Hwang - GHz-THz Electronics - Spring Review 2012

1 DISTRIBUTION A: Approved for public release; distribution is unlimited. 15 February 2012

Integrity Service Excellence

Jim Hwang

Program Manager

AFOSR/RSE

Air Force Research Laboratory

GHz-THz Electronics

08 MAR 2012

2 DISTRIBUTION A: Approved for public release; distribution is unlimited.

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.


I. THz Electronics

DARPA

DARPA

ONR III-N THz

ONR DEFINE

AFOSR

X’tal

Reliability

•Sub-millimeter-wave radar & imaging

•Space situation awareness

•Chemical/biological/nuclear sensing

•Ultra-wideband communications

•Ultra-high-speed on-board and

front-end data processing

Intel

IBM

Cutoff Frequency

(Po

wer)

THz


Intel’s High-k FinFETs

Pro

du

cti

on

De

ve

lop

me

nt

Channel

Source Drain

Gate

Stack

e

S

d

k

V

QC 0


Challenges for THz Electronics

•Highly strained

growth

•Single-phase

ternary

•P doping


Covalent Semiconductors

Covalent Semiconductors


InAlN Molecular Beam Epitaxy Jim Speck, UC Santa Barbara

X-ray diffraction confirms lattice match Cross-sectional transmission electron

microscopy reveals columnar structure

17% In mole fract.

140nm thickness

Scanning transmission electron

microscopy shows nano-network

Atomic probe confirms

composition variation

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


P-Doped InGaN Alan Doolittle, Georgia Tech

GaN:Mg Constant resistivity when

doped 1019/cm3

GaN

GaN

GaN

GaN

GaN

In0.4Ga0.6N

In0.2Ga0.8N

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

1020/cm3 Mg and >50% temperature-independent activation

Plan: Mitigate electrical leakage via metal-decorated dislocations


Hot Electrons/Phonons in GaN Hadis Morkoc, Virginia Commonwealth

Pla

sm

on

Reso

nan

ce

P

eak

Ve

locit

y I ~ nv

Optimum electron

concentration for

plasmon resonance

and optical-acoustic

phonon decay

2700K Electrons

Acoustic

phonons

2400K

optical

phonons

Power Supply

300K heat sink

Objective: Optimize electron density

Approach: Understand interaction of hot

electrons and phonons

Result: Explained limits of many GaN devices

Plan: Dual-well channel


Limit of AlN/GaN HEMTs Grace Xing & Debdeep Jena, Notre Dame

Regrown contact with Rs<0.1Ω-mm

Reduce

gate length Control

surface

states

Increase 2DEG mobility

Add AlN back barrier

Year

Speed (GHz)

400

600

‘11 ‘10 2007

200

‘09

NiCT

HRL MIT

Notre Dame

‘12

Objective: THz AlN/GaN HEMTs

Approach: Outlined below

Results: 370GHz cutoff frequency

Plan: Verify/improve phonon-

limited velocity model


II. Novel GHz Electronics

DARPA

DARPA

ONR III-N THz

ONR DEFINE

ZnO MOSFET

AFOSR

Nano-Oxide

DARPA

MESO

ONR

Extreme E

ARO

Interact TI

ONR

Coupled Φ

NSF

DMR

DTRA

Rad-Hard E

Industry

Thin-Film E

AFOSR

X’tal

Reliability

IBM

Intel

Breakdown,

Power

Cutoff Frequency


Ionic vs. Covalent Semiconductors

Covalent Semiconductors •Transparent Electronics: ZnO, MgO, InGa3Zn5O5

•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


Challenges for THz Electronics

•Highly strained

growth

•Single-phase

ternary

•P doping


Merits of Ionic Semiconductors

Covalent Semiconductor

Ionic Semiconductor

Mo

bilit

y

Ionicity

Ionic Covalent

•Less demanding on crystalline perfectness

•Deposition on almost any substrate at low temp.

•Radiation hard, fault tolerant, self healing

•High electron concentration with correlated transport

•Metal-insulator transition with high on-off ratio

•Wide bandgap for high power and transparency

•Topological effects

•SWAP-C and conforming

Challenges

•Composition and

purity control

•Transport not well

understood


Transport in ZnO Dave Look, Wright State

24

26

28

30

32

0 100 200 300

m*0.30

0.34

0.40

Fitting parameters:

ND = 1.45 x 10

21 cm

-3

NA = 1.71 x 10

20 cm

-3

m* = 0.34m0

T (K)

(

cm

2/V

s)

Pulse Laser

Deposition

in Ar

SIMS

Positron

Kane model

•[VZn ] = 1.7x1020

cm-3 gives

E(formation) =

0.2 eV; provides

accurate check

on theory (DFT)

•Reduced [VZn ]

with Zn anneals:

got = 1.4x10-4

-cm, 3rd best in

world

•Future: create

GaZn donors by

filling VZn with Ga

•Future: apply

methods to other

TMOs

µ (ND, NA, m*, T)

Mobili

ty


LG=1.2m

Grain

Boundaries

Nanocrystalline

ZnO

PLD

World’s 1st microwave thin-film transistor

ZnO Thin-Film Transistors Burhan Bayraktaroglu, AFRL/RYDD

Record Performance

150°C deposition

110 cm2/V.s electron mobility

875mA/mm current density

9.5W/mm dc power density

1012 on/off ratio

60mV/dec sub-threshold slope

10 GHz cut-off frequency

Plan

•Room-temp.

deposition

•High-k gate

insulator

•MgZnO/ZnO

hetero-

junction

Objective: Exploit unique electronic

properties of nanocrystalline ZnO films

Approach:

•Theoretical doping & mobility models

• Pulsed laser deposition (PLD)

• Ga doping in Ar at low temperatures


Correlated Oxide Field-Effect Devices Shriram Ramanathan, Harvard

Estimated

power-delay

product

VO2 Mott FET

vs. Si MOSFET

MBE

SmNiO3

LaAlO3

Temperature (°C)

Objective: Fundamental understanding of field-effect

switches utilizing ultra-fast (ps) reversible metal-

insulator (Mott) transition in correlated oxides

Approach: Fabricate field-effect transistors with oxide

channels and investigate device characteristics

Result: High-quality SmNiO3 grown by molecular-

beam epitaxy on LaAlO3 for room-temperature

transition

Plan: Electronic transport measurement on thin-film

hetero-junctions of different oxides


III. Reconfigurable Electronics

Challenges: Understand

interaction between

electromagnetic waves,

electrons, plasmons and

phonons on nm scale

•Multiple electronic, magnetic and optical functions for UAV/MAV

•Meta-materials, artificial dielectrics, ferrites, multi-ferroics, nano-magnetics, MEMS/NEMS


EuO-Based Multiferroics Darrell Schlom, Cornell

= 0.6eV

Andreev reflection of

>96% spin-polarized

carriers from EuO to Nb

0

0.5

1

20 40 60 80 100 120 140

No

rma

lize

d M

ag

ne

tizati

on

(a.u

.)

Temperature (K)

5% La-doped

5% Lu-doped

5% Gd-doped

Insulator

Metal

Fe

rro

ma

gn

eti

c

Pa

ram

ag

ne

tic

Objective: Enhance and

exploit exceptional

spintronic, optical, and

magnetic properties of

EuO, including highest

∆R/R of any metal-insulator

transition, greatest spin-

splitting of any

semiconductor, and 2nd

highest of spin

polarization.

Approach: Reduce defects

in EuO films to enable

controlled doping.

Combine strain and doping

to boost Curie temperature.

Results: Demonstrated

controlled rare-earth

doping of EuO.

Plan: Apply misfit strain to

boost Curie temperature


Topological Insulators Yoichi Ando, Osaka U.

Unexpected

mass

acquisition of

Dirac fermions

on TlBi(S,Se)2

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

•To discover better TI materials

•To detect surface spin currents

Approaches:

•Explore ternary chalcogenides

•Fabricate TI-ferromagnet devices

•Precise transport measurements


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


I. Covalent Semiconductors • Transition bulk growth and reliability projects via STTRs

• Push to THz via highly-strained thin-film growth, surface

passivation, and high-k gate stack

II. Ionic Semiconductors • Push oxide electronics to high GHz range

• Emphasize thin-film heterostructures

• Explore extreme carrier concentration

• Understand and overcome mobility limitation

• Explore metal-insulator transition & topological insulators

III. Reconfigurable Electronics • Buildup program next year

Take Away Messages

High-k Gate

Multi-Ferroics

Complex

Oxides

Oxide Electronics

Technology

Hwang - GHz-THz Electronics - Spring Review 2012