EP0335487A2
Expired / Lapsed
EP
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Data storage using state transformable materials
Assignee: International Business Machines Corp
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Filing: 1989-02-15
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Granted: —
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Expires: 2009-02-15
Abstract
Abstract A method for recording, reading and erasing data bits in a data storage device is described. Using extended scanning tunnelling microscopy (STM) techniques, a tunnelling electron current by resistive heating selectively melts discrete areas of a state-transformable film; then heat is dissipated rapidly, writing data bits by changing the film in the areas from a first state to a second state wherein an electronic property, such as conductance, work function or band gap, in the areas is changed. Again, using extended STM techniques, the effect of this changed electronic property of the film on the tunnelling current is measured for reading the written data bits. Minimising the effect of blemishes on the material is effected, during operation in STM constant current mode by measuring dI/dV or dI/ds, and during operation in STM variable current (constant gap) mode by measuring (dI/dV)/I or (dI/ds)/I. Also, by using extended STM techniques, data bits can be selectively erased by resistance heating the film to a temperature higher than the crystallisation temperature for a sufficient period of time, restoring selected discrete areas to the first state and each affected electronic property substantially to its original condition.
Inventors
- 👤 John Stuart Foster
- 👤 Kurt Allan Rubin
- 👤 Daniel Rugar
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 17:01
CPC Classifications
G; G11; G11B; G11B9/00; G11B9/12; G11B9/14; G11B9/1463; G11B9/149; B; B82; B82Y; B82Y10/00; G11B9/1472; Y; Y10; Y10S; Y10S977/00; Y10S977/902; Y10S977/932; Y10S977/943; Y10S977/947
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
199 words
A method of recording and reading data bits in a data storage device, the method comprising the steps of: indexing an STM probe tip, connected to voltage pulse generating circuitry and tunnelling current sensing circuitry, to overlie selected discrete areas of a film of state-transformable material on a substrate, together comprising a storage medium; and for recording a data bit of one significance, applying voltage pulses to the STM probe tip to induce current pulses of sufficient magnitude, selectively heating the currently overlaid discrete area of the film to a preselected temperature, and then cooling the areas at a rapid rate for changing the material in the area from a first state thereof to a second state thereof wherein an electronic property is changed in the discrete areas from one value to a substantially different value, leaving the overlaid area unaltered for recording a data bit of the other significance, thereby causing data bits to be written at the areas; and for reading a data bit, using the probe tip and tunnelling current sensing circuitry to sense the film at the overlaid discrete area to determine if the electronic property had been changed to the different value, or not.
Claim 2
Independent Claim
199 words
A method of recording and reading data bits in a data storage device, the method comprising the steps of: indexing an STM probe tip, connected to voltage pulse generating circuitry and tunnelling current sensing circuitry, to overlie selected discrete areas of a film of state-transformable material on a substrate, together comprising a storage medium; and for recording a data bit of one significance, applying voltage pulses to the STM probe tip to induce current pulses of sufficient magnitude, selectively heating the currently overlaid discrete area of the film to a preselected temperature, and then cooling the areas at a rapid rate for changing the material in the area from a first state thereof to a second state thereof wherein an electronic property is changed in the discrete areas from one value to a substantially different value, leaving the overlaid area unaltered for recording a data bit of the other significance, thereby causing data bits to be written at the areas; and for reading a data bit, using the probe tip and tunnelling current sensing circuitry to sense the film at the overlaid discrete area to determine if the electronic property had been changed to the different value, or not.
Claim 3
Dependent Claim
87 words
A method as claimed in claim 1, further including the step of: for erasing recorded data at the overlaid discrete area, applying to the probe tip a voltage pulse that induces a current of sufficient magnitude to heat that area of the film to and only to a temperature lower than the preselected temperature for a period of time sufficient to allow the material to return to the first state to restore the electronic property to substantially the value representing a data bit of the other significance.
Claim 4
Independent Claim
45 words
A method as claimed in either preceding claim, wherein the storage medium composition is chosen so that, following each such selective heating, the material and substrate in combination inherently dissipate heat at the rapid rate to inhibit restoration of the material to its first state.
Claim 5
Independent Claim
20 words
A method as claimed in any preceding claim, wherein the preselected temperature is above the melting temperature of the material.
Claim 6
Independent Claim
71 words
A method as claimed in any preceding claim, wherein the film material is taken from the group consisting of GeTe, (GeTe) 100-z Sn z , where z is between 0 and 30, Sb₂Te₃, GaSb, Sb₂Se, SnTe, PbTe, SbSe, BiSe, GeSe, Te₅₀Ge (50-x) Sn x , where x is between 0 and 10, (Ga 100-y In y )Sb, where y is between 0 and 100, and doped and undoped Ge and Si.
Claim 7
Independent Claim
30 words
A method as claimed in any of claims 1 to 4, wherein the film material is stable in one of the states and metastable in the other of the states.
Claim 8
Independent Claim
30 words
A method as claimed in any of claims 1 to 4, wherein the film material is crystalline in one of the states and amorphous in the other of the states.
Claim 9
Independent Claim
37 words
A method as claimed in any of claims 1 to 4, wherein the film material is stable crystalline in one of the states or metastable crystalline in the other of the states, such as, for example, AgZn.
Claim 10
Independent Claim
25 words
A method as claimed in any preceding claim, wherein the electronic property is taken from the group consisting of conductance, work function and band gap.
Claim 11
Independent Claim
89 words
A method as claimed in any preceding claim, further including the steps, during the sensing step, of: applying to the tip a DC bias voltage at which the slope, dI/dV, of the current vs. voltage curve for the film differs significantly according to the state of the film; superimposing an AC voltage on the DC bias voltage; and sensing the amplitude of the AC component of the readout signal from the film, and hence the value of dI/dV, to determine the conductance and hence state of the discrete areas.
Claim 12
Dependent Claim
35 words
A method as claimed in claim 10, wherein, during sensing, the STM probe is operated in constant current mode, whereby the effect of blemishes in topography of the film on the readout signal is minimised.
Claim 13
Dependent Claim
36 words
A method as claimed in claim 10 or claim 11, wherein, during amplitude sensing, the AC voltage signal and the readout signal from the film are mixed and then filtered to provide the dI/dV readout signal.
Claim 14
Dependent Claim
68 words
A method as claimed in claim 10, further including the steps, during the sensing step, of: operating the STM probe in a variable current mode; sensing the STM tunnelling current, I, as read from the film; and passing the current, I, and the dI/dV signal through divider circuitry to provide a (dI/dV)/I readout signal in which the effect of blemishes in the topography of the film is minimised.
Claim 15
Independent Claim
59 words
A method as claimed in any of claims 1 to 9, further including the steps, during the sensing step, of: modulating the spacing, s, between the tip and film; measuring the tunnelling current, I; and measuring dI/ds to provide a readout signal indicative of changes in work function of the film and hence the state of the discrete areas.
Claim 16
Dependent Claim
36 words
A method as claimed in claim 14, wherein, during sensing, the STM probe is operated in a constant current mode whereby the effect of blemishes in topography of the film on the readout signal is minimised.
Claim 17
Dependent Claim
46 words
A method as claimed in claim 14, further including, in the sensing step, the steps of: operating the STM probe in a variable current mode; and measuring (dI/ds)/I to provide a readout signal in which the effect of blemishes in topography of the film is minimised.
Claim 18
Independent Claim
21 words
A method as claimed in any preceding claim, wherein the probe tip is positive relative to the polarity of the film.
References Cited (Backward Citations)
No citation records indexed.
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