10 th International Vacuum Electronics Conference (IVEC2009) April 28 - 30 th 2009
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Transcript of 10 th International Vacuum Electronics Conference (IVEC2009) April 28 - 30 th 2009
Experimental, Numerical, and Analytical Studies of a Staggered Double Vane Structure for THz
Application
10th International Vacuum Electronics Conference
(IVEC2009)April 28 - 30th 2009
(Presentation #: 1558344)
Young-Min Shin, Larry R. Barnett, Jinfeng Zhao, Diana Gamzina, and Neville C. Luhmann Jr.
Department of Applied Science, University of California-Davis (UCD), CA 95616, USA
17:00 Tuesday, Session 8 - THz
Supported by the DARPA HiFIVE program through a subcontract from Teledyne Scientific.
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Overview
• Motivation and Goal
• Cathode and Electron Gun
• Circuit Design and Analysis
• Interaction Circuit Fabrication
- KMPR UV LIGA
- High Precision CNC Machining
• Cold-Test Setup
• Summary and Future Plans
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220 GHz Sheet Beam TWT
- Vacuum Electronic Circuit ElementsA. High current density, long-life cathode (UCD and Teledyne Scientific)
Tungsten-Scandate Nanopowder cathodes capable of 80 A/cm2
B. High aspect-ratio electron beam (CPI and Teledyne-MEC)Elliptical cathode with beam compression produces 7:1 aspect
ratio beam for SBTWT, 25:1 aspect ratio beam for beam-stickC. High efficiency interaction structure (UCD and Teledyne Scientific)
Novel staggered vane interaction structure at 220 GHz shows 50 GHz bandwidth, 13 dB/cm gain, and 100 W output
D. High power MMIC driver (Teledyne Scientific and UCSB)InP based solid state amplifier 50 mW output at 220 GHz
E. High efficiency thermal management (Teledyne Scientific)Integrated cooling channels around MEMS interaction structure
• MEMS-Integrated High Power Vacuum Amplifier for THz Communication and Sensing Systems
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Nano-Composite Cathode
1150oC for 800 hrs (33 days)UCD Cathode: 80A/cm2 fully space charge limited
• Current Density versus Cathode Button Voltage
After Furnace Sinter: Grain size in matrix is 272 nm and very uniform
• Scandate Nano-Composite (Sc2O3-W) Cathode
Nanograin(100-200 nm)
tungsten
+
Osmium / Rhenium and Scandium /
Yttrium Oxide Cryogenic Milling: incorporation of emission enhancing compounds
Spark Plasma Sintering
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Current:-3 kA-Pressure:--3 kN- 50 kNAtmosphere:--Vacuum
Sol-gel Method
1000 100001
10
100
7543
80
1150o
C-Cathode #3
1150o
C-Cathode #2-311X
400
Cur
rent
den
sity
(A/c
m2 )
Voltage (V)
604030
20
2000 4000
2
Cathode #2---Spectra-Mat 311X
Cathode #3---UCD powder+Spectra-Mat recipe
1000 100001
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7543
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1150o
C-Cathode #3
1150o
C-Cathode #3
1100o
C-Cathode #3
1100o
C-Cathode #3
1150o
C-Cathode #2-311X
1150o
C-Cathode #2-311X
1100o
C-Cathode #2-311X
1100o
C-Cathode #2-311X
400
Cur
rent
den
sity
(A/c
m2 )
Voltage (V)
604030
20
2000 4000
2
Cathode #2---Spectra-Mat 311XCathode #3---UCD powder+Spectra-Mat recipe
EDX Analysis on the SpectraMat 311X Surface
See Zhao et al., Session 23 - Cathodes II
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Cathode Testing at UC Davis
High Current Density Operation of Spectra-Mat: 311X
• At 1272 °Cb the emission at 50 A/cm2 is
still only about 70% SCL • Even at 30 A/cm2 it takes at least 1250 °Cb to reach ~90% SCL
2000 3000 4000 5000 6000 7000
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Cur
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sity
(A/c
m2 )
Voltage (V)
1100oC 1150oC 1180oC 1203oC 1252oC 1273oC
20
1500 3000 4500 6000
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Cathode #1 (UCD pellet and Procedure+Impregnated by Spectra-Mat)
Cur
rent
den
sity
(A/c
m2 )
Voltage (V)
1050oC 1000oC 950oC
UC Davis Cathode
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Cathode Testing at UC Davis
Cathode TestingRapid button test
Multiple rapid cathode life test facility
New High PerveanceCathode Life Test Vehicle
System operational
Three 3.0 P CLTVs completed
Cathode testing and life testing underway at UC Davis: eight vehicles operational with another four nearing completion
G. Scheitrum and A. Hasse
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Overview of Interaction Structure
Machined WSBK Circuit
Circuit Dimensions:Beam Tunnel (b x h) 770 x 150 µmVane Period (d) 460 µmVane Height (L) 270 µmVane Thickness (d-a) 115 µmVane Width (h) 770 µm
Approach: Staggered double vane structure provides large bandwidth and good coupling to sheet electron beam
Beam Size: 700 μm × 100 μm (7 : 1), 400 A/cm2
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Overview of Interaction Structure
Comparison of double vane structures
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Circuit Design and Analysis
- Operating Conditions Beam Voltage (Ve)= 20 kV Beam current (Ie) = 0.25 A Center frequency (fc) = 220 GHz Opt. phase-shift () = 2.5 (n = 1)
- Dimensional Parameters L = 270 m h = 770 m b = 150 m d = 460 m
- Bandwidth (Cold) ~ 70 GHz (30%)
* Larry R. Barnett and Young-Min Shin, US Patent Application No. 60979392, Oct. 12 (2007)
• 3D Model
Transmission Loss :~ - 0.6dB (avg.) Attenuation: ~ 0.15dB/cm (avg.)
• Dispersion and Transmission Graphs
• MAGIC3D PIC Simulation Analysis
150 ~ 275W
1) Larry R. Barnett and Young-Min Shin, US Patent Application No. 60979392, Oct. 12 (2007) 2) Young-Min Shin and Larry R. Barnett, Appl. Phys. Lett. 92, 091501 (2008). 3) Young-Min Shin, Larry R. Barnett, and Neville C. Luhmann Jr., Appl. Phys. Lett. 93, 221503 (2008)4) Young-Min Shin, Larry R. Barnett, and Neville C. Luhmann Jr., IEEE Trans. Elec. Dev. (in press), (May. 2009)
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Broadband Coupler
• Tapered Transition (Vane Width)
• Ka-band circuits
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MAGIC3D: Gain and Stability
Growth Rate ~ 14dB/cm
30dB
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Sensitivity Studies• Misalignment Effect
dy dz
• Off-Centered Beam Effect
x
yz
x
yz
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KMPR UV LIGA Process
• MEMS Facility• UV-LIGANorthern California Nanotechnology Center (NCNC) @ UCD
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UV LIGA Technical Issues
• Underexposure
• Overexposure
• Non-Uniform Resist Thickness
wrinkles
• Heavy table that can absorb vibrations and can be leveled
• Stone hotplate with low thermal expansion coefficient that can also be leveled accurately
• Lapped and polished copper substrate with thickness deviation of less than 1 µm over the circuit area
Results: Film Thickness Uniformity Improvement(1) Over the 4” wafer : 5 m(2) Over the circuit area (25 × 25 mm) : ~ 1 - 2 m(3) Lapped and polished to within 0.25 µm(4) Less than 1 µm undercut after mold removal
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Surface Roughness Analysis of Resistivity versus S21 and S11
• 10 mm long BS circuit model
• Transmission (S21) Graph
• Reflection (S11) Graph • Resistivity versus S21/S11
Only 1 dB in S21 and S11 is changed by up to 5 × Resistivity (OHFC) Interaction circuit is insensitive to surface conditions (roughness)
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Sensitivity Analysis of Fabrication Errors
• Sidewall Slope versus Frequency Deviation
• Undercut versus Frequency Deviation
θ
Undercut ( 40 m) Frequency Deviation ( 2 %) Undercut size of UV LIGA mold is much smaller : ~ 10 – 20 m
Sidewall Slope (> 2) Frequency Deviation (> 2 %) Vertical sidewall of less than 2 can be controlled by common photo-lithography process.
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Process Optimization
- Before Softbake - Right After Heating - After 4.5 hr Soft-bake
* 1 fringe = 0.25 m
• System Setup for Process Optimization
- Autocollimator
(Leveling)
- Large Hotplate(Rapid Production)
- Copper Substrate Flatness Analysis
• UV Lithography • Mold Removal
6 wafers/cycle Thickness Uniformity : 1 m over the circuit (25 mm)
Dimensional accuracy : 3 m, sidewall slope: 90 ± 2
Mold removal efficiency: 90 %
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Completed Circuit and Analysis
• UV LIGA Fabricated BS Circuit
- AFM-Measured Surface Roughness
• Line Resolution and Surface Roughness
- Line Resolution Pattern Images
Aspect ratio ~ 10 : 1
Surface Roughness ~ 50 - 100 m
Young-Min Shin, Diana Gamzina, Larry R. Barnett, and Neville C. Luhmann Jr. “UV Lithography and Molding Fabrication of Ultra-Thick Micrometallic Structure using a KMPR Photoresist ”, IEEE J. Microelec. Micro. Sys. (MEMS) (submitted, 2009)
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Required Surface Roughness
• Frequency versus Required Skin Depth for Device Operation
220GHz (~0.14 µm)
(2)
(3)
(1) LIGA-(Cu) : 70 nm(2) DRIE-(plated Si) : 100 nm(3) LIGA-(PMMA Mold) : 20 nm
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Summary and Future Plans
• Accomplishments– Sc2O3-W Nano-Powder Cathode A. Maximum Emission Current Density: ~ 80 A/cm2 at 1150 oC (Full Space Charge
Limited) B. Life-Time: 768 hrs (950 oC), 800 hrs (1150 oC) C. ~ 50 A/cm2 at 1050 oC – Sheet Beam Gun Design (CPI and Teledyne-MEC)– Circuit Design and Analysis A. Operational Bandwidth : 70 GHz (30%) @ 220 GHz B. Output Coupling Bandwidth: 66 GHz (88%) C. MAGIC3D Simulation: Power Growth Rate (14 dB/cm), Max. Efficiency (5%)– MEMS Fabrication A. UV LIGA : Critical Dimensions ( 5 m), Surface Roughness (~ 50-100 nm),
Aspect Ratio (~ 10 : 1) – CNC Fabrication
• Research Schedule– 750 A/cm2 and 25 : 1 Sheet Beam Transport Test – 220 GHz Circuit Cold-Test