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CMOS THz Detectors for CMOS THz Detectors for ImagingImaging

1CEA-LETI, MINATEC, Grenoble, FRANCE

2University of Montpellier, FRANCE

F. Schuster1,2, D. Coquillat2, H. Videlier2, M.Sakowicz2, JP. Rostaing1, B. Dupont1, B. Giffard1,

W. Knap2

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Outline

I. Introduction and Background

II. Detector Implementation

III. Detector Characterization

IV. THz Transmission Imaging

V. Summary

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I. Introduction and Background

• THz radiation:– THz band: 300GHz – 3THz, λ0 = 1mm -100µm– Unique physical properties– Applications

• Non-destructive testing/ quality control• Security imaging• Wireless communications

106 108 1010 1012 1014 1016 1018 f [Hz]

radio & µ waves IR UV X-ray

THz

VIS

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I. Introduction and Background

• FETs as THz detectors– Rectification of THz radiation

• Radiation coupling: antenna or grating• Theories: Dyakonov-Shur plasma wave theory;

distributed resistive self-mixing

Vgs

Ua

∆U

• Vgs: gate bias• Ua: irradiation

induced ac voltage• ∆U: photoresponse

GDS

THz , modulated

: fmod

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I. Introduction and Background

• Si CMOS THz detectors– First demonstration in 2004, Knap group – Focal plane arrays in 2008, Pfeiffer & Roskos groups– This work: single detectors and arrays for 0.3-1.05 THz

[1] Tauk et al. APL, 2006

650GHz Focal Plane Array [2]Single FETS at 700GHz [1]

[2] Öjefors et al. ESSCIRC, 2010

0 0.2 0.4 0.6 Vgs,V

200

100

0Res

pons

ivity

, V/W Lg=300nm

Lg=200nm

Lg=130nm

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II. Detector Implementation• Test chip micrograph

– 0.13µm CMOS– Bulk Si substrate

– 210µm pixel pitch– Pixel variants

• FET, antenna• amplifiers

– 3x4 pixel imager prototype: amps + multiplexing

2.2 mm

2.2

mm

210 µm 190 µm

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II. Detector Implementation• Pixel architecture

Bow tieantenna

Vout

– Bow tie antenna in metal back end

– Rectifying nMOSFET, variations:L=130nm – 300nm, W=250nm – 10µm

– Optional: in pixel baseband amplifier, G=31dB

FET ∆U

optional

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II. Detector Implementation• Amplifier schematic

– pMOSFETs– MIM capacitor for

feed back– G=31dB, 2MHz BW– Low consumption

97µW@1.2V– Low input noise:

16nV/Hz0.5@30kHz

∆U Vout

Vdd

bias

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II. Detector Implementation• Pixel micrograph

210 µm

210

µm

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II. Detector Implementation• 3x4 pixel imager with multiplexing

Shift Register

Clk 1Rst 1

Clk 2Rst 2

Shi

ft R

egis

terPixel

Array Output

• Pixel multiplexing with:– 2 shift registers– 2 clock, 2 reset

signals

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II. Detector Implementation• Pixel multiplexing

– Shift register with D-flip-flops

ClkRst

D QSD

C

D QSD

C

D Q

CDC

D Q

CDC

D Q

CDC

D Q

CDC

D Q

CDC

D Q

CDC

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III. Detector Characterization • Set-up

Lock-In

THzSource

Test Chip on Translation Stage

ParabolicMirror Plane

Mirror

Ref.Chopper

X,Y

Vout

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III. Detector Characterization • Set-up

THzSource

Imager

ParabolicMirrors

Chopper

Translation Stage

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III. Detector Characterization • Set-up: beam power measurement

– THz power meter, Thomas Keating– Large aperture: 3 x 4cm

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III. Detector Characterization • Results 1/5: pixels without amplifier

Raster scan image of source beam at 300GHz

Used for responsivity calculation

Vgs=0.1V

Pbeam=0.8mW Adet = (pixel pitch)2

detAP

dydxU

Rbeam

image

v ⋅

∆=∫∫

Vgs=0.1V

Pbeam=2mW

∆Umax = 19mV

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III. Detector Characterization • Results 2/5: pixels without amplifier

Responsivity & NEP at 300GHz

0.0 0.2 0.4 0.60

1k

2k

3k

4k

5k

0.0 0.2 0.4 0.6

10p

100p

1n

10n

Vgs

(V)

R

v (V

/W)

C14, 125µm C5, 125µm C14, 370µm x 2 C15, 125µm x 10

substrate

Vgs

(V)

C14, 125µm C5, 125µm C14, 370µm / 2 C15, 125µm / 10

N

EP

(W

/Hz0.

5 )

vds RRTkNEP /4=

NEPmin=8 pW/Hz0.5

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III. Detector Characterization • Results 3/5: pixel C14 without amplifier

Responsivity from 270- 1050 GHz

300 400 500 600 700 800 900100010

100

1k

10k

Rv (

V/W

)

Frequency (GHz)

1 2 3 4 51

2

3

4

5

C14, 125um

Vgs

=0.2V

1050GHz, 180µW Beam

∆∆∆∆U (V)Y p

ositi

on (m

m)

X position (mm)

0.017µ34µ51µ68µ

34µ

Rv,max =5kV/W

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III. Detector Characterization • Results 4/5: pixel with amplifier,

Raster scan image of source beam at 300GHz

X position (mm)

Y p

ositi

on (

mm

)

Vout (V)

Vgs=0.1V

Pbeam=0.8mW

Vout,max = 165mV

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III. Detector Characterization • Results 5/5: pixel with amplifier

Detector signal & responsivity at 300GHz

Rv,max = 90kV/W

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IV. THz Imaging• Transmission imaging of objects

Object on Translation Stage

Lock-In

THzSource

Test Chip on Translation Stage

ParabolicMirror Plane

Mirror

Ref.Chopper

X,Y

Vout

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IV. THz Imaging, 300GHz• chocolate with metal object inside

→ application: food control

Metal wire

225x300 scanned points

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IV. THz Imaging, 300GHz• tree leaves → agriculture: water saving

225x600 scanned points

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V. Summary

• Demonstration of sensitive THz detectors & 3x4 pixel array in CMOS– nMOSFET THz detectors– Integrated broad band bow tie antennas

– Pixel consumption <100µW– High responsivities: 90kV/W @300GHz,

1.8kV/W @1.05THz

– Low NEP: <10pW/Hz0.5 @300GHz– High quality THz images @300GHz

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Recent Publications

[1] F. Schuster, A. Dupret, W. Knap et al. A Broadband THz Imager in a Low-cost CMOS Technology. International Solid-State Circuits Conference, 2011.

[2] F. Schuster, D. Coquillat, W. Knap et al.Broadband terahertz imaging with highly sensitive silicon CMOS detectors. Opt. Expr.vol. 19, pp. 7827–7832, 2011.

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Acknowledgements

• Partial funding from:– French Ministry of Defense– STMicroelectronics through Nano

2012 Project

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Thank you!Questions?