1. Portable Source with Free-Electron Beams for 0.1 to 10 THz
Hans W.P. Koops
Shihab Al Daffaie*, Hans L. Hartnagel*
HaWilKo GmbH Ober-Ramstadt Ober-Ramstadt, *IMP-MWE of TUD Technische Universität Darmstadt , Germany
WOCSDICE 2012

2. Miniaturized THz Source WOCSDICE 2012
Contents
Motivation, present THz sources, Tasks of today
Method for Miniaturization EBIP
Miniaturized FEL-Smith Purcell THz source
Miniaturized THz source with free electron beams using the Dynatron principle
Tunable THz source with Dynatron oscillator and double triode power transmitter
Acknowledgements
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

3. Miniaturized THz Source WOCSDICE 2012
Motivation
New tools with Terahertz (THz) technologies promise to enhance
Chemical, Biological, Nuclear, Radiological and Explosive (CBNRE)
detection capability in homeland security applications.
The key benefits of THz are that many chemical and organic molecules
have distinctive absorption spectra in the THz range
Electromagnetic THz radiation (3 μm - 3 mm) is safe for humans The transparency of the atmosphere for THz is limited to a few meters
Recent developments are in detectors and sources
quantum cascade lasers (CL),
optically pumped terahertz lasers (OPTL)
gyrotrons, backward wave oscillators (BWO), Clinotrons,
GUNN and Schottky diode frequency multipliers.
Despite of previous developments, the technology is far from mature
A compact, tunable, high peak power THz radiation source
is needed for 0.1 to 10 THz
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

4. Miniaturized THz Source WOCSDICE 2012
FBOS : Free Beam Oscillator Sources BWO: Backward Wave Oscillators OPTL: Optically pumped THz lasers CL: Cascade lasers
FBOS
OPTL CL
Gyrotrons
BWO
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

5. Miniaturized THz Source WOCSDICE 2012
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

6. Nanocrystalline Material Free standing structures
Fe-Sources
Ionizers
Current switches
Micro-triodes
THz-Oscillator
Thrusters
FEL, X-Ray
Nanocrystalline Material Free standing structures
Triode
FE-source, extractor and
focusing lens
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

7. Characteristics of EBID Materials and Emitters:
3 D D D D
Nano-crystalline compound material of metal nano-crystals in an insulating matrix
2 nm edge roughness , Crystal size < 4 nm diameter
Size-quantization generates in single crystals O-d electron gas
Conduction by variable range hopping of electrons, tunneling
No Ohmic conduction mechanism as all other metals have!
Current density up to 20 MA/cm² in wires with 100 nm diameter, < 5 µm long
(3d electron gas metals segregate at current densities > 250 kA/cm² (Al)!)
Very high brightness field electron emitters, up to 1 mA per tip!
Highly sensitive photo-resistors
Compound materials with high refractive index
Crystals are to small to support high energy phonons, < 15 meV
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

8. THz Microtriode to operate in air
The mean free path between air molecules at 1 bar is 0.3 µm.
A microtriode of 0.3 µm length does not require a vacuum,
since there is ultra high vacuum between the gas molecules.
The cathode-grid capacitance of a microtriode is 0.24 fF.
Such a triode can switch and amplify in the THz regime.
Schematic and constructed microtriode (to be tested)
At 20 µA electron current and 1 THz is the S/N = 11
EBID construction in <10 min on a prefabricated chip
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

9. High Brightness Field Emitters by EBID
Deposition from Au or Pt precursor renders high current emitters
Current density in emitter rod of 20 nm diameter at 10 µA is J >3 MA/cm²
In the tip the current density is J> 300 MA/cm². All at room temperature
Tips are fabricated with an enlarged footprint to allow at 300 K a
current density J < 0.25 MA/cm², not to evaporate the Au or Mo base
Author
Current mA
Gate Voltage V
First emission V
Spindt SRI
10 µA/180 V
100V
Kretz DTAG
1 mA / 22V
12 V
Floreani NaWoTec
1.3m A / 70 V
15 V
Sellmair NaWoTec
32 µA / 100 V
Planar gate
70V
High Tc NbSn Superconductors work at 40 K and explode at J > 1 MA/cm²
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

10. FEL- Principle and Experimental Layout Filip Floreani 2000 at NaWoTec GmbH
Field emitter
cathode
Grid, D
>80 periods
Anode
Electrostatic lens
and ion mirror
l -
Smith-Purcell radiation
Electron
beam
A free eelectron beam
induces a surface charge
oscillating in the metal grating
This emits THz radiation
Proposed :
2 µm Grating, 100 V to 1000 V beam voltage, Efficiency 0.1 %
At >30 µA, 1000 V = 30 mW : output power >30 µW
Using multiple parallel sources and beams : at 3 mA , 1000 V :
Efficiency of 3 mW is possible.
Top view of field emitter with electron optics
Wiring pattern with grating
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

11. Field Emitter Characteristics Results of Filip Floreani 2000 at NaWoTec GmbH
I-V-curves of field
emission experiments
Right value axis refers to Pt 2
Fowler-Nordheim plots
indicate field emission
Pt 2
Pt 1
Au 1
Au 2
Pt 2
Au/C and Pt/C nanogranular field emitters
Pt – Emitter delivered up to 1.3 mA
Current from 1 tip at 10-5 mb !
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

12. Miniaturized THz Source WOCSDICE 2012
Dynatron, a RF signal oscillator by Albert W. Hull, 1918 at General Electric Res. Lab. Ua C L I A K G E
C = 10 - 16
Farad (3 x10 m )
L = 10 11
Henry ( 5 x 6
f = 2 THz B
Oscillator
THz-Source
Oscillator voltage swing around E
Primary electrons impinging to the anode release secondary electrons.
They drop back to the grid and lower the emitted anode current : negative I/V slope.
Depending on the secondary emission corfficient of the anode material at E, the point
of I = 0, the secondary electron current becomes larger than the primary curent.
With the action of the LC-oscillator the anode voltage ocillates around E.
The negative resistance in the tube I/V curve compensates and balances
resistive losses of the RLC oscillator for continuous self excited oscillations.
Such oscillators have been used for RADAR in WWII to control transmitter antennas (<3GHz)
A miniaturized Dynatron can serve as a voltage oscillator operating at THz
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

13. Miniaturized THz Source WOCSDICE 2012
Layout of the THz IR radiation source
Two free beam micro-triodes are controlled by the oscillator voltage, but with by C12 reversed voltage with opposite phase and beam direction. They emit electron pulses as THz emitters inside a resonator.
The IR radiation emitter aperture
matches the travel of the electron pulse, which is acellerated to the voltage A, in ½ period of the oscillator voltage
Time K1 K2 I C L A Ua G K E K1 K2
C12
A A B1 B2
Fabrication by lithography and EBID with 0D-material (HaWilKo Patent 2010).
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

14. Characteristics for IR-sources in the 0.2 to 10 THz range
Stability requirements of electrostatic elements limits the usable voltage
in miniaturized beam sources
Experimentally 100 V can be used with metal line distances as small as 1 µm.
Electrons reach by acceleration to 100 V a speed of 6 µm / psec.
The oscillator voltage cuts the DC beam in charge pulses of half a wavelength in
length, which corresponds to half the time span of a period.
For example: at 500 GHz the pulse length is 1 psec.
To clearly separate the two electric fields, each beam must pass an aperture of 6 µm
diameter located in the center of the resonator through which the electric and the
magnetic field of the Hertz Dipole radiation is delivered into the resonator having a
dimension of half a wavelength, which is 300 µm at 500 GHz.
Frequency
THz
Wavelength µm
Resonator
E0 µm
1 Electron pulse at 300 V travels µm
= IR window µm
S/N at
1 mA DC
0.2
1500
750 45
173
0.5
600
300 18
77,5 1
150 9 54 5 60 30
1,8
24,6 10 15
0,9 17
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

15. Power of Miniaturized THz sources
The output of the electron beams can reach up to 100 mW
(1 mA current and 100 V total accelerating voltage by battery )
Klystrons deliver from free flying bunched electrons 47% of the beam power as THz-IR radiation[7].
Bunched beams from Dynatron sources can deliver DC 47 mW of IR radiation power per mA field emitter source current.
At 10 THz the signal to noise (S/N = sqrt N) is 17 for a 1 mA beam, delivering 300 electrons per pulse of 0.05 ps duration in each direction. The emitted power is 1 mA x 100 V x 0.47 = 47mW
Beams can be placed on 1 µm pitch, several parallel beams can cross the IR window in parallel. This results in 12 mA total current, which corresponds to 0,56 W emitted source power
Coupled systems can emit > 1 W DC IR power
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

16. Miniaturized THz Source WOCSDICE 2012
Dynatron Oscillator controlled Power Beams in Resonator l/2 E[10]with forward and backward beams
Triode with
Oscillator
Voltage
amplifiers
The electron beams emit like an antenna electromagnetic radiation
The transmitter antenna suffers no resistive loss !
Multiple antiparallel beams increase the output power
THz transparent lenses focus the IR-beam, e.g. for Scanners
Varying the Dynatron Oscillator L-C- and the resonator-dimensions mechanically e.g. with NITINOL muscles allows to build a powerful tuneable source for 0.1THz to 10 THz
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

17. Schematic of a 200 GHz source for a body scanner
1 mm
Emitted power : 1.12 W
Dimensions: 4 x 4 x 6 mm³
The radiation emitted from the
resonator to both sides is aligned
by reflectors and focused by lenses.
The source is pumped by a Getter
pumping unit below the resonator,
or a miniaturized Orbitron pump;
It can be manufactured in large
numbers with micro systems
fabrication technology.
The transfer of the WW2 Dynatron to the miniaturized design requires considering the effects of stray capacitances and inductances and may change the specifics of the proposed design.
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

18. Miniaturized THz Source WOCSDICE 2012
Fieldemission Triode
Test structure for a Dynatron triode.
The 2 needle tips make contact to the emitter and extractor connector lines for electrical measurements.
The Dynatron anode is powered by a
deposited metal line resistive divider.
Emitter (lower tower with tip) and extractor
The emitter- extractor gap is 200 nm.
The extractor is deposited as a gate of
quadratic shape. The emitter tip radius is 25 nm.
Material Pt/C deposit
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

19. Tilted view of Triode (Pt/C) with RAITH 3D module
Emitter (front) andExtractor (back) Tilt 70° for height measurement using 3D-module
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

20. Miniaturized THz Source WOCSDICE 2012
Dynatron Triode Field Emission Measurement in Situ wit needle prober shows field emission Fowler Nordheim Diagram confirms field emission
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

21. Miniaturized THz Source WOCSDICE 2012
Potential and emitted electron beams in miniaturized triode
r = 25 nm
3 emission sites on front facet
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

22. Miniaturized THz Source WOCSDICE 2012
Acknowledgements
The authors are thankful for:
Simulations by Achmed Al-Mudhafar using CST Software (Particle- and Microwave Studios) which show that considering stray capacitances and inductances can even be beneficial for the technical realization of the miniaturized THz source.
Cooperation with Dr. Nouvertné and Dr. Rudzinski and the RAITH GmbH in Dortmund, Germany, who fabricated and characterized with the RAITH E-Line Lithography several triode structures for a Dynatron THz source by Electron Beam Induced Deposition as 3-dimensional very high resolution structures .
Using the built in 2 needle prober direct in-situ measurement of the electrical characteristics was performed to characterize the total structure after deposition.
This capability of the RAITH E-Line system enhances the development speed for a quite complicated structure very much.
Thank You Questions
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

23. Miniaturized THz Source WOCSDICE 2012
References
[1] M.R. Leahy-Hoppa et al. / Chemical Physics Letters 434 (2007) 227–230 (John Hopkins Univ. Laurel MD, Baltimore MD, USA)
[2] “Dynatron”: FR A (Philips NV) 22. November 1924 ( ) and “H. Barkhausen, in Elektronenröhren Bd. 1 (1945) S.75 , Bd.3 (1935), S.73ff, Hirzel Verlag Leipzig Karl Willy Wagner „Erzeugung von Kippschwingungen durch das Dynatron“ Dietrich’sche Verlagsbuch-
handlung, Klemm, Wiesbaden, 1947, 530ff.,
[3] H.W.P. Koops “Electronic tube…” WO patent 97/33295 ( )
[4] J. Kretz et.al. Microelectronic Engineering 23(1994)
[5] H.W.P. Koops, „Verfahren und Vorrichtung zur Herstellung von Korpuskularstrahlsystemen“ DE 10 302 794 A1,
[6] H.W.P. Koops “THz radiation with free electron beams” EP application HaWilKo GmbH 2010
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

24. NiTiNol Material Characteristics
Ni Ti NOL: Nickel- Tin -alloy was discovered by Naval Ordonance Laboratory in 1930, when searching for new materials for submarines
Memory metal changes with temperature from martensite to austinit strcuture and contracts up to 4 % axially, or 14% perpendicular to the wire
Temperature rise by Joules heating with current flow converts electrical power effectively into structural change with a strong force.
A heated wire must be pulled by a low weight or spring into it‘s stretched structure when cooling down
If no force is applied the wire stays in the hot structure even after cooling down. A new heating cycle revives the wire to act as a memory metal
NiTiNOL or Flexinol is employed as stunts
in medicine and as muscles in robotics, as
well as in the car industry
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

25. Miniaturized THz Source WOCSDICE 2012
Work cycle of NiTiNOL A memory metal as power engine for movements is changing the crystal structure with temperature
Nitinol is availablle in form of thin wires (e.g. 0,25 mm wire, 4 cm long)
300g spring expansion
as delivered
expanded
1 Contracted
by heating
Power is supplied
by a current which
heats the wire.
Work cycle
2,5 kg contraction
force
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

26. Miniaturized THz Source WOCSDICE 2012
Tuneable THz Dynatron Source with NiTiNOL -stage for current driven fine tuning of the resonator, anode and oscillator
Getter material and Resonator tuning stage located in the pump chamber
Base plate
and housing
NiTiNOL
Friction stabilized
point of bar rotation
Pull right
Pull left
NiTiNOL
Getter
pump
Tuning of the resonator and oscillator by moving the wall and oscillator parts
( is also possible in the perpendicular direction by a second stage)
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

27. Miniaturized THz Source WOCSDICE 2012
Triode Experiment
Electrical connection of FE-source
with nanomanipulators
Emitter and extractor on gold-electrodes
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

28. Miniaturized THz Source WOCSDICE 2012
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

29. Miniaturized THz Source WOCSDICE 2012
Z-x at y =0 Cath: 10 Extr 20 Anode 15 V
Cathode with ball
with base cylinder 25 nm and ball end with 12,5 nm radius
Extractor in 200 nm distance
y-z an x=0
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012

30. Miniaturized THz Source WOCSDICE 2012
Measurement at 1.8 µm high structure, emitter at 1 µm height
Bent structure
Stiff structure
Hans W.P. Koops HaWilKo GmbH Germany
Miniaturized THz Source WOCSDICE 2012