Spin-torque devices for Information-CommunicationTechnology Alina Deac Seite 1 Prof. Peter Mustermann Institut xxxxx www.hzdr.de
Evolution of mobile ICT devices Principal trends: 1. Constant miniaturization for increased portability; 2. Exponential increase in the volume of data stored and transmitted; 3. Reduced power consumption for extended autonomy and Green-ICT applications. Page 2
Evolution of mobile ICT devices Principal trends: 1. Constant miniaturization for increased portability; 2. Exponential increase in the volume of data stored and transmitted; 3. Reduced power consumption for extended autonomy and Green-ICT applications. 1956 2013 New physics + Technological progress IBM RAMAC 305: 5 MB Toshiba Canvio Basic 3.0: 2 TB, 190 $ Page 3
Evolution of mobile ICT devices Principal trends: 1. Constant miniaturization for increased portability; 2. Exponential increase in the volume of data stored and transmitted; 3. Reduced power consumption for extended autonomy and Green-ICT applications. DynaTAC prototype, 1973 Iphone 6 New physics + Technological progress Page 4
Goal: Demonstrate the viability of spin-torque devices as tunable oscillators for wireless applications in the sub-thz and THz range. Theory/new materials New physics Integration Page 5
Applications: Mobile communication devices: > 35% emails opened on phones today. Radar and security appliations. Anti-collision car systems. Wireless internet in densely populated/disaster-prone areas. Remote hospitals. Immersive audio-video entertainment systems Technology for wireless devices > 70 GHz = priority 1/40 for emerging technologies under EU FET-PROACTIVE initiative (06/2014). Page 6
Background / Intro: Spin-polarized currents Electrical current crossing a ferromagnetic metal can gain a spin polarization. Page 7
Background / Intro: Giant Magneto-Resistance (GMR) Page 8
Background / Intro: Giant Magneto-Resistance (GMR) Page 9
Background / Intro: Giant Magneto-Resistance (GMR) R P rr 2 RAP RP r R GMR R AP r R R 2 P The resistance of the multilayer depends on the magnetic configuration : GMR (Fert, Gruenberg, Nobel Prize 2007). Page 10
State-of-the-art: Spin-Momentum Transfer (SMT) ~1nm Polarizing layer Polarizing layer Free layer Free layer Conduction electrons Angular momentum transfer from the spin current to the magnetization Torque SMT: The magnetic configuration can be manipulated under electrical bias (Slonczewski, Berger 1996). Page 11
State-of-the-art: Spin-Momentum Transfer (SMT) SMT: The magnetic configuration can be manipulated under electrical bias (Slonczewski, Berger 1996). Angular momentum transfer from the spin current to the magnetization Torque Switching for non-volatile storage devices; Precession for tuneable wireless communication. Page 12
Resistance Switching: SMT-RAM (2D storage) AP "1" 0" free P polarizer ON ON Excellent write performance (sub-ns write time, perfect write selectivity). High TMR (>200%), stable up to 400 C (60 min). Unlimited endurance (>10 16 cycles). No leakage currents. Scalability well below 10nm, write power ~ lateral size. Up to 6x reduction in die size/megabyte compared to SRAM in microprocessors (cf Avalanche Technology).. Page 13 Current
Switching: Racetrack memory (3D storage) SMT in non-homogeneous structures: current-induced domain-wall motion. (Parkin, Science 2008) Page 14
Precession: Tuneable wireless communication Output power ~ 1 μw, increases as device size is reduced. f ~ H k (1-10 GHz for Co, Fe, Ni ), Q factor ~ 100-1000. Tuneabiliy: > 10% * f. Power efficiency: 10-2. Page 15 Deac, Nature Phys. 2008
Goal: Demonstrate the viability of spin-torque devices as tunable oscillators for wireless applications in the sub-thz and THz range. Page 16
Goal (materials): To this end we will explore: new materials (MPI-cpfs, MPI-Halle); identified through new theoretical calculations (MPI-cpfs); and investigated using unique facilities and expertise (HZDR, TUD). Page 17
Magnetisation (MA/m) Preliminary results: Mn 3 Ga unpatterned films freq / THz 0.4 0.3 0.2 0.1 0.0-0.1-0.2-0.3 IP scan (VSM) Lin. fit OOP scan 4.38 T S07 MnGa 4.45 T -0.4-15 -10-5 0 5 10 15 Applied Field (T) 0.144 0.142 0.140 0.138 0.136 Sample: SO7 MnGa Field at 30deg out of plane (60deg to normal) 6 7 8 9 10 11 12 13 H (koe) f ~ H k : SMT oscillators based on high anisotropy perpendicular anisotropy materials can bridge the THz gap for wireless communication. Page 18
Goal (devices): Integrate new materials into singledomain/ domain wall (networks of) SMT oscillators (MPI-cpfs, MPI- Halle, HZDR). Page 19
Goal (devices): Integrate new materials into singledomain/ domain wall (networks of) SMT oscillators (MPI-cpfs, MPI- Halle, HZDR). Integrate/analyze/optimize devices in realistic (wireless) circuits (TUD, HZDR).. Page 20
Goal (devices): Integrate new materials into singledomain/ domain wall (networks of) SMT oscillators (MPI-cpfs, MPI- Halle, HZDR). Integrate/analyze/optimize devices in realistic (wireless) circuits (TUD, HZDR). Path G. Explore alternative fabrication methods: ALD for cylindrical wires, ion irradiation. (IFW, HZDR) Paths A and B. Page 21
Other applications for SMT devices Write heads for hard-drives; Read heads for hard-drives; Logic devices, memristors, negative resistors, field sensors, voltage amplifiers, random number generators... Page 22
Background / Intro: Spin-polarized currents Electronic structure of Co : exchange splitting Spin up d sub-band completely filled. d states at Fermi level contain only spin down electrons scattering mostly affects spin down electrons; high resistivity spin up electrons: low resistivity, carry most of electrical current Electrical current crossing a ferromagnetic metal can gain a spin polarization. Page 23