Phase‐Change Materials for Antenna Systems
Characteristics
Challenges Capabilities
Dimitris E. Anagnostou*, Tarron Teeslink
Nelson Sepúlveda†, David Torres†
*Email: [email protected] South Dakota School of Mines and Technology
†Michigan State University
Dimitris E. Anagnostou
[email protected]
Antenna Systems Conference, Las Vegas, NV, Nov. 4-5, 2015
Nov. 5, 2015
1
What is a Phase Change or Phase Transition?
• The transformation of a thermodynamic system from one phase to another through heat transfer.
‐ Phase transitions usually occur as a function of Temperature and Pressure.
‐ Commonly observed as changes between the four (4) states of matter (solid, liquid, gas, plasma).
• Solid‐to‐solid phase transitions can also occur in solid molecules that can rearrange their structure:
• Amorphous Structure ↔ Crystal Structure
• Crystal Structure ↔ Different Crystal Structure
• Amorphous Structure ↔ Different Amorphous Structure
Dimitris E. Anagnostou
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Nov. 5, 2015
2
What are phase‐change materials (PCMs)?
• Materials that absorb and release thermal energy during the process of melting and freezing.
(solidliquid (heat absorbed) // released if cooled.
• PCMs are oxide‐based “strongly correlated electron systems” that typically have partially filled 3d‐, 4d‐, or 4f shells (e.g. transition metal oxides). • PCMs have unusual properties that classical theory does not explain, and that arise from their complex intrinsic interactions between electrons, spins, orbitals, and phonons:
‐
‐
‐
‐
Sodium Acetate heating pad: When it crystallizes, it warms up.
high‐TC superconductivity
colossal magnetoresistance spin polarization, and metal–insulator phase transitions (MITs). MITs = orders‐of‐magnitude change in electrical (σ,ρ) and dielectric (εr) properties. • MITs are actuated by external excitations:
Temperature
Pressure
E‐field
H‐field. Dimitris E. Anagnostou
The electron–electron and electron–ion interactions in materials.
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Nov. 5, 2015
3
Phase Transition of H2O
• Familiar example: melting‐‐freezing water
– At T 0C 32°F), water changes from
liquid phase
 to 
solid phase (ice)
(no structure)
(hexagonal crystalline structure)
• Ice molecules can exhibit up to 16 different phases (packing geometries), depending on temperature and pressure. • During a phase transition certain material properties change discontinuously. E.g. Volume (bottles explode in freezer). [http://www.education.vic.gov.au/PublishingImages/school/teachers
/teachingresources/discipline/science/samples/threephasewater.jpg]
[http://classconnection.s3.amazonaws.com/478/flashcards/3105478/png/ice_vs_water-1414C6D926B6024CEE7.png]
Dimitris E. Anagnostou
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[http://www.chem1.com/acad/sci/aboutwater.html]
Nov. 5, 2015
4
Phase Transition of VO2
• VO2 goes through a solid‐to‐solid phase transition at 68°C. • When heated, its crystal structure rearranges  changes σ and εr.
• The low temperature structure prevents e- conduction (like an insulator) • The high temperature structure allows easy conduction (like a metal)
 these result in useful electrical switching properties. Above 68°C (right), in the conducting phase, large vibrational motions (phonons) stabilize the
tetragonal crystal structure (phase) and free up conduction electrons indicating the VO2 is metal.
[J.D. Budai et al., (ORNL), Nature 515, 535-539 (2014).]
Dimitris E. Anagnostou
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Nov. 5, 2015
5
Phase Transition of VO2
•
VO2 is the smart material with the transition temperature
closest (but not “too” close) to room temperature. • This makes VO2 ideal for practical applications, where low power is necessary to induce the phase change. Above 68°C (right), in the conducting phase, large vibrational motions (phonons) stabilize the
tetragonal crystal structure (phase) and free up conduction electrons indicating the VO2 is metal.
[J.D. Budai et al., (ORNL), Nature 515, 535-539 (2014).]
Dimitris E. Anagnostou
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Nov. 5, 2015
6
Phase Transition of VO2
• Many of the material’s properties (electrical, optical, mechanical, and magnetic) are very abrupt and exhibit hysteresis across the phase change, which makes this "smart material" a "smart multifunctional material". • Hysteresis gives the material memory capability which allows for programming electrical, mechanical, and optical states.
3 orders of magnitude change in resistance R.
Dimitris E. Anagnostou
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Nov. 5, 2015
7
Recent Developments and Applications
VO2‐based Micromanipulator developed at MSU (video): •
•
•
•
•
•
Pick, Drag & Drop
Micro‐assembly
Flexibility Demonstration
Amphibious Manipulation
Micro‐Puncture
Bio‐manipulation
Dimitris E. Anagnostou
[http://www.egr.msu.edu/~nelsons/Micromanipulator]
[email protected]
Nov. 5, 2015
8
Recent Developments and Applications
Thermal imaging using resistive heaters
(video). Using VO2 for programmable thermal
image projectors (video)
Programming images in VO2: Given the multifunctionality of VO2, not only mechanical states in MEMS can be programmed using VO2. It turns out that the phase change of VO2 also comes with a drastic change in the optical properties of the material for wavelengths in the infrared (IR) regime. Michigan State University has successfully used this property to program optical states in VO2 by scanning a red laser over the film and project IR images.
[http://www.egr.msu.edu/~nelsons/Thermal-images-resistive-heater]
[http://www.egr.msu.edu/~nelsons/Prog-thermal-images]
Dimitris E. Anagnostou
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Nov. 5, 2015
9
Recent Developments and Applications
• Microactuators bend at frequencies as fast as 6 KHz. • Potential applications: High-Work Density Microactuators with Phase Transition
Activated Nanolayer Bimorphs. Scale bar is 50 μm Nano Lett.
12, 6302 (2012)
(Video) - VO2 microactuator [https://www.youtube.com/watch?v=0dIs_kgOhig]
Dimitris E. Anagnostou
–
–
–
–
–
Microelectromechanical systems
Microfluidics
Robotics
Drug delivery
Artificial muscles.
(Video) - VO2 MEMS laser-actuated microgripper
[https://www.youtube.com/watch?v=QoDhfRI-VNk ]
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Nov. 5, 2015
10
Recent Developments and Applications
(Video) - VO2 moving switch, 1Hz and 2000 Hz.
(Video) - VO2 MEMS series microgrippers
[https://www.youtube.com/watch?v=FkG5-qpJ914]
[https://www.youtube.com/watch?v=MIgz7424L_E]
(Video) – Contracting / Expanding VO2 Spiral
http://www.slate.com/articles/video/video/2013/12/vanadium_dioxide_video_shows_supermaterial_moving_an_object_much_bigger.html
Dimitris E. Anagnostou
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Nov. 5, 2015
11
Other Applications and Uses
Heating and Cooling:
Thermal energy storage
Conditioning of buildings, such as 'ice‐storage'
Heat pump systems
Solar power plants
Passive storage in bioclimatic building/architecture (HDPE, paraffin)
Cooling of food, beverages, coffee, wine, milk products, green houses
Energy Savings:
Waste heat recovery
Off‐peak power utilization: Heating hot water and Cooling
Medical applications: Artificial muscles
Transportation of blood, operating tables, hot‐cold therapies
Clothing: Human body cooling under bulky clothing or costumes. Food: Thermal protection of food: transport, hotel trade, ice‐cream, etc.
Chemistry: Smoothing exothermic temperature peaks in chemical reactions
Air/Space:
Missile guidance
Spacecraft thermal systems
Turbine Inlet Chilling with thermal energy storage
Vehicles: Thermal comfort in vehicles
Electronics:
Thermal protection of electronic devices
Computer cooling
Cooling of heat and electrical engines
Telecommunications: Telecom shelters in tropical regions (keep the indoor air cold by absorbing heat generated by equipment).
Antennas: ??? Dimitris E. Anagnostou
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Nov. 5, 2015
12
Reconfigurable Antennas
Polarization [F. Yang, et al, 2005]
Frequency [Anagnostou et al., US Patent 7589674 (2009)]
Pattern
[Herrera, et.al ,2003]
Pattern Reconfigurable Microstrip
[Ouyang et al., PIERS, 2008]
Achieved using:
Variable Reactive
Loading or DTCs
Varactors/FET DTCs Varactor Loaded Tunable Printed PIFA
[Liang et al., ©PIERS, 2009]
Digitally Tuned Capacitor equivalent circuit. Industrial use below 3 GHz.
[Peregrine Semicond. PE64904 Spec. Sheet]
Dimitris E. Anagnostou
Structural or Mechanical Changes
Material Changes
Switches
Extendable Parts
Movable Parts
Rotational Parts
Ferrites
Ferroelectrics
(until recently)
PIN Diodes
MEMS
MEMS Vee Antenna, [Chiao et al. et al., ©IEEE 1999]
Ferroelectric reconfigurable leaky‐wave antenna [Lovat et al, ©IEEE 2006]
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Nov. 5, 2015
13
Reconfigurable Antennas
Switches:
PIN Diodes
+ Can have
1 bias line
‐ Non‐linear, no wideband apps
‐ Low fc < 10 GHz
Huff et al., IEEE/ACES 2005
RF‐MEMS
+ Low‐loss
+ Linear
+ Wide bandwidth
‐ Need 2‐line Biasing Pre‐Packaged
Huff et al., IEEE TAP (2006)
Integrated
Using RF as bias line
‐ Floating ground ‐ Reliability With DC bias lines
‐ Bias lines ‐ High reliability
λ/4 μstrip bias lines Narrowband
Kingsley et al. IEEE JMEMS 2007
Nikolaou et al., IEEE TAP 2009
Cetiner et al., IEEE TAP 2010
λ/4 μstrip Anagnostou et al., IEEE TAP bias lines 2006
Narrowband
Anagnostou et al., IEEE APS 2010
Challenge: Very few reconfigurable antennas have been implemented!
Dimitris E. Anagnostou
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Nov. 5, 2015
14
Biasing of Reconfigurable Antennas
This is an example of a typical
biasing network comprised of a λ/4 transmission line and a radial stub. Such networks limit
the tuning bandwidth range to
values around 20% to 25% or
less. A varactor varies the capacitance C to tune a microstrip antenna in a continuous (non‐discrete) range.
Varactor tuning: 2.4–0.4 pF.
Voltage range: 0‐30 V
Tuning range: Δf = 22%
Gain: 5 ± 0.5 dBi
[Bhartia and Bahl, Microw. Journal, 1982].
Dimitris E. Anagnostou
1‐λ slot with two FETs.
Tuning range: 10% at 10 GHz. ‘B’: Slot excitation (center crossover). ‘A,C’: FET bias ckt Zin_10GHz = 0‐25j Ω (0.6 pF), placed near slot ends at low‐Z points to prevent mismatch & field changes. Voltage tuning: Vgs~freq = 0 ‐ 0.6V, Vds = 0 ‐ 0.4V
[Kawasaki and Itoh, 1991].
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Nov. 5, 2015
15
Biasing of MEMS Reconfigurable Arrays
Polarization MEMS‐reconfigurable 2x2 array.
Radial stubs used for biasing. Tuning Range < 2% (Δf ≈ 0%). [G. Wang, et al., IET MAP, 2011]
Electronic scanned array with 14 GHz MEMS phase‐
shifters. Radial stubs used for biasing. Tuning Range < 2%. (Δf ≈ 0%).
[D. Chung et al., IEEE APS 2007]
[N. Kingsley et al., Trans. Microw. Theory Tech., 2005]
Dimitris E. Anagnostou
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Nov. 5, 2015
16
Biasing of Reconfigurable Filters
Single switch reconfigurable Dual‐mode reconfigurable BPF with variable BW using a filter with center dual‐mode triangular patch frequency control.
[C. Lugo et al., IEEE MWCL, 2006] resonator. [C. Lugo et al., IEEE MTT‐IMS, 2005] Six‐state filter with frequency and BW control.
Creates 2 fractional bandwidths A common characteristic of many of these components is at 3 center frequencies (9, 10, and 11 GHz). [C. Lugo et al., IEEE, 2006] Tuning Range ≈ 15%.
that they require biasing, either through hi‐res bias lines or using RF circuits that often limit their bandwidth.
Dimitris E. Anagnostou
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Nov. 5, 2015
17
Other Biasing Mechanisms for Antennas
Other biasing solutions are often design‐specific and involve significant design effort and complexity
(a) Layout of PIN diode switch bias network for frequency‐
reconfigurable slot antenna, and (b) its RF equivalent circuit. Equivalent circuit of tunable matching network and UWB antenna with ‐ control bias voltage VBIAS
‐ series capacitor
‐ shunt inductor L, and ‐ varactor.
[Chin‐Lung Yang and Chieh‐Sen Li, 2011]
[Peroulis et al., IEEE Trans. on AP, 2005].
Dimitris E. Anagnostou
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Nov. 5, 2015
18
Other Biasing Mechanisms for Antennas
Pattern‐reconfigurable spiral microstrip antenna model, including vias, lumped components, tuning and bias stubs, and simplified switch model incl. thin wires over Si chips to approximate the switches. Digitally‐Tuned Capacitors (DTCs) for multi‐band wireless. The tunable matching network:
‐ UltraCMOS DTCs, ‐ three tunable components, ‐ biasing, and control circuitry
is integrated onto a single die, and the DTCs are controlled through a serial interface. Frequencies: 698‐960 MHz 1710‐2170 MHz Tuning range: ≈25%
[R. Whatley, Electronic Design, Mar. 2012 Broadside and End‐Fire Radiation with MEMS Equivalent transmission line circuits for determining the bias and matching networks for the antenna. [Huff and Bernhard, ©IEEE 2006].
Dimitris E. Anagnostou
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Nov. 5, 2015
19
Reconfigurable Wire Antennas (Pros/Cons)
Dipole with Photoconductive Silicon Switches
MEMS Band‐Reject UWB Antenna
8 GHz, 14 GHz, and 25 GHz Reconfigurable Self‐Similar Antenna
Switches diced from a hi-res
Si wafer (ρ>6000 Ω·cm).
∆f = 39%
[Panagamuwa et al., IEEE Trans. AP, 2006]
Pros: Cons:
[Anagnostou et al., IEEE Trans. AP, 2014]
[Anagnostou et al., IEEE Trans. AP, 2006]
integrated MEMS  excellent performance, > 25% tuning range possible.
Packaged MEMS  Fragile Integrated MEMS  Very fragile
No ground plane  non‐directional radiation pattern
High‐Temp (550C), cleanroom lithography (MEMS require high‐resistive bias lines (e.g. AZO) that are sometimes deposited at high temperatures (CCVD).
Dimitris E. Anagnostou
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Nov. 5, 2015
20
Reconfigurable Apertures (MEMS, Diodes) (Pros/Cons)
Diodes alter slot circumference  Tuning
Diodes OFF: Large slot flow
Diodes ON: Small slot  fhigh
[Gheethan, MSc Thesis, SDSMT 2009]
[Anagnostou et al., IEEE AWPL, 2009]
[Ankireddy et al., Journal Appl. Phys, 2013]
0
-5
[B. Cetiner et al., IEEE Trans AP, ]2010.
S11[dB]
-10
-15
-20
-25
Measured (diodes off)
Simulated (diodes off)
Measured (diodes on)
Simulated (diodes on)
-30
4.5
5.0
5.5
6.0
6.5
Frequency [GHz]
Reconfigurable CFSA antennas on FR4 and on flexible Kapton™ using direct‐write.
Frequency reconfigurable annular slot (2.4 and 5.2 GHz). MEMS: 350μm x 650μm. Dimitris E. Anagnostou
Pros: • Apertures allow for simpler DC biasing (λ/4 stub, hi‐Res lines, etc)
• More Metal  Less ohmic losses (limited by diode performance)
• Gain > dipole (G ≈ 4.5 dBi) • Low cost, easy to fabricate and measure
• Broadband and dual‐band.
Cons: • Non‐directional Pattern, Bulky Structure
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Nov. 5, 2015
21
Biasing and Control of Adaptive Arrays
Antenna2
Flex sensor
Circuit
input
Circuit
outputs
Control
Circuit
Array feed
More complex designs offer added functionality. Here, an entire microprocessor and control circuit are used to control the phase‐shifters of a frequency reconfigurable adaptive array.
The CFSA elements allow wide frequency reconfigurability.
[D. Anagnostou and M. Iskander., IEEE Aerospace Conf., 2015]
Dimitris E. Anagnostou
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Nov. 5, 2015
22
Reconfigurable Trade Space
“There are multiple dimensions in this trade-off space, including
- reconfiguration speed
 ~10 μsec (down to 2 nsec reported)
- power consumption
 1 W to 1 mW
- actuation requirements (V or I)
 (80 mA, 20V)
- fabrication complexity
 easier than MEMS
- durability
 excellent
- device lifetime
 excellent
- complexity of control & bias network
network non-existent (non-contact lines)
- weight, size, cost,
 less than most components
- dynamic range
 N/A
- sensitivity
 N/A
- … and of course performance.”
 very good; potentially excellent
J. Bernhardt, “Reconfigurable Antennas”, Morgan Claypool Pub., 2006.
… and Vanadium Dioxide helps address or improve many of these parameters.
Dimitris E. Anagnostou
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Nov. 5, 2015
23
Why VO2 Antennas?
The reversible MIT transition of VO2 has attracted much interest during the past decade. Early results showed a low‐loss VO2 RF switch [1].
So, we wanted to study “if” and “how” VO2 can be used in antennas.
[1] Dumas-Bouchiat, et.al , Appl. Phys. Lett., 2007
Dimitris E. Anagnostou
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Nov. 5, 2015
24
VO2 Characteristics – RF Switch
Shunt switch Series switch
[1] Dumas-Bouchiat, et.al , Appl. Phys. Lett., 2007
Dimitris E. Anagnostou
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Nov. 5, 2015
25
VO2 Characteristics – RF Switch
↖ S21 “On” (cooled)
S21 “Off” (heated) ↗
Shuntconfiguration
• IL‘ON’ 0.8to1.7dB* inactive
• ISO‘OFF’ 25dB active
• L1 1000μm
↖ S21 “On” (heated) Seriesconfiguration
• IL‘ON’ 3dB* active
• ISO‘OFF’ ‐20dB inactive
• L2 500μm
S21 “Off” (cooled) ↗
*0.8dBofthemeasuredloss
isduetotheCPWline
[1] Dumas-Bouchiat, et.al , Appl. Phys. Lett., 2007
Dimitris E. Anagnostou
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Nov. 5, 2015
26
VO2 RF Switch vs MEMS Switch
S21 “On” (cooled)
S21 “Off” (heated)
S21 “On” (heated)
S21 “Off” (cooled)
- Higher losses
- Excellent isolation
MEMS
MEMS insertion
insertion loss
loss (-0.2dB
(-0.2dB at
at 15
15 GHz)
GHz)
MEMS
isolation
(20dB
at
14
GHz)
MEMS isolation (20dB at 14 GHz)
VO2 insertion loss (0.6 to 2 dB approx.)
VO2 isolation (25 to 40 dB approx.)
Main plot from: Rebeiz G., 11th Canadian Semiconductor Technology Conference, Ottawa, Canada , August 18-22, 2003.
Dimitris E. Anagnostou
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Nov. 5, 2015
27
VO2 RF Switch vs MEMS and DIODE
S21 “On” (cooled)
S21 “Off” (heated)
Disclaimer:Valuesareindicative.Theyarenotusedtoexemplifypreferenceofonetechnologyoveranother
andthey maynotreflectthelateststateoftheartofaspecificcomponentor manufacturer.
VO2 Switch [1]
MEMS Switch [2]
PIN/FET Switch [3] Shunt configuration
• IL‘ON’ 0.8dBto1.7dB*
• ISO‘OFF’ 25dB
• L1 1000μm
• Linearity:Excellent
Shunt configuration
• IL‘ON’ ~0.6dB
• ISO‘OFF’ 20dB
• Length 350μm
• Linearity:Excellent
Shunt configuration • IL‘ON’ [email protected],1.2dB@5GHz
• ISO‘OFF’ 30to1dB
• Length 2mmpackaged
• Linearity:Poor
Series configuration
• IL‘ON’ 3dB*
• ISO‘OFF’ ‐20dB
• L2 500μm
• Linearity:Excellent
Series configuration
• IL‘ON’ 0.3dB
• ISO‘OFF’ ‐15dB
• Length 350μm
• Linearity:Excellent
Series configuration
• IL‘ON’ [email protected], 5dB@5GHz
• ISO‘OFF’ 40to3dB
• Length 2mmpackaged
• Linearity:Poor
Actuation:55– 90mA
Power:10mW– 1W est.
Switchingtime:2ns–10μs
CutoffFrequency:N/Ayet
Reliability:Excellent
Durability:Excellent thin‐film
Hysterisis:Yes programmable
Hotswitching:Possibly
Decoupledbiasingmechanism
nomorebandwidthlimitations
Actuation:~40V
Power:~0.1mW
Switchingtime:1–300msec
CutoffFrequency:~40GHz
Reliability:BillionsCycles
Durability:Average
Hysterisis:No
Hotswitching:No
Biasnetworkandlines.
Actuation:0.7V,1mA, FET:0.3‐0.4V
Power:~1mW
Switchingtime:nsec
CutoffFrequency: 10GHz
Reliability:Excellent
Durability:Average
Hysterisis:No
Hotswitching:No 4
Biasnetworkandlines.
S21 “On” (heated)
S21 “Off” (cooled)
[2] Muldavin et al., IEEE Trans MTT, 2000
[1] [Dumas-Bouchiat, et.al , Appl. Phys. Lett., 2007]
[3] Avago Tech. AN-922 Application Note.http://www.pmirf.com/Products/Switches/
ApplicationNotes-PINDiodeSwitches.htm
[4] http://faculty.frostburg.edu/phys/latta/ee/qsk5/hotswitching/hotswitching.html
*andtheILcanbefurtherreducedusingthickerVO2
Dimitris E. Anagnostou
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Nov. 5, 2015
28
VO2 Characteristics – Actuation Actuation:
1. Convective heating (first designs)
2. Conductive heating
3. Joule heating (new designs) 4. Photo‐thermally 5. Voltage biasing
6. Ultra‐fast optical excitation
1.,2.
http://www.roasterproject.com/2010/01/heat‐transfer‐the‐basics/
[1] ACS Nano, 5:10102-7 (2011).
[2] J Appl. Phys., 108, 113115 (2010).
[3] IEEE/ASME J MEMS, 23,1, 243-251 (2014).
[4] Smart Mater. and Struct., 21, 105009, (2012).
[5] Phys. Rev. B, 84, 241410(R), (2010).
[6] Phys. Rev. Lett., 87, 237401, (2001).
4.
3.
Miguel V. Vitorino et al., Scientific Reports 5, 7818 (2015)/
http://www.nature.com/articles/srep07818/figures/4
6.
http://s23.postimg.org/9dmd136nf/paper2.png
Major VO2 Advantage: Remote actuation = “decouple” the bias network from design!
Dimitris E. Anagnostou
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Nov. 5, 2015
29
VO2 Characteristics – Actuation An E‐MIT (electrically driven MIT) can happen at nanoseconds and, potentially, even faster. A 2 ns rise time switch has been reported [1].
Switching speed is limited by
‐ device dimensions
‐ parasitic resistance and capacitance of both circuits ‐ VO2 itself rather than the intrinsic switching speed of VO2. Also, by growing VO2 directly on a metal electrode the contact resistance can be minimized, and the spacing between electrodes can be reduced to hundreds of nanometers (instead of μm and mm).
The transient measurement of VO2 E‐MIT switching in an out‐of‐plane thin‐film device showing ~2‐ns rise time [1].
[1] Y. Zhou, X. Chen, C. Ko, Z. Yang, C. Mouli, and S. Ramanathan,
“Voltage-triggered ultrafast phase transition in vanadium dioxide
switches,” IEEE Electron Device Lett., vol. 34, no. 2, pp. 220–222, 2013.
Dimitris E. Anagnostou
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Nov. 5, 2015
30
VO2 Characteristics – Resistance
VO2 on C‐type Sapphire substrate. (Inset: on SiO2/Si).
Resistivity ρ from [1]:
• 200 nm thick VO2
• ρSapphire = 5.5∙10‐2 (inactive) to 7∙10‐5 Ω∙cm (active)
• ρSiO2
= 5.0∙10‐1 (inactive) to 3∙10‐3 Ω∙cm (active)
[1] Dumas-Bouchiat, et.al , Appl. Phys. Lett., 2007
Three orders of magnitude change in resistivity. L=W (square)
then R=Rs
L
Calculated square patch resistance Rsq_saph 2750Ω (inactive) for a square patch
Rsq_saph 3.5Ω (active) for a square patch
t
W
Figure modified from:
https://upload.wikimedia.org/wikipedia/commons
/6/68/Resistivity_geometry.png
Dimitris E. Anagnostou
[email protected]
Hypothesis:
The significant drop in ρ
allows the creation of VO2‐based reconfigurable antennas, where thin‐
films replace RF components and attempt
to overcome their intrinsic limitations (i.e tuning range & complexity). Nov. 5, 2015
31
VO2 Characteristics – Resistance
First Design
VO2 1 mm2
L=W (square)
then R=Rs
L
Calculated square patch resistance (200 squares)
Rsq_saph 2750Ω (inactive) for a square patch
Rsq_saph 3.5Ω (active) for a square patch
(Used in first antennas)
W
Rsq/N
or
N Rsq /R
(N: # squares)
1 2 3
Heated
Cooled
• VO2 was included correctly in antenna design
• Failed first fabrication
• Measured: 300,000 Ω/□ inactive, 6000 Ω/□ active (1000x higher resistance!)
Figure modified from:
https://upload.wikimedia.org/wikipedia/commons
/6/68/Resistivity_geometry.png
Rsq
With these values we can determine the R of a
N patch from the # squares contained in it, or
determine the # of squares needed to achieve a
desired patch R value.
Dimitris E. Anagnostou
Resistivity (Ω-cm)
t
0.01
0.001
0.0001
0.00001
30 40 50 60 70 80 90 100
Temperature (°C)
Still, we measured similar hysteresis and performance of about 3‐orders of magnitude drop in resistivity.
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Nov. 5, 2015
32
VO2 Characteristics – Permittivity
Capacitance measurement of a layered hafnium oxide VO2 capacitor [2].
HfO2
VO2
HfO2
VO2
HfO2
[2] Z. Yang, et.al ,Phys Rev. B., 2010
• ԑr ≈ 36 at room temperature
• ԑr ≈ 30000 at 100 °C
By varying both ρ and εr
VO2 opens up a new design space where new antenna configurations may be possible.
Dimitris E. Anagnostou
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Nov. 5, 2015
33
The “How” ‐ Fabrication and Characteristics
Pulsed Laser Deposition
f=10Hz
4 J/cm2
KrF Laser
=248nm
T=550°C
P=50 mTorr
O2
15 sccm
Ar
10 sccm
Vacuum
Pump
We deposit VO2 by PLD (one of the best known techniques for growing high quality thin‐films). Vanadium has multiple stable oxide states, so growing stoichiometric VO2 (1V:2O) is not a trivial task; but we have managed to get the right conditions to get VO2 of high quality and highly oriented. Sputtering is another way to deposit VO2. It is commercially viable, and compatible with most standard microfabrication procedures.
Dimitris E. Anagnostou
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Nov. 5, 2015
34
The “How” ‐ Fabrication and Characteristics
Pulsed Laser Deposition
$0.2 ‐ $0.5 each mm2 (est.)
Cost:
Time to fabricate: 1‐day in a university cleanroom or commercial laboratory using standard photolithography + a PVD system (physical vapor deposition) to grow the VO2. Thickness: Thin‐film thickness: 1 nm to 1,000 nm.
Typically 200 nm to 600 nm for best performance.
Resolution: From ~10 nm wide traces to entire wafer. (Results with 4 μm, 20 μm and an entire 2‐inch wafer are shown here)
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
35
VO2 Reconfigurable Antennas
• Classes of Antennas
• VO2 Wire‐Class Antenna
• VO2 Aperture‐Class Antenna
• More results
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
36
Wire Class Antenna Application
With the new resistance modeling in place we began designing two distinct antenna prototypes to represent common antenna classes. The first was the Wire‐Class. • Very similar to dipole
• Approximately 2 dBi gain
• Frequency defined by L
• Bow angle affects frequency and bandwidth
• Increased width over dipole  allows larger aspect ratios of VO2
Bowtie antenna with labeled dimensions.
•
•
•
•
Toroidal radiation pattern
VO2: 200 nm thick, 20 μm × 1.3 mm.
0.558 mm thick Al2O3 (Sapphire) substrate (εr = 11.5) VO2 model: 300,000 Ω/□  6,000 Ω/□
H1/Wv = 65 squares (Rcold ≈ 4.5 kOhm, Rhot ≈ 100 Ohm)
[T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna
Using Metal-Insulator Transition in Vanadium Dioxide”. IEEE AWPL, vol. 14, 2015, pp. 1381-1384.]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
37
Wire Class Antenna Application
VO2‐Bowtie, Current Distribution
Large
Reflections
Inactive: VO2 creates open‐circuits  block RF current flow to edges.
Highest frequency.
─ E‐plane
─ H‐plane
Inactive Active
• Maintains pattern shape
Active: VO2 creates short‐circuits  allow RF current flow to edges. Lowest frequency.
|S11| VO2‐Simulated results
• Δf = 4.71 GHz  4.57 GHz (140 MHz)
• Gcold = ‐0.24 dBi (mostly due to mut. coupling)
• Ghot = ‐1.41 dBi (due to VO2, C reactance & high εr)
Simulated |S11| of bowtie antenna.
[T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna
Using Metal-Insulator Transition in Vanadium Dioxide”. IEEE AWPL, vol. 14, 2015, pp. 1381-1384.]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
38
Wire Class Antenna Application
Fabricated VO2‐based bowtie antenna prototype.
[T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna
Using Metal-Insulator Transition in Vanadium Dioxide”. IEEE AWPL, vol. 14, 2015, pp. 1381-1384.]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
39
Wire Class Antenna Application
Measured vs simulated |S11|
E-plane (inactive)
E-plane (active)
Simulated
fsim: 4.71 GHz  4.57 GHz (140 MHz)
Gsim: -0.24 dBi (inactive), -1.41 dBi (active)
H-plane (inactive
H-plane (active)
• Freq. dropped due to not modeling the high εr => Calong_VO2 ↑ => leff ↑.
• Also increased G means the actual Rsq is < 6,000 Ω/sq, possibly due to
increased thickness or purity of deposited VO2.
*Proof-of-Concept*
Dimitris E. Anagnostou
Measured
fmeas: 4.67 GHz  4.52 GHz (150 MHz)
Gmeas: 0.14 dBi (inactive), -0.67 dBi (active)
Efficiency: ‘cold’ ~48.9%, ‘hot’ ~40.7%, due to
the VO2 ‘capacitor’ and sapphire high εr.
VO2 Loss: ‘hot’ ~ 17% (measured)
[T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna
Using Metal-Insulator Transition in Vanadium Dioxide”. IEEE AWPL, vol. 14, 2015, pp. 1381-1384.]
[email protected]
Nov. 5, 2015
40
VO2 Reconfigurable Antennas
• Classes of Antennas
• VO2 Wire‐Class Antenna
• VO2 Aperture‐Class Antenna
• More results
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
41
Aperture Class Antenna Application
To fully investigate the use of VO2 in reconfigurable antennas, we wanted to test it with a complementary, Aperture‐Class antenna, and this time increase the tuning bandwidth.
• Frequency defined by aperture perimeter C.
ԑ
1
,
2
2
• Pattern similar to 2‐dipole array
• Gain approximately 3.5dBi to 4 dBi (more directive)
• More metal  reduced loss
CFSA antenna with labeled dimensions.
•
•
•
•
VO2: 200 nm thick, 4 μm × 1.3mm
0.558 mm thick Al2O3 (Sapphire) substrate (εr = 11.5) VO2 model: 300,000 Ω/□  6,000 Ω/□
H1/Wv = 325 squares (Rcold ≈ 920 Ohm, Rhot ≈ 18 Ohm)
• Reconfigured in the opposite manner:
• VO2 activation reduces the frequency.
• Current can select to travel from 2 paths: 1. through the VO2, or 2. around the slot. [T.S Teeslink, MSc Thesis, SDSMT, 2015]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
42
Aperture Class Antenna Application
VO2‐CFSA, Current Distribution
Current around full aperture
Inactive
Current through VO2 patches
Active
─ E‐plane
─ H‐plane
Inactive Active
VO2‐Simulated results
• Δf = 4.27 GHz  6.53 GHz (2.26 GHz)
• Gcold = 1.34 dBi (mostly mutual coupling)
• Ghot = 0.07 dBi (mostly ohmic losses on VO2)
[T.S Teeslink, MSc Thesis, SDSMT, 2015]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
43
Aperture Class Antenna Application
Fabricated VO2‐based CFSA antenna prototype (measurements pending).
[T.S Teeslink, MSc Thesis, SDSMT, 2015]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
44
Aperture Class Antenna Application
Measured vs simulated |S11|
Fabricated VO2‐based CFSA prototype.
E-plane (inactive)
Simulated
E-plane (active)
fsim: 4.27 GHz  6.53 GHz (2.26 GHz)
Gsim: 1.34 dBi (inactive), 0.07 dBi (active)
Measured
fmeas: 4.1 GHz  7.15 GHz (3.05 GHz)
Gmeas: 1.73 dBi (inactive), 1.65 dBi (active)
H-plane (inactive)
H-plane (active)
• Higher Gain, possibly due to higher VO2 quality (3rd fabrication).
• Some reflections from large SMA prevented pure toroidal pattern.
Efficiency: ‘cold’ ~68%, ‘hot’ ~64.5 %, due to
the VO2 capacitor, lower resistive losses.
VO2 Loss: ‘hot’ ~ 5.5 % (measured)
*Proof-of-Concept for Aperture Antenna*
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
45
VO2 Reconfigurable Antennas
• Classes of Antennas
• VO2 Wire‐Class Antenna
• VO2 Aperture‐Class Antenna
• More VO2 results
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
46
Can we reduce the practical transition time? Integrated resistive heaters
Heater: 5μm
Via size: 1.5 mm
Imax_meas_90C = 84 mA
V = 20.7 V
Power = 1.74 W
CFSA3
Circ_CFSA
Heater: 5μm
Via size: 1.5 mm
Imax_meas_90C = 71 mA
V = 22.81 V
Power = 1.62 W
•
Platinum heater lines under the VO2 through vias on the SiO2 isolation layer. •
No need for additional resistors or to design frequency‐dependent biasing networks. Measured max current of
heater to reach 90 C.
Switchingtimeofresistiveheater:10μs for3μm× 100μmVO2,measured
~40μs for5μm× 1.3mmVO2,estimated
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
47
Can we reduce the practical transition time? Fabricated VO2 Antenna prototypes with integrated resistive heaters (currently being characterized at SDSM&T) for faster actuation.
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
48
Can we Control and “Tune” the Transition? Transition States Measurement
Measured |S11| at intermediate temperatures during the phase‐transition, showing the gradual transition from the cooled (blue) to the heated (red) state. This measurement helps observe quantitatively the effect of the phase transition on the antenna. The indicated temperature is approximate.
[T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna Using
Metal-Insulator Transition in Vanadium Dioxide”. IEEE AWPL, vol. 14, 2015, pp. 1381-1384.]
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
49
Can we Print VO2 Inks? Ink‐jet printing of VO2
[Contact: Prof. W. Cross at SDSMT: [email protected]]
QR code
200 nm
SEM of tungsten‐doped (12 %) VO2 nanoparticles. Vanadium Distribution Tungsten Distribution
Synthesis [1]: 4 M HCl and hydrazine hydrochloride added to a V2O5 solution  Blue Vanadyl chloride, mix w/ tungstic acid & add to sodium bicarbonate  Purple solution, wash in ethanol, heat at 500 °C for 1‐hour  crystalline VO2
SPACT logo
Prototypes of VO2 nanoparticles were printed easily with the Optomec M3D Aerosol Jet printer. [1] Zifei Peng et al.,J of Phys Chem., 2007.
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
50
Can we alter the Transition Temperature? VO2 Transition at Room Temperature [Prof. W. Cross at SDSMT: [email protected]]
QR code
Transition temperature of the 12 wt% tungsten‐
doped VO2 NPTs: Not well defined. Some NPTs transitioned at room temperature, but the majority from 35C ‐ 60C indicating varying amounts of W‐
doping.
SPACT logo
Prototypes of VO2 nanoparticles were printed easily with the Optomec M3D Aerosol Jet printer. •
•
•
VO2 nanoparticles could be manufactured using a solvothermal process. Doping of the nanoparticles was possible, although control of the doping level has yet to be achieved.
The nanoparticles could be printed using the Optomec M3D. [1] Zifei Peng et al.,J of Phys Chem., 2007.
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
51
Can the Heat Damage the Cables? Effects may depend on the heating method:
1) Resistive heaters: No effect to nearby components
2) Convective heating: Possible effect to nearby parts if overheated. But most wires and components are rated to > 68 C
 Standard coax cables (e.g. RG‐58, RG‐59) rated ‐40 C to +80 C.
 Military cables rated ‐55 C to +105 C.
http://www.awcwire.com/productspec.aspx?id=rg58/u
http://www.awcwire.com/productspec.aspx?id=rg59/u
]http://www.militarywire.org/singleconductor.htm
 SMA connectors (e.g. by Amphenol) rated ‐65C to +165C. http://www.amphenolrf.com/products/sma.asp?N=0&sid=54B06B80360E17F&
 PTFE (Teflon) is often used as insulation in coaxial cables, rated to +160 C.
http://www.daconsystems.com/teflon‐insulated‐wire.
 Many PIN diodes rated to +125 C.
http://www.diodes.com/datasheets/PAM2303.pdf
 Most common dielectrics easily withstand +100 C or higher.
So VO2 is “cable‐friendly”
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
52
Can we Reduce the Losses?
SPST RF Switch with 600 nm VO2 [4]
ILON = 0.2 dB at 50 GHz (0.5dB at 110 GHz) Heater: 10 μm × 2 μm.
ISOOFF = 21.5 dB at 50 GHz (15 dB at 110 GHz). tON/OFF = 2 μs
PON < 20mW (or 8 mA, 2V)
RON = 1 Ohm, ROFF = 17 kOhm
Thicker VO2  reduced losses.
Model for worst case scenario of resistivity per square
200nm VO2  300 kOhm vs 6 kOhm
400nm VO2  150 kOhm vs 3 kOhm
600nm VO2  100 kOhm vs 2 kOhm
800nm VO2  75 kOhm vs 1.5 kOhm
1000nm VO2  60 kOhm vs 1.2 kOhm
Application: 2‐bit phase‐shifter circuit at 50 GHz with two
SP4T switches, and its phase‐shifter insertion loss, return loss, phase shift, and group delay.
[4] C. Hillman et al., Teledyne / UCSB, IEEE IMS 2014
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
53
Conclusions
•
Proof of concept of VO2 antennas was demonstrated •
VO2: Interesting & promising material for RF applications
• We have barely scratched the surface in this presentation. Ongoing research to reduce the losses and accurately control the resistivity will enable new designs, new components and …
• … new fundamental building blocks in RF design
• Exciting new devices and new applications that we may have not yet imagined will be coming up.
Publications from this research:
[1] T.S Teeslink, D. Torres, J.L Ebel, N. Sepulveda, D.E Anagnostou, “Reconfigureable Bowtie Antenna Using Metal-Insulator Transition in Vanadium
Dioxide”. Antennas and Wireless Propagation Letters, IEEE, vol. 14, 2015, pp. 1381-1384.
[2] T.S Teeslink, D. Torres, M. Chryssomallis, N. Sepulveda, D.E. Anagnostou, “Reconfigurable Antenna Prototype Utilizing the Phase Change
Characteristics of Vanadium Dioxide”. 2015 IEEE APS/URSI International Symposium, Vancouver, BC, Canada, July 19-24 2015.
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
54
Acknowledgements
MSU Collaborators:
(left) Prof. Nelson Sepulveda, [email protected]
(right) PhD student David Torres
Dr. Xiao Ding
Dr. Shengwen (Kevin) Zhang
Dr. Arash Rashidi
Dr. RongLin Li
Dr. Muhannad Al-Tarrifi
Dr. Mina Iskander
Dr. Ben Braaten
SDSMT Students:
Tarron Teeslink (MSEE’15) (left)
Brenden Dixon (center)
Nathan Kovarik (right)
Tarron Teeslink, MSc
Md. Abu Numan Al-Mobin, MSc
Md. Akhter Hossan, MSc
Ahmad A. Gheethan, MSc
Ramila Shrestha, MSc,
‐ NSF awards #1310400, #1310257
‐ South Dakota State EPSCoR
Nathan Kovarik
Brenden Dixon
Lek Ojoawo
Jeremiah Sutton
Peter Wang
Matthew Daniel
Sierra Rasmussen
Yaakov Cohen
Mason Cover (NASA Award)
Andrew Carpenter
Curtis Wynia
Richard Handoko
Cole Deichert
Thank you for your Attention!
Questions, feedback and suggestions are always welcome!
Dimitris E. Anagnostou
[email protected]
Nov. 5, 2015
55