Next Generation Memory DevicesFlorida International University Miami, Florida, U.S.A.Center for Nanoscale Magnetic DevicesSakhrat Khizroev

Outline BackgroundPerpendicular Magnetic RecordingThree-dimensional Magnetic RecordingProtein-based memorySummary

BackgroundTraditionally, Scaling Laws were followed to advance data storage technologies ScalingAt 1 Gbit/in2 information density, bit sizes are: 400 x 1600 nm2At 100 Gbit/in2 : 40 x 160 nm2At 1 Tbit/in2 : 13 x 52 nm2

Scaling: Smaller Transducers and MediaAt 1 Tbit/in2 information density, Bit Sizes are: 13 x 52 nm2

Superparamagnetic LimitMagneticgrainsBit transitionSNR ~ log(N), N - number of grains per bitWhile scaling, need to preserve number of grains per bit to preserve SNRGrain size is reduced for higher areal densities:

HProbability of magnetization reversal due to thermal fluctuations:Thermally stable media:Relaxation time = = 72 sec for KuV/kT=40 = 3.6x109 years for KuV/kT = 60Media Stability

SuperparamagnetismIf a

In a typical longitudinal recording layer the magnetic anisotropy axes of individual grains are randomly oriented in the plane of the filmIn perpendicular recording layer the anisotropy axis is relatively well aligned (

Nanoscale Device: Tbit/in2 Recording Transducer*LongitudinalPerpendicularBit Sizes: 13 x 52 nm2 *S. Khizroev, D. Litvinov, Physics of perpendicular recording: writing process, Appl. Phys. Reviews Focused Review, JAP 95 (9), 4521 (2004).

In perpendicular recording the write process effectively occurs in the gap (Write Field < 4pMS)In longitudinal recording the write process is done with the fringing fields (Write Field < 2pMS)Gap Versus Fringing Field WritingHigher areal density media requires higher write fields !!!*S. Khizroev and D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

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FIB to Trim Regular Transducers into Nanoscale Devices*FIB Etch to Define a NanoprobeFIB DepositionThe most critical step is to make a probe with Nanoscale dimensions*S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).

Numerical Calculations**Jointly with Integrated Inc. ,a group at Durham University, UK, and groups at Carnegie Mellon UniversityLongitudinalPerpendicularModeled Fields (Quantum-mechanical)Gallium Ion Implantation

Longitudinal Transducerwith a 30 nm WidthPerpendicular Transducerwith a 60 nm WidthFIB-fabricated Nanoscale Transducers*Note: It takes ~ 10 minutes to make one such device in the University environment*S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).

Control of Gallium Diffusion*AFMMFM3 x 105 Ions/cm22 x 106 Ions/cm2Ion DoseNOTE: Although NO texture change is observed through AFM, substantial magnetic grain change is seen through MFMdoseincrease*D. Litvinov, E. Svedberg, T. Ambrose, F. Chen, E. Schlesinger, J. Bain, and S. Khizroev, Ion implantation of magnetic thin-films and nanostructures, JMMM 277 (3-4), xxx (2004).

The process how to make Nano-precision patterns with FIB wasshared with a few companies and successfully implemented by:Carnegie Mellon University, IBM, Seagate, and others500 nm500 nmSidewall A Part of a Device made in the Industry before the process was implementedSame Device made withthe process implementedNanoscale FIB Process* *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).

Dynamic Kerr Measurement of the Field from a Nanoscale Transducer*CharacterizationKerr-Image Snap-Shots for a SPH Transducer (Near-field Kerr Microscopy)*These experiments were repeated at Seagate, CMU, and IBM*D. Litvinov, J. Wolfson, J. Bain, R. White, R. Chomko, R. Chantrell, and S. Khizroev, Dynamics of perpendicular recording, IEEE Trans. Magn. 37 (4), 1376-8 ( 2001).

CharacterizationIon image of a FIB-fabricated and magnetically active 3-nm-long feature MFM image of recorded nanoscale magnetic "dots"

Perpendicular Recording with Bit Widths of less than 65 nm*130 nm~400 ktpiCoB/Pd multilayerCoCrPtTa alloy~190 ktpiCurrent state-of-the-art longitudinal recording is

Perpendicular Recording promises to defer the superparamagnetic limit to ~ 1 Terabit/in2 Heat-Assisted and Patterned Media are still 2-D limited and relatively slowIt is expected that Moores law will inevitably reach its limit between 2010 and 2020 Time to stack multiple active layers on top of each other3-D Magnetic Recording is a data storage form of 3-D integrationConventional and 3-D Recording MediaNote: Each cell is 50 x 50 nm2Three-dimensional Magnetic Recording

3-D Magnetic RecordingThe development of 3-D magnetic recording is divided into two phases:Multi-level Recording: not optimally utilized 3-D space Note: Effective areal density increase is by a factor of Log2L (where L is the number of signal levels)

3-D Recording: each magnetic layer is separately addressedNote: Effective areal density increase is by a factor of N (where N is the number of recording layers)Note: Each cell is 50 x 50 nm2Note: These are not active layersLead Ph.D. Graduate Student: Yazan Hijazi, Sakhrat Khizroev

Recording HeadThe current in the single pole head is varied to vary the recording fieldEach recording is performed via two pulses: 1) a cell is saturated and 2) the information is recordedSchematics of a TransducerSimulated Recording Field

Playback HeadThe playback head is designed to preferably read the vertical field component which is dominant in this caseStray Field from 3D MediumDifferential Reader ConfigurationElectronic Images of FIB-fabricated Transducer

Multi-level Recording on a Continuous MediumMajor Disadvantages:Every time a track is recorded into the bottom layer, there are side regions in the top layer in which the earlier recorded information is lost because of the overlapping side regionThe superparamagnetic limitRecording Step 1:Recording Step 2:Recording Step 3:

Multi-level Recording on a Patterned MediumPatterned Media by Toh-Ming LuNote 1: The tilt angle can be controlled via deposition conditionNote 2: The inter-layer separation should be sufficient to break the quantum-mechanical exchange couplingFIB-etched Patterned MediumNote: Each cell is ~50 x 50 nm2

Multi-level Recording on a Patterned Medium: WritingNote 2: The inter-layer separation should be sufficient to break the quantum-mechanical exchange couplingMicromagnetic Simulation Illustrating Two Cases of Interlayer Separation: a) < 1 nm and b) > 2 nmRecording Field ProfileM upM downe.a.

Multi-level Recording on a Patterned Medium: WritingH= -H1>Hc >H2H4>Hc >H51234512345123451234512345H3>Hc >H4H2>Hc >H3Recording Field Profiles in Individual Layers at a Given Current ValueHc

Multi-level Recording on a Patterned Medium: PlaybackMagnetic Charge Representation of the Playback Process1095Simulated Stray Field from a 3-D Medium at different levels of recording

MFM Images of Two Types of MediaEach cell is ~ 60 x 60 nm2

Note 2: The demagnetization field could be fairly large for some configuration. Special bit encoding should be considered to avoid the unfavorable bit configuration.Hdemag >> 4MsSNR LimitationsPatterned Media (ideally, fabrication technique limited)Electronic noise sources are 10 Ohm GMR Sensor and 0.2 nV/sqrt(Hz) preamp noise over a 500 MHz CTF bandwidth at 1 Gbit/secNote 1: Special encoding channels should be used to reduce BER

Soft UnderlayerThree-dimensional RecordingSchematic Diagrams of a 3-D Memory DeviceBiasing Conductor for Layer Identification during Writing2-D Recording/Reading Grid (similar to MRAM)

Magnetically-induced WritingNote: The current in the biasing conductor is continuously decreased from the maximum to zero to identify individual layers starting from the top to the bottomK-th layer is identified(K-1)-th layer is identified

Thermally-induced WritingSimulation by Roman Chomko(jointly with Seagate Research)

3-D ReadingActive layers: MRAM devices stacked togetherDifferent ImplementationsMagnetic Resonance FMCoCrPtTa alloyMagnetic Resonance FM

CoCrPtTa alloyElectron Image of Smart Nano-probe (made via FIB)Comparative MFM Images of Atomic-size Information obtained by the Conventional State-of-the-art MFM (left) and the FIU-developed Smart Nano-probe3-D Reading: Magnetic Resonance Force Microscopyrf-coil

3-D Reading: Magnetically-induced Reading*Note 1: Through the variation of the softness of the SUL, one can vary the sensitivity field of each cellSensitivity Field with a Free SUL (red) and Saturated SUL (black)According to the Reciprocity principle, the signal in each cell is given by ExpressionNote 2: Effective physical scanning in the vertical direction is produced via the variation of the softness of the SUL. Thus, each layer could be independently addressed*Provisional patent filed with US PTO on August 4th 2004

Recorded Pattern in Layer 6Parallel Set of Signals at Ibias = 0 (A turn)

Recorded Pattern in Layer 4Parallel Set of Signals at Ibias = 1.56 (A turn)

Recorded Pattern in Layer 2Parallel Set of Signals at Ibias = 5.85 (A turn)

Summary on 3-D Magnetic RecordingThe study of 3-D magnetic recording has been initiatedDuring the last year, the PIs have authored 8 peer-review papers on the underlying physics of magnetic and magneto-thermal recordingSpecific designs of 3-D magnetic devices have been proposedThe university is in the process of filing a patent on the proposed mechanism.CommitmentWithin two years, demonstrate an experimental prototype of a stable (for at least 50 years at room temperature) 3-D magnetic memory with at least ten recording layers with an effective areal density of at least 1 Terabit/in2 and a data rate faster than 2 Gbit/sec

Protein-based MemoryWhy Protein? Naturally occurring residues of proteins (Bacteriorhodopsin (bR) mutants) in the form of molecules with a diameter of less than 3 nm (more than 100 times smaller than polymeric material used to DVDs) demonstrate unprecedented thermal stability at room temperature (critical advantage over magnetic storage, correspond to areal densities of much beyond 10 Terabit/in2 Unprecedented recyclablity of protein medium: it can be rewritten more than 10 million times (more than 1000 times better than CD/DVD) The light-sensitive properties of proteins integrated with the modern semiconductor laser technology provide a relatively straightforward control of recording and retrieving information from the protein media. Much faster time response of protein media (as compared to magnetic media): the time response in the protein media is in the picosecond region (as compared to the nanosecond region in magnetic media) Economical Non-volatile

*R. R. Birge, Scientific American, 90-95, March 1995Schematics of a halobacterial cell and its functional devicesSalinos del Rio on Lanzarote IslandWild-life Bacteriorhodopsine (bR) produced by Halobacteria

Goal is to demonstrate the feasibility of recording/storing/retrieving information on/from photochromic proteins at areal densities of above 1 Terabit/in2 and data rates of above 10 Gigahertz. Approach (2-D Single Molecule Level instead of 3-D) is to take advantage of the 2-D stability of BR media to record on one surface at a single-molecule level or/and use a stack of layers to record in 3-D and take advantage of the most advanced nanoscale recording system so called heat-assisted magnetic recording (HAMR) based on the near-field optical recording transducerProtein-based MemoryProblems with Protein Media: Early proteins were unstable (Solved with discovery of bacteriorhodopsin) Polymers, on which protein structures are made, are less stable than proteins themselves It is not trivial to immobilize proteins in 3-D Holographic methods are not perfected for ultra-high densities (far from competing with magnetic)

Data Recording/Retrieval in Protein-Based StorageThermal Cycle with Two Stable States

Fig. Writing digital 1. Transition A B.Two photon absorption causes transition to intermediate state, which then relax to the second stable state B.Cascade two photon absorption.Note: Using two photon and other nonlinear processes makes possible remote writing digital information inside optical media volume. It is applicable for nonvolatile multi-layered optical memory.Recording Mechanism: Two photon processes

Earlier Proposed Protein Memory**R. R. Birge, Scientific American, 90-95, March 1995Parallel Data Access (page by page via positioning of the green light)Issues:Optics never could record high densities3-D media are not trivial to immobilize

All the above-described methods of recording/retrieving data are quite complicated and it is hard to see whether they will be implemented and if yes, when. In fact, so far no physical demonstration of ultra-high density recording has been made!

The PIs propose first, to use a bit-by-bit 2-D type of recording to demonstrate the feasibility of the protein-based storage (it is trivial to immobilize 2-D media);then, to apply one of the available parallel data recording/retrieving mechanism (e.g. holographic).To accomplish this goal, the PIs use the transducer design earlier developed for heat-assisted magnetic recording (HAMR)*. HAMR is the most advanced recording mechanism proposed so far. The PIs have pioneered one of the most efficient design of the transducer for HAMRThe Proposed Solution to Demonstrate the Feasibility of Protein Based Storage*T. McDaniel, W. Challener, Issues in heat-assisted perpendicular recording, IEEE Trans. Magn. 39 (4), 1972-9 (2003).

Air-bearing-surface (ABS) view of laser diode with a thin layer of Al with FIB-etched "C" shape apertureNovel Recording Transducer for Areal Densities Above 1 Terabit/in2Electron Image of FIB-fabricated Apertureless TransducerNote: Focused ion beam (FIB) is used to fabricate apertureless transducers (with aperture dimensions of less than 100 nm

Two-Dimensional Protein Media Easy to fabricate* Naturally stable Optical spectra of a gelatin-mixed BR film in two states, the ground state and one of the intermediate M states**The spectra were recorded with a Varian CARY 50 spectrophotometer.The decay absorption signal in the excited M-state measured at a wavelength of 410 nm*A gelatin-mixed bR film under study was fabricated by Lars LindvoldNote: Patented approach to immobilize proteins Into stable thin-film recording media (H. Arjomandi, V. Renugopalakrishnan)AFM Image of a 2-D Pattern with a 2.4-nm Period

Custom-made Near-field System built around Aurora-3 by DIExperimental setup to record and read information on/from proteinsSchematic DiagramNote: The modular structure of the system allows simultaneously using more than one (currently, up to four) sources (red to blue lasers, UV lamps) to conduct photons through a fiber to the sample in the near-field regime. In addition, as described below, the system will allow implementing diode lasers assembled right at the air bearing surfaces (ABS) of the recording probes attached to the SPMs cantilever.

Early Results: Reading Tracks from Photochromic BR Media* The signal is the absorbed power in the detector system in the reflection modeNear-field Optical Readback SignalNarrowest track is ~ 100 nm

1 Tbit/in210 Tbit/in250 Tbit/in2100 Gbit/in21. Perpendicular Recording2. Use smaller Grains&Deal with Write Field Problem (~10x gain)Heat Assisted Magnetic Recording (HAMR)E.g. high anisotropy 3 nm FePt grains3. Single Grain per Bit Recording combined with HAMR (~5x gain)Patterned Media4. 3-D Magnetic Recording5. Protein-based Memory (Single-Molecule Recording)Ultimate Recording Density > 50 Tbit/in2 conceivableSummary0. End to Longitudinal Recording