THz/sub-THz direct detector challenges: rectification and thermal

detectors for active imagingF. Sizov, V. Reva, O. Golenkov, V. Petriakov, A. Shevchik-Shekera,

S. Korinets, M. Sakhno, I. Lysiuk, V. Zabudsky, S. Bunchuk, S. Dvoretskii

Institutes of Semiconductor PhysicsKiev (Ukraine), Novosibirsk (Russia)

MIKON-2014, Gdansk, 18 June, 2014

THz technologies starting to be important for some applications and they can be added to existing X-ray and IR technologies e.g. in:

But one of the drawbacks of THz vision technologies now is large acquisition time (up several minutes for systems with single detetor).

To increase the acquisition speed but be cost-effective uncooled detector arrays are needed.

- Security applications (detection of threats and weapons), - Nondestructrive testing (electronics industry, corrosion analysis, agro-food control, …), - Medicine and Biology (e.g. pharmaceutical quality control, skin cancer, …), - Telecommunications.Possible THz imaging

applications.

(a,b): Time domain spectroscopy (TDS), (c) Direct (passive) imaging, and (d) Heterodyne imaging.

THz imaging technologies

a) - Active and Passive Coherent Millimeter and THz Wave Imaging; b) - Pre-amplified Direct Detection Imaging; c) - Incoherent Un-amplified Direct Detection Imaging.

Simplified schematic of heterodyne receiver architecture. Can be passive and active.

Simplified schematic of a pre-amplified direct detection receiver (as a rule limited to W-band). Can be passive and active.

Simplified schematic of un-preamplified direct detection receiver. Low-temperature can be passive. Un-cooled – active.

Current status of the “uncooled” THz imaging technology

Image plane

Аd

D

f (at l >> f)l

Aоb

j

Sop

Instantaneous FOV

Optical system sketch.

To estimate NEP needed for a passive system

For 1 0.85 mm, /0.3, =1 and NEDT 0.1 K NEP1 1.310-12 W/Hz1/2. For 1 3.0 mm, NEP2 410-13 W/Hz1/2.

For frame rate fr =10 Hz, the integration time for detector tint 10-1 s and the noise equivalent bandwidth fe =(2tint)-1 5 Hz. Then for pixel

NEP1610-13 W/Hz1/2 and NEP2 210-13 W/Hz1/2. If = 0.3 then these values should be multiplied by 1/2 0.55.

4

dT

)Т,(PANEDT

NEP

u

co

d

Earth atmosphere transparency from visible to radiofrequency band regions [A.H. Lettington, et.al., Proc. SPIE 4719, 327-340

(2002)]. Also spectral radiances of blackbodies with temperature T6000

K (Sun) and T300 K (Earth) are shown .

10000

1000

100

10

1

0.1

0.01

0.00110 100 1,000 10,000 100,000

Frequency (GHz)

Pow

er (

mW

)

~n-2~n2

THz gap THz gap with respect to source technology: ( ) quantum cascade lasers (QCL) are progressing downward from high frequencies, the lowest n = 1.2 THz, T = 110 K – CW, T = 163 K – pulsed; ( ) frequency multipliers dominate other electronic devices ( ) above about 150 GHz (after T.W. Crowe, et.al., IEEE J. Solid-State Circuits 40, 2104–2110 (2005))

Curves that define BLIP performance are calculated for diffraction limited beams

taking into account that AТ is an invariant of optical system with coherent (heterodyne) detectors. Effective receiving of diffraction limited beams at the

entrance of the optical system is defined by AТ = 2, where АТ is a circle aperture area and (sr) is a solid angle. For system with direct detection detectors it is possible AT > 2 and as a rule it is, and that is a benefit of direct detection

systems in a case of broad-band radiation (e.g. in vision systems).

1940 1950 1960 1970 1980 1990 2000 2010

10-10

10-12

10-14

10-16

10-18

10-20

BLIP-ground imaging

BLIP-ground / =300 spectroscopyn n

BLIP-space / =1000n n

Year

Noi

se e

quiv

alen

t pow

er (

W/H

z)

1/2

Low-temperature bolometers NEP improve a factor of two

every two years

Si PIN

SWIR HgCdTe

MWIR HgCdTe

LWIRHgCdTe

InGaAs

InSb

Si:As BIBSi:Sb BIB

0.1 1 10 100 1000

1000

100

10

1

0.1

Ope

ratin

g te

mpe

ratu

re (

K)

Wavelength ( m)m

Ge:Ga stressed

Ge:Ga

Operating temperatures for low-background detectors. Longer wavelength detection - lower operating temperature for (After A. Rogalski, in: THz and Security

Applications, Springer, 2014).

But for THz/sub-THz applications it is desirable use of cost-effective uncooled detectors.

1 10 100 1000Wavelength ( m)m

10000

1000

100

10

NE

P (

pW) Calculation

SNR=1TV/4 (320x240),49.5- m pitch, NECmTV/4 (320x240),23.5- m pitch, Leti

(160x120), 23.5- m pitch, INO

m

m

Microbolometer NEP spectral dependence for THz FPAs (reprinted from A. Rogalski, in: “THz and Security Applications,” Springer, 2014).

IR and THz vision technologies are different in many aspects (i) IR technologies now are passive and THz technologies can be passive

only with sensitive detectors in some applications.

(ii) The sizes of IR sensitive elements, as a rule, are larger or comparable with the wavelength but the sizes of THz/sub-THz sensitive elements are smaller (at n ≤ 3 THz) the wavelength and, as a rule, they require antennas use.

(iii)Differences in physics of signal registration processes and constraints, especially when integrated in large arrays (systems), and many details not important when constructing IR arrays are crucial when making up THz arrays (e.g. antennas, substrate permittivities, their thickness, lenses etc.).

Different physical phenomena are present that calls for multidisciplinary special knowledge.

Three detector types were considered: MCT narrow-gap bolometers, SBDs, and FETs (HEMTs).

141 GHz, without Si lens, d=400 mm.

141 GHz, without Si lens, d=350 mm.

Equivalent circuits for electrical matching with antenna

~

ZA

VA

CP

RS

ZS

G,in

t~

ZA

VA

CP

RS

RD

~

ZA

VA

RHEB

RS

Si - FETSBD MCT- HEB

RS ~ 200 ÷ 500

ZIN ~ 103 ÷ 104

RS ~ 20 ÷ 100

ZIN ~ 1000 ÷ 2000

RS ~ 20 ÷ 100

ZIN ~ 100 ÷ 1000

ZA ~ 50 ÷ 200

Simplified schematic representations with basic parasitic components. ZA - antenna impedance; VA - antenna voltage amplitude; RS = RG + Rsource in FET is

the active series (parasitic) resistance of FET, where RG is the gate active resistance; RS in SBD and MCT-HEB is series parasitic active resistance; RD is

SBD differential active resistance; CP is the parasitic reactance (usually capacitive), ZGS,int is internal source-gate impedance.

Long channel, LCH>Leff, Zero-bias HEB

MCT hot electron bolometer Electrons in MCT bolometer are heated by electromagnetic wave field changing the bolometer resistance

Three free carrier effects are responsible for MCT bolometer response:

-Dember effect (photodiffusion effect) contribution;-Thermoelectromotive contribution;-Free carriers concentration changes.

They are differently temperature dependent that may cause the change of the response sign on temperature.

(V. Dobrovolski, F. Sizov, Opto-Electr. Rev., 18, 250 (2010))

MCT bolometers

F. Sizov, V. Petriakov, et.al., Appl. Phys. Lett. 101, 082108 (2012)Signal profile dependence at

detector displacement

1500

200

600

Sensitive element 60x30µmContact pads

Quartz substrate

Antenna

In bumps

Quartz substrate

Metallization

Epilayer

GaAs substrate

Bolometer

Linear hybrid array of hot electron bolometers with antennas on quartz substrate for radiation frequency

n ~ 125 – 145 GHz. Quartz substrate ( ~ 4.8) thickness is 200 mm.

Example of linear hybrid array of hot electron MCT bolometers on GaAs substrate with antennas on quartz substrate for radiation frequency n ~

125 – 145 GHz. Quartz substrate ( ~ 4.8) thickness d=200 mm

A

a)

b)

Schematic of glass fibre laminate wafer with microlens and sensitive element (a), microlenses and sensitive elements (MCT microbolometers on the back side of microlenses) with antennas on GaAs substrate and fiber glass wafer (b).

126 128 130 132 134 136 138 140 142 144 1460123456789

1011121314

U,

mV

n, GHz

# 1 # 2 # 3

Ibias=5mA

Signal frequency dependences for 3 MCT microbolometers with Si lenses immersed into glass fibre laminate wafer by 1 mm. S/N ~> 3104, Ibias=3 mA, with lock-in.

0 2 4 6 8 10 120,0

0,2

0,4

0,6

0,8

1,0

Noise = 160 nV/Hz1/2

SNR = 750 ( = 6.5 mm)

MCT HEBT = 78 K x = 0.214

n ~ 5*1014 cm-3

S = 60 x 20 mm2

S, a

.u.

, mm0 2 4 6 8 10 12

0,0

0,2

0,4

0,6

0,8

1,0

Noise = 17 nV/Hz1/2

SNR = 50 ( = 5 mm)

MCT HEBT = 300 K x = 0.214Intrinsic conductivity

S = 60 x 20 mm2

S, a

.u.

, mm

MCT THz/sub-THz detector IR responsivity spectra a) T = 78 K, b) T = 300 K

a) b)

00 600 1200 1800 2400 3000 3600-200

-150

-100

-50

0

50

100 143 GHz

131 GHz

T = 293 K, ~ 50, W = 20 mm, L = 2 mm

V, a

rb. u

n

, degree

FET Long Channel detectors

0,0 0,5 1,0 1,5 2,00,0

0,2

0,4

0,6

0,8

1,0

W = 1 mmL = 1 mm

I DS, a

.u.

VGS

, V

ddVGS

140 GHz

64 GHZ

0,0 0,5 1,0 1,5 2,00,0

0,2

0,4

0,6

0,8

1,0

W = 8 mmL = 1 mm

I DS, a

.u.

VGS

, V

0,8 1,0 1,2 1,4 1,6 1,8 2,00,0

0,2

0,4

0,6

0,8

1,0

140 GHz

64 GHz

W = 1 mmL = 1 mmf Z

, a.u

.

VGS

, V0,8 1,0 1,2 1,4 1,6 1,8 2,0

0,0

0,2

0,4

0,6

0,8

1,0

W = 8 mmL = 1 mm

f Z, a

.u.

VGS

, V

Dependencies of drain-source currents and effective coefficient fz on FET channel dimensions and radiation frequency

Antennas, 265-375 GHz.

0.0

50.0µ

100.0µ

150.0µ

200.0µ

0

30

60

90

120

150

180

210

240

270

300

330

0.0

50.0µ

100.0µ

150.0µ

200.0µ

U (

V)

2-10

E

Sample 1 Line 1 Transistor 7

50.0µ

100.0µ

150.0µ

200.0µ

250.0µ

300.0µ

350.0µ0 15

30

45

60

75

90

105

120

135

150165180

50.0µ

100.0µ

150.0µ

200.0µ

250.0µ

300.0µ

350.0µ

U (

V)

T5

E

Sample 1 Line 1 Transistor 5

E

(Exp. data of W. Knap, D. But, et.al.).

Vdet = Pant,maxRV,intaL22

,int ,int,int 12

Re /

Re /

SG SGin

in SG SG SG

Z ZP Z

P Z Z Z

Power transmission coefficient is ratio of power absorbed in internal part of transistor Pin,int to power Pin that is absorbed in transistor as a whole.

1/2 3/2

1 2 3

1

1c c c

-2

c1SR

-1

c2 2 P SC R

3/23 )2( S

2Pс RС 2

CH

ox

R

C

a is an antenna transfer coefficient, L is loading matching coefficient.

RVmeas ~Vdet ~n-2 if wide aperture antennas are used (or, for example,

in experiments lenses are used), RVmeas ~Vdet ~n-4 in other cases.

a~0.2 at Zant~(100 - j100) , n77 GHz, L ~1 at voltmeter Rinput~10 M

202

1el elV I

p S

R RC R

is in the range of ~10-40 A/W for almost every transistor. For SBD at T=300 K and n = 1, RI,int=19.3 A/W is a max figure.

0elIR

MOSFET and SBD as mm-wave/THz detector

Responsivity RVIO (n) as a function of radiation frequency in the linear region for pulsed detection measurement. Dots are experimental data of FET detectors (HEMT) at Iir = 10 W/cm2. Line is fitting with n = 2. [D. But, W. Knap,

et.al., JAP, 115 (2014)]. Vdet ~ω-2 if wide aperture antennas are used (or, for example, in experiments lenses are used), Signal ~ ω -4 in other cases (Sakhno

M, et.al. J Appl Phys (2013).

FET NEPel improvement performance when going from 1 µm technology, W/L=20/2 (mm) to 0.35 µm technology, W/L=1/1 (mm).

0 10 20 3010-12

10-11

10-10

10-9

10-8

1-mm, W/L=20/2 (mm) 1-mm, W/L=4/2 (mm) 0.35-mm, W/L=1/1 (mm) SBD

NE

Pop

t , W/H

z0.5

n, 1011 Hz

15

17

14

1418

18

6

19

19

19

2

1

20

21

2159

NEPopt with antenna impedance Zant=(100–j100) Ω (taken into account parasitics). Open marks - for Si FET detectors and filled marks - for SBD detectors.

M. Sakhno, A. Golenkov, F. Sizov, JAP, 114, 164503 (2013).

One-chip eight-element THz/sub-THz linear array with antennas, amplification and information

processing circuits.

FET THZ/sub-THz detectors (Si-KMOP, 0.35 mm design rules)

Output signals of eight-element linear array under Gaussian beam.

-5 -4 -3 -2 -1 0101

102

103

104

105

GaNS1, g7d9

VDS

=50 mV

RC

H,

VDS

,V

-6 -5 -4 -3 -20

5

10

15

20 VDS

= 0 V,

Rload

= 10 Mfmod

= 331 Hz

n = 140 GHz

PTHz ~ 0.071 W/cm2

GaN, T = 300 K, S1, g7d9

VGS = -4.6 V

SV ~ 46 V/W

NEP ~ 10-10 W/Hz1/2

VD

S, m

V

VGS

, V

-5 -4 -3 -2 -1 00

1

2

3

GaNS1, g7d9

VDS

=50 mVI DS, m

A

VGS

, V

GaN HEMT detectors

Authors are thankful to K. Zhuravlev and J. Gumenjuk for supplying GaN

transistors

W/L~100

Detector n, GHz Output Resp., SV Noise NEP, W/Hz1/2

MCT 138 11 mV(Ibias=5 mA)

~140 V/W(Ibias=5 mA)

~37 nV/Hz1/2 (Ibias=5 mA)

~2.6·10-10

(G8 dBi)

Si-FETwithout antenna

140 VDS ~ 60 mV ~200 V/W UJN ~ 90 nV/Hz1/2

~5 10-10

(G = 1, = 1)

GaN HEMT 140 ~46 ~10-10

Conventional SBD

(GaAs)without antenna

139 58 mV(Vbias =585

mV)

~800 V/W ~360 nV/Hz1/2

(Vbias=585 mV)

~5.7·10-10

(G1.05 dBi)

Zero-biased SBD

150 – 440 Vbias= 0 SV = 300-1000 V/W

- 2·10-11÷5·10-12

Zero-biased SBD

(InGaAs/InP)

320 Vbias= 0 120÷200 V/W

- 5·10-10÷1·10-11

Parameters of sub/THz detectors investigated

Pictures of lighter at n 150 GHz by existing incoherent un-amplified direct detection single detector prototype with MCT bolometer. a) – lighter in envelope, b) – lighter in envelope behind the gypsum plasterboard of d = 12 mm, c) – visible region. Two medicine pills in the thick non-transparent envelope of different form and

dimensions. In the upper pill the small (~2x2 mm) dielectric item (d~0.3 mm) is imbedded. Dark rings around pills seem arise due to the phase differences

between the beams in air and in pills. Right – example of leafs imaging

Visible

n GHz

n GHz

Imaging examples obtained with single FET and MCT uncooled bolometer system

F. Sizov, V. Zabudsky, et.al., Optic. Eng., 52, # 3 (2013)

27

Lighter in envelope behind gypsum plasterboard of d = 12 mm, SNR ~ 41 dB

SNR ~ 54 dB

1

2

3

Lighter (1), electric cable (2) and a bit of metal sheet (3) in opaque envelope in reflection configuration through the gypsum plasterboard with d=12 mm (radiation passes twice through plasterboard) at n 150 GHz.

-Uncooled MCT, FET and HEMT detectors and arrays can be applied in active THz/sub-THz direct detection systems;

- Long channel FET detector performance is mainly limited by parasitic effects;

- FET, SBD and MCT detectors performance is proportional to n-2 or to n-4 in dependence on the antenna type and measurement procedure;

- FET detector performance can be improved with the design rules advance due to lowering the parasitic effects;

Partly these investigations were supported by NATO contract

SfP 984544.

Conclusions