quantum engineered field-effect transistors for warm, wide-bandwidth, near quantum-limited terahertz...
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![Page 1: Quantum engineered field-effect transistors for warm, wide-bandwidth, near quantum-limited Terahertz heterodyne receivers Mark Sherwin UCSB Physics Department](https://reader036.vdocument.in/reader036/viewer/2022062321/56649dc95503460f94abf0c7/html5/thumbnails/1.jpg)
Quantum engineered field-effect transistors for warm, wide-bandwidth,
near quantum-limitedTerahertz heterodyne receivers
Mark Sherwin
UCSB
Physics Department
and
Institute for Terahertz Science and Technology
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Herschel Space Observatory
Bilpratt et. al., A&A 518 L1 (2010)
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Heterodyne Instrument for Far Infrared (HIFI)
Th. De Grauw, et. al., A&A 518 L6 (2010)
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HIFI spectrum of Orion hot core
Th. De Grauw, et. al., A&A 518 L6 (2010)
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35Cl/37Cl ratio in dense molecular clouds
J. Cernicharo et. al., A&A L115 (2010)
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H2O in cometary atmosphere
3x105 km
P. Hartogh et. al., A&A 518, L150 (2010)
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Coherent detection (e. g., heterodyne mixing)
Frequency
Sig
nal
fLO= 1 THz to 5 THz
fsigfIF = 1 - 10 GHz
• Receiver Noise:
Top = TA+ TM + TAmp / M
• Integration Time:
(TR)2
Mixer
TM
M
PLO
fLO
TAmpfIF
IF AmpBackend
SpectrometerfIF = | fLO - fsig|
HETERODYNE RECEIVERf / f = 107 - 108
Quantum Limit
(double sideband)TM≥hf/2kB
TQ= 25K @ 1 THz
TA
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DSB system noise temperature on HIFI
Th. De Grauw, et. al., A&A 518 L6 (2010) Operating temperature 1.7K
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Heterodyne receivers for future missions
• Higher frequency (HD @ 2.7 THz, [email protected] THz)
• Lower noise
• High temperature operation (40-100K)
• Wider bandwidth (>15 GHz vs. 4 GHz for phonon-cooled HEB)
• Low LO power
• Arrays
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Superconducting hot-electron bolometers
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Superconducting hot-electron bolometers
Theory, proposed mixers
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Proposed mixers
• Mixer noise temperature (classical theory): 200K DSB
• Operating temperature: Top=30-100K
• LO frequency: 1.5-5 THz
• IF bandwidth: >15 GHz
• LO power requirement: – ~1 µW@ Top=30K
– ~100µW@ Top =100K
• Planar, suitable for arrays
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Quantum-engineered FET as hot-electron bolometer
SourceDrain
IF
THz
Front gate (to antenna)
Back gate (to antenna)
absorberdetector
“Tunable antenna-coupled intersubband terahertz (TACIT) sensor”
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Relevant physics in quantum wells
• Absorption: intersubband transition in quantum well
• Detection: temperature-dependent mobility of 2-D electron gas
IF
THz
absorber
IF
THzdetector
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Example: intersubband absorption in square quantum well
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Intersubband absorption in square well
0 20 40 60 80Position (nm)
Ene
rgy
(meV
)250
150
50
0
100
200
Al0.3Ga0.7AsGaAs
in-plane wavevector k
Ene
rgy
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Absorption vs. dc electric field, constant Ns
2.4 THz 4.8 THz
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Absorption peak vs. dc electric field, charge density
Experiment:Williams et. al., PRL, 2001)
Theory:Ullrich and Vignale Ibid.
ns=1010 cm-2
ns=13x1010 cm-2
Time-dependent Local density approximationAll parameters from experiment
Frequency (T
Hz)2.4
4.8
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Intersubband absorption below 1 THz
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Detection: temperature-dependent mobility
IF
THzdetection
• Mobility of 2-D electron gases vs. temperature
• Mobility determined by electron temperature Te.
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Detection
• Hot-electron bolometric
IF
THzdetection
1R||
dR||
dT
⎛
⎝ ⎜
⎞
⎠ ⎟ ≡γ =0.01−0.03K−1@50K
ρ=dVdP
=IR||γT1
CV
=IR||γT1
1NSAkB
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Speed
• Phonon cooling
• Diffusion cooling– 20 GHz IF bandwidth demonstrated in 4µm long millimeter-wave mixer. (M.
Lee et. al., APL 2001)
J. N. Heyman et. al., PRL 74, 2682 (1995)
109
1010
1011
0 0.04 0.08 0.12
1/T (K-1)
50 25 10
T (K)IF
bandwidth (G
Hz)
0.16
1.6
16
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Coupling efficiency: impedance of active region
LV(t)
Area ACharge Q+ + + + + + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -2-DEG=
Dipole sheeton springs
On resonance
€
C =ε 0εA
L
R =q2
ε 2ε 02m *
Ns f12n(T)
2πf( )2A2Γ
R can be 20 in future designs
C can be tuned out byrf embedding circuit design
Source-Load coupling can be>90%!
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The math
€
Z ω( ) =Vω
Iω
€
Z(ω*) =Vω*
Iω*
=L
iω*εε0A+
NSe2 f12n(T )ε 2ε0
2Am *ω*2 2Γ=
1iω*C
+ Rzz
€
= 1iωεε0A
L −χ 2D ω( )
εε0
⎛
⎝ ⎜
⎞
⎠ ⎟€
Vω = EωL − P2D /εε0€
χ2D ω( ) =NSe2 f12n(T )
m *1
ω*2 −ω2 + i2ωΓ
€
P2D(ω) = χ 2D(ω)Eω
M. Sherwin et. al., Proceedings of 2002 Monterey Submm workshop
LV(t)
Area ACharge Q+ + + + + + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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Can couple efficiently to ~10,000 electrons!
LV(t)
Area ACharge Q+ + + + + + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -2-DEG=
Dipole sheeton springs
On resonance
49 Ohms*
18 Ohms*
*on resonance for high-quality 40 nm square well, Te=50 K, f=2.3 THz, A=5µm2,L=0.15 µm
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Theory for NEP, TM
• NEP (direct detector)
– =insertion loss, =1/R(dR/dT), NS= sheet density, A=active region area
• Double sideband noise temperature (mixer)€
NEP = α −12kB
NS A
τ
4
γ 2+ Te
2
€
TM = α −1 4
γ 2Te
+ Te
⎛
⎝ ⎜
⎞
⎠ ⎟
M. Sherwin et. al., Proceedings of 2002 Monterey Submm workshop
Johnson noise Thermal conductionnoise
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Performance limits for TACIT mixer
10,000 electrons106 cm2V-s @ low temp.Bulk LO phonon scattering
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First-generation devices
• Twin slot coupled to coplanar waveguide
• Demonstrated direct detection, electric field tuning
• Difficult fabrication with very low yield
• Quantum well far from optimal
• Microwave embedding circuit far from optimal
• Collaboration with W. R. McGrath, Paolo Focardi
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Completed TACIT detector
Source
Drain
Front gate bias line
Back gate bias line
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10nm
130
nm
10.8 nm
197
nm
500
nm
1000
nm
200
nm
70 n
m9 nm
70 n
m
3 nm
0.5
mm
subs
trat
e
buff
er
etch
sto
p
cap Si d
elta
Dop
ing
(101
2 c
m-2)
Coupled quantum wellsba
rrie
rs
cap
GaAs Al0.3Ga0.7As
Sample structure design and growth
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Intersubband absorption characterization
THz in (FTIR) THz out
bolometer
1.6 THzDesign frequency
theory
Electrons in quantum well
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Fabrication of 1st generationTACIT detector
Epoxy Bond and Stop-Etch (EBASE), Sandia
1. Process front side
2. Epoxy bond to GaAs wafer
3. Etch away substrate
4. Process back side, etch vias
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Experimental Set Up
IF
THz
GaAs Host Substrate
Silicon LensUCSB Free Electron Laser at 40-80 cm-1
Sample in a Helium Flow Cryostat, T=20-100K
Current amplifierSources and measures channel
oscilloscope
0 V
Gate Voltage
0
5
10
15
-5 0 5 10 15
Signal /mV
Time/ microseconds
5s, 1mW
0
10
20
30
40
50
-5 0 5 10 15
Signal /mV
Time/ microseconds
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Response to fast THz pulses
1.5 ns 3.5 ns
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Tunability with gate voltage
300
400
500
600
700
800
900
1000
0.25
0.26
0.27
0.28
0.29
0.3
0.31
0.32
0.33-1 -0.5 0 0.5 1 1.5
signal/ nanoAmps
signal/milliVolts
front gate - back gate Voltage
Sample ATb=100KTe~120Kf=1.53 THzFEL
Sample BTb=77KTe~100Kf=1.6 THzMoleculargas laser
Pho
tocu
rren
t (n
A)
Photovoltage (m
V)
Charge density held constant.
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Origin of “double peak”
2000 2100 2200 2300 2400 2500-50
0
50
100
150
200
250
300field = -0.2 mV/Angstrom
Energy / meV
2000 2100 2200 2300 2400 2500
field = 0.2 mV/Angstrom
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
45
50
55
60
65
70
Intersubband Resonance
Frequency /THz
Intersubband Resonance
Frequency /cm
-1
-0.2 -0.1 0 0.1 0.2
Electric field (mV/Angstrom)
Inte
rsub
band
ab
sorp
tion
fre
quen
cy (
TH
z)
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New design*
• Easier fabrication• Eliminate some parasitics• Can rapidly iterate to optimize
Inspired by Chris McKenney’s thesis, Cleland group.
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TACIT mixer development strategy
• Microwave engineering• MBE growth of wafers with high mobility,
narrow intersubband linewidth.• Develop fabrication process• Test and iterate
40
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TACIT specs to enable new missions
• High-temperature operation• Wide bandwidth• High frequency• Low noise
41
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Herschel cryogenics
• Herschel– Large dewar drives up mission costs– Duration limited to 3.5 years
42
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Long-duration mission with cryocooler
• Atmospheric Infrared Sounder (AIRS)– Detectors @ 58K– Long-lifetime cryocooler– Launched 2002
43
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Potential platforms for TACIT mixers
• Explorer-class missions– Astrophysics– Planetary science
• Long-duration ballooning• SOFIA
44
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Summary and conclusions
• THz heterodyne spectroscopy: important science• TACIT mixers offer improvements over state of art
• Timely to develop TACIT mixers in concert with new mission concepts
45
Superconducting HEB actual
TACIT mixer theory
Operating temp. 2K 30-100K
Bandwidth 4 GHz >15 GHz
Noise temperature @ 2.5 THz
1000K 200K
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Acknowledgments
• W. R. McGrath (JPL): Antenna design• P. Focardi (JPL): Antenna impedance, mode matching
theory• G. B. Serapiglia (UCSB->law school): processing,
characterization, experiments• Sangwoo Kim (UCSB-> Tanner Research Labs): room-
temperature devices.• M. Hanson (UCSB): sample growth• A. C. Gossard (UCSB): sample growthFunding: NASA, NSF
46
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Insertion losses for this device and experiment
• Matching antenna pattern– Only 4% coupled into antenna mode*– Device fried before could be improved– Mode matching can be increased to >90%+
Antennapattern
Illumination pattern
*Computed following Goldsmith, “Quasioptical systems”
+Focardi, McGrath and Neto, IEEE MTT 2004.
Zload=(1.7-i39)
Pin
€
PLoad
PIn
=1−ZS − ZL
*
ZS + ZL
2Zsource=(20-i40)
• Matching antenna and load impedances- Only 2.5% coupled from antenna into load
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Responsivity at Tbath=80K
• Roptical=V/Pin=0.1 V/W
• Rinternal=Roptical/(total insertion loss)=107±75 V/W
• Relectrical
• Theory: Rinternal =(1100±400) V/W€
Relectrical =
V
I−
dV
dI
⎛
⎝ ⎜
⎞
⎠ ⎟
2V= (400 ±150)V /W
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Electrical transport data
This sample
106 mobility2-DEG
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Electrical transport data