Nanodevices for THz Applications
Tomás González University of Salamanca, Spain
Research Group on Semiconductor Devices THz Nanodevices at USAL
Research Group on Semiconductor Devices - Modeling of nanodevices for THz applications - Design of optimized structures (feedback to technology)
THz Laboratory - Detection and emission of THz radiation from plasma wave nanodevices - Time-domain spectroscopy and imaging in the THz range
T. González - Nanodevices for THz Applications December 12, 2012 Research Group on Semiconductor Devices
http://campus.usal.es/~gelec/ CONTACT: Prof. Tomás González ([email protected]) Staff: 8 permanent researchers, 3 post-doc, 2 students Collaborations with several EU (IEMN, Chalmers, Manchester, Montpellier, etc.) and USA Labs. (Rochester)
Monte Carlo simulation of high-frequency nanodevices InGaAs/InAlAs, InAs/AlSb and GaN/AlGaN HEMTs
RESEARCH LINES
(FP6 project METAMOS) InGaAs based THz ballistic nanodevices (FP5 project NANOTERA ) Advanced Si MOSFETs
100nm TBJs YBJs MUX/DEMUX SSDs
Coordinator of the FP7 STREP Project ROOTHz (FP7-243845) Characterization Laboratory (DC-GHz) Semiconductor Nanodevices for Room Temperature THz Emission and Detection - http://www.roothz.eu/
GaN diodes InGaAs/InAlAs diode Research Group on Semiconductor Devices EQUIPMENT Computer Clusters Probe station (Cascade M150)
Keithley 4200: DC and pulsed VNA Agilent PNA-X: measurements (Keithley 4225) RF measurements up to 43.5 GHz THz Laboratory
Contact: Dr. Yahya Meziani ([email protected])
Plasma-wave nanodevices
A glimpse of the considered structures:
Doubly interdigitated grating Strained Si/SiGe n-MODFET gates in III-V HEMT
THz detectors based on Graphene transistors THz Laboratory
Si/SiGe MODFETs used as sensors in THz signals detection
Si/SiGe MODFETs used as sensors in THz imaging THz Laboratory
Facilities
Terahertz Spectroscopy System Probestation
THz-Time Domain Spectroscopy System: EKSPLA Cascade Summit 11000B manual probestation with
Spectrometer+Ti:Sapphire Laser (Spectra-Physics) FemtoGuard® and PurelineTM technologies (200mm-chuck)
THz imaging: Gunn Diode at 0.2TH + frequency tripler + Agilent B1500 (4 SMUs, 1 multifreq CMU and 1 WG/FMU
OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs)
Conclusions / Perspectives
T. González - Nanodevices for THz Applications December 12, 2012 The THz Band
1 THz = 1012 Hz THz range (100 GHz to 10 THz) (300 GHz to 3 THz, 1 - 0.1 mm)
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications
THz radiation can penetrate poor weather, dust and smoke far better than infrared or visible systems.
Aeronautics: guidance and landing Satellite Telemetry
Image of sea surface temperature (European Space Agency)
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: medical diagnosis
THz radiation can penetrate organic materials without ionizing
Readily absorbed by water: distinguish between materials with varying water content
Medical imaging
Skin Cancer Detection
Courtesy of Teraview Courtesy of Teraview
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: security
THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: testing
THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls
Non-destructive testing: integrated circuit package inspection
Courtesy of Teraview
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: security
THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls
THz radiation can penetrate organic materials without ionizing
Weapon or Explosive Detection (metallic or non metallic)
Courtesy of Qinetiq Courtesy of Qinetiq Courtesy of Thruvision
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: security
THz radiation can penetrate dielectrics such as windows, paper, clothing and in certain instances even walls
Full-body security screening, body scanners
Passive Detection - no THz source is needed
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: spectroscopy
THz radiation can be used to identify spectral fingerprints of explosives, narcotics, or active pharmaceutical ingredients THz Spectroscopy
Active Detection - THz sources are needed (narrow or broadband)
Driving force of THz technology so far: spectroscopy, imaging, sensing
T. González - Nanodevices for THz Applications December 12, 2012 Potential applications: communications
T. González - Nanodevices for THz Applications December 12, 2012 Evolving THz market
T. González - Nanodevices for THz Applications December 12, 2012 The THz gap
PHOTONICS THz Gap ELECTRONICS
All-optical sources All-electronic sources • Mixing lasers with close frequencies • Gunn diodes + frequency multipliers (Schottky diodes) • Excitation of semiconductors or superconductors with fs laser pulses • Quantum cascade lasers Very low power in the THz range
Bulky and expensive equipment Backward wave oscillators - BWOs Useful for spectroscopy and sensing, but (vacuum electronic device) not for communications
T. González - Nanodevices for THz Applications December 12, 2012 The THz gap
Signal generation at THz frequencies
500 GHz – 5 THz
Quantum cascade lasers (QCL) QCL at cryogenic T Frequency multipliers _ Other electronic devices: amplifiers, RTDs, IMPATT and Gunn diodes
SemiconductorPROBLEM Nanodevices for RoomLack Temperature of a compact, THz room-temperature, The THz Gap Emissionhigh-power, and semiconductor Detection (ROOTHztunable source Project) Source: T. H. Crowe, W. L. Bishop, D. W. Porterfield, J. L. Hesler, and R. M. Weikle “Opening the Terahertz Window with Integrated Diode Circuits” IEEE J. Solid-State Circuits 40, 2104 (2005)
T. González - Nanodevices for THz Applications December 12, 2012 OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs)
Conclusions / Perspectives
T. González - Nanodevices for THz Applications December 12, 2012 The Project
Semiconductor Nanodevices for Room Temperature THz Emission and Detection (ROOTHz Project)
• Funded under: 7th FWP (Seventh Framework Programme) • Area: FET Open (ICT-2007.8.0) • Project Reference: 243845 • Total cost: 2.1 M€ • EU contribution: 1.57 M€ • Execution: from 1st January 2010 to 30th June 2013 • Duration: 42 months • Website: www.roothz.eu
T. González - Nanodevices for THz Applications December 12, 2012 Partners
J. Grahn Chalmers University of Technology Gothenburg, Sweden A.M. Song The University of Manchester Manchester, UK
C. Gaquiere Coordinator: J. Mateos Institut d’Electronique Microélectronique University of Salamanca et de Nanotechnologie, Lille, France Salamanca, Spain
T. González - Nanodevices for THz Applications December 12, 2012 Semiconductor nanodevices in ROOTHz
Final objective: fabrication of THz detectors and emitters with the same technology
Self Switching Diodes (SSDs)
Ohmic Ohmic
Contact Contact Contact Contact Insulating Trenches Current
Cap Layer Top View Barrier Channel Narrow Bandgap Buffer Wide Bandgap Semiconductors (NBG): Semiconductors (WBG): InGaAs/AlInAs GaN/AlGaN InAs/AlSbSlot Diodes (Ungated HEMTs)
T. González - Nanodevices for THz Applications December 12, 2012 OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs)
Conclusions / Perspectives
T. González - Nanodevices for THz Applications December 12, 2012 Self-Switching Diodes (SSDs)
1 µm 3.0 2.5 W approx. 60 nm 2.0 A) W approx. 70 nm
1.5 1.0
Current ( 0.5 0.0 -0.5 -3 -2 -1 0 1 2 3 V (V)
– – – – – nanochannel d doping + + + + + InP – + InP – – – – – + + + + + InGaAs
V<0, channel closed V>0, channel open InP - substrate InGaAs channel
T. González - Nanodevices for THz Applications December 12, 2012 Self-Switching Diodes (SSDs)
Simple technological Tuneable threshold voltage process: etching of insulating from almost zero to more than trenches on a semiconductor ten volts by adjusting the surface channel width
Easy downscaling and parallelization: THz Adequate geometry operation can be for the onset of Gunn obtained oscillations
T. González - Nanodevices for THz Applications December 12, 2012 Self-Switching Diodes (SSDs)
• THz Detection: non-linear I-V characteristics Use of NBG materials (Room Temperature ballistic transport) for increased sensitivity and broadband
• THz Emission: Gunn Effect in InGaAs, and GaN !! Use of WBG materials for increased power and frequency
• Planar geometry (and antennas) allow for a better coupling
• Parallelization for enhanced performances (and correct thermal management)
T. González - Nanodevices for THz Applications December 12, 2012 OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs) SSDs as THz detectors Conclusions / Persp. SSDs as THz emitters
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: experiments
B 20 V 16
12 A) 8 2DEG 4
Current( 0 4 diodes in 3 m -4 parallel -1.0 -0.5 0.0 0.5 1.0 Voltage (V) 0 1 mm -5 RoomResponsivity temperature 1330THz V/W detection @ 12 K -10 -15 150 mV/mW Free Electron
Laser at 1.5 THz -20 -25 -30 300 mV/mW T = 300 K Output DC Voltage (mV) Voltage DC Output -35 0.0 0.2 0.4 0.6 0.8 C. Balocco et al., Appl. Phys. Lett. 98, 223501 (2011) Bias Current (A)
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: experiments
V
2DEG THz imaging using black body radiation
4 diodes in 3 m parallel
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: experiments
Interdigital InGaAs mesa with 2000 etched SSDs
600nm
106 ) 5 1/2 10 1/f noise • Corner frequency below 100 kHz 104 even at relatively high biases 103 200 nA 2 1/2 10 300 nA • NEP @ 110 GHz ~ 65 pW/Hz comparable to SBD 500 nA 101 1 A 2 A
Voltage noise (nV/Hz no bias 100 100m 1 10 100 1k 10k Noise can be reduced by increasing Frequency (Hz) the number of SSDs in parallel
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: Monte Carlo simulations
• THz Detection: non-linear I-V characteristics Use of NBG materials (Room Temperature ballistic transport) for increased sensitivity and broadband. Possibility for RESONANT DETECTION
2.0 AC to DC 1.4 THz W =20 nm 1.5 rectification V In0.53Ga0.47As T=300 K Vo=0.25 V
1.0
WC=50 nm
0.5
Rectified DC current(A/m) V=V sen(2pf) WH=5 nm o I 0.0
175 nm LC=250 nm 175 nm 0.1 1 Frequency (THz)
Enhanced rectification in the THz range (tunable by geometry)
T. González - Nanodevices for THz Applications December 12, 2012 THz dynamics in SSDs: pump-probe experiments
Schematics of electro-optic Sampling beam (EO) sampling 800 nm
EO crystal fs laser excitation beam 400 nm
Experiments done at Univ. of Rochester Bias by Jie Zhang and Roman Sobolewski
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: pump-probe experiments
3000 8
6
2000 Experimental 4
2 1000 0
Current (A/m) Current V=1.0 V -2
0 u.) (a. Experimental V=0.0 V -4 V=-1.0 V -1000 -6 15 17 19 21 23 Time (ps)
MC simulations predict a much sharper peak THz oscillations may be emitted from the (1/3 FWHM), but the shape is similar excitation of the SSDs with fs-lasers
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz detectors: InAs technology
Progress in InAs SSDs technological process
higher mobility improved responsivity and fc
29 nm
38 nm
650 nm
T. González - Nanodevices for THz Applications December 12, 2012 OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs) SSDs as THz detectors Conclusions / Persp. SSDs as THz emitters
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz emitters: Gunn oscillations
(a)
• Suitable geometry: vertical trench focuses n+ n- n n+ the electric field at the cathode side of the channel, and anode voltage increases electron
concentration onset of domains and propagation along the channel (b) Cointegration with detectors
• Material: GaN channels
High saturation velocity, low energy relaxation time high frequency High threshold field high power Planar design SSDs in parallel facilitates heat dissipation
T. González - Nanodevices for THz Applications December 12, 2012 SSDs as THz emitters: Monte Carlo simulations
Monte Carlo Simulations 2.0 60 V (a) WV=100 nm GaN T=300 1.6 K Gunn WC=75 nm 1.2 50 V Oscillations
W =50 nm I (mA) H in GaN 0.8 40 V SSDs 150 nm LC=900 nm 500 nm 30 V 0.4 10 15 20 25 30 35 40 45 50 Time (ps) 1.0 450 (b) 0.8
0.6 400 0.4
I (mA) 0.2 350
0.0 (GHz) Frequency 300 -0.2 -40 -20 0 20 40 60 25 30 35 40 45 50 55 60 65 V (V) V (V) Oscillation frequencies above 400 GHz (voltage controlled and tunable by geometry)
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 1 of GaN SSDs
16 parallel GaN SSDs
Unexpectedly high surface charge too low electron concentration in the channel no Gunn oscillation observed (on probe electrical measurements) Monte Carlo constant surface charge model fails new model (self-consistent model) in order to fit the experimental results
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 2 of GaN SSDs
New strategies in the design
Wider square SSDs V-Shape SSDs
(a) 100 nm (b)
100 nm 4 00 nm
W=500 nm, 750 nm Win=350 nm 50nm 4 =
out 50 nm 400 nm 50 nm W V-shape GaN SSDs
200 nm L= 500 nm 450 nm 200 nm L=500 nm 450 nm
1.5 1.5 L= 500 nm L= 500 nm L= 500 nm
1.0 W=500 nm W=750 nm Win=350 nm 1.0 W =450 nm 0.5 out 0.5
0.0 (a) (b) (c) 0.0 -0.5 -0.5
Current (mA) Current Experimental Experimental Experimental (mA) Current -1.0 MC MC MC -1.0 -1.5 -1.5 -10 -5 0 5 10 15 20 -10 -5 0 5 10 15 20 -10 -5 0 5 10 15 20 Bias (V) Bias (V) Bias (V) New Monte Carlo Self-consistent surface charge model GOOD AGREEMENT T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 2 of GaN SSDs
New strategies in the design
Wider square SSDs V-Shape SSDs
(a) 100 nm (b)
100 nm 4 00 nm
W=500 nm, 750 nm Win=350 nm 50nm 4 =
out 50 nm 400 nm 50 nm W V-shape GaN SSDs
200 nm L= 500 nm 450 nm 200 nm L=500 nm 450 nm
Square SSDs: W ≥ 500 nm to provide Gunn oscillations (much wider that initially expected!!) VERY STRONG HEATING
V-shaped SSDs facilitate the onset of oscillations: Heating is much o Lower threshold voltage (30V instead of 50V in square SSDs) reduced with o Narrower channels are needed (W ≥ 200 nm) the V-shape geometry
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 2 of GaN SSDs
Free space measurements (devices with antenna mounted on PCB and Si lens)
Pulsed-mode measurements developed In spite of large effort in characterization of emission in RF and THz no evidence of oscillations were found in Run 2
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 3 of GaN SSDs
Run 3 fabricated
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 3 of GaN SSDs
Bow-tie Emission not perpendicular Z ~ 75 Ω
720 µm 4 µm
Integration with adequately Equiangular spiral designed Emission perpendicular Z ~ 120 Ω broadband antennas 1.8 mm
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 3 of GaN SSDs
Good control of the technology
T. González - Nanodevices for THz Applications December 12, 2012 Experimental results: Run 3 of GaN SSDs
Free-space characterization Structures designed for optimized heating
Higher bias can be applied (above the threshold for the onset of oscillations)
No emission observed yet Guided-wave characterization under probes
T. González - Nanodevices for THz Applications December 12, 2012 Desynchronization of the oscillations: MC simulations
Single SSD
2-SSDs
4-SSDs
More SSDs in parallel, more An external resonator is pronounced desynchronization needed for synchronization
T. González - Nanodevices for THz Applications December 12, 2012 Resonant circuit modeling
• Series and parallel RLC circuits already implemented
• Circuit equations (solved in the time domain) coupled to the MC current
The voltage between terminals is fixed by the RLC circuit
T. González - Nanodevices for THz Applications December 12, 2012 Resonant circuit modeling
Resonant frequency f0=1/(2pLC) 0.20 Constant quality factor Q=117.8 300K 0.15 500K
C (fF) L (nH) R (MW) f0 0.10 Heating is not 0.073 33.0 2.5 102.3 blocking the
0.061 27.5 2.5 122.7 (%) Efficiency 0.05 oscillations 0.050 22.5 2.5 150.1 0.00 0.042 19.0 2.5 177.7 100 200 300 400 500 600 0.039 17.5 2.5 192.9 f0 (GHz) 0.031 14.0 2.5 241.1 0.022 10.0 2.5 337.6 Crosstalk capacitance 0.020 9.0 2.5 375.1 New design iteration of about 5 fF can kill with integrated 0.017 7.5 2.5 450.2 the oscillations resonant circuit 0.010 4.5 2.5 750.3 needed For N parallel diodes C×N, L/N and R/N Very small Around 100 SSDs in parallel capacitances needed to avoid its effect
T. González - Nanodevices for THz Applications December 12, 2012 OutlineOutline
Introduction. Importance of THz
ROOTHz Project
Self Switching Diodes (SSDs)
Conclusions / Perspectives
T. González - Nanodevices for THz Applications December 12, 2012 Future work
THz detection:
• Fabrication, THz characterization and optimization of InAs SSDs as detectors
• Spectral characterization of the responsivity of the SSDs (InGaAs, GaN and InAs) Identification of plasma resonances
• GaN SSDs as THz detectors (two patents filed): - Mixing of THz signals (heterodyne detection) - Direct demodulation of THz signals (ultra-high bandwidth detection)
• Graphene SSDs
THz emission (main focus):
• High frequency (>900 GHz) FTIR cryogenic detection
• Design and fabrication of optimized structures with resonant circuits
T. González - Nanodevices for THz Applications December 12, 2012 Acknowledgements
ROOTHz: Semiconductor Nanodevices for Room Temperature THz Emission and Detection www.roothz.eu
J. Mateos A. M. Song C. Gaquiere J. Grahn S. Pérez A. Rezazadeh G. Ducournau P. A. Nilsson B. G. Vasallo M. Hallsall P. Sangaré H. Rodilla I. Íñiguez-de la-Torre C. Balocco A. Westlund J. Millithaler L. Zhang H. Zhao A. Íñiguez-de la-Torre Y. Alimi S. García
J. Torres L. Varani Jie Zhang P. Nouvel Roman Sobolewski A. Penot Institut d’Électronique du Sud Université Montpellier II
T. González - Nanodevices for THz Applications December 12, 2012 Thanks for the attention !
T. González - Nanodevices for THz Applications December 12, 2012 T. González - Nanodevices for THz Applications December 12, 2012