IEEE 802.15 <subject>

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
High Power Miniature CVD Diamond-Based
Submillimeter/Terahertz Signal Sources Date
Submitted 31 October, 2008 Source Gerald T.
Mearini Company Teraphysics Corporation Address
110 Alpha Park, Cleveland, OH 44143 Voice
440.573.0008 FAX [phone], E-Mail
mearini_at_teraphysics.com Re Abstract
Teraphysics has developed a miniature
submillimeter signal source, named TERATRONTM ,
comprised of solid CVD diamond structures
produced by replicating lithographically
fabricated Si molds, and assembled using modern
liquid crystal display techniques. The device
represents a novel reinvention of a backward wave
oscillator and a merger of vacuum electronics
with modern microfabrication and computer
modeling techniques. Two prototype versions, 300
GHz and 650 GHz, have been fabricated and are
capable of producing 20 30 mW of output power,
tunable over a 20 range. The final assemblies
are powered from a nominal 2 Watt power supply,
with physical dimensions measuring approximately
2 cubed weighing approximately 3 pounds. The
TERATRONTM will serve as a signal source to
enable commercialization of applications such as
real-time high resolution images of concealed
weapons, unambiguous spectroscopic identification
of chem/bio agents, pathogens and explosives, and
early detection of skin and breast cancer.
Purpose Source Development Update and
Overview Notice This document has been prepared
to assist the IEEE P802.15. It is offered as a
basis for discussion and is not binding on the
contributing individual(s) or organization(s).
The material in this document is subject to
change in form and content after further study.
The contributor(s) reserve(s) the right to add,
amend or withdraw material contained
herein. Release The contributor acknowledges and
accepts that this contribution becomes the
property of IEEE and may be made publicly
available by P802.15.
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Acknowledgements

• Funding
• NASA JPL
• Defense Advanced Research Projects Agency
• Army Research Office
• Air Force Office of Scientific Research
• Collaborators
• Teraphysics (C. Kory)
• RTI International (D. Malta, M. Lueck, K.
  Gilchrist)
• Hana Microdisplays (S. Worthington)
• Applied Diamond Lab (J. Tabeling)
• SRI International (C. Spindt, C. Holland)
• Naval Research Laboratory (J. Butler)

TERAPHYSICS
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Biplanar Interdigital BWO (Patented 2007)

• First proposed to NASA JPL in 2002
• Convergence of vacuum electronics, computer
  modeling and microfabrication
• Interdigital structure formed on two planes
• Diamond structure selectively metallized
• Electric waves travel in the space between the
  planes
• Electron beam passes between the planes and gives
  up energy to the electric waves

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Thermal-Mechanical Advantages of Diamond

• Highest known thermal conductivity
• Relatively low permittivity
• High strength
• Artificial diamond can be grown in place using
  chemical vapor deposition (CVD)
• CVD diamond forms intimate thermal bond with
  substrate
• Unique application by Teraphysics

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Fabrication Scheme
Micro fabrication performed at RTI
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100 mm Wafer Layout
300 GHz 6 V2 and 6 V2A
11 650 GHz V3
11 650 GHz V2
10 650 GHz VI
Designed for wafer scale production
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Patented Fabrication Process

• Intricate structure designed on computer
• Computer model transferred to silicon foundry
• Negative of structure fabricated in silicon
• Diamond grown into silicon molds
• Silicon dissolved in acid leaving diamond replica
  of computer model
• Direct transfer from computer file to diamond
  structure

Diamond slow wave circuit
Dimensions 71.5 µm long, 86.5 µm high, 15.6 µm
wide, 23.4 pitch
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Two Views of Selective Metallization
SEM
Optical Microscope
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Laser Dicing of BWO Bodies
Accurate repeatable process
100 mm quarter wafer after dicing
Adaptable to wafer scale production
A Bucket of BWOs
100 yield on Lot 5, completed Oct. 22
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BWO Layout
Anode 1
Anode 2
Slow Wave Circuit
Diamond Wall
?
Electron Beam Path
Antenna
Field Emitter on Mesa
Electron gun, slow wave circuit and antenna
fabricated as an integrated diamond structure.
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Diamond BWO End View
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Field Emitter Layout
SRI International
Base
Mesa is etched after field emitter is formed,
greatly reducing yield.
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Alignment Accuracy
Hana Microdisplays
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Assembly Steps
Leaded 650 GHz V2B
650 GHz V1B BWO in alumina cradle
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Exploded View of BWO Assembly
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Assembled BWO in Magnetic Circuit
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Remedial Action OmniProbe
Cathode mount

• Silicon chips 220x800 micron diced at SRI
• Tungsten needle inserted into silicon die
• Micropositioner aligns die with mount
• Die inserted into mount
• Tungsten needle removed
• Applicable to future manufacturability

Die in BWO body
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Remedial Action Thermionic Gun Design for Planar
BWO
Diamond forks to facilitate alignment
Field emission gun removed with laser dicing
Computer simulations for optimized design
500
Alignment of gun and circuit challenging
Miniature thermionic gun layout
Cathode
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Planar BWO Project Technology Innovations

• Computer-aided design of gun, circuit, and
  antenna
• Transfer CAD file to Si mask to diamond structure
• DRIE of SOI wafers to create Si mold
• CVD growth of diamond structures in Si mold
• Grow flat, transparent diamond of correct
  thickness
• Self masking of diamond structure for selective
  metallization
• Vertical metallization of gun electrodes
• Fabrication of field emitter arrays
• Laser dicing of individual BWO halves
• Prototype BWOs assembled using LCD technology
• Application of micromanipulator for cathode
  insertion
• Design of miniature thermionic electron gun
• Demonstrate BWO operation

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Predicted Characteristics of Planar BWO

• Continuous wave operation
• Frequency is continuously voltage tunable
• Voltage 6 kV, current 2.0 mA
• BWO power 26 mW at 6 kV, 125 mW at 12 kV
• Efficiency 1.8 (10x improvement)
• Mass of magnetic circuit 1.6 kg
• Designed for wafer scale production

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Next Generation Conventional Helical Slow Wave
Circuit

• Most commonly used slow wave circuit.
• Advantages wide bandwidth, high efficiency,
  moderate power, broad manufacturing base, vast
  expository literature.
• Fabricated by winding wire or tape around a
  mandrel.
• Supported in center of barrel by dielectric rods.
• Seldom fabricated for applications above 50 GHz
  because of high beam interception and mechanical
  and thermal stress

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Lithographically Fabricated Helical Slow Wave
Circuits

• Helix fabricated lithographically
• Diamond dielectric support structure
• Electron gun and barrel fabricated as a unit
• Wafer-level economies of scale
• 160 BWOs from four 100 mm wafers
• Output power radiated directly from circuit
• Electron beam encircles helix
• Applicable to W-band and sub mm devices

Patent Application Submitted Feb. 2008
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Doubly Convergent Electron Gun
Side cut through view of electron gun designed at
95 GHz
Beam trajectories through gun showing double
convergence
Doubly Convergent Gun First the beamlets are
focused to increase current density. At the same
time the beamlets must be drawn into trajectories
of reduced radius, parallel to the axis.
Provisional Patent Application
End view of particles through circuit showing
100 beam transmission
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Novel Helical Circuit Design and Fabrication
Golden helix supported by a diamond sheet in a
diamond box that has been selectively metallized
on the inside
The electron beam passes through space above and
below helix
Fabrication process flow
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Isotropic Etch and Selective Metallization of
Circular Trenches
Depth and shape of trench controlled by etch
conditions.
Mold for half helix
Half helix
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Au/Au Die Bonding
Half helix with bonding bumps
Helix section after bonding
Complete helix has 306 bonds 100 yield
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Accidents Will Happen
The bonds did not break!
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Helix Perspective
Diameter of human hair
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Fabrication of Helix on Diamond Sheet
Trench etched in diamond sheet
Half helix on diamond sheet
Simulation of RF currents in helix
Helix on diamond sheet
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Iterative Helical Design and Fabrication
Gold helix bonded to diamond sheet
Electroplated gold helix in silicon trench
without diamond sheet
Three simulated helices having the same RF
properties illustrating the capability to design
the circuit around the resulting fabricated
helices
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Masks for Diamond Box
Dark green areas are oxide and resist (final
ridge height of 190 um), blue areas are resist
only (final ridge height of 100 um)
Wafer Die
Matching top and bottom device pairs
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SEM images from wafer 2
Low mag SEM image of wafer 2 showing the
waveguide coupler area
SEM image of the waveguide and slow wave circuit
areas
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Helical BWO Assembly
A golden coil supported by a diamond sheet and
suspended within a diamond box
Four 100 mm wafers will produce 160 BWOs in a
single operation
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Summary

• These concepts extend the applicable frequency
  range of the helical slow wave circuit by more
  than an order of magnitude.
• Computer modeling of idealized structures is
  starting point for development.
• Feasibility of essential fabrication procedures
  is demonstrated.
• Computer simulations and fabrication experiments
  are proceeding iteratively for a 95 GHz TWT
  (AFOSR) and a 650 GHz BWO (ARO).
• 650 GHz is not the upper limit for the
  lithographically fabricated helix.
• Proposal to DARPA pending for TWTs at 670, 830
  and 1030 GHz.
• Family of devices with higher power and frequency
  enables a wide range of applications

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Properties of THz Radiation Relevant to Major
Applications

• Harmless nonionizing radiation
• All warm bodies naturally emit THz radiation
• THz radiation will pass through clothing (and
  bandages)
• Complex molecules can be identified by their
  resonant signatures in THz band
• Speed and attenuation of light in water (and
  blood) changes dramatically in THz band
• Distinctively different propagation in different
  types of human tissue
• Selective heating below surface of the skin
  possible
• THz radiation strongly attenuated in atmosphere
• High frequency implies broad bandwidth and very
  high wireless data transmission rates

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Potential Applications
Medical Wound Imaging THz radiation will pass
through bandages, allowing medical personnel to
inspect wounds without disturbing healing
process. In Situ Cancer Imaging During surgery
THz radiation reflects from a tumor differently
because it contains an abnormal concentration of
blood. Skin Cancer Imaging THz radiation can
provide images of cancers growing on or near
surface of skin. Mammography THz radiation may
be able to detect and identify abnormalities in
breast tissue without subjecting patient to
invasive procedures. Prostate Cancer Detection
THz radiation may be able to detect and identify
abnormalities in prostate tissue with greater
resolution throughout entire volume of organ.
Pharmaceuticals THz radiation can be used to
identify counterfeit drugs, point of sale
confirmation of drug identity, verify thickness
and density of coatings on time release capsules,
and provide quality assurance. Dentistry THz
radiation may be able to provide images of dental
carries without subjecting patient or the medial
practitioner to ionizing radiation. Cosmetics
THz radiation has been proposed as means to heat
subcutaneous collagen to smooth wrinkled skin.

• Homeland Security
• Devices will enable sensing at safe distance of
  weapons and other contraband hidden under
  clothing of persons approaching military
  checkpoints or entrances to critical facilities,
  airport terminals, etc.
• These systems may make it possible to accurately
  identify in real time the distinct signatures of
  complex molecular substances present in the
  environment such as dispersed aerosols and toxic
  gases.
• Communications
• The wide bandwidth of these TWTs will enable
  secure very high data rate wireless
  interconnections between computers or in enclosed
  spaces such as aircraft cockpits.
• Space Science
• NASA determines the composition of dark
  space in the universe by detecting the
  characteristic resonances of molecules in deep
  space using a highly sensitive spectrometer. THz
  radiation has been used to inspect the tiles on
  the space shuttle.
• Electronics
• Detection of defects in materials and
  microprocessor circuits using time delayed
  reflectometry.