1. Sakhrat Khizroev - Center for Nanoscale Information Devices Next Generation Memory Devices Florida International University Miami, Florida, U.S.A. Center for Nanoscale Magnetic Devices Sakhrat Khizroev

2. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 2 Outline  Background  Perpendicular Magnetic Recording  Three-dimensional Magnetic Recording  Protein-based memory  Summary

3. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 3 Background Traditionally, Scaling Laws were followed to advance data storage technologies Scaling At 1 Gbit/in 2 information density, bit sizes are: 400 x 1600 nm 2 At 100 Gbit/in 2 : 40 x 160 nm 2 At 1 Tbit/in 2 : 13 x 52 nm 2

4. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 4 Scaling: Smaller Transducers and Media Flying Height 5 nm Head Smoke Particle Fingerprint Human Hair 75,000nm Media 10-100nm Disk Substrate At 1 Tbit/in 2 information density, Bit Sizes are: 13 x 52 nm 2

5. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 6 H  Probability of magnetization reversal due to thermal fluctuations: Thermally stable media: Relaxation time =  = 72 sec for K u V/kT=40  = 3.6x10 9 years for K u V/kT = 60 Media Stability

7. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 7 Superparamagnetism If a<a minimum, medium becomes thermally unstable leading to severe deterioration of recorded data over time. Approaches to avoid superparamagnetic instabilities: Decrease a minimum by increasing K U Increase a by decreasing the number of grains per bit Demagnetization fields in transitions shorten the relaxation time Perpendicular Recording* Patterned Media HAMR *S. Khizroev and D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

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

9. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 9 Nanoscale Device: Tbit/in 2 Recording Transducer* Longitudinal Perpendicular Bit Sizes: 13 x 52 nm 2 *S. Khizroev, D. Litvinov, “Physics of perpendicular recording: writing process,” Appl. Phys. Reviews – Focused Review, JAP 95 (9), 4521 (2004).

10. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 10 In perpendicular recording the write process effectively occurs in the gap (Write Field < 4  M S ) In longitudinal recording the write process is done with the fringing fields (Write Field < 2  M S ) Gap Versus Fringing Field Writing Higher areal density media requires higher write fields !!! *S. Khizroev and D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.

11. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 11 FIB to Trim Regular Transducers into Nanoscale Devices* FIB Etch to Define a NanoprobeFIB Deposition The most critical step is to make a probe with Nanoscale dimensions *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).

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

13. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 13 Longitudinal Transducer with a 30 nm Width Perpendicular Transducer with a 60 nm Width FIB-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).

14. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 14 Control of Gallium Diffusion* AFM MFM 3 x 10 5 Ions/cm 2 2 x 10 6 Ions/cm 2 Ion Dose NOTE: Although NO texture change is observed through AFM, substantial magnetic grain change is seen through MFM dose increase *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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 15 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 500 nm Side wall A Part of a Device made in the Industry before the process was implemented Same Device made with the process implemented Nanoscale FIB Process* *S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).

16. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 16 Dynamic Kerr Measurement of the Field from a Nanoscale Transducer* Characterization Kerr-Image Snap-Shots for a SPH Transducer (Near-field Kerr Microscopy) Glass Substrate Media Stack Microscope Writer *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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 17 Characterization Ion image of a FIB-fabricated and magnetically active 3-nm-long feature MFM image of recorded nanoscale magnetic "dots"

18. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 18 Perpendicular Recording with Bit Widths of less than 65 nm* 130 nm ~400 ktpi CoB/Pd multilayer CoCrPtTa alloy ~190 ktpi Current “state-of-the-art” longitudinal recording is <100ktpi 400 nm Writer Reader MFM Images of Nanoscale Size Information *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 23 rd 2002. The FIB-made transducer

19. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 19 Perpendicular Recording promises to defer the superparamagnetic limit to ~ 1 Terabit/in 2 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 nm 2 Three-dimensional Magnetic Recording

20. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 20 3-D Magnetic Recording The development of 3-D magnetic recording is divided into two phases: 1.Multi-level Recording: not optimally utilized 3-D space Note: Effective areal density increase is by a factor of Log 2 L (where L is the number of signal levels) 2.3-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: Each cell is 50 x 50 nm 2 Note: These are not active layers Lead Ph.D. Graduate Student: Yazan Hijazi, Sakhrat Khizroev

21. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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 Schematics of a Transducer Simulated Recording Field

22. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 23 Multi-level Recording on a Continuous Medium 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 1: Recording Step 2: Recording Step 3:

24. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 24 Multi-level Recording on a 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 FIB-etched Patterned Medium Note: Each cell is ~50 x 50 nm 2

25. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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) 2 nm Recording Field Profile M up M down e.a.

26. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 26 Multi-level Recording on a Patterned Medium: Writing H= -  H 1 >H c >H 2 H 4 >H c >H 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 H 3 >H c >H 4 H 2 >H c >H 3 Recording Field Profiles in Individual Layers at a Given Current Value HcHc

27. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 28 MFM Images of Two Types of Media Each cell is ~ 60 x 60 nm 2

29. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 29 Note 2: The demagnetization field could be fairly large for some configuration. Special bit encoding should be considered to avoid the unfavorable bit configuration. H demag >> 4  M s 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

30. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 30 Soft Underlayer 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)

31. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 31 Magnetically-induced Writing 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 K-th layer is identified (K-1)-th layer is identified

32. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 32 Thermally-induced Writing Simulation by Roman Chomko (jointly with Seagate Research)

33. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 33 3-D Reading  Active layers: MRAM devices stacked together Different Implementations  Magnetic Resonance FM CoCrPtTa alloy  Magnetic Resonance FM

34. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 34 CoCrPtTa alloy Electron 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-probe 3-D Reading: Magnetic Resonance Force Microscopy rf-coil

35. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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) According to the Reciprocity principle, the signal in each cell is given by Expression 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 *Provisional patent filed with US PTO on August 4 th 2004

36. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 36 Recorded Pattern in Layer 6 Parallel Set of Signals at I bias = 0 (A turn)

37. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 37 Recorded Pattern in Layer 4 Parallel Set of Signals at I bias = 1.56 (A turn)

38. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 38 Recorded Pattern in Layer 2 Parallel Set of Signals at I bias = 5.85 (A turn)

39. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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/in 2 and a data rate faster than 2 Gbit/sec

40. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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/in 2 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 41 *R. R. Birge, Scientific American, 90-95, March 1995 Schematics of a halobacterial cell and its functional devices Salinos del Rio on Lanzarote Island Wild-life Bacteriorhodopsine (bR) produced by Halobacteria

42. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 42 Goal is to demonstrate the feasibility of recording/storing/retrieving information on/from photochromic proteins at areal densities of above 1 Terabit/in 2 and data rates of above 10 Gigahertz. Approach (2-D Single Molecule Level instead of 3-D) is 1)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 2)take advantage of the most advanced nanoscale recording system – so called heat-assisted magnetic recording (HAMR) based on the near-field optical recording transducer Protein-based Memory 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)

43. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 43 Data Recording/Retrieval in Protein-Based Storage Thermal Cycle with Two Stable States

44. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 44 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. h 1 State A State B Intermediate 1 h 2 State A State B Intermediate 2 h 1 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

45. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 45 Earlier Proposed Protein Memory* *R. R. Birge, Scientific American, 90-95, March 1995 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

46. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 46 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 The 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).

47. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 47 Air-bearing-surface (ABS) view of laser diode with a thin layer of Al with FIB-etched "C" shape aperture Novel Recording Transducer for Areal Densities Above 1 Terabit/in 2 Electron Image of FIB-fabricated Apertureless Transducer Note: Focused ion beam (FIB) is used to fabricate “apertureless” transducers (with aperture dimensions of less than 100 nm << than the wavelength)* < 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 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* *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 Lindvold Note: 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

49. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 49 Custom-made Near-field System built around Aurora-3 by DI Experimental setup to record and read information on/from proteins 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. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 50 Early Results: Reading Tracks from Photochromic BR Media * The signal is the absorbed power in the detector system in the reflection mode Near-field Optical Readback Signal Narrowest track is ~ 100 nm

51. Sakhrat Khizroev - Center for Nanoscale Information Devices Page 51 1 Tbit/in 2 10 Tbit/in 2 50 Tbit/in 2 100 Gbit/in 2 1. Perpendicular Recording 2. Use smaller Grains&Deal with Write Field Problem (~10x gain) Heat Assisted Magnetic Recording (HAMR) E.g. high anisotropy 3 nm FePt grains 3. Single Grain per Bit Recording combined with HAMR (~5x gain) Patterned Media 4. 3-D Magnetic Recording 5. Protein-based Memory (Single-Molecule Recording) Ultimate Recording Density > 50 Tbit/in 2 conceivable Summary 0. End to Longitudinal Recording