Tecnologie TeraHertz per la Sicurezza Aldo Di Carlo, Dept. Electr. Eng. Univ. Rome Tor Vergata (ITAY) In collaboration with: Francesca Brunetti,, Claudio Paoloni, Maria etizia Teranova, Matteo Cirillo Univ. of Rome Tor Vergata A. Fiorello,, M. Dispenza,, F. Ricci, F. Gemma,, C. Falessi (SEEX-SI) SI) TechFOr 2010, 18 Maggio, Fiera di Roma "Tecnologie Abilitanti e Sistemi per la Sicurezza: il contributo delle Università e dei Centri di Ricerca"
What is Terahertz (THz)? Visible Radio Microwave T-rays Infrared UV X-rays 10 8 10 9 10 10 10 11 10 12 10 13 10 14 10 15 10 16 10 17 Frequency (Hz) 1 THz frequency = 300 μm wavelength or 33 cm -1 or 4.1 mev or T = 48 K Also known as Far-Infrared or sub-millimeter
THz for Scanning Explosives / Bio-Chem Agents THz transmits through most non-metallic materials: plastic, paper, clothing THz yields transmission / reflection spectra of targets J. Chen et al Rensselaer Polytechnic Institute From GHz to THz frequencies, numerous organic molecules exhibit strong absorption and dispersion due to rotational and vibrational transitions. These transitions are specific to the targets and enable T-ray fingerprinting.
Drug Detection by THz spectroscopic Imaging
The THz-Bridge project (ENEA)
T-ray images
Wide Area Surveillance THz - low energy radiation - non-ionizing no damage to biological tissue (for typical conditions) differentiation of target compounds based on THz color Imaging and color information combination will reduce false alarm rate. THz applications require a higher output power
THz source technology: an overview Up to now the leading technology for THz sources are 1) Quantum Cascade aser, 2) photomixing, 3) electronic upconversion. All of them are limited to very low output powers (< 1 mw@ THz). Output Power (mw) 100000 10000 1000 100 10 1 0.1 0.01 D G IA A D I I A II DI G GG GG G I I I A A AA A D I G G D GI D DD GG GG GG I D D DD D G A D D TD G D T TTT D DD D D ~f -2.5 T T D G T T D I GG D T T D T ~f -3 R R R THz POWER?? T T T T T ~f 2 Q Q QQ QC results Q Μ Ge 100 1000 10000 100000 = aser Q = QC Ge = p -Ge laser D = Doubler T = Tripler G = Gunn Diode I = Impatt Diode R = RTD A = Amplifier Cooled Pulse d Output Frequency (GHz)
Our activities for THz generation We are developing two strategies for THz Generation 1) NanoTriodes (NMP project) Here the active component is a microscructured triode with CNT as electron sources. The triode could be used for both amplifier and oscillator circuits 2) TWT amplifiers (FP7 OPTHER project) Here we develop an amplifier based on micromachined TWT approach using CNT based cold cathodes
Nanotriode: Spindt type Anode Grid CNTs Cathode Oxide Metal SiO 2 P-doped Silicon
NanoTriode device realization Anode Grid Grid c SiO 2 Si b Fe a For the device realization it was planned a 3 alignment process that allows to realize: SiO 2 Etching Catalyst deposition Grid electrode deposition
Nanotriode: array detail Metal Grid Oxide Silicon
Nanotriode Array: CNT growth Before the CNT growth After the CNT growth
Diode mesurements Current (A) 275µ 250µ 225µ 200µ 175µ 150µ 125µ 100µ 75µ 50µ 25µ 0 160 μm 150 μm 130 μm 60 μm 35,0m 30,0m 25,0m 20,0m 15,0m 10,0m 5,0m 0,0 Current density (A/cm 2 ) 400 500 600 700 800 900 1000 Voltage (V) I-V measurement for several anode-cathode distance
Triode measurements Current Iac (A) 1,0µ Vga 120V Vga 100V Vga 75V 800,0n Vga 50V Vga 25V Vga 0V 600,0n 400,0n 200,0n 0,0-1000 -800-600 -400-200 Voltage Vca (V) Anodic Characteristics Current Iac (A) 1,0µ Vca -1000V Vca -900V 800,0n Vca -800V Vca -700V Vca -600V 600,0n 400,0n 200,0n 0,0 0 20 40 60 80 100 120 Voltage Vga (V) Output Characteristics Cathode-Structure Distance: 100 μm Grid-Anode Distance: 3 μm Gate turn-on voltage: 40 V gm=20 ns
THz modulation - Cross-bar triode (patent) Griglia "HIGH FREQUENCY TRIODE-TYPE TYPE FIED EMISSION DEVICE AND PROCESS FOR MANUFACTURING THE SAME" PCT/IT2007/000931 Di Carlo et al Catodo Pattern d emissioned CNT can grown on a patterned area. This allow for a reduction of grid- cathode capacitance Griglia Anodo Catodo Guida Coplanare Catodo Griglia Micro strip
The FP7 - OPTHER approach Current development OPTHER THZ source THz amplifier High power THz radiation QC Electronic upconversion Optical downconversion Example THz input Vacuum electronics amplifiers based on advanced nano/microtechnologies THz output QC sources Vane loaded tube (TWT) OPTHER Consortium: Univ. of Rome Tor Vergata (Italy, Coordinator) TU Denmark, CNRS (France), SEEX-SI SI (ITAY), THAES-RT & ED (France)
The THz amplifier Input Signal Generation of THz Efficient coupling Different sources Waveguide Input port THz drive signal Electron beam Beam size Beam-THz coupling Electron beam Output port Output Signal Measurement Output matching Cathode Microwave structure Collector Cold Cathode CNT Growth Substrate patterning Alignment Interaction structure DRIE SU-8 Bonding Packaging collector
SWCNT Emitters Raman Raman data clearly show the presence of Single walled carbon nanotubes
Optimization of Field Emission 1,0m 4,0 800,0µ nano patterned cathode micro patterned cathode 3,5 3,0 Current (A) 600,0µ 400,0µ 200,0µ 3.5 A/cm 2 0.44 A/cm 2 2,5 2,0 1,5 1,0 0,5 Current density (A/cm 2 ) 0,0 0,0 200 400 600 800 1000 Voltage (V)
New CNT cold cathode design Extraction part Extraction grid Cathode array SWCNT Conductive substrate Focussing part Anode Focusing grids Beam energy Maximum beam radius 8.48 kev 40 µm @ B = 1T; 29.2 µm @ B = 1.5 T Current density @ max beam radius 146.3 A/cm 2 Perveance 0.00547 µp Transparency 100% Cathode
Slow-wave structure realization (Selex) H=66μm H=150μm SU-8 8 + electroplating p=26μm-32 32μm =20mm
Final OPTHER THz Amplifier
Conclusions THz radiation is very suited for security applications Our objective is to increase the THz power to enable more advanced T-ray T applications This is achieved by an innovative amplification scheme of THz radiation based on nanotechnology enhanced vacuum electronics (Nanotriodes( and TWT) Carbon Nanotube based cathodes could be used in both nanotriodes and micromachined TWT