Dr. Jim Hwang presents an overview of his program - GHz-THz Electronics - at the AFOSR 2012 Spring Review.

1. GHz-THz Electronics
08 MAR 2012
Jim Hwang
Program Manager
AFOSR/RSE
Integrity  Service  Excellence Air Force Research Laboratory
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2. 2012 AFOSR SPRING REVIEW
NAME: Jim Hwang
BRIEF DESCRIPTION OF PORTFOLIO: GHz-THz Electronics
LIST SUB-AREAS IN PORTFOLIO:
I. THz Electronics – Material and device breakthroughs for transistors based on conventional
semiconductors (e.g., group IV elements or group III-V compounds with covalent bonds) to
operate at THz frequencies with adequate power. Challenges exist mainly in perfecting
crystalline structure and interfaces.
II. Novel GHz Electronics – Material and device breakthroughs for transistors based on novel
semiconductors (e.g., transition-metal oxides with ionic bonds) to operate at GHz
frequencies with high power. Challenges exist mainly in controlling purity and stoichiometry,
as well as in understanding doping/transport.
III. Reconfigurable Electronics – Material and device breakthroughs for meta-materials,
artificial dielectrics, ferrites, multi-ferroics, nano-magnetics, and micro/nano
electromechanical systems to perform multiple electronic, magnetic and optical functions.
Challenges exist mainly in understanding the interaction between electromagnetic waves,
electrons, plasmons and phonons on nanometer scale.
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3. I. THz Electronics
• Sub-millimeter-wave radar & imaging
• Space situation awareness
• Chemical/biological/nuclear sensing
• Ultra-wideband communications
X’tal
Reliability • Ultra-high-speed on-board and
AFOSR front-end data processing
DARPA
ONR III-N THz
ONR DEFINE
DARPA
(Power)
Intel
IBM
THz
Cutoff Frequency
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4. Intel’s High-k FinFETs
Development
Production
Gate
S Stack
Q k 0
Drain C 
Source e
V d
Channel
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5. Challenges for THz Electronics
•Highly strained
growth
•Single-phase
ternary
•P doping
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6. Covalent Semiconductors
Covalent
Semiconductors
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7. InAlN Molecular Beam Epitaxy
Jim Speck, UC Santa Barbara
Cross-sectional transmission electron Scanning transmission electron
X-ray diffraction confirms lattice match
microscopy reveals columnar structure microscopy shows nano-network
17% In mole fract.
140nm thickness
GaN
peak
•First extensive study of phase
separation in nitrides
•Nano-network may be useful for
thermoelectrics
•Homogeneous InAlN grown by
NH3 MBE and MOCVD perhaps by
suppressing In ad-layer at higher
growth temperatures
Atomic probe confirms
composition variation
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8. P-Doped InGaN
Alan Doolittle, Georgia Tech
Objective: P-type GaN or InGaN for HBT
Approach: Optimize MBE temperature and flux to prevent surface
segregation/decomposition & to provide optimum Mg substitutional sites
Results: Breakthrough in single-phase, high-quality InGaN doped with GaN
1020/cm3 Mg and >50% temperature-independent activation
Plan: Mitigate electrical leakage via metal-decorated dislocations
GaN
In0.2Ga0.8N
GaN
GaN
In0.4Ga0.6N
Constant resistivity when GaN
GaN:Mg doped 1019/cm3
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9. Hot Electrons/Phonons in GaN
Hadis Morkoc, Virginia Commonwealth
Objective: Optimize electron density
Resonance
Approach: Understand interaction of hot
Plasmon
electrons and phonons
Result: Explained limits of many GaN devices
Plan: Dual-well channel
Power Supply
2700K Electrons
Optimum electron
2400K concentration for I ~ nv
Acoustic
Velocity
Peak
optical plasmon resonance phonons
phonons and optical-acoustic
phonon decay
300K heat sink
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10. Limit of AlN/GaN HEMTs
Grace Xing & Debdeep Jena, Notre Dame
Speed (GHz)
Objective: THz AlN/GaN HEMTs
600
Approach: Outlined below
400
Results: 370GHz cutoff frequency
HRL
MIT
Plan: Verify/improve phonon-
200 NiCT limited velocity model
Notre Dame
Year
2007 ‘09 ‘10 ‘11 ‘12 Regrown contact with Rs<0.1Ω-mm
Reduce
Control gate length
surface
states
Increase 2DEG mobility
Add AlN back barrier
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11. II. Novel GHz Electronics
Breakdown,
Power
Nano-Oxide X’tal
Reliability
AFOSR AFOSR
MESO ZnO MOSFET
DARPA DARPA
Extreme E ONR III-N THz
ONR DEFINE
ONR
Coupled Φ
ONR DARPA
Interact TI Intel
IBM
ARO
Rad-Hard E
DTRA
DMR
NSF
Cutoff Frequency
Thin-Film E
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12. Ionic vs. Covalent Semiconductors
Covalent
• Transparent Electronics: ZnO, MgO, InGa3Zn5O5 Semiconductors
• Heterojunctions: MgZnO/ZnO, LaAlO3/SrTiO3
• Multiferroics: BiFeO3, EuO,
• Metal-Insulator Transition: VO2, SmNiO3, NdNiO3,
• Topological Insulators: Bi2Se3, Bi2Te3, Bi1-xSex,
• Other Chalcogenides: sulfides, selenides, tellurides
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13. Challenges for THz Electronics
•Highly strained
growth
•Single-phase
ternary
•P doping
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14. Merits of Ionic Semiconductors
• Less demanding on crystalline perfectness Challenges
• Deposition on almost any substrate at low temp. •Composition and
• Radiation hard, fault tolerant, self healing
• High electron concentration with correlated transport purity control
Mobility
• Metal-insulator transition with high on-off ratio •Transport not well
• Wide bandgap for high power and transparency
• Topological effects understood
• SWAP-C and conforming
Covalent Semiconductor
Ionic Covalent
Ionicity
Ionic Semiconductor
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15. Transport in ZnO
Dave Look, Wright State
•[VZn ] = 1.7x1020
Pulse Laser cm-3 gives
32 Deposition E(formation) =
in Ar 0.2 eV; provides
accurate check
30
Mobility  (cm /V s)
on theory (DFT)
µ (ND, NA, m*, T) •Reduced [VZn ]
2
Fitting parameters: m* with Zn anneals:
28 21 -3 0.30 got  = 1.4x10-4
ND = 1.45 x 10 cm SIMS
20 -3
-cm, 3rd best in
NA = 1.71 x 10 cm Positron 0.34 world
26 m* = 0.34m0 Kane model •Future: create
0.40 GaZn donors by
filling VZn with Ga
24 •Future: apply
0 100 200 300 methods to other
TMOs
T (K)
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16. ZnO Thin-Film Transistors
Burhan Bayraktaroglu, AFRL/RYDD
Objective: Exploit unique electronic PLD Grain
properties of nanocrystalline ZnO films Boundaries
Approach:
• Theoretical doping & mobility models
• Pulsed laser deposition (PLD)
• Ga doping in Ar at low temperatures
Nanocrystalline
World’s 1st microwave thin-film transistor ZnO
Plan
Record Performance
•Room-temp.
150°C deposition
deposition
110 cm2/V.s electron mobility
•High-k gate
875mA/mm current density
insulator
9.5W/mm dc power density
•MgZnO/ZnO
1012 on/off ratio
hetero-
60mV/dec sub-threshold slope
junction
10 GHz cut-off frequency
LG=1.2m
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17. Correlated Oxide Field-Effect Devices
Shriram Ramanathan, Harvard
Objective: Fundamental understanding of field-effect MBE
switches utilizing ultra-fast (ps) reversible metal- Estimated
power-delay SmNiO3
insulator (Mott) transition in correlated oxides
Approach: Fabricate field-effect transistors with oxide
channels and investigate device characteristics product
Result: High-quality SmNiO3 grown by molecular- VO2 Mott FET
beam epitaxy on LaAlO3 for room-temperature
transition vs. Si MOSFET
Plan: Electronic transport measurement on thin-film
LaAlO3
hetero-junctions of different oxides
Temperature (°C)
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18. III. Reconfigurable Electronics
•Multiple electronic, magnetic and optical functions for UAV/MAV
•Meta-materials, artificial dielectrics, ferrites, multi-ferroics, nano-magnetics, MEMS/NEMS
Challenges: Understand
interaction between
electromagnetic waves,
electrons, plasmons and
phonons on nm scale
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19. EuO-Based Multiferroics
Darrell Schlom, Cornell
1
Normalized Magnetization (a.u.)
Objective: Enhance and
Ferromagnetic
exploit exceptional
5% Gd-doped
spintronic, optical, and
Paramagnetic
magnetic properties of 0.5
EuO, including highest
5% Lu-doped
∆R/R of any metal-insulator
transition, greatest spin- 5% La-doped
= 0.6eV
splitting of any
semiconductor, and 2nd 0
20 40 60 80 100 120 140
highest of spin Temperature (K)
polarization.
Approach: Reduce defects
in EuO films to enable Insulator
Andreev reflection of
controlled doping. Metal
>96% spin-polarized
Combine strain and doping
carriers from EuO to Nb
to boost Curie temperature.
Results: Demonstrated
controlled rare-earth
doping of EuO.
Plan: Apply misfit strain to
boost Curie temperature
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20. Topological Insulators
Yoichi Ando, Osaka U.
Phenomena:
• Insulating bulk with metallic surface
• Massless Dirac fermions 
high-mobility transistor
• Dissipationless spin current 
Low-loss spintronics
Objectives:
• To explore novel physics
• To minimize bulk current Unexpected
• To discover better TI materials mass
• To detect surface spin currents acquisition of
Approaches: Dirac fermions
• Explore ternary chalcogenides
• Fabricate TI-ferromagnet devices
on TlBi(S,Se)2
• Precise transport measurements
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21. Collaboration
• AFOSR
• Kitt Reinhardt – Eletro-thermal/thermo-electric effects
• Gernot Pomrenke – THz optics, microwave photonics, reconfigurable electronics
• Harold Weinstock – Nanoscale oxides, spintronics
• Seng Hong (AOARD) – Osaka U.
• Scott Dudley (EOARD) – SPI Lithuania
• ONR
• Dan Green – >95% overlap of interest
• Paul Maki – GaN
• ARO
• Marc Ulrich – Physics of topological insulators
• DARPA
• Jeff Rogers – Topological insulator devices
• John Albrecht – THz electronics, GaN
• Bill Chappell – Adaptive RF technology, RF-FPGA
• DTRA
• Don Silversmith – Rad-hard electronics
• Tony Esposito & Kiki Ikossi – THz applications
• NSF
• Samir El-Ghazaly – THz electronics
• Anu Kaul – 2D materials & devices beyond graphene
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22. Take Away Messages
I. Covalent Semiconductors
• Transition bulk growth and reliability projects via STTRs
• Push to THz via highly-strained thin-film growth, surface High-k Gate
passivation, and high-k gate stack
Complex
Oxides
II. Ionic Semiconductors
• Push oxide electronics to high GHz range
• Emphasize thin-film heterostructures
Oxide Electronics
• Explore extreme carrier concentration
• Understand and overcome mobility limitation
• Explore metal-insulator transition & topological insulators
III. Reconfigurable Electronics
• Buildup program next year Multi-Ferroics
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