystallizable material and a plurality of layers of crystallization inhibiting material disposed in alternating, generally coextensive relationship; and,

#FIG. 2 is a schematic representation of an apparatus as adapted for the preparation of multilayered articles in accord with the principles of the instant invention.

#Referring now to FIG. 1A, there is shown in cross section a multilayered structure 10 configured in accord with the principles of the instant invention. The structure includes a layer of an amorphous crystallizable material 12 and a layer of a crystallization inhibiting material 14. The amorphous crystallizable material 12 is a material which is capable of existing in either the crystalline or amorphous state and which may be switched from one state to another by the application of the proper form and amount of energy thereto. In accord with the principles of the instant invention, the temperature at which the amorphous form of the material forming the layer 12 is switched to the crystalline state is substantially elevated. While there are no stringent limitations on the dimension of the crystallizable layer, it has been generally found that layer thicknesses in excess of 200 angstroms, the inhibition of crystallization is less than for thinner layers. Accordingly, in the practice of the instant invention, layers of less than 200 angstroms thickness are preferred.

#It should be noted that heretofore conventional thought in the disciplines of amorphous thin film materials ran counter the principles of the instant invention. The general observation was that a thin layer of amorphous material has its crystallization temperature lowered when it is in contact with a layer of another material; see, for example, the paper of Herd, et al, entitled: "Metal Contact Induced Crystallization In Films Of Amorphous Silicon And Germanium." Journal of Non-Crystalline Solids 7 (1972) pp. 309-327. Consequently, our finding that the crystallization of layers of amorphous materials can be retarded by the presence of an inhibiting layer is novel and unexpected.

#There are a wide variety of materials capable of existing in either the amorphous or crystalline state; accordingly, the instant invention may be practiced with any such material. By way of illustration and not limitation, some of the materials which may be employed for the fabrication of the crystallizable layer 12 include: tellurium, selenium, germanium, arsenic, and silicon as well as alloys and other materials containing the aforementioned elements. It should be noted that as used herein the term "element containing material" and its equivalents are meant to refer to the pure form of the element as well as all compounds, mixtures, alloys, and molecular species which include the specified element.