terahertz imaging and security...

Erich Grossman, [email protected]

TeraTOP, Haifa, Nov., 2011

Terahertz and Mmw Imaging

Erich Grossman

National Institute of Standards & Technology

Optoelectronics Division

Charles Dietlein (now at Army Research Lab)

Arttu Luukanen (now at Millilab/VTT)

Aaron J. Miller (now at Albion College)

Also Zoya Popovic (Univ. of Colorado)

mailto:[email protected]



Outline

• Background and History

– THz Gap, Radio Astronomy

– Terrestrial applications (esp. concealed weapons detection), requirements

• Our Contributions :

– Uncooled antenna-coupled microbolometers

• Narrowband for active systems

• Single-pixel active imaging: phenomenology

• 2D Staring array : real-time video imaging

– Cryogenic microbolometers

• Ultrawideband for passive systems

• Single-pixel passive imaging: phenomenology

• Tools for measurement: ABC source and THz CVF

• 8-channel modular camera

• 64-channel, realtime, conical scanned camera

• The Current State-of-the-Art : Passive and Active Imaging

– System Architectures, Detection Matrix

– Example Systems and Components

• Conclusions




The “THz Gap”

CO2

Electronics Lasers

Electronics

• Classical region

(hv << kT)

• Critical dimensions << λ

Optics

• Quantum region

(hv >> kT)

• Critical dimensions > λ

THz / Sub MMW

• Transition region:

hv ~ kT

Electronics


(hv << kT)


• Atmosphere transparent

Optics

• Quantum region

(hv >> kT)



THz / Sub MMW


hv ~ kT

• Narrow, poor

transparency windows

Electronics


(hv << kT)



• Sources readily available

Optics

• Quantum region

(hv >> kT)



• Sources available

(many at specific λ)

THz / Sub MMW


hv ~ kT

• Narrow, poor

transparency windows

• Only weak sources

available

Courtesy, Dr. Mark Rosker, DARPA/MTO



TeraTOP, Haifa, Nov., 2011 4

Introduction – a Bit of History

Hertz: spark gap generator

1880s – Bose – down to 5mm

1890s – Rubens – far IR mercury lamp,

restrahlen filter, for measurement

of Planck spectrum (UV

catastrophe)

Horn!

Apparatus demonstrated to the

British Royal Society in 1897

D. Emerson, MTT Trans. Dec. 1997

Measured IV curves for an iron point-contact

junction – 0.4V knee voltage!

Different curves are for different initial currents.

Straight line is a resistor.




Radio Astronomy (First Imaging Application)

(credit M.Heller)

CO images of Taurus

molecular clouds

• Millimeter/submillimeter

spectral components dominate

the spectrum of planets, young

stars, many distant galaxies.

• Most of the observed

transitions of the 125 known

interstellar molecules lie in the

mm/submm spectral region—

here some 17,000 lines are

seen in a small portion of the

spectrum at 2mm.




Radio Astronomy

Two Main Detection Schemes for Astronomical Sub-/mm Radiation:

• Incoherent detection -> bolometer

• total power detection

• no phase information -> only used on single antenna

• Coherent detection -> heterodyne receiver

• frequency conversion

• total power detection

• spectral information preserved

• phase information -> single antenna and interferometer

• SIS: most sensitive coherent detector in mm/submm wavelength range

(sensitivity close to quantum limit - a few hn/k )

• relative bandwidth ~ 25 - 30 % (-> 10 ALMA bands)

• fixed tuned / tuning elements

• Double sideband (DSB) / single sideband (SSB) / sideband separating (2SB)

• two main types of structure:

• waveguide: high efficiency, difficult fabrication at high frequencies

• planar (“quasi-optical”): simpler fabrication




Radio Astronomy Continues: ALMA

Operational 2013 (Early Science in 2010)

Plano Chajnantor, Northern Chile,

5000m elevation

50 12-m telescopes

+

ACA: 12 7-m + 4 12-m

Atacama Large

Millimeter/submillimeter Array

International astronomy facility,

partnership between Europe, North

America and Japan, in cooperation

with Chile (2003,2006)

Courtesy for ALMA info:

Dr. Eric Bryerton

NRAO

Bands 1-2 HEMT Bands 3-10 SIS




Radio Astronomy Technology Spinoff

1995: Millitech catalog

(but scanned single pixel required 30 min)

Circa 1990, Millitech founded by 4 FCRAO radio astronomers,

offering ~100 GHz components and systems

Obtained with

Schottky-diode

heterodyne receiver

Application based on partial

transparency of clothing at mmw

Terrestrial Imaging Apps:

exploit THz penetration

of materials




Penetration of Clothing

• Variation between clothing types

• (and wet vs. dry, Huegenin ’96)

• Smooth rolloff of transmission at

higher frequency

• Typical (one-way) –

• 1 dB at 100 GHz,

• 5-10 dB at 1 THz

• Scattering has been less studied

• key for active imaging, texture ~ l

Grossman, Dietlein,

Chisum, Luukanen,

Bjarnason, and Brown,

―Spectral Decom-

position of Ultra-

wideband THz

Imagery‖, Proc. SPIE,

v.6548 (2007)

"Millimeter-wave, terahertz, and mid-infrared transmission

through common clothing" , J. E. Bjarnason, T. L. J. Chan,

A. W. M. Lee, M. A. Celis, and E. R. Brown, Appl. Phys.

Lett. vol. 85 (no. 4), pp. 519-521. [2004]

300 mm




Fog, Smoke, etc. is Transparent to Mm-waves/THz

Visible clear Visible 50mvis PMMW




X-ray Backscatter – Alternative to Submm Imaging

“X-ray vision shows air passengers naked”

Susan Hallowell, director of the Transportation

Security Administration's security laboratory,

demonstrated the system which bounces X-rays off

her skin.

To the eye, she is dressed in a skirt and blazer. On the

monitor, she is naked - except for a gun and a bomb

that she hid under her outfit.

"It does basically make you look fat and naked - but

you see all this stuff," she said.

[New York Times, July 2003]

―Last month [Sept. 2011] the Transportation Security Administration ordered over $40

million worth of body scanners to outfit even more of the nation’s airports with enhanced

security screens. All 300 of the new machines ordered are millimeter-wave machines --

rather than backscatter X-ray machines, that have been controversial due to their use of

radiation.‖ Forbes Magazine, Oct 2011

8 years later..




Motivation for Submm Security Imaging

R (range)

D (diam.)

l Res = (R/D)

• To image (detect and recognize) threats

• concealed on the person beneath clothing

at standoff range, e.g. 5 – 100 m

• Portal detection, e.g. airports

• Short range + controlled environment

• Now (since Dec 2009) reasonably covered by

• X-ray Backscatter (Rapiscan, dev.1990’s)

• ―Mmw‖ (30 GHz) Holographic Imaging (L-

3/Safeview/PNNL)

• Large-scale

deployment

underway




Application Requirements

Users need

• Image quality (ROC curve)

• NETD and spatial resolution

• High throughput

• Frame rate and FOV

• Privacy and Safety

• Footprint and Range

• Range

• Low cost

•1/e absorption length comparable to interesting

application range, 10’s of m.(See Wallace, Proc.

SPIE 2006)

• Technical drivers

• Penetration, spatial resolution

• Atmospheric transmission

• Technological maturity




Spatial Resolution, Angular Diversity

• What’s possible - Diffraction-limit

D = 1 m (practical maximum) implies 3 mrad at 100 GHz

resolution > 2.5 cm at 8 m range knife, gun, or explosive ?

> 6 cm at 20 m

> 15 cm at 50 which person ?

• What’s Interesting – U.S. Export Control Classifications:

• Resolution < 0.5 mrad ITAR-forbidden

• 0.5 mrad <Resolution < 1 mrad (ECCN 2A984)

• Resolution > 1 mrad no restrictions

Higher frequency (> 100 GHz) Needed

• Angular Subtense (―angle diversity‖) is key in defining

physics of standoff imaging – determines spatial resolution

• Radar: monostatic, bistatic, and multistatic

• In optical and IR, BRDF

• For portal screening, sub-wavelength resolution

• It differentiates between standoff architectures,

• sparse-aperture vs filled,

• active vs. passive (since passive receives from sky or background)

R (range)

D (diam.)

filled aperture

geometry

Portal

geometry




Our Contributions,

2001-2010




2001 - Single-pixel Active 100 GHz Imager

target detector

assembly

scanning mirror

chopped

CW source

pulsed source

• Image acquired in 20 s, limited by

mechanical stage

• Goal : qualify system (target reflectance,

spatial resolution, sensitivity, etc.)

• Conclusion 1 : Orientation of target and

TX/RX geometry (mono/bi-static) are critical

Metal knife

Ceramic

(YSZ) knife

Internal

resonances

Red, Green =

different

incidence

angles

specular peaks

Amplitude-only, active imaging




Compare Illumination Modes

Conclusion #2 : Illumination mode (temporal) has little influence on qualitative

image quality.

(All are amplitude-only, active imaging)




Antenna-coupled Microbolometers

• A thermally isolated, resistive termination for a lithographed antenna

• Signal coupled to the bolometer changes its temperature: T=Pinc/G

• A DC current is used to sense the resistance of the bolometer, given by R=R0(1+T)R0(1+I2)

• Electrical responsivity Se=I

• Noise contributions:

– Phonon noise

– Johnson noise

– 1/f noise

– Amplifier noise

• For room temperature devices, NEP is limited by Johnson noise

bias

Be

T

GTkNEP

24

thermal conductance

G

Bath at

T0

T0+T

Za Earlier work on ACMBs

Tong 1983

Rebeiz 1990

Hu 1996




2003, 120-element Microbolometer Arrays

160 um 55 um

4.75 mm array pitch

• ACMB arrays are simple and cheap

• 4 mask layers + 1 backside etch

• no semiconductors

• Si substrates (large diam. possible)

• ACMB arrays are frequency extensible

• microantenna alone to > 30THz

• substrate thickness dominates design

• ACMB performance is adequate for

active systems

• NEP ~ 50-100 pW/Hz1/2

• Speed ~ 400 kHz

• pixel count limited by real estate,

now ~ 100

• This speed can be traded for pixel count

via scanning

•Prior mmw ACMB arrays

• Tong (1983)

• Rebeiz (1990)

• Hu (1996)

and many others

1.6 x 10 x .02 mm

bolometer

• Single-pixel imaging too slow,

• Developed antenna-coupled

microbolometer focalplane arrays

• Built realtime 100 GHz active system




Airbridge

Airbridge Microbolometers

• FPA microbolometers, Nb, 300K

• 5-10 V/W-mA

• 25-50 V/W

• 400 kHz

• Airbridge, Nb, 300K

• 40 – 80 V/W-mA

• 100 V/W, 25 pW/Hz1/2

• 50 kHz

• Airbridge, NbN and Nb, 4K

• NbN: no response at 300K

• 250-500 A/W

• 100 kHz

• Optimum (for 1D scanned system)

• maximize V/W consistent with

• ~ 20-40 kHz bandwidth 10 micron airbridge,

Nb strip passivated in SiO2,

Released with XeF2 etch

Of underlying Si

C.R. Dietlein, A. Luukanen, J.S. Penttila,H. Sipola, L. Gronberg, H. Seppa, P.

Helisto, and E.N.Grossman, ―Performance Comparison of Nb and NbN

Antenna-coupled Microbolometers‖, Proc. SPIE, v 6549 (2007)




Air-Bridge Bolometers

Pattern Antenna

Pattern Bolometer

Deposit Insulator

Pattern Wiring

Substrate Etch

Air Gap Photoresist

Aluminum

Bolometer Metal

SiO2 Insulator

GNb < 2 μW/K

Gair < 3 μW/K

Gox < 2 μW/K




Substrate-Supported dv/di vs. T

70

80

90

100

110

120

-6 -4 -2 0 2 4 6

dv

/di

[Ω

]

Bias Current [mA]

100C 90C

70C

60C

50C

40C

30C 20C

10C

0C

Differential Resistance vs. Substrate Temperature • Au antenna metal

• Maximum Ibias ≈ 4.5 mA

• G ≈ 50 μW/K

• Johnson-noise limited

• = 400 ns

• TCR = 0.2 % per degree K

• β = 3-5 V/(W·mA)

• Responsivity ≈ 20 V/W

Time [µs]

0 1 2 3 4 5 6

Sig

nal

[a.

u.]




Active Imaging System, Block Diagram

• “Brute-force” repetition of

120 channels amplification

and gated integration (8

chan. per card

• Real-time readout

•ASIC-able

• ―Brute-force‖ 120-channel electronics

noise limited by bolometer Johnson noise




3-D Illumination System

• Illuminate from X, Y, and Z directions

• Detect from (1,1,1) direction

• Source pulse trains are interlaced in time

Map of point source (open ended WR-10)

• Conclusions

• Clutter-limited (skin return comparable to

threat)

• Realtime motion tracking greatly improves

detectability for marginal SNR and

resolution

• Large field-of-view required (20k image

pixels or more)




Video imagery: Suicide bomber




Video imagery: point source movie




Passive Imaging

with Ultrawideband Crygenic Bolometersd




2005, Single-pixel Passive Imaging

• Ambient illumination is naturally diffuse, not directional

• outdoor vs. indoor are different

• wide angular subtense, specular effects small

• incoherent, so speckle effects absent

• But signals are very weak (~x1000 below IR)

• requires, either cryogenic

or coherent operation

• ultrawide bandwidth important

(0.2-1.8 THz spiral antenna)

• Signals measured in radiometric temperature, sensitivity in noise-

equivalent temperature difference (NETD), as in IR

Image from Qinetiq (UK)

94 GHz Passive Imager (2003)

Several companies now sell passive imagers for

100-200 GHz (Millivision, Brijot, Thruvision etc.)




Superconducting Hotspot Bolometer

• Voltage bias, combined with Tbath<Tc

negative electro-thermal feedback (ETF)

maintains constant dissipation

• Formation of a N-state hot spot in the middle

of a suspended superconducting bridge

• Bias dissipation (DC) takes place in the N

state spot, RF dissipated also in the

superconducting region

• Bias power modulates the size of the hot-spot

modulation of R modulation of current

through the bridge

S S

Tc

xln/20

A. Luukanen, J.P. Pekola, Applied Physics Letters, Volume 82(22), pp. 3970-3972

(2003).

A. Luukanen, R. H. Hadfield, A. J. Miller, E. N. Grossman, ―A Superconducting

Antenna-coupled Microbolometer for Terahertz Applications‖ Proc. SPIE Vol. 5411, p.

121-126, (2004)

A. Luukanen, E.N. Grossman, A.J. Miller, P. Helisto, J.S. Pentilla, H. Sipola, and H.

Seppa, ―An Ultra-low noise Superconducting Antenna-coupled Microbolometer with a

Room-temperature readout‖, IEEE Microwave and Wireless Components Lett. V16(8),

p.464 (2006)




Principle of Operation

• Dark current-voltage

characteristics given by

I(V)~Pbias/V + V/Rn

• ETF can be characterized by a

loop gain L

• L >> 1 (low end of I(V)),

conventional TES, impedance low,

SQUID readout

• L=1 (minimum of I(V)), dV/dI high,

uncooled readout possible

• Responsivity [A/W]

– SIdI/dP=-1/V L/(L+1)

RZ

RZ

I

V

dI

dV

I

V

dI

dV

dR

dP

R

PL

• Modeling: 1-D diffusion of

heat

0

0

,2

2

2

2

2

)2/(,)2/(,0

2/

2/,

TlTTlTdx

dT

lxPdx

Td

lxPjdx

Td

cn

x

nopt

nopt

S S ln

l

bathcNe

bathc

opto

eeN

TTGRVp

TTG

Pp

pppppR

VVI

2

0

2

00

,

41)1(

21)(




Broadband Microbolometers

• Bolometer materials: • non-stoichiometric NbN (VTT), Tc=5-7K • thin (20-30 nm) Nb (NIST), Tc=5-7K • similar performance, stability and

longevity of films depends on growth • normal Rn sets P(saturation)

• freely suspended in vacuum to reduce

thermal conductance to ~10-8 W/K

• Bolometer bandwidth,

• planar antenna design

• self-similar, self-complementary

spiral, 0.2-1.8 THz

• Quasi-optic substrate lens design

• (waveguides inherently narrowband)




Planar Antenna/Substrate Lens

• Eliminates coupling into substrate modes

for planar antennas on dielectric half-space

~95% coupling into Si (n=3.4)

• Developed early 1980’s, Rutledge et al.

• Very widely adopted in THz systems, esp.

(nearly all) Time-Domain spectrometers

• Spiral, square-spiral, log-periodic,

bowtie, and other antennas

―true‖ hyper-

hemisphere

(aplanatic)

―extended‖

hemisphere or

―sythesized

ellipse‖

C.R. Dietlein, J.Chisum, M. Ramirez, A. Luukanen, E.N.

Grossman, and Z. Popovic, ―Integrated Microbolometer

Character-ization from 95-650 GHz‖Intl. Microwave Symposium

Proc. p.1165-68 (2007)

A. Tamminen, J. Ala-Laurinen, A. Luukanen, E.N. Grossman,

and A. Raisanen, ―Chjaracterization of Antenna-coupled

Microbolometers for Terahertz Imaging‖, Proc. 5th ESA

Workshop on Mmw Technology (2009)

109, 240,

and 650 GHz

f

deg-THz5.4FWHM

f

deg-THz9FWHM

4mm lens

2mm lens




Other Superconducting Bolometers

S. Cibella, M. Ortolani, R.Leoini, G. Torrioli, L. Mahler, J.Xu,

A. Treducci, H.E. Beere, and D.A. Ritchie, ―Wide Dynamic

Range Terahertz Detector Pixel for Active Spectroscpoic

imaging with Quantum Cascade Lasers‖, Appl. Phys. Lett.,

v95, p213501 (2009) CNR, Rome

Y. Ren, W. Miao,Q.-J.,Yao, W. Zhang, and S.-C. Shi,

―Terahertz Direct Detection Characteristics of a

Superconducting NbN Bolometer‖, Chin. Phys. Lett.,

v28(1), p010702 (2011), Purple Mountain, Nanjing

• Hotspot microbolbolometers

have been picked up by other

groups

• TES bolometers in wide use for

radioastronomy instruments

• also superconducting,

resistive, V-biased

• isothermal, in mid-transition

• SQUID readout

• Kinetic inductance (KID)

detectors also in development

for radioastronomy, uwave

readout




Resistive Readout

• I(V) measurements at 4 K:

– Voltage bias provided by current

biasing a cool shunt resistor (10

)

– A 10 series resistance RL

used to probe the device current

– Good fits with the theoretical

model

– G=5 nW/K

– Bias power 25 nW ( optical

saturation power = 2000 K) 1 10

10

100 Measured Model fit

Curr

ent [mA

]

Voltage [mv]

G=5 nW/KR

N=195

=0.05 %/K

I0

Rshunt Rde

t

RL

I

0 5 10 15 20 25

0

50

100

150

200

250

Re

sis

tance

[]

Voltage [mV]




Experimental Setup, ―Wet‖ LHe Cryostat

Detector&

Substrate

lens assy

4 K cold

plate

4K

fluorogold

low-pass

filter

Teflon

window 4K radia-

tion shield

• Optical setup: – 30 cm diameter spherical mirror, f=25 cm

(aperture underfilled:

– f=68.5 mm diameter PTFE lens

– Optical chopper to circumvent amplifier 1/f noise

• No bath temperature control whatsoever




Calibration target (hot

water in styrofoam cup)

Ceramic knife

Thick collar

Folds in clothing Silhouette

of sleeve

Silhouette

of arm

Absolutely Calibrated Passive 0.1-1 THz images

Mm-wave anechoic

material (AN-72)

Handgun

Zipper-assembly

on jacket

Detector NETD = 105 mK, (ref 30Hz)

Indoor scene fluctuations greater

340 K

290 K




NIST is distributing source at no cost to

anyone with legitimate measurement

needs

• Overall size: 53 cm x 27 cm x 50 cm

• Entrance aperture 20 cm x 20 cm

Aqueous Blackbody

Calibration (ABC) Source Accuracy of Radiometric Temperature

for 40 C Signal (Twater – Tambient)

Traceable Test and Measurement for Submm Imagers

C.R. Dietlein, Z. Popovic, and E.N. Grossman,

―Aqueous Blackbody Calibration Source for Mmw/Thz

Metrology‖, Appl. Optics, v47(3), pp. 5604-5615 (2008)




Resolution Measurement for Submm Imagers

50% visibility

at 6.5 mm

• Radiometric temperature NETD via high emissivity

blackbody (next-generation hot water in styrofoam cup)

• Spatial resolution via 4-bar resolution target implemented

in Cu on kapton




What NETD is Needed for Indoor CWD?

Add white noise to 200 mK image, to simulate higher NETD

0.5 K

2 K 5 K

1 K

C.R. Dietlein, A. Luukanen, F. Meyer, Z. Popovic,

and E.N. Grossman, ―Phenomenology of Passive Broadband THz Images‖

Proc. 4th ESA Workshop on Mm-Waves, Helsinki, (2006)

Key criterion is the

detection/resolution of clutter,

not of threat items




Terahertz Circular Variable Filter

• Low-cost THz Monochrometer

based on frequency-selective surfaces

• Commercially patterned on 25 mm

kapton, up to 60 x 90 cm

• 50 mm min linewidth provides

operation to 880 GHz, in octave bands

• Linear center frequency-vs-angle,

not linear dimensional scaling with angle

(thickness is constant)

220 GHz

440 GHz

330 GHz 330 GHz




VTT Transimpedance Bolometer Readout

• Readout of 4 K, ~50 devices problematic with

uncooled electronics

• Transimpedance amplifier provides

“virtual” voltage bias thru feedback

• 1 nV/Hz1/2 uncooled amp noise

translates to negligible current noise

near minimum in I-V

• smooth minimum due to internal

bridge thermal gradient




Making Broadband Imaging Practical

• Speed (20 minutes per image with single pixel)

• arrays

• fast scanning and readout

• Cryogenics (liquid helium requires Ph.D’s)

• Range

• Without sacrificing NETD

or spatial resolution

5mm

24 mm

• NETD = 110mK (ref 30 Hz),

• =0.5 ms ~ 15 kpix at 100 ms/pixel

(20 min)

• spatial resolution ~6 mm




• Modular, not monolithic, approach

8-element, quasi-optic

detector package (3mm pitch)

• Uncooled transimpedance readout

yields detector-limited sensitivity (!)

• 8-element System is mobile, for

indoor/outdoor phenomenology, varying

environment etc. Presently used for

detector screening.

• Modularity also has advantages for

larger arrays

• Allows for imperfect detector yield

• Allows focalplane reconfiguration

• Allows curved focalplanes

(corrects field curvature)

2007, 8-channel Passive Imager

E.N. Grossman, C.R. Dietlein, J.E. Bjarnason,M.D. Ramirez, M. Leivo, J. Penttila,

P. Helisto, and A. Luukanen, ―imaging with Modular Linear Arrays of Cryogenic Nb

Bolometers‖ Proc. SPIE v6948,p6948-05 (2008)




2007, 8-channel Raster-scan Camera

• Astigmatism (barely) visible in

sharpness of H and V edges

• Small, 100mW JT cryocooler

• Uses single 1x8 module

• Flex wiring and VTT trans-

impedance readout

• Off-axis spherical primary

Depth of Field using Edges of

ABC Source

4K, 100 mW

$25 kUS

30,000 hr MTBF

• ~2-3 minute acquisition




8-channel Images, Range 2-4m

Spatial Resolution and Penetration

• Ultrawide bandwidth implies

more penetration and less resolution from low f

more resolution and less penetration from high f

Better resolution on exposed

fingers than on hidden handgun

Ceramic knife




4bar target

beneath sweater

Wallet

And cellphone

Small keychain

Other Images, Range ~ 2m

Ceramic knife

Gun, beneath

fleece and jeans Empty pockets

PIC080215160534.dat

50 100 150 200 250 300 350

50

100

150

200

250

T shirt , polar fleece, and jeans

• Note Stripes

• Flatfield/calibration

algorithms critical




2008-present, Realtime PEATCam

(with VTT, Helsinki, A. Luukanen)

• Linear array, with conical scanner.

• Preserve ultrawideband response and NETD

– High frequencies see fine features on surface,

low frequencies see deeper.

• Specifications:

– Range – 8m

– Field-of-View - 2m x 4m (h x w)

– Real-time operation – 10 frame/s

– NETD < 0.5 K per frame

– Spectral range 0.2 – 1.8 THz,




What’s Conical Scanning ?

• Angular deflection at aperture plane, rotate about

undeflected axis (1 rotation=1 frame)

• Produces ―stadium‖-shaped fields of view

• Common for realtime imaging with

low channel count

• But introduces

non-uniform sampling

all channels

read out

simultaneously

red and blue

channels

syncopated




2009 : 64-channel Conical-scan

Camera (w/ VTT Helsinki) ABC Source aperture

8 m Range

•System running up to 10 frame/s

(since Sept 09)

• NETD = 1.25 K (ref. 1 frame)

• Conical scan gives nonuniform

sampling of target plane

• Large FOV (4m x 2m) but

coarse sampling

Footprint:

1.10 m (w)

0.97 m (d)

1.79 m (h)

Remote display

& compressor

64-element array

(central 8 modules)




64-channel Conical-scan Camera

Footprint:

1.10 m (w)

0.97 m (d)

1.79 m (h)

Remote display

& compressor

64-element array

(central 8 modules)

Acquisition/Control

Computer

(Display computer is

remote)

• All-reflective Optics

• Conical Scanner

– In-line, balanced,

– Perimeter driven, no central obscuration

– non-uniform sampling




Example Video (2010)

• Note higher image noise at edge of array (center of image)

• VTT videos omit those channels (black hole at center)

• 8 m Range

• 5 fps

• Realtime

coord. transform

• 14.7 data-kpixels (230 x 64)

interpolated to

8 image-kpixels (64 x 128)

• No image processing, flat-fielding,

or averaging (yet)




Video: Concealed Gun under a fleece jacket -

5 m, 6 fps S

canner

angle

Channel #

Gain

Eq

Coord

.

Transf




Video: GSM phone in fleece pocket-5 m, 5 fps

Mozilla Firefox.lnk




Peanuts under cotton pullover




ID

card

belt

System Performance: Sensitivity

Nscan = 1/16 -1/2

eoptics= 1/3

Using s from noise in image,

Mean NETD (ref window) = 38 mK Referred to target plane

38 mK -> 1.8K




System performance : Stability

• The stability of the system is

evaluated by measuring the

channel-wise Allan variance

• Stray light is the dominant

source of 1/f-noise by far;

limits integration to <10s

• All channels indicate Allan

variance scaling consistent

with white noise No

significant drifts present

• Allows for smart integration

routines for reducing NETD

on stationary targets

10-1

100

101

102

-0.5

0

0.5

1

1.5

Integration time [s]Norm

alized C

hannel -

wis

e s

tandard

devia

tion

Channels 17-48;Tbath = 7K, fframe

=5.7 Hz

Data: Arttu

Luukanen

VTT




Array: Optical Performance

• Pattern, NETD, using

blackbody sources (not

monochromatic)

• Efficiencies referred to

cryostat window

• Obscuration, aperture

Illumination, atmospheric

propagation add to total

efficiency and spatial

resolution

Typical wideband ―pattern‖

Best-fit

Gaussian

Residual

Measured

Beam




The Current State-of-the-Art :



TeraTOP, Haifa, Nov., 2011 [email protected]

System Architectures

Scanned Staring Aperture

Synthesis

Passive

(radiometry)

NIST/VTT,

Qinetiq

HRL,TSC

UDel (PSI),

PNNL

Active

Incoherent

(amplitude only)

NIST THz

Electronics

(NGC,TSC,

NRL), PNNL Coherent JPL

Level of Parallelism is

Semi-continuous

(can scan a small array)

How to

Get 20 kpix?

What is source

Of contrast




Detector

Technology

Examples Sensitivity Cost and

Complexity

Cryogenic

Coherent RX

• SIS heterodyne

• Cryo HEMT

Near quantum-

limited

(Tn[K] ~ f[GHz])

Huge

Uncooled

Coherent RX

• HEMT

• HBT

Excellent

Tn[K] ~ 10f[GHz]

Huge, but

improving

Cryogenic

(4K)Thermal

• Hotspot bolometer

• TES and KID

Good (4K)

5-50 fW/Hz1/2

Moderate

Uncooled diode • Zero-bias diode

• Schottky diode

moderate

1-10 pW/Hz1/2

Moderate

Uncooled Thermal • uncooled

microbolometer

• pyroelectric

poor

0.1 – 1 nW/Hz1/2

Tiny

Detector Approaches (2011)

Arrays (>100 element)

Low

Medium

High

Bandwidth

~10 GHz

~100 GHz

>1 THz




Coherent Systems require Coherent Receivers

• Terahertz Monolithic Integrated Circuits (TMICs)

• Low-noise Amplifiers and Power Amplifiers based on

HEMT or HBT Transistors

M. Rodwell, H. Le, and B. Brar, Proc. IEEE, v96, p271

(2008) ―InP Bipolar IC’s: Roadmaps, Frequency Limits,

and Manufacturable Technologies‖

W. Deal, X,B. Mei, K.H. Leong, V. Radisic, S. Sarkozy,

and R. Lai, ―THz Monolithic Integrated Circuits using

InP high Electron Mobility Transistors‖,Trans. THz Sci.

and Tech. v1(1), p.25-33 (2011)

• Transistor figures of merit

• fT : frequency at which current gain

h21 = 1

• fmax : frequency at which max avail.

gain MAG = 1

IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 1, SEPTEMBER 2011 25

THz Monolithic Integrated Circuits Using InP

High Electron Mobility TransistorsWilliam Deal, Senior Member, IEEE, X. B. Mei, Kevin M. K. H. Leong, Vesna Radisic, Senior Member, IEEE,

S. Sarkozy, Member, IEEE, and Richard Lai, Fellow, IEEE

(Invited Paper)

Abstract—In this paper, background describing THz monolithicintegrated circuits using InP HEMT is presented. This three-ter-

minal transistor technology has been used to realize amplifiers,mixers, and multipliers operating at 670 GHz. Transistor andprocessing technology, packaging technology, and circuit results

at 670 GHz are described. The paper concludes with initial resultsfrom a 670-GHz InP HEMT receiver and trends for InP HEMT

components.

Index Terms—Active semiconductor circuit, solid-state sensor,

solid-state source, three-terminal device.

I. INTRODUCTION

IN THE LAST few years, the development of THz

transistor technologies [1] has pushed operating frequen-

cies of amplifiers well into the sub-millimeter wave range.

The first demonstrations of sub-millimeter amplification were

undertaken at the 340-GHz atmospheric window using InP

HEMT [2] and MHEMT [3] technologies. Amplification has

now been demonstrated above the 300-GHz sub-millimeter

wave threshold, with work in the 460–500 GHz range recently

reported including a HEMT amplifier with 11.4-dB packaged

gain [4], and noise figure of 11.7 dB [5], and a 16.1-dB gain

amplifier measured on-wafer at 460 GHz [6]. Amplification

has also been shown above 500 GHz with a cascode amplifier

reported in [7], which reached a packaged gain of 10 dB at

550 GHz.

A variety of fundamental advancements are necessary to

make this progress possible. First, transistors with extremely

high are essential for demonstrating gain at 670 GHz.

Secondly, a tailored MMIC process for realizing the matching

integrated and biasing networks. Third, specialized packaging

techniques are required for getting the signals in and out of

the circuit. The background for these is all described in this

Manuscript received March 07, 2011; accepted April 14, 2011. Date of cur-rent version August 31, 2011. This work was supported by the DARPA THzElectronics Program and Army Research Laboratory under the DARPA Con-tract No. HR0011-09-C-0062. The views, opinions, and/or findings containedin this article/presentation are those of the author/presenter and should not beinterpreted as representing the official views or policies, either expressed or im-plied, of the Defense Advanced Research Projects Agency or the Department ofDefense. Approved for Public Release, Distribution Unlimited.

The authors are with the Northrop Grumman Corporation, Redondo Beach,CA 90278 USA (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TTHZ.2011.2159539

Fig. 1. Scanning Electron Tunneling (SEM) image of 30-nm InP HEMT gate.

paper. These results include 670-GHz amplifier and mixer

results. The paper concludes with initial results on an all InP

HEMT receiver operating at 670 GHz and some circuit scaling

predictions.

In this paper, we provide background into the fundamental

developments which now make amplifiers and other types of

electronic circuits possible at 670 GHz using InP HEMT tran-

sistors. In addition to the 30-nm InP HEMT transistors (Fig. 1),

the physical features of these integrated circuits are aggressively

scaled with frequency. For this reason, we refer to these inte-

grated circuits operating close to 1 THz as “Terahertz Mono-

lithic Integrated Circuits”, or “TMICs”.

As a final comment, it should be noted that all of the 670 GHz

results in this paper have been taken at room temperature and

represent either first or second iteration results on a newly de-

veloped 30-nm InP process. For the presented application, the

technology is therefore still relatively in its infancy for Terahertz

applications. We therefore expect additional improvements to be

made over time as the technology matures.

II. THZ INP HEMT DEVICE

Critical for reaching Terahertz operational frequencies for in-

tegrated circuits are transistors with sufficiently high . This

paper describes development of amplifiers targeting 670 GHz.

As a rule of thumb, transistor should be 50–100% higher

than the design frequency. Therefore, 1–1.3 THz tran-

sistors are necessary. In this section, 30-nm InP HEMTs are

described.

2156-342X/$26.00 © 2011 IEEE

addressed in [10]. There is no expectation that veff will

decreasein HBTswith very thin baseor collector depletion

layers. In bulk (nonplanar) point-contact Schottky diodes,

the finite skin depth s ¼ ð2=! o Þ1=2

in doped semi-

conductor layers, the dielectric relaxation frequency

! d ¼ =" , the scattering frequency (the inverse of the

momentum relaxation time) ! s ¼ q=m , and the plasma

resonance frequency ! p ¼ ð! s! dÞ1=2

all impair the

diode responsivity at frequencies near 20 THz [36]. Here

¼ 1= ¼ q n is the conductivity, o the permeability,

" the permittivity of the semiconductor, and m the

carrier effective mass. For the HBT emitter and

collector layers, n-InGaAs at 3.5 1019=cm3 doping,

! s=2 ¼ 7 THz, ! s=2 ¼ 7 THz, and ! p=2 ¼ 74 THz.

For HBT base layers, p-InGaAs at 7 1019=cm3 doping,

! s=2 ¼, ! s=2 ¼ 12 THz, and ! p=2 ¼ 31 THz. Even at

5 THz, the skin depth in such layerswell exceeds the base

and subcollector layer thicknesses; hence semiconductor skin

effect has negligible effect on HBT bandwidth. Because ! d

and ! p far exceed anticipated HBT bandwidths, the emitter,

base, and subcollector bulk resistivities all can be

approximated as j! ¼ ð1þ j! =! sÞ [36]. Even this effect

is negligible. Because the HBT lateral dimensions must be

reduced in proportion to the inverse square of increases in

device bandwidth, even given bulk resistivities increasing

with frequency, base and collector contact resistivities will

dominate over bulk semiconductor resistivities. To reiter-

ate, achievable metal–semiconductor contact resistivities

and device thermal resistivity are the primary limits faced

in scaling HBTs for terahertz bandwidths.

D. Representative Mesa HBT ResultsWe show two representative results for HBTs fabricat-

ed in a simple mesa fabrication sequence. This process

flow (Fig. 5) employs mesa etches to define junctions and

metal depositions to define self-aligned contacts. Mesa

processes incur difficulties in yield of large ICs, but their

simplicity facilitates exploratory device fabrication.

Fig. 6 shows a device scanning electron microscope

(SEM) image and Fig. 7 results. Griffith et al. [37]

reported initial results with HBTs at 250-nm WeV having

Fig. 5. Mesa HBT process f low. (a) Emit ter metal deposit ion.

(b) Emit ter etch and self-al igned base contact metal deposit ion

by l if toff . (c) Base mesa etch, collector mesa etch, and

collector contact deposit ion.

Fig. 6. SEM images (top view and closeup of emit ter-base junct ion)

of a simple mesa DHBT. The emit ter and base contact w idths

are 400 and 150 nm, respect ively. The emit ter -base junct ion

width is 300 nm.

Fig. 7. Measured microwave gains and common-emit ter

character ist ics of representat ive mesa DHBTs. (a) Gains of a DHBT

having Tc ¼ 150 nm, Tb ¼ 30 nm, and We ¼ 250 nm, biased at

Je ¼ 12 mA= m2. (b) Gains of a DHBT having Tc ¼ 60 nm, Tb ¼ 14 nm,

and We ¼ 400 nm, biased at Je ¼ 13 mA= m2. DCcommon-emit ter

character ist ics of the HBT having (c) Tc ¼ 150 nm and (d) Tc ¼ 60 nm

are also shown.

Rodwel l et al .: InP Bipolar ICs

276 Pr oceedings of t he IEEE | Vol. 96, No. 2, February 2008

fT=600 GHz; fmax=1.2THz (2011)

fT=380 GHz; fmax=0.8 THz (2010)




• 300 GHz LNAs and PA’s, ~2007-2010

• now being embedded in systems

• 650 GHz TMICs under development now

• NF~15dB, Ps~1mW with 20 dB gain

•655 µm

375 µm

•Passive TMIC Technology: •High compaction. •HEMT to HEMT spacing of 10 µm.

• Transistor Technology:

• 30 nm InP HEMT

10 µm

DEAL et al.: THZ MONOLITHIC INTEGRATED CIRCUITS USING InP HEMTs 31

Fig. 20. Northrop Grumman InP HEMT noise temperature trend chart.

Fig. 21. Plot of measured output power versus frequency for 30- and 35-nmInP HEMT.

Note that some of the data presented here is previously unpub-

lished due to the rapid advances in the field, but are included

here to give a good snapshot of current technology capabilities

for both low noise and power amplification. Although signifi-

cant work has been made in other transistor technologies, we

have restricted our data to include only the 30- and35-nm InP

HEMT process at NGAS.

Low noise amplifier results are shown in Fig. 20, along with

a citation for the measurement. Note that [18] and [20] are pre-

viously unreported results. From these results, referenced to

the TMIC, noise temperature increases fairly linearly with fre-

quency. The packaged results show more rapid increase with

frequency due to the increased packaging loss with frequency.

Measured power output results are shown in Fig. 21 across

frequency. Due to the greater challenge in developing power

amplifiers at Terahertz frequencies, less data is available. In fact,

the highest frequency data point is taken from data measured

on a low noise amplifier. Note that we are currently developing

higher power amplifiers, and project that considerably better

power will soon be available at 670 GHz. All of these results

are taken at room temperature and off-chip power combining is

not used.

VIII. CONCLUSION

In this paper, the background describing development of am-

plifiers at 670 GHz using InP High Electron Mobility Transis-

tors is described. This includes high InP HEMT transis-

tors, a MMIC process tailored to Terahertz integrated circuits,

packaging techniques and various circuit types which have been

realized in InP HEMT at 670 GHz. The paper concludes with an

initial description of a 670-GHz InP HEMT receiver and a sum-

mary of 30- and 35-nm InP HEMT benchmarks accomplished

over the last five years.

From the results of the paper, it is clear that three-terminal

transistors are becoming a viable circuit technology at frequen-

cies approaching 1 Terahertz for low noise amplification, power

amplification, and frequency conversion. A significant benefit

for using a HEMT process for all of these functions is integra-

tion of multiple functions on a single chip, which will eliminate

interconnect losses between components, thus improving per-

formance and simplifying packaging.

ACKNOWLEDGMENT

The authors would like to thank Dr. J. Albrecht and Dr.

M. Rosker of DARPA, and Dr. A. Hung of ARL and to

acknowledge the many contributions that make this type of

technology demonstration possible, including NGAS contribu-

tors in HEMT, EBL, MBE, processing, layout, machining, and

test groups, ARL THz laboratory for providing test support,

as well as the guidance of R. Kagiwada, A. Oki, O. Fordham,

and A. Gutierrez. The authors would also like to thank R.

Lin and G. Chattopadhyay of the Jet Propulsion Laboratory,

California Institute of Technology, for making the noise figure

measurements.

REFERENCES

[1] R. Lai, X. B. Mei, W. R. Deal, W. Yoshida, Y. M. Kim, P. H. Liu, J.Lee, J. Uyeda, V. Radisic, M. Lange, T. Gaier, L. Samoska, and A.Fung, “Sub 50 nm InP HEMT device with Fmax greater than 1 THz,”in Proc. IEEE IEDM Conf. Dig., Dec. 2007, pp. 609–611.

[2] W. R. Deal, X. B. Mei, V. Radisic, W. Yoshida, P. H. Liu, J. Uyeda,Barsky, T. Gaier, A. Fung, and R. Lai, “Demonstration of a S-MMICLNA with 16-dB gain at 340-GHz,” in Proc. IEEE CSIC Conf. Dig.,Oct. 2007, pp. 1–4.

[3] A. Tessmann, A. Leuther, V. Hurm, H. Massler, M. Zink, M. Kuri, M.Riessle, R. Losch, M. Schlechtweg, and O. Ambacher, “A 300 GHzmHEMT amplifier module,” in Proc. IEEE IRPM Conf. Dig., May2009, pp. 196–199.

[4] W. R. Deal, K. Leong, V. Radisic, S. Sarkozy, B. Gorospe, J. Lee, P. H.Liu, W. Yoshida, J. Zhou, M. Lange, J. Uyeda, R. Lai, and X. B. Mei,“0.48 THz Amplification with InP HEMT Transistors,” IEEE Microw.Wireless Compon. Lett., vol. 19, no. 5, pp. 289–291, May 2010.

[5] W. R. Deal, “Solid-state Amplifiers for Terahertz Electronics,” in Proc.IEEE MTT-S Int.Symp. Dig., May 2010, pp. 1122–1125.

[6] A. Tessmann, A. Leuther, R. Loesch, M. Seelmann-Eggbert, and H.Massler, “Ametamorphic HEMT S-MMIC amplifier with 16.1 dB gainat 460 GHz,” in Proc. IEEE CSIC Conf. Dig., Oct. 2010, pp. 245–248.

[7] W. R. Deal, K. Leong, X. B. Mei, S. Sarkozy, V. Radisic, J. Lee, P.H. Liu, W. Yoshida, J. Zhou, and M. Lange, “Scaling of InP HEMTcascode integrated circuits to THz frequencies,” in Proc. IEEE CSICConf. Dig., Oct. 2010, pp. 195–198.

[8] K. Leong, W. R. Deal, V. Radisic, X. B. Mei, J. Uyeda, L.Samoska, A. Fung, T. Gaier, and R. Lai, “A 340–380 GHz inte-grated CB-CPW-to-waveguide transition for sub millimeter-waveMMIC packaging,” IEEE Microw. Wireless Compon. Lett., vol. 19,no. 6, pp. 413–415, Jun. 2009.

[9] P. H. Siegel, R. P. R. P. Smith, M. C. Graidis, and S. C. Martin,“2.5 THz GaAs monolithic membrane-diode mixer,” IEEE Trans.Microwave Theory Tech., vol. 47, no. 5, pp. 596–604, May 1999.

[10] S. M. Marazita, W. L. Bishop, J. L. Hui, W. E. Bowen, and T. W.Crowe, “Integrated GaAs Schottky mixers by spin-on-dielectric waferbonding,” IEEE Trans. Electron Dev., vol. 47, no. 6, pp. 1152–1157,Jun. 2000.

[11] Y. C. Leong and S. Weinreb, “Full band waveguide-to-microstrip probetransitions,” in Proc. IEEE MTT-S Dig., Jun. 1999, pp. 1435–1438.

0

25

50

75

100

125

150

0.000

0.250

0.500

0.750

1.000

1.250

1.500

620.0 640.0 660.0 680.0

Po

we

r De

nsity

[mW

/m

m]

Me

asu

red

Po

we

r [m

W]

Frequency [GHz]

Power at Flange Output

Power from Transistor

Transistor Power Density




(Sparse) Aperture-plane (Phased) Arrays

• Inspired by Radioastronomical interferometry (VLA, ALMA)

• Circumvents spatial resolution/aperture size tradeoff

Figure 3: Schematic representation of the distributed aperture imager (left). The two-dimensional form factor makes it

possible to attach the detectors conformally to the airframe (right).

2. OPTICAL CONFIGURATION

The unique property of our imaging system approach is the upconversion of the millimeter wave signal to optical

frequencies using electro-optical modulators. This approach is feasible because the optically upconverted signal

maintains both amplitude and phase information of the mmW signal. By shifting to optical frequencies, optical fibers

can be used for signal routing while the Fourier transform property of a lens can be exploited to effect image synthesis.

The image thus formed can then be readily captured using an optical camera. In this way, a compact and lightweight

system may be realized that leverages readily available optical components, such as lasers, optical modulators, and

optical add-drop multiplexers (OADM). The latter item is an optical filter with very narrow passband and high out-of

band rejection, which is used for stripping the sideband signal from the carrier.

freq.

Int.

Laser Optical Modulator Bandpass FilterPhotodetector

MMW Antenna

DC

c c

c+ fc- f c+ f

freq. freq. freq.

Int. Int. Int.

freq.

Int.


MMW Antenna

DC

c c

c+ fc- f c+ f

freq. freq. freq.

Int. Int. Int.

Figure 4: Principle of operation for a mmW imager based on optical upconversion. In this case a single detector

channel is shown; for the distributed aperture imager, the many channels are optically recombined to produce an image.

The optical upconversion process is schematically illustrated in figure 4. A laser operates as an optical power supply

producing a quasi-monochromatic output that feeds an electro-optic modulator. Millimeter wave radiation that is

collected by an antenna is also fed to the modulator, where it creates upper and lower sidebands on the carrier by the

non-linear behavior of the modulator. The resulting signal is shown in figure 5. The optical carrier is then suppressed

T. Dillon, C. Schuetz, R.D.Martin, D.L.Stein,J. Samluk,

D.Makrides, m> Mirotznik, and D. Prather, ―Optical

Configuration of an Upconverted Millimeter-wave Distributed

Aperture Imaging System‖, Proc. SPIE, v7485(2009)

Figure 3: Schematic representation of the distributed aperture imager (left). The two-dimensional form factor makes it

possible to attach the detectors conformally to the airframe (right).

2. OPTICAL CONFIGURATION

The unique property of our imaging system approach is the upconversion of the millimeter wave signal to optical

frequencies using electro-optical modulators. This approach is feasible because the optically upconverted signal

maintains both amplitude and phase information of the mmW signal. By shifting to optical frequencies, optical fibers

can be used for signal routing while the Fourier transform property of a lens can be exploited to effect image synthesis.

The image thus formed can then be readily captured using an optical camera. In this way, a compact and lightweight

system may be realized that leverages readily available optical components, such as lasers, optical modulators, and

optical add-drop multiplexers (OADM). The latter item is an optical filter with very narrow passband and high out-of

band rejection, which is used for stripping the sideband signal from the carrier.

freq.

Int.


MMW Antenna

DC

c c

c+ fc- f c+ f

freq. freq. freq.

Int. Int. Int.

freq.

Int.


MMW Antenna

DC

c c

c+ fc- f c+ f

freq. freq. freq.

Int. Int. Int.

Figure 4: Principle of operation for a mmW imager based on optical upconversion. In this case a single detector

channel is shown; for the distributed aperture imager, the many channels are optically recombined to produce an image.

The optical upconversion process is schematically illustrated in figure 4. A laser operates as an optical power supply

producing a quasi-monochromatic output that feeds an electro-optic modulator. Millimeter wave radiation that is

collected by an antenna is also fed to the modulator, where it creates upper and lower sidebands on the carrier by the

non-linear behavior of the modulator. The resulting signal is shown in figure 5. The optical carrier is then suppressed

Optical filter

Optical lens and focal plane array

(multichannel correlator)




Radar Imaging with Coherent Receivers

K.B. Cooper, R.J. Dengler, N. Llombart, B.

Thomas, G. Chattopadhyay, and P. Siegel, ―THz

Imaging Radar for Standoff Personnel Screening‖,

Trans. THz Sci. and Tech. v1(1), p169-182 (2011)

• FMCW and Pulsed

• range information vs amplitude only

• range resolution ~ (bandwidth)-1

• scanning speed

• Implemented in ―conventional‖ ie Schottky diode multiplier and

mixer technology; naturally adapts to the TMIC technology

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B=@>FBFGDHNE?D@EOF72bRI< REO?IWK?KFG=BFF=G?HP A?GIB?< ?@=EFA

=>=?@GEEOF LDAP2

!@= GNLGF̂ NF@ECB=< F GODS @?@Z?>2 : XIY0 EOF GNLaFIEO=G

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EOF FA>F DCEOF 41 ( K?KFG?GGE?HHT?G?LHF2 #O?GGEBF=W?@> FCR

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E?D@2ZDBEOF LFGE?< =>F ^N=H?EP OFBF0= E=B>FES DNHAO=TF EDLF

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GODS G0GD< F?@CDB< =E?D@=LDNE=ID@IF=HFADLaFIE?GGE?HH=T=?HR

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GE=@A?@> DNEG?AF EOF B=A=BiG! FHADCT?FS EDGODS EOF K?KFG?@

EOF DKE?I=H?< =>F2

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BFTF=H?@> = O?AAF@< DIWO=@A>N@=@ALD< L LFHE2

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KH?I=EFAH=PFB?@> DCEOF a=IWFE0TFGE0GO?BE0=@A! @=HHP GW?@2#OF

B=@>F EDEOF C=BEOFGEDCEOFGF0KBFGN< FAEDLF =EDB@F=BEOFGW?@

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KHDG?TF GE?< NH=@EI=@=HGD LF F=G?HP BFTF=HFA S ?EO #* ; B=A=B

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Z?>2k2#OFC=GEFBCB=< FB=EFG=HGDKFB< ?ET?AFDGF̂ NF@IFGDCE=BR

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?@EOFB=@>F 727 2X#OFFHFT=E?D@F@AKD?@EGS FBFGH?>OEHP DTFBR

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GODS G0GD< F?@CDB< =E?D@=LDNE=ID@IF=HFADLaFIE?GGE?HH=T=?HR

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E?D@2Z?@=HHP0EOF CB=< FGDCZ?>2: XFY=@AXCYGODS = B=A=B?< =>F

DCEOF K?KFGS ?EO @D ID@IF=H?@> a=IWFE0=GS FHH=GEOF GNLaFIE

GE=@A?@> DNEG?AF EOF B=A=BiG! FHADCT?FS EDGODS EOF K?KFG?@

EOF DKE?I=H?< =>F2

FMCW: range encoded

In (IF) frequency




Focal Plane Arrays of Diode-based Detectors

M.E. Stickley and M.E.Filipkowski,‖Microantenna Arrays:

Technology and Applications MIATA, An Overview‖

Proc. SPIE v5619 (2004)

• Originated in 2004-2006 program on

monolithic arrays of 100-200GHz

detectors for passive imaging

• Antimonide backward tunnel (HRL)

• ErAs Schottky diode (Teledyne)

• NETD’s achieved 2-5 K




Focal Plane Arrays of Diode-based Detectors

D.J. Burdette, J. Alverbro, Z. Zhang, P. Fay, Y. Ni, P.

Potet, K. Sertel, G. Trichopoulos, K. Topalli, J. Volakis,

H.L. Mosbacker, ―Development of an 80x64 pixel,

Broadband, Real-time Imager‖, Proc. SPIE v8023(2011)

• Current development focused on tunnel diodes,

for higher freq. (Traycer)




Some Conclusions

• At low frequencies (100 GHz), scenes are very specular

• Active, amplitude-only systems are problematic • 360-degree subtense systems (portals) an exception

• Radar systems that image range (not intensity) OK • Require coherent reception with bandwidth ~1/(range resolution)

• Millirad resolution requires higher frequency or distributed

apertures

• Passive imaging requires NETD <0.5K (indoors)

• Cryogenic or coherent detector arrays needed • Modularity advantageous: robust reconfigurable, conformable

• Conical scanning enables high framerate, but leads to

nonuniform sampling

• TMIC receivers provide plausible path to arrays of

coherent receivers




Lessons for SiGe/CMOS and III-V

• For passive (indoor) imaging, NETD need implies

significant bandwidth challenge. • NETD = Tn (BW*tframe)

-1/2

• For BW = 15 GHz and NF = 12 dB (DARPA benchmarks)

NETD = 0.2 K,

BW > 50 GHz should be goal for passive imagers!

• For active imaging, simple and low-cost reflectarrays

may be easiest route to realtime imagers with

adequate FOV

for 100 % optics and atmo efficiency!

-> Can easily miss 0.5 K requirement


terahertz imaging and security...

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