Nanometer-Scale Erasable Recording Using Atomic Force Microscope     on Phase Change Media

Kado, H.; Tohda, Takao

doi:10.1143/jjap.36.523

Cited by 36 publications

(25 citation statements)

References 14 publications

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“…[21] Conductive marks in an insulating surrounding were written using an AFM. It was shown that a conductive mark could also be (once) erased by applying a low dc voltage (-1 V) to the tip, but for rewriting a higher voltage (3 V) was used.…”

Section: Communicationmentioning

confidence: 99%

“…Polarity-dependent resistance switching was not reported in Ref. [21] and information on cyclability and data retention was not presented. Only current images were shown, but no topographic images.…”

Section: Communicationmentioning

confidence: 99%

“…Impetus to data-storage technologies has been given by AFM since data writing down to 20 nm is readily possible, and AFM has potential to read/erase the data. [20][21][22][23][24][25][26][27] AFM data writing can occur via thermal or electrothermal means. The former technique so far led to a potential data density of 3.3 Tb inch -2 although it is not yet functional.…”

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Nanoscale Electrolytic Switching in Phase‐Change Chalcogenide Films

et al. 2007

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This Communication presents the important finding that certain chalcogenide materials, well-known from rewritable optical recording, allow resistive memory states that are a combination of two electrically-induced (reversible) switching processes, i.e., an actual amorphous-crystalline phase transformation and a (electrolytic) polarity-dependent resistance change. Nanometer-sized crystalline marks were written electrically in amorphous Ge 2 Sb 2+x Te 5 films using atomic force microscopy (AFM), and their resistance was found to depend on the polarity of the applied voltage with a resistance difference of three orders of magnitude. However, no contrast in current has been detected between the crystalline higherresistance state and the surrounding amorphous phase. This resistance switching is reversible for bias voltages well below the threshold voltage required to induce the phase transformation. The switching mechanism is attributed to the solidstate electrolytic behavior due to the presence of excess Sb in the films. Our results render exciting technological opportunities for data storage and encryption by combining both switching concepts.Following his seminal work in 1968, [1] Ovshinsky demonstrated in chalcogenide alloys a fast reversible transformation between amorphous and crystalline phases induced by electrical or optical (laser) pulses. [2][3][4] The two phases exhibited clear contrast in electrical and optical properties and, hence, these materials were suggested for binary data-storage applications. However, it took considerable time before rewritable optical compact discs (CD) and digital versatile discs (DVD) based on these findings came to the market. In recent years, the main focus of phase-change data-storage research returned to resistance switching. So-called chalcogenide or phase-change random access memory (CRAM/PRAM) and ovonic unified memory (OUM) based on the phase-dependent resistance switching are currently under intense investigations, [5][6][7][8][9][10][11][12][13] because they show great promise as next-generation nonvolatile solid-state memory replacing flash memory. In certain chalcogenides a special phenomenon of polaritydependent resistance switching (induced by an electric field) has been identified. [14][15][16][17][18][19] This is related to the solid-state electrolytic character and high ionic conductivities of chalcogenides, and hence is called ionic/electrolytic switching. For one polarity, the chalcogenide medium is electrically conductive by forming conducting filamentary pathways between electrodes, whereas for the reverse polarity it becomes relatively insulative or at least less conductive because of rupture of the previously formed electrical pathways. Memory elements (or structures) based on this switching have been demonstrated in some Ag-saturated chalcogenides including Ag-S, [14,15] AgGe-Se, [16,17] Ag-Ge-Te, [18] and Ag-In-Sb-Te. [19] This switching seems more attractive for applications than phase-dependent switching, because i) it can be performed at lower volta...

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Section: Communicationmentioning

confidence: 99%

Section: Communicationmentioning

confidence: 99%

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confidence: 99%

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Nanoscale Electrolytic Switching in Phase‐Change Chalcogenide Films

et al. 2007

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“…These probes are used to induce semipermanent, nanoscale changes in storage media to record the binary data. One approach involved using highly conductive tips, either in contact ͑using modified atomic force microscope tips͒ [1][2][3] or in close proximity ͑using scanning tunneling microscope tips͒ 1,4,5 to a phase-change medium to deliver a current that, through Joule heating, induces stable amorphous or crystalline phase transformations to record information. Using these techniques, it was shown that it is possible to record stable crystalline marks in an amorphous material with diameters less than 50 nm.…”

Section: Introductionmentioning

confidence: 99%

A slope-theory approach to electrical probe recording on phase-change media

Aziz

Wright

2005

Journal of Applied Physics

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A theoretical approach to predicting the spatial extent of the amorphous to crystalline transition region during the probe recording process on phase-change storage media is presented. The extent of this transition region determines the ultimate achievable linear density for data storage using phase-change materials. The approach has parallels with the slope theory used to find magnetic transition lengths in magnetic recording, and shows that the amorphous to crystalline transition length can be minimized by reducing the thickness of the phase-change layer, by minimizing lateral heat flow, and by maximizing the ratio of the activation energy for crystallization to the transition temperature E c / T t .

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“…Kado and Tohda [12,13] have reported reversible recording in amorphous GeSb 2 Te 4 films using an AFM with conducting cantilevers, and detect a drop of the electrical resistance of the films when exposed to electrical pulses of −4 V. Ueno and Gan et al studied the microstructure and morphology of recorded marks in micro area by TEM [14] and X-ray diffraction [15][16][17][18], but it is difficult to relocation the recorded marks due to its small size. Ishiyama [19] evaluated the size of phase-change bits by their frictional contrast and deemed it an effective resort for in situ phase-change observation.…”

Section: Introductionmentioning

confidence: 99%