Method of storing and retrieving binary information

Details Method of storing and retrieving binary information Method of storing and retrieving binary information

1999-07-07

2002-05-21

Phan, Trong (Department: 2818)

Static information storage and retrieval

Radiant energy

Electron beam

C365S106000

Reexamination Certificate

active

06392915

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of storing and retrieving information, and in particular a method of storing and retrieving binary signals by changing the geometry of individual crystals within a suitable material by thermal means.
BACKGROUND OF THE INVENTION
Memory systems currently employed by digital computers or other microprocessors rely on the use of magnetic and opto-magnetic media to write, store and read binary information. Technological development of electronic data processing has required an increase in the capacity and operational speed of data storage or memory systems. A modem personal computer may have a hard disc storage system that has a capacity of several giga-bytes; this can be increased by installing a higher density disk drive, by networking a series of computers or by sharing a high capacity server system. However, the operating speed, which determines the time taken to store or retrieve information, does not increase proportionally with the overall data storage capacity.
The present invention seeks to use the property of structural change in certain materials to store information which can be accessed by digital computers and the like.
Many materials have a structure whose essential crystalline geometry or volume may change due to thermal variations. The crystalline changes in steel alloys, as an example, is well documented in the published literature. A change from an austentic to martensitic crystalline form is one of the mechanisms whereby physical changes to the properties of the steel may be brought about. Hardness, elastic properties, toughness and other attributes may be generated by suitable heat-treatment in appropriate steel alloys. Other metal alloys exhibit these changes and are equally well known.
Certain metal alloys known as shape memory alloys are capable of changing their crystalline geometry and structure when heated, but, unlike the example of steel, shape memory alloys simply revert back to the original lower temperature crystalline format if allowed to cool to an appropriate temperature. Typically, the temperature range where this crystalline change may be arranged to occur is between −200° C. to 150° C. The actual temperature range depends upon the elemental constituents that the alloy is comprised of.
A shape memory alloy may be configured with a shape by constraining the material in a required geometry and heating to a memorising temperature for a short period. The temperature of the annealed material is then rapidly reduced, ideally to 0 to 5° C. A geometrical shape is now set within the structure of the material and can be recovered, consequent to mechanical deformation, by heating the material to a recovery transformation point, determined largely by the elemental composition.
Shape recovery is facilitated by a reversion of the crystalline structure of the material from martensite to austenite. In a martensite condition, the shape memory alloy has a rhomboidal form. Above the thermal transition point a conversion to the austenite phase occurs producing a body centred cubic lattice crystal form. The crystalline form will however show a phase change without mechanical deformation and this can be demonstrated by raising or lowering the temperature above or below the transformation point. The crystalline change results from the thermal energy input.
The temperature differential between martensite and austenite phases may be as much as 100 degrees Celsius with some alloys, for example Iron/Manganese/Silicon, or as little as 4 to 5 degrees Celsius with other alloys, for example Indium/Titanium. The range across all shape memory alloys from the lowest temperature martensite form to the highest temperature austenite form is approximately 400 degrees Celsius.
EP 0734017 (Hewlett-Packard Company) discloses a device for storing information (for example binary information) on a storage medium using field emitters. The field emitters, which emit beams of electrons from very sharp points, change the state of a storage area on the storage medium and thereby write information onto it. The storage medium is preferably a material whose structural state can be changed from crystalline to amorphous by electron beams, such as germanium telluride and ternary alloys based on germanium telluride.
EP 0378443 (Sharp Kabushiki Kaisha) discloses a method for recording and reproducing information on a recording medium by irradiating the medium with an electromagnetic wave such as visible radiation or by using an electron beam in order to vary the “work function” of the recording medium. The medium is preferably a material whose structure can reversibly change such as an alloy of telluride or indium.
EP 0335487 (International Business Machines Corporation) relates to a method for recording, reading and erasing data bits in a data storage device by using extended scanning tunnelling microscopy in order to selectively heat and then rapidly cool discreet areas of the film in order to change an electronic property of the area such as conductance, work function or band gap. Preferred data storage devices are substrates with a thin film of a compound material which undergoes reversible amorphous to crystalline phase transformations. Such materials include germanium telluride.
WO 97/44780 (International Business Machines Corporation) discloses a storage information method in which small indentations are made in a shape memory alloy layer by mechanical deformation using a local probe. The indents can be removed by locally heating the alloy layer to or above its transformation temperature. An example of a shape memory alloy is the binary titanium
ickel alloy.
U.S. Pat. No. 4,888,758 (Scruggs) discloses a storage information system in which a laser is used to melt discrete regions of a recording medium such as a tungsten-nickel-boron alloy. The regions then cool into an amorphous state and this can be detected using X-rays or an electron beam in order to read the information.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method of storing information on a material, comprising the step of selectively heating individual crystals of said material in order to effect a structural change in each said crystal, wherein the information stored on said material is encoded in the arrangement of changed and unchanged crystals. Preferably, the crystals of said material are notionally grouped in sets of eight crystals, such that each set comprises a byte of eight bits of encoded information.
It has been discovered that the smallest unit within a metal alloy that will exhibit a geometrical change is a single crystal comprised of the constitutive crystalline elements. For example, in the case of a body centred cubic lattice of nickel/titanium, the individual crystal elements are the nickel and titanium atoms, which are disposed on the corners and faces of a notional cube. Thus each crystal consists of fourteen atoms (seven titanium atoms and seven nickel atoms ion the case of an equi-atomic alloy). If the heating means can be directed to an individual crystal in order to heat it to, or above, its transition point, then the crystalline form of the crystal will change.
In the example of nickel/titanium alloy, the geometrical structure of the crystal changes from rhomboidal to body-centred cubic. Each crystal can be thought of as a ‘bit’ of information, with a crystal in a rhomboidal form representing a ‘0’, and a crystal in a body-centred cubic form representing a ‘1’, in binary code. In this manner, binary information can be encoded by changing the crystal geometry, and the storage density on a given surface area of material can be maximised.
For example, the letter ‘A’ might be encoded in binary format as 10000001, the letter ‘B’ as 10000010, the letter ‘C’ as 10000011, and so on up to the letter ‘Z’ as 10011010. It will be appreciated that other encoding schemes may be employed. Complete alpha-numeric or other coded and translatable information may be generated by addressing groups of eight crys

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