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Next Generation Memory Devices

Next Generation Memory Devices. Sakhrat Khizroev. Center for Nanoscale Magnetic Devices. Florida International University Miami, Florida, U.S.A. Outline. Background Perpendicular Magnetic Recording Three-dimensional Magnetic Recording Protein-based memory Summary. Background.

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Next Generation Memory Devices

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  1. Next GenerationMemoryDevices Sakhrat Khizroev Center for Nanoscale Magnetic Devices Florida International University Miami, Florida, U.S.A.

  2. Outline • Background • Perpendicular Magnetic Recording • Three-dimensional Magnetic Recording • Protein-based memory • Summary

  3. Background Traditionally, Scaling Laws were followed to advance data storage technologies Scaling At 1 Gbit/in2 information density, bit sizes are: 400 x 1600 nm2 At 100 Gbit/in2 : 40 x 160 nm2 At 1 Tbit/in2 : 13 x 52 nm2

  4. Scaling: Smaller Transducers and Media Human Hair 75,000nm Smoke Particle Head Fingerprint Flying Height 5 nm Media 10-100nm Disk Substrate At 1 Tbit/in2 information density, Bit Sizes are: 13 x 52 nm2

  5. Superparamagnetic Limit Magnetic grains Bit transition SNR ~ log(N), N - number of grains per bit While scaling, need to preserve number of grains per bit to preserve SNR Grain size is reduced for higher areal densities:

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

  7. Superparamagnetism If a<aminimum, medium becomes thermally unstable leading to severe deterioration of recorded data over time. Approaches to avoid superparamagnetic instabilities: • Decrease aminimum by increasing KU • Increase a by decreasing the number of grains per bit • Demagnetization fields in transitions shorten the relaxation time HAMR Patterned Media Perpendicular Recording* *S. Khizroevand D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

  8. Perpendicular Recording*: Well-defined Anisotropy Magnetic grains In a typical longitudinal recording layer the magnetic anisotropy axes of individual grains are randomly oriented in the plane of the film 2D random medium In perpendicular recording layer the anisotropy axis is relatively well aligned (<2-4 degrees) perpendicular to the plane of the film oriented medium Substantially relaxes the requirements for write field gradients Can use thicker recording layer - better thermal stability !!! (increased V in KUV/kBT ratio) *S. Khizroevand D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

  9. Nanoscale Device: Tbit/in2 Recording Transducer* Perpendicular Longitudinal Bit Sizes: 13 x 52 nm2 *S. Khizroev, D. Litvinov, “Physics of perpendicular recording: writing process,” Appl. Phys. Reviews – Focused Review, JAP95 (9), 4521 (2004).

  10. Gap Versus Fringing Field Writing Higher areal density media requires higher write fields !!! 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) *S. Khizroevand D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

  11. FIB to Trim Regular Transducers into Nanoscale Devices* The most critical step is to make a probe with Nanoscale dimensions FIB Etch to Define a Nanoprobe FIB Deposition *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology14, R7-15 (2004).

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

  13. FIB-fabricated Nanoscale Transducers* Longitudinal Transducer with a 30 nm Width Perpendicular Transducer with a 60 nm Width Note: It takes ~ 10 minutes to make one such device in the University environment *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology14, R7-15 (2004).

  14. Control of Gallium Diffusion* Ion Dose AFM MFM 2 x 106 Ions/cm2 dose increase 3 x 105 Ions/cm2 NOTE: Although NO texture change is observed through AFM, substantial magnetic grain change is seen through MFM *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).

  15. Nanoscale FIB Process* The process how to make Nano-precision patterns with FIB was shared with a few companies and successfully implemented by: Carnegie Mellon University, IBM, Seagate, and others A Part of a Device made in the Industry before the process was implemented Same Device made with the process implemented Side wall 500 nm 500 nm *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology14, R7-15 (2004).

  16. Writer Media Stack Glass Substrate Microscope Characterization Dynamic Kerr Measurement of the Field from a Nanoscale Transducer* Kerr-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).

  17. Characterization Ion image of a FIB-fabricated and magnetically active 3-nm-long feature MFM image of recorded nanoscale magnetic "dots"

  18. Perpendicular Recording with Bit Widths of less than 65 nm* Writer Reader MFM Images of Nanoscale Size Information ~190 ktpi CoCrPtTa alloy 400 nm CoB/Pd multilayer ~400 ktpi 130 nm The FIB-made transducer Current “state-of-the-art” longitudinal recording is <100ktpi *S. Khizroev, D. A. Thompson, M. H. Kryder, and D. Litvinov, Appl. Phys. Lett. 81 (12), 2256 (2002); Editor's choice for the Virtual Journal of Nanoscale Science & Technology, Sep 23rd 2002.

  19. Three-dimensional Magnetic Recording • Perpendicular Recording promises to defer the superparamagnetic limit to ~ 1 Terabit/in2 • Heat-Assisted and Patterned Media are still 2-D limited and relatively slow It is expected that Moore’s law will inevitably reach its limit between 2010 and 2020  Time to stack multiple active layers on top of each other 3-D Magnetic Recording is a data storage form of 3-D integration Conventional and 3-D Recording Media Note: Each cell is 50 x 50 nm2

  20. 3-D Magnetic Recording Lead Ph.D. Graduate Student: Yazan Hijazi, Sakhrat Khizroev • The 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 addressed • Note: Effective areal density increase is by a factor of N (where N is the number of recording layers) Note: These are not active layers Note: Each cell is 50 x 50 nm2

  21. Recording Head The current in the single pole head is varied to vary the recording field Each recording is performed via two pulses: 1) a cell is saturated and 2) the information is recorded Simulated Recording Field Schematics of a Transducer

  22. Playback Head The playback head is designed to preferably read the vertical field component which is dominant in this case Stray Field from 3D Medium Differential Reader Configuration Electronic Images of FIB-fabricated Transducer

  23. Multi-level Recording on a Continuous Medium Recording Step 2: Recording Step 1: • Major 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 region • The superparamagnetic limit Recording Step 3:

  24. Multi-level Recording on a Patterned Medium FIB-etched Patterned Medium Patterned Media by Toh-Ming Lu Note 1: The tilt angle can be controlled via deposition condition Note 2: The inter-layer separation should be sufficient to break the quantum-mechanical “exchange” coupling Note: Each cell is ~50 x 50 nm2

  25. Multi-level Recording on a Patterned Medium: Writing Note 2: The inter-layer separation should be sufficient to break the quantum-mechanical “exchange” coupling Micromagnetic Simulation Illustrating Two Cases of Interlayer Separation: a) < 1 nm and b) > 2 nm e.a. M up M down Recording Field Profile

  26. Multi-level Recording on a Patterned Medium: Writing H= - H1>Hc >H2 Recording Field Profiles in Individual Layers at a Given Current Value 1 1 2 2 3 3 4 4 Hc 5 5 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 H4>Hc >H5 H3>Hc >H4 H2>Hc >H3

  27. Multi-level Recording on a Patterned Medium: Playback Magnetic “Charge” Representation of the Playback Process “10” “9” “5” Simulated Stray Field from a 3-D Medium at different levels of recording

  28. MFM Images of Two Types of Media Each cell is ~ 60 x 60 nm2

  29. SNR Limitations • Patterned 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/sec Note 1: Special encoding channels should be used to reduce BER 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 >> 4Ms

  30. Three-dimensional Recording Schematic Diagrams of a 3-D Memory Device Biasing Conductor for Layer Identification during Writing 2-D Recording/Reading Grid (similar to MRAM) Soft Underlayer

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

  32. Thermally-induced Writing (jointly with Seagate Research) Simulation by Roman Chomko

  33. 3-D Reading Different Implementations • Active layers: MRAM devices stacked together • Magnetic Resonance FM • Magnetic Resonance FM CoCrPtTa alloy

  34. 3-D Reading: Magnetic Resonance Force Microscopy Comparative MFM Images of Atomic-size Information obtained by the Conventional State-of-the-art MFM (left) and the FIU-developed “Smart” Nano-probe rf-coil CoCrPtTa alloy Electron Image of “Smart” Nano-probe(made via FIB)

  35. 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 cell Sensitivity Field with a “Free” SUL (red) and “Saturated” SUL (black) Note 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 According to the Reciprocity principle, the signal in each cell is given by Expression *Provisional patent filed with US PTO on August 4th 2004

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

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

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

  39. Summary on 3-D Magnetic Recording • The study of 3-D magnetic recording has been initiated • During the last year, the PIs have authored 8 peer-review papers on the underlying physics of magnetic and magneto-thermal recording • Specific designs of 3-D magnetic devices have been proposed • The university is in the process of filing a patent on the proposed mechanism. Commitment Within 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

  40. Protein-based Memory • Why 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

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

  42. Protein-based Memory 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. • Problems 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) • 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 transducer

  43. Data Recording/Retrieval in Protein-Based Storage Thermal Cycle with Two Stable States

  44. Intermediate 2 Intermediate 1 h2 h2 h1 h1 State A State B State A State B Recording Mechanism: Two photon processes 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.

  45. Earlier Proposed Protein Memory* Parallel Data Access (page by page via positioning of the green light) Issues: • Optics never could record high densities • 3-D media are not trivial to immobilize *R. R. Birge, Scientific American, 90-95, March 1995

  46. The Proposed Solution to Demonstrate the Feasibility of Protein Based Storage • 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 HAMR *T. McDaniel, W. Challener, “Issues in heat-assisted perpendicular recording,” IEEE Trans. Magn.39 (4), 1972-9 (2003).

  47. Novel Recording Transducer for Areal Densities Above 1 Terabit/in2 Note: Focused ion beam (FIB) is used to fabricate “apertureless” transducers (with aperture dimensions of less than 100 nm << than the wavelength)* Electron Image of FIB-fabricated Apertureless Transducer Air-bearing-surface (ABS) view of laser diode with a thin layer of Al with FIB-etched "C" shape aperture < 90 nm In-house made *F. Chen, A. Itagi, J. A. Bain, D. D. Stancil, and T. E. Schlesinger, “Imaging of optical field confinement in ridge waveguides fabricated on very-small-aperture laser,” Appl. Phys. Lett. 83 (16), 3245 (2003).

  48. 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* AFM Image of a 2-D Pattern with a 2.4-nm Period The decay absorption signal in the excited M-state measured at a wavelength of 410 nm Note: Patented approach to immobilize proteins Into stable thin-film recording media (H. Arjomandi, V. Renugopalakrishnan) *A gelatin-mixed bR film under study was fabricated by Lars Lindvold *The spectra were recorded with a Varian CARY 50 spectrophotometer.

  49. Experimental setup to record and read information on/from proteins Custom-made Near-field System built around Aurora-3 by DI Schematic Diagram Note: 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 SPM’s cantilever.

  50. Early Results: Reading Tracks from Photochromic BR Media Near-field Optical Readback Signal Narrowest track is ~ 100 nm * The signal is the absorbed power in the detector system in the reflection mode

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