Magnetic Spin Devices: 7 Years From Lab To Product. Jim Daughton, NVE Corporation. Symposium X, MRS 2004 Fall Meeting

Transcription

1 Magnetic Spin Devices: 7 Years From Lab To Product Jim Daughton, NVE Corporation Symposium X, MRS 2004 Fall Meeting Boston, MA December 1, 2004

2 Outline of Presentation Early Discoveries to 1995 Resulting Products Potential Products New Discoveries Future Products

3 Giant Magnetoresistance (1988) Simultaneous Discovery Fert(France) Grunberg (Germany) Multi-Layer Devices Ferromagnetic Materials Previous Magnetoresistance Materials Anisotropic Magnetoresistance ~ 2% Magnetoresistance R.T. Thin Films Current Direction Much Higher Magnetoresistance Observed

4 NVE GMR Multilayer Cross-Section Magnetic Layers AF Coupled Antiparallel - High Resistance Magnetic Field Overcomes Coupling Parallel - Low Resistance

5 Typical Characteristic resistance (kohm) applied field (Oe)

6 New Outlook For Magnetoresistance Conduction Electrons In FM s - Polarized Same Direction - Spin Up Opposite Direction to M - Spin Down Spin Up Electrons - A Longer MFP Spin Down Electrons - Shorter MFP Conduction Between Ferromagnetic Bodies Depends On How They Are Magnetized.

7 Spin Valve (1990) I High Coercivity FM Layer Copper Low Coercivity FM Layer I Antiparallel M s - Higher Resistance Parallel M s - Lower Resistance Magnetoresistance ~ 6% Initially Easy to Switch Soft Layer

8 Pinning With An Anti-Ferromagnet Anti-Ferromagnet Coupling Interface Substrate Ferromagnet Cool To Below Neel Temperature In A Field Ferromagnet Can Be Pinned To High Fields

9 Synthetic Antiferromagnet (SAF) Ferromagnet 6-10 A Ruthenium Ferromagnet Thin Inner Layer of Certain Materials (Ru) Very High Antiparallel Coupling (~2500 Oe) Pin One FM Layer - Really Pinned M s

10 Tunneling Magnetoresistance (1995) Magnetic Film Conductor Magnetic Film Lower Resistance Parallel Magnetizations Electron Motion Magnetic Film Insulator Magnetic Film Higher Tunneling Current Magnetic Film Conductor Magnetic Film Anti-Parallel Magnetizations Magnetic Film Insulator Magnetic Film Higher Resistance Lower Tunneling Current Practical Devices - Moodera, Miyizaki Much Higher Magneto-Resistance

11 GMR Bridge Sensor (Two Shown) Flux Concentrators GMR Resistors (In Gap) Shielded Resistors Wire Bonding Pads

12 GMR Read Heads (1996) Most Commercial Heads - Tsang et al (IBM,1994) Spin Valves - Pinned and Soft Layer Pinned Layer Magnetization Across Stripe Senses Vertical Fields New Additions - Pinned SAF and NOL

13 GMR Isolators (1998) Spin Valve Sensor Used For Ground Isolation

14 MRAM Concept Magnetic Hysteresis For Data Storage Material Properties - Anisotropy, Coercivity Shape Magnetoresistance of Storage Element - Readout Magnetic Elements on Integrated Circuit Advantages Doesn t Wear Out With Writing (Unlike Flash) Nonvolatile (Unlike SRAM or DRAM) Writes Fast (Unlike Flash)

15 GMR MRAM Pseudo-Spin Valve

16 Motorola Figure TMR MRAM

17 MRAM Products (2004?) Many Developers - Two Near Products Motorola (Freescale) Samples 2003 Limited Production Y/E 2004 or Mbit Capacity Cypress Semiconductor Samples - Early K bit Capacity

18 MRAM Scaling Challenge Road Map Projections Year Lithography (µm) Cell Size (µm 2 ) Capacity (bits) 1G 2G 4G 8G Stability Requires Es/kT >~50:1 Small Volume High Energy Density Write Currents Get Big (Conventional Designs) Transistors Are Big (~2 X 5mA) Heating in Narrow Conductors

19 Still Higher TMR Over 200% Challenges Understanding of TMR 2P 1 P 2 /1 - P 1 P 2 Parkin et. al., Nature (2004) Believed P 1, P 2 Understood Obviously Overconfident Large On-Off Ratios Possible!!

20 Spin Momentum Transfer (SMT) 70 nm free layer fixed layer Cu Cu Py (2 nm) Cu (6 nm) Py (20 nm) 130 nm 5.5 dv/di [Ohm] 5.3 dv/di [Ohm] Magnetic Field [G] Current [ma] Bob Buhrman, Dan Ralph, et.al. Cornell

21 Spins in Semiconductors (SPINS) Ferromagnetic Semiconductors Light-Induced Spin LED Sensing Ferromagnetic Injection

22 Thermally Assisted MRAM Chip Operating Temperature Required Thermal Rise Write

23 Two Methods For T-MRAMT

24 Possible Implementation

25 SMT Written MRAM 70 nm free layer fixed layer Cu Cu Py (2 nm) Cu (6 nm) Py (20 nm) 130 nm 5.5 dv/di [Ohm] 5.3 dv/di [Ohm] Magnetic Field [G] Current [ma] Bob Buhrman, Dan Ralph, et.al. Cornell

26 Spin Waves - Spin Transfer Oscillator Absorbed angular momentum: Torque Active layer (thin): Free Polarizing layer (thick): Fixed point contact W. H. Rippard et al PRL 92, (2004) precessional excitation H e - 2r radiating spin-waves Amplitude (nv/hz 1/2 ) Review of metal based spintronics: Stephen Russek ma 5.5 ma 7.5 ma 4.5 ma 8.5 ma 4.0 ma Frequency (GHz)

27 Future Products High Density MRAM- Will Scale Thermally Assisted Writing Spin Momentum Transfer Magnetic Logic - High On/Off Ratio TMR SPINS Program (Spins In Semiconductors) Semiconductor/Light Spin Transfer Oscillator Magnetic Transistor- Storage