09-30-2010 “Gate” Materials for Nonvolatile Electronics WIN Nonvolatile Electronics Kang L. Wang Raytheon Professor of Physical Sciences and Electronics NA & W Raytheon Professor of Physical Sciences and Electronics Device Research Laboratory (DRL) Directors FEN Western Institute of Nanoelectronics - WIN Center on Functional Engineered Nano Architectonics – FENA California NanoSystems Institute - CNSI California NanoSystems Institute CNSI University of California - Los Angeles (E-mail: [email protected]) 1
Transcript
09-30-2010
“Gate” Materials for Nonvolatile Electronics
WIN
Nonvolatile Electronics
Kang L. WangRaytheon Professor of Physical Sciences and Electronics
NA
& W Raytheon Professor of Physical Sciences and Electronics
Device Research Laboratory (DRL)Directors
FEN
Western Institute of Nanoelectronics - WINCenter on Functional Engineered Nano Architectonics – FENA
California NanoSystems Institute - CNSICalifornia NanoSystems Institute CNSIUniversity of California - Los Angeles
How much energy is needed to make an on or off switch?
Gate
Substrat
Source Drain
Nonvolatile
e Volatile!!
Dynamic energy: E=kTln(2)= 3x10-21 J
Nonvolatile
2WINStatic energy: Leakage due to tunneling
Advantages of non-Volatile Electronics
No Static dissipation No Booting! Bootingo oot g Instant on Computers mostly idle
Booting
Computers mostly idle (>98%)
GreenGreen
3WIN
OutlineNon-Volatile ElectronicsNon Volatile ElectronicsSpintronics – collective, nanomagnetism Gate oxide in spintronics: Gate controlledGate oxide in spintronics: Gate controlled
ferromagnetism SPIN FET: Gate controlled ferromagnetism with Al2O3
M O t i t t ll d f ti MgO to improve gate controlled ferromagnetism
Tunneling oxide in spintronics: spin injection and detection MgO growth on Ge Symmetry properties Spin injection structure and spin detection in Ge Spin injection structure and spin detection in Ge
Spin torque Transfer Memory Dielectrics for CMOS
4WIN
Dielectrics for CMOS Traditional gate oxide SiO2 and high k dielectric oxides Learning from tunneling
Nanomaterials for nonvolatile electronics
Low or no standby dissipation Low or no standby dissipation Low dynamics power dissipation Examples -- Enabling collective
spintronics – nanomagnetsNanomagnetic materials for Spin FETHigh speed, low energy memory – STTNano magnetic control by electric field: spin
wave –non-equilibrium case
Integrated with CMOS to form nonvolatile electronics
5WIN
Spintronics
Wh Low Power
Nonvolatile Logics
Why? Low power, variability & nonvolatilityNo current flow
Nonvolatile Logics Green (low power)
Collective effect MACRO - Relays
Quantum interactionexchange interaction
Room temperature Room temperature
Low variability Low quantum Low quantum fluctuations High yield and lower T ( 500C) i
Transition metal dopedTransition metal-dopedSemiconductors
(III Mn)-VEG
EGEF
(III,Mn)-VI Group IV diluted-magnetic semiconductors Integration to Si substrates
Well developed Si microelectronics
(III,Mn) V(Ga, Mn)-As(Ge, Mn)
EF
EG (III,Mn) VI(Zn,Mn)-Se(Ge,Mn)
Well developed Si microelectronics Add more functions or options to Si IC Si-based spintronics
Fundamental studies for spin in group IV materials
MM
9WIN
Fundamental studies for spin in group IV materials Nanostructures
BB
Major Milestones of FCFM in Mn(In/Ga)As,MnGe
In 2000, Ohno, Electric-field control of FM, Nature. In 2003, Chiba, Electrical manipulation of magnetization
reversal in a ferromagnetic semiconductor Sciencereversal in a ferromagnetic semiconductor, Science. In 2007, Our group, Electric field control magnetic phase
transition in nanostructured MnxGe1-x, APL.x 1 x, In 2008, Chiba, Magnetization vector manipulation by electric
fields , Nature.f In 2009, Ohno, Experimental probing of the interplay between
FM and localization in (Ga, Mn)As, Nature Physics. In 2010 Our group Electrical field controlled FM in MnGe QDsIn 2010, Our group, Electrical field controlled FM in MnGe QDs,
Nature Materials.
10WIN
Enabling NanostructuresThe use of nanostructures affording the
Better control of physics –
The use of nanostructures affording the following advantages:
MgOQD
wetting wetting
B Au
Improved carrier density control
Carrier mediated
wetting wetting
E1
Ground state for QDsGround state for wetting
Carrier mediated ferromagnetism through quantum confinements (Bohr orbital) P iti
E5
Si
E1*
orbital) Improved materials properties
for dissimilar or lattice h d l
Position x
mismatched materials – Strain accommodated &
misfit dislocations and other
11WIN
defects minimized
MOS like basic structure for FCFM
VgVgVgVgVg
MnGe QDsAuAuAuAuAu
Al2O3 40 nm
p Si ( 1018 cm-3)
Al2O3 40 nm
p Si ( 1018 cm-3)
Al2O3 40 nm
p Si ( 1018 cm-3)
Al2O3 40 nm
p Si ( 1018 cm-3)
Al2O3 40 nmAl2O3 40 nm
p Si ( 1018 cm-3)p Si ( 1018 cm-3)p Si ( 1018 cm-3)p Si ( 1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)p-Si (~1018 cm-3)
AuAuAuAuAu
12WIN
Choice of Oxides in Spintronics Devices
Al O Al2O3
Advantages: ALD process, simple and compatible Advantages: ALD process, simple and compatible with Si CMOS process
Disadvantages: Amorphous, no symmetry induced i filt i ff tspin filtering effect
M O ( ill l b t l t ) MgO (will elaborate later) Advantages:
• atomic sharp interface with Ge• atomic sharp interface with Ge• single crystalline by Epitaxy• symmetry induced spin filtering and efficient spin filtering
13WIN
Challenge: Epitaxial growth
MnGe DMS quantum dotsObjective: to Obtain High Curie Temperature DMS QDs
OutlineNon-Volatile ElectronicsNon Volatile ElectronicsSpintronics – collective, nanomagnetism Gate oxide in spintronics: Gate controlledGate oxide in spintronics: Gate controlled
ferromagnetism Gate controlled ferromagnetism with Al2O3
I d t t ll d f ti ith M O Improved gate controlled ferromagnetism with MgO
Tunneling oxide in spintronics: spin injection and detection Al2O3 ,MgO growth on Ge Symmetry properties Spin injection structure and spin detection in Ge Spin injection structure and spin detection in Ge
Spin torque Transfer Memory Oxide in CMOS
23WIN
Oxide in CMOS Traditional gate oxide SiO2 and high k dielectric oxides Learning from tunneling
Spin Injection and Detection Challengesg
Fermi level pinning of Ge surface Temperature dependent RA product Low spin injection efficiency
Our approaches Depin Fermi level using Al O or MgO Depin Fermi level using Al2O3 or MgO Use surface doping to optimize RA product Epitaxially grow high quality MgO as spin filterEpitaxially grow high quality MgO as spin filter
Fermi level depinning by
metalthin oxiden-Ge
metal
insertion of a thin oxide layer n-Ge
24WIN
Fermi Level Depinning Using Al2O3
• Before Al oxide insertion, the Fermi levels are closely pinned at the valence band, resulting a high Schottky barrier (~0.6 eV) for all metal/n-Ge contacts.
• After insertion of an Al oxide layer, the Schottky barrier heights decrease from ~0.6 eV to 0.39 eV, 0.23 eV and 0.18 eV for Ni, Co and Fe Schottkydiodes, respectively.
25WIN
• The reverse current of Co/n-Ge contact increases significantly due to the reduced Schottky barrier height.
Y. Zhou and et al. Appl. Phys. Lett. 93, 202105(2008).
Fermi level depinning of Ge surfacemetal
n-Ge
metalthin oxiden-Ge
metal
Fermi level depinning by insertion of a thin oxide layer
Ion implantation was performed to highly dope the Ge surface layer for tunneling transportlayer for tunneling transport.
The RA products are optimized for prospective spin injection.
27WIN Y. Zhou and et al. Appl. Phys. Lett. 94, 242104(2009).
p p p j
Epitaxial Growth of MgO on Ge
Why MgO?MgO enhances the spin injection efficiency due to the symmetry induced spin filtering.
Why epitaxy films?To achieve single crystalline structure and atomicallysmooth interface for spin injection.
28WIN
Symmetry filtering effect in Fe/MgO/Fe MTJ
y45°
y
x’y’y
x
Prerequisite for symmetry filtering:
Single crystalline structure –wavefunction theory can be appliedwavefunction theory can be applied.
45 degree in-plane rotation – leading to a much higher decay rate (filtering) for minority spin states
29WIN Ref: W. H. Butler and et al. PRB 63, 054416 (2001)
for minority spin states.
Single crystalline MgO grown on Ge
Fe[110](001)
MgO[100](001)
Ge[110](001) 2 nm
Fe
MgO
Single crystalline and atomicallysmooth MgO is epitaxially grownon Ge in UHV under optimized
ditiGe
condition.
The unique 45 degree rotationbetween MgO and Ge unit cellminimi es the lattice mismatch and
30WIN
minimizes the lattice mismatch andenhances spin filtering.
W. Han, Y. Zhou and et al. J. Crys. Growth. 312, 44(2009).
Fermi Level Depinning using MgO
M O (0 5 3 )Fe
Schottky barrier is significantly reduced by insertion of an ultrathin MgO between Fe and n Ge
n-GeMgO (0.5-3nm)
Ohmic contact
MgO between Fe and n-Ge.
MgO terminates the dangling bond at the Ge surface, leading to a depinned
31WIN
Ohmic contact
Y. Zhou and et al. Appl. Phys. Letts. 96, 102103 (2010)
Fermi level favoring electronic transport.
Ideal Structure for Spin Injection in Ge
Fe
High doping layer (2E19 cm-3, 15nm)MgO (2 nm)
Fe
Device layer (1E16 cm-3, 300 nm)
Transition layer (1E16 to 2E19 cm-3, 15nm)
Atlas simulation of spin injection structure based on Fe/MgO/n-Ge
Use epitaxy grown Ge device layer and highly doped layer to minimize defects and dopant diffusion caused by ion implantation and annealing
32WIN
annealing.
Use Epitaxy grown MgO and Fe to ensure high quality interface for spin injection.
OutlineNon-Volatile ElectronicsNon Volatile ElectronicsSpintronics – collective, nanomagnetism Gate oxide in spintronics: Gate controlledGate oxide in spintronics: Gate controlled
ferromagnetism Gate controlled ferromagnetism with Al2O3
I d t t ll d f ti ith M O Improved gate controlled ferromagnetism with MgO
Tunneling oxide in spintronics: spin injection and detection Al2O3 ,MgO growth on Ge Symmetry properties Spin injection structure and spin detection in Ge Spin injection structure and spin detection in Ge
Spin torque Transfer Memory Oxide in CMOS
33WIN3
Oxide in CMOS Traditional gate oxide SiO2 and high k dielectric oxides Learning from tunneling
Magnetic memory
A 10.8×10.8 cm card of core memory of 64x64 bits, as used in a CDC6600(ca 1965)
MRAM using Osted field
Too much power!
34WIN
(ca. 1965) Too much power!
Illustration of magnetization switching using spin transfer torque
Applications of nanoscience in:BiomedicineBiomedicineDevicesEnergy
W ld l di t fWorld-leading center for:Innovation & understandingEducationCommercialization
120 faculty (science, eng, medicine, health, art)
43WIN
y ( , g, , , )17,000 m2 adjacent to science, e ng, & medicine>$120M/y grants + strong Calif. & UC support
Developing and Applying World-Class ToolsNine core labs extend the state-of-the-art and make the tools of nanoscience available to the community
Advanced Light Microscopy (STED, multiphoton)Macro-Scale Optical Imaging Laboratoryp g g yNano and Pico Characterization (scanning probes)Electron Imaging Center for NanoMachinesMolecular Screening Shared ResourceIntegrated Systems Nanofabrication Cleanroom(includes bio suites)(includes bio suites)Integrated NanoMaterials Lab (MBE)Center for Quantum Research
