1. OPTICALLY DRIVEN THZ AMPLIFIERS Vacuum tubes for THz applications Claudio Paoloni Dept. of Electronic Engineering, University of Roma Tor Vergata, Via del Politecnico 1, 00133 Roma Italy Carter Fest 14 July 2010

2. OPTICALLY DRIVEN THZ AMPLIFIERS - Why THz? - Opther project overview - Carbon Nanotube cold cathode - SWS for THz applications: - Corrugated rectangular waveguide - Narrow corrugation rectangular waveguide - Double corrugation rectangular waveguide SWS - Technology Summary Carter Fest 14 July 2010

3. OPTICALLY DRIVEN THZ AMPLIFIERS THz region Why THz? Carter Fest 14 July 2010 OPTICALLY DRIVEN THZ AMPLIFIERS

4. THz applications: Extracting material properties unavailable by using other frequency bands - Security Detection and recognition of dangerous or toxic substances - Early diagnosis in medicine (in vivo tissue recognition) - Imaging - Communications But power is needed! Why THz? Carter Fest 14 July 2010

5. OPTICALLY DRIVEN THZ AMPLIFIERS THz region devices Why THz? Carter Fest 14 July 2010 OPTICALLY DRIVEN THZ AMPLIFIERS

6. OPTHER - Optically Driven THz Amplifier European project devoted to the design and realization of THz Vacuum Amplifiers University of Rome Tor Vergata (Coordinator) École Polytechnique, Thales Research & Technology, Thales Electron Devices CNRS, France, Selex-SI, Rome, Italy, Physikalisches Institut, Universität Frankfurt, Germany Main points: - Carbon nanotube cold cathode - Sheet beam or cylindrical beam - High aspect-ratio lithographic process (LIGA, DRIE and UV/SU8) - Low beam voltage (better < 12 kV) -Main target of OPTHER amplifier: -Operating frequency : in the band 0.3 to 2 THz -Gain : 10 to 20 dB -Output power : > 10 mW ( 10 dBm ) -Lightweight, Portable, Opther Project Carter Fest 14 July 2010

7. OPTICALLY DRIVEN THZ AMPLIFIERS OPTHER - Optically Driven THz Amplifier Why an amplifier? Amplifier is independent on the THz sources. From a system point of view it is important to have amplifiers Can be used for communication purposes Can amplify CW and pulses. Amplifiers can be used in the receiver part of the system. Backward wave oscillators are also considered Opther Project Carter Fest 14 July 2010

8. OPTICALLY DRIVEN THZ AMPLIFIERS Problems to solve: -Design of an electron gun based on CNT cold cathode -Losses The surface roughness of metal could be more than one skin depth, leading to an unpredictable increase of the expected theoretical losses -Lithographic processes are suitable for SWS supporting sheet beams -SWS supporting a cylindrical beam realizable by lithographic process with minimum number of steps -Design method faster than 3-D simulation Opther Project Carter Fest 14 July 2010

9. OPTICALLY DRIVEN THZ AMPLIFIERS Carbon nanotube cold cathode CNT Growth Stabilized and optimized growth conditions for vertically-aligned CNTs are achieved by using several techniques: Microwave Plasma Enhanced CVD (MW-PECVD) Hot Filament CVD (HF-CVD) Thermal CVD (T-CVD). Process was developed for uniform growth of individual CNTs of nm- scale diameter based on patterning of Ni dots for proper emission efficiency Carter Fest 14 July 2010

10. OPTICALLY DRIVEN THZ AMPLIFIERS Carbon nanotube cold cathode CNT Growth Carter Fest 14 July 2010 Thermal + Microwave CVD Hot filament CVD Thermal CVD Single wall CNT Multi wall CNT

11. OPTICALLY DRIVEN THZ AMPLIFIERS Carbon nanotube cold cathode CNT Growth Carter Fest 14 July 2010 Synthesis on nanometric patterns 150 nm spot diameter Growth of CNT samples with integrated grid

12. OPTICALLY DRIVEN THZ AMPLIFIERS Carbon nanotube cold cathode Carter Fest 14 July 2010 Field emission from micrometric patterns Field emission from nanometric patterns Diode field emission measurements

13. OPTICALLY DRIVEN THZ AMPLIFIERS Slow wave structures for THz devices Carter Fest 14 July 2010 SWS for Sheet beam: Corrugated waveguide SWS Narrow corrugation rectangular waveguide SWS SWS Cylindrical beam: Double corrugation rectangular waveguide SWS

14. OPTICALLY DRIVEN THZ AMPLIFIERS Corrugated waveguide SWS Carter Fest 14 July 2010 Period 50  m Corrugation width 240  m Corrugation height 60  m Beam Voltage 12 kV Beam Current 8 mA Beam 80 x 20  m Magnetic field 0.8 T Period number 185 (9.25 mm)

15. OPTICALLY DRIVEN THZ AMPLIFIERS Corrugated waveguide SWS Carter Fest 14 July 2010 3D particle-in-cells simulation

16. OPTICALLY DRIVEN THZ AMPLIFIERS Corrugated waveguide SWS Carter Fest 14 July 2010 1THz Backward wave oscillator

17. OPTICALLY DRIVEN THZ AMPLIFIERS Corrugated waveguide SWS Carter Fest 14 July 2010 1THz Backward wave oscillator

18. OPTICALLY DRIVEN THZ AMPLIFIERS Narrow corrugation rectangular waveguide SWS Carter Fest 14 July 2010

19. OPTICALLY DRIVEN THZ AMPLIFIERS Narrow corrugation rectangular waveguide SWS Carter Fest 14 July 2010 643 GHz Amplifier Period 54  m Corrugation width 120  m Corrugation height 100  m Beam Voltage 16.8 kV Beam Current 0.8 mA Beam 20 x 5  m Magnetic field 0.8 T Input power 1 mW Period number 300

20. OPTICALLY DRIVEN THZ AMPLIFIERS How a corrugated waveguide SWS can support a cylindrical beam? Double corrugation rectangular waveguide SWS Carter Fest 14 July 2010

21. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Carter Fest 14 July 2010

22. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Characteristics: - Supports a cylindrical electron beam - Good interaction impedance in forward and backward wave mode - Easy to realize by micromachining or photolytographic processes (LIGA, DRIE, UV/SU8) - Good assembly feasibility Carter Fest 14 July 2010

23. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Geometrical parameter sensitivity: Carter Fest 14 July 2010

24. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Geometrical parameter sensitivity: Carter Fest 14 July 2010

25. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Carter Fest 14 July 2010

26. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation rectangular waveguide SWS Design guidelines: - The height h and the period p mainly affect the dispersion curve behavior and therefore the operating frequency for a given beam voltage. - The distance between the corrugations g determines the intensity of the E z field and, consequently, the interaction impedance level. - The width of the corrugations affects in opposite way the losses and the interaction impedance. The wider the corrugations, the higher the losses and the lower the interaction impedance. - An increase of the height of the waveguide b determines slightly higher interaction impedance and lower losses. The opportunity to act on so many geometric parameters demonstrates a great flexibility of the double corrugation SWS to achieve the best compromise of cold parameters. Carter Fest 14 July 2010

27. OPTICALLY DRIVEN THZ AMPLIFIERS Double corrugation waveguide characteristics 450 GHz Amplifier Beam Voltage 10 kV Beam Current 4 mA Beam Radius30 μm Magnetic field 0.8 T Input power 4 mW Structure length 15 mm Output power target20 dBm Carter Fest 14 July 2010

28. OPTICALLY DRIVEN THZ AMPLIFIERS Cold parameters and beam line Carter Fest 14 July 2010 450 GHz Amplifier

29. OPTICALLY DRIVEN THZ AMPLIFIERS Magic 3-D simulaton for maximum gain at the given length 450 GHz Amplifier

30. OPTICALLY DRIVEN THZ AMPLIFIERS Carter Fest 14 July 2010 1 THz Backward wave oscillator Beam Voltage 10 kV Beam Current 4 mA Beam Radius20 μm Magnetic field 0.8 T Period number 180 (7.2 mm)

31. OPTICALLY DRIVEN THZ AMPLIFIERS Carter Fest 14 July 2010 1 THz Backward wave oscillator

32. OPTICALLY DRIVEN THZ AMPLIFIERS Technology Microfabrication technique: UV/SU-8 lithography (Selex/SI) Carter Fest 14 July 2010

33. OPTICALLY DRIVEN THZ AMPLIFIERS Technology Microfabrication technique: LIGA - German acronym of lithography, electroplating and molding. (Thales TRT) Carter Fest 14 July 2010

34. OPTICALLY DRIVEN THZ AMPLIFIERS Conclusions - Carbon nanotubes are a as promising solution for cold cathode electron gun. - Different SWSs for THz applications have been presented supporting sheet beam and cylindrical beam. - THz vacuum device (BWO and Amplifiers) simulations have shown relevant perfomance. - The fabrication phase is in progress. Carter Fest 14 July 2010

35. OPTICALLY DRIVEN THZ AMPLIFIERS People Francesca Brunetti a Aldo Di Carlo a (Project Coordinator), Mauro Mineo a and Giacomo Ulisse a, a University of Rome Tor Vergata, Rome, Italy, C.-S. Cojocarua b, A. de Rossi c, M. Dispenza d, D. Dolfi c, A. Durand e, A. Fiorello d, A. Gohier b, P. Guiset c, M. Korantia f, V. Krozer g, P. Legagneux c,,R. Marchesin e, S. Megtert h, F. Bouamrane h, K. Pham e, J.P. Schnell c, A. Secchi d, E. Tamburri a, M.L.Terranova a b LPICM - École Polytechnique, (UMR 7647) CNRS, Palaiseau, France c Thales Research & Technology, Palaiseau, France d Selex-SI, Rome, Italy, e Thales Electron Devices, Vélizy, France, f Technical University of Denmark, Copenaghen Denmark g Physikalisches Institut, Universität Frankfurt, Frankfurt am Main, Germany h UMR137 CNRS/Thales, Palaiseau, France Carter Fest 14 July 2010

36. OPTICALLY DRIVEN THZ AMPLIFIERS Acknowledgments This work is supported by European Community FP7 Opther Project. Carter Fest 14 July 2010 www.opther.eu

37. OPTICALLY DRIVEN THZ AMPLIFIERS Acknowledgments Thank you for your attention! My gratitude to the organizers of this wondeful day in honor of our distinguished friend Richard Carter Carter Fest 14 July 2010